Hot answers tagged

160

That one thing is to unload the rotor too much (i.e. "push on the stick"): From explainxkcd: ... Unfortunately, as soon as the rotor stops spinning, the whole aircraft falls like a brick and the rotor may be impossible to restart in flight. This is a situation that should be avoided at all costs. Normally it is not a problem since the weight of the ...


71

Stall was an unfortunate choice of words for an engine that suddenly quits since the aerodynamic stall in aviation means something very different and isn't related to the aircraft engine at all1. To a non-pilot, an aerodynamic stall can best be described as the situation where there is not enough air flowing over the wings to create the amount of lift ...


55

A deep stall or a super stall is a condition where the wake of the wing impinges on the tail surface and renders it almost ineffective. The wing is fully stalled, so the airflow on its upper surface separates right after the leading edge, which produces a wide wake of decelerated, turbulent air. Consequently, the dynamic pressure at the tail surface is much ...


48

Audible Warning On light aircraft there is a reed (much like used on a musical wind instrument) mounted on one wing root, which is angled such that at the Angle of Attack which would cause a stall, the reed "plays" which can be heard in the cockpit. Here is a view of where this system is mounted on a Cessna: (source: weekendcfii.com) On some aircraft, ...


43

I believe you are confusing the wing angle of attack with the pitch of the aircraft. Aircraft moving at a slow, near-stall speed, despite pointing the nose up, will still be traveling more or less horizontally. Their VSI instrument will read near zero. Whereas, if you take an aircraft moving quickly and pull the nose up to the same angle, the aircraft ...


42

All airplanes can glide, if they couldn't they wouldn't be able to fly in the first place. When you glide an aircraft you are converting height into airspeed, which you can use to move across the ground. How far you can go across the ground for height lost is called the glide ratio for the aircraft. Gliders have a very high glide ratio as their wings are ...


42

The main thing that is required for a stall recovery is just the ability to drop the nose to decrease angle-of-attack and regain airspeed (and, of course, adding power helps, too.) Except in the case of deep stall, there is still sufficient air flowing over the horizontal stabilizers (and, thus, the elevators) in an airliner to push the nose down during a ...


38

The stall speed your source is referring to may be the speed for a clean stall which means with the flaps are in flight position (= 0°). Flaps on powered planes usually increase lift as well as drag. This means basically that you can fly slower and stall happens at a lower speed. Here are the speeds from the F-8D flight manual (big pdf): From the chart, ...


38

Why do car manufacturers install seat belts? Shouldn't licensed drivers be well aware that they should slow down when it's raining or snowing and that they shouldn't run through red lights or stop signs? A better analogy: Why do car manufacturers install anti-lock break systems? Shouldn't drivers know that when their brakes lock up they should release ...


35

In 727 and 747-100/200 aircraft and their simulators for the two airlines I flew those aircraft for up to my retirement in 1999, all stall training was done in simulators, never in the actual aircraft. Stall training in the sim consisted of slowing (or otherwise loading up the wing) until the stick shaker started. Recovery was accomplished by unloading the ...


34

An engine stall and an aerodynamic stall are completely different. In aviation, an engine stall is referred to as an engine failure, and an aerodynamic stall is simply referred to as a stall. For Nerds An aerodynamic stall happens when the wing stops producing lift because the Angle of Attack is too high. This is usually, but not always, caused by pulling ...


33

All airplanes can glide. Some glide better than others. A very old reference I read talked about engine-out landings in military aircraft. Their procedure was arrive at the airfield at X feet, circle once and land. Trainers like the T-33 needed 2,500 feet, other aircraft needed 3,500-5,000 feet. An F-104, which is basically an engine with fins, needed 20,...


32

Stalls occur based on a wing's angle of attack rather than the aircraft's airspeed. (In fact, one of the basic facts that all pilots learn in their initial training is that an airplane can stall at any airspeed). The A330 measures angle of attack using vanes mounted on the fuselage: However, below 60 knots, these vanes become ineffective. During the ...


32

The immediate cause of a stall is the detachement of the airflow from the wing: Image from NASA This happens when your Angle of Attack is too high. How can the AoA become too high? --For level flight: Given a certain velocity, you will have a certain AoA that will provide the lift needed for level flight. The lower the velocity, the higher this AoA. ...


32

Large commercial aircraft typically rely on either Angle of Attack (AoA) Vanes or Differential Pitot Tubes (Smart Probes (PDF)) to supply input to flight computers for the purpose of calculating AoA. AOA Vane When the computer(s) calculate an AoA nearing the critical angle, an impending stall is communicated to the pilots. There are visual indications, ...


32

No because aircraft are categorized by their speed at the runway threshold (1.3 times stall speed). VAT —Speed at threshold used by ICAO (1.3 times stall speed in the landing configuration at maximum certificated landing mass) By knowing the category, ATC is able to use appropriate speeds. The category is not actually listed anywhere, so the controller ...


31

The correct way to recover from a stall is counter intuitive, not because pilots are trying to climb, but because the nose of the airplane drops due to the loss of lift and aircraft design. 99.999% of the time (when the aircraft is not in a stall), if the nose drops, you simply pull back in order to raise it and this muscle memory is built over time. ...


31

For the stalled flight to recover, the nose needs to be pointed in the airstream, and then the aircraft pulled up with load factor below the ultimate load. From the accident report: The recordings stopped at 2 h 14 min 28. The last recorded values were a vertical speed of -10,912 ft/min, a ground speed of 107 kt, pitch attitude of 16.2 degrees nose-up ...


28

Your airspeed does not remain constant because of inertia: it takes more time for the airplane to adapt to the new relative wind, compared to the time it takes for the wind to change. Example One: you're flying 80 knots and the headwind is 20 knots. Over a time of 3 minutes, the headwind gradually reduces from 20 knots to 10 knots. Since the change is ...


26

Yes, all aircraft have a glide ratio. On many of the higher-performance fighters, it's 1:1 at best (1 foot altitude traded for one foot forward gliding). Many of the newer fighter aircraft are intentionally unstable. They aren't really flown by the pilot; they're flown by a Flight Control Computer System (FLCCS) which depends on electrical and hydraulic ...


26

The short answer is that we want to warn the pilots about an impending stall well prior to an actual stall condition. From a safety perspective, waiting until the airflow starts to separate, or at the onset of buffeting, it's already too late. By using AOA we can set a very conservative threshold. This AOA threshold can be adjusted by taking into account ...


24

I think this is more common than you might think in a C182. The 182 is much more nose-heavy than a 172 (which is particularly noticeable in the flare) and this seems to limit the amount of upward pitch authority the elevator has at low speeds. The only stalls I've done in a 182 are much as you described - you can hold full back-elevator and you just sort of ...


23

To be certifiable, airplanes have to have some kind of cues to warn when you are getting close to a stall, and have decent behaviour during the stall, because nobody is perfect. Airplanes with very strong physical cues prior to stall, like the whole airframe shaking, and good behaviour during a stall, like a good natural pitch over tendency with immediate ...


22

Short Version An accelerated stall is a stall that occurs at an airspeed higher than normal due to a higher load factor (g loading). Longer Version When an aircraft is in a bank or when pulling back on the yoke quickly, the wing has to create additional lift to support the aircraft since the load factor has increased. This increases the angle of attack ...


22

For a parcel of air to generate a lift force as it flows over the wing requires the wing to tip that air parcel's momentum vector downwards slightly; the reaction force that the wing experiences as it does this is what we measure as lift. In the case where the airflow over the top of the wing separates from it, the parcels of air flowing by do not get ...


21

An airliner certainly has the ability to recover from a stall, given sufficient height and power. Moreover stall recovery isn't about maneuverability as such. A fighter jet is more difficult to recover from a stall than a Cessna 150, but the Cessna is much less maneuverable. (That is one among many reasons people learn to fly on Cessna 150s and not on ...


21

A prolonged series of steep turns will not produce a stall in subsequent straight and level flight. "after perhaps twenty turns have been completed, it will stall: stall, mark you, out of level flight with cruising throttle!" In this case "level flight" means not climbing or descending while still in a steep turn. Stopping the turn by rolling level ...


21

I believe what the comic is referencing is Mast Bumping. Rotor blades are very flexible, and for a bunch of reasons, are free to pivot around the mast.(The shaft the blades are spinning around) In normal flight, the blades are held taut by centrifugal forces and the weight of the rotor craft they are supporting. If a pilot were to suddenly push down on the ...


21

This is a well known problem with gyrocopters. The first answer was partially correct in that the problem was caused by pushing the stick forward and unloading the rotor. However, the problem wasn't a slowing down of the blade. The actual problem was that many of these gyrocopters would tumble under these conditions. If you were close to the ground you would ...


19

The FAA publishes Advisory Circular 20-151A, which says in section 2-17(a): Because TCAS II can only accept a limited number of inputs related to airplane performance, it’s not possible to automatically inhibit CLIMB and INCREASE CLIMB RAs in all cases where it may be appropriate to inhibit such RAs. In these cases, TCAS II may command maneuvers ...


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