The conventional explantion is that the wing is curved on top. This curve means that the air has to travel farther than the air on the underside. Because the air is less dense on top there is greater air pressure on the under side of the wing and this is what gives the wing lift. I see one potentily serious flaw with this line of reasoning. In order for the molecules to move up and over the wing they must first strike the wing and then bounce upwards. This collision will mean that a downward force will be exerted on the wing. I would think that this downward force would cancel out any potential vacuum that is created in the above explanation. Is the theory more complex than this? Are there other forces, such as Van der Waals forces, involved? What am I missing?