Re: WING FEATHER ATTACHMENT

["Tim Williams" <twilliams_alpha@hotmail.com>]

Jim Cunningham wrote:

> > surface (patagium) strung between the fore- and hindlimbs and
> > contiguous with the body wall on each side of the body.  Hence, the 
> patagia
> > meet the torso to form a single effective gliding surface.
>
> Is it a gliding surface, a parachuting surface, or a vortex generation 
> surface?

To me a gliding surface is one that generates an airfoil - such as the 
cambered patagium of a gliding mammal, or the wing of a bird with its 
asymmetric feathers.  In other words, a gliding surface creates aerodynamic 
lift.

As for "a vortex generation surface", to me vortex generation is the 
function of an airfoil during gliding.  Lift is generated by the creation of 
a pressure differential over the wing surface: the lowest pressure occurs 
over the upper wing surface, and the highest pressure under the wing.  A 
vortex is created which "sucks" the wing upwards.

A parachuting surface simply facilitates a controlled or retarded fall by 
creating drag (air resistance) during the object's (such as animal's) fall 
to the earth.  A parachuting surface creates aerodynamic drag.

Modern gliders may use both lift and drag, AFAIK, while in the air.  But 
gliding is what they do best, and that is what the patagium is designed for 
- and the asymmetric vanes of wing feathers.


Regards, Tim


----------------------------------------------------------------------

Timothy J. Williams

USDA-ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163



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