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Re: four winged Archaeopteryx
On Fri, Sep 29, 2006 at 12:54:08PM -0700, James R. Cunningham scripsit:
> Graydon wrote:
> > but proposing an immobile aerodynamic feather _and expecting to work
> > for flight_ is a very strong claim.
> Note that I have no objection to mobile aerodynamic feathers and
> realize that many are, but by analogy, does the statement below mean
> that proposing immobile fixed wings for aircraft would be a very
> strong claim? I note in passing, that immobile fixed wings are not
> unusual in aircraft, and that they are expected to work for flight.
Really immobile fixed wings for aircraft didn't work; it was only when
somebody figured out (at a minimum) wing warping and (much better)
ailerons than powered flight was a success, and that had to be
accompanied by the ability to design aircraft as a whole for flight
Modern aircraft wings -- as I'm sure you know better than I do -- have
all sorts of flaps and slats and control surfaces, and while they're
immobile as structures (usually -- swing wings do exist) the wing isn't
immobile as an aerodynamic surface. Nor is the wing the
thrust-producing mechanism in an aircraft, which it is with birds.
The guys who built a working ornithopter *definitely* couldn't get
it to work with an immobile wing surface; the wing they ended up with
had to change shape for the thing to fly.
What I should probably have said was something like "expecting a
immobile tail surface to work for bird flight is a very strong claim"; a
fixed frond tail would have uniform drag and be a uniform contribution
to flight stability.
So you either have an Archie that can't fly with lost feathers/feather
damage to the tail, maybe can't turn without heroic effort, and is in
serious trouble with gusty winds (or anything else which applies an
assymetric airflow to the tail), or you've got an Archie with some
ability to adjust the tail surface to cope with conditions.
I suppose it's possible to assert that, so early in the history of bird
flight, the ability to cope with tail damage might not have existed,
but I'm still going to assert that there must have been a strong
selective pressure for the ability in a volant species, even one
restricted to burst flight for predator escape.