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Re: Hone and Benton 2007 (their second paper)



Comments inserted below. Caution, my tongue may be in cheek, and that interferes with my typing (so does most everything else -- typing's not my bag....)
JimC


----- Original Message ----- From: "Tim Williams" <twilliams_alpha@hotmail.com>
To: <dinosaur@usc.edu>
Sent: Monday, May 28, 2007 4:52 PM
Subject: Re: Hone and Benton 2007 (their second paper)



If I was a pterosaur, and I was dropping out of the tree as a means of achieving flight speed - would I open my wings during this 'drop', or would I keep them closed? I was thinking that by keeping the wings folded, I would achieve flight speed sooner, since open wings would only create drag during the brief descent.

For a large pterosaur, wouldn't that require a very specialized tree shape, in order to keep tree limbs from whacking the wings or vice versa? :-)


For an animal the size of Hatzegopteryx or Q northropi, the wings would only create a total drag of about 12 to 15 pounds at cruise speed and cruise lift coefficients. You could orient them so that they would start pitching the animal from a vertical path to a horizontal path as it gained speed. In other words, start out head down. At someone's request, I once calculated that a tree only a few hundred feet tall should adequately suffice for northropi to perform this maneuver without assistance from flapping, with most of the height consumed in a circular transition from vertical to horizontal flight. It would help if the tree had only two limbs, preferably located at the top. One treelimb would be for supporting the forelimbs, and the other, the hindlimbs. Keep in mind also that pterosaur wings don't fold as closely as bird wings, so climbing the tree is clumsier and more difficult for pterosaurs as well.

But if my wings are already open during the 'drop', then they are already positioned for the downstroke.

True. And it makes access to trees with only two limbs even more important.

However, in both cases, the vertical descent prior to reaching cruising speed is quite short. You can see it if you look for it, however. Like arboreal birds, a tree-dwelling pterosaur would not require a gravity assisted launch, but it saves energy if you happen to be at a high point already.

I agree, but suspect that most pterosaurs launched from ground level.

So in this situation too, would pterosaur wings be open or closed during the vertical descent, prior to reaching cruising speed?

You would want to open them well below cruise speed, in order to control the loading and prevent structural damage to the wings.