[cap-talk] OT: Re: - theoretical/practical (Flight of the Bumblebee)

[Jim Dennis]

On Mon, Feb 27, 2006 at 12:31:25AM +0000, David Hopwood wrote:
 
> (I remember, even as a small child, being intensely irritated when told the
> anecdote that "Scientists Say That Bumble-Bees Can't Fly". It was quite clear
> to me that it was the anti-scientific views motivating the popularity of the
> anecdote, not any inadequacies of physics or of theory in general, that were
> more of a problem. See <http://www.keelynet.com/interact/archive/00001691.htm>
> for some discussion of this anecdote, and the mechanisms by which insects
> generate vortices to provide additional lift.)
 

 I remember having mostly the same reaction.  It was obvious to me
 that the aerodynamic models couldn't be that flawed (they work for
 planes, kites, etc) and it seemed obvious to me that this was a case
 of misapplying the equations to the wrong scale.

 Even as a little kid (less than 10 years old) it was obvious to me that
 the density of air in proportion to the mass of a housefly, bee or other
 insect make their "flight" far more akin to swimming than to aerodynamics 
 on the macro scale.

 Of course the theoretical work to model these micro-aerodynamics wasn't
 done until about 20 years later -- but I'm sure that the gist of it was
 obvious to anyone who applied any thought to it at all.

 Following the link you provided I notice that it doesn't include some
 of the most fascinating results from the recent research on the topic.
 In some issue of New Scientist or SciAm or some such I so some
 interesting diagrams and captions on the flight modeling of houseflies.
 From what I read the wing stroke is actually far more complex than
 you'd initially suppose.  It turns out that they generate lift and
 thrust on the backstroke as well as the forward/downstroke.

 Basically the wing flips over on the upstroke, and performs a sort
 of lemniscate (figure eight) arc, entraining some air flow into vortices
 back and down as the wings swing back just before they flip back over 
 for the normal forward/downstroke.  A few minutes tracing some arcs with 
 a fan and concentrating on how you can flip it eddge-wise for streamlined
 cuts through the air to position it for forward and backward flapping
 should give you the sense of how that all works on an intuitive level.

-- 
Jim Dennis