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Re: Thoughts on the new Czerkas book (long)




Patrick Norton wrote:

> If selection pressures among small feathered (primarily) bipedal
> archosaurs were biased toward aerodynamic performance in general, the
> overall effectiveness of the lift and/or thrust potential of an
> airfoil surface was probably the most significant factor.  Selective
> improvements in 'flight' performance (such as the asymmetry of the
> flight feathers
>
> >>the advantage of asymmetry is in controlling the variation of the
> pitching moment couple  between the loaded and unloaded conditions, to
> reduce the tendency to flutter uncontrollably.  This can be
> accomplished in several ways, asymmetry being just one of them.
> Actually, you do want the feather to 'flutter' during the cycle, but
> in a very slow and controlled manner, synched with the flight stroke.
> This mode is not normally called flutter.  However, in common usage
> the term 'flutter' is taken to apply to very high frequency,
> uncontrolled cyclic pitch variations.  As an aside, this type of
> flutter is unrelated to the so-called 'flutter stroke' which involves
> deliberate cyclic momentum reversals.<<
>
>
> and, later, the alula, and even later, the fusion of the
> carpometacarpus) seem reasonable as more derived characters. PTN

>>I agree.  I suspect that as the fingers became less useful for other
purposes, as a weight-saving device, the alula replaced the remaining
and somewhat similar flight function provided by the fingers.  Was the
transition sudden, or gradual?  It could be made to work either way.<<