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Re: Controversial
From: ah596@FreeNet.Carleton.CA (Max Feil)
Date: 1996/01/24
MessageID: DLo9Av.14H@freenet.carleton.ca#4/4
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Note that explanations of lift based on Bernoulli (speed vs. pressure) and
those based on Newton's Laws (action-reaction from air redirected down) are
really much the same. The Bernoulli equation is just the integral form of the
momentum equation (F=mA). Therefore it is not correct to say, as many do, that
"not all of lift is explained by Bernoulli's principle". Newton's laws and
Bernoulli's principle are physical laws that coexist quite nicely, each
describing aspects of what is happening as air flows past a wing. Bernoulli's
principle can be used to explain 100% of lift, as long as incorrect reasons for
speed changes are not stated first!
Finally, it is worth mentioning that the way the top of a wing produces lift is
the same as the way the bottom of a wing produces lift. Many other explanations
separate the two into "Bernoulli/venturi" lift for the top and "air deflection"
lift for the bottom, whereas in reality the air simply curves along either
surface in a very similar manner. Bernoulli's principle applies fully in both
cases. The air going over the top will speed up as it enters the lower pressure
region, and the air going under the wing will slow down as it enters the higher
pressure region. The top of the wing ends up being the better lift producer,
usually producing about twice as much lift as the bottom of the wing.
There, that's it. For more detailed information and some discussions on the
ideas I have presented above, consult the Sci.aeronautics archives on this
subject, some of which are available from me. In my next article I plan to talk
about what goes into determining the correct center of gravity for an airplane,
which may help you figure out where to place the CG on that radical new and
odd-looking design you're working on!
Cheers!
Max
--
Max Feil
ah596@freenet.carleton.ca
Ottawa, Canada.
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