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Re: Great in the air, not so good underwater

----- Original Message ----- From: "don ohmes" <d_ohmes@yahoo.com>
To: <dinosaur@usc.edu>
Sent: Saturday, December 09, 2006 10:35 PM
Subject: Re: Great in the air, not so good underwater

Testing the load-carrying capacity of
pigeon-sized birds at increased pressures might clarify the
relationship between size, flight medium density and performance in flapping fliers,
just as variable-density wind tunnels were once used to manipulate the Re
number when designing airplane wings. Astonishingly (to me), this has apparently never been done, although it appears straightforward.

I was under the impression that it had been done, by testing flight capability at reduced pressures. For flight at larger Reynolds numbers, where viscous effects are not as important, load carrying capability will increase approximately as the density, and flight speeds with the square root of the density ratio.


On the peer-reviewed level--

R. Dudley, P. Chai, and others performed experiments within the last decade with hummingbirds and reduced flight-medium density which in my opinion can only be classified as elegant. Of particular interest is confirmation of the intuitive perception that wing-stroke amplitude and frequency increase as flight-medium density decreases. The corollary is that increased atmospheric density reduces wing-stroke amplitude/frequency, with obvious implications for take-off scenarios in large animals with long wings.