|MLA Citation:||Bloomfield, Louis A. "Question 575"|
How Everything Works 19 Jan 2018. 19 Jan 2018 <http://howeverythingworks.org/print1.php?QNum=575>.
In a paper airplane, the most important effect is a rise in pressure below the wings. To understand why this pressure rise occurs, think about the movement of air from the perspective of a bug that's riding on the airplane. To the bug, the air is flowing toward the front of the airplane. As this stream of air encounters the undersurface of the wing, the air slows down. You can think of this air as hitting a slanted wall. Whenever a moving stream of air slows down, its pressure rises. You experience this pressure rise when you hold your hand out of the window of a moving car and feel the slowing air push your hand toward the back of the car.
The dynamics of the air above the wing is more complicated and depends on the design of the wing. But in any case, the air above the wing doesn't slow down and its pressure never rises above atmospheric pressure. In a well-designed wing, it actually drops below atmospheric pressure! Since the air pressure rises under the paper airplane's wing and doesn't rise above the airplane's wing, the wing experiences an upward force due to pressure. It's this upward force that supports the airplane.