Comment on Yep, it's me

CuriousRefugee@lemmy.ml ⁨3⁩ ⁨weeks⁩ ago

• Samvega@lemmy.blahaj.zone ⁨3⁩ ⁨weeks⁩ ago

  I’ve heard the Bernoulli’s principle is not that important for how planes fly.

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  • CuriousRefugee@lemmy.ml ⁨3⁩ ⁨weeks⁩ ago

    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.

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    • Samvega@lemmy.blahaj.zone ⁨3⁩ ⁨weeks⁩ ago

      This is fascinating, thank you. I understand that Bernoulli’s principle is involved, but it is not the sole nor even the most important factor in fixed-wing aircraft flight (if I’m using terms properly), and you’ve added some interesting context.

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      • SkyezOpen@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

        Fun exercise to demonstrate bernoullis principle that I love to whip out. Take two pieces of paper and hold them from the top so that they’re hanging parallel to each other. Blow air between them. Most people expect them to go apart due to the air coming at them, but the higher velocity causing lower pressure means the static air on the outside of the papers actually pushes them together.

        I went to a science center that had a demonstration with two heavy stone balls and an air cannon. The cannon was powerful enough that the balls actually touched. Mind blowing.

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    • DogWater@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

      Can you talk about acrobatic plane wings design theory?

      Do wings designed to work inverted rely on angle of attack and airspeed while inverted? Are there big concessions for regular flight performance in order for the wing to work inverted?

      Always wondered

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    • Zoop@beehaw.org ⁨3⁩ ⁨weeks⁩ ago

      I wish I had a cool family member like you when I was a kid! Thanks for being you. :)

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  • sir_pronoun@lemmy.world ⁨3⁩ ⁨weeks⁩ ago

    Ooh don’t fight THAT battle in front of your children

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    • Samvega@lemmy.blahaj.zone ⁨3⁩ ⁨weeks⁩ ago

      Yes, the truth is a battle, but only because people force it to be so.

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