Originally Posted by
bfisk
There's your problem.
You need to be a bit more precise - a wing will always stall at the same AoA as long as it's in the same configuration. Changing the configuration will change the properties of the airfoil and alter the lift and drag coefficients and - curves.
Stall AoA will also change as a function of ... Mach number, Reynolds number, load (twist and bending of wing), sideslip if present, proximity to the ground (lower stalling angle in ground effect), general condition of wing (steps, gaps, damage, etc.), roll/yaw/pitch rates, and I'm sure I've missed some.
Furthermore, the simplified explanations given by various people above shouldn't say "the
wing stalls ..." but rather "the
aerofoil stalls ..." - notions of local AoA relative to changing camber lines are reasonable approximations when talking of a 2-dimensional aerofoil section but become pretty much meaningless when considering a real 3-dimensional wing. For example, the flap extends (usually) only over part of the span. So, when I deploy the flaps, do I consider the camber to change or not - the OB wing hasn't had any geometrical change, and if the stall is actually still outboard then the effect of the flap movement may not fit the simplified explanation at all.
Because of that, AoA for an aircraft is pretty much always defined in terms of the fuselage reference relative to the airflow, and is not shifted around in definition by wing configuration changes. Otherwise the standard relationship:
pitch attitude=AoA plus gamma
would not hold.