Re: Glider questions

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

dbensen wrote:

> Sigh, all right I be more specific.
> How big can the airfoils (feathers) on the arms and tail of small archosaurs 
> be
> to alter lift and aerodynamics enough to be beneficial to the archosaur?

Pretty small.

> Remember the butterfly-wing experiments?  It was found that big wings are good
> for lift and really big wings are better, but small wings, i.e. the
> intermediate stage between having no wings at all and having fully developed
> wings, have no beneficial effect on aerodynamics at all.

This is a function of Reynolds number.

> Also, it was found
> that chitonous extensions of the exoskeleton of insects acted as radiators 
> made
> their heat-regualtion more efficient.  For this purpose, small extensions were
> okay, and medium extensions were better, but past a certain size, larger and
> larger extensions were no more efficient heat-regulators than were smaller
> ones.

This is a function of the specific heat of air.  The same is true of the cooling
fins on aircraft engines.

>  The cutoff point for the usefulness of different sizes of extensions for
> different reasons were the SAME

This is a coincidence.

> .  That is, the point at which the extensions
> became no longer useful as heat regulators was the same as the point were they
> started to become useful as wings.

See above. No conclusion regarding a relation between wing and radiator size 
can be
drawn from this.

>  Therefor, we can assume that primitive
> insects evolved heat regulators that, through selection, became larger and
> larger, and at a certain point, became useful as wings.

That is certainly a feasible possiblity, but it doesn't follow from the
relationship described, and the assumption resembles a leap of faith.

> If we find out this sort of data for birds, perhaps a similar scenario can be
> drawn up for them.

As I mentioned the other night, try a scenario that allows an incease in the 
zenith
angle of the lateral force vector between the foot and the ground (that enhances
the ability to turn).  However, I think a several of independent uses came 
together
by happy serindipity to trigger the development of the functional avian wing.  I
realize that this might not be the most parsiomonious path to flight, but think 
the
several adaptations required to become an effective glider are less likely.

> I'm sorry, but I don't remember the reference on that butterfly thing, 
> although
> I know I read it in a Gould article.

No problem.

Jim