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Re: The "ideal" Eumaniraptoran arm motion



-----Original Message-----
From: James R. Cunningham <jrccea@bellsouth.net>
To: larryf@capital.net <larryf@capital.net>
Cc: Pharris Nicholas J <pharrinj@plu.edu>; Jeffrey Martz
<jeffmartz@earthlink.net>; dinosaur@usc.edu <dinosaur@usc.edu>
Date: Wednesday, March 03, 1999 10:35 AM
Subject: Re: The "ideal" Eumaniraptoran arm motion


>
>
>Larry Febo wrote:
>
>snipped
>
>> <Bear in mind that the drag produced by hauling wings or slabs of
cardboard
>> through the air is greatly determined by the angle at which you do it.
If
>> you hold the cardboard/feathers vertically, it is very difficult, but if
>> you slide the wing through the air horizontally (which, because of the
>> semilunate carpal block, is the plane in which maniraptoriform arms were
>> made to operate), it is not that hard.>
>
>Yes.
>
>> Gee,...wish I could draw a diagram. There seems to be some
>> confusion...(maybe mine).OK, lets say the vertebral column is a straight
>> axis (for the sake of simplification).And the wing motion, when this axis
is
>> parallel to the ground (as in a bird in flight) causes most drag with the
>> downstroke (towards the earths surface).
>
>No.  The drag component is approximately parallel to the free stream
velocity
>rotated by the induced angle of attack (not the actual AOA), just as lift
is
>approximately perpendicular to that plane.  The thing that's of interest
here is
>the J ratio.  Most drag does not occur during the downstroke -- it occurs
during
>the last half of the upstroke, which is the reason birds, bats, and
pterosaurs
>dump all their lift at that point in the recovery stroke when using the
vortex
>ring gait, and dump part of it when generating a continuous vortex at
higher
>flight speeds (they are actively controlling induced drag, which is a
function
>of lift, and goes to zero when lift goes to zero - retraction of the
wingtip
>during the upstroke simultaneously reduces profile drag to some extent, as
does
>the reduction in free stream velocity during the upstroke).  During the
>downstroke, the drag component is rotated upward to some extent, and the
>vertical component of drag is percieved by the animal as a contribution to
lift,
>just as the forward component of the lift rotation is percieved as thrust.
>
>> Now, in a Theropod bolt upright (an exaggeration), with the same arm
motion,
>> and feather alignment, chasing prey, the drag would be caused with the
>> feathered arms being brought together in the direction of the prey ( also
>> the direction of travel).
>
>Not necessarily; the feathers will pronate aeroelastically to reduce that
>component unless they are deliberately restrained to maintain it.
>
>> Therefore, there would be significant drag that would oppose the forward
>> motion of a theropod chasing down prey....at least at the final moment
>> (assuming its arms were tucked) when it reaches out to grab the prey.
>>
>> More likely, the theropod was leaning somewhat in the forward direction
with
>> axis at what?...about 45 degrees?  Still there would be significant
amount
>> of drag.
>
>For a big, fast animal, only a pound or two.For a small animal (even one
fast
>for its size), only a few ounces.
>Best wishes,
>Jim
>
>
>
Well, I gotta admit, sounds a lot better than that stick diagram I tried to
draw out in my head. ...Got some of the angles wrong too ...I think (I`ll
admit that before someone else "carches" me). In actuality, I see the result
of the wing type motion is not that far off from a bird in flight,  maybe
only a bit more "drag" produced . Still, ...it seems that the claws, when
brought together, would only be able to grab at things fairly close to the
ground, when in a running position. Anything large, would be in reach of the
jaws before the hands. Why such a limited motion in one plane?? Can that be
called optimal? You`d think it had time to evolve more freedom of movement
in the shoulder girdle.
And the thought that this "optimal" restricted motion "just happened" to be
the ideal for avian flight.........it`s just too hard for me to buy it.