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Was Bernoulli wrong?


Doug G.

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This has actually been known for years upon years upon years. We just can't seem to shake the misconception, despite it being well known to engineers.

 

There are parts in the FAA books that talk about downward deflection of air from the wings, though there are still some references to common beliefs too. The truth is, airplanes fly using *several* factors, not just bernoulli's principle. 

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The problem isn't that Bernouilli was wrong, but that the application of his principles and its relationship to the generation of lift is misunderstood and oversimplified (and the application of Newton's Laws even more so).  I've been blogging about this quite a bit, and there's a good discussion from NASA Glenn about this issue (Included in the links below):
https://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html
https://t.co/p0wVcIOK6r
https://t.co/zJTaFF1Hq8

 

The downward deflection of air..which we all know as downwash..is a manifestation of a real (three dimensional) wing and is a result of the production of lift by the wing.  It doesn't exist in the production of lift if you look at a 2d infinite span. People keep trying to ascribe it as the action in the Newtonian action-reaction explanation of lift; but that's false.  If you just have to go there, the action is the reduction of pressure above the wing (that is typically the bigger driver than the increase in positive pressure below) and the reaction is the wing moving upward from the force generated.  Downwash is the driver behind induced drag and that's why engineers design things like winglets to reduce it.  You can calculate lift using Newton's laws only, but you must calculate the momentum change of the air in the entire system, and that's a bitch of a thing to do. It's easier to simply measure the pressure distributions in a wind tunnel and then do an integration of areas to come up with the forces.

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I think we need to go back to the basics on this! Remember manually rolling your window down on the family 57 Chevy and flying your hand?

 

The answer to flight as I see it is lots of wind pushing your hand up! Forces smashing your hand making it rise!

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