The above is not the same thing as saying that "planes fly on compressed air ". I agree with your pressure difference statement. It's really all about action/reaction and pressure differences. Sometimes I think you make some statements just to cause controversy. And you suckered me right in again! [sm=crying.gif]

Sure the pressure is higher near the "bottom" of the wing during a positive wall, but it's quite a bit lower near the "top". This causes air to MOVE in an attempt to equalize the pressure again. It takes energy to get air to move, and that energy is supplied by the airplane's movment. So your "planes fly on compressed air " statement tells only part of the story, so I put my hackles up. You're enjoying this, I can tell.[sm=punching.gif]