Originally Posted by
GE 90
Not sure what kind of wing you are thinking of. Lift is created at 0 degrees AOA by the action of air passing over the top surface at a higher speed than under it.
True for a cambered airfoil.
For a symmetrical airfoil, at 0 degrees AOA, the air passes over top and bottom surface at equal speeds, so lift is 0 by symmetry. For an asymmetrical airfoil, lift does not have to be zero at exactly 0 degrees AoA - and for cambered airfoils, it is positive. However, for every cambered airfoil, there is an angle of attack where lift does equal zero, this being less than 360 degrees - but normally much closer to 360 than 270 degrees. Anyway, AOA of cambered airfoil is often defined so as to be 0 at zero lift... (though it seems to me that such definition cannot be independent of Mach).
Originally Posted by
GE 90
This causes a lower pressure area to form above the wing thus sucking the a/c into the air.
And at the same time, a high pressure area forms under the wing, pushing the a/c into the air.
Originally Posted by
GE 90
If you increase the AOA until the air separates the lift is lost so it is only the engines thrust pushing up that will act against the weight.
But there is still the high pressure area under wing. The only time the engine thrust remains the only force counteracting weight is when the AoA is about 90 degrees, so that the lift is directed horizontally.
Originally Posted by
GE 90
At close to Mach1 the air over the top of the wing will be supersonic and so will form a shockwave. As the air hits the shockwave it is squashed and so creates a high pressure area. (The reverse of what you want on top of the wing.)
The air hitting the actual underside of the wing is still squashed against the underside and forms high pressure area. Which is what you want under the wing.