Let’s have a moment of silence for one of the co-founders of modern flight: Wilbur Wright passed on to the great baggage claim in the sky exactly one hundred years ago this month. Poor Wilbur may have succumbed to typhus in 1912, but his invention, we will be reminded this month, lives on. May is also the month we commemorate paper airplanes (May 26 is National Paper Airplane Day!) and the beginning of the summer travel season (Memorial Day is the busiest flying weekend of the year so far). So come fly with Jeopardy! champ Ken Jennings as he debunks some commonly held—but thoroughly untrue—beliefs about airplanes and aviation. He’ll make sure your historical facts are in the upright and locked position, and that your scientific understanding is securely stowed in the overhead bins or under the seat in front of you.
Airplane Myth #4: Planes Fly Because Air Takes the Same Amount of Time to Pass Over the Wing as Under It.
I was on Jeopardy! for like six months or so—how is it possible that I never know the answer to anything my own children ask me? Yesterday my son wanted to know if snails are born with their shells already on. Are you kidding me? Luckily, he accepted “Hey, who wants to watch cartoons?” as a correct answer. The last time we flew somewhere, the kids wanted me to explain how planes fly. We were sitting over the wing, so I was happy to explain that air takes the same amount of time to travel in a curved path over the top of an airfoil as it does to go under it, which creates lower pressure above the wing. The higher pressure under the wing generates the lift that pushes the plane upward.
This story is how airfoils were explained to me back in grade school science textbooks, and is so widespread nowadays that even pilot’s training manuals use it. The diagrams look so convincing: of course those two streams of air are going to meet at the back of the wing at the same time! Unfortunately, the “equal time-transit fallacy,” as engineers call it, is bunk. There’s no physical reason why parcels of air should “rejoin” after passing over and under the wing. In fact, it’s possible to design an airfoil that works perfectly well even without a curved top. If you’ve ever tried to hold onto a piece of cardstock or plywood on a windy day, you know that lift can be generated even by a “wing” that’s totally flat.
It’s true that there’s less pressure on the upper surfaces of a wing than on the lower one, but the air passing over a wing is always traveling much faster than the “equal time” fallacy would require. The actual aerodynamics of lift are incredibly complicated, and the equations aren’t likely to interest a curious nine-year-old. Perhaps the easiest (correct) explanation uses Newton’s laws. If the wing is deflecting the air that passes it, then, according to Isaac Newton, the air must push back on the wing, right? “Equal and opposite reaction” and all that. The key is to design a wing shape that deflects air down, therefore pushing the wing up. (Oh, and snails are born with tiny little proto-shells, it turns out.)
Quick Quiz: Speaking of wings: the third founding member of Paul McCartney’s band Wings, Denny Laine, was a veteran of what other group?
Ken Jennings is the author of Brainiac, Ken Jennings's Trivia Almanac, and Maphead. He's also the proud owner of an underwhelming Bag o' Crap. Follow him at ken-jennings.com or on Twitter as @KenJennings.
Public domain photo: "Le Bris' flying machine, photographed by Gaspard-Félix Tournachon aka Nadar in 1868", taken from Wikimedia Commons.