[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: 11th specimen of Archaeopteryx



On 10/30/2011 1:07 AM, Habib, Michael wrote:

Ah, I see. Yes, that's a nice simple approach to the problem.  Pretty amusing.

Yes. At the time, there was no lit to cite even though the physics are clear -- a flier that is competent at one density may fail entirely at a lesser density -- or even a higher density.

Large pressurized flight chambers are expensive to build, a vacuum pump (and chamber) were not available, and have potentially confounding problems relative to O2 level -- so this was a very quick/cheap way to prove the obvious.

About 10$, iirc -- although I needed a tire pump and valve stems anyway, so I guess you could say it was all a freebie.

Higher density does change the wing loading threshold, but the effect is 
greater in insects (especially rapid flappers like bees) than in other flyers, 
so your model system was particularly well chosen.

The density of the flight medium does indeed limit wingloading at given speed w/ given design specs -- what amazes me is that many people reject the idea that living fliers will alter their morphology in predictable ways over time to adapt/optimize to a given density or range of densities.

But to get back on topic -- 1) models are very nice, but there is no need to speculate on how a lack of inboard feathers affects performance. It should be investigated empirically.

2) 'turning/agility scenarios' are weak in my view because although mathematically significant forces may be generated by proto-wings in "terrestrial" scenarios -- even in the absence of a full upstroke -- they cannot be applied in timely fashion. Even in humans stride frequencies are 3 or 4 steps per second, and in posited pre-birds would be much higher. Air being compressible, and circulation slow to build, it is much quicker and much more economical to simply plant one foot and change direction.

3) nor do I see fighting scenarios as compelling, in the absence of a full upstroke -- no boxer draws his hand back behind his head to strike a blow -- so where does incremental selection toward a full upstroke come from?

You may wonder why people want to "put Archie into trees", but given that: a) no terrestrial animal that is physically able to work it's way into a tree, yet does not occasionally do so comes readily to mind -- I have observed turtles, alligators, dogs, foxes, goats, leopards, lions, bears, rats, coons and 300 lb rednecks in trees at various heights and comfort levels -- b) "perching adaptions" are only useful on small limbs -- most plants over 3m in height have limbs large enough to sleep on, and c) Archie-types had claws fore-and-aft plus teeth, and so could indeed climb, however laboriously.

So I wonder why the drive to make poor old Archie sleep on the ground. It seems dangerous to me, and run-around-on-the-ground, sleep-in-trees lifestyles seem to be popular even today.

As previously stated -- a limited powerstroke really takes the steam out of ground-up muscle-powered scenarios.