source
stringlengths 620
29.3k
| target
stringlengths 12
1.24k
|
|---|---|
Why would a commercial flight make banked turns five minutes before landing / low altitude? As a passenger on a commercial flight into Essaouira From London Luton a short while ago, I noticed the aircraft made several quite steep banked turns, all to left, very close to landing. When I say close I mean about five minutes before we touched the runway, and I'd estimate 600-1500 feet off the ground at most. It was possible to make out individual bushes in detail in the scrub. What was more concerning was that the terrain became undulating and was rising into rounded hills with a height difference of around 250 feet. Sky was clear, and I don't remember any turbulence near the airport. Is it normal to bank that close to the ground? I thought an approach was lined up further out and higher up. <Q> As denizhanedeer said, it was a circling approach. <S> There is only one charted IFR approach to ESU. <S> It comes in from the northwest and would line up for a straight-in approach to runway 16. <S> Depending on the wind the pilot may have needed runway 34 (same runway from the opposite end) so they would circle around to line up with it. <S> This flight did just that. <S> (It might even be your actual flight, Easyjet 2039 on 5/17/2016) <S> It did a short hold at the final approach fix to lose altitude then circled to land on runway 34. <S> It landed at 4:09 UTC. <S> It did the first left turn at 4:06 and 1850 ft. <S> The image here shows it during the second turn at 4:07 and 1475 feet. <S> The altitudes given are MSL. <S> The terrain rises pretty quickly there. <S> I'm guesstimating from some topo maps that at the area of the turns it rises to 175-200 feet. <S> So 1475 ft MSL would be as low as 1275 ft above ground level. <A> Now, I'm not an ATP, but as a pilot I know that sometimes I (and commercial airlines) will make "S" turns on final for spacing. <S> There are minimum times between an aircraft taking off/landing and another aircraft landing behind them due to wake turbulence. <S> Instead of making the aircraft go-around (which would take quite a bit of time), they may be asked to slow down as much as safely possible and make the s-turns for spacing. <A> Given that the sky was clear and there are no charted visual approaches in the Moroccan Aeronautical Information Publication for Essaouira (GMMI) -- <S> what I suspect happened was that ATC gave your flight a vector or vectors to a visual final approach after having them descend to the area Minimum Vectoring Altitude. <S> (The Minimum Vectoring Altitude for an area can be lower than the published procedure altitudes.) <S> Also: while "normal" approaches line up early, airspace or terrain <S> constraints mean there are procedures that call for turns much lower and later than the vectoring your flight receieved. <S> Examples include the main instrument approaches to runway 19 at Reagan National (KDCA). <A> I don't know the type of aircraft but most probably you were not so close to ground. <S> In normal stabilised approach it would be approximately 1:30 minutes from 1500 ft to ground. <S> In old days we were making timing approaches for defined ground speeds. <S> So Second part : Airliners don't make step turns unless otherwise there is emergency. <S> Bank limit for turn 33 degrees for airbus and after that you need to push even more to 67 degrees without slip control. <S> Also you definitely feel the turn due to increased G. <S> My option, you may have seen a nice circle to land operation, wind condition may not be the best option for approach runway, either pilot or ATC may ask to circle another runway which is close to ground, but again in safe altitude. <S> 500 ft above the ground an airliner must be aligned and stabilised, unless safety issues. <S> Above requirements are for conducting a safe flight, depends on carrier and pilot they may have push limits more if you think that you were closer than 500 ft. <S> Especially in Africa, there are many non-precision approaches and you may need to make approach to one runway and circle to land another one. <S> I could not find official charts of ESU. <S> Never been there but hope it helps. <S> Cheers,
|
If you make a step turn so close to ground you need to apply a lot of thrust due to load factor to achieve level flight.
|
Does the expression "stall speed" have a definition? I read, not only on this site, that the stall speed of an airfoil doesn't exist, and I usually make the effort to stay away from this expression. While an airfoil can stall at any airspeed, it's clear that the stall speed refers to the airspeed at which the stall occurs in an horizontal 1G flight. Stall speeds for B747-200 (n=1). ( Source ). This speed is the lowest one that can generate a vertical component of lift equal to the weight with the airfoil at its stall angle of attack. I would compare this implicit assumption with the maximum airspeed of an aircraft: It's clear we are assuming at least an horizontal flight and a standard atmosphere, etc, else this speed can be anything too. So what's wrong with this definition of the "stall speed"? Is the stall speed defined in the aerodynamics field? Example of use: Stall Speed (Dr. Mustafa Cavcar). <Q> Indeed, "the stall speed of an airfoil doesn't exist." <S> But the stall speed of an airplane does exist, though it's dependent on the aircraft weight $W$, load factor $n_z$, configuration (e.g., flaps position) and the air density. <S> This variability makes it disadvantageous (for pilots---even dangerous) to think of an airplane's stall in terms of a definite stall speed <S> $v_{Stall}$, as if it were a constant characteristic of the type. <S> What are (roughly) constant are the stall angle of attack and the stall lift coefficient $c_{L_{Stall}}$. <S> The equilibrium equation for the forces acting on the airplane <S> In stall in its symmetry plane and perpendicular to its velocity is: $$n_z\cdot W = \frac{1}{2}\cdot\rho\cdot <S> v^2_{Stall}\cdot S_{ref}\cdot <S> c_{L_{Stall}}$$ <S> Doing the algebra, one can easily exspress the stall speed in terms of the remaining parameters ($\rho$ = density of air, $S_{ref}$ = reference area) <S> The resulting expression will explain (i) that for an airplane, stall speed does exist; (ii) <S> the nature of its dependences and (iii) that for an airfoil, to which force equilibrium does not apply, there is no "stall speed." <A> Flap settings Center of gravity position. <S> However, for regulations the simplification of a single stall speed is helpful; here it is the minimum speed at which the aircraft can be controlled with idle power. <S> Note that the definition for stall speed in the US regulations for GA aircraft ( Part23 subpart B §23.49 ) is quite vague, allowing for details like the flight mass and altitude <S> being in the condition existing in the test, in which V$_{SO}$ and V$_{S1}$ are being used; At least the center of gravity needs to be in the position which results in the highest stall speed (normally most forward). <S> The controllability condition can result in the stall speed not being at the highest lift coefficient, but at the elevator control limit. <S> Note also that it is not determined in level flight, but with engines idle or providing no thrust. <S> Your linked example is rather theoretical - the lift curve slope of an airplane rarely looks so nice and clean like in the example. <S> If you test a wing with a constant cross section in the wind tunnel, the resulting lift curve slope allows to define a maximum lift coefficient, and with this you can calculate a theoretical stall speed when adding wing loading and absolute size (for the Reynolds number). <S> But the stall speed as measured in flight test will be different and most likely higher. <A> 'Stall speed' is defined only with respect to the aircraft as it is the case where it has a physical meaning. <S> We define stall as the point where the airfoil or wing stops producing the necessary lift due to flow separation <S> (This is an extremely simple definition, which will suffice for now), i.e where the lift coefficient is maximum. <S> lift coefficient. <S> Basically, we are using the stall speed because it is directly available to the pilot <S> i.e. it is a derived quantity, based on the angle of attack, configuration etc. <S> among others. <S> On by itself, the value has no meaning, as you pointed it out yourself. <S> Now, coming to the airfoil, the same (or similar) definition cannot be used as there is no way of saying lift equals weight due to the nature of airfoil itself. <S> Thus, the stall speed is a performance term, not an aerodynamic one. <A> A stall speed can be predicted if the other variables that are factors for a stall at any given speed are known. <S> Obviously, the point of discussion with stall speed is to make sure everyone has awareness that it isn't a fixed number, and it is definitely not the authoritative variable regarding the point at which an airfoil will stall; that would be the angle of attack. <S> The reason we need to acknowledge the existence of an estimated stall speed during common, predictable flight conditions is because the airspeed is going to be one of the pilot's primary focus points during critical phases of flight where a stall presents a greater risk. <S> Attempting to utilize a speed is just more practical. <S> There are virtually unlimited stall speeds, so in the same way we refer to a number divided by zero as "undefined," stall speed is also numerically undefined. <S> Yes, it has a literary definition, but no, it doesn't have a numerical definition, just a reference point for various operational configurations in different aircraft.
|
For aircraft, the stall speed is given as where the wing reaches the max. There is not a single stall speed, because stall depends on Angle of Attack Pitch rate Mach number Reynolds number Load factor
|
Why do naval jet aircraft need to have strengthened undercarriages? I've read several times that the navy versions of jet aircraft need to have a strengthened undercarriage. Here is one example , and another . I've always just automatically assumed this was needed because aircraft landings are "rough". That is, the aircraft smacks down hard on the carrier deck (or so went my assumption). Now I find myself questioning this. Naval jets land by catching a wire that brakes them hard. They may also takeoff with a catapult, which is some running device that pulls the nose gear forward at high g's. So, what is the real reason that naval versions of jets need a strengthened undercarriage? <Q> The landing on carrier is indeed hard. <S> The reason is not the deceleration (which is handled by the hook), but the touch-down. <S> Since the deck is short, the wires can't be spaced very far apart, so the aircraft must touch down very precisely. <S> Since the precision is better at steeper angle, the aircraft landing on carrier do not flare. <S> At all. <S> So they hit the deck at more than twice the vertical speed compared to typical landing on decent runway. <A> I'm not sure why "Naval jets land by catching a wire that brakes them hard. <S> They may also takeoff with a catapult, which is some running device that pulls the nose gear forward at high g's. <S> " would make you question your assumption that carrier "landings are 'rough'". <S> In addition to Jan Hudec's description of the landing process , your statement about takeoffs is reasonably accurate, as well. <S> According to Wiki, the C-13-1 catapult (used on many Nimitz class carriers) can shoot 80,000 lbs to 140 knots in 310 feet generating 2.81g with a total force of 225,140 lb (Thanks reirab!). <S> All that stress goes through the nose gear. <S> Between the launch and the landing, there are considerably higher forces on the undercarriage of the plane, thus it needs to be considerably stronger than that of an equivalent land-based aircraft. <A> It's the first reason you list: the aircraft hit the deck hard.
|
It's not just the undercarriage; the whole airframe has to be ruggedized to withstand the greater shock of carrier landings.
|
Do I need to get a new AFSP approval if I change to a new part 61 instructor? I have an AFSP (TSA) approval to train with a part 61 provider. I want to transfer from them to an individual part 61 CFI. Do I need to go through the AFSP approval process again? <Q> Yes , you will need to apply for AFSP approval for your new training provider. <S> The Application Guide for the AFSP says in step 7: <S> It is possible for a Candidate to have several active training requests at a given time. <S> These requests may be for the same or different flight training providers. <S> Each training request form will be processed separately; AFSP approval is valid only for the Provider listed in the application. <A> Yes you do. <S> I've had two Germans and an Indian receive training from me while here on visas. <S> I was freelance, and they all had to go through ASFP. <S> There must be a new training request submitted each time a student in this situation changes training providers, and yes, I had to register with flightschoolcandidates.gov as a flight training provider and was involved with the students' application processes. <A> Yes, every flight school change is a new request according to the AOPA FAQ for aliens . <S> You might not need to give fingerprints but you will have to pay the 130$ registration fee again to go to a different flight school. <A> You can't transfer an approval <S> so yes, you need to get a new one. <S> From AFSP's Application Guide : <S> TSA cannot transfer your training event request from one flight training provider to another flight training provider. <S> TSA approval is valid only for the flight training provider listed on the training event request. <S> You may desire to build more flight hours than the flight training provider can accommodate. <S> You may train simultaneously with more than one flight training provider; however, you must submit a flight training event request for each provider.
|
So if you needed AFSP approval for your original training provider, you will need a new approval to switch to a different provider.
|
What is the difference between dry operating weight and dry operating mass? What is the difference between dry operating mass and dry operating weight in the context of rotorcraft? What is the formula for converting mass to weight? <Q> Weight is a force. <S> Mass is a property of matter. <S> Acceleration makes mass produce a force. <S> Specifically, a mass in the gravitational field of Earth effects a weight force on its support. <S> The relation between both is the gravitational acceleration g, which is standardized to 9.80665 m/s² (approximately 32.174 ft/s²), as in Weight = <S> Mass · g. <A> The problem occurs due to lazy terminology. <S> In aviation both normally mean the same thing: The reading you would get if you put the empty aircraft onto a large weighing device (scales, or whatever). <S> This is normally given in kilograms (kg) or pounds (lb). <S> This trouble arises because both of these quantities are actually masses, the weights would be in Newtons (N) or pounds-force (lbf). <S> To transform the mass into a weight you multiply by the local gravity, g, which is usually assumed to be 9.81m/s2. <S> A similar problem exists when at home: If you weigh yourself on standard bathroom scales you will normally see a value in kilograms (i.e: A mass), but the scales actually measure a force. <S> This means if you use the same scales on another planet you will get a different value in kilograms, which is nonsensical. <S> The same goes for aviation: Weight and mass are being used interchangeably, which is incorrect. <A> Weight = Mass x Gravity. <S> In typical aviation terms, in an operational sense, you don't need to worry about mass (unless you're talking about a spacecraft...)
|
edit - And to specifically answer your question: Dry weight and dry mass mean the same thing in this context.
|
Are commercial pilots incentivized to reduce fuel consumption? Commercial airlines spend a lot of their operating income on fuel, so in order to maximize shareholder value presumably like to use as little fuel as is safely possible. Are commercial pilots ever given incentives (e.g. financial, performance review) for reducing fuel usage, or given dis-incentives for excessive fuel usage? <Q> There have been, at various times, and with various carriers, incentive programs set up to encourage pilots to save fuel, improve on-time performance, or some combination of the two. <S> An example of a fuel-saving incentives program existed at the former Continental Airlines in the early 90s, where pilots would be paid a bonus for using less fuel than planned. <S> The problem was that it wreaked havoc with the schedule itself, as pilots would simply dial back to economy cruise thrust settings, saving fuel but taking noticeably longer to reach their destinations. <S> Ironically enough, it was called the "Green Incentive Program" (don't ask). <S> And it was a can of worms. <S> I vaguely remember other airlines experimenting with incentives programs relating to fuel consumption and on-time performance, but it's been several years since I left the industry and can't recall any other examples. <S> In short, yes they do get implemented fairly regularly, but they can be very problematic due to the difficulty in properly designing and managing them (incentivization is a complex problem). <S> Lastly, since another poster has brought this up, dispatchers do indeed perform most, if not all the flight planning, but the PIC (i.e. Captain of the flight) has the option of overriding most everything the dispatcher plans and arranges for (subject to the carrier's Operational Specifications), including amount of fuel to be carried. <S> Basically, if the Captain decides that the plane is to be filled with as much fuel as it can carry up to MTOW, that's what's going to happen. <S> Might not be the most business-savvy (or even prudent) decision, but it's part of their prerogative as PIC (i.e. the person ultimately responsible for the craft, crew, passengers, and goods onboard). <A> It's seems like you are talking about part 121 operations which is like delta to Chicago and Atlanta and daily passenger operations. <S> The pilots don't really do the weight and balance(fuel required). <S> Dispatchers do the calculations and then it's sent to the pilots <S> and they double check the math. <S> I'm gonna say they don't because it's already at mins. <S> Then you have other factors like it's cheaper to buy fuel at this airport <S> so I will top of the tanks so you can fly to another airport and back. <A> After the collapse of the USSR and break-up of Aeroflot into smaller regional entities, there was (reportedly) a widespread practice of such incentives. <S> Or rather, disincentives to 'waste' fuel. <S> Say, a pilot could be penalised for doing such 'unnecessary' thing as a go-around. <S> This was often unofficial or semi-official, but still put pressure on pilots to compromise safety. <S> It is believed such practice may have contributed to some accidents in the 90s. <A> Incentivising pilots for reducing fuel requests was definitely not the done thing in Australia when I worked at a commercial airline. <S> The responsibility and final decision making of the captain was absolute. <S> For those pilots perceived to load up too much 'granny gas' as it was called, we used to make charts showing them where they were ranked amongst their fleet type colleagues for putting in more fuel than planned. <S> For the 'bottom' say 5-10% of 'overloaders', they were called in for a meeting with the fleet captain, and shown where they sat in the ranking tables. <S> The pilots found the process endlessly fascinating, but both the company and the crew were aware these conversations were not 'directive' in anyway, just a 'hey here's where you sit <S> : do you think our planning parameters are perhaps too tight?' <S> or 'have you just been getting many marginal weather flight rosters lately?'. <S> This was almost always enough to get the outliers to change their ways slightly (we tracked that too). <S> Everyone felt that this was an important part of a good safety culture, and never under question, even during tough financial times. <S> Had any bozo tried to tell a pilot how to plan their gas, they'd have been given very short shrift by the pilot concerned, but I'm not aware of that even happening, despite the presence of some genuine 'overloaders'!
|
An example of an actual-vs-scheduled block incentive program intended to help with on-time performance existed at Silver Airways in their Beech 1900D fleet, whereby pilots would be paid a bonus for each minute they were able to shave off a baseline target time. But at no point were they incentivised to reduce their additional fuel requests, and no-one in management would even ask: the tech crew's charge over their aircraft on the day of operation was absolute, and this was understood by both management and the pilots.
|
Why does this plane not pitch up after a dive? I've tested my RC plane yesterday. It's a canard. After hand launching, the plane goes straight, then I change the elevator to go down and it's going down, but when I pitch up the canard doesn't work and the plane crashes. The plane is at full throttle. When diving the plane slightly rotates to right. Controls tested before flight. Edit: Airfoil is a NACA 2412, but tips gets a little thick (all cutting, sanding is done by hand) No incidences. One servo for the canard and one servo for the ailerons. No thrust angle. The plane: CG is just in front of the vertical stabilizer (the little cross in the image) <Q> How floppy (non-rigid) are the wings and the canard surfaces? <S> The wing looks to be sagging under its own weight! <S> Tail heaviness causes the plane to tend towards going or falling flat like a leaf; it's usually strongest (leeast recoverable) <S> when under the influence of negative G's. <S> It doesn't matter whether the craft is upright or inverted; it's still "negative G's" including the caused airflows. <S> Still, my best guess is weak surface rigidity. <S> Good luck with your cool project!!! <A> Thank you for giving more information, but I still have to resort to speculation. <S> Here are some things you might want to consider: A rear-mounted prop stabilizes the aircraft. <S> Full throttle limits your control power. <S> You would had a better chance of recovery with engine idle. <S> No incidence means that the plane needs to compensate for the c.g. location with elevator deflection alone. <S> If your plane is statically stable, it would need to be trimmed with some elevator-down deflection for straight flight. <S> This limits the maximum possible canard lift and your nose-up control power. <S> Better give the canard a few degrees of positive incidence. <S> However, from the picture it might well be that you use a full-flying canard. <S> In that case, the incidence is set automatically by trimming, and a nose-up command means increasing the incidence further. <S> Now the control commands do not change the camber of the canard wing which reduces both the amounts of maximum and minimum lift possible. <S> Better use a canard with a stabilizer-elevator combination to increase control power. <S> You talk of cutting and sanding. <S> Are the wings and canard made from styrofoam? <S> Then @TipStall is right: The plane lacks stiffness. <S> Commanding a descent (what you described as "going down") increased the dynamic pressure and thus the forces warping wings and canard. <S> For now, I think you suffered a canard wing stall, but I am not able to say why. <S> Either it was aeroelasticity (twisting of wing and canard) or insufficient control power. <S> In that case, use a stabilizer-elevator combination for the canard, throttle your engine and maybe consider a less stable aircraft by shifting <S> the c.g. <S> back a bit. <A> I would suspect a combination of a very nose heavy CG, and not enough up elevator control throw, but it's impossible to determine based on the information given. <A> To add to Greg's answer (which points to the two most obvious suspects), I'd say that a typical stable canard should have a higher incidence on the canard than on the wing. <S> You can offset it with a constant pitch up trim, but apparently you don't have enough of it (for the chosen CG position).
|
My vote is that the surfaces aren't rigid enough and get twisted so much that the control surfaces can't overcome the effect. My thought too is that you're tail heavy, tail heavy will pitch both ways and you can get stuck in either positive or negative stall (or tuck).
|
Has anybody done gliding experiments with exact replicas of the birds or other real world flying creatures? The most obvious way to verify if birds are stable or not in at least gliding flight would be to make the exact rigid model of the bird (including weight distribution) and launch it into flight. The simplest approach that even early aircraft inventors may have tried is to use a frozen real bird. Are there any references about anybody trying such experiments? Pure logical or mathematical analysis is outside the topic of this question. <Q> The closest I know of are several attempts to build models of pterosaurs . <S> Since the head with its long beak is ahead of their center of gravity, the configuration is statically unstable in yaw and needs continuous control corrections. <S> On the other hand, this instability provides very quick responses. <S> This YouTube movie contains footage of a Pterodactyl model made by Paul MacCready in flight. <S> Note that Paul had attached a conventional tail for the first flights to statically stabilize the model in pitch and yaw. <S> Later in the flights this tail was removed. <S> The small skin area between the legs was most likely not sufficient for pitch stabilization, and small changes in wing sweep were used to stabilize the animals in pitch, just like modern birds still do. <S> Another branch, the Rhamphorhynchoidea , had a tail which provided additional lateral and longitudinal control. <S> Palaeobiologists are still arguing, however, whether the tip of the tail was oriented horizontally or vertically in flight. <A> One of his papers is referenced in this broad review: Lentink & Biewener 2010 One of his earlier papers is copied here: Hoey, 1992, American Institute of Aeronautics & Astronautics <S> The topics include some discussion of low static stability of the model and the lack of vertical surfaces in real birds, as well as unknowns such as wing profile. <A> I don't know about birds but researchers have been working for a long time to replicate insect flight. <S> This article talks about how 3D printing has made this much easier. <S> It has a video of a working replica hovering. <S> They call it an ornithopter. <S> Technically "ornitho-" means "bird," <S> but I guess entomopter didn't have the right ring to it. <S> I remember reading something back in the 80's about spy agencies trying to develop a "fly on the wall" cyber-insect that could get in through air ducts or other tight spaces.
|
A number of experiments and papers by Robert Hoey (from the early 1990s on) have used models of flat-winged soaring birds such as ravens.
|
Can a Diesel Aircraft engine be run on Car Diesel? What are the operational differences between normal diesel fuel used in cars and the Jet-A diesel type fuel used for some prop aircraft such as the Diamond DA62? I know that aircraft use Jet-A fuel, but could an airplane be run on car diesel? <Q> In at least some cases, yes. <S> Continental's CD-155 diesel engine will run on auto diesel, Jet A or any mixture of both: <S> The CD-155 is certified for the use of both jet fuel and diesel (DIN EN590) and is running with the two fuels in any mixture ratio. <S> EN590 is the European standard for auto diesel . <S> The Gemini 125 engine can run on Jet A and diesel according to their website, as can the Austro AE300 . <S> So it seems that in general, aircraft diesel engines can indeed run on auto diesel. <A> Have heard delightful testimony of this from some owners of diesel cars who worked at an airport. <S> The Austro diesel engine in a Diamond aircraft is an adaptation of a Mercedes car diesel engine. <S> Runs fine on both car diesel and jet A-1. <A> Some more examples of (ultra-light) planes running on car diesel: <S> FlyEco developes a diesel engine (derived from the Mercedes-Benz Smart car), running on diesel and jet A-1. <S> The FlyEco engine was further incoperated with Siemens into a hybrid experimental plane , which unfortunately crashed.
|
Yes, and diesel cars can run on aviation jet fuel.
|
How is a horizontal stabilizer attached to the fuselage and works as a trimmable Horizontal Tail as well? I am trying to figure out how does the horizontal stab attached itself to the plane and moves up and down? Is the HS attached by the rear spar and to the fuselage? <Q> Fighter aircraft usually have their tailplane connected to the fuselage with a single pivot joint, as visible in this F-15 drawing: <S> Passenger aircraft often have a horizontal tailplane which is a single part, and as such, the entire stabilizer is being trimmed by an actuator around a pivot, as can be seen in this 727 drawing. <S> The actuating system is different on newer aircraft, but the idea is the same. <A> The stabilizer is hinged at the quarter-chord point of the tail surface and has a second, movable attachment point. <S> This second point can be moved up and down, generally by turning a spindle on which a nut rides which moves the second attachment point. <S> A300 stabilizer root ( source ) <S> On this picture (sorry, was the best I could find now) <S> you see the stabilizer being attached to the bulkhead ahead of the APU. <S> Ahead of it, near the left edge of the drawing, you see the vertical spindle which moves the forward attachment point. <S> It turns according to trim commands from the flight control computer or from the cockpit. <A> The Lockheed Jetstar does this (next time you look at a Jetstar, look for the silver strip of metal below the horiz. <S> stab.) <S> but more commonly, the Mooney M20 series uses this mechanism, illustrated below:
|
Apart from those listed above, some unique aircraft have the horizontal stabilizer attached solid to the vertical stabilizer and then the entire pair pivots around a point on the empennage.
|
Why are airports like Roswell and Fresno so popular for flight tests? I recently visited Roswell, NM, and was surprised at how many flight tests have been performed there. Even the fatal Gulfstream flight test crash happened there. My research shows that a lot of flight tests happen at places like San Bernardino, Roswell, Fresno, and Moses Lake. My research turned up only simplistic explanations for why these airports are so popular like "Boeing chose the San Bernardino facility because of three factors: hangar size, availability and weather." (Source: The Sun News ) Is that really all they consider in determining flight test locations? I've heard that you can't do flight tests at just any airport, though I haven't been able to find any relevant legal restrictions. The airport choice doesn't even seem to be just the obvious factors like weather, runway length, and GA availability. (I also don't care about specialized testing that would require unusual airports like long runways or specific temperatures.) There are a few dozen low-volume long runways in the arid American West and similar regions. Why are just a few so popular? Are there any FAA (or EASA) restrictions on doing flight tests at any old airport? <Q> You can do flight tests from almost any airport, but it helps if: <S> The weather is dry and stable, the field is not too far from the factory, there is a large unpopulated area nearby, and you have support facilities available. <S> The support facilities were installed by the Air Force, and the other factors were already taken care of by Mother Nature in the case of places like Fresno or Roswell. <S> If you look at Lancaster, the next town near the vast Edwards Air Force base, the driving distance to Los Angeles is only 70 miles. <S> This should help to explain why Edwards is today the main Air Force test base. <S> Once you have a long runway and some experienced flight test engineers in place, other manufacturers will also converge on this location in order to make their flight testing more predictable and effective. <A> The FAA does regulate "where" flight test can be performed, in 14 CFR Part 91 , which says: §91.305 Flight test areas. <S> No person may flight test an aircraft except over open water, or sparsely populated areas, having light air traffic. <S> Application of this rule differs depending on the stage of flight test. <S> The FAA also provides guidance on how to extrapolate takeoff data in Advisory Circular 23-8C . <S> In particular: When the basic takeoff tests are accomplished between sea level and approximately 3,000 feet, the maximum allowable extrapolation limits are 6,000 feet above and 3,000 feet below the test field elevation. <S> Therefore the elevation of the field at which testing is performed matters a great deal. <S> In addition to the length of the runway and stable weather conditions, the elevation of Roswell, NM (~3,500 feet) allows for a greater range of extrapolation than an airport closer to sea level. <A> For a couple of your specific examples: Roswell is specifically chosen for braking performance tests because it is one of the few remaining >10,000 foot long ungrooved runways in the US. <S> Braking performance testing requires ungrooved pavement for the wet runway data. <S> Moses Lake is the closest (relatively) low traffic airport with a long runway to the Boeing factories, and the weather in eastern Washington is generally better than west of the mountains (especially in winter), making it a convenient choice for tests. <S> San Bernardino (and Victorville) are lower traffic airports in Southern California with facilities for a transport category aircraft. <S> Southern California tends to have better weather than Seattle in the winter, so some tests get moved down there depending on time of year. <S> They provide access to the restricted airspace at Edwards (R-2508) and off the coast (W-291). <S> A lot of the test flights out of KSBD head out over the water.
|
Given that the distance from Los Angeles, a major aviation industry hub, to Fresno is only a bit more than 200 miles, flight testing in predictable weather and over the open terrain west of Fresno becomes very attractive.
|
Why does fuel consumption decrease with increasing aircraft altitude? I have a chart where the thrust ($F$) and the thrust-specific fuel consumption (TSFC) are plotted against the aircraft flying speed, for several altitudes (i.e. sea level, 3000 meters and 11000 meters). This is for a generic turbojet. I don't know the source of the image, I apologize for that. At the left, we see that the thrust decreases with altitude. At the right, we observe that the TSFC actually decreases with altitude as well. However, I think this is counter-intuitive. I understand that $F$ decreases with altitude, since density (and therefore mass flow rate) decreases when the airplane goes up. What I don't understand is that the TSFC, defined as: $$\text{TSFC}\equiv\dfrac{\text{fuel mass flow rate}}{F}$$ decreases with altitude. In other words, the higher we fly, the more thermodynamically-efficient the airplane is. How does that happen? From a pure mathematical point of view , it doesn't make sense that TSFC decreases with altitude since, following the aforementioned formula, $F$ is decreasing, which leads me to think that the fuel mass flow rate diminishes with altitude faster than thrust. In a nutshell: why does the TSFC decreases with the flying altitude, having the last equation into consideration? <Q> I can't provide the math, but yes, this is correct. <S> Fuel flow decreases as air density decreases. <S> The engine becomes more efficient because of the greater temperature differential between inlet and exhaust gases combined with the lower fuel flow. <A> Gas turbine engine works more efficiently at higher altitudes Altitude increases - Air density reduces - Mass flosw reduces - <S> Maximum thrust reduces. <S> To maintain thrust as altitude increases - Compressors must rotate faster. <S> Hight altitude - Less air density - Lesser resistance - Less fuel required to spin the compressor faster. <S> There is an optimum altitude in reference to speed and thrust which increases as weight reduces. <S> Altitude increase <S> - Maintaining a constant TAS - Reduction in fuel flow and SFC from sea level up to the optimum altitude. <S> for more information visit <S> http://www.theairlinepilots.com/forum/viewtopic.php?t=476 <A> Multiple parameters have a role in this, but high altitudes are not the best operating conditions in general for an engine: see hot and high tests, but are the best for an aircraft ! <A> Less oxygen is present at higher altitudes, so not decreasing the fuel flow during climb will eventually throw the air to fuel mixture so far out of balance that the engine will run rough or even shut down or flame out. <S> By definition you will get better fuel economy at higher altitudes <S> but I would not say it is "more efficient" due to the significant reduction in power that can actually be developed due to the lack of oxygen. <S> Any engine will produce more power as a direct result of fuel burn and maximum available oxygen at sea level. <S> However, in jet engines one must take into account EGT temperature differentials and the resulting expansion of exhaust gases that do produce additional thrust dependent on greater temperature differences.
|
High altitude means - less thrust because of lower air density - less power in the gas generator due to less oxygen density - far less losses from air resistance to the fuselage
|
Why are test crashes not made harder on the airframe? This is one of the videos of the crash: 727 Test Crash . It seems it was more of a hard landing without gears. Why wouldn't the experimenters have made it more of a really hard crash if they needed to study the effects of a crash on a plane? Would slamming down the plane really hard (maybe even nose down) given a more realistic scenario and more valuable data rather than making it soft? <Q> If the plane crashes with high vertical speed, the decelerations involved are so insanely huge that there is absolutely no way to make it survivable. <S> That is well explained in Even after years of research, why are planes unable to keep passengers alive in case of a fiery crash? . <S> However in many cases the aircraft is still, at least partially, controllable, so a crash-landing can be made. <S> And that is the case where survivability can be improved by careful design, so <S> that is the case they were testing. <S> This is also relevant for accidents on landing where the aircraft simply does not have that much vertical speed. <S> Together these scenarios cover more accident cases than the out of control scenario. <A> <A> Would slamming down the plane really hard (maybe even nose down) given a more realistic scenario and more valuable data rather than making it soft? <S> Gone, everything is gone then. <S> What are you going to try to improve from the outcome of such a test? <S> Forget the real airplanes I have never been able to salvage a model aircraft that crashed nose down for any reason whatsoever. <S> I have on many times crash landed a model safely that had its landing gear malfunction <S> and that's the practice that gives you valuable lessons for future landings. <S> If you had an airplane without a landing gear and you wanted to study how can you improve chances of its survivability you would want to make a survivable attempt in the first place. <S> You wouldn't want to crash it hard deliberately and then try to pick up pieces of the landing gear to find out what could you have done better. <A> The basic principle of the airworthiness regulations is risk analysis. <S> If you can demonstrate that a particular scenario has a sufficiently low risk of ever happening, you don't need to consider the consequences if it does happen. <S> As an order of magnitude, "sufficiently low risk" means you might expect something to happen at most once during the full lifetime of all the aircraft of that type - which may be a period of 50 years or more for a popular aircraft type where thousands of aircraft were manufactured. <S> Landing a partly controllable aircraft with the gear up is more likely to happen than that "extremely rare" probability, so you need to demonstrate what the consequences are, hence the test. <S> But there are thousands of possible but extremely unlikely scenarios that could (and most likely would) lead to the loss of the aircraft. <S> For those scenarios, you design to reduce the risk of the event happening at all, not to deal with the consequences if it does happen. <S> A topical example: you don't try to design planes that will survive explosions in mid flight. <S> Rather, you try to design systems to ensure that planes don't carry explosive material in the first place.
|
Because they wanted to analyse survivability, making the crash non survivable would have defeated the point.
|
How long does flight planning take / when is it done / how is it done? When I left an A320 today, the fuel truck was already there and refueling the aircraft. (At least, the hose was connected.) Also, a FA said they will fly back within 40 minutes. This isn't much time, and I wonder if they start to refuel the aircraft before actually calculating the required amount. (Since it's a 4h flight, they'll need quite some fuel.) So I'd like to know how much time is needed for flight planning of an airliner. Maybe some planning for the next flight can already be done in advance during the current flight? Maybe some part can already be done by others? Or does the entire process take just a few minutes today? It's also not clear to me what is done during flight planning. Of course planning the route, including possible ways to divert the aircraft, and amount of fuel. What else? EDIT: To make it more clear: I'm asking about the work the pilots have to do to prepare for the next flight <Q> The pilots don't do the flight planning. <S> On a quick turnaround, one pilot goes to a printer to retrieve the flight plan. <S> The other stays with the aircraft and prepares for the next flight. <S> Sometimes someone will bring the flight plan directly to the aircraft. <S> Some airlines have stopped using paper flight plans and instead download to an iPad. <S> The pilots review the flight plan to ensure it meets all requirements, and can request a reroute, or additional fuel it <S> they feel it is needed. <A> When is flight planning done? <S> Anytime convenient! <S> Honestly. <S> You can plan for a trip 3 hours later, tomorrow, next week, or even next month. <S> There're already pre-defined airways on most areas <S> you'll fly above; you just need to lookup the charts and select yourself a route. <S> Now, unlike a family road trip, commercial flights are flown everyday. <S> Every pilot assigned to the flight will make that trip. <S> So, no, pilots do not arrive at the gate, being told " Your next hop is going to Hawaii ", then grab the charts, lay them out on a nice big table, and figure out which waypoints to go. <S> Somebody at the company has already done that for them. <S> That somebody is called a dispatcher. <S> And remember, it's the same route flown over and over again, day by day. <S> You only have to plan once. <S> When do I know how much fuel to take? <S> To figure that out, you need to know how much cargo and how many passengers are going on this flight. <S> When will you know that? <S> A few hours before departure, you already have a good estimate (given that usually x% of passengers will turn up). <S> By the time check-in for this flight is closed, you have the exact number. <S> Just plug in that number into a calculator and you'll get your fuel requirement. <S> Even without computers, this calculation takes only a minute. <S> Pilots' responsibility <S> The pilots (in particular the captain) has the final and unquestionable authority over any matter of the flight, including its flight plan. <S> That said, pilots are not the ones who come up with the initial plan. <S> In airline operations, the pilots' responsibility is to adjust the plan as necessary. <S> For example, if bad weather is expected at the destination, the captain might request extra contingency fuel. <S> So in short, the pilots' responsibility include: <S> Familiar themselves with the planned route Review the weather forecast and NOTAMs, and adjust the flight plan if necessary Verify <S> the weight and balance is appropriate (taking into consideration cargo, fuel and passengers. <S> Again, somebody has already done the calculation for them.) <S> That's not much, indeed. <A> Well, a 40 minute turnaround time can be quite short to leave time for planning. <S> Mind you <S> it's not just about choosing an appropriate flight route, but weather considerations, reading Notams, winds, choosing an appropriate flight level, deciding on extra fuel, choosing takeoff alternates, en-route alts, destinations alts <S> , then the w/x and Notams for those alternates, etc. <S> It can probably be done in 30 minutes , but it will be hairy. <S> Normally all my sectors (legs?) are pre-planned/read/briefed at the beginning of a work day. <S> Deciding on most important factors before we even go to the plane. <S> Then, when we have to do a 40' (30'?) <S> turnaround it makes it all much easier. <S> Most times we can call ground handling companies via VHF before we even land, informing them in advance of the services we need (including the amount of refuelling). <S> How long does flight planning take Computers print an OFP in probably under 1 minute. <S> Then maybe 5-10 minutes for the pilots to read <S> /change/understand/brief. <S> when is it done At the beginning of the work day <S> how is it done? <S> uhm <S> .. see above <S> I'm asking about the work the pilots have to do to prepare for the next flight <S> Ok, different question as it is not so much planning related: <S> Refuel <S> walk-around check prepare the FMC (in one way or another) <S> review the mass&balance loadsheet <S> compute takeoff speeds review and brief the departure and you are good to do. <S> Did I forget anything?
|
It is done 1-2 hours before the flight by dispatchers using computer software.
|
How do the cabin noise levels of the A380 and the 777 300 ER compare? I couldn't find any official comparison for noise level (dB) in Airbus A380 versus the Boeing 777 300 ER. Does anyone have some info about it? Which one is better in terms of acoustic isolation? <Q> From a luxury round the world flight on several different models of aircraft on several different airlines, a traveler used the exact same sound meter at his seat in either business or first class to measure ambient noise level during cruise. <S> Here is a chart I made of his measurements, including carrier and age of aircraft. <S> As you can see, long haul aircraft are quieter than short. <S> Carrier and age of aircraft also seem to make a difference. <S> For this set of measurements, the b773 is 3db (or 25%) louder than the a380. <A> As a passenger: In the forward bulkhead section of economy class (lower deck) there is almost no engine noise in the A380. <S> If you listen carefully, you can hear it. <S> I was actually surprised at how quiet it was that I didn't need my noise cancelling headphones. <S> In the upper deck, there is no engine noise to speak of. <S> In the forward section of the 777 (normally this is business class) <S> the noise is a loud but muffled (think of a speaker under a pillow), but not as loud as in the entire economy class cabin. <S> In economy class the noise is atrocious on the 777. <S> Note that both flights were on Emirates. <A> I can tell you that in economy, the 777 noise was, in my opinion, almost unbearable. <S> The A380 was almost silent. <S> I have been on both on long haul to the uk, and their is a world of difference in the noise levels. <S> Will never fly 777 again. <A> This is a very difficult question to answer, but lets assume that you're flying during cruise, eliminating as much airframe noise as possible (landing gear, flaps, slats and spoilers) <S> then the position of you in the aircraft is of importance as well. <S> The further you go to the front the more silent your flight will be. <S> Since the A380 also has an upper deck this will be even more silent. <S> Then during the flight it is important to know if the crew is doing some catching up so flying faster than normal, this will indeed be more noisy. <S> further more I found it harder to notice that we were in fact flying than in the 777. <S> Every movement feels more dampened which contributes to the overall feel on board. <S> In business class the 777 is more quiet than the 787 in business class when the crew is making up for lost time by flying at a higher speed. <S> To conclude: It greatly depends on your position in the aircraft, aft equals more noise Cruising speed, higher speed than normal equals more noise Engine type, airlines have for most the option to choose between 2 or 3 engine manufactures. <S> Personal perception, during the night you're maybe less tolerant to noise than during the day and during the night there is less noise from the cabin to muffle the engine noise. <A> In my recent travels, I have been lucky to get a host of aircrafts. <S> 777-300ER X 2 (9W)&(SIA), A330-300 X 2 (QANTAS), A350-900 <S> X 1 <S> (SIA), A380-800 <S> X 2 <S> (SIA) seated at various positions. <S> I must say that the A380-800 is a class apart! <S> take a bow Airbus! <S> I had always been partial to the Boeing, but the A380 had taken my heart away. <S> I was seated at the lower deck the 1st time I boarded an A380. <S> Honestly, I had no clue <S> when the aircraft was at rotate speed and through out my 6 hours in it, I could virtually feel no sound at all. <S> Note that I was at the front aft of the economy section. <S> I could enjoy a great view of the Changi airport while the A380 banked almost 360 during a summer sunset. <S> I surprisingly found no difference between the noise levels of the 777-300ER & the A350-900 (shocked) <S> I was rather hoping to find the same db levels on the A350-900 as the A380-800 <S> since conceptually it was a newer aircraft but was bitterly disappointed. <S> On my way back I was at the upper deck and re-lived that experience of a virtually noise free cabin! <S> Thank you Airbus and thank you Singapore Airlines. <S> My next would be an A380-800 on Qatar airways! <S> Looking forward to it already. <S> -Nik <A> I have just returned B/Class from the UK and both the 380 and the 777 were used. <S> The 777 for 14 hrs and the 380 for 6hrs. <A> Not a frequent flyer <S> but I've done quite a few SYD-LHR-SYD flights over the years (all economy). <S> No matter the carrier (SIA, BA, EK) the 777 regardless of model is my least favourite thing to fly on - <S> the noise just does not stop and it isn't a pleasant noise either. <S> Give me an A380 any day or night.
|
The difference between the two aircraft was amazing the 380 noise levels are only a quarter of the 777, in the 380 ear plugs were not needed however in the 777 you did plus the audio head phones further reduced the noise in the 777 was unbearable and sleep was not at all possible. So with this I can give you only my opinion and then overall the A380 is a bit more silent on board,
|
Could a plane land inside or on top of another plane in flight? I'm sorry if this is a little fantastical, but I'm just wondering if this type of maneuver is possible in any way. I understand if this question gets pulled. I'm trying to make a little action-animation-cgi and just wondering if this was ever a last-resort option for maybe two planes, maybe one is a bit larger than the other but maybe similar speeds could be maintained for the one plane that is running out of fuel could latch-on somehow. <Q> Parasite Fighter <S> The Space Shuttle was routinely transported on the back of two specially equipped B747s. <S> Shuttle Carrier Aircraft <A> The Navy has already done this using airships. <S> Here is a video showing launch and recovery. <S> USS Macon launching a recovering aircraft. <A> Let me take a stab at the "inside another plane part". <S> One of the smallest trainer planes is the Cessna 172, with a wingspan of 36'. <S> One of the biggest cargo planes is the C-5 Galaxy, with an inside diameter of 19'. <S> So right there, you'd be hard-pressed to find a small plane that could even fit inside a larger plane. <S> The next problem is airspeed: <S> The C-172 needs to travel at least 40 kts to maintain flight, and this is 40kts relative to the air it is in , so if it were inside the cargohold of a larger plane, it needs to be traveling 40 kts faster than the larger plane. <S> I couldn't find a canonical reference for the C5 Galaxy's minimum speed, but I can estimate it around 140 kts. <S> This means that on approach to the host-plane, the smaller plane would need to be doing about 180 kts relative to the outside air. <S> That is around the fastest speed the Cessna is capable of; it would need to be in a considerable descent at full power to achieve that speed. <S> The propeller would be turning about 2700 RPM. <S> On the transition from outside the host to inside the host, the small plane needs to slow its propeller from 180kts (2700 RPM) to only 40 kts(1200 RPM). <S> The propeller needs to slow to landing speed nearly instantaneously, otherwise the fast propeller would accelerate the smaller plane relative to its host. <S> Essentially, the parasite-plane would need to be in a considerable descent at full power to make an approach speed. <S> Then as it enters the host-plane, it would need to level off and slow its propeller drastically. <S> This seems incredibly risky. <S> Once you're inside the larger plane, the Cessna has a published landing roll out of about 500 feet. <S> The C-5 Galaxy has a length of around 250 feet. <S> So you'd need some sort of arrester cable system, like found on aircraft carriers. <S> cannot go fast enough to catch up to a big plane's minimum speed. <S> The airspeed transition from outside a big plane to inside a big plane is extreme and sudden. <S> There isn't a lot of space in a big plane for a landing roll out. <S> So, I would generally say "No", landing inside a larger plane seems impossible. <A> Something similar has happened before; see Pardo's Push . <S> Two F-4 fighters were on a mission over Vietnam when they got hit with anti-aircraft fire. <S> One jet lost too much fuel to be able to make it back to a tanker or air base. <S> The pilot of the other jet, Captain Bob Pardo, used the canopy of his jet to push on the tail hook of the other jet. <S> This was certainly a "last resort" situation. <S> It slowed their rate of descent just enough for them to fly further back to base. <S> Both pilots bailed out and were rescued, eventually being awarded the Silver Star .
|
The airforce used to have Parasite Fighters that could be launched and then recovered by a larger aircraft. So, in summary: Most big planes are not big enough to fit small planes inside Small planes
|
Why do you have to keep your seat belt fastened after landing? What's the point of the usual "please keep your seat belt fastened until the aircraft stops completely (at the gate)" in large passenger aircrafts? Since the plane is on the ground, it is not moving very quick. Even if it stopped abruptly, the seat belt won't prevent me from banging my head against the seat in front of me since it's a two-point seat belt. The only reason I can think of is if two aircraft collided with each other, which could potentially generate enough force for the seat belt to be useful. Though, I could argue that when a plane is taxiing to the gate, it has to abide to a certain speed limit, which would render any kind of collision not serious enough to be prevented by two-point seat belts. <Q> Ground operations are just as dangerous as air operations. <S> Strictly speaking the deadliest aviation incident actually happened on the ground (not saying seatbelt played a role or not however severe accidents do happen on the ground). <S> The comments cover things well, ( keeping people seated , keeping people from accessing over head compartments etc.) <S> Planes are not safe simply because they are on the ground, they are only safe from flight related incidents <S> and once on the ground they are susceptible to ground related incidents. <S> By some estimates 27,000 ground incidents happen a year. <S> The fact remains there are plenty of things to hit on the ground and plenty that can go wrong in taxi. <S> These accidents are classified by ICAO under (RAMP) and (GCOL) codes (and potentially others). <S> Boeing has a breakdown of accidents by flight category <S> (taxi and ground ops make up about 10%). <S> Furthermore here in the US under the FAA FAR 91.107 as well as FAR 121.311 <S> in the commercial case(basically the same wording) requires it ... <S> (3) Except as provided in this paragraph, each person on board a U.S.-registered civil aircraft (except a free balloon that incorporates a basket or gondola or an airship type certificated before November 2, 1987) must occupy an approved seat or berth with a safety belt and, if installed, shoulder harness, properly secured about him or her during movement on the surface , takeoff, and landing. <S> For seaplane and float equipped rotorcraft operations during movement on the surface, the person pushing off the seaplane or rotorcraft from the dock and the person mooring the seaplane or rotorcraft at the dock are excepted from the preceding seating and safety belt requirements.... <A> Twice, I've had vehicles (the tractors that tow the baggage carts) cut sharply in front of me as I've taxied toward the gate. <S> The individual driving the tractor was either oblivious or reckless -- either way, foolish in the extreme -- but no matter what his issues are, I'll do everything I can to avert the risk of a collision. <S> And that means using the wheel brakes that can stop the aircraft when it's moving nearly 200 mph... and using their full braking capability, right now. <S> If anyone were standing, he'd have a face full of bulkhead or floor before he had an opportunity to react. <S> If he were retrieving luggage from an overhead bin, the chance that he'd be able to control the bag are probably pretty slight, and now it's a projectile coming down on the back of somebody's head. <S> Even our Flight Attendants stay seated as we taxi in to the gate, simply because of the risk that the pilot may need to bring the aircraft to an immediate, even violent, stop with no warning. <S> It's pretty rare, but when it happens, it happens hard. <S> Taxiing out for takeoff, you've left the congested gate area behind, and this risk is lower, but after landing, you're heading to the most congested area with the greatest opportunity for something or someone to intrude into the path of the aircraft. <S> So, yes, by all means, please do follow the Flight Attendants' instruction, and example, and remain seated with your seatbelt fastened until we're parked at the gate. <S> The face or other body parts you save, might be your own! <A> The passengers may finally be relaxing because the wings didn't fall off and <S> the Italian mathematician in has packed away his terrifying scribblings , but the aircraft has entered a new environment with new risks, and the crew are certainly not thinking "There, done that, work's over." <S> A stationary or slow-moving aircraft is at risk from a fuel, oil and even other fluid leaks in a way that one that's flying isn't. <S> A newly-landed aircraft has new, different stresses on its structure. <S> One that's just landed has hot engines, brakes and tyres. <S> Tyres in particular, but also other components, can and do catch fire. <S> Unlike when it's in the air, an aircraft heading to the terminal is in close proximity to buildings and other obstacles, some of which also move around themselves. <S> For any number of reasons aircraft may need to be evacuated, or manoeuvred violently shortly after landing. <S> Those are not circumstances in which you want 200 people standing up, blocking each other's view of the cabin crew, talking loudly, pulling luggage out of overhead compartments, putting objects in the aisle. <S> The safe place for people to be is sitting quietly in their seats, until the doors are opened and they are invited to get up and leave.
|
A plane that has just landed is actually in a new and vulnerable condition.
|
Why are trailing-edge control surfaces usually split? I've noticed on many military and commercial jets, the trailing edge control surfaces (ailerons and flaps) are separate from each other. Why is this? Can't both serve the same function? It would save weight and complexity if one combined control surface ran the length of the trailing edge, instead of being split in half. A particular example I found is the F-102 Delta Dagger . There's no conventional tail to experience disrupted airflow, so why have separate ailerons and flaps? A similar idea that I know exists is the V-tail, such as in the F-117, which has "ruddervators"---combined elevators/rudders. It can still control yaw and pitch at the same time by somehow averaging the deflections. Presumably, combining and averaging ailerons and flaps should be even simpler, since they're both deflecting on the same axis. <Q> Same reason you have split ailerons on most big airliners. <S> It also allows for finer control (in fly-by-wire cases) as well. <S> Like a lever, a small deflection of the outboard surface results is higher rate pitch/roll (in this delta wing <S> elevon <S> example) compared to same deflection of the inboard surface. <A> There is no "usually" here. <S> For every aircraft with split control surfaces you come up with, I believe it would be possible to come up with an aircraft that either has one combined control surface (eg F-16 has flaperons), an aircraft that has some kind of a combination (eg F-18, which has an inboard flap and an outboard flaperon as can be seen <S> here - warning headphones users - ) or even an aircraft that doesn't even use ailerons ( <S> eg F-14, that only uses elevons and spoilers on the top of the wing for roll authority). <S> What you may consider to be less complex structurally might end up being more complex as much as the Fly-By-Wire software logic is concerned. <A> It would save weight and complexity if one combined control surface ran the length of the trailing edge, instead of being split in half. <S> If the trailing edge real estate is there, it makes sense to split control surfaces along their functionality. <S> The issue is maximum deflection: at full flaps, a flaperon cannot command any additional aileron down input. <S> Combining two or more surfaces poses issues such as identified in this answer. <S> Having said that, combining control surface functionality and applying computer controlled functionality means that the flight controls can be reconfigured, in case of battle damage for instance. <S> That would increase weight and complexity, and also redundancy and survivability.
|
The inboard surfaces deflect at higher speeds and the outboard ones are locked, reducing the twisting (torque) forces on the wings.
|
Why do the F/A-18 and the F-22 Raptor have horizontal stabilizer as well as canted rudders for pitch control? F/A-18, F-22 Raptor have a horizontal tailplane as well as canted rudders? Why can't the horizontal tailplane done away with (as in the F-117) and have only the ruddervators for pitch control? <Q> They're very different aircraft, built to different requirements, meant to fill very different roles. <S> Large tails are good for pitch authority and high-alpha---which are good for maneuvering and dogfighting, but not very relevant to the F-117's missions. <S> The F-117 was a medium-altitude, tactical bomber <S> that spent its life trucking around a pair of large, 2000 lb bombs. <S> It wasn't expected to tango with opposing fighters, so maneuverability was less important, thus the small tail and very modest T/W ratio. <S> Stealth kept it alive, not fancy footwork. <S> The Hornet classic (and Super Hornet thereafter) is a multirole fighter , expected to perform everything from fleet defense, SEAD, interdiction, recon, and of course CAS. <S> It was made to handle extremely well at low-speed and high AOA. <S> Pitch-rate and nose-pointing is very good---it will easily turn inside an F-16, albeit briefly <S> (turn rate v. turn radius). <S> Low-speed controllability is also crucial for landing on carriers. <S> This is why it needs large tails <S> The Raptor is an air superiority fighter (with some multirole capability). <S> Its job is going toe-to-toe with anyone else in the air. <S> So all the classic performance parameters matter: <S> T/W, acceleration, top speed, climb rate, turn rate and turn radius. <S> It will out-turn a Hornet (instantaneous and sustained) and out-run an F-16 despite being twice as heavy as either. <S> Large tails are even more important for control here, especially the very high altitudes at which the F-22 can fly. <S> In other words, the Raptor and Hornet need to be pretty nimble---the F-117 does not. <S> Here's a Super Hornet giving a little show. <S> Watch it yank its nose around at 4:35 and 5:00. <A> The rudders on modern fighters are canted mostly to reduce their radar cross section . <S> A straight vertical tail would produce a corner reflector in combination with the fuselage or the wing and would send radar waves straight back to their source. <S> To reduce the detection radius, such a behavior must be avoided. <S> The first aircraft to use this trick was the SR-71. <S> On the F-18 an additional reason was to move the tips of the vertical tails into the lateral position of the chine vortex: The wing's big leading edge extension produces a strong vortex at high angle of attack which improves the effectiveness of the tails and gives better yaw control. <S> However, the bursting of the vortex would cause heavy buffeting, and an additional fix was needed to improve the fatigue life of the tails. <S> Just look at Boeing's entry to the JSF competition : The X-32 was initially planned as a delta with only vertical tails, but when the Navy refined their carrier operation requirements, Boeing had to add a conventional horizontal tail to achieve the required angle of attack and minimum speed. <S> Boeing X-32 <S> (left, source ) and the planned production version (right, source ) with the added horizontal tail. <S> The F-117 was an Air Force plane with very limited agility, so it could get away with a tailless design. <S> Real fighters and carrier airplanes cannot. <S> Giving the horizontal tail dihedral reduces its effectiveness in two ways: Angle of attack changes from pitch variations are reduced by the cosine of the dihedral angle, and the vertical component of the aerodynamic force is also reduced by the cosine of the dihedral angle. <S> Note that the drag of a V-tail depends on the total lift created, regardless of its direction. <S> Only the horizontal component is effective for pitch control, so a steeply angled V-tail is very ineffective for pitch control. <S> In air combat the high drag will reduce performance when it is needed most. <A> The design philosophy of the F-117 was different from that of the F-22 (or F-18, which was not intended to be a stealth aircraft). <S> The main design driver of <S> the F-117 (in fact, practically the only one) was to reduce the RCS- the result being a distinctly non-aerodynamic design. <S> The inclusion of separate horizontal stabilizers would've reduced the effectiveness of the design. <S> The F-117 utilized the four elevons (a combination of ailerons and elevators) in lieu of the horizontal stabilizer, due to their location far back in the fuselage. <S> No horizontal stabilizers were ever considered in the development of F-117. <S> The F-22, on the other had was a supersonic, high performance combat aircraft, which would require horizontal stabilizers for maneuverability (it is a super-maneuverable fighter which uses thrust vectoring). <S> In absence of horizontal stabilizer, it would be very difficult for the F-22 or F-18 to reach their performance objectives, particularly for the carrier borne F-18. <S> In fact, there was a variant of F-117 which was designed to have a horizontal stabilizer- <S> the unbuilt A/F-117X, which was expected to be a multi-mission aircraft (unlike F-117, which could barely do anything other than lob bombs). <S> One main reason this design had a horizontal stabilizer was that the F-117 had quite high approach speeds, as the elevons didn't double up as flaps. <S> The revised tail had horizontal stabilizers similar to F-22, which was used to reduce the descent rate and control the approach angle, which wouldn't have been possible with the original F-117.
|
The horizontal tail is a necessity for pitch control and to trim the flap moments in the landing configuration.
|
Why there is such a strong correlation between the range of an airliner and its passenger capacity? Why we rarely see an A320 (or equivalent aircraft) on a long route with all premium business seats or an A380 (or equivalent aircraft) with high density seating and on a short route? On top of that, it is a much easier task to design a long range light aircraft and a short range heavy/high capacity aircraft, so why have no airliners (as far as I know) ever been designed with these characteristics in mind? <Q> A big part of the difference in range between small and large aircraft is simply mathematical. <S> When you make a 3D object larger, area increases with the square of length while volume increases with the cube. <S> The A320 has a wingspan of 35.8m, carries 150 (2-class), and carries 24,210L of fuel (standard). <S> The A380 has a wingspan of 79.75m, about twice the dimensions of the A320. <S> However, the passenger capacity increases by a factor of 4 to 644 (2-class), and the fuel capacity increases by over a factor of 10 to 320,000L. <S> There is simply more room for fuel in a larger aircraft. <S> Smaller aircraft may have options to carry additional fuel talks to increase range. <S> Note that this trend also applies to business jets despite their market having less of a correlation between range and passenger demand. <S> In addition to the geometrical constraints, airlines have other reasons for not operating large planes on short routes , or vice versa, more often. <A> There are five points that need to be addressed on the graph of range vs capacity, not just two. <S> Short and thin. <S> These routes are flown by small aircraft such as puddlejumpers and regional jets as well as smaller mainline aircraft, and represent the spokes in the classical hub-and-spoke model (Savannah-Atlanta or Bordeaux-Paris for instance). <S> Service frequencies are low to modest, and competition is generally fairly limited, with one or a few carriers on the route. <S> Short and fat. <S> These routes mainly exist in areas where there are large cities close together, but land/sea connectivity has a tough time competing due to geographical or political issues. <S> Examples of this include Tokyo-Osaka and Taiwan-Hong Kong. <S> Oftentimes, service frequencies are high, competition is fierce, and <S> both narrowbody and densely configured widebody (2-class seating at best) aircraft can be found. <S> Long and fat. <S> These are your classical, long-haul hub-to-hub routes such as London-New York or Los Angeles-Sydney. <S> Most of these flights are on traditional 3-class or 4-class configured widebody aircraft, and see relatively infrequent service compared to shorter routes. <S> Long and thin. <S> These routes are introduced to relieve congestion from major hubs, usually in international markets. <S> An example would be Newark-Glasgow, bypassing the otherwise-obligatory plane change at Heathrow or Amsterdam. <S> Other examples of this pattern include US domestic long-hauls. <S> In the middle. <S> Most short-to-intermediate haul mainline flying is this way -- these may be busy hub-to-spoke connections, or inter-hub flights that aren't fat enough or long enough to sustain the use of larger aircraft. <S> LCC networks (Southwest, JetBlue, Ryanair, Easyjet) center around these types of routes because they work well for a homogenous fleet (vs. hub and spoke networks, which require smaller planes for the spokes and bigger planes for hub-to-hub). <A> Basically the airlines need keep their planes always flying, parking them idle on the airport just costs money. <S> Parking a big plane and waiting a complete day until it gets full with passengers is expensive, flying a small plane a long time while passengers already waiting for the next flight is lost money. <S> In the past big planes were build for short and medium-routes, like the B747-100SR/300-SR or the A300 <S> (first time two aisles one a twin-engine?). <S> The 747-SR was used a lot inside Japan , while the A300 founds it first customers inside USA. <S> But the airlines don't buy them anymore. <S> Consider that on short routes you are often connecting smaller airports with fewer passengers per trip, therefore a smaller plane is more efficient. <S> On the other side, most jet-engines become more efficient when they are bigger, furthermore long boarding times are not a problem on long distance flights. <S> Also, one, two or three flights during a day on long routes are okay for passengers on long routes (selecting a round about departure/arrival), while on short routes you may need a flight every hour (selecting exact departure/arrival). <S> Notable exceptions are current B737-700ER and A319LR, both can fly around 10.000 km. <S> I don't know the sales figures, but I think only customers with special needs buy them. <A> There are two design reasons for this: <S> Airline routes <S> In the hub-and-spoke system most large airlines use, larger volumes of passengers are concentrated into a few airport hubs then moved greater distances between hubs. <S> In that system, there is little need for long distance/small passenger aircraft. <S> Fuel Capacity <S> A larger plane can carry more fuel and thus go farther. <S> Yes, you can get a 737 configured for business that can go as far as an early 747 <S> but, when loaded like that, it cannot carry very many people. <S> A BBJ 737 with full fuel can only carry about 2500 lbs—about 15 passengers with no bags, no food, no nothing. <A> In general as an aircraft gets bigger, with more passengers, the bigger the wing has to be to carry all of that extra load. <S> As the wing gets longer, the root has to increase in thickness quite a bit due to the increased bending moment (also due to the increased load going into the wing). <S> As the wingspan gets longer, the wing chord usually increases at the root as well (on commercial aircraft). <S> Finally, since the wing root has has gotten thicker and longer, the center wing under the fuselage has also gotten taller and longer. <S> Considering the vast majority of fuel is stored in the wings and center wing on commercial aircraft (on many that is the only location of storage), and nearly all of the wing between the spars is dedicated to fuel storage, a higher capacity aircraft just has far more fuel storage volume available. <S> Of course you could put a huge wing on a small aircraft to give it a lot of range, but I think the other answers have done a good job of explaining why that isn't done.
|
Using small planes allows for more frequent service and more flexibility even if there is enough demand to use a smaller number of larger aircraft.
|
Why does the speed of commercial airliners fluctuate, sometimes as high as 1,060 km/h or as low as 800 km/h? I've noticed that (long-haul) airliners sometimes travel at as high as 1000 km/h (I believe I've even seen 1040 km/h), but usually they fly closer to 800 km/h, for most of the trip. This seems odd to me. I would understand this if it was due to wind speed; however, usually those that travel slowly seem to do so for most if not all of the journey, regardless of the direction of travel (e.g. even if they are going up to the north pole and back down, and whether the net direction is west or east). I find it nearly impossible to explain this using wind speed. Similarly, given that the speed of sound is around 1,060 km/h at 12 km above sea level, I find it equally uncompelling to reason that they need to go at less than mach 0.8 due to the speed of sound. I would understand it if they limited themselves to (say) mach 0.95 (obviously you don't want to do mach 0.99 due to variability etc.), but I routinely see top speeds that are around mach 0.8 for cross-continental flights, and I don't understand why. So, what's the real reason? <Q> There are three different speeds that are of relevance here: <S> Groundspeed- <S> This is probably the speed indicated to the passenger. <S> For them, this is the most relevant as it determines the time taken for the trip Airspeed- <S> This is the speed of relevance to the flight crew and is used for flight. <S> Local airspeed- <S> This determines the maximum speed of (subsonic) airliners. <S> a result of the air being accelerated over the wing. <S> As a result, the local airspeed over the wing can exceed Mach 1 quite a bit before the airspeed of the airliner goes anywhere near that. <S> The result of such local supersonic flow would be a rapid rise of drag at the drag divergence <S> Mach number (which is greater than the critical Mach number ). <S> Image taken from notes of Advanced Aerodynamics by Professor H.M. Atassi of University of Notre Dame <S> In order to avoid the drag penalty, the airliners fly at speeds below the drag divergence Mach number. <S> The reason is reduced speed is not the free-stream Mach number- <S> it is the local Mach number, which should be kept below the Drag divergence Mach number. <A> Information displayed to passengers through the entertainment system often gives the aircraft ground speed rather than airspeed. <S> Wind affects the ground speed, you're right about that. <S> Few things out of the way first. <S> Pilots do not use ground speed for flying, instead they use indicated airspeed . <S> Mach number is not derived from the ground speed, as it is dependent on air temperature, instead it is derived from the true airspeed . <S> Notice we already have two kinds of airspeed. <S> There are more still. <S> Aircraft type (for example 737 vs. 777) determines "top speed". <S> Not all airliners are the same. <S> Those two types range from Mach 0.77 to Mach 0.85, roughly. <S> In less words than Wikipedia which I linked: Indicated airspeed tells the pilot the aerodynamically relevant speed to be used for flying. <S> True airspeed is the actual speed relative to the surrounding atmosphere. <S> From the true airspeed, add or subtract tail or headwind, <S> and you get ground speed from that. <S> Typical wind experienced by the regular subsonic airliner is fast (+100 km/h). <S> The tail or headwind component would vary depending on the plane's direction and the wind's direction. <S> Finally, Mach number is a function of temperature and true airspeed (notice, not ground speed). <S> The higher you are, the colder it is. <S> Also very important, Mach number is a ratio, never a speed . <S> Since the speed of sound varies as the atmosphere changes density and temperature at the different altitudes. <S> Here's a nice story , a 1200 km/h subsonic flight. <S> Summary: <S> Pilots don't use ground speed (for flying), mach number is not a speed. <A> It is all about the wind. <S> If you check schedules, you'll see that for example USA-Europe flights are way shorter (about an hour, say) than Europe -USA. <S> This is due to the jetstream. <S> I found it even more significant in the Southern hemisphere, when flying Australia-New Zealand (and back) or Santiago-Buenos Aires. <S> As mentioned in the other answers, no commercial jet goes anywhere near mach 1. <S> The ground speed <S> you are shown may be close to the speed of sound (it could even be higher, if the wind were strong enough), but <S> the actual airspeed of the aircraft (its speed relative to the air mass) <S> is way less than that (around mach 0.8 for the bigger jets, and less for many smaller comercial aircraft). <A> Similarly, given that the speed of sound is around 1,060 km/h at 12 km above sea level, I find it equally uncompelling to reason that they need to go at less than mach 0.8 due to the speed of sound. <S> I would understand it if they limited themselves to (say) <S> mach 0.95 <S> (obviously you don't want to do mach 0.99 due to variability etc.), but I routinely see top speeds that are around mach 0.8 for cross-continental flights, and I don't understand why. <S> What matters is the speed of the air passing the plane. <S> As the other answers have explained, the numbers you see in the cabin are typically speed over the ground, rather than speed through the air, so a big component of the difference is whether the plane has a headwind or a tailwind, which can easily add or subtract 100km/h at cruise altitude. <S> The other thing you need to look at is not just the plane's speed through the air but the speed of the airflow over the plane. <S> How are those things different? <S> The point is that, as a plane pushes through a mass of air, air has to move out of the way of the big metal thing. <S> This means that the air passing over the plane will be moving quite a bit faster than the plane's speed relative to the air. <S> Thus, even a plane moving quite a bit below Mach 1 can have supersonic air flowing over it. <S> The reason you don't fly at Mach 0.99 is not because a gust of headwind might take you over the speed of sound, but because you'd already be experiencing supersonic airflow 100% of the time, at that speed. <A> There are other factors that people already mentioned. <S> On modern jets the flight computer can be programmed for efficiency during the route. <S> One of the reasons why mach 0.6-0.8 is used is it is sufficiently fast without burning a lot more fuel. <S> The 777 if I remember correctly uses about 30% more fuel fully loaded to accelerate to 0.87 (edited) mach than at 0.7 mach at around 11.5 km. <S> That's a lot of fuel to save yourself less than 20% of time. <S> That extra fuel would result in more expensive tickets, in an industry which is trying to keep ticket prices to the minimum to compete.
|
The reason is that the local airspeed over the wings are higher compared to the undisturbed flow-
|
Is a fixed wing more efficient in reaching a certain altitude than rotary wing? Given the limited amount of energy (battery or fuel) let's reach the maximum possible altitude! Rotary wing aircraft pushes the air directly downwards and propels itself straight up. Fixed wing, however, must gain forward speed to produce lift, so it wastes some energy for unnecessary circling and associated drag. Anyway, eventually, its wings must somehow push the air downwards to gain altitude (that's what Newton says), energy-wise is it really different from rotary wing? (especially when circling really tightly?) Moreover, imagine our fixed might wants to pitch up really hard and has powerful engine - at some point this makes it similar to rotary wing, in that the thrust direction becomes more and more vertical. Oh, so the distinction might be not that obvious! Anyway, the question is, for this specific requirement of going just up, is the fixed wing still more energy efficient to reach a certain altitude than a rotary wing and why? <Q> A helicopter in forward flight is more efficient than a helicopter in vertical hover, due to less induced drag (and more form drag which becomes a problem at high fwd speed). <S> When the helicopter is in forward flight, the rotor disk has the same characteristics as a fixed wing: less induced drag, higher form drag. <S> But it will be a circular wing, which is always less efficient than a beautiful slender fixed wing. <S> The slenderer (is that a word?) <S> the better. <A> The first human powered airplane flew in 1977, and a later version https://en.wikipedia.org/wiki/MacCready_Gossamer_Albatross in 1979. <S> The first human powered helicopter flew in 1989. <S> The Wikipedia article mentions several endurance records (measured in minutes), but no distance records. <S> It stands to reason that if a rotary wing were more efficient, human powered helicopters would have been built prior to human powered fixed wing aircraft and would have accomplished more. <A> It is worth noting that on a fixed wing aircraft the aerofoil shape of the wing creates low and high pressure rather than, as you said " its wings must somehow push the air downwards to gain altitude " <S> Technically speaking the Rotors on Helicopters are much the same (aerofoil) shape as wings on a fixed wing aircraft. <S> The difference is they're forced to move through the air at speed by the engines thereby creating low and high pressure in much the same way. <S> Fixed wing aircraft can and do fly higher. <S> I'm not sure if helicopters can safely reach the top of Mount Everest, whereas fixed wing aircraft fly over the top of it daily. <S> I believe (and could be wrong) air density at higher altitudes <S> will not support the weight of a helicopter without the rotors rotating faster (there is a limit to how fast they can go) to produce more lift. <A> Most "conventional" helicopters (those with a tail rotor or fan) cannot be as efficient as a fixed wing in any flight regime. <S> This is because the tail rotor or fan uses a considerable amount of the power available to counter torque and to control the helicopter in yaw. <S> This power contributes nothing towards climbing or forward speed. <S> For all helicopters, the lift drag ratio is less than for fixed wing. <S> In order to climb to high altitudes, more lift must be generated which can only be done by increasing the pitch of the blades. <S> The rotor RPM is limited by two effects; a, dissymmetry of lift and b, a large increase of drag as the tips approach supersonic. <S> These limits means that increasing pitch is the only way to continue to climb and eventually, you will simply run out of angle of attack as drag overcomes the ability of the engine to deliver power.
|
Fixed wing aircraft are more efficient than forward flying helicopters because: The rotor flow in forward flight causes fearsomely complex aerodynamic interactions in flow with the fuselage and other components, which causes a particular type of drag that a fixed wing simply does not have.
|
Could the experience of inflatable structures in boats be applied to large aircraft design? Inflatable structures in boats have proved extremely successful and versatile since they began to find widespread use in the 1930s. I'm aware that experiments have been made with inflatable wings - very light, delicate structures mainly on human-powered and unmanned aerial vehicles. On boats, they're used differently: in some cases they form the main structure of the craft itself, in some, the craft has a rigid hull and the rest of the structure is inflatable, but either way, the inflatable sections are very far from delicate. Experience gained with multiple air cells in inflatable engineering means that it's now possible to build effectively rigid structures, that are extremely tough, reliable and resilient. Their behaviour in failure modes is well-known. Many large aircraft have built-in air compressors - the engines - that could keep the inflatable structures correctly pressured at all stages of a flight. Materials science has produced enormous improvements in the longevity and resistance to chemicals/sunlight/temperature ranges of the rubber skins of inflatable structures. What opportunities are there for designing parts of an aircraft as inflatable structures (perhaps winglets, or undercarriage doors)? Is there any research or experimentation into more heavy-duty use of inflatable engineering in aircraft? <Q> We now have experimental use of inflatables in space as well as for boats. <S> If an aircraft's engines are responsible for the inflation of any aerodynamic or structural part of the aircraft, however, one would have to answer what happens if the engines stop. <S> A conventional aircraft whose engines fail at a sufficiently high altitude can glide for some time, giving the crew a chance to restart the engines; it may even be landed without engine power if necessary. <S> This is a very bad time for the aircraft to lose aerodynamic performance or structural strength--for example, for the winglets to deflate just when the crew need the best possible glide slope. <S> Unlike boats or spacecraft, moreover, most conventional aircraft are intended to descend from altitudes of low pressure to altitudes of high pressure. <S> If the amount of gas in an inflatable structure is held constant, one has to balance structural rigidity at low altitudes against the stress on the fabric from the much greater pressure difference at high altitudes. <S> If the amount is not constant, it has to be replenished during descent. <S> The engines cannot be relied on to do this, since the reason for descent may be engine failure. <S> Gas could be supplied from high-pressure cylinders, but those can be heavy. <S> For an aircraft not intended to climb very high, these concerns are less severe. <A> It has been done: https://en.wikipedia.org/wiki/Goodyear_Inflatoplane <S> It was intended as something that could be dropped to pilots behind enemy lines for escape purposes. <S> Never got popular as if the pressure dropped the structure failed. <A> Their behavior in failure modes is well-known-- in the paraglider case, many pilots have had the pleasure of experiencing it first-hand. <S> (Ok, I see you specifically said LARGE aircraft design. <S> Sorry for the side-track... ) <A> In a way, aeroplane structures have pioneered using pressure differential for structural benefit. <S> The fuselage of an airliner is under pressure and functions as a pressure vessel. <S> In flight, the fuselage is supported by the wings - nose and tail want to sag down from gravity forces, creating tension in the upper section and compression in the lower section. <S> Compression stresses require reinforcements against buckling, and structures can be constructed lighter if compression forces are reduced. <S> And this is what the internal air pressure does: <S> it pre-loads the fuselage structure under universal tension stress. <S> Compression stresses at the lower fuselage segment are considerably reduced, or replaced by a reduction in tension forces. <S> Inflatable structures are beneficial because of the elimination of buckling: flimsy plastic that buckles in all directions will obtain universal stiffness when under tension stress from the inflation pressure, and this is where potential weight gains could be obtained. <S> But without the air pressure the structure would collapse, and this is where the concept might not be very suitable for aeronautical purposes. <S> Safety. <S> The overpressure in an airliner fuselage is an essential design demand for the passengers to be able to survive the conditions at cruise altitude in reasonable comfort. <S> But introducing a potential failure point only to save weight is a different matter <S> - I'm not saying it could not be done, but it would require a large effort in safety analysis.
|
A paraglider (or powered parachute or powered paraglider) is an example of a popular style of inflatable aircraft.
|
What is a skidding turn (vs slipping turn)? I am trying to understand the concept of 1) What qualifies a turn to be skidding or slipping 2) how we need to give elevator back pressure if we do not want to 'slip' the turn. While browsing for answer I read that skidding occurs in the absence of back pressure. Why does it occur when there is no elevator back pressure. I understand that when you bank to turn, you reduce the lift component and not giving back pressure might make the aircraft nose low. But how does that make a skidding turn. Also what causes the turn to slip? <Q> The terms "slip" and "skid" refer to two different types of uncoordinated <S> turn - neither has much to do with the elevator, instead both depend on what the rudder is doing: <S> Skids <S> In a skid you have too much rudder input for the turn - the aircraft starts to pivot into the turn. <S> Because the aircraft is effectively pivoting about its center of lift while flying you can think of a skid as the outside wing advancing (seeing a faster relative wind), while the inside wing is retreating (seeing a slower relative wind). <S> The inside wing thus generates less lift, and the plane starts to bank into the turn. <S> If you try to correct for that bank using aileron to raise the wing your elevator deflection effectively increases the angle of attack on that low wing, with its reduced relative wind -- do that aggressively enough and the inside (retreating) wing stalls while the outside (advancing) wing is still generating lift, and you enter a spin. <S> Slips <S> A slip is the same thing in the opposite direction: You have too little rudder input for the turn, and the aircraft is pivoting out of the turn: <S> In a slip the inside (low) wing is advancing, and the outside wing is retreating, so the inside wing is moving faster, generating more lift, and trying to level the plane. <S> If you try to hold the inside wing down with aileron input you are increasing the angle of attack on the outside (high) wing to keep it up. <S> If the outside wing stalls because of this it will drop the aircraft into something closer to a wings-level attitude, which will also bring you out of the turn. <S> This is why slips are said to be spin-resistant : The stall encourages the aircraft back into a more stable configuration (coordinated flight) rather than a less-stable one (spin). <S> The images here are taken from BoldMethod's "Why skids are more dangerous than slips" article, which is a great read and also has a better and more comprehensive explanation of the aerodynamics involved. <S> My explanation above is a vast oversimplification, but the advancing/retreating wings and difference in relative wind is the one that got the idea to stick in my head <S> so maybe it will help you out too. <A> (1) When you turn with no rudder there is natural tendency to skid slip, slide away into the center of the turn. <S> The tail swings in and nose goes out. <S> This is bad because the inner side of the plane (the side inside the turn) hits the air and you get drag. <S> (2) To counteract this tendency, the pilot applies rudder to pull the tail nose in. <S> The whole idea is to keep the fuselage in line with the direction of motion and prevent undue drag. <S> (3) <S> In any turn, without making a correction, you will lose altitude. <S> This is because when you bank, less profile is facing downwards so your resistance to gravity decreases. <S> Imagine if you banked to 90-degrees, what would happen? <S> You would plummet like a rock. <S> The same thing happens whenever you bank, you decrease your ground-facing air resistance. <S> There are two ways to counteract this: pull the stick back and/or apply power. <S> This helps you maintain altitude at the cost of airspeed. <S> A better practice is to increase power. <S> By increasing power slightly you can maintain altitude in a turn without sacrificing speed. <S> In any low-altitude maneuver, for example, when taking off, you should always increase power when turning, if you are not at maximum power already. <S> (4) <S> Back pressure on the stick has nothing to do with skidding or slipping. <S> It is purely a move to maintain altitude during a turn. <A> A skidding turn is an uncoordinated turn causing the plane to skid to the outside of the turn. <S> A turn in an airplane is accomplished by shifting some of the lift from up to a vector in the desired direction. <S> The rudder is used to help coordinate the turn. <S> During the turn there is more lift on the outside wing than the inside wing. <S> That creates a yawing effect that the rudder is used to overcome. <S> There are times when a very small direction change can be accomplished using just the rudder. <S> But primarily a turn happens because lift is vectored to one direction or the other. <S> That is why when you turn a certain amount of back pressure is required on the elevator. <S> You are removing some of the lift from up, to right or left. <S> The steeper the turn, the more upward lift you are sacrificing for more right or left direction. <S> A slip is the opposite of a skid. <S> It is an uncoordinated turn wherein the airplane slides into the turn. <S> In either case, it is the rudder that is used to overcome the adverse yawing effect of a turn, not the elevator. <S> The elevator is used to overcome the loss of upward lift. <S> Uncoordinated slow speed turns during the landing sequence are probably the most common reason for small plane crashes. <S> The point when the airplane turns from the base leg to the final leg of landing is, in my opinion, the most dangerous part of flying. <S> An uncoordinated slow steep turn is an invitation to a spin which happens too low to the ground to overcome.
|
The general practice is to put back pressure on the stick.
|
Are GA airports typically accessible 24/7? Is access to GA airports 24/7? I always thought it was. Every airport I've visited had gate-codes to open gates after hours. But I recently started planning a flight to Salina, KS (KSLN), and the local FBO told me field access shuts down entirely at 10p.m. As a transient flight, I'd have no way back to my plane after that. I'm skeptical, as I believed airport access was 24/7. Am I just completely mistaken in that belief? <Q> There are no standard federal rules for the same reason that there aren't any for when gas stations should open and close: they're private (or state-owned) businesses. <S> So before going somewhere new <S> it's always good to call and ask about opening hours, access etc. <S> If there are multiple FBOs at the field, you can call them all: one might be open 24 hours a day even if another one isn't. <S> One specific point about Salina is that the TSA may be limiting access. <S> The AOPA airport directory says that KSLN is under security directive <S> SD-8G , i.e. the TSA limits access to the apron. <S> That means you might need an authorized escort - most likely someone from the FBO - to and from your aircraft. <S> If the FBO shuts at night there may be no one there, but FBOs in general are usually good at making special arrangements if needed. <S> And although your question seems to be about ground access, I guess it's worth stating the obvious: airports are accessible 24x7 from the air. <S> Nothing stops you landing at 3am, filling up at the self-service pumps and then taking off again. <S> But watch out for local practices like voluntary noise abatement curfews, e.g. at KPDK : <S> Pilots are encouraged not to fly between the hours of 11 p.m. and 6 <S> a.m. <S> Due to FAA Regulations, PDK cannot implement a mandatory curfew at this time. <S> It's still legal to land or depart there during curfew hours, but you'll really annoy the airport management, FBOs, and local pilots who have to deal with the complaints from local residents. <A> You may want to call the airport manager if there is one that is not at the FBO. <S> If there are multiple FBO's on the field try another one, they may have 24/7 access. <A> Define "accessible". <S> If you need ground access to your aircraft, that depends on gate code / FBO availability (or whether the FBO is willing to give you access through a code-locked side door). <S> If you mean accessible for arrivals and departures, there will usually be a note in the Chart Supplement (formerly the AF/D) as to what the restrictions (if any) are. <S> For example, KSNA (Orange County in SoCal) has a restriction of "WHEN ATCT CLSD NO LCL TRNG <S> OR TOUCH & GO OPNS."
|
The general answer is that the airport manager is in charge of ground access (unless the TSA is involved; see below) and individual FBOs can open or not whenever they like. This will vary from field to field and I do not think there is a regulation on the matter.
|
Why do some flights make turns shortly after takeoff? I have seen that flights will make a turn, after traveling some large distance (say after some kilometers), but that can be done before. Why not flying directly like in 2 ? I am not expecting a passenger flight to do like fighter jets and perform nearly vertical take-offs, or some other manoeuvrers. Are these flights restricted to do so, or is there any reason to behave so? Or did I misunderstand something? <Q> It is mostly standardized procedures. <S> I take as example Amsterdam airport (AMS), but the following is applicable to most, if not all, major commercial airports. <S> Let's look at the departure charts , <S> in particular this one: as you can see, if an airplane is departing via that runway, it MUST follow one of the two specified paths to exit the airspace of the airport through the "ANDIK" waypoint. <S> It has different paths for the other exit waypoints, but they are similarly defined and limited in number. <S> In the link you will find similar charts for each of the runways. <S> Within restrictions due to factors like terrain, noise abatement over populated areas (as Dan's mentions in his answer ), areas restricted due to security and safety (over city centres, government and military installations, nuclear power plants and such) or used for other purposes (military operations, space launch and such), these routes are defined so they don't intersect (much). <S> This ensures arriving and departing aircraft don't come close to each other, which greatly reduces the risk of collision and allows responsibility for different routes to be split among several controllers who can each handle their assigned routes mostly independently of the others. <S> Weather conditions and other factors will dictate which runways are used, but the runway will dictate how the airplane will exit the airport's airspace, after the appropriate exit waypoint has been selected (you generally would not use a waypoint on the north side if you have to go south). <S> So, to summarize: you have a limited amount of exit <S> waypoints <S> you have a limited amount of runways weather will restrict your choice <S> (well, the airport's tower will do this for you) of runway <S> your destination will restrict your choice of exit waypoint for each runway-waypoint pair you will have one or two possible routes <S> This results in the kind of behaviour you have observed. <A> Aircraft are routed based on all manner of different things. <S> It's much easier for controllers to manage aircraft if everyone is following a similar route, and so there are generic routes defined. <S> This is especially true in and out of airports - imagine if dozens of planes were simply arriving in any direction they like, it would be very chaotic to deal with. <S> Noise Abatement. <S> Many areas have noise abatement procedures, where aircraft are either restricted from flying over or the number or flights is limited. <S> It's not uncommon for aircraft to have to fly around certain places. <S> Weather Avoidance. <S> For comfort and safety, aircraft will sometimes be routed around certain types of weather. <A> This isn't an answer, just an addition to @federico's answer. <S> The following image shows departing aircraft from international airports near my location, Düsseldorf (red) and Cologne (blue). <S> The data was recorded over 24h from flightradar24 and put on a map together with some beacons. <S> The dotted lines indicate the angles mentioned below. <S> Looking into the departure charts for Düsseldorf , one finds for take-offs to south-west this, in layman’s words: Turn hard right and fly away from NOR at 0 <S> ° Turn right to LMA <S> (Roughly, there are more points not shown in the map, and more than one route), then depending on destination turn left to 203° or 209°. <S> Turn left and fly to NOR at 174°, then turn left to GMH at 86 <S> ° <S> Finally, there's a chart showing all this together, though this is more about noise: <S> For cologne it's obvious that there are similar rules. <S> It's also clear that the flights from Düsseldorf to south-east are guided around Cologne by flying a little towards GMH first. <S> So, not an answer, just to show that aircraft fly as they are intended to do, though there are a few exemptions. <A> Just like you can't drive your car straight from point A to point B because there might not be a direct road between the points, aircraft can't necessarily fly from point A to point B because there might not be airways that directly connect the points. <S> Also, most traffic between major airports will follows established procedures. <S> These are either Standard Information Departure (SID) - for flights departing or Standard Terminal Arrival Route(s) <S> (STAR or STARS), for flights arriving. <S> These standard departure and arrivals procedures are put in place based on the geography, weather or other restrictions at or near the airport and don't have to coincide with the flight's arrival or departure direction. <A> Just one clear answer why it is also done on short trips <S> (so not depending on the earths curvature that much): Airplanes have the allowance to fly on a flight level (FL), given in feet / 100 AND refering to an imaginary surface level where the standard pressure of 101325Pa is located. <S> So FL 130 is 13000 feet above the level with 101325Pa ambient pressure.
|
Some turns are only allowed at that FL to avoid collisions with other airplanes. Just off the top of my head, here are some of the more common reasons: Standardised routing.
|
Why do you never see any other planes in the sky whilst flying? I was just wondering as I passed the airport this morning why, whilst we are flying, do we never see any other planes nearby? There must be millions of planes and millions of people flying each day, I appreciate the sky is massive but these planes must follow roughly the same routes so how is it that they never seem to pass by any other aircraft? <Q> If you're not seeing them, you're not looking. <S> I see planes all the time when flying commercial. <S> Obviously, I see them a lot more when close to a major center, and a lot less when in the sparse parts of the Pacific Northwest (Montana, Idaho, Oregon, Washington). <S> I think spotting them may take some practice. <S> Visually, a plane 10+ miles away is a very small dot, and easily missed. <S> Try looking for contrails and be sure to look at altitudes above and below you. <S> Scan the sky in narrow, 10 <S> ° concentrated "fields of view" to scan from left-to-right all the way across the sky. <A> The image above is taken over Germany, and the other aircraft is just a bit higher: <S> Of you look at site like Flightradar24.com , you'll see aircraft following the same route, and close enough to allow each other being seen by passengers. <S> Screenshot (look at the scale): <A> Aircraft are usually routed one in front of the other, often at different flight levels. <S> Situations where another aircraft would be flying alongside yours, where they would be easily visible, are fairly rare. <S> They do happen though. <S> I was flying from Chicago to Boston last Thanksgiving and there was another heavy alongside about 2000 feet below and 3000 feet to port. <S> If aircraft are on an intersecting airway, they will generally be several miles away, so they will be very small, and will usually be at different flight level. <A> That's not true, you DO see other planes in the sky. <S> I fly very infrequently (on average probably 1 flight a year) but I've seen other planes in flight. <S> I remember on one flight, my airplane entered a quite steep bank to the left, I was sitting by the right side window, and I saw another passenger jet fly past above me, it was rather close, probably a 1000ft altitude difference.
|
Sometimes you have two for the price of one: From my personal experience, seeing other aircraft is really common, as already commented and answered, even far from busy airports.
|
Are turboprops more efficient than piston engines (thrust per fuel consumption)? I want to compare two types of engines: Turboprops and piston engines. I want to know which one is more efficient. There are many types of efficiencies, so I will specify: thrust (in newtons) per fuel consumption (kg/second). Right now I don't care about power/weight ratio or max speed or horsepower. Those are all valid concerns for aircraft design, but I'm trying to pick exactly one criteria and figure which engine is more efficient in its terms and its terms alone. I don't want to mix criteria. I want to focus on one aspect, get an answer to it, then move on to the others later. A complication is that piston engines usually give their output in horsepower. I have no idea why this is. What's ultimately needed is thrust. I realize that a propeller engine's job is to create torque, and thrust will depend on blade length and airspeed. In that case, I can't understand why those engines don't specify their output in torque. Citing engines that actually exist (and citing their specs) will answer this question as long as the choices are modern, good engines. (I did not include turbojets or turbofans for fear of being too broad. I picked two propeller engines and don't want to mix them with jet engines.) One more thing. I realize that engines are capable of varying levels of thrust. It's my understanding that max thrust is usually more in efficient than cruising thrust. Therefore, I will ask for thrust/fuel-consumption figures of an engine at typical cruise conditions. <Q> No, piston engines are more efficient. <S> Their output is given in kilowatts or HP because this does not change much with speed, unlike the thrust of a propeller. <S> By running a piston engine a few times on a dynamometer stand you can get reasonable numbers which are valid over the full operating range. <S> If you want to characterize them by their thrust, you would need to look at an engine-propeller combination at one particular speed, which is not very helpful. <S> Now you ask for specs of contemporary engines. <S> The funny thing is that the efficiency of aviation piston engines has not changed much over the last decades. <S> If you assume 250 g of fuel per kWh at full power for gasoline engines, this figure holds already for good WW II-era engines like the Jumo 213 <S> A which was run on 87 octane gasoline. <S> The low octane number restricted compression to 6.93:1, while the higher octane number of contemporary AVGAS allows for an 8.5:1 compression ratio in engines like the Lycoming O-360 , which consumes 280 g of fuel per kWh. <S> Adding fuel injection enabled Lycoming to reduce fuel burn to 240 g per kWh in the IO-390 , which was first run in 2002. <S> Diesel engines are even more efficient; they typically consume 220 g per kWh. <S> This low value was already possible with the venerable Jumo 205 of the 1930s which consumed only 213 g per kWh at its most efficient speed. <S> Modern aerodiesels run at similar efficiency: <S> The Thielert range of engines which have been taken over by Continental consume 220 g per kWh . <S> Even the best turboprops rarely achieve less than 300 g per kWh. <S> The most modern version of the venerable Pratt&Whitney PT6 consumes 308 g per kWh, and only very recent developments can close the gap to piston engines. <S> The Progress D27 claims a specific fuel consumption of 231 g per kWh while the Europrop TP400 one of 237 g per kWh. <S> Note that here the remaining thrust from the exhaust has been converted into an equivalent power rating to achieve such good values. <A> There is no small turbine engine that has anywhere near the specific fuel consumption (Lbs/Hp?Hr or Grams/Kw/Hr) of a gasoline or diesel aircraft engine. <S> Turbines are light (lbs/Hp or KG/Kw) but burn considerably more fuel. <S> Turbines are also extremely smooth, almost no vibration. <S> But as to efficiency, even our antique technology small aviation piston engines, turbines just aren't very good. <S> Typically the smaller the turbine the worse the specific fuel consumption. <S> So the Allison, now Rolls, C250 family, are terrible, sometimes getting 0.8 Lbs/ <S> Hp/Hr in low cruise setting. <S> The big turbines, like the AE2100, can get down to 0.4, but these engines are rated at 5,000hp, much too big for light aircraft. <S> One particularly troublesome aspect of turbine specific fuel consumption is that it is worse at lower power settings. <S> This is one of the reasons that most turbine aircraft tend to fly as high as possible, because at high altitude they are running much closer to max power to achieve best aerodynamic efficiency. <S> Piston engines tend to achieve their best specific fuel consumption at relatively low power settings, so flying low and slow does not hurt range nearly as much as on a turbine aircraft. <S> With several new diesel aircraft engines coming into use the efficiency of piston aircraft engines has gotten much better. <S> Some of these diesels have specific fuel consumption in the 0.35 lb/ <S> Hp/Hr range, better than even the most efficient large aircraft turbines, and close to half of a small turboprop at low cruise. <A> Turbines aren't as efficient as piston mills, but the difference isn't as much as you might think if you consider the improved performance. <S> At optimum altitude, the Meridian [turboprop] burns about 31 gph compared to 20 gph on the Mirage [piston], roughly 50% more. <S> That's because piston engines are more efficient and offer a lower specific fuel consumption (.43 lbs./hp/hr) compared to turbines (.58 lbs./shp/hr). <S> Source: planeandpilotmag.com <S> But a turboprop can fly faster, i.e., get there on less fuel. <A> If you want to rate an engine by the thrust it makes, you must know the propeller efficiency at the given criteria for your test. <S> The engine performance and thrust performance both change with altitude and speed. <S> Only a jet engine or turbofan engine should be rated by thrust, and even then, it changes with altitude and speed. <S> Don't accept book numbers for prop efficiency, because it changes all over the map. <A> I went and broke down how much fuel is burned to create one hp in the lycoming 720 vs the pt6 and the piston engine came out to be between 7-8 percent more efficient than the turboprop. <S> Pt6 approximately 088-.089 gallons per HP per hourLycoming 720 approximately. <S> 081-.082 gallons per HP per hour <A> Above graph is from Torenbeek, Synthesis of Subsonic Airplane Design: Fig. <S> 4-1 shows the quantity of fuel used per hour by some representative examples in the categories mentioned above, the figures being for cruising flight at a given thrust which is equal to the drag. <S> The graph shows that turboprop engines have a slightly higher fuel consumption than piston engines, which at the time of publishing of the book were exclusively avgas engines. <S> The graph shows the state-of-the-art of 40 years ago.
|
So for the fuel consumption criteria, a piston engine is more efficient.
|
Why is the VFR traffic pattern area at some airports different from its IFR circling approach area? Take Half Moon Bay Airport (KHAF) as an example. Under VFR, the traffic pattern is right pattern for RWY 30 and left pattern for RWY 12. This implies the downwind leg is to the EAST of the RWY 12-30, and therefore we should fly over the land at TPA 999'. However, looking at the IFR plates, both RNAV (GPS) Y Runway 30 and RNAV (GPS) Y Runway 12 indicate we are required to circle WEST over the water at 800', since that " Circling NA east of Rwy 12/30 ". I understand it is likely that we have more vertical room over the water since there are no obstacles there. However, I don't get the reason to require VFR traffic over the land. Is it for VFR/IFR traffic separation? Some reasons that I came up with Favors the water, against the land: Terrain/Obstacles, Noise Abatement. Favors the land, against the water: Marine Sanctuary Protection. <Q> It looks like you have a few different questions here. <S> As a caveat, I know nothing about Half Moon Bay <S> so these are (educated) guesses to some extent. <S> Someone with personal experience at KHAF could probably give better answers. <S> Why is circling always west of the runway at KHAF? <S> Circling areas are planned according to the TERPS criteria (see section 2-7-1); the formulas are in the document, but the basic idea is to make sure that there are no obstructions to circling within a certain distance of the runway . <S> It looks very likely that at KHAF the terrain east of the field rises too sharply to allow safe circling there: the minimum allowed in the TERPS is 1.3nm/1.5sm/2.4km, and Google Maps shows that there's definitely rising terrain within that distance. <S> Why is the pattern always east of the runway at KHAF? <S> I don't know for sure. <S> Noise abatement is obviously a concern at KHAF but then as you said, why not put the pattern to the west, over the ocean? <S> The most obvious reason is that Half Moon Bay is in the Monterey Bay National Marine Sanctuary and flying over national parks below 2000' AGL is discouraged . <S> Another possible reason is to avoid directing light, single-engine aircraft to fly over water unnecessarily. <S> Why - in general - would a certain area be used for the pattern but not for circling? <S> There's no reason why one area should always be suitable for both needs. <S> In particular, circling requires guaranteed obstacle clearance within a certain distance from the runway. <S> VFR pilots should be able to see and avoid, but obviously that assumption isn't possible for IFR. <S> If you fly a circling approach at minimums then you might even go back into cloud while circling ( and then go missed ); in that scenario you really don't want to have to worry about terrain or obstacles being anywhere nearby. <A> 99% of the time <S> it’s Runway 30, and there are noise abatement procedures (pdf) for the east side traffic pattern as well. <A> I live in Moss Beach next to KHAF. <S> Specifically, they want the VFR traffic over land because of the Fitzgerald Marine Reserve to the NW of 30. <S> There's a huge pack of seals <S> w/ cubs on the beach <S> , so they'd rather keep the noise over the residential areas. <S> You wouldn't want to send IFR traffic over that land though, not with Montara Mountain to the N <S> and it getting steep pretty quickly to the NE.
|
It’s because of the marine sanctuary.
|
Is a recoil start (hand propping) allowed if it isn't mentioned in the aircraft manual? Is a recoil start (hand propping) allowed without it being referenced in the aircraft manual? In a Cessna 150, for example. <Q> You didn't say exactly what "allowed" means, <S> e.g. do you mean approved by the manufacturer, or legal in a certain country? <S> But if you're asking is it legal in the US (under FAA regulations), then the answer is yes. <S> AOPA has a nice article on exactly this question, called <S> Hand propping: A legal primer . <S> It says: <S> There is no specific FAA regulation that applies to hand propping an airplane, either to prohibit it or to direct how it is to be done <S> But: The FAA contends that hand propping is a two-person operation and has expressed this view in the Airplane Flying Handbook <S> (FAA-H-8083-3A) under the section titled “Hand propping.” <S> Of course, this publication is not regulatory, but the NTSB was surely influenced by it in a 1983 legal decision. <S> In that case, the FAA sought to suspend a pilot’s certificate for being careless or reckless when, while attempting to start a VariEze experimental aircraft, it “got away” and ran into a parked aircraft. <S> The NTSB concluded that the pilot had violated 14 CFR 91.13 (careless and reckless operation): <S> The board affirmed the administrative law judge’s finding that there had been a 91.10 (now 91.13) violation <S> That means that hand propping itself isn't illegal, but doing it wrongly and against the FAA's general procedures could get you in trouble: <S> There have been at least two previously issued NTSB (full board) decisions and one subsequent decision that refer to these generally accepted procedures and precautions for hand propping. <S> The precedent has been set. <S> So, hand proppers beware; if you fail to follow proper precautions and the airplane gets away, the FAA might pursue action against you for being careless or reckless. <A> It might be stupid, but it's not illegal. <S> There is an important distinction to be made here. <S> The manufacturer can state that hand propping "is not recommended" but that is not a binding statement and hand propping is still permitted...though not recommended. <S> Simply because a procedure is not recommended does not mean it's prohibited. <S> Now, if the manufacturer places a limitation of "no hand propping" in the limitations section (the real, formal section of the POH called "Limitations"), then the procedure is not authorized at all. <S> I know of no airplane with this limitation because it's not really a problem. <S> I think our good friends physics and Darwin take care of that for us. <S> I've never seen a person hand prop a GTSIO-520 (physics) <S> but if someone manages to hand prop a large piston engine I doubt we'll ever hear about it (Darwin). <S> Smaller piston engines are actually easy to hand prop. <S> Hand propping of O-170s (Continental A series) and O-190s (Continental C series) is actually quite common because many of the airplanes equipped with these engines lack electrical systems to power starters. <S> The C-150 uses a Lycoming O-200 <S> which is only 10 cubic inches larger than the Continental O-190s. <S> The O-200 is rarely hand propped, however, because the aircraft that use it generally have electrical systems and starters. <S> Why hand prop when you can just use a key? <A> When I was flying skydivers we had occasion to hand prop a Cessna 182. <S> That's almost a 500 cubic inch engine, and hand propping it is definitely NOT in the manual. <S> But all reciprocating aircraft engines have impulse-coupled magnetos, so you don't really have to turn them quickly to get them to fire. <S> When you move the propeller through the sweet spot, the mag will unwind and cause a spark. <S> The coupling makes a ticking noise that you can hear. <S> If there's fuel in the jug when the magneto fires it will kick, and that's usually enough to start it.
|
Unless an operation is prohibited by regulation, the laws of physics, or the limitations section of the POH/AFM, it's not illegal.
|
How are wooden aircraft protected from lightning strikes? A wooden aircraft is not conductive and if a lightning hits the wood it will instantaneously ignite. How would you protect a wooden aircraft from this occurrence? <Q> By not flying through thunderstorms. <S> For a small aircraft, the lightning is not the most hazardous part of a cumulonimbus (Cb) cloud system. <S> Mature Cb clouds have huge updrafts underneath them, which can cause enough turbulence to upset most aircraft. <S> Heavy rain and hail is also commonplace underneath Cb clouds. <S> Even the rain can be heavy enough to damage wooden propellers and any components on your leading edge (such as the leading-edge slats <S> found on the Tiger Moths I fly). <S> Hail can put holes in your canvas, which are expensive to repair - if you manage to get the aircraft home at all. <S> This turbulence and rain persists for a much longer period and across a wider area than the thunderstorm itself. <S> For these reasons, the chief protection against thunderstorms is by training and procedure: student pilots are taught to avoid Cb clouds when they're visible, and to plan flights to avoid areas where Cb are forecast. <S> Weather forecasts and reports specially call out Cb clouds to help with this, and ATIS messages often warn of "cumulonimbus cloud in the vicinity of the aerodrome". <S> Protecting a wooden aircraft specifically against lightning is not hugely worthwhile, because it's unlikely to be able to stay in the vicinity of the Cb cloud for long enough to be at risk of a lightning strike. <S> It just wooden happen. <A> Additional physics-y information: trees attract lightning strikes because they are reasonably well conductive, especially the living tissue between the bark and the heartwood. <S> Also because one end is well-grounded through its roots, which extend down to damp conductive soil. <S> So they are natural lightning conductors. <S> Wood once dried and turned into timber is not a good conductor, and a plane in flight is not grounded at one end. <S> So it's much less attractive to lightning than a living tree. <S> A metal plane is more likely to be struck than a wooden one because it is a near-perfect conductor and offers the lightning an much easier path than through air. <S> However, for the same reason, a lightning strike doesn't often cause any damage to a metal plane. <S> I'd expect that a wooden plane could be downed by a lightning strike, and lightning strikes are not always closely associated with cumulonimbus clouds. <S> Look up " positive lightning " (a.k.a. "a bolt from the blue", literal meaning thereof). <S> This is mercifully rare. <S> Wikipedia reports that it has downed at least one glider. <S> I'd also guess that a jet engine's high temperature exhaust creates something of an ionization trail behind it, equivalent to trailing some considerable length of wire behind the plane. <S> A piston engine, much less so. <A> It is undeniable that an airplane manufactured from wood or other materials that are good insulators would probably suffer considerably more damage to the structure from a direct lightning strike but they have been certified as to protect critical structure, fuel tanks and other components from massive electrostatic discharges. <A> By not building wood aircraft <S> But there is a way: build them like a composite aircraft. <S> There are very few wood airplanes left, for one thing. <S> So the problem is solved by building mostly metal airplanes for past 70 years or so. <S> While wood planes are excellent when new (wood is strong, light, and elastic) they have a fatal flaw: they rot on exposure to moisture. <S> (And, they are expensive to build.) <S> As it happens, wood planes are still built in tiny numbers, and yes, they are vulnerable to lightning. <S> But lightning by definition comes from thunderstorms and these must be avoided for other reasons anyway. <S> The few handmade wooden planes that are registered these days are light planes that rarely fly in instrument conditions and so the chance of blundering into a storm cell is really low. <S> It would be possible to build a protected wood plane. <S> One could laminate a conductive screen on surfaces in the same manner as used on certified glass and other composite aircraft. <S> However, I would guess that no one has ever done that. <A> Wood airplanes do have steel control cables and rods, which can conduct a strike through one side of the aircraft to the other if the skin is penetrated, which is still destructive to the wood structure at that point. <S> Burning or fire? <S> Possibly if the strike is strong and penetrates the right places. <S> That's why it's a good idea to install grounded static wicks in proper strategic trailing edge locations. <S> There are modern and sleek kit planes out there today. <S> Very sharp-looking, and pretty quick too. <A> An article from Flying Magazine hints that lightning strikes do not affect wood-and-fabric planes. <S> That there are almost no reported cases, and the only case they know of, resulted in a damage to a wing-tip. <S> Source , go to page 6. <S> It's worth mentioning that big composite (non-conductive) planes ( <S> e.g. 787) could suffer from lightnings if it weren't for special coatings , per Boeing. <A> There are also conductive paints that cause the skin of the plane to carry the charge regardless of its composition. <S> I would suspect that conductive paints that lead to static dischargers could also be used on wooden structures with cloth skins.
|
Well, first off a wooden aircraft is not totally manufactured from wood; it does have metallic or otherwise conductive components throughout the airframe and is engineered with conductive pathways throughout the airframe for electrostatic dispersion and lightning protection as per the requirements of 14 CFR 23.1306, 25.1316, 27.1316, and 29.1316.
|
Why would pilots "call the company" after an aborted takeoff? I was skimming through the RealATC videos on YouTube today and watched this one . In it there are two flights taking off from Chicago-Midway ( KMDW ); Delta flight DAL1328/DL1328 and SouthWest's SWA3828/WN3828. They are each taking off from crossing runways (4R and 31C). For some reason, even though SWA3828 is given clearance to take off, the Delta flight also starts its own rollout. After the call to abort is given, both aircraft abort takeoff and are able to then safely leave their respective runways in order to taxi back to the proper starting point. One of the aircraft states it will need a few minutes to check for heated brakes. Then both aircraft state they will need to " call company " for some unspecified reason. Why would both planes need to call company? My guess is to recalculate fuel used to determine if they will have enough fuel to continue the trip. Why else might they need to do so? <Q> An RTO can happen for any reason, mechanical, FOD, ATC error, etc. <S> The boss (airline operations) will want to know what happened. <S> Safety Is everyone safe? <S> Is anyone in immediate danger? <S> Prepare documents for the NTSB investigation. <S> Time <S> How much time will be lost (e.g. to cool the brakes); this can affect the schedule of this particular plane days ahead. <S> Especially if maintenance is required. <S> Notify the destination airport of the delay, and also publish the delay for the next flight from said destination airport. <S> If not, get on the phone with airlines who can help. <S> Find a replacement plane and send it over there. <S> Get the all-clear from an airline engineer that the hot brakes won't affect another attempt. <S> It depends on how hot they are. <S> If a delay is expected, start the clock, airlines can keep passengers on a stationary plane for so long, I guess it's two hours. <S> Been there, it's awful. <S> If it will take more, find them a gate, if no gate is available, get the stairs and a bus. <S> Whose fault was it? <S> Get a grip on the PR before things get out of hand, i.e. tweet. <S> If anyone is suspected of not doing their job properly, start an investigation. <S> If the ATC is at fault, send them the bill. <S> If it is another airline's fault, call the insurance company. <S> Fuel <S> Not really an issue for an aborted take-off after few seconds of take-off thrust, but nonetheless run the numbers again. <S> Both in the cockpit and in the ops center. <A> While many of the answers shared "may" be partially correct, there is a compliance issue that requires the "call company" to occur. <S> The Dispatch Release (the document that permits the flight to be operated) under Part 121 is valid for one operation. <S> When the aircraft took the runway for the purpose of takeoff and then aborted that takeoff, and then left the runway surface, that Dispatch Release is no longer valid, and would require either a revalidation or issuance of a new Dispatch Release. <A> Almost certainly refers to calling station ops in order to get a gate. <S> After a rejected takeoff, even at fairly low speed, it's common to need to let the brakes cool, and if they aren't so hot as to be dangerous, cooling at the gate is preferred -- allows passengers a chance to get off & use a real restroom, buy food, etc. <S> Since Ops has the picture of what gates won't be needed for the next XX minutes, the crew calls them to determine where they need to go next.
|
Maintenance Make sure the airline's maintenance stationed at the airport can deal with the issue.
|
What is the relation between pressure and airflow speed above an airfoil? Does decreased pressure on the top surface of an aerofoil cause high velocity airflow or does the high speed airflow result in decreased pressure? <Q> Above the wing, decreased pressure causes the air to accelerate. <S> But it is the plane's velocity that causes the decrease in pressure above the wing. <S> Much like pressure gradients are the cause of wind. <S> Or when a fast truck on a highway punches a hole in the air, the air behind the truck rushes in to the lower pressure area. <S> So when a fast truck/airfoil causes low pressure, the air rushes in / speeds up. <S> Source: Wikipedia <S> More information here (NASA). <S> What happens in a stall, is the drag from the airflow separation outweighs the lift. <S> But the pressure is still lower above the wing. <S> Leading-edge root extension and delta wings can make better use of high angles of attack. <S> The NASA link above explains the true relation between airflow speed and pressure, but that's not the only cause of lift, is what I mean. <A> Both pressure and velocity are related: The total energy of an air molecule outside of the boundary layer is constant and the sum of its pressure and its velocity component. <S> Mathematically, the energy per unit of volume is $$\frac{\rho}{2}\cdot <S> v^2 + p = const$$ which is actually the simplest form of Bernoulli's equation which neglects changes in altitude and temperature. <S> In the end, it's not this causes that, but both components fluctuate in sync and combine to a constant total. <S> Nomenclature: $\rho\:\:$ density <S> $v\:\:$ <S> speed <S> $p\:\:$ pressure <A> Reducing the cross-section area <S> When air encounters the airfoil, the streamlines over the top surface are compressed, because the surface is an obstacle pushing them vertically upwards, and the rest of the atmosphere prevents them from moving freely in block upwards. <S> Note this reduction of area is widely accepted as real, but is not well explained. <S> This would work the same way for the other side of the cylinder, as atmosphere pressure exerts in any direction, normal to the surface. <S> Increasing speed <S> If we assume a simplified case of little change in density (nearly incompressible fluid), the same quantity of air must go through a smaller area in the same time, and to do that it "must" accelerate. <S> This is similar to what happens to water in a garden hose: <S> When squeezing the extremity water accelerates at this location relative to the rest of the hose. <S> Decreasing pressure <S> If we still assume a nearly incompressible fluid, and neglect the effect of viscosity then, per Euler's equation , an infinitesimal variation of velocity $dV$ leads to a variation of pressure $dP$ equal to $-\rho VdV$ ($\rho$ <S> the air density, $V$ the velocity). <S> Therefore a cross-section area reduction leads to a velocity increase, which in turn leads to a pressure decrease. <S> If you need to put a name on this effect, then this is Bernoulli's principle ! <S> More on Euler and Bernoulli equations: Fluid Mechanics, Euler And Bernoulli Equations <S> Which one change first, pressure or speed? <S> Pressure and velocity in a fluid carry some energy (pressure energy, which is a kind of potential energy, and kinetic energy). <S> The total energy is constant. <S> The obstacle changes the ratio between potential energy (pressure) and kinetic energy (speed). <S> None change first. <S> It's like action and reaction, their existence is linked and simultaneous.
|
Bernoulli's principle states that within a steady airflow of constant energy, when the air flows through a region of lower pressure it speeds up and vice versa. We see pressure varies inversely to the velocity.
|
Why did this plane fly in a zigzag pattern? I was tracking flight NKS739 from LAX to SEA this morning and saw that it made some some odd turns. If you look at the track from FlightRadar24.com you can see that it was heading toward SEA then it took a large turn to the right then to the left then returned to its original course. This does not look like the usual technical glitch from Flightradar24, and FlightAware shows the same track. There was no weather anywhere in the area. There were many aircraft in the area at the time and none of them made any unusual turns. There are no MOA's in the area (most of it is over a national forest) and none of the other aircraft seem to be avoiding anything in the area. I tried to see if LiveATC.net had a recording but that's Seattle center's area and they don't appear to have a feed for ZSE. I can't come up with any reason for such an odd deviation. The aircraft arrived in SEA and there didn't seem to be any problem. It immediately turned around and made another flight which was uneventful. Is there anything that might explain this deviation? Is it just a glitch? <Q> Alrighty then, that took some detective work. <S> Here's another flight around the same time, SkyWest 4458, which arrived 2 minutes later. <S> Notice <S> it's one deviation, compared to two deviations in your example. <S> Weather seemed fine, but KSEA has TBFM (Time Based Flow Management) since Aug 2013. <S> If the ATC asks a plane to delay its arrival time, the way it's done is to deviate from the route, then get back on it again— <S> that's if slowing down alone won't meet the time target. <S> Pilots then use the RTA (Required Time of Arrival) function of the FMC. <S> Initially the function was rarely used, but now with NextGen in the U.S., SESAR in Europe, and similar systems elsewhere, it is frequently used. <S> It can be arranged way ahead of the airport, i.e., it can be ordered by the approach controller, yet the center controller of another ARTCC delivers the message. <S> It looks exactly like that. <S> Deviate, if not enough, deviate the other way. <S> Behind the Scenes <S> The system is called ERAM ( En-Route Automation Modernization ). <S> ERAM detects future conflicts, and based on that, traffic is asked to speed up, slow down, or deviate to slow down further. <S> It reduces/eliminates hold time. <S> Europe—the first to use it in 2012—refers to it as initial 4D trajectory management . <S> Planes arrive at waypoints at agreed times. <S> For whatever reason—most probably sudden traffic influx—they were asked to slow down. <S> The difference between this, and the regular vectoring/doglegging in the terminal area , is the way it is predicted, coordinated, and then relayed to airplanes far from the airport. <S> Below you can see as the jet turned, it slowed down as well. <S> The initial upward spike is just the tailwind when the plane turned. <S> Source: flightradar24.com <A> It is a typical dogleg used to increase spacing between aircraft or delay their arrival. <S> If the airport does not have enough capacity to handle incoming traffic, the air traffic controllers have basically two options to delay arriving aircraft: reduce their speed increase their path length Speed reduction works, but only when the distance to travel is still long. <S> And even then it can only absorb a few minutes as the minimum speed of aircraft is still quite high. <S> At very low speeds the fuel consumption increases drastically, making slow flight unattractive. <S> Increase of path length is more versatile, it allows for much more time to be added to the flight (fuel is the limiting factor). <S> Basically two types of path lengthening are used: holding patterns and dog legs. <S> In a holding pattern, ATC can stack multiple aircraft on top of each other. <S> A full circuit in a holding pattern takes about 5 minutes so it is a way of absorbing much delay. <S> When not so much delay is needed, the dog-leg is preferred. <S> By vectoring the aircraft 30 - 60 degrees off-course and then back to the original track, the controller can accurately control the delay and spacing between aircraft. <S> This is used in the initial approach phase and when vectoring to the final approach. <S> Often it is used in combination with speed control; slow flight reduces the size of the dog-leg. <S> However, airlines prefer to fly the optimum endurance speed during such a phase to minimize fuel consumption. <S> In case of the flight you were tracking, the aircraft was vectored right of its track, then back to cross to the left of its original track and finally back onto the original track. <S> The added distance was approximately 65 nautical miles, which would be about 11 minutes extra flying time. <A> DeltaLima hits the mark. <S> I used to work there. <S> TBFM issued directly to the aircraft is still in the early stages. <S> I believe most delays are managed by the controllers vectoring, holding or issuing speeds. <S> BTW- speeds are only effective for absorbing very small delays because it takes too much time to work. <S> Old ATC rule; use vectors to get your spacing, speed to keep it. <S> The "dog leg" vectoring going on looks like it's occurring in the second tier sector, sector 46 (two sectors away from the approach control boundary). <S> The first tier sector may have been at capacity forcing the delays to be pushed out to the high altitude sectors. <S> FYI - we used to figure about 5 minutes for one turn in hold. <S> Holding needs to be handled at lower altitudes just to keep the plane in the box. <S> I saw someone issue a hold to a 747 at FL390 once and it took the better part of the state to complete one turn!
|
Undoubtedly traffic management delays going on for some reason, either too much traffic or reduced runway capacity.
|
In what ways do air traffic controllers communicate with pilots in class A airspace? I know they use two-way radio, but is that the only communication pilots receive from air traffic controllers? Also, in general in class A airspace, how often do pilots hear from air traffic controllers? <Q> HF is used in oceanic areas, but it is in decline. <S> Data comms are also used, it's called CPDLC ( Controller–pilot data link communications ). <S> The ATC sends a digital message to the pilot, and they respond the same way. <S> Too Much Static Noise (HF) <S> On long flights, the controller can grab the crew's attention by poking them using SELCAL . <S> Too much static noise for a long time is tiring to listen to. <S> Chatter <S> Most of the chatter is handing off the plane from one controller to another. <S> If there's bad weather en-route, the pilot will ask to deviate. <S> That's another type of chatter. <S> Also climb, step-climb , and descent instructions. <S> When flying over areas not covered by radar, position reports are also provided by the crew and confirmed by the controllers. <S> PIREP 's—or pilot reports—often include information like "watch out there's icing , tell the folks behind me." <S> Traffic separation instructions and traffic advisory information are also quite common. <A> A VHF or UHF radio. <S> Class A airspace operates under IFR, so pilots must be on a filed light plan, cleared by ATC and maintain two way communications with ATC at all times. <S> That and hand signals don't work too well at 33,000 feet. <A> VHF & UHF in domestic airspace, HF transoceanic. <S> Digital communications Controller/Pilot Data Link (CPDLC) have been used over water for some time and are in the process of being implemented domestically as "Datacomm". <S> Over water is satellite communications while domestic digital will be carried over ARINC/SITA cell phone type networks. <S> Datacomm is being fielded for Clearance Delivery at large terminals first with en route communications to follow. <S> As far as the towers go, I think they may still have light guns for signaling aircraft that lack radios.
|
Changes to route are also relayed. Methods VHF radio is one method.
|
Partial Serial numbers on Military Aircraft - what combination is unique? Modern US military aircraft have partial serial numbers painted on their tails. Interestingly, it seems these serial numbers are actually not quite enough to be unique on their own, being comprised of only the year the aircraft was ordered, followed by the last 3 digits (usually) of the serial number. On occasionally this is not a unique combination by itself. Is there a specific combination of tail markings that is guaranteed to be unique? For example, if one combines the branch markings (such as 'AF' for Air Force) and/or the base code (such as 'AZ' for Arizona National Guard), would that be guaranteed to be unique?Thanks so much for any insight. <Q> I can only address the AF system, but I assume the other services systems are similar. <S> The AF serial numbers for vehicles (the system applies to all vehicles including ground vehicles) are made up of the letters "AF" followed by the contracted delivery year (2 digits) followed by a sequential number that restarts at 1 every year. <S> The pic below is of an F-22 assigned to the 1st Fighter Wing (the FF code). <S> So this aircraft was purchased in 2008. <S> The sequence number is 161, and would have been assigned from a block of numbers provided in the contract. <S> The contracting officer was given the block by the office that keeps the master list. <S> It's worth noting that the paperwork and the data plate is where it has to be complete. <S> What's painted on the a/c is just used for the convenience of the crews. <S> For some a/c such as KC-135's and B-52's whose production run was less than 10 years <S> , they often just us the last digit of the year and the sequence number. <S> Most of the tankers I see have a 5 digit number that starts with 2, for 1962. <S> In a fighter squadron, most 'local' documentation just refers to the last 3 digits. <S> example: 061 and 813 were how we referenced two of the F-16s in the test squadron. <A> If I remember correctly, military aircraft do not identify themselves by those painted serial numbers in radio communication. <S> Combine that with the odds of a squadron having two a/c of the same make/model 1,000 serial numbers apart, and the reality is that this is a non-issue. <A> Each service uses its own method. <S> There's a nice summary of how serial numbers are assigned to military aircraft here. <S> The US Army began in 1991 to use year/sequence number. <S> Example: 92-00518 Bell-Textron OH-58D(I) <S> Kiowa Warrior delivered in 1991. <S> The bureau number is typically a six digit number that remains with the aircraft/airframe for its entire life, and is assigned once it has been delivered to the government. <S> A given Bureau Number may have different side numbers painted on it, depending upon which squadron it is assigned to. <S> For example: An SH-60B Seahawk assigned the bureau number 1613xx would have a two digit side number , typically painted on the forward fuselage just below the door on both sides ... <S> if it was assigned to a West Coast squadron. <S> " <S> Tactical Call Sign Lonewolf 45" <S> If it were assigned to an East Coast Squadron, it would have a three digit side number. <S> (Tactical call sign "Proud Warrior 430")
|
The US Navy uses two numbers to identify the aircraft: the Bureau Number, and the side number/call sign.
|
Do any airplanes really have this piece Tom Cruise is hanging onto in this movie? The piece Tom Cruise is holding onto on this moving plane seems useless as a component, maybe even inductive of drag. Is this a real airplane component, or just a film prop? I don't know the model of the airplane; I'm hoping maybe the shape is recognizable to some of you, or maybe it's even a "no-brainer". <Q> The plane is an Airbus A400M Atlas , a four-engine turboprop military transport aircraft. <S> I'm referring to this page , and there the stunt is well described. <S> About the door, here's an explanation: <S> Visible in the released image, the A400M's new side door deflectors were added to the development aircraft fleet after initial tests with the ramp and side doors open resulted in high noise levels and turbulence inside the cargo hold, says Fernando Alonso, Airbus Military's senior vice-president flight and integration test centre. <A> Civilian jump planes often have some sort of similar (but much simpler) deflector in front of the door used for exiting the aircraft. <S> It's not difficult to hold yourself on the plane, but a jump plane slows down when dropping jumpers, and the engines don't have anything like the prop blast of this plane. <S> I have no idea what the blast would be like in the situation in this film, but hanging on the outside of an airplane in flight with just the strength of your hands is nothing exotic - skydivers do it all the time. <S> Source: almost forty years as a skydiver and skydiver pilot. <A> Combat drops happen under rough conditions and with speeds that can be greater than "clear-and-sunny" civilian fun drops.
|
It's a blast deflector as said above, but most importantly, it's a blast deflector for combat drops .
|
What is the longest range single-pilot certified (FAA and/or EASA) business jet? I suspect the single-pilot business jet with the longest range is the SyberJet SJ30x : NBAA IFR Range with 100 nm Alternate M 0.76 (1 pilot + 2 passengers; passenger/pilot at 90 kg each) 2,575 nmi (4,769 km). But I am not sure; also, there are many negative reviews regarding SyberJet company and its aircraft of which, by the way, only a dozen have been produced for now. Are there any single-pilot certified jet with longer range in comparison with SyberJet SJ30x? <Q> I consulted Aviation Week's "Business Airplane's 2012" and the only other light jets listed with a long range are the Embraer Phenom 300 with a range of 1,954 nm, and the Cessna Citation CJ4 with a range of 1,913 nm. <S> The Cessna CJ3 comes in at a respectable 1,869 nm. <S> The PC-24, which is still undergoing certification in 2016, is listed here with an NBAA range of 1,950 nm. <S> All of these are (or will be) single-pilot certified in at least one cockpit configuration, to my knowledge. <S> Is there any reason you're restricting this to jets and not turboprops? <S> (Speed is one of the biggest differences between the two categories.) <S> The King Air 350IER has a range of 2,239 nm. <S> Several other turboprops have ranges that are comparable to average light business jets, like the PC-12 NG which has a range of 1,544 nm. <S> Here's a graph of my own making to show these statistics: <S> For any readers unfamiliar with the restrictions regarding FAA approval for single-pilot operations, here's a good source: http://www.flyingmag.com/single-pilot-jets . <S> The biggest stipulation is that transport category aircraft (12,500+ lb MTOW or not commuter category) are assumed to be two-pilot aircraft. <S> Note: all ranges listed here except <S> the PC-24's range are NBAA IFR max fuel ranges w/ 100 nm alternate as listed in Aviation Week's "Business Airplanes 2012" <A> There are only a hand full of single pilot jets in production currently and the SJ30x seems to have the longest range by far. <S> The other competitors in the space, the Cessna Citation Mustang , <S> Depending on how far you are willing to stretch the planes you include many military fighters, many of which you can own (which are generally single pilot planes) have a range that competes with or exceeds the SJ30x. <S> There is another caveat to this as well. <S> All of these planes can in theory be fitted with ferry tanks which can greatly extend their range for a single mission. <S> Its generally impractical to do this on a constant basis but it can be done in one off scenarios. <A> The CJ4 is, with nearly 2000 nm. <S> Some would say the SyberJet SJ30 <S> but since you can't buy one yet <S> And in turboprops the Beechcraft 350ER. <A> The SyberJet doesn't exist for practical purposes. <S> The design has changed hands through at least 4 different manufacturers and only about 15 were ever built IIRC. <S> Try looking for one on www.controller.com for one <S> and you'll see that the brand isn't even listed because they've never sold one used. <S> If you want a long range single pilot jet, the best game in town is the Citation S/II with the Williams Engine FJ-44 <S> engine mods by Sierra (called the Super S/II) or similar modder. <S> They can hold ~5800lbs of fuel and with the new engines, they climb faster, cruise faster, and burn less fuel. <S> They can go 2300-2600nm, depending on the upgrades. <S> This is basically the same airframe as the Citation 1 & Mustang (500/501 airframe) and Citation II & Bravo <S> (550 airframe, longer than 500), but with more fuel capacity and a very efficient supercritical wing. <S> The Citation Super S/II (Sierra's modded plane) has a maximum takeoff weight of 15000lbs, so it has stricter standards to meet than a "Part 23" aircraft which must be under 12500lbs. <S> There is no jet that you can actually buy that weighs under 125000bs and can go 2600nm <S> that I'm aware of, and believe me I have looked. <S> That makes the Super S/II the closest thing I've found to an affordable single-pilot jet for long missions.
|
There aren't any civilian, current-production jets that come close to the range of the SJ30 for single pilot operations based on my research, although one or two turboprops have comparable ranges. The Honda Jet and the D-Jet come in roughly in the 1300-1500 mile mark which is far less than the SJ30x. the Cessna CJ4 is the winner in jets.
|
What are the options for installing ADS-B OUT in a Cessna Citation to meet the regulations? So I have a friend that works for a company that owns a Cessna Citation. His company is looking to comply with the ADS-B regulations. He has been given the task of making a business case for actually doing this, but so far the only thing he's turning up is companies that want to sell the Garmin solution (GTX-345). The specific questions: Are there other manufacturers of ADS-B equipment that are recommended (by AOPA, FAA, or any other respectable group)? What companies (again, respectable) would do installations? Maybe towards the Northeast since that's where he is located. What sort of considerations do you have to look out for in upgrading to ADS-B? I am assuming it's a transponder replacement that you end up doing, but it also has to tie into a bunch of other equipment. What are the gotchas? <Q> It depends on what kind of Citation you are talking about. <S> Textron is focussing on creating Service Bulletins (SB) for installation of ADS-B on recent models (up to 15-20 years old). <S> For the Cessna Citation a SB is available for the following models: <S> Pro Line 21 <S> CJ1 <S> + <S> : SB525A-34-90 CJ2 <S> +: SB525A-34-41 <S> CJ3: SB525B-34-26 <S> CJ4: <S> SB525C-34-09 R1 <S> Encore+ <S> : <S> SB560-34-163 XLS+: <S> SB560XL-34-76 <S> Sovereign Primus EPIC: <S> SB680-34-33 R1 <S> Citation X Primus 2000: <S> SB750-34-58 <S> For the followingCessna Citation SB's are under development (when the presentation was given) <S> Ultra, Encore, XL, XLS Primus 1000; expected Q2 2016; Prerequisite: Universal FMS with SBAS LPV <S> Mustang G1000 <S> ; expected Q2 2016 <S> It is possible to install another transponder than advised by Cessna. <S> However if it hasn't been done already, you have to go through a Supplemental Type Certificate (STC) process for that which makes it rather expensive. <S> It also wouldn't be supported by Cessna, which will impact the resale value of the aircraft. <S> You may offset the cost of the STC by offering it to other Citation operators, but then you are suddenly in a whole different kind of business. <S> Other considerations to take into account are support of future operations, mainly LPV approaches using the same GPS receiver. <S> Since all offers seem to prefer the Garmin GTX, I assume the aircraft is a Cessna Citation CJ1 or CJ2 with a non-Collins FMS. <S> Cessna has a STC for this aircraft that is based on the Garmin GTX. <A> Are there other manufacturers of ADS-B equipment that are recommended (by AOPA, FAA, or any other respectable group)? <S> but Garmin is a very highly respected avionics maker. <S> What companies (again, respectable) would do installations? <S> Maybe towards the Northeast <S> since that's where he is located. <S> Any decent avionics shop should be able to do the install. <S> I presume someone does the maintenance on the plane currently, they should be more than capable of an install like this or have a go to avionics shop that can help out. <S> As mentioned in the comments Cessna may have someone or be able to point you to someone. <S> What sort of considerations do you have to look out for in upgrading to ADS-B? <S> I am assuming it's a transponder replacement that you end up doing, but it also has to tie into a bunch of other equipment. <S> What are the gotchas? <S> ADS-B may be able to play well with your other equipment but that cant be answered unless you tell us what the plane is currently outfitted with. <S> If it is an older cockpit with steam gauges and traditional radios there is not much to wire it into. <S> However if its a new glass cockpit there may be more options for wiring it in. <A> From my understanding, there's a difference between updating the CJ2 and CJ2+. <S> The straight 2 can get Garmin ES transponders and a GTN-750. <S> But the 2+ has more integrated avionics, and must have a Collins solution that is more expensive and complicated. <S> Ironically, the older the jet, the easier it is to update to ADS-B. <S> The early 500/550 series Citations had a ADS-B solution 2 years ago. <S> I've heard the Beech Premier is a real problem, because it requires new antennas, and the composite construction makes retrofitting difficult. <S> Also, not jets, but the G series Bonanza and Baron owners are getting the runaround with updating the G1000. <A> When looking for potential ADS-B Out installations, one might consider first looking at the FAA's website of approved installations. <S> After doing a search there, contact a vendor who may offer that solution. <S> They also maintain a searchable database by aircraft: <S> Searchable database <S> This information is directly from the manufacturers and provided by the FAA.
|
In cooperation with avionics manufacturers, the FAA maintains a list of approved installations: List of certified ADS-B Out installations. I found a presentation by Textron (ppt) that discusses ADS-B installation for various models. There are other makers out there making transponders
|
Why is the trailing edge sweep angle smaller at the wing root? Many airliners have a distinct unswept part at the wing root at the trailing edge. See for example this image from Wikimedia of a B737-400. Other examples include the B777, A320, Embrear 145, and many more. Virtually all airliners have at least some degree of less sweep at the wing root. Why is there a part of less sweep at the wing root (to facilitate engine mount; Aerodynamic reasons)? Why does a completely unswept part seem to be a preferred choice for this part of less sweep, as opposed to any other sweep angle than zero? <Q> There are two main reasons: <S> If wing taper and sweep remain constant over the full span, the lift distribution will show a distinct drop at the center. <S> This is called the " Mitteneffekt ". <S> The remedy is to locally increase the wing chord near the root and to decrease the wing's sweep angle. <S> This "fills up" the dimple in the lift distribution and reduces induced drag. <S> Large aircraft need heavy wing spars, and increasing chord near the root gives the spar more height while the relative thickness of the airfoil can remain unchanged. <S> A higher spar is structurally more efficient, so increasing its height at the root saves weight. <S> Since the relative thickness determines the maximum operating Mach number, it cannot be increased locally without hurting the whole wing. <S> The better alternative is to disproportionally increase wing chord at the root. <S> The unswept trailing edge near the root is a consequence of Boeing's flap track mechanism. <S> Boeing Fowler flaps move perpendicular to the hinge line, and an unswept hinge line avoids lateral movement of the flap. <S> Another consequence is a gap between the inner and outer flaps in order to allow both to move back without colliding. <S> Boeing fills the gap with a high-speed aileron. <S> Airbus flaps move in flight direction and leave the sweep angle of the trailing edge free. <S> Also, they don't need a gap between the flap segments left and right of a sweep change of the hinge line. <A> Two other (minor) reasons for this: Landing gear storage <S> The main landing gear is positioned just behind the aircraft's center of gravity. <S> For most aircraft with wing-mounted engines this is near the trailing edge of the wing root. <S> Flap effectiveness <S> Another benefit of a low trailing edge sweep angle is that the effectiveness of the inboard trailing edge flap is higher. <S> The maximum $C_L$ of the flaps decreases with increasing sweep angle. <S> ( http://adg.stanford.edu/aa241/highlift/clmaxest.html ) <A> I think it is also about arranging the wing spars. <S> Due to the swept wings they meet at an angle in the middle and must handle a high torque. <S> This can be reduced by either having an A connecting piece or leading the spar in the unswept part.
|
In order to have enough space for the landing gear when it is retracted, and to have a part of the wing structure that is dedicated to support the landing gear, this part of the wing has a larger chord, and thus a smaller trailing edge sweep angle. Swept wings suffer from interference at the center of the wing.
|
Why must IFR be cancelled? Watching flying videos and listening to LiveATC, you will sometimes hear a pilot cancel IFR approach. Why does the ATC care if you are on IFR or VFR? So long as you get on the ground safely, it seems like it wouldn't matter if you were looking at instruments or out the window. Surely the "radar service" is still running for other aircraft, so it seems it's merely a formality to indicate how a craft was navigating in the event there's an accident. Is there another reason I'm not thinking about? <Q> It's all about making sure everybody knows what's going on. <S> While you are on an instrument approach and thus flying IFR, ATC is responsible for spacing you, giving instructions on heading and speed in order to fit you in with other inbound aircraft. <S> In that situation they expect you to confirm and follow those instructions, and if you don't it makes for a lot of headaches. <S> If you're on a visual approach, such as when you've cancelled your IFR flight plan after descending below sparse clouds with the runway now in plain sight, then the tower knows not to give you spacing instructions; they instead space IFR traffic around you, while other VFR traffic just has to maintain their separation minima from you. <S> Knowing that you're on a visual approach means ATC won't waste their breath trying to get you to adjust your airspeed, altitude or course to follow a traffic pattern; they'll just give those instructions to other aircraft in the pattern to maintain a steady traffic flow. <S> ... <S> unless you're in Class B space. <S> If you are flying into a Bravo airport, you can still request a visual approach, but approach control has to OK that change (especially for airliners), and ATC is still required to provide separation services to you whether you're VFR or IFR, so they can still give you instructions regarding your airspeed to make sure you fit into the IFR traffic pattern. <S> This may, at times, require an uncomfortably fast landing for GA pilots being spaced in between commercial airliners at a busy time. <S> Some Class Bs like Phoenix or DFW will have a runway more or less reserved for smaller aircraft <S> so there's less disturbance to commercial airliners with higher approach speeds, but not all airports have that luxury; if you want to land your small single at O'Hare or Dulles, you'll probably find yourself spaced in-between airliners and forced to very precisely time your approach so you can touch down and clear the runway in time for the plane behind you to take off. <S> If traffic is heavy, you may not get in if you greet them with "Hello O'Hare Approach, Piper 354 Alpha...". <S> As soon as the O'Hare controllers hear your GA small-prop callsign, if the pattern's too busy they'll deny you Bravo entry and recommend you head for a smaller airport like Chicago Exec or Gary. <A> There's really no "must" for in-flight cancellation - If you want to you can continue under IFR all the way to the ground, even if you've broken out and are in VMC, and then close your IFR flight plan once you're on the ground (by radio if still in contact with ATC, or by telephone). <S> (You must however cancel your IFR flight plan at some point or <S> ATC will assume you have made a smoking hole in the vicinity of the runway and send people looking for you.) <S> Pilots <S> may cancel IFR in-flight if they've broken out of the clouds and are operating in VMC (with all appropriate visibility and cloud clearance requirements met, and the weather such that the pilot can continue to meet them until they land). <S> The big advantage of cancelling in-flight is that it helps out ATC. <S> When operating IFR at a non-towered field operations are handled on a one-plane-at-a-time basis: If you are on approach under IFR ATC can't take another IFR aircraft - inbound our outbound - until the last one they authorized departs the area or calls in to cancel IFR. <S> If that aircraft cancels "early" (in flight, because they found VMC under the clouds) they can bring another IFR aircraft onto the approach, which avoids having to stack them up in holds or other traffic management tricks. <A> I've never heard of a requirement to cancel IFR per se. <S> That's left to the PIC's discretion. <S> I do know that if you are flying an instrument approach into an untowered airport, controlled airspace around the airport ends at 700' AGL i.e. the transition between Class E Airspace and Class G Airspace at which point ARTCC can no longer provide control and radar services in this airspace. <S> The flight plan does continue to operate under instrument flight rules as required, particularly if you have to go missed as you will immediately switch from the CTAF back to center or approach and declare missed. <S> This is not a problem with a towered airport as you will be immediately handed over from ARTCC or approach control to the tower for the rest of the approach and landing. <S> As mentioned above this can help alleviate workload for approach controllers as well. <A> IFR flight requires separation minima to be applied by ATC. <S> By cancelling IFR, you relieve ATC of the restrictions incumbent with instrument traffic requirements.
|
Sometimes pilots will cancel an IFR flight plan when arriving at an airport if the local weather accommodates VFR flying for reasons of expediency; you can quickly enter the VFR traffic pattern and land as opposed to being vectored out to an initial approach fix for flying an instrument approach. When an aircraft reverts to VFR (cancels IFR), the pilot takes on the responsibility for separation from other traffic.
|
Can a passenger force a Go Around? Sorry if this question is too stupid, but I wonder what would happen if a passenger on the first row just behind the cockpit (ie. on a 737) starts screaming "GO AROUND" when the plane is about to touch down. Can it confuse the pilots? <Q> Not likely. <S> Pilots wear headphones, so we cannot hear the idle prattle of the pax in the hold. <S> In any case, we don't take orders from passengers. <S> Think about that for a second <S> : would you like it if aircraft pilots followed the instructions of a crazy screaming passenger? <S> What if there were TWO crazy screaming passengers giving contradictory commands? <S> Which one should we obey? <S> In any case, nowadays cockpit doors are closed during flight anyway. <A> Unless he’s shouting “cow on the runway”, I don’t even hear my copilot on finals as he mutters “too fast/slow”, “too high/low”, “left a bit”, etc., but I hear fine as we taxi <S> and he says “Coffee’s on me”. <A> The authorities don't react kindly to that kind of crap in a post 9/11 world. <A> The chosen answer is correct so far, no doubt. <S> But in my eyes, it lacks some generality and an important point: While it is certainly true for a 737 that a pilot won't hear you and therefore take no action, I'd add that is can be true for smaller aircrafts when you hear the passenger as they may even can speak over the intercom (say a Cessna 172). <S> As a pilot, you have to decide, if you realize that it was a passenger screaming "go around", if you take action. <S> You train a lot of things as a pilot, one of the most important one is to make a go around as fast as possible if anyone screams it (normally co-pilot, flight student etc) and <S> you do <S> not think about whether it is right or not <S> (you assume he had a good reason) because there is no time, you better focus on the maneuver. <S> The conclusion is nearly the same as mentioned in other answers with the small addition that, if the pilot hears you, you may trigger <S> it's trained reflexes and he will make a go-around. <A> If there is a legitimate need for a go-around like an emergency that the pilots can't see but the passenger can or landing at the wrong airport, then it might influence the pilots. <S> However, that might not happen because of the conditions described by @Tyler Durden's answer.
|
No, but the passenger is likely to be arrested for causing such a disruption and face serious charges.
|
Are "Tally-ho" and "no joy" acceptable ATC terms for civil operations? I keep meaning to ask this question. I heard "Tally-ho" used for the first time by a pilot on Liveatc.net. I know these are pretty standard phrases in military aviation but I wondered if civil pilots use them. Are they acceptable under either FAA or ICAO standards? If not, what's the likelihood a controller will know what you mean? <Q> As a private pilot, I have heard "Tally-ho" and other pseudo (British?) <S> military phrases used when talking to ATC. <S> I understand "Tally-ho" to be equivalent to "target(s) in sight" or "inbound" or even in some cases "affirmative", and that's the problem. <S> It is important to be clear and precise when communicating on the radio, however, the folks working at ATC seem to understand these phrases. <S> FAA: <S> I've read the AIM - Aeronautical Information Manual and Pilot's handbook of aeronautical knowlage <S> (Both available for free download from the FAA's website) <S> and I don't remember seeing these phrases anywhere. <S> Other texts caution against using these colorful phrases instead of standard phraseology because problems stemming from varied interpretations. <S> It is important to be clear and precise when communicating on the radio. <S> I think the correct terminology is: "Traffic In Sight" and "Negative contact" <A> No, they aren't considered acceptable although you do hear them from time to time. <S> Neither term is in <S> the P/CG and the AIM 4-2-1 says: Good phraseology enhances safety and is the mark of a professional pilot. <S> Jargon, chatter, and “CB” slang have no place in ATC communications. <S> The Pilot/Controller Glossary is the same glossary used in FAA Order JO 7110.65, Air Traffic Control. <S> We recommend that it be studied and reviewed from time to time to sharpen your communication skills. <S> In other words, if it isn't in the P/CG then don't use it. <S> Of course in reality some pilots do use military terms for whatever reason (force of habit?) <S> but it's definitely discouraged. <A> NO.Not an acceptable term. <S> Only a tiny (and rapidly diminishing) number across the globe appreciate its original 1930's context. <S> Some commonsense and logical analysis:"Land Ho" means "land in sight!" <S> "Tally" is another word for a score - or for a count of sorts. <S> It follows that somebody announcing "Tally Ho" is excitedly anticipating racking up a score. <S> This could be foxes or Messerschmitts. <S> Of course, this only makes sense in the context of a heart-felt outburst in the heat of the moment in old England - or a place influenced by old English culture. <S> Use of "Tally Ho" in civil aviation makes no sense at all. <S> How would you intend to "rack up" the score? <S> Tally Ho is believed to be based on a French expression from way back: <S> https://en.wikipedia.org/wiki/Tally-ho <S> It is the nature of humanity to bend language out of shape... <S> What do you call an AERObatic machine designed by AEROnautical engineers?Not an AEROplane? <A> Worse <S> yet, they are not even true military terms. <S> While "Tally" does mean you have the enemy in sight, notice there is no "Ho" attached to it. <S> Since you are up there <S> and NOT shooting at people <S> you should use the term "Visual" when you can see the aircraft being referenced. <S> Visual is not only a military term, meaning you see a friendly <S> but it is also used in civilian aviation and means EXACTLY the same thing. <S> But! <S> It's just easier to say, "Tower, traffic in sight." <S> Roger, Wilco (will comply) are great words that mean things. <S> I use them all the time. <S> Telling ATC your fuel is "Bingo" will get you killed, declare an emergency instead. <S> Fly safe! <S> Blue skies! <A> "Tally Ho!" was adopted by US military pilots during WWII, from British fighter pilots. <S> Who in turn had adopted it from fox hunting. <S> The US pilots must have just liked the sound of it, although it was an official part of the lexicon of British pilots . <S> They used lots of other lovely quaint terms. " <S> Angels" for flight level, "Bogeys" for enemy aircraft. <S> And the Navy had a particular anti-submarine manoeuvre they called "Raspberry"! <S> Nothing like some jolly fun during a war old boy. <S> You still hear "Tally Ho" used by military pilots on both sides of the Atlantic, with the same meaning it had in WWII.
|
As stated earlier by others - the term has no official recognition and would only serve to confuse. Apart from anything else, many pilots have no military background (or are foreigners) and have no idea what these or other slang/military phrases might mean. "No Joy" or "Tally-Ho" are not acceptable when talking on aviation bands.
|
(Why) Do airliners travel together sometimes? While browsing through the planes in FlightRadar (once again), I've noticed that sometimes some airliners from the same airline company seem to travel "together" on long distance flights to destinations located relatively close to each other (Like Finnair from Helsinki to Hong Kong and to Singapore or to different Japanese cities). The planes were separated vertically by about 2000ft but otherwise quite close to each other. Is there any advantage to this or a good reason? Or is this a pure coincidence? <Q> I do not have inside knowledge of Finnair operations, but I would expect that they have a limited number of staff who speak Japanese, and <S> so logistically running the check in desks for several flights to Japan at the same time allows the airline to schedule checkin staff with appropriate language skills to cover the appropriate flights. <S> There are also restrictions at both Helsinki and in many Japanese airports that restrict night operations and aircraft on the ground overnight do not earn the airline money. <S> As a result, there is a limited range of flight times that ensure that the aircraft are operating continually. <A> In the hours up to the departures of these long range flights, many short- and medium range feeder flights will arrive at Helsinki, with a lot of passengers who are transferring to the long range flights. <S> It basically enables them to operate an efficient spoke-hub model . <S> Looking at flight schedules for Helsinki as an example, a lot of transfer passengers from all across Europe will arrive on these flights between 15:00 and 16:00: Major European arrivals 15:00 Budapest and Berlin 15:05 Barcelona <S> 15:10 Dusseldorf, Frankfurt and Manchester 15:15 Brussels, London and Amsterdam 15:20 Stockholm <S> 15:25 Milan <S> 15:30 Madrid <S> 15:35 München <S> 15:40 Oslo and Nice <S> 15:45 Warsaw and Rome <S> 15:50 Hamburg 15:55 Copenhagen <S> And will then transfer to the various long distance flights that depart between 17:00 and 17:35: <S> Long distance departures 17:00 AY67 to Guangzhou 17:15 AY73 to Tokyo and AY79 to Nagoya 17:20 AY57 to Shanghai 17:25 AY77 to Osaka 17:30 AY41 to Seoul 17:35 AY89 to Bangkok Because the long distance departures are bundles so closely, it is possible to create short transfer times from all major European airports to any of the long distance flights. <A> It is just coincidence that they are close together. <S> The dispatchers plan the most efficient routing and it is no surprise that aircraft would follow the same routing.
|
They do this to allow convenient transfer times for passengers at major hubs (in this specific case, Helsinki).
|
What role, if any, does visual aesthetics play in the design of modern airliners? Another way of asking the question: Are there any distinctly identifiable features of particular modern airliners that are there for design reasons that have less to do with engineering than with appearance? or: Could one look at at a modern airliner, and point out something in its design, however small or large, that is there because "it looked good"? To be clear about a few points: By modern I mean since the 707. In visual aesthetics I only want to include physical form - contours, placement of parts, proportions etc - and specifically want to exclude livery, colour, and so on. I'm not interested in inessential matters like the design of the interior, but in the airframe, engines and so on. I'd be pretty surprised to discover that any aspects of design allowed aesthetics to trump engineering consideration, but perhaps there are examples where aesthetics played a part because the choices, from an engineering point of view, were equally viable. <Q> A friend of mine, who did the design of the Gulfstream G650 canopy, designed the cockpit windows on that jet after the lines of an Aston Martin sports car. <S> I suspect there are a few other features like that in various aircraft. <S> That being said, despite the aircraft design mantra of 'if it looks good it will fly good' most the the design choices made in aircraft is very utilitarian. <S> Aerospace engineers - and in particular the management at the major OEMs - are some of the most boring, unimaginative SOBs you will ever meet. <S> They generally leave creativity to the marketing departments and make every effort to pound flat any nail that sticks out. <S> The only exception to that rule that I can think of was Burt Rutan of Scaled Composites, who when his own way and designed unique planes as virtual works of art - but also were highly functional with great performance and capabilities. <S> From the Vari-EZ to Spaceship One, that guy is in a league of his own. <A> You may want to check out this article . <S> Function aside I agree with them that to me the Boeing nose has always been more pointed than the airbus nose. <S> Airbus Nose ( source ) Boeing Nose ( source ) <S> There is of course engineering decisions for this decision, but as to which one is the "correct" way to build a nose you may not find an answer. <S> If we look over at small planes, the most identifiable feature that I can think of <S> is the inverted shaped rudder on almost every Mooney ever produced. <S> Some think this was done for esthetic reasons <S> but there are actually lots of aerodynamic reasons <S> Al Mooney chose the design. <S> Since you put the hard cut at the 707, you will get mostly planes that were designed in the modern age where function over form ruled and our knowledge of aerodynamics was far beyond what it was in the 50 years before that. <S> Earlier planes, designed in an era when aerodynamic knowledge was far less are more likely to have "just for esthetic" things. <A> Winglets may be a good example. <S> Not entirely aesthetical (hardly anything in aviation is), but the undue attention given to them is certainly driven more by the look rather than use. <A> I can't speak much to airframe design, but I can say that in the case of the engines, basically zero consideration is given to aesthetics. <S> Some of the designs do end up looking quite visually appealing <S> (e.g. GE90 fan blade in Museum of Modern Art ). <S> However, that is entirely a happy coincidence. <S> The biggest three concerns are fuel burn, weight, and cost. <S> Fuel burn is such a huge driver that if the choice were between A) <S> hideously ugly design that made fuel efficiency better by 0.001% or B) <S> beautiful elegant design that made fuel efficiency worse by 0.001%, <S> option A would win every time hands down. <S> The only engine feature where aesthetics might be given some consideration is the paint scheme on the front of the spinner, but you said you weren't considering paint.
|
Depending on if you consider the cockpit "inessential" since its an interior part of the design there are some very easily identifiable cockpit features when we are talking about the Boeing/Airbus comparison.
|
Why evacuate wing at the front side after water landing? When looking at the following Transavia B737 safety cards, I noticed that after a water landing, passengers who evacuate via the overwing exits should leave the wing at the front, while during evacuations on land they should leave via the rear side of the wing. It is clear for me why normal evacuations need to go via the rear side of the wing, but why does a water evacuation need to happen via the front side? Does it have to do with the center of gravity position, in an attempt to keep it is far forward as possible so that the tail doesn't sink? Because in the second picture the rear exits are prohibited from use too. ( images cut pictures at this source ) <Q> When I worked as a flight attendant back in the 80's we were told that water landings frequently resulted in very damaged trailing edges to the wings. <S> Flaps and spoilers will most likely have been deployed prior to landing and the velocity of the water impacting these extended surfaces would tear them up badly, along with the hinges and fairings that support them. <S> To avoid serious injury to passengers from ragged sheet metal, we were to direct them off the leading edge of the wing. <S> This wouldn't be a problem with an evacuation on land so in that case we would direct them off the trailing edge. <S> The upper wing surface makes a good slide and a more natural and controlled drop to the ground. <S> Edit: <S> I forgot to mention that additionally, water landings mean passengers would be wearing life vests and life rafts would be deployed. <S> Jagged sheet metal would make short work of these inflated devices as well. <A> An answer that I once received from a flight attendant <S> (I don't remember the airline or plane model, it was long ago) was that in the event of a water landing passengers would be able to assist each other if they were all together. <S> Thus, passengers leave by the front of the wings in the direction of the other usable exits. <S> Otherwise, the wings would separate the passengers into groups. <A> It all depends on the design of the exits as well as how the aircraft floats in the water prior to succumbing. <A> Additionally to @PJnoes answer, I spot that the path to the front of the wing is dangerously close to the (possibly hot) engines. <S> That's less likely an issue when they are immerged into cooling water and may explain that going towards the tail of the aircraft is preferred in case of a landing on the ground. <A> For comparison, here's a picture I've taken of an emergency card onboard an Airbus A319. <S> Slides from the wings are deployed after emergency landings both on land and on water. <S> I guess the slides have to be specially protected against damaged trailing edge of the wings, as discussed above. <S> (Image source: Own work)
|
It may have been determined that it would be easier for people to deplane at the leading edge of wing it water as opposed to the trailing edge for that reason.
|
Do modern aircraft have the functionality for the pilots to look behind the aircraft? Basically like the functionality of a rear-view mirror in a car. It's made known that pilots have all the information, hence they might not need the feature, but my question is to know if such a feature exists in modern commercial airlines. <Q> Some do, some don't. <S> It depends by the type of the aircraft and by the need to see behind the aircraft itself. <S> Just as an example, this is a render of a Boeing F/A-18E "Super-Hornet" cockpit: <S> As already stated in comments, aircraft usually don't "power-back" and there is no overtaking like in cars (where cars from behind can overtake you just from left or right) <S> , so usually there is no need of mirrors inside a cockpit. <S> In a military aircraft, mirrors increase your situational awareness, but with a wide Field-of-View (FoV), details or a distant aircraft or missile cannot be seen with a narrow FoV, <S> a smaller portion of the sky is visible Just for reference, the F-16 or the F-22, both featuring a single piece canopy, don't have rear view mirrors. <S> The pilot must turn the head as much as he/ <S> she can and look behind. <A> Almost all tow planes have rear view mirrors mounted in them so they can see the glider and the tow rope. <S> You can see mirrors mounted on the cowlings of these Piper Pawnee tow planes. <A> There is one example that I can think of. <S> The Norhrop Grumman AN / AAQ-37 Distributed Aperture System, Developed for the F-35 airplane, this sensor suite for the aircraft consists of six visible and infrared cameras placed at points around the fuselage. <S> The images which these cameras create are fed to a central processor, which not only uses the information for automated functions such as missile launch warnings, but also creates a 360deg picture of the space around the jet projected directly onto the visor of the pilot's half million dollar helmet. <S> http://www.northropgrumman.com/capabilities/anaaq37f35/pages/default.aspx
|
On the canopy's frame are located three adjustable mirrors (like the one on the windshield of a car) the pilot can use to see what's happening behind him.
|
How do pilots set the exact amount of thrust needed for a reduced power takeoff? I know jet-powered airplanes very rarely use 100% available power for takeoff, and most often reduce power to increase engine life. How does a pilot set thrust to an exact level? The airplanes I'm referring to are common commercial jets such as A320/B737 types. If they'd set it manually with thrust levers, there are some complications: there are no placards on them. If you try setting revs via the displays, revs and temperatures do not change instantaneously, and looking at the indicators and adjusting the lever would be a dangerous distraction during take-off (imagine: the engines roaring, the brakes are applied and tires are rubbing against the asphalt; or the plane is rolling, and the pilot is looking at the gauges). On the other hand, if a limit is set via FMS, how does it know when to add more power if it's urgently needed? <Q> The EMB-145 used a combination of FADEC settings and the thrust levers to select the desired thrust and to signify the need for additional thrust. <S> If you pushed the thrust levers past the detent to "max" this would give you extra thrust. <S> The mode the FADEC is operating in is selected by a button in the cockpit that cycles through the available modes. <S> For takeoff power the modes were "ALT T/O", "T/O" and "E-T/O" which gave you 90%, 100% and 107% thrust for takeoff when the thrust levers were in the detent. <S> If advanced past the detent this would put the mode into a reserve mode and depending on model would give you up to 110% or 117% thrust. <S> Setting the exact amount of thrust needed was up to the engine FADEC units, our job was just to tell it what thrust mode it was in <S> and it scaled the output of the thrust levels to that mode. <S> Flying a 90% thrust takeoff, a normal rated climb and then reducing to cruise levels only required initially setting the thrust levers into the detent and adjusting the FADEC mode. <A> Usually power output for a jet engine is gauged from its low pressure turbine speed. <S> In turbofans, this corresponds to the fan speed, displayed as N1 . <S> In general, the derated takeoff thrust will be selected based on performance calculations done prior to flight, taking into account weight, runway available, climb performance and ambient atmospherics, which will determine the appropriate N1 speed to set during the takeoff roll. <S> There exist two types of derated thrust operations: fixed and variable. <S> Fixed derate is a pre-set derated thrust by the engine OEM. <S> Variable derate offers the flight crew the ability to select the derated thrust from a range of values. <S> For more information, consult AC 25-13 on this. <S> So also is this presentation from Boeing , which includes how thes factor are loaded into to the FMS, which then computes a corresponding N1 value and displays this on EICAS, as does this presentation for Airbus . <A> caseys answer nicely describes the procedure for the Embraer 145. <S> Since you specifically mentioned the Boeing 737 and Airbus A320, here is how it works for these aircraft: <S> Boeing 737 <S> All Boeing aircraft have autothrottles with servo motors which move the thrust levers in the cockpit. <S> This system is also used to set takeoff thrust: <S> During the preflight, the desired derating is selected in the CDU (see left image below). <S> When starting the takeoff roll, the thrust levers are advanced to about 40% N1. <S> After the engines are stabilized, the TOGA button on the thrust lever (see right images below) is pressed and the autothrottle becomes active. <S> The servo motors then move the thrust levers to the desired position. <S> Airbus A320 Airbus aircraft do not move the thrust levers with autothrottle engaged. <S> The thrust levers usually remain in the CL (climb) detent during flight and the autothrottle sets the desired thrust directly. <S> The takoff procedure starts similar to the 737, until the engines have stabilized. <S> Then, the thrust levers are moved into the FLX/MCT (flex/max. <S> continous) detent (see image below). <S> This will set the derated thrust. <S> For maximum takeoff thrust, the thrust levers can be placed into the TOGA detent.
|
The thrust levers had a detent that selected "100%" thrust for the given mode the FADEC is operating in.
|
Would there be any advantages to a wing with a concave upper surface? A wing with a concave upper surface could have the same area as one with the normal convex shape of an aerofoil. I can think of many potential disadvantages: additional complexity of design and construction, reduced volume for fuel tanks, having rain fill up rather than run off the the wing. Could there be any advantages to such a design? Has it ever been tried, or studied? For clarity, this is the kind of cross-section I have in mind. Yes, it's ugly, and I don't think that better draughtsmanship would improve it. <Q> The idea behind this design seems to be that the principal cause of liftof a wing is that the top has a larger area than the bottom, so if wesubstitute a top surface with a different shape but the same area, we willstill get similar lift. <S> This is the idea behind the equal-transit-time theory of lift,which is incorrect, disagreeing in several ways <S> withwith actual observations of air flowing past airfoils and thelift forces that result. <S> NASA has produced a basic but thorough refutation of this theory; among the points they make are <S> The lift predicted by the "Equal Transit" theory is much less than the observed lift, because the velocity is too low. <S> The actual velocity over the top of an airfoil is much faster than that predicted by the "Longer Path" theory and particles moving over the top arrive at the trailing edge before particles moving under the airfoil. <S> and There are modern, low-drag airfoils which produce lift on which the bottom surface is actually longer than the top. <S> What you generally want in an airfoil is for it to establish streamlinesthat carry the air at very high speed over the top and shoot it downwardpast the trailing edge. <S> The speed is not determined by the surface areaor length along the top surface; the speed is determined by other things,and two air molecules that start near each other but go on different sidesof the wing (one on top, one on the bottom) get to the trailing edge when their respective speeds carry them there, generally not at the same time as each other. <S> Putting a big hollow space on top of the wingwhere the air can pile up and then forcing it over a second hump to getto the trailing edge seems counterproductive. <S> But I am not an airfoil designer, and I don't know exactly what the result would be. <A> A wing with an inward (concave) surface on the top will generate negative lift for many positive angles of attack, and really not much lift at all. <S> Curving the top surface is basically creating an upside down airfoil (because lift is negative). <S> Take a look at a 0° angle-of-attack on a wing with a -14.24% camber: <S> You can see we are generating a lot of negative lift (-3955 lbs) and a lot of drag, resulting in a large (negative) L/D ratio. <S> Lets increase the AoA until we get a slightly positive lift coefficient: <S> You can see that the AoA is extreme for a small amount of lift, barely overcoming drag. <S> The AoA of 15.2° is required which brings the airfoil basically into stall because the flow is going to quickly separate from the wing. <S> Compare all this to a "normal" airfoil: <S> At a small 3.5° AoA, you are generating 1000+ lbs of lift and only 90lbs of drag, with a L/D ratio of 11+. <S> If you would like to play around with airfoils and see the results like I have above, you can download NASA's FoilSim Program <A> Well, wing produces lift by accelerating the air downward. <S> That's a result of third law of motion (principle of action and reaction). <S> And it applies at each point along the wing— <S> the lower the pressure, the higher the lift, but also the downward acceleration of the air flowing over the wing. <S> Now that only works to a certain point. <S> If the surface curves too fast, the air won't be able to follow it any more due to inertia, will detach and the pocket underneath will fill with stagnant air at ambient pressure, eliminating the suction and the lift with it. <S> That is stall. <S> Normal wing distributes the acceleration of the air along the chord. <S> However, as the air follows your shape, it would accelerate downward a lot in the first part, then return up somewhat before the second hump and accelerate downward a lot again over the second hump. <S> Your wing needs higher curvature at the two humps to compensate for the concave part generating negative lift. <S> Mainly the first hump is critical, because increasing angle of attack only increases the curvature near the leading edge (while flaps increase it further aft). <S> So I would expect your wing to stall earlier. <S> I would also expect the wing to have higher form drag, because there would be more changes to the flow conditions and each such change means losing some energy to viscosity. <S> Also above compares wings with the same coefficient of lift. <S> To achieve it, your wing would probably have to be thicker as it needs to compensate for the negative lift in the middle part. <S> Which is another reason for having higher form drag, too. <S> No advantage in sight anywhere.
|
It might just lead to the wing stalling at relatively low angles of attack,which would limit the amount of lift you can get from it.
|
How do pilots estimate glideslope visually without PAPIs? If my (enthusiast-level) understanding is correct, on instrument approach there are specific glideslope paths a plane is expected to follow. On ILS this is self-evident, but (again, if I read approach plates correctly), VOR DME approaches also entail a certain altitude that must be crossed at given DME distances. I assume, crews estimate their rate of descent based on their ground speed etc. Now, when visually, apart from PAPI lights, is there any other way of estimating the correct glideslope? With C172s and 55 knots, I expect it's easier to simply crawl to the runway and adjust accordingly. But how does it work when you have a B737 or A320 landing on a 6000ft/1800mt runway without PAPI lights? I expect a certain kind of precision is required, but does it come merely with experience, or is there some other way? <Q> There's no instrument you need for a good approach angle in good weather, it's all done by eye. <S> When you train as a pilot you develop a sight picture of what a good approach looks like, and you develop a sense of what a runway looks like when you get too low or too high. <A> A landing approach in good weather can be judged visually in pretty much any kind of aircraft: The exact sight picture will vary (the view from the flight deck of an A380 is obviously different than from the cockpit of a Cessna 152 - you're higher up among other things), but the basic geometry of what you're looking at is similar. <S> The best illustrations I've found for this are below: Broadly we can break these images down into the 3 categories a VASI gives us (High, Correct, and Low): <S> High/Steep <S> If you are high and your approach path is therefore steep <S> The runway will look long, skinny, and relatively rectangular. <S> Terrain/buildings near the airport will also look "flat" since you're looking down on them. <S> "Correct" (on altitude / on glide path) <S> If you are at the correct altitude for your position on the approach and therefore are flying a normal descent angle to the runway everything will look "normal" -- <S> The runway has a trapezoidal shape as it recedes into the distance, and the markings/terrain will look as you expect for a normal landing. <S> Normal in this case is something you learn judge largely by experience and all the bad landings you made as a student, though there are some tricks to help you estimate the angle . <S> Low/Shallow <S> If you are below the normal approach path and flying at a shallow angle the runway and terrain/buildings begin to resemble what they look like when you're on the ground: The runway is wide and flat, and the markings generally appear larger than you would expect on a normal approach. <S> Buildings/terrain around the airport also start looking more and more like they do when you're sitting on the runway. <S> Taken to its most extreme the sight picture for a low approach looks like you're standing on the ground at the runway threshold (or a few yards before it), but in good weather there are sufficient visual cues that a pilot shouldn't get into that situation. <A> Commercial carriers (questioner mentioned B737 or A320) <S> generally use runways that have some form of instrument approach (ILS and/or VOR/DME and/or GPS RNAV). <S> Those aircraft also have baro-VNAV, which essentially creates a glide slope without an ILS. <S> Whatever form of guide is available, it can be used on an advisory basis when cleared for a visual approach operation. <A> It should be done by sight picture and all pilots eventually get there. <S> On a standard glidepath of 3 degrees you will descend 319 ft/nm. <S> Most pilots will round to 300 ft <S> /nm <S> though I have seen European approach charts with a SCDA at 320 ft/nm. <S> If you know your distance to the runway, do the math. <S> Typically the FAF is 5nm from the runway <S> so that is roughly 1500 ft agl. <S> Try to descend so that you are 1200 ft agl at 4nm <S> and so on.
|
It comes from experience and practice combining with the human brain's excellent spatial processing capabilities.
|
Why is the drogue parachute jettisoned on the runway? Why is the drogue parachute of a military plane jettisoned on the runway? Why not drag it to the parking area for safe removal, inspection, and repacking? <Q> For several reasons. <S> First to protect the drogue from damage by scraping on the pavement second to prevent it from becoming snagged on nearby objects third to prevent metal components on the drogue from hitting and damaging the tail of the aircraft, and fourth to make it easier to taxi back to the ramp without the need for higher power setting to overcome the drag and prevent damage to the drogue from this jet blast. <A> Anyone who jettisons a DRAG chute on the runway will be roundly jeered by his mates, ops in the tower, "guest lecturers" (your flight lead, boss, etc) and ground crews. <S> Chutes are jettisoned OFF the runway at a point and place designated not to close the runway for FOD and to allow retrieval by recovery crews. <S> That being said, there MAY be a reason in some operations for dropping the drag chute prematurely. <S> There is usually a fair size "ramp" or "apron" immediately off the runway where this chore is done, without screwing up the taxiways to and from the RW/parking. <S> It is often a "de-arming" area, where safety pins and other securing devices are installed on combat aircraft with ordnance aboard. <S> A DROGUE chute is one that helps extract a main chute from a pre-packed storage container (drag chute bay, parachute container in ejection seat, or seat/back/chest pack, etc). <S> There is no discernible drag from a drag chute at low speeds, but you can't count on the exhaust to keep the chute reliably inflated, off the ground, or from becoming entangled in lights, equiptment, etc on the way back to the chocks. <S> The recovery crews WISH the pilot could bring it back to the parking apron.... <A> Chutes are jettisoned after clearing off the runway in the designated area. <S> The reason for jettisoning chutes is so that they do not scrape on the operating surface and wear off. <S> Dragging them along may result in damaging the lights or other objects. <S> Also it is an additonal weight being carried by the aircraft, which generates drag and slows down taxy back to the apron.
|
One downside to jettisoning the drogue at a lower speed (< 40 kts) is that it now creates a FOD hazard on the runway and requires a waiting cleanup crew to retrieve it before another recovery is possible.
|
Why do fighter pilots wear helmets? I notice that fighter pilots wear helmets, although pilots of aircraft like C-130s do not. What is the purpose of this? I have heard that it could be helpful in the event of an ejection, but considering the explosive force of an ejection, if you hit your head I would be surprised if a helmet made any difference. <Q> There are several reasons: <S> A helmet provides head protection. <S> If the pilot needs to eject the airplane, helmet is needed to protect from wind blast, in addition to what I mentioned #1. <S> Helmets play an important role in noise attenuation. <S> The mic and headphones are mounted in the helmet. <S> Many helmets contain a sun visor, hence the pilot does not require to use sunglasses. <S> Modern helmets have a mounted display, night vision support. <S> The latest ones help to see the pilot in any direction they desire, and even through the airplane. <S> Oxygen supply mask can be directly mounted to the helmet. <A> In addition to ejection it's to protect the pilot's head from impacts against the inside of the cockpit in case of sudden maneuvering or loss of control. <S> Many aerobatic pilots wear helmets for this reason as well. <A> Primarily to protect the pilot's head from windblast and and trauma from blunt object impact in the event of an ejection and parachute landing. <S> The current generation helmets do not offer ballistic protection against enemy fire <A> There was at least one case when a helmet saved a helicopter pilot's life, namely a RAF's Chinook HC4 pilot . <S> In short, Flight Lieutenant Ian Fortune was injured while extracting some soldiers in Afganistan. <S> An enemy bullet basically struck his helmet above the upper rim, crushing it and sending parts of the helmet and visor into his face, but nevertheless saving his life and leaving him more or less operational and conscious. <S> Fun fact: <S> the helicopter he was flying, serial number ZA718, has enough stories to tell to have his own nickname and Wikipedia page :). <A> Keep in mind that a pilot can eject at 500kts+, or possibly even supersonic. <S> The helmet and faceplate keeps the pilot's face from being seriously damaged by high speed airflow. <S> Helmet also protects the pilot's skull if they strike the seat after separation, or when they impact the ground... same purpose as a motorcycle helmet... <S> the human skull can be fractured by as little as a 15mph impact, and head injuries tend to be more serious (or fatal) than similar impacts elsewhere on the body. <S> Today, the helmet also doubles as a HUD mount, with the faceplate being the screen. <S> In the F35, the helmet/HUD combination is reported to cost over $400k, but it does give the pilot to 'see' through the aircraft... tracking opponents that would otherwise be blocked from the pilot's view.
|
A fighter airplane can make many sudden turns and a helmet provides reduction of the risk of a head injury.
|
Where can one buy old 737 parts? I'm trying to build a home cockpit for the PMDG 737-800. I'm looking for some landing gear position indicator lights but I don't know where to get them from. I've tried ebay and amazon, but it returned no promising results. The other alternative is of course to make them. Does anyone know where I could have something like this made? <Q> Airliner parts have a tiny market outside of the airline and maintenance businesses (in the sense thst the general public generates no demand) which means that there probably aren't many places to shop for unairworthy (read: cheap) spares. <S> I would place "want to buy" ads on Barnstormers and maybe cruise the site from time to time clicking through relevent categories. <S> I did see one ad offering 737-200 parts <S> but you'll have to contact the seller to see exactly what they have <S> and how much they want. <S> You could certainly buy a new part but <S> you will not like the price tag. <S> I imagine that an unairworthy spare for an -800 series will be hard to find compared to a -200, for example, because of the quantity of inoperative junk parts generated thus far by the respective fleets. <S> Good luck! <A> There are effectively 3 types of used airplane parts, Red Tag: component is scrap or unusable Yellow Tag: component is serviceable and airworthy <S> Green Tag: component is not airworthy but is repairable when you are looking at aircraft parts most of what you will see is green and yellow tags as they are generally what is worth selling as they still have life. <S> These parts are pricey as they still carry air worthy value. <S> Most used aircraft parts come from air frames being parted out which often occurs at a bone yard . <S> These same facilities also scrap some parts (red tag them). <S> Since red tag parts carry little aviation value they can sometimes be had for cheap. <S> You should contact the various large dismantlers with a list of what you are looking for and inform them that you would like red tag parts for a home simulator. <S> If you are just looking for instrumentation (which is in some regards generic to all aircraft) it may be worth a trip to your local airfield/maintenance facility to ask what they have lying around. <S> I would reach out to this guy and ask him where he got his stuff <S> (I know some came from a bone yard). <S> I would read this , but take note of the fact that there is an active effort to physically destroy red tag parts so they don't make it back into circulation (unfortunately this has happened in the past due to fraud). <S> This limits the public sale of these kinds of parts but there is not necessarily any law that I know of requiring the parts to be destroyed <S> so you may just need to contact the right people at the right time. <A> Try cockpitsimparts.co.uk. <S> I built my whole 737-800 from this site. <S> Sells most things you will need at a very good price! <S> Depends where you are I suppose. <S> They are based in Cardiff UK.Everything is made from plastic but looks pretty real!
|
There is a very large market for used airplane parts but you need to understand the types of parts you can buy.
|
Why the lack of faster piston-powered planes? There aren't very many fast piston airplanes in production. By "fast" I mean, if you look back in the early to mid 20th century, before turbines won out, there were lots of piston airplanes in production that pushed the practical velocity limit of propeller-driven aircraft, cruising 360+ knots in military planes, sometimes as fast as 330 knots in commercial airliners. And this was with a terrible understanding of aerodynamics and piston engines compared to today. Today, for both singles and twins, the fastest speeds around aren't much higher than 200 knots. ~240 knots in the case of the very fastest couple available airplanes like the Cessna 400 and fastest Mooney. There are indications that with modern materials and engineering, much faster speeds can be achieved using piston engines already available. The Cobalt CO50 Valkyrie design claims to push a spacious 4 person cabin up to 260 knots with a single 350hp engine. The recently-certified Diamond DA-62 can move a spacious 7 passenger cabin at ~200 knots using only a pair of 180hp engines. Why aren't there more faster piston airplanes available? Would the market not be interested in piston powered planes that could do 300 knots? Shouldn't you be able to make almost those speeds for a very small plane powered by a single commonplace 350hp engine? Shouldn't you be able to make those speeds in a more spacious plane with a pair of commonplace 350hp engines? My understanding of the marketplace is that the #1 reason people choose piston is cost. And isn't the cost of operating piston engines, even two piston engines versus a single turboprop, much much lower? How much does a 350hp turbocharged piston engine cost brand new, 50k-60k dollars? So even buying a pair of them is 100k-120k dollars. And then how much does a single comparable turbine engine cost? ~800k dollars with proportionately higher rebuild costs per flight hour? Plus 20%+ higher SFC than a piston? Basically, I see the Piper M600 listed at 2.8M USD, or the TBM930 listed at 3.9M USD, and I don't understand why it would be hard to achieve nearly the same performance for a fraction of the price using a pair of cheap piston engines. For example the Piper M350 has the same 6 passenger cabin as the M600 and also includes pressurization, and with a single 350hp engine makes over 210 knots on a very old airframe with a list price of under 1.2M USD. If you basically built the same airplane but reoptimized for twin engines and using modern materials and aerodynamics, shouldn't you be able to achieve near 300 knots by adding another piston engine? And shouldn't you be able to sell the resulting airplane for well under 2M USD and with a significantly advantaged SFC and therefore range and payload than the M600? <Q> The power requirement of an airplane grows with the cube of speed. <S> When you fly fast with an airplane which needs to comply with a set minimum speed imposed by regulations , your drag coefficient is nearly constant, so flying faster does two things to a propeller aircraft: <S> Drag goes up with dynamic pressure, which is proportional to speed squared <S> Thrust goes down with the inverse of speed. <S> Power is thrust times speed, so <S> if the the 350 hp get you to 210 knots, doubling the installed power can only bring you to 264 knots. <S> A turbine can still make limited use of the increased dynamic pressure by ram recovery , so here the thrust decrease over speed is not quite as bad as for piston engines. <S> Expressed in an equation, the power $P$ demand for a given speed $v$ is:$$P = <S> \frac{D\cdot <S> v}{\eta_{Prop}} = <S> \frac{\rho\cdot v^2\cdot S_{ref}\cdot <S> c_D\cdot v}{2\cdot \eta_{Prop}} \rightarrow <S> v <S> = \sqrt[\Large{3}{}]{\frac{2\cdot <S> P\cdot\eta_{Prop}}{\rho\cdot S_{ref}\cdot <S> c_D}}$$ <S> If you want to fly fast with better efficiency, you need to increase the minimum speed - note that the landing speed of many fast piston aircraft was around 100 mph. <S> Now you need a long runway, and for operation in bad weather or at night infrastructure for instrumented approaches, and you will end up at airports where turbine fuel is easy to get and cheap , but piston fuel will be hard to find and expensive. <S> As with all expensive machinery, you need to use it often to justify the expense. <S> Now your fuel cost will factor in, and will make a piston engine rather unattractive. <S> Fast piston aircraft were only built while turbines were not yet available. <S> As soon as turbines emerged, all fast piston designs were obsolete. <S> And aerodynamics in the early 1940s were already very advanced; engineers back then built airplanes which would be impossible to design with the engineers of today. <S> Back then, they got fully manually controlled airplanes into the air when today everyone would refuse to do it without hydraulic boosters at only half the flight speed. <S> They could design cooling ducts which actually increased thrust , an art which is (almost) lost today. <A> But the converse applies to jets, which is why you don't really see jets cruising around at 5000 ft. <S> A piston engine is pretty complex and has quite a few moving parts that are moving in a somewhat violent fashion. <S> A piston changes direction every stroke, and the combustion that drives each stroke is a different force and purpose than that of a jet engine. <S> Those dynamics change a bit with the type of engine (a rotary engine is different than an inline engine), but it still requires a combustion to force a piston to push a propeller to drive the aircraft. <S> The mechanics are much more complex than a jet engine (which essentially just brings air in, compresses it, lights it on fire to Bernoulli it, and uses that exhaust to turn the compressors [usually]). <S> (I found some nifty engine animations at http://www.animatedengines.com ) <S> Also, propellers and jets move an airplane differently. <S> A propeller is no different than any other airfoil. <S> Its primary mode of motion is by decreasing the pressure on one side, causing movement towards that lower pressure. <S> A prop feels like a big fan, but most of its motion is pulling the aircraft. <S> However, a jet functions by pushing the aircraft. <S> Because of this difference, a propeller can reach its upper performance limitation at a slower speed than a jet will. <S> Again the converse applies and a jet can reach its lower performance limit at a slower speed than a prop will. <S> This allows a turbine engine to fly faster. <S> Lastly, a piston engine will likely weigh more than a comparable turbine engine. <S> And in an airplane, weight makes a difference in pretty much everything. <A> If you want a fast propeller-driven aircraft, it's much easier to use a turboprop engine than a large piston engine. <S> the turboprop is lighter and more compact <S> it produces less vibration <S> it produces less noise <S> it's more reliable (the moving parts count drops from thousands to tens = less to go wrong) <S> it's easier to build a high-performance turboprop. <S> Late WW2 piston engines operated at the edge of what was possible at the time. <S> They needed special high-octane fuel to prevent detonation (and even then, backfires were somewhat common on e.g. the Griffon).
|
A piston means a propeller, and a propeller is more efficient at lower altitude and much less efficient at higher altitudes (that's part of why there are variable pitch propellers ).
|
Is it currently possible to build a jet engine with 1,050 kN of thrust? (236,049 lbf) Do we currently have the engineering know-how to build a 1,050 kN jet engine? This question originated from the idea of changing a 4-engine aircraft into 2-engines. I chose the A380 since it seems to have the highest takeoff weight. One A380 engine produces a max of 350 kN. If one engine goes out, the A380 still has 1050 kN available, and per regulations that should be enough even for takeoff. So if we switch to a two-engine aircraft, per regulation we need enough thrust for takeoff even if one engine dies, which means each engine would need 1,050 kN max. I read this and this . They're in the same context of reducing a 4-engine plane to 2-engines, but do not answer the question if 1050 kN is achievable for a single engine. <Q> The limit to the size of turbomachinery is considerably larger than the size of current aero engines. <S> To estimate how large cores can get, we can look at power plant SCGT. <S> You can get heavy frame turbines as large as 576 MWe for the SGT5 (this is half of a typical nuclear reactor at 1000 MWe). <S> The aeroderivative LM6000 delivers 40 MWe out of a 270 kN turbofan core, and the largest aeroderivative, Industrial Trent 60 , provides 60-70 MWe out of a 415 kN thrust turbofan core. <S> This would suggest an thrust equivalent of 3.5-4 MN or 800,000-900,000 lbf for the SGT5. <S> You can't just fly a frame turbine like this, except in the hold: it's slow to spin up, its speed is on the low side, and it's not certified to aviation standards. <S> But that's just a matter of design. <S> It simply shows the amount of power that can be crammed into a single turbine core. <S> So, could we make a 1 MN engine? <S> Yes, we are making cores with several times the power. <S> Could we make an airworthy 1 MN engine? <S> With effort, perhaps, of course it would cost money to develop. <S> Would it be as good as the engines we have? <S> That's the million dollar question. <S> Or it would be, and more of a billion dollar one, if there were a market for it. <A> Is it currently possible to build an engine with 1050kN? <S> No, because there's no design for it, because nobody has asked for it. <S> Jet engine design is not a matter of scaling up existing designs, you can't just drag the corner and make it bigger. <S> You have to model the forces involved to understand what your materials requirements might be, blades, etc. <S> I would expect an engine that powerful would pose some serious engineering challenges which would need to be resolved. <S> provided there's enough investment. <S> Of course it would require an airplane to be designed to use it - an engine that powerful is going to be very big, you'd need more ground clearance below the wing, or a different engine placement to situate those engines, plus stronger wing structures to handle the forces. <A> are, the unit cost would also be huge and it (assuming a high-bypass design) would be enormous so hard to fit onto a plane anywhere. <S> All these combined give the real reason such a thing doesn't exist: given the compromises required, no-one wants one. <A> Technically yes. <S> Economically no. <S> While the Meganewton engine is feasible, the number you could sell is so low that nobody will put money into its development. <S> Unless some military feels it needs this engine no matter what, it will not be done. <A> Currently, no. <S> The most powerful turbofan engines in production today produce in excess of 120,000lb, but to go from this to 236,000lb in one step would be too much of an engineering challenge and too big a commercial risk.
|
As far as I'm aware there's no technical reason why not, but designing an engine with double the thrust of the current most powerful (GE90-115) would take a vast amount of money and time, especially as nothing on a similar scale has been done so it could not be a derivative design like many engines Jet engines have been getting progressively bigger over time, so I have no doubt that if there was a need it could be done
|
Can a jet cruise with asymmetric thrust? If a twin turbojet aircraft has an engine failure during takeoff, does it return for landing or does it continue to cruise with asymmetric thrust? <Q> As a practical matter, the aircraft will probably land ASAP. <S> Having lost an engine pretty clearly qualifies as an emergency for twin-engine aircraft! <S> That said, the aircraft would be capable of cruising with asymetric thrust. <S> Rudder is applied to keep the aircraft flying straight. <A> Aircraft are allowed to takeoff in weather conditions that are below landing limits. <S> So yes, with an engine failure after takeoff, twin engine aircraft may plan a "Takeoff Alternate" up to one hour flight time away. <A> The jet will take off, but declare an urgent situation and either land as soon as practical if the aircraft is below gross landing weight or be directed to a holding area to either dump off or burn off fuel until the a/c is below gross landing weight, and then land as soon as practical.
|
In cruise, modern twin jet airliners like the B777 and A330 are designed to fly ETOPS ("Extended-range Twin-engine Operational Performance Standards") for up to 330 minutes engine to a suitable landing field on ONE engine.
|
How would one define or explain the term "unloading the controls?" I've heard people say "unload the controls" or "unload the wing/propeller." What does this mean exactly? It is usually followed by releasing back pressure on the elevators or starting/ending a turn. <Q> When maneuvering the aircraft by deflecting the control surfaces with the stick, the wing with the downward aileron and the tail will generate additional lift, which increases the load on that wing (using the ailerons) and on the tailplane (using the elevator). <S> Unload the controls <S> is a request to neutralize the pressure on the controls. <S> Usually this means bringing the stick back to the center position, reducing the controls surface deflection, the amount of lift generated, and therefore reducing the aerodynamic load on the wings and tailplane. <A> You: unload a wing by pitching forward unload a propeller by pitching forward, reducing power, or flattening blade angle (increasing RPM) <S> The typical reason to "unload" is to provide greater a margin from a stall or to reduce torque on an engine. <S> The term unload is easily understood from a bicyclist's perspective. <S> When a steep hill flattens or a bike is shifted into lower gear, the bicyclist experiences unloading. <S> In conventional aircraft, control force (called stick force gradient) exists to inhibit pilot over-control. <S> Control force is proportionate to the lift being produced and to aircraft speed. <S> Therefore, to say "unload the controls", is the same as saying to "unload the lift on that surface". <A> When you are manipulating the airplane, for example in a turn, you're increasing the aerodynamic loading of the wings. <S> In a 30-degree level turn, the loading is 1.3G, i.e. 1.3 times the weight of the aircraft in straight-and-level flight. <S> In a 60 degrees level turn, the loading is 2G. <S> If the plane is flying with excessive aerodynamic loading for a continued amount of time, it can end up in a stall. <S> This is because to achieve a higher loading, the angle of attack must be increased; eventually it may exceed the critical angle of attack. <S> With a higher angle of attack, the airframe will also produce more drag, with slows the aircraft down. <S> Excessive loading can also lead to structural failure, as you are asking the wing / elevator structure to provide more lift, increasing the stress of the airframe. <S> "Unload the wings" is a general term meaning "to reduce the lift produced by the wings". <S> You're asking too much from the airplane . <S> The action to execute depends on the state of the aircraft. <S> If you're in a level turn, reducing the bank angle reduces wing loading. <S> If you're pulling up, easing back pressure on the yoke / stick reduces wing loading. <S> In aerial dogfighting, "unloading" means to ease back on the stick and allow the airplane to pick up speed. <S> High-G loading bleeds off energy very quickly. <S> A pilot must manage his energy during a fight. <S> If he keeps making very sharp turns, the high aerodynamic loading of the airframe will slow the aircraft down; and slow moving targets are easy targets.
|
Unload means immediately reduce the lift being produced by a lifting surface.
|
Why don't airliners use noise cancelling? Some cars have started using noise cancelling in their cabins, through the speaker system. It's a well established technique for dealing with low frequency noise like engine rumble and wind noise. So why don't modern airliners use it? <Q> First, some airliners do use it - the Bombardier Q400 uses a NVS (Noise and Vibration Suppression) system to reduce cabin noise. <S> Basically, it uses devices called Active Tuned Vibration Absorbers (ATVAs) mounted on the fuselage frames to 'cancel' the vibrations from propellers and outside noise, thereby quieting the cabin. <S> However, there are some issues with using active noise cancellation in aircraft: <S> If the waves turn out to be in phase in a region, the sound would be doubled - not a good result. <S> A significant contributor to the noise inside the cabin is the wind outside; this is usually random and the frequency spectrum is also quite wide, resulting in difficulties in noise cancellation. <S> Noise cancellation is effective mostly when the frequency of the source is constant, which is not usually the case (the props are an exception - they lend themselves well to noise suppression) <S> Instead of active noise cancellation, aircraft manufacturers are putting more energy in reducing the noise itself: <S> Better engines, which has lesser noise through the use of chevrons, etc. <S> Better modelling of aircraft, so that the fuselage design minimizes the noise due to wind. <S> Better damping and cabin design, so the noise produced (for example, due to air conditioning and ventilation) is reduced. <A> “It's a well established technique for dealing with low frequency noise” – exactly. <S> Noise cancellation works precisely if, and only if, the area you try to shield from the noise is significantly smaller than the wavelength of the sound you try to cancel, because then you can ensure that the anti-sound signal will in fact interfere everywhere destructively with the environment noise. <S> Wavelength scales as $\lambda = \tfrac{c_{\mathrm{s}}}{\nu}$, so it gets ever smaller as the frequency $\nu$ increases. <S> ($c_{\mathrm{s}} \approx 343\:\mathrm{\tfrac{m}s}$ is the speed of sound.) <S> As soon as the size of the room you try to apply this to is larger than the wavelength, it is inevitable † that the artificial signal will in fact interfere constructively on half the space, i.e. it will in many spots actually make the problem worse than it was by itself! <S> In a car, you can go quite far – the space is really small, and LF rumble has a generous wavelength – up to ~100 <S> Hz you can be sure that it at least won't interfere constructively anywhere in the cabin. <S> Quite different in case of an airliner – not only is the cabin much bigger, also, jet noise has much more high-pitched components. <S> Hence it is completely hopeless trying to cancel this sound with open speakers. <S> It is possible to cancel it directly at the ear, with noise-cancelling headphones . <S> But these are already available individually, so it's not something the airline needs to worry about! <S> † <S> Unless you can exactly predict the direction of the interference noise. <S> That is only possible if you know a priori the exact phase of the source noise. <S> As said in the other answer, this is actually possible to some degree with turboprops (which also have more low-frequency components), but not for jets. <A> The main problem in a large cabin is, "What do you cancel?" <S> The noise in an aircraft is different depending upon where you sit. <S> The engine noise is different whether you are in front of the engine or behind it. <S> Canceling the noise in one place in the cabin would increase the noise in another.
|
The aircraft cabin is quite big and complex, and it would be very difficult to achieve noise cancellation over the entire volume; as active noise cancellation depends on the cancellation of sound waves using opposite phase, it works best in small, confined spaces.
|
Why don't aircraft (commercial and military) use reflective visor windshields? Just like those used on an astronaut's helmet, these reflective visors can help in better visibility when facing the sun (or any bright light source). But the windshields of most aircraft (commercial and military) look transparent from both sides. The whole point behind the question is to find out if it was experimented and if yes, why was it dropped? <Q> At night these materials could potentially blind the pilot, so you would have to make these materials retractable somehow, which would add complexity and weight. <S> Over time these coating would be damaged by airborne debris, smashed bugs, and regular wear and tear. <S> Add to this that ever pilot would have different tinting needs - <S> some people with less sensitive eyesight would need less tinting and others more. <S> It's far cheaper and more effective for people to simply buy sunglasses. <A> How would that supposed to be working? <S> If you were normal glasses, you never ever thought about wearing sun glasses all the time, right? <S> Because in so many situation, you do not need sun glasses. <S> As pointed out, even astronauts don't use it if they are not exposed to the sun <S> (it's like a sun glass to them). <S> So it's an obvious decision to let the pilots wear sunglasses. <S> The only thing that comes near to what you may think, are "sun visors" These are adjustable and work like a big sun glass. <S> They are however not overlayed with gold like no sun glass is. <S> This is simply because there is no need for such a strong protection. <S> We have the atmosphere that reduces the sunlight even further, the astronauts don't. <A> Go for a drive at night, with your headlights off and sunglasses on. <S> Actually, don't. <S> I don't want you to die. <S> Now imagine doing the same thing while landing a highly flammable tin-can with hundreds of lives counting on you, except this time the sunglasses are glued to your face. <S> You can see how this is a terrible idea for anything but daytime flight, right? <A> I'll assume you're referring to astronaut helmets only because of their sunglasses-like reflective properties against visual light, not other wavelengths. <S> There are some small efforts by manufacturers to add some reflective coatings to their windshields. <S> The 787 has a window coating by PPG that had a gold-based heating film that also reflected infrared light- useful because a cockpit can heat up quickly. <S> Military jets like the F-16 can have golden-tinted " <S> Have Glass" cockpit windows but that's to reduce radar cross section , not to filter visual light. <S> There are <S> several reasons visible-light reflective windshields are never seen. <S> The first is that optically it's very difficult to have reflection only go one way. <S> Reflective coatings work well for sunglasses and some car windows because the light coming in can be assumed to be much brighter than the light going out, so glare from inside is not a huge problem. <S> In an aircraft, where that tiny light on the horizon could be a several-ton aircraft closing in fast, the requirements for night vision are a bit higher. <S> It should be noted that, for cars, reflective or tinted windshields are illegal in the USA for a number of reasons, including visibility. <S> The second reason is that bright outside light is a solved problem, so we don't have to resort to desperate measures like permanent reflective tinting. <S> Sunglasses use by pilots, <S> even though not strictly necessary , is so widespread there's literally a style of sunglasses named "aviators" and the FAA has a safety brochure on selecting sunglasses ( <S> AM-400-05/1 ). <S> If the pilot doesn't like sunglasses, they can use sun visors and sun screens that may be part of the aircraft or provided by the airline . <A> (This answer pertains to military application) <S> A reflective windshield would increase the chances of the aircraft being seen. <S> This is often NOT desirable in military application. <S> The enemy being able to see that very shiny canopy reflecting light at them would increase the chance of being shot at. <S> Even a regular fighter jet's canopy reflections can be a detriment to the pilot. <S> Dirty canopies reflect more light, and it is a crew chief's responsibility to keep that canopy clean, both to prevent the pilot from having issues seeing, and to prevent them from being seen. <S> As a crew chief, I'd been blamed more than once for my pilot 'losing' in training missions because he was easily seen by others due to reflections off his canopy (I wasn't always too keen on polishing them.)
|
Reflective materials cut down the amount of light let into the cockpit, which is useful in very bright sunlight, but would be undesirable at night. Add this that these coatings are expensive - outfitting them would be a significant cost.
|
How safe are airplane tours of the Grand Canyon? I'm curious as a complete layperson who's looking at scenic flights with Scenic or Papillon . I'm not afraid of flying on commercial airplanes, but this is a private, single-engine flight around the Grand Canyon. I think the company has had a bit of a history of crashes with its helicopter program over the past 15 years as well. The tour is two 45 minute flights, I haven't booked it yet. Should I be worried? <Q> It used to be worse. <S> (Comforting, I know) <S> Back in the day (1956), commercial airliners traveling coast to coast would often give their passengers a little tour of the Grand Canyon on the way to their destination <S> (air travel was still a novelty). <S> When a mid-air collision between two passenger planes occurred, the government invested in a $250 million upgrade (1960 dollars!) <S> of the air traffic control (ATC) system. <S> One could say that the crash resulted in the 1958 creation of the Federal Aviation Agency (now Administration) to oversee air safety. <S> One of the things the FAA did was create a Special Flight Rules Area (SFRA) around the Grand Canyon and make a specific chart just for the area. <S> Additionally, they created approved commercial tour routes (see the orange routes below) <S> In addition to commercial sight-seeing tours being more regulated, there is a lot more training, documentation and procedures available for pilots with the main interest being safety. <S> For example, the following notice is printed on the chart (References 14 CFR Part 93 <S> Subpart U which gives minimum altitude restrictions, both for safety and noise abatement!) <S> https://skyvector.com/?ll=35.7929449938479,-112.79126822365794&chart=231&zoom=2 <S> And of course, as mentioned in another answer, commercial operators, even if they are operating what looks like a "small private plane" are subject to increased mechanical inspections and regulations. <S> One thing to look for when you arrive is the level of professionalism exhibited by the crew (it might just be a single pilot), but also the people checking you in and working with you to get you on your flight. <S> There is something called a "culture of safety" in aviation that, while the unforeseen can always happen, if there is a culture of safety, preventable incidents can be minimized or eliminated. <A> Like many other fun things, there is going to be a risk associated with it. <S> However, I would rank this risk as being pretty low. <S> I would like to split my analysis into two sections. <S> (1) General Health Risks in the Grand Canyon and (2) Aviation risks in the grand canyon. <S> General Health Risks <S> In The Grand Canyon <S> You are far more likely to die of heat exhaustion or falling in the Grand Canyon than you are from a plane crash. <S> Admittedly, this might have to do with the quantity of people exposing themselves to the elements, rather than the number who take an airplane, but the point is that all manners of seeing the Grand Canyon will have a certain level of risk associated with them. <S> Aviation Risks in the Grand Canyon <S> As you noted, there have been several Helicopter incidents in the past. <S> However, there have been substantially fewer Fixed Wing incidents. <S> From what I can tell , there have been two incidents in the past 10 years with regards to aviation tours in the Grand Canyon area. <S> In one incident there were no injuries. <S> In the other, there was one fatality and several other minor injuries. <S> Try comparing that to general automotive statistics! <S> My Advice <S> In fact, it might even be the safest method to see the Grand Canyon, in comparison to helicopters (higher incidence rate), Mule's (substantial number of deaths per year), and hiking (risking exposure to the elements). <S> In the past 10 years only one individual has died on one of these Grand Canyon air tours. <S> I would personally take those odds and enjoy the view! <A> Flying over the canyon is relatively dangerous. <S> Over the years there have been 65 fatal crashes of various aircraft in and around the canyon causing a total of 379 deaths. <S> All the deaths are either known or believed to have been flights involving sight seeing. <S> If we subtract out the 128 deaths from the 1956 crash, that leaves 251 deaths in 60 years, or approximately 4+ deaths per year. <S> If we estimate that approximately 500,000 people take an air tour every year, then the chance of dying on an air tour is about 1 in 100,000 visitors. <S> The overall death rate for all visitors, air and foot is 1 in 400,000 (National Park Service statistics).
|
An air tour of the Grand Canyon sounds like a great time and the risk of injury is negligible.
|
Is the A330F main deck cargo compartment pressurized? If not, what is the purpose of the structural cargo access door? I know there is a related question already asking if cargo holds in general are pressurized . My question is specifically about the A330-243F in the below photograph. That looks like a pressure withstanding door/bulkhead dividing the fore crew compartment from the aft cargo compartment. Is that correct, and does it mean the aft cargo compartment is not pressurized? It's also possible both are pressurized and it's an airtight door for fire/fumes control. Source As mentioned in the linked question, it's likely both compartments are pressurized because of the efficient shape of the pressure vessel and so that the same pressurization system can be used across both passenger and cargo variants. <Q> You're correct- for cargo aircraft derived from passenger planes, the cabin is pressurized. <S> This reduces the complexity and certification requirements. <S> Also, this allows for easy conversion too. <S> The thick door may be due to two reasons: To improve load carrying/transferring capacity- airbus talks about ... <S> the aircraft’s reinforced fuselage and doors, which increase shear and bending/running loads.. <S> also, the thick door will help protecting the crew should the cargo move forward in flight. <S> To act like an airtight seal between the cabin and cockpit, so that it prevents smoke ingress into cockpit and to enable the crew to extinguish fire. <S> FAA Class E (for cargo aircraft) requires isoaltion between the cargo compartment and cockpit. <S> Another thing to note is that even a number of military 'cargo' aircraft have pressurized cabins (An-124, I think is among exceptions), as they are also used in Medivac and causality evacuation roles- <S> these require the cabin pressure to be set higher than normal. <A> The wall is a rigid barrier behind the supernumerary section that serves two purposes. <S> The first purpose is protect the supernumerary area and cockpit from cargo shifting forward during an accident. <S> The barriers are rated to be able to hold back a full load of cargo at crash loads (9G*). <S> This allows for the primary cargo securing system to only have to handle flight loads, making it lighter and less bulky, meaning more cargo can be carried. <S> The second purpose is to act as a smoke and air barrier. <S> If a fire is detected in the cargo area, airflow to the compartment is shutoff. <S> The rigid barrier then prevents smoke from crossing into the supernumerary/cockpit and keeps fresh air from crossing into the cargo area. <S> Loss of fresh air should lead to the fire extinguishing, some aircraft will also depressurize the aircraft to extinguish a main deck fire. <S> See 14 CFR 25.857 Paragraph (e).(4)-(5) (note that main deck cargo is a Class E cargo compartment). <S> The door is not pressure rated. <S> *The crash landing loading of 9G is defined by 14 CFR 25.561 . <S> Although the FARs do not directly mandate that the barrier be used as crash barrier, it does mandate that the cargo subjected to 9G <S> would not injure crew or block their egress path. <S> Using a rigid barrier to react the crash loads is a design decision made to optimize cargo capacity. <A> In the good old days there was no wall, instead there was a net which was designed to prevent any loose load from coming into the galley/supernumerary seating area (commonly referred to as a G-net. <S> There was also a smoke barrier which was affixed by velcro to the prevent any smoke from entering the aforementioned area. <S> Even the 747 combis had the net and smoke screen. <S> The aft wall had no load restraint capabilities and apart from making things look nice it served as a form of insulation against cold and noise. <S> The net was not ideal as it could not prevent the movement of sharp/pointed objects as the lattice of the net was quite big, around 8-10 inches IIRC. <S> So if you had a load of pipes or bars you had to have <S> x number of compressible load ULDs (cargo which was of a certain density) which would act as the barrier to prevent the pipes/bars from going thru the g-net and into the galley/supernumerary seating area. <S> Certification requirements changed and I believe it is now mandatory for new build/newly converted to cargo aircraft to have a fixed bulkhead. <S> This is not so much a pressurisation issue but more to prevent smoke and cargo from entering the galley/cockpit.
|
The door is used to allow access to the cargo area during loading and during flight for various reasons.
|
What happens to cabin pressurisation when the engines fail? I was reading about the cabin pressurisation mechanism from Wikipedia and another article here . According to both of them, the aircraft's engine plays a vital role in the pressurisation process. My question is: I have come across many air crash investigation articles mentioning that all the engines of an aircraft had failed, but the pilots were able to glide the aircraft and safely land it with no casualties. How is it possible for everyone onboard the aircraft to survive without cabin pressurisation (with all engines out) ? UPDATE: What if a safe landing area is a bit too far? After losing altitude, the aircraft can't obviously gain altitude. Won't the plane crash due to low altitude (the descent is fast) gliding?So, isn't it better to maintain (sufficient) altitude to reach an emergency destination? I hope the altitude can be maintained provided cabin pressurisation is intact. But, how is this achieved in commercial aircrafts? <Q> Closing the outflow valve would seal up the plane, so it wouldn't depressurize immediately. <S> Once the pressure falls below a safe threshold the oxygen masks would drop. <S> The masks are good for about 15 minutes. <S> Air Transat flight 236 which ran out of fuel over the Atlantic holds the record for the longest unpowered glide in an airliner. <S> It lasted about 19 minutes. <S> The APU can provide pressurization, but if you're out of fuel that won't work either. <S> Air Transat was running off the RAT and I doubt that can provide pressurization. <S> BUT if you factor in the outflow valves being closed and the last part of the glide being below 10,000 feet the oxygen masks will provide ample time for the passengers to stay safe. <A> During this period, the pilots will initiate descent to lower altitudes (10000' or lowest safe altitude permitted by terrain) where the passengers can breathe without cabin pressurization. <S> The cabin pressurization system is controlled by an outflow valve, which is shut in case the pressure differential goes above certain value or the pressure altitude rises above a certain value. <S> This prevents the loss of air in cabin. <S> The air coming to the cabin is prevented from going in the opposite direction by check valves. <S> Commercial aircraft usually carry supplemental oxygen, which is fed via masks in the cabin (which drop automatically once the pressure altitude reached 15000' or can be dropped by crew before that). <S> As the supply is limited , the crew (who will don their masks first) will get the aircraft to low altitudes. <A> Oxygen for breathing is all that is required to survive the decent. <S> That's what all the little masks that drop down are all about... don't forget to pull the little string. <S> It may not be enough to keep you conscious in the event of a full loss of cabin pressure at cruising altitude but it will keep you alive.
|
If the engines of the aircraft fail, the APU can supply the required air for some time.
|
How do airports manage gate assignments for aircraft? Today, some companies like Delair, SITA and INDRA provide airport Resource Management Systems (RMS) for gate allocations, which show information as a Gantt Chart. I know that air traffic controllers use a flight progress strip to track flights under their control, but how was parking managed in the past without today's RMS solutions? What do dispatchers use for gate management? If it's manual, what is the process? <Q> Depends on the airport. <S> Some airports assign blocks of gates to specific airlines, and they then assign them to flights (usually on an as-needed or first-come-first-serve basis). <S> Other airports assign them all themselves, again usually on an as-needed or first-come-first-serve basis. <S> Of course there are categories of gates as well, size and capacity determine what aircraft types can be handled by specific gates. <S> In theory at least, and no doubt small airports do it that way, it can be handled all with pen and paper. <S> Larger airports of course will have some sort of computerized system for it, either purchased off the shelf or something they had custom built for them. <A> Depending on the airport, an airline may lease gates(s) and have exclusive rights to manage that particular gate or parking location. <S> Typically there is always common use gates, which are allocated based on advance schedules submitted to the airport authority for approval. <S> Gate management software is often used. <A> It's based on all the usual variables (gate aircraft type capacity etc.). <S> I'm aware of one that prioritises certain flights based on distance to expected take-off runway (to minimise taxi time), but it's a standard optimisation problem solved using software. <S> If the process is manual, it's based on the heuristic knowledge of the dispatchers ie. can seem a bit random, but works! <S> I was always amazed at the skill of the 'ops' guys when they did the gate planning manually. <S> They managed to squeeze everything in perfectly, but it was not something they could explain as a process: just something they knew how to do after years of experience.
|
Most airlines or airports (if they control gate allocation) have their own software to do this.
|
Do "water bomber" aircraft pilots have more relaxed rules? I have no exposure to aviation regulations, but I'm curious if some rules are different for emergency aircraft pilots. Similar to ambulance drivers and police officers being allowed to speed or run red lights for the sake of emergencies. Specifically, this video shows a water bomber very close the ground and bystanders during an approach: My gut tells me two things: A) that this plane is dangerously close to the ground, and B) that this would be a serious incident, representing some sort of strike against the pilot's record. Please correct me if I'm wrong about either point. If either are true, though, is the situation treated differently for emergency pilots? Are they trained to go that close to the ground, like police officers are trained to handle a car at higher speeds? And are their rules different for that reason? I'm not sure how much the answer would vary country to country, aircraft to aircraft, or even situation to situation. So if the question is too broad, assume the United States or Canada even though that's not where the video is from, and assume a water bomber pilot in a situation just like this. <Q> All aircrews have to comply with laws and regulations, unless they have a waiver that makes them exempt for certain regulations. <S> Aerial Fire Fighting need to fly lower than the minimum safety altitude in order to pick up water, so they will have a written permanent waiver to do so. <S> This is similar to ATO's conducting training for student pilots. <S> They can be allowed to fly below the minimum safety altitude (in Germany: 500ft) for the purpose of training engine failures and attempted emergency landings in fields. <S> In all honesty, it does not look like recklessness to me, it looks like the pilot miscalculated his approach and came in too low and with not enough speed, as he bounces off the water surfaces instead of doing a proper flare. <A> If this had taken place at a controlled airport, the crew would most likely be disciplined, but since it was outside of an airport and no damage or injury occurred, it's likely nothing will happen. <S> What they did was reckless, but as long as they caused no damage to their aircraft or to anyone on the ground there is nothing to punish them for. <S> At an airport they could be punished for deviating from procedure, but otherwise nothing. <S> (This is according to FAA guidelines, not sure what the DGAC guidelines are.) <A> In the USA wild land fires are covered by "temporary flight restrictions" which restrict access by general aviation. <S> Fire related flights set transponder code 1255 <S> so ATC can identify them. <S> This is to avoid midair collisions.
|
As for altitude, in the USA over sparsely populated areas and open water there is no low altitude restriction other than staying 500 feet from a building or boat. No, law enforcement and fire department aircraft have to comply with all of the same safety guidelines that regular aircraft do.
|
Are tail strike landings preferable for an emergency landing on water? In this video , would it have been better if the pilot had attempted a tail-strike landing instead of a normal flare? <Q> While there probably is an "ideal" attitude to impact water, and it would be nice to crash-land with exactly the correct attitude... <S> it's very much a secondary consideration. <S> By far the most important thing, when landing on water, is to land slowly . <S> As such, your aim should be to land (/crash) with whatever attitude gives the lowest possible ground speed/descent rate at the point of impact. <S> If that means a "normal" flare, do a normal flare. <S> If that means a harsher flare with a tail strike, do that instead. <S> The point is that you're in an emergency situation, and your biggest priority is to get the speed <S> right: you likely don't have the luxury of trying to fine-tune your angle of impact and flare. <S> Additionally, you always have the risk of over-flaring and stalling into the water instead, which is a worse end result. <S> So <S> yes, it may - with some airframes - be beneficial to have a tail strike, but you're far better off just keeping the aircraft under the best control possible and reducing your speed as far as possible <A> Remember, impacting the water will slow your plane down very quickly, which will take away all the lift your wings are generating. <S> Thus, it would likely drop the front of the plane into the water, possibly at a very high speed. <S> The best practice would be to land as slowly as you can ( like Jon Story said ), while doing the best you can to keep the plane level with the water (though, as Jon stated, that would be a secondary consideration to keeping the speed low.) <A> It's pretty dependent on the structural integrity of the airplane, and water-landings aren't an exact science to begin with. <S> This will ensure that the aircraft doesn't flip tail-over-nose when it does finally settle in the water (if, for example, the "landing" speed is too high). <S> Put the tail in the water at too high of an AoA though, and the sudden deceleration of the tail will cause the nose to slam into the water quickly. <S> Alternately, it can break the tail off the aircraft. <S> This would allow water to flood into the aircraft, causing it to quickly sink. <S> Definitely not optimum if you have passengers to evacuate. <A> A fixed gear aircraft like that in the video will almost certainly flip over no matter what technique is used. <S> The main wheels are well below the aircraft's center of mass, are going to contact the water while the aircraft is still moving forward at a significant airspeed, and will create a very large drag force as soon as they do. <S> It all adds up to an upset moment far larger than the tail can counteract, so the aircraft will at the very least upend, if not rotate all the way onto its back as in the video. <S> The picture can be more favorable for a retractable gear aircraft if the wheels are up at ditching. <S> Even then, it's possible for aquatic drag forces to create a large enough pitching moment to cause the nose of the aircraft to "dig in". <S> Touching tail first will probably make little difference. <S> For the aircraft to settle rather than slam onto the water, the wings have to be generating enough lift to support it, which means the aircraft still has to be at flying speed at the moment it contacts the water, which means huge drag for whatever is in contact with the water.
|
If the tail of an aircraft can withstand the sudden deceleration of striking the water without breaking off, then a tail-first landing should be ok, if the AoA is still close to level. Having your tail hit the water first probably isn't the best idea. It would be preferable to avoid such an impact.
|
What is the viability of stacking passengers in an airplane cabin? I've came across on youtube a new design for stacking passengers in an airplane cabin, that looks at first sight interesting. What would be the advantages and drawbacks of such a design? Why this is not common in today's airplanes? <Q> I see several challenges with this design, both technological and not: <S> Making that design safe enough will be difficult, the structure you add in the cabin would need to be strong enough to maintain rigidity in a crash. <S> That much rigidity would add weight, and would add loads to the structure <S> The pod walls will make it hard to get by people in the single narrow aisle. <S> In an open design you can squeeze by people in the aisle, in a walled design you'd have no place to go <S> Parents with small children and families traveling together would have a hard time with this design as there's no more than 2 seats together, and limited space for sky cots <S> Access to a sick passenger would be restricted <S> Passengers with limited mobility would have a hard time getting into and out of these pods <S> Comfort is the biggest problem I see with this design. <S> Anyone in one of those pods is spam in a can with limited visibility and movement. <S> Personally I think it looks awful <S> and I would go out of my way to avoid flying with an airline using it <A> The problems I can see with that design: Increased structural weight : all things remaining the same, you will have less payload availability for luggage/cargo. <S> Cabin servicing <S> you either add an elevated kitchen (more weight) or you have to go up those stairs with the carts every time you want to service the cabin. <S> Possible claustrophobia <S> those modules look tiny, and the center rows are quite different from a car where you can open the window. <S> Possibly longer evacuation times <S> And people will try to get their belongings from under those seats. <S> You will have to demonstrate that this does not adversely affect the prescribed evacuation times. <S> Now that you have added screenshots, and that I have more time to look at them, I would add that <S> there is no consideration of the oxygen masks , where are they going to fit? <S> For both bottom and top row there does not seem to be the required space. <A> The video shows the seat-pitch at 42". <S> Current seat pitch is typically around 30-33". <S> I'm pretty skeptical that you can increase seat-pitch by 10" and still increase seating, no matter how much seats are stacked on top of each other. <S> Also, the video shows seating in a 2-2-2-2 configuration, with 3 aisles. <S> Typical wide-body seating is 2-4-2, 2-5-2, 3-3-3, or 3-4-3 with 2 aisles. <S> This implies the seats would be even narrower than current seats. <S> And current seats are already pretty narrow for most average sized people. <S> Typical wide-bodies have overhead bins inboard and outboard (4 overhead bins per row). <S> This diagram shows the outboard overhead bins, as normal, but no inboard overhead bins. <S> There is some small space above the upper-deck seating, but none for the lower-deck seating. <S> In my estimation, they're cramming more passengers into narrower seats, with less luggage space. <S> It is an interesting video, but I want to see Numbers and Math to back up the pictures. <A> The depicted seating configuration wouldn't fit in a typical wide body aircraft. <S> It would require a jumbo platform, such as the 747 or 380. <S> A wide body aircraft can only do 2+4+2 seating, whereas this configuration requires another 15" aisle. <S> Further, this configuration appears to suggest additional walls and structural components that would increase the width. <S> If you move to a jumbo platform, you find they're already stacking passengers in two levels, so there's no advantage there. <S> Further, there isn't enough height for the elevated aisleway without significantly impinging on the aircraft backbone. <S> You may be able to convince the aircraft company to build a widebody with two separate backbones, but that would increase weight, assembly costs, and would limit the ability to route cables, hoses, ducts, and other necessary items through the area above the cabin. <S> Lastly, you'd have to increase the amount of wiring, lighting, ducting, and emergency equipment to support the additional passengers. <S> This may involve more than simply space considerations. <S> This doesn't even begin to approach considerations for claustrophobia, evacuation, loading, and so forth. <A> I could think of 2 reasons not yet mentioned by the other answers. <S> 1) <S> The "passenger leg room and capacity increased by 6.4%" would turn into "passenger leg room unchanged and capacity increased by 9.3%" or some such thing. <S> If an airline can stuff you in a bit tighter, they will probably try it. <S> So really not much would improve for the passengers. <S> 2) <S> Many airlines are still using airplanes that are fairly old. <S> This would likely only be possible if the entire airplane was redesigned to fit this which would mean it would only be seen 10 years in the future at the earliest.
|
This design would greatly limit carry-on storage to only what could fit under the seat in front of you Airplanes are incredibly expensive to build. you are increasing the passengers, making them lay down more (more time to get up/out of those compartments), and maintaining the same volume.
|
Was a 7300-mile non-stop flight possible in 1979? I'm listening to the On Wings of Eagles audiobook by Ken Follett and found some information about a non-stop transatlantic flight between Teheran (IKA) and Dallas (DFW). GCM says that this is 7,300 miles and Google says that's 11,750 km. Was there any aircraft capable of performing such a flight in 1979? If yes, then which one? It was expected to travel with about 10-15 people on board and non-stop flight seems to be essential (at least to the author, because I completely don't understand the reasons why such a flight couldn't take a re-fueling break at some European airport once clear of the dangerous zone of Iran's / Middle East's airspace). The author's choice of either a Boeing 707 or 727 seems to be completely incorrect, as according to Wikipedia there wasn't any version of either of those aircraft capable of flying 7,300 miles non-stop (or I'm missing something). The longest range mentioned is 10,650 km in the case of the B707-320B. <Q> Even for zero payload, no B707 model is able to fly more than 6000nmi <S> (11111km). <S> B727 even has less range. <S> However, Iranair planned to run Tehran-LAX flight, which length is 12222km, but never materialized because of 1979 revolution. <S> The flight could have been operated by the 747SP (introduced in 1976), similar to their Tehran-JFK route. <A> Just about any plane out there could be fitted with Ferry Tanks allowing for ranges that are well outside its quoted maximum range. <S> As you mention the aircraft only needs to hold 10-15 people, in the spirit of completeness for what its worth a plane like a 747 can fly a lot farther if there is only 15 people on board and the rest of the plane is effectively a flying fuel tank. <S> While this may not be the immediate case there the idea is similar. <A> Sure. <S> A B-36 produced from 1946 and onwards has a range of approx. <S> 10.000 miles according to Wikiepdia: <S> https://en.wikipedia.org/wiki/Convair_B-36_Peacemaker#Specifications_.28B-36J-III.29 <S> According to the book "B-36 - Cold War Shield" <S> a regular long-range crew numbered around 15 people, plus possible obeservers.
|
Sure it was possible as for the list of planes that depends on if you consider the planes in their base configuration or not.
|
What are these symbols on the runway? As just a passenger, not a pilot, this may be a very basic question, but when I am on an airplane leaving the terminal, it goes over a symbol on the tarmac that looks like this: Also I see signs on the side of the runway pointing to those markers. On a related note, there is a similar sign near the gate that looks like this: What do these signs mean? <Q> The first one is the holding position marking. <S> It denotes the entrance from the taxiway into the runway. <S> The dashed lines are in the side of the runway. <S> The second one is the non movement area boundary mainly for vehicles, which divides the movement and non-movement areas of boundary- <S> the movement area is on the dashed line, for moving into which you'll need ATC clearance. <S> Images from FAA Guide to Ground Vehicle Operations <A> Here's the big book of everything: <S> http://www.faa.gov/air_traffic/publications/media/AIM_Basic_4-03-14.pdf <S> Your first example is a runway hold. <S> That is the physical boundary of the runway. <S> See page 112 (PDF). <S> The second is a non-movement area boundary. <S> This is the the boundary of where ATC controls. <S> For example, they may park the snow plows beyond this boundary. <S> When they plow crosses the boundary, it needs to be in radio contact with the ground controller in the tower. <S> See page 114. <A> As mins said in his comment, it's a "holding position" marking; it denotes the entrance to runway from a taxiway. <S> It's like the solid white line at a traffic light, except that pilots don't usually roll over it while waiting to be cleared onto the runway (waiting for the light to go green). <S> It is on the side of a sign pilots will see when exiting an RSA (Runway Safety Area) or OFZ (Obstacle Free Zone). <S> Here's a reference of the various airport markings.
|
The sign you saw is a "Runway Safety Area / OFZ and Runway Approach Area Boundary".
|
Where can I find reliable data on maximum turn rates for jet fighters? I'm looking for reliable data on maximum instantaneous turn rates for jet fighters, something coming from reliable sources, ideally official flight manuals or specifications. I can't seem to find anything. I've seen reports of turn rates around 35°/s for some fighters (F-22, Typhoon, Rafale) but I don't know whether those can be trusted: https://defenseissues.wordpress.com/2014/01/11/comparing-modern-western-fighters/ If possible I'd like to have data on fighters with exceptionally high maximum turn rates, but really, anything would be welcome. Even information on old, retired fighters would be nice, and I guess that's more likely to be declassified. Failing that, a lower bound would be useful. I don't know if turn rates make much sense for helicopters, but that information would also have some value. <Q> Imformation on the F-22, particularly performance and mission systems data remains classified, as with the F-35 airplane. <S> To the best of my knowledge there isn't much technical data available to the public on those subjects. <S> Now flight manuals for older fighter aircraft are readily available to the general public. <S> Janes/IHS is not a great source for this stuff; their entries are more on the level of intelligence briefs and encyclopedia entries and are not likely to contain the information you ar looking for. <A> While it's an interesting question, the actual answers are not very meaningful. <S> Max instantaneous turn rate is a corner condition where you will give up all your energy leaving you very vulnerable. <S> The key to fighter maneuverability is energy management. <S> A good discussion on fighter maneuverability is available at this link . <S> Additionally, I would suggest researching Col, John Boyd, USAF. <S> He did much of the early research in energy management. <A> You need to look up Flight Data on the F-16. <S> It was designed to be an Agile Fighter aircraft using specific formulas for aircraft energy Calculations. <S> The flight data is also NOT Classified: NASA is a public organization and required to disclose it's information, and ran a series of High Performance tests with an F-16 and through a Wind Tunnel that are publicly available (but that I don't have a link to at the moment.
|
PublicIntelligence.net is a great source for these documents, as they have them for the F-14, F-16, F/A-18E/F, AV-8B, A-10, just to name a few.
|
Why don't aircraft fly over Tibet? If you open www.flightradar24.com or their app, then this is what the scene commonly looks like: As you can see, the South-Central China area is strangely empty and the aircraft look to take a circular route around it instead (like this Emirates A380 to Incheon): So, my question is why don't aircraft fly over that area? Also, I occasionally see some China Air Force aircraft going to that area.. <Q> Where possible, aircraft prefer to take paths along great arcs , which are the shortest distance between two points on the surface of a sphere (such as Earth.) <S> In short, there simply aren't many common air routes between city pairs where the shortest path passes over central China. <S> If you look at the first image posted in the question, you will see that the flights into China are primarily flying either to or from Europe or Eastern North America (the ones crossing over Mongolia,) Japan or Western North America (the ones crossing over the Sea of Japan and East China Sea,) India (the ones flying over South China,) the Middle East (the ones flying over North China,) or Australia/Philippines/Thailand/Indonesia/Oceania/etc. <S> (the ones coming in from the South.) <S> For your great arc path to pass over Central China, you'd need to be going to or from central China itself (which isn't terribly populated,) Siberia (which is even less populated,) the Central Indian Ocean (which is open ocean with Antarctica on the other side,) or the mountainous region between China and India (which also doesn't have a lot of air traffic.) <S> So, there's normally just not much reason to fly there and, thus, not much reason for China to have airways there. <S> For the specific example that was shown in the question of the Emirates flight, the arc on which its flight path is shown across Northern China is, in fact, very close to the great arc between Dubai and Incheon, which looks like this: Great Circle Path from DXB-ICN <S> Source: <S> gcmap.com <S> This map should give you something of an idea for how unpopulated Western China is: China, as seen on Google Maps Source: Google Maps <A> Because there is only 1 airway ( B345 ) in Tibet. <S> Source: <S> Chinese AIP - 15 Jan 2019 <S> China (PRC) creates 2 sets of Aeronautical Charts, AIP and NAIP. <S> AIP is aeronautical charts only listing airways for International flight. <S> It is open for public and foreign organisations. <S> NAIP is a confidential and more accurate aeronautical charts listing airways for both International and Domestic flight. <S> Its standard is different from AIP. <A> According to FlightRadar24, I see Flight TV9886 of Tibet Airlines flying into Lhasa right now. <S> So, the answer seems to be that they do when they need to.
|
While Him's answer is correct, part of the reason that there aren't many airways over central China is just that there's rarely a reason to fly there.
|
Can radars detect small drones? I've just started working with weather radars and such. With weather radars, it is possible to detect bird migrations with a specific algorithm and a lot of information about birds, but it would be a problem to detect a single bird (depending on the bird size) because of the radar's resolution. I am wondering, if you have a place or a secret base that you don't really want the population to see whats in that area and take photos of the inside of the area or spy, is there a way to detect small drones with radar signals if you pack a few radars around your place or military base? If so, how? <Q> Depends entirely on the drones. <S> If the radar system is known and the drone is designed not to be detected by this particular radar system, then the drone can only be detected in exceptional circumstances. <S> Small size would be one way , but in order to be effective, big is better. <S> Detection has many aspects, and one of them is how soon detection happens. <S> If all you need is to stay undetected while you approach the target, only the frontal aspect needs to be considered. <S> If, however, you want to stay undetected for the whole mission, the task becomes much, much harder. <S> The radar systems in operation during the Eighties along the Iron Curtain could already detect single, large birds. <S> Adding computerized signal processing and networking of several radar stations has improved detection performance many times over since then. <S> See this question for more details. <A> Aveillant is manufacturing radars that have a high resolution and continously cover a volume of airspace in which it detects and tracks objects including drones. <S> Their system was tested in Monaco earlier this year and they were able to detect small drones up to 5 km away. <S> Later this year they will install a permanent radar setup. <S> The Gamekeeper radar is designed to detect targets down to 0.01m2 cross section and has a range of up to 5km. <S> Holographic Radar technology does not scan across an area as a traditional radar does, but continuously floodlights a volume of space, gathering 3D position and motion information from all targets, all of the time. <S> This gives a detection and tracking capability beyond that possible with other radars. <S> Source <S> The technology they use is different from typical primary radars used for ATC. <A> Radar detection of rotorcraft may be done by looking at the Doppler returns and seeing double sidebands caused by advancing and retreating rotors. <S> The same is true for quadrotor type drones, though the radar returns from small plastic rotors may be very small.
|
Yes, small drones can be detected by radar, if the radar is designed for it.
|
In general terms, is a Constant Speed Propellor equiped aircraft more expensive to maintain? I've been looking at possibly buying a used Mooney M20 or a used Cessna 172 . One of the big differences between the two is that the Cessna is a fixed prop , and the Mooney is a constant speed propellor . While CSPs sound really nifty and efficient...I can't help but wonder if they would be more expensive to maintain. Both in terms of regular maintenance and just the fact that it has more parts that can break. Is a CSP more expensive to maintain than a fixed pitch prop? And why? If you can include some numbers that relate to the planes mentioned, that'd be cool too... <Q> Yes, they are more expensive because they are more complex. <S> I would not avoid buying a plane simply because it has a CS prop because, in the grand scheme of airplane ownership, CS prop maintenance has a small impact on your hourly cost. <S> Maybe ~$1/hr for a piston single with repetitive ADs. <S> Now, the maintenance of a CS prop can range from a simple visual inspection of about \$100 USD to a complete replacement of the prop (up to \$15,000 USD, maybe more for large props). <S> An owner will likely not do an "overhaul" when the prop reaches TBO but will instead opt for an IRAN (Inspect, Repair As Necessary). <S> This is typically a little cheaper than a full blown overhaul and, from a practical perspective, extends the life of the propeller as an overhaul would. <S> At some point you'll end up grinding blades and balancing the prop but that's not annual maintenance. <S> I've seen the cost quoted at around \$1,500 USD for a high performance piston single IRAN which comes to less than $1/hr for a private owner. <S> All in, a CS prop only adds a small amount to the hourly operating cost. <S> In my opinion, the performance gains are worth the cost in most cases. <A> One thing about constant speed props that nobody has mentioned is that there is also a cost savings. <S> a fixed pitch prop is like a one speed transmission, where constant speed prop can be adjusted for the current need (climb vs cruise). <S> This means that, at least in theory, you can either go faster at a given rate of fuel flow, or burn less fuel at a given speed. <S> Whether or not this makes constant speed props cheaper in the long run probably depends a lot on the plane and the frequency and style in which you fly. <A> ACPilot hit it on the head in a general sense but ill add to that a bit to more directly cover the direct parts of the question as well as the aircraft in question. <S> I don't know which Mooney you are looking at <S> but if you are also looking at 172's I can assume you are looking at the M20C's D's and E's possibly J models (although the C's and D's are closest to the 172). <S> The older variants of these planes along with being CS props are subject to an AD that requires 100 hour eddy current inspections . <S> This makes these props more expensive to maintain than even their non AD counterparts. <S> But for this particular case the AD can add quite a bit of cost. <S> It should be noted that there is a Non-AD prop available for these airframes and many have been converted.
|
As mentioned the CS props can be more expensive simply because they have moving parts.
|
May an uncertificated pilot log non-PIC flight time for future certification? Let’s suppose I as a PIC take a friend up flying with me and this friend does not have a pilots license. Now let’s suppose I teach him how to control the airplane and let him fly for a while. I even go on a cross country flight and let him fly most of it. Looking at the regulations regarding aeronautical experience for a private certificate, CFR 61.109, it states that the pilot must log 40 hours total flight time, 20 hours of instruction and 10 solo. CFR 61.51 outlines documenting aeronautical experience and has caveats for the type of flight time but nothing for this type of situation however, 61.109 does not stipulate that all of the flight time come from solo or instruction. So here is the question. May an uncertificated pilot log non-PIC flight time and use it towards a certificate when another pilot lets him fly the plane as the sole manipulator of the controls? <Q> Your friend can't log any time because he isn't licensed and qualified to fly the aircraft and assuming that you aren't a CFI then he isn't receiving training either. <S> He's just a passenger, although if he wants to record the time for his own purposes that's fine, it just doesn't count for anything as far as the FAA's concerned. <S> First, 14 CFR 1.1 says that flight time is time acting as a pilot, not just time in an aircraft: <S> Flight time means: <S> (1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing; <S> So your friend needs to log time as a pilot. <S> Obviously without a certificate there's no way to log PIC or SIC time, so that leaves training time. <S> The regulations for that are in 14 CFR 61.51 (my emphasis). <S> (h) <S> Logging training time . <S> (1) <S> A person may log training time when that person receives training from an authorized instructor in an aircraft, flight simulator, or flight training device. <A> I assume you are not an instructor, so no. <S> §61.51 Pilot logbooks . <S> (h) <S> Logging training time. <S> (1) <A> Student pilots can only log authorized solo hours plus dual instruction hours, i.e. you must be a CFI for it to count toward dual instruction hours. <S> Answer is no.
|
A person may log training time when that person receives training from an authorized instructor in an aircraft, flight simulator, or flight training device.
|
What is the difference between reversible and irreversible controls? What is the difference between reversible and irreversible controls ? <Q> For example the cable linkages in a light aircraft up to an MD-80. <S> Irreversible is when there is a hydraulic power control unit in the way, it can be mechanical or fly-by-wire. <S> And such controls would sometimes need an artificial feel system to relay how much force is being applied. <S> It is found in airplanes that cannot be steered by just muscles. <S> A good way to picture it, is what happens if you move an aileron by hand, would the yoke turn as a result or no. <S> Superman might be needed for a 747's rudder, but still, the rudder pedals won't budge. <S> More information here and here . <S> Source: <S> airlinebuzz.com <S> Photo shows an unpowered rudder that was swung by the wind, in the cockpit the rudder pedals would show the neutral position, hence irreversible. <A> It is easy to understand it if you think this way: <S> The control force goes 'forward' from the yoke/stick/pedals to the control surface (e.g. rudder). <S> The (mostly) aerodynamic reaction travels 'back' ( reverse ) from the surface to the yoke/rudder. <S> On many (mostly heavy and/or very fast) aircraft this force link is broken at some point: your muscle force as such doesn't reach the surface, and, more importantly, the reaction doesn't reach you. ' <S> More importantly' because this reaction is the main reason for such arrangement: it is simply too great. <S> So, you don't feel true reaction. <S> This arrangement is called 'irreversible'. <S> The link is replaced by powered boosters or actuators of some sort, and the reaction is often also recreated (to some comfortable levels) by active or passive means. <S> Note <S> though that reversible control does not preclude from some automation: the control system may vary the linkage, the autopilot may add its own inputs, trim may change. <S> This may modify <S> the reaction (even down to zero), but in the end there is a hard link, and you can generally feel the changes of force. <A> Reversible means: at the flight controls, the aeroforces at the surface can be felt. <S> The hinge moments exerted onto the control surfaces (ailerons, elevator, rudder) by the airflow are fed back (reversed) to the pilot - holding the control surface at a certain angle requires a pilot force at the stick, creating a moment at the stick that equates the aerodynamic hinge moment at the control surface hinge. <S> Irreversible means: <S> the pilot cannot feel the forces and moments that the airflow exerts on the control surfaces. <S> They will definitely need some sort of artificial feel that links force to control position: humans have very precise force transducers in his hands, but no position transducers. <S> So in order to get an intuitive measure of how much the flying control is deflected, an artificial resistance force is exerted by a spring based feel system. <S> Deflecting a valve that results in oil flow that deflects a rudder, requires no force at all by itself. <S> A limp light stick at M 0.85: not a good idea <S> , that's why the artificial feel system is required. <S> Irreversible flight controls are usually hydraulically powered, but not every hydraulically powered flight control is irreversible. <S> Aeroforces have a couple of desirable feel characteristics that are not easy to mechanically reproduce, mainly the stiffening up of the spring force as the aircraft picks up speed. <S> In some aircraft the hydraulic actuators act as boosters: they amplify (boost) <S> the control forces of the pilot. <S> In the F100 the elevator is powered for 1/3 by the pilot and for 2/3 by the hydraulic actuator, and the pilots feel the airforces directly but only part of them. <S> No artificial feel system required. <S> Some aircraft have irreversible flying controls with artificial q-feel, which stiffens up the spring gradient when IAS picks up, just like with reversible controls. <S> The B737 pitch control column for instance.
|
Reversible is when there is a direct linkage from controls to control surfaces.
|
Why is white light more visible than red and green on this Cessna model on a sunny day? Source: https://i.ytimg.com/vi/hNgu1vypV3g/hqdefault.jpg VS Why is the white Landing light more visible on a fine sunny day and not the other two? I would have assumed the Red one to be most visible during flight, followed by Green but from a distance on a sunny day you can only see the white Landing LED very clearly but neither of the other two. Could it simply be because of the intensity of white light being more (having 2 bulbs) as compared to the other two having 1 bulb each? This picture does illustrate the position of lights but since it was taken in a dark setting it doesn't do justice to how it appears during the day. Those red and green lights are not visible at all from any distance beyond a few meters. When its a little dark (evening / cloudy) they are clearly visible. Please Note : It is not really so that I expect to see all these 3 lights clearly on a bright day, obviously against sun light they stand no chance. I am just curious as to why the colored ones are far less visible than the white one. <Q> The navigation lights are meant to give away the airplane's orientation (i.e. which direction it is travelling) at night. <S> The red and green lights are small. <S> Their purpose is to be observable from a long distance, which only requires a small light. <S> For the same reason, the anti-collision red lights of tall structures are small as well. <S> The landing lights (white light) are meant to illuminate the runway, taxiway or any terrain in front of the aircraft. <S> The light must travel to a certain distance in front of the aircraft then bounce back. <S> They are very bright. <S> To experience that, go to a busy airport at night and stand near the approach end of a runway. <S> In fact, standing next to an airliner with its landing lights fully on would likely damage your eyes. <S> Landing lights must also be turned on when any aircraft enters an active runway. <S> Here they serve the same purpose of turning on the headlights of your car at night: to make sure others can see you. <S> This regulation came after an airliner landed on an occupied runway at night. <S> It was determined that the plane on the ground blended in with the runway lights, and the pilots of the landing aircraft were unable to spot it. <S> Had the plane turned on its landing lights, the very bright light source would have give away their position and alerted the crew to abort its landing. <S> The model is simply a replica of the real life scenario. <A> Navigation or Position Lights are meant to be used at night-time and can be used when precipitation or weather in general deteriorates to the point where the lights will help you identify an aircraft's position, distance and orientation of the aircraft. <S> During daylight operation, the use of navigation lights is not required as you can identify the shape of an aircraft against the horizon or background. <S> Navigation lights are also installed at the sides of the aircraft, spanning a range of 110° measured from the extended centerline of the aircraft to each side. <S> It also is of higher intensity than the navigation lights, as it needs to give a pointed illumination for a larger area in front of the aircraft, rather than giving a steady and 110° wide illumination. <S> (Image Source: Wikipedia - Author: Trex2001 Clem Tillier) <A> The OP asks why the white "landing light" is more readily visible during the day than the red or green nav lights. <S> The primary reason for the white light being more recognizable in this instance is that it is providing more photons than the green or red lights. <S> The landing or taxi lights consume more power and produce more light than the nav lights. <S> In general, the eye sensitivity is a function of the photons received, adjusted for the sensitivity of the eye for the color(s) received, and adjusted for contrast (brightness gradient). <S> The peak photoresponsivity of the human eye is about 560 nm, which is a green-blue color and shifts to 507 nm at night, which is more blue. <S> The white light of the landing light is comprised of most or all colors which the eye is sensitive to, normally considered colors with wavelengths ranging from 400nm (violet) to 700nm (red), where nm is the wavelength of the light, nanometers, not nautical miles. <S> But to be clear, the visibility is a function of amount of radiation emitted, adjusted for the sensitivity of the eye, and in the OP case, the answer is simply that the landing lights have a much higher level of emissions than the nav lights. <S> As a tangentially relevant aside, the human eye, when night accommodated, has a very high quantum efficiency. <S> Quantum efficiency is the ability to convert a photon (the smallest unit or packet of light) into a neural response which is recognized by the brain. <S> Once impressed by the ability to observe lit cigarettes from 5000 ft and higher altitudes while doing surveillance work, I later investigated the responsiveness of the human eye. <S> In general, a younger eye can reliably detect single photons. <S> Things like available nutrients affect that, those nutrients including oxygen. <S> Lay on the ground on a moonless night, and look at the stars, and then take a breath or two of oxygen, and suddenly there will be many more stars. <S> To summarize, the reason the white light cited by the OP is more visible is that it is giving off more photons which are detectable to the observer.
|
The landing light however is pointed directly along that extended centerline, which makes it easier to spot if the aircraft is approaching you.
|
When is QFE used? When is QFE , instead of QNH, used for the altimeter setting? QFE: If you set the subscale of your altimeter to read ... millibars, the instrument would indicate its height above aerodrome elevation (above threshold, runway number ...).—Wikipedia It seems like a good setting for flying in Class G, as the pilot would get height above ground level near the reporting station. <Q> It is used in aerobatic competition. <S> It is much safer and easier to read AGL altitude directly from the altimeter than to attempt to do the arithmetic immediately prior to performing a maneuver. <S> I normally fly out of a field at an elevation of 1000'. <S> If I were to fly a contest in Colorado where field elevation is 8000' or higher, my altimeter will show an unusually high reading even when I'm still on the ground. <S> If I reset to QFE I still have to deal with density altitude considerations but at least I will have unambiguous altitude information. <A> In the UK at least, QFE is used primarily by the military. <S> There are still a number of airfields which are used by both the military and civilian flights (eg, RAF Northolt ) and flying in there <S> you will be given a QFE. <S> As a civilian pilot, you are only likely to be given a QFE on joining to land at an airfield, and while in the circuit. <A> From <S> Pooleys Air Navigation Manual:"It is very convenient for circuit operations if the altimeter can be set to indicate height above aerodrome level (aal). <S> This means that a 1,000ft circuit at, for example, Leicester airfield (elevation 469 ft) can be achieved with the altimeter indicating 1,000 ft rather than 1,469 ft if QNH was set in the subscale. <S> It is a satisfactory procedure in the UK to set QFE in the subscale when flying in the circuit".
|
In the UK, General Aviation traffic typically uses QFE in the circuit, and regional QNH in the cruise.
|
What effect would there be if the brakes were locked at touchdown? I'm imagining if you had a panicky passenger sitting in the right seat who had both feet firmly on the brakes while landing. Unless you had a crosswind and needed rudder as you touched down it's possible you wouldn't be aware of it. Or if there was a malfunction causing them to be locked. How likely is it that could cause you to have a bad day? What if only one side was locked up (which seems worse to me)? I'm mainly asking about small aircraft. Would it be any different for an airliner? What if you were aware of it? What action would you take? <Q> I've seen it happen many times (ask any rental place about this). <S> You get a big bald spot cut into the tread. <S> Sometimes it goes all the way through the tire. <S> If it happened on one side, you'd likely get a ground loop. <A> It's mostly harmless in a nose wheel configuration. <S> You quickly blow all tires and slide along the runway on your wheel hubs until the aircraft comes to a rest. <S> Crosswind will make the experience worse, because at lower speed you have less rudder authority and the aircraft might leave the runway. <S> Here it is best to step on the other brake <S> so both cause the same braking force. <S> But this is peanuts when compared to a tailwheel configuration. <S> Here the consequence is a headstand right after you put some load on the wheels, which can be right at touchdown when you come down with some sink speed. <S> Depending on the speed of the aircraft when this happens and the length of the fuselage nose, the aircraft might even flip on its back. <S> Now this is sure to ruin your day. <S> I've witnessed this once with a Polish Yak-12 which landed on soft ground - nothing more. <S> The pilot climbed out unhurt from his inverted position, but damage to the aircraft was extensive. <S> This was the occasion when I learned the worst Polish cursing ever. <S> If only one side is locked in case of a taildragger, I am unsure what will happen first: Ground loop or headstand. <S> Details depend on the wheel track and the attitude at touchdown. <S> Be sure to touchdown at the lowest possible speed and with the highest nose-up incidence possible to increase the resistance of the aircraft against flippig over. <S> Unload the locked wheel with ailerons, so you touch down on the working wheel only, but make sure that you do this with as little sideslip angle as possible. <S> Flying a gentle turn while touching down will help - just place the touchdown point at the moment when the aircraft is aligned with the runway (I know - easier said than done). <S> Touching down on one main wheel of a taildragger with some lateral speed by sideslipping into the direction of the working wheel will quickly roll the aircraft into the direction of the lateral speed, which helps to unload the locked wheel but might end up in a three-point landing: One wheel, wingtip and fuselage nose. <S> Again, this is sure to ruin your day. <S> That is what is colloquially called a "headstand" <S> (Picture source ) <A> When Air Transat Flight 326 glided into the Azores after fuel exhaustion over the Atlantic, the pilots were unsure whether they would be able to apply the brakes on their Airbus 330 more than once, and their anti-skid systems were inoperative. <S> So they applied the brakes and held them, locking the wheels. <S> The results, from the accident report: <S> The tires quickly abraded and deflated at a point between about 300 and 450 feet beyond the second and final touch down. <S> The segments of the main wheels contacting the pavement were worn down to the bearing journals, the left, rear, inboard wheel detached from the axle. <S> Both left and right brake anti-torque links attachment horns on the bottom segments of the main oleos also contacted the pavement; the horns were abraded to the point that some of the links separated from the oleo resulting in the rotation of at least one brake carrier. <S> Shedding of brake and wheel components during the landing run also resulted in a combination of punctures and impact damage to the airframe and left engine nacelle. <S> ... <S> CFR [Crash Fire Rescue] reported that there was fire visible coming from themain wheels, and responded to put out the fire. <S> At 06:46, CFR reported that the evacuation was in progress and that some signs of fire still existed in the left main wheels. <S> By 06:54, all fires were extinguished; the areas around the main wheels continued to be monitored due to the fire hazard associated with the damaged wheels and hot brakes. <S> However, the airline stayed on the runway, and everyone survived. <S> (Two passengers were hospitalized due to their injuries.) <A> If that happens to an airliner(full brakes at touchdown), a lot can happen.1- <S> depending on the landing speed, the wheel struts could break off2- if the struts resist such enormous load and bending force, the n the wheels will wear and burst due to friction and then most certainly burn depending on the condition of the runway(wet or dry).
|
If only one side is locked you will risk a ground loop.
|
Why was the U-2 so different from the SR-71? Both were designed for the same goals: taking photographs at high altitude, avoiding radar. Both were designed by the same company with a few years apart. Yet one is a "jet glider", with large wingspan, small chord, subsonic, and the other is a ultra high speed, delta wing airplane. Why did these two planes took such different approaches to perform similar tasks? What would be the pros/cons of each? The SR-71 was developed later, so it could be seen as a better approach, yet it was retired, while the U-2 is still in use. <Q> When U-2 was developed, the requirement was for an aircraft which would fly high at 70,000' due to the (mistaken) belief that the Soviets would be able to detect and engage aircraft only below that altitudes. <S> Once the U-2 entered service however, it became obvious that they could detect U-2 (they complained about the overflights, though misidentifying the aircraft), and once an aircraft was shot down , it became obvious that U2 isn't going to be of much help. <S> SR-71, which came later, was the result of a requirement which expected it to not only fly higher, but more importantly, faster . <S> Interestingly, the Soviets went the same way with the Mig-25R . <S> The main reason for the retirement of spy aircraft was the advent of reconnaissance satellites, which are immune to being shot down (not that it is impossible, but no one has done it except in tests). <S> Spy aircraft are still operated only over areas where the threat from anti-aircraft systems are extremely limited or non-existent. <S> At the time of its retirement, the USAF accepted that even the SR-71 is not invulnerable : <S> In congressional testimony, Air Force Chief of Staff <S> Gen. Larry D. Welch identified the increased survivability of reconnaissance satellites, SR-71 vulnerability to the Soviet SAM-5 surface-to-air missile and the cost of maintaining the SR-71 fleet. <S> As for why U2 has outlived the SR-71, the main reason is the operating costs- <S> the operating costs of SR-71 is quoted to be anywhere from \$85,000 to \$200,000 per hour , while the U-2 costs much less than that (incidentally, U-2s operating cost is less than that of its proposed replacement, the RQ-4 Global Hawk ). <S> From the same source as above : The Air Force decision to retire the Blackbirds in 1990 is based on several factors. ... <S> The cost factor is the most significant to the Air Force because it limits expenditures in other areas. <S> Reagan Administration Air Force Secretary Edward C. Aldridge Jr. estimated that the money used to operate the SR-71 fleet could operate and maintain two tactical fighter wings. <A> First off, the U2 was an earlier design, and engineered around the philosophy that the primary threat to a reconnaissance aircraft were cannon armed fighters. <S> Kelly's thinking was that if he could design an airplane which could fly far higher than existing turbojet powered fighters, the aircraft could not be shot down and could conduct reconnaissance missions with impunity. <S> Then came Sputnik and the dawn of the missile age. <S> Lockheed had quietly begun to investigate higher and faster flying design which could nullify the threat of missiles using solid fuel boosters and sustainer motor to reach the altitudes the U2 flew at but the U2 continued to fly over the USSR and with great success. <S> And it all worked great until May, 1960 when a CIA pilot named Francis Gary Powers was shot down over the Soviet Union by an SA-2 surface to air missile. <S> At this point there was an impetus to acquire a newer faster aircraft for strategic reconnaissance. <S> The idea being that the plane could fly so high and so fast that a ground launched missile system would not pack the energy needed to overtake and shoot down the new aircraft. <S> This was the genesis of the A-12 Oxcart program, which struggled through a 7 year long development and flight test program before entering service with the CIA; a two seat advanced derivative of the A-12 went into service with the USAF as the SR-71 Blackbird. <S> Officially there have never been overflights of the Soviet Union by either the A-12 or the SR-71 due to the political risks but Blackbirds did officially overfly North Vietnam, China, Eastern European communist bloc countries, Lybia, Egypt and North Korea and were shot at multiple times using advanced Soviet made SAM systems - all without a single loss. <A> The main idea was completely different behind the 2 designs. <S> Neither could (at the time, and to a large extend still) reach the operational altitude of the U-2.The Soviets tried many times to shoot one down, but it wasn't until Gary Powers (due to a navigational gamble he took to get out of the USSR in time to make a daylight landing at his intended destination, which had him fly near a Soviet SAM site) was shot down by the newly fielded strategic SAM capability of the USSR (designed against American bombers) that the idea was shown to have outlived its usefulness. <S> The SR-71 was then rushed through design and production to be completely different, flying not just very high but also very fast. <S> AND its operational concept relied far more on side looking sensors so the aircraft could remain outside the target country or area and look in from the relative safety of friendly airspace (under the assumption, which was never broken by the USSR or China, that the USSR would not shoot at aircraft outside of its airspace. <S> Later the D-21 project intended to add a deep penetration drone to the back of the SR-71 which could overfly China or the USSR and later be recovered. <S> Several of these drones were lost, causing top secret technology to fall into enemy hands, and the D-21 program was shut down.
|
The U-2 was designed in an era when the main threat to aircraft were anti aircraft guns and gun carrying point interceptors. Because the requirements were different.
|
Will portable Stratus ADS-B In receivers operate normally from the passenger cabin of a commercial airliner? Are ADS-B In receivers such as Stratus or Stratux permitted to be used along with other portable electronic devices at cruise altitude on commercial airliners? Will they receive GPS and ADS-B signals in the passenger cabin to be able to track progress on ForeFlight, for example? Source: Appareo <Q> The receiver will work in the cabin but the reception is really poor. <S> GPS will only work if it has enough satellites in view, so a window seat is best. <S> The signal is severely attenuated by the windows. <S> I have brought ADS-B receivers with me on various flights but in my experience you will not get a proper ADS-B signal from aircraft further than about 20-30NM away. <S> Whether it is permitted or not depends on the airline and the country of operation. <A> This would include GPS and ADS-B receivers. <S> Here is one example Devices that are NOT permitted for use: [...] <S> - radio receivers and transmitters <A> I've brought my Stratus on several trips. <S> Inside an airliner, you'll really only get signal if you leave the thing pressed against a window the entire trip. <S> Otherwise, you probably won't even get GPS lock, forget about ADS-B. TBH, there really isn't a lot to see once you get further away from the airport. <S> No one has ever made a fuss about me using it, typically they are just more curious as they see whats on my iPad. <S> Once I was sitting next to an off duty captain, once he saw what I was looking at we ended up chatting the entire trip. <S> So... generally it shouldn't be a problem, but you should always follow the direction and instruction of the flight crew, commercial or not.
|
Although not banned by the FAA, virtually all major air-carriers have company policies that prohibit anything that sends or receives a signal.
|
Do I have to notify ATC if I go-around when I was cleared for a touch and go? If I was cleared for a touch and go and go-around on short final or just before touchdown, do I have to notify ATC? I still would have made a takeoff after the touchdown during a touch and go, so it's basically the same when I start the climb a few seconds earlier isn't it? <Q> From the Instrument Procedures Handbook , page 4-41 (as part of the Missed Approach section), there is a quote about what to do when you need to go around when operating beyond the missed approach point: <S> In the event a balked (rejected) landing occurs at a position <S> other than the published missed approach point, the pilot should contact <S> ATC as soon as possible to obtain an amended clearance. <S> I have seen several other references in FAA documents which say to "contact ATC as soon as practical" in similar situations, but nothing which specifically says to do it any time that a go around is initiated by the pilot (i.e. under VFR). <S> That being said, if you have received a specific clearance (for a touch and go), and decide that you prefer to do something else (low approach/go-around), you should always receive an amended clearance first. <S> If you know ahead of time, your best option is probably to request the "option", in which case you have a clearance to do either one. <S> On the other hand, if the reason for the go-around is due to a safety issue then execute the go-around immediately when needed, and follow the above guidance to contact ATC as soon as practical if they don't call you first. <S> I was taught by my flight instructor to always report it, and the tower certainly needs to know about it in order to provide proper separation with other aircraft operating in the area. <S> If nothing else, it is a "best practice" to ensure that the person in the tower doesn't get distracted and not notice that you didn't land. <A> If you are on IFR and cleared for the touch and go or "the option", then you should already have received climb out instructions, which would apply whether you actually touched down or not. <S> So there's no issue from a clearance perspective. <S> The reason for announcing it is that going around instead of touching down can significantly change the pattern spacing. <S> If you are following close behind another aircraft, going around would put you much closer. <S> Tower may ask you to extend upwind a bit. <S> Like Dingo_Chaser said though, Aviate Navigate, Communicate. <S> If you've got your hands full then don't worry about it. <A> From my experience and conversations with my CFI, I think it's more of a courtesy to the tower and to the other planes in the area, so they know what to expect. <S> After all, if it's at a controlled airport, the tower will have a visual on you during your landing. <A> The general answer is: yes, you have to notify ATC that you are going around. <S> This is clearly stated in the ICAO Manual of Radiotelephony (doc 9432) <S> (emphasis mine): <S> 4.8.3 <S> In the event that the missed approach is initiated by the pilot, the phrase “GOING AROUND” shall be used. <S> Note the use of the word "shall", which denotes a mandatory action. <S> This applies equally to approaches with the intention to land and approaches for touch and goes (since not stated otherwise). <S> As others have pointed out, you should always focus on flying the aircraft first before worrying talking on the radio. <S> Make sure you have the situation under control before talking to ATC. <S> Note that the other answers posted so far <S> only focus on local rules in the USA. <S> The answer I have provided here is general since it is based on ICAO SARPs, and applies to the entire world, except for specific countries which have decided to not follow certain international standards. <A> Required , no. <S> But it's always a good idea. <S> In the Airman's Handbook, it says that you should always contact the tower when a missed approach procedure must be executed. <S> The purpose for this is to alert the tower of any air or ground conditions that caused you to abort the landing attempt, which they may not be aware of. <S> However, remember your priorities: Aviate, Navigate, Communicate. <S> Your first priority is to fly the plane. <S> Your second priority is to point the plane where it needs to go and to avoid any potential collisions with other planes. <S> Once you have accomplished both of those and still have mental and physical capacity, you can talk to whomever might need to know what you're doing. <S> This is all just as true of a T&G as for an actual landing. <S> If you can't T&G because someone pulled onto the numbers right in front of you, the tower will want to know that even if it was just a "practice landing attempt". <S> But, a T&G is even more mentally demanding than a normal landing, because it's a landing followed immediately by a takeoff, and your first priority is to handle the plane in a safe manner for everyone involved.
|
From my experience, it is definitely good airmanship to advise the tower (and thereby other aircraft) of your intentions if you are doing something unexpected.
|
Are Boeing 737 winglets adjustable from the cockpit? As I taxied past some Southwest 737s during a recent trip I saw what appeared to be different angles of the winglets relative to the wing. Are winglets adjustable, are they arranged differently from Port to Starboard, or is it an optical illusion? <Q> Winglets are fixed to the ends of the aircraft. <S> As can be seen below, the winglet has no movable parts and is fixed to the end of the wings. <S> http://www.sae.org/dlymagazineimages/2861_2313_ACT.jpg <S> Boeing 737 winglet; image from sae.org <S> The port and starboard side winglets would not be much different, usually (except that they are mirror images externally). <S> Interestingly though, Boeing has filed a patent for an adjustable winglet . <S> Airbus is also working on a similar project, called the morphlet. <S> Both of these are geared towards reducing drag and saving fuel. <A> You may have just seen aircraft with different models of winglets. <S> According to this site <S> there are four different models of winglets. <S> 737-200 <S> Mini-Winglets <S> 737 <S> Classic/NG Blended Winglets <S> 737 <S> NG Split Scimitar Winglets <S> 737 <S> MAX Advanced Technology Winglets <A> <A> 737 winglets are not adjustable. <S> There are several configurations in the fleet, as noted by @TomMcW, but they are all fixed. <S> Airbus and other commercial aircraft winglets are also fixed. <S> The only winglets with control actuation I've seen in actual use are on "flying wing" configurations like the Swift: <S> Studies (e.g. AIAA 2003-4069 ) show that for classic (tube-and-wing) aircraft, incorporating control deflections into an otherwise optimized winglet reduces the best lift to drag ratio. <A> 737 winglets are not, to my knowledge, adjustable. <S> However, some aircraft do have adjustable winglets, like the XB-70 <A> No. <S> The winglet is a fixed structure.
|
All winglets are permanently fixed to the wings and are not adjustable. What you'd seen is an optical illusion.
|
Which aircraft have made notable use of lateral asymmetry? I'm asking about functional asymmetry - doors on one side but not the other wouldn't count. Examples I can think of three examples: experiments with oblique wing designs, such as NASA's utterly hideous AD-1 , designed apparently by Burt Rutan displaced fuselage designs, such as the Blohm & Voss BV 141 or (another Burt Rutan aircraft), the Boomerang all single-propeller aircraft, in which the torque of the engine exerts asymmetrical forces on the aircraft Symmetrical asymmetry doesn't count (Then there are some that I don't think really count - for example, the Wright brothers' Flyer 1 placed the engine and the pilot side-by-side, but since they were intended to balance each other out and the twin propellors were symmetrically placed, that counts as an attempt at symmetry as far as I am concerned!) Other examples, and the reason for their asymmetrical design Are there any other good examples? The more ugly and wrong-looking, the better. I'm interested in the problems that the asymmetry aimed to solve - for example, oblique wing designs aimed to procure aerodynamic advantages (which turned out to be at the expense of handling issues), or Rutan's Boomerang which "was intended to be a multi-engine aircraft that in the event of failure of a single engine would not become dangerously difficult to control due to asymmetric thrust" ( Wikipedia ) Visual reference Just for reference, here's the AD-1 ( NASA, via Wikipedia ): ... and the BV 141 ( Deutsche Bundesarchiv, via Wikipedia ): <Q> A good example of experimental aircraft is the NASA F-16XL F-16XL with supersonic laminar flow control experiment (black area on left wing, front) or "glove. <S> " <S> Image from nasa.gov Aircraft used as engine test beds are usually asymmetric. <S> The following image shows a B-47 Stratojet used as engine test bed for the the Orenda engine earmarked for Avro Arrow program. <S> Image from <S> silverhawkauthor.com <S> A closeup of the rear: <S> Image from google <S> English Electric Canberra <S> PR9s had offset canopies. <S> By MilborneOne <S> - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=13266605 <S> So did the de Havilland Sea Vixens . <S> By Yeovilton_Vixen_2009-001.tif : <S> Nigel Ish derivative work: Cobatfor - This file was derived from Yeovilton Vixen 2009-001.tif : , CC BY-SA 3.0, <S> https://commons.wikimedia.org/w/index.php?curid=19477903 <S> Of course, all 'conventional' helicopters (with tail rotors on one side) are asymmetric, but I don't think that's what you're after here. <S> Also, see this page and the Wikipedia page on asymmetric aircraft . <S> As a disclaimer, I wouldn't call any of these aircraft 'ugly'. <A> All aircraft with external storage that dump only one become instantly asymmetrical. <S> A particularly extreme example might be the Heinkel He-111 H22, which was designed to carry a V1 to a launching point in order to attack targets beyond the reach of the fixed launch catapults, or the B-52 used to carry the X-15 aloft. <S> Heinkel He-111 H22 with FZG-76 <S> (picture source ) <S> Even after dropping the cruise missile, the He-111 H remained an asymmetrical configuration, because the tip of its glazed nose was offset to one side, so the front gunner would obstruct the pilot's view less. <S> Inside view of the He-111 cockpit (picture source ). <S> B-52 <S> just after launch of <S> the X-15 (picture source ) <S> Also here the aircraft remained asymmetrical after having launched the X-15 due to the large pylon used for carrying the X-15. <A> Another Rutan design (I think his earliest asymmetric) was the Ares "mudfighter" with a 25mm cannon on one side of the cockpit, and the turbojet air intake on the other. <S> The design was intended to keep the pressure waves and nasty combustion gasses from the cannon from being ingested by the engine. <S> The NASA X-15 <S> Active wasn't asymmetric by design, but was designed to induce asymmetries (to simulate failures, or damage, up to and including loss of an entire wing). <A> The M.C.202 actually had wings of different sizes to compensate the engine/propeller rotation: <S> As rightfully requested, here are some pictures from the video: <A> two wings are not at the same position along the length of the aircraft. <S> To save weight, their non-tapered spars are bolted together in the fuselage, so one wing is one spar thickness ahead of the other. <S> With a wingspan of over 100 feet, it isn't very noticeable. <S> It also has two vertical stabilizers but only the starboard one has a movable rudder. <S> To cut down on questions about that, they put a line on the port one that looks like a rudder gap using an ink marker (lighter than paint!). <S> Lower cruise drag and weight at the cost of terrible rudder performance asymmetry (right rudder response was fine; left rudder response almost nonexistent). <S> This learned from conversations with Dick Rutan, the Voyager's pilot, in 1985/1986.
|
There are quite a few asymmetric aircraft, most of which are, experimental engine test beds The Rutan Voyager (World Flight, 1986)
|
Were inclined runways ever under consideration? A long time ago I read an article (in Popular Science, probably) of a plan for an airport runway constructed on a grade, so that one end was ten stories higher than the other. The idea was to save gas: at takeoff, the plane would be going downhill and get a speed boost from gravity. When landing, the plane would be going uphill , and take less engine power to stop because gravity is slowing it down. Did anyone ever research or actually test this plan? Does it seem practical? <Q> The first reason is wind: It helps to take off and land with a headwind. <S> If the runway slope is on one end, this has to be the end where the take-off run starts and where the landing run ends. <S> Since both are in the same direction, this scheme now needs twice the runway length, the first half for landings and the second half for take-offs. <S> The next reason is the magnitude of what can be saved. <S> The energy from the height change $∆h$ can be translated into a speed gain $∆v$ by this formula: <S> $$∆v = <S> \sqrt{2\cdot g\cdot ∆h}$$ <S> Let the ten stories be a height of 40 meters, and <S> your speed gain is only 28 m/s. <S> This was significant in the age of propeller aircraft, but jets need much higher speeds to get airborne - 150 knots or more. <S> In sane units this is 77 m/s, and since the energy is proportional to the speed squared, the 40 m slope will save only 13% of the energy needed for take-off. <S> It is simply not worth it. <S> Now look at the operational consequences: The landing has to be performed such that the aircraft has slowed down to 28 m/s when it reaches the foot of the slope. <S> If it is still too fast, it will overshoot and roll down the other side, and if it is too slow, it needs to run up the engines in order to climb up the slope, expending the energy it hopes to save at take-off. <S> No, practical is not what I would call this. <A> It's never been planned as such due to the usefulness of flying approaches into the opposite end of the runway when winds favor so. <S> That being said there are a number of inclined one-way in / one-way-out runways in the world, mainly in remote and mountainous areas. <S> The most notorious of which is Courchevel airport in the French alps. <S> Like Gustaf III on St Barts, Courchevel requires special training and a logbook endorsement to fly approaches into. <A> many one-way strips in New Guinea with slopes up to 17%. <S> As in the alps, commercial operations restricted to pilots with five trips under supervision, preferably under different weather conditions. <S> An exemption, which I had, was supposed to require 1000 hrs in PNG and endorsement into 50 strips. <S> I didn't get to that many . <S> Wind direction irrelevant, accept what it is and compensate. <S> On the steeper strips, full power at touch-down or you won't get to the top.
|
Yes, it does work, but cannot really be called practical. Not practical for econoomic advantage, but there is an advantage if you are building airstips in the mountains - the strip doesn't have to be so long!
|
Does windmill restart often work for airliner engines? There seems to be a certain class of airline accident where an airliner engine flames out followed by further unfortunate events. Very often, pilots are recorded as having attempted to restart a failed engine by windmilling, which seems to involve attempting to restart an engine from the rotation due to the passage of air due to airspeed. In accident reports this rarely ever succeeds, leaving the impression of a rather worthless exercise. But, of course, there's a massive bias here because these are the reports of accidents and if the windmill start worked, things wouldn't have deteriorated. So, in rough terms, how desperate is attempting a windmill start. Is it in the land-on-water level of optimism, or something which usually succeeds which we never hear about? <Q> Fuel starvation, bird ingestion, etc., do not count. <S> ( YouTube ) <S> In-flight shutdown. <S> In-flight restart is tested as part of the aircraft certification, and it must work. <S> In the link above is a video showing the procedure in a 777F simulator. <S> Engine Restart Capability - § 25.903 <S> (e). <S> Tests should be conducted to determine that inflight restarting can be accomplished within the envelope provided. <S> Restarts at the conditions of the critical corners of the envelope and at or near the high altitude extremes of the envelope should be conducted to verify the boundary conditions of the envelope ( FAA ). <S> Examples of successful restarts: <S> On British Airways Flight 9 , all four jets on a 747 failed after entering a volcanic ash cloud, all 4 were restarted after exiting the ash cloud. <S> One of the four failed shorty after, but volcanic ash is sticky, the particles are very small, they melt, and they clog moving parts. <S> So three out of four isn't bad at all. <S> For KLM Flight 867 (a mirror of BA 9) it was four out of four successful restarts. <A> Windmill starts are a rather last-resort type of thing. <S> Lots of things have to go wrong before pilots will be attempting that. <S> First, an engine has to fail. <S> Since airliners are required to have at least 2 engines, and be able to fly on one engine, this isn't a dire emergency. <S> Pilots will work the associated checklists. <S> If there is no apparent issue they may attempt to restart the engine using bleed air from the running engine. <S> If there is an issue they will leave it shut down. <S> With thousands of planes in the air, this sort of thing happens pretty much daily. <S> The chances of the other engine failing are very low , and generally due to some common circumstances that affect both engines . <S> Pilots may be more aggressive in trying to get even a damaged engine started, as a damaged one is better then none at all. <S> The APU may be started and used to help start the engines as well. <S> But this takes time, which tends to be running out when gliding with no engines running. <S> As ymb1 pointed out , engines are required as part of certification to demonstrate windmill starts. <S> Issues that can prevent this from working tend to get the attention of the safety folks. <S> This establishes limits and guidelines that are put into the aircraft checklists. <S> Pilots know that if they maintain a certain air speed, the engines should reach a certain RPM, which will allow them to be started. <S> Of course if multiple engines have already failed, there is a chance that this issue will prevent a restart. <A> As Oscar Wilde said, "pure and simple truth" is rarely pure and never simple... <S> The "not-so-simple" part is that engines don't just flame out for no reason. <S> They only flame out because something is abnormal, either with the engine itself or with the environment (ash clouds, sandstorms, torrential rain, fuel supply, etc). <S> Therefore, the probability of a successful engine restart is already compromised in some unknown manner by the fact that it stopped. <S> Deliberately shutting down an undamaged, low-life engine and demonstrating that it will relight, as part of the flight test certification program, is about as good a test as is practicable (there is no way any flight test program will go around looking for volcanic ash clouds to fly through, water ingestion tests done on an engine on a test stand on the ground can't be followed by a windmill relight test, etc) <S> but it's not necessarily completely representative of a real-life engine relight situation. <A> The problem with windmill starts on a gas turbine is - <S> it requires a fairly high airspeed, as mentioned in this bit on starting aircraft engines . <S> Typically, the APU, itself a smaller turboshaft engine, has an electric/battery start, while high pressure bleed air from it or another running engine or a ground supply is used to start a main engine. <S> If your only option is a windmill start, it means you have no bleed air from another running engine, or the APU, as in all of them have failed. <S> Quite probably, you've run out of fuel, so a windmill start is a waste of time. <S> APU's tend to start far more quickly than main engines, so if you don't have the time to start the APU, you probably don't have the altitude to swap for airspeed to try a windmill start. <S> The last thing you want to do if you're in that shape is lose more altitude than necessary when you have no power, and no other way to restart your engines. <S> Windmill starts on piston/prop planes in the 1930's and 1940's <S> were performed, usually when the electric starter on one engine of a four engine aircraft had failed while the aircraft was parked. <S> They would take off unladen on three engines, with the fourth prop feathered, and use the airflow to crank that engine to a start, then land and pick up whatever they were carrying and go on their way. <S> Or, WW2 fighter aircraft would windmill start when the pilot dropped external tanks but forgot to switch fuel supply to the main tanks. <S> They'd just change the fuel settings, nose down and reset prop pitch, and fire the engine back up. <S> In some cases, it was quicker than an electric start, or in the case of naval aircraft that used a high pressure shotgun shell starter, it was the only way to restart the engine in flight.
|
If the engine isn't damaged, and the restart altitude/speed are followed, the engine should start.
|
How were bullets fired through the propeller in the Focke Wulf 190? In WWII there was a plane called the Focke-Wulf Fw 190 . It was designed by an engineer called Kurt Tank . How is it possible that the Fw 190 fires through the propeller from 4 different places as you can see in the picture below? There are two machine guns right in front of the pilot, and one at either side on the wing, close to the body of the plane. <Q> Note: <S> See Peter Kämpf's answer for specifically how the Fw 190 Achieved this Electronically <S> This answer is specific to how this was achieved via mechanical means in earlier aircraft and not specific to the Fw 190. <S> Source: <S> Kaiserliches Patentampt (Imperial German patent Office) / Franz Schneider - Patentschrift <S> No. 276396, 1913 First published in Flugsport" (1914) <S> and in many places since, Public Domain, [From Wikipedia] <S> Interestingly, the linkage between the propeller and the gun is achieved with a spinning drive shaft rather than a reciprocating rod. <S> The impulses needed to operate the trigger, or in this case to prevent the trigger from operating, were produced by a cam wheel with two lobes at 180 <S> ° apart situated at the gun itself, since the gun is interrupted by both blades of the propeller. <S> These have been around since before 1920, long before the aircraft you mention in your original post. <S> The one on the Fokker (not Focke-Wulff, but still German) differs a little bit from the patent image above: Source: <S> By Gsl - Version with English text of Image: <S> Interrupter_gear_diagram.png, Public Domain But not significantly, the basic idea is that the trigger mechanism follows a cam lobe which is tied to the propeller shaft. <S> When the cam lobe spins, the trigger is allowed to fire the gun only when the propeller isn't "in the way". <S> See Wikipedia Article on the Synchronization Gear for more information. <A> The Internet is incredible. <S> I found a PDF of the manual for the armament of the Fw-190 online here . <S> In it, the components are described sufficiently to be sure that synchronization in the FW-190 was achieved electrically. <S> General arrangement of the armament in the Fw-190 <S> (picture source ). <S> The pipes running to the wing cannons feed hot air from the engine to the ammunition box to keep the temperature there above -35°. <S> Detail view of the Sicherungs- und Verteilerkasten SVK-2 (circuit breaker and distribution box) for the MG 151/20 in the wing root <S> (picture source ). <S> Clearly, the weapon was electrically controlled. <S> The Wikipedia page on gun synchronization already mentions that with firing rates above 400 rounds/minute, mechanical synchronization became unreliable, and at the end of WW I, the first electrical gun synchronization by Siemens was used in LVG attack planes, and Aviatik employed their own system. <S> The much higher firing rate of WW II guns required electrical synchronization, and only some Russian fighters continued to use mechanical synchronization into and even beyond WW II. <A> Since WWI, there was a device called a Synchronisation Gear which staggered the firing of the gun so that it would not hit the propeller of the plane. <A> I can't seem to locate the reference but the synchronizing gear was not at first used with the forward firing gun. <S> The inventor of the forward firing gun had steel plates mounted to his propellers to deflect the occasional round that might hit the prop. <S> This was satisfactory right up until he got his prop shot off. <S> That's when the synchronizing systems were sought out.
|
It's called a "Synchronization Gear" and it allows the gun to fire only when the blade is not in front of the barrel.
|
Can a pilot act as cabin crew member? If several standby cabin crew members called in sick and there are no more available can standby pilot called to perform cabin crew member duties? Probably it would be more economical than postpone flight let say with 200 passengers... <Q> For the U.S., can a non-cabin crew act as a cabin crew? <S> Yes , except for safety duties. <S> U.S. air carriers periodically use company employees in the cabins of its aircraft for the purpose of conducting certain passenger service activities, such as serving beverages, conducting customer relations, or acting as translators. <S> These persons are not assigned to flights to perform safety duties . <S> These company employees are not acting in the capacity of an F/A nor are they, in general, trained or qualified to act as a F/A. <S> The regulations do not prohibit the use of non-F/A personnel by an air carrier. <S> However, their presence could conceivably interfere with the F/ <S> As if they were not properly instructed. <S> Source: <S> FAA <S> My interpretation is technically yes, especially that pilots are trained in safety duties. <S> But that's not to say there wouldn't be a union rule against it. <A> I'm not sure if this is possible. <S> Cabin crew are trained for a number of things including handling of emergency situations, which are different from what the flight crew receives. <S> Also, there is no reason to believe that the flight crew is proficient in various duties of the cabin crew (like performing safety demonstration, etc) as their duties are distinct. <S> On the regulation side, the certification requirements are different. <S> For example, the FAA requires the cabin crew to have a certificate of demonstrated proficiency . <S> In the fall of 2003, Congress established a flight attendant certification requirement in the Vision 100-Century of Aviation Reauthorization Act. <S> The act requires that after December 11, 2004, no person may serve as a flight attendant aboard an aircraft of an air carrier unless that person holds a certificate of Demonstrated Proficiency (certificate) issued by the FAA. <S> This would mean that the flight crew can't operate as cabin crew (unless they have the certificate), atleast in US. <A> The Answer for your question is NO. <S> Pilots are not trained to serve passengers, but I think that was not What you were referring. <S> After this command the pilots have to leave the aircraft, so in this case the pilots can help the flight attendants with the passenger evacuation. <S> Sometimes asking the flight attendant to jump off in the scape slide and help the passengers at the other side of the slides. <S> Remember that this is a quick procedure as a time to evacuate any commercial aircraft is 90 seconds by regulation. <S> Hope this help ;)
|
Pilots can and must help flight attendants in emergency, this does not mean they are working as a flight attendant, in case of an emergency the pilots will finish all the emergency check lists turn off engines, APU and Battery as part of the check list procedure and after that will communicate the evacuation of the aircraft.
|
Why are the wings of some planes changing width? I was travelling recently in a Boeing 737 and I noticed one thing that I didn't understand. After the takeoff the wing flaps started retracting into/under the wing, making it narrower. The opposite happened before the landing. You can see what I mean in this video: The question is: Why are the flaps hiding into/under the wing? I understand that the bigger wing area is better during takeoff and landing. But why is the wings' size reduced during the cruise? Shouldn't bigger wings provide better lift during the entire flight? Some clarification after comments: I'm asking specifically why are the flaps retracted and not just remain parallel to the wing <Q> Well, yes, bigger wings to provide better lift, but the also produce more induced drag in the process. <S> The wings on an airliner are optimized for cruise in high subsonic and transonic flight where a slender, swept wing works well. <S> While this is great for cruise flight, the trade-off is this style of wing requires a very high approach speed for landings which in turn require very long runways to accelerate the airplane on to reach rotation speed for takeoff or to decelerate the aircraft on once it has landed. <S> The Boeing Company successfully addressed these problems in the early 1960 with the development of the 727 airplane as a regional airliner. <S> It made use of a type of flaps called Fowler flaps (see Fig 1) in concert with leading edge extensions. <S> Fowler flaps. <S> These style of flaps consist of a series of segments attached to tracks or support linkages running chordwise, allowing the flaps segments to extend and retract by rolling along said tracks. <S> Fig 1. <S> Typical Fowler flap installation <S> When deployed these give the effect of changing the airfoil shape from a slender, slightly cambered airfoil into a wide airfoil with a large camber. <S> Fowler flaps have an additional advantage to them in that partial deployment creates a large increase in lift with limited additional drag, very useful for takeoff, while when fully deployed they create a lot of drag in addition to higher lift. <A> Bigger wings also produce more drag. <S> Instead, flying faster (in cruise) produces the required lift. <S> For any given object, the bigger it is, the more drag it produces. <S> Since a plane spends most of its time in cruise, the wings are designed with a lift-to-drag ratio that suits cruising. <S> For slow flying (take-offs and landings), high-lift devices are then used, they come in many flavors. <A> This is important both on take-off and, especially, landing where the aircraft is moving relatively slowly. <S> The trade off is that flaps dramatically increase the drag. <S> Bear in mind, that commercial airliners spend most of their flight time cruising at, more or less, constant speed and altitude. <S> At cruise, there is no value in 'more' lift, they need exactly enough lift to support their weight at an efficient cruising speed. <S> So, the wing shape is designed to do this with the minimum possible drag. <S> Flaps increase the lift at low speed so the aircraft still has enough lift to support its own weight when approaching for landing without needing to be traveling at a speed which would make safe landing more difficult and require a very long runway to slow down after touchdown. <A> The "flaps up" configuration represents the wing's base shape. <S> This is the shape designed to produce the intended flight characteristics including required lift at minimum drag under the aircraft's designed cruising flight conditions (airspeed/altitude). <S> Take-off and landing is best performed at the lowest speeds which are practically attainable (take-off and landing distances increase dramatically and non-linearly with speed). <S> The "flaps down" configurations (note the plural) increase the effective wing area, but also change its profile. <S> Extending flaps increase lift but also increase drag. <S> Most aircraft have multiple flap settings, providing a progression between "clean" (flaps up) and full flaps. <S> Full flaps are only used for landing where high drag is desirable because it helps slow the plane down after touchdown. <S> Intermediate settings are used for take-off because they aid lift with a minimal drag penalty and are used in the early stages of approach as the aircraft is slowing down. <S> Flaps aren't simply enlarging the wing. <S> Most flap designs leave gaps when fully or mostly extended. <S> These gaps allow some air from under the wing to flow up through the gap and join the air moving over the top of the wing. <S> This helps the airflow remain "attached" to the top surface of the flap. <S> Without this feature, air on the top surface can "detach", become turbulent, and no longer aid lift.
|
Flaps are a way of changing the shape of the wing so that it is able to provide more lift at lower speeds and higher angles of attack.
|
How can planes with the same stall speed and power-to-weight ratio have such different takeoff field length, climb rate, glide ratio, etc? I am interested in better understanding the performance differences between different planes that seem to be similar in many important ways but that differ greatly in performance. For example, take single engine turboprops A, B, and C that all have a regulation stall speed minimum of 61 knots, and that all have similar power to weight ratios at takeoff. Turboprop A has a takeoff field length of 1,200', B is 1,600', C is 2,400'. If they all have the same stall speed (and a similar lift-to-weight ratio, I would think) and similar power to weight ratios, shouldn't they have similar takeoff field length requirements? Lancair Evolution 550hp at takeoff (750hp in flight) 4,550 lbs MTOW max speed ~295 knots 1,200' field length ~10:1 glide ratio Epic E1000 960hp at takeoff (1200hp in flight) 7,500 lbs MTOW ~330 knots max speed 1,600' field length ~17:1 glide ratio Daher TBM 900* 850hp 7,400 lbs MTOW ~330 knots max speed 2,400' field length *65 kts stall speed http://www.flyingmag.com/pilot-reports/turboprops/tbm-850-even-faster If these planes have the same stall speed (and therefore, my intuition would think, similar ratios of lift to weight and drag), and have similar ratios of power-to-weight, how can they have such different field length requirements and glide ratios? EDIT: UPDATED INFO Stall speed is as defined by the FAA for Part 23 aircraft certification. Here's a link to how the FAA requires the stall speed to be validated. Wikipedia defines this V s0 speed as: Stall speed or minimum flight speed in landing configuration. <Q> Are we comparing apples to oranges again? <S> The differences in take-off length are far too big with such similar performance numbers, and I agree that they should be closer together - if we are really comparing the same thing. <S> Take-off means that the aircraft has to gain an energy difference with a potential and a kinetic component. <S> FAR 23.53 demands a height of 50ft, and FAR 23.51 a speed of 1.2$\cdot\text v_{S}$, but adds more conditions that could be significant here. <S> If the speed for continued safe flight is found to be higher, that speed must be used as the basis of the take-off performance. <S> The 61 kts stall speed limit only applies to aircraft below 6000 <S> lbs MTOW <S> , so two of the three are not constrained by this limit. <S> Interestingly, the heavier aircraft have longer take-off lengths. <S> If the airplane weighs more than 6000 lbs and is certified in the commuter category, FAR 23.59 comes into force. <S> It relaxes the height requirement (35 ft instead of 50) but adds a factor of 1.15 to the demonstrated length. <S> If all take-off distances would had been determined with the same rules and if the stall speed in take-off configuration would be equal between all three types, the take-off distance would be very similar. <S> But I am sure both conditions are not met. <A> You need to dig a little deeper here, we need area, aspect ratio and airfoil type of wing AND propeller. <S> For example, a low aspect wing will stall at a lower airspeed, but not glide as efficiently as a high aspect wing. <S> The Lancair and Epic bear comparison here. <S> Also, check into slat and flap configurations available for low speed flight on all types. <S> The Daher may be able to "hang everything out" for a low speed airline-like landing, but may have a smaller, lower aspect wing than the Epic, there for, poorer takeoff performance. <A> This is likely a difference in optimization, contrasting speed and efficiency at cruise with other performance parameters like acceleration on the runway or stall characteristics. <S> As for the prime mover, a turbo-jet is best at high speeds and less efficiently creates thrust at taxi speeds, a high bypass turbo fan is best at medium speeds and is reasonable at taxi speed. <S> A propeller can be designed/selected for a target performance, with a climb prop(optimized for low speeds) you will get much more thrust at low speeds for quicker 0-60 times and steeper climbs but you will suffer reduced cruise speed and efficiency while operating at higher rpm. <S> Adjustable pitch props help provide good low speed and cruise performance <S> but the still have an optimum sweet spot. <S> At the extremes of fixed pitch you have the STOL performance of bush planes that will nearly hover with a slight headwind and a top speed of 80, and Reno air racers that may actually get out and push to get the plane moving because at low-taxi speed the prop is almost completely stalled and needs some relative airflow to get a useful angle of attack <S> but they have a top speed of 3-400.
|
Total drag will make some difference, design optimization of the prime mover will likely be a big factor, and as others have said stall speeds may be stated for different high lift device configurations, brakes, spoilers.
|
Checklists before take off - how often must they be performed? Friday I was on a plane from MXP to Prague, should have been a 737-400, and the take off was preceded by something I'm not sure what it was: probably a pre-flight checklist, but it's the first time I see something like this: The plane got pushed back by a tractor from ramps to apron - at least, I think it was the apron- and turned (still by the tractor) in the right direction for the taxiway Engines thrust was increased and decreased a few times, keeping them at "high" levels for a bit Control surfaces were checked as usual I'm used to pilots checking control's surfaces either while still at ramps or on the taxiway while waiting for their turn to take off, or just at the beginning of the runway, but never seen anything different and never seen "testing" the engines that way, and it got me wondered about check list frequencies. Was that routine some kind of checklist? And if so, is there a specific regulation about how often it must be performed? (and, by the way...I know that it's possibile to load fuel even with passenger on board, but...testing engines with plane full loaded? Isn't it a bit too dangerous?) <Q> For an airline crew, the Before Takeoff Checklist is performed once before every takeoff. <S> There is normally no "run up" associated with such a checklist for jet aircraft. <S> Depending on what else is going on, there are reasons that engine power might be advanced then reduced, and it would be speculation as to what the reason for that was on your particular flight. <A> The amount of times they do the checklist is not important. <S> There's things that are repeated between checklists. <S> For example, some aircraft have control surface checks both on the ramp and while taxiing. <S> Regarding the engine run-up, the pilot would not do it if it was hazardous to passengers. <S> Engine run-ups are usually performed somewhere between the ramp and takeoff. <S> Engine run-ups are a must. <S> Other reasons for engine run-ups could be carb cleansing (for non-fuel injection pistons), engine temperature adjustments, etc. <A> Engines thrust was increased and decreased a few times, keeping them at "high" levels for a bit <S> This could be as a result of a recent maintenance note on the aircraft, which resulted in some configuration changes or modifications to the engines, thrusts, throttles or any number of things in the middle. <S> If my memory is correct, the 737-400 is not a fly-by-wire aircraft; so there is a lot of mechanical stuff going on. <S> So it could be simple run up to verify things in the mechanics <S> log. <S> I'm used to pilots checking control's surfaces either while still at ramps or on the taxiway while waiting for their turn to take off, or just at the beginning of the runway, but never seen anything different and never seen "testing" the engines that way, and it got me wondered about check list frequencies. <S> Unless some extraordinary exception is in place, control surfaces are not checked at the gate or at the ramp; simply because most of these test have to be performed post engine startup in order to ensure all systems and redundancies are tested. <S> If flight controls are being tested (ie, full range being tested) on the runway <S> this is definitely not normal. <S> (and, by the way...I know that it's possibile to load fuel even with passenger on board, but...testing engines with plane full loaded? <S> Isn't it a bit too dangerous?) <S> Most commercial airplanes can be fueled with the engines running (but at idle), but for safety reasons, it is almost never done. <S> Having passengers on board during refueling happens quite often. <S> You'll know its going on because the crew will inform passengers to be seated. <S> So a taxi checklist is done before each taxi, takeoff before each takeoff and so on.
|
Regarding your main question about checklists - they must be performed once at the respected stage of flight.
|
Why do airliners have "pressure bulkheads"? Image source: FAA What part of the fuselage aft of the bulkhead would leak pressure? Or is it just there to reduce stresses? How does a DC-9/MD-80/90 incorporate aft bulkheads when there's a staircase in the way? ( Image source ) <Q> What part aft of the bulkhead would leak pressure? <S> That's a partial misunderstanding of what a bulkhead is there for. <S> You could build the aft cone section to keep the pressure, but it would be a much heavier solution. <S> The shape of the final aft section is not well suited to resist pressurization stresses: the best shape is a sphere; the cylinder (with spherical terminations) comes a close second. <S> The conical shape would require serious stiffeners to survive pressurization cycles for the whole life of the aircraft; the bulkhead solves this problem by using a shape that is naturally more resistant to stresses - and thus can be built with less material - leading to less weight, and hence fuel savings (in addition to the increased safety). <A> You can think of an airliner (or any other pressurized airplane, or a submarine) as a pressurized container with control surfaces and a nosecone stuck to it. <S> Rather like a submarine, an airliner has a floor with seats, a nose to make it aerodynamic, wings for lift, and a tail section for control <S> (yes, I know I am way oversimplifying it, and that's the whole point) <S> So the bulkhead IS the "tank" and the tail is just added to it. <S> As for why it is shaped that way, it was answered in the other posts. <S> A sphere is stronger and so it is used for deep subs for instance. <S> This image might help you picture what I mean; it's easy to see the "tank": <A> Pressure bulkheads are the primary structure members which combined with a fuselage or cabin provide a sealed pressure vessel and carry the fwd and aft pressure loads <S> when the cabin is pressurized - think of them <S> kind of like the end caps on a cylindrical air storage tanks on an air compressor. <S> As for the aft stairs on a DC-9 or a 727, the stairs are aft of the aft pressure bulkheads and accessed through a pressure door in the aft pressure bulkhead, as in the example from a 727 below. <A> A dome is one of the most resilient and versatile shapes in engineering. <S> It is the ideal shape to resist internal cabin pressure. <S> When you blow a balloon it fills out into a sphere too. <S> So the bulkhead can be built with highest efficiency weighing the least. <S> As for the steps, they have latches and when closed snap tight, similar to the main doors. <S> And become a continuous integrated shell with the fuselage. <A> I think what isn't clearly mentioned in other answers (despite those answers being correct) is that the structure rearwards of the aft bulkhead isn't pressurised. <S> Whilst at cruise level <S> the cabin will be maintaining a pressure equivalent to roughly the altitude of 8,000ft (cred @ vasin1987); the structure rearward of the aft bulkhead i.e. the tail cone, will be at the cruise altitude's external atmosphere's pressure. <S> Therefor there is no pressure to leak out of that tail cone section of the fuselage as the outside and inside pressure for that section of fuselage are the same. <S> As others have mentioned, the justification for this would be the costs and challenges in making a difficult shape capable of resisting the pressure imposed on it. <S> NB, I wouldn't advise opening the bulkhead's pressure door at cruise altitude because on one side will be the cabin pressure and on the other the external atmosphere's pressure!
|
It is also an integral structural member of the frame to help stability of fuselage against local buckling and articulate transition to tail section which is a totally different geometry.
|
Do planes have odometers? I'm curious to know if planes have distance counters similar to the ones in cars indicating how many kilometres/miles the plane has flown since being put in service. <Q> A Hobbs meter measures the time spent in a general aviation aircraft with the power on. <S> Planes differ in that time <S> is easier to record than distance. <S> For a given airspeed, the distance covered by the aircraft depends on the wind, altitude, and other factors. <S> Modern airliners would record the period each engine has run, flight time, cycles (one cycle is one pressurization/depressurization cycle), etc., digitally . <S> Those records are then used to track the time between overhauls (TBO). <S> Same as with cars. <S> For small planes, a tach timer is used to record the revolutions the engine has made, this one is used for TBO. <S> ( Source ) Image of tach timer. <A> No, there's no odometer to measure distance on an airplane because it is not a good measure for maintenance. <S> An airplane's body (wings, fuselage, etc) will require more or less frequent maintenance based on the stresses placed on it and how it is flown. <S> Take for example 2 scenarios, both with identical models of Cessna 172. <S> In the first case the airplane is part of a training organization and mostly flown by student pilots. <S> It will be subjected to plenty of hard landings, and the engine will have lots of time at full RPM. <S> The second airplane is flown by a retired air force pilot who does lots of cross country. <S> Over the same distance the first airplane will need significantly more maintenance than the second. <S> Distance is also hard to measure because the air moves . <S> In a car the odometer is changed by tire rotation, which is directly measureable against the ground, but the air is a mass which is constantly going from place to place. <S> Again take two scenarios, both in which an airplane must fly 300 nautical miles at an airspeed of 100kt. <S> In the first case there is a 30kt headwind, in the second a 30kt tailwind. <S> In the case of the headwind the ground speed is 70kt and the trip takes about 4 hrs 20 mins. <S> In the second case the ground speed is 130kt and the trip takes about 2 hours and 20 minutes. <S> The distance over the ground is exactly the same but one trip takes almost double the time of the other because the distance through the moving air mass is much longer. <A> We use engine time. <S> The tach keeps track of engine time and that is what is recorded in required logs and <S> what dictates maintenance cycles, part 135 overhauls etc. <S> Hobbs is only used for pilot log books and serves no regulatory purpose. <S> -Robert
|
Airplane engines have a service life which is determined by the number of rotations it has made or the number of hours it has been operating.
|
What is the benefit or motivation for having Class G airspace? I'm looking at the differences between Class E and Class G ( AIM 3-2-6 ) airspace in the United States and I get that there are different flight condition requirements depending on AGL/MSL altitudes, but if you're outside a Mode C veil and around an untowered airport (So you don't need a transponder, don't need a radio), why not make everything Class E? I think the answer came to me while writing this out...is it this simple? Does Class G exist because for whatever reason (Radar services not available, technical reasons, etc.) ATC is unable to provide IFR separation services in that area, so it has to be deemed "uncontrolled?" Is there some other reason why Class G exists besides being a catch-all? Class G airspace (uncontrolled) is that portion of airspace that has not been designated as Class A, Class B, Class C, Class D, or Class E airspace. Like is there some benefit that you get when you're in Class G instead of Class E? The only thing I could think of is that the flight visibility is less than 3 miles but more than 1, it's daytime and the cloud deck is lower than 500 feet AGL (since you just need to be clear of clouds and 1 SM visibility), you could take off VFR in Class G and you couldn't take off in Class E. (However, you'd still have to be sure not to be engaged in Careless or reckless operation (14 CFR § 91.13).) <Q> You can also fly Ifr without a clearance in G. Remember that the entire purpose of airspace is to keep us from hitting airliners. <S> It is not about keeping GA planes apart. <S> When you look at wx mins that is clear. <S> The FAA gives us the freedom to fly around in low vis so long as we stay out of the areas you'd find airliners. <S> -Robert <S> CFII <A> Airspace classifications above G exist to protect commerce. <S> (The FAA exists to protect commerce.) <S> That is primarily IFR operations, as well as carriers and others that utilize ATC services. <S> The protections include around congested airports (towers, radar service areas) and airspace for route structures. <S> Just 50 years ago, there was much more uncontrolled airspace in CONUS. <S> Air routes (Victor airways) were protected, and airspace moved to higher classification levels, and along with it NAVAID facilities were implemented, better radio coverage for FSS and ATC, as well as more terminal and enroute radar service areas. <S> FAA Order JO 7400.11B is an example of the FAA issuing orders classifying airspace for the purpose of serving airports and their instrument approaches. <S> Other airspace, such as Class A was defined by broad regulation. <S> When I was first instrument rated, it was possible to make substantial trips IFR, without a requirement to file flight plans. <S> The airspace was uncontrolled, and little or no ATC services were available. <S> Flight plans could be filed for search and rescue, but separation services were not available. <S> FSS stations and their remotes (RCO) were a primary link for IFR operations in uncontrolled (now Class G) airspace. <S> It is noteworthy that radar coverage is not necessary for airspace to be classified as controlled airspace. <S> It is true that some airspace, for example, Class C, is defined by the existence of radar services. <S> If radar goes down, then class C reverts to Class D and class E. <S> But in general the classification of airspace is done to support the operations and the services rendered in that airspace. <S> https://www.faa.gov/air_traffic/nas/nynjphl_redesign/documentation/feis/media/Appendix_A-National_Airspace_System_Overview.pdf <S> https://www.faa.gov/documentLibrary/media/Order/JO_7400.11B.pdf <A> Class D and above require good weather, and permission, to enter. <S> Class E airspace requires good weather only. <S> Class G airspace requires not much. <S> That's the benefit/difference of Class G. <A> All airspace was originally uncontrolled. <S> Then planes started crashing into each other, especially in bad weather, and someone got the bright idea of having controllers to track where planes were and keep them separated. <S> Yay! <S> Those controllers expect to be paid and need radar/radio equipment, though, so it was only done where there was enough danger to justify that expense, e.g. around busy airfields. <S> As planes got faster, a low-altitude speed limit was added so that new danger was limited to high altitudes, which are cheaper to control due to physics. <S> But traffic kept growing, so they kept adding more and more radar/radio coverage to enable control at lower and lower altitudes. <S> There's still a limit to budgets, though, so most of the last bit near the ground remains uncontrolled--now called class G. <S> In some countries, it's actually a rather large part of the lower airspace because they simply haven't thrown as much money at radar/radio coverage as others have, and that's often (but not always) linked to lower traffic density and correspondingly lower collision risk.
|
Rather there is the need to be able to control that airspace to assure the separation and provide weather services for aircraft.
|
If planes can go faster, why don't airlines fly faster? I came across this page where a DC-8 set a record in 1964 for a 12h24m flight from Montreal to Tokyo. Last year I flew to Tokyo from Montreal and it took 9h from Vancouver (where I had a layover) I suspect the answer is along the lines of "for safety reasons", but surely in the 5 decades since that record airplane design and safety protocols have improved such that today's planes can fly faster and safer. Am I mistaken in that airlines today don't fly at the fastest the airplanes can ? If so why not ? <Q> The key issue that determines the aircraft speed is economics. <S> Airlines fly the aircraft that make most sense economically- <S> which is rarely, if ever, the fastest speed possible (more speed equals more drag usually, which reduces fuel economy). <S> The top speed of the (subsonic) aircraft has changed only a little in the past few decades- <S> most developments have been geared up towards improving fuel efficiency, not increasing speed (speed alone doesn't make economic sense to airlines; look at what happened to Concorde). <S> There is another issue here- <S> most of the passenger aircraft fly in high subsonic (transonic) regime. <S> As a result, the airliners are flown below the drag divergence mach number , beyond which the drag increases rapidly. <S> This limits the aircraft speed. <S> As a related point, due to the high altitudes at which the aircraft are flown is that there is little speed range to chose from between the stall speed (lowest speed possible) and critical mach number (highest speed possible beyond which flow separates due to local supersonic flow). <S> This limits the practical options available to the pilot. <A> It costs lots of fuel, and hence money. <S> Drag scales with the square of velocity, and you have to overcome drag with thrust. <S> Moreover, currently airliners fly just below the transonic range, where the drag increases much faster. <S> In addition, to carry the extra fuel that is needed to be faster towards the end of the journey, you have to carry additional extra fuel during the early portion of the flight. <S> Are you willing to pay for all that extra fuel, just to slightly reduce the flight time? <S> Are there enough people that want to pay that and can afford it, so that the airliners will not fly empty? <A> The record was set on the return flight. <S> This will be faster as the plane will be flying in tailwind , increasing its ground speed. <S> Nowadays Tokyo to Vancouver (7h57) plus Vancouver to Montreal (4h11) totals 12h8m, it beats the record despite having to take off twice, change to a slower plane, and fly at least 430 NM more than a direct flight. <S> (gcmap.com) <A> We've previously had this discussion with the reason Concorde is no longer in service. <S> The basics: Design complexity increases with speed and heat, driving up costs. <S> Government regulators won't allow for supersonic flight over land, engine efficiency limits range to approximately 4000 NM, so Pacific routes are limited and all SSTs (Super Sonic Transports) so far have been commercial disasters requiring considerable government subsidies to keep them operational.
|
More fuel efficient the aircraft is, better the range/passenger capacity, making airlines more money.
|
Why does the Piper Cherokee (PA-28-140) engine have such low horsepower despite the very large displacement? I'm sure this question could apply to many other plane engines, but specifically I'm looking at the Piper Cherokee PA-28-140. Surprisingly, it appears that the engine used, the Lycoming O-320 , has ~320 cubic inches of displacement but only puts out 150hp. When comparing the horsepower per cubic inch of displacement (CID), the ratio is quite low. We have the technology (and already used it in vehicles in the 50's, 60's etc.) to achieve a better efficiency than that. Why is this engine (and perhaps other models) so inefficient? <Q> Aviation engines run at near max RPM through out the flight. <S> A car on the other hand doesn't use the full RPM spectrum except in bursts. <S> 1 <S> If a car engine was utilized the same way an aviation engine is, it won't last long. <S> So an aviation engine is sturdier , heavier, and weaker (hp) for the same displacement, but also provides higher torque (big cylinders). <S> 2 <S> Formula One engines have small displacement, very light weight, yet deliver near a 1,000 hp. <S> But they don't last long either. <S> Something like 15 hours of racing and practice sessions. <S> Further reading: Do Car Engines Make Good Airplane Engines? <S> 1 <S> Piston planes run at near max RPM because they don't have and don't need gearboxes . <S> 2 <S> Same era <S> alloys and technology. <A> One reason is not so much <S> can you build a reciprocating engine with higher horsepower or better efficiency , but can it do so with a very high reliability for extended periods . <S> Most automobile engines are run on average at 20% power with very brief higher power outputs whereas aircraft engines are routinely operated at 65-85% power and are expected to have a mean time between overhauls of around 2000 hours at these power settings. <S> To accomplish this, most aviation engines operate at slower speeds and much greater displacements than traditional automobile engines do. <A> A modern aircraft propeller must be designed so that the tip speed is less than supersonic so as to avoid issues with noise and performance. <S> Most small plane propellers are about 6 feet in diameter and are thus limited to about 2700 RPM. <S> The engine designer may thus connect the crankshaft directly to the propeller and limit engine speed to about 2700 rpm, or use an intermediate gearbox to allow higher crankshaft speeds. <S> As a result, a high-speed engine plus robust gearbox is often not worth the extra complexity as compared to a simpler direct drive solution. <S> (see "Continental Tiara" and "Porsche PFM 3200") <S> Of course, as engine power is proportional to the product of the torque and speed of rotation, the slower turning engine produces less power for a given displacement. <S> But experience has shown that slower-turning direct drive units are often as light and more durable for a given power output when compared to geared units. <A> RPM, RPM, RPM. <S> If you want 1,000 HP out of 1.5L, you run it as 10,000 rpm. <S> An earlier poster referenced prop tip speeds being a limiting factor - true. <S> However, there are geared aircraft engines which permit the engine to run at higher RPM without overspeeding the prop. <S> These are the same displacement as their non-geared brethren but make more horsepower for the simple reason that they are burning more fuel/air and making more heat. <S> They are also more expensive to maintain and are seen on larger twins where they remain cheaper than adding another engine. <S> Not related directly to horsepower, but the design of A/C engines have a greater bore to stroke ratio then auto engines - typically 4:3 while auto engines are closer to square or with even longer stroke.
|
Because the propeller has very high rotational inertia and wants to turn at a constant speed while the engine supplies power in a few pulses during each revolution, the wear and tear on a gearbox may be quite extreme.
|
Can a light glider without thermal protection land from the orbit, starting from the orbital speed? I ask about a glider without any special thermal protection (pilot in the space suit), so both answers to the other question do not cover the topic. When the glider enters the atmosphere, it starts generating lift. Could this lift keep the glider high enough, in low density air, and this way prevent the heat damage? The glider then would fly a long distance, losing speed and altitude slowly, until reaching speed and elevation at which it can safely land. Seems that lots of lift could be generated at speed and air density where the metal burns already. Is there any analysis ever been done if such landing is possible? <Q> No. <S> The stagnation point temperature goes up with the square of true air speed. <S> Temperature dissipation is proportional to true air speed and density. <S> Lift is proportional to the square of airspeed and density. <S> The lower wing loading of a glider (compared to the Shuttle, for example) means that all of the reentry will be slower, but that is not necessarily an advantage. <S> Note that the Shuttle needed external cooling to prevent heat stored in the heat shield to dissipate into the Shuttle's structure. <S> If the glider flies a longer reentry, it will be closer to thermal equilibrium. <S> Also, the aerodynamic shape of a glider is a disadvantage here because the lowest heat load is possible with a blunt object - this is why reentry vehicles look like they do. <S> Just to give you an idea what temperatures are involved: <S> If we express speed as Mach number, a typical reentry speed would be Mach 25. <S> This makes the reentry temperature at the stagnation point $$T_s <S> = <S> T_{\infty}\cdot \left(1 + \frac{\gamma-1}{2}\cdot Ma^2 \right) <S> = <S> 126\cdot <S> T_{\infty}$$at Mach 25. <S> If we assume 195K at the edge of space , this comes out to 24,570K - theoretically, because ionization effects will cause the eventual temperature to be lower and the ratio of specific heats <S> $\gamma = c_p <S> / <S> c_v$ is no longer constant. <S> To calculate the real value needs a non-equilibrium gas model since the nose radius of typical glider wings and tail surfaces is in the order of one centimeter. <S> The distance between the detached shock wave and the structure is too small for the gas molecules to reach equilibrium. <S> On the other hand, the epoxy resins used in glider construction cure at room temperature first and are then tempered at about 60°C. <S> The glass transition temperature <S> $\text{T}_g$ of such resins is at best a couple of degrees above the curing temperature. <S> $\text{T}_g$ marks the onset of weakening of the composite matrix, and heating the glider above <S> it will permanently damage it. <S> Given that the glider will stay for dozens of minutes in air of a temperature of several thousand degrees and has no thermal protection will make sure that all which reaches the ground is a charred lump of material. <A> Remember that temperature of a gas is related to the speed of its molecules. <S> When the molecules hit an object moving 25000 feet per second and bounce, that gives them a temperature of many, many thousands of degrees (C or F). <S> A balsa object would char and be destroyed. <S> A glider would have to be designed to have good lift to drag at Mach 22+, not a minor trick. <S> And when it loses only 30% of its speed, it will need to support half its weight as it will no longer have orbital speed. <S> That equates to significant lift, thus significant drag and since power is speed times force, very large dissipated power that will appear as heating. <S> So, sorry, but heat shielding is necessary to prevent thermal destruction. <A> Yes. <S> With enough wing span-to-weight ratio it should be able to shed the speed in the most upper atmosphere, skipping without losing altitude for considerably longer than it would take the space shuttle to shed speed. <S> Would a balloon pop if the entry was shallow enough? <S> With a pressure of .00001 <S> atmosphere <S> no one has tried it; yes <S> it is just possible. <S> Getting it to orbit would be impossible, but constructing it in space for entry is possible. <S> This was the closest picture to what I am talking about showing that there is a material capable of withstanding entry faster than orbital speeds. <S> The one I am thinking of would be much bigger and wing shaped and can land without a parachute like a stalled landing. <S> It would not need parachutes or retrorockets because of the surface-to-weight ratio. <S> https://www.newscientist.com/article/dn10288-inflatable-cushions-to-act-as-spacecraft-heat-shields/
|
A wing shaped blimp that weighs much lighter than air at ground level should work.
|
How do manufacturers/kit providers determine Vne? Vne defines the maximum indicated airspeed which should not be exceeded . And clearly, doing so would result in "bad things" happening like flutter, etc. Presumably manufacturers do some sort of design work to determine likely Vne but how do they test for that? Exceeding Vne would put the aircraft into a structural failure situation would it not? <Q> $V_{ne}$ is typically set to about 90% of $V_D$, the maximum design dive speed. <S> This difference provides a safety margin. <S> Above $V_D$, damage may occur due to flutter or structural failure, or <S> controllability considerations may make the aircraft unflyable. <S> The aircraft is not guaranteed to fall apart at $V_D$ due to additional structural and manufacturing margins. <S> During flight test, the aircraft is flown above $V_{ne}$, up to, or close to, $V_D$. Appropriate safety precautions are taken, e.g. parachute. <S> Any failure below $V_D$ indicates a design or manufacturing issue that must be resolved prior to certification. <S> The limitation to flight below $V_{ne}$ (as opposed to $V_D$) during regular operations provides protection against airspeed measurement errors, pilot errors and some margin against structural degradation over the lifetime of the aircraft. <A> It is exactly as pericynthion says. <S> VD is one of the so called design speeds defined at design time. <S> Many of the structural/aeroelastic characteristics have to be demonstrated at speeds up to VD during flight test. <S> However VD is for certification flight testing only. <S> Normal operation is limited to VNE. <S> However VNE is for light aircraft only. <S> Larger aircraft have VMO instead. <A> The generic answer is: Design Cruising Speed (Vc) = <S> 33 <S> * Sqrt (wing loading) <S> Design Dive Speed (Vd <S> ) = 1.4 <S> * <S> Vc <S> Never Exceed Speed (Vne) <S> = <S> 0.9 <S> * <S> Vd <S> Then empiric testing (wind tunnel or test pilot) is done to test and expand those. <S> Actual formulas are in the F.A.R. <S> FAR/ <S> JAR-23 and <S> a reference page with this question answered is in this forum .
|
Military and advanced civil design does finite analysis based on the material properties in a computer simulation to calculate failure at stress points based on the materials used and predict flutter but that's beyond any simple answer and in industry is done by entire teams of individuals.
|
Could a pick up truck save a plane with failed landing gear? I recently saw this fictionalized video. While it's not real, I do wonder if this could be possible, even if not the best way to handle the situation. <Q> For the Boeing 727 that you see there, that whole procedure is impossible with a pickup truck. <S> Given that the 727 is operating at its Operating Empty Weight, 102,900 lb OEW for the 727-200 advanced, and the force on the nose gear is somewhere around 10% at rest, that would put it way over the limit for that particular truck model (Nissan Frontier at 4,690 to 5,816 lbs GVWR ). <S> That would be even less pretty for the truck since the force at touchdown on the nosegear should be higher. <S> Also, according to this thread , the maximum speed for that truck is about 95 mph. <S> Assuming that this Yahoo Answers is correct, the landing speed of a 727 is 130 to 150 knots (150 to 170 mph). <S> This is way greater than the speed of any pickup truck. <S> I had to make a response like this some time ago as well to the exact same video someone had a question about. <S> However, you could land a GA plane on a pickup truck if you had the right equipment. <S> Nitpick on the video: if the plane's nose gear didn't deploy all the way, then truck or no truck, it should have collapsed on impact. <A> Depends. <S> A large aircraft, no. <S> A jetliner weighs well over 50,000 lbs on landing and wouldn't even fit on a flatbed. <S> CGI films like '405' are spectacular but unrealistic. <S> Now it is possible for a light airplane to do this, or potentially land the whole airplane on a moving truck with a very skilled pilot in the cockpit. <S> A friend of mine in Alabama does an air show act with this kind of stunt using a piper cub. <S> See 13:00 into the video. <S> Granted Greg is a very senior air show pilot with more combined flight time than anyone reading this and the average GA pilot will probably not have the skill to pull this off successfully. <S> Landing gear problems, especially problems extending the nose wheel seem pretty hair raising but can usually resolve with a belly landing and relatively minor damage as demonstrated by this A320 making an emergency landing at LAX in 2005 after the nose wheel steering failed. <S> Even a complete failure to the landing gear to extend can be remedied with a belly landing on a smooth, long runway without nearby obstacles. <S> The jet will touch down most likely on the tail and engine nacelles, making the rupture of the wing box and fuel spillage and fire relatively low. <S> This is aided by crash and fire crews at the ready to foam down the airplane after it has stopped to keep the risk of an ignition source to a minimum. <A> But in some cases yes . <S> In that case the gear was not collapsed but since the relative speed of the truck and plane were the same it really does not matter if there was landing gear there other than to provide prop clearence . <S> You could of course attempt a maneuver like this . <A> I personally saw a truck - which had mattresses on the bed - accept the nose of a high wing twin engine turboprop with nose gear stuck up during landing and without incident! <S> This happened one afternoon at Anchorage International Airport and many years ago! <S> It was bigger than an Aerocommander but smaller than the commuter turboprops! <S> The Anchorage tower might have a record of the incident?
|
It depends on the size of the plane.
|
Has there ever been a fully automated takeoff, cruise, and landing of a large aircraft similar to commercial airliners? Has there ever been a fully automated takeoff, cruise, and landing of a large aircraft similar to commercial airliners? In fact, has there ever been a fully automatic flight of any pure aircraft whatsoever? This is gonna sound crazy, but the only thing I know that comes close is the Soviet Space Shuttle Buran. It launched unmanned and returned successfully under computer control, including its glide and landing. So I'm interested in automatic aircraft similar to large commercial airlines. BTW, remote control toy planes wouldn't count because that is not automated (a person is manually controlling it). <Q> The book The Glass Cage describes a fully autopilot-controlled military test flight in 1947. <S> The plane was a C-54 Skymaster with seven men aboard. <S> According to this source, the pilot aligned the plane on the runway for takeoff, but the takeoff, course control, and landing were performed by autopilot with no human engagement. <S> See also this report from the Chicago Tribune at the time. <A> Fully autonomous flights have been demonstrated- <S> but not not in 'large commercial' aircraft. <S> The Dassault Aviation AVE-D 'Petit_Duc' drone has demonstrated fully autonomous flight : <S> The flight, watched by representatives of France's Délégation Générale pour l'Armement (DGA) armaments procurement agency, comprised a completely automated sequence: roll from parking spot, runway alignment, takeoff, in-flight maneuvers, landing, braking and rolling back to the parking apron. <S> Helicopters also have demonstrated this ability. <S> this time, the helicopter did it entirely on its own — with no humans involved. <S> It was the first fully autonomous flight of a full-sized chopper, ever. <S> Unmanned Little bird, image from <S> wired.com <S> Note <S> : I've considered only those where it is explicitly mentioned that 'full' flight was autonomous. <S> Not the capability alone. <A> Not as big as a commercial airliner (but bigger than many people realise), at the time of its introduction into the USAF, Global Hawk flew from Edwards Air Base in California to Australia without any human control (including takeoff and landing). <S> Following incidents like 9/11 and GermanWings, it would be sensible to introduce a feature into all passenger airliners now to automatically land at the nearest airport - and once the feature had been invoked, it could not be revoked. <S> Better yet, largely remove most of the pilot's work. <A> There is no current aircraft capable of fully automated flight in all stages of flight as equipped and operated according to the POH. <S> The closest you can get is from climb out to landing. <S> Currently you could fly the takeoff and activate the auto pilot once established on climb out (probably some time after the gear came up or around then). <S> Let the FMS fly the plane, then setup the auto-land to take it home. <S> But you still need to get it off the ground. <S> There are various ways to guide a plane in flight via automated systems. <S> Most modern airliners contain an FMS unit capable of using a variety of navigation methods and control of steering. <S> Smaller planes that don't utilize an FMS may have GPSS (GPS Steering) . <S> GPS Steering is becoming more common on smaller planes from what I have seen. <S> Auto-land capabilities have been around for some time, one of the earliest planes to have it was the Concorde . <S> There are many airframes that now contain auto-land capabilities <S> but they are not utilized all the time . <S> It should be noted that all of these things need to be programed by the pilot before the flight. <S> Any deviations by ATC while in route would also need to be programed.
|
A Boeing-modified MD530F helicopter has demonstrated fully autonomous flight : ...
|
Does a headwind affect the climb gradient? When studying for my German PPL exam, I came across this question: For those that do not speak German I'll try to translate the question, but bear with me as it is kinda picky what I'm trying to get across here: During flight on a straight track with constant speed headwind will increase the gradient of climb headwind will decrease the gradient of climb headwind will increase the distance needed to descent 50m headwind does not affect the gradient of climb at all As you can see answer 4 is supposed to be the correct one. I disagree, so I started searching for a reason, yet I couldn't find anything useful. Let me explain my train of thoughts: I didn't really know the "gradient of climb", I always used the two terms "angle of climb" and "rate of climb". Thus I'm trying to figure out which one the gradient of climb is. Common sense makes me think it is the same as the angle of climb (gradient does just sound like an angle). This opinion is supported by SIDs, which have a PDG (Procedure Design Gradient) that is given in percent, just like the gradient of climb. Assuming the gradient of climb is indeed the same as the angle of climb, the only way for the "correct" answer to be confirmed is by taking the distance traveled during the climb relative to the air, not to the ground (angle of climb is defined as the height gained divided by the horizontal distance traveled in a certain amount of time). This would mean that it is used with IAS, rather than GS, which in my opinion absolutely makes no sense ("Hey look, that mountain is 10NM away, we are climbing with 600 ft/min. and going 100 KIAS and need 3500ft more to go over the top, we're all good!" - Well, add a tailwind of 25kts, the pilot would still think he's good to go but it'd result in CFIT...). The question I have is: How is answer 4 the correct one? <Q> The gradient of climb is the ratio of the increase of altitude to horizontal distance through the air, not over the ground. <S> The definition used by the UK CAA in CAP 698 is: Climb Gradient <S> The ratio, in the same units of measurement, expressed as a percentage, as obtained from the formula: - $$\text{Gradient} = <S> \frac{\text{Change in Height}}{\text{Horizontal Distance}} \times <S> 100 \% <S> $$ <S> Climb gradient is not the same as rate of climb, although they are related. <S> Rate of climb is altitude over a period of time, gradient is climb over distance travelled. <S> There is another question which covers the difference in more detail. <A> I could not find a technical definition for Gradient of Climb. <S> But from the FAA's Pilot Handbook the closest thing is Angle of Climb (AOC). <S> How it differs from a jet to a prop, and that TAS and Thrust Excess (T E ) are the only factors. <S> Wind is not a factor. <S> The text mentions flight path, which is the result of Angle of Attack and TAS. <S> AOC is a comparison of altitude gained relative to distance traveled. <S> AOC is the inclination (angle) of the flight path. <S> Achieving the maximum AOC (TAS at the T E , i.e., V y ) will ensure the aircraft is at its steepest flight path. <S> Any headwind then is a bonus. <S> Wind does not change the maximum attainable AOC. <S> With the pilot the frame of reference, a headwind slows down the flight (it takes longer to reach the obstacle), but the AOC remains the same: <S> The same idea is used for descents and working out the top of descent. <S> Good luck! <A> Climb Gradient IS affected by the wind component along the flight track. <S> Rate of Climb is not. <S> The gradient changes with the wind because wind affects your ground speed, and gradient is basically (rate of climb)/(ground speed). <S> Rate of Climb and Ground Speed expressed in the same units, of course.
|
If you have a headwind or a tailwind it makes no difference to your climb gradient because your airplane is moving relative to the air mass.
|
Why does flight duration differ for the same flight? I was checking the flight duration between two places over a 2-3 month period. The flight duration for the same flight is different for different months. For example, some days the flight takes 13 hrs 10 minutes and some other days it's 12 hrs over the same distance. How does this happen? Moreover, this data is available long before the departure of the flight; I am curious to know the reason. What are the factors that decide this? <Q> Several possible reasons: different equipment (not every aircraft flies at the same speed) different routing known seasonal changes in high altitude winds (which can prompt routing changes) <S> extra time built in in some periods for historically experienced frequent delays during those periods (e.g. in summer when a lot of inexperienced travelers with small children are expected, boarding and deplaning tends to take longer than in spring and autumn when there's more business travel). <S> I'm sure there are other reasons as well. <A> I'll expand on the other answers here. <S> Wind: <S> The biggest factor in this is wind. <S> Winds at common cruising altitude can sometimes reach well into the 100 Knot spectrum. <S> Keep in mind that this can be in any direction. <S> So lets say a long haul flight has a 100 Knot headwind half the year and a 100 Knot tail wind for the other half. <S> That's a 200 Knot ground speed difference which can really make an impact on flight time. <S> ATC Holds Vary : <S> ATC for various reasons may put a plane into a holding pattern on arrival. <S> This may add to the time spent in the air for a given flight depending on the hold. <S> Landing Slots: <S> There are 5 high density airports here in the US (and presumably others elsewhere) that require planed ahead landing slots. <S> If the slot time changes but the departure time remains the same an airline may chose to slow the plane a bit (or speed it up a bit) to compensate. <S> Since not every flight on a given route is loaded equally there may be efficiency gained or lost as a result of loading. <A> I was hoping for a specific example, but based on your statement that some days the flight takes 13 hrs 10 minutes and some other days it's 12 hrs over the same distance <S> I suspect that you are determining the flight duration from the published schedules available to the public, that use local times for arrivals and departures, thus I would like to add a possible alternative to the ones proposed in the other answers: <S> Daylight Saving Time : different countries enter/leave (if they use it) <S> DST in different dates. <S> Example: the US and the UK change to DST 2 weeks apart, having a difference of only 4 hours between New York and London in that period, while normally they have 5.
|
Aircraft Loading: Aircraft efficiency (and subsequently speed) will vary a bit with the loading of the aircraft.
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.