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

and embed some kind of a tension
member in them,

See..thats the whole problem..I just want something that doesnt require
any poles because I almost always camp where there are trees and the
poles add a lot of weight. Not so much of a problem in the boat but I
also like to use my equipment for hiking.
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. True, it does not take advantage of the arch effect of a
catenary parabaloid, but it doesn't need to. I find it hard to believe
that the only company that sells such a thing is Campmor and their price
is too high. A big square of rain fly material with a few loops or
grommets should do the job just fine...for less money.

"steveJ" wrote in message
...
and embed some kind of a tension
member in them,

See..thats the whole problem..I just want something that doesnt require
any poles because I almost always camp where there are trees and the
poles add a lot of weight.

Don't need no steenking poles. Unless you have hiking poles or your canoe
pole breaks down.

Nuthin' in my rant that said anythin' 'bout poles. I use mine poleless
whenever I can.

Not so much of a problem in the boat but I
also like to use my equipment for hiking.
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. A properly done wing will be quiet
and stable in the wind, will shed water reliably, and will shed snow with a
kick from below.

True, it does not take advantage of the arch effect of a
catenary parabaloid, but it doesn't need to.

If you don't think so, then you're all set with a tarp. People have been
happy with flat tarps for centuries. Civilization marches on.

I find it hard to believe
that the only company that sells such a thing is Campmor and their price
is too high. A big square of rain fly material with a few loops or
grommets should do the job just fine...for less money.

I haven't seen Campmor's, so I don't have an opinion. I conspicuously
avoided mentioning brands.

Fred

So what's the "tension member" if not a pole?

Fred Klingener wrote:
"steveJ" wrote in message
...

and embed some kind of a tension
member in them,

See..thats the whole problem..I just want something that doesnt require
any poles because I almost always camp where there are trees and the
poles add a lot of weight.


Don't need no steenking poles. Unless you have hiking poles or your canoe
pole breaks down.

Nuthin' in my rant that said anythin' 'bout poles. I use mine poleless
whenever I can.


Not so much of a problem in the boat but I
also like to use my equipment for hiking.
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. A properly done wing will be quiet
and stable in the wind, will shed water reliably, and will shed snow with a
kick from below.


True, it does not take advantage of the arch effect of a
catenary parabaloid, but it doesn't need to.


If you don't think so, then you're all set with a tarp. People have been
happy with flat tarps for centuries. Civilization marches on.


I find it hard to believe
that the only company that sells such a thing is Campmor and their price
is too high. A big square of rain fly material with a few loops or
grommets should do the job just fine...for less money.


I haven't seen Campmor's, so I don't have an opinion. I conspicuously
avoided mentioning brands.

Fred

"steveJ" wrote in message
...

Fred Klingener wrote:
"steveJ" wrote in message
...

and embed some kind of a tension
member in them,

See..thats the whole problem..I just want something that doesnt require
any poles because I almost always camp where there are trees and the
poles add a lot of weight.


Don't need no steenking poles. . . .

So what's the "tension member" if not a pole?

Sorry for the engineering bull****. The 'tension member' can just be a cord
or cable passing through a tunnel sewn in the edge. Just like the hardware
store blue tarps, except, to make the membrane work, curved.

Fred

"Fred Klingener" wrote in message m...

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.

I'm feeling pretty good about having bought a relatively inexpensive
($80) no-name Campmor wing 4 or 5 years ago. Campmor doesn't seem to
sell that 'wing anymore (I don't see it in their catelogue anyway);
too bad, 'cause I believe they got it right.

The one we have is a simple 16x16 and it does everything you say about
a correctly designed parawing. It's drum tight when erected properly,
ain't no way it'll lay flat on the ground (it is more or less
impossible to fold up; we usually fold it about half way and then just
kinda crunch and stuff).

I'm sold on the functionality of a parawing though, and can't imagine
going back to a flat tarp*. The only downside I've found to a parawing
is the reduction of covered space due to the shape and necessity to
have two corners set low - I find our 16x16 provides just enough space
for four people, a kitchen area and a small bit of gear.

* Although we still carry a blue poly 8x10 piece of junk for rough
uses I wouldn't subject our 'wing to, using the poly job as a cover
for the woodpile, or ground tarp for staging gear when packing or
unpacking, or set up vertically as a windbreak...