Why is every student pilot taught that an aircraft stalls at a critical angle of attack??

Question

isnt it true that a stall is not just a result of the critical angle being exceeded,but is completely dependant on the thrust produced by aircraft in flight?If the airspeed is less that the stalling speed,the aicraft stalls but just because of no lift which is a result of inadequate thrust,while for a fighter jet,stalling is rare.

Answer 1

Stalls are categorised as normal stalls when the wing loses lift due to any reason and  the 'high speed stall' which is induced under high "G" conditions, being the result again of airflow breaking off from the wings.

The stall is a result of the critical angle being exceeded and also due to not enough power to sustain flight. At high angles of attack with full power and not enough forward airspeed the aircraft will also stall.

Fighters are equally prone to stalling as other aircraft. That is the reason fighter pilots are taught to fly smoothly and apply back pressure gently and keeping the high speed stall in mind. Stalling a modern fighter in a dog fight can be disastrous.

Answer 2

It seems that way but, in fact, it all comes down to angle of attack. The faster you're going, the better the wing functions. When a plane is level and you drop below a certain speed, the force of gravity overcomes the weakened lifting force of the wings. As this happens, the plane begins to drop. This downward motion increases the wing's angle of attack until the wing stalls. In fighters, this happens just the same, but is easier to aviod because it's easier to keep your speed up with so much power. Basically, the decreased lift at low speeds lets the wings fall into a stall. It's a different circumstance than pulling the nose up too hard, but the same thing happens to the wing.

Answer 3

The angle of attack is the point where that air flow over the wing separates from the surface and lift is lost. If the plane is not going fast enough to generate enough lift to maintain it's altitude is not the point of angle of attack.

Making comparisons to fighter jets is not valid, the wings on fighter are more control surfaces then wings. Any aircraft that can accelerate going straight up is not using lift generated by its wings to fly.

Answer 4

Just to add to what everyone else has said, the main error in your reasoning is the statement that "no lift which is the result of inadequate thrust". In an airplane, thrust has nothing to do with lift, except that thrust produces airspeed. Lift results from airspeed, the aerodynamics of the wing, and the angles between the relative airflow and the wing.

A stall is not a matter of not having enough lift to stay level, otherwise every descent would be a stall. So if a plane is in a stalled or non-stalled configuration, and you increase just the airspeed, it it still stalled or not stalled just the same.

A "stall speed" presumes you are attempting to keep the plane in level flight. To do this with a given wing configuration and a given weight, you need to get that wing to produce lift equal to the weight. As the speed goes down, the angle required to produce that much lift increases. So to keep a plane in level flight as it slows down, you have to pitch up. Eventually, if you keep slowing down and pitching up, you will reach the critical angle and stall. We call the speed at which the angle becomes critical the "stall speed".

But it's important that pilots know that they can stall even above the stall speed -- if they exceed the critical angle.

Consider a dive bomber. He may have maximum thrust and plenty of airspeed going straight down. If you pitches the plane horizontal too quickly, such that the relative wind is still upward, he will stall. He can have full thrust, high airspeed, and still fall like a rock because the relative wind now has a 90-degree angle with respect to the wing.

A plane stalls when the relative wind is wrong -- not along the wings but at a steep angle to them.

Hope that helps.

Answer 5

airplanes surf on the hydrogen bonds within the water vapor moles. air temp, density, altitude and humidity parameters determine how much water vapor is available to sustain hydrogen bonding at a particular angle of attack- independent of speed-. High angle of attack causes more resistance as the wall of hydrogen bonds build up on the bottom surfaces. (same as a surf board)  that is why flaring out on landing causes the plane bottom surfaces to catch more support on the hydrogen bonds as speed is reduced. Lift is the mechanics of surfing on hydrogen bonds.

Answer 6

No, a stall has absolutely nothing to do with thrust.  The reason that every student pilot is taught that an aircraft stalls at the critical angle of attack is because it does.  That's the ONLY thing that induces a stall.

Stall speed is just a calculation of what the airspeed would be at the critical angle of attack in level (1G) flight.

How do you maintain level flight with the power off?  You have to increase back pressure on the controls to increase the angle of attack.  The increased angle of attack increases the coefficient of lift, allowing level flight at lower airspeeds until the critical angle of attack is reached.  At that point, the coefficient of lift drops of sharply.  That's a stall.

Answer 7

Any aircraft can stall whenever its wings exceeds its critical angle of attack. In the case of fighter jets, this is an exception because thrust directly opposes weight in a vertical climb.

Keep in mind that two things other than aircraft design increase/decrease lift=

1. Airflow over the wing. More air, more lift. This can come from a more dense air, e.g. cold air at sea level, or this can come from a faster airflow.

2. Angle of attack. Lift steadily increases as AoA increases until the critical angle of attack, in which lift dramatically decreases while drag likewise increases.

When an aircraft slows, the wings reduce less lift, as a result, the angle of attack must be increased in order to produce more lift. When it speeds up, the angle of attack must be decreased so it doesn't produce too much lift.

This is the main reason why stalls are based on speed.

However, the aircraft can reach critical angle of attack in other methods as well.

If the load factors increase, this also increases the angle of attack. Remenber, increasing load factors is like increasing weight. If the airplane is heavier, you need a higher angle of attack for the wings to produce enough lift to hold the airplane up.

This is known as an "acceleration stall" which occurs during steep banking turns. As you increase the bank in a turn, load factors increase, as load factors increase, the airplane is being slung out to the side, or downwards relative to the airplane, which creates a larger difference between its flight path and the angle of the wing into it, aka angle of attack.

Answer 8

imagine a SU27 performing a tail-stand.

The airplane is not falling, so the wing isn't stalled... right?

In a textbook tail-stand, the angle of attack is 90 degrees, or infinite, depending who you ask. Either way, the angle of attack is far, far past the critical angle of attack. So, the wing is good and stalled.

To answer your question, this jet flies the tail-stand using dramatic thrust, but the wing is still stalled. Very stalled.

Answer 9

then why are gliders able to fly, using your rationale they wouldn't be able to fly at all because they dont produce any thrust. at the end of the day the main criterion is the critical angle.

Answer 10

Is it time for a flight lesson?

"....for a fighter jet, stalling is rare"?  If it is rare it is because a stall is not usually a good tactic, can make the plane less maneuverable, can make the plane very vulnerable, and in some planes cannot always be recovered from.

Answer 11

Everyone appears to be assuming the aircraft is climbing, or in level flight. The critical angle of attack is the angle at which airflow separates and the wing ceases to generate lift. This can happen at any airspeed and any angle relative to the horizon. In other words, you can be flying straight down at 200 knots and stall the wing trying to stop the dive. If you are too close to the ground as with any stall, you will crash.

Answer 12

Any aircraft can stall, and pilots must learn how to recover from, and understand, stalls. Without this knowledge the pilot will sooner or later die from lack of knowledge.

Regards,

Dan

Answer 13

No matter what the airplane is, a stall occurs when you exceed the critical angle of attack.  Thats why alot of airplanes have an AOA indicatior (because that's the only for sure reference as to when the aircraft wing will stall).  It's confusing, but I'm pretty sure that holds true for all airplanes.

Answer 14

Stalling has no DIRECT link to gravity, thrust or attitude – sure, if you maintain level flight with less thrust than drag you’re going to decelerate and eventually stall.

It is purely a function of the angle of attack of the wing – if you let the AoA build to the stall AoA (very simply - when airflow breaks away from rather than ‘follows’ the wing) then the wing will stall irrespective of the speed, thrust or attitude.

The comparison to fighter aircraft is valid, although there are some ‘strange’ aerodynamics going on under certain conditions with certain aircraft. Some fighters simply won’t stall, but that’s a bit outside the box!

Answer 15

Stalls have ABSOLUTELY NOTHING TO DO WITH ENGINE POWER SETTING.

They are purely an aerodynamic factor and are reached ONLY when the critical angle of attack is exceeded.

So in answer to your question, yes student pilots are taught that an aircraft stalls at a critical angle of attack.  Because it does.  If you are underneath the critical angle of attack, you are not stalled.  If you exceed it, you are stalled.  That's what a stall IS.

Let me say it again...A stall has nothing to do with the engine power setting, or thrust produced, or even airspeed (though airspeed certainly is related to angle of attack).  A stall can occur at any airspeed, with any power setting, in any attitude.

AND to add to this, a wing continues to produce a significant amount of lift EVEN AFTER the stall occurs.  Its not like it stops being a wing and stops making lift.  So to say that a stall occurs because there is no lift is also wrong.