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



Comments inserted
JimC

----- Original Message ----- From: "Roberto Takata" <rmtakata@gmail.com>
To: "jrc" <jrccea@bellsouth.net>
Sent: Wednesday, June 25, 2008 6:11 PM
Subject: Re: Archie a non-flyer? (was:Re: origin of bats/reply 2 to TMK)



One will have problem if do not restrict flow direction in the
analysis - specially if consider a flow parallell to gravity
acceleration.

One will have a problem if they do restrict flow direction. With that restriction, you are no longer modeling what's happening to the airfoil.


Snip.

But so let's go put Bernouilli effect in a zero-cambered wing. We will
regard two situations: I) positive angle of attack and II) negative
angle of attack. Where the air is accelerated in (I), and where the
air is accelerated in (II)?

For a non-cambered wing at positive angle of attack, the leading stagnation line shifts away from the leading edge to a line on the lower surface near the leading edge, and the flow above that line reverses, accelerates forward, around the leading edge, and aft over the top of the wing at high velocity. The flow below the stagnation line goes aft along the bottom of the wing at lower velocity, thus setting up the standard circulation for upward lift. Note that two particles that reach the stagnation line at the same time and then seperate, one going around the top and the other going around the bottom -- do not reach the trailing edge at the same time.


For a non-cambered wing at negative angle of attack, the leading stagnation line shifts away from the leading edge to a line on the upper surface near the leading edge, and the flow below that line reverses, accelerates forward, around the leading edge and aft under the bottom of the wing at high velocity. The flow above the stagnation line goes aft along the top of the wing at lower velocity, thus setting up the standard circulation for downward lift. Note that two particles that reach the stagnation line at the same time and then seperate, one going around the bottom and the other going around the top -- do not reach the trailing edge at the same time.
JimC