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Re: Patagium attachment Was: Re: Pterosaur.net

It would probably help in understanding. Jim, if this model wing of yours is a 
deep wing attached to the ankles or a shallow wing attached at mid thigh. I'm 
guessing the former because you mentioned, "Increasing the inner wing tension 
of the retracted wings during a dive by use of hindlimb positioning..." 

If the latter, there would not be as much "inner wing" to consider (so, less 
flutter). And no connection to the hind limb (so, fewer mental calculations for 
the pterosaur). Two other advantages if one is looking for "reasons".  

Moving the [tip of the] pteroid anteriorly means it no longer is pointing 
directly at the deltopectoral crest? Certain preaxial carpals (as in 
Nyctosaurus) would constrain such movement (see JVP 29(4) for an image). And 
once again you're pulling at a "fabric" with a "knitting needle," inviting 
disaster IMHO.

David Peters

--- On Tue, 1/19/10, jrc <jrccea@bellsouth.net> wrote:

> From: jrc <jrccea@bellsouth.net>
> Subject: Re: Patagium attachment Was: Re: Pterosaur.net
> To: davidpeters@att.net, "Mark Witton" <Mark.Witton@port.ac.uk>
> Cc: dinosaur@usc.edu, "Mike Hanson" <mhanson54@comcast.net>
> Date: Tuesday, January 19, 2010, 8:10 AM
> This might be a good place to mention
> that although pterosaurs could and almost certainly did use
> wing retraction to reduce profile drag, it doesn't work
> quite the same way as in birds and bats.  In
> pterosaurs, there is an additonal requirement to reconfigure
> the inner wing appropriately to control the nonlinear
> interaction between the inner wing tension (both spanwise
> and chordwise) and the outer wing tension.  For
> example, if the inner wing membrane is allowed to slacken
> during the retraction, then the outer wing will slacken to a
> lesser degree thereby increasing the outer wing pressure
> jump which increases the outer wing camber, requiring that
> the aoa of the outer wing be reduced, which moves the line
> of maximum membrane camber aftward.  If left
> uncompensated, this can reduce the flutter margin and 
g the
> inner wing tension of the retracted wings during a dive by
> use of hindlimb positioning has implications for uropatagium
> tension, flutter, and drag that put constraints on the
> articular positioning of the hindlimbs so that neither the
> wing nor the uropatagium will flutter.  There are
> several ways the animal can accomplish this, and several
> other ways that will keep one of the surfaces from
> fluttering while triggering flutter in the other.  I've
> not looked at Mark's drawing to see if his positioning
> appears to comply with  the constraints -- I'm simply
> using this as an opportunity to point out that the
> relationships are quite nonlinear.  For example,
> folding at the metacarpophalangeal joint will require
> simultaneous anterior deflection of the pteroid in order to
> constrain the reduction in tension of the outer wing and its
> associated increase in pressure jump and camberline
> reshaping (which can be done).  These things ain't
> airplanes, birds, or bats and one should not emulate the
> others too closely when working on pterosaur flight
> mechanics.
> JimC
> ----- Original Message ----- From: "David Peters" <davidpeters@att.net>
> To: "Mark Witton" <Mark.Witton@port.ac.uk>
> Cc: <dinosaur@usc.edu>;
> "Mike Hanson" <mhanson54@comcast.net>
> Sent: Monday, January 18, 2010 9:57 PM
> Subject: Re: Patagium attachment Was: Re: Pterosaur.net
> >> As for the
> >> posture of the legs in the Darwinopterus image,
> the animal is meant to
> >> be diving, swooping its wings back and narrowing
> the uropatagia to
> >> lessen the wing area and minimise profile drag:
> why not use the legs as
> >> extra control devices to alter the shape of the
> wings?
> > 
> > Sorry, I didn't understand the dive concept. For me a
> diving pterosaur, like a diving bird and bat, would have
> folded its wings posteriorly at the metacarpophalangeal
> joint. I thought Darwinopterus was raising the wingtips in a
> V shape. If it IS diving, it is overextending the elbow and
> the fully deployed and limp bra
g to
> flutter like a flag on a speeding car IMHO.