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Re: BBC Horizon on Ostrom's "New" idea.



 

John V Jackson wrote:

Ostrom claimed: "Gliders depend on a stable/immobile airfoil to support the lifting surface. Flapping flight depends on flexibility in that airfoil surface, and that’s what birds possess." This view unavoidably implies that John astonishingly does not appreciate that moving airfoils also give vertical lift to flapping birds in horizontal flight.

I've had both verbal and written communication with Ostrom on this subject.  He appears to be very much aware of and appreciate the function of moving airfoils.  JRC
 
 

Another argument for "Ground up" was illustrated by the difficulty hummingbirds have when flying in low-density helium-rich air. Since there was thought to have been more oxygen in the Jurassic atmosphere, and oxygen is heavier than nitrogen, this is supposed to show flying was easier.

While it's true that oxygen is heavier than nitrogen, this isn't the point here.  The oxygen didn't replace the nitrogen, it was present in addition, thereby increasing the total atmospheric mass, substantially lowering the density altitude relative to the present day standard atmosphere.  Performance variation with density altitude is well understood and practically demonstrated every time aircraft (and birds, etc.) take off.  JRC