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Re: flight stroke
David Marjanovic wrote:
> Sure, if the center of gravity is behind the center
> of lift. (Ebel thinks just this was the case in
> Archie, which was therefore unable to glide
> according to him.) Where the cg was in extinct
> animals with unknown pneumaticity etc. etc. is...
> let's say challenging to test. :-)
Well, it was probably somewhere in the area just in
front of the acetabulum. This should hold true of
hypothetical arboreal theropods. Gliders like flying
geckos, Dracos, and various marsupials seem to place
their wings or patagia near the center of their bodies
or evenly distribute them. Since theropods couldn't
splay their legs to the sides, it would force them to
put their lift surfaces either toward the tail or on
the arms. The elongate femoral feathers may prove to
be gliding surfaces in Jehol Deinonychosaurs, though.
The whole point of evolving longer arm feathers may
just be to bring your center of lift closer to your
center of gravity.
> I don't think so. Moving the wings downwards or
> upwards _once_, or tucking them in, so that they
> produce less lift, should be enough, shouldn't it?
Exactly! If you find your forebody beginning to climb,
1.) Create drag beneath your body by holding your
wings low or
2.) Move your arms/wings up or
3.) Angle your wings forward diagonally
These options would work, but the byproduct is that it
decreases the efficiency of your lifting surface. So,
flapping is a way to correct your flight posture
without losing your lift surface. It's a temporary
fix. Tucking the wings in is not an option. The goal
is to maximize glide time. Tucking will give you a
boost because you start to fall, but you don't want to
lose altitude. What happens after you lift or drop
your arms? The stalling effect will start all over
again, and you'll be forced to do something about it.
If anything, raising or lowering the arms (and leaving
them in that position) will just slow you down, and
intensify the stall effect. Repetitive flapping is the
only way to get your body level and keep it that way
if you're gliding with a big heavy tail. At least
that's how I see it.
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