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From: Henry Spencer <>
Subject: Re: unstable craft (was Re: Aerospike engine...)
Date: Sun, 8 Mar 1998 03:21:09 GMT

In article <6dqgl0$hhf$>,  <> wrote:
>Well, there are theories about forward swept wings reducing drag
>in transsonic or supersonic flight... they're aerodynamically unstable.

The problem with forward sweep is not instability so much as aeroelastic
divergence:  when they flex up, their angle of attack increases (versus
conventional sweep, in which it decreases), which tends to make them flex
further.  Putting in enough stiffness to fight that tendency makes them
unacceptably heavy if built with conventional materials.  But you can do
strange things with composites, and in particular you can build a wing
which will twist as it flexes, avoiding the problem.  The X-29 was built
to test that concept in flight.

Unfortunately, as I understand it, the X-29 didn't work out all that well.
The tailored composites in the wings worked okay, but overall performance
of the forward-swept wings wasn't nearly as good as people had hoped, and
the concept no longer looks particularly attractive.
Being the last man on the Moon                  |     Henry Spencer
is a very dubious honor. -- Gene Cernan         |

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