Dec
18
2017

Airplane Wings and Bernoulli’s Theorem

I don’t understand how Bernoulli’s theorem works with airplane wings.

The top of the wing is curved. Therefore, the air going past the top has a longer path to travel. Which means that it is moving faster than the air going past the bottom of the wing. Which, by the theorem, means it is lower pressure. Which means that the pressure differential pushes the wing upwards.

But why does having a longer path imply greater speed? Why does the air that is going over the top of the wing need to end up at the back of the wing in the same time as the air traveling over the bottom of the wing? Why doesn’t it all travel at the same speed with no differential in pressure? This inquiring mind wants to know.

Late update: A knowledgeable friend said that Bernoulli is part of it, but there are other effects in play, particularly at the edge and tips of the wing. If it was just Bernoulli, there would be no need to taper the wings as you move to their tips, or angle them towards the back of the plane.

And hey, XKCD also says it’s more complicated! So maybe this blog post is just knowledge dropping…

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