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Re: poling dangers


----- Original Message ----- From: "David Peters" <davidrpeters@earthlink.net>
To: <dinosaur@usc.edu>; <mhabib5@jhmi.edu>
Sent: Monday, April 17, 2006 5:34 AM
Subject: Re: poling dangers


First, everything flexes in panic. Flexion of the humerus brings the already
folded wing forward to the surface in a configuration the pterosaur
might also use to rest on dry ground.

Let's keep in mind that the forces generated by doing this are more than 800 times greater than when done in air at the same speed and configuration. So we are saying that the animal does this very slowly when in water, in order that the forces match the power available. Does that jive with the panic situation?


The once relaxed femora splayed
at the surface, immediately flex (adduct), forcing the hips up and the
shoulders down. So far, not good ? but wait... Taking advantage of the
imminent bounce back, the neck rapidly elevates which helps rotate the
anterior torso momentarily and elevate the shoulders.

The head and neck rotating rapidly upward will rotate the body nose down and lower the shoulders.

At the same time
the thighs abduct creating a low pressure situation between the knees,
which sucks the posterior torso down, which elevates the shoulders in
this bizarre version of see-saw. This is how I see Q. raising the
shoulders above the surface. Momentarily freed from the water, the wings
snap laterally and start flapping, but only employing the top half of
the beat cycle in order to avoid reentering the water.

How do you generate enough thrust to remain aloft and above stall speed using this upper half only technique? Even swans are heavily loaded enough that they have to use a very sophisticated lower stroke to assist acceleration during the takeoff run (swans can't do a burst takeoff from water -- they are too heavily loaded). During the lattermost part of the downstroke, swans are actually hovercrafting and accelerating the air trapped underneath the body for additional jet thrust augmentation. Put a harness on them that would stop the latter part of the downstroke and they wouldn't be able to get off. So how would the more heavily loaded pterosaurs make up for the difference?

Once airborne, danger over. 

Not until you are above the height that predators can reach.

Does this work for you? It's all speculation on my part. Hadn't thought
of this until painted into a corner. Could be all wrong.

Dave, one of the things that I like about you (even when I disagree), is that you're always willing to think outside the box, and you're always willing to let everyone watch you do it. That takes guts, and is admirable.

All the best,
Jim