Re: Flying birds

Date:         24 May 99 01:52:33 
From:         Don Stauffer <>
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?

If one were to measure the pressure under a heavier than air flying
object one will find that the downwash exists that eventually creates a
slightly higher pressure on any surface below the object.  Now, in free
air that field extends theoretically to infinite distances.  However, in
a completely enclosed container, the integration need only be carried out
over the cabin floor.  When the birds are in flight, the pressure on the
floor will be somewhat above ambient, so the plane will weigh the same.

Don Stauffer in Minneapolis