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Re: CNN: how first birds flew



Although I think it unlikely that in very early feathered theropods the
wing feathers could have made much addition to spead, maneuverability
is a more likely candidate for a characteristic that would give the bearer
an advantage. The positioning of the feathers on the arms allows considerable
leverage. Gauthier was quoted in an article as saying that "a physicist" had
calculated the effects of protowings as maneuvering tools about 10 years ago..
Can anyone give me a citation for the article by "the physicist"? I have
not been able to find it.
-Gus Derkits

James R. Cunningham wrote:

> 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).
>
> Cheers,
> JimC