Why Do Airplane Wings Generate Lift?

Travel Blog  •  Rob Verger  •  02.24.09 | 11:33 AM ET

Photo by neologism, via Flick (Creative Commons)

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.

Rob Verger

Rob Verger is a frequent contributor to World Hum and the site's former air travel blogger. His articles and photographs have appeared in the Boston Globe and other publications, and he's a former undergraduate writing instructor at Columbia University. If you like, .(JavaScript must be enabled to view this email address) or follow him on Twitter.

3 Comments for Why Do Airplane Wings Generate Lift?

Chris 02.24.09 | 3:36 PM ET

It’s funny that after 100 years of flight we still aren’t totally sure why it works. Basic Fluid Dynamics says Bernoulli is right and faster moving-fluid always yields lower pressure, which in the case of a wing gives you lift.  The criticism is correct though, there is nothing that should particularly drive particles to reconnect behind the wing at the same time. The Newtonian approach is obviously valid, otherwise control surfaces wouldn’t work as they do. But Bernoulli explains things like wingtip vortices and supersonic wing design better than Newton. This is why I like rocketry more - it’s a lot more straightforward.

Saad Barood 02.25.09 | 4:39 AM ET

Chris wrote: “This is why I like rocketry more - itís a lot more straightforward.”

It’s truly FAST way to get out of all the riddle :)

Chris 02.25.09 | 11:33 AM ET

“Itís truly FAST way to get out of all the riddle :)”

Unfortunately there is a lot more chemistry involved!

Commenting is not available in this weblog entry.