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Re: WING FEATHER ATTACHMENT
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
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
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
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
appropriately? Note that I'm not saying that they needed to do this, only that
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
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
> 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?
think they tend to use low aspect ratio vortex lift, which is physically
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
> > 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
> 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,