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Re: CNN: how first birds flew
Thomas R. Holtz, Jr. wrote:
> This is a Reuters news article. It is not the original paper. Neither you
> nor I nor anyone on this list (with one or two lurker exceptions, probably)
> have seen the paper, nor its data, nor the model they used. (Okay, I've
> seen an early version of the model at the Ostrom Symposium).
> If we have problems with the reportage, than it is appropriate to take apart
> the article. If we have problems with the science, we should wait until we
> see the freakin' paper, dammit!!
Tom's making a good point here. I too, saw the early version at the Ostrom
Symposium. Though I think the animal could have taken off that way, I don't
think he HAD to.
Archie's weight appears to have been on the loose order of 0.4405 pounds, give
or take quite a bit, and his span was about 1.929 feet.
Based on the expected inertia of the wing, a bird that size would be expected to
have a flapping frequency up around 8-10 beats per second, but let's assume that
Archie couldn't achieve that beat frequency from a standing start because of the
lack of a supracoracoideus (in flight, he could probably come close because of
the aerodynamic lift available early in the upstroke, but I haven't calculated
that). Very arbitrarily assuming Archie had a 0.10 pectoral mass fraction, then
if he could achieve the following flapping frequencies, he would have needed the
following supplemental horizontal velocities to take off.
Flapping Running/leaping Rate of climb available
Hertz supplement mph feet per minute
4.0 4.77 0
5.0 1.77 0
5.3 0 0
7.25 0 126.7
Please note that take-off ability is largely a function of wingspan, not wing
area, which is why I didn't show the wing area above. Playing with any
reasonable assumption of pectoral mass fraction within about 50% of 0.10 leads
to the conclusion that Archie was able to take off at will by either running or
leaping (from either the ground or the trees), and was able to do so with
essentially no ground run. Because of the lack of a supracoracoideus, and the
resulting inability to generate lift through trailing edge momentum reversal
with Kutta violation, I would expect he would have to land running unless there
were a gentle breeze blowing. Because of the relative lengths of the bones in
the foot (not my specialty, so treat it as a hunch on my part), I suspect Archie
was fairly comfortable both on the ground and in the trees. Personally, I tend
to agree with Kathleen Earl of Brown University that Archie had sufficient leg
strength to achieve the required initial velocity by leaping rather than
running. Which implies that he could have done it either way, at will, or could
have leaped from a tree. Bear in mind that because he does have some flapping
ability, he doesn't have to run or leap at anything like his steady-state
non-flapping stall speed to launch.
Also bear in mind that I haven't seen the Nature paper either. Though I
personally lean toward ground-based flight origins, I don't think Archie, taken
alone, answers or can answer the question. The only point I'm making here is
that there's more than one way to skin a cat (with apologies to my cat Ozma, who
may have cringed when I said that).