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168

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 ...


72

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 ...


58

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 ...


49

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 ...


47

It isn't practical for a number of reasons: Intentional stalls are inherently dangerous. Stall-spin accidents are a major cause of accidents, stall recognition and recovery are taught specifically to avoid stalls. Some airplanes have docile stall characteristics, but even those can still bite you. A Cessna 172 will drop a wing if mishandled, especially ...


44

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 ...


43

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 ...


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 ...


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 ...


37

You have misunderstood. Lowering the stall speed means that, whereas your stall speed at a given configuration was e.g. 150 knots, the stall speed now is 138 knots. This does not mean 'it is "easier" for the plane to reach this new lower speed'. It only means you can slow down more without stalling. Moreover, keep in mind that dumping fuel lowers ...


36

This is called stall hysteresis. You have two different situations and the flow reacts differently in each of them. When increasing the AOA The flow is attached to the wing and the boundary layer is resisting the adverse pressure gradient as much as possible. At some point the flow detach from your profile and you have stalled let's say at 18°. At this point ...


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 ...


34

As far as I can tell, NASA has never given a straight-forward answer to this question. The theoretical stall AoA is likely in the 33-40° range (see reason for that guess below). However, at operational airspeeds, the orbiter becomes aerodynamically unstable at a lower angle of attack than the stall angle. Therefore, the stall angle never mattered for shuttle ...


34

If the cables break on an elevator (and the safety brakes fail), you won't be in true freefall. You'll still have friction from wind resistance, from the guide rollers on the rails, etc. The same is true in an airplane. Even if you're falling straight down, you'll still have wind resistance. In addition, lift doesn't just drop straight to zero when the wing ...


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,...


33

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 ...


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

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 ...


31

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 ...


30

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 ...


29

The instinct drilled into a pilot's head from the beginning as the primary response is "lower the nose" to lower AOA. If you learn in a glider, that's the only option, so it's easy to drill the instinct into peoples' heads (one reason that glider training before power is so good for pilot skills later). In a power plane, it's lower the nose and add as much ...


27

Yes, but the challenge is managing the asymmetric thrust effects when applying power during the stall recovery. Pilots are trained in the sim for two stall (actually, just stick shaker onset) situations: high altitude and low altitude. Low altitude stall recovery training is normally done by slowing until the stick shaker starts, then adding max thrust ...


26

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 ...


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

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 ...


26

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 ...


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