Some research on wiki, google and this forum seem the state that planes fly because of Bernouilli, i.e., the acceleration of the air on the top of the wing because of the increased path. Just to discuss a little bit, as other threads seem just dead. Wings, sails and rudders work in the same way. This is clear. As a sailor, I think that increased path is negligible so it doesn't explain the power obtained from the wind. On the other hand, it is not possible to catch a sailship by following the same path (assuming close-hauled sailing), as second boat will receive the wind from the front. It is not only that air is slower below the wing and faster over the wing. The air is changing direction both below and above the wing. The same for a sail or a rudder. Air is accelerated downwards (not meaning that v is increased, just a change in direction) to follow the obstacle (wing, sail or rudder). Importantly, above the wing air increases its velocity because cross section is increased to fill the space behind the wing. At the trailing edge, air is flowing downwards for both flows. I find strange that most pictures of these flows do not show this effect. What do you think?