Re: The origin of flight: from the water up (still short!)

["James R. Cunningham" <jrccea@bellsouth.net>]

David Marjanovic wrote:

> > > When the wings are below a certain relative size, flight is impossible.
> >
> > Doesn't that depend to some extent on the airspeed?  And size relative to
> what?
>
> The wings of birds generate both lift and thrust, so which airspeed can be
> reached with what amount of force depends on the wing area and shape.

When they're gliding it is gravity that generates the thrust, not the wings per
se.  If you need to carry more weight, you simply increase the rate of descent.
For a given wing (ignoring structural strength issues) if you need to carry
twice the weight, you simply increase the rate of descent by about 41%.
Flapping and continued level flight are a different issue.

> Because Big Q has a few more elements that can grow, such as the wing finger,
> I assume.

Oh.  I had assumed it may have also had something to do with mechanical loading
of the skeletal spar and membrane.

> > >     - If the tail with its long rectrices was used for steering in Archie,
>
> > > it would have been rather difficult to move if it would have been longer.
> >
> > I rather doubt that it's primary purpose was for steering, but it probably
> > could > have been used for that too.  Why would it have been more difficult
> to
> > move if  it were longer?  I presume you are talking about moving while in
> flight?
>
> Oh, sorry, I'm talking about moving underwater. When the tail is too long
> there, it requires excessive power to be moved (except in the plane of the
> rectrices).

Why is it relatively much different than in air?  At these speeds, both are
incompressible fluids and dynamic lift and drag forces are changing
proportionally to the density (a factor of about 800).  Do we know that the tail
mobility was constrained such that it was impossible to use the tail feathers to
move the tail in more than the pitch axis?  What about the roll axis or yaw
axis?  Note that I don't personally believe that archie was a swimmer.  I'm just
thinking about the fluid mechanics in the two mediums.

> I don't think so. I'm just suggesting a possible test, cheaper than a wind
> channel, for how having an Archie tail influences manoeuverability in water.
> :-)

Doesn't this presume that a rigid, artificial archie tail functions identically
with a living tail?  Are are you planning incorporation of internal mobility to
make the hypothetical simulation more 'realistic'?  If the latter, my concerns
would go away.