Re: Fw: avian flight

["Rob Gay" <rob_redwing@hotmail.com>]

> That's it. Ebel has addressed this mathematically. First he refutes the
possibility that *Archaeopteryx* could have parachuted: When assuming 
present air density (small changes there would hardly alter the outcome), a 
weight of 250 g and a wing area of 479 cm² (too low), Archie's speed of 
descent was 9.13[8233248 in my calculation with the same formula] m/s, 
"corresponding to a free fall from a height of 4.2 m, would hardly be 
acceptable to a bird with delicate bones"<
SNIP
> "Even if the rate of descent may be rather low in a good glider, in
any case the total kinetic energy must be annihilated when arriving on the 
ground or on a branch. An impression of this problem is given by an  
albatross which has to land in calm air, but often tumbles over.<
But, isn't the albatross "a bird with delicate bones"? No one said that 
Archie would make delivate, graceful landings. Why couldn't _Archaeopteryx_ 
make the same sort of controlled crash on landing?

> This corresponds to a free fall from a height of 8.5 m and would probably 
> lead to an injury [rather, death] if the speed could not be reduced prior 
> to touch-down.<
Surprise, surprise. I bet that if you dropped an unfrozen supermarket 
chicken from a height of 8.5m, it would have some serious injuries as well. 
So...
> However, the available mechanisms for speed reduction are restricted, since 
> the maximum lift coefficient during landing could hardly be greater [what 
> an understatement] than the maximum drag coefficient of cD-max = 1,4 of a 
> cup-shaped parachute.<
Not quite sure what this means (icky math. I'm working on it though). 
However, why would it be impossible for Archie to rotate it's body (in the 
air) to the verticle, so that the wings and tail are perpendicular to the 
direction of travel (basically stall a moment before landing). I think some 
modern birds do something similar, when landing on a narrow perch.

> Here also the not yet evolved wingstroke cannot serve as an escape from the 
> dilemma [means: Gliding can't be a precursor stage to flapping if gliders 
> already need to flap].<
This is an assumption. How do we know flapping hadn't already evoloved for 
some other purpose (display?). But, it seems like a common reaction from 
most animals that jump/are dropped from a height (my cat comes to mind, no, 
I don't throw her off ledges to test this hypothesis). Why would Archie be 
an exception?
Also, all this talk of landing leaves out how the animal would land in the 
water. I think that an impact with water would cause as much, if not more 
damage to the animal if it wasn't able to slow down. Flying things hitting 
the water, even at a relatively low angle, end up looking bad if they canoot 
decelerate before impact (Saw video footage of an airplane test ditch in the 
ocean...).

> Furthermore, considerations regarding the origin of flight must take into 
> account that at the beginning of the evolution the wing area must have been 
> substantially smaller than that of *Archaeopteryx*.<
True. But this means that there had to be some pressure to enlarge the 
feathers, which I don't think would be present in an aquatic environment 
(see my earlier message on the topic).

> To be able to fly up a landing site in a curve so that the speed is 
> completely reduced at arrival, as Recent birds can do, requires completely 
> developed flight abilities. [Coffin for trees-down]<
I don't see how this is so. This assumes that the animal is flying to the 
tree, and not climbing (If I'm reading this statement correctly).

> Yes. *Archaeopteryx* was found in sea sediments.<
I was under the impression that Solenhofen was a lagoonal, near shore 
environment This would mean that...
> there is no advantage a semi-aquatic insectivore would have over a 
> terrestrial one in there.<

Anyways, these are my thoughts...
Peace,
Rob

Student of Geology
Northern Arizona University
P.O. Box 20840
Flagstaff, Az. 86011
AIM: TarryAGoat
"A _Coelophysis_ with feathers?"

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