Re: Flight again (was Re: The Lizard of Oz)

["David Marjanovic" <david.marjanovic@gmx.at>]

> > , and non-pygostylians had reasonably long tails
> > that put the center of gravity in a more stable position.
>
> I must be misunderstanding your concept here.  It sounds like you're
saying that
> moving cg aft with respect to the center of lift is stabilizing, but
moving it
> forward is stabilizing, and moving it aft is destabilizing.  Again, I must
be
> misinterpreting what you said.

I wanted to say that a sizable tail in bipedal dinosaurs brings the center
of gravity into the plane between the hip joints, whereas in pygostylians it
is farther in front. This stabilizes them in flight and makes gliding phases
possible, but for bipedal standing and landing without toppling over a
measurable tail should be better, no?

> > Good argument. But the fuzz seems not to slow down the tennis balls
> > significantly,
>
> Fuzz allows you to speed the ball up significantly because the geometry of
the
> court and net is such that you can't apply a great deal of speed to the
ball
> unless you also apply some spin to help bring the ball down.  You can't
put as
> much power on a defuzzed ball because it will go long (though it does so
at a
> VERY respectable speed).  However, if you aren't interested in getting the
ball
> into the court -- you can hit a worn, new ball much faster than a fresh
ball.

Does this mean that the fuzz makes the ball _faster_?

> > and the effects of spin-induced drag -- flying in curves and
> > such -- can be achieved equally well with a smooth soccer ball.
>
> I think you're omitting differences in size, speed, Reynolds number, and
seam
> patterns.

Ermmmm... yep :-]

> I can testify from personal experience (average about 20-30 hours a
> week for 5 years) that spin-induced drag does not work as well when the
tennis
> ball is smooth.
>
> Cheers,
>
> Jim

Once more bowing to your superior knowledge of aerodynamics,

David :-)