Why is the critical AoA of most flaps 40° when most airfoils stall at 15°? A plain flap deflected 40 degrees is largely stalled (...)


Flaps stall at 40° according to an answer on Quora, why is this so when typical airfoils stall at 15°?
Flaps are located in the downwash of a wing. Their local angle of attack is not equal to their deflection angle, but equal to the deflection angle minus the angle the downwash leaves the trailing edge of the wing.