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Re: pterosaur femora sprawl
----- Original Message -----
From: "Mike Habib" <firstname.lastname@example.org>
To: "Christopher Taylor" <email@example.com>
Cc: <firstname.lastname@example.org>; "'dinosaur mailing list'" <email@example.com>
Sent: Tuesday, June 03, 2008 11:48 AM
Subject: Re: pterosaur femora sprawl
I suspect that your confusion comes from trying to force the poor critter
to deploy the wings too early (based simply on the fact that I get that
bit of confusion a lot).
I do too.
A quad launching pterosaur would leap first, and then deploy the wings
near the max height of the ballistic path.
They would start the deployment immediately upon the hands leaving the
ground, but the deployment takes a bit of time (about a quarter second for
the bigger pterosaurs). They can't start significantly unfolding the wings
till a line drawn from the shoulder to the wingfinger pivot is high enough
that the wingtip will clear the ground by the time it is unfolded. Once the
outer wings start to unfold, a significant amount of lift is generated, and
it starts happening before the animal reaches max height on the ballistic
path, and it also increases the leap height over the ballistic height. Max
extension does happen at about max height of the ballistic path though (In
other words, I'm not disagreeing with Mike -- just pointing out that the
wings start doing their thing before they are fully deployed and that that
starts happening fairly early. At the time that the hands leave the ground,
for a big pterosaur (Quetz, Hatz, etc.), the vertical component of the
animal's velocity is about 7 to 8 Meters/second, so that the ballistic path
would raise the cg about 2.3 to 3.3 meters during an elapsed time of about
0.68 to 0.82 seconds. This is over twice the duration of a downstroke, so
there is plenty of time for the animal to initiate the first downstroke and
be on his way before the ballistic path reconnects with the ground (read
that as 'no kersplat required'.....)
There is a tendency, I think, to expect that birds flap themselves into
the air, and that being bipedal somehow makes ground clearance less
difficult. Remember, though, that most living ground-launchers use a
leap-first, flap-second kinematic, as it is.
In fact, quad launching *reduces* the problems of clearing the ground,
Indeed it does. Well said, Mike.
because the leap impulse is so much more powerful than a bipedal leap -
it is birds that actually should have the most trouble clearing the