In practice, AoA is just a parameter describing the orientation of the wing relative to the (undisturbed) flow. The absolute angle is completely meaningless as it is just a parameter in function of the lift/drag coefficient. For example: one can define AoA=0 when the imaginary line between the attack edge and stream edge is parallel to the flow, or calibrate it so AoA=0 means the orientation that gives zero lift and minimum drag. The latter is better defined, though I am not sure what aeronautic engineers use.
AOA= angle of attack. What this means is the wing's relative angle to the oncomming wind. the oncomming wind is created by the aircraft's foward motion, thus it is exactly 180 degrees opposite to the aircraft's flight path. i'm not sure about the aircraft in here, or real combat aircraft, but modern general aviation aircraft when flying straight and level, generely have about 1 or 2 degrees AOA. when the wing exceeds 17 degrees, the air seperates from the top of the wing(see Lusche's post and diagram above), and this is what causes the wing to lose lift. Go offline and climb to about 5,000 feet, level out, and let the speed stabalize. Now GENTLY start pulling back on the stick, and you'll notice the aircraft climbs nicely, although losing speed. level out and stabalize speed again. now YANK the stick, and you'll notice the aircraft shudders heavily(or stalls)and you should hear a loud buzzer(warning of the stall). that's because when you were pulling gently, you were changing the flight path of the plane gradually enough that it never exceeded the critical AOA. when you yanked it, you took and angled the wing to a point past the critical AOA. another thing to demo this......when you're driving, stick your hand out the window....flat palm, facing down, and perfectly level. when you don't feel any lift at all on your hand, that's 0 degrees.....angle the foward facing part upward slightly, and you feel the wind trying to lift your hand up..you've now got a wing at 1 or 2 degrees. keep lifting the foward facing part of your hand upward, and it'll reach a point where the wind simply pushes your hand back.....that's the critical AOA, and at that point the wind seperated from the top of your hand, causing loss of lift.
definitly refer back to Lusche's diagram up top too........it's a very good visual description......oo..and the other thing is, your airplane does not know which way is up, only you do, so whatever you do in level flight, to cause the plane to stall, will also cause it to stall in a turn.
i hope this helps some.
<<S>>
