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Re: Patagium attachment Was: Re: Pterosaur.net



Oops.
The statement in my previous post "Both a shallow and a narrow wing"
should read "Both a shallow and a broad wing"
(corrected below)
JimC

----- Original Message ----- From: "jrc" <jrccea@bellsouth.net> To: "David Peters" <davidpeters@att.net>; "Mark Witton" <Mark.Witton@port.ac.uk>
Cc: <dinosaur@usc.edu>; "Mike Hanson" <mhanson54@comcast.net>
Sent: Tuesday, January 19, 2010 9:54 AM
Subject: Re: Patagium attachment Was: Re: Pterosaur.net


The same statement applies to either a deep or a shallow wing, as long as the aft wingroot of that wing is attached to the hindlimb in some fashion. Both a shallow and a broad wing will be subject to flutter when partially retracted, unless the wing (and hindlimbs in some cases) is configured to inhibit it). I think there may be a misperception of how the pteroid and membrane interact to modulate forces and stresses in the wing.

Needless to say, the exact interplay of interactions varies from species to species, and also between individuals of a specific species.
JimC

----- Original Message ----- From: "David Peters" <davidpeters@att.net>
To: "Mark Witton" <Mark.Witton@port.ac.uk>; "jrc" <jrccea@bellsouth.net>
Cc: <dinosaur@usc.edu>; "Mike Hanson" <mhanson54@comcast.net>
Sent: Tuesday, January 19, 2010 9:27 AM
Subject: 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
davidpeters@att.net


--- 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 will
not necessarily reduce profile drag. Increasing 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 brachiopatagia are going to
flutter like a flag on a speeding car IMHO.