Re: pteros have lift-off

[Michael Habib <mhabib5@jhmi.edu>]

David Peters wrote:

> > ......... There aren't any known pterosaurs with roughly a 3x longer 
> > wing.
>
> Yes, there are, in relation to torso length. Not absolute length. 
> We're modeling here. So everything is to scale with a torso length as 
> a more or less common unit.

Wing length relative to torso length doesn't really have a huge impact 
on ground clearance issues (aside from the absolute wing length).  And 
I think you've overestimated - I can't think of any species with a full 
3x relative wingspan compared to Quetzalcoatlus sp.  By that metric, 
there should be something out there with half the torso length, but a 
27.5 foot wingspan.  That's pretty extreme.


> Unfortunately, that's really not where I'm looking for clearance. 
> Let's move the video back a few frames and see if there is this thing 
> called wing clearance much earlier in the launch -- closer to where 
> the hands are still only inches to feet above the ground and rising 
> quickly.

Well, if the hands were at the ground, and then they are rising - where 
is a ground clearance issue going to arise?  It could only possibly 
happen if the wing finger was moved into flight position immediately, 
which it wouldn't be.  In fact, taking the extreme case - we can simply 
model the wing finger as staying fully folded until the top of the 
upstroke.  It probably doesn't actually do that, because opening a bit 
earlier saves energy by utilizing inertial unfolding, but every 
pterosaur I've looked at so far *could* do that if wanted.  So that's 
the most straight-forward sequence (and one that works just fine, 
simply not the most optimal): leap, unfold at the top of the upstroke, 
downstroke.

> You mentioned the animal has .72 seconds to bring the wing to the 
> beginning of the first downstroke. I'm wondering what the wing finger 
> is doing at .1, .2, .3, and .4 seconds into the launch.

It's still completely folded until about 0.25, more than likely.  But, 
if it wants, our leaping pterosaur can simply leave the wing finger 
folded up until the 0.7 mark when it begins to downstroke.  It makes 
the initial upstroke faster anyway.

Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181
habib@jhmi.edu