3 ms·

That's not correct, then the upper surface of the wing would not have effect on lift, when in fact it contributes over half of it.

Retric 11y ago
All the low pressure above a wing does is reduce a downward force it does not provide lift. Drop a piece of paper and it drifts slowly. Drop a book and it falls fast. In your model the paper is supported by the air below and pulled up by the void behind it. However, if you put a piece of paper behind a book it sticks to it and is not pulled up. Thus, all lift comes from the bottom. Edit: You can do the same thing with a piece of paper on top of a wing. PS: The same is true if you pick up a piece of paper with a vacuum. Even if it seems like the suction is providing lift all the force is from outside air.
- JumpCrisscross 11y ago
  > All the low pressure above a wing does is reduce a downward force it does not provide lift. NASA explains why the "skipping stone" theory of lift is incorrect well [1]. In summary, the upper surface does generate lift. [1] https://www.grc.nasa.gov/www/k-12/airplane/wrong2.html https://www.grc.nasa.gov/www/k-12/airplane/wrong2.html
  - Retric 11y ago
    I did say the top of the wing reduced a downward force, unlike the skipping stone theory. But, that's not lift. Do you think individual air molecules are going to magically hold the top of the wing and pull? Now, you can use an inaccurate model of what's going on. And mathematically it looks like the top of a wing provides lift. But, physically that's not what is happening. PS: This is only an issue, because we think an aircraft as zero forces acting on it when it's sitting still on a runway. Instead of being under ~2100 pounds of force per square foot on all sides from air.
    - Gravityloss 11y ago
      I think you've changed definitions on the fly. Both the higher pressure on the bottom and the lower pressure on the top contribute to the lift. If you use a suction cup to lift a piece of horizontal glass, well, I think most reasonable people would say it contributes a force. Maybe you'd say no it doesn't, you don't actually lift it, you just provide a lower pressure at the top allowing the bottom air pressure to push it up... Well duh, of course.
      - Retric 11y ago
        I don't think science should care what 'reasonable people' believe, because reasonable people are often wrong. The whole point is to build accurate models of the world and perpetuating a myth is harmful in the long term. PS: Can you point to where you think I changed definitions? I may have been less than clear.
        Gravityloss 11y ago
        Your definition of lift is very different from the commonly accepted one. If an aircraft that weighs 1000 kg flies level, then the lift has to be 9800 newtons. That means the lift is the sum of the effect from both the bottom overpressure and the top underpressure. You can check it from any dictionary. https://en.wikipedia.org/wiki/Lift_%28force%29 https://en.wikipedia.org/wiki/Lift_%28force%29
        Retric 11y ago
        In level flight every actual force vector above the wing is lowering the magnatude of lift. If you owe 2000$ and have 2200$ your net worth is positive 200$. But, people don't talk about debt as adding to your net worth even if it's part of the equation debt is reducing the result not increasing it. PS: I agree you don't need to model the 2.1 tons per square foot of force in most situations. But, just because you ignore something does not mean it goes away.

Retric 11y ago

All the low pressure above a wing does is reduce a downward force it does not provide lift. Drop a piece of paper and it drifts slowly. Drop a book and it falls fast. In your model the paper is supported by the air below and pulled up by the void behind it. However, if you put a piece of paper behind a book it sticks to it and is not pulled up. Thus, all lift comes from the bottom. Edit: You can do the same thing with a piece of paper on top of a wing. PS: The same is true if you pick up a piece of paper with a vacuum. Even if it seems like the suction is providing lift all the force is from outside air.

JumpCrisscross 11y ago
> All the low pressure above a wing does is reduce a downward force it does not provide lift. NASA explains why the "skipping stone" theory of lift is incorrect well [1]. In summary, the upper surface does generate lift. [1] https://www.grc.nasa.gov/www/k-12/airplane/wrong2.html https://www.grc.nasa.gov/www/k-12/airplane/wrong2.html
- Retric 11y ago
  I did say the top of the wing reduced a downward force, unlike the skipping stone theory. But, that's not lift. Do you think individual air molecules are going to magically hold the top of the wing and pull? Now, you can use an inaccurate model of what's going on. And mathematically it looks like the top of a wing provides lift. But, physically that's not what is happening. PS: This is only an issue, because we think an aircraft as zero forces acting on it when it's sitting still on a runway. Instead of being under ~2100 pounds of force per square foot on all sides from air.
  - Gravityloss 11y ago
    I think you've changed definitions on the fly. Both the higher pressure on the bottom and the lower pressure on the top contribute to the lift. If you use a suction cup to lift a piece of horizontal glass, well, I think most reasonable people would say it contributes a force. Maybe you'd say no it doesn't, you don't actually lift it, you just provide a lower pressure at the top allowing the bottom air pressure to push it up... Well duh, of course.
    - Retric 11y ago
      I don't think science should care what 'reasonable people' believe, because reasonable people are often wrong. The whole point is to build accurate models of the world and perpetuating a myth is harmful in the long term. PS: Can you point to where you think I changed definitions? I may have been less than clear.
      - Gravityloss 11y ago
        Your definition of lift is very different from the commonly accepted one. If an aircraft that weighs 1000 kg flies level, then the lift has to be 9800 newtons. That means the lift is the sum of the effect from both the bottom overpressure and the top underpressure. You can check it from any dictionary. https://en.wikipedia.org/wiki/Lift_%28force%29 https://en.wikipedia.org/wiki/Lift_%28force%29
        Retric 11y ago
        In level flight every actual force vector above the wing is lowering the magnatude of lift. If you owe 2000$ and have 2200$ your net worth is positive 200$. But, people don't talk about debt as adding to your net worth even if it's part of the equation debt is reducing the result not increasing it. PS: I agree you don't need to model the 2.1 tons per square foot of force in most situations. But, just because you ignore something does not mean it goes away.