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Re: Senter 2006, Confuciusornis, and humeral mobility



On Mar 24, 2011, at 12:31 AM, Jason Brougham wrote:

>> I already did the calculations; they're actually pretty easy.
>> Granted, I'm just doing a rough version.  However, the results are not
>> promising for powered flight with a non-elevated forelimb.
> 
> Hmm. Interesting. By "not promising" what are we talkin', percentage wise?
> How much more lift would we need, you know, given a range of finger
> flexibilities from 10 degrees at each of the two finger joints to 90
> degrees at each of the finger joints?

Interesting question.  I'm getting roughly 33% too little force to effectively 
push against drag, assuming a profile drag coefficient similar to a modern 
mid-sized bird (crows).  To answer your question, what we'd need to do is 
estimate the amount of additional speed at the primaries for each of those 
joint flexibilities, and add that to the distal acceleration.  I just ran it 
for 5 and 10, and neither was enough, but that's not surprising because it 
doesn't really add much acceleration.  Of course, this is only talking about 
the distal wing, anyway.  Granted, the distal wing provides most of the 
propulsive force, but the inboard wing still needs to generate substantial 
circulation.  If span-wise flow can be initiated by a big snap at the hand this 
might help, but it needs to be a big snap and early in the wing cycle.


> Also, in your calculations, how many of the primary feathers, and thus how
> much of the wing area, did you put on the first phalanx, how many on the
> second, and how many on the metacarpal? Give me the numbers of feathers
> and the surface area of each that you plugged into your equations so I can
> check them out for you.

I did not break it down that far; I have a wing area of 0.12 m^2 and a span of 
1.2 meters (using quite a large specimen I measured in 2007).  I have feather 
measurements for that specimen, as well, but I just did it quick and dirty - 
using what I have, I get that about 30% of the wing area is hand wing.  I just 
built in the potential excursion by adding some acceleration to the hand wing.  
It isn't actually necessary to get the lift per feather unless we're doing a 
feather bending strength analysis.  I'm taking it for granted that the feather 
strength was sufficient (going with the rebuttal paper, as it were).  Any data 
checking you can provide would be excellent.

Cheers,

--Mike H.


Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181