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Re: vaulting pterosaur launch, questions



I would be very interested in knowing what sort of environment pterosaurs and archaeopteryx's ancestors evolved in.
I don't know how the later ones started flying (birds today will both do a running takeoff, or just leap into the air), but I highly doubt the first ones to begin to fly just leapt into the air.

I'm not sure we should be so quick to consider a leaping launch unlikely as the basal state. It is sometimes perceived as "harder" than a running launch, but this is largely a misinterpretation. (See post in reply to Tim Williams). Running launch in modern birds shows up as a derived state in very particular groups, the vast majority of which are semi-aquatic.


Going away from paleontology, and into aviation:
Birds always take off into the wind

This isn't strictly true; birds often launch without any steady wind or gusts, or may launch at various angles to the oncoming wind depending on what they wish to do (though I grant that they prefer launching into the wind when applicable). Incidentally, I assume by wind that you are referring to gusts: a steady wind won't help much for sustaining flight (though, at launch, the steady wind will transiently act as a gust, and therefore be temporarily useful).


, a 9 mph wind would be enough to make up the difference between the 2 m/s running speed, and 6 m/s stall speed.

Yes, a 9 mph wind/gust could go a long way towards getting a basal bird off the ground - it need not use a running launch to utilize the gust, however, and using a leaping launch would help in the sense that the gust might be brief.



The local weather and terrain can dramatically effect how easy it is to fly.

Absolutely.

Early hang-gliders had horrendous glide ratios (like 4:1), and pretty bad sink rates- but could still soar coastal dunes with sufficient wind. If I recall, that was about the estimated glide ratio of Microraptor...

True, but I think they may have had the AR wrong on that Microraptor model (just a personal gripe).


Such an arboreal glider should be able to fly in the ridge lift, and could then perhaps develop further flight adaptations.

An interesting thought. I do note, however, that a dedicated glider (i.e. unpowered) might find itself very far from a refuge when it finally landed, should it be reliant on ridge lift from nearby dunes and cliffs. Also keep in mind that the basal glider morphology for the bat side of things, at least, may very well have had a very low AR and thus been pretty inefficient at extracting energy from atmospheric conditions and external lift sources. Still, things like ridge lift are often overlooked; good to consider.


If you are interested in seeing just how "easy" flight is at coastal dunes, you might want to check out these videos on youtube showing real examples of completely unpowered coastal soaring in aircraft with sink rates and glide ratios far worse than the majority of birds:

Thanks for the video links! Fun stuff. I do note, just as an aside, that not all biological soaring forms maximize glide ratio or minimize sink rate. In particular, low sink rates aren't always an advantage. Not shooting you down (or suggesting you don't know it already) - those are good parameters for comparison and you make an excellent point - I'm just throwing it out there for those that don't fly gliders and such.


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