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Re: Pterosaur size
----- Original Message -----
From: "don ohmes" <firstname.lastname@example.org>
Sent: Saturday, December 16, 2006 6:06 PM
Subject: Pterosaur size
To verify our points of agreement; the big girls existed (11m or bigger
Yes, though the max estimated span for birds is on the loose order of 6.5-7
they could fly,
and the upper size limits of volancy generally are
constrained by launch and landing capability?
Yes. launch more than landing.
So, anyhow, what are you using for wingload?
Depends upon the animal. Since pterosaurs tend to have similar aspect
ratios, and somewhat differently from birds (which show more variation in
planform), their wingloading tends to increase with wingspan. For Qn, it's
roughly 4.3 pounds per square foot, or about 21 Kg/S.M. -- about the same as
the most heavily loaded birds, but greater than the largest volant birds.
However, for both birds and pterosaurs weight can vary substantially during
the course of a single flight (as much as 50% for some birds).
Relative to a given process, selection occurs at the point of maximum
And at points of average stress, and minimum stress, and so on, ad
and it isn’t surprising that you don’t observe a large change in behavior
morphology from the point of maximum stress to the point of least stress.
The appropriate question is; how will they
perform in a habitat range of .5atm-.85atm, or .68-1.15atms?
It depends mostly on their launch technique. For example, I once calculated
whether pterosaurs could fly on Mars (where surface pressure is about the
same as at 110,000 feet here. It turns out that if you could supply them
with oxygen, keep their blood from boiling due to the low pressure, and keep
them from freezing -- some of them could. But they couldn't launch or land.
Well, actually -- they could land, but not in one piece.
To use an analogy-- I weigh 100kg,
and like to jog on the beach (boy, I wish, but that’s why I like thought
I can identify. I weigh about 97 Kg.
Once a week, I run a marathon with 15kg strapped on my back. I am
optimized to running weekly carrying 15 kg, and therefore finish my
which is good for me ‘cause I’ll die if I don’t. The beach of course, is
the beach. You observe my performance and notice that I seem to be using
the same running style 7 days a week. You reason that I can easily cope
15% change in my weight.
Well, no -- that's not an apt analogy for what we've been talking about.
Wrong. This observation tells you nothing about my
ability to cope with a lifestyle wherein I weigh 115kg on the beach, and
while running my mandatory Saturday marathon. Granted, a day at the beach
is just a day at
the beach, but Saturdays are a bitch. Or more to the point, how much are
chances of a long life improved if I weigh 85kg and marathon at 98…
improvements in ambient conditions lead to small improvements in athletic
lead to very large improvement in the probability of success, and by the
a bird flying in +15% has lost 15% of its weight.
Ur, uhh, No. It doesn't work quite that way.
That is the equivalent of the
real me losing 36 lbs. Makes a HUGE difference.
Let me ask a flight question. Let us arbitrarily assume that you are a
bird, or a winged whatever, and that from a height of 1000 feet in no-lift
conditions, you can glide a distance of 20,000 feet. Now, let's add 15% to
your weight. Without flapping, how far can you glide in the same
conditions? Now, let's reduce your weight by 15%. How far?
and the Andes. Blackbirds that nest at 2500’ have lower
wingloads than sealevel nesters.
Not for any reason to do with flight -- it's actually to do with launch, and
the variation between individuals or for one individual over time -- varies
by more than the difference in density due to the 2500' change in altitude.
Seems like if you could determine minimum launch density, you could adjust
to sealevel, and get a eco-perspective on max viable swan size.
That's true, for their present bauplan.
Checking is good, right?