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Cake day: August 1st, 2023

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  • Yes, there’s a bit of a myth around Bernoulli’s principle (faster moving fluids have lower pressure) and how much it matters for lift in plane wings. It came up in the conversation because I was trying to describe what air pressure is in general, and made an analogy to a pan flute (he plays flute in band).

    Disclaimer: I’m an aerospace engineer, but I do not claim to be an expert on topic.

    But for plane wings, the myth is really that the air above the wing moves faster because the curved surface is longer. That’s pretty much dead wrong, but is still in tons of textbooks. The air above the wing does move faster, but it’s because of a bunch of complicated physics that to be honest, I don’t really understand any more. I may have even been taught wrongly in college. But the result is that there is a velocity difference on a cambered wing even when it’s flat, and thus Bernoulli’s principle does apply, and there is a pressure difference giving you lift.

    But that speed difference is mostly important at cruising altitude, when the wings aren’t angled, and it’s positively correlated with airspeed, so the thrust matters way more. When you’re climbing, the angle matters more. The camber (curvature) of the wing, the airspeed, and the angle of attack all lead to that pressure difference, along with a few other things like circulation, which is also caused by a sharp edge at the back of the wing. But everything kind of works together to generate that pressure difference and hence the lift that can combat gravity. It’s actually pretty hard to try and dumb it down without saying things that aren’t wrong.