Re: Cost in Aquatic Birds (the big one)

["Mokele mbembe" <mokele_mbembe@hotmail.com>]

> From: "David Marjanovic" <david.marjanovic@gmx.at>
> >From: "Jaime A. Headden" <qilongia@yahoo.com>
> > Hair-like rachis and barbs
> > develope as an effect of primitive structures being influenced by drag.
> This should be testable experimentally :-)

It's already well known in aerodynamics, as i recall.  Drag can, in some 
cases, be significantly reduced by adding something to cause boundary layer 
turbulence.  If the aerodynamics are such that the boundary layer would 
separate from the body in question, use of wires, hairs, etc to cause the 
smooth boundary layer to become turbulent will reduce the drag by preventing 
rather nasty vorticies from forming.

Highly aerodynamic things don't need this, as their boundary layer just 
slides off.  However, something like a theropod isn't quite so aerodynamic, 
and, without hairs or barbs, the boundary layer separates and forms a 
drag-inducing vortex (aka "parasite drag").  With the hairs, this additional 
drag force doesn't come into effect, since what was once a flat sheet of 
almost isobaric air becomes turbulent and unable to form single, large 
vorticies.

Hope this helps. or at least doesn't waste too much bandwidth. :)

Henry Astley

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