Originally Posted by
jonkster
If the dropping wing is stalled and you are adding aileron to pick it up you are asking (depending on type) for something it may not give, in fact depending on type you may get exactly the reverse of what you want - the stall on that wing gets deeper and the wing drops more and the yaw increases.
Except that, as covered in the paragraph before the one you have extracted, in reality it's not a whole wing that stalls - a stall develops somewhere on the wing and in many cases the region with the aileron will stall last (because aeroplane designers have put a bit of thought into the design).
And while we're here - another similar depressingly common myth/misunderstanding is the idea that deflecting an aileron downwards increases the angle of attack of that part of a wing and risks stalling it of the wing is close to it's stalling AoA. This is not true. A lowered aileron is just a flap, and no one says "if you're close to the stall for <deity's> sake down't lower the flaps because you'll stall the wings!"
The lowered aileron is a flap, and just adds camber to the wing which will probably*
increase the stalling AoA of that part of the wing and delay the stall.
There is a convention that *defines* the AoA strictly in terms of a line drawn through the centre of the LE radius and the tip of the TE, but that's just a geometric convention for ease of drawing. It isn't an aerodynamic datum.
PDR
* Government Health Warning: Airfoils vary. Your aeroplane could be at risk if you make assumptions about the behaviour of an airfoil. Consult your airfoil's lift polar before relying on rules of thumb about its behaviour...