Re: vaulting pterosaur launch, questions

[Mike Habib <habib@jhmi.edu>]

> I think the physical requirements for a standing/leaping launch are  
> greater than a running launch.

Do you have any particular mechanical parameters in mind?  I don't  
think the physical requirements are actually greater.


> While it may be easier for a bird with the neccesary adaptations, I  
> would think a standing launch would be a more derived form of  
> flight, and the basal launch technique would either be running into  
> the wind, down a slope, or dropping from a high perch.


Dropping from a perch (i.e. gravity assisted launch) seems plausible  
as a basal launch strategy, assuming arboreal, gliding ancestry.   
Running into the wind or down slopes strike me as much less likely, as  
the specific requirements of terrain and conditions seem unlikely to  
be met with enough regularity.  And, if wind was truly required, then  
leaping into the wind would be just as good as running into it.

> But archeaoptyrx could sustain flight, the problem was getting  
> airborne and the trouble it would have flapping its wings on the  
> ground, right? a running start into a head wind could be sufficient  
> to get airborne to allow for weak flapping to do the rest.

It's ability to sustain flight is not certain, though it should have  
been able to cruise for a bit.  The problem is indeed largely with  
launch, and that is likely best solved by leaping for an animal with  
its build.  The running start into the wind might do the trick, but  
jumping into the wind would probably do even better.

> True, but I think any animal that does a leaping takeoff from the  
> ground, is already adapted for flight, I have a hard time beleiving  
> it is the basal launch technique

Well, running launch is only present as a derived state in living  
birds.  Granted, the basal state in neornithines is already heavily  
flight adapted, but I still don't see why leaping should not be the  
basal launch technique.  For an animal with long hindlimbs, like  
Archaeopteryx, a leaping launch provides similar launch velocity, with  
greater clearance for the wings, over less launch distance, in a  
shorter period of time (as compared to a running launch).


>    I'm not talking shear here (30 knots consistent straight in is at  
> my limit, if not just above it), but smooth laminar flow over  
> elevated coastal terrain.

If you're not experiencing gusts or shear, then where are you  
extracting your energy?  I was under the impression that you were  
referring to deflected air at ridge features, which would be a form of  
shear energy.

> Coastal lift is the most consistent lift I know of, and presents in  
> my view the lowest barrier to controlled flight. This doesn't mean  
> thats how it happened, but I wouldn't be surprized if controlled  
> flight arose from pterosaurs or therepods living near the beach, or  
> consistent wind.

Not a bad thought.

> Of course birds do that as well, and it isn't a requirement.  
> However, as with the Wright brothers, you can't very well have  
> powered flight until you can have controlled flight.
> The transition form has to be viable, and I think a coastal soaring  
> unpowered flight form is viable.
> At least more viable than something clumsily flapping to extend its  
> glide between trees.

I don't entirely disagree, but for sake of argument I do note that  
extended, controlled marine soaring among modern birds is actually a  
fairly derived and control-intensive exercise.


> Among human foot launched flight, a lot of the time all you need to  
> do is walk to the edge of a coastal dune with a neutral/negative  
> angle of attack, and then increase angle of attack at the edge, and  
> away you go- no leaping or running required at all. It should get  
> even easier as it is scaled down.
> A an early bird or pterosaur need not neccesarily run or leap at at  
> all, just waddle up to the edge and unfold its wings

Indeed; a gust over a ridge is a powerful source of energy.  I doubt  
that pterosaurs launched bipedally (see earlier posts in the thread)  
so I rather imagine that pterosaurs didn't waddle up to cliffs and  
unfold the wings in quite that manner, but a bipedal or quad leap off  
a ridge into a strong gust would be a decent way to get airborne,  
presuming that the aforementioned incipient flight was not intended as  
a method of escape (since reliance on ridges for your getaway is  
unlikely to be sustainable).


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