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Re: Origin of flight



In a message dated 98-04-30 03:12:21 EDT, Patrick.Norton@state.me.us writes:

<< There are two kinds of lift. A typical wing (bird or plane) has its long   
 axis perpendicular to the airflow (ie, a long "leading edge"), a cambered   
 upper surface and a flat, or relatively flat, lower surface. This allows   
 the wing to function as an airfoil. >>

Right. The tail is certainly not an airfoil in the same sense that the wings
are. The lift generated at the tail is mainly the result of the airstream
pushing up against the lower surfaces of the tail feathers, which are arranged
transversely to the vertebral column. There should be some Bernoulli lift
across the tail feathers themselves, but probably not a heck of a lot. Drag is
reduced somewhat when the dihedral is positive, which is why I believe the
tail feathers were arranged this way (everything is squashed flat in all the
specimens, so there's no direct evidence of this). This lift tends to keep the
tail horizontal during flight; the restoring force on the tail increases both
when the tail drops and when the tail rises, as would happen when the animal
pitches forward. (This, incidentally, answers the question about pitching
forward in another post.) The horizontal tail, in turn, keeps the animal's
body more or less horizontal during flight.