I another thread,
"Mike McCrea" wrote in message
om...
I'd suggest a coated-nylon parawing. For just the two of you a 12x12
parawing would provide plenty of room for two bodies, some gear and
even a kitchen area...

A lot of years ago, a friend and I invented parawings, we doped out the
math, and we cobbled up a few with hand awls and duct tape. They worked as
intended. Beautifully.

Very shortly after that, the commercial versions started appearing, and I
eagerly bought successive versions, hoping for one that worked as well as
the prototypes but was lighter, more durable, and didn't look like it had
been stolen from a migrant camp.

Not to be, alas. Even though some come with grand sales fluff that talked
about 'hyperbolic paraboloids" and 'catenaries,' suggesting that the
designers really understand the stuff, the nylon itself reveals no real
grasp of the principles. Not the ones I've bought and tried to use anyway.

The functional requirements are pretty simple: produce a more or less
rectangular membrane that is taut everywhere when you pull the four corners,
one diagonal high and the other low.

The nylon topology you need to meet these requirements is pretty
straightforward: 1.) to get the membrane in tension at the edges, you have
to cut them in a curve that looks something like a catenary (the shape of
the main cables in a suspension bridge) and embed some kind of a tension
member in them, and 2.) tuck the membrane to produce the saddle shape (this
is where the 'hyperbolic paraboloid' comes in). In practice, whether you're
sewing nylon or ducttaping poly sheet, 2.) is accomplished by cutting strips
or patches in a shape that falls out of the topology, and joining them
together.

AFAICFigure it, no commercial wing gets 2.) right. If you do get it right,
the thing won't lie flat on the ground, and it's troublesome to fold, but
once it's up, it's a marvel of set-it-and-forget-it comfort even in some
pretty terrible conditions.

There. I feel better now.

Fred Klingener