Why Do Airplane Wings Generate Lift?
Travel Blog • Rob Verger • 02.24.09 | 11:33 AM ET
Believe it or not, there is something of a long-time scientific debate about why airplane wings work. There are two ways of looking at why a wing generates lift, and neither is perfect. The first and most common method has to do with Bernoulli’s principle. (How Stuff Works has a more thorough explanation.)
The second way has to do with Newtonian physics, and simply put, this theory basically proposes that air deflected off the bottom of the wing is what keeps the plane in flight. For every action there is an equal and opposite reaction, and the wing’s reaction to the deflected air is to move upwards.
But I’ll focus here on the Bernoulli explanation. (Although some say that Bernoulli is not the best way to explain why wings work, I find it interesting, so here goes.) Bernoulli’s principle basically states that faster-moving fluid—and here, think of air as a fluid—creates an area of lower pressure. A quick experiment to illustrate this: Take a piece of paper and hold it parallel to and a few inches away from a vertical surface, like a wall. Now blow hard between the wall and the paper. The quick-moving air you produced between the wall and paper created an area of low pressure that drew the paper towards the wall.
In the case of an airplane’s wing, Bernoulli’s principle applies because air traveling over the curved surface of the wing actually moves faster over the top of the wing than the bottom. (Why? Let’s say there are two molecules of air that both hit the front of the wing at the same time. One goes over the top, one below. Because the one going over the top has to travel a longer distance, it should need to travel faster to reach the other side at the same time the bottom particle does.) The faster-moving air over the top of the wing creates an area of low pressure above the wing and one of high pressure below it, and—like the paper that was drawn towards the wall—the wings are drawn upwards.
What’s the problem with this theory? One rebuttal goes like this: Those two hypothetical particles that supposedly need to meet at the other side at the same time? There’s no reason why they should “need” to do to that.
Anyway, rest assured, wings work. They just do.