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Re: *Archaeopteryx* Is Not A Penguin



Jaime, I mostly agree with you, with a couple of minor exceptions.

Jaime A. Headden wrote:

> Having a longer feather or
> flight-surface will increase drag by increasing the aspect ratio
> of the structure.

The relationship you describe is not linear.  Having a longer feather or flight
surface will DECREASE induced drag by increasing the aspect rato of the
structure, when the feather is transverse to the free stream.  Due to the
changing proportions of induced and profile drag, Increasing aspect ratio will
generally reduce total drag at high lift coefficients while increasing it at low
lift coefficients.  Increased aspect ratio makes a wing MORE efficient and will
normally improve rate of climb and glide ratio while reducing top speed.  This
is why birds retract the wings during high speed flight, so they can have their
cake and eat it too (adjustable aspect ratio).

> The feather itself acts to increase drag in the
> water, and will trap water between the barbs and barbules,
> making it more difficult to move the arm or tail,

Not necessarily.  They may in some circumstances be used to control the surface
texture, modifying the energy contained in the boundary layer in a way that
reduces total friction.  For example, creating a surface texture similar to
shark's skin using protrusions with a regular repeating array can increase skin
friction by about 10%, while using the identical protrusions in a semi-repeating
pattern with random variations can reduce skin friction by about the same
amount.  The situation is not as straight-forward as you describe.