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Re: 11th specimen of Archaeopteryx



On Oct 27, 2011, at 5:00 PM, David Marjanovic wrote:

>> This is certainly not impossible, but it should be noted that any
>> model suggesting a "limited flapping" precursor needs to consider the
>> potential for appropriately manipulating vorticity on the wing (and,
>> in this case, rapidly increasing circulation and abruptly reducing it
>> - otherwise, the animal loses more than it gains). I have yet to see
>> this even whispered in the literature with regards to early birds,
>> which is pretty concerning.
>> 
>> Cheers,
>> 
>> --Mike H.
> 
> By "increasing circulation", do you mean a downstroke or an upstroke or...?

I mean increasing the circulation component of the airflow over the wing.  
Producing lift requires that a circulation component be added to the 
translational flow.  In order to push up and forward more than down and 
backwards, a flapping flyer needs to have more circulation produced on the 
downstroke than on the upstroke.  The tricky bit is that those changes don't 
happen instantaneously.  In fact, those changes in vorticity on the wing can be 
quite sluggish (relatively speaking) without special kinematic mechanisms for 
rapidly changing circulation patterns.  This important characteristic of 
flapping flight is rather under-appreciated in most paleontological 
examinations of animal flight.

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