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Re: Quetz wing questions
Mark, I've taken a quick look at your Qn-giraffe drawing, and assuming the
human height at 1.75 M, have made a few rough measurements on the drawing.
I was only able to measure two of the three dimensions due to foreshortening
into the plane of the drawing, so your dimensions are actually a bit larger
than I recite here.
Your humerus appears to be about 20% longer than life. If you use the
square-cube rule for volume, that would make your volume too great by a
factor of 1.73
Your r/u appears to be about 15% longer than life. Same s-c rule, volume
too great by factor of 1.52
Your MCIV is about 15% short. Volume factor of 61%. Not all that much mass
associated with MCIV though.
PhIV-1 and outer wing are short, but I didn't measure them in the drawing.
Again, not all that much associated mass.
Your torso seems to be a minimum of about 38% too long, for a torso volume
too large by a factor of about 2.63 or more.
For talking purposes only, lets just take a quick average of only the
humerus and r/u volumes 0.5*(1.73+1.52)=1.625 , ignore the larger torso
discrepency, and assume the whole thing is large by that 1.625 "average"
amount, which would imply a mass of 250Kg/1.625=154Kg. Probably by
coincidence, this is fairly close to the guestimate of 150Kg that I usually
use for Qn, based on the wing area and optimal lift coefficient for the
aspect ratio that I use. Needless to say, mathematical rigor is sorely
lacking in the numbers I used above, so what I've just said is strictly for
talking purposes -- but, in short; I think your 250Kg estimate may be a bit
heavy. As an aside, when I do pterosaur mass estimates, I take a series of
cross sections, actually distribute each of those sections into proportions
of bone, fat, muscle/ligaments/tendons, air sacs, marrow, voids, lung
tissue, skin, etc. and apply seperate densities to each. When I do so, I
find that the all-up weight of a pterosaur tends to be approximately similar
to that of an albatross with the same wing span (which isn't really all that
much of a coincidence, aerodynamics and atmospheric physics being what it
is....). I have not used this technique for Qn yet.
Please don't take this the wrong way. I like what you've done very much and
encourage you to pursue it.
All the best,
----- Original Message -----
From: "Mark Witton" <Mark.Witton@port.ac.uk>
Sent: Wednesday, January 16, 2008 3:11 AM
Subject: Re: Quetz wing questions
Hi all (particularly Jim),
"My projection of 150 Kg is based on
optimal CL for the aspect ratio that I generate, and his is based on
estimate (which I haven't seen -- can anyone send me a copy of Mark's
calculations or summary ? )."
A brief overview of my mass work can be found at:
It's entirely irreverant and informal, but it should give you some gist
of where I'm coming from. The slightly less informal paper is in review
at the moment.
Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Tel: (44)2392 842418
jrc <email@example.com> 15/01/08 10:29 PM >>>