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



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

Leading edge vortices (LEVs) are actually known in several birds and bats now, as well. This is predictable, of course: we can expect LEV use in just about any flapping flyers with the proper leading edge shape that fly in the prerequisite Reynolds Number range. In fact, since most flying animals have a sharp leading edge, at least outboard, LEV usage is probably pretty ubiquitous, though it is presumably less pronounced in the larger birds and bats. The turbulent boundary layer does help the LEV stay attached to the wing, but I wouldn't describe it as "drag over the wing", per se. Effects that are associated with increased lift or drag coefficients need not be a direct result of increased drag or lift.



--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?

The asymmetric structure results in reduced mass requirements because the resultant shape is more resistant to twisting under aerodynamic load. A symmetric feather can be built to resist the loads just as well, but at the cost of being more robust, and thus more massive. Therefore, an asymmetric feather is structurally advantageous in terms of material distribution.


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?

What exactly do you mean by "airflux" in this case?


Cheers,

--Mike


Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280-0181 habib@jhmi.edu