[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: pterosaur take-off analog



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