Stalls - Angle of Attack versus Vstall

Gary Drescher wrote:
"Stubby" wrote in message
. ..
Don't forget the stall is caused by the elevator losing lift.

No, that's incorrect. There is such a thing as an elevator stall, but it's
very different from a normal stall. In typical small planes, an elevator
stall does not occur unless there is tail icing, or else a CG that's too far
forward when you apply substantial up elevator.

If you have an elevator stall during a landing flare, the nose snaps
abruptly downward, potentially damaging the nose gear.

That's why the nose drops.

No, not in a normal stall. Rather, the wings produce insufficient lift and
so the plane accelerates downward. The plane weathervanes into the new
relative wind, dropping the nose.


There's more to it than that. The centre of pressure is
well behind the centre of gravity in normal flight, and as the AOA is
increased and the boundary layer begins to break up toward the aft wing
surface, the centre of pressure moves forward somewhat, helping to
raise the nose further. At the stall break, where the airflow over the
wing more or less completely breaks down, the CP moves aft again, the
stab/elevator can't hold the nose up against the suddenly increased
nose-down force, and the nose drops. That's not to say the elevator
stalled; it didn't, and elevators don't stall except under unusual
circumstances such as airframe icing or poor design such as the early
Cardinal's stabilator, where the thing would stall in the flare and
drop the nosewheel hard on the runway, sometimes breaking it. Cessna
added slots to the stab to fix that by preventing stab stall.
A stalled elevator would result in the airplane nosing
completely over onto its back in flight, since the stab/elevator's AOA
would increase as it came up, stalling it further, and control would be
totally lost. You'd never get that airplane certified.

Dan