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



On Wed, Jun 25, 2008 at 9:50 AM, jrc <jrccea@bellsouth.net> wrote:
> --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.

Indeed my original response could be interpreted that way. It would be
better that I've said "by avoiding partially turbulent airflux" or
more properly "by reducing turbulent airflux".

>> 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?

That model is more well stablished for insect flight.
http://www.nature.com/nature/journal/v384/n6610/abs/384626a0.html

> --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.

Reducing feather mass? Reducing feather total area?

>> 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,

With no effect on airflux?

[]s,

Roberto Takata