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

[Mike Habib <habib@jhmi.edu>]

> 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