[304065]

Gentlemen,

Stalling, or exceeding the wing's critical angle of attack, is not a function of airspeed, whether indicated, calibrated or true. It is only a function of angle of attack. If you exceed the critical angle of attack, whether at 10 knots or 10,000, the wing will depart flight.

This is a pretty common misconception, caused by the fact that pitch is related to airspeed. You climb to altitude, pull on the carb heat, retard the throttle to idle and pull back the stick to maintain altitude. Airspeed decays. Five knots above the stall you feel the pre-stall buffet and the warning horn comes on. At the break, you look up and the airspeed indicator is showing, say, 40 knots. So you think, low speed made me stall. Actually what happened is that in order to maintain altitude you had to continue increasing angle of attack until you reached the critical value.

So you dance on the rudders to avoid inducing a spin, and the nose comes forward. You push the stick forward slightly to break the stall and resume level flight at MCA with the horn going off. Airspeed continues to decay, and pre-stall buffet comes in. This time, you apply full throttle, and the stall is averted. Airspeed picked up when you put the throttle in. Did airspeed save you from the stall? Well yes, sort of, because when you came in with the throttle, you increased airflow over the back of the wing, which had the same effect as decreasing angle of attack in inhibiting flow separation.

Now you climb to altitude again, and this time, you push the nose over into a shallow dive until the airspeed indicator reaches 85 knots. As soon as you nail the entry speed, you abruptly pull in full aft stick and push the left rudder all the way to the floor. With the airspeed indicator reading 85 KIAS, the aircraft departs flight and experiences a rapid rotation to inverted. You hold those control inputs until you see the horizon coming around to the three o'clock position, then you feed in forward stick and apply full right rudder and roll out level Congratulations, you just did a snap roll, sort of a "forward spin" in which the wing departed flight with unequal lift on both wings (when stalled, they still produce lift, but WAY less than when in normal flight) and the aircraft rolled rapidly to the left.

At high altitude, the "coffin corner" finds the a/c between mach overspeed and aerodynamic stall. There is a very narrow operating window here, not just found in spyplanes, but in commercial jets as well! You DO NOT want to stall a swept-wing aircraft at high altitude. Those who have done so report taking 15,000 feet to get it back.