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My point in my last post was mostly to call attention to the distinction between
parachuting, gliding, and vortex lift.

Michael Bruce Habib wrote:

> 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?

> 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 
the wing.  Is that your assumption?

> > >  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.

>  The animal spins because nothing on
> the rear of the animal is acting as a gliding surface.
> That is, resistance is far greater towards the shoulder
> than around the hips and pelvic area, so the torso becomes
> a pivot point.

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.

> > > Modern gliders all use broad surfaces across all four limbs, so that the 
> > > braking
> > > force  is applied across most of the animal and a broad membrane.

Describe that as it applies to Diomedes exulans please. And please pardon me if 
misspelled that -- I didn't look it up, and spelling isn't one of my talents 
and eating are).

> > Are you referring to parachuting rather than gliding?
> 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.

> > Er uh, I wouldn't tell a sailplane pilot that.
> Neither would I, she (or he) would not be pleased.  But
> gliding marsupials and rodents don't glide like a sailplane, they parachute 
> (very
> well, but it is still not a sailplane model).

They seem to use vortex lift, a different technique than sailplanes and frigate 
use, but gliding nontheless.

>  Yes, again, true gliders do.  But modern "gliding" animals
> are parachuters, as mentioned.

> > >  Gliding possums, squirrels, and others all show
> > > this same technique.  All of these gliders have very low
> > > terminal velocities in free-fall, thanks to the gliding
> > > surface.

Is it thanks to the gliding surface, or thanks to the parachuting surface?  
Actually, I
think they tend to use low aspect ratio vortex lift, which is physically 
distinct from
both high aspect ratio gliding and parachuting.

> > Good gliding surfaces don't inherently produce low terminal velocity.
> True.  But good parachuting surfaces have to.

Yes, but they are not using the same mechanisms for lift production.

>  At least, they have to be able to, or else it gets really messy when
> the landing part of the trip occurs.  (I have this really
> sick image of exploding possums in my head now...)

Ooh, and now I have this image of possums gaining altitude in a tornado prior 
to the
splat.  Yuck

> > On some days even a crappy glider can accomplish it.
> Agreed, but only the manmade variety.  A possum glider or
> flying squirrel would be hard pressed to use atmospheric
> lift.  The don't get high enough, and (more importantly),
> are not in the air long enough. They are also too heavy.

Now that depends upon the amount of atmospheric lift.  I'm not sure what the 
descent rate of a flying squirrel is, but I've been in updrafts that I think 
might have
exceeded it.

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

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?

> so your model may work better than I expect.

What model is that?  I didn't realise that I had expressed one.

>  (This relative mass difference could be checked rather easily.  I
> may be able to verify it directly, actually, if you wish to find out).

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 
flight mechanics of late-Cretaceous pterosaurs.

All the best,