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Creation of Lift

MtrHedAP

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What is the largest contributor to creation of lift? Bernouli or Newton? In all my readings Bernouli has always been stressed while they merely mention Newton's third law. NASA's website says that the creation of lift is flawd in theories and common misinterpretations. They say that as the fluid is bent Newtons 3rd law is the primary contributor as the air flows over the top of the wing it flows down with the curvature and since it flows down it causes the reaction to go up. This is a new theory for me and is different from the old hand out the window of a car scenario. Anybody know more about this or what they are saying and can bring this further into light.
 

VNugget

suck squeeze bang blow
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It isn't one or the other... that is a false dichotomy.

Imagine if someone asked you what is the largest contributor to a car's acceleration force: torque produced from the engine, or friction between the drive wheels and the road? You can't say it's one or the other, or a certain percentage of both. Both are required steps along the "chain of events" if you will, and both account for 100% of the car's acceleration force.

Likewise, both the pressure differential across the wing surface as predicted by Bernoulli, and the air downwash reaction each account for 100% of the lift force.

Newton's 3rd law: Every action has an equal and opposite reaction. If the air is imparting 1000 lb. of lift on the wing in the up direction, then the wing is imparting 1000 lb. of force on the air in the down direction.

Newton's 2nd law: Force = mass x acceleration. That air has 1000 lb. of force acting on it downward, so if it has mass then it must be accelerated in that direction. If it isn't, there can not be a lift force.

Don't get me wrong, I'm not advocating the "bullets bouncing off a surface" analogy. If it were true, then the maximum lift angle of attack would be 45 degrees. It of course isn't. Most of the lift does come from airflow over the top surface. But that's just the mechanics of it. In the end, there has to be a downash reaction against which lift acts.

That all said, none of it is as important for a student to understand as the final result of it all, the AOA-Lift relationship. I wouldn't really care if they accounted for lift with pixie dust, as long as they can draw that graph, intimately understand what it means, and instinctively apply it in the airplane.
 

Goose Egg

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We all know what the greatest contributor of lift is:


$$$$$$

That should settle the debate.
 

MtrHedAP

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May 17, 2005
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Thanks for the replies. I would also not expect a student to understand it as much in detail. I teach the standard simple ways of lift. I was just thinking that I might be neglecting something and actually teaching something wrong. I agree they are both necessary and you dont need to understand it completely to fly an airplane.

This all came about in a garage over a few beers with a couple of my pilot buddies. Funny how everybody has a different theory when you've had a few.
 
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