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Re: Archie a non-flyer? (was:Re: origin of bats/reply 2 to TMK)




----- Original Message ----- From: "Roberto Takata" <rmtakata@gmail.com>
To: "Michael Habib" <mhabib5@jhmi.edu>
Cc: <dinosaur@usc.edu>
Sent: Wednesday, June 25, 2008 3:29 AM
Subject: Re: Archie a non-flyer? (was:Re: origin of bats/reply 2 to TMK)



> Not the cross section shape - ok, if you have a cross section shape
that is circular it will not work.

--It will if the circular shape is rotating in a 'topspin' direction.... :-)

But as far as you note that the
curvature could be greater in the bottom face of the wing (the
negative or reverse camber), we could dismiss the widespread talk that
the air flowing faster over upper face of the wing than over the
bottom face creates a differential pressure (by Bernouilli effect)
that creates lift.

Not at all. You are ignoring the vertical translation of the stagnation line that is located just below the leading edge nose (for a wing that is lifting upward). Bernoulli effect works fine -- it's just that it is a bear to establish the appropriate boundary conditions for its use. For example, the assumption is often made that the flow splits at the nose rather than the forward stagnation line, and that the particles reach the trailing edge at the same time. Neither of those assumptions is true. The camber acts to impact the angle of attack at zero lift and slightly extends the range between zero lift and the critical angle of attack. There are methods that are much easier to apply than Bernoulli's, but Bernoulli works if you want to put the effort into it.
JimC