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Why does the U.S. have so many general-aviation aircraft? In a comment on my previous question about the paucity of South Korean general-aviation aircraft in the 1990s, @Pondlife pointed out (in response to my comparison between the numbers of GA aircraft per capita in South Korea and the United States) that, in their words : Considering that just over 50% of the world's GA aircraft are in the US perhaps you should be asking why the US has so many, rather than why South Korea has so few? :-) Why does the U.S. have such an extreme abundance of general-aviation aircraft (210,000 out of the total world population of 416,000 GA aircraft in 2016, according to the provided link), amounting to one GA aircraft for every 1,540 U.S. citizens (a per-capita abundance more than ten times the global average of one GA aircraft per 17,950 humans)? <Q> Part of the reason is also historical. <S> After World War II was over there was a large number of veterans with flying experience returning to a country that suddenly had a massive surplus of small trainer aircraft. <S> While the US expended huge amounts of resources on World War II, it was largely untouched by the destruction that many other countries suffered. <S> This meant that instead of having to rebuild, the US could focus on growing the economy. <S> Though GA declined in the Great Depression and was suspended during World War II, there had been a similar situation after World War I that had gotten the industry started. <S> Small aircraft were much simpler then, with a much lower cost to build and certify. <S> This made general aviation relatively much cheaper. <S> Also, while the US certainly had a highway system, the interstate highway system had yet to be built. <S> Commercial aviation service was not nearly at the scale it is today and was still fairly expensive. <S> This made general aviation a much more reasonable option for traveling around a large country. <A> It is said that airplanes fly because of money and the Bernoulli effect, in that order. <S> So the first cause is simply that there's a lot of wealth in the USA to support what is essentially a rich person's hobby. <S> There are also a lot of airplanes still flying that were built during the boom years of aviation to support interest in the novelty of plane ownership (which is much less a novelty today), which tends to hold down the purchase price of a small plane. <A> Combination of two factors Wealth, particularly long term. <S> A large number of general aviation aircraft flying today are quite old 70's and 80's equipment makes up a large portion of the market and even 40's and 50's equipment can be found easily. <S> Area and population density. <S> Europe and the Asian Pacific are densely populated areas. <S> Cities are close to one another meaning commute times are short and airspace is highly regulated (those airports are close together as well). <S> This makes it harder to fly and leaves less incentive as one is less likely to have a particular route in mind. <S> The only a few wealthy countries have large amounts of land, Australia, Canada, and the USA.
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The USA is a wealthy country that has been that way since the invention of flight. In addition, gasoline is much less expensive here than in western Europe so the operating costs will be lower.
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Has there ever been an airliner design involving reducing generator load by installing solar panels? Has there ever been a trial/project/design, in which solar panels were incorporated in the design of a commerical airliner (e.g. on the wings), with the aim to reduce fuel consumption by lowering the generator workload? If no, why not? <Q> If no, why not? <S> While I can't say categorically that it's not happened, I'm pretty sure. <S> Solar radiance is approx. <S> 1kW/m^2. <S> A 737 has approximately 100m^2 wing area . <S> Solar cells are approximately 20% effective . <S> If you covered the entire wings in solar panels, that would work out to 20kW of electrical power at best. <S> At night, it would be close to zero extra power. <S> Jet fuel contains <S> ~43MJ/kg of energy. <S> 20kW is 20kJ/s. <S> For a 2 hour flight, the total energy produced would be 144MJ, or comparable to energy in 3-4 kilograms of jet fuel. <S> Turbines is not 100% efficient, so let's say that with all losses in engine, 25% of the power in the fuel is available as electricity. <S> That means you'd need 12kg of fuel to provide the same amount of electricity as the solar panels. <S> 12kg of fuel. <S> That's probably far less than the solar cells will weigh, probably by a factor of at least ten. <S> In addition, the you don't have to carry around already burnt fuel, unlike solar cells, which you will have to carry around. <S> Edit: I found another answer on this site, that claims extra fuel use is on the order of 0.125kg/kWh. <S> I don't know if that's correct or not, nor do I really care. <S> It doesn't change the conclusion, it only makes jet fuel even more favorable. <S> In short the amount of power provided by solar cells is tiny compared to the energy contained in jet fuel. <S> And that doesn't even touch on the mechanical requirements of a wing... <A> No, there are several reasons: <S> Fragility v <S> Efficiency v Weight: <S> the most efficient solar panels are rigid and heavy, which is bad for a wing structure. <S> Flexible and light panels do exist, but they are half the efficiency. <S> They also have limitations to how much flexing they really can take, the constant flexing of a wing, vibrations, cycles between hot and extreme cold at altitude all make it a punishing environment for that kind of technology. <S> Covering the fuselage would mean less flexing, but then you'd only have a few panels positioned right at any one time to create electricity <S> Weight: <S> In addition to the weight of the panels themselves you have all the other technology to make them work, like regulators, power conditioners, power storage, delivery wiring <S> Complexity: This is yet another system to maintain, and it would be complicated to do so. <S> If a panel breaks you'd have to take apart the wing to get at it <S> Cost: you'd need solar panels that are efficient, flexible, durable and light. <S> That all adds up to expensive panels, far more than is worth it <S> Limited window of use <S> : Obviously solar panels are no good at night, but they are also only generate electricity when they are oriented at least partly towards the sun. <S> If you're going to cover the wing then the sun must be a good 30-40 <S> ° up before you'll get appreciable power from them <S> So it's a lot of weight and cost for a technology that isn't going to generate power for much of the time the airplane is in use. <A> Not purely on topic <S> but there is a solar airplane. <S> Also it would have to be economically feasible to even be considered. <S> Here's an article from 2016 about a solar airplane that traveled the globe. <S> https://www.theguardian.com/environment/2016/jul/26/solar-impulse-plane-makes-history-completing-round-the-world-trip <A> I once worked for a company that made electronics for commercial aircraft (flight deck printers, Ethernet switches, digital chart recorders). <S> In addition to what others have mentioned on this thread, you also have to account for the fact that if a product is manufactured for aircraft in the US, it must comply AS9100 and FAR, and whatever standard the EU is using nowadays. <S> This includes rigorous testing to ensure that, not only is the device safe, but also that the device will not interfere with any of the critical systems of the aircraft. <A> One consideration that makes solar aircraft less feasible is that the figure of 1kw/m2 is for sunlight striking the solar panel square on - i.e. perpendicular to the panel. <S> Unless you're flying in the tropics at noon, an aircraft's wings won't meet that. <S> Their insolation (the amount of power from sunlight) drops with the cosine of the angle from vertical incidence. <S> Regarding doubling 747 wingspan for two seats - how many passengers will settle for a 45 MPH / 39 knot / 72 kph flight speed (i.e. New York to London in 77 hours if no headwind)?
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Solar supported airliner isn't out of the realm of possibilities, just solar tech isn't there yet.
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What is the meaning of "Steer 1-2-0" in WWII texts? I am reading some texts about WWII and English operators tell the pilots to "Steer 1-2-0". Can anyone help with the meaning of 'steer' here? Is it a synonym of 'direction', 'heading' or 'vector'? <Q> To "steer" means to change the aircraft's track (the direction of movement of the aircraft) to a certain degree in relation to the lines of meridian (north–south lines). <S> The units are degrees from north in a clockwise direction. <S> North is 0°, east is 90°, south is 180°, and west is 270°. <S> Note that, due to wind forces, track is not the same as the heading (where the nose is pointing). <A> Yes. ' <S> Source: <S> reading lots of books on WW2. <S> The term is still in use on ships , not so much in aviation any more. <A> The modern ATC phraseology is "Fly heading 1-2-0".
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to steer ' = 'to change course to', and the number is a compass heading.
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What is the offset in a seaplane's hull? I noticed there is a little offset in a seaplane's hull (highlighted in the following picture). I suppose this is useful as it exists in all the seaplanes I know. It appears to be neither a hydrodynamic nor aerodynamic feature. I could not find clue by myself as I don't know this feature's name. My question, what is its name and purpose? ( wikimedia.org ) <Q> Without it, you'd have to fight against the buoyancy of the rear end of the hull when you rotate for takeoff. <S> However, a seaplane float or hull must be designed to permit the seaplane to be rotated or pitched up to increase the wing's angle of attack and gain the most lift for takeoffs and landings. <S> Thus, the underside of the float or hull has a sudden break in its longitudinal lines at the approximate point around which the seaplane rotates into the lift off attitude. <S> This break, called a "step," also provides a means of interrupting the capillary or adhesive properties of the water. <S> The water can then flow freely behind the step, resulting in minimum surface friction so the seaplane can lift out of the water. <S> The steps are located slightly behind the airplane's centre of gravity, approximately at the point where the main wheels of a landplane are located. <S> If the steps were located to[o] far aft or forward of this point, it would be difficult, if not impossible, to rotate the airplane into a pitch-up attitude prior to planing (rising partly out of the water while moving at high speed) or lift off. <S> Although steps are necessary, the sharp break along the float's or hull's underside causes structural stress concentration, and in flight produces considerable drag because of the eddying turbulence it creates in the airflow. <A> It's called a hull step. <S> Below is with and without: <S> It reduces water drag. <S> As the plane gains speed and the aft body is lifted, only the forward hull will be in contact with the water. <S> Source: <S> Laté 631 Replica - Chapter 3 - Hydrodynamics <A> As everybody has said, it's called a 'step'. <S> But it's nothing to do with buoyancy <S> , it's to do with the opposite effect - water suction. <S> Without the step you will never get the airplane off the water simply due to the suction of the water clinging onto the airplane. <S> The step forces a break in the water-suction, in the case of the Catalina above probably halving it, which then allows the lift of the airplane to overpower the remaining water suction. <A> Landing and taking off is done on the step. <S> During the takeoff, the aircraft is rotated forward until it is planing on the float or hull portion forward of the step; less surface is in contact with the water. <S> A notable increase in acceleration can be felt as the aircraft rises and rotates onto the step, and then a further slingshot effect felt as the remaining drag ends as the float or hull separates entirely from the water. <S> Land is the reverse; the landing is made on the step, or the section of the float or hull forward of the step; high speed water taxi is done "on the step," and low speed taxi is done by reducing power until the aircraft sinks deeper into the water in a condition known as "plowing." <S> The step is a hydrodynamic feature which causes a break in laminar flow along the float or hull; with an adequate increase in speed this serves to decrease drag along the portion of the hull or float aft of the step. <S> For simplicity when flying seaplanes, operation on the forward area is simply referred to as "on the step."
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That's called the step .
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Do airline pilots ever risk not hearing communication directed to them specifically, from traffic controllers? I gather pilots communicate regularly with air traffic controllers within air traffic controllers' jurisdiction or airspace as they enter the space, during their time in that space and as they leave. In some or most instances, they will not land in that air space, they are simply passing through and may encounter lots and lots of regional and international air traffic. They are routinely directed by air traffic controllers to fly at a certain direction, increase or decrease altitude for safety in order to avoid collisions and accidents. In most instances, auto pilot is engaged and I assume the headphones come off, for flights longer than say 2 hours or even 1 hour. Speaker phone may be on but pilots can read a book or watch a movie on their laptop or revise their reading on knowledge of their ever changing craft. At a certain frequency. I gather lots of communication to planes occurs and listening to all of them can become tedious and may require too much concentration. In this light, do airline pilots ever risk not hearing communication directed to them specifically, from traffic controllers of space they are flying past on cruise? Does a light or sound or siren switch on when a message is directed at them and I assume they differentiate communication directed at them by their call sign, e.g., American Airlines Flight 200. Is there a risk they might not hear it and how is that risk mitigated? <Q> There is a ton of radio communication during the taxi, takeoff and departure phases, and then again during the arrival, landing and taxi phases. <S> Pilots are generally very busy at these times and 100% focused. <S> Airlines have two pilots, and one will be flying while the other works the radios and monitors various instruments. <S> Cruise is another matter. <S> There generally isn't a lot to do other than keep an eye on the autopilot. <S> The pilots will take turns eating, resting, going to the lav, etc. <S> Radio work usually involves little more than getting handed from one frequency to the next. <S> They may get rerouted due to traffic or weather, but it only takes a few seconds to update the autopilot. <S> Either way, pilots do occasionally miss radio calls. <S> So does ATC for that matter. <S> It's common enough that nobody gets worried about once or twice, though it's annoying. <S> If it's a real radio problem, there are procedures for both sides to follow to keep everyone safe. <S> There (usually) isn't any sort of light or tone when someone is calling you. <S> However, the standard format is "called station, calling station, message", so with a little training, your brain can quickly tell whether the message is for you. <S> If so, it "tunes in" and you consciously hear the message; if not, it "tunes out" and the message is just background noise. <A> When a pilot is given instructions, clearances etc. <S> from a controller, the pilot has to acknowledge they've heard it and certain items need to be read back to the controller. <S> If the controller doesn't hear anything they will repeat their message and keep trying to contact the aircraft. <S> The rules for UK readbacks are included in a CAA document CAP413 , along with other conventions and standards for communication between flight radio telephony stations <S> It's not that uncommon, these days, for fighter aircraft to be scrambled to intercept unresponsive aircraft <S> There is less communication that you'd expect once you've made contact with a controller and been given your clearances. <S> It isn't an onerous task to listen in to all the chat and respond when you hear your callsign <A> For example, in small aircraft normally the pilot will often hear nothing from ATCC unless they have specifically requested flight following. <S> Small VFR aircraft usually fly with a 1200 transponder code which is generic, and in that case it is tricky for an ATCC to even contact the plane at all. <S> For larger aircraft, usually a separation is guaranteed from instructions at the beginning of flight and contact <S> is only necessary if something changes, so your guess that they talk to the pilots "regularly" is not really correct. <S> Note that most commercial aircraft monitor 121.5 in addition to their assigned frequency and an ATCC will always try that if they are getting no response on an assigned frequency. <S> So, big planes have to screw up twice to go incommunicado completely. <S> If an aircraft is unresponsive, then what happens depends on a lot of different factors. <S> The bigger the aircraft, the more actively ATC will react. <S> If it is a small aircraft on IFR, then ATC will assume the pilot is on the wrong frequency and just steer other aircraft around them. <S> If that causes a big problem, the offending pilot will get written up. <S> Usually the pilot will figure out he is out of contact once he gets closer to civilization. <S> If it is a heavy, ATC will make repeated attempts to contact and do the same thing as with a smaller plane: steer others around them. <S> If the heavy is unresponsive and deviates from its flight plan or remains unresponsive for a long time, then fighter aircraft will be scrambled to intercept and observe them. <S> By "they" I mean the captain and first officer.
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Normally pilots do not communicate much with ATCC between airports. Obviously, if a commercial crew with a lot of passengers goes unresponsive for so long that it requires an intercept, they are going to get in trouble.
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Why isn't airport relocation done gradually? Recently Istanbul airport (IST) was relocated from Atatürk over 2 days. Munich Franz Josef Strauss (MUC) was also moved overnight from Munich Riem . Doesn't it cause chaos, since most employees are new to the place and equipment, work procedures are not well established? E.g. some people do not have badges with correct security clearance. Why not do it gradually over longer time? Move airline by airline -- smaller first, bigger later. <Q> Gradual relocation essentially mean having to staff and equip nearly two full airports during the transition period. <S> It is also annoying for the travelers that want to transfer planes and need to relocate to the other airport. <S> They would then need to get transported to or from the new location and through security again unless a small short hop flight is established during the transition. <S> In IST's case it's 35 km distance between the old and new location. <S> Having two busy airports close to each other is also a bigger challenge for air traffic control than a really busy one and a calm one. <S> The solution to the issues you mention can be solved by thorough preparation. <S> Like making sure all the old badges work (or having the new ones passed out as they come in for their first day at the new location), make sure everyone knows where they need to report for work in the new location. <S> Perhaps having some extra trouble shooters on hand to fix teething issues. <A> Moving airline by airline doesn't help that much: <S> You still have the same chaos, just on a per-airline basis. <S> The airports you mention are dominated by large carriers that have turned them into hubs (Turkish Airlines and Lufthansa). <S> Even if you move all the other airlines one by one, you still have much of the pain of the big move when you move the largest airline. <S> And it has disadvantages: <S> Connections: <S> A large percentage of traffic through these hub airports are connecting passengers, and thanks to airline alliances and partnerships, many are connecting between flights from different airlines. <S> Very few passengers (and even fewer high-paying business travelers) will willingly break their journey to go for a drive across a famously traffic-congested city to change airports. <S> Customers will abandon your airport and fly other routes while this is going on. <S> Equipment: When Denver International Airport moved, there was a massive overnight caravan "of more than 10,000 baggage carts, plane tugs, fire engines, catering trucks, de-icing machines and untold truckloads of tickets, tags and gift shop sundries" to the new airport. <S> A similar operation occurred in Istanbul . <S> If both airports must operate simultaneously, a fleet of equipment must be maintained at both airports during the overlap period. <S> Much of this equipment is expensive, long-lasting, and will be difficult to sell or dispose of after the old airport is closed down. <S> Staff <S> : There's not an exact linear relationship of airport staffing to the number of flights. <S> Many staff may work for contracted ground handling companies and serve flights from more than one airline. <S> They can't be in two places at once. <S> This is still done to a limited extent though. <S> Turkish Airlines operated a few flights out of New Istanbul Airport for several months prior to the big move, which allowed them to test systems and familiarize staff with the new airport. <S> Some of these disadvantages can be mitigated by limiting the number of flights and choosing them strategically. <A> Exactly that was done at Montreal Mirabel airport, a fabulous, spacious new replacement airport for Montreal Dorval (Trudeau). <S> Montreal used to be Canada's main international hub. <S> International flights were banned from the old airport, as incentive for airlines to move all operations to Mirabel. <S> But they lacked the political strength to fully close the old airport, and never finished the high-speed-rail connection (or even highways) to Mirabel. <S> Passengers needed to take an hourlong bus ride and re-clear security. <S> This was so irksome that instead of consolidating at Mirabel, operators simply sent their international flights to Toronto instead, making it Canada's main hub. <S> They lost so many flights that Montreal didn't need two airports anymore, and they consolidated back at Trudeau. <S> Mirabel's main terminal was scrapped and it's a race track now. <S> A few cargo operations remain. <S> Then you have the case of Kai Tak, where they "threw the switch" properly, but due to teething pains, threw the cargo operations back to Kai Tak for a short while. <S> Then there is Berlin . <A> My experience is when KUL moved from Subang (now SZB) to the new KL Intl Airport (KLIA). <S> The moving date was declared way in advance, I seem to remember the date was locked more than 6 months before, and a lot of airlines rescheduled their ops especially the nightstopping aircraft. <S> Obviously Malaysia Airlines had to ferry a bunch of planes over but its a 10minute hop and done in the early hours so not much of an issue. <S> Some of the ground equipment was ferried over earlier in the day (of the last day of Subang operations) but everything else was moved over once the last flight of the day was completed. <S> I'm talking motorised stairs, K-loaders, belt-loaders, tractors, trolleys, dollies the works. <S> It was quite a convoy of flat loaders. <S> Stuff that could be driven on public roads were given temporary permits so you saw motorised steps and water/toilet trucks on the public highways! <S> The biggest change was moving from a host (MH) checkin environment to a homegrown common-use system which was integrated with the Baggage Handling System (BHS). <S> The first days baggage handling was chaos with a lot of bags not making their flights. <S> A lot of items can't be duplicated not only in terms of equipment but also in manpower and its easier to make a clean cut and manage the problems for a 24hour period than drawing the pain over a period of weeks.
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Gradually moving between airports is a living nightmare for connecting travelers.
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Does an rc plane tail also have airfoil or is it just flat material? I've chosen an airfoil for the wing, now i'm confused weather i should do the same for tail or just attach a flat piece of wood as tail. I'm going for conventional tail design.This is my first ever plane so sorry for the dumb question. <Q> A flat piece of wood with rounded edges will work fine. <S> In fact most fabric light aircraft get by with what is effectively a flat surface wind deflector, like this Super Cub. <A> Flat plate will be adequate as most r/c planes are overpowered and do not require perfectefficiency to enjoy. <S> Much more important are the proportions of wing, Hstab, elevator, and elevator throw. <S> Finer points can come later. <S> See what other planes similar to your build have. <S> If it is your first plane, you may be far better off buying a ready to fly. <S> Gain some experience. <S> There are so many variables it is best to start with an easy trainer and hook up with an instructor or somebody with experience. <S> These can be found at local radio control flying clubs. <S> In the mean time, you can build simple gliders and experiment with designs. <S> As in the earlydays of flight, the thin undercambered wing will give amazingly slow glides. <S> Also, check out R/C Groups on the web. <A> A flat piece of wood is technically not an airfoil due to the lack of curvature, but it may help to think of it as an airfoil with a very, very bad lift:drag ratio. <S> The tail needs a certain amount of lift to stabilize the plane, so the more drag you incur in getting that lift, the more power you will need to overcome it. <S> But the tail is small compared to the wing, so its overall effect on efficiency is also small. <S> Is it better for you to add a little more power every time your plane flies or to add a lot more effort once while building it? <S> Only you can answer that. <A> Some full scale aircrafts with humans in them also have one flat airfoil as horizontal and vertical stabilizer. <S> For instance : Laser 230 aerobatic aircraft. <S> ( source )
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The tail's job of producing downforce doesn't require the lift coefficients or angle of attack range required of the main wing, so the actual airfoil shape is not that important especially at low speeds, even more so under the low Reynolds numbers ("thick" air) that RC airplanes work at.
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Why doesn't Stratolaunch have connected tailplanes like it has connected wings? As a complete layman, the design of the Stratolaunch airplane, especially when reminding myself of its size, seems too flimsy, in that the only connection between the two fuselages is the center wing. Apart from apparently trusting their materials and connections, what might the reasons have been for Dynetics engineers to not also connect the tailplanes? Also, are there no aerodynamic disadvantages to having that many more trailing edges (if that's the terminology used)? <Q> There is indeed an Eigenmode possible on the Stratolaunch which does not exist on regular airplanes: If the two fuselages pitch in opposite direction, thereby twisting the center wing. <S> If that happens at the torsional eigenfrequency of the center wing, flutter might be possible. <S> Stratolaunch in flight (picture source ) <S> Given the pitch damping of the horizontal tails, however, this scenario is rather unlikely. <S> I bet the elevators have plenty of mass balance to avoid this flutter case. <S> Underbalanced, their dynamic response would support flutter, but overbalancing would dampen this flutter mode. <S> Connecting the tails would not make much of a difference and would even reduce pitch damping somewhat in the above mentioned case. <S> Similar configurations used both, a connection horizontal tail (F-82 <S> Twin Mustang) or individual tails (He-111 Zwilling). <S> North American F-82 <S> Twin Mustang (image source ) <S> Heinkel 111 Z (image source ) <A> That's not how airplanes work. <S> An airplane is the wing first , everything else just hangs on the wing in flight. <S> The correct way to look at an airplane is to imagine the wing without all the attachments, then add them one by one as weights. <S> The engines are a semi-exception in that they also pull forward at their attachment points. <S> The fuselages, on the other hand, are just fuel tanks, and also carry control forces from the tail surfaces. <S> Placing two heavy fuel tanks (fuselages) <S> a considerable distance apart is much more structurally efficient for the wing than only placing one in the center. <S> That's the reason it's done that way. <S> As for why the tailplanes aren't connected, the right question is "why should they be". <S> There are multiple possible reasons for such a decisions, and a number of twin-boom aircraft where they are connected, often with a lifting surface that acts as a second wing. <S> But the Stratolaunch is a twin-fuselage aircraft with conventional tails, and in this case it would cost a lot of extra weight to connect the tailplanes. <S> It's only on the ground that the aircraft rests on its wheels and the wing rests on the two fuselages. <S> And indeed, a twin-fuselage arrangement does make ground handling more complicated, and on the ground the wing is subject to some forces arising from out-of-sync loads on the fuselages. <S> But given this aircraft's mission, that's a minor concern. <A> It’s mainly because the load is shared between two fuselages like in mechanics the load of a bridge is shared among its towers sharing the bending moments
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It's inefficient from the payload perspective (the payload, be it live or cargo, prefers one big tube), but the Stratolaunch carries its payload slung between the twin fuselages.
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When communicating altitude with a '9' in it, should it be pronounced "nine hundred" or "niner hundred"? It sounds a little odd, but trying to understand if that's the recommended way to communicate. E.g. 9900"Nine-thousand-nine-hundred"vs"Niner-thousand-niner-hundred" <Q> In the UK, the RT rules for the ANO are in <S> Cap 413 and section 2.13.2 states: <S> All numbers used in the transmission of altitude, height, cloud height, visibility and runway visual range information which contain whole hundreds and whole thousands shall be transmitted by pronouncing each digit in the number of hundreds or thousands followed by the word HUNDRED or TOUSAND as appropriate. <S> Combinations of thousands and whole hundreds shall be transmitted by pronouncing each digit in the number of thousands followed by the word TOUSAND and the number of hundreds followed by the word HUNDRED; examples of this convention are as follows: <S> Table 5 Number <S> Transmitted as Pronounced as 10 <S> One Zero <S> WUN ZERO100 <S> One Hundred WUN HUN DRED 2 500 <S> Two Thousand Five Hundred <S> TOO TOUSAND FIFE <S> HUNDRED 11 000 <S> One One Thousand WUN WUN TOUSAND 25 000 <S> Two <S> Five Thousand <S> TOO FIFE <S> TOUSAND <S> There isn't a specific example of NINER here, but given that the examples do actually use their prescribed pronounciations, you'd expect NINER to be used too. <S> I can't remember hearing it but the other conventions seem to be adhered to by professional pilots in the UK (we Sunday afternoon bimblers are not as good at it). <S> Non-native english speakers are very exact in their use of the published pronounciation <S> No doubt there will be a professional along in a minute, who can give you a more authoritative answer EDIT: <S> The reason I can't remember hearing "Niner-thousand-niner-hundred" may be because, in the UK, it would be above the transition level? <A> Several numbers are not pronounced the way they are in English. <S> Niner is the most obvious and most US pilots use it. <S> In my experience, tree and fife are heard less often. <S> I don’t recall ever hearing anyone say fower. <S> From Wikipedia <S> The NATO phonetic alphabet, officially denoted as the International Radiotelephony Spelling Alphabet, and also commonly known as the ICAO phonetic alphabet, and in a variation also known officially as the ITU phonetic alphabet and figure code, is the most widely used radiotelephone spelling alphabet. <A> ATC should always use the correct pronunciation and phraseology. <S> Pilots aren't as consistent <S> , at least if they're native English speakers; as long as we're understood (the primary goal of communication), we can get away with a lot of shortcuts. <S> NINER HUNDRED doesn't come up often since we usually fly at multiples of 500 feet, but I'd expect the same tendency when it does. <S> I've never noticed US pilots using TREE, FOWER, FIFE or TOUSAND, though. <S> Unlike NINER, those aren't easily distinguished unless you're listening for them specifically. <S> They seem to be used mainly by pilots whose native languages don't have the sounds necessary for the normal English versions. <A> NINER is an artifact of the "phwa phwa phwa bwa bwa what-the-hell-did-he-say" days of radio telephony, with vacuum tube equipment and carbon microphones and raspy, garbled, muffled audio, to prevent it from being mistaken for the number five. <S> With the FM radio quality audio of modern avionics, it's not really required any more and sometimes you hear it <S> and sometimes you don't. <S> No controller will scold you for saying nine instead of niner.
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In the US, NINER THOUSAND is used by most pilots, but you'll hear NINE occasionally.
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Can a drone be seen on TCAS? On condition that the pilot reports to ATC, an aircraft's TCAS sees a drone in the vicinity. How can the pilot be sure that it was a drone on TCAS? What kind of symbol is shown on TCAS that can be identified as a drone? Or is it just a primary radar target pick up by TCAS? <Q> No, a drone will normally not be visible on an aircraft TCAS. <S> The TCAS system is based entirely on direct communication between aircraft transponders, so both parties (aircraft and drone) must have a transponder in order for TCAS to work. <S> If a pilot reports a drone near the aircraft, what he means is that he (visually) has seen a drone out the window, not that it is indicated on an instrument anywhere. <S> Besides, TCAS does not know different aircraft types, so even if a drone had a transponder and it was presented on a TCAS, the pilot would have no way of knowing that it was a drone (as opposed to any other aircraft). <S> Or just primary radar target pick up by TCAS. <S> TCAS is <S> NOT a radar. <S> It is not able to display anything without a transponder. <S> And even ground based primary radars will not necessarily pick up a small drone. <A> TCAS is based on aircraft transponders, so unless the drone has one installed it cannot be seen by TCAS. <S> At least no commercial drones intended for consumers have transponders installed. <S> On the other hand drones are not allowed in airspaces used by airliners so there should not be a need for one. <A> It's already been said TCAS is not a radar, but how come it knows the bearing, and how does it work with the different transponder types? <S> Radar <S> A basic ground secondary surveillance radar sends an interrogation signal as it sweeps the sky, and the transponders in the direction of sending reply. <S> TCAS <S> A TCAS system is similar, by having an on board directional antenna, the plane sends interrogation signals, and airborne transponders reply to it. <S> The reply delay would indicate the distance, the reply will contain the barometric pressure (which is used to discern the altitude difference), and the directional antenna will display the relative bearing. <S> The bearing is informative only (for display), and its resolution is not used in the decision making. <S> White diamonds show other traffic with +/- <S> relative altitude in hundreds of feet and arrows would indicate climb/descent ( flickr.com ). <S> Cooperative <S> The TCAS' decision (conflict resolution advice) can be cooperative as well in Mode S . <S> So if a TCAS of one plane says "climb", this information is sent, so the other TCAS in conflict would order the opposite, for example. <S> Once an RA has been issued, the vertical sense (direction) of the RA is coordinated with other ACAS II equipped aircraft via a mode S link, so that two aircraft choose complementary manoeuvres. <S> ( SKYbrary ) <S> Drones <S> So if the unmanned aerial vehicle does not have at least a barometric transponder (Mode C) system, TCAS equipped aircraft won't offer conflict resolution. <S> ACAS II will not detect non-transponder-equipped aircraft and will not issue any resolution advice for traffic without altitude reporting transponder. <S> ( SKYbrary ) <S> ADS-B <S> But what about having only an ADS-B transponder on the UAV? <S> TCAS still needs Mode C/S on the other plane, ADS-B only permits fewer interrogations. <S> Hybrid surveillance does not make use of ADS– <S> B's aircraft flight information in the TCAS conflict detection algorithms; ADS–B is used only to identify aircraft that can safely be interrogated at a lower rate. <S> ( Wikipedia ) <S> Further reading: https://www.skybrary.aero/index.php/Airborne_Collision_Avoidance_System_(ACAS)
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Normal drones do not have transponders, so they will not be visible on TCAS.
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For length in aircraft design, and in weight and balance manuals, what measurement unit does Airbus use? What length measurement unit does Airbus use for aircraft design and in their weight and balance manuals? Meters or centimeters? Possibly they use both like Boeing does for, say, feet plus inches for overall length and wingspan but just inches for a position along the longitudinal axis for crew, pax, and cargo locations? For example 1821.0 inches for the lower hold aftmost ULD position on a 747. <Q> Structures are soft metric. <S> Airbus uses inch hardware so some measurements make sense in inches but are drawn with an ugly mm number. <S> The coordinate system is in metric. <S> The rest of the aircraft is hard metric. <S> For example, MTOW and fuel capacity is in a nice number of kg. <S> Documentation and instrumentation is localized according to the operator. <S> Mass, as in fuel, can be switched between kg and lbs on ECAM, and all the manuals and W&B will follow. <S> There's a few units that aren't localized, most notably pressure is always in PSI and engine oil <S> is always given in quarts (probably since it comes in quart cans). <A> In the FCOM for the A320 <S> the dimensions are listed in both decimal meters and in feet+inches. <S> source: <S> A320 FCOM <A> I think the operations manuals are available in metric and imperial units for the operator to choose.
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The (few) design drawings I‘ve seen were in millimeters; however I can’t confirm whether that’s the uniform standard.
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Why in helicopter autorotation phase the opposing torque is eliminated? As you many know, according to Newton's 3rd law for every action there is an equal and opposite reaction, as the main rotor of a helicopter turns in one direction, the fuselage tends to rotate in opposite direction but when there is no engine power during autorotation, there is no torque reaction, why??? <Q> Because the engine is not applying power to the rotors. <S> No engine power means there will be no torque pushing the airframe in the opposite direction. <S> In auto, the main rotor essentially becomes a pinwheel, kept moving by the air rushing past it... <S> Auto doesn't really power the rotors, it keeps them moving so that the spinning rotor creates air resistance and slows the descent of the helicopter, and maintains enough inertia in the blades to flare and stop the descent. <S> Of course, that inertia is only sufficient for one attempt at flaring and stopping descent. <A> Because the torque to spin it is being generated within the rotor itself, being a forward thrust component of the lift being generated by the spinning blades, like any gliding aircraft. <S> An autorotating rotor is like two gliders with velcro wingtips going toward each other in opposite directions, who when they pass each other hook wingtips and start to spin around each other, still gliding and moving forward, but forced into a circle who's axis is their inboard wing tips. <S> What ever rotational force is transmitted to the airframe (a tiny amount) is actually in the same direction as the rotor's rotation; not a torque reaction, just friction drag from the main shaft bearings and sprag clutch. <A>
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In autorotation, the engine and gearbox are not applying any turning force, or torque to the rotor system, so therefore there is no torque reaction in the opposite direction.
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What is the definining line between a helicopter and a drone a person can ride in? When I say drone in this context I don't mean an unmanned aircraft. I'm not sure what the terminology of a drone that has been adapted to carry a person? Is this picture below considered a helicopter or what? What if it ran on petroleum? If not, then how is the separation between a VTOL aircraft and helicopter defined? Would a Chinook that can fly itself be a drone? <Q> A helicopter is an aircraft in which thrust and lift are provided by rotors. <S> A drone is an unmanned, self-piloted or remotely-controlled aircraft, which can use rotors to provide thrust and lift, but can also use other means such as propellers or turbines. <S> To put it in simpler terms, a helicopter can only be a helicopter, regardless of whether it has a human inside or not. <S> A drone can be any kind of aircraft. <A> I would just call it a VTOL aircraft. <S> Those kind of multi-rotor VTOLs do kind of blur <S> the line between VTOL and helicopter, but a practical way to define them could be to separate them by a key capability; the ability to glide. <S> A helicopter has a rotary wing that is driven forward by a power source like an airplane, but can also change pitch and glide downhill, like an airplane. <S> A rotor is just two fuselage-less airplanes joined at the wingtips being driven in a circle by a twisting force applied at the wing tip instead of a propeller out at mid span. <S> A multi-rotor VTOL with small fixed pitch rotors can't glide, which is why you won't get me in one unless it has multiple levels of redundancy with NO single-points-of-failure or double-points-of-failure modes for that matter (like say being able to take damage to both rotors on one corner for example, and still maintain control). <A> There is no automatic separation between the two, it is possible for an aircraft to be both a drone and a helicopter. <S> Drone only refers to how the vehicle is piloted, and helicopter only refers to how it flies. <S> (Battery vs petroleum vs any other power source is a third, separate modifier, too.) <S> (Note: <S> Unmanned means not having any crew on board. <S> You can still have passengers, they don't count.) <A> When I say drone in this context <S> I don't mean an unmanned aircraft. <S> Drones are unmanned aircraft which can receive flight path control (rather than controls directly affecting the control surfaces/rotors). <S> Method of generating lift, engine technology and size are not a factor - after WW1 some biplanes became drones and various air forces have converting more modern end-of-life fighters to drones, either for attack or for target practice . <S> I'm not sure what the terminology of a drone that has been adapted to carry a person? <S> Passenger carrying unmanned aerial vehicle or ' passenger drone ' Is this picture below considered a helicopter or what? <S> What. <S> I'd call it a rotorcraft (UK terminology used, e.g. in CAA larger UAS guide ), or more specifically a large octocopter. <S> I tend not to call things helicopters if they don't have helicopter controls ( cyclic and collective driving a swashplate), but I can't find an authority on whether that is what makes a helicopter. <S> Electric multi-rotor craft use differential rotor speed to manoeuvre instead. <S> What if it ran on petroleum? <S> I suspect it would fall out of the sky - it would be hard to get the control responsiveness from eight small petrol engines or one large one and an eight way variable transmission that would allow it to be stable. <S> You could change it from an octocopter to an eight rotor helicopter by adding swashplates, but with the other changes to make that happen it would be a different thing.
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The vehicle in your picture is an unmanned aircraft, a drone, a helicopter, a quadcoptor, and a VTOL vehicle all at once.
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An appropriate way to practice ATC communications I'm a PPL trainee and I'm looking for a way to improve my radio communication. https://www.liveatc.net/ is a great way to practice but I can't fully understand the conversation between the unit and the aerodrome. If it just had subtitles or general documentation about it, would be great. <Q> I used to pick out a tail number and then pretended to be that aircraft. <S> When ATC gave instructions, I would say back what I think the response should be. <S> If there are terms or phrases you dont understand, you should be able to look them up in the Pilot/Controller Glossary here: <S> https://www.faa.gov/air_traffic/publications/media/pcg_10-12-17.pdf <S> ATC and pilots should do their best to use the official phraseology in the glossary. <S> However, the goal of communication on the radio should be clarity. <S> If there is something you want to say but dont know how, just say it plainly without worrying about the 'official' wording. <A> If you use MS Flight Simulator on your computer (which you should be) you should look into VATSIM , which is a virtual air traffic control system for people who use Flight Simulator online. <S> A lot of VATSIM controllers are real controllers, and there are all kinds of resources. <A> To improve your communications you need to fly . <S> There's a world of difference between practicing on the ground and actually saying it in the air, when you are Aviating and Navigating <S> , There are times you will sound like Porky Pig on speed which is an unavoidable part of being a student and nothing to worry about. <S> Don't get me wrong, practice is useful, what I found was that the act of saying was not as important as knowing what to say. <S> For that I built a list of the common calls I was likely to be asked to make and thought about the responses. <A> a) Get an airband receiver and listen to ATC whenever you have the opportunity.b) Armchair flying and self-talk ... <S> sounds funny but does work extremely well!
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Live ATC is an excellent way to listen and get familiar with your local airports procedures.
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Why was the Spitfire's elliptical wing almost uncopied by other aircraft of World War 2? The Spitfire was one of the most successful designs of its day, with flying qualities of a similar standard to the other best designs of the era. In its decade of production from 1936 it grew bigger , stronger and faster . Yet there seems to be almost no appetite from any of the major aircraft-manufacturing powers to emulate its most iconic feature. In fact, there is only one mass-produced aircraft of that time with an elliptical wing, the American P-47 Thunderbolt . Nothing German or Japanese, and nothing more from the British either. In a period where every manufacturer was trying to gain every last bit of advantage, it seems odd that a prime design feature attracted so little appetite to copy. There are good explanations here on the aerodynamics or performance of the elliptical wing. Why is it so rare when it demonstrably works so well? Source <Q> Interestingly, I couldn't find an answer to this question on the website, but I've found an answer of Peter Kämpf on Quora . <S> He brings forth the same arguments I wanted to mention, so I'll repeat them here. <S> Elliptical wings are very good - aerodynamically. <S> If you want to minimize induced drag for a given lift requirement, you end up with an elliptical wing. <S> But a plane is not only aerodynamics. <S> You also have to consider: <S> Weight, an elliptical wing is not structurally efficient, and will lead to a higher weight, which leads to higher lift requirements which will lead to more induced drag, even with a very efficient wing. <S> Controllability, where and how the wing stalls determines if you're able to recover from a stall. <S> Elliptical wings stall tip first, leading to bad stall behavior. <S> Manufacturability, a fully elliptical wing is very hard to make, with its double curves. <S> This will make the wing more expensive. <S> If you include these factors, you'll see that you'll end up with a compromise. <S> If you use wing taper (which is somewhat close to the aerodynamic optimal shape) but much easier to make and much lighter <S> you'll see that you'll end up with a better design overall. <S> An analysis of how the design of a wing changes if you include the structural requirements was done by Jones and can be found here . <A> Well the short answer is the elliptical wing was used on a lot more aircraft than this article lets on. <S> The following all used an elliptical wing and there are others too: <S> German Heinkel 112 fighter <S> German Heinkel 111 bomber <S> German Heinkel 70 US P35 US P43 Italian Reggiane 2000 Japanese Aichi D3A "Val" dive bomber British Hawker Tempest <A> Short answer: <S> A trapezoid wing with a defined geometric or aerodynamic twist can get very close to an elliptical lift distribution (optimal lift distribution over the wingspan, therefore the primary goal of the wing design). <A> A lot of planes still use elliptical wings - sort of. <S> What the maths tell us is that the most efficient wing configuration for a given wing span should have an elliptical lift distribution <S> *. <S> The most obvious way to implement this is to make your wings elliptical. <S> But aircraft designers learned from the experience of manufacturing the Spitfire that elliptical wings are more difficult to manufacture leading to increased cost and manufacturing time. <S> So later in the war when resources became tight and everyone assumed that they were racing the Germans to build better, faster planes designers deliberately chose to use straight wings to ease production and reduce costs. <S> The P51 Mustang was designed this way. <S> But we have learned that making your wing elliptical isn't the only way to have elliptical lift distribution. <S> To get elliptical lift distribution you can: Make your wing more elliptical Add washout to tune lift distribution along the wing Change airfoil profile from root to tip to change lift distribution <S> Do any combination of the above (eg. washout + rounded tips) <S> So a lot of planes still use elliptical wings. <S> Especially when fuel economy is one of the main driving design objective. <S> It's just that they don't look elliptical. <S> * note: There is evidence that this may not be accurate. <S> It is true that if you fix your wingspan the maths will output an elliptical distribution but if you fix your weight (ie. lift at cruise) <S> the most efficient distribution turns out to be something else (something bell shaped) <S> but you end up needing to extend your wingspan <A> The main drawback of the Spitfire's elliptical wing was the the amount of labour required to build it. <S> Overall the Spitfire required about five times as many man-hours to build as the nearest German equivalent, the Messerschmitt Bf 109.
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Elliptical wings are too expensive to manufacture.
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Is it cheaper to drop cargo than to land it? Is it more fuel efficient to drop cargo onto a runway from the air en route to a final destination than to land and unload it using a more fuel efficient plane? <Q> That scenario only makes sense if your airplane stays at cruising altitude: although taxi and takeoff does use up fuel it's really the ascent to cruise that takes the most. <S> You aren't really going to be able to drop cargo accurately from cruising altitude, so you'll have to descend pretty low, then you'll need to climb up again, and that would suck up lots of fuel and make it much less efficient a method of delivery. <S> Add to that <S> the weight and cost of the parachute mechanisms as well as the massive protective packaging the cargo would need to survive the jolt (2-3 Gs when it hits the ground) and the whole thing becomes pretty uneconomical. <S> The military only air drops cargo when there's no other alternative - now you know why. <A> Looking purely at operational cost of the aircraft, yes. <S> You save time, burn less fuel, don't have to pay for the landing etc. <S> But dropping the cargo makes the cargo more expensive. <S> You have to provide parachutes (and return them after use, inspect them etc). <S> You have to combine cargo into parachute loads. <S> You have to package the cargo for a hard landing, getting pulled over on its side by the parachute after landing etc. <S> Commercial cargo aircraft usually don't have one, so you have to switch to more expensive military aircraft (Hercules, C-17). <S> And occasionally a parachute won't work and the cargo will dig a crater. <S> You can also go for low-altitude horizontal extraction , but that also has its cost, and entertaining failure modes . <A> The main advantage of landing is that the plane can then carry another cargo on the return journey. <S> Flying an empty plane back home is extremely inefficient and halves the range of the plane. <S> Air dropping might make sense for a large number of relatively small but urgent packages with lots of destinations along a route, but even then the plane would be mostly empty towards the end. <S> Dropping a load by parachute is fairly difficult, but loading a plane in the air is a real challenge! <A> Outside of any of the difficulties associated with dropping cargo out of a plane at altitude, the answer is still 'it depends'. <S> For long distance flights, a large part of the initial weight of the plane is due to the fuel load, not the cargo. <S> This fuel weight imposes a penalty on both climb- and cruise performance. <S> It may be beneficial to land halfway and refuel, so that on both legs of the journey, less fuel has to be carried. <S> This is also why refuelling is typically done at every stop (unless poor availability or high fuel costs forces 'tankering' - landing with enough fuel left to do a return flight or the next leg as well). <S> However, in that case you might as well use road or rail transport. <S> The only remaining use case, which is unsurprisingly the only use case in reality, is to drop cargo if no other means of delivery are available - for example, conflict zones, disasters, etc. <A> Depends entirely on the constraints. <S> So: "Sometimes" or "maybe". <S> There are a few effects that make landing more fuel efficient: <S> On long trips refueling midway is fuel efficient, even if it involves landing. <S> Saving a second trip by loading new cargo midway is even more fuel efficient. <S> Having lower weight cargo due to absence of air drop packaging is fuel efficient. <S> Saving a trip due to tightly packed cargo is fuel efficient. <S> Related: <S> Dropping a parachute over a runway from high altitude can disrupt air traffic for a significant amount of time. <S> Dropping a parachute over a runway from low altitude means having to climb again, which is not fuel efficient. <S> There are many (contrived?) <S> scenarios where none of these arguments come into play - in those scenarios air drop is indeed more fuel efficient. <S> These scenarios would usually involve short distances, inherently air droppable cargo, runways that see very low amounts of traffic, and machines that will stay at relatively low altitude during most or all of the trip.
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The only use case for commercial cargo drops seems to be if you need to deliver cargo at a number of closely spaced airports (in which case the short hops would be fuel-inefficient). You have to use an aircraft suited for airborne dropping (i.e. with a tail ramp).
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Is it required to be an ATP and work for an airline to be a Captain? I'm just curious if the ATP certificate and working for an airline are prerequisites to being a Captain, or could you have such a title as a PPL or a CPL? <Q> The key phrase, legally speaking, is "pilot in command". <S> On a multi-crew aircraft the PIC is normally given the honorific title of Captain, but what really matters is the legal status of PIC where an aircraft legally requires more than one crew. <S> In general to be PIC of a multi-crew a/c <S> you need an ATPL. <S> Operators may operate single-pilot aircraft like Caravans as if they were multi-crew with two pilots and call the PIC Capt, but again that's just an honorific title and in that case the PIC can be just a CPL. <S> Like DLH says, a PPL or CPL can call themselves anything they want; Captain, Great Exalted Poobah, Zontar The Munificent, whatever. <A> The title "Captain" is not a title bestowed by the FAA. <S> The airlines themselves bestow that title for an ATP rated pilot who has seniority and is shown to be proficient for the airplane flown. <S> A pilot could be deemed "captain" for one flight and "first officer" for another. <S> In the US a pilot must have an ATP certificate to be a "first officer" or "captain". <S> Could somebody bestow that title on a pilot with only a PPL or CPL? <S> I suppose so, but calling somebody Captain doesn't really say anything about their credentials. <A> When Pan-Am created the first modern airline, most passengers of that era were familiar with the practice of ships having a naval-uniformed "Captain" and/or "First Officer" that greeted them on boarding. <S> Pan-Am decided to copy that practice by dressing the pilots of their "flying boats" dress in the same uniforms and use the same titles, in hopes this would set themselves apart from barnstormers (who frequently killed themselves and their passengers) as a "professional" outfit and put passengers at ease. <S> Other airlines soon copied the practice, and it has survived to this day despite the move to land-based planes long ago. <S> However, the titles have absolutely no legal status, unlike with ships. <S> Legally, what matters for flying is the "Pilot in Command" and, for aircraft that require one, the "Second in Command". <S> For example, a student pilot can be "Pilot in Command" of a single-engine trainer as long as they are not carrying passengers and have the correct endorsements from their instructor. <A> There are a tiny number of people who are rich enough to fly what we think of as airliners for their own amusement. <S> If they are not flying for profit they do not need ATP licenses, nor to work for an airline, and can be called "Captain" by any standard.
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The type of pilot license required for each varies by country, type/size of aircraft, and whether the flight is scheduled, charter or private.
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How can I best prepare for my first lesson on stalls? I am a flight student preparing to practice stalls and stall recovery in a Tecnam P-2002. I have already done spin recovery. On top of that, what preparation techniques have others found useful? <Q> Just do some reading on stalls and really get to know the 2002's Operating Manual, especially the numbers and limitations. <S> Be careful about trying to show that you already know it all. <S> If a student has taken the time to learn the operating manual and knows all the important numbers and limitations by heart, and can recite emergency drills etc while under stress, the instructor will way more impressed than if a student tries to show they already know how to do the lesson. <A> First, the low-hanging fruit: has your instructor provided you any homework for the upcoming lesson? <S> If so, have you done it ? <S> I'm an instructor, and believe me, it's very easy to tell which students are doing their homework and which aren't. <S> As John K says , doing the assigned work beforehand is a fantastic way to impress your instructor. <S> If there's no assigned work, you could ask for some . <S> Unless your instructor is very new to the field, he or she probably has several resources besides the "standard" textbook that you could look at. <S> I know here in the USA <S> there's at minimum the FAA book, the Jeppesen book, and the Rod Machado book, and each one explains the same concept a little differently. <S> A variety of views often helps with mastering a concept - <S> if you don't understand a topic from one source, you might understand it with another. <S> Have you been chair flying? <S> Learning numbers is good but flying is an active physical process. <S> Find a quiet place, sit in a chair with your eyes closed, envision the cockpit, and then actually move your hands to the places that they would go during the maneuver. <S> Taking five minutes to remember how to do it on the ground (for free) is much better than taking five minutes to remember how to do it in the air. <S> Are you training alone or are there others in your class? <S> One of the best ways to learn something is to try to teach it to others. <S> If you have classmates, try to arrange a small study group that meets regularly. <S> Each person chooses a topic and then does their best to explain it to the group. <S> I will warn you, it's very hard to get a group of people to agree to this, at least around here. <A> Two great answers already, but I’d like to add that besides doing your homework be there on time and listen to your instructor ! <S> S/he will be telling you what you need to do. <S> Not many more frustrating things for an instructor than a student who is so eager to please/show off that they don’t listen to the instructions.
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You will impress your instructor most by being eager to learn and learning quickly, and by having done book work beforehand. That being said, just read up, and really learn the manual.
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What type of aircraft would fly with an orange light at night? I know planes usually fly with red lights which seem small in the sky, but last night i saw a bright orange blinking light traveling through the sky; it was bigger then a star but was orange. I thought it might be a helicopter, although I read it could have been a comet or a meteor. <Q> While normally red in colour, anti collision lights can often appear more or less orange, depending on the background and atmospheric conditions. <S> It is impossible to determine the aircraft type just based on the fact that it has a orange light on it, since almost all aircraft have reddish orange anti collision lights. <A> The flame used to heat the balloon is orange, and most balloons are translucent enough that the whole balloon can appear orange when the flame is lit. <S> There wouldn't be a blinking orange light, but the flame is often used in short bursts to keep the balloon inflated, so it would be intermittent. <S> Balloons don't move very fast, so if it was really "travelling across the sky" as you describe, perhaps this isn't the answer. <S> A meteor (which you've already guessed at) moves a lot faster, but tends to glow orange or white for a few seconds and then disappear: I don't think I've ever seen a blinking one. <A> Orange isn't a standard color for aircraft lighting. <S> Best guess would be reflected sunlight on a metallic aircraft, although any number of other explanations are at least possible. <A> In this new era of widespread droning, anything is possible. <S> People can and do put all kinds of non-authorized lighting on drones. <S> Maybe you saw a drone, possibly flown by an amateur hobbyist in a manner non-compliant with regulations.
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Others have mentioned red anti-collision beacons that might look orange in certain environmental conditions, but there's only one kind of aircraft that shows an intermittent orange light: balloons.
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How useful are the AOA Indexers and indicators for jet pilots and civillians? I dont see them neccessary unless you are landing on a aircraft carrier. I just don't know a lot about them. I understand what they do but they just dont seem neccessary unless you are landing a jet to an aircraft carrier where every bit of precise information is neccessary. And now I see them on the Cessna 172SP planes. Long story short. How important they are for aircraft carrier pilots and Cessna students/pilots? <Q> They’re super useful once you get used to them. <S> No matter your weight, if you fly at the right AOA you’ll have the right stall margin. <S> It is easier to see the indexer than the ASI, for control on approach. <S> It acts like a pitch rate indicator too, if you are rough with the nose, so it helps to smooth out the flying. <S> Responds much faster than the ASI. <S> If you are maneuvering aggressively, it will give you that stall margin too. <S> Update with nice paper from AIAA Journal of Aircraft: "Low-Cost Accurate Angle-of-Attack System", Borja Martos and David F. Rogers, Journal of Aircraft 2018 55:2, 660-665 ... <S> The angle of attack for maximum lift-to-drag ratio corresponds to maximum range and maximum glide ratio for a piston engine- propeller aircraft. <S> Hence, in a fuel critical situation and/or an engine failure situation, it is critical that the pilot have accurate access to this angle of attack. <S> With today’s fuel costs, the Carson cruise [1] angle of attack, which represents the most efficient way to fly fast with the least increase in fuel consumption, is of significant interest. <S> The angle of attack for maximum lift-to-drag ratio does not depend on density altitude, weight, or load factor but only on aircraft design parameters and aircraft configuration. <S> Similarly, the angles of attack for minimum power required and Carson cruise depend only on aircraft design parameters and configuration... <S> Therefore, a low-cost, accurate, full envelope, easy to flight calibrate angle-of-attack system is a transformative technology for light general aviation aircraft. <A> Accidental stalls are fairly common, especially for new pilots, and that's why we have stall warning devices--and train pilots to immediately recover as soon as they hear/see them. <S> However, simple devices don't tell you anything until you're right on the edge. <S> For more complete information, you need an AOA sensor. <S> Once you have that sensor, why not display that information to the pilot? <S> If you have a glass cockpit, the cost of adding one more data item on the display is pretty much zero, and it might be useful to some pilots--regardless of whether they're flying a trainer, an airliner, or a fighter. <A> Planes that fly off aircraft carriers rely on them heavily. <S> They not only have indexer lights in the cockpit, but they also have them on the outside of the plane (usually on the nose gear doors) so the Landing Signals Officer on the boat can see them as well. <S> Depending on the aircraft, they might not even turn on unless the landing gear is down, because they're calibrated for approach speeds. <S> We also have two independent pitot-static systems, so a loss of all airspeed indications is a remote (but not impossible) scenario.
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On the planes I'm more familiar with, we rarely use it at all because it's a real pain to calibrate.
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May the Class-E-to-surface airspace near Eagle County Regional airport (KEGE) and Marshall AAF (KFRI) be ignored when the tower is open? May the Class-E-to-surface designation indicated by the dashed magenta lines outside the dashed blue circle at Eagle County Regional airport (KEGE) be ignored when the tower is open? Likewise at Marshall AAF (KFRI) ? Normally we would consider a dashed magenta line that does not actually enclose the airport whose approaches it protects to denote a Class-E-to-surface "extension", i.e. E4 airspace. The "extension" would be described in the E4 section of the "Airspace Designations And Reporting Points" document (FAA Order 7400.11C) , typically with no comment about effective hours. Meanwhile, if the tower is not open 24 hours, the area in the dashed blue circle will be typically described in the Class D section of Order 7400.11C and ALSO in the E2 section of 7400.11C, with a note in each section to see the A/FD for the effective hours of that designation. Here is an example of an airport with airspace designated in this manner: KMFR . The relevant pages in JO 7400.11C are E-80, E-189, and D-65. The dimensions of the E-2 airspace are identical to the dimensions of Class D airspace, except for the absence of any altitude ceiling on the Class D. The E-4 "extensions" are in effect 24/7, whether the tower is open or closed. But at KEGE and KFRI that's not what was done. There is no listing for the airspace within the dashed magenta line in the E4 section of JO_7400.11C. Instead, a single area of Class-E-to-surface "Surface Area designated for an airport", i.e. E2 airspace, is defined that includes the area in the dashed blue circle AND the area in the dashed magenta line that abuts the dashed blue circle. (Page E-70 KEGE, page E-16 KFRI). There's a note that the dates and times that the E2 will be in effect will be published in the A/FD: for example, for KEGE we read "This Class E airspace area is effective during the specific dates and times established in advance by a Notice to Airmen. The effective date and time will thereafter be continuously published in the Airport/Facility Directory.AMENDMENTS 11/23/06 71 FR 46077 (Revised)" Naturally, the airspace in the dashed blue circle is also described in the Class D section of Order 7400.11C (page D-59 KEGE, page D6 KFRI), with a note to see the A/FD for the effective times. The A/FD (for KEGE) says "AIRSPACE: CLASS D svc 1400–0200Z‡; other times CLASS E." No E4 airspace has been designated for KEGE or KFRI. So the area in the dashed blue circle is Class D when the tower is open and E2 when the tower is closed. And the area enclosed by the dashed magenta line, has, oddly, been designated not as E4 airspace as per normal practice, but rather as part of the same E2 airspace that is only in effect when the tower is closed. So it seems that the entire E2 airspace should vanish when the tower is open, and should therefore simply become Class G up to 700' AGL. Surely this is not what is actually intended. Is the intention that the area inside dashed magenta border but outside the dashed blue circle stays E2 the whole time, while the area inside the dashed blue circle and below 9100' MSL at KEGE or below 3600' MSL at KFRI falls out of the E2 as if it were cut with a cookie cutter, and turns into Class D, when the tower is open? Here's one problem with that idea-- There are about twenty other airports in the US where the airspace designation is similar to KEGE and KFRI, but a little different. One such example is KUNV-- University Park at State College PA -- --for the others, see this related answer: What are all the US airports where E4 "extensions" change to E2 and become part of a larger E2 "surface area" when the tower closes for the night? . Taking KUNV as an example, the airspace enclosed by the dashed magenta lines is designated in order 7400.11C (page E-171) as E4 airspace, with a note to see the A/FD for the effective hours. There's ALSO a designation of E2 airspace (page E-37) that includes the exact same airspace AS WELL AS the area in the dashed blue circle, with a note to see the A/FD for the effective hours. And the area in the dashed blue circle is also described in the Class D section of Order 7400.11C (page D-23), with a note to see the A/FD for the effective hours. The note in the A/FD simply says "AIRSPACE: CLASS D svc 1100–0300Z‡; other times CLASS E." Clearly, in this case it was felt that the entire E2 airspace would vanish as a single unit when the Class D airspace was in effect, hence the need to also have an E4 airspace designation to protect the airspace in the dashed magenta projections when the tower is open. The same situation applies at the other 20 airports listed in the linked answer. Added note-- it is interesting to note that on the FAA's LAANC map for authorization for sUAS (drone, model airplane) flight the projecting "extensions" at KEGE and KFRI are NOT covered by the grid squares that indicate the areas where pre-authorization is required. All other E2 airspace IS covered by the grid square that indicate that pre-authorization is required, EXCEPT for part-time E2 airspace that changes to E4 whenever the adjacent control tower is open, i.e. the twenty or so airports described above. This tends to suggest that the airspace within the dashed magenta line at KEGE and KFRI is not treated as E2 airspace when the tower is open, at least in relation to FAR 107.41. However this doesn't really bear on whether this airspace still functions as some form of Class-E-to-surface airspace when the tower is open in relation to other FAR's. One shouldn't read too much into the depiction on the LAANC map. See also this related question: May an ultralight vehicle pass directly above KEGE at 9200 MSL at 1600Z with no prior authorization without violating FAR 103.17? Are there any other airports where the airspace designations have been set up similar to KEGE and KFRI? <Q> The short answer is "No." <S> The explanation: Class E airspace is not related to tower operations, it's related to ATC. <S> In this case, the dashed area of the Class E is protecting the precision approach to runway 25. <S> The surrounding shaded magenta area is the transition zone. <A> It appears that the best description of the airspace designations at KEGE and KFRI is that they exactly like the 21 other airports listed here <S> What are all the US airports where E4 "extensions" change to E2 and become part of a larger E2 "surface area" when the tower closes for the night? <S> , except that no E4 description has been provided to cover the area in the rectangular projection to the east during the time that the tower is open and the E2 airspace is not in effect. <S> Technically, as the descriptions have been written, it appears that there is no Class-E-to-surface airspace in the dashed magenta projections when the tower is open. <S> It's not clear whether this is an oversight (mistake), or whether the airspace planners simply made a presumption at KEGE and KFRI that all the E2 airspace would remain in effect 24/7 except for the particular portion that is superseded by the Class D when the tower is open. <S> In the latter case, it's not clear that that presumption is actually consistent with what was actually published in the "Airspace Designations and Reported Points" document. <S> At KEGE I've verified that local ATC treats the airspace as if there is Class-E-to-surface airspace in the projection to the east 24/7, and the same is surely true at KFRI. <S> It would be interesting to know of any other airports where the airspace designations have been handled in this manner. <A> No. <S> The Class E surface area is part of approach corridor for the instrument approaches into that airport so additional control and weather minimums are needed for this. <S> As such that block of airspace remains Class E 24 hours a day, whether the tower at KEGE is operative or not.
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Whether there has been a mistake in the airspace designations or not, it makes no sense for the airspace within the dashed magenta extensions at these airports not to be treated as Class-E-to-surface airspace when the control tower is open.
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Why are thrust reversers not used to slow down to taxi speeds? In reading this question ( Would more throttle when using reverse thrust reduce stopping distance? ), it prompted me to remember that on many of my flights (typically on 737s or CRJ type aircraft), it seems that thrust reversers are used for a few seconds after landing, but then are deactivated while the aircraft is still rolling at high speed. The pilot then utilizes the regular brakes to slow down to taxi speeds. I am wondering why the pilot does not continue to use thrust reversers down to approximately taxi speeds, to reduce the amount of brake usage (and heating of the brakes) needed. My only guess would be to possibly avoid the reversers kicking up FOD back into the engine inlets at lower ground speeds, but not sure if that's the real reason or not. <Q> A minimum max reverse power speed is often an airplane operating limitation. <S> It's mostly related to FOD (mostly sand grains and small gravel) and on some designs there may be compressor stall issues due to flow disruptions. <S> On the CRJ 700 max reverse is limited to 75kt although you can use up to 60% N1 down to zero speed. <S> On a 900 you have to be at idle below 60kt. <S> In practice, you start to come off max reverse during the landing roll transition from high energy to low energy (on the RJs, there is a speed call at 90 kts for this). <S> You come down to idle not too quickly and linger at idle for a second before stowing them; if you just slam the levers down to stow position, the reversers stow while the fan is still producing a lot of energy and you actually get a little kick of acceleration, which feels like you let off the brakes for a moment. <A> To avoid kicking up rocks and debris for potential damage and ingestion, along with hot gas ingestion. <S> Also not needed. <S> Kinetic energy is proportional to velocity squared, so once you've knocked off the high velocities, most of the energy is gone. <S> Brakes are fine from there. <A> I believe its to prevent sucking in hot air from the reverser back into the the inlet. <S> For example for the JA-37 <S> that is the reason why you are not allowed to thrust up very much at low speeds with reverser on. <A> Thrust reversers are very effective at high speed and have poor retardation at lower speeds. <S> Using the brakes in the landing roll gives them about a tenth or less of the wear that they get taxing for take-off, and greatly reduces the wear they experience taxying to the terminal. <S> Paradoxically, using the brakes in landing reduces brake wear compared to not using it at all in the landing rollout. <S> So the reversers increase your safety margin, which is always a good thing, whilst using the brakes as well reduces brake wear. <S> There is almost no increase in brake wear if brakes (with or without spoilers/lift dumpers) are used in the landing roll without reversers being deployed. <S> It's debatable whether or not reversers are worth the trouble, but they sure can help when things go wrong. <S> But as discussed, they also impose their own risks and costs. <S> Fortunately, they are MELable, and dependant on the airline, locking pins may be carried for pilot use in locking them out if need be for the MEL.
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You can use idle reverse, which gives a little bit of braking, while taxiing if the alternative is riding the brakes and overheating them, say like a taxi along a downhill slope or along a slick icy surface where braking is marginal, and you don't want to taxi single engine, and in a pinch you may use reversers to try you save your butt if you start sliding off an icy taxiway with no braking control.
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How do carbureted and fuel injected engines compare in high altitude? I couldn't find enough information on the internet for this topic. What I found can be paraphrased as: Carburetor means easy engine start while fuel injected means manual fuel start up and carburetors are cheaper. So how do carbureted planes compare against the fuel injected ones for GA purposes especially in long distance cold high altitude flights? I looked for the M-9 Series and the specs doesn't reveal much. <Q> Disadvantages of fuel injection: <S> You need to do a business case. <S> It's possibly not worth the price. <S> The Bendix fuel injection system used on the Lyc is a fairly crude (by car standards) mechanical constant flow system, and <S> the specific fuel consumption is perhaps 5-10% lower, maybe, at best, .4 <S> lb/hp/hr <S> vs .44 <S> or so for a carb (cars are in the high .3s <S> , diesels in the low .3s). <S> Lets be generous and say the fuel burn is 9 gal/hr instead of 10. <S> At 100 hrs a year that's a $500-550 saving. <S> If you spend 5000 extra for the injected engine, it's 10 years just to break even. <S> Hopefully the fuel injected option is a lot cheaper than that, or you do enough flying to recoup the extra price much faster. <S> You prime by pressurizing the system with the fuel pump (using the mixture) to inject fuel pretty much where the primer would be on a carbureted engine; so far so good, but it's a somewhat more finicky procedure and easy to flood. <S> There's a little bit of a pucker factor issue because you have a high pressure fuel distribution system snaking around the engine <S> (yes there are primer lines on a carb engine but they aren't pressurized) <S> so there is a higher fire risk due to a fuel leak <S> (it's the main reason carbureted engines are always updraft - nobody puts the carb on top). <S> When the engine is hot and sitting on hot day, you can get vapor lock in the distribution manifold and lines, sizzling away like a pan of bacon in the plenum of the cowling, making the engine really hard to start. <S> If you're on floats drifting away from a dock after pushing off and frantically trying to start the dang thing before you drift into the rocks, it becomes a big deal. <S> My personal opinion is the fuel burn reduction is not worth the costs, extra failure modes, and loss of simplicity <S> and I prefer carburetors, for simple, low speed airplanes at least. <A> Fuel injected engines make use of a fuel metering unit which directly injects fuel into each cylinder of the engine. <S> Advantages to carbureted engines: <S> Simpler Easier to start than fuel injected engines, especially when hot. <S> Disadvantages of carbureted engines: <S> Carburetors use Bernoulli principle to draw fuel into Venturi, resulting in a temperature drop, which can result in carburetor icing. <S> Less uniform control of fuel air mixture entering cylinders. <A> Performance wise, both types perform similarly at high altitude. <S> Without turbocharging/turbonormalizing, neither will have enough air at altitude to create the same horsepower they can make at low altitude. <S> Basic chemistry/physics there.
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Carbureted engines make use of a carburetor to mix fuel and intake air prior to administrating the airflow to the engine intake manifold.
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How useful is skyscrapers and high buildings lighting to get a visual reference for pilots by night? (not obstruction lights, just general lights) I would like to know how useful is skyscrapers and high buildings lighting to get a visual reference for helicopter and small planes pilots by night in cities like New York. This is different from obstruction lights. I'm talking about shapes and colors. <Q> Three building lighting examples that I often used were: <S> When flying Metroliners for a commuter airline that operated to Walla Walla, WA, I would call for a visual approach to the airport when I saw the Washington State Penitentiary. <S> It's distinctive pattern of bright lights, especially those around its perimeter, made it stick out like a sore thumb. <S> When flying night freight in 727s, from many miles out, we could see the blue neon lighting outlining the Sofitel Hotel just across the road from the southwest corner of Miami International Airport. <S> Back in the late 1990s, the high rise hotels along the beach at Tel Aviv had a distinctive pattern. <S> Head just to the south of them <S> and you were lined up for Ben Gurion airport when approaching from the west. <S> Really, if you go into most urban airports regularly at night, you learn to recognize the pattern of the lights and can use them to orient yourself. <S> Freeways with heavy traffic are also helpful. <S> Interstate 5 running south from Albany, OR to Eugene, OR has a 33 mile straight stretch that produces a line of headlights. <S> Aircraft approaching from the north can aim about 15° right of that line and be headed to the Eugene Airport. <A> Lights at night can be useful in VFR conditions, but if conditions are less than ideal, it can be dangerous to rely on external lights. <S> For example, if its pitch black and you can see a light which you think is on the ground near the airport and <S> actually its a star? <S> Spacial disorientation can occur very easily in poor visibility. <S> This is the top google search result just now <S> http://hartzellprop.com/5-tips-avoiding-spatial-disorientation-night-flying/ <S> I would say having some instrument flying skills even if you are not instrument rated is a good thing for night flying. <S> If an area is very dark with no lighting whatsoever, are you sure where you are? <S> The dark area could be a mountain that you are about to run into. <S> If you are on final approach and the runway lights go out, you could have descended too far and there is ground between you and the airport. <S> Night flying in anything other than perfect VFR conditions can be challenging especially if the pilot doesn't do much of it. <A> In addition to the direct visual references provided by building and street lighting, in major urban areas the overall light pollution often provides enough light to see terrain and unlit obstructions. <S> I commute across the Los Angeles basin by Lancair daily, and if it's overcast or slightly hazy <S> the reflected and scattered city lights provide almost as much general illumination as one would get from a good moon on a clear night in an unpopulated area.
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Buildings and their lights can be very useful to aircraft in VFR conditions at night to orient themselves regardless of the type of aircraft.
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Why does the headset man not get on the tractor? As far as I can see, the pushback operation of a passenger aircraft is carried out by a similar application at many airports. It's a towbarless tractor and driver who pushes the aircraft together with a headset man connected to the aircraft walking next to the tractor. It's strange for me to walk for minutes instead of getting on the tractor. The task of the headset man getting on a tractor will make both time efficient and less tiring. And it’ll be more faster than conventional push-out as well. Isn’t it? (Source: wikimedia.org ) <Q> The "headset man" is a wing walker, and he is there for a reason <S> - he is not just someone who needs a ride to where the aircraft is being pushed to. <S> Essentially, he is an extra pair of eyes for the tow driver. <S> This task cannot be performed from within the tow truck since the view from there is relatively limited. <A> Costs, effectivity, and safety are the main concerns. <S> If that person now has to drive a tractor around the tarmac, the airport would have to pay for tens and hundreds of tractors and their maintenance costs (such as fuel etc). <S> The person driving the tractor also has to focus on the road, and you can't move around as you wish with a tractor on an airport to observe. <S> If you are elevated on a tractor, you may not be able to observe what's going on under the aircraft. <S> Is there a fire? <S> A spark or two? <S> We may never now. <S> Safety concerns are a thing too; how close can the tractor come to the aircraft? <S> What happens if they colllide? <S> That's extra costs for the airport. <S> The person in the tractor has to be connected to the aircraft via a wire <S> so range is a question here. <S> Airport vehicles have to have a beacon light during movement. <S> This is to alert vehicles around (including planes) that they are moving and could be a risk. <S> If a plane pushes back during night, a light of another vehicle could be mistaken for the truck which elevates the risks of an accident happening. <S> Those are the debatable reasons I could think of. <A> Actually the "headset man" is the line maintenance a.k.a. mechanic. <S> The headset is plugged into the airplane and is in direct communication with the cockpit. <S> It's more precisely known as a "telephone". <S> Callsigns are usually "cockpit" for cockpit and "ground" for the mechanic. <S> "Ground" informs the "cockpit" when to release the parking brakes (when it is connected to the paymover and chocks are off).Cockpit tells "ground" when done and in which direction to pushback the plane. <S> He walks beside the airplane so he has a better and less obstructed view of the airplane surroundings, he clears the crew for the engine start up checking that the engines are clear and monitors it. <S> He also supervises the tow bar disconnection and removes the nose gear pin. <S> He checks everything is clear (trucks, people, etc.) and clears the plane to taxi after showing the crew the pin so that they can visually confirm it has been removed.
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He needs be able to see everything going on around the aircraft to avoid collisions with other aircraft or stationary objects.
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Limitations of bird flight as an aircraft design What is it that stops man from duplicating Bird Flight as Engineering? After all, birds do not require separate propullsion! They use the same wings for propulsion and navigation. My question could be broad. Is it far-fetched ? With solar energy harnessed and electronic control systems, SHOULD we not take a re-look at bird flight, at least as personal carriers or even as a short-haul option ? <Q> The movement of the bird wing during the flight is very complex. <S> Not just the trajectory matters, the shape of the wing itself changes as it moves. <S> Angle of attack changes continuously. <S> It is definitely not just about flapping up and down. <S> For a long time, this limited the possibilities of building such machines, while with recent technology it seems possible. <S> This complex movement also restricts the maximum speed possible, as even small birds cannot beat the wings more than about 80 times per second. <S> The fastest birds, such as the white-throated needletail, may reach 105 mph (168 km/h) in horizontal flight that would not be impressive for an aircraft. <A> It has been looked at. <S> This class of aircraft is called an ornithopter . <S> Scale model ornithopters can be made to work, manned ornithopters are few and far between. <S> A big problem with a large ornithopter is that you're replacing a static structure (the wing) with a large, reciprocating mass. <S> The structure gets a lot heavier and each joint is a point of failure. <S> you have to convert the high-speed rotating motion of the engines to low-speed linear motion, which means (heavy) hydraulics and large losses <S> imagine the complexity of a wing that's articulated, and at the same time needs to be able to change its profile multiple times per second at each point of its span. <S> You soon end up with an aircraft that can't carry anything because the wing is stuffed with hydraulics. <S> on a bird, the wings are a large fraction of the total area and weight of the bird. <S> It has a small payload. <S> Scaling up the concept only makes this worse (square/cube law). <A> It wasn't until the idea of flying stopped trying to incorporate bird-like flapping movements that it started to see any kind of success. <S> Wing-propulsion is a dead-end for human flight. <S> In fact, for large birds, wing-propulsion is also not as efficient as it is for smaller birds, because of the way that scaling works - if you double a length, you get four times the area, and eight times the volume (and mass). <S> Larger birds tend to spend most of their flight soaring, making use of the movement of air itself - and many of them, far from flapping, are able to lock their wings into place. <S> There are many aspects of bird flight that have successfully informed human flight, but using wings for propulsion is not one of them. <A> For the use of wings for both propulsion and sustaining flight, it has already been done as ornithopter <S> For the use of flexible wing for control, it is currently under research. <S> For example, I can cite the NASA dynamic Control Surfaces and Active Wing Shaping Control . <S> For the solar energy, I may add that gliders and birds use thermals.
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Much of the early history of attempted flight is about failure inspired by bird flight.
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Is the seat-belt sign activation when a pilot goes to the lavatory standard procedure? Yesterday, I took an inter-European commercial flight with a popular budget airline. Before take-off, the captain announced that the First Officer would be taking the entire flight today. During the middle of the approximately 2 hour cruise, the seat-belt sign came on. The flight attendant, who was next to me at the time, quickly turned to look at the front of the cabin. The captain came out of the cockpit, a flight attendant took his place and locked the door behind him, he spoke over the PA system and asked everyone to fasten their seat-belts. A couple of people stayed up and he firmly told them, again over the PA, to sit down and fasten their seat belts. Despite largely overcoming my fear of flying recently, I was slightly alarmed at this point, so I asked the flight attendant if we were expecting some turbulence. He told me that no, we weren't and that the seat-belt was only because the captain needed to use the restroom. Sure enough the captain used the restroom, came out, re-entered the cockpit and a few minutes later turned the light off. My question - is this standard procedure or is it likely the flight attendant was giving me the 'passenger friendly' version of the story? I have since wondered if it was the FOs first 'solo' flight and if that might have been related. <Q> In the US they do very similar theater when a pilot needs to relieve himself. <S> There is an announcement that nobody is allowed to come forward, and grim looking flight attendants are blocking the aisles with coffee trolleys. <S> The details surely depend on the airline. <S> Each of these procedures goes back to some bad incident. <S> The cockpit doors are locked since 9/11. <S> Since Germanwings 9525 (PIC on toilet, co-pilot had a death wish, cockpit door locked), a flight attendant has to replace the pilot in the cockpit. <S> I'm not sure if there was an incident calling for body-guarding a pilot outside of the cockpit, but maybe someone can comment. <S> Even though it is much more likely to get killed by your angry spouse or just falling down the stairs at home, security procedure theater is in fashion, and it is just getting worse and worse. <S> Yes, it is very plausible that the seat-belt sign activation in your flight was standard procedure to ensure that the PIC could pee in peace. <S> This photo of Thomas Cook Airlines (UK) is courtesy of TripAdvisor <S> Some similar reports found in the depth of the internet: <S> boards.ie in August 2013: <S> Noticed this last night on a Ryanair flight. <S> Internal phone call to stewardess was then followed by the fasten seat belt sign going on. <S> We were forced to sit down with a by then crying baby (who had been just about dozing off being rocked whilst standing up) <S> Once we were all sat down <S> cockpit door opens, one of the pilots exits and was replaced by an air hostess in the cockpit. <S> He visits the loo, comes back out, rings in, door opens, swaps with the air hostess <S> and then the lights go back off. <S> Not a hint of turbulence during the time period involved. <S> [...] <S> flyertalk.com <S> in August 2008: <S> In the middle of a flight today from LAX-ORD, the seat belt sign was turned on and the pilot or co-pilot came out of the cockpit to use the bathroom. <S> As soon as the pilot went back into the cockpit, the seat belt sign was turned off. <S> It was perfectly smooth throughout this portion of the flight, so it was obvious that the seat belt sign was turned on just for the pilot to use the facilities. <S> [...] <A> This is standard procedure when a pilot needs to use the lavatory (bathroom). <S> The area near the front lavatory is blocked off by cabin crew, so you cannot get into this area. <S> The pilot unlocks the cockpit door, steps out, and goes into the lav. <S> a cabin crew member takes his place, and the cockpit door is closed. <S> reverse steps 1-3. <S> Why step 1? <S> To avoid a rush on the cockpit by malefactors. <S> This change occurred after 9/11 -- prior to that, "The Book" on dealing with hijackers said to give them cockpit access, because they'd never done anything bad with it. <S> Why step 3? <S> So the remaining pilot is not alone in the cockpit. <S> This was strongly disputed by the unions and doubters, and there wasn't data-recorder data. <S> There was after a burst of them: 2013 LAM 470 <S> (data recovered), 2014 <S> Malaysian 370 <S> (suspected; no data) and 2015 <S> Germanwings 9525 <S> (data recovered). <S> Nobody could deny it anymore, and everyone applied the rule. <S> Interestingly, Tom Clancy predicted both 9/11 and the emotionally distraught solo pilot, in his 1994 book Debt of Honor . <S> By the way, the reason the copilot took the flight was that he needs a certain number of takeoffs, landings and hours of flight to keep his skills up. <A> Airlines are free to add any safety procedures they deem necessary for safety-of-flight situations. <S> If that is what they did, it's likely standard procedure for that airline. <A> A couple of years ago, I witnessed the same 'procedure' but without as much of the 'theater': During a very smooth flight, the 'fasten seatbelts' lights went on, people got to their seats, and a couple of minutes later, while I was still wondering why we should secure ourselves in the seats mid-flight in perfect weather conditions, the cockpit door opened and a pilot went straight to the lavatory. <S> Sure enough, shortly after he was back in the cockpit, the seatbelt lights turned off. <S> I thought of it as a rather elegant, unspectacular way to make sure the restrooms are vacant before the pilot leaves the cockpit. <S> I pictured the alternative of the pilot having to stand in front of the lavatory door, waiting for 10 minutes for the old lady to fix her make-up, and concluded that I prefer the pilot to be in the cockpit instead of standing there waiting for the lavatory to become vacant. <A> Crews usually work together for several days as a unit, and the CA and FO usually alternate flying each leg. <S> This allows each to stay current and for the FO's skills to grow through critique by the CA and by observing the CA, depending on whose leg it is. <S> In the event of emergency, though, the CA will usually take over. <S> Part of the reason the FO is there is to handle things if the CA is somehow incapacitated, so he is necessarily fully qualified to fly the plane alone. <S> However, for security and safety reasons, both pilots are required to remain in the cockpit except during brief periods during cruise, such as the one you describe. <S> It is remotely possible that it was the FO's first revenue flight in type; after all, everyone has a first day at any new job. <S> But there is nothing in your story that would indicate that was true in this case. <S> It just sounds like the CA needed to use the restroom, nothing more complicated than that.
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In some airlines, this has been standard practice for years, because of fear of accidents suspected to be solo pilots making a horrible mistake .
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Are there any current projects/plans for a VTOL passenger airliner? I was very surprised to see there's a seemingly underway project for a VTOL "business aircraft" that seats a few people. http://xtiaircraft.com , https://www.startengine.com/xti-aircraft They assert they've done a 65% scale test. I realize historically there have been a couple military transport-sized VTOL aircraft, and there's one or two small ones today. Is anyone contemplating a regional airliner or even full-size airliner VTOL concept? <Q> US patent 9,475,585 describes a Tilt-Rotor Vertical-Lift Aircraft . <S> This patent was awarded to Boeing on October 25, 2016. <S> The subject aircraft may be anything from a personal aircraft to a regional commercial aircraft for at least 100 passengers. <S> The two tilt rotors (36) are powered by a number of turbine engines (40) which are fix mounted under the wings. <S> The novelties claimed by this patent are about the transmission of power from the power plants (engines) to the rotors. <S> Figure 1 - in vertical mode: Figure <S> 2 - in horizontal mode: Images source: <S> United States Patent and Trademark Office, www.uspto.gov <S> Of course, the filing of a patent is an evidence that a company is spending at least some limited resources to the subject. <S> However, this does not mean that Boeing is actually developing such an aircraft. <A> VTOL airliners were looked at in the 1960s. <S> The Hawker Siddeley HS.141 , for example: The idea was dismissed for several reasons that still hold today: lots of engines which use lots of fuel and are costly to buy and maintain massive loss of payload (because of all the engines that are dead weight during most of the flight) <S> jet-borne VTOL is very loud (e.g. the Harrier was one of the loudest aircraft ever), and VTOL only makes sense if you can land in population centers rather than out-of-the-way airfields. <S> so you'd run into noise regulations. <S> Electric motors have one big advantage over the turbines used until now: turbines are inefficient when they run at low throttle settings, so if you use one engine for takeoff and cruise, it's running inefficiently for much of the flight. <S> Electric motor efficiency is high throughout its power range. <S> Whether it's viable remains to be seen, XTI hasn't published full specifications. <A> There probably won't be because of simple economics. <S> (Even I can understand them, must be simple and obvious.) <S> Basically even a regional air liner transports a significant amount of people on a regular basis. <S> It is not designed for single transports of single groups, it is designed to serve sustained needs. <S> This means there must be sustained ground transport infrastructure in place at the end points for those groups of people to travel to, gather, embark, disembark, scatter and travel to their destinations. <S> In other words you need an airport with infrastructure to handle passenger traffic. <S> If you have an airport, you might as well build a runway. <S> It is basically a specialized road for aircraft and you need to build roads anyway. <S> If you have a runway, conventional take off and landing will be much more economical than a vertical one. <S> That is without the extra mass of the VTOL hardware factored in. <S> Thus the kinds of places it makes sense to use VTOL passenger craft and the kinds of places it makes sense to use air liners, even regional ones, are mutually exclusive.
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The amount of traffic is either too low for service by airliners or too high for not building a proper runway that makes VTOL unnecessary waste to make sense.
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How can air launched UAV's be decelerated? I am working on disaster relief drones for a college project. I was thinking about having multiple set of drones launched from an aerial vehicle over the disaster prone area. That's when I came across a big challenge. How would you effectively decelerate a UAV that is air launched from an aircraft which is flying at a much greater speed than the maximum allowable speed of the UAV? The stall speed of the aircraft is much larger than the maximum speed of the UAV (assuming, it has to be a very low cost UAV and hence the idea of having a parachute for deceleration is not very effective). I would be glad if anyone could suggest me simple and robust ways to do achieve this. <Q> ......the same way you decelerate any other kind of aircraft. <S> Once released from the Mothership at idle power, it slows down until reaching an appropriate cruise speed thence power is increased to maintain speed. <S> If the release speed of too high for the UAV, one might use some kind of a frangible capsule equipped with a drag chute or other high drag device of some sort to enclose the drone during launch, thence the capsule fractures once the speed is slow enough, releasing the drone to begin flight under its own power. <A> Another would be to deploy the UAV inside some sort of canister that only falls away at a safe airspeed, letting the drone then fly away. <A> You can just let drag take care of it. <S> Granted <S> this means that you need to have the drone sturdy enough to handle that headwind. <S> Too high speed is only a real problem when you go to maneuver the drone. <S> Straight and level flight and gently adjustments is less of a problem. <S> The next option is to launch upwards in a climb and wait until the drone has bled enough speed that it can safely maneuver <S> it's way down. <S> A set of speedbrakes in the tail can help keep the drone stable until the speed drops enough for normal flight.
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One way might be to design the UAV to be deployed with flight control surfaces folded, use a parachute to decelerate, unfold the flight control surfaces at a safe speed and release the parachute.
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Planes returned to base after dumping fuel due toilet issues A colleague of mine experienced this and I was astonished. Flying KLM from PVG to AMS a couple of hours into take off toilets became full. The pilot dumped fuel and returned to PVG. All passengers were re-booked next day. Funnily, she had the same issue fly from JFK to LHR last year. (Probability that she was on both planes - amusing) Thinking of aviation fuel, environment, cost of re-flying passengers. I wonder why the aircraft makers not allow dumping 'contents' of 'toilet tank' (on the open sea) instead of dumping gallons of fuel. I just wonder how often does such issues happen? Would toilet tank emptying not be checked before take off? <Q> It is usually the responsibility of the Purser or In Charge Flight Attendant to check the waste tank volume when they prepare for each flight. <S> On most aircraft there is a control panel with a display that shows the actual waste volume. <S> Here are some possible reasons why the waste tanks became full: They were not checked before the fight <S> They were not emptied on the ground <S> They malfunctioned and ran continuously <S> The display on the waste control panel malfunctioned <S> In any case these tanks can not be emptied while airborne, and the only course of action is to land and have the tanks emptied or serviced. <S> On a long haul flight like PVG to AMS the crew would not have been legal to continue their duty day after returning to PVG and the flight would have to be cancelled or delayed until a new rested crew could be found to operate the flight. <A> Airliner toilets cannot be emptied in flight. <S> The valve is on the outside, and can only be accessed by ground crew. <S> Besides, two hours of flying would not have filled the toilets. <S> It is much more likely that the ground crew at PVG forgot to empty them before the next leg to AMS, or their toilet service cart was not working at the time. <A> I wonder why the aircraft makers not allow dumping 'contents' of 'toilet tank' (on the open sea) instead of dumping gallons of fuel. <S> If you are implying that the waste should be dumped to allow the flight to continue, then the additional complexity, weight and cost that would go into a mid-air waste-pumping device makes it completely impractical. <S> The waste tanks are intended to be big enough for any flight, and should start empty if the ground-crew handles it properly. <S> A waste-pumping mechanism would need certification and regular maintenance, and take from the weight and fuel capacity of the plane. <S> It would very rarely get used, and is better handled just by reliable ground service.
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An aircraft with full lavatory waste tanks can not continue on it's flight as it is a requirement to have a specified number of serviceable toilets on every flight.
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What is the backup for a glass cockpit, if a plane loses power to the displays/controls? I'm assuming there is still power to the rest of the plane - maybe it's an unrealistic scenario. <Q> I'll answer this question as "If the glass cockpit instrument fail, what are the backup? <S> " <S> This answer will also be General Aviation oriented (as I'm a PPL student) <S> The short answer is redundancy . <S> At first, let's look at a G1000 (standard GA glass cockpit) architecture : <S> The most important components are : One (or multiple for redundancy) AHRS : gives information about Attitude and Heading of the aircraft, thanks to electronic gyrometres / accelerometres / magnetometres. <S> One (or multiple) <S> And two Integrated Avionics Unit, that collect data from AHRS / ADC, and generate the content displayed on screen. <S> Now, Although the two screens usually don't display the same informations (PFD and MFD), These two systems are standalone : in case of a screen / Avionic unit failure, the second can take other. <S> Here the goal is to remove all single points of failure. <S> But what if the whole EFIS fails ? <S> The definition of "essential" depends of the type of flight (day VFR, night VFR or IFR?). <S> For some aircraft, there backups are traditional (steam gauge) instruments / others have independent electronic systems, like the new Cirrus SR22 G6 : all electric ! <S> And in the case of a complete electrical failure? <S> Depends of the aircraft. <S> In my case, I fly the Robin DR401 (certified for night VFR): <S> The EFIS is a Garmin G500 (smaller version of G1000) along with a GTN650 GPS. <S> With such a cockpit, even if I have a complete loss of electrical power, backup instuments would still work : Altitude, Airspeed and Vertical Speed indicator don't require any power to operate ; So does the slip/skid indicator (a simple ball) And the Attitude indicator gyro is powered by a vacuum pump, linked to the engine ; it would thus still operate. <S> In that case I'd be more concerned about the loss of radio / transponder / flaps control / trim than the loss of instruments! <S> To summarise, Glass Cockpits are designed to avoid the creation of single point of failure, to reduce the risk of complete loss of instruments, thanks to redundant system / backup instruments / displays... <S> And for all-electric planes, I guess backup power supplies! <A> Depends on the plane. <S> In my plane, I still have the airspeed indicator, altimeter, vertical speed indicator, turn/slip indicator, compass, and a hand held radio that I can use for comm's, none of which are connected to the electric supply that runs the panel displays. <S> Engine controls are still manual, as is the ailerons/elevator/fins. <S> For night flying, a flashlight or two are kept handy as well. <S> So fly the plane, figure out where you're going, communicate. <S> (Aviate, navigate,communicate). <S> Also, I have dual Garmin G5s which are battery backed up, so I might lose the radios, but my main gyro's will still be active for 4 hours in case <S> I lose the other stuff while IFR. <A> In airliners is a bit different than in General Aviation aircraft, since you have room for a lot more backup systems. <S> Nevertheless, when you lose power on all engines, your glass cockpit screens go black immediately. <S> But don't worry, you always have an independent instrument called ISFD ( Integrated Standby Flight Display for Boeing) or ISIS ( Integrated Standby Instrument System for Airbus) which gives you the basic flight parameters in order to keep flying while trying to recover your systems. <S> Right in that moment, the aircraft will realize of the problem and automatically will release the RAT (Ram Air Turbine) which is a little propeller that drops from the belly of the aircraft providing emergency power for the electric and hydraulic systems. <S> Eventually, the emergency checklists will guide you to switch on the APU (if you haven't done it yet, like wisely did Capt. <S> Sully). <S> The APU will be running within a few minutes and you will recover all your glass cockpit capability. <S> At that point you will be already troubleshooting your engines or.... <S> looking for a spot to land in the Hudson :) <A> Not explicitly mentioned in the other answers yet: <S> in almost all cases the electrical power systems feeding the displays and sensors have redundancy in one form or another. <S> Sometimes this is a separate engine-driven alternator or generator, sometimes a backup battery dedicated to a subset of the EFIS hardware that can run it for an hour or so if the main alternator or battery fails (that's the case in the Dynon system in my Lancair).
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It is required by law to have backup of essential instruments. Air Data Computer: gives information regarding airspeed / vertical speed / altitude, thanks to static / dynamic pressure informations.
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How could the B-29 bomber back up under its own power? I was watching some footage of the Enola gay I was interested in the part where the plane was backing up over the bomb (starts around 18:27). It appears to be doing this under its own power with the propellers running. Could the B-29 reverse some propellers to do this? <Q> Some B-29s had reversible pitch propellers. <S> Wikipedia B-29 <S> Variants <S> Moreover, engine packages changed; including the type of propellers and range of the variable pitch. <S> A notable example were the eventual 65 airframes (up to 1947's end) for the Silverplate and successor-name "Saddletree" specifications; built for the Manhattan Project with Curtiss Electric reversible pitch propellers. <S> Army Air Forces tests reversible propellers for B-29 bomber <A> Although I can't find direct hard documentary evidence, I'll make the case that that B-29 has Curtis Electric reversing propellers thusly: <S> We know that Curtis had a reversing version of its electric propeller during WWII because the Consolidated had them for the inboard engines of the Coronado flying boat. <S> The B-29 in the video is clearly backing up under its own power, and you can tell at least two engines are higher RPM from the blade strobing. <S> It's not the wind blowing it back. <S> The B-29 had a free castering unsteerable nose wheel and you can see that steering is being done by ground crew manhandling a towbar for fine steering, probably assisted (or hindered) by bits of braking by the pilot. <S> Looks like a pretty tricky task. <S> There were many field mods done on the B-29 <S> and things like installing reversing props in the field as an upgrade would certainly have been done late in the war. <S> And you can bet that Enola Gay had all of the latest and greatest field mods. <S> As field mods they were probably covered by Flight Manual Supplements and that sort of documentation can be very hard to track down. <A> Many planes have props that can be set to a negative angle, for braking during landing. <S> So, that could also be used to reverse under its own power.
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All the B-29s used for the Atomic bomb missions had reversible pitch propellers.
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What is an "all-weather" aircraft? I've read a few times that such-and-such a plane is an "all-weather" aircraft, for example : The McDonnell Douglas F/A-18 Hornet is a twin-engine, supersonic, all-weather, carrier-capable, multirole combat jet. This is quite intriguing and a rather odd thing to specify. A fighter that couldn't be operated in for example rain (perhaps because it might dissolve, rust or leak) wouldn't seem to be much of an asset to one's air force. Similarly, I would not expect a supersonic fighter to be unable to deal with gusty winds, or a heatwave, or really, anything else the weather might be expected to throw at it. What sort of jet would not be an "all-weather" aircraft? <Q> “All-weather” is a little bit of a hold-over from the WWII days where severe weather was much more of a threat to the aircraft. <S> Between less reliable engines, delicate and finicky instruments like artificial horizons, and limited anti-ice technology, flying in adverse conditions was much harder then. <S> Becoming completely disoriented in low visibility was almost a death sentence. <S> Special planes were made with the sole purpose of fighting at night, and certain designs were better than others for all-weather operation. <S> Nowadays, world class military aircraft are all pretty much all-weather because of the 70 years of avionics, propulsion and airframe improvement. <A> Up to WW2, aircraft operations were highly dependent on weather. <S> navigation used ground observations to correct for drift etc. <S> military aircraft needed optical observations to find their targets (on ground or in the air). <S> This limited aircraft use to daytime and put an upper limit to the amount of clouds that were acceptable. <S> A target completely covered in low-level cloud meant you couldn't find it. <S> The same goes for the landing. <S> You had to find the airfield visually. <S> Descending blindly through clouds could end up with you crashing into the nearby hill. <S> Then in WW2, radar and radio navigation aids were used for the first time. <S> This allowed some aircraft (the ones with proper equipment) to function day and night. <S> The equipment was too large and expensive to be installed in every aircraft, so you got a bifurcation: a large amount of day fighters (without radar), and some night fighters (with radar). <S> Similarly, bombers were flown in groups where only some of them had radio navigation (Pathfinders) and the rest followed the leader. <S> Later on, the equipment got cheaper and smaller, and from the 1960s night fighters ceased to exist as a separate class: pretty much all new fighters were all-weather capable. <S> So an all-weather aircraft needs radar, accurate navigation, and an ILS. <A> All-weather fighter aircraft means it can operate in low-visibility such as night time. <S> For example F-16 was envisioned as a cheap day-fighter, but ended up being an all-weather fighter. <S> See: https://en.wikipedia.org/wiki/Night_fighter <A> This means airborne intercept radar and homing missiles, vs older fighters that relied more on the pilot's vision and guns.
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In the context of a fighter this can mean not only that the aircraft can operate safely in (almost) all weather conditions, but that it can be effective in combat in weather also.
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What does the future of the weather radars look like? Planes had weather radars for a long time (Dassault Falcon and Learjet35A) which was useful since you either had to ask ATC, listen the ATIS frequency or ask the flight advisory before flight planning in order to learn the weather. But we are living at a time of two way transponder communications and more and more of the world (At least the USA) are employing more weather stations and satellites are continously monitoring the world which makes the weather information more and more accessible and in flight Wi-Fi finally arrived! So. are there plans about sending weather information through two way transponders in the future? Will this hamper the importance of weather radars? <Q> In the USA, planes with ADS-B can receive FAA transmitted weather from ground stations for display in the cockpit. <S> It can lag by several minutes. <S> https://www.faa.gov/nextgen/programs/adsb/pilot/ <S> Planes with XM weather can receive more timely weather from satellite feed for display in the cockpit. <S> Airborne radar has the advantage of being the most immediate, but you may not be able to see much past what is immediately in front of you, so combining that with ground/satellite feed to give you a view of what is farther ahead would be the best of both. <S> I have ADS-B in my plane, but I don't do any extreme weather flying, just climbing thru cloud layers to get to nicer weather on top, or dropping thru a layer to land. <S> I'm not out there trying to dodge thunderstorms and heavy rainstorms. <S> If the weather is that bad, I can wait it out. <A> Since both ground based and airborne weather radar is all about bouncing radio waves off water, the issue is, do you want to send the radio waves from your airplane or from a ground antenna somewhere in the region. <S> Well, there are advantages and disadvantages to both; one presents a weather "big picture", the other tells you what is going on right in front. <S> If you have choose, you want an airborne system because that's what is best able to keep you out of trouble right now. <S> Pilots flying IFR without weather radar could rely on ATC's weather radar for guidance in staying away from severe weather, but this was never considered optimal and airborne radar has always been preferred. <S> The Storm Scope thunderstorm detection system, that locates and maps lightning strikes, came out in the 70s as a way for light aircraft that couldn't install airborne radar to dodge cells with higher confidence than just advice from ATC. <S> It has its own deficiencies because the really bad stuff is usually associated with water more than electrical charges so Storm Scope couldn't always be depended on the keep you out of the worst of a storm, although it was better than nothing. <A> What I also foresee is the integration of information coming from: <S> Airborne weather radar Ground based terminal radars <S> Satellite radars <S> Other sources like LiDAR or thermal sensors. <S> Each of them has advantages and disadvantages. <S> For example, one of the most dangerous disadvantages of airborne radars is the "attenuation", which hides the weather behind a strong signal. <S> There has been accidents in the past directly related to this limitation. <S> The radar technology itself has a huge limitation to detect certain types of dangerous weather conditions, for example ice crystals, even in high concentrations. <S> In order to overcome such limitations, the future weather systems most probably will relay and integrate radar along with other technologies like LiDAR ( Laser Imaging Detection and Ranging ). <S> There is a lot of research nowadays using LiDAR to study weather, it wouldn't be a surprise to see that in the aviation industry in the near future.
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I'd say that what you WILL see though (or are seeing already) is a seamless integration of airborne and ground weather radar via various data channels, as well as electrical storm activity, into aircraft displays, to provide the accurate possible presentation.
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Is it possible for a person to fly with mechanical wings attached to his torso? I’ve seen several adaptations of this concept in fiction from the tales of Icarus to Falcon in the MCU. But is it possible in reality for an average human to be able to fly through the air by wearing these gadgets? If it is possible, then how would this work? <Q> You could reasonably call a hang glider "wings strapped to the torso" for this purpose -- hence the answer is "yes, sort of." <S> With a well designed glider, one can launch from sloping ground and soar on slope lift or thermals, limited by oxygen requirements and fatigue. <S> Hang gliders have done cross country flights running to many hours, stayed up literally dawn to dusk on ridge lift, and flown high enough for the pilot to require oxygen (and then some, I believe the altitude record is around 18,000 feet). <S> None of this, of course, is powered by the pilot, using either arms or legs, but this is clearly "wings strapped to the torso. <S> " <S> Add a small engine and you get a modern ultralight/microlight, or something like Rocketman's jet powered wings. <S> The latter, especially, is still pretty clearly "wings strapped to the torso." <A> Humans aren't strong enough to fly using their arms to flap a wing . <S> In other words, humans make terrible hummingbirds. <S> You can build an ultralight aircraft that's pedal-powered <S> (human leg muscles are much stronger had have better endurance than arms), but this is still on the edge of human capability. <S> These aircraft will fly low and slowly, and the distance record is ~115 km. <S> Add an engine (or glide from high altitude), and it becomes feasible to use a wingsuit (or a rigid wing attached to a harness). <A> Assuming you mean wings attached to one's arms: Only trained gymnasts are capable of holding the Iron Cross for a short period of time (see Rings_(gymnastics) ). <S> With the Iron Cross, the center of force counteracting gravitational acceleration is one arm length away from the center of mass. <S> Depending on the aspect ratio of the wings attached to one's arms, it'll be harder or lighter to hold your wing compared to the Iron Cross, for non-vertically accelerated flight. <S> (ref. <S> Force_and_levers ) <S> Therefore you only see wing-suits with very low aspect ratio wings in use. <A> You didn't specify whether engines were allowed, but Jetman: https://www.youtube.com/results?search_query=jetman
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According to Usherwood, for a human to take flight on flapping wings, “your body would have to be made almost entirely of muscle.”
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Does Nitrogen inside commercial airliner wheels prevent blowouts on touchdown? I just watched the first episode of Inside Mighty Machine where civil engineer-turned-host, Chad Zdenek, discussed innovations of the 747. One innovation he discussed was the increased number of wheels and trucks, along with this tidbit: When the 747 touches down, the wheels must accelerate from 0 to 150 mph in a heartbeat, making them skid before they start to spin. That's why they smoke on touchdown. That friction causes heat to build inside the wheel, creating the risk of an explosion, so the 747's tires are filled with nitrogen, an inert gas which, unlike oxygen, won't aid combustion. That helps protect the plane from blowouts and keep landings safe. That seems like an oversimplification and backhandedly suggests that the alternative is to fill the tires with pure oxygen—a surefire recipe for combustion I would think. So, (1) is nitrogen really "the thin line" between safe landings and blowouts on modern commercial airliners and (2) is nitrogen landing gear inflation a legitimate innovation of the 747? <Q> Apart from the paragraph you quoted, here are a few more reasons. <S> Dry nitrogen is specified for aircraft use. <S> I believe the rules say that any gas used cannot exceed 5% oxygen content. <S> Because its dry it reduces corrosion. <S> Nitrogen moleculeas are slightly larger than oxygen and takes longer to escape.. hence tyres stay inflated longer. <S> But more importantly, nitrogen has a lower rate of expansion/contraction than normal air. <S> An aircraft wheel has to live in sub-zero (at 40,000ft) and blistering <S> hot (IIRC <S> about 500deg C will trigger hot brakes warning). <S> A gas with a low expansion rate cf temp is desirable. <S> This trait has been put to good use by unscrupulous 'performance auto shops' which claim better handling with nitrogen in the tyres... <A> There is some truth in the claim about inerting. <S> Mostly, blowouts are as a result of high temperatures weakening the rim and tyre and increasing gas pressure within it, rather than being the result of chemical explosions. <S> However, overheated tyres can decompose to produce gaseous products that can explode in air at high pressure and temperature and there have been airworthiness directives related to this (see, e.g., FAA Advisory Circular 20-97B ). <S> Of course, the outside of the tyre is bathed in oxygen anyway, but at much lower pressure, so there's much less of it around. <A> In addition to what the current answers mention, it should be noted that the danger is not merely theoretical, though blowouts on touchdown aren't necessarily the primary concern. <S> Mexicana flight 940 was the deadliest 727 accident as well as the deadliest accident on Mexican soil with 167 deaths. <S> Accident investigators found that a tire had been serviced with regular air instead of pure Nitrogen. <S> A brake malfunctioned and overheated during the takeoff run. <S> This caused the tire to heat up to the point that the oxygen in the tire chemically reacted with the tire itself to the point that the tire exploded fifteen minutes after takeoff. <S> This severed hydraulic, fuel, and electrical lines, which then resulted in an in-flight fire at cruising altitude. <S> The pilots declared an emergency and tried to return to Mexico City, but ultimately lost control and crashed into a mountain before they could get back to MEX, killing everyone on board.
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Also, having oxygen in the tyres will oxidize the rubber to some extent, weakening it.
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What is the largest (size) solid object ever dropped from an airplane to impact the ground in freefall? What is the record for the largest single solid item that has ever been dropped from an airplane at free fall to the ground? Here, "free fall" means falling vertically, or nearly vertically falling allowing some leeway for expected horizontal movement such as the ground speed of the plane doing the drop, winds, or unintended Magnus effect among other things, and allows for normal atmospheric air resistance. The object being dropped should be payload, not part of the vehicle doing the dropping. The object should not be designed with the intent to generate lift. For example, the above mentioned Magnus effect would disqualify if a machine was purposely built to spin with the intention of generating lift. This includes things with wings, parachutes, landing thrusters, etc. The object must have hit the ground in an uncontrolled descent in the past. In other words, satellites in free-fall orbit around the Earth do not count unless they fell to the ground and then got re-launched into orbit again ( unlikely ). Objects that burn up in the atmosphere do not reach the ground as a single solid object, so they do not count unless any possibly remaining fragment that may reach the ground is still the biggest object to be dropped and reach the ground in its destroyed state ( unlikely ). The item does not have to have been intentionally dropped. For example, if it were dropped with a parachute, but the parachute failed to deploy, that counts. Bombs easily count as long as they don't have a parachute, thrusters, wings or any other design factor that is intended to generate lift. Last, but not least, "largest" means greatest volume, not heaviest. <Q> <A> If you consider the space shuttle an aircraft its self, the external tank was dropped after it was depleted and broke up on impact to the Indian ocean . <S> The heavy early version weight 58,000 LBS empty and 1.68 Million LBS fully loaded. <S> While not heavier than the shuttle it was volumetrically larger. <A> If we're counting the Space Shuttle orbiter , then I'd say it's probably that's probably the winner at around 150,000 pounds. <S> As Juan's answer describes, it was dropped from the Shuttle Carrier Aircraft for glide testing before the first shuttle launches. <S> The orbiter 'glides' about as well as the average brick, so <S> this seems like it should count. <S> Other possible contenders I can think of: Pegasus XL , an air-launched rocket. <S> It is dropped from an aircraft, after which point its rocket motor ignites to launch a satellite into orbit. <S> Approximately 51,000 pounds. <S> The Minuteman 1b inter-continental ballistic missile. <S> While normally launched from the ground, a test was conducted on 24 October 1974 in which one was dropped and launched from the cargo bay of a C-5 Galaxy . <S> According to the USAF, the dropped missile stack weighed 86,000 pounds. <S> The absurdly-large Russian fusion bomb RDS-220, better known in the West as " Tsar Bomba ," coming in around 60,000 pounds. <S> It's also worth noting that all of these may be soon blown out of the water if Stratolaunch Systems gets their way. <S> The Stratolaunch Carrier Aircraft is capable of dropping 550,000 pounds of rocket stack payload. <S> The first test flight of the carrier aircraft has been completed, but it hasn't dropped a payload yet. <A> A good candidate here is the US T-12 cloudmaker ( https://en.wikipedia.org/wiki/T-12_Cloudmaker ) at 43,600 lbs. <A> Not dropped from an aircraft, and was part of the vehicle but Saturn V’s first stage was jettisoned at the weight of more than 360000 lbs or 160000 kgs. <S> On Apollo 11 the mass of the first stage was 363425 lbs when jettisoned. <S> After that, it fell freely to the ocean. <S> Source: http://apollo11nasa.blogspot.com/2012/07/saturn-v-inert-weight-or-dry-weight-or_22.html?m=1 <A> The MOAB prototype was 30 feet long and 40 inches in diameter and hard landed. <S> It seems to qualify, but it is a GBU with gridfins, so not totally a dumb bomb. <S> It has almost the same envelope volume as the T12. <S> You'd need an accurate scan of the two to figure out which had the greater volume. <S> I also seem to recall that large seaplanes were developed to carry boats out to bombed naval vessels. <S> These weren't little rafts, these were plank on frame, wooden, ocean capable lifeboats with diesel engines that could be airdropped. <S> It also sounds like failed air drops could qualify - extraction chute functions normally, Main shoots or pallets fail completely. <S> That has certainly happened a few time. <S> Several of the D-Day invasion towed gliders suffered catastrophic structural failures while being towed, and became qualifying items as they were jettisoned. <A> Since you have edited the question to require both "free-fall" and "second use in this fashion" (implying intentional dropping ), the answer is "none". <S> Things aren't dropped out of airplanes on purpose twice.
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I can't think of anything dropped from an aircraft larger than the US Space Shuttle when it was dropped from a specially modified 747 during the testing phases of development.
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What are some of the longest flights without modern navigation systems? Context: As a private pilot, I enjoy preparing my flights with a mix of paper charts and iPad apps. In flight, my navigation is now often very assisted by the G1000 or iPad, relegating the paper maps to backup. But I remember that, when I was only using paper maps during training, the workload could quickly rise and that I was sometimes exhausted after a short navigation because of that. What are the longest (either by time or distance) known flights ever flown without any "modern" navigation system ? I'm interested by flights that comply to the following criteria: Did not use any GPS or inertial navigation system (maps and stars are ok) Radio navigation is ok (but bonus point if the aircraft is not equipped for that) Have only one leg Take off and landing fields can be the same if the flight was long enough to require actual navigation (recon missions, circumnavigation...) Can be historical stories (war heroes, military experiment, pioneers...) as well as modern ones (record attempts...) May have a flight crew as large as Pilot + Co-Pilot + Navigator + Engineer, but... ...don't have any rest period for the crew (no backup crew on board) <Q> It seems reasonable to assume that no modern navigation means were used in 1931. <S> However, the flight was mostly local, so navigation was not really required. <S> The all time record is from Dick Rutan and Jeanna Yeager in 1986. <S> The latter was only functioning for approximately 4 hours per day, because the GPS constellation was not yet complete and many satellites were missing. <S> The Double Sunrise flights seem to qualify, with times in the air between 27 and 33 hours. <A> While a slightly shorter distance than the Rutan Voyager, in 1949 the Lucky Lady II did the first nonstop circumnavigation (using air-to-air refueling). <S> Flight time was 94 hours 1 minute, and a distance of 23,452 mi (37,742 km). <S> Looks like it predates any airplane use of Inertial navigation systems . <S> Unfortunately this flight had multiple pilots on board, and so fails the "backup crew" rule, <S> but I think is still worth mentioning. <A> The first thing that came to my mind was the Pan Am Clipper flights, especially those operating about the Pacific / China. <S> https://www.clipperflyingboats.com/transpacific-airline-service
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This list of flight endurance record on Wikipedia lists as number 3 an endurance record of 84 hours 32 minutes between May 25th and 28th 1931. The Rutan Voyager had state-of-the-art navigation on board, including an Omega Navigation System and a GPS receiver.
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Can a helicopter mask itself from radar? I have read somewhere that if a helicopter is traveling under 100 km/h and below 5 meters AGL then most radars will ignore it. From what I understand of this process, the radars can pick up things like cars and vehicles driving on the ground and thus need to ignore certain signals if they are traveling below a certain speed and height. Is this actually the case, though? Does this also apply to military-grade radars? Edit: This is not asking if a helicopter can fly under the radars coverage, but whether the helicopter can using techniques to notch its signal from being displayed as a contact on a radar operator's screen. <Q> Note that for advanced radar systems, moving helicopters might always be distinguishable from cars and other objects, due to the fact that helicopters have moving rotors. <S> While I have no information on military systems, I know the systems by robinradar can separate drones from birds by using doppler shift techniques. <S> Doing this on an actual, full-size helicopter without rotor guards should be a lot easier than on a drone. <S> This means avoiding detection by moving slow and staying low might not work, unless you can stay out of the line of sight of the radar system. <A> The answer is yes (in most cases) but it has little to do with the helicopter itself. <S> 5 meters (~16.5 feet) <S> AGL is quite low to the ground. <S> Chances are you are simply below the radar horizon for whatever the local radar facility is. <S> At that height you are even below trees, buildings and the like. <S> This of course is affected by the distance to the radar unit as well as having a clear line of sight to it. <S> So being on an airfield or very close to a radar facility you may very well be visible. <S> Military grade radars are bound by the same laws of physics as civilian ones, so yes it applies. <S> Like any electronic system, radar units are susceptible to noise and do implement filters but they tend to be for general "noise" exclusively filtering out helicopters flying <100km/h and under 5 meters is a somewhat specific constraint. <A> The JSTARS (Joint Surveillance Target Attack Radar System) <S> military radar developed and used from 1991 was particularly good at identifying helicopters. <S> JSTARS was designed to identify moving objects on the ground, such as tank columns and supply convoys used by the Iraqi forces during Operation Desert Storm. <S> It used a doppler radar suspended below a large aircraft and, as such, it had generally better line-of-sight capabilities compared to ground based radars. <S> Using doppler, any movement was highlighted, especially the rotational movement of the rotors, which meant that even if a helicopter were sitting on the ground with its rotors idling, it was still seen by JSTARS operators. <S> Helicopters trying to fly slowly in order to avoid air tracking radar systems would make it far more likely that they'd be identified by a GMTI (Ground Moving Target Indicator) system. <A> A helicopter is no different from anything else. <S> And radar doesn't care whether you're in a helicopter or whatever. <S> All the radar cares about is whether you're reflecting energy back to its reception antenna. <S> A helicopter will do that, IF it's in line of sight to the antenna (and to the sending antenna, which may be somewhere else). <S> At 5m above the ground, a helicopter or indeed anything would have to be pretty close to the radar installation to do that, not only due to the curvature of the earth but the transmission angle of the radar installation, terrain features, etc.. <S> For example even a low rise in the terrain, like an earthen berm protecting the radar installation, or some trees standing around it, a shack or house in the vicinity, would be enough to hide something from detection. <S> This to prevent cluttering the displays with radar returns from birds, cars, motor cycles, and things like that. <S> But that's a function of the display unit, not the radar receiver. <S> It still gets all those returns, there's just a software filter between it and the screen that declutters the data for easier interpretation by the radar operator, who should have an option to tweak or even turn off that decluttering as needed.
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And yes, many radar installations can be set up to ignore things that don't have at least a certain speed and/or are below a certain altitude.
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What could be the cause of an uncommanded roll at high speed? I have a problem with a T-38. There is uncommanded roll to the left when the aircraft flies at 250 knots. But as the aircraft speed goes up around 500 knots, the uncommanded roll is now to the right. During 500 knots we could control the plane with 15-20 aileron trims. What may be the problem? We have replaced a lot of systems and cylinders. And we changed the travel limits of aileron, flap, rudder, and horizontal stabilizer. But no change has been observed. <Q> I once went on-site to troubleshoot an airliner with an uncommanded roll problem. <S> The operator had rigged this and rigged that and were in the process of ordering new aileron power control units, pretty much out of desperation. <S> I asked about the trim actuator, which they had replaced with a known good unit off another aircraft, making them think that couldn't be the problem. <S> I centered the trim and went to look at the position of the rig pin holes in the aileron control circuit. <S> They were mis-aligned. <S> The trim actuator on this airplane was an electric linear type with an internal Linear Variable Displacement Transducer (LVDT), that supplied the position signal to the cockpit trim indicator (or EICAS in this case), that was "dithering", that is, the signal was drifting around. <S> When you thought the trim was centered, it was actually offset, and this error would randomly change as the actuator was moved. <S> On the original airplane the actuator was installed on, the dithering wasn't enough to cause a snag to be raised by the flight crew <S> so its internal problem went undetected. <S> The variations in roll you saw at speed may be some other phenomenon, or it just could have been coincidental variations in the trim indication on that flight. <S> So, if it was me, the trim system itself would be an item to cross off the list before proceeding to more desperate measures. <S> Do a thorough functional test of the trim system and its indication, and also look for things like backlash within the actuator itself or in the linkage. <A> Generally, the rudder will have more authority at lower speeds, while aileron will gain authority as speed increases. <S> Based on that, I'd suggest verifying the rigging of the airframe; look for a fin, rudder, or rudder trim that's generating yaw in the direction of your lower speed uncommanded roll (yaw will produce roll due to whatever mechanism provides roll stability). <S> The aileron trim that offsets that uncommanded yaw will overpower it as speed increases, producing your uncommanded roll in the opposite direction. <A> If the flight control is a hydraulic system, have you changed the fluid recently, if yes you need to purge the system for air bubbles, otherwise you need to check the fluid quality for impurity. <A> http://www.aiaahouston.org/Horizons/ATS2019-Presentation-SS-Tang.pdf <S> This presentation was given in AIAA Houston Section Annual Technical Symposium (ATS) at NASA Johnson Space Center, Gilruth Center. <S> A new discovered root cause for uncommanded roll, pitch and yaw was given. <S> A technical paper was presented and a live demonstration was shown in the 2019 AIAA AVIATION FORUM and EXPOSITION. <S> A Youtube video shows this phenomenon. <S> Hope <S> this may help you to understand the uncommanded roll. <S> Actually, it was not "uncommanded". <S> It was indirectly commanded.
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If this were a model aircraft with a wide speed range (like, say, a hand launch glider), I'd expect this to be a cross-trim problem.
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How can I fix the stalling of an RC plane after the addition of floats? I'm modifying a RC plane into a bi-plane with floats and it keeps stalling. I don't have a bigger battery or better motor to add so how do I fix this? This is the biggest challenge I've ever faced. <Q> Your model is based on the FX-803 Piper Cub model shown in this video . <S> It's made from expanded polystyrene wings and fuselage, with a two channel radio that controls thrust from two motors mounted below the wing, with overall thrust controlling pitch and differential thrust controlling yaw. <S> There are no moving control surfaces, and the propeller on the nose is a cosmetic windmilling attachment. <S> Your extra wing, lashed on with elastic bands, may or may not produce lift, but adds additional weight and drag below the thrust line, inducing a significant nose down moment. <S> Your carved foam floats add additional drag even further from the thrust line exacerbating the nose-down problem, and further increasing the weight. <S> The original model was built and trimmed to give flying characteristics that could be controlled by simple thrust adjustments. <S> There is no moving surface with which to counter the added drag, and even if there were, it is unlikely it would have sufficient authority to overcome the problem. <S> The modifications may also have moved the centre of gravity significantly, possibly beyond the point where it is fixable. <S> The model shown in the video has sprightly performance on limited power. <S> The additional weight and drag you have added could easily overwhelm the available power. <S> Realistically, I doubt you will be able to get this to fly. <S> If you do, please come back and post a video! <A> This plane appears to have no moving control surfaces at all-- it appears to be controlled purely by differential thrust from the two wing-mounted motors. <S> You could consider modifying the horizontal stabilizer to give the plane an elevator, even if just works as a ground-adjustable trimming device. <S> You need to fix the elevator in a slightly lowered position to counteract the stalling tendency you are experiencing. <S> Don't overdo it! <S> It could be as simple as piece of stiff cardboard taped to the back of the horizontal stabilizer, that you can bend into a lowered position. <S> In fact it looks like you may have already done something like this with the vertical fin, to give some right rudder trim. <S> Or you could just try moving the CG forward by adding weight to the nose. <S> This is probably the best solution as will enhance pitch stability as well as help address the trim issue. <S> Again, don't overdo it! <S> Small changes will be best-- Or try a combination of both approaches. <A> OK! <S> Is there a doctor in the house! <S> Try moving the lower wing back until it stops pitching up. <S> " <S> Staggering" the wings may alsoreduce interference between the two, which may be part of the problem once it starts to pitch up. <S> It should fly better overall with the lower wing further back. <S> Try this modification and hand launch to test. <S> If it works, then reset your floats as needed.
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You could try adding a fixed elevator to provide significant down force at the tail, but this will further compound the drag issue, and could also affect centre of gravity.
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What happens if you do emergency landing on a US base in middle of the ocean? A theoretical situation. I fly from Honolulu International to the Bejing but my private jet gets fuel starvation and then I land on the Wake Island airstrip. What happens next? Would the military give me fuel or they would give me shelter and tell me to stay? Did such things ever happen? <Q> Wake Island has had aircraft divert there before, as it serves as an ETOPS diversion airport. <S> Per the remarks on AirNav and the NOTAMs: <S> RSTD: <S> VERY LIMITED OPERATIONS STATUS, AVBL FOR EMERG LDG AND MIN PRIORITY TFC. <S> TRAN ALERT: <S> SVCG FEES RQD. <S> TRAN SVC HRS <S> 2000-0400Z (0800L-1600L) <S> TUE-SAT. <S> CLSD SUN, MON, HOL. <S> FUEL: <S> FLIGHT CREW REQUIRED TO ASSIST IN REFUELING. <S> J5(MIL). <S> FLUID - W, SP, PRESAIR. <S> It's possible you could plan to fly through there with prior permission, as with most military fields. <S> AirNav reports 2% of the average of 49 operations per day are transient general aviation, <S> so it's not entirely military, but government and contractors probably make up most of this. <S> If your emergency is just that you forgot to have enough fuel, you should be able to get more fuel and depart again, for a fee. <S> If there is a fuel leak or some other maintenance issue, you could be in for a longer stay. <S> RSTD: <S> NO AIRCRAFT MAINTENANCE AVBL. <S> As with the airliner that diverted, maintenance equipment and personnel will have to be flown in for any work that needs to be done. <S> You should be in contact with Oakland ARTCC through San Francisco ARINC in the oceanic airspace, and can call base operations ahead of time to advise of your needs. <S> If it's outside of their normal staffing hours, they need at least 30 minutes notice to open back up. <A> Landing at a military base is not off limits to civilian aircraft but typically requires some pre-approval. <S> If you came diving in with out any radio announcements and on an apparent crash course the situation may not play out in your favor. <S> But a stable glide in approach with announcements should be safe. <S> You will have lots of questions to answer on the ground though. <S> I’m sure you will be scolded quite a bit for departing without enough fuel and an FAA/NTSB incident report will need to be filled out. <S> Fuel may be a bit tricky (although I’m sure you can get some). <S> It’s likely that you will have to submit some forms etc etc <S> but it’s unlikely they will keep you stranded. <A> Many years ago, I had an unexpected landing at a non-towered military base. <S> I did not need fuel which made things easy. <S> The base stored nuclear weapons, and we were escorted at all times, until we were able to depart. <S> Security was annoyed, but polite. <S> Since we did not leave the ramp, there was no paperwork that we needed, however we did provide the MPs identification, and an explanation as to why we needed to land there. <S> That was several decades before 2001, so the welcoming committee might have a slightly different posture today. <S> From a subjective standpoint, people are human, and aircraft are imperfect machines, and there has to be recognition of that. <S> Long established maritime law recognizes that. <S> Also, the ramp personnel explained that obtaining fuel would have been problematic and potentially required substantial delay. <A> The military understands that a distressed aircraft is a priority situation in terms of safety. <S> When you are an emergency aircraft, all available resources will be provided to you. <S> Once the emergency is complete, the situation will change depending on where you are and what resources are available. <S> They will follow some security protocols initially and it will be slow and cumbersome. <S> Then you’ll have the FAA to deal with. <S> But you’ll be safe, and as a guy who has been a distressed aircraft and damaged a plane on landing, you’ll be one happy camper to be uninjured and healthy. <S> Long story short, passing up a safe landing area just because it’s military is crazy. <S> “Who are you and why did you land here?” <S> “My name is Jon <S> and I had an inflight emergency that forced me to land here.”
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In an emergency situation (and declared over the radio) most military facilities will be helpful. If it’s a base there may be no way to actually sell you the fuel as the military is not really a retailer.
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Why don't B747s start takeoffs with full throttle? Why does the 747 start takeoff with partial power and increase to full throttle later down the runway, when the A380 for example starts on full? Source This is not the same question as: Is it possible that derated thrust takeoffs are safer than normal takeoffs? Why don't airliners use full throttle on takeoff? <Q> The other answers are spot on, but I'd like to address one part, which is the "later down the runway. <S> " It is by no means "later." <S> ( YouTube ) <S> In the frame grab above of a 747-400 (taken at 1:12), the captain had already called out "takeoff thrust," the TO/GA system had set the pre-programmed thrust setting, and the 747 wasn't even at the piano keys. <S> (Auditory cues can be misleading to passengers or air side spotters.) <S> Typically, a low thrust setting is set to make sure all the engines are responding in the same way, and more importantly, will have uniform application of thrust thereafter. <S> This can be done with (standing takeoff) or without the brakes on, $^1 <S> $ or during a rolling takeoff. <S> Then it is TO/GA time. <S> (In tail-wind conditions, the procedure may vary.) <S> Here's <S> another video by JustPlanes from inside the cockpit. <S> Again TO/GA was pressed while the plane was at a crawling pace far from being anywhere later down the runway. <S> $^1 <S> $ <S> Boeing 747-400 FCTM § 3.4 <A> I can't give a 747 specific answer, but generally, on some engines it's desirable to let the engines stabilize at a moderate power setting, with the N1 equalized there, before advancing them to TOGA thrust. <S> It helps to make sure the engines will all get to TO thrust at the same time, which is important to avoid yawing motions early in the roll. <S> The crew may hold the brakes and do it, not releasing brakes until the move to TOGA, or they may do it on the roll, which is probably what you were seeing. <S> There may also be limitations in the event of strong crosswinds against going to TOGA while stopped with the wind blowing from the side beyond a certain angle and above a certain speed, requiring that kind of rolling takeoff procedure (to minimize flow disruptions to which a particular engine may be sensitive). <A> Mentour Pilot talks about this in his video . <S> The answer is Stabilization . <S> It takes an engine several seconds to spool up from idle to TO/GA. <S> That's long enough that the engines don't get there at the same time . <S> The difference can be enough to make asymmetrical thrust yaw the airplane on a slick runway. <S> Whereas, spooling up from mid-thrust to TO/GA happens very quickly, and so the time of differential thrust is too short to matter. <S> The time from idle to mid-thrust is most of the total time to TO/GA. <S> So they command mid-thrust <S> , wait for both engines to catch up and equalize, then punch it. <S> They can't correct with rudder because it's ineffectual at low airspeed. <S> They can't correct with differential braking because dragging brakes only works if you're moving. <S> This is a throwback to the old piston engine planes which would run up the engines and wait to see they all stabilize, perform properly and are equal. <S> They find out about carb problems or fouled plugs before they are rolling down the runway. <A> Typically you run the engines to 60% N1 or so, then do a final sweep of the gauges for abnormalities prior to advancing to either maximum rated thrust or a lower pre determined rating. <S> It’s a means to verify everything works correctly one final time before committing to the takeoff roll. <A> Some engine types on the 747 are not capable of running at the maximum N1 (fan) speed with no forward speed to increase the air flow into the engine, especially at low altitudes and low temperatures. <S> In other words, the engine is at maximum power for the operating conditions it is in, but it is not operating at the maximum <S> RPM <S> the fan is designed for. <A> Rolling take-off..recommended practice if the runway is long enough as its easier on the airframe and also on the pax. <S> Standing on the brakes and running up to take-off power is only done on shorter runways. <S> As the 747s mostly operate from bigger airports you would not normally see this. <S> If you've never experienced it and don't know whats happening it can be a bit disturbing as the noise and vibration increases a lot <S> and there's a lot of initial acceleration when the pilot gets off the brakes. <S> The last few I've been on were on smaller aircraft (a 737 and an ATR 72).. <S> exciting to say the least! <S> Anilv <A> Another reason is foreign object debris (FOD), which is easily picked up by the outboard engines. <S> This can be avoided by delaying the spool up to full thrust. <A> It's not an interceptor/air superiority fighter that needs to be up in the air 10 minutes ago nor is it taking off from an aircraft carrier which has a limited amount of runway length <S> so you need a catapult (steam atm mostly but electromagnetic <S> ones are being developed (and I think they are deployed on the USN's newest carriers)). <S> For other missions taking of with the afterburner (if you have one) and engine(s) at max isn't the most efficient way.
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You don't want to push the engine to the limit of the operating envelope and then have a gust of cross-wind that causes a compressor surge by disrupting the inlet air flow, until you have enough forward speed to prevent that sort of event from happening.
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Is it possible to design a GA plane with a 5' -10' wing span? We see sparrows with 6" wing span land on a dime, yet it seems there no GA planes you can buy or build from a kit with short bodies, short wing spans, something with a 20' landing/takeoff roll, something with folding wings you can drive out of your garage, take off from your driveway ( if you live in a non built up area) and land almost anywhere at 20mph. It seems like GA is dying, but I think a lot more people would be interested in flying if GA planes were way more useful. Yes, there was the BD5 which was nice and small, not STOL though, the Alaskan bush pilots are taking off/landing in 10' ( yeah!!) in their super cubs, a standard Zenith 701 STOL which can take off in 25' with a good headwind, but all have large spans Using the Cri Cri as an example Cri Cri Monoplane: , I think it has a span of 15’ and a chord of 2’ for a wing area of 30 ft2. Cri Cri biplane: Now imagine converting it into a biplane with a span of 1/2 or 7.5’, same chord. Cri chi triplane: Now take the Cri Cri monoplane and reduce the span to 1/3, or 5', same chord. Why can't we have planes with 5-10' wing spans. Is it impossible to design roll stability into a plane with such a short wing span? Is there any other reason, like 50% effectiveness, etc. at low span due to span wise flow, instead of chord wise flow, etc. Looking at Selig's work on multi element racing car wings, their spans are only 5', with a cl of up to 4.5!! He does mention they need huge end plates to avoid span wise flow. <Q> They can, its just not a very efficient size for one that needs to cary people. <S> this one and some planes that don't have wings at all... <S> But smaller wing spans means a thicker wing, at some point you will run into a drag issue, a roll stability issue or both. <S> When it comes to aircraft people tend to be concerned with efficiency as air travel has always been about going far, fast, and for a similar cost to what you can on another means of transport. <S> As such efficient designs win out over novel ones or ones that provide some means of limited added benefit. <S> On any note most of the supporting infrastructure has been designed for planes with substantial wing spans so aircraft width in the GA market is not really a huge issue. <S> Saying a narrower wing is "way more useful" <S> depends on your use case. <A> Part of the reason is that bird wings can deform a lot, under detailed muscular control, while aircraft wings are usually stiff structures of metal, with at best a few controllable flaps & slots. <S> If you made a model of a sparrow that just held its wings out in a fixed position, it would not be able to land on a dime. <S> Then there's the matter of thrust to weight ratio, and the general square-cube law. <S> Sparrows don't weigh much at all, so they can take off and land with relatively little power. <S> (And hummingbirds are even better.) <S> Large birds like albatrosses & condors have trouble getting off the ground, and mostly fly by soaring. <S> A human-carrying aircraft would have to weigh at least a factor of 10 more than the largest (flying) bird... <A> The shorter your wingspan, the longer your landing roll is going to be. <S> Wide chord wings rely on lower angles of attack and higher airspeeds to work well. <S> Stacked wings work at slow speeds, and indeed allow for shorter spans, but their lift doesn't increase linearly with the number of wings. <S> Also, lift falls quicker than linear with reduced spans, as the fuselage and areas close to it don't contribute as much lift as the clean mid section of the wing. <S> They are also draggy and heavy, and at some point it becomes easier to just go to a rotary wing. <S> 5 ft wide racing car wings can produce enough lift to support a car - at 200 mph. <S> At 200 mph, you're looking at takeoff/landing roll of about a mile. <S> This would be of some utility to the few of us who benefit from a mile-long driveway, but since a plane with no wingspan is a pig to fly, you might as well fly a regular one with that much private land. <S> The 10' takeoff video was filmed with probably 40 mph of headwind. <S> This much headwind is difficult to produce reliably, but you don't have to be the god of winds to do it - all you need is an aircraft carrier, which you turn into the wind and run at full speed. <S> So the very few of us with a pond large enough for such a toy can similarly benefit from 10' takeoffs at any time. <S> And for the majority of us who don't get to play with toys like that <S> , if you want your plane to land like a sparrow, you have to have it the size and the weight of a sparrow. <S> A sparrow weighs just over an ounce, and scaling one up from a 6" to 6' wingspan would produce an aircraft weighing about 10 pounds gross. <S> Such a radical weight loss can be challenging for most pilots, but many UAV and fixed-wing drones in this weight class can indeed be launched simply with a hand toss. <S> If they had arms of their own - that is, if their wings could flap like a bird's - they could do away with even that.
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The simple answer is that everything comes with a trade off, there are plenty of planes with small wing spans like this one , and
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How does this RC helicopter keep itself upright? I have this (cheap, beginner-level) RC helicopter: It has 3 controls: one for climbing and descending (collective throttle), one for yawing (differential throttle), and one for pitching (the tail rotor control). There's no roll control. This helicopter seems to have a very strong tendency to stay upright. Even if you grab it by the skids in mid-air and tilt it slightly, it will right itself (after first flying in whichever direction you tilted it in). As shown in the picture, the helicopter has two coaxial main rotors and one tail rotor. The tail rotor is pointed vertically, so that it produces a pitching moment. The lower main rotor is fixed-pitch, but the upper rotor has cyclic pitch controlled by a weighted "balance bar". The balance bar itself is mounted about 45° ahead of the rotor. The balance bar is on a hinge so that the ends can move up and down relative to the shaft. If one end of the balance bar goes up, then the blade closer to it is automatically set to a coarser pitch; meanwhile, as the other end goes down, the blade closer to that end is set to a finer pitch. It seems very unlikely that this helicopter has any electronic accelerometers or gyroscopes. So, how does this helicopter keep itself upright? Here's what I can figure out myself: Suppose that the fuselage accidentally rolls to the right while the balance bar remains upright. Then the rotor's cyclic pitch will be set so that each blade is coarsest when it's in the forward right position, and finest when it's in the rear left position. This will produce a left rolling moment, which will tend to bring the helicopter upright again. (It will also produce an up pitching moment... or maybe a down pitching moment, thanks to phase lag? Or no pitching moment at all? I don't know.) Suppose that the fuselage and the balance bar both accidentally roll to the right. This will cause the helicopter to fly to the right... which will somehow cause it to right itself? But I don't understand the details of why this will happen. By the way, I've noticed that the helicopter has a tendency to fly in clockwise circles, especially after being disturbed. (It doesn't yaw during this circular motion; it simply moves in a circle while maintaining a constant heading.) I bet that this tendency is caused by the balance bar somehow, but I don't know how. (Someone may be tempted to answer, "It rights itself because the rotors are above the center of gravity." That explanation doesn't work, though, because the only way an aircraft can right itself is by means of torque. The rotors will generate this torque somehow , but they won't generate it by virtue of being located above the center of gravity.) <Q> The rotor is gyro stabilized. <S> The balance bar is the gyro. <S> If the machine rolls right, the balance bar wants to stay in a level plane and generates a correction by influencing the rotor blades to go where the balance bar wants to be. <S> The Bell 2 blade teetering rotor system used on the '47 and the Huey used a much smaller version of the same thing, to provide a little bit of inherent stability to the rotor disc, without inhibiting pilot control. <A> These rotors exert torque via the mechanism in item 1 in this answer , and the body will align itself with the top rotor. <S> But the other way around as well: the rotor aligns itself with the shaft, it just depends on what it controlled, the rotor angle (like in a regular helicopter through cyclic pitch) or the body angle. <S> So top rotor and shaft will return to be perpendicular to each other after a disturbance or a control input. <S> Torques exerted by the body are instantaneous, torques exerted by the top rotor have a time delay due to the inertia in the stabiliser bar. <S> The helicopter is flown by body tilt. <S> Pitch direction: body tilts, upper rotor follows, in a controlled way, resulting in longitudinal movement. <S> Roll direction: <S> no control input possible. <S> Once there is lateral movement, the helicopter can right itself if the aerodynamic drag on the rotor assembly is larger than drag on the body - if the other way around, the helicopter will speed up and tilt itself more and more until it crashes. <S> Notice <S> that the pendulum fallacy does not apply to helicopters: they can align rotor thrust away from the CoG, like a hang glider does when canting the wing, and create a rolling or pitching moment that way. <S> On the flight in a circle without changing yaw (with the helicopter flying backwards halfway in the circle): thanks to @ZeissIkon in a comment: The "flies in circles without changing heading after being disturbed" behavior is most likely due to precession of the balance bar. <S> Disturb the fuselage/rotor shaft, some of that disturbance propagates into the balance bar; once the body has righted, the balance bar continues in a very slightly tilted plane, and the slight righting force from the shaft causes it to precess. <S> – Zeiss Ikon <A> Having read the other answers, I've come to my own hypothesis as to how the helicopter keeps itself upright. <S> The process is: Suppose that the entire helicopter, including the balance bar, accidentally tilts. <S> For the sake of example, suppose it banks to the right. <S> Now the rotors are no longer generating lift straight up; they are generating lift up and to the right. <S> So, the helicopter begins to accelerate to the right. <S> Now the helicopter is experiencing relative wind from the right. <S> The upper part of the helicopter (the rotors) has more drag than the lower part (the fuselage), so this relative wind causes the helicopter to roll left again. <S> The above process has positive dynamic stability, so the helicopter will return to a level attitude and stay there until it's disturbed again.
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The top rotor is a hinge offset rotor with a very serious stabiliser bar.
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Could a helicopter fly like a plane this way? Could a wing be added to a helicopter to allow the entire craft to tip 90 degrees forward allowing it to fly faster like a plane using a fixed wing and leaning into the wing for lift? I understand that there would be major modifications to be made but would there be any benefit? <Q> You've described a tail-sitter aircraft. <S> Instead of a helicopter that tilts sideways to cruise, it's a airplane that can sit on its tail and uses thrust to take off vertically, before transitioning to fixed-wing horizontal flight. <S> This makes more sense since a plane spends more time in cruise than takeoff. <S> They were first demonstrated by Nazi Germany during WWII. <S> You can also use a single centerline engine. <S> Existing designs use contra-rotating propellers or jet thrust vectoring for anti-torque instead of the helicopter tail rotor. <S> The idea has been revived recently for UAVs, which don't have the occupant comfort problem: Aerovironment SkyTote <S> (US Government photo) <A> There would certainly be a great benefit in occupant comfort! <S> The aircraft would get greatly increased drag of its large frontal cross-section and lose most of the lift that the rotary wing normally produces. <S> It's not just a propeller turned upwards, but an actual wing, producing lift on the same principles. <S> Helicopters require far less power to fly forward than to hover thanks to this dynamic lift. <S> Some occupants don't appreciate the improved ergonomics of the depicted position and prefer that only the rotor is tilted forward. <S> To them, the solution is tiltrotors like <S> the V-22 - you get to use the rotors as huge propellers, but not the massive drag from tilting the entire plane. <S> Note the rotors are also sized somewhat smaller than for a pure helicopter, and still their size is a source of extra drag in flight. <S> In the drone world, when designing from scratch, there's been a much more elegant solution - the Parrot Swing . <S> And yes, it's probably the first aircraft to look like the X-wing for entirely practical reasons. <S> But remember that quadcopters (drones) are not normal helicopters ; they use differential thrust from simple fixed propellers for control, not complicated rotor assemblies that keep each blade at proper pitch. <S> Simply attaching big wings to a heli won't let it fly this way for long, but special craft that take off as helicopters and fly like planes can and have been built. <A> It would be far simpler just to add wings and tilt only the rotor 90 degrees, and not the entire fuselage. <S> Drag would be much lower, and the occupants wouldn't have to endure hanging down in their seats. <S> You could call it... a tilt-rotor. <A> You could. <S> But in the advent of tiltrotor aircraft why would you want to? <S> What you propose is grossly inefficient, awkward for the occupants and counterproductive in terms of drag. <A> This picture of the BV-37 came up that somewhat proves my concept, but the wing moves forward in flight and the helicopter leans onto the wing some. <S> I wanted to know if the wings span was long enough if the rotor blades could serve as a propeller and the wing provide lift.
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A major benefit over the tiltrotor or tiltwing is that you don't need the bearings that can support the thrust of the engines or lift of the wings.
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Why don’t airliners have temporary liveries? For buses, it’s quite common to have plastic foil with advertisements on them, but I’ve never seen that on an aircraft. Looking at how aggressively some airlines try to save money, they probably already came up with the idea to sell the space on the side of their aircraft for advertisement purposes – so why did they not do it? Is there any technical reason to not have temporary liveries? <Q> They do have temporary liveries. <S> This is very common in wet lease operators, where an aircraft is flown for an airline during a peak period or when their planes are down for maintenance. <S> Airlines want customers to feel they are getting the brand-name product they are paying for; they don't want customers to board a generic white jet. <S> An airplane will be painted and decals applied only for several months. <S> Just like motor vehicles, 3M makes aircraft film wraps, including models specifically for short-term use . <S> You can expect ANA's jet for the 2020 Tokyo Olympics to be returned to normal shortly after the Olympics are over. <S> You can see Lufthansa and Egyptair dressed their planes up for the World Cup. <S> Egyptair's photographic livery can only be done by printing onto a decal. <S> This video shows Alaska Airlines paint essentially an ad for Disneyland and the Cars movie franchise. <S> They paint the simpler parts like the clouds and the large solid areas, but at 1:28 you can see them apply decals of the characters' faces. <S> They say it took 29 days to paint. <S> This is another video where they're simply applying a decal to advertise another movie. <S> So, no, there is no technical reason not to have a temporary livery and such schemes are done regularly. <S> It's merely an issue of marketing and customer impressions. <A> The time needed to apply and remove the advertisements would cost too much money. <S> As long as the aircraft is on the ground, it cannot earn revenue. <S> Better to forgo the small profits from ads for larger profits from operating the aircraft. <A> 1) For a typical urban bus, that plastic foil has to stay on at maybe a max of around 60 mph. <S> For a commercial jet, it'd have to stay on at 600 mph. <S> And suppose it starts ripping off and gets tangled in the elevator... <S> 2) <S> You could repaint the plane at a cost of $50-200K <S> How much does it cost to give an airliner a fresh coat of paint? <S> but the ad would only be seen by the small number of people at the airports, so hardly cost-effective. <A> Building upon jamesqf answer, I'd like to add: 3) <S> The number of people seeing bus on the streets while moving between stops could be simplified as sum of traffic size + population working and living along its route. <S> For every bus you get a very rough estimate of a thousand potential advertisement targets every minute. <S> And who sees the plane? <S> Only its passengers when they're boarding. <S> People waving their goodbyes usually are too far to read the advertisement, not to mention ppl seeing the plane inflight. <S> That amounts to one to several hundred advertisement targets per several hours, or even whole day in case of longer routes. <S> The increased cost leads to a fraction of market penetration. <S> Totally not worth it. <A> They have been using temporary liveries for decades. <S> Rock group Yes famously had one produced on film for their US tour in 197x and half way across the Atlantic it started peeling off and flapping towards one of the engines. <S> YouTube for Rick Wakeman telling this story as he does it so well in his inimitable style <A> A city bus is a city bus, but an airline wants to advertise its own brand with its own livery. <S> Some people dislike ads, so that could create a negative perception of the airline. <S> An airplane is much larger and more expensive to have out of service. <S> There's also lower benefit. <S> Buses with advertisements spend most of their time in the city and on roads, surrounded by people they can advertise to. <S> Airplanes spend most of their time in the air, where nobody else gets close enough to see them very well for very long. <S> They do get some exposure near the airport as they are landing or departing, and to people in the terminals. <S> However, some airlines do put advertising on their planes. <S> It's usually something with a connection to a flag carrier's country, as with Air New Zealand and The Hobbit, or a partner of the airline. <S> Airlines will commonly have some aircraft painted in a livery of their alliance. <S> ANA has had many special liveries, such as Star Wars and Pokemon. <S> There are certainly outliers, though. <S> They have a history of advertising on their planes , and did announce in 2013 they would be selling advertising space on their planes, <S> but I couldn't find any recent examples other than partners.
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The airline tries to make it as appealing as possible, because in addition to advertising something, they are also drawing attention to their own brand. Part of the reason is cost. Ryanair is famous for eking out every bit of revenue that they can come up with, and advertise throughout the cabin. It is also common to have a livery for a special event, say the Olympics. Part of the reason is branding.
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What's the name of this light airplane? The propeller of this light airplane almost looks like a triangle, so I'm interested in knowing its performance but I need help in identifying this plane because I don't even know her name. <Q> Looks like the "Homebuilt Hornet, one-off wonder plane" on the cover of the March edition of the Australian Sport Pilot Magazine . <S> The article can be found on pages 34-37 . <A> The fuselage was made from two canoes, and it's powered by a 80hp Jabiru engine. <S> It featured in the March edition of Australian Sport Pilot, where you can see more pictures and read something about it's history. <A> Jabiru in Australia seems to be engine manufacturer. <S> They also supply propellers. <S> https://jabiru.net.au/propellers/ <S> The prop pictured doesn't too much like the 2200 Wooden Laminate they offer for the 80 HP 2200 <S> Aero Engine <S> https://jabiru.net.au/wp-content/uploads/2018/05/2200-Aero-Engine-Flyer.compressed.pdf <S> To my eye, it doesn't look triangular.
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The aircraft is a Hornet, built as a one-off by Australian Colin Jamieson.
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Is it possible to fly backward if you have really strong headwind? Is it possible to fly a plane backwards if you have a really really strong headwind? I mean when you are aloft, you have positive airspeed and airflow over the wings but you have negative ground speed. <Q> Yes, certainly! <S> Example videos: from ground (noisy, better turn down your volume) from cockpit <S> However, note that headwind cannot cause a plane to fly backwards through the surrounding air. <S> Constant wind does not affect airspeed. <A> Yes, I have done this many times in hang gliders, and at least once in a Cessna 152. <S> In the latter case, the wind aloft was much stronger than at the ground-- <S> it would be foolish to take off or even taxi in a ground-level wind strong enough to fly a light plane backwards. <S> You may enjoy this video of flight at zero groundspeed (I am not the pilot!) <S> -- Note the lack of any obstructions that would create turbulence upwind of the glider. <S> Also, the stable marine airmass, chilled from below by the cold ocean water, contributed to the smooth, gust-free conditions seen here. <S> In many other situations it would be unsafe to maneuver near the ground at low airspeed in wind this strong. <A> Been there, done that. <S> A poorly forecast cold front once had me flying backwards in a Cessna 172 over Altoona, IFR (instrument flight rules) at night. <S> Center asked me several times to verify my heading. <S> Then when it was clear to them, they asked me my intentions. <S> I told them I had lots of fuel and could continue to wait things out for an hour or so. <S> The winds let up in about 20 minutes. <S> The controller (and all the other big boys on center frequency) were kind of incredulous. <S> The controller eventually gave me a EFC <S> (Expect further clearance) time, which made sense. <S> On that trip the anemometer at Rocky Mount, NC broke at 140 mph, according to FSS (Flight service station). <S> A secondary problem was mountain wave over the Blue Ridge mountains and to a lesser extent over Pennsylvania. <S> That required a block airspace clearance because the updrafts exceeded my descent capability, and the downdrafts far exceeded the climb capability. <S> There was however no problem maintaining the IFR (instrument flight rules) minimum altitudes and the MVA (minimum vectoring altitude) for center. <A> Yes. <S> When aloft, an aircraft only cares about how the air is flowing over its wings; how fast the air is moving relative to the ground is irrelevant. <A> Indeed. <S> When I was a child in the 1960's I was fishing at a bridge off the eastern end of Isla Grande Airport (TJIG) in San Juan, Puerto Rico. <S> I saw a huge, dark and tall column of something turning and churning all the way at the other end of the airport, and flagged down a policeman walking his beat to tell him that I thought it was a fire. <S> His eyes grew huge, grabbed me and ran for safety in the nearby Club Náutico marina building. <S> It was a water spout -- a tornado coming in from San Juan Bay. <S> I clearly remember seeing two aircraft trying to land on runway 27 and ending up flying backwards -- a PRANG Huey helo and a Cessna 172. <S> One of them crashed somewhere else, but I don't remember which one or where. <S> That was a sight I will never forget -- that and the one of my mom frantically looking for me because the spot where I was was now covered in zinc roofing. <S> At that same airport, many years later, I witnessed an Aeronca 7AC "Champ" trying to land in a strong headwind and coming to a dead hover over the water close to the runway 9 threshold. <S> Try as he might, the pilot could not make any forward progress -- the engine was not powerful enough to develop enough airspeed. <S> It was a very stupid landing attempt, IMO. <S> He turned west and landed at Arecibo Airport (TJAB). <S> Once the winds calmed he came back. <A> Yes, if there are really strong winds, the aircraft can fly backwards relative to the ground , but never relative to the air . <S> This is because an aircraft always needs a minimum wind flow over its wings in order to keep flying. <S> If it's flying backwards relative to the air, there would be 0 flow or even negative wind flow over the wing. <A> This can happen with a glider (sailplane) winch-launching into a strong wind. <S> Once the glider is airborne, and up into the faster wind, the winch can be slowed to a stop, and even payed-out again. <S> For obvious reasons, this is called 'kiting', or a 'kite launch'. <S> Some pre-planning or radio communication between the winch driver and pilot is useful to get the maximum height out of this manoeuvre. <A> Is it possible to fly a plane backwards if you have really really strong headwind <S> Definition of "fly backward": "tail facing direction of travel". <S> Yes, it's possible, even with a fast plane (jet) and light headwind; easier vertically. <S> Proof: <S> " F-22Raptor flies backwards! " <S> " F-22 Raptor Slides <S> Backwards <S> At 2015 Melbourne Air Show " " Sukhoi Su-35S Super-Flanker Extreme Flight Demonstration incl. <S> Insane Kulbit Maneuver!!! <S> " <S> " Full size plane doing 3D " or " Skip Stewart - Entire Performance - Battle Creek 2011 " Easier with RC - " Fighter Jet does AMAZING stunts! " or " 3D Jet Tail Touch " <A>
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If your airspeed is lower than the speed of the headwind, the aircraft will fly backwards relative to the ground. Yes it is possible and here is some evidence Flying Backwards
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Do ailerons on opposite wings move together? It seems nicely symmetrical that opposite ailerons would be locked togther, so that when the left wing's ailerons move up, those on the right wing would move down, by the same amount and at the same speed. Is this in fact generally the case on aeroplanes? Or can they be moved independently, or at different rates or to different positions (and what advantage would that offer)? Finally, are there any aeroplanes on which they can be moved in the same direction? <Q> On most general aviation airplanes, and other cable-controlled aircraft, they move together and for that matter are cross linked to the same physical cable. <S> You can see this nicely on the control diagram for the B-24 ( source ) <S> Some ailerons are designed to counteract adverse yaw and may move such that they are asymmetrical to the flow over the wing. <S> 1) <S> Differential Ailerons: <S> One aileron is raised a greater distance than the other aileron is lowered. <S> The extra upward aileron movement produces more drag change than an increase in AOA on the downward aileron. <S> This produces an increase in drag on the descending wing, which reduces adverse yaw. <S> 2) <S> Frise Ailerons: <S> The aileron being raised pivots on an offset hinge. <S> The leading edge of the aileron is now pushed into the airflow, creating drag and reducing adverse yaw. <S> In this case, frise ailerons are using form drag to counter induced drag. <S> But not all aircraft contain such systems. <S> Fly-by-wire systems are theoretically capable of deflecting any control surface as they see fit and may not move symmetrically but generally speaking their direction of movement is opposite. <S> Some fly-by-wire aircraft even have split ailerons which may see parts of a give aileron deflect differently. <S> This answer covers that quite nicely. <S> If you really want to go back, the 1912 Farman HF.20 had single action ailerons <S> that only deflected downward and were pushed back into position by the airflow. <S> I would say (if these count as ailerons) that they do in fact not move in tandem. <S> There were some other early designs covered here <S> that worked a bit differently than modern ailerons. <S> As for your second point, aircraft that have elevons, which serve as both the elevator and the aileron (mostly delta wing stuff like the Concorde and other high speed airframes), can move the surfaces in the same direction. <S> Generally other surfaces are employed for the use case of needing to move both ailerons in the same direction (speed brakes). <A> Or can they be moved ... at different rates ... ? <S> I saw a power glider (maybe an SF-28 or an RF-5) where the ailerons moved with a different rate. <S> The reason was an effect whose German name translates to "negative turn effect", but I don't know the correct English word for it: <S> If you operate the ailerons to the right, the ailerons work in a way that the left wing produces more lift and therefore more air resistance than the right one. <S> Therefore operating the ailerons to the right will also have a similar effect as operating the rudder to the left. <S> (For this reason the rudder has to be operated to the right together with the ailerons to compensate that effect.) <S> The power glider I have seen was built in a way that the left aileron only did a much smaller motion then the right one when putting the stick to the right. <S> By doing so, the right aileron worked like an air brake so the air resistance of both wings was nearly equal and there was no "negative turn effect". <S> Finally, are there any aeroplanes on which they can be moved in the same direction? <S> There are airplanes that use "flapperons": <S> This means that the same part is used as flap and as aileron. <S> Being used as flaps, the flapperons move in the same direction; being used as ailerons, they move in different directions. <A> But the movement usually isn't equal on both sides. <S> Moving the aileron down increases the wings camber and therefore lift, which also comes with drag. <S> This drag produces a yawing effect opposite to the desired turning direction. <S> This is known as adverse aileron yaw, and needs to be overcome by coordinated use of the rudder when banking. <S> There are a few different ways of reducing this adverse yaw, the most common of which is known as differential ailerons. <S> This is where the aileron that deflects up has a greater range of movement than the one that deflects down, reducing the drag on that side for the same banking force. <S> On a side note, airliners don't use ailerons at all at high speeds, because doing so will twist the wing. <S> Spoilers are used instead for roll control in cruise as they are closer to the wing root, thus providing less twist. <S> They operate only by deflecting up on the one side.
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The basic principle of ailerons is that the aileron on the down-going wing will deflect up, and the aileron on the up-going wing will deflect down.
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Could a person damage a jet airliner - from the outside - with their bare hands? Given just a small hammer, I'm pretty sure I could disable a large airliner with a few well-placed blows. What about with my bare hands? In other words, are there any parts of a large aeroplane that are: exposed delicate enough that they could be damaged without using tools critical to the plane's operation? The only think I can think of are the pitot tubes and angle of attack sensors. (Throwing oneself into the engines while they are idling does not count.) <Q> Yes, a few possibilities... <S> Brake hydraulic and electrical sensor lines located on some landing gear. <S> Covering pitot system sensor holes Pressing or hitting the pitot tube (on most airliners you will need a ladder) Letting air or hydraulic fluid out - under inflating tires or cylinders Bending or mis-adjusting bellcranks/control arms or changing the linkage geometry. <S> Damaging fuel vents <S> I am not sure of what your definition of "exposed" is but most airliners allow the E&E (electrical & equipment) bay usually located above or behind the nose gear and gear doors to be opened and closed from external control panels for ground crews. <S> This allows access to most the computers, batteries and thousands of wire bundles. <S> It may also give access to lines, cables, pumps, switches, and sensors. <S> Maintenance and inspection panels, engine cowls and fuel distribution panels expose or control critical systems. <A> I expect blade antennas could be damaged with a good blow (or several) from the side. <S> Or disconnecting the cannon plugs - although without further damage, that by itself could be reconnected. <A> Yes, it can happen. <S> All they'd have to do is pick up some gravel or some other pieces of FOD (Foreign Object Debris) and throw them into the engine intakes. <S> It's probably not going to cause catastrophic damage immediately, but it will significantly increase the maintenance required to keep them operating. <S> I've actually heard a story about this happening once by some maintenance engineers who were upset about their overtime hours being cut, but a quick Google search isn't turning anything up - possibly because they were quietly fired after they got caught on camera and the news organizations never heard about it.
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Putting foreign objects under or between the rotors of brake pads Opening the gear doors of some airlines exposes the air-packs, generators, converters and aux turbine with it's associated mechanisms. Any number of wire bundles & hydraulic lines in the wheel well could probably be damaged with enough determined yanking on them.
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How can pilots sleep or rest merely 1 hour after takeoff? I screenshot this YouTube video . Because the A380 just attained FL250, the flight obviously commenced less than an hour ago. At 14:28 the relief captain ( Robert Juelicher ) leaves the cockpit. At 14:37, ATC clears the flight to climb to FL320. Doubtless, relief pilots are legally mandated to have well and sufficiently rested and slept before their flight. So how can Juelicher be expected to sleep or rest 1 hour just into the flight? Or did the Pilot-in-Command (Juergens Raps exhibited below in the screenshot) mis-speak? Is Juelicher expected to merely fritter away time (e.g. read a book) until his shift, not necessarily to sleep? <Q> The military has been teaching people how to fall asleep fast for a long time and its quite doable. <S> Keep in mind this pilot did not start working one hour ago, if he is relived after 1 hour he is likely at the end of his duty shift and may have been flying for the previous 7 hours and awake for some more time than that. <S> Pilots hop time zones frequently so just because its daytime outside the aircraft does not mean that pilot started off his duty time in that time zone or even on that continent that day. <S> The relief pilots may have woken up just before the flight and had a nice hour to relax before "going to work". <S> The crew rest area is pretty nicely isolated and free of light and distractions making it an ideal place to sleep. <A> I do not believe the captain mis-spoke. <S> Just like Dave answered, a pilot going on duty and expected to be the “relief” pilot would usually not wake up, rested and fresh as a start to the flight. <S> He/she would have planned (and the airline’s scheduling dept. will have considered) to arrive “legally” rested since their last shift but ideally not at the pilot’s cycle of “early morning” after a full night’s sleep. <S> Consider this: Similar to the way you, as a passenger preparing to depart on an international flight might stay up extra late the night before (or get up extra early) to “force” your internal clock closer to the time zone of your destination, this pilot would have done the same. <S> Pilots have the additional consideration that they might spend very little time at the destination and consider the length of the next route they are assigned. <A> I do a lot of long-haul flying. <S> I have a 13.5 hour trip tomorrow. <S> I will not be sleeping on the flight. <S> Some crew do. <S> For certain operations, adequate sleep facilities must be provided. <S> There is neither a requirement that the pilot sleep, nor is it always possible. <S> Moving between time zones, and flying both sides of the clock means that frequently I'm just not going to be sleeping. <S> It's not uncommon to take off east bound and turn a long night into a very short one, with nearly two days of daylight, or fly the other direction and never leave night, or to gain a day or lose a day. <S> There are tips and tricks in hotels, using light or backout curtains, sleeping when able, avoiding caffeine, etc...but <S> the bottom line is that I find that I may not sleep when rest is available, because I can't. <S> On long trips, I don't like to sleep, and usually don't. <S> Some pilots operate under regulations that allow a 30 hour duty day, and I've seen a lot of those. <S> Long days. <S> When home, I get tired in the middle of the day, sometimes, and often stay up all night. <S> For crews going to a rest area, it's a matter of juggling crew to ensure no one exceeds their legal time in the pilot seat, and going to a dark area to lay quietly with a little music, or a set of earplugs and a comfortable temperature... <S> it's a matter of doing what one must. <S> If one has regular trips scheduled, then one can learn to sleep. <S> I mean literally right after takeoff. <S> Once, departing Honolulu, before the landing gear was up. <S> I kid not.
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I knew a captain many years ago who would fall asleep right after takeoff.
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Are ham radio contacts allowed from inside an airplane? This question probably lies in the middle ground between Amateur Radio.SE and Aviation.SE . I have seen a couple of videos where ham radio contacts are made with people on board a commercial aircraft while in flight. In one of the videos , contact is established trough the 2-meter band (VHF) with a passenger carrying his hand-held transceiver on board the flight, while in the other video , contact is made trough the 20-meter band (HF) with the captain of the airplane using the airplane's radio transceiver. I am curious about what do regulations say in this regard. Are ham radio contacts allowed from inside an airplane? <Q> Two-way radios are just like any other communications device. <S> Also, if the captain determines that something you are doing with your communications device is interfering with aircraft communications or navigation, he may order the flight crew to confiscate your device until after landing, and you may be subject to criminal charges. <A> The regulations say that for any flight on an IFR flight plan (which includes all commercial airline flights) <S> the captain (PIC) is responsible for determining if any electronic device will interfere with the airplane's instruments or communication. <S> If the PIC determines that it will not interfere, they can give permission to use the device in flight. <S> Regular VFR (like small airplanes) have no such restrictions on determining interference, but the PIC can still decide if you can use it or not. <A> In private aircraft, absolutely! <S> In my 40+ years as an amateur (W0BTU), I have heard and worked many hams in single and dual engine private aircraft. <S> (aeronautical mobiles). <A> There are several good reasons to prohibit the use of ham radio transmitters on commercial flights. <S> They were largely detailed in a QST magazine article in August 1996 titled “An Aeronautical Antenna Farm” (I remembered that because I worked at the ARRL at the time). <S> Basically the bottom line is that there is too much risk of interference to critical aircraft communication and navigation systems. <S> The article references FAA Advisory Circular 91.21. <S> While this is not a regulation per se it certainly seems like something all commercial carriers would follow. <S> The current revision (2017) of this circular is here: https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91.21-1D.pdf
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If the captain says all such devices must be in flight mode at any particular moment during the flight, you are not allowed to use it and could be arrested if you do.
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How strong someone should be in order to fly without "power steering"? Planes these days use fly by wire systems while older ones had a mix of hydraulics with electronic assistance like the MD-11 (And maybe 737-800?). But what would happen if you lost the electronic systems and you had to fly manually? I remember an incident of this happening in a MD-11 and pilots using raw muscle power to operate the flying surfaces (And using something like 10 kilos of force only to keep the yoke in place) or putting 10 kilos of force to the yoke constantly (My memory isnt exactly bad. It was a months ago) So How much raw muscle power is needed to fly an MD-11 or an 737-800 without assistance for 10 minutes and then land? Through two pilots or as a single person. <Q> You can't. <S> Most of these airplanes are flown with hydraulically powered control surfaces with no mechanical input possible from the cockpit flight controls. <S> The flight controls just operate servo control valves in the hydraulic actuators, like the bucket on a front end loader but <S> a little fancier. <S> If it's FBW, the FBW system does the same thing at the actuators using torque motors operated by the FBW computers to drive the servo control valves. <S> There will be two, or three, hydraulic actuators driving each control surface. <S> The flight controls in the cockpit just control the extension/retraction of the actuators. <S> Control feel in these airplane comes from spring devices in the control circuit to simulate "air loads". <S> There is no direct connection between the pilot and the dynamic forces acting on the control surface. <A> Only small planes can fly without power actuation. <S> The largest size airliner that can be flown manually would be about a B737, which actually has manual back-up for the elevator & ailerons as in this answer . <S> The B737 uses a balance tab to assist in lowering the hinge moments during manual actuation. <S> In a much larger aeroplane like the DC-10, there is no practical amount of reducing hinge moments with servo tabs or other means, and flight control surfaces are deflected using hydraulic power only. <S> This is schematically as follows: <S> When the pilot moves the stick, they deflect an input linkage which opens the servo valve of one or more hydraulic actuators. <S> These then deflect, moving the output end, thereby closing the servo valve again. <S> As long as there is enough total hydraulic pressure to overcome the aeroforce hinge moments, the actuator moves the control surface without any effort from the pilot required at all. <S> In fact this would be so very light that artificial feel springs are mounted. <S> However, in some circumstances the actuators cannot overcome the control hinge moments, for instance due to: <S> Having to fight one of the other actuators, for instance because of a hardcover servo valve failure; Hydraulic pressure loss in one or more of the actuators; Mis-trim and high airspeed cause surface blow-down, as in several recent crashes. <S> Note that in this case, when the pilot pulls on the stick, they first deflect the servo valve until it hits the stop, and this now becomes the fixed hinge point of the input linkage. <S> Further stick deflection results in direct manual surface deflection, against the hinge moments caused by the aeroforces and against oil still slushing around in the hydraulic system. <S> A DC-10 did manage to actually land after total hydraulic failure by using differential engine thrust, not manual actuation. <A> As a complement information to Koyovis answer, please note On large airplanes, it is rather <S> a <S> « servo tab » that will do the job you are asking for, in case of hydraulic failure rather than assisting the normal force that moves the elevator, it becomes the sole force that makes the elevator move. <S> Therefore during normal flight it acts like a balance tab, in case of failure it becomes the sole active force. <S> Like the balance tab, the servo tab moves in the opposite direction of the flight control’s trailing edge. <S> Please refer to the following website: https://www.flight-mechanic.com/flight-controls-tabs/
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If you lose all of the hydraulic actuators, you lose the control surface. Like mentioned, in large aircraft with no measures to lighten hinge moments, the flight crew cannot practically control the flight path using manual force.
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Why are Vertical tails generally tapered? I'm just intrigued to know why the vertical tail of a majority of aircraft is tapered? Is it due to aerodynamics, structural design or due to some instrumentation or multiple other reasons? <Q> The vertical tail and the horizontal tail are wings, and follow the same construction rules. <S> The span-wise lift distribution is much better if the wing is tapered: more lift at the root, less at the tip. <S> Vortex induced drag is lower. <S> As a reference, from Torenbeek: pages 232 & 233 It is observed that nowadays there are basically three forms of straight wings: the tapered wing, the untapered (rectangular) wing and the wing with a prismatic inner portion and a tapered outboard portion. <S> About taper for wings (and for tail surfaces): Tapered wings have been adopted for the majority of aircraft since they offer an efficient solution on account of their low induced drag, high maximum lift, low structural weight... <S> (and) <S> acceptable stalling characteristics can be obtained, provided the wing is not too sharply tapered. <S> Untapered wings are inferior and cheap: <S> The untapered wing is attractive from the point of view of manufacture, since only one airfoil contour is involved; this simplifies jigging as there are no compound curvatures. <S> It is aerodynamically inferior to the tapered wing, but may nevertheless be the logical choice for inexpensive private aircraft, where the utilization factor is low and initial cost and cheapness of components are important. <A> There are obvioius aerodynamic and structural advantages for taper (and sweep), but also remember that a signficant factor in a vertical tail's shape is what comes down to... styling. <S> The fin and rudder form maybe a third of the airplane's shape in profile and the "look" that defines it. <S> Designers aren't machines; they are humans with a sense of aesthetics like anybody else, and there is a bit of art to it, and one of the great things about aviation is artistic forms flow naturally from efficient shapes, like teardrops and tapered and swept surfaces. <S> Any designer will consider the look as part of the overall shape of the tail to some degree or another. <S> Now, the Pilatus Porter uses a constant chord vertical tail and it works perfectly fine and is cheaper and simpler to build and in most light low speed airplanes that is a more important factor than the aerodynamic ones. <S> But it looks incredibly ugly, and who the hell wants to build something ugly unless you've decided to make that part of your brand, or you don't care about the look at all, or the plane was designed by a committee with no sense of aesthetics. <S> Since the 50s, on GA aircraft, sweep became associated with "modern" and high performance, since on high performance aircraft that was actually true. <S> Between 1950 and 1966, Cessna's tails went from: <S> and it made not the slightest difference in the airplanes' handling or performance. <S> It was strictly for looks. <S> From a manufacturing and aerodynamic perspective, they should have stuck with the middle square tapered one used from the mid 50s to the early 60s, but in the mid 60s swept tails were all the rage in GA. <A> A little quandary here (again thanks for John's artwork) for the designer: Earliest tail Pros - very strong with desirable Prandtl style trailing edge and swept forward edge, low aspect ratio and high stall AOA. <S> No accident <S> this was the tail of the Bf 109. <S> Cons - not as effective at generating lift as a straight wing <S> (ASE readers should be seeing this trend), lots of area for cross wind "weather vaning". <S> The fillet seen in the P 51 would also improve high AOA lift. <S> Squarish tail Pros - again, very strong, low aspect ratio, high stall AOA. <S> Reliable and easy to make. <S> Cons - not as effective in lifting, there for needs to be bigger (drag, weather vaning). <S> Swept wing tail Pros - Stylish, better spanwise load distribution (thanks Peter), more efficient at generating lift (same lift for smaller size). <S> Less weather vaning. <S> Cons - will stall at a lower AOA, and because of its greater length, is not nearly as strong. <S> This is why airline pilots cannot rudder aggressively, particularly at high speeds. <S> It will break. <S> So, aerodynamicly, the tapered tail gets a plus for looks and lifting efficiency, but a minus for strength and high AOA performance. <S> The first two, particularly the earliest one, may be a better pick, particularly for aerobatics.
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The wing can be built lighter, root area is larger, torsion stiffness is higher.
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Is this one of the engines from the 9/11 aircraft? I ran across an interesting set of post-9/11 photos and I noticed this picture in particular: The closest item on the truck looks a bit like an airplane engine, but I can't tell for sure. Is it one of the engines from the 9/11 aircraft? <Q> They are definitely not jet engines. <S> They look more like electric motors or generators or blower units or something. <A> It's too big and too intact. <S> In a turbofan engine, you see the fan upfront. <S> The casing (nacelle) surrounding the engine would not survive. <S> And the remaining core that runs <S> the engine is much smaller compared to the fan and engine, in diameter and length, respectively. <S> For comparison, this is the remaining core from the 737 Max crash in Ethiopia (lower-right corner): ( france24.com ) <A> These are very large electric motors, used in HVAC plants or water distribution, probably. <S> Or possibly main generators out of a diesel gen-set. <S> They are very dense and tough by design, though certainly beat to snot; they may have been inside a building that collapsed. <S> They are on the trailer together because they are going a scrapper who specializes in hacking copper out of motors. <S> Copper is worth $4-8 a kilo depending on market. <S> They use copper for such windings because copper has the best conductivity per volume , for more efficient use of the magnetic fields. <S> Such a thing is far too heavy and dense to be any part of any airplane. <S> Generally speaking, copper's density works against it in aviation applications; aluminum delivers the same conductivity at almost half the weight (although at nearly double the volume, but volume is not as important as weight). <A> Here is one of the motors from 2 other angles. <S> It's on exhibit at the 9/11 World Trade Center Memorial & Museum . <S> Photo 1 <S> (Source "More Than Route 66" blog) : <S> Next to the radio tower was an elevator shaft motor also recovered from the rubble. <S> The motor was most likely from one of the express or service elevators from inside the north tower. <S> Photo 2 <S> (Source Edward Stojakovic) : 9/11 Memorial Museum - Elevator Motor <A> Unlike many of the others who have responded here, I have relatively little expertise in identifying motors and wouldn't be able to distinguish a pump motor from a high-torque lift motor at a glance. <S> I'm not even very expert when it comes to jet engines. <S> However, I do think that one reasonably reliable heuristic is this: if it appears to be attached to a large block of concrete, it is almost certainly not part of an airliner . <S> On that basis I think I can say with confidence that these are not jet engines.
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Those are Elevator shaft motors , they're wound for high starting torque, not like most pump motors.
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On a axial flow turbo fan or turbo jet engine what comes first the rotor or the stator? I've been let to understand that one stage consists of a row of rotors and stators. But I'm not sure which comes first? Does the front fan blades make the first part of the stage (rotor) with a stator section behind? And so on.. Or on a fan engine with a booster the first stage is the stator and then rotor (after the fan blades). Secondly do all engines have inlet guide vanes? I'm assuming not or we would physically see them in front of the the big fan engines or do they appear later on.. Maybe in the HP section? Hope this makes sense and any images with an explanation would be appreciated. Thanks <Q> There are two aspects to consider here: <S> The aerodynamic principle: <S> The constructive aspects: Constructive aspects to be considered are: a) <S> Pre-rotation of air before the rotor: <S> in order to reduce the relative speed of the airflow on the rotor blades (to avoid the shock waves of supersonic airflow) <S> a set of stators can be placed in front of the rotor; this will rotate the air towards the direction of rotation, reducing by this the relative speed of the airflow on the rotor blades; even in such cases a stator stage is required after the rotor. <S> b) Bearing location: <S> some designs put the bearing behind the rotor, other designs put the bearing in front of the rotor; in such case the bearing before the rotor needs to be supported by a system of vanes. <S> Consequently, many smaller diameter (or high speed military design) engines will take advantage of a) and b) above and have a stator in front of the first stage compressor. <S> To answer the same questions on turbines, there the aerodynamic principle requires to have first a set of stators and then a rotor. <A> Rotor, then stator, in as many subsequent pairs as the engine is designed to contain. <S> Source: https://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node92.html <A> In an axial compressor, the air is compressed by grabbing it with a moving blade and squeezing it against a fixed surface. <S> This is a very simplified representation, of course, but it gets the idea across. <S> For this reason, the rotor goes first, the stator follows. <S> Inlet guide vanes are only present in some engines. <S> They do not replace a stator, only make the rotor more efficient, but add their own drag.
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The simple aerodynamic principle requires a compressor stage to have first a rotor followed by a stator.
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Why cruise at 7000' in an A319? I was on a flight from Philadelphia (KPHL) to Boston (KBOS), after some delay and some change of route due to weather, the captain announced that we will be cruising at 7000' due to delays in the area. The history of the flight is here: https://flightaware.com/live/flight/AAL2606/history/20190618/2235Z/KPHL/KBOS My question is two fold: Why cruise so low with such an aircraft (A319)? What is the impact on fuel consumption, knowing that we were also slower? <Q> The only reason for your flight to operate at such low altitude is because it is cheaper for them to do so . <S> As you said it is due to weather, other route/altitude may not be available. <S> They can cancel the flight but that is likely to be costly. <S> They may have to find accomodation for you and crew until they can put you to the next flight. <S> Sub-optimal flight maybe better than no flight in this case. <S> They may need that aircraft at that location the next day. <S> If they choose to cancel your flight today, they will have to find a way to have this aircraft or another aircraft to fill in for the required flight the next day. <S> They might as well fly a slightly more expensive flight at lower altitude rather than fly an empty plane to Boston. <S> It is possible for them to wait for weather to improve <S> but there is an issue of crew working hour. <S> A pilot cannot work more than 8 hours in a day without provision for additional crew. <S> They may approach that limit and the wait for weather to improve might means the airline has to provide another crew for the flight and might mess up crew schedule for the next few days. <S> So for the airline, in this case, flying lower and slower maybe a better option for them. <S> Hence higher fuel comsumption is better than no flight. <A> I used the playback function of Flightradar24 for the 18th at 23:00 UTC , and the amount of traffic above 10,000' (filtering by altitude) seemed very normal compared to other days. <S> I'm baffled as to why they flew so low, but I can address your fuel question in some detail. <S> The difference in fuel consumption is ~693 kg of fuel, and would cost an extra ~$415, which is certainly not disastrous, but can be a good profit on another short-haul flight (volume economics). <S> The decision to go ahead and fly low, as has been covered, is not just about fuel. <S> There is a myriad of direct and indirect costs associated with cancelling a flight, and its knock-on effects. <S> How I arrived at the fuel figure: <S> The distance flown was ~360 NM (nautical miles). <S> The more direct no-weather route takes 307 NM. <S> I'm limited by 10,000'/29,000' as the upper/lower limits of low/high cruise figures. <S> Cruising at a weight of 50 tonnes: <S> At 10,000' each engine burns 1028 kg/h while doing 280 knots true airspeed ( <S> indicated airspeed is 242). <S> At 29,000' each engine burns 1305 kg/h while doing 462 knots true airspeed. <S> Now to subtract the distance and fuel used in the climb/descent: <S> Climbing : <S> To 10,000' takes 11 NM and 336 kg of fuel (at a brake release weight of 52 tonnes). <S> To 29,000' takes 66 NM and 970 kg of fuel. <S> Descending : <S> From 10,000' takes 23 NM and burns 48 kg. <S> From 29,000' takes 64 NM and burns 114 kg. <S> Total: <S> For 10,000', that leaves 326 NM of cruise, which would take 2393 kg (two engines). <S> Adding the climb/descent fuel would be a total of <S> 2777 kg (trip fuel). <S> For 29,000', that leaves 177 NM of cruise (using the shorter distance), which would take 1000 kg (two engines). <S> Adding the climb/descent fuel would be a total of <S> 2084 kg (trip fuel). <S> Note: <S> spending the shortest time in cruise (a flight that is mostly a climb followed by a few minutes in cruise) is the right strategy for short-haul flights, see: What should be the minimum time spent in cruise (for e.g. a B737)? <A> IFR flights are subject to congestion management at the ARTCC level, which means they have to wait their turn in line to be allowed into the airspace. <S> That used to be done with holds (and still is in many other countries), but the US will slow down aircraft, reroute them or even delay takeoff to avoid holds, which saves fuel and therefore money. <S> Most likely in this case, they were facing a long wait on the ground due to congestion in ZNY and/or ZBW. <S> However, if a flight stays low enough, it may be in contact with various TRACON facilities the entire way and never talk to an ARTCC, which means it can avoid the congestion and therefore leave immediately. <S> This typically requires flying below 10k MSL for the entire trip, which is the normal boundary between the two. <S> (It varies between 9k and 12k.) <S> In fact, doing this in the NE US is so common that they've developed an entire suite of preferred Terminal En-route Control (TEC) routes to make it easier for both pilots and controllers. <S> Using TEC routes burns more fuel because the planes are flying lower and slower than normal, which is inefficient for turbine aircraft, but in some cases the airlines may decide that's better (i.e. less bad) than delaying or canceling a flight. <A> That’s a typical alternate route to KBOS by sending them direct to FJC VORTAC thence routed eastward. <S> I suspect the real reasons for this are reduction of traffic congestion for NYC arrivals by ATC. <S> On lighter days, they’re typically given the ROBUC3 arrival into KBOS immediately after departure from KPHL. <A> If they had an issue with the pressurization system, they'd fly that low. <S> Why not cancel the flight? <S> Well, that'd cost money. <S> It'd be cheaper for them to fly low, eat the extra fuel costs and make buck on passenger fare. <S> Who knows, maybe the part needed was nearby so they were going to have to route the plane there anyways.
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It was because they could get there faster on a " TEC route ."
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Why were the first airplanes "backwards"? In the question Is the location of an aircraft spoiler really that vital? the accepted answer states "Surfaces behind the CoG act as stabilisers, keeping the nose pointing forward. An aeroplane has vertical and horizontal tail surfaces at the back just for this purpose." I agree that this seems straightforward, to a layman (me). So why then were so many of the first aircraft built 'backwards'. Taking a look at the Wright Flyer Image (C) Bay Images as an example. There are many other examples from the earliest days of aviation. Why did many put the elevators up front, thereby destabilizing the whole thing? <Q> "Backwards" is relative, there are modern aircraft that have forward placed elevator i.e. canard designs that fly quite successfully ( source ) <S> As for why its not more popular you can read up more on that in <S> why are there no production canard GA aircraft? <S> and Why is the Tu-144 the only commercial airplane with canard configuration? <S> as well as in the answers to lots of 'canard' questions on this site . <S> As for why the Wrights did it this way, NASA offers an explanation <S> The placement of the elevators at the front of aircraft is rather unique for the Wright flyer. <S> Modern aircraft typically have the elevator at the rear, attached to the horizontal stabilizer. <S> The Wright's placed their elevator at the front to provide protection to the pilot in the event of a crash. <S> (The pilot of this aircraft lies next to the engine on the lower wing.) <S> So they were not necessarily backwards so much as different considerations were taken under advisement during the design. <A> I am not sure you are correct that most early planes placed the elevator at the front. <S> For example, Otto Lilienthal's gliders had the tail at the rear. <S> The Wright brothers were strongly influenced by Lilienthal's work, but were also very anxious to avoid his fate, and believed they would obtain control he lacked by placing the elevator at the front (amongst other things). <S> It turned out that their Flyer was in fact very unstable, and difficult to control well - but controllable enough. <S> They also apparently felt that a tail at the rear would be more susceptible to landing damage. <A> It's not destabilizing to put the elevator or horizontal "tail" in front, as long as you place the CG sufficiently forward that a large portion of the wing itself is well behind the CG and effectively acting as a tail. <S> The fact that the forward elevator or canard is trimmed to generate positive lift, is what allows you to place the CG well forward in this manner. <A> Remember that the aviation pioneers were inventing the skills required to fly while refining their designs. <S> It would be a great help to actually see the position of the elevator while trying to relate its movements to the results. <S> We relate control pressures (which we sense in our hands and feet) to the aircraft movements to sense how we are doing and we learn that from instructors and through practice on well designed aircraft. <S> The Wrights were trying to figure it all out as they went. <A> They were not backwards, they had a huge horizontal stabiliser at the aft section!. <S> Angular accelerations are relative to the CoG. <S> If there is only one aerodynamic surface, it must be behind the CoG in order to self stabilise. <S> If there are two of them, like in the plane through the Y-axis, basically the same stipulation holds: that the total centre of lift is behind the CoG.
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But there is also a static performance advantage when the elevator is placed forward. Lifting wings have a natural tendency to flip tail over nose because of the way the pressure is distributed.
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Is it legal to bring your own survival gear aboard an airliner? Is it legal to bring your own survival gear aboard an airliner? Considering the sobering article by William Langewiesche that is appearing in the July 2019 edition of "The Atlantic", one might want to consider bringing: Oxygen canister with regulator and pressure breathing mask Parachute <Q> It has been done. <S> No, it's not going to save you. <S> You are not going to be able to jump out of an airliner. <S> Unless your name is D.B.Cooper , and you're hijacking the last flying 727 with a rear exit door, <S> that is. <S> Again. <S> No, it's not legal to bring a pressurized container onboard a passenger jet. <S> When you want to fly with a pressurized tank (say, a pony or deco bottle for tec diving), you have to unscrew the valve and bring it separately. <S> This is to ensure you can't bring explosives or poisons inside the tank. <S> Yes, if you could bring an oxygen or nitrox container (less fire hazard than pure O2), combined with a firefighter SCBA, it could improve your odds of survival in the very marginal event of a fire-related accident, in which the plane manages to land intact enough for you to don it. <S> No, none of these are practical measures. <S> If you want to somewhat improve your odds without impractical means, wear comfortable leather shoes without heels, cotton clothing, and a fanny pack for your papers, so that you're not tempted to reach for your luggage in an emergency. <S> One specialized item that has been considered for inclusion on airliners as safety equipment is fire hoods. <S> There are portable smoke hoods that can give you a couple minutes' protection for evacuation. <S> They don't include air or oxygen, only a simplistic filter, which is still a solid step above just holding your breath. <A> Some are. <S> I have traveled with a parachute as carry-on. <S> Got some strange looks from the crew and the pax who recognized what it was, but there's no rule against that. <S> I also regularly bring along my EPIRB emergency GPS-enabled beacon, which works worldwide, also in carry-on. <S> Nobody ever questions that either. <S> Depending on where I travel I also bring water sanitizing tablets and a Lifestraw, and pills for the occasional case of (insert_your_favorite_dead_chief's_name_here) Revenge. <A> Compressed or liquid oxygen containers are not allowed. <S> This is governed by 14 CFR § 125.219 - Oxygen and portable oxygen concentrators for medical use by passengers.
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In the US you can carry approved portable oxygen concentrators on board, which would probably be of no use in a depressurization scenario. Yes, it's legal to bring a parachute, if you can fit it within the permitted carry-on limits.
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Are gliders susceptible to bird strikes? Gliders don't travel at the high speeds that make bird strikes so devastating in airliners. However, they are also smaller, lighter and softer, and can still move pretty swiftly. Are they also vulnerable to bird strikes? What happens when a large bird collides with a glider? <Q> This is a detached glider's tail after hitting a 10 kg vulture: <S> The accident was <S> caused when the crew lost control of <S> the airplane following the loss of a part of the tail assembly after the vertical stabilizer on the airplane struck a griffon vulture head-on. <S> Some countries are more susceptible to this kind of accidents than others. <S> In Spain, which has a large population of vultures, I routinely hear about fatal accidents due to bird strikes. <A> You aren't going fast enough for it to be a problem for fibreglass and gelcoat unless the bird is quite large, like a large eagle or vulture. <S> You encounter birds all the time in a glider. <S> You soar with them. <S> You spot one thermalling, you join him. <S> A hawk or eagle will pretty much ignore you unless you pass within 10 ft. <S> I encountered a large brown soaring bird, probably a juvenile bald eagle (they don't get white heads until they are several years old), last week at about 3000 ft in a thermal and passed under it several times, close enough to see it looking back and forth to keep track of me. <S> Then he was gone... <S> To them a glider is just another big bird. <S> On tow, you have the tug in front making a racket that drives birds away, so that's not a problem unless the tug runs through a flock of gulls or something on departure. <S> Some eagles have been known to dive and attack gliders if you fly under them. <S> Bad news for the bird if it takes on the leading edge. <S> I've never heard of a composite glider being substantially damaged by a bird strike <S> but I suppose it's happened and could be a problem if a large bird hit the horizontal tail or the wing while diving. <S> For me, bird encounters are always the highlight of any soaring flight. <A> I had a glider collision with what I believe was a golden eagle (possibly a juvenile bald eagle). <S> It dove at me while I was thermalling. <S> I think it was trying to scare me, but must have misjudged and slammed into my leading edge. <S> Did quite a bit of damage, but didn't affect flight characteristics <S> and I was able to land safely. <S> Unfortunately I watched the body of the eagle fall a couple thousand feet to the ground.
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Gliders, as every other aircraft, are susceptible to bird strikes.
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Does propwash increase pitch stability? Here is a polar for a piston single-engine aircraft: (This is lifted from a Russian manual for Yak-52 , so $C_x$ is drag, $C_D$ , and $C_y$ is lift, $C_L$ ). 1 is the 'normal' case without propwash. 2 is nominal, and 3 is the max takeoff power. It is evident that the whole lift curve slope $C_L^{\alpha}$ is increased significantly (by some 30%) as the engine revs up, with $C_{L_{max}}$ reaching 2. But what immediately follows, amongst other things, is that the AoA (pitch) stability should increase accordingly: it is proportional to $C_L^{\alpha}$ (as well as to the distance from NP to CG). However, somehow I've never seen this fact mentioned explicitly, despite it being quite significant. Can anyone confirm it, either from literature of experience flying higher-powered prop aircraft? (It may not be very obvious to feel the difference because other conditions are rarely the same between idle and full power, but the closest approximation I can think of is glide descent vs full power climb at the same speed: the aircraft should be 'stiffer' and possibly more oscillatory in pitch at full power. However, propwash over tail may mask this effect; perhaps a twin is a better testbed for this...) <Q> There is not an obvious answer to this. <S> I'll outline three effects (among others): Placement of thrust line. <S> If the thrust line is placed below the CG, it will have a destabilizing effect; the converse is true. <S> That's why wing mounted engines tend to destabilize aircraft as throttles are increased. <S> But that's not the title of your question. <S> The local increase in flow from prop wash increases the wing lift slope. <S> This tends to decrease the pitch stability. <S> An increase in lift has an associated increase in downwash as a function of AOA. <S> This also tends to decrease stability. <S> This tends to increase the pitch stability. <S> The neutral point contribution is as follows (cited from Etkins, Dynamics of Flight): $$h_n=h_{n_{wb}}+\frac{a_t}{a}\overline{V_H}(1-\frac{\partial\epsilon}{\partial\alpha})-\frac{1}{a}\frac{\partial C_{m_p}}{\partial\alpha}$$ where <S> $h_n$ is the location of neutral point, <S> $h_{n_{wb}}$ is <S> the wingbody aerodynamic center (AC), $\overline{V_H}$ is the tail volume with respect to the wingbody AC, <S> $a_t$ is tail lift slope, $a$ <S> is the total aircraft lift slope, $\epsilon$ is downwash on the tail, <S> $C_{m_p}$ is the pitch moment contribution from thrust. <S> Forget about thrust line for a moment, then we have: $$ <S> h_n=h_{n_{wb}}+\frac{a_t}{a}\overline{V_H}(1-\frac{\partial\epsilon}{\partial\alpha})$$ <S> Therefore, increasing the wing lift slope decreases the neutral point, as will an increase in downwash. <S> Increasing the tail lift slope has the opposite effect. <S> So there is no blanket statement. <A> No. <S> Only for pusher types it does. <S> Pitch stability is the change in pitching moment over angle of attack. <S> The polar doesn't mention this and I would expect that pitch stability de creases with power. <S> Pitch stability is $$\frac{X_N - X_S}{l_{\mu}} = <S> -\frac{c_{M\alpha}}{c_{L\alpha}}$$ and with an increase in $c_{L\alpha}$ <S> the absolute value of the whole term should become smaller. <S> That would be normal for tractor propeller aircraft, see this answer . <S> Note especially the reference to an old NACA report ( NACA TN 2586 ) on this by John L. Crigler and Jean Gilman, called Propellers in Pitch and Yaw. <S> for the stability with free-floating elevator. <S> Both should decrease with power on. <A> Thanks for including the identity of the aircraft. <S> The Yak 52 is a low wing single engined tractor design. <S> The graph indicates prop blast over WING increases its lift at a given angle of attack. <S> It does not seem possible to infer anything else from that graph and I would not wish to guess. <S> The prop blast could affect the horizontal stabilizer trim and improve the directional stability, which includes pitch (and yaw). <S> This would be a reasonable generic assumption for all aircraft of this design, with the caveat that prop flow swirl could also have effects on the empennage as well. <S> However, I doubt the Yak designers would leave it with borderline stability without prop blast. <S> The test would be to glide it. <S> Under power, trim may have to be adjusted, as is normal for aircraft of this type.
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The local increase in flow from prop wash increases the tail lift slope. In order to measure pitch stability in flight just measure the stick travel needed to trim different airspeeds for the fixed-stick stability or the stick force needed to trim different airspeeds (without changing the trim setting, of course!)
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How does the A350 variable camber system decrease drag? Just curious how the A350 reduces drag/fuel burn by extending the flaps ever so slightly during cruise. Everything I've read about extending flaps says that extending them pushes the centre of pressure rearwards. This causes a pitching down moment, which means you need to increase the AoA, but this affects drag and fuel burn negatively (a pitch up command increases the down force from the tailplane which has the result of increasing the effective weight of the plane, which requires an even higher AoA to compensate, which also increases the induced drag). Here's how it works as per the ( A350 Flight Deck and Systems Briefing for Pilots ) Differential Flap Setting and Variable Camber The Differential Flap Setting and Variable Camber enable to optimize the loads and drag on the wings. Small flaps deflections (4° maximum) either symmetrically or asymmetrically, enable to automatically: Optimize the wing camber to reduce wing loads and drag Perform an optimized Lateral Trim function. <Q> Henning Strüber, one of the Airbus engineers behind this system, has written a paper on it. <S> In cruise: This can be applied in early cruise phases to shift the center of lift more inboard and by that reducing the wing root bending moment, which can be transferred into a structural weight saving. <S> A plane that can be built lighter will have lower drag [for the same payload]. <S> For a heavy and/or a hot and high takeoff: <S> In high-lift configuration a more outboard loaded lift distribution can be achieved to reduce induced drag during take-off. <S> For how that works, see here . <S> The answer there by @PeterKämpf confirms that outboard loading requires a heavy wing relative to the whole mass (scaling laws work for an insect, but not for an albatross or an airplane). <S> So those two regimes may appear to be contradictory: if the cruise system allows a lighter wing, then how can that lighter wing achieve more outboard lift for a heavy takeoff. <S> Accounting for the gust loads in cruise is the key here, which are smaller for takeoffs. <S> (Thanks to @PeterKämpf for this insight; see comment posted below.) <A> Just complementing the answer from @ares which is quite good and refers to the main effect. <S> I would like to refer to another "secondary" effect that implies also drag reduction. <S> When designing an airplane the structure is designed taking into account several factors, one of them, is the maximum load that the airplane can be exposed to. <S> Airbus has designed a system that during flight optimises the loads over the wing. <S> Let's say, for example, that, without the variable cambering system we have a determined maximum load <S> (let's say A). <S> Using the variable cambering system the airplane is capable of reducing the load A (maybe increasing drag) to B (being B < A). <S> So, when designing the structure, assuming that the variable cambering system will be used, the airplane will use B as design point and not A. <S> As B < A the size and weight of the structure with the variable cambering system will be lighter. <S> A lighter structure will imply less lift force needed and so less drag produced to achieve such lift. <S> So, from a design optimization point of view, the variable cambering system is, essentially, providing new design variables which will allow a better opitmization of the airplane, reducing the drag. <S> Essentially, @ares has properly described the "active" mechanism, and I have described a "passive" one. <A> Briefly speaking, there at two types of drag: profile drag and induced drag. <S> Profile drag can be said to be composed of viscous drag and shock-wave drag (these two often interact). <S> Induced drag is a result of the local effective velocities on the wing due to the -vortex- circulation. <S> I don't know what is your background <S> and thus I won't go more in depth. <S> I will just mention that, if you want to simplify things, profile drag can be seen as the drag that a 2D airfoil would have, while induced drag is a measure of the efficiency of a wing geometry. <S> In reality, these two types of drag may strongly interact when the aspect ratio of wings is small. <S> For example, it is well known that elliptical spanload distributions are optimal (when induced drag is the objective). <S> This 'elliptical spanload' can be reproduced if you design a wing of i) constant chord with elliptical distribution of twist, ii) elliptical distribution of chord with constant twist, iii) <S> a combination of twist and chord that gives an elliptical distribution. <S> What AIRBUS says, is that we can vary the chord in-flight to optimize spanload and root-bending moment. <S> Now, if you change camber, you will also optimize for profile drag (because camber is a property of the 2D airfoil) and twist (in the sense of aerodynamic twist). <S> For commercial jets, flying in transonic conditions, this means that the camber is modified to reduce shock-wave drag loss. <S> Clarification : <S> Aerodynamic twist refers to changes in camber along the span. <S> It is often more efficient to change the airfoil shape along the span instead of using the same airfoil at a different angle. <S> If you want more details, please let me know.
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What they actually do, in simple terms, is to optimize for induced drag and possibly control, i.e. stability and flight controls by changing the chord distribution.
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How to estimate the altitude of an aircraft at a given distance from a runway? What altitude should a heavy class commercial freighter be at on a descent path 17 nautical miles from a runway? (Say SDF airport) <Q> Straight in, on glidepath, about 6000' above the runway. <S> Straight-in & fast, below glidepath at 3000 to 4000 feet above the runway. <S> That's based on about 3 miles per thousand feet <S> is a standard glidepath, and it takes in the ballpark of 5 miles at idle power & level flight to slow from 250 knots to a configuration for starting down the glideslope. <S> Those are ballpark numbers; a heavy aircraft slows less rapidly than a lightweight one does, headwinds can shorten those distances, while a tailwind at altitude can extend them. <S> And there are techniques to slow a little faster than that, and you can leave the power in & slow down over a (much) longer distance if desired. <S> But for ballpark values, those are good approximations. <A> The final descent phase is flown at approximately three degrees flight path angle. <S> $17 <S> \cdot <S> \tan(3^\circ) <S> \approx 0.89$ <S> If the aircraft has 17 track miles to go to the runway, and it is on a continuous descent of 3 degrees, it will have an altitude of approximately 0.89 miles above the runway elevation. <S> Assuming nautical miles here, that translates to approximately 5400 feet. <S> However, it may be that the approach contains horizontal flight segments, in which case the altitude may be lower at 17 track miles to go. <S> If one is 17 miles from the airport and the aircraft is not flying straight to the runway but has to make one or more turns, then the number of track miles to go will be higher than 17 and consequently the aircraft will be higher. <S> Please note that the altitude given on tracking websites is typically derived by a pressure altimeter, uncorrected for the local atmosphere. <S> This pressure altitude is different than the geometric altitude of the aircraft. <S> To acquire the exact (GPS measured) <S> height, a subscription is required. <A> It all depends... <S> But in many cases, airplanes adhere to specific patterns - and these can differ from airport to airport. <S> While the normal glideslope is around 3° it might vary. <S> For a start, one might look up the charts of the airport in question. <S> But at this distance, most planes are not on the glideslope yet - often they capture is from below at somewhat above 10 nm. <S> But they might also be on a continuous descent - and it is hard to tell by eye at such a distance if the airplane is flying level or descending. <S> Crosswind and weight do actually have little impact on the glideslope, as in most cases (at least commercial traffic) <S> this is fixed and in most cases, pilots don't deviate from regulations... <A> Checking the charts for KSDF ILS RW17L (just the one I picked by random) <S> @16.9 NM <S> the altitude would be at or (slightly) above 5000ft MSL when using the default approach. <S> See https://aeronav.faa.gov/d-tpp/1907/00239IL17L.PDF
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Instead of estimating, one can use a flight track website such as FlightRadar 24 to get the exact height of the aircraft.
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What's the difference between an airplane that stalls nose down or just mushes in a stall? What's the difference between an airplane that stalls nose down or just mushes in a stall? I understand most GA planes go nose down after a stall, but some GA planesdon't drop their nose at all, they mush (they just drop in altitude). How are these planes different? Is their CM curve near horizontal, instead of negative, so that they fly almost neutral with little static margin? Or do they have a high horizontal tail volume and so with stick back, they just stay almost horizontal, or other? <Q> Take a look at the sketch below illustrating three different pitching moment characteristics: <S> In all the cases, you can assume that the CLmax occurs around 12deg AOA (not presented here). <S> Cm1 is the aircraft that would present a distinct nose-down upon reaching CLmax. <S> This is also known as a pitch bucket, because of its shape, and is good for stall identification and recovery as the aircraft tends to un-stall itself. <S> Cm2 is the mushy case. <S> With increasing aft column pressure, the AOA will continue to increase, while the airspeed may stagnate. <S> No stall identification is naturally provided to the pilot. <S> Cm3 is anything from stick lightening to outright pitch up, depending on the aggressiveness of the instability. <S> This is a common characteristic for high speed aircraft that have large LE sweep and the stall does not originate from the root of the wing. <S> As mentioned by Carlo, the degree of nose-down or nose-up would also be CG dependent. <S> Aft CG would always have smaller pitch bucket and worse pitch up (if exist). <A> It's different planes and different flying conditions. <S> Picture a plane trying to do a quarter loop. <S> Without sufficient energy it will not make it to 90 degrees (pointed straight up). <S> Now, considering most GA planes have a thrust to weight ratio of around 0.20 to 0.25, what affects how far into the "loop" we go before stalling? <S> Do we "mush" or pitch down sharply? <S> Energy is entry speed, so if we dive and then pull up at full power (zoom) we will go higher into the loop, maybe even completing it. <S> But if you don't make it to 90 degrees, the plane loses airspeed, stalls (with continued elevator deflection), sinks, and pitches sharply down. <S> Two factors contribute to pitch down. <S> At full stall center of lift moves back to 50% chord and tail volume (as plane sinks) will "flip" the nose down. <S> Now picture entering the loop with no power or zoom, your plane does not nearly go as high to vertical <S> , it simply loses airspeed and does a much gentler "mush". <S> Other factors include elevator authority. <S> The B-52 bomber has a comparatively "weak" elevator compared with an Extra 300. <S> You don't want to stall one of those. <S> And light weight, which enables a much sharper loop entry. <S> Also placement of the CG. <S> Many trainer aircraft, including the Cessna 172, as set up for students with a forward CG (within limits) to "weaken" elevator pitch up authority and encourage "mush". <S> But even with the 172, if CG is aft, stall characteristics can change dramaticly. <A> That behavior is going to largely depend upon where the CG is located. <S> A fwd CG should offer a sharp break in the stall with the nose abruptly pitching down when the stall occurs. <S> An aft CG loads airplane will have a more demur, mushing and sinking stall and, in extremes cases where the CG is aft of the approved range, may be unrecoverable simply because both wing and tailplane have stalled and aerodynamic forces no longer permit the pilot to lower the nose to break the stall. <A> The simple answer is that it depends on the degree to which the airplane is stalled. <S> When an airplane is in the stalled regime the lift on the wings does not go to zero but usually gradually decreases (see graphic). <S> The horizontal stabilizer cannot support the weight of the nose on its own and needs a contribution from the wings to keep the nose from dropping. <S> If you stall more deeply, then the wing cannot support the weight (or more specifically the moment of force due to gravity) at the nose. <S> * Graphic taken from See How it Flies Website <S> In the Piper Cherokee that I fly the plane will break when I stall it aggressively <S> (lots of back pressure on the yoke) but will mush if I stall it more gradually.
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If the wing is not producing enough lift to support the weight of the plane but producing enough lift to keep the nose in the air then you have a mushing stall situation. You are absolutely right that it has to do with the pitching moment (Cm) characteristics of the aircraft.
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Why do most airliners have underwing engines, while business jets have rear-mounted engines? Why have modern airliners converged on a configuration with two or occasionally four underwing engines, while modern business jets have converged on a configuration with two or occasionally three rear-mounted engines? I am of course aware of the many past airliners with rear-mounted engines, with the DC-9 and MD-80 and later derivatives continuing into production until rather recently, but it still seems fair to say that the underwing configuration dominates modern airliner design. Meanwhile business jets exclusively use the rear-engine design, unless one counts small airliners put into business service such as the Boeing Business Jet. Does the underwing engine design simply not scale down well to something the size of a smaller business jet? Here's a related question with good answers but still doesn't really answer my question-- How does the mounting location of a jet engine affect aircraft performance? One key factor now occurring to me is that business jets are boarded with self-contained airstair doors/ steps so a fuselage sitting high off the ground would be problematic. Airliners with long fuselages perhaps may need rather long landing gear to provide adequate ground clearance for rotation anyway-- although the DC-9 / MD-80 with its wing and landing gear far to the rear did sit rather low to the ground-- still in the airliner situation perhaps there simply is not as much benefit to having a low-sitting fuselage as there is in the business jet situation. Of peripheral interest is this Wikipedia article on "airstairs" , pointing out some cases where full-blown airliners are equipped with airstairs. One of the more interesting lines is: The most unusual airstair design was found on the Lockheed L-1011, which was a full-height airstair which was stored in a cargo compartment and allowed access from the right aft passenger door to the ground. This design was ultimately so large and heavy, and it took up valuable cargo space, that it was rarely used. <Q> Underwing engines have more advantages for larger planes, but there must be enough room underneath the wing to mount them. <S> This was tested by Boeing in the 1960s, when they designed the B737 and had <S> two competing teams pre-design both configurations. <S> The underwing config won. <S> When Airbus designed the A320 two decades later, the underwing config won again with engines that were a good amount wider. <S> Image source. <S> Advantages of underwing mount: <S> If the pods stick out forward of the wing, the backwards aerodynamic twisting moment is also reduced: lighter construction. <S> The engines can be easily reached for maintenance. <S> All of the fuselage can be used for useful load - tail mounted engines <S> have structural reinforcements in the fuselage between the engines. <S> Advantages of fuselage mount: <S> The yawing moment of a single engine fail is smaller, allowing for a smaller vertical tail. <S> Fuselage can be lower to the ground and allow for low door sill height. <S> Landing gear can therefore be shorter. <S> Clean wing configuration. <S> Lower trim change due to thrust. <S> Less noise in most of the cabin. <S> In smaller planes, the wing bending & twisting moment is a relatively smaller constructive issue than in larger planes. <S> And indeed, being closer to the ground allows for easier boarding via air stairs. <A> The terminal comes to the door you might say, so it doesn't matter so much how far off the ground it is. <S> And absent a terminal gate, you can always use an external staircase you move to the plane for the passengers/cattle to climb. <S> Business aircraft are designed to be boarded from the surface, traveling from limo to cabin in a luxurious, exclusive manner, usually using an airstair door. <S> You need a fuselage close to the surface for an airstair door to work. <S> This pretty much precludes underslung engines. <S> And if you did insist on trying to squeeze in a set of underslung engines under the wings, they'd be so close to the surface they'd ingest every sand grain and pebble. <A> Ground clearance <S> The single reason why an underwing design is unfeasible for smaller jets is just ground cleareance. <S> There are several reasons why smaller jets have lower ground clearance. <S> For once, higher ground clearance requires longer landing gears. <S> These have to be stored in flight and take up valueable space and weigh more. <S> On larger planes, the gear has to be sturdier anyways thus they need heavier and larger gears anyways since they have longer fuselages and more overall weight. <S> In turn this reduces maximum range and payload of the aircraft and that is generally something you'd want to avoid. <S> Also a lot of smaller jets operate on smaller airports. <S> Smaller airports have fewer gates with passenger bridges / stairs available (if they have any at all) and using a gate with one usally is attached to quite a hefty fee. <S> Considering that many business jets also have long durations of waiting on the ground, they are unlikely to ever be used at a gate with a passenger bridge anyways. <S> Thus passengers have to be able to (dis-)embark easily without stairs / passenger bridges as they often will use GA parking spaces. <S> You can see that mostly on smaller jetliners too like the smaller Embraer or the McDonnell Douglas planes. <S> The smaller designs tend to use rear mounted engines as they have a very low clearance below their wings.
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Engines mounted in pods underneath the wing reduce the upward bending moment of lift creation, and therefore allows for lighter construction. Airliners are designed for loading from elevated passageways at airport terminals.
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Why are overwing engines so rare? This comment to a question about underwing vs rear-mounted engines notes the existence of a rarely used third option: overwing engines . There seems to be very few planes using those. What are the disadvantages that makes it so unpopular, and what are the advantages that made it worth building those few planes? <Q> The biggest reason is the negative (or spoiling) effect of having a body "in the way" and disrupting the flow field above the wing. <S> A wing makes lift by redirecting a very large package of air downward (actually, up a bit, then down a lot) as the wing moves along, and most of the package of redirected air (which ends up as downwash) is above the wing. <S> (Otherwise, the wing would just be an air deflector and a flat sheet of plywood would do the job.) <S> Disruptions to this upper flow have to be minimized. <S> Look at any tactical fighter, like a Skyraider , festooned with rockets and bombs and tanks under the wing almost across the entire span. <S> The disruptive effects of all those shapes on the underside have minimal effect other than parasitic drag. <S> Put them on top and they act like spoilers and the airplane would never get off the ground. <S> On airplanes that do put the engines on top, either the engine is so far aft that it minimizes the effect and it might was well be mounted on tail pylons (like the Honda Jet), or the engines are mounted way forward to minimize the effect, plus gain from having the high velocity fan stream across the top, or <S> it's propeller driven and <S> the propeller flow field mitigates the effect, or, it was done anyway and the design was unsuccessful. <A> The main advantages are keeping the engines clear of ground debris to avoid FOD and providing additional lift for STOL operations, as can be seen in the An-72. <S> These requirements are rare for civilian airliners operating out of modern airports, and are more common for military transport types and regional jets operating in remote areas. <S> The greatest disadvantage is the complicated maintenance, which requires stairs to even begin to inspect the engine. <S> Furthermore, with the proliferation of composite structures in aviation, it is desirable to avoid the risk of a mechanic dropping a wrench on such a surface, and having technicians regularly working over the wing is a surefire way to end up replacing panels due to tool damage. <A> Another reason overwing engines are not favored for passenger planes <S> is that instead of shielding the passengers from engine noise by the wing (as in the case of underslung engines) you have the noise source(s) on the same side of the wing as the passengers, which makes for a noisier cabin. <S> In addition, suspending an engine on a pylon under the wing allows the engine to be shed off by gravity in case of an inextinguishable fire that destroys the engine. <S> It's not clear you could exploit this effect with engines mounted above the upper surface of the wing. <A> When they are low to the ground you can detach the engines with relative ease compared to lifting them up from above the wing. <S> This makes maintenance inspections quicker and thus cheaper. <S> During the walk around pilots can easily look into the engine intake, even grab the fan blades and turn them. <S> You can have visual gauges like an oil level indicator at eye level. <S> In case of a fire hot burning oil doesn't drop down onto the wing and in case of an uncontained engine failure (e.g. turbine disk rupture) <S> you at least have the wing in the way of the debris before it hits the cabin.
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The reason why engines are mounted under the wing is easy maintenance access and easy visual inspection.
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Why do airports remove/realign runways? When looking at Google Earth, I often find myself looking for airports. I often notice that no matter what size airport, over time many of them have abandoned old runways and built new runways in different directions. It doesn't matter between rural and urban, so residential doesn't seem to be the cause. Is it that the wind direction changed from decades ago? Did they decide that sunlight matters more or less at some point in time? Anything to do with Earth's magnetic field? <Q> In some cases the prevailing winds change and certain runways fall out of use. <S> Since airports tend to be land limited they may wish to use the land for hangars or other facilities so the runways are eventually decommissioned. <S> In other cases it could a noise abatement issue, many airports predate the property development that often surrounds them. <S> It may be in the best interest of the local neighborhood to change the runway orientation to one that creates less noise and pollution over homes or businesses. <S> In some cases runways may be moved to comply with changing regulations as was the case at Aniak Airport, where an existing runway no longer complied with obstacle clearance regulations. <S> Magnetic shift generally wont cause a runway move but it may cause a runway re-number since the runways are numbered as per their magnetic heading. <A> Three runways (or pairs) <S> 60 degrees apart was very common. <S> Where land was limited, two runways (or two pairs) at 90 degrees was almost as good. <S> These generic designs could be built very quickly almost anywhere and work well regardless of the prevailing winds, which was particularly important when building hundreds of them in a hurry during WWII. <S> However, the needs are different. <S> Modern jets need longer runways than WWII planes but aren't as sensitive to crosswinds. <S> And there is now decades of data on which runways were used the most at each airport, so only those were extended. <S> At the same time, traffic has grown, and building new runways parallel to the main one(s) adds capacity faster than it adds costs, so it makes sense. <S> Some airports kept the intersecting runway(s), but it(they) don't provide anywhere near the capacity now, still cost a lot to maintain and take up valuable land that could be reused for fancy new terminals or hangars, so many airports have ripped some or all of them out. <A> In the US, one of the most common reasons to abandon one or more runways is that a large military airbase built for intensive World War 2-era training has passed into civilian hands-- county, municipal, or private ownership-- and it is too expensive to maintain all the runways, especially considering the vast reduction in traffic. <S> For example, if you visit the airnav page for SN76 and look at the aerial photo, you'll see the short stretch of fresh blacktop on the one maintained runway, with remnants of a vast system of other runways and taxiways still clearly visible. <S> This former military airfield is now privately owned. <S> This explanation wouldn't apply to small airports though-- <S> there would at least be some visible evidence that a larger airport had once been there! <A> Some airports have had to rebuild runways as the size and weight of planes using them has increased. <S> Occasionally, the underground geology under the old runway may not be suitable to support the newer heavier planes. <S> For example, a runway built near the water may be on soft or marshy ground. <S> This ground may need to be reinforced to handle heavier planes. <S> Also, it is generally not desirable to take a runway out of service completely while rebuilding it <S> so you will build a new runway nearby and then decommission the old when one when the new one is complete. <A> Multiple reasons. <S> 1) Changes in prevailing local winds can necessitate new runways though this is probably the least desirable reason to do this as runways cost between \$1-\$3 million per mile, depending on type, layout capacity, etc. <S> 2) Airport expansion and upgrades to accommodate larger heavier traffic. <S> Sometimes this is possible to simply upgrade or lengthen an existing runway. <S> Often times preliminary civil engineering studies conclude this is not practical and a site for a brand new runway is chosen. <S> One prime example of this was Van Nuys airport (KVNY).
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In some cases it also becomes expensive to maintain a runway that may not see much use and it will be shut down.
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When do flights get cancelled due to fog? When flights get cancelled due to fog, what triggers the cancellation? Fog is too thick, too wide-spread, blocks the view of tall buildings or other landmarks? Or is the problem the type of air traffic? Too many helicopters or small-ish aircraft? <Q> Other answers have addressed the case of weather that's too bad for flights to operate, but another situation that can occur is congestion. <S> Take a look at the Average Arrival Rate chart for San Francisco International Airport (SFO) (more details on this in this blog post by an airline dispatcher ). <S> During visual conditions with favorable winds, they can operate in normal flow and accept 54+ arrivals/hour into two parallel runways, with departures using the perpendicular runways in between arrivals. <S> But that only works when the cloud ceilings are above 3,000-3,500ft. <S> That procedure relies on aircraft being able to visually see and avoid each other when flying in close proximity . <S> If there's fog (or low stratus clouds that don't touch the ground, as is typical), that can't happen; you can't send jets blindly into a cloud 750 feet apart from each other. <S> If the clouds are high enough (per the chart, a minimum ceiling of 1,600ft and 4mi visibility), they can use a special SOIA procedure (Simultaneous Offset Instrument Approach)—essentially a guided, monitored way to direct jets into a cloud 2,000 feet apart—and accept around 36 arrivals/hour. <S> And if the weather is too poor for that, the average arrival rate can drop to 25 arrivals/hour or below. <S> The extra procedures and spacing required to safely manage traffic in the weather reduces the airport's capacity. <S> When this happens, there's nothing that stops any specific commercial flight from using the airport—they all have the necessary technology to land in most cloudy conditions—, but the airport's capacity is now too low to accommodate everyone. <S> The FAA will impose a ground delay program to meter traffic into the airport until conditions improve (otherwise you end up with too many flights circling and diverting to other airports, causing many other problems), and the result is flight delays and cancellations. <A> For landing aircraft, the Instrument Approach Procedures available will dictate the required ceiling (height of clouds above ground) and visibility (horizontal). <S> The most common approach type for airlines is an Instrument Landing System (ILS). <S> ILS Category <S> I requires a ceiling of at least 200 feet and visibility of at least 1800 feet. <S> With special equipment on the ground and in the plane plus specially trained crews, this can be improved to Category II at 100/1200, Category IIIA at 50/700, or Category IIIB at 50/300. <S> "Fog" is defined as a cloud at ground level, though, so these requirements still wouldn't be met. <S> ILS Category IIIC theoretically allows landing with 0/0, but the standard has never been implemented and will probably be rescinded. <S> If the weather doesn't meet the minima for any approach procedure, arriving aircraft cannot legally land and must divert elsewhere. <S> If such conditions are forecast for when they plan to arrive, there is also likely to be a ground delay program that prevents them from even taking off. <S> For departing aircraft, airlines are not allowed to take off from an airport where they cannot legally land in the event a problem forces them to return. <S> Private pilots are allowed to do so, but few will unless they know the fog is localized, which is common in coastal areas. <A> At bigger airports when it's foggy, the limits are set by light transmissiometers along the runway that measure the horizontal visibility, giving a value called Runway Visual Range (RVR). <S> You follow Low Visibility departure procedures, which include minimum RVR requirements as well as certain runway lighting requirements, departure alternate airport requirements (because you can't return to that airport to land if something goes bad on the departure) <S> etc, that have to be met. <S> Or the available runway doesn't have the low vis equipment requirements. <S> Or there is no usable departure alternate airport. <S> Or the departure may also be cancelled due to fog forecast at the destination.
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So if the departure is cancelled due to fog, it's probably because the RVR is too low (too foggy along the runway itself) for whatever procedure the crew is qualified for.
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Why is a reduction in lift called 'drag'? Induced drag is high pressure air 'leaking' to the upper part of the wing (low pressure zone) creating a vortex which means the area of the wing tip with the vortex can't create lift. Drag on the other hand is the opposition to the flow of air. Why is induced drag called a drag when it doesn't oppose oncoming air but instead reduces wing lift? Same thing applies to interference drag, high pressure air from the top wing of a biplane leaking to the low pressure of the wing underneath it hence reducing lift , yet it's called drag when it actually reduces lift. So my question again is why is interference drag called a drag when in reality, it reduces lift and does not oppose oncoming air? <Q> Induced drag is unrelated to leaking and vortex creation. <S> It exists even in a wind tunnel where the wingtips touch the walls and thus prevent leaking and vortices. <S> Then what is induced drag? <S> To create lift, the wing needs to be at some angle with respect to airflow (or be asymmetric), so the force vector points mostly upwards but also somewhat aft. <S> Forces that point aft are generally called drag. <S> Induced drag is thus a 'real' drag, not a reduction in lift. <A> Induced drag is indeed related to vortices. <S> However, I would not characterize the effect as: a vortex which means the area of the wing tip with the vortex can't create lift Instead, imagine that each section of the wing generates a vortex, which induces downwash/upwash (downward or upward flow of air) on another section of the wing. <S> Because of the finite span of the wing and, as you put it, vortex rollover at the tip, there is a net downwash generated at each section of the wing. <S> Another way to visualize downwash is to think of it as an additional flow incidence on the wing, or an induced angle of attack ( $\alpha_i$ ). <S> Since the induced flow acts downward, it reduces the effective AOA on each section: ( https://www.theairlinepilots.com/forum/viewtopic.php?f=26&t=366 ) Not only does the induced AOA decrease lift, it also points the lift vector rearward from the reference flow. <S> The sum of that component from every wing section is the induced drag. <S> You also mentioned interference drag. <S> This drag is separate from the classical induced drag and is related to vortices/eddies created by the joining of two surfaces. <A> All lift production causes drag, and induced drag is the blanket term for this. <S> It's not specific to the wingtip vortex. <S> It doesn't necessarily "oppose oncoming air", but it is a force that acts rearwards on the aircraft, so it's drag. <S> Interference drag is a question of perspective. <S> It's like induced drag, but it's not producing lift. <S> You're seeing that from the point-of-view of the lift it's not producing: "if this were productive, induced drag, it would be generating this much lift, so it must be a reduction in lift". <S> But it's not producing a downward force on the aircraft, it's producing a rearward force on the aircraft. <S> You could choose to see all parasitic drag in the same way: "if this were a lifting-body airframe, and all this parasitic drag were induced drag with the same L/D ratio, it would be generating this much lift," but it's not very helpful to think that way. <S> It might lead you to think that you shouldn't get any parasitic drag (or any interference drag) when the wings aren't producing any lift (e.g. when stalled), and then you'd be wrong. <A> No induced drag is a horizontal vector component of the lift line, which itself is a resultant force vector from altering the momentum of air flowing around an airfoil or other lifting surface. <S> You’re on an interesting track there as both lift and drag are resultant forces from altering the momentum of air moving around an object. <S> Lift is just described as the sum of all forces in the direction opposing gravity While drag is the sum of all forces opposing the force of thrust on an aircraft. <A> Thinking of lift and drag as “causing” each other is—by definition—technically flawed. <S> Lift and drag are the “final” “result” of the magnitude of various pressure forces acting on the airfoil in various directions, resolved into two directions: parallel to the direction of airfoil travel and perpendicular to the direction of airfoil travel. <S> The former is called Drag, the latter is called Lift. <S> Being perpendicular to each other, lift cannot possibly cause or reduce or increase drag, and vice versa. <S> If you are looking for the factors that will affect the magnitude of the final lift force or drag force, you need to talk about what will change the magnitude or direction of any of the various pressure forces that are produced on the airfoil. <A> The reduction of lift is not called drag. <S> Lift is the sum of the forces acting to oppose the (apparent) force of gravity. <S> Drag is the sum of forces acting to reduce momentum. <S> Induced drag is anything that has the consequence of causing more drag (such as vortices coming off the wing-tips). <S> These answers might address a lot of your questions
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Induced drag is the drag caused by producing lift.
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Can a gas turbine be able to switch from torque to thrust? Can a turbine engine be switched from providing torque (like a helicopter) to the rotor to transfer power to provide exhaust thrust (like a jet plane)? Related: BV-347 upgrade this way? <Q> For example, the GE CF6 , which powers aircraft such as the 747, 767, and A330, has a gas turbine variant called the LM6000 that provides around 50 MW of power. <S> If you want to provide thrust from the exhaust, you're talking about a turbojet, which will require a lot of changes. <S> A gas turbine like that in the CF6 is designed to extract most of the power out of the exhaust gas to drive a load such as a fan or a generator. <S> Just removing that load is going to cause the engine to be unstable. <S> Each stage in a turbine engine is dependent on the stages around it for smooth operation and even small changes can cause problems. <S> You might be able to salvage the high speed spool but the rest will have to be redesigned to provide a stable compressor section and provide most of the thrust from exhaust. <S> Turbojets are very loud and only start to be an efficient choice at high speeds. <S> Even modern fighter jets are powered by low-bypass turbofans. <A> Most turbine engines designed to drive some sort of mechanical system such as a hydraulic pump and electrical generators are not designed to provide thrust because their fuel controller can only run it at one speed. <S> In other words, there is no throttle. <S> Also, the internal components may not be designed for that type of application. <S> So while it is in theory possible, it can be expensive and can result in some interesting failure modes that will entertain people standing far away. <A> I suppose the F135-PW-400 powerplant on the F-35B does just that. <S> A turbine engine is used to create high enthalpy gas which can either pass through a turbine to produce mechanical work or pass through a diffuser to accelerate it and create a reaction impulse. <S> General Electric has designed power generation gas turbines which use the gas core from the GE F404 fighter engine changing from a thrust application to a power application. <S> As to doing this on the fly, other than the F-35B application I don’t know of a gas turbine which can dynamically change between the two. <S> High bypass turbofans do get a small portion of their total thrust from a hot diffuser for turbine exhaust gases as do turbopropeller engines. <S> But a total dynamic shift from one to the other? <S> No <S> I’m not aware of that.
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The main way to convert a gas turbine to provide thrust rather than shaft horsepower is to attach a large fan or propeller in place of the previous load.
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What is the best option when the headwind exceeds the maximum airspeed? In a previous question, Mongo described flying his Cessna with a negative ground speed in a head wind. In this situation, what is the correct thing for a pilot to do, if there is nowhere to land downwind and upwind ground speed is negative? Other answers on that page show that, for very light aircraft, descending will not always get you to a low enough wind speed that you can fly forwards. <Q> Before even taking off, a pilot is required to get a weather briefing, including winds. <S> Wind speeds are usually predictable and well known. <S> If a pilot was flying against strong headwinds, with no good landing alternate, he screwed up his flight planning before he even started the engine. <S> A headwind doesn't even have to be strong enough for negative GS, just strong enough to cause concern. <S> Winds vary by altitude in both strength and direction. <A> This question is actually applicable to a power off emergency gliding situation, where your best option may be behind you. <S> The way the question is worded (and one of the reasons light GA air craft are generally designed with one wing and a bit more speed than old time Jennys) is that progress upwind will drain your energy source (be it altitude or fuel) <S> much faster than downwind <S> (note going downwind does not necessarily mean LANDING downwind). <S> Nor is this question in the realm of the impossible, as I once witnessed a light GA (152 or 172) on final inching into a 35 knot headwind in Armarillo, Texas one fine day (windmills are doing great out there). <S> So, going upwind is out. <S> On your way upwind, always try to pick out possible landing sites like open fields or interstate highways. <S> If there is no where to land from where you came from, that would be a poor trip plan. <S> Changing altitude may be an option, though going lower may be more turbulent. <S> Abort <S> ASAP if weather is marginal. <A> If you are flying into a headwind, that means that there is an area of High pressure to your right. <S> Frequently, as you leave move further away from the low pressure area, the winds will diminish. <S> This isn't always the case, but it is the PICs responsibility to check weather conditions along the route and the routes to any alternate destinations.
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If a pilot does find himself in such a situation, changing altitude by a few thousand feet, higher or lower, can very likely change both the wind direction and speed to something that is manageable.
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Do helicopters need a class B entry clearance when air / hover taxiing? You're a helicopter pilot at a class B airport. You'd like to taxi to another parking spot. The ground controller could either give you a hover taxi clearance or an air taxi clearance, depending on the situation. Either way will get you off the ground and (technically) gets you to enter the class B airspace. Would you need to obtain a class B entry clearance prior to requesting your taxi clearance? <Q> No. <A> You need to be cleared into Class B airspace. <S> Are you suggesting that a helicopter on the ground at a Class B airspace FBO is not in Class B airspace? <A> Technically, even with wheels on the ground anything above the surface is in class B airspace if you are at the primary airport. <S> I have never been a helicopter PIC in class B <S> so I cannot answer definitively, but if there is no intent to fly and you are cleared to airtaxi by ATC, (albeit a ground controller) that should be sufficient. <S> If you are actually facing this situation it wouldn't hurt to call on a landline ahead of time to clarify expectations with your local controllers. <S> In any case you wouldn't need to make a separate radio call for class B entry. <S> If you are truly concerned, this could be accomplished all at once. <S> For example: "(callsign) request airtaxi in Bravo airspace from _ to _ ." <S> Then you have it on tape.
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Hover taxiing with a helicopter follows the same regulations as taxiing with an aircraft (or helicopter) on wheels.
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Why are the flaperons on the 787 located so far in-board? Why are the flaperons positioned in between the outboard and inboard flaps (see 2nd picture)? Why not have them located as far outboard as possible to achieve maximum roll authority? I would think the order would be more efficient if the main flaps were both inboard, followed by the flaperons, followed by the ailerons. Thoughts? In a previous post "How does the particular piece of flap behind an engine on a B777 work?", Peter Kampf explains the flaps would have a gap b/w them when extended because they extend perpendicular to the hinge line and the trailing edge is non co-linear. However, the 737 tackles this problem just fine (see 1st picture) so I don't think it fully captures why the flaperon is placed where it is on the 787 and 777. <Q> Quoting the answer @fooot linked to : <S> At high speed, the outboard ailerons are locked and all roll control is achieved by deflecting the inboard ailerons (and spoilers, if needed). <S> This helps to reduce wing torsion and twist. <S> Yes, roll authority will be larger once the force is applied further away from the fuselage (/ roll axis), but the cost at which this comes (wing twist) is larger than that benefit. <A> The 737 has quite a complicated tracked mechanism to deploy its Fowler flaps. <S> I think it's designed to allow all elements of the flaps to move parallel to each other, as opposed to perpendicular to the trailing edge. <S> That prevents the flaps from jamming into each other at the inside corner. <S> The 787, on the other hand, has quite simple dropped hinged flaps. <S> This is part of a long standing trend since the mechanically complex 747 of simplifying flap mechanisms by using more sophisticated aerodynamic design. <S> 2 <S> So the flaps proper move a little bit aft as they extend, <S> but I think the flaperon hinge isn't dropped, so that it doesn't extend aft and crunch into the flaps. <S> This video shows that the trailing edge of the flaps moves aft, but that the flaperon does not. <S> 787 Flaps during landing <S> While jet wash would make the flaps more effective, it would also require them to be much stronger and heavier. <S> Since it doesn't extend so far down and aft, the jet wash is a convenient place to put the flaperon. <S> This NASA paper is long, but a very readable survey of the various flap mechanisms used up until the 777. <S> High-Lift Systems on Commercial Subsonic Airliners - Peter Rudolph <A> I strongly suspect that the locking of the ailerons is because the aileron aeroelastic reversal speeds don't meet the margins required under Part 25 of 14CFR.
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I think part of the reason for the placement of the 777 flaperon is that it moves the Fowler flaps away from the jet wash. I can't speak for the designers on the true rationale, but one of the considerations would be a balance between control reversal speeds and roll rate requirements at high speed.
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Why aren't aircraft cabins pressurized to sea level pressure? From an article on WHO's website: Although aircraft cabins are pressurized, cabin air pressure at cruising altitude is lower than air pressure at sea level. At typical cruising altitudes in the range 11 000–12 200 m (36 000–40 000 feet), air pressure in the cabin is equivalent to the outside air pressure at 1800–2400 m (6000–8000 feet) above sea level. Why aren't cabins completely pressurized, but instead to 6000-8000', seeing that many passengers wouldn't have to endure sometimes painful popping in the ears? <Q> Two reasons: Longevity and weight. <S> Which really come down to just weight. <S> Airframes have a limited fatigue life, measured in flight cycles. <S> The main driving factor for airliner airframe wear is pressurizing and depressurizing them. <S> Each millibar of difference between cabin pressure and outside pressure effectively consumes some percentage of the airframe's fatigue life. <S> Reducing the cabin altitude means increasing this pressure difference, and thus consuming more of the airframe's life. <S> This could be compensated for with sturdier construction, which adds weight. <S> It would also consume a little more bleed air, requiring slightly heavier packs, which, as well as weight, means a loss of efficiency. <S> Luxury business jets often maintain a lower cabin altitude, such as 4,000 ft. <S> This eats into their flight cycles, so they can still be switched to the usual 8,000 ft for flights without the owner/VIP inside. <S> Carbon fiber has a much longer fatigue life, so CFRP fuselages can afford to lower the cabin altitude to 6,000 ft. <S> This pressure altitude can also be maintained in other airliners at flight levels well below their ceiling. <S> The optimum compromise point is subject to a lot of debate . <S> The highest cabin altitude that could be permitted is 15,000 ft, above which hypoxia-induced loss of consciousness can occur. <S> The regulatory bodies have settled at 8,000 ft, so that's what the manufacturers targeted with most of their aluminum airliners, and that's where airlines prefer to run them even if they have a choice, to get more life out of their planes. <A> The higher the pressure differential between inside and outside, the more stress is put on the plane, which reduces lifespan, and the stronger it needs to be, which increases weight. <S> More weight means more fuel burn and shorter range. <S> All of these factors would combine to increase the overall cost of operation--and eventually fares. <S> Many passengers don't even notice the higher cabin altitude, especially the frequent fliers who account for the vast majority of airline revenue, so there is little financial incentive to change. <A> In all seriousness the weight of the extra air might well be on par with a layer of paint, or heavier, and we are often told that airliners are sometimes left partially unpainted (e.g. on undersides) to save weight. <S> Of course the extra structure required by the extra pressurization would also add weight.
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Because the extra air would add extra weight!
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Does temperature affect dynamic pressure? Taking off on a cold day (5°C), it can take 10 seconds to reach rotation speed but on a hot day (40°C) degrees it will take longer to reach the same speed. Is this due to the dynamic pressure? How does temperature affect it? <Q> Dynamic pressure <S> q <S> $ = <S> ½ <S> \cdot <S> \rho <S> \cdot V^2 $ <S> The molar form of the ideal gas law: pressure p = <S> $\rho \cdot R \cdot T$ , with R = gas constant and T in <S> degree K $$\rho = <S> \frac{p}{R \cdot <S> T} \tag{1}$$ Eliminate <S> $\rho$ from dynamic pressure: $$q = \frac{p}{2R \cdot T} <S> \cdot <S> V^2 \tag{2}$$ From (2) we can see that if temperature increases, dynamic pressure decreases linearly. <S> In a deleted answer @xxavier mentions correctly that Indicated Air Speed is a measure of dynamic pressure, so let’s compare the two situations. <S> 5 <S> °C = <S> 292K, 40°C = 327K, TO true airspeed on a cold day = <S> $V_c$ , on a hot day = <S> $V_h$ <S> $$ \frac{p}{2R <S> \cdot 292} <S> \cdot V_c^2 = \frac{p}{2R \cdot 327} \cdot <S> V_h^2$$ <S> $$ V_h^2 = \frac{327}{292} <S> \cdot V_c^2 = <S> > <S> V_h = \sqrt{\frac{327}{292}} \cdot V_c <S> $$ $$ V_h = 1.058 <S> V_c \tag{3}$$ <S> So to reach the same IAS, TAS must be 6% higher. <S> But there are more ways that dynamic pressure affects time to reach rotation IAS: <S> The propeller thrust is proportional to air density: simple momentum theory models thrust as <S> $T = C_T <S> \cdot <S> ½ \rho <S> A <S> \cdot <S> (\Omega R)^2$ . <S> Again density $\rho$ which decreases linearly with temperature according to (1). <S> Propeller thrust reduces with factor (292/327), integrated over time until $V_h$ is reached. <S> 11% less thrust to reach a 6% higher velocity. <S> The engine has less dense air to operate with. <S> From this site: <S> When your engine is not equipped with a turbo- or supercharger it will also suffer from the less dense air. <S> Each intake stroke (which is by volume) will contain less air molecules and thus less power can be developed by the engine (due to the fixed fuel / air ratio). <S> So yes, dynamic pressure plays a role, but the real underlying cause is the less dense air everywhere. <S> Also in the dynamic pressure. <S> Notes: <S> All above comparisons at equal static pressure $p$ . <S> $V_c$ and $V_h$ are actual true airspeeds, not indicated speeds. <A> Sure, when it's hot the indicated airspeed is lower than normal for a given true airspeed, due to reduced air density, and air density is indeed a factor in dynamic pressure. <S> The relationship between air temperature and indicated airspeed is same as the relationship between air temperature and dynamic pressure, and both are due to the relationship between air temperature and air density. <S> Of course, power and thrust are also less on a hot day. <S> That has to do with air density too, but not in a way that directly involves dynamic pressure. <A> Dynamic pressure q = <S> $\frac{1}{2}\rho \cdot u^2$ , with <S> $\rho$ is density, u is flow speed. <S> It is a measure of aerodynamic pressure at a given speed and is expressed in pascals or psi. <S> This value is the origin of the term "Max Q", which is the maximum aerodynamic stress a rocket experiences when launched and is accelerating through the atmosphere. <S> Since it has a density term, it is part of your answer, but the solution is not usually described with the term Dynamic Pressure, it is described as Density Altitude. <S> Density Altitude is Pressure altitude corrected for temperature. <S> So you get your pressure altitude by setting your altimeter to 29.92 and reading the altitude. <S> Then Density Altitude is calculated as P + (120x(OAT-standard temperature)) <S> Standard temperature is 15 Celsius at sea level, BUT it decreases 2 C with every 1000 feet of altitude. <S> So now pressure and temperature on a 40 C day make you "high and hot". <S> What this does is give your prop less air to "bite" at max rpm, resulting in less thrust. <S> With less thrust, your plane will take longer to reach its rotation speed due to slower acceleration ( a = f/m ), and because it will have to accelerate to a higher speed to get enough IAS to lift off.
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Yes, temperature affects dynamic pressure by affecting air density: it reduces with increasing temperature.
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Should I have one hand on the throttle during engine ignition? I'm training in a Cessna 172 for my private pilot license (PPL). My flight instructor recommended that I keep my checklist in one hand (so that I can keep looking outside with my peripheral vision) and turn the magneto key with the other. The other day another instructor told me that the checklist should be on my lap and my right hand should be on the throttle, in case I find the setting too high on starting the engine and I need to decrease power immediately.He sounded like this was something very obvious and said I'll fail my checkride immediately if I didn't have my hand on the throttle. To be as safe as possible I could put my checklist down, start the engine with the right hand on the throttle, then pick up the checklist again, but is this really what I should be doing, and if I don't will I really fail my checkride? <Q> Yes hand on throttle when starting, always, except on engines with fuel injection where you have to have it on the mixture because you start on idle cutoff and move it up as the engine catches. <S> In any case, you shouldn't be reading checklist items during the start; you just learn what to do and do it so you can be in total control. <S> Back to the checklist after the engine is running and you are satisfied it's running properly on its own <S> and you can divert your attention to other things. <S> Whoever was telling you to hold the checklist during the start is... <S> well... an idiot. <S> I don't think you'll fail a checkride, but will probably get marked down a bit for that item. <S> Most checkride fails are because a series of screw-ups accumulates and drops your overall score, not because of a single item, unless the single item is something critical and screwing it up is dangerous, like taxing onto a runway with an airplane on final or making a really bad judgement call or leaving out a critical item. <S> When you do your check ride, you will probably be convinced at the end you failed, if you made this little mistake and that little mistake, and will be shocked to hear "you passed". <S> Because unless you do something that shows the examiner you're dangerous, it's the overall scoring that counts. <A> It is of the opinion of the FAA that you should, according to the airplane flying handbook When activating the starter, the wheel brakes must be depressed and <S> one hand is to be kept on the throttle to manage the initial starting engine speed <S> This is merely a suggestion, there is no hard regulation on the books saying you should. <S> Although if something were to happen as a result you could be in violation of § 91.13 Careless or reckless operation. <A> That is what kneeboards are for. <S> I'd be surprised if you haven't seen one, but just in case, here is what I am talking about: <S> When you clip the checklist to the kneeboard, you are holding it. <S> When I fly, the only time I actually touch the checklist is to turn it over (when it is two sided) or to point at items as I do them. <S> As to whether you should hold the throttle, I will give the rather unsatisfying answer of " <S> That is what I was always taught." <S> That said, an examiner is going to be following the Private Pilot ACS (assuming you are in the US) and is going to be evaluating you on those items, of which, keeping your hand on the throttle during engine start is not a part. <S> IOW <S> , Engine start, taxing, takeoff, climb, descents, traffic pattern and, of course, landing. <S> YMMV as it probably also depends on the airplane, whether you have an autopilot, etc. <A> I'd like to answer by offering a counter-question for you. <S> I think we can agree that the seconds surrounding the engine start is one of the few really critical moments in getting an airplane off the ground. <S> Sure, the rest is important as well, but you can usually afford to lose a few seconds during, say, the magneto check, or while lining up on the runway for departure. <S> If we can agree on that, then the question for you becomes: does holding the checklist in your hand during engine <S> start somehow help you start the engine in a safer manner? <S> Maybe, in some roundabout way, it can be argued that it does. <S> But in this specific case, there seems to be a much more direct argument that can be made that holding the throttle will help you react much more quickly in case, say, it's mis-set and the plane lurches forward when the engine takes. <S> (You probably should verify that the throttle is set to idle, or very close to idle, before <S> you begin starting the engine, but this is part of the belt-and-suspenders attitude <S> you'll see a lot in aviation.) <S> When in doubt, always refer to an approved checklist. <S> If the checklist doesn't say, then make a judgement call on what's more likely to make an emergent situation easier to handle, or what is more likely to improve aviation safety, and go with that. <S> If you're having trouble working that out, talk to your instructor. <S> I really recommend getting into the habit of not asking just what to do; rather, ask why to do it in some particular way. <S> You're paying for your instructor's time, and their experience in these matters; as long as you're learning, they can handle the occasional "dumb" question. <S> Also, the checklist probably calls for you to somehow verify that the engine is healthy immediately after starting it. <S> In the airplane I fly, the immediate check is for the oil pressure to be within limits. <S> It pays to read ahead a little before starting the engine, so that you can proceed immediately with those immediately-after-start checklist items. <S> The checklist is a tool to help you remember each and every step, but you are allowed to read ahead when doing so is beneficial. <S> Just don't forget any of the steps.
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Personally, my hand stays on the throttle during all parts of a flight that don't involve cruising.
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What would be the impact of replacing the engines on the 737 MAX, not just reworking MCAS? There has obviously been a lot of focus on the MCAS failure following from the 737 MAX crashes. However, the MCAS appears to be a compensating control for design decisions, specifically the replacement of the CFM56-7BE engines on 737NG with the much larger, more efficient LEAP-1B. That in turn necessitated a higher ground clearance. In lieu of redesigning the landing gear to provide greater clearance (and raising the overall height of the plane), the engine pylon was redesigned, moving the engine further ahead of the wing and closer in line with the wing surface. There were other changes as well. The re-positioned engines changed the thrust line. The resulting control characteristics were compensated for in software, with the MCAS addressing a very specific negative flight characteristic. Notwithstanding the new engines being more efficient (resulting in lower operating costs), is it possible and what would be the impact of retrofitting the existing fleet of 737 MAX with an engine and pylon in the previous position ? Could for example, the CFM56-7BE and pylon be retrofitted? There are plenty of plane models offered with multiple engine configurations, though I imagine they are fit off a similar pylon / housing. If I were an operator of MAX fleet in which the public has lost confidence in flying on , I'd like some other option than scrapping the fleet. Edit/Addenda: I don't know anyone is planning to scrap the fleet and it's far too early to suggest what the final outcome may be as this story plays out. There have definitely been order cancellations , orders lost and questions surrounding the plane's certification . You can't cancel an already delivered/completed order; it would be difficult to force Boeing to buy them back and replace them (with what?). IF Boeing offered to "retrofit the MAX as an NG-like", it might be the best possible outcome for all. It certainly seems less drastic than Boeing starting from a completely different base design or losing customers to Airbus. <Q> Possible? <S> Yes. <S> Economically feasible, not even close. <S> Right now, Boeing has to re-do one thing, and it will take a few months. <S> To re-engine the plane would take several years at the least. <S> However much money it is losing right now <S> , it is a drop in the bucket compared to the cost of what you propose. <A> Near as I know the answer is no, not without additional changes to the type certificate and it would make more sense to add additional hardware and software fixes to the 737 Max’s flight control software before attempting anything that drastic. <S> Just a sad part of the bloodletting Boeing is having to undergo for years of bad business practices at BCA. <S> What they should have done was design and build a clean sheet airplane back in 2011. <S> But that’s water under the bridge. <A> Yes they can be re-engined to B737NG configuration, while retaining the aerodynamic improvements made. <S> From wikipedia : The new winglet is 9 ft 6 in (2.90 m) <S> high.[34] <S> Other improvements include a re-contoured tail cone, revised auxiliary power unit inlet and exhaust, aft-body vortex generators removal and other small aerodynamic improvements <S> Technically possible and with small improvements over the NG, but not including the main benefit of the larger bypass ratio of the LEAP engine. <S> Also not very good for PR. <A> None of that is going to happen. <S> There will be a fix and it will be software based one, way or another, however long it takes. <S> The problem isn't really the pitch behavior problem that MCAS was designed to address; it's the way MCAS and its architecture was designed and certified. <S> There are even stranger software band-aids out there on other designs. <S> The 747-8 uses a software based solution for wing "flutter" (more of a vibration/oscillation than flutter) where the tip shakes up and down at 3 or 5 hz or so in certain regimes. <S> Rather than redesign the wing to increase its torsional stiffness, they use the FBW computer to actively oppose the vibration with outboard aileron inputs (which is normally inactive at this point), transparently to the crew.
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To re-engine the plane, you would basically have to re-do a large amount of the FAR 25 certification.
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Consequences of stalling while sideslipping in a glider? In a glider, sometimes it's useful to do a side slip with crossed controls. However, when that happens, the pitot tube angle is out of line and the ASI goes to zero, therefore losing any indication of the current airspeed until the sideslip is interrupted. During this maneuver, what would happen if I were not to keep proper control of the attitude, and thus airspeed, and were to stall the wings? would the glider spin, or would the unusual attitude prevent it? Edit: The duplicate question does not necessarily responds as it seems to address powered airplanes, where other factors may be in play. My question targets specifically gliders. <Q> How aggressively would depend on the glider's actual stall behavior, some being more benign than others, but say you were in a glider with an abrupt stall with minimal warning and a sharp nose drop. <S> That sort of glider would spin if you didn't initiate recovery right away. <S> This isn't such a big problem, because the nice thing about gliders is you don't have power to confuse things when it comes to pitch attitude vs speed. <S> For a given configuration (weight/CG etc), if attitude X gives speed Y than you can be certain that any time you pitch to attitude to X <S> you will get speed Y, with or without an airspeed indicator. <S> So, if you are on final at 50 kt, and want to side slip, just make sure you lower the nose a couple of degrees during the slip and control the pitch attitude, so that you will maintain somewhere around 50kt with the additional drag and there is very little risk of stalling and spinning. <S> Easy peasy. <S> You also have the other impending stall cues, like softening controls, noise dying off, and such, so if you are aware and on top of things there shouldn't be a problem and it would take some ham fisted flying to really mess up. <S> If you are getting trained well, there should be dedicated no-airspeed instruction and practice and once you are considered a proficient pilot you should have no problem with flying safely with no airspeed for all maneuvers (if you sent me out in a power plane on some kind of wacky challenge, and told me I could only have one operating flight instrument, my choice would be a compass). <A> Firstly, I would find a way to keep that airspeed info coming. <S> Loss of airspeed info certainly could be very dangerous, especially if you are slipping into your landing approach in any kind of winds. <S> That being said, if you are cross controlled (ailerons in rudder away), as soon as you feel a buffet center the ailerons and rudder, and PITCH DOWN. <S> If you haven't started yawing, you are OK. <S> If you have, use that rudder! <S> Breaking/preventing the stall by pitching down is critical, as is controlling yaw with the rudder. <S> Do not worry about your bank, you can carefully roll out after the stall is definitely broken. <S> Only then can you safely use aileron inputs. <S> Provided proper inputs (especially centering ailerons) <S> are done at stall warning, spin should not develop if the CG is set up correctly and the glider is of a stable design. <S> I would worry a lot more about my airspeed indicator. <S> Remember, the best way to know the consequences of a stall is to try it with a qualified instructor at a safe altitude. <S> This is the best way to learn the slow flight characteristics of your plane. <S> If your design is docile enough, simply relaxing the elevator may be enough when you feel the buffet, but practicing up high will help fine tune your technique tremendously. <A> I would suggest you take some dual spin training, and then go carefully perform some constant-heading cross-controlled stalls at altitude in all the gliders you will be flying, with the intent of exploring the flight characteristics up to the point of the stall break. <S> (Don't intentionally take things further than the stall break unless spins are allowed in that glider, and you are competent in spin recovery.) <S> I would suggest that in a constant-heading slip or a slipping turn with the yaw string blowing toward the outside of the turn (as opposed to a skidding turn with the yaw string blowing toward the inside of the turn), in most gliders you'll find that if you relax the aft stick pressure as soon as the nose begins to drop in the stall, the glider will not spin. <S> (Please add a note to the end of this answer listing any glider types where you find this not to be true!) <S> In general, if you are slipping to lose altitude, you'll get the best results if you carry some excess airspeed-- keep that nose down. <S> But note that a normal crosswind landing, using the wing-down method, does end up with the aircraft slowing to near stall speed in uncoordinated (slipping) flight. <S> In most gliders this is considered to be an acceptable landing technique. <S> Here is a related answer: <S> What happens in a stall during a slip? <S> The last paragraph of this answer also has some related content: <S> Is this paragraph about the dihedral effect in the FAA's Glider Flying Handbook correct?
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Yes if you were to stall the airplane while in a side slip it will probably depart, or start to depart, into a spin.
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Why is the UH-60 tail rotor canted? The Sikorsky UH-60 (S-70) has a tail rotor that is canted 20 degrees upwards. Why is that? Picture source <Q> John K and Koyovis 's answers are both correct. <S> However, as a former pilot of the UH-60 and a mechanical engineer here is a simpler version. <S> A helicopter must be balanced. <S> If the front is much heavier than the tail, then it can't fly safely as the nose is too low. <S> If the tail it too heavy, then the same. <S> The point of balance is called the center of gravity. <S> The tail boom on a helicopter is very long. <S> If you were to add one pound to the tail vs one pound to the nose, the pound on the tail would more impact due to the length of the tail boom. <S> In engineering this is called the "moment arm" By canting the tail boom, the tail rotor actually lifts the tail boom. <S> There isn't that much lift, but since the tail boom is so long it has a pronounced effect. <S> This gives the aircrew more latitude in loading the helicopter. <S> With the extra lift provided by the tail rotor, we can put more load (troops, fuel, etc.) <S> behind the rotor mast and still keep the center of gravity in acceptable limits. <A> A guy in my glider club used to fly them. <S> It's something to do with achieving a vertical lift component of several hundred pounds from the tail rotor's thrust, and that and the large horizontal tail allow a large C.G. range by helicopter standards, as well as adding a bit to the total vertical lift capability. <S> There is some kind of mixing system in the control system to deal with various cross coupling effects due to interactions between the tail surface and the canted tail rotor and main rotor, but which is transparent to the pilot. <S> I snooped around and found a paper that talks about the advantages of canted tail rotors here . <A> I came across this in Ray Prouty's book, Helicopter Performance, Stability and Control. <S> The best position for the centre of gravity on a single rotor helicopter is slightly ahead of the main rotor shaft. <S> In some cases, (an) aft C.G. position is forced by design considerations even during preliminary design. <S> A classic example of this is the Sikorsky UH-60A. <S> As explained in reference 10.13, this helicopter was limited in overall length by the requirement to load it into a C-130 without major disassembly. <S> With the rotor sized by the vertical climb requirement, the air transportability requirement dictated a short nose. <S> This and the desire to carry all the fuel behind the main cabin, led to a centre of gravity range of more than 15 inches, all located aft of the main rotor. <S> Sikorsky more or less satisfactorily solved the resultant trim problem by canting the tail rotor, as explained during the discussion of tail rotor design. <S> Note that in the design phase, it would have been a lot simpler to shift the CoG forward by constructing a longer nose, but this was not possible and the more complicated canted rotor option had to be implemented. <S> With a large useable range of CoG as a result. <S> Downside : <S> the canted tail rotor introduces cross coupling between yaw and pitch, but since there are two control mechanisms for pitch (cyclic control as well) <S> the pitch response to pedal input can be tuned by a control mixer. <S> The stabilator helps at forward speed - it is also in the downwash of the tail rotor and can redirect some vertical tail thrust in the hover. <S> Upside : <S> tilting thrust at small angles has large trigonometric effects. <S> Thrust in the yaw direction reduces with (1 - cos20 <S> ) = 6%, at a gain in the pitch direction of sin20 = <S> 34% of tail rotor thrust. <A> The stabilator has a decided effect on effective lift with the tail rotor. <S> It has a large range of travel, both up and down. <S> This travel combined with the tail rotor thrust augmented by the 20 degree cant makes it a very balanced assembly. <S> The UH-1 had a limited movement sync elevator mounted forward of the tail rotor arc which provided stability but not increased lift. <S> This was how it was explained to me by a design engineer with Sikorsky and who was also an Army Aviator. <A> In addition to the answer put forth siting Ray Prouty <S> (The Man) tail rotors are canted in order to compensate for the forward tilt of the main rotor mast, allowing for a more level hover attitude.
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You could say that it turns the machine into a sort-of quasi tandem rotor helicopter, with just a little bit of tandem-ness.
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How did pilots avoid thunderstorms and related weather before “reliable” airborne weather radar was introduced on airliners? How did airline and or mail pilots avoid hazardous weather especially at night before airborne weather radar systems were in use? <Q> They looked out the window! <S> If you are talking about a developing thunderstorm, especially during the day, they can be quite easy to see in front of you provided decent visibility. <S> Here is some good footage of what it looks like to fly around a towering cell , you will note its fairly easy to see. <S> At night, lightning, even in the clouds tends to be a prominent effect and is a good indicator of "dont fly there" . <S> Here is a good picture of that effect (as well as a little story about flying around it) . <S> Of course, summer haze , the dark of a moonless night, shifty weather , or just plain old mistakes sometimes lands planes right where they should not be sometimes with disastrous results . <S> Here is an interesting report on thunderstorms and aircrafts from 1948 that may have some interesting info for you. <A> I´ll second John K´s recommendation of Fate is the Hunter for a first hand account of flying in the 30s and 40s. <S> The style can be a bit too laden in floritures, trying to lend a certain mystique to flying that still existed when it was published, but the content is sound and if you want a glimpse into the aviation world of that era, it is a great read. <S> Experience handed down orally by more senior airmen that were familiar with a particular route. <S> The poorly understood impact of icing on an airframe made weather seem like less of a danger than it really was. <S> Since CVRs and data recorders were still far in the future, many weather-related accidents were unsolved. <A> Read the book <S> "Fate Is The Hunter" by Ernie Gann, who was flying DC-2s and 3s for American. <S> One of the all time great aviation books. <S> In the 30s, they just blundered right through thunderstorms if they couldn't be visually avoided because they were embedded in cloud or it was at night, and hung on for dear life.
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To summarize some of the main points: Reports of winds aloft were reports of the local conditions relayed by radio from aircrews flying in the area of operations and served to inform following pilots.
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What is the purpose of the fuel shutoff valve? Most GA planes have a fuel shutoff valve which I don't quite understand the purpose of. Does it cut the fuel flow with the mixture.My theory is to prevent fuel flow at earlier stage for safety reasons? <Q> It's both a maintenance and safety feature. <S> You need a way to cut off fuel flow to the engine compartment, either to work on the engine, or because of a fire at the engine, or because you are doing a forced landing and it helps reduce the risk of your entire fuel contents seeping onto your hot engine if you bend things a bit putting it down and a fuel line gets broken. <S> So you will always have a shutoff valve, and it's always somewhere upstream of the firewall. <A> Fuel shutoff valves are a hold over from the days of float style carburetors (and necessary on any float style carb system). <S> With a float style carb when the fuel is on the bowl will fill up until the float floats up and shuts the flow off. <S> Since gasoline becomes a vapor at ambient temperature the small pool in the carb will be constantly evaporating. <S> As such the float will sink and refill the bowl. <S> Given enough time this will drain the fuel tank. <S> This vaporous fuel also fills the intake and can cause backfires or intake fires. <S> The mixture is adjusted post bowl and merely leans you to the point of cutout which may not truly be a full stoppage of fuel. <S> For fuel injected systems or systems that use some kind of blow through carb a shutoff valve is not strictly necessary for leak reasons but JohnK makes some good points on when its used for safety reasons. <S> Some of these systems will also allow small paths for fuel to escape so a shutoff is often implemented to ensure total fuel stoppage. <A> The less technical, but accurate, answer is to meet the certification requirements of the FARs. <S> Specifically, FAR 23.2430 is Airworthiness Standards for Fuel systems. <S> It reads in part: <S> (a)Each fuel system must-...(5) " <S> Provide a means to safely remove or isolate the fuel stored in the system from the airplane" <A> Here are two examples of high wing fuel systems. <S> The left is a from a 1973 Cessna 177, the right from a later model Cessna 172. <S> You can see in the 177 the fuel cutoff is earlier in the system, before the fuel system is pressurized, while in the later plane it is after the fuel pumps.
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Either way, fuel is cutoff after the header tank to limit the amount of fuel available in case of an engine fire that could result from a crash.
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Are glider winch launches rarer in the USA than in the rest of the world? Why? I had heard before that winch-launching gliders was a relatively rare practice in the USA, while quite common in the rest of the world. My data is mostly anecdotal, but I do know gliding clubs in Europe that exclusively use winches. A recent post in The Hangar reminded me of this: Tanner claims their club owns the first winch launcher sold by Tost to a USA customer, and that they have not used it in years. As far as I know general aviation scene in the Asia-Pacific region takes after that in the US, but I have no concrete knowledge. Is winch launching relatively rarer in the USA than in the rest of the world? If so, why? How does it compare to other regions? <Q> To expand on Quiet Flyer's answer, it's technical and economic at the same time. <S> Technical: <S> Winch is limiting because you are deposited in the same spot over the field, whereas a tow, if the pilot knows what he's doing, can take you to a thermal up to a few miles from the field. <S> Plus you can get towed higher. <S> If you had to choose the launch method that gives the highest probability for a successful flight, aerotow's a no-brainer. <S> Economic: Because of the higher average individual purchasing power in the US (and Canada to more or less the same degree) of disposable income (for example, power flying is a middle class, even lower middle class, activity in the US and Canada, and an upper middle class activity in EU), glider pilots can afford the higher cost of a tow, but which is still cheaper than a tow in Europe because overall operating costs for power planes are less. <S> So given the choice between paying 15-20 bucks for a winch launch to hopefully 2000 ft (if you have a runway long enough to fit the cable) and 30-40 bucks to be hauled to 3000 feet in a Pawnee, whose pilot, if reasonably skilled, will find and drop you off right at a thermal, most North American glider pilots will pay the 30-40 for the tow. <S> So the result is there is very little market demand for winch operations in North America, except with some small clubs in out of the way places without the money and resources to run a tow plane. <A> Is winch launching relatively rarer in the USA than in the rest of the world? <S> Definitely. <S> If so, why? <A> This is strongly influenced by the overwhelming number of airports in the United States compared to other countries. <S> According to chartsbin, which pulled it's data from the CIA world factbook , in 2010 there were 43,982 airports in the world, of which 34 percent (15079) are in the United States. <S> The US also tops the world in unpaved airfields with 9,885. <S> The next highest country on that list was Brazil with 3346 and only Mexico in the group topping 1000. <S> Couple all of this with the US accounting for less than 5 percent of the world population and one thing becomes clear... <S> there are just a lot more places to aerotow from in the US than the rest of the world. <S> I would guess (will try to backup with stats later) that the US also accounts for a much bigger proportion of GA (and thus tow capable) <S> airplanes as well. <S> As an aside <S> , so far all of my 150+ glider flights have been aerotow. <S> I look forward at some point to try winch launching... <S> I've heard it is quite a rush! <A> Watching YouTube videos like this one , I get the impression that car towing is quite popular in the USA - especially for instruction flights. <S> The reason why car towing is done instead of winch launching is simple: <S> Car towing is quite simple: You require a powerful SUV that you can buy at the next car dealer. <S> Winch launching requires a winch. <S> I have read that a winch costs more than 300 thousand EUR (350 thousand USD). <S> Because of this high price most clubs here in Germany try to build their winches themselves and sometimes fail due to the lack of engineering skills. <S> (Years ago I myself was a member of a club who failed.) <S> So if you have the choice between winch launch and car towing, you will probably decide to do car towing. <S> However, here in Germany car towing is nearly never done because of the airfield sizes: <S> Using a winch a runway length of 950m is sufficient to lift a glider to 1100ft GND. <S> I have read that a runway length of 1700m is enough for 2000ft GND. <S> The runway length of 2000m in the YouTube video was only sufficient for 700ft GND using car towing. <S> This means that car towing requires much longer runways than winch launching. <S> A typical airfield here in Germany has a runway length of 600m, however, winch launching is only done on airfields with runway lengths of 800m and longer. <S> Europe is rather densely populated <S> so there is simply no space left to build (general aviation) airfields with longer runways.
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At least in part because airplane fuel, as well as some other costs associated with powered aviation, are cheaper in the US than in many other countries.
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What is the lowest-speed bogey a jet fighter can intercept/escort? Jet fighters are made to cruise at a high subsonic speed, even at a supersonic speed (supercruise?). It means that they can be flown comfortably at relatively high speeds. Jet fighters are often used to intercept aircraft, whatever the reason (assistance, escort from national to international airspace, check an unresponsive aircraft,...). General aviation aircraft can cruise at a slow speed compared to jet fighter. Moreover, if needing assistance, it may fly even slower. I imagine it is possible that a GA aircraft needing assistance cannot fly at a speed above the stall speed of a jet fighter. I know that some countries dispatch choppers to intercept slow aircraft to handle such situation. I imagine the military doesn't fly their jets at stall speeds when close to another aircraft (a margin is needed). Is there a speed below which a jet fighter cannot intercept another aircraft? Otherwise, how do they do it? (I imagine you can orbit above another aircraft but it is less convenient to guide it safely to an airport) <Q> There is nothing stopping a faster jet from flying a zigzag pattern behind an intercept target if the goal is to remain in close contact with it, but a large difference in airspeeds would indeed hamper some tasks like observing the cabin for signs of life or unlawful interference. <S> So the answer is yes, a jet fighter cannot perform all the tasks involved in a typical interception of an unresponsive aircraft if the speed delta is too high. <S> For reference, the takeoff speeds of 4.5 generation fighters like the F-16 are in the 130 kt (240 km/h) region, while the takeoff speed of something like a C172 is around 60 kt (111 km/h). <S> The exact weapon and fuel load of the fighter will of course have an impact, but fighters scrambled for an intercept are typically light and with an almost clean configuration. <S> I have deliberately used takeoff speeds instead of landing speeds to factor in a margin of safety in regards to control authority; both speeds are among the lowest an aircraft can sustain, but during close approaches to a potentially hostile aircraft, some maneuverability is required. <S> Still, 100+ <S> km/h is a substantial speed gap, and has led to issues in the past : <S> The Po-2 is also the only biplane credited with a documented jet-kill, as one Lockheed F-94 Starfire was lost while slowing down to 161 km/h (100 mph) – below its stall speed – during an intercept in order to engage the low flying Po-2. <A> This is within the speed range of medium to higher performance GA aircraft, but a bit too fast for most fixed pitch prop, fixed landing gear aircraft in common use. <S> Additionally, there is almost no assistance a military jet could provide to a GA aircraft that would require the two to be in close formation at matching airspeed. <S> The nearest situation necessitating actual close formation flight would be to provide visual verification whether landing gear were fully extended. <S> While close up inspection of an over-center lock is possible to confirm, a general up, down, or stuck halfway assessment is possible from quite a bit further. <S> Even if it were ideal or possible, unbriefed formation flight between dissimilar aircraft with a GA pilot of unknown proficiency presents its own set of risks. <S> Communication relay to ATC, assigning headings or leading a lost-comm pilot to a hole in the clouds, etc. are legit forms of assistance that could be provided from an interceptor orbiting higher overhead, or leading on at a slightly higher airspeed. <A> Military fighter jets are actually not all that fast, when they aren't supersonic. <S> Their cruise speeds are below the cruise speed of airliners. <S> Supersonic flight is mostly meant for interception, while combat speeds are subsonic. <S> Below their cruise and maneuvering speeds, there is considerable margin to an actual stall. <S> It depends on weight and altitude, so there is no one answer, but it goes down to 100 knots and below. <S> The most popular GA aircraft, the Cessna 172, has an official cruise speed of 122 knots. <S> This is within the operating limits of most jet fighters, except when overloaded or at altitude above that of GA aircraft. <S> So there is a sufficient amount of overlap between GA and jet speeds, if both want to stay alongside. <S> However, a GA aircraft can operate much slower, and jet fighters generally won't be able to maintain a steady position close to their stall speeds. <S> While their TWR can be close to 1, the typical fighter aircraft is simply not controllable at a 45-degree angle of attack. <S> Make no mistake, a fighter won't lose a GA plane, but it won't be able to maintain a steady position next to it. <S> Fighters with thrust vectoring, which are still rare, could sustain mostly side-by-side contact with a GA aircraft. <S> The Pugachev's Cobra maneuver can slow a supermaneuverable plane to near-zero airspeed, although it will have to get back to its stall speed after. <S> That said, a helicopter is still more practical for assisting a GA airplane, not least because it's much more likely to be able to land near the plane's crash site to help pull the occupants out.
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Some fighters are quite controllable at high AoA at speeds lower than optimal for approach, but it is unlikely that a fighter pilot would be comfortable flying formation at such a slow speed. Depending on aircraft type and weight, flaps down approach speeds for most military fighters is in the range of 120 to 150 KIAS. The best-range cruise speed for most fighters in the range of 300 knots, due to high drag.
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Why does RPM for a fixed-pitch propeller change with an aircraft's pitch? Talking bout a C-152 - If I pitch the aircraft down, and without adjusting the throttle, the RPM would show an increase. Pitch up, and without adjusting the throttle, the RPM shows a decrease. I've been told that by pitching down you increase the amount of airflow your engine is receiving while pitching up decreases the amount of airflow, or that the propeller at different pitch attitudes either forces more air or acts against the air entering the intake ports, or that it's because of the propeller angle of attack. <Q> The driving variable here is airspeed, not pitch attitude per se. <S> Your airplane naturally goes faster when you put the stick forward and decrease the wing's angle-of-attack, and this changes the prop rpm. <S> Your pitch input is changing the wing's angle-of-attack which leads to an airspeed change. <S> Even with the engine switched off, the aircraft would fly (glide) at a higher airspeed with the stick forward than with the stick aft. <S> And for a given throttle position, a fixed-pitch prop turns faster at a high airspeed than at a low airspeed. <S> Just as a wind turbine does. <S> Your tachometer can be used as an airspeed indicator. <S> The key factor is the speed of the air flowing through the propeller disk-- with a fixed-pitch prop, this dwarfs any effect related to the amount of air being forced into the engine. <S> And yes, this effect can be explained in terms of the angle-of-attack of the propeller blades. <S> Increasing the airspeed decreases the angle-of-attack of the propeller blades, "unloading" them, or in extreme cases subjecting them to negative loading so that the prop is driving the motor rather than vice versa. <S> In a fast dive at a low power setting, the wind (airflow) is making the prop move, not the other way around, and you'd pick up more airspeed if the prop fell off. <S> But even at a lower airspeed and higher power setting, the speed of the oncoming airflow has big influence on the speed of the prop's rotation. <A> Consider what happens when you move this propeller from a stable cruise condition to a dive. <S> In a dive, the incoming airstream increases, so a propeller with a fixed geometric pitch will have a smaller effective angle of attack. <S> It will then generate less lift and drag, and thus need less torque to rotate. <S> Consider this paint.exe marvel: <S> An increasing forward speed component tends to align the airflow with the propeller blade, reducing its angle of attack. <S> Since the rpm of the propeller-engine combination is stabilized where the torque output of the engine equals the torque requirement of the propeller, the rpm will increase to the new equilibrium. <A> Because your hydrostatic load changed The RPM changed instantly because the hydrostatic load on your prop changed. <S> Because air is a fluid . <S> Effectively, your prop is a fluid coupling. <S> An example of "not a fluid" is an engine geared to cogs on a rack railway. <S> An RPM change must match a speed change. <S> Not here. <S> Compare to your car's automatic transmission torque converter- <S> the most common fluid coupling in normal life. <S> It intentionally has "slip" so the engine can idle at 600 rpm while the car is stopped. <S> This slip varies by engine force: if you push the accelerator, the engine will rev more while still stopped. <S> On a slight downhill, it slips less, and on a steep downhill, it can actually push (windmill??) <S> the engine <S> *. <S> There is a relationship between throttle position, engine RPM, and hydrostatic load (resistance). <S> Your propeller is the engine side of a torque converter. <S> When you pitch down, you change induced drag, i.e. the airflow is resisting less . <S> You have instantly removed hydrostatic load from the prop, so the engine RPM instantly increases. <S> Put it another way, at any given altitude, weight, pitch and throttle position, the airplane will seek to "balance out" at a particular RPM and airspeed. <S> But it won't get there instantly . <S> You can change pitch angle very quickly, but it takes awhile for airspeed to change. <S> So in that moment when you have pitched down and you have not gained airspeed, the air is resisting less (because the airplane wants to go downward on its own, like going down a hill on a bike)... <S> so the RPM must increase. <S> Again, air is not a rack railway. <S> * however you can't "windmill" start an automatic transmission car. <S> That's because the gears are engaged hydraulically by a pump on the engine side...
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Because airspeed influences the effective angle of attack of your propeller blades.
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While waiting for a delayed outbound flight how can I guess where's the inbound plane? This summer in Mykonos our flight back to FCO was delayed and nobody at the airport could communicate reliable estimates on when it would be. In that case I managed to find the FCO-JMK inbound flight on FR24 and saw it left FCO with 2 hours delay, so our own would have been at least that. In bigger airports with more connections you might not be able to guess which airplane will become yours. I guess the registration number of the plane assigned to my flight will be available some time (maybe a few hours?) before as per the flight plan. Is there a reliable public accessible source for that? When I have the assigned RegNum I can use plane finder, FR24 or whatever to see if it's on its way and have a rough estimate of when it will land and then be available for my flight. Apologies for my English. Thank you <Q> It's difficult to find out what the inbound aircraft is, unless you are at a small airport and/or the airline you are flying on is only operating a few routes from the airport. <S> When you are at a big airport and/or the airline is operating many routes there, you have no way of telling where your aircraft is. <S> For smaller airports, you can effectively find the inbound aircraft by using the appropriate filters in FR24. <S> Note that in some cases the aircraft planned for a flight can be changed last minute. <S> This typically happens when aircraft are significantly delayed inbound to their hub / main base and the airline decides to minimise the outbound delay costs by assiging a different aircraft. <A> Some tools provide this information. <S> For example, I have found FlightAware to be generally accurate. <S> Some airline's services (online or mobile) services also provide the information. <S> Information might well not be available to the public for some airlines. <A> Is there a reliable public accessible source for that? <S> No, there isn't. <S> The registration is listed in the ATC flightplan, which is not publicly available. <S> One such airport is Frankfurt, and I if I recall correctly, at least some other German airports do the same. <S> If you download the mobile app for the particular airport, you will be able to find the registration. <S> FlightRadar24 also sometimes have it available, and sometimes the airline might even show it somewhere <S> (app, website, ...) <S> But a reliable public accessible source? <S> No, unfortunately not.
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Some airports do publish the registration of flights, enabling you to find the right aircraft using a bit of investigative skills.
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Why did this aircraft do a ‘spiral’ before landing? There was this WizzAir flight two days ago, from BUD to PMI, and right before landing it did a ‘spiral’ like maneuver. I’ve attached a screenshot. Why did it do that? It looks strange. <Q> The flight was on the 28th, and before orbiting it was around 12:00 UTC. <S> By using the playback function of FR24, this is the view: <S> The flight in question was 2383 with call-sign WZZ1161 <S> (FlightAware permalink ). <S> The boxes with numbers and arrows indicate the flight level and either climbing or descending. <S> As you can see, two busy streams were approaching the airport from the north. <S> This orbiting as opposed to a holding track (race track shaped) is common and its phraseology can be : for spacing orbit left for spacing <S> make a 360 turn left <S> Fast forward: <S> And a Ryanair flight did the same before continuing the approach. <S> It was just heavy traffic <S> and it's quite common over Heathrow (live as of writing this): <A> At the time WZZ1161 / <S> W62383 arrived at Palma de Mallorca (PMI), it was rush hour. <S> To sequence the aircraft for final approach, Air Traffic Control usually give aircraft vectors (headings) to increase their path lenght so that they line up with the runway at the right time, with the appropriate amount of spacing from the preceding aircaft. <S> In case of peak traffic a lot of time may need to be absorbed before the final approach can start. <S> Since vectoring causes high workload for the air traffic controller (multiple instructions, aircraft moving all over the area) <S> ATC resorts to putting aircraft in holding patterns or instruct simple 360 degree orbits. <S> In the screenshot below you can see 6 aircraft on approach to PMI at the time that WZZ1161 was arriving. <S> All had complex vectors and/or 360 degree orbits as part of their approach. <S> There were just too many aircraft arriving for the airport to handle it efficiently. <A> The only published Standard Terminal Arrival Routes (STARs) over Menorca are coming from the RIXOT and MORSS <S> waypoints as shown in the following Jeppesen chart: <S> It looks like your plane was coming in from RIXOT (where it should have been at FL230 or below). <S> The only published holding is over the Capdepera VOR (CDP), but your plane was circling before reaching that point, meaning it was either instructed to circle there by ATC or requested to do so themselves. <S> The likely reason for circling (as discussed in the comments) is to bleed off some altitude, which raises the question why the aircraft was too high in the first place. <S> This could have been due to traffic, i.e. ATC does not allow an early descent due to conflicts with other planes, or because the crew expected to fly the full procedure. <S> In the chart above, you can see that the RIXOT 2M arrival goes all the way to the Mallorca VOR (MJV), which is south of the airport. <S> This would typically be flown when approaching on runway 06L/06R. <S> If the wind direction just recently changed, the airport would switch to landing on 24L/24R instead. <S> While there are published approaches to these runways from MJV , it is much more common to approach via CDP or get radar vectors to final approach. <S> If the crew expected an approach to 06L/06R, they would suddenly be at a much too high altitude. <S> The best way to reduce the altitude now, is to circle before accepting radar vectors on to final. <A> Its actually called an 'orbit' as in "left hand orbit for traffic". <S> This is if you're far out enough.. too near <S> and you'll be going around.
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Another reason for the 'spin' is to give time for the aircraft in front to either take-off (departure) or get off (landing) the runway.
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Why don't short runways use (downhill) ramps for takeoff? This is a followup on question: Why don't short runways use ramps for takeoff? There are multiple answers to that question that answer why an uphill ramp at the end of the runway does not make sense. But what about going the other way? I would imagine a downhill ramp at the beginning of the takeoff roll could give the aircraft more energy on takeoff (converting potential energy to speed), and that could indeed improve takeoff performance. This would be useful at places where extending the runway is not possible. How the aircraft would get up there is another question, but worst case scenario it could always back-taxi on the runway before turning around and taking off. Is this practice ever used? If not, what are the reasons? <Q> it could always back-taxi on the runway before turning around and taking off. <S> So ... that would limit the steepness of the slope significantly, and thus the potential benefit. <S> Most other aspects are already covered by Bjelleklang's answer: Landing aircraft would either have to clear the obstacle before being able to touch down, or they'd fall over the edge if they don't brake in time (rather than, as these days, get stuck in the grass behind the runway end) <A> Many of the arguments against using a ramp from the other question is valid for this as well. <S> If the ramp is above ground, aircraft taxiing for take-off would also have to overcome the upward slope, meaning that more fuel is needed for taxi. <S> You'd also need a ramp at the opposite end; the runway would basically look like a stretched out 'U'. <S> A possibly unintended consequence of this is that the aircraft would at some point reach the point where the runway begins to slope upwards again, resulting in the aircraft either having to abort or use additional power to get airborne. <S> To avoid such a case you would have to stretch out the runway <S> so this isn't an issue, and if the goal is to reduce the runway length the current design is more efficient. <S> Alternatively you could create a separate runway for each direction, but then you'd be faced with potential crashes whenever a pilot tries to land in the wrong direction. <S> This would also result in difficulties for airports located in built-up areas where there simply isn't available room for additional airport infrastructure. <S> If you keep the ramps on ground level and the runway center below you'd also need working drainage pumps whenever it rains or snows. <S> If not, the runway would quickly be reduced to a pond with very wide roads leading into it. <S> Depending on where in the world you are, water might seep in from the surrounding terrain as well, making reliable drainage even more important. <S> This is generally avoided by building runways with a slightly raised centerline so that water runs out to the sides so that you can use "passive" drainage systems such as pipes, ditches, pools etc where no machinery is required. <S> There are some airports such as Lukla where one end of the runway is substantially higher than the other, but due to surrounding terrain it is only possible to land and take-off from opposite directions. <S> Landing aircraft can use the upward slope for an additional braking effect, while aircraft taking off will get a speed boost from the downward slope. <A> Here's an example of a sloped up runway, midway down looking southwest. <S> The end is definitely sloped up. <S> We're typically off the ground well before that tho, the runway is 3110 feet long. <S> Taking off from that end towards the northeast, going downhill to start will help with the takeoff acceleration. <A> A "relaxed definition" of this concept is in use today on aircraft carriers. <S> Notice <S> the ramp in question is essentially a mechanical device to increase the total thrust force on the aircraft, which increases acceleration. <S> This is also exactly the same as pitching an airborne aircraft down, or launching a model aircraft by throwing it. <S> RATO can help too. <S> The energy input for higher rate of acceleration: <S> F = ma total = <S> ma thrust + ma gravity, steam catapult, thrown with hand etc. <S> The result is higher air speed for a given distance as compared with no "ramp". <S> The practicality of building such a device would be questioned. <S> Generally, it's landing distance that is limiting. <S> But many soaring birds take it one step further, they simply jump off a cliff (disclaimer: attempting without certified wings may be hazardous to your health).
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Any ramp means a height difference between the ramp itself and the runway, for it to actually make a big difference I suspect a fairly long slope from the ramp to the runway is needed, and this will obstruct the runway for landing aircraft.
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How and why does the ATR-72 sometimes use reverse thrust to push back from its parking position? Travelling with Czech Airlines via Prague in an ATR-72 I have already experienced multiple times that instead of pushback service the planes simply used their reverse thrust to leave their parking position, even doing a 90° degree turn while rolling backwards. Personal experience as well as a Google search show that this is rather uncommon. What makes the ATR-72 special to be able to perform such kind of manoeuvre? <Q> This is particularly true for turbofan engines mounted under the wings. <S> Turboprop engines tend to be mounted on high wings (such as on the ATR-72), and they tend to serve smaller airports where an airline may not have tugs available for pushback. <S> Regional and private jets, which often have fuselage-mounted engines, also tend to serve such smaller airports. <S> These planes were designed with the engines mounted higher specifically to reduce the risk of ingesting FOD, thus allowing them to safely power back when needed. <S> Note that powering back still burns a lot of fuel, and even with high engines the FOD risk isn't zero, so when operating at larger airports that do have tugs available, airlines will generally use them. <A> Pushback via reverse thrust is problematic for turbofans, as they kick up lots of debris, which could be ingested into the engine or hit something laying around. <S> Presumably the ATR as a turboprop doesn't create as much wind, and with a turboprop the reverse thrust is blowing from the front of the engine, so there's no chance the debris will reach the intake. <S> Most modern commercial airliners are prohibited to power back. <S> Ground operations in aircraft fitted with high-bypass engines are usually restricted to idle and low-idle operations (enough to make the craft start moving, after which momentum enables further movement with idle only). <S> Aircraft capable of power back are predominantly thus turboprops, several operators of these allow their crews to operate accordingly. <S> Is a powerback allowed by airlines as a safe maneuver? <S> Related: Is it possible to use thrust reversers to taxi backwards? <A> Just about any turboprop or piston engine airplane with reversing propellers can do it, as the airplane doesn't care whether BETA reverse is being used on the ramp or a taxiway or a runway. <S> You normally use DISCING (flat prop blades to make zero thrust) when taxiing when you want slow down or when you are stopped. <S> To go backwards, you just move the powers back out of DISCING a touch. <S> You kick up FOD on the ramp, which a TP can draw in almost as easily as a jet. <S> Gate areas are a garden of zipper tags from luggage and will do major damage to a TP if they get past the particle separator in the nacelle, which is more likely on the ground without a high velocity air stream to let the separator do its job. <S> The airline has probably made the business decision to take the risk of FOD damage to avoid having to use tugs for pushback. <S> When you want to stop backing up, you should not use brakes, lest you tip back. <S> You use forward power. <A> You can do powerbacks with basically any commercial turboprop, not really uncommon at all. <S> We did it regularly with our F50s <S> and we still performing it nowadays sometimes (even though quite rarely) with our DH8Ds when there is no towbar available. <S> Never heard about the problem of ingesting FOD, we never experienced this. <S> The only thing you have to be careful about is NOT to use the normal brakes for stopping or you will end up with a tailstrike. <S> Instead one has to go back to DISC.
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As other answers note, for most aircraft, the risk of the engines ingesting FOD while powering back is too high.
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What is the most 'environmentally friendly' way to learn to fly? As this question indicates, I've been thinking recently about the environmental impact of flying (since when automated cars are the only means of ground transport, aviation will be responsible for most greenhouse emissions). So, as an amateur, novice pilot, I would like to know which is more environmentally friendly, learning in a glider or learning in a single engine prop (Piper Tomahawk, Cessna and the like)? At first it seems obvious, the glider doesn't have an engine while the latter does. But if we assume the launch method of the glider is tow rope, this would be powered by a single engine prop, using more fuel than it would if it wasn't towing, plus the climb is the most fuel-expensive part of the flight anyway, leading me to think there might not actually be that much difference. Clarification on this issue would be greatly appreciated. <Q> Here are some options for flying in an environmentally friendly way: Use an electric trainer: Since last year the all electric trainer aircraft Pipistrel Alpha Electro has FAA certification . <S> Assuming the batteries are charged with renewable energy, this would mean no greenhouse gas emissions at all (excluding manufacturing). <S> It will probably still take some time <S> until larger all electric aircraft with higher ranges are available, but Airbus has already started research . <S> Use a glider with a winch: <S> Assuming the winch is powered by renewable energy, this would also result in no greenhouse gas emissions. <S> While winch launches are less common in the US , this might change in the future. <S> If you use a glider with tow plane, it will depend on how long you can fly with the glider. <S> Assuming good thermals you could stay in the air for quite a while, which would easily be better for the environment than a single engine prop plane. <S> But for training (where you would presumably want many takeoffs and landings), I agree with you that the tow plane would now use more fuel because it has to drag the glider along. <A> <A> Learnt to fly a solar powered hot air balloon <S> The UK's International Balloon Fiesta in Bristol is a celebration of all things hot air ballooning, but this year it's taken a big stride into the future. <S> August 6th saw the maiden public flight of the world's first hybrid hot air balloon, which flies by heating regular air from the sun alone. <S> Source <S> In theory, fly forever with no fuel costs. <A> The answers by Bianfable are pretty good. <S> I'd add one more option: <S> Use a powered glider. <S> There are gliders with a small engine, electric or otherwise. <S> Some look like propeller planes with glider wings, some have a much smaller engine and a retractable or foldable propeller. <S> My favourite example is this one. <S> These can take off under their own power, which is less energy-intense than even a winch start, but they can then still stay aloft without using the engine, provided the weather is suitable. <S> I think they're probably also good for beginners as it's much easier to get out of situations where an unexpected change of wind direction prevents you from making it back to base... <A> The answer is pretty simple. <S> A foot-launched glider (paraglider, hang-glider or ultralight) launched from a hill has zero emissions from the flight itself. <S> It doesn't get more environmentally friendly than that! <A> "which is more environmentally friendly, learning in a glider or learning in a single engine prop (Piper Tomahawk, Cessna and the like)?" <S> I think you can combine the two. <S> Glider for learning basic stuff in the airport environment and nearby (launching however the local method is, in my area that seems to be tow plane), and then small engine (100 HP) for the longer trips where there is more navigation skills and radio work/electronics (ADS-B Out) required for the controlled airspace/tower interaction. <A> The primary source of pollution from single engine propeller airplanes is the avgas used as fuel. <S> Avgas is typically gasoline with tetraethyllead <S> (TEL), a lead-containing additive used to reduce engine knock. <S> The most environmentally friendly way to learn to fly, short of using a fully electric airplane, is to use an engine which supports unleaded automotive gasoline, mogas, natively. <S> For such engines, you will usually need to use gasoline without any ethanol, as it will damage an engine not designed for it. <A> Depends on your definition of "fly". <S> If you simply mean flying a plane-like object around in they sky, the fuel spent on a glider tow might only be 5-10 minutes worth, and on a good day you can stay up practicing your technique for hours. <S> Your up-time-to-fuel ratio can pretty low, though I can't say the environmental impact of the manufacture of the two planes involved. <A> A significant part of the environmental cost of the airplane is building it in the first place . <S> That becomes relevant in a crash. <S> A gentle crash saves the airframe, a rough crash makes you buy another airplane. <S> Therefore, glider training is an environmental win, because it makes you better trained to gracefully recover from an engine-out situation, giving you a good eye for less destructive off-airport landing fields, and better at managing energy to get to such a spot. <A> By using flight simulator where possible. <S> A very high end computer with multiple CPUs and several video cards maybe would use 1500 W of power under full load (this is how much the most powerful PC power supplies are rated). <S> Maybe multiple large monitors would use few hundreds more. <S> This is next to nothing in comparison to 75000 W required for launching even a glider. <S> Of course, simulators can only replace part of the training but especially in cases when somebody has enough hours but for some reason not enough skills to pass the test, this could probably work. <S> This answer assumes certified simulators like this one for CESSNA 172, certified . <S> I mean, not a PC running a star wars computer game with just mouse and keyboard attached.
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Running the simulator is definitely more environment friendly than running even a small aircraft. By using as much simulator time as possible.
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What is it exactly about flying a Flyboard across the English channel that made Zapata's thighs burn? CNN's French inventor makes 'beautiful' flight across Channel on hoverboard reports that: "French inventor Franky Zapata has successfully crossed the Channel on a jet-powered hoverboard for the first time, after a failed attempt last month. Later in the article it says: The inventor said that he tried to "take pleasure in not thinking about the pain," even though "his thighs were burning." What is it exactly about flying a Flyboard across the English channel that made Zapata's thighs burn? 20 minutes of standing shouldn't be that stressing, what is it exactly about flying this board that requires so much muscle activity that it would be painful? <Q> He's using the angle of his legs to control the attitude of the platform (and as a result, the direction he's flying in). <S> So he can't take a relaxed pose, he's standing with his knees slightly bent the whole time. <A> This is what he said after the 1st attempt <S> "When you fly with your body, even your hands affect the direction you want to go in. <S> You feel the turbulence and the air through your fingers," Zapata told CNN. <S> "It's like becoming a bird. <S> But it's also very hard. <S> I have to fight against the wind with my legs <S> so there's pain too. <S> It's not as peaceful as it looks." <S> https://www.cnn.com/travel/article/franky-zapata-flyboard-channel-gbr-intl/index.html <S> I imagine it's like a long ski run, where you're compressed down with every bump & turn. <A> There is another bit of information worth mentioning in the CNN link in CrossRoads' answer <S> The flyboard looks like a chunky skateboard and is powered by five small engines. <S> It is fueled by kerosene, which Zapata carried 104 pounds [47 kg] of in his backpack . <S> I believe that carrying a 50 kg backpack and balancing on a jet powered air skateboard combined delivers some serious strain on the pilot's legs. <A> There is no ground; he is responsible for balance during the whole high-speed flight. <S> Imagine putting a large ball on a freight car of a speeding train and standing on top of it.
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Do a mile long run at high speeds and you really feel it in the thighs.
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Why do private jets such as Gulfstream fly higher than other civilian jets? I heard in a TV show that private jets such as Gulfstream can fly at about 50,000 ft, higher than other civil jets. Is it an aerodynamic reason (lighter aircraft to be sustained in a less dense air) or does it depend on the fact that a smaller fuselage is more resistant to lower outside pressure at a higher altitude? I think that – if possible – flying higher, in order to fly faster and with lower fuel flow, is always better. Am I correct? <Q> There are several reasons and none of them really have to do with a private jet being more aerodynamic than a commercial jet. <S> Commercial jets also carry more fuel which needs to be burned off to lighten the plane to go higher. <S> It’s easier to pressurize smaller cabins than larger ones <S> (this is a significant factor for commercial jets). <S> Flying higher is usually better for avoiding weather that can even affect commercial airliners in the 30ks. <S> There is much less traffic up above 40k and it allows the private jets to fly more direct routes at a faster speed and more safely as well. <A> There are three main factors that let corporate jets with 50000 <S> + ceilings get up that high. <S> First and most importantly, they have very large wings. <S> Partly this is because of the need for fuel volume for range requirements, but it's mainly that you need the extra wing area to be able to fly that high with a reasonably efficient indicated airspeed at 50000 ft <S> (500 kt TAS is <S> only 250 kt indicated at FL500) at reasonable weights. <S> Next they use turbofan engines like the BR700 with lower bypass ratios than airliners because a lower bypass ratio is somewhat more efficient in very thin air. <S> Lastly, they operate with higher cabin pressure differentials, 9-10 psi rather than around 8 psi to get an 8000 ft cabin at 50+ thousand feet. <S> The structure has be a bit heavier to handle the pressure differential, but not that much because they are designed for way less cycles than an airliner, 3-500 cycles per year vs 2-3000 cycles for a regional airliner. <S> If you took a corporate jet as-is and put in a regular interior and started running it 4 or 5 flights per day flogging it like a mule, it'd start breaking down in short order. <S> Conversely, corporate aircraft created as conversions of regional airliners designed for 3000 cycles per year will run pretty much forever in the light duty corporate role. <A> I think the other important factor that the others haven't addressed is Mach number. <S> The speed of sound is doesn't change much with altitude (it actually drops slightly due to reducing temperature) and if a plane gets too close to it, shockwaves start to form in areas where the airflow is accelerated (such as on the top of the wing) causing a lot of excess drag. <S> By flying higher, a plane gets a higher ground speed and true air speed for the same indicated air speed (IAS). <S> However the limit is when the true air speed (TAS) results in a Mach number that starts to cause shock waves. <S> To go higher, a plane has to reduce its indicated air speed to maintain the same Mach number. <S> Therefore the limiting height is when IAS approaches stall speed at the same time as the Mach number limit is reached. <S> (see Coffin Corner ) <S> Now private jets are usually designed to use smaller runways than big airliners, so they have a slower stall speed (due to relatively large wings for their weight). <S> Their maximum Mach number is similar (an easy way to tell is that the angle of wing sweep is similar) <S> so the height at which minimum IAS = maximum TAS is higher. <S> EDIT: <S> True air speed (TAS) is the actual speed of the air, similar to the aircraft's ground speed (after allowing for wind). <S> Indicated air speed (IAS) is the effective aerodynamic air speed, or "how much force you'd feel if you stuck your hand out the window". <S> IAS falls relative to TAS as the air gets thinner.
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Private jets have better power to weight ratio than commercial jets so it is easier to ascend to greater heights.
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What accidents have had crew accustomization to warnings among their causes? A non-answer on this question claimed that: the idea that maneuvering with the stall warning activated will somehow damage us, causing us to ignore its warning when the chips are down and AOA is up, is just silly which sounds wrong to me, as I vaguely remember reading about crews becoming accustomed to frequent warnings, spurious or real, and disregarding them when they became critical. Which, if any, aviation accidents or incidents have had among their direct or contributing causes a crew that ignored a warning due to being used to it being spurious or unimportant? I am looking for substantiated answers only, remember that this site is not a venue to speculate on aviation accidents. <Q> A notable accident was the Helios Airways Flight 522 crash, where the pressurization system was turned off and the pilots ignored the warning horn because they thought it was the takeoff config warning. <S> From the Wikipedia page: As the aircraft climbed, the pressure inside the cabin gradually decreased. <S> As it passed through an altitude of 12,040 feet (3,670 m), the cabin altitude warning horn sounded. <S> The warning should have prompted the crew to stop climbing, but it was misidentified by the crew as a take-off configuration warning, which signals that the aircraft is not ready for take-off, and can only sound on the ground. <S> The official accident report explains the source of the confusion in more detail (emphasis mine): <S> The Board examined the flight crew’s actions to disengage the autopilot and auto-throttle, and to retard the throttles upon onset of the warning horn. <S> Given that the expected reaction to a cabin altitude warning horn would have been to stop the climb (there was no evidence to this effect), the Board considered such actions to signify that the flight crew reacted to the warning horn as if it had been a Takeoff Configuration Warning <S> (the two failures use the same warning horn sound) . <S> [...] <S> The warning horn was designed to signal two distinctly different situations. <S> The Board considered the role of experience in interpreting and reacting to the warning horn. <S> In the course of his career, a pilot is generally likely to only hear the warning horn when it is associated with a takeoff and a takeoff configuration problem. <S> [...] <S> Most pilots are not very likely to experience a cabin pressurization problem and the associated warning horn at any time during their line flying. <S> Conclusion: <S> Never use the same warning for multiple situations, if the pilots will only get used to one of them, otherwiese they will ignore the warning for the other situtations! <A> The aircraft descended below minimums on approach and impacted terrain, in this case a water body, short of the runway. <S> Among the contributing factors, the BEA listed "De-activation of EGPWS audible warnings due to nuisance alerts" . <S> The following is taken from the translation of the report provided by AVHerald, so I cannot confirm its accuracy; the original report can be found here if any French speakers want to double check. <S> Emphasis mine : <S> The BEA reported the EGPWS was found fully and properly working, however, even on the previous flights the EGPWS had been sounding premature terrain warnings obviously related to an incorrect altitude reported by the Air Data Computer. <S> A difference of about 700 feet between altitudes reported by ADC and radio altimeter was recorded. <S> While the GPS data appeared correct and agree with the radio altimeter, the ADC data transmitted via ARINC 204 bus appeared incorrect. <S> The BEA annotated: "The regular presence of untimely (premature) Alerts from the EGPWS may have encouraged the crew to ignore these alerts, probably going so far as to disable them." <S> Also: <S> The EGPWS nuisance alerts were confirmed to have been present for a number of flights, however, had never been reported to the company . <S> Therefore no action to identify and correct the malfunction were undertaken. <S> A reliable Terrain Warning would certainly have made the crew aware of the vertical profile and correct their flight path to climb. <A> “The crew seemed to have disregarded and talked over all the caution annunciations. <S> The crew had experienced those type of cautions on previous flights and perceived them as nuisance alerts with no resultant consequence. ” <A> On May 9th, 2012, a Sukhoi Sukhoi Superjet 100-95 on a demonstration flight in Indonesia crashed into a mountain while in clouds. <S> The Terrain Awareness and Warning System (TAWS) gave warnings, and the crew could have still avoided the terrain up to 24 seconds after the first warning, but they ignored and then inhibited the warnings, commenting that it must be a database issue. <S> The crew had believed in their brief that there was no high terrain nearby and then became disoriented. <S> On April 10th, 2010, a Polish Air Force Tu-154 crashed during landing. <S> As they were landing at a military field, it was not in the TAWS database. <S> This meant that the system did not recognize that they were trying to land and started giving alerts. <S> Rather than using proper procedure and engaging the "terrain inhibit" function, the crew changed the captain's altimeter setting, telling the system it was higher than it actually was. <S> They later ignored multiple TAWS warnings and did not follow proper go-around procedures until it was too late.
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Just last year the crash of an Air Niugini flight was directly related to pilots ignoring warnings The captain and first officer ignored a total of 17 audible warnings that they were flying too low. A Valan Air Cargo An-26 crashed in Cote de Ivoire on the 14th of October, 2017 , while performing a charter flight.
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How much does it cost extra to fly with one additional passenger? How much does it cost to fly an airplane (like a Boeing or Airbus) when there's one extra passenger there, at an average speed of 475–500 knots (880–926 km/h; 547–575 mph)? That is, about 100kg extra, including clothes and luggage. <Q> I am basing the following calculations on the excellent answer by Peter Kämpf to this question: How much of an improvement would a 1% weight decrease on an airplane be to the industry? . <S> We can approximate the fuel usage with the Breguet equation $$ m_\mathrm{TO} = <S> m_\mathrm{Landing} <S> \cdot \exp <S> \left( \frac{R \cdot g <S> \cdot b_f}{v \cdot L/D} \right) , $$ <S> where: <S> $m_\mathrm{TO}$ is the total mass at takeoff <S> $m_\mathrm{Landing}$ is the total mass at landing <S> $R$ <S> is the distance flown $b_f = 0.000018 \mathrm{kg} / <S> \mathrm{Ns}$ <S> is the fuel <S> burn <S> $v=250 <S> \mathrm{m}/\mathrm{s}$ <S> (about 900 km/h) is the velocity <S> $L <S> /D=18$ is the lift to drag ratio <S> Assuming a fully loaded A320 ( OEW $ = 42.6 \, <S> \mathrm{t}$ with <S> $ 19.9 \, <S> \mathrm{t}$ <S> payload and $3 \, <S> \mathrm{t}$ <S> reserve fuel <S> $\Rightarrow m_\mathrm{Landing} = <S> 65.5 \, \mathrm{t}$ ) <S> , we can do the calculation for the fuel ( $m_\mathrm{TO} - m_\mathrm{Landing}$ ) with and without an extra 100 kg and compare for different distances <S> $R$ : <S> Note: this equation become increasingly inaccurate towards small distances because the takeoff, which uses more fuel, is not taken into account here. <S> Using the given speed, this can be converted to different flight times: And by multiplying with the current jet fuel price of 616 US Dollars per metric ton, we get the additional cost of a 100 kg passenger per flight time: <A> This depends - among others - on the size and speed of the airplane, as well as the total trip duration. <S> Yielding some 40 to 50 extra kgs of fuel for a trip of 10 hours, that is in accordance with the calculation done by @PerlDuck . <S> This answer over-simplifies stuff a lot, of course, but it's a bit easier for back-of-the-envelope calculations. <A> I just stumbled across this FAA document that provides details on the incremental fuel burn due to additional weight. <S> As noted above, incremental fuel burn related to an increase in aircraft weight was calculated for selected aircraft types and selected stage lengths. <S> The aircraft types selected present a sampling of the most common aircraft in use within each economic values category. <S> Mission lengths were based on typical mission lengths for each aircraft type, as observed in FY 2013 ATSBM data. <S> For most aircraft models, multiple mission lengths were analyzed. <S> A weight penalty of 500 pounds was used for most larger narrow-body and wide-body jet aircraft, while a weight penalty of 200 pounds was used for most smaller narrow-body, regional jet and turboprop aircraft. <S> In a few cases, these weight penalties did not produce reliable results so a different weight penalty was used. <S> Table 6-1 presents the results for all large commercial aircraft (including both passenger and all-cargo aircraft). <S> The table presents the aircraft type, passenger or cargo configuration, the stage lengths analyzed, the weight penalty and the incremental fuel burn in pounds per flight. <S> In addition, the incremental fuel burn per pound of weight added is also calculated in U.S. gallons per flight. <S> The incremental fuel burn in gallons per hour per pound of weight added is calculated by dividing the incremental fuel burn per flight per pound of weight added by the flight time. <S> Also shown is the total flight time for the specific mission analyzed.
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As a rule of thumb (based on fuel consumption data of a major airline), I've been working with 4 to 5% per hour of flight time (for jets).
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Does a 4 bladed prop have almost twice the thrust of a 2 bladed prop? Does a 4 bladed prop have almost twice the thrust of a 2 bladed prop? As a general rule, I'm told GA planes generate 4 lbs of thrust per horsepower. (Source: Zenith School of Airplane Design, Flying on your own Wings) So if you use a 4 bladed prop, does it generate anything close to 8 lbs of thrust per hp? In other words, say for an ultralight, where you're only flying 60 mph, and prop drag isn't an issue, can you use an engine with half the horsepower, or some other fraction thereof? Will that shorten my takeoff roll? Conceptually, takeoff roll is just the distance to accelerate from zero to my minimum takeoff speed. Since F=ma, then a=F/m, so if I want to accelerate twice as fast, I need twice the force, or thrust ( probably more than twice the thrust, to overcome rolling drag, etc.) Is this correct, at least conceptually? Just to summarize: In the GA world, I'm told as a general rule, props develop 4 lbs of thrust per hp. So, for 160 hp, I get 640 lbs of thrust, or is this not correct? In the STOL world, with 8' props, I'm told, they get 8 lbs of thrust per hp. So, for 160 hp, I get 1,280 lbs of thrust. Well, I'd rather have a 160 HP engine and prop that produces 1,280 lbs of thrust than 640lbs of thrust. So... if I take my 8 ft 2 bladed prop, chop it in half to get a 4' 4 bladed prop ( same overall "wing area"), I'll still get 1,280 lbs of thrust ( less a few % for inefficiency), instead of 640 lbs of thrust. Is this correct? If not, what value of thrust should I expect, roughly? Or are these rough estimates incorrect? <Q> At the same size and rpm, a 4-bladed prop will require twice the horsepower to drive, approximately. <S> Due to blade interference, it will always generate less than twice the thrust. <S> So lbs thrust per hp will generally slightly decrease, as long as the propeller is in its optimal tip airspeed band. <S> If the propeller was overly fast initially, slowing it down and going with more blades to compensate can result in small thrust/hp gains (+X percent, not X times). <S> This will generally apply to aircraft originally designed with much less power and later modified. <S> There are a few legitimate cases where design size is less than the aerodynamically optimal size. <S> One is clearance to the ground or between the props (in quads). <S> Another is turbofans: the drag of the nacelle overcomes the benefits of lower disc loading. <S> Even for airliners there's a push for wider fans, but the "open fan" idea (basically a turboprop) was scaled down to geared fans and the Ultrafan for noise reasons. <S> In helicopters, at some point, the blades become so long and so far apart that adding more blades beats the weight and bulk of longer blades. <S> The more blades, the worse, so going up to 4 is not such a big deal as doubling it again to 8. <S> For small aircraft with low power/weight ratios, where 2 blades fit easily, that's generally the best configuration. <A> This is not conceptually correct, for the following reason: Doubling the number of blades on your prop <S> will not double the thrust unless your engine is powerful enough to drive the prop at the same speed as the 2-bladed case . <S> For small planes with fixed-pitch props, a prop and engine combination is chosen for a given aircraft so that when the engine is running at its maximum RPM setting and full throttle, the prop is absorbing the full power output of the engine. <S> If one then adds some more blades to the prop, the engine will be loaded down too heavily for it to run at its maximum power setting and the power output of the engine will go down and so will the thrust generated by the prop. <A> There is no free lunch here. <S> Adding blades does not somehow cause the engine to produce more power. <S> It just means that each blade gets a smaller fraction of that power and thus produces less thrust, and total thrust would remain constant. <S> Actually, due to interference, total thrust actually goes down a bit when you add blades. <S> The main reason to accept that inefficiency is that any fewer couldn't absorb all the power coming from the engine, typically due to ground clearance or tip speed, so you don't really have a choice. <A> As I read this there are really two questions being asked here. <S> 1) Does a 4 bladed prop have almost twice the thrust of a 2 bladed prop? <S> Basically <S> yes, if the propeller rotation rate, blade length, inflow velocity, and blade pitch all remain the same. <S> There will be some losses for interference between blades, but those can be neglected to first order. <S> Going from 2 blades to 4 will also, those same things being equal, double the required torque, which will also double the shaft power required to spin the prop at that same RPM. <S> If you double your number of propeller blades AND double the size of the engine, you will nearly double your thrust. <S> This should significantly reduce the takeoff roll. <S> 2) <S> Can I add blades to my propeller to compensate or allow for a reduction in engine power? <S> The answer to this is a more nuanced <S> no. <S> At the most basic level, the useful flow power of a propeller $P_{flow} = <S> TV_\infty = <S> P_\mathrm{shaft}\eta_{p}$ <S> Restated, <S> $T = \frac{P_\mathrm{shaft}\eta_{p}}{V_\infty}$ <S> This shows that, for a given amount of engine power at some airspeed, the useful thrust you can get is driven by your propeller efficiency at that flight condition. <S> In general, a well-designed 4-bladed propeller is about as efficient as a well-designed 2-bladed propeller. <S> More blades is desirable when you need more thrust in a small diameter, less blades gives you a slight efficiency benefit because of the reduced losses from blade-blade interactions. <S> But one won't give 2x the efficiency of the other. <S> Prop efficiency varies widely, depending on the operating condition and design details. <S> The converse may also be true. <S> QPROP is a good, open-source tool for playing around with the effect of changing the number of propellers blades, operating condition, and other design details. <S> The theory document also lays out the fundamental relationships clearly.
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So a specific 4-bladed propeller might very well give more thrust than a 2-bladed propeller on the same engine, depending on how well-matched it is to the engine and the design details of the propeller.
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What are the abandoned technologies in aviation industry And technologies has come to end of to their life cycle Especially technologies that developed for aviation. This could be a manufacturing technology or an engine rather than avionics or sensors. <Q> The biggest one that comes to mind for me is Cathode Ray Tube technology for cockpit displays. <S> There are a number of companies offering LCD units to upgrade CRT units under STC and this is happening across the airline industry. <S> Mechanically, not that much. <S> Light aircraft are still built today with magnetos that use points and condensers like tractors from the 40s. <S> They are simple and work. <S> The business is very conservative, a vital self-preservation characteristic in such a life-or-death environment, and things that are simple, work, and are easy to fix and easy to diagnose, and let you know when they are degrading, are hard to replace. <A> Venturi tubes to drive vacuum gyros. <S> One could say the vacuum drive as such is abandoned, but the current C172S still has it. <S> Corrugated skin. <S> Photo by Stefan Krause, from Wikimedia <S> Of course, we need to exclude vintage and replica aircraft: one could probably find some flying with any technology. <A> I was thinking more navigation related - ADF, NDB, LORAN, VOR getting there. <S> Incandescent light bulbs going away, being replaced by LEDs.
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Rockwell Collins (called something else now) has ceased production of CRT displays and users of Proline CRT Primary Flight Displays, Secondary Flight Displays and EICAS systems are in a scramble to replace the CRTs when they wear out. Another one could be navaids like Non Directional Beacons that are starting to go the way of the A/N Range and the related receivers, and eventually other analog navigation equipment. Vacuum pumps & vacuum driven gyros going away too.
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What determines a plane's range? When a planes maximum range is specified, is fuel [capacity] the only constraint or what else is taken into account? Would it always or ever be the case that a greater fuel capacity will increase range? Interesting long-flight story of 64 days in the air, but it doesn't get too technical: https://jalopnik.com/how-a-slot-machine-mechanic-flew-150-000-miles-over-64-5971433 <Q> As also stated in this answer: <S> Range is a function of MTOW and empty weight, according to the Breguet Equation for a jet: $$R=\frac{V}{c_T} \cdot \frac{L}{D} \cdot <S> ln\frac{W_i}{W_i-W_f}$$ with <S> ${c_T}$ = specific fuel consumption, $W_i$ = initial weight, <S> $W_f$ = fuel weight, $L$ = lift, $D$ = drag. <S> What increases range if other factors remain constant: <S> Higher speed <S> $V$ Lower specific fuel consumption. <S> Higher lift/drag ratio. <S> The weight ratio can be because of fuel weight used during the flight, but of course chucking ballast overboard helps as well. <A> Somewhere in the fine print in the airplane's specs will be the Mach# and altitude that the maximum range is based on. <S> Most airplanes can't be flown with full fuel AND a full cabin without being overweight, so you have to horse trade. <S> A corporate jet with fuel for 5 hours endurance may only be able to carry 3/4 of the passenger complement to get max range, or conversely be limited to 4 hours if the cabin is full. <S> Such a jet may have an option for a long range fuel tank add-on, increasing endurance to 6 or 7 hours, and if that tank is also full, the passenger load may be cut down to just a few passengers. <A> Optimizing each of these variables will lead to the most efficient results. <S> Generally speaking greater fuel capacity will increase range, which is why auxiliary tanks are sometimes used. <S> There are a great many design factors that influence each of these three variables, but that is beyond the scope of the question. <S> Additionally, environmental factors such as wind will affect actual performance. <A> Would it always or ever be the case that a greater fuel capacity will increase range? <S> The problem for a flight without external assistance is you have to carry the fuel (and any other consumables but fuel is by far the most significant consumable). <S> You can add more tanks (and ferry pilots do), but ultimately you reach a point where your takeoff weight is at the aircrafts limits. <S> You could make the whole aircraft bigger, but then it needs more fuel, so you haven't really gained much. <S> The 64 day flight you linked was not unassisted. <S> They received fuel and supplies from a truck on the ground during the flight. <S> It also sounds like it was rather unsafe, with the article reporting that one of the pilots dozed off at the controls due to inadequate sleeping arrangements.
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The airplane's published range will be based on distance that can be flown in still air (excluding winds in other words) with full fuel, departing at max gross weight, when flown at some optimized cruise speed or mach#, at a specified flight level, with normal IFR fuel reserves (fuel to go from A to B, fly an approach, do a missed approach, proceed to alternate, fly an approach there, and land, with, for a jet, 30 minutes remaining after all that), in standard ISA atmospheric conditions. Higher TakeOff/Landing weight ratio. Speed, fuel capacity, and burn rate are the only three factors that determine range.
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Under which condition is a forward CG most critical? This question is from CFI written exam. (6824) “Under which condition is a forward CG most critical?” The answer is “Forward CG is most critical during landing. If it is too far forward, the elevators may not have enough power to get the tail down for a proper approach and flare.” I don’t know why if CG is too forward, the elevators may be less effective. In my mind, if something has longer arm, that one becomes more effective like teeter-totter. That would be great if someone could help me! <Q> One intuitive way to think about this is that the pitching motion of a rigid body occurs at its CG. <S> At forward CG, the elevator, which pitches the aircraft up, indeed has a longer moment arm. <S> On the other hand, however, the wing lift vector, which tends to pitch the aircraft down, also has a longer moment arm. <S> The proportion of change of the wing lift moment arm is quite a bit more than that of the elevator, for the same change in CG. <S> In the end, the wing lift, which is also quite a bit larger, wins this race. <S> Hence, forward CG is more critical for maneuvering. <S> Strange that it says landing, which I assume is the flare portion, is the most critical condition. <S> I would've thought takeoff rotation would be equally bad, especially if you have a mistrim. <A> The elevator is producing downward lift. <S> It is you pushing down at one end of the teeter totter. <S> Your kid is sitting on the other end of the teeter totter, and the teeter totter's center of gravity is somewhere between the pivot and your kid. <S> If you stop pushing down, he drops. <S> If your kid moves farther out, say by leaning back, you may not have the strength to keep pushing down and down he goes. <S> Having the CG too far forward is like your kid moved farther out than you can handle. <S> This is a problem when the horizontal tail is working at the limit of its strength you might say, at low speed and with the elevator at maximum deflection, without any slipstream blowing on it. <A> By too far do you mean outside the fwd limit? <S> If yes then is a question of the elevator having insufficient 'arm' to counter the increased 'arm' of the (too fwd)CG. <S> Airlines usually add a bit onto the manufacturer's limit as the manufacturer limits are based on static conditions (no movement of load) but airlines usually have people and equipment(galley carts) going thru the cabin in flight so the airlines will add some buffer.
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If the CG is within limits or even 'on' the fwd limit then the airplane should have no problems with elevator effectiveness. When the CG is too far forward, it can't push down hard enough to hold the nose up at the normal landing speed, and has to go faster to do so.
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Are any jet engines used in combat aircraft water cooled? Are any jet engines used in combat aircraft water cooled? If they are not, and instead are air cooled, how can the engine ensure consistent cooling? Wouldn't the airflow passing through whatever radiator implementation it has be greatly affected by the airspeed? Consider low subsonic numbers with heavy maneuvering in a dogfight, vs. mach 2 sustained flight? While I can imagine that variable air inlet for the radiator would change the airflow, I really have no idea how this would work. I'm also aware that certain rocket engines, e.g. the F-1 allow the fuel itself to circle around the thrust chamber to cool it. Perhaps a similar system is used in jet engines. <Q> Jet engines are cooled and temperature managed by the mass air flow itself which is used to surround and limit the boundaries of the flame, keeping it away from the burner can walls, and dilute the heat of the flame as it passes to the turbine (only a minority of the mass airflow's oxygen is actually burned - which is why afterburners work; there's lots of leftover oxygen to work with). <S> If you're talking about using a closed liquid cooling system with heat exchangers taking heat from the burner can and turbine somehow, well, I've never heard of a water jacketed burner can, and how you could use liquid in a closed system to cool a turbine, who knows. <S> Liquid cooling was used in the past as supplemental cooling to increase available power by spraying water directly into the mass flow as mentioned here , but in that case the water is a consumable. <A> The thing most in need of cooling inside a jet engine is usually the high pressure turbine blades. <S> The air entering the first stage of the turbine is in the neighborhood of 2500F ( https://en.wikipedia.org/wiki/Turbine_blade ). <S> This is often higher than the melting temperature of the blades themselves. <S> These blades are cooled using air bled off from the high pressure compressor, which is typically at a "cool" temperature of 1000F or so. <S> Water would not be much help in cooling here, as it would instantly vaporize. <S> EDIT : <S> @hobbes <S> I was about to say the same thing. <S> Beyond that, where does all of the water come from? <S> You'll have to bring it with you on the plane. <S> Based on data from here ( https://leehamnews.com/2017/01/27/bjorns-corner-aircraft-engines-operation-part-2/ ) <S> a CFM56 core has a mass flow rate at cruise of about 50 pounds/s. <S> 1-3% of that is used for turbine cooling, so let's just call it 1 pounds/s. <S> So during a two hour flight, you are using about 7200 pounds of air for cooling. <S> Let's say that water is 10x efficient at cooling, so if you replace air cooling with water cooling, you need to carry 720 pounds of water along with you for each engine, plus a tank to store it in, a pump, and tubing. <S> Overall at least 1500 pounds increase to overall aircraft weight. <S> That means you can either carry less passengers (less revenue) or have to carry more fuel (more expense). <S> That's a big hit versus air cooling which is basically free in terms of weight. <A> The closest I could find for closed-cyle fluid cooling was a 1975 NASA study for supersonic aircraft, but this used no radiators, and wasn't for the engine. <S> Instead, circulating refrigerant moved heat from the wing and fuselage to the fuel tank containing liquid hydrogen, in the hope that titanium skins could be replaced with cheaper aluminum. <S> The conclusion was that this would help only at airspeeds much greater than Mach 3. <S> Even for piston-powered aircraft (and NASCAR automobiles for that matter), the drag due to airflow through a radiator can be enormous. <S> Some 1930's racing aircraft used radiators inset flush to the wings for this reason. <S> It may just be that the jet engine's mass airflow suffices, so there's no justification for the extra complexity and weight of a dedicated heat exchanger. <A> The KC-135 used to have water cooling during takeoff to increase thrust during a critical phase of flight (decreasing runway required and increasing max weight). <S> When the KC-135 transitioned to the R-model, the new high bypass engines no longer required water cooling. <S> The MQ-9 is a combat aircraft, and has a turboprop, and therefor is technically a jet. <A> If you mean liquid cooling like the piston engine in your car then no, as stated above boundary layer air cooling is used to keep vanes cool, shape the flame in the combustion chamber to stop it touching anything. <S> There is a large amount of air available and means to control it. <S> The Pegasus engine in the Harrier uses water methanol as a thrust augmentation system, cooling the compressor air, making it more dense, making more power. <S> See here :- <S> How does jet engine water injection work?
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The extended range variant uses an alcohol-water injection system for takeoffs at high gross weights in certain environmental conditions in order to provide cooling for max thrust at takeoff.
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Does taking a long time to solo mean that I'll take a long time for training in general? I have a fairly high (in my research - 80hrs and counting) flight hours and still no solo, with landings having been a major reason. There is definitely progress - but I am not convinced I'll solo before 100. I am 43 in decent shape and reasonably coordinated (no red flags). In addition to being expensive and frustrating it begs a question whether any subsequent flying activities like an instrument rating would also take significantly longer (thus being more expensive and frustrating) and - more importantly - whether it is an indicator that my future piloting skills will always be mediocre. My CFI says that "everyone hits a plateau" but I am concerned that past may be an indicator for future... Couple notes to address comments- I have passed my medical- Hours were spread over 10 months and there was a 2-3 month lull (due to weather + ski season) in winter and 1 month break in summer. Otherwise I was pretty religious about 2-3/week lessons.- I actually changed CFI at about 50hr mark and quite like how my current CFI teaches So while it would be nice to look at outside issues - I think the problem is more likely to lie with me than with others... Now back to my original questions... Any thoughts? <Q> Yes, that much time pre-solo is a huge red flag. <S> Either: You do not have the right aptitude for flying <S> Your instructor is incompetent, or Your instructor is deliberately milking you. <S> If the instructor hasn't already had a frank discussion with you about your progress and prospects by this point, that would indicate #2 or #3. <A> It depends on few factors. <S> If you had some pauses in your flying or if you are unable to keep the regular pace in your lessons, that may slow you down. <S> Flight students tend to lose coordination fast. <S> I suppose that you have passed your medical? <S> There is an eye condition that may prevent you from seeing the depth correctly. <S> I hope that this is not the case as this usually disqualifies you to be a pilot. <S> I am 47 myself. <S> Very young people tend to advance faster before first solo as they are able to learn coordination faster. <S> During the route flying older people have more patience and general knowledge, so they advance faster. <S> That is not the same set of skill. <S> In the end, you should discuss that subject with your instructor. <S> Your hours are a bit long for the first solo, so it might be smart to discuss the root cause. <S> This "open end" situation leads to frustration. <S> You might lose motives and they may lose a student. <S> It looks to me that tis is a good time for the "next steps" conversation. <S> In the end, I know some people that were in the same situation as you and they are great instructors now. <A> At the risk of answering a question with a question, what about "landings" is holding you back? <S> 2 recommendations: <S> First, fly the plane all the way down to the ground. <S> A landing doesn't just happen, you control every step. <S> Break the landing pattern down into parts and gain proficiency at each one. <S> "Landing" will be much less stressful, rather than "facing it" as one stressful event. <S> Second, at this point, before flying, sit down with your instructor and be perfectly clear <S> you WANT control of the plane and DO want to get past this step so you can solo, when you feel you are ready. <S> This can be worked out by incrementally gaining proficiency in entering downwind, lowering to approach speed, judging glide angle, controlling flaps and power, stable final approach, rounding out, flaring and landing. <S> Try to focus on your weakest point, and work to improve it. <S> Your instructor should not "jump in" unless you need help. <S> Do lots of touch and goes and work to gain confidence in each step. <S> Not everyone solos after 20 hours. <A> I would second the responses that say, "Not necessarily. <S> " It really does depend on what's holding you back, but in general, the ability to master the skills of landing are quite different from all of the knowledge/memory items required for cross country, decision-making, etc. <S> Also, and this may be completely irrelevant for you, but I heard about a person who struggled for so long to make a good landing her CFI was ready to give up on her - told her she just wasn't cut out to fly. <S> Another CFI did one flight with her, got her a pillow to sit on so she could see the ground, and she soloed within another hour or two of lessons. <S> Just to say, it could be something pretty simple.
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If you have 80 flight hours logged and no solo, unless there is some unusual extenuating factor (e.g. those 80 hours were spread over many years), something is seriously wrong.
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