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Re: Arms into wings




Ralph W. Miller III wrote:

> It is well known that the airfoil shape is perfectly suited to the task of
> providing lift on the wing of an animal or vehicle which is propelling itself
> forward.  This ubiquitous shape is evident in avian primary remiges and 
> rectrices
> (feathers), in the shape of the bird wing itself, as well as all manner of 
> other
> forms (including airplane wings, frisbees and propellers).  To demonstrate the
> effectiveness of the airfoil (to a classroom of first grade students), I 
> fitted a
> styrofoam (polystryrene foam) airfoil shape with straws which enabled the 
> form to
> go smoothly up or down a set of brass rods.  The styrofoam rose with ease 
> when an
> electric fan directed a stream of air at the airfoil.  I had also attempted 
> the
> same with a flat block of styrofoam, for comparison, and it failed to rise.

There may have been a problem with your initial flat plate angle of attack.  
Flat
plates and cambered airfoils both have the same lift increment with increasing 
angle of
attack (CL increases by approximately 0.1 with each degree of AOA increment).  
The only
difference between flat plates and cambered airfoils as lifting devices is the 
AOA of
zero lift, the CLmax value, and a bit of drag.

> The funny thing is that the airfoil rose whether the breeze was directed 
> toward the
> fore or aft end, as the curve remains atop the airfoil either way!  (On the 
> other
> hand, an upside down airfoil wouldn't work at all)!

Actually, it will -- and quite handily at that.  But the AOA is increased by 
twice the
AOA of zero lift.

> Hence even a symmetrical feather would produce some lift; the familiar 
> airfoil shape
> of modern avian flight
> feathers is "merely" an important refinement.  The _Caudipteryx_ feather style
> would therefore confer some degree of aerodynamic function, in spite of its 
> less
> than optimal shape.  In actual flight, the trimmer leading vane of an avian 
> fight
> feather would be sturdier in the face of the wind, and would be easier to 
> control
> than the broader vane (were the feathers to be reversed on a bird).

Yep, you're quite right.  It's also well known that the significant advantage 
of the
asymmetric feather is in the reduced biological cost of the molt rather than 
the minor
mechanical energy cost of flight due to the extra weight of the symmetric 
feather.

JimC

> --
> Ralph W. Miller III  <gbabcock@best.com>