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



Comments inserted.

----- Original Message ----- From: "Roberto Takata" <rmtakata@gmail.com>
To: <jrccea@bellsouth.net>
Sent: Wednesday, June 25, 2008 4:08 AM
Subject: Re: Fw: Archie a non-flyer? (was:Re: origin of bats/reply 2 to TMK)



On Tue, Jun 24, 2008 at 11:11 PM, jrc <jrccea@bellsouth.net> wrote:
But, the flow is turbulent in both cases, both across and behind the wing.
It's not laminar. You may be thinking about the difference between
turbulent attached and turbulent seperated flow.

You don't need laminar flux, just that the turbulence be *reduced*.

--My original post responded to your comment that asymmetric feathers reduce drag by asking, " By what mechanism does it reduce drag?"
Your response was, "By avoiding turbulent airflux."
I took that to mean avoiding both turbulent attached (high drag) and turbulent seperated (very high drag) flow, which implies laminar flow. Since the feathers don't see significant laminar flow, that triggered my series of responses.


Drag *over* the wing could help creating lift (or, eventually,
thrust), but drag *behind* wing, in most case is not a good idea.

--Could you elaborate on that, please?

Although it is not possible to avoid *completely* the drag direct to
backwards, if it was *reduced* it could save much energy -

--That is true. :-)

and so, a
mechanism that do it could bring a selective advantage. (Chartajee ant
others say that asymmetric feathers improve lift, more than reduce
drag.)

--Asymmetric feathers shift the point of maximum t/c ratio forward, with the usual results. However, shifting it aftward usually results in lower drag. I would speculate that the evolution of asymmetric feathers had more to do with reducing feather mass than reducing drag or increasing lift.


Does any one have created a mechanical model of a avian wing with
symmetrical and assymetrical feather to see what happens during a wing
stroke? Or have simulated it in computer?

Not to the best of my knowledge. However, with the exception of mass effects (and at very high lift coefficients), the wings would operate much the same even if the individual feathers were shaped like planks,
JimC