What Makes a Wing Work?
Let's use a wing to help get a better understanding of lift at subsonic speeds. With a typical subsonic wing, the upper surface is more curved than the lower surface.
The curved upper surface constricts the flow of air more than the flatter lower surface, causing the air above the wing to speed up more than the air below. The faster the air speeds up, the lower its pressure becomes. So the faster moving air above has less pressure than the slower moving air below. (Remember, this relationship between pressure and speed is called Bernoulli’s principle.) The higher air pressure below pushes the wing up—lift. Any further increase in the speed of the air will increase the difference in pressure and increase the lifting force on the wing.