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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,
JimC



----- Original Message ----- From: "Mark Witton" <Mark.Witton@port.ac.uk>
To: <dinosaur@usc.edu>
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
Mark's
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:

http://www.flickr.com/photos/markwitton/1386125619/

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.

So long,

Mark

--

Mark Witton

Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road
Portsmouth
PO1 3QL

Tel: (44)2392 842418
E-mail: Mark.Witton@port.ac.uk
jrc <jrccea@bellsouth.net> 15/01/08 10:29 PM >>>
Comments inserted.
JimC