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Re: Science feather strength debate

On Nov 1, 2010, at 8:28 PM, Erik Boehm wrote:

> If the wing is generating lift, and the bird has just completed a downward 
> stroke, would not the wings rise back up? In a fixd wing aircraft, if your 
> wing spar is too weak, and snaps, the wings "fold up"
> Sure, powering the up stroke could increase the flapping rate, and provide 
> forward thrust too, but I can't believe it if flapped its wings down, that 
> its wing would just stay that way, with massive anhedral.
> I don't see the lack of a powered upstroke as a convincing argument against 
> some form of flapping behavior (I can see it as an argument about the upper 
> limits to what sort of power it could get by flapping)

The wings will tend to rise passively via lift, yes, but this is not 
necessarily sufficient.  The upstroke for flying animals is more than a 
positional reset; during slow speed flight, for example, it is also used to 
pull the wings out of circulation.  In some gaits it is also important the the 
upstroke occur in less time than the power stroke.  Furthermore, while derived 
birds have kinematic solutions to build circulation quickly at the beginning of 
each power phase (that is, countering Wagner Effects), there is still some 
delay in generation of full lift (not to mention that some of the WE counters 
require elevation of the wing) - this means that a bird that could not raise 
the forelimb above the shoulder might have had difficulty in building much 
circulation on a given power stroke.


--Mike Habib

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