Re: pterosaur take-off analog

[Mike Habib <habib@jhmi.edu>]

On Oct 5, 2009, at 12:27 PM, Erik Boehm wrote:

> >
> I think with sufficient wind, biped vs quad becomes a non issue, as  
> the animal won't need to "locomote" in any fashion along the ground,  
> just spread its wings and flap, this of course assumes it can get  
> its wings high enough above the ground that the air isn't slowed too  
> much due to the boundry layer/wind gradient.

Jim already covered the gust/wind launching issue quite well, so I  
won't belabor the point too much here.  However, I do want to point  
out that large (i.e. heavily loaded) flying animals generally need  
some translational velocity from the launch impulse to make the  
overall takeoff sequence feasible: they cannot keep themselves up just  
by flapping once gusted into the air.  This is why birds generate most  
of their lift force from the hindlimbs (80-90% for most species): at  
small sizes, they just need clearance for the flapping stroke, but as  
size increases, there is a increasing reliance on initial  
translational velocity.  There is also the problem that most (if not  
all) pterosaurs, if placed in a stable bipedal posture, generally have  
their wings forced into an inappropriately high angle of attack for  
flapping flight.  Finally, keep in mind the weights involved:  
Quetzalcoatlus northropi was likely at least 150 kg in mass; it's  
maximum fueled mass likely exceeded 200 kg.  With enough wind or other  
special conditions, all sorts of things are possible, but all else  
being equal, I see no reason to expect that any pterosaurs bothered to  
biped launch with any regularity.

Cheers,

--Mike



Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181