ORIGINAL: ccab17
Heres an explanation from a beginner:
Air is a mass. All airplanes have the ability to create thrust. With thrust, the plane pushes against the air (a mass) and the air (mass) pushes back against the plane. Wings are shaped to create lift, like you had described. With thrust, the orientation of the plane does not matter (whether it is upside down or not), as long as it is going in a forward manner. Am i right?
No.
It is theoretically possible to design a wing for a plane that will NOT let it fly upside down but fly OK upright.
You could throw all the thrust you want at the plane, but upside down you'd still have almost no lift.
( assuming of course you are not producing SO much thrust that you've basically turned the plane into a ballistic missile ).
Most airfoils DO provide lift when inverted, but some are MUCH better than others.
Symmetrical airfoils tend to do the best job, while a flat bottomed wing will not produce as much lift when inverted... hence the extra required speed ( which generates the missing lift ).
As stated AOA also needs to be changed when the wing is inverted.