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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