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Re: More on Argentavis



If this research was done in the same manner as Chatterjee's pterosaur work (which is what it sounds like), then they are applying helicopter momentum theory as the framework for flight ability estimates. It is essentially a particular model for estimating how momentum is imparted to the air for a flyer of a given size and wing shape. It can get rather complex, but the previous applications of the technique to pterosaurs were pretty simplistic, to the best of my recollection. Unfortunately, Chatterjee's estimates and assumptions regarding pterosaur launch and cruising ability had a number of problems, including some estimates of body mass that are probably impossible (like 70 kg for Quetzalcoatlus northropi).

I'll have to look at that actual paper before I form any opinions or critiques. Chatterjee has done a lot of good work, but I rather doubt the accuracy of some of his conclusions regarding pterosaurs (including body weights, relative muscle composition, and launch kinematic). This work may have fewer errors, but from the review article I am concerned that the launch model may be inappropriate. Specifically, launching for birds with low wing loadings is as much a leaping problem as a flapping one (especially for the early launch phase). The hind limb mechanics are critical in avian launch, and I noticed a lack of mention of any hind limb analysis in the review. That might just be an oversight of the Nat. Geo writer, though, so I don't want to jump to conclusions.

I'll grab the full paper tonight, and perhaps toss out some thoughts soon. I'd be quite interested to hear what others here think of the paper and the methods.

Cheers,

--Mike




On Tuesday, July 3, 2007, at 03:14 PM, Mark Hallett wrote:

Guy, Interesting news. I'm curious as to how the
researchers determined that A. couldn't, or would have
had trouble flying-- perhaps I'm remembering this
incorrectly or incompletely, but wasn't there an
aeronautics engineer who stated many years ago that
according to the laws of flight dynamics, a bumblebee
should in theory be incapable of flight? --Mark
--- Guy Leahy <xrciseguy@sbcglobal.net> wrote:

http://news.nationalgeographic.com/news/2007/07/070702-biggest- bird.html





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