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Again, I have caused confusion.  My apologies...

> > I was implying that this would not be enough surface to
> > slow the animal's rate of fall.  Not a very broad gliding
> > surface is presented by the distal feathers only.
> Why would it need to be broad?  And by broad, do you mean substantial chord, 
> or do you
> mean substantial span?

I mean substantial span.

> > Therefore, when the animal leaps, it does not make much
> > difference in terms of how hard it hits at the end, or in
> > staying aloft.  It just makes a cool whooshing noise.
> This seems to presume that the force production is primarily from drag rather 
> than from
> imparting a downward component to the velocity vector of the freestream 
> passing across
> the wing.  Is that your assumption?

Yes, that was indeed my assumption.  I was making this 
assumption because I did not believe we were assuming the 
animal had a full wing, or advanced wing elements, which I 
assumed (perhaps erroneously) would be needed to produce a 
stable freestream across the wing. 

> > > >  If anything, the arms would be forced back towards the shoulders,
> > The gliding surface is not anchored to anything other than
> > the forearm.  Therefore, when the animal leaps, pressure is
> > exterted only on the arm, which would be forced backwards,
> > causing it to spin.
> Why?  I'd expect the muscles of  the shoulder, humerus, and forearm to resist 
> this, just
> as they do in modern birds and bats.

Yes, and modern birds and bats have full wings, with 
powerful flight muscles to work them.  The original 
assumption involved an animal with distal wing components 

> Why wouldn't he swing the wing forward slightly at the shoulder and then 
> aftward at the
> wrist, providing him with a swept, stable planform with the center of lift 
> still located
> appropriately?  Note that I'm not saying that they needed to do this, only 
> that it would
> provide a stable solution to the scenario you suggest.

Point taken, fair enough.

> > All modern "gliding" animals actually use parachuting,
> > good call on making the distinction. I should have made it
> > before.
> Again, I wouldn't say that the wandering albatross or the frigate bird are 
> using
> parachuting, though I would include them among the very best gliders.

An albatross or frigate bird still has very good powered 
flight.  While they do soar for long distances, they have 
the ability to control themselves much more while aloft 
than the mostly landbound animal I was imagining with the 
distally feathered arms.  These birds also have a very 
different wing type from the primitive glider originally 
assumed.  Basically, the flight apparatus on a soaring bird 
and a gliding theropod or basal bird seem very different in 
my mind.  The aspect ratios are completely different for 

> However, it occurs to me now that these animals might have
> a much greater mass, relative to volume, than a sailplane

>A higher density?

Yes, a higher density.

> (as they are mammals, not avian species). They might also
> be lighter per volume than an avian or near avian animal,

>A lower density?

Yes, thank you again.  I was trying to imply a lower 
density.  Can't think lately, can I?

>Truth to tell, I'm not particularly curious.  I just 
>responded to the physical
>distinctions between parachuting, gliding, and vortex 
>lift.  My personal bag is the
>flight mechanics of late-Cretaceous pterosaurs.

Very nice.  I am not all that curious either, really, but 
just in case you were...

Michael Habib
Student, Biology Department
University of Virginia