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Why do cargo aircraft still have floors? Even with dedicated cargo aircraft built as cargo aircraft (rather than converted from a passenger-carrying configuration), the cabin is virtually always still divided into an upper and a lower lobe (which would, on a passenger aircraft, be the passenger cabin and the cargo hold, respectively) by a floor located a third to a half of the way from the bottom of the fuselage, drastically reducing the maximum size of the cargo that can be carried and making it much harder to transport round outsize cargo (such as, for instance, large high-bypass turbofan engines as are used on essentially all modern jetliners) by air. Given that the essential structural members of a large modern jet are the skin itself; longitudinal longerons running the length of the fuselage just beneath the skin; and circumferential frames encircling the fuselage just beneath the skin; it should be possible to remove the floor, and thus dramatically increase the freighter's ability to carry very large objects, without significantly compromising the fuselage's structural integrity (the middle of the cabin would still be partially occluded at the bottom - or the top, or the middle, depending - by the center portion of the wingbox, but there would, nevertheless, be a considerable increase in the outsize-cargo capacity ahead of and behind the wings). Why isn't this done? Is the floor left in to facilitate possible future conversion to a passenger aircraft? <Q> Because the overwhelming amount of cargo is fairly small and floors allow easy loading of both decks at the same time which is more important than the ability to load big cargo on occasion. <S> By having floors you can load standard cargo containers quickly and efficiently . <S> It also gives you the ability to standardize the containers with a reasonable degree of reuse most importantly they can fit into the lower deck of a passenger aircraft with out modification. <S> Passenger airlines make a lot of money moving commercial cargo. <S> When it comes to flying around big, cumbersome cargo there are simply aircraft designed and built for such a task like the Airbus Beluga ( source ) <A> Because most cargo aircraft are derived from passenger aircraft. <S> All dedicated cargo designs have no extra floor: They carry the payload on the fuselage bottom structure. <S> Comparison of transport aircraft cross sections aft of wing drawn to the same scale ( <S> picture source ). <S> The <S> C-5 and C-17 <S> are dedicated military cargo designs and their round bottom is not only for aerodynamics, but also to fair the structure needed for carrying the cargo floor bending moments. <S> The Boeing 747-400 is a passenger aircraft which is also used as a cargo aircraft. <S> Even many aircraft which seem to be specially designed for cargo duties have in fact a passenger-carrying origin , and applying more than structurally superficial changes would cost too much for the limited number of aircraft needed. <S> Most freighters started their life as passenger aircraft and only small changes are efficient; redesigning the fuselage is completely uneconomical. <A> Also the space under the floors is full of components, avionics, ducting yadda yadda. <S> Ya gotta put it somewhere. <S> Lots of airliners have underfloor cargo holds though. <S> The passenger aspect is also a factor. <S> You could design a cargo only airplane with only a very skinny floor section as low as possible that would take specialized circular containers, but then that's all it could do.
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On most transport aircraft the floor structure, especially the beams along the sides, is a key part of the fuselage as a load bearing pipe whos lower half is under compression and benefits from the stiffening.
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why are turboprop/turboshaft engines rated only in horsepower and never in ft-lbs of torque like diesel engines or electric motors? I realize torque and horsepower are essentially the same measurement since horsepower is simply torque over time. But I'm curious as to why diesel engines or electric motors always provide torque ratings whereas turboprop engines are only rated in horsepower. Is there any reason for this? <Q> Have a look at any performance curves of a piston engine and this will be evident. <S> Hence, to define in a few numbers the maximum performance of the engine, you need to give both figures. <S> However, turboprop engines for propeller aircraft, and turboshaft for helicopters, operate differently. <S> Maximum efficiency for a rotor or propeller occurs at a certain RPM. <S> Operating at different RPMs is inefficient. <S> Hence, propellers and helicopter rotors are designed to operate at a fixed RPM. <S> As load changes, the blade pitch angle is changed so it “bites” into more or less air. <S> Hence, RPM can be kept constant, despite the load (and hence torque demand) changing. <S> Now, since the power turbine is running at a constant fixed RPM, only 1 performance figure is needed (SHP or TQ) because the other can simply be derived from it. <S> Torque is just as important in a turboshaft or turboprop as a piston engine. <S> These engines all have a torque sensor that usually works by measuring the twist in the power turbine shaft. <S> Most helicopters do an engine performance check daily that involves reading TQ of the gauge prior to flight to ensure adequate performance. <A> Because it's less useful for aviation application. <S> For diesel and electric, or ground vehicle and industrial motors in general, lack of peak torque is a problem (engine/motor stall), but for aviation, there's never a condition that you can stall a turbine. <S> Usually you stall the propeller way before you stall a turbine. <S> Or, put it another way, an aviation turbine is rarely found short of torque. <S> However torque is still an important performance metric and will be stated in the data sheet, but simply isn't actively marketed as much as diesel and electric motor. <A> Torque and horsepower are different measurements. <S> Horsepower is a measure of power, where one horsepower equals 746 watts. <S> Torque is a rotational force, which might be akin to voltage. <S> One can have large amounts of torque, but if a shaft will not turn, no work is done. <S> Work is accomplished by power. <S> One may frequently see torque specifications for diesels, because they tend have different operating characteristics. <S> For example, in common diesel engines, max torque may appear at substantially lower RPMs than on a comparable gasoline (Otto cycle) engine. <S> With similarly sized gas and diesel engines, the gas engine usually has a higher horsepower rating, and always at a higher RPM. <S> The torque rating of a diesel engine or an electric motor are merely forces which the device can apply, at a certain RPM. <S> They are not power ratings. <S> Horsepower and torque are important attributes when designing propulsion systems, so that the drive requirements (eg. propeller, fan, or wheels on the road) can be matched effectively to the power plant (eg. <S> engine, motor or rubberband).
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The reason a Diesel engine has a torque figure and a horsepower power figure is because max torque and max horsepower occur at different engine RPMs.
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Can the CG move out of bounds as fuel is used? I've never bothered to check the weight and balance when the tanks are empty. I always assume that if the Center of Gravity is within range when the tanks are full, then it will remain within range as the flight progresses. Am I correct? Should I compute the W&B on both ends? I know some airliners have complex fuel systems which require fuel to be moved around during flight (e.g. B747-100, Concorde). I am interesting in small aircraft in general, i.e. General Aviation and perhaps personal and up to regional jets. <Q> With a straight wing aircraft with all the fuel in the wings, the fuel is close enough to the C of G across the span of the tanks that the C of G shift as fuel is consumed is insignificant. <S> When this is the case, the weight and balance chart won't have any special requirements to show C of G shift, relative to the fore/aft limits, from fuel burn. <S> If there is an aux tank that is forward or aft, the effects of its fuel level on C of G will be included in the airplane's weight and balance, and there may be limits on loading of cabin or cargo incorporated into the weight and balance data, and special instructions for C of G calculations when it's being used along with curve added to the wight and balance graph. <S> On swept wing airplanes, sweep and dihedral in wing tanks causes C of G to move forward as fuel is burned (level drops in the tips first, which are aft). <S> The C of G charts of swept wing airplanes will include a fuel burn curve to show the C of G location variation with fuel burn. <S> If no center tank, the curve will slant or curve to represent the forward shift, and if there is a center tank it will have a kind of sideways V shape as the C of G moves aft and then forward as the pounds of fuel load declines. <S> If it's something like a 172, there isn't going to be any major shift. <S> If it's something like a Taylorcraft with a nose tank, C of G will shift aft as fuel is burned. <S> To keep things simple, there may be a baggage restriction that is intended to prevent exceeding the aft limit when the tank is empty at the end of a trip. <A> Should I compute the W&B on both ends? <S> Yes, you should generally always compute W&B on both ends of the flight. <S> If for no other reason that you may want to know where your CG falls when you land as even within limits it can greatly change handling of the aircraft. <S> If you are currently training you should encourage your instructor to setup situations where you can fly the aircraft at different loads, perhaps bring a friend along to ride in the back and fill the tanks or you and your instructor a very light fuel load and some pattern laps. <S> I always assume that if the Center of Gravity is within range when the tanks are full, then it will remain within range as the flight progresses. <S> This depends on the airframe and you should consult the POH that accompanies the airframe . <S> It really depends on the tank configuration, the fuel load, and the aircraft load. <S> For example the Bonanza has tip tanks that actually increase useful load which can have a pretty big CG impact. <S> While some GA planes have their tanks mounted fairly center mass and the burn has little impact. <S> In the various PA-28's and 172's I have flown, generally with myself and a passenger, they are fairly hard to push out of CG limits just by burning fuel. <S> However there are plenty of bigger GA planes that have more complex fuel systems, and extra bag compartments that allow potential CG issues. <A> It's not general aviation, but the P-51 had enough of a CG shift as fuel as used to be worthy of mention in the Pilot's Handbook ( reference ) The fuselage tank should be used for takeoff and climb to to a safe altitude as it is the most direct system to the engine and is on a higher plane in relation to the engine. <S> Use of the fuselage tank will also move the C.G. of the airplane forward to a more desirable position for flight. <S> and also The stability of the plane improves rapidly as fuel is expended from the fuselage tank.
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On swept wing airplanes with a center tank, the center tank is almost always burned first and it causes an aft shift of C of G as its fuel is burned, followed by a forward shift as the wings are consumed. Bottom line is, do whatever the weight and balance chart for the airplane says to do.
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Why should autofeather only be used for take off on the Dash-8 Q400? The Bombardier Dash-8 Q400 FCOM says (emphasis mine): The autofeather system provides automatically initiated propeller feathering following an engine failure during take-off, and power uptrim of the operating engine (Figure 12.22-5). Autofeather is selected on for take off only , using the AUTOFEATHER switchlight on the engine instrument panel. (source: smartcockpit.com ) It only says autofeather should be used for take off only, but fails to explain why. I would assume autofeather would also be useful when landing. The uptrim (automatic power increase for remaining engine) might not, but it is independent anyway: Uptrim is triggered (regardless of autofeather selection) [...] Why should autofeather not be selected during landing? <Q> It's because the critical case that autofeather caters to is engine failure right after V1, on takeoff, where the normal identify/feather drill uses up precious time. <S> An engine failure on a missed approach or go-around starts well above the low energy state of an engine failure after V1 and there is much more time and energy margin to do the normal feathering procedure. <S> The system is quite sensitive and there are risks associated with having the autofeather system armed and "ready to fire" you might say. <S> Mainly, having it put a prop in feather when you don't want it to. <S> Or even BOTH props in feather. <S> That risk outweighs the benefit of having it armed outside of the take-off case. <S> It's a bit like having a policy of taking a firearm off SAFE only when there is a critical need to able to fire instantly when clearing a house. <A> Please refer to the following very interesting Website: https://assets.publishing.service.gov.uk/media/5422ed34e5274a1317000179/dft_avsafety_pdf_500839.pdf <S> You may read: <S> The commander's decision to delay the selection of climb power was the initiating event in the sequence which started with the failure of the first officer to disarm the autofeather <S> systemand allowed a train of events to occur which could have had more serious consequences. <S> It is clear that had the standard practice of 'autofeather disarm - select climb power' occurred at the normal point, this incident would not have happened Clearly the objective of limiting the use of this feature, is to reduce human factors consequences, while keeping its advantage in the most critical phase. <A> It could also be that Bombardier decided it wasn’t worth the cost of certification. <S> An engine failure immediately after or during go around was unlikely, just like moments after V1. <S> However, the certifying agencies do not give them any choice for the later.
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There is no point to use autofeather when there is no great benefit of that because: Multiplying the phases where you rely on it, is multiplying the risk to forget it armed, and this feature being forgotten has been a source of incidents that could have turned into dramatic accidents.
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Why did narrowbody jetliners take so long to switch over to high-bypass engines? High-bypass turbofans were introduced into the airliner market around 1970, when the first widebody jetliners were released (the 747 was first, followed in rapid succession by the DC-10, L-1011, and A300); however, narrowbodies continued to rely on low-bypass turbofans (primarily the Pratt & Whitney JT8D ) for considerably longer. To the best of my knowledge, the first narrowbody powered by high-bypass engines was the DC-8-70 (a re-engining of the DC-8-60), which entered service in 1982; the first narrowbody built with high-bypass turbofans, the 757, did not enter service until 1983. As for the other narrowbodies of the time: 707, 720, 1-11, F28: No high-bypass version ever became available (although high-bypass versions of the 707 and 1-11 were proposed, they never entered production). 727: The only 727s that ever flew with high-bypass engines were four 727-100s reengined and renamed 727-100QFs in 1992. 737: The first high-bypass version, the 737-300, was only introduced in 1984. DC-9: Stubbornly held onto the JT8D into the mid-1990s, only switching to high-bypass engines with the DC-9-90. What kept the narrowbodies from immediately, or almost immediately, taking advantage of the greater power and lesser fuel consumption and noise of high-bypass turbofans? <Q> The effort in developing new technology and designs, plus the cost of building a larger fan add cost. <S> Then all of the new technology is inherently less reliable than existing proven designs. <S> The JT9D was notoriously unreliable, causing major problems in the development of the 747. <S> Development problems and spiraling costs from the RB211 bankrupted Rolls-Royce, had huge failure rates, nearly causing an accident (Eastern Airlines Flight 855), and ultimately killing the L1011. <S> CF6 fan disk failures caused National Airlines 27, sucking a passenger out the window, and the fatal United Sioux City crash. <S> Even what we think of as the most reliable engine today, the CFM56, when new had a fan failure leading to a fatal crash (Kegsworth), combined with water ingestion issues that nearly lead to a crash (TACA 110). <S> When you have such compromised technology, you narrow it in the place that makes sense. <S> High bypass engines brought high efficiency, reducing fuel burn. <S> They also had more thrust, allowing heavier planes, carrying more fuel. <S> Both advantages combine to enable long-haul direct flights which passengers like. <S> These are flown with widebodies, so naturally these engines were used in widebodies. <S> Short-haul narrowbodies carry less fuel per flight, and can refuel frequently, so there wasn't an advantage here. <S> Only as the compromises with high-bypass engines were solved, then did the technology trickle down. <S> You see a similar thing today with carbon fiber composite fuselages. <S> They're expensive to build, expensive to fix, and there is uncertainty over long-term costs. <S> But the weight savings opens up ultra-long-haul flights, hence the A350 and 787. <A> There was no suitable high-bypass-ratio turbofan engine available. <S> What were the narrow bodies flying in the 1960s and 70s? <S> Here is a list: Sud Aviation Caravelle <S> Boeing 707 Douglas DC-8 <S> Hawker-Siddeley Trident <S> BAC <S> One-Eleven Boeing 727 <S> Tupolev 134 Tupolev 154 <S> Douglas DC-9 Vickers VC-10 <S> Ilyushin <S> Il-62 <S> Boeing 737 <S> The thrust needed for those aircraft, about 10 tons per engine, was not covered by the first generation of high-bypass-ratio engines. <S> Remember, their development was started with the Heavy Logistics System (CX-HLS) program which eventually resulted in the General Electric TF-39 and the C-5 Galaxy . <S> The maximum thrust of the TF-39 (43,300 lbf or 193 kN) is twice that of the Pratt & Whitney JT8D (21,000 lbf or 93.4 kN) <S> which powered the Boeing 707, 727 and 737, the DC-8 and -9 and the Mercure. <S> Another result of the CX program was the Pratt & Whitney JT9D <S> which was in the same thrust class as the TF-39 and its civilian spin-off CF6. <S> Other early engines with higher bypass ratio like the General Electric <S> CF700 were much too small with 4,200 lbf or 18.68 kN static thrust and did not offer enough of a jump in bypass ratio to become interesting for airliners. <S> It was not before the CFM56 became available in the 1980s that a suitable high-bypass-ratio engine in the 10-ton class existed. <S> One reason for the long development time of the CFM56 was the delay in an export license for the engine core technology which was derived from the military F101 design. <S> And when the CFM56 entered the market, it was first used <S> to re-engine old Boeing KC-135 (the engines for the French KC-135s were the first big order), 707 and DC-8 aircraft which benefited much more from the new engine than the smaller mid- and short-range airliners. <S> The competition to the CFM56 ( IAE V2500 and Pratt & Whitney 6000 series ) <S> both entered the market much later. <S> There simply was no suitable engine available any sooner! <A> One reason would be that high bypass engines tend to be larger, especially having a larger diameter. <S> This requires often quite significant redesign of the aircraft to fit them when the aircraft wasn't designed with them in mind from the outset. <S> The 737 for example required a longer undercarriage to allow the larger diameter engines to fit under the wing. <S> Aircraft with tail mounted engines require almost certainly strengthening of the rear fuselage, especially the mounting pylons and their support structures, which adds weight, changes the center of gravity, etc. <S> etc.. <S> It probably just wasn't worth the cost until noise regulations made aircraft with turbojets harder to sell and operate.
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Early high-bypass engines were expensive and unreliable.
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How is the change of moment handled in a Weight and Balance calculation with a swept wing aircraft? I'm writing a weight and balance calculator for a charter operation. Every aircraft I've ever flight planned for has all the tanks on the same moment arm, so I don't know how you calculate the W&B for an aircraft that has swept wings. Do they have one tank on each wing whose moment changes as it drains, or do they have multiple tanks? And if they have multiple tanks, so you have to calculate for 'drain the forward tanks first' and 'drain the rearward tanks first' and plot both of those on envelope? <Q> In supplement to @Dave's answer and as he said depending on the airplane, the complexity of calculating the c.g. can vary greatly. <S> The manufacturer of every large aircraft I've programmed weight & balance for has had tables for each tank. <S> In Boeing's case for the 747-400, each table line is a tank volume in gallons and the tank c.g. <S> at that volume in inches. <S> For example, and using JSON notation since the OP is JavaScript fluent: {"vol":3200,"ba":1453.7},{"vol":3250,"ba":1454.8},{"vol":3300,"ba":1456.0},{"vol":3350,"ba":1457.2},{"vol":3400,"ba":1458.4},{"vol":3450,"ba":1459.7}, "vol" is the fuel volume in the tank in gallons <S> "ba" is the balance arm at that volume in inches Since fuel is loaded by weight, one has to use the fuel density to convert to volume. <S> Typically, at least for large aircraft, you have to satisfy the c.g. envelope for: zero fuel weight <S> ramp weight after fueling takeoff weight landing weight <S> Also there has to be provision for carrying ballast fuel if that is necessary. <A> You will need to consult the POH for the airframe in question and see what it says in regards to fuel burn from tanks at different moment arms. <S> Ultimately you will need to program in the variable factor of fuel burn. <S> It sounds like the program will have more inputs than just the weight of the passengers, fuel, and cargo. <S> The end user will also need to input their planed fuel burn schedule and the order of the tanks they intended to burn off of. <S> Once you have all this info you can compute inflight CG at different times. <S> What you are going to end up with is a piecewise system that describes your WB at various points in the flight. <S> One of the contributors here <S> @Terry built a WB app for some 747 variants that he used when he flew. <S> You can find it here , it might be worth reaching out to him if he does not add an answer here. <A> Most twin engine jets have one very long tank in each wing for each engine and often a center tank that feeds both. <S> The fuel shifts forward as fuel is consumed from the wings (dihedral plus sweep), and aft as fuel is consumed from the center tank, if installed (always before the wings, so if there is a center tank the C of G moves aft until the tank is dry and forward as the wings are consumed). <S> When you do the load sheets on a swept wing airplane <S> the fuel moment/mass curve will be integrated into the chart data so that an accurate fuel moment/mass value is applied to the C of G calculation for takeoff. <S> Also, some form of the fuel curve will be overlaid onto the C of G limits chart to confirm that the C of G shift will stay in limits as fuel is burned during the flight. <S> This is especially important for jets with center fuel tanks, because you may be able to load it with a marginally aft G of G, such that the aircraft is technically in C of G limits at takeoff with a full fuel load, but as the center tank is burned off the C of G could move past the aft limit temporarily until some of the wing fuel is burned off. <S> The result is the C of G with center tank at zero will determine the aft limit for freight/pax.
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The manufacturer's weights engineering group will determine the overall fuel load's center of gravity moment for different fuel volumes and plot the results on a chart as a curve.
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Can longer paths consume less fuel than the (shorter) great circle path? Is the most fuel-efficient route between points A and B always along a great circle ? Although somewhat counter-intuitive, this comment on an aviation blog seems to suggest that longer paths ( in terms of geographic distance covered ) can save fuel: Oceanic Flights these days are not restricted to the old “defined great circle routes”. Modern computerised flight planning systems definately take weather into account, and go searching for the best winds (tailwinds) or least adverse (headwinds). Particularly in the case of westbound flights across the Indian Ocean, where headwinds are often ferocious, the tracks actually flight planned, and actually flown, are often a long way off “great circle” routes. <Q> That depends how you define longer in aviation. <S> As you can look at it geographically or on the clock. <S> If you can take advantage of a big tail wind 20 miles south of the geographically shortest route or at a slightly higher altitude you may burn a bit of fuel getting there but on long haul flights you can make up for the burn, and even gain quite a bit by taking advantage of the winds <S> Similarly headwinds can really kill your efficiency even over short distances. <A> On a flat plane, the shortest distance between any two points is a straight line, right? <S> So if you were at A and wanted to get to B in as few steps as possible, you would walk a straight line. <S> But what if there's a moving sidewalk along that route, going the wrong way? <S> Now is the path of fewest steps still a straight line? <S> Probably not: by adding a few steps at the start and end, you can bypass the moving sidewalk and avoid the extra steps it would force you to take. <S> The moving sidewalk essentially added more ground, so that the shortest path via a tape measure is not the shortest path by steps taken. <S> The idea is the same with headwinds. <S> The shortest path as measured by the ground is not the same as the amount of air you fly though, because the headwind effectively add more air. <S> Since the engine is working on the surrounding air, not the ground under you, the fuel consumption is based on how much air you fly through -- not how much ground that happens to cover. <A> Yes, the shortest route by distance (great circle route) is very often not the most fuel efficient route to take. <S> An aircraft at a given speed, altitude and weight will burn a predictable amount of fuel per hour, regardless of the distance traveled. <S> It follows that the less time in the air, the less fuel is burned (generally speaking, and if flying economically). <S> If there is a tailwind, the aircraft will travel faster without using any extra fuel, needing less time to go from point A to B, ergo less fuel consumed. <S> So a pilot or dispatcher will review the forecast winds, and if they are strong enough, will detour from the direct great circle route to take advantage of them (or get out of their way if it is a headwind). <S> Anecdotally, I would predict that almost every single long haul flight flying east/westwards will deviate from the GC route due to winds (as opposed to other route changes like airspace restrictions). <A> You begin with a great circle route as the default. <S> Then you adjust it to account for the presence of either favorable or unfavorable winds.
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The hard answer is no, the most fuel efficient route is the one that has the aircraft in the air for the shortest amount of time.
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Can I fly through these military airfields' class C airspace? I am a low time private pilot now based in Pensacola. I’m a bit unsure how the Class C of PNS/NAS Whiting Field is handled. As you can see they all overlap. PNS is a civilian field while the others are military. If I was going to fly VFR to the northeast, can I fly through the Class C of Whiting field? I always get flight following when departing. <Q> When entering Class C Airspace: Since all the airfields are Class C you would need to contact the approach control prior to entering. <S> Approach control should be able to direct you appropriately from there. <S> Approach control would handle traffic at all three airports. <S> If there is nothing going on at the military field then approach control could let you cross over the field. <S> When Departing Pensacola Field: When departing Pensacola field you can request a Northeast departure through Clearance Delivery. <S> You could be granted the request to fly Northeast directly from the airport or they could make you fly East for a while then make a turn North to avoid the military airport. <S> Nevertheless you have to follow ATCs instructions whenever you are in Class C airspace. <S> Side Note: <S> It is fairly common that when you have military airfield close to a Class C airport, the class C airspace will be extended over the military fields as well so that one approach control would handle all the traffic and deconflict traffic for all of the fields. <S> A similar situation exists for the Tucson area where the Class C includes Tucson International and Davis Monthan AFB. <A> If I was going to fly VFR to the northeast can I fly through the Class C of Whiting field? <S> As long as you contact the NDZ tower/approach control and they respond to your call <S> you are cleared through the Class C as you would be through any class C. <S> However also to the northeast you will find R-2915A and the Eglin base area which has some special rules. <S> The FAA offers a nice course/overview on it you can find here. <S> Generally speaking you are allowed to fly close to military bases and into their airspace so long as that airspace is not prohibited or a hot restricted area. <A> When departing KPNS (or any class B/C), you'll call Clearance Delivery before taxi and tell them which direction you want to depart, and they'll give you a squawk code and <S> (maybe) what heading and altitude to fly immediately after takeoff. <S> Then you call Ground to taxi as usual. <S> After takeoff, KPNS Tower will hand you off to Departure, who will likely give you a new heading and/or altitude once you're on radar. <S> Ideally, you'll have climbed above the other Towers' airspace within a few miles and thus can stay with Departure the entire way out. <S> If your climb performance sucks, they may turn you to avoid a handoff, or they might have a local agreement that lets them handle you anyway, e.g. if you're just going to clip a corner on the way up. <S> The key point is that as long as you're talking to ATC, they'll hand you off to whoever controls wherever you're headed next without you having to worry (much) about who that may be ahead of time. <S> All those complicated lines are mostly just for folks trying to fly without talking to ATC.
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If the military airfield does not want civilian aircraft to cross the field for any reason approach control will direct you around it.
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From which rating would it be easier to transition to an Osprey? Fixed-wing or rotary-wing? If the future of flight was to be on aircraft that were a hybrid of fixed-wing and rotary-wing (for example the Osprey), assuming they had similar technical abilities and the same number of flight hours, who would have an easier time flying an Osprey? Or to put it another way, is the Osprey closer to a plane or to a helicopter? <Q> The Osprey is closer to a helicopter and if I was going to chose from a fixed wing pilot or rotary pilot to train on it <S> I'd choose the rotary pilot. <S> A helicopter pilot could master fixed wing cruising flight in the Osprey far easier than a fixed wing pilot could master hovering the Osprey (you can pretty much train a monkey to fly an airplane in cruising flight - airplane physical demands are mostly when you slow down). <A> I believe the FAA considers the Osprey or the AW-609 to be a powered lift category aircraft per §1.1. <S> Therefore if you were an Osprey pilot and you completed the conversion of your military pilot certificate and ratings, you would hold an FAA commercial certificate in the powered lift category and class with an instrument powered lift rating. <S> Given that your primary flight training (if you’re former USAF/USN) was in airplanes, they may add airplane single engine land as well with an instrument airplane rating too. <S> If the FAA’s policy stands, powered lift is a hybrid of airplane and rotorcraft helicopter aircraft but so different that the FAA considers it to be its own category and requires meeting the aeronautical experience requirements and passing a practical exam before being able to serve as PIC in such an aircraft. <A> Generally, in my opinion a vehicle like ospery is resembling an aircraft charateristic more than a helicopter. <S> From the flight physics perspective, ospery is behaving "completely" like an aircraft in most of its flight time (cruise phase), while at take-off and landing, the vehicle is operating in a "similar" manner to a helicopter. <S> For example, most of helicopters use their tail rotor for providing directional contol, while ospery does not have any tail rotor. <S> A helicopter uses its primary rotors for vertival, longitudinal and lateral movements, while ospery uses them only for the vertical and longitudinal motions. <S> For this reason, it seems different skills than flying a helicopter are required to be able to land an ospery. <S> Generally, I think the capability of landing or taking off vertically would not essentially make it a helicopter, as nobody considers the F-35B (the USMC version) as a helicopter. <S> But, I acknowledge that the rotors may be misleading in the ospery case.
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The rotary wing physical skill set is so much more demanding than the fixed wing one.
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What are the areas of an aircraft that suffers most from G forces? i want to ask this time as to "what are the areas of an aircraft that feels or suffers the most from G forces?". i am asking this in terms of structural design and physical limits of the pilot(the position and seat angle) and the plane.please try not to limit the airplane model to simple light-aircraft,try to expand it near to military Aviation and other else. if possible, please try not to use high-falutin words since i'm having a hard time with words in English. If you can not understand this clearly, i am sorry for my poor English and Grammar, and also i want to elaborate more, but i can't translate it properly at the moment. <Q> In this case we'll say a single engine light aircraft. <S> Wing root spar fittings on a cantilever wing - the bottom in tension and the top in compression. <S> For a high wing airplane with struts, it will be the strut attachments at each end that join the strut to the fuselage and wing. <S> The roots of the horizontal tail, same except upside down - bottom in compression and top in tension. <S> Engine mount attachment to the firewall - top mount in tension and the bottom mount in compression. <S> Those are the points where flight loads from a lot of mass are concentrated at a single point or set of points during high G loading and are where the structural elements will be heaviest. <S> For most other areas the loads are distributed over more of a large area. <A> Wing attachment points. <S> (spars and struts) <S> Not every answer requires paragraphs of postulating and philosophizing. <S> Reference: <S> 115 years of heavier-than-air aviation accident reports. <S> In 2002 all large air tankers were grounded after two of them had wing spar failures a month apart. <S> Both were large, 4-engine ex-military airplanes. <S> Five days ago the FAA proposed an AD on Piper wing spars because the wings keep falling off. <S> Lowell Bayles was killed in a Gee Bee racer in 1931 when the wing spar failed and the wing ripped off. <S> In 2012 the EASA issued an AD on the A380 because of cracking in the wing spars after they “found cracks in almost all of the planes inspected”. <S> This is a straightforward question with a simple answer. <S> All airplane types and sizes have the same major mode of structural failure due to stresses imposed by the force known as "Gs". <A> G forces are forces caused by the acceleration of a mass. <S> The one acceleration all parts are subjected to all the time is gravitational acceleration, and here John K's answer gives the right direction. <S> However, there are other accelerations at work which might cause higher loads still. <S> Any fast, cyclic movement will cause accelerations which can become higher than those of gravity, especially when the acceleration is vertical so gravity comes on top. <S> Obvious candidates are: Flutter: <S> Here, certification requires the mass balance of control surfaces to withstand 24g ( JAR 23.659 ). <S> That does not mean that in every flutter case this acceleration is reached, but that there have been cases where a stronger mounting of the balance mass could have prevented an accident. <S> In case of flutter, the concentrated mass of the mass balance could be ripped off if not adequately secured to the control surface, rendering it ineffective. <S> Imbalance: This could be the rotating part itself (propeller, engine) or some structural member which is excited at one of its eigenfrequencies. <S> Especially in helicopters, some vibration and shaking is always present and will create local stresses which can easily surpass those of gravity if a part is not well balanced. <S> Repeated, cyclic stresses will let the vibrating part accumulate creeping damage until it breaks suddenly and unexpectedly. <S> Excuse my use of technical terms - please copy and paste the answer into Google Translate if you need help.
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Basically 3 places on an airplane see very high concentrations of stress in a small area from in-flight G loads.
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Can ATC terminate flight following AND approve (arbitrary) frequency change while still inside Class C airspace? Unusual (for me) event inside Class C. Can ATC terminate flight following inside Class C and approve frequency change. Background: Requested and received VFR FF at 6500 msl prior to approaching ONT Class C (top is at 5000). Intent was to over-fly ONT and not enter Class C, however after reaching north of the field, ATC said “free to descend altitude at your descretion ” (Point A). My response, “6500 ft decending to 4500”. At about point B, I dropped into Class C and continued to 4500. After leveling off, still in Class C, ATC said “Squawk VFR, frequency change approved.” I responded “Squawking VFR, and immediately departing Class C to the North”. (Point C) His response, “You don’t have to do that as the tower still has you on radar.” I said “departing Class C to the north” Here is my confusion: First squawking VFR is not an issue, I’ll squawk whatever is requested and maintain my own flight separation but when he said “frequency change approved” I would no longer be in radio contact in Class C if I actually did as approved. This would mean, to me, I am illegally in their airspace. What am I missing??? <Q> Jim S asks an interesting question. <S> Can ATC ask you to do something which is contrary to the regulations? <S> The practice of advising aircraft to switch to advisory frequency and squawk VFR is common here, in Class C airspace, and I have experienced it in Class B airspace as well. <S> Discussing this with the ATC supervisor once, it was explained to me this way: The controller knows where you are going, knows your intent, and believes that he can manage the traffic in the area effectively if you leave the frequency. <S> So for the controller it is an issue of risk and workload management. <S> With students, this creates a good learning opportunity to have them "monitor" one radio, while using another. <S> No official guidance on this, but it is common practice. <S> So if you are not familiar with this, have an experienced pilot or CFI demo it to you. <S> Keep in mind that this is the same process for IFR aircraft making approaches to non-towered airports. <S> Arguably, ATC can authorize deviations from 91.130, as @DaveCFII points out. <S> Certainly that covers temporary frequency changes to check WX and things like that, but it could be interpreted to have broader scope <S> is that it could be used to terminate communications near to the point where an aircraft leaves Class C. <S> Having said this, I would prefer that ATC state something like, "communications deviation approved. <S> " <S> Of course that will not happen on a busy frequency. <S> Having said all this, it is important to remember that the pilot has final authority over a flight, and the FAA in the Granby LOI makes it clear that ATC does not have the requirement to point out to pilots what regulations apply to their operation. <S> So a pilot who is uncomfortable with this procedure, might monitor ATC on one radio, and broadcast their intents on the advisory frequency. <S> This way they can fully comply with the regulations. <S> Most aircraft have dual COM radios. <S> If not, delay your frequency change until you are clear of Class C, to remain in strict compliance. <S> Ref: Granby LOI https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/data/interps/2006/granby%20-%20(2006)%20legal%20interpretation.pdf <A> The requirement to maintain two-way radio communications is FAR 91.130(c) . <S> But regulations have to be read as parts of a whole. <S> Read 91.130(a), which says: <S> Unless otherwise authorized by ATC , each aircraft operation in Class C airspace must be conducted in compliance with this section... <S> "Frequency Change Approved" is ATC authorization to deviate from the requirements of 91.130(c). <A> Were you perhaps inbound to CCB ? <S> If so, I agree with the comment by @StephenS : <S> That once you are cleared all the way out of the airspace, ATC will release you by effectively saying, "I'm not going to have anything more to tell you, you don't really need to stay on frequency anymore" (even if this might be a technical violation under 91.130.) <S> Because ATC expects you to go to the CTAF frequency, they know where to find you. <S> They may well be monitoring that frequency, and can broadcast on it if needed. <S> If you have dual radios, and want to be extra safe, keep ATC on Radio #1, and start your CTAF calls on Radio #2. <S> Double-check your mic-setting with each transmission <S> , so you know which frequency you're transmitting on. <S> You can still hear ATC if they try to reach you even after approving a change.
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The answer is they can, and just because they do, does not change the regulations.
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How can I use an ADS-B receiver to make my aircraft visible in Flightradar24? I recently bought a SENTRY ADS-B receiver for the aircraft in order to track the flight. How could I make Flightradar24 or Flightaware show my aircraft and how to register my aircraft on the website? <Q> ADS-B is broadcasted by many aircraft and contains flight and aircraft information. <S> This can easily be received and decoded, either by dedicated devices or a simple 20 bucks TV USB dongle. <S> All information is then sent to flightradar and other sites by the members of their community. <S> (there are also other sources for their data) <S> However, once ADS-B is broadcasted and received by any receiver working for flightradar, the aircraft appears on their map. <S> There is no need to register your self, in fact, you have to opt-out if you prefer to be invisible. <S> Now, you write about a receiver, and also a short visit of the product page shows that your device is a receiver only . <S> Together with the built-in GPS it might just warn you about other near aircraft (which do broadcast ADS-B). <S> You will need an ADS-B sender to find yourself on flightradar. <S> In the US, ADS-B Out is required to be installed (by Jan 1, 2020), it cannot be a portable unit. <S> ADS-B <S> In can be a portable unit. <A> The ADS-B Out market has quite a few options. <S> Some, like the uAvionix, are small and can be installed in place of a winglight or a taillight and include the GPS receiver for position gathering. <S> See skyBeacon, tailBeacon here: https://uavionix.com/ <S> Others, like some of the Garmin products, are intended to be wired in to the existing transponder and use that antenna for sending position information. <S> Garmin also has numerous In/Out products also, including transponders, such as the GTX345, which I just installed to replace my very old King transponder which I wasn't sure actually worked anymore after the plane sat in storage for 12 years. <S> https://www.garmin.com/en-US/search/?query=ads-b <A> That is how they track planes. <S> You shouldn't need to "register" your plane with them unless you want to hide it from others. <S> They may not show it by default anyway if you're not on an IFR flight plan, but that's just a viewer setting. <S> ADS-B <S> "In" isn't required unless you are in an area with poor coverage and want to contribute. <S> How (and if) to set that up would merit a separate question.
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For FR24, FA and other flight tracking websites to "see" your aircraft, it will need to have a Mode S transponder (or UAT transmitter if in the US) with ADS-B "Out" installed.
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What would happen if I exceeded mach 1 over a regulated area? What would happen if I exceeded mach 1 over a regulated area? Are there any penalties in place for this violation? Would ATC actually know I’m flying supersonic or would they have to go out of their way to check my groundspeed and work out my approximate air speed? <Q> It would be a violation of 14 CFR 91.817 § 91.817 Civil aircraft sonic boom. <S> (a) <S> No person may operate a civil aircraft in the United States at a true flight Mach number greater than 1 except in compliance with conditions and limitations in an authorization to exceed Mach 1 issued to the operator under appendix B of this part. <S> It would be extremely easy to track such an aircraft, and the pilot would be dealt with upon landing. <A> <A> Well, they might well find out what you did, but it won't be from ATC radar that they get the first clue. <S> If you're flying SR-71 speeds, then yeah they'd notice, but the difference between M 0.95 and M 1.05 isn't enough that they'd see it, or care. <S> You'd be far more likely to be "busted" based on noise complaints from the ground, which could be followed up by checking the ATC replay to determine who was flying "there" at that time. <S> But if nobody from the ground complains about the boom, the chance that radar by itself would catch a slightly supersonic excursion is pretty remote. <A> As an ATCO, if you turn IAS/Mach datum off from Mode S, trust in your answer to the question <S> "report Mach number" is all I can do, as long as you aren't catching yr preceding traffic flying @ same mach # !!!! <S> But I am still unable to guess if you are @ .90 or 1.01. <S> Happy new 2019
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ATC radar wouldn't catch it, since they see ground speed and know neither your head/tail wind component nor the exact temperature at your altitude (which determines the speed of sound). Depending on the place and altitudes this took place at, the FAA would certainly cite you on 91.817 and 91.13 careless and reckless operation, and may recommend disciplinary action, including suspension or revocation of airman certificates and ratings.
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Why are the leading edges of wings not always made as 'sharp' as possible? Why is an airplane's wing (the leading edge) not made as sharp as possible to break the air, in the same way that a ship's hull is made sharp to easily break the water? This is unlike Concorde's nose and most jet fighters' noses, which are made very sharp. <Q> A blunter (less sharp) leading edge allows the wing to operate effectively for a wider range of angles of attack (AoA). <S> The angle of attack is the angle between the approaching airflow and the chord line (as illustrated below) <S> As you can see, the air has to curve around the leading edge on the upper side of the airfoil. <S> This curvature accelerates the flow and thus creates an area of reduced pressure and thus contributes to the lift of the airfoil. <S> A sharper leading edge will cause a more intense curvature of the flow and therefore reduce the local pressure even further. <S> A higher angle of attack will also cause a more intense curvature of the flow with the same effects. <S> Here's the problem: In order to reach pressure equality between the upper and lower side at the trailing edge of the wing, the pressure will have to increase again as you move further towards the trailing edge. <S> The boundary layer of the flow doesn't like this at all. <S> Strong pressure gradients will cause the boundary layer detach (generally, the boundary layer is already turbulent for commercial aircraft). <S> A detached boundary layer (stall) causes a drastic increase in drag and decrease in lift and is therefore highly undesirable. <S> To increase the range of angles of attack at wich the boundary layer stays attached and to allow for a more gradual transition between normal flow and stall, the designers favour a quite blunt leading edge for most commercial and general aviation aircraft. <S> This will increase the drag at zero AoA, but won't force the air to follow a high curvature at positive AoAs. <S> Supersonic aircraft such as the Concorde and fighter aircraft have to deal with a new type of drag called wave drag. <S> Generally wave drag can be reduced by having sharp leading edges. <S> Most boats also have to fight against some kind of wave drag (although the fluid dynamics are very different) and therefore also have sharp hulls. <S> This is a broad generalisation and there are a lot more things to consider in reality. <S> If you want I can go into more detail. <A> As long as the aircraft flies subsonically, a sharp leading edge doesn't really have much advantage. <S> Far more important for reducing drag is to keep the flow as laminar as possible. <S> This works only in the subsonic / transsonic region, because the pressure-forwarding travels as a sound wave, i.e. against a subsonic stream the wedge can be built up against the stream direction, but against a supersonic stream this is not possible. <S> That's why supersonic planes have sharp leading edges, but this leads to its own engineering challenges. <S> Sharp edges in general are less structurally robust and they can easily disrupt the laminar flow. <S> † <S> Actually, this high-pressure region is not wedge-shaped at all, rather it's a smoothly decaying “baffle”. <S> The crucial point is that it makes a pressure gradient that's pointing up for the air approaching above the center line, and down for the air approaching below it. <S> This accelerates the air out of the way of the wing, so not much of it actually hits the surface. <S> You can look at the pressure in some CFD simulations. <S> https://www.google.com/search?q=airfoil+cfd+pressure <A> Rounder leading edges help the air follow the wing under high angles of attack, they are cheaper and easier to manufacture, and thicker wings are structurally stronger, reducing the weight used for structural rigidity by a big margin. <S> Like almost everything in aviation/engineering, it's all about trade-offs. <S> Clearly, the advantages mentioned above are more important than the sleekness of sharp leading edges. <A> Because at subsonic speeds, the best way to "break the air" is to start pushing it out of the way in front of the wing. <S> The wings with the round noses travel below the speed of sound, the wings with the sharp noses go faster than the speed of sound. <S> The speed of sound is actually the speed of a disturbance in the air, and if the wing approaches at a slower rate it can announce its presence and start pushing air out of the way. <S> If the wing approaches faster than the speed of sound, the air does not know that the wing is approaching until it is actually there, and will split suddenly and sharply with a shock wave. <S> The best wingtip shape here is the one that cuts through air like a knife. <S> Image source Notice <S> that in boats, only the bow at the surface has a sharp knife-like edge like supersonic wings have, under water the bow is rounded. <S> Water at the surface behaves like air at supersonic speeds, because there water can be easily shocked into the third dimension, above water level. <S> Deeper down water cannot be easily compressed, and the lowest resistance bow shape is rounded, like a subsonic wing traveling through air that behaves in an incompressible way. <A> The shape of the wing helps determine the lift it creates, and the reaction of the wing when the plane is pitched up enough to stop producing lift (or stalls). <S> Everything is a tradeoff. <S> Small enough curve to make sufficient lift and be aerodynamic, but not quick to stall when flying slower for landing. <S> Sharp noses help with flying faster than the speed of sound. <S> The Concorde and the jet fighter are designed for fast flight, the airliner is not. <S> The more rounded nose also allows for weather radar to be installed. <S> In even larger planes, the nose can be tilted up for cargo loading as well.
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Simplifying the physics a lot, you can imagine that before a round leading edge, an additional “wedge” † of only slightly higher-pressure air is built up, which can divert the flow around the wing almost as efficiently as a sharp edge would.
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Can pilots choose runway and landing direction? Pilots normally receive landing clearance for a specific runway assigned by ATC . Absent an emergency , can pilots of commercial flights (depending on the wind conditions for example) choose a different runway the landing direction for this runway or both ? If no, why not ? If yes, ( and still assuming nothing is wrong with the aircraft ) how does the pilot get his wish ? Can (s)he .. simply choose (i.e. just communicate the choice to ATC, which has to accept it) ? request it / ask for it (but ATC has the final say) ? insist on it ? (analogous to " telling ATC you are altering heading for weather " ) In the last 2 cases, does the pilot need to name a specific reason ? <Q> Pilots can request a particular runway approach course and landing <S> but in a controlled environment they are at the mercy of ATC. <S> At high traffic (read busy) <S> commercial airports they are unlikely to get their request. <S> As far as I know, shy of an emergency declaration you cannot insist on a non standard runway and expect to get it. <S> At a quiet class C or D airport they may very well get what they ask for. <S> I did this a lot during my training at a quiet class D airport. <S> If the winds were favorable to one runway but my instructor wanted to practice cross wind approaches we would request the non standard runway and if no one was around they would often grant it. <S> Generally you don't want to fly the non preferred runway if there are windy conditions as landing with a tail wind <S> can be dangerous. <A> To avoid all the Class this and that stuff, just think of controlled (tower with a clearance required) and uncontrolled airports. <S> If a controlled airport, the runway is assigned by the tower controller, normally based on the favorable wind. <S> Thing is, you don't HAVE to do what the controller says if it puts you in danger, and the controller doesn't HAVE to let you go where you want if it screws up his/her flow, and you could say there is always potential for a Mexican standoff situation, in theory. <S> In practice, there will be some mutually agreed resolution, the controller wanting everything to flow smoothly and safely, and the airplane crew wanting to get where they're going without getting violated and without being forced into something dangerous. <S> So say you are given a clearance to land on runway 9, landing east, but you want to land on runway 18, landing south. <S> So you ask for 18 and see if you get it. <S> The controller decides whether it will cramp his/her day and says yes or no (probably yes 99% of the time). <S> If no, your choices are to either land on 9, go elsewhere, or declare an emergency, in which case the decks are cleared for you <S> but you may have to justify yourself later. <S> In the big picture, common sense is supposed to prevail. <S> At uncontrolled airports, it's uncontrolled, so knock yourself out. <S> You land on whatever runway you feel like, keeping in mind certain rules and protocols for uncontrolled aerodromes, like pattern (circuit) rules, IFR arrival announcement requirements etc etc. <S> Say everybody is landing on 9 and you want to land on 27 going the other way, forcing an airplane landing on 9 to take evasive action. <S> Probably you'll just get the finger from someone, but there's a possibility somebody will report you for breaking regulations on traffic etiquette and you will have to answer for it, but there is no ATC around <S> so trouble won't come from them. <A> [Adapted from a comment I previously posted] <S> I have an anecdote which bears on this, at least for the case of takeoff. <S> In 1988 I was on a flight leaving O’Hare and the radio comms were on one of the audio channels while we waited to taxi. <S> Among the traffic we heard was something which caused me a bit of concern: a pilot being told to use a runway he thought was too short. <S> He started off requesting "runway ZZ" and the controller simply responded "prepare to taxi to runway AA". <S> After a second similar request that was also refused ("ignored" may be more accurate), the pilot said, Tower, I am X thousand lbs <S> , I need Y thousand ft, I need runway ZZ. <S> The controller finally agreed, with real annoyance in his voice. <S> I've long since forgotton the exact runway numbers, and I don't know whether the current runways have evolved since that time, but then as now O'Hare was a busy place, so I can easily imagine that allowing an oddball departure on a cross runways would require significant delays. <S> Still, I was struck by how this pilot had to really insist on the runway he needed. <S> Within the same 20-minute session we also heard a pilot barge into a queue, in front of a plane he was clearly (twice) told to get behind . <S> The tower said "get in behind the Company Nine" and in this big Texas voice the pilot responded "Roger, in front of the Company Nine"; tower said "negative, behind the Company Nine" and the pilot came back " <S> Yessir, right in front of the Nine" and the Tower just said "Ok, fine.". <S> So maybe there's a culture of low-grade pushiness that the controllers are prepared for. <S> And they lost track of a plane, telling an aircraft to queue behind another that just wasn’t in the queue at all. <S> Which objectively seems kind of odd, too, but it was the least of it that evening.
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Normally, you use the runway assigned by the controller, unless you have a reason to use another one.
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What’s the setting range altimeters can handle? What’s the setting range altimeters can handle? Is there a standard requiring a certain range for aircraft to be certified? Are there many occasions where a QNH is so high or low that airplanes have problems handling that? <Q> The stand-alone altimeters in older aircraft and small GA aircraft (panel mounted "steam gauge") are certificated to SAE AS392C, Altimeter, Pressure Actuated Sensitive Type. <S> The specified scale range is "at least 28.1 - 30.99 inches of Hg (946 - 1049 millibars)". <S> This standard was updated in 2016 to require compliance with SAE AS8009C, Pressure Altitude Systems. <S> Altimeters built to this standard have a specified range of 27.50 - 31.50 inches of Hg (931.3 to 1066.7 mb). <S> Aircraft with "glass cockpits" use Air Data Computers certificated to SAE AS8002A, AIR DATA COMPUTER - MINIMUM PERFORMANCE STANDARD. <S> Barometric corrected altitude correction is covered by Table 2, which defines a range of 22.00 - 30.98 inches of Hg or 745 - 1049 millibars. <A> The pressure ranges for altimeters in the United States are set forth in a technical standing order. <S> For example TSO-C10b <S> in turn references SAE standard AS392C , which indicates the following performance parameters: Type <S> I : range to 35,000 feet Type II : <S> range to 50,000 feet <S> Both adjustable from 28.1 to 30.99 inHg. <S> These parameters have regulatory consequences, notably FAR 91.144 , which restricts flight operations when the barometric pressure exceeds the upper limit set in the TSO. <S> I have found no regulation for the bottom end, I suppose because the weather would be discouragingly foul. <A> It is very dependent on the type of altimeter. <S> A lot of standard GA altimeters are rated from -15,000ft to 50,000ft based on a mechanical range rather than a pressure limitation. <S> For example, on an older model of an aircraft from 1979 a barometer reading of 25.69 was taken from the aircrafts altimeter. <S> At uncorrected station pressure, this would be 71,000ft. <S> Thus altimeter limits are altitude based, not pressure based* <S> * <S> In most cases.
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There are actually multiple different answers depending on the specific type of altimeter system and what standard applies.
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Disadvantages of using thrust vectoring only in an aircraft with variable rotation nacelles such as the X-19 Take a quad tilt rotor aircraft such as the curtiss-wright X-19 or even a bi-tilt aircraft such as the V-22. What would be the advantages or disadvantages of using thrust vectoring only for control of roll, pitch and yaw assuming for a moment that there is no added mechanical complexity in individually tilting each nacelle a variable rotation and assuming each nacelle can tilt 180 degrees from full vertical producing downward thrust (lift) to reverse vertical, essentially sending the aircraft downwards. In theory, the front two nacelles would control pitch by rotating up or down simultaneously while the back two nacelles would control roll by each nacelle tilting oppositely. Combined all nacelles would be capably of controlling yaw or by changing the thrust being generated on each side of the aircraft, a yaw moment could be generated. of course there are clear issues in the form of Cost, mechanical complexity, control of the aircraft in an engine out scenario, gyroscopic moments and control generally but purely from a flight mechanics perspective, what are the advantages or disadvantages of removing ailerons and using thrust vectoring to control the flight of such an aircraft. Currently, it is my belief is it would allow the use of highly complex airfoil geometries that would increase the efficiency of the aircraft in flight as airfoils would no longer be necessary and perhaps increase maneuverability of what i would imagine to be large aircraft but there is no drawbacks other than those previously mentioned however, would thrust vectoring produce less turning moments than ailerons? I look forward to any and all replies, thank you. <Q> There is one disadvantage: it makes control dependent on engines running. <S> This disadvantage effectively precludes using it on any aircraft carrying people. <S> Usual requirement for a critical system, which controls are, is that the probability of fatal failure must be estimated to be less than $10^{-9}$ per hour of operation. <S> Turbine engines themselves have, IIRC, risk of failure on order of $10^{-4}$ , so for independent failures you can get below $10^{-9}$ with double redundancy, but common causes—which means mainly various problems with fuel—are included as well <S> and the risk is not low enough. <S> And even triple redundancy is a lot. <A> It is my belief <S> is it would allow the use of highly complex airfoil geometries that would increase the efficiency of the aircraft. <S> The best airfoil is one that adaptively changes shape to meet current requirements (read: flaps or flaperons that run the entire length of the wing). <S> What would be the advantages of using thrust vectoring only for control of roll, pitch and yaw? <S> That's how the V-22 works. <S> During horizontal short field takeoffs, the engines are angled forward and upward and the flaps are fully deflected to generate maximum lift. <S> Pitch and roll control are provided by thrust vectoring and differential thrust (the V-22 has conventional swashplates). <S> Below is an image of a V-22 during takeoff. <S> ( source ) <A> More control of the aircraft. <S> The disadvantages: Everything else. <S> You mention increased efficiency, but I don't see how that would be possible. <S> The most efficient aircraft are those which generate lift over a large span. <S> This is because the air you move doesn't need to be accelerated as fast when you are moving large volumes of air at a time. <S> This why gliders for example have such long wing spans. <S> The problem with gliders however, is they need very long runways to take off and land. <S> To get the best of both worlds many aircraft use wings which change airfoils depending on what the aircraft is doing. <S> For example deploying flaps during takeoff. <S> In flight ailerons might cause a bit of parasitic drag, but it's certainly less than 4 rotating propellers pushing in different directions would be. <S> If you wanted to get even more lift out a standard wing to have shorter takeoff you could use flaperons. <S> Which are basically ailerons that extended the entire wing and are used for control and generating lift. <S> One aircraft I can think of which merges both worlds together is the V-22. <S> It has 2 rotating propellers which can provide differential thrust, and an airfoil with a solid flap built in to make takeoff as short/efficient as possible. <S> However outside of the specific military roles this aircraft provides, I don't see much use for it for the general public. <S> I you really need that kind of control helicopters are always available.
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There are simply no propulsion systems that would be as reliable. The advantages: Short/Vertical takeoff.
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Can a bird strike destroy the stealth capability of F-35? There is a video according to which a F-35 aircraft has been struck by a bird in Israel. This, allegedly, disabled its stealth capability. More than a year earlier, two storks allegedly damaged another F-35 and made "maintenance work" necessary. Can a bird that lives in Israel and surroundings actually make a F-35 lose its stealth abilities? <Q> The F-35 is a plane that relies on safety via stealth, rather than armor. <S> The F-35 fuselage can be dented much like any other plane. <S> The F-35 uses a variety of methods to reduce the its radar signature, most of which revolve around the "skin" of the fuselage - the way the fuselage is physically shaped is meant to reduce the reflection of radar, and there are various paint and material considerations as well. <S> When at any considerable speed, a bird strike will tear right into the fuselage. <S> Take for example the following picture of a bird strike on a separate military fighter. <S> When the fuselage is damaged in this way, the radar waves are no longer being strategically reflected or absorbed, and the aircraft becomes suddenly very visible on radar. <A> The answer is yes. <S> The damage done and to what extent the airplane’s <S> RCS was compromised depends on the type of bird that hit, the location of the hit, the speed at which the impact took place and the total damage done. <S> If this compromises the shape and external RAM coatings, The airplanes RCS will increase dramatically. <S> This can be repaired, though I don’t know if the Israelis as yet have the facilities to do so at this time. <S> That video strikes me more as conspiracies and speculation than reported fact. <S> I would take it with a grain of salt. <A> There have been numerous losses of military aircraft as a result of bird strikes, including multi-engined types. <S> If a bird can cause serious damage, this suggests that an intentional collision with a small UCAV weighing, say, 100kg would result in loss of the aircraft in most cases. <S> It used to be claimed that the B2 bomber had a radar signature that was similar to a large insect. <S> Taken literally, this would mean that if a large insect became stuck on the nose of the aircraft, it's radar signature would be doubled.
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Birdstrike can puncture holes in airframes, shatter canopies, damage engines and wreak all kinds of havoc.
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How is the effect of wind on arrival time handled? If a commercial plane encounters strong tailwinds, would the pilots set the autopilot for a fixed arrival time (if that is possible), or would it be ok to arrive way ahead of schedule? I imagine this could disturb airport operations, and that there are fuel economy considerations: if I was the airline, I would try to minimize fuel consumption. But if I were ATC, random arrival times could cause chaos. Passengers in turn would probably be happy to arrive as fast as possible. It seems like there are conflicting interests. <Q> It will depend on constraints at the arrival airport. <S> If there are no constraints, they will choose a speed that minimizes fuel burn, and arrive early if that's how it works out. <S> It's possible that the arrival airport may have constraints on arrival volume. <S> As you pointed out, for busier areas, if aircraft arrive earlier than expected, it could cause things to get backed up. <S> In that case ATC may have an aircraft adjust their speed or enter a hold in order to delay their arrival until capacity allows. <S> Slowing down early is more efficient than arriving too soon and having to fly a holding pattern. <S> In areas without radar coverage, such as oceanic crossings, aircraft may be required to hold a certain airspeed in order to maintain separation from aircraft ahead and behind. <S> In this case a pilot may not have much choice until they exit the oceanic airspace, and any adjustments would have to be made after that point. <S> ATC will do their best to ensure the safe and expeditious flow of traffic, but safety has to come first. <S> While a pilot can choose to not follow ATC instructions in the case of an emergency, and in the interest of safety pilots have some amount of discretion in declaring emergencies as they see necessary, doing so just to reduce cost or for convenience would not be acceptable and may attract some scrutiny . <S> It's also possible that there would be constraints on the ground at the arrival airport. <S> If the aircraft is scheduled to arrive at a certain gate at a certain time, and it arrives early, there may be another aircraft still occupying the gate, or support staff may not be ready to receive the aircraft. <S> This would require the pilots to coordinate with the airline. <S> If alternate arrangements can't be made, the airline might actually prefer the aircraft to be not arrive early. <S> They would probably prefer to sit on the ground, with the engines off if possible, as that burns much less fuel than doing the waiting in the air. <A> Given a strong tailwind and freedom by ATC, most pilots will aim for the most fuel efficient power setting, to reduce costs ; they are part of a business after all. <A> It depends... <S> If I was a miles per gallon tightwad and was flight planning for a certain mach # in order to get there in a certain time, and found myself in a high altitude jet stream with a crazy tailwind, I might decide to slow down closer to the "min drag" speed of my plane to improve the air miles per gallon, knowing I can still arrive at the planned time. <S> Otherwise, I would just take the early arrival as a bonus. <S> However, if I'm heading for a saturated-traffic airport like Chicago, and an unexpected tailwind is going to make me arrive 20 minutes before the arrival time expected by ATC from the flight plan filed (and where I may have a reservation time slot assigned), and that arrival is going to add too much to the incoming crowd, ATC will probably put me in a hold to delay my arrival, which I won't have any choice about unless I request a fuel-state priority or declare an emergency. <S> Better to be on the ground sitting on the ramp, with one engine shut down and one idling, as you sit for 15 minutes waiting for the gate you arrived early at to become free.
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One thing you can be certain of is that the airline itself will not on its own accord do anything to increase its fuel burn just to avoid arriving early; only if ATC forces it to.
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How can I know DME distance? When I fly 12000ft, how can I know a distance from DME station?Is there any formula to know or measure distance from DEM? <Q> If your radio has DME installed, then it is shown on the instruments <A> Just to be clear, when you are asked for your DME from a station or using a DME fix, what is being expected is that you use what you see as the distance in nautical miles on the DME readout of your instrumentation. <S> You're not expected to use your altitude to come up with the distance along the ground using trigonometry. <S> It's the slant distance <S> they're expecting you to report and use regardless of your altitude and the actual distance over the ground. <S> I lifted the image off a Google search for "images of dme instrumentation", and they got it from https://www.cfinotebook.net/graphics/avionics-and-instruments/distance-measuring-equipment/DME-Slant-Range-Distance.jpg <A> DME is a slant distance.
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If you are asking for a lateral distance, that could be done using simple trigonometry taking the slant distance and field elevation of the DME station, and aircraft altitude to compute an azimuth from the station, thence a lateral offset can be computed.
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Would there be a purpose for a set of compressors in an electric turbo fan? This is actually a two part question. Would there be a purpose to a compressor in an electric turbofan where there is no need for a combustion chamber, and if not, is there then a purpose for a bypass as well? Sorry if I'm unclear, as i am not an industry professional perhaps my wording may not be clear. What I mean to say is that in a regular turbofan engine there are compressors that push air into a combustion chamber with higher density (presumably to get more potential energy per volume of air) where fuel is introduced and ignited to create higher pressure/kinetic energy to run the turbines, which in turn move the front compressors and the fan. However, in an electrically driven fan, since there is no combustion happening, and the fan is driven by an electric motor, does the engine then need the compressors? Do they perform any benefit in a system that does not use combustion to create pressure? Then if not, is there any benefit to the bypass system in an electrically driven fan engine? Or does it make more sense to simply switch to a ducted fan system? <Q> No. <S> If there is no combustion chamber and no turbine, then you do not need a compressor. <S> Just drive a big ducted fan (or propellor, your choice) with your electric motor. <A> There won't be an electric turbofan as it doesn't make sense to make one. <S> A jet engine is designed to burn fuel and turn it into propulsion, compressors squash air so it can be mixed with fuel. <S> If you take the fuel away and replace it with an electric motor an engine would be designed along completely different principles. <A> Yes, if you want to go super sonic. <S> This effectively gives you the performance characteristics of a low-bypass turbofan or a turbojet: 1) low cross section and high thrust to cross section ratio (low supersonic drag) 2) achieving very high nozzle velocity by jetting the high pressure flow out of the nozzle (useful at high speed) 3) <S> Flow increases pressure but not velocity when moving through the engine, so that all stages operates in the subsonic region. <S> Important if your intake is not far from transonic when the airplane is supersonic. <S> 4) Poor economy. <S> In the perceivable future it's hard to imagine any jet engine not powered by a turbine (piston ICE, electric, nuclear, etc, any shaft engine except a turbine). <S> Especially the focus now on electric airplanes is to improve range, and both supersonic and jet kills the range, so practically the answer is still "No".
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The only purpose of the compressor is to provide high pressure air for the combustion chamber and turbine.
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Is the MD-11's third engine slightly nose up? From my visual inspection, the third engine (the engine on the horizontal stabilizer) is slightly "nose up", especially compared to the engines on the wing. That means, the front part of the engine is lifted slightly. Am I correct? If yes, what is the intention? <Q> Yes, there is a slight tilt to the engine. <S> Engines are heavy, so placing them on the tail shifts the center of mass towards the tail, which is not good for stability. <S> To counter this, aircraft with rear engines often tilt the engines slightly, so the thrust they produce can offset their own weight, helping with stability. <S> It's extremely slight though, as large angles can produce major pitch oscillations with power changes (something known as pitch coupling). <A> I believe it has a 4deg incline to align the exhaust with the drag from the fuselage. <S> It appears more because the inlet is higher than the engine. <S> http://drawingdatabase.com/mcdonnell-douglas-md-11/ <A> The third engine of the tri-jet is simply pushing the tail up as thrust is applied. <S> This is something very beneficial in the event of a power-on stall as it assists the elevator in lowering the nose. <S> Adding up thrust in the back to compensate for weight imbalance would have to be questioned from an engineering point of view, as failure of this engine would create a dangerous aft CG imbalance. <S> It is wise not to rely on thrust or trim to correct an out of saferange CG. <S> Better to move the wing back a bit, as long as it is still directionally stable.
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It may be for the same reason down thrust angle is commonly put into tractor engine mounts - to compensate for pitch up tendency of air craft as they accelerate from added thrust leading to increased velocity.
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What is the maximum angle between an airplane and runway centerline when touching down at a crab angle in a crosswind landing? What is the maximum angle between the airplane's heading to the runway when an airplane is being landing sideway due to crosswind? <Q> A B777 (as in your photo) would generally have a maximum crab angle of about 16 degrees when approaching and landing at the Maximum Demonstrated Crosswind Component of 38 knots. <S> A 38 knot crosswind is not limiting and can be exceeded provided you apply a sideslip or crab correction at touchdown. <S> It is however limiting if you plan to touchdown maintaining the crab. <S> E6B Heading, Ground Speed, And Wind Correction Angle <S> By using a sideslip or crab correction at touchdown, Airliners will sometimes approach and land when the wind exceeds the Maximum Demonstrated Crosswind Component. <S> If the crosswind component was 50 knots and the aircraft was had a lower approach speed (due to light weight), the crab angle during approach could be as much as 25 degrees. <A> Usually the aircraft's AFM limitations give a maximum crosswind component (a lateral vector derived from wind direction and speed you get from using a chart) with a statement that it is the maximum "demonstrated" component and is not considered limiting. <S> It's simply the maximum component that was able to be tested during cert testing. <S> For crosswind components beyond that, it's not "illegal" to land from an exceeding aircraft limitations standpoint, but airlines may designate the demonstrated maximum component from the AFM as a hard limit for crews to observe as a policy. <A> The answer varies according to the plane's design. <S> Some planes are constructed with landing gear so robust and flexible that significant crosswinds will not overstress them during a crabbed landing (Ercoupe). <S> Other planes are constructed with swiveling mains so the plane lands at a crab angle but the gear tracks straight down the runway (Lockheed C-5A). <A> No airplane touches down sideways, some may approach at and angle but generally the goal is to touch down with the airframe in line with the orientation of the runway. <S> What you see is a crabbed approach and the aircraft will straighten out prior to touching down. <S> As Greg notes in the comments this angle is defined (and variable per aircraft) by the crosswind component. <S> The maximum angle desired is 0 as anything above that will add side loads to the gear that are generally not a good thing. <S> As the FAA notes in their Airplane Flying Handbook ... <S> The crab method is executed by establishing a heading (crab) toward the wind with the wings level so that the airplane’s ground track remains aligned with the centerline of the runway. <S> This crab angle is maintained until just prior to touchdown, when the longitudinal axis of the airplane must be aligned with the runway to avoid sideward contact of the wheels with the runway . <S> Practically an aircraft can touch down a bit off the longitudinal axis and with proper control <S> you can straighten it out but its generally not great for the airframe or gear. <S> Poor longitudinal control in a tail wheel can also lead to ground looping. <S> The exception to this is the B52 which can actually touch down sideways although the gear is in line with the runway.
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There isn't a maximum crab angle (you aren't supposed to touch down crabbed to the extent you can prevent it) and there usually isn't a maximum crosswind component either on most airplanes as a "legal" limitation.
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Is a mode C transponder required underneath Class C airspace? FAR 91.215 states that a mode C transponder is required for... all aircraft in all airspace above the ceiling and within the lateral boundaries of a Class B or Class C airspace area designated for an airport upward to 10,000 feet MSL My flight instructor and I disagree on how this regulation is interpreted. He says that I need a transponder to fly underneath class C. I understand it to mean that I only need and transponder if I am both above and within the lateral boundaries (i.e. overflying the airspace). Which is the correct interpretation? <Q> You are correct. <S> In fact, if you read a little further in that reg, you'll see that is one of the places where aircraft built with no electrical system are allowed to fly at all! <A> The reg. <S> states that IN or ABOVE CLASS C airspace when class C IS active a MODEC transponder is required, if CLASS C is not active you are in CLASS E airspace and a transponder is NOT required below 10.000 ft MSL,Unless you are in the MODE C VEIL. <A> This is dependent on where you are and the specifics of the airspace and onboard equipment. <S> If your aircraft was certificated with an operative engine driven electrical system, you are allowed to fly under a Class C shelf without an operative transponder. <S> See §91.215(b)(4). <S> If your aircraft was not certificated with an operative engine-driven electrical system AND you are operating within the Mode C veil of an airport described in Part 91, Appendix D(1), you may conduct operations within the Mode C veil, provided they are conducted outside of the Class B and C airspace. <S> Below the ceiling of the class B or C airspace, or 10,000 ft MSL, whichever is higher. <S> See §91.215(b)(3).
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You do not need a transponder to operate under Class C airspace if there are no other overlapping airspace areas where a transponder is required.
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Why is this video of a G36 Bonanza taking off so scary? Why is this video of a G36 Bonanza so 'scary'? If they had clipped the top of the trees, would it really have brought the plane down? (And even if yes, it looks pretty survivable). <Q> Because those trees will kill them <S> If you look at this document regarding the Bonanza G36 performance <S> you will note that the lowest stall speed written is 61 kts. <S> 61 kts is 112 kph or 71 mph. <S> We can assume they were going a little bit faster than that but let us say 110 kph / 70 mph. <S> In that clip, they are just barely keeping airborne. <S> This means the aircraft is extremely sensitive to disruptions. <S> Any loss of power — even partial — or getting knocked back by a collision and thus losing a few knots or upsetting the aerodynamics of the aircraft, is very likely to send it crashing into the trees. <S> Going 110 kph / 70 mph into a tree is rarely survivable even in a car, and then you have to remember that cars these days are built to withstand crashes while at least keeping the occupants alive, but that assumes crashing into something wide, that distributes the forces over a wide area, and that gives way, like another car. <S> Trees fail that on both accounts. <S> A G36 does not even come close to any such structural integrity in case of a crash. <S> The cabin will crumple like figurative tin foil, sending the occupants smashing into the trunks of the trees, or throwing them clear of the aircraft only to then smack into other trees or the ground from several meters up and at a high speed. <S> And that is going to be fatal. <S> Hence, this is scary because if they clip a tree they are very likely to die . <A> They Trimmed the Margins to Zero <S> In this video, the aircraft takes off and flies a straight course through the trees and continues a shallow climb out. <S> To the uninitiated, this may appear innocuous, until one realizes that the aircraft was performing at it's maximum limits with near zero room for error. <S> The voice and narration of this video does a good job breaking down what happened in this scenario, to recap in writing: <S> The pilots appear to have calculated the takeoff performance, found it to be adequate and made their attempt. <S> Their calculations were likely correct, but sufficiently lacking in margin so as to excite those on board who were cognizant of the situation. <S> It is reasonable to assume that aircraft performance tables are generated under near ideal and non-threatening conditions. <S> It is also reasonble to assume that: A pilot who flies recreationally may not be able to squeeze every bit of rated performance out of their aircraft. <S> Mistakes can be made in the calculation of weight and balance which affect performance. <S> Conditions may change between the time calculations are made and time of takeoff. <S> Near the end of the commentary, the pilots can be heard verbalizing their learning experience. <S> I think the lessons of the experience are not lost on them. <S> Lessons of aircraft performance are somewhat frightening to me as an aspiring instructor. <S> Training usually occurs at one airport, often with a long runway, with one aircraft or type of aircraft and one loading scenario. <S> If the training is compressed into a few months, the student may not even be exposed to a significant range of weather conditions. <S> I intend to teach my students to be awake to the amount of runway they are using and load the aircraft in multiple configurations as part of the training. <S> I think many pilots have a moment of nervous surprise the first time they experience narrowing margins. <S> I would like it to be less of a surprise. <S> Learn from this video, and from this other one, which had a less fortunate ending: <A> What makes it scary is just how close they did come to an accident. <S> They attempted a takeoff using the performance calculations listed in the POH on a hot day at high field elevation. <S> That’s fine assuming EVERYTHING works out just like the book ie no errors in calculating performance, aircraft and engine in peak condition, field atmospherics, perfect short field takeoff technique, etc. <S> But as the video showed, they came damned close to clipping the tree tops on climbout. <S> The aircraft in question was a turbonormalized G36 departing from Mears Airport (3W5) in Concrete, Washington. <S> The small country airport is located in a river valley surrounded by mountains. <S> According to the pilot the performance calculations show that the aircraft could do it, and so he attempted to try it. <S> Fortunately he managed to weave his way through the trees at just under stall speed to get clear of obstacles and clean up and accelerate the aircraft out of the reverse side of the power curve. <S> The film is scary because it shows just how close he came to having a controlled flight into terrain or striking obstacles. <S> Mountainous terrain quite often has downdrafts coming through the valleys on the windward side. <S> Had he encountered one, he would have never made it. <S> The airport is built on a small flat land surrounded by rough terrain. <S> The likelihood of survival in a situation like that, particularly in a high-performance airplane like a bonanza climbing out at 80+ knots, is not great.
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Had a pilot collided with the treestops at the end of the runway, there was a good chance that he would have lost control and crashed.
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Why do we say certain things three times (e.g., "Mayday, Mayday, Mayday"), rather than two or four? Repetition is a key characteristic of communication in the control tower, cockpit, and control room. Some phrases, like "Mayday" get repeated. The speaker says the same thing three times. We know this is for redundancy. Why exactly three times ? Why not twice or four times? Is there research suggesting three is the most effective number, or is there a historical reason for the convention? <Q> Yep, the critical commands are repeated 3 times. <S> This ensures there is ABSOLUTELY zero doubt in anyone's mind (especially on a big crew airplane) of what needs to be done in a critical situation. <S> It also standardizes these criticalities across different aircraft and aircrew cultures. <S> "Bail out, bail out, bail out" "Eject, eject, eject" "Abort abort abort" " Pan-pan, pan-pan, pan-pan . <S> " <S> I was 27 years a USAF pilot, and this is how the training has worked for over 50 years. <S> I only saw these terms used 2-3 times, but it certainly gets your attention and amps up the sense of urgency. <S> A little history: back in the day of very poor radio communications, it was necessary to repeat to "get someone's attention" or in the event a single "mayday" <S> didn't come across when the transmit button was pressed. <A> The use of Mayday dates back to 1923 when it was first used because it sounded like the French word m'aider, which means “Help me." <S> In those early days of radio it was necessary to repeat things sometimes because of interference on the frequency from various potential sources. <S> The "rule of three" is rooted in research conducted in 1890 by Hermann Ebbinghaus, a German psychologist. <S> Ebbinghuas studied how many rehearsals were necessary for his test subjects to memorize a list of nonsense syllables. <S> He came up with three as the optimal number, and that became a rule of thumb in many other things, such as advertising. <S> Here's a cool video that adds information on Mayday and Pan Pan . <A> There are no instances in normal conversation where the same word is repeated three times consecutively. <S> In order to prevent a critical command or order from being issued or heard accidentally, a command is given three times in order to verify that it is being given intentionally. <S> Going to the moon? <S> “Launch! <S> Launch! <S> Launch!” <A> I assume it's for redundancy. <S> Assuming the voice signal is very noisy, the listener might hear two different things, the first and second time. <S> The third repetition can then be used to decide which of the two versions heard is more likely to be the correct one. <S> Majority voting with three signals is very common in redundant systems. <S> In computing it is called TMR (triple modular redundancy). <S> https://en.wikipedia.org/wiki/Triple_modular_redundancy <A> Because human brains are slow and easily distracted? <S> The first time you heard it - you started listening. <S> The second time you heard it - you started listening properly, because you know it's important <S> The third time confirmed you heard what you thought you heard? <S> This is just my unresearched perception of what's going on, and why we naturally settled on saying thing 3 times when it's imperative that it's heard properly.
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Procedure calls for the mayday distress signal to be said three times in a row so that it won't be mistaken for another word or phrase that sounds similar under noisy conditions.
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Why not make the touchdown zone of runways wider than the rest? Reasons: Save money by making the rest of the runway narrower Larger margin of error left and right Easier to turn around, if necessary And if the reason that it isn't done is merely for regulation/legal reasons: Is this something that would be practical if it were allowed? <Q> Because most runways already are as narrow as safely feasible. <S> Let us look at your question piece by piece: <S> Save money by making the rest of the runway narrower <S> You seem to be assuming we are currently deliberately wasting asphalt on making runways wider than needed, and could build them narrower. <S> As they say on Wikipedia: [citation needed]. <S> Larger margin of error left and right <S> The touchdown zone is the whole runway, as long as the aircraft in question can stop afterwards, so if you start down this alley you'll find it cheaper to complete the runway in the same width. <S> Easier to turn around, if necessary <S> This is already done by including turn pads, on top of the nominal width. <S> For an example, see: OGZ <A> <A> At least a few runways are divided by length. <S> For example, once at Boeing Field (BFI) four general aviation light aircraft were cleared to land approximately at once on two runways. <S> My VFR landing clearance was to land in the first half of runway 14R while another aircraft above and slightly ahead of me had to stay at 500 AGL <S> (? <S> I forget the exact number) until the threshold and then land on the second half. <S> The left runway had something similar occurring at about the same time. <S> Having irregular width runways doesn't help this much. <S> Also it is difficult to imagine that the non-ends would be graded any differently. <S> In the overall project of constructing a runway, it is highly likely that the land preparation, utilities, and grading are like 80% of the cost of the surface. <S> A forum exchange breakdown of a Canadian 7000 x 100 foot runway is: $ 250,000 <S> geotechnical analysis$ <S> 4,000,000 gravel (60 cm of 7.5 cm minus, 25 cm 1 cm minus) <S> $ 2,500,000 <S> labor and equipment rental$ <S> 100,000 quality testing (compaction, etc.) <S> $ 2,000,000 asphalt (15 cm)$ 200,000 lighting $ 10,000 <S> painted markings <S> ----------$ <S> 9,060,000 <S> total <S> Would making the shape narrower increase any of those costs? <S> Probably. <S> Certainly less materials should decrease the overall cost, and maybe labor could be economized. <S> For strong crosswind landings, I usually use all of whatever width there is!
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Because planes that landed towards the edge of the touch-down zone would run off the side of the runway when it narrowed.
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Can horizontal stabilizer trim be worked independently (each side)? I notice most jetliners have a big trim wheel on each side of the center console. This wheel is black with white stripes, and notably turns on its own via the autopilot. Two large trim wheels: And obviously, most jetliners have two horizontal stabilizers or stabilators. Can each side be trimmed independently of each other? That is, does each big wheel control one stabiliz/ator and can they be unlocked and operated in different directions if need be? <Q> No. <S> Theoretically you could have <S> the left and right stab move independently <S> so there is still some trim authority if one jams, but would be structurally way more complex and quite heavy, your trim authority would still be cut in half, and there isn't really a strong need to do that from a risk perspective. <S> There may be aircraft out there that are like that, but most moving stabs are single surfaces usually operated by a big electric jack screw. <S> The required redundancy is provided by redundant control channels for the trim system, dual drive motors for the screw jack that drives the stab, and a dual load path design in the acme thread and the trunnion (the "nut" part of the jack), and in the attachments that connect the trunnion to the stab and the actuator assembly to the structure. <S> The only single point of failure would be for the hinge of the stab itself to completely seize, and the risk of that is low enough that it doesn't need to be accounted for in the system architecture. <S> Two independent stab surfaces would require an attachment to the fuselage or fin that allows independent movement of each surface while cantilevered off the root structure, which would require a pretty heavy and complex center structure for not a lot of gain safety wise. <A> I don't know why one would want split stabilizer/stabilator control in a jet airliner. <S> Not having the same up/down input on both sides would make the plane want to rotate from the tail, fighting any inputs coming from the ailerons and/or wing spoilers. <A> One side moving to a position while the other side is floating ( following the air flow) won’t be harmful. <S> As an exemple on the A320, if one elevator is faulty and the other is active, the faulty one will be floating. <S> Similarly on the A320 if both elevators are faulty due to computers failures, both elevators will be centered (aligned with the THS), pitch is THS controlled in this case
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Splitting the stabilizer would be structurally dangerous if one side is controlled while the other is fixed.
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How much clearance is provided when taking off over a 50 foot obstacle? When performing a takeoff over a 50' obstacle, how much clearance is provided between the obstacle and the aircraft and where can that be found? <Q> Calculated figures for take-off distance required (TODR) are to only just clear a 50-foot obstacle at that distance (with gear down), and figures provided by aerodromes for take-off distance available (TODA) are the measured distance to the obstacle, with no extra clearance added. <S> If there's any uncertainty when they measure TODA, they'll give the most pessimistic value. <S> The obstacle may be further away than the given TODA but no closer. <S> Measuring distances is easy with modern equipment so it's likely to be an exact figure. <S> However, it's rare for the first obstacle to be exactly 50 feet high. <S> If the obstacle is (say) only 30 feet high, you get 20 feet of separation for free. <S> Be sure to apply the standard safety factor (e.g. 1.33) when comparing your calculated TODR with the published TODA, to ensure you get plenty of separation over the obstacle. <S> As StephenS points out, if there are any significant obstacles in your take-off path, it's good practice to go for a best-angle climb until you overfly them. <A> The answer is provided in FAR Part 23. <S> There is no conservatism involved. <S> § <S> 23.2115 Takeoff performance. <S> (b) For single engine airplanes and levels 1, 2, and 3 low-speed multiengine airplanes, takeoff performance includes the determination of ground roll and initial climb distance to 50 feet (15 meters) above the takeoff surface. <A> There is no specific clearance height since the takeoff distance, runway length, etc. will vary widely. <S> The point of calling out that scenario in training is to get pilots used to thinking about obstacles at all <S> and, when obstacles do exist, make it a habit to climb out at best angle until clear of said obstacles (even though that may be just a few seconds if only 50ft) rather than automatically climbing at best rate as they're used to.
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The distance provided is what the airplane can do.
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Would a flight consisting of solely first-class passengers be cancelled due to center-of-gravity issues? Consider any modern jetliner (narrow-body and widebody separately) in a standard 2 or 3 class configuration. If somehow only first-class or business-class passengers bought seats, would that plane be impossible to fly because all the weight is focused up front? And since they are premium-class they can't be moved aft for load-balancing. If this is (practically) impossible, then doesn't that suggest there is a minimum number of economy passengers required as "ballast" for every premium passenger? I suspect one answer might be that the flight wouldn't be profitable anyway with few-to-none economy seats sold, so it would be cancelled. But let's suppose in that case the aircraft needed to be flown anyway because it was required to be at the destination airport, profitably or not. Doesn't that suggest there is a maximum "premium-only" passenger count that would actually be less than the number of premium seats? I.e they would have to tell some premium passengers "sorry you're bumped, or you can go to economy" despite the plane being 80% empty? <Q> It is much more difficult to load a plane so that the center of gravity ends up being too far forward than too far aft. <S> Excessive weight forward can almost always be counteracted by increased trim on the stabilizer. <S> When small GA planes crash due to Balance, its almost always too much rear-weight, not too much forward-weight. <S> Especially in the case you describe, the pax probably have luggage, and the luggage can be loaded in the rear of the plane for balance. <A> Generalized statements like the above sometimes have exceptions, but I'd be surprised if that one did. <S> I worked a weight and balance for a 747-400F putting the equivalent of 72 pax at 200 lb each in the forward quarter of the airplane. <S> That moved the c.g. %mac from 30.8 to 22.4, still well aft of the zero fuel weight forward c.g. limit of 16.0. <S> Then I put in 200000 lb of fuel, 2000 for taxi <S> , 170000 burn. <S> The forward c.g. limits for the taxi envelope, takeoff envelope, and landing envelope were still not exceeded. <S> The moral of the story thus far is that passengers take up a lot of room, but they don't weigh much relatively speaking. <S> However, when I loaded 350000 lb of fuel, it put the taxi c.g. <S> at 10.9, just forward of its limit of 11.0, and the takeoff c.g. <S> at 10.8, just forward of its limit of 11.0. <S> I fixed the out of limits condition by putting in 50 lbs of baggage for each pax, splitting the weight between K48L and K48R, the two aftmost lower cargo ULD positions. <S> If you want to take a look at the test load with the 350000 lb of fuel but before adding in the bags, go to https://terryliittschwager.com/WB/index.php . <S> Once there and after dismissing the initial message window, select the SERVER Load at the top of the list. <S> It has a false date of 2222-01-08 to keep it at the top. <S> You can fix the out of limits condition by scrolling down to K48L and K48R and putting 1800 lb in each. <A> The passengers don't weigh enough to seriously affect the weight & balance, especially since there are usually less than 20 people in first class. <S> I was on a Pan Am flight soon before its demise, and there were maybe 10 people on the plane. <S> They invited everyone up to first class, after all the baggage had been loaded, so there was no compensating for the shifted passenger load.
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As has been noted in the previous answer and comments to date, you can compensate (if you need to) for a first class loaded with pax but with the rest of the cabin empty by putting the pax bags in the rear.
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Why didn’t the Captain of Cathay Pacific flight 780 shut down engine 1 and land with a more reasonable speed? In the approach phase, engine 1 of Cathay Pacific flight 780 got stuck at about 70% N1 and it forced the crew to do an overspeed landing (230knots). Why didn't they shut it off by turning the fuel pumps off? Is there a backup mechanism if the fuel valve fails like in this scenario? <Q> You can find the full incident report here and this topic is touched upon briefly, but in short they had little to no time to entertain any other options but a full speed landing. <S> It was not until the aircraft [was] on the final descent for landing that the Commander realised they could not reduce the thrust on the number 1 engine. <S> The speed was not controllable and from that point, there was no time for the crew to consider other strategy nor procedure to cope with such emergency situation. <S> and more in the conclusion section... <S> t. <S> At that stage, there was no time for the flight crew to consider other strategy nor procedure to cope with such emergency situation. <S> The flight crew concentrated on flying the aircraft for a safe landing. <S> First off, the engine was throwing errors throughout the flight and they were talking to the maintenance team at other points. <S> Ultimately, the proper steps were taken and everything was done by the book. <S> They were prepared for an engine-out landing. <S> When you have a runaway engine malfunction (or throttle stuck at full) shutting down prior to landing may not be the right decision if the running engine provides no immediate safety risk. <S> If you shut down a problematic engine in flight you run the serious risk of not being able to get it started again. <S> Considering that most airports have a bit (or a lot) of extra runway, EMAS systems and often land at the end of the runway, coming in overspeed and burning through your tires and brakes may be safer than cutting the engine and potentially falling short of the runway. <A> Engine #2 wasn't doing its job <S> either Had the situation just been engine #1 stuck at high thrust, with engine 2 normally controllable, than what you describe would be a reasonable response to the situation. <S> However, that was not the case with CX780 -- during approach, Engine #2 was stuck at 17% N1 (or rather below idle) and thus delivering effectively nil thrust. <S> As a result, the pilots dared not shut down engine #1 until they were safely stopped on the ground. <A> From the incident report section 1.1.4: a. <S> At 0519 hrs during the descent to a cleared level of FL230, ECAM messages “ENG 1 CTL SYS FAULT” and “ENG 2 STALL” were annunciated within a short period of time. <S> According to the Commander, a light “pop” sound was heard and some “ozone” and “burning” smell was detected shortly before the ECAM message “ENG 2 STALL” <S> Then later: e. <S> At 0530 hrs, when the aircraft was approximately 45 nm southeast from VHHH and was about to level off at 8,000 ft AMSL, ECAM message “ENG 1 STALL” was annunciated. <S> So now both engines are out, they started the APU and successfully managed to restart #1: h. <S> The crew moved the thrust levers to check the engine control but there was no direct response from the engines. <S> The No. 1 engine speed eventually increased to about 74% N1 with the No. 1 thrust lever in the CLB (climb) detent position. <S> The No. 2 engine speed remained at sub-idle about 17% N1, with the No. 2 t hrust lever at the IDLE position. <S> Engine 2 was out of action, producing no power, engine 1 had failed, but was temporarily working although they couldn't adjust power, if they'd shut that down too they'd have been gliding and probably would have crashed with total loss of life. <S> They didn't have the power to climb and had one shot at landing, so they made damn sure they got it on the runway, not a bad landing considering the circumstances. <S> On a humorous note, another example of pilot understatement: l. <S> At 0539 hrs, the Commander made another PA advising the passengers of having “small problem with the engines” with small vibrations and requesting them to remain seated and follow the directions from the cabin crew. <A> Aside from what Unrec. <S> and GdD point out, even if the other engine had been running perfectly... <S> A frequent problem with twin engine airplanes is shutting down the wrong engine . <S> Nobody ever expects or plans to shut down the wrong engine, but it happens anyway. <S> So a crew is very cautious to shutdown an engine that is working. <A> 1 <S> : Source: [...] <S> The aircraft then rolled left seven degrees and pitched down to -2.5 degrees at the second touchdown during which, the lower cowling of No. 1 engine contacted the runway surface. <S> Spoilers deployed automatically. <S> Both engine thrust reversers were selected by the Commander. <S> Only No. 1 engine thrust reverser was deployed successfully and ECAM message “ENG 2 REV FAULT” was annunciated. <S> Maximum manual braking was applied. ... <S> [ Accident report , page 26. <S> Engine #1 was the one that was stuck at 74% N 1 .]
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I could be wrong but reverse thrust from the running engine helped to stop the plane 1 as it was approaching at a great speed way over the recommended landing speed, so shutting the running engine off right at approach would have made the plane to overshoot the runway, making the situation worse.
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Why do carburetors tend to produce richer mixture at higher altitude? The pressure drop in the venturi is proportional to air density and the fuel is at ambient pressure in the float chamber, so I would expect the fuel flow to reduce proportionally with density, and that response to preserve the fuel-air ratio over changing altitude. But in practice that does not seem to be the case. Proper response to altitude requires additional modification that most carburetors don't have, so the pilot usually has to lean out the engine as they climb. What am I missing here? (Update) More specifically, I would expect that at the same RPM, the volume flow rate will be the same—because the engine pulls in its displacement per revolution. Now velocity in the venturi $v$ is just $$ v = \frac{\dot V}{A} $$ Where $\dot V$ is the volume flow rate and $A$ is the cross-section of the venturi. So it will also be the same independent of altitude. Since dynamic pressure $$ p_d = \frac 1 2 \rho v^2 $$ And that is also the pressure that pulls in the fuel (when the float chamber is open to ambient pressure). Substituting mass flow $$ \dot m = \rho v $$ $$ p_d = \dot m \frac 1 2 v $$ and as long as $v$ is mostly constant, $$ p_d \sim \dot m $$ This still leaves open the dependence of fuel flow on $p_d$ . If the relation is reasonably close to linear, it should mean the venturi mixes properly by mass. I can see a reason why higher pressure should cause less than linear increase in fuel flow, but not much why it should cause more than linear increase in fuel flow—but that is what the actual behaviour would need. Note: Did you notice the extra $v$ conspicuously missing from the last equation? That suggests the mixture should become richer with throttle opening—which is actually the reason there are extra fuel jets after the throttle that pull in extra fuel when the throttle is at idle and slightly above. It might also explan what is going on here, but would require explaining why the speed should increase when the density is lower. <Q> The simple reason is that high altitude changes the density of air, but not the density of fuel. <S> Most simple carburetors use a simple venturi design that mixes air and fuel by VOLUME. <S> But, the correct air/fuel mixture must be based on MASS, not Volume. <S> If the air/fuel Volume is correct at sea level, it will be too rich at altitude. <S> This is because a given volume of air will have less Mass at high altitude, while a given volume of fuel will have the same Mass at high altitude. <S> Aircraft carburetors have a mixture control to "lean" the volume of fuel to the volume of air, and are then able to maintain the correct air/fuel ratio at all altitudes. <A> Leaning is not done to counter carburetors that do not "preserve the fuel-air ratio over changing altitude". <S> The [operationally] ideal stoichiometry (air:fuel ratio) is not fixed, it depends on what is being sought. <S> Leaning is done because it provides better fuel consumption when less than full power is needed (see graph below), which coincides with cruise. <S> Rich mixtures also burn cooler, so leaning becomes practicable and easier on the engine in the colder air of the cruise altitudes. <A> It's not pressure that forces fuel into the venturi as much as the vacuum pressure sucking it out. <S> Fuel is pumped or gravity fed to the carb, but then it's metered into the bowl by the float. <S> Fuel sits in the bowl before getting pulled into the jets and then into the venturi. <S> Airplane engine carbs are generally tuned so at sea level they deliver slightly over the ideal ratio, this is done by restricting the fuel flow. <S> If it wasn't restricted the engine would run rich on the ground. <S> As density altitude increases the amount of air going through the venturi decreases, but the air still can hold more fuel so the mixture richens even though there's less pressure.
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There is air in the bowl, sure, and as that air pressure decreases with altitude there is a bit of a decrease in the pressure behind the fuel, however the part you may be missing is that air can mix with a much higher ratio of fuel than what is ideal for an engine.
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Why do heavy departures wait 5-10 minutes on the runway at ZRH? I'm frequently travelling to Zürich for business and I usually make my schedule so that I have at least an hour to do some planespotting and photographing at the ZRH airport. Whenever I came to the airport, the runway usage was the same: RWY14 for all the landings, RWY28 for almost all the takeoffs, while RWY16 was used by heavies for takeoffs (usually the flights to Asia or to the USA). I noticed that once a heavy aircraft lines up at RWY16, it waits for some 5-10 minutes before it starts rolling (although it is already way behind its scheduled departure time). The only possible explanation that I could think of was that its engines would cause severe turbulence for the airplanes which are landing at RWY14 and that it has to wait for a significant gap between the landings. Am I right? Or if not, does anyone know the real reason for these delays? <Q> The usual reason is, that departures from runway 16 are not allowed to climb straight ahead due to noise restrictions over downtown Zurich. <S> Instead they need to turn left, where they cross the departure path of runway 14. <S> So if there are arrivals on 14, no departures on 16 are cleared, as in the case of a go around on runway 14, its departure sector must remain free. <S> I've been watching planes stuck for half an hour at the line up 16 for that reason. <S> Imagine that waste of fuel... <S> ZRH's runway capacity, despite having 3 runways, is thus actually lower than for a parallel 2-runway setup (think about London Heathrow e.g.). <A> ( Airbus ) <S> An A380's jet blast at take-off affects 540 m behind the plane. <S> (The yellow contour is 16 m/s.) <S> There is enough space behind runway 16 . <S> In general (ZRH aside), there's an easy fix for jet blasts -- jet blast deflectors . <S> Today around 1:50 pm UTC, an Emirates A380 <S> (Dubai isn't affected by delays due to curfews so that removes one variable) departed right away after lining up. <S> It was preceded by a smaller jet from runway 28, which intersects 16: ( Flightradar24 ) <S> One possible explanation for the delays that you witness is waiting for runway 28 to be clear. <S> Flights bound to European airports are on tighter schedules due to airspace congestion, so it's possible they get priority. <S> Keep an eye on the activity of runway 28 on your next trip. <A> I don't know, but I have what I think is a reasonable guess. <S> First, if separation (wake turbulence mitigation) was the reason, then why would ATC block a perfectly servicable runway by having an aircraft line up and just sit there for upwards of 10 minutes? <S> It would make far more sense to have the aircraft taxi and hold short of the runway, than to line up and wait, until there is a likely large enough gap in the traffic. <S> Even if the first aircraft is holding short at the threshold of 16, unable to take off due to say separation concerns, it would still be possible to allow another aircraft to enter the runway from the next taxiway down, backtrack then line up, or to land on 16, if ATC wants to do so. <S> (I would argue that this is probably inappropriate for other reasons, but at least the takeoff scenario looks no more complex than would be a takeoff on 14.) <S> Second, notice that 10/28 and 16/34 intersect at about a third of the runway from one end. <S> (A third down the runway on 10 and 34, two thirds down the runway on 16 and 28.) <S> Even not considering winds, this would severely limit ATC's ability to safely use those two runways simultaneously, especially for heavier airplanes, as they would need to consider also the situation at the intersection in the case of a successful or a rejected takeoff or, in the case of a landing, an airplane either landing long or executing a missed approach. <S> All of these add complexity and risk. <S> The ATC mantra is safe, orderly, expedient, in that order . <S> Safety comes first, so anything that compromises safety in the name of expediency is going to be a no-go from the start. <S> If the airplane was "well behind" its scheduled departure time, yet just sits on the runway for a good ten minutes, my first guess would be that whatever caused the initial delay might be causing further delay before the pilots feel comfortable beginning their takeoff roll, or before ATC clears them to begin the takeoff roll. <S> As an aside, engines don't cause wake turbulence per se; wings providing significant lift do. <A> There are many reasons that departures from runway 16 might be delayed. <S> If an arrival to runway 14 has to go around, it would not have adequate separation from an aircraft taking off from runway 16. <S> There would need to be a adequate spacing in the arrivals to allow for a departure from runway 16. <S> Departures from runway 16 will interfere with departures from runway 28. <S> They may prefer to get some departures off of runway 28 at closer spacing rather than make them all wait for wake turbulence. <S> As ymb1's answer shows, if both aircraft are departing to the north/east, their paths will also cross in the air. <S> So if the controller decides to get the departures off of runway 28, they would need to wait for the last aircraft to get far enough east that there will be room for the departure from runway 16. <S> It's also possible that the aircraft have to wait for release so they can be integrated into the traffic flow. <S> If they are significantly late, they may have lost their original spot in the flow, and it could take time before another opening can be made for them. <S> This extends all the way to having a gate available at the arrival airport. <S> Any of these reasons could cause delays from departures from runway 16. <S> Air traffic control would have them line up and wait so they are ready to go as soon as conditions allow. <S> It sounds like heavy departures are the only use for the runway at the time, and if there's an emergency there are two other runways that ATC can use. <S> ATC knows the traffic flow, and that they can afford to have an aircraft sitting on runway 16 waiting for takeoff.
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In addition, smaller aircraft departing from runway 28 would have a required delay after a large aircraft departing from runway 16, due to wake turbulence.
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Do any airports have runways or taxiways that cross active rail lines at grade? Gibraltar has a runway which crosses an active road at grade (which, due to the peninsula’s geography and the resulting constraints on the airport’s location, happens to be the main road connecting Spain and Gibraltar, thus bringing traffic between the two to a halt whenever the runway is in use), which got me wondering: are there any airports with runways (or, for that matter, taxiways) which have grade crossings with active railroad lines? <Q> There is at least one: <S> In Gisborne, New Zealand, there is a freight rail line which crosses the south end of runway 14/32 at Gisborne Airport (GIS). <S> It appears to still be an active line for freight (logging) haulage , as well as occasional passenger excursions . <S> Image source: Google Maps , plus own annotation. <S> This article has some additional pictures and info as well. <A> There is another place too, Manakara East Madagascar. <S> Both train and airport are still active. <A> There’s at least another one (not an active crossing anymore though): <S> Wynyard Airport, on Tasmania's north-western coast, was quite unusual in that it was one of the few airports in the world to have a railway crossing on a runway. <S> See link. <S> Edit: <S> Further down my favourite search engine‘s results, there’s evidence that very question has been discussed elsewhere . <A> Not sure if Filton is still in use as Airbus industries no longer fly their Beluga Airbus from there. <S> As a train driver, i worked freight locos across the branch line. <S> We had a signal either side of the runway interlocked with a signal cabin.
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Their is a lightly used freight line crossing the runway at Filton airport, Bristol, UK.
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Does the movement of the magnetic poles affect aviation? Recently I read that Earth's magnetic pole moves quite significantly, several kilometers. Do these changes affect aviation, i.e. for pilots landing their airplanes? <Q> I don't think magnetic shifting affects the pilots directly, but it does force airports to re-number their runways because of the fact that runways derive their numbers from their magnetic headings. <S> Other than that <S> , I don't know of any direct effect this would have on the landing itself, as approaches rely on the ILS's radio signals or direct visual contact with the runway. <A> Not really. <S> Yes, there are changes, but they are small, regarding the size of earth. <S> So sometimes they have to renumber runway designations, as they roughly represent the magnetic runway heading. <S> And you get updated maps and airfield charts all the time, where the variation is adjusted - among all the other stuff, <S> that changes like frequencies, obstacles, noise abatement procedures etc. <S> If you live close to the poles, it might affect you harder, but luckily this regions are not that densely populated. <S> I'm from central Europe, here the variation changes about a half degree per year. <S> You don't actually recognize it, considering all the whisky-compasses used in planes are barely usable to hold a 5 degree heading... <S> Landings are mostly unaffected, as you either use ground based systems like ILS, satellite navigation or make a visual approach. <S> You should croscheck the runway designator with your actual heading to avoid landing in the wrong direction or on wrong runway. <S> But this is not affected by the change of the poles positions. <S> Ignoring a sometimes proposed complete pole flipover, at least... <A> The motion of the pole by a few kilometers sounds dramatic. <S> But given the size of the earth represents fairly small changes in the orientation of the magnetic field. <S> Away from the poles, these changes are much harder to detect. <S> Also, the changes that you mention are not sudden. <S> They're normally measured over years. <S> Lots of other things change in that period of time as well (like runway configurations, changes in obstructions, etc.) <S> So pilots are already used to having to update their information (like charts) periodically. <S> When necessary, the magnetic field information is updated on them. <S> This does mean that the name of a runway might differ from its magnetic orientation over time until it is renamed. <S> And of course, navigation by non-magnetic means (radio signals, GPS, etc.) are not affected.
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While the position of the pole does wander by a bit, this doesn't cause major problems for aviation for several reasons.
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Is 'bouncing' an airliner on landing in high winds a deliberate technique, or something always unexpected? Last week, 767 landing at Newark, high winds, a good deal of rocking in the last few minutes, some passengers quite distressed. The landing was harder and noisier than usual, and we immediately floated upwards, must have been a couple of seconds before we landed again. The question I have is - in these circumstances (high winds), would the pilots have been flying the landing with a little less flare than usual and anticipating the bounce as a way of shrugging off some speed / energy; or, is it something you never quite know if it's going to happen or not, and would rather didn't happen at all? <Q> Bouncing a landing is neither intentional nor desirable. <S> There are several reasons why a student pilot might bounce, but for a professional pilot, it's most likely related to wind gusts, which are a challenge no matter how much training and experience you have. <S> Gusts are by their nature unpredictable, and if one hits the plane right as it's touching down, it can suddenly lurch upward and/or downward, resulting in a bounce. <S> That's probably also why your plane was "rocking" before landing. <A> Bounces are bad news on airliners because you are becoming airborne again just as the lift dumpers pop out, which makes the second touchdown even more exciting and often leads to hard landing inspections, and in extreme cases broken gears. <S> The lift dump spoilers are supposed to limit bouncing tendency, but if you come down hard enough there is so much energy stored and released they don't come out fast enough or <S> they are ineffective initially when they do or on some airplanes they won't even be triggered until the nose wheel is down. <S> When you have a significant bounce on a jet you aren't supposed to try to save the landing. <S> It should be "go around - set thrust" and get out of there. <S> It's called a "Balked Landing" which is a go-around initiated in a low energy state close to the ground. <S> You MUST get the lift dumpers retracted, or prevent them from coming out, and setting go-around thrust will do that. <S> You may touch down again and probably will, but you are supposed to continue with the go around. <S> There was an Air Canada Jazz RJ that bounced on landing and they tried to save the landing, but the bounce was so high and the lift dumpers were out <S> so they collapsed one of the main gears on the second landing. <S> Like everything, there are nuances; <S> a little skip, maybe only one gear touched, maybe they feel a balked landing procedure is more dangerous in gusty crosswinds than just landing, so a lot of crews will try to save it. <S> So maybe this crew did a bad thing, maybe not. <S> Without a lot more details, hard to say. <A> Bouncing is far better than "pancaking" from 15 feet off the ground because you were going too slow. <S> The difference is only a few knots in airspeed, especially for light GA aircraft. <S> Landing in gusty or variable winds will never be a perfect science. <S> A light bounce only means the pilot erred on the side of caution, with plenty of runway to do it. <A> Usually bouncing is completely undesirable, because this will increase your landing distance quite significantly to the extend you might overrun the runway if you don’t go around.... <S> so better avoid it...
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The reason an aircraft "bounces" on touch down is that it is going too fast to "settle" on the runway.
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What vertical separation is required in a holding stack to avoid wake turbulence? Sometimes in my free time I play Endless ATC, a game where one acts as the approach and departure controller. In the game (as in real life) the controller is forced to put planes in a holding stack, separated vertically by 1000 feet. Is this vertical separation - 1000 feet - enough on its own to prevent one plane's wake turbulence from affecting the plane immediately below? Or is it possible that I've accidentally had planes fly in each other's wake turbulence? If so/if not, then what's the minimum vertical separation necessary to ensure one plane's wake turbulence doesn't affect the next plane in the holding stack? <Q> The minimum vertical separation in a holding stack is no different from the minimal vertical separation used elsewhere. <S> This is almost universally 1000 feet. <S> 2000 feet is also needed if a non-RVSM equipped aircraft (such as certain older military planes) is flying above FL290. <S> However, not many holding stacks grow to above FL290. <S> A point to consider is the fact that aircraft produce the most wake turbulence when they are flying slowly for landing . <S> So since 1000 feet is enough during approach, it should also be plenty in a holding stack. <S> There has been some evidence that 1000 feet of vertical separation may not be enough for certain, heavy aircraft types. <S> In 2017, a Challenger jet had an accident after passing 1000 feet below an Airbus A380 during cruise, presumably because the smaller business jet hit the wake turbulence from the A380. <S> See AVHerald for details. <S> However, this has not (yet) resulted in changed separation minima. <S> Also remember that wind can have a significant effect on the spread and dissipation of wake turbulence, so on days with a certain wind direction and velocity, the wake turbulence may survive longer than other days. <A> From some of the ATC feeds I've seen transcribed controllers seem to prefer 2000 feet separation. <S> Which makes sense if you consider that airplanes aren't going to hold on the exact altitude (which would then lead to violation of separation) and think about what can happen to airplanes in a holding stack. <S> Using 2000' separation also lets the controller move the entire stack down 1000' in a single series of commands instead of needing to wait until each aircraft has descended to its new altitude. <A> The minimum separation in a holding stack is still 1.000ft. <S> Given that wake turbulence vortices move with the wind direction, you would have to fly the holding pattern with a direct headwind or tailwind to hit one. <S> Or your speed difference between two aircraft in the same pattern by pure chance correlates to the wind speed and direction. <S> If you have enough space, you can surely work with 2.000ft, but 1.000ft will remain the minimum separation.
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But the answer to your question remains the same: the vertical separation to be applied in a holding stack (below FL290 and during RVSM) is 1000 feet. In countries where Reduced Vertical Separation Minima (RVSM) has not been implemented, 2000 feet of vertical separation is required above FL290. 1000 feet is not enough to prevent planes from "flying in each other's wake turbulence" as you say, but in most cases it should be enough to ensure that the wake turbulence has weakened enough to not pose any threat to the lower aircraft.
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Can a turbofan run without the fan to provide power without thrust? Is it possible for a turbofan jet - like on a 747 - to run without the fan, if for example you just want the thrust from the internal jet to use to heat up water, not to use as thrust? <Q> No , the fan is directly connected to the outer compressor and turbine (N1). <S> There is no direct connection to the inner compressor and turbine (N2), which could run independently, but there is no switch to somehow stop the N1 rotation in a 747 (and I am not sure, if it would run properly anyway). <S> Some turboprops (e.g. ATR-72) can run an engine without the propeller ( Hotel Mode , see <S> e.g. this question), which is connected to the engine via a gearbox. <S> While there are also geared turbofans, you cannot completely disconnect the gearbox from the core engine. <S> As the other answers have said, it is however possible to build a jet engine without a fan in the first place. <S> The Boeing 747 even has one in the tail: the Auxiliary Power Unit (APU), which will provide electricity and bleed air while the main engines are not running. <A> Yes, it is possible, in fact it is pretty common. <S> It is called a turboshaft engine or gas turbine. <S> You can find examples of their use in: APUs <S> An acronym for Auxiliary Power Units, these are probably the closest to what you have in mind, this is a jet engine, usually quite small, that is used to provide onboard power and sometimes hydraulic pressure. <S> You can often find these located in the tail cone of modern airliners, with the exhaust at the cusp of the cone. <S> Helicopter engines <S> Most helicopters worldwide are powered by this form of jet engine, optimized for mechanical output, since helicopters generally do not benefit from exhaust jets. <S> Otherwise it is very much a jet engine that drives a helicopter rotor (via multiple gearboxes to reduce rpm) instead of a fan. <S> Tank engines <S> Just like the helicopter version, although with different optimizations. <S> You can find these in the M1 Abrams and the T-80, among others. <S> Electrical power plants <S> The generation process at most modern gas-fired electrical plants involves a gas turbine that works like an upscaled turboshaft, although usually in combination with other systems . <A> Yes.
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A turbofan without the fan would be called a turboshaft engine .
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On the 737NG, after deployment of spoilers automatically after landing, do the spoilers automatically go back down? So, I was just wondering whether the spoilers on a 737-800, after automatic deployment when landing, will go back down automatically, or need manual input by pilots for the spoilers to go down. <Q> The spoilers on the 737 after auto deploy will re-stow automatically based on TLP (thrust lever position). <S> This is a function for a rejected landing which will automatically lower the boards & retract the levers for go around... <S> most pilots after taxi off the runway quickly advance the throttle to let the actuator reset the system in leu of pushing the lever forward (it has a clutch in the linkage to allow manual positioning as well) <A> It should depend on the aircraft. <S> In the EA-6B Prowler the spoilers deployed when 3 conditions were met: Switch armed, weight on wheels, and throttles at the idle stop. <S> (this presumes hydraulic pressure is available to actuate them...) <S> Adding any amount of power, even just enough to taxi, would cause them to retract if they were armed. <S> The post landing checklist called for the switch to be turned off, so they would then retract and not fluctuate up and down during taxi due to throttle movement. <S> I would imagine others work similar to this, but if you want a more detailed answer for a certain aircraft you will have to specify which particular one you are interested in. <A> To add to Michael's answer, on pretty much all modern airliners they retract automatically after completion of the landing and are disarmed until re-armed on a subsequent take-off. <S> There will also be some kind of manual override to manually disarm them. <S> It's the end of this timer cycle you are seeing when the spoilers come down as you are pulling onto the taxiway.
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There is usually a timer cycle of say 30 or 40 seconds after deployment, while still on the ground, at which point they retract and disarm.
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How to reverse course when there is no published course reversal? Coming from the SW on the RNAV RWY 15 KONO, how do I align myself with the final approach course? There is only one IAF and no published course reversal. Is it up to me how I get established inbound?[RNAV 15] <Q> If the approach doesn't contain a published course reversal (ie PT barb or Hold-In-Lieu), the approach must be flown straight in. <S> In this case, you will either get vectors-to-final or you will get cleared via one of the feeder routes. <A> It's a RNAV approach. <S> You just fly to PIYID waypoint and that's all. <S> I think all those reversals very useful when there was no RNAV <S> and there was no other reliable way to establish on the final approach course unless you had VOR's and NDB's not at the airport to assist with that. <S> Now it does not make sense. <S> Why to fly more miles if you can fly this approach as published directly. <S> There are 3 real life situations: <S> If you fly commercially you will have a flight plan that will end at PIYID. <S> If it is uncontrolled airport probably it will make sense to go directly to PIYID... or other waypoint. <A> "Approach, (callsign) request 3 mile offset to the west at CEYTA for alignment." <S> The offset you request will be what is necessary to execute a roughly 180 deg turn to the inbound course. <S> Keep it snug, but don't cheat yourself out of the space needed to make a comfortable turn in IMC with a little bit of wings level time before you hit the fix. <S> ATC knows you can't get there and pivot in place, and are usually very accommodating if it is clear what you are asking.
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If you just fly somewhere and ask tower for the approach you will get direct to PIYID.
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Why does the B-52 have such a tiny rudder? The B-52 (aka Stratofortress, aka Grey Lady, aka BUFF) has a minuscule rudder for an aircraft of its size and wing-mounted engine placement: Compare to, for instance, the rudder on a 747: The B-52’s rudder is so small that it can’t be used to decrab the aircraft during a crosswind landing, meaning that it had to be designed to stay crabbed throughout the landing roll, forcing the designers to use a fully-steerable dual-bicycle landing gear layout (plus wingtip outrigger gears that are there solely to keep it from tipping over) instead of the conventional tricycle arrangement. Why, then, did the B-52’s designers give it such a small rudder? One could argue that, because it has four engines on each side, rather than one or two or three, it doesn’t need a large rudder, because the thrust differential (and, thus, yawing moment) in the event of an engine failure would be minimal). However, if you look more closely, that argument doesn’t hold up, because the B-52’s eight engines are mounted in conjoined pods, two engines per pylon, which virtually guarantees that an engine failure will also take out the engine right next to it; 1 thus, one would expect that the design case for the B-52’s rudder would be a double engine failure of both engines on one pylon, rather than the improbable case of one engine failing and somehow managing to leave the one next to it completely intact. So why isn’t the B-52’s rudder bigger? 1 : For instance, the danger of cascading engine failures is one of the main reasons why no airliner designed after 1960 has ever used conjoined engine pods . <Q> There are two reasons and they date back to the early designs for the aircraft. <S> Keep in mind the tail is different now than when it was originally designed. <S> Boeing has originally planned for an all moving vertical stabilizer but engineers doubted its reliability and the systems to operate it simply would not fit in the tail at the time. <S> The engineers shortened everything to create a more stable situation as is noted in this passage: Concerning the rudder, the situation is much worse. <S> The B-52 rudder and elevator have an exceptionally narrow chord. <S> Most airplanes have at least a 25% chord, which allows sufficient power and effectiveness in both yaw and pitch during takeoff, landing, and asymmetric conditions. <S> The same is not true of the B-52 with its 10% chord rudder and elevator. <S> The chord was reduced because original designs of the aircraft had the tail exceeding critical Mach prior to the wing. <S> The chord of the tail was reduced to ensure that the wing reached critical Mach first.[15] <S> The original designers knew that the rudder was underpowered. <S> An aircraft the size of the B‑52 requires a massive rudder that does not exist. <S> This rudder is insufficient for the basic needs of the aircraft, let alone for asymmetric engine-out scenarios. <S> Original plans called for an all moving vertical tail, the first of its kind. <S> However, Boeing doubted the reliability of the hydraulic actuators necessary to achieve this. <S> Therefore, Boeing designed, built, and incorporated the yaw-adjustable cross-wind landing gear,[16] what is known to B‑52 aviators as ‘cross-wind crab.’ <S> This system allows the B-52 to operate during normal conditions of take-off and landing in crosswinds. <S> However, the true problem was asymmetry. <A> Several factors come into play: <S> Having 8 of them, asymmetric thrust after an engine failure - which is often the dimensioning case for the size of the vertical stabilizer - is not much of a problem. <S> Lateral control is primarily maintained by operation of spoilers . <S> Apparently , an all movable vertical tail was to be used but didn't make it because of doubts about the reliability of hydraulic actuators. <A> I have a vague recollection that the entire empennage was reduced in size due to the introduction of computer-control of stability and manoeuvrability. <S> The monitoring/ detection of and response to out-of datum attitudes meant that large control inputs were no longer required. <S> I think this lead to a weight saving in the order of several tons. <S> The concept had a fancy name- <S> something like Control Configured Vehicle. <S> If this is not totally correct- apologies; I'm recalling stuff from 50 years ago. <S> Not many large aircraft have direct physical connection between inputs and outputs, even considering hydraulic, pneumatic or electric servo actuation. <S> Pilots request a function and the computers rationalise and deliver the signals to the functions.
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More importantly the original designs had sufficiently larger control tabs but this lead to an elevators and a rudder that had a lower critical mach number than the wing (i.e. the empennage would stall first). The design was also too heavy for the tail structure to sustain.
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ATC calling out regional airlines in traffic advisories: phonetic or "aircraft paint" airline used? When ATC points out traffic that is a regional airline (e.g. Compass, Envoy, SkyWest, etc.), do they use the phonetic callsign of the airline, or do they use the callsign of the airline that they are operating as (how the plane is painted)? The plane that a regional airline flies might be painted differently, depending on which airline they are flying for. My thinking: 1) Pros of using the "aircraft paint": aircraft who are flying in VMC can spot each other more easily. 2) Pros of using the phonetic callsign: aircraft are on the same frequency in the same phase of flight, so they are more situationally aware if you use their phonetic callsign because they have probably already heard it in another transmission. <Q> The call-sign is not used – it's as useful as saying the tail number if it's a GA plane ;) <S> The information given to the pilot is in FAA <S> JO 7110.65 <S> – section 2-1-21. <S> TRAFFIC ADVISORIES. <S> Azimuth (o'clock position), or cardinal position (e.g., northeast) if moving rapidly Distance Direction and/or relative motion (e.g., southwest bound, converging) If known, type and altitude. <S> Example: ATC: <S> [You], traffic, 12 o'clock, 10 miles, opposite direction, Boeing 737, one thousand above. <S> A comment by @user71659 remarked that Cockpit Display of Traffic Information (CDTI) can be used to follow traffic, and hence a call-sign/tail number would be given. <S> This notice was cancelled in May of 2016 and was only to authorized users. <A> In addition to the answers already here, aircraft "paint" scheme is often called between multiple jets in order to differentiate if there are a few of them in close proximity (on the ground). <S> They don't have to be regional, either. " <S> Delta 1921, follow the United-colored Boeing 757 ahead and to your right. <S> " <S> Delta 1921 would then know they are not to follow the Fedex-colored 757 but the United colored one. <S> In the air, paint scheme is often used when pointing out traffic. <S> " <S> Traffic 9 o'clock and 5 miles, south bound a Delta-colored Boeing 717 descending out of 4 thousand, report that traffic in sight. <S> " <S> Both of these situations help differentiate between other traffic the pilots might see. <A> Depends on what you mean by “point out.” <S> A point-out, in an air traffic sense, is a technical term, meaning coordination between two controllers where one controllers traffic will entered another’s airspace but control will not be transferred. <S> In that case, call signs, positions and altitudes are used. <S> Calling airborne traffic to other pilots: direction, distance, direction of flight altitude and type of aircraft <S> On ground: all the above. <S> Paint job of the airline, type, location... <S> anything goes. <S> I’ve used call signs as well, as in “you’re number 20 for departure, following an opposite direction xxx, call sign is yyy. <A> They would use the aircraft's actual call sign, ie. <S> Endeavor or Brickyard. <S> This is because often they are looking for traffic several miles away, and unless it's an all-white British Airways A380, you probably won't be able to tell the color anyway. <A> In the air, they don't bother; if you're close enough to read the paint, you're probably dead. <S> They do give the type (if known) <S> so you have an idea of what size plane you're looking for, though. <S> On the ground, they definitely call the paint--when they know it. <S> This can cause confusion when a plane's paint doesn't match its callsign.
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More often, however, ATC will just call the type of aircraft (737, A330) and its bearing and distance rather than say the airline it flies for. For carriers known to use multiple paint schemes, they just call the type unless they can see the paint themselves from the tower.
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How do I keep a C172 straight on the centerline during landing/rollout? During rollout upon touching down, I'd often find myself veering off the runway centreline to the left. Every time I input rudder, I have this feeling that I am getting pulled out of the turn (while that is normal just like turning round a corner at high speeds in a car), and that the aircraft might just flip over. But you see I know my limitations of the car, and that it won't flip unless I yank the steering wheel. My instructors tell me to just simply keep my feet active, but it's the fear of too much input that will cause me to lose directional control of my aircraft. Upon touching with my main wheels, to maintain centreline, should I just really apply rudder without fear, even though I feel, and visually believe, that I am going to flip over? What correct techniques should one apply to keep the aircraft straight during the rollout? <Q> My guess here would be that you are not truly tracking the centerline of the runway on final or on roundout. <S> There’s an easy way to solve that when flying final: if the runway centerline appears pure vertical from your perspective in the airplane while stationary in your field of view, you are tracking the centerline. <S> If it has a slight angle to it or is translating, then you’re not totally on centerline. <S> The differences can be subtle, but can lead to flying a serpentine track toward the runway on final, during roundout, and during ground roll. <S> It can also result in a touchdown with a slight drift to it which indicates poor piloting technique. <S> Remember the more corrections you need to make to do this closer to the runway threshold, the more difficult the approach becomes and the more likely errors in technique will grow unchecked. <S> Once on a stable final approach, observe the runway centerline and judge if it is a vertical, straight line. <S> If so, you’re tracking straight down the centerline. <S> If not, use shallow, coordinated turns to align the airplane so. <S> This technique will also work when flying a crabbed final in crosswind conditions. <S> As you roundout, remember you are in slow flight at an increased AoA, so the propeller will tend to pull the airplane’s nose to the left. <S> Use additional right rudder to prevent this and track straight. <S> After touchdown, use quick precise feetwork for rudder inputs - think “happy feet happy feet happy feet” - to track centerline. <S> Also, if doing a crosswind landing, DON’T RELAX AILERON PRESSURE AFTER <S> TOUCHDOWN or the airplane will tend to veer off centerline rapidly. <A> The chance of flipping due to too much rudder is a very real concern, and perfectly valid. <S> Flipping can happen quite suddenly due to crosswinds, so you are right to be cautious. <S> My advice: <S> On landing, make sure you hold full back elevator. <S> Many students have a tendency to think they've landed the plane, and then let go of the aerodynamic surfaces like the elevator. <S> Pilots have a saying, "Fly the plane all the way to the gate!" <S> Never treat the plane like a car: <S> It is always "flying", even on the ground. <S> Holding the elevator full-back after landing takes a lot of pressure off the nose wheel, which makes steering easier and the plane more stable. <S> It also provides a lot of aerodynamic breaking (you have a large metal board sticking up into the wind) which slows the plane down a lot, in a stable, safe manner. <S> Also, don't necessarily try to stick to the centerline like glue. <S> If you try too hard, you may make drastic and sudden rudder changes which can flip the plane. <S> Instead, work on constantly adjusting towards the centerline. <S> If you're off too the left, use right rudder to aim back towards the centerline; not to hit the centerline immediately, but to adjust your course towards it over the next 2 seconds. <S> Then re-evaluate <S> , and adjust your course closer to the centerline again, never actually getting 100% on the line, but always moving closer and closer to it. <A> "Trikes" can flip forward left or right, which is why many people prefer "quads" (or having the single wheel in the rear). <S> However, with 2 main wheels down only rudder input will still swing the nose left or right with little danger of flipping. <S> When you are at landing speed and after mains touch down, the rudder is your friend, use it. <S> If you are slightly off center, continue controlling the aircraft as it slows down (this includes aileron inputs too) and keep "flying" the plane until it rolls to a complete stop. <S> But abrupt inputs or sharp swerves are not needed. <S> Easy does it, and differential braking is also helpful. <S> As you gain experience, you will feel more comfortable with its limits. <S> I would not rule out a taxiing lesson to test and refine your ground control techniques.
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To counter this, first, remember to get the final approach stabilized ie on centerline, on glidepath, and on airspeed as soon as possible after rolling out from the base to final turn. Remember, fly the airplane all the way through the landing, including the complete rollout. Very good advice to hold nose gear off while your are slowing down.
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Can we change light aircraft skin from aluminum to foam and fiberglass? Can we change the skin and wings of light aircraft from aluminum to foam and fiberglass composite in zenith ch 750 ? <Q> Yes. <S> No. <S> A little bit of yes, but overwhelmingly a NO. <S> Not because of any intrinsic properties of fiberglass, but simply because of the level of knowledge involved in redesigning an aircraft of this scale, and the fatal consequences of getting it wrong. <A> I would also check into the weight of the resulting structure. <S> Foam is disappointingly heavy and weak compared with cantilever balsa (and air spaces) construction. <S> Epoxy and fiberglass can be used to reinforce key areas such as wing roots. <S> But stressed skin over a metal framework is a time honored aircraft construction method. <S> Light carbon composites (technically including wood) are making inroads for future designsas they offer considerable strength that foam does not have and corrosion resistance <S> that metals lack. <S> Layers of different types of materials are famously used in Mongol bows and show how something like a wing could be built to be both strong and flexible. <S> Plywood is another example. <S> One thing about aluminum is the thinness of the sheets that fiberglass would have difficulty matching. <S> Weight savings is crucial in aircraft. <A> Possibly. <S> The right foam, the right resins, the right fiberglass or better fiber such as carbon fiber, layered and cross braced in the right way. <S> Done wrong, the least of your problems could be a wing that is heavier than the original. <S> It's not an automatic win, you can't just lay up an aluminum shape in fiberglass and call it a day. <S> It needs to be re-engineered based on all the properties of the new material. <S> Ask anyone who's re-decked a wood sun-deck with Trex! <S> Foam doesn't have any particular strength. <S> It is just a filler / shape-holder to hold the composite in the right shape while it cures. <S> It does help the composite stay where it belongs, but not much - that would depend on tensile or compressive strength of foam, and that is laughable, especially over years. <S> On something like a boat, which requires ballast to even hit its minimum desired weight, you just leave the foam or wood "forms" in place for life. <S> This is also done in house construction using foam molds for concrete; the foam is left in place for insulation value and ease of attaching siding/drywall. <S> Where weight matters, one effective strategy in composite fabrication is to use a foam that dissolves in a solvent that does not attack the composite, <S> e.g. The way gasoline will dissolve polystyrene but not some epoxy resins. <S> Then wash out the finished product in the solvent, causing the foam to dissolve. <S> In a modern industrial environment that would be recovered, separated and reused. <S> This sort of thing is already done at foam-cup plants, which use pentane as a blowing agent for polystyrene.
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It's possible to design and build an aircraft like the CH-750 with fiberglass instead of aluminum, but it's so far above the skill and qualifications of anyone who would ask the question on the web - as opposed to starting by modeling it in ANSYS - that the only realistic answer is "no".
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Is there a practical carbon-free jet fuel? For example, when I want to use a small turbojet or low bypass turbofan as both the APU and bleed air supplier for blown flaps, ailerons, elevators, (like the ShinMaywa US-2 amphibious plane) and rudders, (and hot wing deicing) there's a lot of internal ducting, and a large number of them are quite narrow, so having soot in them is like having thrombus in capillaries, so it's best that it doesn't contain so much as a single carbon atom in it. EDIT: OK, the small engine mentioned above is used as a gas generator , not for thrust , that's the main engines' job. For the sake of the argument, let us assume the main engines are not available for bleed air like in real-life large airliners because they are say mounted on gimbals in a tilt-turboprop. If this sounds artificial, how about having a complete set of blown surfaces so the tilt-turboprop can have control authorities in pitch, roll, and yaw at airspeed 0 knots , i.e. when it's taking off vertically. Being a tilt-turboprop means it can not have helicopter-like variable pitch propellers like the V22 Osprey and has to rely on external measures for attitude control. EDIT: It doesn't matter how weak the alternative fuel is as long as it can support the small jet engine's N1 RPM. It is only for the small engine. <Q> A different fuel is not necessary. <S> Even the most extreme experiment in diverted jet engine output, the Hunting H.126 did not divert its exhaust flow, it just tapped off compressed air. <S> Its takeoff speed was 52 km/h. <S> All aircraft need forward thrust, and with modern high-bypass turbofans you can get massive amounts of compressed air <S> that's more than enough for blowing any surface you want. <S> The BAe Harrier is a good example; the front nozzles of the Pegasus blow compressed air and match the thrust of the jet exhaust in the rear nozzles. <S> Fuels roughly fall into 3 categories: hydrocarbons (everything from methane to jet fuel and diesel). <S> They all contain carbon. <S> Some leave less soot than others: methane is relatively clean. <S> But it's a gas at room temperature, which makes it difficult to store (you need heavy high-pressure tanks). <S> Hydrogen. <S> Clean, but very difficult to store (needing even heavier high-pressure tanks than methane), and explosive in a wide range of circumstances. <S> Oddballs like hydrazine and hypergolics. <S> They're all nasty, toxic fuels that require specialized handling which make them unsuitable for civilian use. <S> Hypergolics are two-part fuels that spontaneously combust when in contact with their counterpart. <S> Some more details on hydrazine : <S> Hydrazine is highly toxic and dangerously unstable <S> Anyone involved in fueling a hydrazine-powered vehicle has to wear a full Hazmat suit. <S> That alone makes it difficult to use a hydrazine-powered aircraft on most airfields as it'd disrupt normal operations. <S> Hydrazine is also inefficient. <S> For jet fuel, you can pull the oxidizer from the surrounding air. <S> Hydrazine has a specific impulse of 220 s, while jet fuel has a specific impulse in the region of 350 s. <S> So you have to carry 350/220 <S> is 1.5 times more fuel to do the same work. <S> The exhaust products of hydrazine are extremely flammable (hydrogen). <S> You could burn that in a jet engine, which would significantly increase the specific impulse. <S> Hydrogen is a bit finicky, but hydrogen-fueled aircraft have been tested. <A> This question is based on a fundamental misunderstanding: by definition, NO bleed air system has combustion byproducts in it. <S> None. <S> Bleed air is tapped, or "bled", from the compressor section before fuel is introduced in the combustion chamber. <S> Which makes sense when considering that bleed air is generally used to run Air Conditioning packs... you don't really want exhaust fumes making their way into the pressurized cabin! <S> Any system that IS taking exhaust gasses & doing something with them, is by definition NOT a "bleed air" system. <S> The solution for the underlying question is similar to what's used in the 737 NG: an APU that burns standard, plentiful, reliable jet fuel, and which turns a generator, and a load compressor. <S> That compressor provides the bleed air to the jet's pneumatic systems, and plenty of it, and quite efficiently. <S> When you put a bleed air load on that APU, the EGT rises, but not because you're stealing cooling air, but because the APU is now burning more fuel to do more work. <S> Great system, works well. <S> But at the end of the day, combustion byproducts are always going to be undesirable to have in a pneumatic system, even if it's "only" a constant supply of water vapor. <S> No fuel will do what the OP envisions, but a different approach toward producing the high-pressure air will work just fine. <A> Many problems need to be solved there but seems less issues than with hydrazine. <S> Burning hydrogen produces just water, so the fuel should be carbon neutral. <S> However not all technologies used to obtain the hydrogen are carbon neutral. <S> Some burning metals like magnesium " slurry fuel" have been tried in about 1950, with the claims it may produce more thrust. <S> Looks like these works did not advance till the flyable prototype. <S> Electric aircraft can be carbon neutral, depending on how was the electricity obtained. <S> They also already fly, from as early as from 1917, but even as of 2019 mostly just as technology demonstrators. <S> Nuclear powered aircraft have been thought about in the past but none were built.
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To answer the question as stated in the header, hydrogen powered aircraft have been tried with some success (they fly since about 1989).
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Is it legal for pilots to transport or use marijuana? More and more states are legalizing the recreational use of marijuana. What does that mean for pilots? Is it legal for pilots to transport marijuana within states that have legalized it? Can pilots use marijuana recreationally if their state allows it? Are there implications for medicals? <Q> Is it legal for pilots to transport marijuana within states that have legalized it? <S> This <S> I'm not sure about. <S> I can't find any FAA regulation or guideline on it, so I think it would depend more on specific state statutes. <S> The problem would lie in going over state lines, obviously, but intra-state transport is unclear. <S> If you were ramp-checked by an FAA inspector and had marijuana on board, they would probably require you to get a drug test, and if failed (according to the next part of this question) you would lose your license (actually your medical, you would keep the license but be unable to use it). <S> Can pilots use marijuana recreationally if their state allows it? <S> Are there implications for medicals? <S> Negative. <S> AME's have marijuana on the DNF/DNI <S> (do not fly/do not issue) <S> list : <S> Controlled Substances <S> (Schedules I - V). <S> An open prescription for chronic or intermittent use of any drug or substance. <S> This includes medical marijuana, even if legally allowed or prescribed under state law. <S> While the guidance just says medical marijuana, I would suppose that it includes legal recreational marijuana as well. <S> Since you would be using a controlled substance on the DNF list, you would not be eligible for flying under the BasicMed either: <S> A diagnosis or medical history of substance dependence is disqualifying unless there is established clinical evidence, satisfactory to the Federal Air Surgeon, of recovery, including sustained total abstinence from the substance(s) for not less than the preceding 2 years. <S> A history of substance abuse within the preceding 2 years is disqualifying. <S> Substance includes alcohol and other drugs (i.e., PCP, sedatives and hypnotics, anxiolytics, marijuana , cocaine, opioids, amphetamines, hallucinogens, and other psychoactive drugs or chemicals) <S> Another way to look at it: Since pilots licenses are issued by a Federal authority, the Federal rules apply. <S> Marijuana is still a Schedule 1 substance (on the same level Federally with Heroin and LSD). <A> §91.19 Carriage of narcotic drugs, marihuana, and depressant or stimulant drugs or substances. <S> (a) Except as provided in paragraph (b) of this section, no person may operate a civil aircraft within the United States with knowledge that narcotic drugs, marihuana, and depressant or stimulant drugs or substances as defined in Federal or State statutes are carried in the aircraft. <S> (b) Paragraph (a) of this section does not apply to any carriage of narcotic drugs, marihuana, and depressant or stimulant drugs or substances authorized by or under any Federal or State statute or by any Federal or State agency. <S> This gets into the classic State versus Federal laws argument. <S> On one hand, if a "permissive" state agency finds it, they will not have any cause to report it. <S> If a non-permissive state agency finds it, they can take action, (fines and jail time) and in addition they can report it to the Feds. <S> If the Feds find it (e.g. customs inspection), or it was reported to them via a state agency; the Federal government's position is that this is a violation and can (and have) take steps to remove your licence. <A> AOPA has a nice article on it here according to them even if legal you cant transport it. <S> As a Schedule <S> I drug <S> , it is treated as illegal under the FARs regardless of whether recreational or medical use is permitted by state law. <S> Several laws and regulations address airman use, possession, and/or carriage of marijuana; the FAA further addresses it in its medical standards. <S> If you use it, even legally or accidentally ingest THC, and the FAA finds out they will pull your medical as was the case for this Colorado based pilot . <S> According to this article since the aircraft is in federal airspace its even illegal for passengers to transport it. <S> Can an aircraft passenger bring legalized marijuana along on a trip, say between two states that have approved legalization? <S> How do pilots, charter companies, and airlines deal with the issue? <S> The answer is fairly clear. <S> All public airports, airspace, and aircraft are governed by federal law and subject to federal law enforcement. <S> Therefore, a passenger may never legally fly on an aircraft with marijuana or products containing marijuana. <S> This is true even if you have a medical marijuana identification card and even if you are flying between two locations in the same state that legalizes the use. <S> By entering the airport, you are entering a federal jurisdiction and from a federal perspective, there is no exception.
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According to Federal laws, marijuana is illegal and your license (or medical) is not valid even if the state you are in allows it legally. So it may be legal to transport it, but you certainly can't be the one using it.
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Was the Space Shuttle aerodynamically neutral while piggybacking, or did the combination act like a giant biplane? Trying to investigate this question, I see that 'Ask the Captain' says: The weight of the shuttle is calculated like any payload. The 747 produces enough lift to fly and to carry the weight of the shuttle. In this respect it is no different than cargo carried inside the airplane. source But of course it is different, since cargo is generally carried inside an aircraft. There was a fairing for the Shuttle's engines for drag reduction, but I'm wondering if the wings of the Shuttle had some aerodynamic contribution to the lifting body, or whether that was all down to the 747's wings. source <Q> This podcast with one of the pilots answers just about every question on the shuttle carrier you could have <S> and it's worth a full listen. <S> But to cover the flight dynamics, I would skip to 50:33 minutes, where the pilot states (please note there is no official transcript of the podcast <S> and I typed this as I listened to it <S> , please see the official podcast for the actual verbiage, but this is close): Markus Voelter (Interviewer): <S> Let's talk a bit about the flying characteristics, did the wings of the shuttle add some extra lift or was it mounted with essentially 0 angle of attack? <S> Arthur C. “Ace” Beall (Pilot): <S> It was mounted with some angle of attack, you can see that as it's sitting. <S> At the speed we were flying, <S> the carrier itself was about 5 degrees nose high. <S> , it was always mounted the same way <S> so we had no basis of comparison. <S> It did, however, create a lot of drag and made the aircraft very top heavy so bank angles were limited. <S> So some lift was generated but at the speeds they were flying, other limitations came into play that were more of a concern. <S> It's also worth noting that when in transport no one was in the space shuttle and the control surfaces were not used in any way. <A> Interestingly enough, for the orbiter separation maneuver to work, the Shuttle would need to have a higher lift to weight ratio than the carrier 747. <S> Plenty of people were probably wringing their hands (including me) over the possibility of the orbiter hitting the V stabupon release, but when you see the video, it isn't even close. <S> This was accomplished with an lighter unloaded orbiter set at a higher angle of attack than the 747. <S> At adequate airspeed, it simply lifted away. <S> The higher AoA tolerance of the delta added to the safety of the manuever. <S> I would imagine they spoiled to lift of the 747 a little too. <A> The space shuttle's wings are small, but they still act like wings. <S> Their lift depends on the actual angle of attack. <S> The space shuttle cannot be neutral for all angles. <S> The engineers had a choice at which precise angle to mount the space shuttle on top of the carrying 747. <S> I would assume that the shuttle is rather close to neutral at cruising speed, to avoid excessive drag. <S> Then it will contribute to the lift when the combination has a larger angle of attack like during start and landing. <S> Yes, this is a huge biplane, but the "upper wings" are designed for returning from earth orbit and landing, not for contributing much lift to the 747 combination.
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The shuttle was creating lift, but how that affected it aerodynamically is hard to say
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Do all aircraft carry depleted uranium as counterweights? I was told that most aircraft had depleted uranium on board as counterweights. I have not seen one myself. Do all current modern aircraft have depleted uranium on board? <Q> From my research, it looks like about 0.1% of all aircraft carry depleted uranium counterweights. <S> The Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials (NUREG-1717) , on page 3–260, gives a table showing that 430 domestic United States aircraft were delivered with depleted uranium counterweights, and says that "A reasonable estimate is that 50% of these aircraft still contain DU counterweights. <S> " <S> So there are about 200 aircraft in the United States which contain depleted uranium counterweights. <S> Meanwhile, the FAA's " Air Traffic by the Numbers " publication says that there are over 200,000 aircraft in the United States currently. <A> That material is dangerous and expensive. <S> It is used only in special situations where the design requirements are stringent and heavily constrained. <S> For example, the C-5A cargo plane used depleted uranium (DU) to counterweight its main control surfaces. <A> No. <S> For example, recently-manufactured modern paragliders and hang gliders contain no uranium.
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So no, very few aircraft use depleted uranium counterweights.
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What is this object in the cockpit of an ultralight? This is a tool (probably) in on an ultralight airplane. Initially I guessed that it is a tilting meter (to level between right and left), but seems it is not as it just a vertical tube filled up with something like liquid. So, what is that and how does it work? <Q> It's an airspeed indicator for ultralights. <S> They are very sensitive and are good down to 10 MPH or less. <S> You'll also see them on hang gliders. <S> See here: https://www.aircraftspruce.com/catalog/inpages/hallwindmeter.php?clickkey=5468 <A> Here's one at Oshkosh 2018, with me blowing about 27 knots into it. <A> I don't see an ASI in the panel. <S> I am unable to confirm this guess, but it could be an airspeed indicator (ASI). <S> Google Dwyer Wind Speed Indicator. <S> The Dwyer is plastic, wider at the bottom, and works by having the wind push a ball up a tube that gets progressively wider near the top. <S> As the airflow pushes the ball up, more air can leak around the ball. <S> Where the ball reaches equilibrium indicates the speed. <S> Edit: <S> @John K beat me to it! <S> Thanks, John!
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It's indeed an airspeed indicator. The pitot inlet is at the bottom and the pitot air pushes a little red plastic disc up and down on a central rod, with a calibrated clearance between the edge of the disc and the walls of the tube.
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What are some Anti-icing solutions for small planes without an on-board system? When flying during the winter, is there anything I can do to increase my margin of safety, such as anti-icing fluid? I've heard of people spraying their aircraft with propylene glycol, but am curious to know if this will do anything to prevent ice after takeoff, especially without a thickener. <Q> There are many things you can do to mitigate the risk of icing, but most involve prevention via avoidance of icing conditions. <S> For example, getting a good weather brief, knowing where the freezing level is, staying away from visible moisture, and finally, recognition and taking evasive action. <S> Pre-flight deicing liquids are not intended to prevent ice accumulation in flight. <S> As you noted, they will just blow off in the slip stream. <S> If you are not instrument rated it gets easier, because if you stay out of clouds you won’t ice up. <S> But if you want to fly IFR in the winter, (or any time you could be IFR in the temperature zone where ice could form) <S> your best method of increasing the safety margin is to arm yourself with knowledge, practice operational risk management, and exercise sound judgment to keep yourself out of icing. <A> Generally light GA aircraft have limited anti ice system, usually limited to just pitot heat. <S> Some newer aircraft have been certified for flight into known icing (FIKI) and make use of chemical deicing methods like TKS “weeping wings” or electrically heated systems like the Kelly ThermaWing. <S> I will caution you that, even if your aircraft is FIKI certified, this is by no means an encouragement to actively enter or remain in icing conditions. <S> Rather it is just an additional layer of protection to allow a pilot to escape icing conditions. <S> GA planes are not transport category machines and do not offer that same level of ice protection that transport catergoy aircraft do. <S> Also note that these system do have their limits. <S> Operate outside of them and anti icing systems can be pretty hazardous, as this photo from an acquaintence of mine shows after having used a TKS system in an SR-22 in temps below that recommended for the system. <S> Even more tragic was this case from New Jersey where a pilot flew a FIKI certified TBM-850 into severe icing conditions and it cost him his life. <S> Again the systems can help if you get into a pinch and need additional time to escape, but the best course of action is to avoid icing conditions in the first place by doing a proper Preflight, setting personal minimums and strictly adhering to them.........and knowing when to say when. <A> In the end, for a VFR pilot, if there is any chance of running into rain in winter, it's all about the freezing level. <S> The criteria for use of heat anti-icing on jets for departure is visible moisture (which can be rain, snow or mist/cloud) below +5C OAT. <S> The pressure drop over the wings causes a small temperature reduction that eats into this margin, so it's actually less than +5C on top of the wings when you are flying in +5C free stream air, especially at lower speeds. <S> Due to the extreme danger of an icing encounter, this margin is probably not really enough for VFR <S> and it would be a good idea to use +10C/5000 ft below freezing level as a planning minimum if there is any risk of a rain encounter on a trip. <S> You would apply this safety margin such that when you check the weather and there is any chance of an encounter with rain, you want to make sure <S> the freezing level is 5000 ft above your planned minimum cruising level to give you at least that +10C safety margin for the entire route. <S> If you can't cruise at least 5000 ft below the freezing level, you have to be sure the air will be free of any visible moisture on your route. <S> A brief encounter with snow is not too bad, from an accumulation risk perspective, if the temperature is well below freezing and the snow is very light, but still best to avoid it because the effect on visibility is severe in anything more than very light snow <S> and it can change from light to not so light pretty fast <S> and it's quite frightening. <S> So stay away from snow. <A> Anti-icing fluid (a different mix of the same chemicals used for de-icing) applied to airliners is only effective at keeping ice from forming on the planes while taxiing and waiting to take off. <S> All that fluid will be blown off the plane by the time it rotates, though. <S> Once in the air, a plane must rely solely on its onboard de-/anti-icing systems until landing. <S> If a plane doesn't have the latter, thenthe former won't do anything of value. <S> If you can't stay out of icing conditions, then stay on the ground until they pass. <S> Period.
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Anti-icing fluids such as TKS are very effective, but the aircraft must be equipped with a system to properly disperse it to be certified for flight into known icing conditions.
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Can a 777X legally be ferried with one or both wingtips folded? The 777X family (777-8/-9/-10) features wingtips that fold up on the ground to let the aircraft fit in tight spaces. These have to be extended and locked in place before a revenue flight can take place, but can a 777X legally be ferried with one or both wingtips in the folded position - for instance, if one of the wingtips is jammed in the up position while at some backcountry airport that doesn't have maintenance facilities for a 777? For the purposes of this question, I'm assuming that it's physically possible to operate the aircraft. The non-folding part is the same length as the wing of a regular 777, so it would still be able to take off safely, just with considerable performance penalties compared to normal, wingtips-folded-down flight. Ferry flights for maintenance purposes can get away with a lot that wouldn't be allowed during line operations (for instance, multi-engine jetliners can be ferried with one engine - or, for quadjets, two - inoperative, and the 747-400 can be ferried with one of its winglets broken off). <Q> As Ron notes in the comments to another answer this is a perfect situation for a Ferry Permit/Special Flight Permit . <S> The FAA via your local FSDO can authorize aircraft to fly for the purpose of being fixed elsewhere via a ferry permit. <S> This question covers whats needed for that . <S> However in some cases it may be cheaper to fly (or drive) in a maintenance team and fix it on site. <S> Moving an empty 777 even short distances means burning quite a bit of Jet-A. <S> For the cost of the reposition it may just be cheaper to send a team (possibly in car) with the parts and tools they need to get the job done. <S> On a similar note its likely that the majority of fields big enough for a 777 to touch down have at least some form of maintenance on hand. <S> Again it may be cheaper for an airline to contract the job to a local shop than bother with the ferry logistics and costs. <S> Boeing also offers these services if you should need them in a pinch as part of the AOG services. <S> Our technical experts will provide on-site, comprehensive and integrated assistance to recover an airplane. <S> Our goal is to quickly and safely return airplanes to service, using methods and procedures that avoid costly secondary damage. <S> From what I can tell they will basically show up with parts and people to get the plane back in the air just about anywhere you can fly it out of. <A> Not with one tip up and one tip down, but it could be possible to ferry with BOTH tips folded, or removed, if Boeing has tested it. <S> A scenario might go like this: <S> Airline can't get one wing tip to unfold, or the tip gets physically damaged somehow, at a location where required equipment is unavailable. <S> Airline contacts <S> Boeing customer support (why not <S> ; they have nothing to lose by asking) and asks if they can get an authorization for a non-revenue ferry flight with both tips folded or removed. <S> There will be an internal discussion within the Boeing engineering/test/customer support organizations. <S> If not, it will probably end there and the airline will have to fly facilities to the airplane instead of the opposite. <S> If they have test documentation that demonstrates that airplane can be flown safely with the tips folded or removed, and the engineering heads who have to sign off have done a risk evaluation and are comfortable (and their relevant FAA counterparts are ok with it), it's theoretically possible that the FAA could issue a one-time ferry permit with a list of operating limitations (such as weight, altitude and speed restrictions). <S> My guess would be a flight with tips removed <S> is the most likely configuration to be authorized, if at all. <S> I'd be surprised if this sort of thing hasn't already been evaluated within Boeing and has been determined to be feasible or not feasible. <S> Only someone within the Boeing engineering organization would know. <A> I don’t believe Boeing authorizes flight of the 777x with a wing fold failure. <S> To be blunt, if you can afford a \$425 million airplane, you can afford a \$30,000-\$40,000 maintenance call where an AOG team is dispatched to the airport to repair the airplane and return it to service. <S> Even if Boeing approved flying the airplane with a wing fold failure, I doubt your Company SOPs, not to mention the insurance underwriters would approve.
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It'll depend on whether Boeing did any experimental flight testing to document the airplane's behavior with tips folded or removed.
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Would a propeller extracting air from a cylinder with holes in it be an ideal lift apparatus for a VTOL aircraft? I am wondering if enough lift can be created for a VTOL aircraft using a propeller that is extracting air from a cylinder which is closed at one end and has holes in the top half of the cylinder. Please reference the conceptual drawing below. I believe that when the propeller is turned on and air is flowing in through the holes and out of the cylinder, there will be low static pressure inside the cylinder and the cylinder will be lifted up by the ambient air pressure outside the cylinder pushing against the bottom half of the cylinder. Lift should occur because the bottom half of the cylinder has a larger surface area compared to surface area of the top half of the cylinder which has holes in it. So, would a propeller extracting air from a cylinder with holes in it be an ideal lift apparatus for a VTOL aircraft? <Q> Already invented by an Italian priest in the 17th century. <S> His version was simpler, having no engines or propellers... https://en.wikipedia.org/wiki/Francesco_Lana_de_Terzi <A> It seems very inefficient. <S> There's a couple of ways to see this. <S> From a momentum perspective, you're doing a a lot of work to accelerate the air downward. <S> But once it gets into the tube, it has to be accelerated upward again because it strikes the bottom. <S> You lose a lot of benefit here. <S> The other perspective is to look at where pressure at the boundary differs from atmospheric. <S> High pressure at the rear. <S> Only contributes to thrust, not lift. <S> Low pressure only above the holes. <S> Very small total area for the pressure to act on, creates a small amount of lift. <S> If you try to increase the area of the holes, the fan can no longer maintain the same low pressure inside. <S> It looks to me like just turning the fan to blow downward and eliminate the tube would be much better. <A> Your design will not work. <S> If you want to reproduce the concept of the Italian priest, then you want no holes in the top surface, because his concept was based on having a vacuum in the spheres (balloons) attached to his ship. <S> Since you have holes, you will not get much reduction in static pressure, because air will flow in trying to refill the tube. <S> And, as pointed out from a momentum perspective, it creates sideways thrust, not downwards thrust. <S> So, no, you will only get a very tiny bit of lift from a very small reduction in static pressure, but even with modern materials, you weight will be orders of magnitude higher. <A> No. <S> When that value is reached, air will start flowing around the propeller blades back into the cylinder. <S> The holes around the circumference will make that "small amount" even smaller: they leak more air into the cylinder. <S> For argument's sake, let's say your idea works. <S> You've closed off the holes in the top and developed a one-way propeller that does not allow air back into the cylinder. <S> You turn on the engine, and the propeller pulls the air pressure in the cylinder all the way to a vacuum. <S> Your cylinder now has to withstand 1 kg/cm 2 of force, i.e. it needs thick walls.
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A propeller can only reduce the air pressure in the cylinder by a small amount.
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Why would a C150 tachometer bounce so much that the needle fell off? On a long flight in a C150E, the tachometer started bouncing a little bit and the severity of the bouncing gradually increased until it was extreme: The tachometer was spinning in loops and making a loud screeching sound. The counter continues to increment. Here's a video of the tachometer in the last 10min of our flight . Just after that video, the needle fell off, but the screeching sound persists and the metal pin at the center still seems to be spinning: What could cause this? I understand the tach needle is not powered by any gear mechanism, but rather a small alternator that converts the angular velocity of the tachometer cable into a current which exerts a force on the needle. This should be highly reliable and I don't see how it could cause this behavior. <Q> Cessna 150s have a mechanical tachometer driven by a mechanical tach drive cable geared to the engine. <S> The tach needle is moved by sensing spinning magnets driven by the tach cable. <S> They do wear out over time and yours has reached the end of its life. <A> Myself I wouldn't be surprised at all to see 54 year old (from 1965) mechanical tachometer with 5000 hours on it starting to break down from all that age and vibration. <S> You can get a new TSO compliant replacement unit for as little as 250 bucks... <S> https://www.aircraftspruce.com/catalog/inpages/mech_tachs.php <S> ... <S> so the broken one in the plane is likely headed for the trash bin. <S> You'd be nuts to get it overhauled unless you can get someone to do it for that price or less. <A> It appears like you have never disassembled a tachometer, now or as a kid. <S> ;-) <S> These old type meters consists of two disks near each other. <S> One is driven to rotate by the cable coming in from the engine (or weels, if measuring the speed of a driving vehicle). <S> The other disk is connected to the needle, and is spring-loaded, so it can't rotate freely. <S> The rotating disk tries to drag the needle-disk along with it, because of magnesizm and currents induced (the actual details are not important, it could be air or a liquid). <S> What matters is that the amount the needle-disk can turn before the force of the spring is equal to the force from the turning wheel, this force is proportional to the speed of the disk. <S> The faster the wheel turn, the further the needle goes. <S> If one of the disks gets bent, or some debris, rust, dirt, bugs gets between the disks, you get the mechanical scratching noise. <S> In this case the needle-disk can start rotating at the same speed as the incoming disk, the spring breaks, and the needle will hit the stop pin from the other side, and will probably break off. <S> So it is "just" opening it, clean out the debris, and fixing a new spring and put the needle back on. <S> I don't have a clue if it is cheaper and at all possible to either fix or replace it, giving that a repaired flight instrument have to be certified, I understand. <S> Also, as the digit drums turned as usual shows, there is nothing wrong with the cable or the drive on the engine. <S> EDIT: If I imagine the worst case, the inside of the cable could be too long, causing the rotating disk to be pressed inwards, ruining the bearing so the two disks touch each other. <S> Or a sealing might have gone bad in the engine end, causing oil to meander inside the cable into the meter. <S> Or the bearings in the meter have finally worn out after many years of use. <A> This exact chain of symptoms happened to me on an automotive speedo - wobble, screech, increaing to extreme wobble, needle falling off, odo still working... exacerbated by low temperature in my case. <S> This is due to old lubricant not having the correct viscosity due to hardening up from age. <S> It was like this for many hours. <S> I put a drop of oil in the right place, and it was fully cured and the repair held for over a year so far. <S> The needle snapped back on, but it took some iterative testing to get it to point correctly. <S> So I expect your unit should be very repairable. <S> Of course, being aviation, this work must be done by someone certified. <S> The crux of the work would be comparable to what I did, but with proper testing and formalities. <A> It might be fixed temporarily by disconnecting the tach drive shaft from the tach head, removing the drive shaft, lubing it, and forcing some oil or grease down the shaft. <S> Or you could replace the entire drive cable assembly. <S> Please note that this level of maintenance is not allowed to be done in the United States by the pilot/owner as preventative maintenance by 14 CFR Section 43. <S> Legally you will need a sign-off by a repairman holding an Airframe and Powerplant license, aka an A&P. <A> Most C-150's had a Stewart Warner tachometer. <S> They are considered disposable because they are assembled by crimping the front bezel on to the case. <S> Also neither an A+P or an IA can work on an instrument. <S> This is a job for a repair station with the correct rating. <S> If you can find such a repair station, they will laugh at you. <S> If you buy a high enough quality tach you might be able to get an instrument shop to paint the markings on the face, otherwise you will have to put them on the glass. <S> Not as nice, <S> but either way you must have both the tachometer and the proper markings.
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The most likely cause of this problem is a lack of lubrication in the drive shaft for the tachometer.
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How is one's hypoxia resistance affected by the time of day? I am doing my PPL course in the Czech Republic and here they have the following question in tests: when during a day is the resistance of a human organism to hypoxia the best? There are 3 possible answers: 3 am 12 am 5 pm What is the correct answer and why? Is a human's ability to resist hypoxia connected somehow with the time of day? FAA book doesn't have a word about it. <Q> As noted by others here, PPL course questions might not be designed according to pure deductive or inductive reasoning. <S> My approach would have been the following: <S> Medical-related aviation questions tend to base their background on "old" studies, so let's have a look at Van Liere, E. J. (1964). <S> Resistance to Hypoxia. <S> Archives of Internal Medicine, 113(3), 418. <S> : <S> As a corollary, it would be anticipated that if the metabolic rate of an animal were elevated, the ability to withstand hypoxia would be decreased. <S> Zarrowetal in 1951 demonstrated that hyperthyroid states decrease tolerance to hypoxia. <S> The thyroid-stimulating hormone (TSH), thyroxin, and dinitrophenol all decrease hypoxic resistance. <S> TSH has a circadian rhythm (24 hour cycle) and levels peak between midnight and 6am (refer to https://medicalsciences.stackexchange.com/a/4034/15791 ). <S> Therefore, 3am and 12am are not an option, which leaves us with 5pm . <S> I'm aware that you stated that the correct answer is 3am, and I'll definitely check back with my medical colleagues on that, but the question in itself is clearly not well-defined within the visible context on this platform. <S> As others mentioned, one measure of gauging the depression of cellular oxidation is metabolic rate, for which in 2014 according to Examining Variations of Resting Metabolic Rate of Adults: <S> A Public Health Perspective <S> no single value for RMR is appropriate for all adults. <S> Last <S> but not least, if we talk about hypobaric hypoxia, conclusions change again. <A> It depends upon what you mean by hypoxia resistance. <S> Keep in mind you may have to take into account hypoxia’s effects on various organs and organ systems of the body and the effects their impairment at different hours. <S> I’m not going to give away an answer for a test, but that is an additional clue for you to go on. <S> Good luck. <A> Half of the challenge behind piloting exams is understanding what the question is asking. <S> I think this is one example of many poorly-worded questions. <S> AFAIK hypoxia doesn't care what time of day it is, it's all about absorbing oxygen. <S> However, some of the symptoms of hypoxia include reduced colour and night vision, which is bad news for night flight. <S> If the question doesn't make sense, look at the answers for clues. <S> Out of the 3 options here, 2 of them are very similar - times where it is nighttime year round, and one where it is daylight (varying with latitude and season of course). <S> So the exam is asking you to choose between day and night, essentially.
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The symptoms of hypoxia are more abundant at night, so I think you have your answer there.
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What are some drawbacks to having a wingtip propeller on an aircraft? I was reading about aircraft concepts that involved wingtip propeller design and was wondering what the drawbacks of such a technology would be. I could not access the full paper but came across this: https://arc.aiaa.org/doi/pdf/10.2514/3.44076 For me, one of my concerns is that if the propeller fails, feathering would be very difficult on the wingtip prop. I am also trying to decide on optimal placement for aircraft propellers in general. Would the drawbacks from having a wingtip propeller outweigh the benefits in high-lift generation and drag reduction? <Q> Feathering isn't really an issue, if you can feather a prop on an engine further inboard you can do it on the tip too. <S> There are 3 major drawbacks that come to mind: <S> The wing structure has to be stronger: engines are heavy, <S> the further out they are the beefier the structure has to be to hold them. <S> Stronger wings mean more weight and possibly a thicker cross section. <S> Neither are good traits in a wing Decreased roll rate: the farther the engines are the greater the moment arm and the slower your roll rate will be. <S> Think about skaters spinning around, the farther their arms from their body <S> the slower they spin. <S> The same principle is at work here, so you need bigger ailerons to give you maneuverability, so more weight, cost and complexity Safety in a single engine failure scenario: engines on the wingtips will cause more yaw in a single engine failure than engines further in board, so you'll need a bigger rudder to counteract it. <S> A bigger rudder means more weight and cost, and there are also limits - eventually you will get to the point you can't counteract the force effectively and an engine failure will cause a loss of control. <S> Yaw onset will be faster as well, giving a pilot less time to react, and there's nothing you can do about that; a bigger rudder doesn't help with reaction time. <S> Mechanical cross-connections could be used to share power across the wing in the case of a single engine failure, like the V-22 Osprey, Chinook helicopter, however these increase weight, cost and complexity. <S> Also, these systems aren't perfect, a single engine failure is still a possibility <A> Moving the thrust (and additional weight) to the wingtips creates more drawbacks than benefits. <S> Yaw - because of the increased moment of inertia (compared to having the engines be closer to the fuselage - the center line of the mass), it would be harder to initiate yaw changes as well as harder to stop or reverse them. <S> Left <S> /right thrust differentials could be used, and that would certainly increase yaw change rate, but then you have to consider the time cost of changing the force of each engine quickly. <S> And it becomes a very serious problem if you have a failure on one side, leaving you with only one wingtip generating all of the thrust. <S> Depending on the geometry of the aircraft and the size of the vertical stabilizer, it might not even be possible to counter the yaw force generated by the one engine producing enough thrust to keep the aircraft flying. <S> Roll - Similar to the yaw problem, the roll rate would be reduced the further the weights were moved away from the center line. <S> The <S> V-22 Osprey is an example of this design. <S> The wings are kept short to minimize the increase to moment of inertia, but the operational requirements of the vehicle (VTOL) required it to have large propellers (rotors), so the wings had to be long enough to keep the prop tips from hitting the fuselage. <S> Additionally, vibration and external (turbulence) effects on the wing structures would have to be considered. <S> Even in normal operating conditions, the wings would be subject to increased vibrations that could create structure failures in some complex compound wave situations. <S> Aircraft designers already deal with this and model these scenarios, but the complexity increases (I suspect exponentially) as the vibrational force is moved further toward the wingtip. <A> Another non-flying attribute that having a wingtip-mounted propeller can drive is landing gear length. <S> Since there are minimum clearance distances for propeller tip to ground during taxiing, and the wings may sag or dip during a turn <S> while taxiing, you may end up having to change your gear length (which can cause other issues in turn). <A> Wrapup of smaller things: <S> This could affect the minimum runway width required. <S> Wings will pass over grass okay, but props/engines could risk blowing dirt/dust/plants about and inhaling them causing FOD. <S> Any obstruction beside the runway could have consequences. <S> Slight increase in fire risk from any sparks from the engine because the spark might drop into shelter rather than dropping onto the hard tarmac of the runway. <S> Increased risk to first responders in the event of an incident/accident because the moving parts may force crash tenders to stand back a bit further slowing the quench time of fire. <S> Engines over grass/soft ground could make landings and take offs slightly quieter as a benefit. <S> I'm unsure if the passengers would find it quieter or louder. <A> Any pilot who has flown long enough has had landings where wingtips came quite close to the ground. <S> In fact in a cross wind landing you should have your wing on the wind side a bit lower than the other wing, which will be in partial shadow from the fuselage. <S> With wingtip propellers now you have less clearance for surprise gusts but more importantly the consequences are far worse. <S> A second disadvantage is collisions on the ground. <S> Wingtip scrapes are relatively common in all sizes of aircraft used by all types of operators. <S> They are nearly always inconsequential. <S> With a wingtip propeller these incidents would cause a lot more damage to both craft and are more likely to cause injury due to flying debris. <S> And of course as others have mentioned, loss of a motor implies that the center of thrust will be very far from the center of mass and aerodynamic center of the aircraft. <S> On takeoff particularly this is not what you want. <S> It is hard enough to manage with regular twins, which have the engines as far inboard as possible. <S> It's just a bad idea.
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To me a showstopper disadvantage of wingtip propellers is that they are potentially disastrous in crosswind or landings, or landings with significant turbulence. You could damage a prop and suddenly have asymmetrical thrust at the worst possible time.
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What is Density Altitude? I'm trying to get a deep understanding of the term: Density Altitude. So I have read the explanations in my instruction book, and online articles. One source explained it differently then the other which confused me. Wikipedia defines Density Altitude as: The density altitude is the altitude relative to standard atmospheric conditions at which the air density would be equal to the indicated air density at the place of observation. In other words, the density altitude is the air density given as a height above mean sea level..". https://en.wikipedia.org/wiki/Density_altitude So if I would believe Wikipedia then I could look at the ISA table to find the altitude by using the pressure. Here is an ISA table: My instruction book (Aerodynamica, prestatieleer en vliegtuigtechniek by Bas Vrijhof on page 112, written in Dutch) claims this: in de ISA is de dichtheidshoogte altijd gelijk aan de drukhoogte Translated to English: in the ISA the density altitude is equal to the pressure altitude. So, let's say I'm flying in an aircraft, the pressure is "22.22 Hg", and the outside air temperature is -0.9°C. The altitude in the ISA would be 8000 ft. The Density Altitude would also be 8000 ft. Skybrary defines Density Altitude as: Density altitude is pressure altitude corrected for temperature. Link: https://www.skybrary.aero/index.php/Density_Altitude This explanation contradicts with the Wikipedia explanation: the air density would be equal to the indicated air density at the place of observation On another wikipedia article I found this: De relatie tussen temperatuur, hoogte en luchtdichtheid kan worden uitgedrukt in density altitude. Translated to English: The relationship between temperature, altitude and air density can be represented as density altitude. Link: https://nl.wikipedia.org/wiki/Opstijgen#Benodigde_snelheid So in short, each source explains Density Altitude in their own manner, some contradict the other which confuse me. So my question is: What is Density Altitude? <Q> The concept of 'density altitude' is kind of like the concept of 'wind chill'. <S> Stick with me here <S> , I'm going somewhere with this. <S> Cold weather is dangerous for the human body, and wind (because of increased heat loss on human skin) makes it worse. <S> But how much worse? <S> Is it worse to be outside in -10C temperatures with a 20 knot wind, or -15C temperatures with a 12 knot wind? <S> The concept of 'wind chill' resolves those two values into a single easy number. <S> Density altitude works the same way. <S> It's difficult and tedious to compare and contrast how an airplane will perform on a 25C day with a pressure of 29.80 at an elevation of 600 MSL, versus a 20C day with a pressure of 30.17 at an elevation of 1250 MSL. <S> We need a way to mash all of these variables into one easy-to-use number. <S> That number is density altitude. <S> So just as I can say "The wind chill is -10C" and it doesn't matter whether it's warm but windy or cold and calm <S> , I can say "The density altitude is 2,000" and everyone will have the same idea of the expected performance of the airplane, no matter what combination of factors led to that result. <S> Once you start thinking of (and using!) <S> density altitude as a simplification tool , its value becomes a lot more obvious. <A> Try this article https://www.aopa.org/training-and-safety/active-pilots/safety-and-technique/weather/density-altitude <S> As a pilot, we like higher Pressure and Cold Temperatures - it makes the air denser so the engine can create more horsepower. <S> High Pressure systems, where the barometer reads above 29.92, and cold air, where the temperature is below 59F (I'm in the US) mean the aircraft will get off the ground sooner and climb better. <S> So - Winter! <S> Ideal flying time from a performance perspective. <S> Summer, we may see the same increased barometer reading, but the higher temperature means the air is less dense (heat makes the air expand), so engine performance suffers. <S> Even worse, if there is a Low Pressure system, combined with high temperatures, can make the airplane feel like it is taking off from a higher altitude. <S> So Density Altitude is the altitude that the airplane thinks it is - the barometer reading with temperature impact added to it. <A> Suppose you are at a given place, with a given temperature, and the barometer shows –for example– <S> 25.84 inches of air pressure. <S> That's precisely the pressure at 4000 ft. altitude within the 'standard atmosphere'. <S> Hence, you may say that the 'density altitude' at that place where you are is exactly 4000 ft. <A> Density Altitude, in a nutshell, tells you how the plane is going to perform, in particular the climb performance for takeoffs or go-arounds. <S> The performance tables in your POH are based on ISA, which for practical purposes no plane ever actually flies in. <S> That means you have to calculate the density altitude for the current conditions and look at that line in the tables to find out what the actual performance will be. <S> If the density altitude is very high (i.e. approaching your service ceiling), it's possible that your plane won't be able to clear obstacles/terrain or, in extreme cases, even get off the runway. <S> This happens frequently to non-turbo pistons in mountains in the summer, and it is occasionally bad enough that even airliners can't take off from airports like PHX and LAS. <S> Any time your planned flight will be High, Hot and Heavy (known as the three H's), you need to consider DA and check the performance tables to determine whether it will be safe. <S> High terrain may mean a different route via mountain passes; Heavy load may mean ditching passengers/cargo or fuel, and Hot may mean waiting until night or early morning. <S> If any of these aren't things you encounter regularly, e.g. because you live in a (relatively) cold and flat region, it would be wise to check with a CFI to refresh your knowledge and double-check your plans before you go. <A> Try this: Density Altitude <S> Defined Types of Altitude Pilots sometimes confuse the term “density altitude” with other definitions of altitude. <S> To review, here are some types of altitude: Indicated Altitude is the altitude shown on the altimeter. <S> True Altitude is height above mean sea level (MSL). <S> Absolute Altitude is height above ground level (AGL). <S> Pressure Altitude is the indicated altitude when an altimeter isset to 29.92 in Hg (1013 hPa in other parts of the world). <S> It isprimarily used in aircraft performance calculations and inhigh-altitude flight. <S> Density Altitude is formally defined as “ pressure altitude correctedfor nonstandard temperature variations. ” <A> The altimeter, although used primarily to give you altitude, is a pressure gauge. <S> Through mathematical trickery in its innards, it will take the pressure and temperature and QNH and give you an altitude reading. <S> When you set 29.92 in the window, then the altimeter is truly measuring pressure, albeit in odd units of "pressure altitude". <S> The reading has a one-to-one correspondence with other units of pressure. <S> Just an odd nonlinear conversion to go from one to the other. <S> Pressure altitude is important, because airfoils fly by pressure. <S> Thinner air but higher speed gives the same pressure, gives the same indicated airspeed. <S> Planes in 1G flight stall at the same IAS, regardless of TAS. <S> When you make the temperature correction to the altimeter reading, you get density altitude. <S> The altimeter is now measuring density not altitude or pressure. <S> Again, just weird units with a nonlinear conversion to other measures of density. <S> Density altitude is important, because it tells you how many atoms of oxygen are in each parcel of air, and engines ingest oxygen to generate thrust. <S> The same pressure but higher temperature and therefore less density, and you get less oxygen atoms per gulp. <S> So to summarize, Density Altitude is actually a measure of density , just an odd one.
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Density altitude is a measure of density.
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How do planes know what altitude they're cruising at? I know that when planes enter the aerodome containing the airfield of destination, the ATIS will tell them an altimeter setting so the system knows how to calculate their altitude above their field; what about in cruise? Do they listen to the ATIS of every sector while cruising as well? <Q> Above Transition Altitude (e.g. this is 5000ft in Germany) <S> the altitude is measured in flight levels (FL) - each FL equals 100ft and is measured above an artificial QNH of 1013,25 hPa. <S> If you cruise for example at FL380 that will be 38000ft above the pressure level of 1013,25 hPa. <S> This system assures that 2 aircraft which are 10 FL apart <S> (e.g. FL370 and FL380) always have the required separation of 1000ft. <S> During descent when passing Transition Level you will change your altimeter setting to local QNH which ATC will tell you. <A> To combine the other two answers: Below the "transition altitude" (which is 18,000 feet in the US, 5,000 feet in Germany), the pilot has to pay attention to the current altimeter setting, and adjust it accordingly. <S> However, they don't have to listen to ATIS/AWOS <S> /etc. <S> , most controllers will give you the current altimeter setting when you check in with them, or when you make some request, or when it changes, or sometimes just for no reason at all. <S> If you're not talking to ATC, though, you would have to get the local altimeter settings from ATIS, or satellite weather, or some other source. <S> If you're above the transition altitude, however, you are supposed to just set your altimeter to a fixed 29.92 inHg or 1013 hPa. <S> The theory is that when you're that high, the distance to the ground doesn't matter. <S> There are no towers to avoid or anything, so you only need to pay attention to the distance between planes. <S> Having one single setting helps relieve the pilots of fast-moving planes from having to constantly adjust their altimeters while still providing vertical separation between aircraft. <A> Do they listen to the ATIS of every sector while cruising as well? <S> These are both set to 29.92 for example <A> In a word: altimeter. <S> It is a device that measures the pressure of the atmosphere. <S> Flight levels are expressed as height above Mean Sea Level or MSL, a worldwide standard of pressure at sea level at a specified temperature or "standard temperature and pressure". <S> The referenced altimeter reading is actual pressure at the surface. <S> Altimeters in aircraft can be adjusted to compensate for local variations in the air pressure so that altimeters in all aircraft display approximately the same readings at consistent heights above the surface in the area. <S> Periodic pressure references and adjustments are necessary as air pressure fluctuates due to weather patterns. <S> Air traffic controllers usually give periodic altimeter settings, especially when first contacted during communication hand-offs. <S> Pilots may also request that information from them. <S> Other sources are ATIS, if a tower-controlled airfield is nearby, En-route Flight Advisory Service (EFAS), and automated weather reporting stations such as ASOS and AWOS. <S> When attempting to land at a controlled airfield, a wise pilot will listen to the ATIS prior to contacting the approach controller. <S> In instrument conditions, having an accurate altimeter setting (among other things) is critical to operating and landing safely.
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Yes, smaller planes listen to ATIS/ASOS/AWOS or ATC while enroute below 18,000 ft (in the US) and adjust the altimeter setting in the Kollsman window accordingly.
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Why does a sport certificate have no distance restriction while recreational does? A recreational pilot certificate only allows flights within 50 miles of home airport. A sport certificate has no distance limits even though it's easier to get - no medical certificate, less flying time and less instruction. What's the reason? <Q> I always got the impression that a recreational pilot certificate was essentially for people who had soloed and did not want to accomplish any other aviation goals save flying around their local airport. <S> Instruction is restricted to pre-solo aeronautical knowledge and skills. <S> It’s pretty limited in capability compared with a private pilot certificate, which explains why there are less than 600 recreational pilots registered by the FAA. <S> And one can expand a recreational pilot certificate to permit PIC on cross country flights over 50 nm, but this will require additional training and logbook endorsements by an instructor <A> To put it short, the Recreational Pilot certificate allows you to fly common aircraft such as the Cessna 152. <S> The Sport Pilot certificate was only created recently (2004), and it restricts the owner to Light Sports Aircraft - 1300 lbs MTOW or less. <S> Pilots on a budget normally get a well-used plane, and that's rarely an option for LSA, just because they're all quite new. <S> Right now a well-used light aircraft can still be bought cheaper than a new LSA. <S> So the Recreational path still has a lower financial entry barrier. <S> Long-term, the Sport cert appears to be meant to displace the Recreational. <S> LSA restrictions are more practical and reasonable, given modern-day technology. <S> Anyone who can't find a LSA that's good enough for them isn't likely to be satisfied with Recreational Pilot restrictions either, and will go for the proper PPL. <A> Because the spirit of the regulations are a bit different and there is some history tied to this. <S> The recreational pilot cert allows you to fly a lot of lighter common GA planes ( <S> J-3 Cub etc.) <S> but limits you to one passenger and a local area. <S> The idea being that the training is reduced a bit <S> but you dont really need to worry about complex navigation, long range weather planning or any of the stuff that comes with flying a capable plane, far. <S> The cert was intended mostly for local weekend fun in aircraft that were already easily rented. <S> The sport pilot cert was intended to birth a whole slew of aircraft but the type never really took off. <S> Since new limitations were in place the hope was makers would build new planes but the reality was that a new sport plane cost well more than a nice used GA plane. <S> You could often take the difference and get a full PPL as well as an instrument rating and still have some left over. <S> Sport planes are fairly useable in some regards and pretty docile so the training was matched to the intended plane more than to complete with recreational. <A> The Recreational Pilot PTS and Sport Pilot PTS look nearly identical, but the key to your question can be found under AREAS OF OPERATION, Section I. PREFLIGHT PREPARATION. <S> Sport Pilots are required to demonstrate "Cross-Country Flight Planning", whereas Recreational Pilots are not. <S> Since they are not required to demonstrate the ability to plan a cross-country flight, unlike Sport or Private pilots, Recreational pilots are not allowed to perform them without an additional endorsement.
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Because a sport pilot certificate requires the applicant to undergo at least three hours of cross country flight training whereas a recreational pilot certificate does not have that requirement.
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Why do airlines seem to go out of business suddenly? FlyBMI are currently in the news for failing and stranding passengers abroad. This is not the first time an airline has halted operations seemingly overnight and left passengers without a way to get home. Why is it that airlines stop operating so suddenly, compared to other businesses which seem to go through a more protracted period of profit warnings, administration... and generally more orderly windup? <Q> Airline operation nowadays is calculated in most cases toward a rather high plane utilization. <S> Even more so on low cost enterprises. <S> Sometimes even 10% less passengers may turn a profitable flight into a loss. <S> Airlines depend on filling up flights - until the last seat and last moment (last minute bookings being, depending on the business plan, even being more profitable). <S> As soon as an airline would announce the intention to close down, new bookings will dry up quick, making next to every flight after this unprofitable. <S> This all is due the fact that, unlike a brick and mortar store, most cost of an airline are operational cost. <S> There is no valuable inventory to be sold of over time, or much existing machinery to be run until the last moment to convert existing materials in (somewhat) higher valuable products, to turn it into cash. <S> For Airlines there is none (No, collector value of in flight magazines don't really count), so shuting down the flights removes next to all further expenses, stoping any further increase of debt. <S> Not to mention, that flying after such an announcement would become almost impossible as each and every supplier would demand cash payment from that moment on - with airport fees and fuel payment most prominent - something a money strapped airline hardly can provide. <S> Airlines that tried to go that way usually postponed the shutdown just by days - and often with planes stuck in all corners of the world, unable to return, not able to sell them, but instead adding more debt in airport parking fees. <A> When you buy an airline ticket, you are buying a promise that at some future date there will be a seat on a plane for you to make your journey. <S> If you have any reason to doubt whether that promise will be fulfilled, the rational thing to do is buy your ticket from a different airline. <S> That is fundamentally different from many other commercial transactions, where you are buying something that can be delivered right now . <S> If a store chain announces that it may have to close next week or next month, that makes no difference to you if you can physically go to the store and carry what you have bought out of the door. <S> If the shop closes the next day you still have what you bought, and it has exactly the same functionality and reliability as it would have if the store were still trading. <A> It's actually not that common and is probably mostly related to the bankruptcy law in the country where the airline is incorporated. <S> Countries that have bankruptcy laws that allow second chance rescue plans like "Chapter 11" in the US (or Company's Creditors Arrangement Act in Canada) typically see the airline go into a bankruptcy process that sees the airline continue as it is reorganized and negotiations go on with creditors. <S> Certainly in North America airlines almost always go with one of these restructuring/reorganization routes once or twice before they disappear and these sudden collapses don't really happen very often. <S> A lot of airplane sales happen because an airline in bankruptcy protection is "restructuring" and part of the restructuring plan involves updating the fleet to something is is newer and cheaper to maintain, so word of a Chapter 11 execution is sometimes not bad news for a manufacturer, when the bankrupt company was flying around old beaters and is now shopping for new machines backed by fresh capital or loans. <S> Possibly FlyBMI has gone through a restructuring already and the options and creditor protections under UK bankruptcy law have already been exhausted. <S> Usually these things go down the drain slowly, then suddenly, so anyone who was not an insider is caught unawares, like passengers.
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Mainly because winding down airline business will turn it into a sudden and from there on increasing loss.
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Why is carburetor heat unnecessary at full throttle? Questions like How does aircraft design affect carburetor ice? show how carburetor mount point affects the relative passive heating of the carburetor by the engine, but I've never learned why full power eliminates the need for carb heat. Looking at how Wikipedia depicts carb ice: Regardless of the carb's mount point on the engine, high throttle wouldn't get rid of the ice on the throttle valve, heat generated by high throttle doesn't affect the temperature of the air flowing in. Further, when the throttle is full open, there is a greater airflow speed across the neck of the carb and hence a greater temperature drop. So, what explains why high throttle eliminates the need for carb heat in Lycoming/Continental engines? Thanks! <Q> The icing you are talking about is called "throttle ice" and actually just forms around the edges and back side of the throttle butterfly. <S> It's not really related to the venturi that is upstream; it's from the pressure drop caused by the restriction of the throttle plate (the high vacuum on the back side you might say) along with the presence of vaporizing fuel, which massively boosts the temperature reduction caused by the pressure drop because the evaporating fuel is absorbing a lot of heat from the air stream. <S> It's the temperature drop from this pressure drop at the butterfly, plus the effect of evaporating fuel, that turns ambient humidity into carb ice. <S> Anyway, when the throttle is wide open, the pressure drop downstream of the butterfly caused by the throttle restriction is minimal. <S> As a result, the chilling effect of the pressure drop and of evaporating fuel is also minimal. <S> Because of this you won't get ice formation as readily (not impossible, just relatively unlikely) when the passage has say only a 5 or 10% restriction at WOT, vs say, an 80% restriction at a low power setting. <S> For a given ambient temperature/humidity, carb ice always forms more easily the more the throttle is closed. <S> One of the worst airplanes for carb ice was the 65 hp J-3 cubs where the carb receives very little conductive or radiant heat from the engine due to the carb mounting and the cowl with the exposed cylinders. <S> Descending with the engine at or near idle on a 65 deg F high humidity evening was begging for a carb ice related stoppage, and liberal use of carb heat was advised even if there were no signs of icing. <S> Carb ice at WOT wasn't too much of a problem, but you can never be sure. <S> Always err a little on the overuse side with carb heat, especially on Continental powered airplanes which are a bit more sensitive to all this due to the way the carb is insulated from the crankcase <S> , at least until you get to know the engine's quirks. <A> Having the throttle at full doesn't eliminate the need for carb heat. <S> It's actually the opposite: with the throttle at full, the drop in air temperature through the Venturi is greatest, so you're (slightly) more likely to develop ice, all else being equal. <S> In general, he reason you're not supposed to use carb heat at full throttle <S> is because it reduces the density of air going into the engine, so it can't produce quite as much power. <S> Presumably you pushed the throttle forward for a reason, so reducing the amount of power <S> right when you need it doesn't make much sense. <S> If you're in a situation where carb ice is a factor, then use the carb heat before <S> you start your climb, so that you have full power available to you during the climb itself. <S> But if you notice that your engine power has started to drop, by all means, go ahead and pull the knob, even if you're in a full-power climb. <A> There is a small risk of carb icing at full throttle but it is a much narrower range of conditions than at partial throttle. <S> Pressure drop causes temperature drop. <S> The purpose of the throttle is to control manifold pressure, a more open throttle creates less pressure drop from ambient outside to inside the manifold so less temperature decrease. <S> The temperature drop must also be enough to condense moisture from the air, if the dew point is much below freezing <S> then there is no point where liquid water forms. <S> Direct formation of ice is like snow it just gets sucked into the hot cylinders, you need a liquid droplet phase for the ice to adhere. <S> So with high dew point and a large pressure drop you get super cooled liquid water droplets that freeze on impact. <S> With low humidity the range for liquid condensation is reduced and with low pressure drop the temperature doesn't drop below freezing. <S> Injected engines actually can develop intake ice however they do not have a venturi and without the additional pressure drop in the venturi <S> the total temperature drop is not as substantial or it occurs in a less critical section <S> so problems caused by icing are not as common. <S> Venturis are more sensitive to ice as they are part of the calibrated fuel metering and mixing system. <S> Fuel evaporation is a contributing factor to the difference in temperature between carbureted and injected systems but it is not a major factor when comparing part throttle to open throttle within a system as the mass of fuel is directly proportional to the mass of air and less fuel evaporates at low temperatures. <S> Also high power settings create more cylinder heat, this heat increases engine temperature and the increased temperature increases the heat transmitted to the intake components both by increased conduction through the manifold and increased infrared radiation.(proportional to the fourth power of absolute temperature[kelvin^4]) <A> One of the reasons for not using carb heat at full throttle is due to the increased risk for detonation due to the temperature increase and reduction in density of the air charge.
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On a fuel injected airplane you only have the butterfly valve without fuel present, and the temperature drop from that alone isn't sufficient, and therefore you don't need carb heat on injected engines (just an alternate air source in case of impact ice on the air intake).
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Can a VFR flight follow an IFR route? Can a VFR flight follow the same route of an approved IFR route (such as those found on Forefight Route Adviser) using waypoints and Victor airways? <Q> Yes. <S> In fact, before GPS came along, if you were flying somewhere and wanted to use your VOR to get from A to B, that's exactly what you did a lot of the time if it was convenient; fly along the victor airways if they were more or less on your route. <S> IFR traffic is only separated from other IFR traffic and when VFR in non positive control airspace you can go wherever you want notwithstanding other restrictions. <A> For low altitude flights ie below FL180, yes you can. <S> You can use either Victor (VOR) or Tango (RNAV) airways. <S> You will fly at VFR altitudes during cruise, but use of these airways on VFR flights is common. <S> For improved safety and traffic separation, pilots are requested to either file and open a VFR flight plan or request flight following when VFR on Victor or Tango airways, especially near navaids or other high density airspace. <S> Victor and Tango Airways can also be used for VFR flight segments during composite flight plans like VFR on top, VFR over the top, etc. <A> When filing a VFR flight plan with an ATS route identifier in it, consider the following:- check that the aircraft is equipped with suitable navigation aid receivers (e.g., ADF, VOR, GPS)- check the lowest altitude permitted for that specific ATS route - make sure the weather / clouds will allow you to climb and maintain the minimum ATS route altitude in VMC at all times- make sure to use VFR altitudes (xx500) , not IFR altitudes (xx000), as mentioned above already- <S> specify the point, where you plan to join and leave the ATS route. <S> If something doesn't match, you can still fly the same direction and use the same navaids, but don't specify the ATS route in your flight plan. <S> Instead, you can specify point along the ATS route with maximm 30 min flight time intervals.
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In the GPS era nobody uses VORs very much any more and you can fly direct almost all the time when VFR (I haven't used the VOR in my plane in eons; mostly I just use a tablet or my phone), but there is nothing to stop you from flying along an airway if you feel like it.
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Does the ditching switch allow an A320 to float indefinitely? I watched a documentary yesterday about the Hudson River ditching of US Airways Flight 1549 . In the documentary, one of the investigators explained that the reason the water was entering so quickly was because the FO did not have time to hit the 'Ditching' switch the A320 is equipped with. This switch closes all vents etc. to prevent water from entering the cabin. If an A320 or similar is ditched and the switch is activated in time, does that totally prevent water from filling the cabin (in a best-case scenario)? I'm thinking if one ditched in the Atlantic and had to wait for hours for help, would it be possible to stay afloat for so long? <Q> The answer is no, not totally, but it would really slow things down. <S> I don't think anybody knows the precise answer because only flat water ditchings seem to result in the airplane stopping in the water in one piece (such as 1549 and a similar one in Malaysia) and flat water incidents (like Malaysia and some airport overruns) are usually in shallows where the ditching valve is moot. <S> But assuming an A320 was able to ditch on open ocean swells without breaking somewhere, certainly it would float for a much longer time, but not forever. <S> Pressure hulls are never absolutely fluid tight; door/hatch seals leak a little bit, and there may be tiny leaks through various entry points below the water line like bleed air shutoff valves, fay-sealed skin laps, rivets, control cable pressure bulkhead fairleads, etc (the older the airframe the leakier). <S> Wing dry bays may be sealed off with a tape made for the purpose but they are not usually totally water tight. <S> Water can migrate into the fuel tanks through the vents. <S> Full fuel or nearly full fuel would be a bonus, fuel being buoyant. <S> You certainly would have a lot more time to get onto the rafts (perhaps Airbus has estimated the theoretical sink time by calculation), but it would sink eventually (it would take quite a few hours, maybe even a day or two), and you aren't going to be staying on board any longer than necessary regardless. <S> (Now, if you ditch in a composite foam sandwich sailplane, well you've got yourself an unsinkable boat right there, and if you took a paddle along, you could actually go places. <S> If I'm in a glider that gets low over rough forested terrain, and there are lakes around, I'm putting it in the water and paddling it to shore with whatever I have at hand). <A> In theory, yes. <S> In practice, no. <S> FAA regulations (specifically, 14 CFR 25.801(d) ) require that, under reasonable water-landing conditions, an airplane must remain afloat long enough for the occupants to evacuate. <S> Most airplane manufacturers don't actually test the ditching performance of their aircraft, but instead rely on the clause of paragraph (c) to let them compare their airplane to a similar one that has been tested. <S> The A320 is certified based on ditching tests of a scale model of an Airbus A300 done in 1974. <S> Under the landing conditions specified in the certification, the A320's fuselage is supposed to remain intact in the event of a water landing, and with the "ditch switch" activated, water entry is supposed to be minimal. <S> (Flotation won't be truly indefinite, but when the main source of water entry is things like leakage around door seals, it's quite possible to stay afloat for days or longer.) <S> If you read the investigation report from US Airways flight 1549 , the specified landing conditions were found to be nearly impossible to attain in the event of a dual engine failure. <S> Flight 1549 actually hit the water with the nose lower than specified, producing a higher vertical speed and a greater glideslope angle, causing significant structural damage. <S> Specifically, a number of lower aft fuselage panels were buckled or torn, letting water freely enter the airplane. <S> In this situation, the use or non-use of the "ditch switch" is irrelevant. <A> NO. <S> Indefinitely is a very, very, long time. <S> In fact it's so long that by the time it's over there's no more water for the aircraft to float in. <S> Heck, there's no more planet for the water to exist on. <S> But even for a shorter period, say hours, it wouldn't work. <S> The switch may close some holes, but the doors would still be opened to allow egress into life rafts. <S> Wave action may break windows and erode door seals pretty quickly. <S> And there has to be some holes still open to allow air circulation into the cabin to prevent everyone inside suffocating. <S> Water can enter through those as well. <S> That's all it is designed to do, and that's all it does. <S> It's not designed as nor does it work to turn the aircraft itself into a life boat for the crew and passengers.
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The switch is there so slow down water ingress to allow more time for evacuation, not completely prevent it.
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What prevents aircraft with a tailcone APU from using tail-mounted airbrakes? The BAe 146 and Fokker F-28 , which are virtually alone among jetliners in lacking thrust reversers, compensate by using large, tail-mounted airbrakes to help slow the aircraft during descent and landing: (Image by Adrian Pingstone at Wikimedia Commons .) According to this answer to a previous question about why we don’t see this on more (and bigger) jetliners, the BAe 146 and F-28 are only able to use tail-mounted airbrakes because, unlike most jetliners, they lack an APU in the tailcone: ...Air brakes such as the RJ100 have only upsides, since they influence drag only, not lift. They're not used everywhere because the bit of fuselage where they are mounted usually houses an APU. (Emphasis added.) But I don’t see why having an APU in the tailcone would preclude the use of tail-mounted airbrakes; the APU is situated in the middle of the tailcone and exhausts out the tip of the tail, 1 while tail-mounted airbrakes are mounted on the sides of the tail and deploy to the left and right: (Image by dtom_cro at Photobucket .) As such, having a tailcone APU shouldn’t necessarily preclude having airbrakes on the sides of the tail; in the 146, the space between the airbrakes is basically empty, with only a light truss supporting the rear collision beacon, but it'd be easy to have something more substantial - such as, for instance, an APU-and-other-machinery-housing structure - in between the petals: What am I missing here? 1 : As @ymb1 points out in their comment , the BAe 146 does have an APU, but its APU obviously does not exhaust out the tip of the tail; that statement regarding APU exhaust placement refers to its location in the vast majority of jetliners in general. 2 2 : That last statement obviously does not apply for jetliners where that real estate is taken up by a full-blown engine (727, Trident, Tu-154, Yak-40, L-1011, Yak-42, etc.). <Q> The airlines prevent them or: <S> the airlines won't buy them if they were offered <S> The photos you have already show an APU in the tail section (exhaust on the starboard side). <S> Adding air brakes requires increased structural integrity (weight; money) and additional system connections (weight; money). <S> When they are of no use, they're simply not added. <S> Why are they of no use? <S> Well, pure air brakes (as opposed to speed-brakes/spoilers) have 1–2 functions (for jetliners): Compensating for the lack of thrust reversers Performing steep approaches when the thrust-to-weight ratio is high (small plane that has too much power). <S> As I noted here : The thrust-to-weight ratio for the RJ100 is 0.28:1, compared to 0.16:1 for the comparable Boeing 717. <S> It's even higher for the smaller RJ's. <S> Neither affect most jetliners (note that the babybus (A318) can be certified for steep approaches, and it doesn't need such an air brake). <S> The airlines would rather carry payload (paying load) and not bother paying for maintenance to regularly check and fix a novel item – not all airports are London City: high thrust-to-weight ratio is good for taking off from short runways and performing steep climbs from in-city airports for noise reduction. <A> The defining factor is not the presence of an APU, but that of a T-tail. <S> Aircraft with a conventional set of stabilisers mounted on the rear of the fuselage cannot use the tail cone for expanding air brakes, as deploying them would distort the airflow over the stabiliser. <S> Note that all aircraft systems add weight and money, and aircraft manufacturers look very closely at where to save weight and money. <S> Do air brakes weigh and cost less than wing slats necessary when lift dumpers are used for airspeed reduction during landing? <S> Two manufacturers of T-tail aircraft determined that it does, with the added advantage of reduced Angle of Attack during approach. <S> Thrust reversers aid in decelerating the aircraft after touch-down. <S> The brakes of a large, heavy aircraft need to work disproportionally harder than those of a lighter and smaller aircraft such as the BAe 146 and Fokker 100. <S> Braking efficiency is improved by deploying lift dumpers, and it may make sense to use these as air brakes during approach. <S> Particularly if stabilisers mounted at the rear fuselage take away the obvious place for mounting the air brakes. <A> There is no technical obstacle to building tail mounted air brakes and APU.The <S> Fokker 70 has a tail air brake, APU and also thrust reversers and spoilers as seen in this great photo from airliners.net: <S> Fokker 70 landing in AMS
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Yes indeed, it is possible to combine an APU with air brakes at the rear of the fuselage.
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Why would the Pakistan airspace closure cancel flights not headed to Pakistan itself? The India-Pakistan feud has heated up again, with Pakistan closing its airspace as a result. I know many international routes fly over Pakistan, and that the closure would cause issues, but this report surprised me: Thousands of people were also stranded by affected airlines that not only land in Pakistan, but fly over its airspace -- one of the major routes from Southeast Asia into Europe. Thai Airways announced that all its European routes "departing near midnight of 27 FEB through early 28 FEB" were canceled "due to sudden closure of Pakistani airspace as a result of tension between India and Pakistan." Why would the airspace closure force flights over it to cancel entirely? I would think you would just reroute them around it. <Q> To give an example of how flights can be affected by this in ways to make them impossible, Iranian airspace is closed from sunset to sunrise (unless things have changed recently).Any aircraft that due to the closure of Pakistani airspace would need to cross Iranian airspace and be unable to do so because of that closure now needs to be cancelled or rescheduled. <S> Or the diversion would cause such a delay in the schedule that it causes too much problems with the overall scheduling of the airline. <S> Such things tend to have a ripple effect. <S> One flight gets delayed by several hours, dozens of others get delayed as a direct result, hundreds more can suffer delays in the end. <S> Also, some airports only operate during daylight hours. <S> A diversion around Pakistan might mean the flight can't make it to one such airports before sunset and thus can't land at its intended destination. <S> Now the airline has 2 options, divert to another airport, arrange for bus or train transport for all the passengers, and in the morning yet another hop to the intended destination to pick up the new passengers, or cancel the flight. <A> Not mentioned in the other answers is simply logistics coordination. <S> If you can't fly over Pakistan, that suggests that maybe you have to fly somewhere else. <S> Perhaps flying around means an overflight of China or Kyrgyzstan. <S> Do they charge overflight fees? <S> Do they require prior permits? <S> Even if the money involved isn't huge, starting up a new route may mean the first time your airline had to work with that country. <S> I'd expect that could take a few days. <S> Even if you already have a relationship with the country from other routes, adding permits and having the accountants approve the route choice would still be required. <S> https://www.jetex.com/overflight-fees-in-asia-pacific/ <A> There are multiple reasons for cancelling instead of rerouting: <S> Take-off & landing slot assignments <S> You may have a pair of slots available and your regularly scheduled flight uses them. <S> Rerouting the flight will take longer and you may no longer make your destination landing slot Departure & arrival gate assignments <S> Likewise, you may no longer have a gate assignment available at the destination airport because the reroute takes too long. <S> Aircraft range. <S> If your flight is near the maximum range by overflying Pakistan, rerouting around it could push the plane past its maximum allowable range. <A> There was an extensive report on the grounding of Thai Airways flights in The Guardian today. <S> To quote: Thai Airways said later on Thursday it would resume flights after gaining permission from China to use its airspace for nearly a dozen flights to Europe set to leave on Thursday afternoon and Friday morning. <S> Quite simply, Thai lacked the necessary permissions. <S> The Chicago Convention on International Civil Aviation established a general right for overflight by foreign aircraft, but many states nonetheless require airlines to acquire permission in advance – including China .
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Also, if the diversion around Pakistani airspace would stretch the endurance of an aircraft beyond what fuel it can carry, it cannot fly the route.
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Why don't American passenger airlines operate dedicated cargo flights any more? I was reading recently that Northwest Airlines was the last American passenger carrier to operate dedicated Cargo aircraft. Why do none of the large US airlines operate dedicated cargo flights anymore? This seems to be common among international Airlines (Lufthansa, China Airlines, Qatar Airways, EVA, etc). Presumably UPS and Fedex's extensive networks have something to do with it? I'm surprised that none of them find it economical, however. <Q> American, Delta, Southwest and United all have thriving cargo shipping operations, but as far as I can tell, no longer have freighters. <S> https://www.aacargo.com <S> https://www.alaskaair.com/content/cargo/general <S> https://www.deltacargo.com <S> https://www.hawaiianaircargo.com <S> https://www.swacargo.com <S> Alaska used to run 737 Combi to ship cargo and passengers in the main cabin on their “Milk Run” up the Alaskan panhandle. <S> They now have dedicated freighters to handle the cargo. <S> https://thepointsguy.com/2017/10/final-flight-alaska-airlines-737-400-combi/ Good luck shipping your parcel. <A> A lot of airlines (USA flagged or not) still ship cargo in the hold along with passengers baggage, for some airlines its a high dollar business . <S> Carriers like UPS, FedEx, etc, have surely put a dent in the plane-full-o-cargo market but for the airlines it actually helps to mitigate risk. <S> If you carry both cargo and passengers you can be assured of a more stable revenue stream across the board. <S> An airline can mitigate a lull in travel or cargo movement by also generating income from the other stream. <S> There is also a lot of differing logistics in moving cargo that a passenger airline may not want to deal with. <S> UPS and FedEx also maintain truck fleets to deal with the package once it gets to an airport. <S> This end to end business model is attractive to consumers. <S> An airline, who may have the space on the plane but not the trucks, can't offer such service and for a given customer this may make or break the deal. <A> The cargo operation (dedicated fleet) requires its own logistical and operational apparatus. <S> According to this article , Lufthansa's cargo operation lost money in 2016 and they were complaining about subsidies to Gulf operators that allow them to undercut airlines like Lufthansa who have marginally profitable cargo divisions. <S> And there's the rub. <S> A good chunk of cargo operations outside the North America are subsidized (certainly the ones operated by government owned or controlled airlines). <S> In the absence of subsidies, and with a harder focus on making every dollar count, in North America it was found to be more efficient to specialize.
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Unless an airline's cargo subsidiary is large enough to get the required economy of scale, along with decent market conditions, it's not worth the trouble and expense. Alaska Airlines, Hawaiian Airlines still have dedicated freighters.
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How to calculate service ceiling and absolute ceiling in PA-44 Seminole? I am hard to understand to calculate service ceiling and absolute ceiling in PA-44 Seminole. Is there anyone know how to calculate it in the condition(T/O weight: 3599.24 L/D weight: 3354.44 PA:2329 Temp:20) <Q> You can use the given chart to define (single engine) ceilings. <S> There should be separate graph for both engines running case. <S> Note: it is important to understand that the definition absolute ceiling is absolute: zero climb rate while service ceiling is defined by local regulations. <S> In Europe, in commercial operations for class B aircraft (which Seminole is) <S> A single engine service ceiling is defined as "positive gradient" so it is the first usable altitude below single engine absolute ceiling. <S> To define required altitude enter the graph from the right from the desired vertical speed, go upwards until you meet your current (or estimated) gross weight. <S> From there draw a horizontal line all the way across the left side of the graph. <S> The point where to local OAT (at an altitude) and your horizontal lines cross is the ceiling according to the selected climb requirement. <S> When interpolating between the altitude lines make sure to go perpendicular between altitude lines - not up and down along the grid. <A> With the chart you uploaded you don't calculate the ceiling, but the climb rate when you have only one engine operating. <S> The TO weight and LD weight don't matter, what you need is the GW (which should lie somewhere between the TO weight and the LD weight). <S> I have added red lines to the chart to show you how to use it: <S> Select your OAT (20°C in your case) <S> Move up until you meet your PA (2329 in your case) <S> Move right until you meet your weight <S> (let's say 3599 at take off) Move down <S> and you get your climb rate (in this case 120ft <S> /min) <S> * <S> * <S> At your LD weight it is 190ft/min NOTE: <S> at the bottom of the chart you see dashed lines with arrows. <S> Those are used to understand the order in which you have to read the chart. <A> Service ceiling I believe is the altitude at which an aircraft will no longer climb at a rate of 100 ft/minute. <S> It should be published in the POH for the plane. <S> For example, in a 1977 Cessna 150 SERVICE CEILING ..... <S> 14, 000 FT <S> That is a single engine, 2 seat propeller plane, with no turbocharging/turbonormalizing. <S> The Seminole POH should have a similar number. <S> Absolute ceiling can be higher but it will take a while to get higher. <S> Use of O2 is required above certain altitutes, and after certain time periods above a lower altitude as well. <S> If one departed a hot California airport at 45C (110F, definitely possible out in the desert areas), say Rosamond Skypark (L00) at 2415ft, then 14000-2400 = <S> 11,600 feet x 2C/1000 <S> ft = 23.2C, and 45C - 23.2C <S> = 21.8C! <S> Will feel nice & cool while airborne, but really hot when that door is opened. <S> We were flying the US southwest a few years ago, July 4th weekend. <S> Flying southeast away from Albquerque, New Mexico, to Carlsbad, Arizona, we couldn't climb above 9,000 ft <S> , my 180 HP normally aspirated engine just couldn't make any more power to get higher. <S> So the rated Service Ceiling for my plane, SERVICE CEILING ------------ <S> 14,600 FT made no difference. <S> 107F on the ground. <S> Hot!
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service ceiling is the altitude where both engines running aircraft is able to climb at 300 ft/min at present gross weight and local OAT.
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Does altitude influence the flight range of an engine driven aircraft? I'm reading a chapter about flight performance during the cruise phase and the influence of altitude. My book (Aerodynamica, prestatieleer en vliegtuigtechniek by Bas Vrijhof on page 155, written in Dutch) describes the following: Naarmate de hoogte toeneemt, neemt de luchtdichheid af. De afnemende luchtdichtheid heeft een effect op het benodigde vermogen, en dus op de prestaties. Om bij een lagere luchtdichtheid te vliegen is meer vermogen nodig. Om bij een lagere luchtdichtheid voldoende lift te houden moet de TAS toenemen, dat kost vermogen. Translated to English: Airdensity decreases with altitude. A decrement in airdensity influences flight performance. To fly at a lower airdensity more engine power is needed. To maintain enough lift at lower airdensity the TAS needs to increase, this comes with the cost of engine power . This is totally clear to me. Then the book says. Endurance... Meer vermogen betekent een hogere brandstofverbruik. De endurance neemt daarom af. Translated: Endurance (amount of fuel per hour), more engine power means a higher fuel consumption . The endurance decreases with an increase in engine power. Again, this is also clear to me. Range... De range verandert niet bij toenemende hoogte. De range is niet afhankelijk van de vlieghoogte. Wel neemt de Vmax range toe als de hoogte toeneemt. Translated: Range (maximum flight distance, amount of fuel per km) doesn't change with an increase in altitude . However, the Vmax range increases with an increase in altitude. The last sentence is confusing me. Because my instincts say that a higher fuel consumption comes with a shorter flight distance. So my question is: Is it really true that the altitude doesn't influence the flight range? Does the book has an error? <Q> Your book may not be wrong, but it is misleading, because the answers depend on the the aircraft type, and the type of engine. <S> (piston, turboprop, turbojet, turbofan) <S> In general: All aircraft have the best range at higher altitudes. <S> Piston powered aircraft have the best endurance at low atitude. <S> (not too low and not too high) <A> Jet engines can make the same horsepower/thrust at basically all altitudes due to their compressors, thus the same fuel burn - <S> this lets them take advantage of the less dense air/less drag at higher altitudes, and perhaps take advantage of jet stream tail winds. <S> Well, maybe not the same, see here for more <S> How does turbojet thrust change with altitude? <S> Smaller planes can be equipped with turbochargers, or turbonormalizers, to make sealevel horsepower at higher altitudes and also take advantage of the thinner air. <S> Non-turbo engines like mine and most small planes are limited to leaning the mixture to keep the engine from running rich/wasting fuel as (generally) climb above 3000 feet. <S> We can't get fully as high to the thinnest air, but we're also burning less fuel once cruise altitude is reached. <A> any aircraft has an optimal altitude for cruising. <S> account for burn at takeoff and landing, then the cruising altitude is the one minimizing the costs. <S> since combustible is the main cost, then is easy to determine which altitude is the economical one, even customized for the trip length and wind direction. <S> however, for practical reasons and separation of air corridors, the economical altitude also depends on imposed constraints related to air traffic. <S> for distances of less than 1000km, <S> the 6000m 675km/h turboprops of small capacity are the most economical. <S> embraer and bombardier are flying those routes.for longer distances, the 11000m 980km/h large airliners are the most economical.for planetary distances, the largest airships are the most economical. <S> the altitude is limited to 11000m.
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Jet powered aircraft have the best endurance at their optimum altitude.
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Why don't flight attendants get tired when passengers can, despite sleeping? This Reddit thread refers to "stressors of flight" (many of these stressors are also present in automobiles) , sudden altitude adjustment, lower cabin humidity. , proximity to strangers . Yet flight attendants face these stressors too, but they don't appear tired? I don't think sleep answers my question. I know that on long flights, they are allowed to sleep in crew rest compartments , while passengers sleep too but still can remain tired. <Q> This is bordering on opinion based as its a bit subjective from person to person but generally speaking flight attendants and pilots are more accustomed to the typical stressors of flight and potentially less subject to them after some time as the human body adjusts. <S> Perhaps more importantly this is also their day job, <S> its what they do. <S> When you get on a flight it may be in the evening, or early in the morning, maybe you are coming off a long work week and really burnt out or that weekend in Vegas really got to you. <S> When you get on a flight you may likely be tired, and small, dry, noisy spaces are not where you want to be. <S> This is not the case for the crew. <S> They are there to do a job, presumably well rested and ready to go. <A> Sitting still is surprisingly tiring. <S> Flight attendants are up and moving around for most of the flight, and that physical activity helps keep them awake. <S> They're also more accustomed to the lower oxygen levels and other physical and mental stresses of flight, similar to pilots, so even if the activity levels were the same, they'd be better able to handle it. <A> FAs receive the same kind of fatigue and circadian rhythm management training that pilots receive, and have similar statutory duty hour requirements that limit time-on-duty and require minimum rest periods between duty, and so on. <S> A Flight Attendant's job is quite unusual, in that the majority of their training, and their real job function, is as kind of an undercover riot control cop, who can expect to spend their entire career working their nominal role as a cabin steward without ever implementing their training except in relatively minor ways. <A> In addition to all the other fine answers, there is also a statistical error in your sample, more precisely in your selection criteria: you have a selection bias in your sample, because you are ignoring all those flight attendants that quit their job because they found it too tiring.
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In other words: one possible reason why flight attends are not constantly tired by flying is because if they were constantly tired by flying, they wouldn't be flight attendants.
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Is the A-10's cannon effective against tanks? Perhaps this isn't on-topic, but is the A-10 effective against tanks (tank armour) when using its cannon? For example, this page claims: Using the cannon, the A-10 is capable of disabling a main battle tank from a range of over 6,500 m. Is that true? If that were so, why does a "main battle tank" (e.g. an M1 Abrams) have a 120 mm gun -- contrast that with the A-10's 30 mm cannon? I thought that in WW2 you needed something like a 75 mm or 88 mm gun to be effective against the then-heavy tank armour. And the gun on a "main battle tank" has if anything increased in size since then -- or converted to missile instead of projectile -- is a 30 mm cannon effective? Is the armour-penetration of an A-10 exaggerated (if it is effective against only e.g. softer armour than main battle tanks)? Does the cannon being mounted in a plane make it especially effective (I'd guess not, the muzzle velocity of a GAU-8 is 1000 m/s and and A-10's airspeed only adds 200 m/s to that)? If it is effective then why isn't that the primary armament of a main battle tank? <Q> Well it depends.... <S> It depends on the tank, where you hit it, what angle you hit it, how far the A-10 was from the tank when it fired, and what kind of ammunition was used. <S> Wikipedia quotes that a GAU-8/A firing the PGU-14/B depleted uranium API ammunition offers the following armor penetration capability. <S> Armor penetration of Armor-Piercing Incendiary ammunition, BHN-300 RHA, attack angle 30 degrees from vertical: 76 mm at 300 meters 69 mm at 600 m 64 mm at 800 m 59 mm at 1,000 <S> m 55 mm at 1,220 <S> m <S> Whether that's a declassified spec with all other known values a secret or a realistic representation is unknown. <S> I'd say it sounds reasonable. <S> Tanks tend to have heavy armor on the front and sides but lighter on the top. <S> Certainly the PGU-14/B could defeat armor on APCs and older generation MBTs. <S> Modern MBTs with advanced composite/reactive armor may be more difficult to crack. <S> While it might not be able to penetrate the chobham hull of an M1A2, it can certainly take out fuel tanks, destroy the engine, etc. <S> Keep in mind that a GAU-8/A can hammer a 5-mil Circle with 70 such rounds with a 1 second burst, provided the pilot has a steady trigger hand. <S> This also can have a cumulative destructive effect on armor plating. <S> While the gun can be employed against armor, the preferred method is to attack tanks using standoff weapons like the AGM-65 Maverick missile. <S> Getting close enough to tank columns to use the gun can be hazardous, especially if the group has mobile AAA/SAM escorts. <A> The thinnest armour on most MBTs is the roof of the turret and hull. <S> The A-10, when it attacks with its cannon, is diving from a fairly high aspect and therefore shooting at the most vulnerable parts, the roof and engine compartment. <S> Also, the rate of fire of the gun is so high and the projectiles are therefore so close together, there is a high probability of multiple hits on the same point. <S> The result is an 30mm depleted uranium AP round, even if it doesn't penetrate the first time, has a good chance of being followed by another right behind it into the divot made by the first one and finishing the job. <S> An old GE video of the GAU8 on a test range shows the effect of follow up rounds hitting the crater made by their predecessors, and basically chewing their way through quite thick armour. <A> In the image below, we see the tracks and the wheels, which are exposed. <S> We see some optical systems for awareness and fire control. <S> If an aircraft manages to damage enough of these exposed systems to render the tank incapable of fulfilling its role, then the tank has been effectively knocked out, despite it being not killed. <S> The quote of the OP talks of disabling, not destroying. <S> Thus, making the tank blind, or unable to move, may be sufficient to disabling it. <S> Image source: Wikimedia Commons <A> First of all adding "only" 200 m/s aircraft speed to 1000 m/s barrel velocity will give 40% more kinetic energy to those depleted uranium rounds. <S> Secondly, an aircraft can attack at many more angles than another tank, more easily finding thinner armor points. <S> Thirdly, even if aircraft could carry an 88mm gun, it has a much higher probability of a miss as it is moving in three dimensions. <S> There for, it fires a guided missile at longer range and closes to point blank with its Gatling, accomplishing its task with multiple hits. <S> A tank on the ground can aim much better with its gun and goes for one good shot. <S> But nothing wrong with helicopters carrying missiles to help out, along with the Warthogs. <S> As long as the A-10 is effective, it will still be around.
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Define effective Using the cannon, the A-10 is capable of disabling a main battle tank from a range of over 6,500 m. While modern battle tanks have quite sophisticated armor protection (for the crew), there are many vital components with less protection.
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how are UAV systems (aircraft+ground facilities) fitted with landing aid system? For commercial aircraft, precise landing aid systems (ILS, GBAS) are required for autolanding, but these navigation systems are too expensive to be used for UAV operations. However, a lot of UAV OEMs have claimed and demoed landing the fixed wing UAV at a runway which is typically used for a Part 23 aircraft. How do these fixed wing UAVs perform and autoland? What kind of landing aided system are installed on the ground or on board? <Q> Each project will have its own specifications. <S> Military UAVs will have different use cases from civilian ones, and, as the comments mention, unmanned does not mean unpiloted. <S> Most of current UAVs are remotely piloted, meaning that there is a front facing camera relaying images to the ground, where a pilot will command flight adjustments to the vehicle to keep it aligned, no special equipment involved (except for the air-ground communication apparatus). <S> The aircraft will be equipped with the usual inertial sensor unit(s) and GNSS receiver(s). <S> For situations where you might have an unpiloted aircraft (that are extremely rare today), it is still solvable by simple INS + GNSS, with the additional requirement that you will have to accurately measure the position of the runway in the GNSS reference system (published charts are not precise enough, as they are created for eye-bearing humans, that can correct the course by sight). <S> This is the method we used <S> and we landed 2 meters from the centerline (the two pilots where there for safety, being it the first attempt). <S> Other projects might include ground-based aid signals akin to an ILS system. <A> A don't know what systems they're using (probably classified). <S> I do know however that military GPS has the "password" to decode the additional GPS frequencies unavailable for civilians, and this gives GPS a much precise location. <S> That should be enough to land a UAV. <S> Civilians can't use this, but most of the absolute error is due to changes in the ionosphere. <S> Relative precision is a lot better. <S> So if you have a receiver at the airstrip, and you broadcast your location, the UAV can calculate its relative position to the airstrip a lot better. <S> This must be good enough as well. <S> Actually, GPS has around 3 meters (10 feet) of error in the open sky on flat ground - incidentally most airstrips has these features - and airstrips are quite big. <S> (Those are based on how I would do it. <S> I don't know enough about UAVs, but I have experience with different GPS systems.) <A> Many UAVs use specialized landing systems. <S> For instance, the Boeing/Insitu Scan Eagle and Blackjack both "land" by snagging a vertical line with a wingtip mounted hook. <S> To do that reliably, the Skyhook retrieval system has a GPS antenna at the top of that line and transmits its location to the incoming UAV which homes in on a location directly underneath the antenna. <S> That it succeeds reliably despite wind turbulence, motion of a ship-board landing and other challenges and has for nearly 20 years strikes me as pretty amazing!
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Smaller UAVs could land based solely on GPS without external help on airstrips built for bigger planes, because that 3m difference is good enough.
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How many serious airline accidents have been caused by design faults alone? That is, in the chain of events that led to death or injuries in an airline accident , how often has a design fault been solely responsible? By a design fault I mean a problem such that even if the equipment: were maintained and operated to the highest possible standards flown in ideal conditions by pilots who committed no errors unaffected by manufacturing defects endured no bad luck eventually it would still inevitably eventually kill or injure its passengers. I can think of only two examples: the early Comet's square windows, and the Boeing 737 rudder power control problem. All the others I can think of include errors of piloting, manufacture, maintenance or just plain bad luck in the chain of causes. Are there others? <Q> The Douglas DC-10 - <S> The door latching mechanism was not robust and the design of the safety indication was flawed. <S> In the Paris incident Douglas tried to blame the handler who closed the bulk compartment door for using excessive force when latching the door but ultimately the design was at fault. <A> I'd say British Airways flight 38 qualifies. <S> Flawed design of the fuel/oil heat exchanger allowed ice to block fuel flow. <S> The aircraft was operated within intended limits and the crew did everything correctly. <S> It was not a maintenance issue nor a manufacturing error. <A> The Douglas DC-6 apparently had a design flaw in the cabin heater that caused one fatal accident and another emergency landing in 1947 before the design was corrected: <S> https://www.pprune.org/archive/index.php/t-355634.html https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_the_Douglas_DC-6 <S> The Lockheed 188 Electra had a design flaw with regards to the engine mounting that caused catastrophic resonance and broke off the wings of two aircraft before it was corrected: https://en.wikipedia.org/wiki/Lockheed_L-188_Electra <A> One of the early ones is the crash of a BFW M.20 on the Berlin-Goerlitz route on April 14, 1931. <S> In a gust the rear fuselage was twisted by 60°, the tail surfaces almost broke off and the aircraft crashed. <S> The crash investigation concluded that the design was good enough to satisfy the certification requirements, but that flight loads exceeded those. <S> As a consequence, the certification loads were doubled. <S> Also, the rudder hard-over with the early Boeing 737s comes to mind. <S> Those accidents caught the poor pilots in a trap. <S> And maybe the first deep stall with the One-Eleven in 1963 . <S> Later accidents with the Hansa Jet and the Trident could had been avoided had the engineers and test pilots studied the One-Eleven accident better. <S> Tupolev did and increased the tail size of their Tu-124A (which became the Tu-134) by 30% as a reaction. <S> The 1991 <S> Lauda Air Boeing 767 uncommanded thrust reverser deployment might also fit. <S> It happened before, in 1990, on the C-5A when the thrust reverser of the No. 1 engine deployed right after takeoff. <S> Similar to Hawker-Siddeley before them, Boeing refused to learn that lesson and tried to cover up this design flaw. <S> Borderline case: <S> It turned out that the engines had not been sufficiently tested and the pilots had insufficient familiarity with the engine instruments, so they came to their wrong conclusions (which would had been correct on the earlier 737s). <A> De Havilland Come t (structural problems, BOAC Flight 783 and 781 crashes in 1954 resulted grounding the entire fleet). <A> Embraer Bandeirante Pitch trim switch causes trim runaway. <S> Crew puts excess stress on control system. <S> Tail breaks off. <S> NTSB report <A> The infamous Boeing 787 battery problem caused at least one emergency landing and evacuation, with a small number of passenger injuries: <S> "There was a battery alert in the cockpit and there was an odd smell detected in the cockpit and cabin, and <S> [the pilot] decided to make an emergency landing," said Osamu Shinobe, an ANA vice president, at a news conference. <S> ANA said that the 129 passengers and eight crew were evacuated, with a number of people sustaining minor injuries. <S> The Reuters news agency reported that five people were injured, while Bloomberg said that one person was sent to hospital. <S> ANA officials were not immediately available to confirm the figures. <A> To answer the title question of how many, we need to check the proper Accident Classification Taxonomy as used by IATA. <S> What you're interested in is the: Latent conditions: Design Design shortcomings <S> Manufacturing defects 10% of the jet accidents are design related $^1$ <S> $^1 <S> $ IATA Safety Report <S> 2017 54th edition (not confined by 2017 or 2013–2017).
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The Kegworth air disaster , when a fan blade on the uprated CFM56 engine of a Boeing 737-400 broke and the different sourcing of flight deck air caused the pilots to shut down the good engine.
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Is it common for automated control systems to use non-redundant sensors? While reading an article about the Lion Air Crash with a Boing 737 Max 8 , I was very surprised by the following paragraph: In designing the 737 Max, Boeing decided to feed M.C.A.S. with data from only one of the two angle of attack sensors at a time, depending on which of two, redundant flight control computers — one on the captain’s side, one on the first officer’s side — happened to be active on that flight. My naive assumption was that any system that is capable of pointing an airplane towards the ground would certainly have redundant sensor input, and switch off if there is serious disagreement between the sensors. Is it common to have non-redundant sensors for this kind of purpose in commercial airplanes? <Q> In general, yes. <S> This matches the fact that pilots flight instruments are fed from a single source as well. <S> Therefore, the autopilot behavior and instruments should have a coherent and predictable response. <S> The main reason is fault isolation. <S> If the flight crew identifies a fault with the captain's instruments, then disabling instrumentation and autoflight functions on the captain's side will guarantee the faulty data will not influence the copilot's instrumentation and controls. <S> If you have the system try to "intelligently" vote, you run the risk of not being able to isolate a faulty sensor, especially in 2 faulty of 3 sensor situations. <S> Another classic problem is how to prevent the voting system from becoming a single point of failure. <S> Instruments are accompanied by a comparator, which detects significant differences between redundant readings and causes an appropriate warning. <S> Most systems treat the warning as binary: the flight crew manually compares all readings and using human logic, decides which are discrepant. <A> The first answer deals with avionics (displays, autopilot, annunciations, stall warning), whose single source failure is usually of minor criticality. <S> If your stall warning misfires, it's not a big deal since the pilot is expected to cross-check against the other sources (co-pilot screen, ISI, etc.), and finally cut off the stick shaker (stick pusher, on the other hand, is a totally different matter). <S> However, for a fly-by-wire aircraft, the other side of the story on automation is flight controls. <S> Since flight control laws modify the handling characteristics behind the scene, much more redundancy is required. <S> By law, any single failure in flight controls, regardless of probability, must not be catastrophic. <S> Then depending on the probability of combinations of failures, they need to be dealt with accordingly, as well. <S> This means that critical sources into the flight control computers must have redundancy. <S> This includes inertial data, air data, AOA, surface positions, etc. <S> The computers themselves must also be redundant and sufficiently different to avoid common mode failures that will knock out all of them at once. <S> Now since MCAS is part of the flight controls, you would think redundancy is required to match the failure probability with its criticality <S> (initially evaluated as hazardous, but not catastrophic). <S> Therein lies the controversy. <A> In general, no. <S> Only in cases where system failure has very little impact on continued safe operation of the aircraft. <S> As mentioned in this question , an analysis needs to be made on: Severity of the consequences of system failure. <S> Exposure time to the failure condition. <S> The failure rate of the hardware. <S> The consequences of a cruise autopilot failing are usually benign (except for some hard-over failures), plus there is lots of reserve in altitude and time for the flight crew to assess what is wrong. <S> In a case like this, a single transducer is tolerable. <S> This answer gives an example of the redundancy in the CATIII autoland system, which has triple redundancy in all systems, including the sensors. <S> It is an example of a critical system, but not the only one. <S> As @Jimmy mentions, flight controls are by definition flight critical.
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Except in certain configurations, namely autoland, autoflight functions are usually fed with one set of sensors.
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How does having a bigger engine placed slightly more forward and higher impact the plane in pitch? I'm asking about general aerodynamics for under-wing twin-jets – I'm not after information/speculation on the Max 8 crashes/systems, but I mention the crash below because of what I see as an unclear (to me at least) explanation: In response to Lion Air Flight 610 , leehamnews.com wrote: All objects on an aircraft placed ahead of the Center of Gravity will contribute to destabilize the aircraft in pitch. But as one commentor wittingly pointed out, wouldn't the fwd engine also move the CG fwd. And then: [G]enerating an angle of attack close to the stall angle of around 14°, the previously neutral engine nacelle generates lift. A lift which is felt by the aircraft as a pitch up moment (as its ahead of the CG line), now stronger than on the 737NG. This destabilizes the MAX in pitch at higher Angles Of Attack (AOA). I read this as insufficient pitch authority, not pitch instability. Going by the text above, I would also imagine the destabilizing force to be a drag from the larger nacelle's bottom, not lift. For example, the relaxed pitch stability of the MD-11 warranted an LSAS system , but not a special anti-stall system. I tried to look for an official explanation for why MCAS was added to understand the general aerodynamics, but the prelim report doesn't mention it. I've presented what has me confused, but the question is the one in the title, wrt general aerodynamics, not 737 Max or MCAS. <Q> This is an "I think" rather than "I know" answer so if you disagree please feel free to explain why. <S> In normal straight and level flight it shouldn't have a significant impact. <S> But at a high AoA, at least a significant portion of the engines are ahead of and crucially, above the CG. <S> The nacelle will be producing both lift and drag the resultant effect of both forces, being above the CG, will be a pitch up moment. <S> Even if this extra force by itself isn't enough to make the aircraft unstable in pitch, it will require the pilots to make a stronger nose-down command, but when you're so close to a stall you want that to be as easy as possible. <A> Placing a bigger (high by pass jet) engine slightly more forward and higher (on the wing) impacts the plane in pitch 2 ways. <S> Moving engine forward moves center of gravity forward, requiring more down force on tail (unless cargo/fuel placement is adjusted). <S> Generally forward CG improves directional stability but can only be trimmed for one speed. <S> The solution to improve pitch stability is to add area behind the center of lift, generally on the horizontal stabilizer. <S> Another solution is to endcap the Hstab (like the B-24 Liberator tail) to make it more effective. <S> Understanding general aerodynamics is key here. <S> A very pitch stable aircraft (where Hstab only allows very slow change in AOA) with a very gentle elevator (ridiculously safe for civilian transports) is what may be far more desirable for this application. <A> Everyone acts like <S> the lift produced by the engine nacelles only acts to increase the amount of down force required of the horizontal tail and pilot effort to cause this increased down force. <S> What is not being talked about is that the lift produced by the engine nacelles is forward of the lift produced by the wing resulting in the total lift vector of the airplane to move forward. <S> As AOA is increased the lift of the nacelles increases in a non-linear fashion (greater than one would expect. <S> I believe that this causes the total airplane center of lift to move forward of the center of gravity. <S> Under this condition an increase in AOA results in a greater pitching moment which can very rapidly result in a runaway condition and stall. <S> The 737 MAX problem is aerodynamic and cannot be fixed by the MCAS which was originally intended to be a longitudinal stability enhancement.
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Moving engine forward creates more area ahead of the center of lift as viewed from directly underneath the aircraft, which affects pitch stability at higher angles of attack.
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Why would a jet engine that runs at temps excess of 2000°C burn when it crashes? Airline engines are designed to work at very high temperatures. Yet, when a plane crashes they're burnt (see below). Is it something in their design? ( bostonherald.com ) <Q> How The Jet Engine Works : <S> Inside the typical commercial jet engine, the fuel burns in the combustion chamber at up to 2000 degrees Celsius. <S> The temperature at which metals in this part of the engine start to melt is 1300 degrees <S> Celsius, so advanced cooling techniques must be used. <S> You can read more about some of those cooling mechanisms in <S> How are temperature differences handled in a jet engine? <S> See also, How do you stop a jet engine melting? <S> : <S> Neil - <S> The normal melting point of the nickel blade alloys that we use in the turbine is typically about 12-1400 degrees. <S> But what you do, and this is the clever bit, is you actually cool these blades. <S> You have internal cooling passages, which effectively has air that flows through <S> and it's about 7-800 degrees. <S> And this cooling air then exits from small little minute holes that have been drilled on the surface of the blade and this air then forms a kind of a film on the surface of the blade, and this technology is typically called a 'film cooling.' <S> What you also do - you coat these blades and typically use something called a thermal barrier coating. <S> The thermal barrier coating, effectively, is ceramic, typically about quarter of a millimeter in thickness, but they have got very, very low thermal conductivity. <S> So, effectively, even though the gas stream is at a much higher air temperature, the effective metal that exists beneath the thermal barrier coating is much colder, and you get thermal grade of the order of about 100 degrees C between the hot and the cold surface. <S> So all of this put together - <S> this whole cooling technology effectively helps to keep the blade below its melting temperature. <S> The engine is designed to manage the intense heat in a controlled way, by restricting it to certain components, injecting cool air around the hot parts, and choosing different materials for different parts of the engine. <S> If the engine is severely damaged, doused in jet fuel, and set on fire, none of those mechanisms function; the entire engine (or whatever is left of it), as opposed to just the portions intended to manage heat, will be hot, and none of the cooling mechanisms will be working. <A> Peter's answer to another question has a nice chart <S> that shows internal jet engine temperatures: <S> You can see that the temperatures are highest by a fairly large factor in the combustion chamber. <S> This means that only the combustion chamber needs to be able to withstand those temperatures. <S> To save weight and often use less expensive and less exotic materials, the rest of the engine may be made out of materials that don't need to withstand such high temperatures. <S> As such, in an accident where jet fuel may be dispersed in an uncontrolled way and burn with as much oxygen as it can get, it's easy to scorch engine parts and anything else around. <S> It also is in part a question of time. <S> The ability to withstand heat varies with time. <S> In a crash of a fairly fueled aircraft that may burn uncontrolled for a long time you are likely to find scorched parts like this. <S> Whereas a plane that runs its tanks try and crashes in a field may not see the same fire marks. <S> However, if the plane hits the ground with enough force the heat generated from the impact can also lead to markings like this . <A> First off, the engine is running around 2000° F (NOT 2000° C/3632° F) only in a few places within it. <S> The Turbine Inlet Temperature (TIT) can be that high but cools rapidly when the exhaust gases are rapidly expanded through the high and low pressure turbines to exit at approx 1000 <S> ° F at the jet pipe (enthalpy is converted into mechanical work here). <S> UPDATE: <S> While I do not have definitive values for the max TIT of a CFM-LEAP engine, a good estimate would be around 1500°- 1600 <S> ° C (2732° - 2912° F) as this represents about the state of the art for gas turbines outside of a few military applications. <S> This source quotes that the Pratt & Whitney F-135 can operate at TITs of 2000 <S> ° C due to its use of a proprietary ceramic coating over single crystal nickel cobalt superalloys for the hot section. <S> It is unclear whether that is a sustained engine power setting or simply a max operating temp prior to destruction. <S> This is NOT representative of a typical aviation gas turbine, which run much cooler. <S> I would stand by my original figure of 1000-1200° <S> C TIT for earlier gas turbines eg PT-6, J85, J79, etc.
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Most sections of the engine are not designed for that high of a temperature and may well oxidize or deform in the post crash fire.
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Where are the grounded 737 Max planes being kept? With various countries grounding the 737 Max, where are they (their carriers) keeping the grounded planes? Are they simply being kept at Gates of various airports (which I doubt since gates are expensive and/or logistical reasons)? Are there "holding areas" at some airports? While I understand some carriers just fly a few of these, what about those carriers with larger fleets, such as ones in China or the EU? <Q> Airports are big enough places that there's room plenty of room to park planes that aren't currently in use, and it's completely normal to have such planes parked at an airport. <S> Just look at a few in Google Maps satellite view. <S> At least in Europe (and presumably elsewhere), the directive banning flights does allow one ferry flight (of up to three legs) to get the plane to a location where any corrective action can be taken. <S> But note that this does not allow moving the plane just to get it to a more convenient storage location. <S> Great Circle Mapper's featured map for 14th March showed the actual location of the 737 MAXes owned by US airlines, as of the previous evening. <S> Those aircraft are spread across around 30 airports in the US and Caribbean. <S> Thanks to Antzi for pointing out the ferry flight exception. <A> Gates (with jetways and all that) are extremely precious. <S> They are only used by passenger aircraft, and even then to load or unload passengers. <S> My last flight had a nice tailwind and arrived early; we had to wait 20 minutes for a gate to open up. <S> During any other times, aircraft are sent to a ramp area , or a chunk of airport area reserved for parking and servicing airplanes. <S> London Heathrow is a very cramped airport with an abnormally tiny ramp area, however here is much of it. <S> Note the special guest near bottom, just right of center. <S> Notice <S> a couple of areas walled off for engine run-up testing . <S> Southwest of here <S> there's additional ramp in the space reserved for Terminal 5D. <S> All in all, Heathrow is very sparse on ramp area; even SFO has more. <S> (SFO also still has the literal ramps for seaplane operations.) <S> Now, busy airports have lots of taxiways that less-busy airports do not need, like taxiway A and B at Heathrow, which provide basically 2-way traffic. <S> If an incident causes reduced activity that makes some of those taxiways redundant, they can park planes on them. <S> Further, if certain runways are expected to be crosswind runways for the duration of a crisis, they can stack those up too. <S> At extremes, Kingman Airport basically took their east-west runway out of service and is using it to store decommissioned RJ's. <S> They used to store more aircraft still . <S> This could also be done temporarily with a crosswind or little-used runway. <S> Also, even if an airplane is grounded, a ferry move may be permitted out of a very cramped airport like Midway to an airport with more ramp space available. <S> Look at this sat photo of the ramp at Victorville (former George AFB). <S> See something familiar? <S> The date is Aug. 25, 2018, and these planes are about 110' long, making these most likely 737-300's (or -700s?). <S> Bet Southwest wishes they had them back right now! <S> The one at far right is about 129' long, making it a -800 or MAX 8. <A> FlightRadar24.com has compiled a list of where (almost) all the grounded 737 MAXs were as-of 17 March 2019. <S> Their page shows airports with 5 or more aircraft and there is a list that's sortable by registration, aircraft type, MSN, airline and airport. <S> The airports with the most are: <S> Guangzhou Baiyun, China (15) <S> Boeing Field, WA, USA (14) Ürümqi Diwopu, China; Windsor, ON, Canada (12 each) <S> Dubai, UAE; Istanbul, Turkey; Beijing Capital, China; William P. Hobby, Houston, TX, USA (10 each) <A> Bloomberg has an Interactive Map showing where the planes are in the USA. <S> You can scroll through the days, and it also shows which flight paths they took to arrive at their "final" destination, and is color coded by carrier. <S> Pretty neat! <S> Edit: Also, they're storing some in the Boeing Employee's Parking Lot :
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They're at whatever airport they were at (or next landed at) when they were grounded.
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Are pilot YouTubers breaking any rules? Recently, I've been watching a few YouTubers (mostly FOs) who make great videos like this: Then I realized... They must spend a lot of time setting up cameras, playing with them, hitting record and stop etc. This could potentially distract them or make them miss something (a warning, a pre flight check etc).. Are they breaking any formal rules doing this? If an accident occurred during filming would they be under investigation due to negligence? <Q> If the FAA considered making videos itself (i.e. separate from any unrelated rule violations within those videos) to be a problem, they would have put a stop to it long ago, either by explicit rulemaking or the catch-all "careless or reckless" when no other rule applies. <S> They haven't, at least with respect to GA pilots--who are allowed to do all sorts or things that charter and airline pilots are not. <S> Several YouTubers I follow have said they mount the cameras and start recording before preflight, don't touch them again until after the plane is down and secured, and edit out the boring parts later that show this. <S> That seems to mitigate the physical safety issues. <S> The other issue is pilot distraction if they're talking to the camera, but I don't see that as any worse than talking to passengers, which is commonly accepted within reason, and is perhaps less of a risk since the camera doesn't talk back. <A> You can get into trouble for your videos. <S> Stevo1Kinevo had to remove all of his videos that were taken on Part 135 trips and had to take a 709 ride. <S> I gather that it wasn’t due to distraction so much as rules related to Part 135. <S> He was also dinged for not using checklists, but he had the raw videos that showed that he does use them. <S> I suppose you could be charged under §91.13 Careless or reckless operation. <S> if you video yourself doing something careless and/or reckless. <A> Outside of a departure or arrival, with the autopilot engaged, and one pilot monitoring, the other pilot can do headstands, play a game on his tablet, read, take a snooze, fill out log books, go for a dump, or... use a video camera. <S> It's not a big deal. <S> I've shot video to pass the time during cruise. <S> The general rule (as in good airmanship) is no screwing around during a higher workload phase like departure or arrival and especially below 10000 ft (including superfluous talking... <S> non-flying chit chat should stop below 10000 ft). <S> During those higher work load phases, if a camera is set up to record, it needs to be set up in a way that doesn't require any attention or cause a distraction. <A> The FAA does have specific regulations that could apply to making videos during part 135 and part 121 flights. <S> As JScarry explained in his answer the part 135 rules may have been used against one prominent Youtuber. <S> 135.100 says (emphasis mine): §135.100 Flight crewmember duties. <S> (a) <S> No certificate holder shall require, nor may any flight crewmember perform, any duties during a critical phase of flight except those duties required for the safe operation of the aircraft. <S> Duties such as company required calls made for such nonsafety related purposes as ordering galley supplies and confirming passenger connections, announcements made to passengers promoting the air carrier or pointing out sights of interest , and filling out company payroll and related records are not required for the safe operation of the aircraft. <S> (b) <S> No flight crewmember may engage in, nor may any pilot in command permit, any activity during a critical phase of flight which could distract any flight crewmember from the performance of his or her duties or which could interfere in any way with the proper conduct of those duties. <S> (c) <S> For the purposes of this section, critical phases of flight includes all ground operations involving taxi, takeoff and landing, and all other flight operations conducted below 10,000 feet, except cruise flight. <S> For part 121, 121.542 says essentially the same thing, with an additional section banning the use of electronic devices at duty stations for non-flight purposes. <S> In any case, clearly recording videos during takeoff and landing in 135/121 flights is no problem; there are hundreds of them on Youtube and airlines even use them in promotional materials. <S> It seems very likely that the FAA's real concern is distraction, i.e. not just recording but actively participating in the video.
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Activities such as eating meals, engaging in nonessential conversations within the cockpit and nonessential communications between the cabin and cockpit crews , and reading publications not related to the proper conduct of the flight are not required for the safe operation of the aircraft. I remember reading or hearing somewhere (maybe reddit) that the FAA went after Steveo1kinevo because he was making videos during part 135 flights that included a lot of commentary during takeoff and landing, i.e. "nonessential conversations" during critical phases of flight.
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Why is not every airplane equipped with 3 angle-of-attack sensors? For critical systems, redundancy is built into the system. It is common knowledge among designers/architects to have three different inputs so in case one is faulty, input from the remaining two can be used to find (and shut off possibly) the faulty one (two against one). Why is not every airplane equipped with 3 angle-of-attack sensors and triple modular voting when these devices are critical for the safety? <Q> Triple redundancy is necessary to detect a fault and exclude it. <S> The system then continues to operate through the fault. <S> The important fact is that the faults they actually detect are identical. <S> Stall events are rare and are normally not expected in flight. <S> There is no immediate hazard if handling augmentation or stall warnings are disabled. <S> Therefore, there is no need for triple redundancy. <S> Simply put, if the system detects an AoA discrepancy, it can simply trip off and stay off until it is repaired on the ground. <S> If the double redundant system is ideally designed, then only a simultaneous fault will escape detection. <S> Note too that if the same simultaneous fault occurs to two sensors in a triple redundant system, then it will also escape detection because it will outvote the correctly operating sensor. <S> Therefore, both systems share the exact same failure mode. <S> It also allows faults in the voting logic (QF 72). <S> Both recent AF and XL fatal accidents are signs of an overreliance of buying 3 of the same box and then calling it "safe". <A> Two AoA sensors are more reliable than three! <S> Let's have a look at probability calculation, and assume the fault probability of one sensor to be p = 0.1 % (per flight, or whatever you like to choose). <S> The probability of the same sensor to work as expected is q = <S> 1 <S> − <S> p = 99.9 %. <S> Two Sensors <S> The probability for no fault: <S> q 2 ≈ 99.8 % a discrepancy (1 fault) <S> : 2 p q ≈ 0.2 % an undetected double fault: p 2 = 10 <S> -6 <S> Three Sensors <S> The probability for no fault: q 3 ≈ 99.7 % 1 <S> recovered fault: 3 <S> p q 2 ≈ 0.3 % undetected faults: 1 − q 3 − 3 p q 2 ≈ 3 · 10 -6 <S> Which solution is preferable? <S> Autonomous system <S> If we were talking about an autonomous system, like a drone or maybe a satellite, we would be looking at the ability of the system to take a decision on its own. <S> A decision cannot be taken with 2 sensors if a discrepancy or a double fault occurs. <S> The probability for that is 0.2 %. <S> 3 sensors if more than 1 fault occurs. <S> The probability for that is 3 · 10 -6 . <S> 3 <S> · 10 -6 is 667 times better than 0.2 %. <S> The autonomous system is better off with three sensors and TMR voting. <S> Aircraft with pilots <S> The situation is different if the system is monitored by a pilot, who can intervene in the case of a discrepancy. <S> A false positive alarm is acceptable. <S> Undetected faults are not acceptable. <S> The likelihood for an undetected fault is 1 · 10 -6 with 2 sensors, and 3 · 10 -6 with 3 sensors. <S> The 2 sensor system is 3 times more reliable under this premise! <S> In addition, a single fault is more obtrusive in the case of the 2 sensor configuration. <S> A single fault with three sensors - if noticed at all - is more easily ignored instead of being eliminated. <A> Regardless of the number of sensors, the pilot must have enough experience to tell what is going and just fly the plane. <S> Checklists may help, but there may not be time. <S> After the first 737 MAX crash, there was an Airworthiness Directive and a Notice to Airmen setting forth the way to deal with stabilizer runaway, whatever the cause, including MCAS. <S> The 2nd crash occurred after the pilots first followed those procedures but then reversed them. <S> MCAS has been fixed. <S> Regulators have stated and certified that point. <S> Pilot training has not been fixed. <S> That's what needs to happen next.
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Double redundancy is used to detect a fault but cannot exclude it, so the system stops operating. Double and triple simultaneous faults can and do occur with common causes including environmental factors (AF 447), maintenance errors (XL 888), and birdstrikes (US 1549).
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Why would a flight no longer considered airworthy be redirected like this? I ran across this tweet covering the saga of Smartwings 1201, a 737 MAX 8 that was apparently redirected from Prague to Ankara after the MAX was grounded by the EU. ( flightaware.com ) It seems like an odd decision to do this. The plane had to divert and apparently spent quite a long time in circling before it was allowed to land in Turkey. Why was it not allowed to land at Prague as scheduled and be grounded there? <Q> There could be a lot of reasons for this... <S> EU closed airspace to 737's MAX 8's on March 12 They needed to go into a holding pattern until ATC figured out where to put them <S> They needed to be in the holding pattern until they could get a landing slot <S> They redirected to an airport with code-share partners so they could rebook passengers without a major fee <S> Edit <S> I'm not sure what is going on with FlightRadar24, but it shows that the plane continued to Prague the next day . <S> It looks like they landed in Ankara then continued on to Prague. <S> I'm not sure if the flight to Prague was just a repositioning flight, or if it had passengers. <S> Edit 2 Turkey subsequently (after this flight) also closed airspace to 737 MAX 8's. <S> The EU closure allows for ferry flights, which are flights without passengers on board. <S> The flight from Ankara to Prague was just a positioning flight so that the aircraft could be serviced when it came time to implement a fix from Boeing. <A> This is just because of the way EASA treated B737 MAX grounding. <S> They just stopped accepting flights with these aircraft into the EU airspace even for already airborne flights with valid flight plans. <S> For this company two flights were involved . <S> On from Cape Verde ended up in Tunisia and one from Dubai in Ankara. <S> Both of them were originally hoping to get to the EU airspace until the perceived misunderstanding clears - because flights already airborne and with valid flight plans should be allowed to finished their flights, right <S> , that sounds logical ... not to EASA... <S> So these aircraft had to land outside EU, get to PAX to the hotels, fly other types of airplanes for them and ferry the MAXes empty home to LKPR. <S> Other airplanes of the same company became stranded out of EU because they were doing flights between two out-of-EU destinations at the time of the ban and had to wait for a day to be allowed to ferry home. <A> There is no evidence that EASA refused Smart Wings QS 1201 to enter EU airspace. <S> The EASA AD does not make any statement about airborne aircraft. <S> Stopping operation mid-air is no option, and a last minute diversion does not contribute to the safety of the passengers. <S> It is more plausible that the airline had a hard time to decide what to do with this flight, considering all implications including but not limited to legal, operational, commercial and reputational aspects. <S> The internal decision process might have looked similar to the flight track as shown in the question. <S> ;) <S> Please see the answer of Paul Saccani in <S> Who decided that the Boeing 737 MAX planes that were airborne when the grounding was issued cannot enter and land in EU air space? <A> In the case of the EASA directive regarding the B737 MAX: all planes have to be grounded and those in flight weren't allowed to enter European Airspace. <S> Therefore, the plane is trying to figure out where to land.
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They were redirected to an airport that had a maintenance facility that the airline uses
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Why do passenger jet manufacturers design their planes with stall prevention systems? I understand why passenger jets use software that overrides pilot inputs that might cause the jet to exceed the flight envelope. But why do passenger jet manufacturers design their planes with stall prevention systems? Shouldn't professional pilots be well aware that a stall is possible when the airspeed is too low, or the angle of attack is too high? <Q> Why do car manufacturers install seat belts? <S> Shouldn't licensed drivers be well aware that they should slow down when it's raining or snowing and that they shouldn't run through red lights or stop signs? <S> A better analogy: <S> Why do car manufacturers install anti-lock break systems? <S> Shouldn't drivers know that when their brakes lock up they should release brake pressure and/or pump the brakes quickly to slow the car down? <S> * <S> *To be fair, I don't think this is actually taught in driver's education (at least in the US) <S> anymore - my kids learned this from me, but never reported being taught and/or practicing when they took driver's ed. <S> One of the many reasons flying is safer than driving. <S> Because accidents happen. <S> Because pilots are human and make mistakes. <S> Because when you're flying in the clouds with no visual references, it's easy to get confused. <S> Because even with stall warning & prevention systems in place, confused pilots will fight the system. <S> AF 447 <A> To be certifiable, airplanes have to have some kind of cues to warn when you are getting close to a stall, and have decent behaviour during the stall, because nobody is perfect. <S> Airplanes with very strong physical cues prior to stall, like the whole airframe shaking, and good behaviour during a stall, like a good natural pitch over tendency with immediate unstalling of the wing, can get away without stall warning and prevention systems. <S> Transport aircraft with highly loaded wings and high performance airfoils may have poor behaviour before the stall (no buffeting or shaking), and poor recovery performance after, and need a little help. <S> The airfoils used for airplanes that fly at near trans-sonic speeds tend to suffer from this because they tend to stall from the leading edge, at which point the wing stops lifting all at once, and there is often no prior buffeting or shaking. <S> The earlier supercritical (higher critical mach <S> #) airfoils developed in the 70s were especially bad for this because they developed a flow separation bubble just aft of the leading edge at high angles of attack, due to the profile that was used to manage the formation of shock waves <S> (the Challenger business jet and CRJ200 Regional Jet is typical). <S> You do not want to experience the natural stall on such an aircraft and some kind of system <S> has to be in place as a backup for mishandling of the airplane by the pilot. <S> For airplanes with mechanical/hydraulic controls, to provide a tactile warning as a substitute or supplement for the airplane shaking (pre-stall buffet), stick shakers are used, which is just a motor with an eccentric weight on the control column. <S> If the post stall behaviour (not much natural pitch over, or worse, settling into an unrecoverable deep stall) is poor, a stick pusher is installed to give the control column a shove just before the natural stall occurs. <S> The stall protection system calculates when to do all this. <S> Most high performance aircraft use shakers, and some use stick pushers. <S> With FBW, the FBW computers intervene directly within the control loop to achieve the same end without having to shake or push the controls. <A> You said you understand systems to prevent the airplane from exceeding the flight envelope. <S> Stall is just another boundary of the flight envelope. <S> The rest of the envelope limitations are listed in the flight manual as well. <S> Shouldn't pilots know not to stall the airplane, just as they know not to over-stress it, or exceed other limitations? <S> Of course. <S> But humans make mistakes, they can get distracted or disoriented. <S> And just as there's little benefit to allowing a pilot to rip the wings off the plane by pitching too fast, there's little benefit from allowing the plane to stall. <S> Here is a selection of aircraft that have crashed due to stalls. <S> South Airlines Flight 8971 Air Algérie 5017 <S> AirAsia QZ8501 <S> Thai Airways International flight 261 <S> Vladivostokavia Flight 352 N452DA <S> Yemenia Airways Flight 626 <S> If stall protection systems are implemented and functioning properly, they can prevent issues. <S> Here are just a few instances where stall protection worked as intended: GoAir 338 Air France 7662 <S> Jetstar 248 <A> The relevant certification requirements, set by the FAA/JAA/CAA etc require that a "large aircraft" that is capable of stalling has an automatic stall warning and recovery system. <S> So the simple answer is "because the rule of law says so". <S> Maybe you could think about re-phrasing the question to ask why the traditional stick shaker and pusher, with a long and satisfactory history, were not used? <S> I expect that Boeing will be having to answer that question to the authorities. <A> And note that stall is directly related to pilot input, because in stable aircraft¹ the angle of attack is directly controlled by elevator and stabilizer position² and stall <S> occurs when the critical for given configuration is exceeded. <S> ¹ <S> All transport aircraft are longitudinally stable. <S> Only unstable aircraft are some new fighters (and some very early experiments). <S> ² <S> The stability makes the aircraft always pitch so as to assume the “trimmed” angle of attack determined by the control surface position. <S> It is a first order feedback, so no oscillations, and it takes really abrupt control input, or severe turbulence, to create a significant momentary deviation.
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Well, stall is a limit to flight envelope, the one exceeding which is most dangerous, so stall prevention system is one of the systems that override pilot input if it would lead to exceeding the flight envelope.
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Why don’t airliners use stabilizer movement to assist with large pitch control inputs? Most large airliners not only have elevators for pitch control, but also moveable horizontal stabilizers. The elevators are used for primary pitch control, with the stabilizers being used to trim the aircraft, and, for some airliners, as an alternate method of emergency pitch control in the event of a loss of elevator control (due to, for instance, a failure of the hydraulic systems powering the elevators, an elevator actuator hardover, or the physical separation of one or both elevators from the aircraft). Due to their much larger size, the stabilizers have a vastly greater maximum control authority than the elevators (which is why large modern airliners can be trimmed throughout very wide center-of-mass longitudinal-position ranges without having to defair the elevators, and why a stabilizer trim failure is generally somewhat inconvenient ); however, despite this, few, if any, large airliners use the stabilizers to assist the elevators when making large longitudinal control inputs (for instance, when taking evasive action to avoid a MAC, or when recovering the aircraft from an upset). Why is this? Airliners can and do use secondary flight controls to augment the primaries in other situations; with roll control, for instance, small inputs are handled by the ailerons alone on most aircraft, while the spoilerons 1 jump in to help the ailerons with larger changes. So why aren’t the horizontal stabilizers called on to assist the elevators when large, sudden changes in pitch are necessary? 1 : A spoileron is the technical term for a spoiler that is also used for roll control in flight (these are usually the same spoilers as those that can be extended symmetrically in flight to slow the aircraft). Essentially all large aircraft, and many smaller aircraft, have them to help with large roll inputs; a few aircraft, such as the Mitsubishi MU-2 , have only spoilerons, with no conventional ailerons. <Q> The elevators hydraulic actuators are quick response devices, the THS is screw operated and therefore is slower to response. <S> Therefore it’s normal to use the elevators for short term action and theTHS for long term action. <S> For safety you can’t rely only on elevators or only on THS. <S> One system should be able to neutralize the other in case of failure. <A> There are no regulations requiring airliners to have this kind of high maneuverability. <S> Airliners are designed to be safe and stable. <S> It's more important that pilots are trained to get out of a situation with unnatural pitch than be able to quickly get into such a situation. <S> Voluntarily adding a new system to automatically move the THS to improve handling in situations that are highly unlikely to occur is not without risk. <S> There must be some additional benefit. <S> In general airliners are more concerned with having too much pitch authority rather than too little, as they spend most of their time in the air at speeds where the elevator has plenty of authority. <S> Fly by wire systems can help this by limiting control inputs to avoid over-stress on the structures. <S> They protect the low end in a similar way by limiting angle of attack. <S> The pitch trim is also not very fast, so it's unlikely that there would be enough thrust to sustain a maneuver that would benefit from moving the entire stabilizer. <S> And at the end of such a maneuver the airplane is left way out of trim, at an extreme pitch attitude, with airspeed either increasing or decreasing dangerously. <S> This might be more dangerous than whatever the pilots were trying to avoid. <A> Remember, airliners are all about passenger comfort. <S> Secondly, one must check the G load stress limits of applying elevator and stabilizer trim for pitch, especially for negative G's. <S> As an emergency evasive maneuver, the pilot may prefer to roll the plane to drop it and pull positive Gs. <S> More so, they would prefer to know what was around them. <S> Airliners are so massive and fast that any abrupt input would most likely be to little, too late.
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At low speeds sudden pitch changes would put the aircraft in danger of stalling, as airliners typically don't have the kind of thrust needed to sustain high pitch attitudes, or the type of wings that operate well at high angles of attack.
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If all control surfaces were disabled, could a passenger plane be controlled by distribution of the passengers? Let's assume that a large military plane has its control surfaces disabled in combat. The engine(s) can still be controlled. There is a substantial number of ground forces being transported. In theory could the plane be flown purely by distribution and redistribution of the weight of the passengers? Note these are military personnel and are used to acting on orders. <Q> There are different degrees of control. <S> The plane could at least be made to crash in a different debris pattern than if the input was not made, and even that's a form of control. <S> As the whether the plane could be controlled enough to land, and do so, as the question states, with all of its control surfaces disabled, let's see. <S> You get considerably pitch control authority, with poor speed and accuracy, but very little direct roll control. <S> Differential thrust provides a decent amount of yaw control. <S> So the first question is: Is the plane already on the glideslope of a straight-in approach to an airstrip? <S> If yes, then passenger movement should, with some luck, suffice to get the plane down to the ground. <S> If not, getting a plane to a suitable landing spot becomes more difficult. <S> Many military transports are designed for rough field landing, so over flat and easy terrain, it should be possible to get some sort of landing that is better than an uncontrolled crash. <S> If the terrain is not so forgiving, it comes down to trying to navigate and fly with greatly reduced control responsiveness and precision, where many inputs will be made wrong, and down to whether they can be corrected in time. <S> To make an analogy, if a driver transporting a blind passenger falls out of the car, can it be controlled from the back seat by moving controls with the passenger's walking stick, acting on advice shouted from cars passing by? <S> That's how trying to fly a plane that way would probably feel. <S> That said, much stranger things have happened. <S> People have fallen out of airplanes without parachutes and survived. <S> Planes have landed themselves smoothly after the pilot has ejected. <S> And landings with a loss of most controls have happened as well. <A> Let us consider the longitudinal stability In a longitudinally stable aircraft, any wanted or unwanted increase in angle of attack will cause the pitching moment on the aircraft to change so that the angle of attack decreases. <S> Similarly, a wanted or unwanted decrease in angle of attack will cause the pitching moment to change so that the angle of attack increases. <S> The above stability is possible provided the aircraft has a stable centre of gravity <S> Modifying the CG by moving the passengers to modify the angle of attack is by definition playing on the instability boundary of the pitching moments, this is possible only with extremely reactive commands, that is with FBW (fly by wire) and not with FBP (fly by passengers). <A> Shifting the center of gravity by sending people fore or aft was once common practice on large airships to change pitch, taking advantage of a lever arm of several hundred feet. <S> It is theoretically possible to do this on a passenger airliner. <S> Altering the CG with a fixed (frozen) elevator trim will have the effect of speeding up or slowing down the aircraft trim speed. <S> Moving weight forward means elevator trim (aerodynamic) <S> needs more airspeed to raise the nose <S> (increase the angle of attack of wing), causing the plane to climb and lose speed, eventually settling into its new trim speed. <S> Moving weight back makes it easier to raise the nose, so the speed stability mechanism (elevator trim) raises the nose at a lower airspeed. <S> The key here is realizing the limitations of this technique. <S> If the weight is too far back, the plane will not pitch down and gain airspeed before stalling. <S> Naturally, a little practice at altitude would help. <S> For a stricken aircraft, control by differential thrust has been demonstrated. <S> Moving weight fore and aft could be tested.
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A practical application of moving passengers would be to help flare the aircraft just before landing.
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Why can’t more older 737s be retrofitted with more newer winglets? Some background: there are four different types of winglet that have been used on various 737s over the years. The mini winglet is used to retrofit 737-200s (one of the two 737 Original variants, the other being the 737-100). It is basically a tiny trapezoidal tab riveted to the rear portion of the wingtip. (Image by Julian Whitelaw at airliners.net , via meisam nemati here at AvSE .) The blended winglet is what most people think of when they hear the word “winglet” - an attachment that looks like someone simply extended the wingtip and then bent it up to near-vertical. It was factory-installed on all 737 Next Generation variants (the 737-600/-700/-800/-900) for the first two decades of production, and has also been retrofitted on most of the 737 Classic models (the 737-300/-400/-500) that remain in service. (Image by Ralf Roletschek at Fahrradtechnik auf fahrradmonteur.de via Wikimedia Commons , modified by Altair78 at Wikimedia Commons .) The split-scimitar winglet has replaced the blended winglet on the last few years of the Next Generation production line; it is shaped somewhat like the blended winglet, but a) is swooshed rearwards at its upper tip, as opposed to the simple trapezoidal tip of the blended winglet, and b) has an additional scimitar-shaped, rearward-swept fin projecting from the outside of the upbend in the winglet. (Image by Mnts at Wikimedia Commons .) The MAX winglet is used on the 737 MAX series (737 MAX 7/8/9/10); it, too, is a split winglet, 1 but of a simpler shape than the split-scimitar winglet, looking much like someone extended the wingtip outwards, then split its upper and lower surfaces away from each other and bent them upwards and downwards, respectively, to form what looks remarkably like a glorified Airbus wingtip fence. (Image by Aka The Beav at Flickr , via Helmy oved at Wikimedia Commons , modified by Altair78 at Wikimedia Commons .) Now for what I’m curious about: Although the 737-100 (the original Original) was produced in smaller numbers than the 737-200 and is no longer in service, it still hung on with various operators past the turn of the millennium; why weren’t any -100s also retrofitted with mini winglets, given that the -200 is basically just a stretched -100 with more fuel capacity? Given that the blended winglet, despite being originally designed for the Next Generation wing, was retrofitted on the vast majority of the Classic fleet with little to no trouble, why couldn’t it also be retrofitted on the remaining Originals, given that the Classics are essentially CFM56-engined, (sometimes) stretched -200s? Seeing as the Next-Generation-designed blended winglet was easily adopted for the earlier Classics, what keeps the split-scimitar winglet, likewise designed for the Next Generation wing, from also being retrofitted to the Classics? (Yes, I know that this is three questions rather than one, but I felt it was better to have one question asking three closely-related questions than to clutter up the homepage with three separate but near-identical questions.) 1 : As for why Boeing went to the trouble of developing two different styles of split winglet for the two in-production 737 families, that’s a different question . <Q> Winglets change the spanwise loading on the wing. <S> By increasing the effective span of the wing, lift is increased towards the tips of the wing. <S> With more lift there, you get an increased bending moment on the wing. <S> All this means <S> is that you can't just put winglets on or change the ones you have. <S> You must retrofit the structure of the wing which is very expensive and requires significant downtime. <S> It also adds a weight penalty which decreases the benefits of the winglet. <S> For example, on the A320, which was already wingtip fence equipped, going to the sharklets requires removing the skin and reinforcing both the tip and the center wing box near the fuselage. <S> This takes the aircraft out of service for 15 days and involves, I've heard, in excess of $1 Million in parts alone. <S> On the 737, the list price for the blended winglets is $1.06 Million . <S> So the answer for why is because it often is not economical to do such a huge modification given the limited lifetimes on older models. <A> In order to develop and test a new product, you have to be sure that there is a sufficient market for it. <S> As you noted, the 737-100 is the most extreme example, where only 30 of the 737-100 were ever built, and the 737-200 saw over 1000. <S> This gave them a market roughly 30 times larger. <S> It probably didn't make sense to certify the mini-winglets on the 737-100 if there were only a handful of airplanes that would use it. <S> By the time the makers of the blended winglet were ready to look at derivatives, the mini-winglet was already available, or soon would be. <S> The development cost may not have supported splitting the market, especially since the mini-winglet was part of a more extensive flap modification that provided other benefits. <S> As for the split scimitar, while airlines have seen the benefit of retrofitting it to the relatively new NG line, they may see less benefit of putting on the older classic line, especially if they are still trying to reach the payoff for paying to put the blended winglets on. <A> Because there is not much point. <S> Winglet increases effective wing span. <S> It is not as good as just increasing the span, but it is simpler to redesign a shorter wing by adding winglet than designing a longer wing, and keeping the wingspan down is useful so the new version can still usie all stands and taxiways the previous version could. <S> However, if the aircraft was designed with appropriate span for its weight and cruise speed, increasing the span is not what you want. <S> While it would decrease the drag at the best lift/drag point, it would push that point to lower speed, and the drag at the original cruise speed would increase. <S> Winglets are added to the newer versions, because they are also given more powerful engines, which allow higher take-off mass. <S> The higher weight requires more lift, which increases the best lift/drag speed, so increasing the span is needed to compensate. <S> And modifying the wing by adding winglets is much easier than making it larger, because while it may still need strengthening the spars, as the bending moments do increase, all the other systems like flaps and ailerons and deicing and fuel system can stay the same.
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Because of how aircraft certification is handled, it doesn't make sense to test a modification for a model that can't sell enough units to pay for itself.
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Why is indicated airspeed rather than ground speed used during the takeoff roll? My instructor asked me this question during my lesson and I couldn't come up with any answers. He asked why do I need to look at the indicated airspeed rather than ground speed when in takeoff roll or as soon as we touchdown? It would be great if you could give me the reference to back it up. <Q> Because wings work on air moving past them, not ground moving below them. <S> Heck, in a 35 knot headwind, the Antonov-2 could be rolling backwards at 2 knots and still take off! <A> Because what determines the amount of lift generated is the indicated airspeed, not the ground speed. <S> As usual, it is always easier to think about an extreme case. <S> If you have an aircraft with V R (speed at rotation for takeoff) of 90 knots, and there is an 80 knots head wind, in theory it will rotate with ground speed of 10 knots even though the indicated airspeed will be 90 knots. <A> Airspeed is always important as it determines lift which keeps you in the air. <S> At the moment of take-off or landing, airspeed is critical because it is the point at which you transition to or from flight; you need to be going fast enough but not too fast so that the transition is positive without being abrupt or overly stressful on aircraft components. <S> This is why there are specified take-off and approach speeds. <S> Ground speed matters in navigation because it determines flight time which affects fuel required to get from A to B. Ground speed is a consideration for take-off and landing (ideally kept to a minimum), which is why it's always preferable to do so into the wind, but ultimately it is airspeed that matters and ground speed is what it is at the moment of take-off or landing. <A> The Wikipedia article on indicated airspeed has a good description. <S> An airspeed indicator is actually more of a "dynamic-pressure" meter, with the dynamic pressure converted to airspeed. <S> Dynamic pressure is <S> $q=\frac{1}{2}\rho V^2$ <S> where $\rho$ is <S> density and $V$ is airspeed. <S> The Wikipedia article on the lift coefficient explains that lift is proportional to dynamic pressure, the area of the wings, and the lift coefficient, which in simplified terms can be considered a function of the angle of attack. <S> $L=\frac{1}{2}\rho V^2 S C_L(\alpha) = <S> qS C_L(\alpha) <S> $ <S> The takeoff speed is the speed at which you will have enough lift to get the airplane off the ground at the angle of attack that the airplane will have post-rotation. <S> So, for a given aircraft at a given weight, wing area, post-rotation angle-of-attack, and lift curve, you will be able to take off at a particular dynamic pressure. <S> In fact, all the aerodynamic forces on the aircraft are proportional to the dynamic pressure. <S> So that's why stall speed, never-exceed-speed (above which the aerodynamic forces could start damaging the aircraft structure), etc. are all given in indicated airspeed - because it's a proxy for dynamic pressure. <S> True airspeed is the speed of the aircraft relative to the air mass it's flying through and can be calculated from indicated airspeed by correcting for density and temperature. <S> Your ground speed is then the true airspeed added to the wind speed. <A> The IAS includes factors such as Wind Component (Tail, Head or Cross), Pressure and Temperature. <S> All these have an influence on your takeoff. <S> The takeoff Speed Vr is calculated as Indicated Airspeed. <S> Imagine you have a Headwind Component of +50. <S> You Groundspeed would be way lower than your Airspeed.
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What counts is the amount of air that flows over the wing in order to takeoff, not the speed relative to the ground.
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How are V speeds spoken? How are V speeds spoken? --Research for my novel. Is it the V and the number or letter notation or is there something more to it? The Wikipedia Page on V Speeds does not delve into the subject matter. I did search the search box, prior to submitting, but nothing has come up. Please don't get angry by my question or restrict my learning. I can always go to a better source--I got a message some of my past questions were not well received. <Q> It Depends on the speed, and in some cases the context it is being announced or discussed, different pilots may also call things out differently depending on op specs or simply the way they are trained. <S> V1 is typically announced as "V One" <S> I typically announce V4 as "Trimming for XXX Knots" Vfe for me is typically " in the white arc, deploying flaps" <S> Vx and Vy are usually discussed as such or some times as "pitch for best angle" or "pitch for best rate" Some of the V speeds are never really announced but important to know. <S> V speed numbers help define the operational envelope of an aircraft but are not always announced or even relevant to announce. <S> For example unless you are in a really bad situation its unlikely you are ever going to announce Vne out loud but its a very important speed to know (and avoid). <A> There are quite a few V-Speeds, not all are spoken during takeoff though You do say: (In some companies: "80 knots" - <S> To inform the PF about the speed) <S> V1 - <S> The speed above which you are not allowed to abort the takeoff under no circumstances. <S> Vr (Spoken "Rotate") <S> - The speed at which the pilot pushes the nose upwards in order to generate lift (In most companies: "positive climb" - <S> To inform the PF that the aircraft is climbing with a positive speed and it is secure to retract the gear) <A> These are the standard calls you use on the RJ. <S> Pilot Not Flying is pilot monitoring and Pilot Flying is pilot on the controls. <S> Typical of jets: <S> PNF: "80 kts" (or 90 or 100 depending on jet - the low energy/high energy braking threshold for rejects) <S> PF says "check". <S> PNF: "V1" (passing decision speed) <S> PNF: "Rotate" (passing Vr. <S> Often V1 and Vr are the same, or so close together and the jet accelerating so fast, you pretty much say them as one word, "Veeonerotate") <S> PNF: "Positive rate" (when the vertical speed indicator comes off zero - PF calls "gear up") <S> PF <S> : "Speed mode" (When passing V2 + 10 or 20 kt - PNF selects speed mode on flight director which gives pitch commands to maintain the set speed) PF: "Heading mode" (if ATC has provided a departure heading - PNF selects HDG on flight director, which gives bank commands to maintain the set heading) OR PF: "Nav mode" (if the departure clearance involves flying routing that is programmed into the FMS - PNF selects NAV in the flight director) Passing 400 ft: PF: "Autopilot on" (PNF engages autopilot; you're not allowed to engage autopilot below that). <S> Hands off the controls. <S> Passing 1000 ft, the PF dials up the speed bug on the flight director, typically 200 kt, and lets the airplane accelerate and calls "Flaps X", and/or "Flaps up" as the retraction speeds are passed. <S> You then continue to 3000 ft and dial the speed up to the normal departure climb speed, usually 230 to 250kt and off you go.
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Vr is typically announced as just "rotate"
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What is the maximum holding time? When arriving at a busy airport, airliners may be stacked in holding patterns, increasing flight time. I know airliners are required to carry extra fuel in case of rerouting (including a safety margin). Once in holding pattern, aircraft may be reordered (not as simple as a FIFO), thus some aircraft may stay longer in their holding pattern. Is there a legal maximum time an aircraft can stay in an holding pattern? If needed, the question may be narrowed to EASA and FAA regulations. <Q> Aircraft stay as long in holding patterns as they have fuel on board. <A> At least in the US, there isn't any maximum holding time. <S> The FAA's ATC Orders 4-6-1(c) <S> give instructions for controllers, and they're allowed to issue an "indefinite" delay: When additional holding is expected at any other fix in your facility’s area, state the fix and your best estimate of the additional delay. <S> [...] <S> When holding is necessary, the phrase “delay indefinite” should be used when an accurate estimate of the delay time and the reason for the delay cannot immediately be determined; i.e., disabled aircraft on the runway, terminal or center sector saturation, weather below landing minimums, etc. <S> The final decision on how long a hold lasts is really made by the pilot, not the controller. <S> If a hold is taking so long that fuel is running low, the pilot can always choose to divert to another airport or declare an emergency for priority handling. <S> This question might also be helpful. <A> Actually that happened recently. <S> For operational/load reasons, JFK needed to use tailwind landing runways, making them too short for the weight of an A380. <S> The A380 asked controllers for a more suitable runway but they were unable to break the flow enough to allow that. <S> (I also wonder if this A380 pilot was conservative, and other A380s were landing while he orbited. <S> Perhaps his particular plane was heavy.) <S> The A380 clearly communicated their time available for holding before they needed to divert. <S> As that time grew closer, controllers said "ain't gonna happen" and they diverted. <S> Anyway, there you see the mechanism: the pilots plan a divert, and from that, they look at fuel and decide how long they can hold. <S> They tell ATC that if it's helpful. <A> There is no time limit. <S> The aircraft may be holding until the pilot requests a diversion, or declares an emergency, which they will do depending on fuel on board. <S> I know airliners are required to carry extra fuel in case of rerouting (including a safety margin). <S> Actually not really. <S> The required fuel is calculated as fuel needed to fly to destination, abort approach there and fly to alternate, certain time holding at alternate , and final fuel reserve. <S> The contingency fuel, for cases of route changes and holding is at pilot discretion. <S> These rules mean that once the contingency fuel is burnt, the aircraft shall divert to alternate unless it is clear they will be able to land soon. <S> The pilots are also supposed to declare fuel emergency when landing with the final fuel reserve still on board is no longer ensured with the distance left and any expected delay. <S> And once that happens, the pilots can leave the hold at their discretion. <S> It should be noted that these days holding usually only occurs when there is some disruption like thunderstorms crossing the airport. <S> In good conditions the flow control mostly takes care of releasing the aircraft for take-off <S> so they arrive at approximately regular intervals and rate that the airport can handle.
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No, there is no limit.
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Is there a general approach for designing a Trimmable Horizontal Stabilizer? What is the general design flow when designing a Trimmable Horizontal Stabilizer (THS) and the attached elevator? I assume you would dimension the max. positive/negative deflections of the THS to meet longitudinal trim requirements over all cg ranges, airspeeds, flap configs and then add the elevators on top of that to fulfill the manoeuverability requirements (pitch rate). But I guess there is more to it. In other words: How do you derive the maximum deflections of THS and elevator each? (compared to a non-moving stabilizer design) I'm not asking for specific formulas, but rather for the general approach. If you can recommend some detailed references about it, I would be really thankful. <Q> You always look at both in combination. <S> The first step is to use tail volumes that have worked before. <S> This is enough for preliminary design. <S> When the design advances further, you have load cases to cover which combine trim and manoeuvring demands and you use trim settings and elevator deflections in combination. <S> The useable deflection range changes with trim settings, because when the tailplane needs to produce a sizeable downforce to trim deflected fowler flaps on the wing, it cannot tolerate the same positive elevator deflection as in straight flight with lightly loaded tailplane. <S> Also, speed, load factor and loading determine the downwash angle on the tail. <S> The useable stabilizer range varies with the downwash angle, so each load case needs to be looked at by itself. <A> Trimmable Horizontal Stabilizors vary from plane to plane. <S> For instances, the Cessna Cardinal has a small tab on the back of the stab that is changed by the pilot using a trim wheel in the cockpit. <S> At high speeds, like 125 knots/145 mph, the Cardinal requires quite a but of push or pull the to change pitch - if you want to climb, you can haul back on the yoke, then dial in some trim to hold the pitch angle. <S> Compared to many Piper Stabilators, it does not expand the full width of the stab. <S> The deflection is designed to be enough so that don't have to hold the stick back while coming in for a landing. <S> Coming down final, you dial in enough trim to fly a steady descent, and then still have stick control left to deal with minor up/down changes as needed from wind burbles & stuff, and then be able to pull back to complete the landing flare. <S> (Top picture is <S> Piper, bottom is Cessna). <A> First is understanding the horizontal stabilizer's function relative to its partner, the wing. <S> Jockey and horse really, perhaps director and symphony. <S> For passenger rated aircraft (and big cargo transports who really don't want to spill the goods), a general approach to design parameters may begin with the following criteria: <S> To control wing AOA and prevent the wing from reaching a stall AOA uncommanded. <S> This means the Hstab must be adequately sized enough to act as a "weathervane", keeping wing AOA (relative wind) constant. <S> To keep net center of lift from drifting too far forward as angle of attack increases. <S> As the wing pitches up, it's Clift moves forward, but as Hstab begins to contribute tail up/nose down torque, properly balanced, the effects cancel. <S> In the event of a full blown stall/sink, to pitch nose down faster than vertical descent increases AOA. <S> Failure to do so puts plane into "deep stall". <S> Designers have a choice of the airfoil approach, the larger flat plate approach, or a combination of the two. <S> A low aspect flat plate might be a safe choice for 3, as it acts in a manner similar to a parachute to push the nose down even if it is fully stalled. <S> Airfoils will work for 1 and 2, but must stall at a higher AOA than the wing. <S> Once the right area is established, determination of maximum deflections may be as follows <S> : no one deflection should be so great as to not be overcome by two others. <S> This is why 3 pitch controllers may be better: Hstab pitch trim (very slow), elevator (weaker than Hstab in normal flight, higher rates available for emergencies), and a fine trim tab (for minor pitch adjustments such as a few knots of airspeed). <S> The pilot(s) control the elevator. <S> If Hstab is designed properly and thrust line is correct, this should make for a very safe and stable aircraft. <S> Although obviously influenced by recent events, a review of basic designs can help engineers stay anchored near the highest of safety standards required for passenger carriers.
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Next, you pick the tailplane size and deflection range which covers all load cases and verify the result in the wind tunnel and flight test.
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When is squawk 1000 assigned in USA? From Are squawk codes used with ADS-B? : Yes, squawk codes are still used and required with ADS-B. The post is 3 years old though. And from Wikipedia List of transponder codes : 1000: Used exclusively by ADS-B aircraft to inhibit Mode 3A transmit (USA) The way I understand that, if the flight will be in complete ADS-B coverage, say a domestic flight, it is assigned 1000. Is 1000 indeed assigned to ADS-B flights, or are they given discrete* codes still? * Oops. I didn't mean discrete as in hex discrete, but the 4-digit one that changes from flight to flight. <Q> Currently, FAA's "fusion" software uses discrete squawk codes to merge targets generated by different surveillance systems, i.e. SSR (often several of them) and ADS-B. <S> They plan to upgrade the software so it can merge targets based on Mode S hex code as well, but (as of early 2019) that hasn't been rolled out yet. <S> Once that is in place, ATC will switch to telling Mode S targets to squawk 1000. <S> Mode A/C targets will still need discrete codes, though, including Mode S aircraft in areas that only have Mode C SSR. <A> 1000 is a blockout code that prevents the ADS-B transmitter from also sending its discrete code, if you enter 1000 on your transponder no Mode 3/ <S> A code is sent in the ADS-B OUT message. <S> Its part of AC-20-165B that outlines ADS-B Mode 3/A Code. <S> Currently ATC automation relies on the Mode 3/A code to identify aircraft under radar surveillance and correlate the target to a flight plan. <S> The mode 3/ <S> A code is a four digit number ranging from 0000 to 7777. <S> Secondary Surveillance Radars (SSR) and ADS-B will concurrently provide surveillance, so the Mode 3/ <S> A code is included in the ADS-B OUT message and is required to be transmitted by § 91.227. <S> Note: <S> ADS-B systems will not transmit the Mode 3/ <S> A code if the Mode 3/ <S> A code is set to 1000. <S> As of last weekend when I was flying (in an ADS-B equipped aircraft through controlled airspace) discrete codes are still being assigned. <S> So then why would you need a squak code that overrides the very function of a transponder by preventing the sending of your "unique" squak? <S> every aircraft is assigned a discrete 24-bit address so ADS-B is capable of unique identification without traditional 4 digit squak codes. <S> ICAO 24-bit Address. <S> The ICAO 24-bit address is a unique address assigned to an aircraft during the registration process. <S> ICAO 24-bit addresses are defined blocks of addresses assigned for participating countries or states worldwide. <S> In the United States, civil aircraft are assigned an address from an encoding scheme based on the aircraft registration number (“N” number). <S> Additional information regarding the 24-bit address can be found in ICAO Annex 10, Part I, Volume III, appendix to Chapter 9, A World-Wide Scheme for the Allocation, Assignment and Application of Aircraft Addresses. <S> Since they don't offer an explanation as to why the 1000 code exists my educated guess is to prevent double target identification in radar systems that are capable of both Mode-A/C/S and ADS-B <A> My last flight, 3/20/2019, discrete codes were being given. <S> For me, one was assigned as I departed a local airport and contacted Burlington (VT) approach, <S> when they thought I was landing, then changed to another when they realized I was not landing there and handed me off to Boston Center for flight following for the rest of the flight.
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I have not heard 1000 assigned in my flights around/thru the Boston (MA) Class B, down to the Cape area, or out to middle of NY state.
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Are taller landing gear bad for aircraft, particulary large airliners? Buiding larger engines for larger aircraft as opposed to smaller but many engines has proved to result in more fuel efficiency.Having established one of the main drawbacks or impediments to building larger engines are ground clearance for engines in light of aircraft/airliners in their current under wing configuration. This configuration in light of current technological advancements seems to offer the greatest advantage in terms of control of the aircraft, stability and weight closest to the center of gravity when flying among other things. If space to store the retracted gear were not a problem due to some new design, are taller gear for airliners necessarily undesirable for landing and take off? Do they present some technical problem if for example they were strengthened, the extra length would present some problematic leverage problems as they get closer to the pivot and "load"? <Q> Tall landing gear has been used in the past: <S> The Tu-114 needed really tall gear to clear the really big props. <S> The drawbacks are extra weight and volume, as described in the other answers. <S> The Tu-114 was so tall, on its first flight to the US (the prototype was used to ferry Nikita Kruschev to the UN for some shoe banging) <S> the available boarding stairs weren't tall enough. <S> That arrival raised some eyebrows in the West because they'd done a nonstop flight from Moscow <S> (the Tu-114 was the first aircraft that made that possible). <A> It's just more weight and volume. <S> The problem really arises when you modify an existing airplane with a new engine that requires more clearance. <S> Changing the engine is not that big a deal (relatively speaking) <S> when it is slung below the wing as its physical interface is through the pylon. <S> It is an appendage. <S> The landing gear are smack, dab in the middle of the fuselage, and changes in that will ripple through far more systems. <S> It is literally right in the middle of things. <A> However, in the vast database of aeronautical endeavor there are solutions worth reviewing (wing? <S> ah, review wing). <S> Yes, many high wing designs would comfortably fit the larger engines. <S> Secondly, the trend towards fewer wing mounted engines has deprived air craft designers of a key safety feature from the tri-jet, using thrust to push the nose down. <S> Nose tractors (prop) have it as down thrust, rear pushers (prop or jet) have it as tail up thrust. <S> Add power nose down. <S> So let's look at the A-10 Warthog. <S> Why not put the two large fan jets back there with future airliners! <S> Notice <S> many major airliner designs trace unbroken lineage all the way back to the Me-262.Every time I see one <S> , I think this is the first jet airliner ever. <S> A great plane indeed. <S> But, with the development of more efficient and larger fan jets, designs such as the Ba-146 and many high winged transport aircraft can be brought into consideration to keep the thrust line in a manageable, safe, and even helpful configuration for wing mounts, if we wish to keep them there. <A> I have no experience in aviation but just from physics, longer landing gear "legs" <S> (I don't know the terminology) would mean that as the aircraft lands and experiences a force perpendicular to the landing gear, the torque on the landing gear would be higher. <S> This could present a challenge in that the structural stability of the landing gear "leg" may be compromised from increased torque, especially if we're talking about a heavier aircraft.
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Taller landing gear do present challenges due to increases in leverage and greater amount of space, but this has already been dealt with in large delta designs such as the XB-70 and is certainly not insurmountable.
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When to turn from crosswind to downwind to base in a circuit? I was told by my instructor that my circuit spacing is inconsistent. I do not know how to look at the runway and use it to judge when to turn downwind and base. As a result, my base leg is sometime high and sometime low. How do you determine when to turn at different leg in a circuit? <Q> Like almost everything (aviation or otherwise), this is just something you learn with practice! <S> I was taught to turn downwind to base when the threshold was between 4 & 5 o'clock (in a RH circuit). <S> Here's a good graphical representation in a LH circuit. <S> ] <S> At the end of your downwind leg, when you once again reach a 45° angle to the runway, do a medium 30° turn onto base. <S> (Image & Text source: <S> http://www.ppl-flight-training.com/circuits-briefing.html ) <S> As for the base leg being high or low - it shouldn't be a problem. <S> You can easily correct this. <S> Too high <S> :reduce power 50-100rpm, lower the nose slightly to maintain speed Too low: Increase the power slightly. <S> As was commented, it is also worth considering the wind direction before you depart. <S> On a perfect day, the wind will be directly down the runway towards you on final. <S> Consider the effect of this on your circuit? <S> I find it useful to draw the circuit, and an arrow with the wind direction. <S> Then consider when to turn early/late as appropriate. <S> Finally remember the GOLDEN rule: You can ALWAYS go around. <S> (Assuming you have a fan up front!) <A> What it entails is developing the "sight picture" in your mind of what the runway looks like from the air when you are 45 degrees off the threshold at the nominal turn point. <S> It's my own personal opinion, but I think that for a brand new student the best method is to start off using a predetermined landmark on the ground to locate yourself precisely for the turn, and concentrate on internalizing the runway sight picture you see from that location. <S> As quickly as you can, you start to replace dependence on the landmark with judging the sight picture of the runway, until you can ignore the landmark but get reasonably close to it by runway eyeballing alone. <S> You must not develop a reliance on landmarks at your local airport as a crutch, because as soon as you go to another airport you're back to square one, but you need a starting point somehow. <S> You will need to be able to locate your turn reasonably well without depending on ground land marks before you can solo, so try to develop the correct sense as fast as possible. <S> They should form a "level" V as shown below. <A> At least you've eliminated fast or slow, which (because energy is proportional to the square of your speed) makes it much more complicated. <S> Trimming to approach speed after turning to base makes it a question of high (reduce power/add flap) or low (add power). <S> Because of wind, landing patterns will never be perfect, but improvements can be made to make them more consistent. <S> It is the distance from the runway on your downwind that needs to be worked on first. <S> Landmarks and old saws such as "half way up the spar" help train your eye, as well as your speed and AGL. <S> Landing can be done in stages (example Cessna 172): <S> Enter downwind at consistent speed (around 100 knots), AGL, and distance from runway. <S> At a chosen point along the runway reduce power and drop to approach speed. <S> Add flaps 10. <S> Work on establishing your best spot to do this. <S> Turn to base and trim to 65 knots, look high or low? <S> Use power and/or flaps to adjust rate of descent to set up your final. <S> If you do this consistently, it should make your approaches much easier. <S> "Good patterns make good landings".
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One way to help with judging the 45 degree aspect of a runway with a well defined threshold edge is to study the apparent angles of the runway edge closest to you and an imaginary line extending along the threshold's edge, relative to the horizon.
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How long to clear the 'suck zone' of a turbofan after start is initiated? I recently found this (IMO funny) picture. All funny and all. But let's make this a real situation. Let's suppose I see my crush and his BF doing this, and I come with this 'genius' idea (alright, it's anything but a genius idea, but still) to start the engine they are sitting on. And no, I am not nice enough to turn the beacon lights on. How likely is it that the engine gains enough suction to suck them in without they noticing it in time (considering the fact they need to standup and run for their lives)? How long does it take for the engine to spool up enough suck a person in? <Q> <A> ( Airbus ) <S> The suck zone ahead of a CFM56 on an A320 is less than 5 meters. <S> The couple have enough time to take a leisurely walk toward the cockpit window. <S> The engine start time takes upwards of a minute (the starter is limited to four 2-minute bursts, followed by a 15 min cool down). <S> Newer engines take longer to start. <S> On the neo with PW1000G engines it's 2.9 m. <S> On the A380 <S> it's, surprisingly, only 4.5 m. <S> How soon can they reunite after a shutdown? <S> It won't be a long wait . <A> WHAT?? <S> ? <S> I CAN'T <S> HEAR <S> YOU <S> I said, let's get away from this loud engine! <S> Before it can even start to turn the fan, the noises the engine must make will be so deafening as to force the people in that location to flee. <S> And even before that, there would be clunks, shakes, and vibration that would be very noticeable, and put even deaf people on notice to clear out. <S> There would be no mistaking the engine starting up. <S> They would have at least 10-15 seconds to clear out.
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A start on a TF all the way to idle is about 20-40 seconds depending on the engine, and the fan itself won't do more than creep a bit until the core actually lights off which is 5-10 seconds, so they'll have lots of time to get down and get away as per @ymb1's diagram, once the wheeEEEEEEEEEEtickticktickticktickticktick starts.
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Why aren’t there any lifting-canard airliners? A lifting-canard aircraft, such as the Long-EZ , is an aircraft with the main wing at the back end of the fuselage and a pair of small, highly-loaded canards attached to the forward fuselage; the canards fly at a higher angle of attack than the main wing, and, consequently, provide a significant amount of lift in addition to pitch control. 1 During a sharp pitchup in a lifting-canard aircraft, the canards, being at a higher angle of attack than the main wing, stall first, causing the aircraft to automatically pitch down before the wing ever stalls. As the wing, with the ailerons on it, remains unstalled throughout, roll control is preserved, without any of the violent rolling inherent in stalled control-tail aircraft. 2 As the canards are stalled, pitch control is lost until they unstall, but, in this case, you don’t need pitch control, because the aircraft pitches down and recovers all on its own, without the need for any manual control inputs; 3 this actually has the benefit of making lifting-canard aircraft practically unstallable (for the main wing, anyways) barring the separation of large parts of the airframe. In addition, as the surface providing most of the aircraft’s lift never stalls, the overall loss of lift when the canards stall is fairly minor, and the aircraft’s handling characteristics remain benign throughout. In contrast, while a control-tail aircraft will usually also pitch down when the main wings stall, this is dependent on the stabiliser trim setting, and, if the center of mass is near the forward limit (necessitating considerable nose-up stabiliser trim), the aircraft may actually pitch up in a stall. Also, if the aircraft does pitch down, it does so quite violently, as the majority of the aircraft’s lift is suddenly lost, and with large, violent, largely-uncontrollable roll oscillations (as the ailerons are located on the main wing, which is stalled). And, because the surfaces used for pitch control are not yet stalled, pitch control is preserved, allowing the pilots to hold the aircraft in the stall . Given the considerable safety advantages of the lifting-canard configuration, why don’t we see any lifting-canard airliners? 1 : As opposed to a control-canard aircraft, such as the Flyer , where the canards fly at a nominally-zero angle of attack, are used only for pitch control, and make these aircraft utter beasts to fly without a computer making constant control inputs. 2 : Aircraft with a tail-mounted horizontal stabiliser and elevator which (nominally) fly at a lower angle of attack than the main wings. Examples include most aircraft ever. 3 : In contrast, control-canard aircraft pitch violently up as they stall (because the main wing, being at a higher angle of attack than the canards, stalls first), and, therefore, require aggressive nose-down control inputs to recover before the canards stall as well and pitch control is effectively lost; lifting-tail aircraft (with a tail-mounted horizontal stabiliser and elevator that fly at a higher angle of attack than the main wings) also pitch up, for the same reason, except that this happens well before the main wings stall, and is coupled with a simultaneous, near-total loss of pitch control as the horizontal tail stalls (making stalls completely unrecoverable for lifting-tail aircraft using only the usual aerodynamic surfaces for control). <Q> Sean I have no idea where you got the idea that the horizontal tail on a conventional aircraft lifts up, like a canard surface but at the opposite end, and can therefore stall and let the nose rise. <S> It's exactly backwards. <S> The tail lifts down. <S> When the airplane stalls, the center of lift of the main wing shifts sharply aft creating a strong nose down pitching moment that the horizontal tail lacks authority to counteract until the plane speeds up, and the nose drops. <S> If the down lifting tail surface itself stalls, that is a disastrous situation and is abnormal for any aircraft. <S> Canards generally suck because they have a host of limitations that negate most of the theoretical benefits <S> and that's why they have been commercial failures. <S> Otherwise, you'd see lots of them. <A> One good reason, is that airliners have main wings with flaps galore dropping down to increase the coefficient of lift at slow speeds. <S> This also greatly increases the nose-down pitch moment, which must now be countered by the already highly loaded canard. <S> Canard stall then becomes the limiting factor on approach speed. <A> None other than the great Clarance Kelly Johnson had similar thoughts in the 1930s, before testing validated the advantages of rear mounted stabilizers. <S> The Achilles heel of canard designs was that once relative wind shifted to beneath the aircraft at high AoA, the lower surface of the canard acts as a lever to push the nose up even further. <S> The US Army Air Force Ascender required additional area to be added behind the CG to counter act this tendency. <S> Secondly, a loaded canard essentially makes the airplane a less efficient biplane. <S> Let's also clarify one very important basic aspect of forward set CG and downforce on tail design. <S> As the plane loses speed, the forward CG pitches the nose DOWN. <S> As the plane gains speed (increasing aerodynamic forces) the elevator trim pitches the nose UP. <S> Notice with a properly designed rear mounted horizontal stabilizer (also validated by around 150 million years of bird evolution) <S> the forward wing also stalls first. <S> It would serve us well to review the design of the horizontal stabilizer/elevator/trim system. <S> Firstly, a review of tail force created at various AOA. <S> Yes, at lower AOA the tail creates DOWN force to balance main wing lift force and CG. <S> What happens at a higher AOA (even without change of trim or elevator input) ?. <S> The tail force of a properly designed horizontal stabilizer of ADEQUATE AREA should begin to generate UP force BEFORE the plane stalls, to compensate for the forward shift of the wing center of lift and help push the nose down. <S> Of course control inputs help this, excessive ones should be unnecessary. <S> Notice <S> the canard design is nothing more than a tiny wing and a giant tail. <S> This is why deltas (lots of rear area, stall at higher AOA) go so well at the back end with canards up front, which also makes a successful supersonic design. <S> But in the fuel efficient high subsonic realm, planes will probably look "the same" for a while, just like birds. <S> But it may be good to keep working on that tail.
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You either need to have a less loaded canard (there goes your natural stability) or flaps on it, or some other aerodynamic kludge.
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Can a civilian purchase a new (Not Retired) fighter jet? Let's take a jet like the F22 for example. Strip all the classified systems/weaponry out of it (civilian wouldn't need that), and just leave the basic aircraft itself. Could a civilian technically purchase this aircraft for personal recreational use/travel? Or are these exclusively contracted to the military? How does that work legally/technically? I've always been curious. There are multiple cases of wealthy civilians purchasing USED fighter jets, sure, but I'm talking about a wealthy civilian who can afford it ordering a shiny new (not retired, there is a difference) personalized, non-armed F22 for personal use. Is that even a legitimate premise? <Q> Certain jets, yes. <S> But not the F22. <S> See current listings: https://www.controller.com/listings/aircraft/for-sale/list/category/10072/turbine-military-aircraft <A> There are several reasons that an individual would not be able to purchase a fighter jet new off the line. <S> The manufacturer is focusing on meeting requirements for their current production contracts. <S> A private order would basically be a one-off for them, which adds complications to production. <S> Although it's possible to "de-militarize" a military jet <S> , that doesn't mean any airplane could be delivered to a civilian. <S> The US allows most military aircraft to be exported to certain countries, but the F-22 was never allowed for foreign sale, not even with limitations on what systems are installed. <S> Sales to private individuals would have even more restrictions. <S> Once the aircraft are available "used," the technology may be less protected. <S> Even then, many challenges remain for operating the aircraft. <S> It would be very difficult to find a location that is qualified to provide service and repairs on such a private plane. <S> Any service would also be fairly expensive. <S> Military jets require much more maintenance time per flight hour than other aircraft. <S> They are also designed to be operated with the help of a ground crew. <S> Of course there are some military aircraft in private hands and they have dealt with these challenges. <S> But it takes an owner with the dedication (and mostly the money) to make it happen. <S> For most any purpose, there are much better options. <S> Business jets are much more comfortable, and you can have someone else fly if you want. <S> They'll also be much cheaper to buy and operate. <S> If you want something more maneuverable, you can buy something like the L-39 , a jet trainer that can be found used, or possibly new . <S> Especially used, it will still be much cheaper than a new fighter and can do just about anything a modern fighter could. <S> A modern fighter can go faster and turn harder, but that's where the special training and equipment become a challenge. <A> A bit of a loaded question, like how are you defining the aircraft; without all the systems and weapons is it still the same aircraft? <S> Do you require the ability to use certain abilities, like supersonic travel or is it more of a collectors item? <S> Anything can be bought if the stack of cash is tall enough, even permission to own a particular jet. <S> Though this permission may have details like it must stay in the national airspace, file special flight plans <S> so the location is always known, and maintenance can only be performed by certain companies. <S> You could even get an F22 built with custom non-classified flight systems, <S> of course this custom development would cost a bit extra, really it would essentially be ordering a one-off experimental that looks like an F22, and we are back to how you define the aircraft. <S> Plenty of other types that are less classified are still in production, such as the F18 and F16 would likely be available to a civilian with more reasonable modifications. <S> Assuming this is for flight over land the speed is limited to less than mach one, and if you don't need the low radar profile, there are better designs for sub-sonic high performance flying. <S> Fighters have many considerations other than pure flight: armor adds weight, aerodynamic effect of externally mounted weapons(and <S> the frame mounting hard-points), weight of the internal weapons, those guns change the balance and useful load, targeting systems, active radar and counter-radar systems, passive radar reflection, heat signature, cameras, flight with damage. <S> All of this detracts from flying performance.
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There may be basic aircraft systems that have restrictions. A pilot would need to get training on the aircraft which would be hard to find outside of the military.
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Why do airplanes bank sharply to the right after air-to-air refueling? Whenever I see videos on YouTube they bank really sharply to the right after disconnecting from the tanker. Why wouldn't they do a more shallow 30-degree bank? See this video for reference: <Q> Fighter jets are very maneuverable, so they may make anything from a shallow bank to a breakaway maneuver . <S> The breakaway is a standard way for fighter jets to exit a formation. <S> It provides a way to safely and quickly gain separation from the other aircraft. <S> In this case the bank is fairly shallow, but when the aircraft disconnects they are already in a shallow right turn, so the total bank angle is a bit larger. <A> Doesn't really look all that aggressive to me, either way the fighter and the tanker are very vulnerable while refueling. <S> Usually there is more than one aircraft waiting to refuel, so the goal of this game is to run as many of the aircraft in formation through refueling as quickly as possible. <S> In order to do that, you need to get your wake out of the way for the next guy to get a smooth approach to the basket. <S> As Fooot says in his answer , the pilot is using a standard "breakaway" maneuver to get out of the formation and wait for the other pilots in the flight to get the fuel and continue with the mission. <S> Plus you just got a full tank of fuel in the world's funnest military equipment... <A> Different air forces may operate with different conventions, but right from basic flight training the RAF classifies banked turns of 20 degrees as "gentle," 40 as "medium" and 60 as "steep," and the most commonly used are "medium". <S> Ref: The RAF Basic Flying Manual (1952 edition) - <S> https://www.t6harvard.com/wp-content/uploads/2017/11/Chapter-3.pdf page 26-27. <S> The video is just a 40 degree banked turn. <S> The aircraft have no problem handling the G loads in 60 degree banked turns, and there are not going to be any complaints from passengers in Business Class that the flight crew spilled their gin and tonic! <A> They do this because there are 3 main parts to an air to air refuel: <S> port observation where they wait to be refueled in a line. <S> refuel area where they actually get refueled. <S> reform area where they wait for the rest of the squadron. <S> After the refuel, they will bank the right to go to the reform area and will wait for the rest of there squadron. <S> Once everyone is refueled then they break from the tanker. <A> A jet joins on one side of the tanker then when its turn comes moves behind to tank then when finished, clears off to the other side. <S> Bear in mind a whole formation may be tanking and need to flow through the same process. <S> The turn after tanking is not a hard turn in fast jet terms. <A> Others seem to have answered the why such a sharp maneuver part of the question, so I will answer the why to the right part. <S> Collision avoidance in aircraft is always by turning to the right when possible. <A> Two aircraft must either be flying in formation, or be far apart, to be safe. <S> While the fighter is in the process of leaving the tanker, it is neither. <S> It therefore moves away quickly using the standard breakaway manoeuvre. <S> Bank really sharply? <S> The video showed a positively leisurely turn in the circumstances. <S> Why to the right? <S> It's standard to approach on the left side of the tanker. <S> That's where other fighters waiting and approaching to refuel will be, so the left is a good side to avoid.
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Keeping the formation in such a way that the pilot can always escape to the right is probably done to ensure safety, as it lines up with the engrained training.
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How to apply the TO/GA time and EGT limits? If there is a published 1) EGT limit and a 2) TO/GA time limit, which one should be applied when the EGT is well below the EGT limit and possibly even below the 'max continuous' EGT. Particularly with consideration of terrain avoidance procedures that require climbing to a high altitude (10,000 ft) for terrain avoidance. <Q> They must be adhered to independently and cannot be traded off between the two. <S> Takeoff performance is calculated so that if a safe altitude above terrain and obstacles cannot be reached within the time limit, aircraft mass must be reduced rather than the TO/GA time increased. <S> Having said that, if things don’t go as planned during takeoff e.g. for reasons not known beforehand, I‘d recommend to bust the time limit rather than fly into the side of a mountain, if the choice is only between the two ... <A> The term may also be ITT limit (Inter Turbine Temperature). <S> On most engines there is usually a 2 minute to 5 minute limit on EGT/ITT and N1 (fan rpm) for both Take-off/Go Around power, and APR (Automatic Performance Reserve) <S> power (the balls-to-the-wall thrust setting the engine automatically goes to when the other engine quits). <S> On most FADEC engines, the most forward thrust lever position will take you into APR for both engines and the FADEC will manage things at those limits for you, so you know you can slam the thrust levers full forward without burning up the engines in an avoidance emergency. <S> Same for TOGA. <S> You just have to observe the time limits. <S> On an older non-FADEC engine, you have to observe the limits and stay within them manually with the thrust levers. <S> On a go around for example, the pilot flying will press the TOGA button, move the thrust levers up to TOGA thrust more or less, and call "set thrust", whereupon the pilot not flying fine tunes the thrust levers to the TOGA setting bugs indicated on the N1 gauges, also monitoring to keep the ITT limits from being exceeded. <S> However, on a Holy Crap Emergency like a cliff in your face, on a non-FADEC engine, where it's balls to the wall or die, you accept you're probably going overspeed and overtemp, and maybe wreck the engines. <S> Too bad for them. <S> In any case, 2 to 5 minutes is plenty. <S> The most likely case where you would even have the engines maxed out for any substantial period that eats into a 2 minute limit significantly would be a windshear escape, but even that might burn up a minute at most (that would require a downburst 2 miles across). <S> The margin between maximum ITT and the ITT seen during TOGA setting is the main (but not only) indicator of engine health and life span. <S> An engine will have a minimum margin, and as it wears out the ITT margin gets slimmer and slimmer until you're at the limit and off it comes. <A> If you are below the EGT Limit, as you specify, then you don't need to worry about this. <S> Then all you need to worry about is any TO/GA Time Limit, assuming you can find out what that is.
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The TO/GA time limit and the EGT limit are hard limits mandated by the approved flight manual.
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What does rudder input control in normal law in an A320? I understand form documentation that in normal law, pedal input is not necessary to keep coordinated flight. It is merely said that using the pedals is not necessary. Later in the documentation it is said that the law for the yaw axis is either normal, alternate or direct (depending on the condition). For the normal law, automatic functions are implemented (yaw damping, coordinated flight). What happens when the pilot provides a non-neutral command on the pedals? Such information is well documented for pitch an roll control (command of load factor and roll rate), but not for yaw. On the A380 , the documentation states that, "A pedal deflection results in a proportional sideslip and bank angle". I found no such precision for the A320, but it seems reasonable to assume the pedals command a sideslip angle. In normal and alternate law on a A320, do the pedals command a sideslip? If not, what do they command? <Q> You are correct. <S> See this presentation for a source, slides 3, 5-6. <S> As a note, on pre-A345/A346 models, the rudder pedals are mechanically connected to the rudder. <S> However, the FBW system adds in an additional input, via the yaw damper servos, to drive the rudder to the position the FBW control loops want. <S> Additional details can be found in Advances In Aircraft Flight Control , M. B. Tischer, page 90: <S> Finally, it was decided that the rudder pedals would command a combination of sideslip and roll angle to restore some of the conventional aircraft behavior. <S> Figure 5 shows that the rudder command is a gain-scheduled proportional control based on sideslip, yaw rate, roll rate, and roll angle. <S> The gain scheduling is based on airspeed and high-lift configuration. <A> Short answer: <S> The flight manual and an incident investigation both confirm that irrespective of the flight conditions, the A320-family pedals command a direct rudder deflection. <S> The rudder pedals on the A320 are mechanical inputs. <S> From the flight manual (DSC-27-10-10): <S> Two pairs of pedals, which are rigidly interconnected, give the pilot mechanical control of the rudder. <S> (Emphasis mine.) <S> And <S> And The rudder travel (max deflection) is speed limited though (given that the computers are functioning). <S> This also agrees with slide 3 linked in @user71659's answer, where the manual input is <S> added to the control law input, but is not a beta angle command. <S> And here's what an incident investigation <S> (PDF page 5) noted in clear terms: <S> Also worth noting is that limiting the A320 rudder the faster the plane is done via the RTLU (Rudder Travel Limit Unit), which is a physical mechanical stop, and not an electronic/mechanical subtraction of a pedal commanded deflection. <A> The rudder deflection is the result of the sum of 2 inputs: the pedals and the yaw damper. <S> Turn coordination is controlled by the yaw damper actuator and has no return to the pedals. <S> Therefore during a turn the pedals won’t move. <S> What happens when the pilot provides a non-neutral command on the pedals? <S> If the pilot acts on the pedals during a turn, the yaw damper action will automatically be reduced to maintain a correct coordination, until the yaw damper action is cancelled. <S> Beyond that during a turn the yaw damper will not do an opposite correction, i.e. if the pilot action is beyond the required amount for a correct coordination. <S> During a leveled flight an action on the pedals is similar to an action on the rudder trim.
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On all Airbus FBW aircraft, the rudder pedals normally control the sideslip angle, beta.
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Why would a flight take a detour on clean weather? I was in a flight recently (march 22nd) from SBCF to SBGR (Brazil). It's usually a 1h10m flight, but mine took roughly 20 minutes more. I saw the flight path in FlightAware and there's an unexpected (to me) detour mid-flight: I looked for other instances of this scheduled flight and there are more extreme cases, such as this one: In this case, the actual flight distance was 833km whereas the straight-line distance is measly 496km. Obviously it would be difficult to pinpoint the exact reason why this happened, but what factors could lead to taking such a different than expected route? <Q> There are lots of reasons flights may not take a direct route, some are but not limited to: <S> It's just the route ATC assigned (for whatever reason they see fit) <S> There is an active military operations area or live firing area they are avoiding, these are not always "active" and may be avoided only sometimes. <S> Some kind of natural event on the ground, wildfire, volcanic eruption, etc. <S> There is a TFR they can't get through <S> these are typically not hard bans on overflight but can be. <S> For smaller aircraft it may be a terrain avoidance issue (generally this is for general aviation sized planes). <A> In both examples, the aircraft was crossing the direct path between origin and destination, sometimes even flying perpendicular to the direct line. <S> It would take more than one obstacle (like severe weather) to explain these patterns. <S> It is very likely that the pilots were deliberately delaying their arrival with respect to traffic congestion at the destination. <S> See <S> Why did this plane fly in a zigzag pattern? . <A> You say it was 'clear weather' but do you have anything to back that up other that what you saw outside the window? <S> The pilots know what's ahead of them <S> and it could be <S> your smooth ride was down to their avoiding some heayy stuff. <S> They could've seen some bad weather on their weather radar or maybe a pilot ahead alerted them.
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If it's an international flight they may not be allowed to overfly the airspace.
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Is it OK to decorate a log book cover? I'm a student pilot and am thinking about putting a tasteful decal on my log book, if for no other reason than to identify it as my own. Is that OK, or would that be frowned upon? Thanks. <Q> I don't belive there is any regulation against it. <S> Keep in mind you may need to show the book to officials at some point so keeping it professional is not a terrible idea <S> (1) Persons must present their pilot certificate, medical certificate, logbook, or any other record required by this part for inspection upon a reasonable request by - (i) <S> The Administrator; (ii) <S> An authorized representative from the National Transportation Safety Board; or (iii) <S> Any Federal, State, or local law enforcement officer. <S> The FAA is more concerned with what you log than what's on the cover of your book . <S> I can't say I have ever seen a log book with a bedazzled cover <S> but I'm sure they are out there. <S> If you are talking about putting a decal that says "Ryan's Log Book" across the cover, that's fine, but <S> a giant glow-in-the-dark unicorn sticker might get you some looks although technically OK. <A> My mother used to wrap my books when I was a kid in school for me. <S> I don't know much about aviation and how this logbook looks, but maybe it's doable to use some kind of a "protective cover" that can be taken off anytime, in case you have to show it on official occasions? <S> Beside making your own from book protection paper, kitchen shelf paper, newspaper or non-sticky plastic foil, you can buy pre-made covers in different sizes. <S> Have a look at a stationery shop, bookstore or at a school supply store. <S> The foils and pre-made covers are available in transparent and different colors and with or without printings (for example maps). <A> If you expect a professional career in aviation, then I would keep it within the envelope of what that community would expect. <S> Another thing to consider, you can have multiple logbooks. <S> For example, I have a separate book for gliders, glider towing and rotorcraft. <S> When instructing, I keep a lesson record, which covers instruction details, evaluation and logged times. <S> Those are summarized on a spreadsheet which I update periodically. <S> My work flying and my personal flying have separate logs as well. <S> The FAA inspectors seem happy with my record keeping and appreciate the segmented logs. <S> Things like night currency, instrument currency, glider currency, are recorded in the rear of the books and can be carried from book to book. <S> My multiple logbook implementation is not for everyone, but I mention it because if one wanted to have something radically unique, you might do so in a separate book. <S> As an example, early in my flying career, I noted the names of people I took up on rides, or had them sign my book. <S> Later, I decided to stop that practice when a significant other started reading the logbook. <S> But to be clear, your logs need only be a reliable record which you can readily use for FAA compliance, negotiating rentals, employment or whatever. <S> Many pro pilots I know used spreadsheets, and their company issues a record for company activity. <S> Similar in the military. <S> In summary, do what you want, but you may wish to maintain a more conventional presentation if you expect to be pursuing activities where your logbooks might get reviewed for employment or other activities.
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It all depends upon how your logbook will be used.
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Are there more accidents in winter months, and if so, why? I was watching The Flight Channel videos and have noticed that the accidents seem to happen more often in winter months (for the Northern Hemisphere). Are there some statistics to back this claim? It seems logical: Winter months means icing on wings, slippery runways, etc. Are there any not so obvious reasons for the increased accident rate during winter? <Q> I'd argue fall and spring bring more unpredictable weather, and slippery runways are year-round in the tropics. <S> That being said, for all jet (commercial) accidents, the weather-related contributing threats are: Meteorology (e.g., failure to identify threats before a flight) 30% Windy conditions 16% Poor visibility 10% Thunderstorms 9% Icing <S> 1% <S> Poor braking action (e.g., slippery runways) <S> 10% (falls under airport facilities, not meteorology) <S> All figures are from PDF page 172 of the IATA 2017 Safety Report . <S> Given the opening statement, [near ground] icing is more attributable to cold winters than the rest. <S> The rest are not limited to Dec–Mar in the Northern Hemisphere. <S> The report does not attribute the seasons to the accidents. <A> Accidents are rarest in winter. <S> In https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx , click "Download all (text)", to get a file <S> AviationData.txt containing 80,000 accidents and 4,000 incidents. <S> Keep only the Accident s, split the | -delimited fields to get mm/dd/yyyy, then split by <S> / to get the month, then count how often each month appears. <S> From a Linux shell: grep Accident AviationData.txt | awk '{split($0,a,"|"); print a[4]}' | awk '{split($0,a,"/"); print a[1]}' <S> | sort | uniq -c <S> Result: <S> 4439 <S> 01 <S> 4697 <S> 02 <S> 5989 <S> 03 <S> 6632 <S> 04 <S> 7838 <S> 05 <S> 8758 <S> 06 <S> 9806 <S> 07 <S> 9223 <S> 08 <S> 7607 <S> 09 <S> 6267 <S> 10 <S> 4922 <S> 11 <S> 4485 <S> 12 Accidents are rarest in January, become smoothly more frequent until July, and then become smoothly rarer until December, i.e., the subsequent January. <S> But is this trend just because summer has more flights? <S> Let's compare apples to apples,instead of 747s to everything including powered parachutes. <S> This table shows that airline passengers have the same trend,about 26% to 31% more in July than January. <S> Numbers that big argue that airline flights have the same distribution. <S> When filtering AviationData.txt to include only Boeing, Airbus, etc,July is about 90% more than January. <S> So summer has 30% more flights than winter, but 90% more accidents. <S> Even after adjusting for this, an airliner flight in winter is only a third as likely to have an accident as a flight in summer. <A> Ill second Camille's answer and add the missing factor of GA vs. Commercial Aviation. <S> The NTSB makes the 2012-2016 data available in spreadsheet format here . <S> If you download that and combine all the accident data you will see that the overall accident data for those years, plotted by month looks something like this: <S> This data set for even the limited years is in line with the other answers larger data sets. <S> But if you limit the data set to only part 121 accidents the trend disappears: For those years April and September were the Safest months to fly but a trend really cant not be observed here. <S> So why does GA cause so many summer accidents? <S> The simple fact is there are substantially more GA flights in the summer.
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Well its simple, *most GA planes dont have ani/deice equipment so winter flying in the northern parts of the country is out of the question for many GA pilots.
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What are the advantages/disadvantages of in-fuselage engines (eg most fighter jets) vs wing/fuselage mounted engines? Most modern jet fighter designs incorporate their engine(s) within the fuselage, while most other medium/large aircraft mount them either under the wings or on the rear fuselage. What are the advantages and disadvantages of in-fuselage jet engine placement, compared to those mounted on the fuselage or wings of an aircraft? <Q> The answer is roll inertia . <S> Fighter aircraft need to maneuver quickly, and one of the most important parameters is roll speed. <S> In order to achieve a high roll rate quickly, low moment of inertia in roll is helpful. <S> Placing the engines on the wing would increase roll inertia without much benefit in air combat. <S> Wing-mounted engines can only be found in designs which were optimized for raw speed, such as the P-38 or the YF-12 . <S> Even the Me-262 was initially designed with fuselage-mounted engines, hence its triangular fuselage cross section. <S> Only when the engines grew in diameter during development had they to be relocated to the wing. <S> Disadvantages of fuselage-mounted engines: <S> Worse accessibility for maintenance. <S> Variants using a different engine cost much more to develop. <S> Engine fires or loss of a turbomachinery blade pose a much bigger threat to the structure. <S> No bending moment relief or flutter damping for the wing. <S> Complex intake geometry with boundary layer splitter plate , unless the intake is in the fuselage nose. <S> The air requirements of high bypass ratio engines cause high losses with side intakes. <S> Note that at supersonic speed the engine can actually benefit from the proximity of a fuselage <S> : The precompression of the forward fuselage of the F-16 or the Dassault Rafale help to increase thrust, especially when it is most needed at high angles of attack (well, those relatively high angles in supersonic turns, that is). <S> Advantages of fuselage-mounted engines: <S> Low moment of inertia in roll. <S> Lower overall surface area, thus lower friction drag, when compared to podded engines. <S> Precompression of the forward fuselage can be used to increase supersonic thrust. <A> Advantages of placement in the fuselage: <S> low drag, which enables high speeds <S> disadvantages: <S> no flexibility in engine installation <S> (you can't easily update the aircraft with a new, larger engine) <S> lots of space taken up by the engines and ducting constraints on the center of gravity (heavy engine in the back, lots of empty ducting in front of the engine) disadvantages of engines under the wing: on aircraft with a low wing (e.g. to make the wing box pass underneath the cabin), you need longer landing gear more drag due to extra frontal area <A> Most fighter jets operate at much lower bypass ratios than commercial jets. <S> At low bypass ratios and high speeds, drag is important, and it's simply more efficient to embed the engine within the airframe. <S> At high bypass ratios, the engine is a large assembly that's difficult to embed. <S> The A-10 has separated nacelle engines, while being a combat (attack) jet. <S> The very large Concorde had nacelles flush to the fuselage. <S> Both were tradeoffs, and in this case supersonic flight does call for reducing the cross-section. <A> You may notice that the primary difference between the two classes of aircraft you mention is maximum designed airspeed. <S> Minimizing radar reflections, withstanding high G loads and other effects also apply. <S> The fighters are also smaller and lighter than many medium or larger aircraft as well.
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To allow supersonic performance, low drag considerations such as the area rule are more easily met with in-fuselage engines. difficult installation (so more time spent on maintenance) lots of noise
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How do conventional missiles fly? With the exception of cruise missiles, most missiles don't have any obvious lifting device. If you watch a missile being fired, prior to its rocket firing it does exactly what you'd expect: momentarily plummet toward the earth. And yet the moment it ignites, it stops falling completely, but without any pitch that you'd expect to counteract gravity; even big missiles like the Phoenix or HARM seem to have gravity-defying characteristics. Missiles that fire on the rail seems to experience no drop at all. AIM-9M launch from an FA-18F source There's a good slow-motion video of the firing of an AMRAAM here . Now this isn't magic, so I presume either a) the little fins make adjustments so that the rocket is, despite appearances, pointing a little downwards or b) the fins are smart enough to configure themselves to provide the lift needed to keep the missile in the air. But it might be neither. The question is - generally, how do conventional missiles fly? <Q> Air-to-Air guided missiles are little airplanes. <S> If there are only fins at the tail, it's a ballistic rocket, basically a fin stabilized artillery shell accelerated by a rocket motor instead of an explosion in a pipe. <S> On missile like AMRAAM, Sidewinder, or Sparrow, the vanes are wings and the missile is a rocket powered aircraft that can climb, descend and turn as required. <S> The vanes/wings don't have to be very big because the thing is going superdupersonic. <S> The X plan form means the wings can support and control the missile equally well in any axial position. <S> The front vanes are movable and do the controlling. <S> It's effectively a rocket powered robot canard aircraft on a suicide mission, really. <S> Since the missile accelerates to >Mach pretty quickly and operates supersonically, the wings/vanes use a supersonic airfoil profile, either biconvex (like the F-104's airfoil) or a diamond profile. <S> The vanes on the AIM-9M look like biconvex airfoils. <S> The missile descends when it is first launched because it's going too slowly for its teeny tiny supersonic wings to do enough lifting, and has to accelerate first. <S> Now, for a change of pace, slow something like an AMRAAM or Sidewinder down to subsonic speed, make the fins bigger and provide control surfaces on the rear ones, power it with a turbojet instead of a rocket except for boosting it into the air, and you have the CL-89 <S> surveillance drone, basically a reconnaissance cruise missile that flies hither and yon at low level taking pictures. <A> The missile's wings are very large for it's mass, and produce a great deal more lift than the wings of the aircraft firing the missile. <S> One thing to note from the OP's linked video is that the F-35 and the chase plane are traveling at the same speed, so the F-35 appears stationary. <S> However, that aircraft is likely traveling in excess of 0.8 Mach. <S> Therefore, upon release, the missile is also traveling at 0.8 Mach . <S> The large wings provide plenty of lift. <S> Some missiles may thrust vector as well. <A> In the video you posted, the missile appears to continue falling even after the motor ignites -- you can see the missile start to overtake the aircraft even as it continues to drop: By the last frame, it appears to have taken a slight nose-up attitude to maintain altitude: <A> Depending on the range and mission of your missile, body lift alone may be enough to keep it aloft. <S> @dotancohen pointed out that a typical missile's wings are large for its mass, but look at the ASRAAM - it has only small tail fins which are there purely for attitude control, rather like an AIM-9X (which already has much smaller wings than the 9M) but with even fewer lifting surfaces. <S> It's extremely slender to reduce drag, probably with the intent that it should retain as much of its energy (and thus speed) as possible. <S> With enough speed, you'll only need a little AoA for the missile fuselage itself to create sufficient lift. <S> This seems to be a typical strategy for short-range missiles, but the ASRAAM takes it to the extreme.
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Missile meant for longer-ranged engagement may employ a lofting profile during the boost phase, opting to use the rocket motor to gain altitude as well, in which case the thrust will directly offset some of the weight of the missile.
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