05-31-2011, 03:55 PM
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#57 (permalink)
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I got a response from the NASA guy. Here is what I sent:
Quote:
Hello- I just found NASA's page debunking the "equal transit time theory". Thank you for posting this. Since I learned about "how wings work" in elementary school it just didn't compute in my mind, and now NASA backs me up. A wing producing lift by being angled to turn flow downward is intuitive and matches what we experience when we stick our hands out a car window or swing a rigid plate through the air.
I have some questions though, and I'm guessing you're the person to ask since you're the editor and and NASA official listed (Incorrect Lift Theory)
1- The airflow speed over the top of the wing isn't higher because of equal transit time, but for some other reason. Is it because in flight, a wing is pitched upward, which causes air hitting the underside to compress and slow down?
2- It says in section 1 that it's not the distance that matters, but it's the turning of airflow that produces lift. But then in section 3 it's vaguely implied that the Bernoulli effect can explain lift if you use the real speed instead of the "equal transit time" speed. I don't understand how both can be correct. You'd have to add the Bernoulli lift due to speed difference to the lift created by the airflow turning.
3- If the air speed difference creates X amount of lift, and airflow turning creates Y amount of lift, what are the relative sizes of X and Y?
4- Is the "Bernoulli effect" here the phenomenon of airflow over the top of the wing being pulled downward to match the curve of the top wing surface? Is that what creates lift, the redirection (which I think Bernoulli predicted), and not the speed difference itself? That's known as the Coanda effect isn't it?
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His reply:
Quote:
Glad you are taking a careful look at all this.
Lift .. and drag are created when a solid object moves through a fluid (gas or liquid). The fluid can’t go through the solid. So it goes around the solid. To move the fluid around the solid you have to subject the fluid to forces. As the fluid goes by the body, there are three conservation laws that must be observed; conservation of mass, conservation of momentum, and conservation of energy. These conservation conditions must be satisfied at every point in the flow, at all times, at the same time. Newton’s laws of motion are expressions of the conservation of momentum. Bernoulli’s law is derived from the conservation of energy. So in any flow problem, Newton’s laws and Bernoulli’s law are satisfied at the same time … they aren’t added together.
Tom
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