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Re: Dinosaur Fore Limb Posture & Evolution of Avian Flapping Flight Stroke

Eike, it is cool, but it might be more useful to use the reduced frequency for your purpose rather than the Strouhal number, since high values of reduced frequency infer that flow geometry is changing rapidly and that unsteady aerodynamic effects would have to be accounted for (rapidly changing flow geometry will change the stall speed). It is difficult to determine Strouhal number in the field, because it is hard to photograph an accurate wingtip amplitude. The reduced frequency is determined similarly to the Strouhal number, but uses the mean chord (wing area/wingspan) as a reference length instead of the flapping amplitude. The reduced frequency is easier to field measure.

----- Original Message ----- From: "evelyn sobielski" <koreke77@yahoo.de>
More fundamental to the origin of the avian flapping flight-stroke is the question of how a symmetrical forelimb posture â required for gliding and flapping flight â evolved from an alternating forelimb motion, evident in all extant bipeds when running except birds."

Cool! One might try and glean some angles to estimate A from here http://www.app.pan.pl/article/item/app51-305.html?pdf=39 and see what minimum f would cause U to exceed stall speed in different taxa.