"Michael Daly" wrote in message
able.rogers.com...
On 30-Jan-2004, "Fred Klingener" wrote:

I think a simple square of fabric supported across the diagonal
between
two trees and stretched across all four corners corners, two to the
trees and two to the ground, works almost as well and is much simpler
to
fabricate.

'Almost.' Which is the whole point. The square, rigged as you
describe, is
slack in the middle, will flap in the wind, and will collect rainwater
and
snow. Hence the interest in topology.

That's right. To convert a flat rectangle into a hyperbolic parabaloid
you have to get the fabric to sustain shear normal to the plane of the
fabric.

Typo? You mean shear in the plane?

You can do it with an elastic solid, but it just can't be done
with a fabric. Hence the cutting and shaping.

Most fabrics will shear to a degree, coated fabrics somewhat less, but you
also need differential stretch. You have use Lycra (do they make waterproof
Lycra?) or else preset the deformation pattern you need with kite-shaped
tiles.

Do you know of a commercial wing that has it right? Any I've seen have the
right ad copy but are flat-cut.

Fred Klingener