[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
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
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
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
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181