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Slack membranes and Wing In Ground Effect (was Re: Comparing T-rex to pterosaurs)

James Cunningham wrote:
> Side loads from wind are not much of a problem if the animal doesn't have
> wing membrane taut at the time, because the slack membrane will simply
> with the wind without producing much force.  And when the wings were
folded in
> terrestrial position, the membranes were not taut.
It looks to me as though a slack membrane would reduce the animal's control
over the crosswinds, not limit their effect, because you essentially have an
M-shape (hip-armpit;armpit-elbow;elbow-wrist;wrist-fingertip) with a loose
skin attached to it all the way round, hanging in between.  There would
surely be a build-up of air pockets in this:  Ok, so the distal end of the
wing would be free of most of this, but it would still receive turbulence as
the air pockets from further up the wing dissipated along it.  Still
inherantly unstable for biped locomotion.
> Also, the spoon-shaped
> joints between PhIV-1&2 and PhIV-2&3 would appear to allow the animal to
> the wingtips rather snugly over the back if it so desired (I'm not
implying that
> it actually did so -- just pointing out that it may be possible)
That might do it, but if it's snugly folded up, you're lacking a rear
stabiliser - it resurrects the whole neck orientation due to lacking a tail
problem that got me started in the first place.  The more I think about
biped locomotion the more I think it seems fraught with difficulties.  I'm
not denying Pterosaurs could do it - just that it seems more trouble than
it's worth.
> > .  And woe betide it should try moving at
> > any speed like this - wing in ground effect would have a field day!
Jim's points in response to this on Wing in ground effect (WIGE from now on)
are absolutely right.  What I meant by wing in ground effect is that walking
or running pterosaurs would have inadvertantly been very bad at it if their
lifting surfaces had been folded up aft of their hips as well as their heads
being heavy.  During flight I'm sure WIGE would have been very useful to
pterosaurs because it's all designed to make a large flier more energy
efficient than a slightly higher altitude, smaller one.  see
http://www.amsc.belvoir.army.mil/ground_effect.htm for some interesting
points about WIGE (sorry, no palaeobits).  What I meant by WIGE having a
field day is that it would be acting on the wings only and would pitch the
body out of the way - ie forward and down where the head wanted to take it
in the first place.

Samuel Barnett