Re: Flying birds

Date:         24 May 99 01:52:34 
From:         Matthew Willshee <mjw44@cam.ac.uk>
Organization: University of Cambridge, England
References:   1
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John Gunnar Enebak wrote:
> You fill a cargo plane with 20 tons of birds, and fly 500 knots at
> 10.000 feet with the birds sitting on the floor of the plane.
>
> Suddenly all the birds start flying around inside the plane. Will the
> plane then loose 20 tons of weight and start a climb?

No - because the birds are held up whilst flying around the plane by a
pressure difference across their wings.  This leads to a pressure force
on the floor of the plane that is higher than that on the roof.  The
weight of the birds is felt through this pressure force.  Each bird's
weight is spread out over a very large area as a very small increase in
pressure, so you can't detect the pressure rise.

Matthew Willshee

--
Matthew Willshee                             E-Mail: mjw44@cam.ac.uk
Churchill College, Cambridge, CB3 0DS              : 96mjw@eng.cam.ac.uk