climbing/skydiving - sailing/flying

[brianvh]

For the record, I pinned her despite the biting. She may have beat me in arm wrestling.

And you may be a big ole dumbass, but you're MY big ole dumbass.

[Tad Eareckson]

But we digress...

Brian,

C'mon. From Post 1 I've stated that the harness suspension replacement was a done deal. Installed, flown, climbed, landed, bonked.

I've done some more testing and found that with 40 millimeters worth of one inch webbing overlap I can hold two thousand pounds. That's a bit of tedious work with the needle and nylon floss but it ain't that huge of big freakin' deal to replace harness suspension and maintain a lot of overkill. I'm sure that Sunny and his sewing machine could do a similar job in seconds.

Yeah, again, maybe not worth a replacement but stop making the new ones wrong.

I don't have wind tunnel privileges, I'm not an aerodynamics genius, and that's the best I can do to squeeze a little more performance out of ships whose design plateau has probably been pretty much maxed out. I'd be surprised if the really hot 2018 comp gliders look radically different from today's crop.

Yeah, I'd forgotten what a wire crew was and wasn't thinking fingers. So far only my nose guy suffers but it's mostly the wing folk upon whom one's survival is dependent.

David,

Another thought...

Yeah, but flying a competition glider reduces both comfort and safety a LOT. The instructors don't start their students out on bladewings.

But if you're going all out for performance...

[brianvh]

One more safety note. Rock climbers know they want some stretch in the ropes, because the deceleration on falling is inversely proportional to the amount of stretch. Theoretical zero stretch means when you fall back into the suspension after a bump you experience theoretical infinite acceleration and infinite force, and one little bump will break the suspension. If you have 1/3 the stretch, you'll be stressing the suspension by 3 times as much force every time your wires go snap when falling out of a thermal.

So you may need a lot more stitching than you think. In fact, the elasticity in the stitching may be the only thing that's keeping you from sudden failure.

[Tad Eareckson]

Brian,

Rock climbers are arresting falls of up to a couple of those ten meter platforms we were just watching in Beijing.

If I get dumped so bad I bounce off the keel I still can't fall as much as three and a half feet.

Climbers, as I said to begin with, are anchoring themselves to granite.

We're anchored to a frame of light weight, flexible, hollow tubing (aluminum and/or carbon) stretching a sail which billows under load supported by a medium of a nitrogen/oxygen(/carbon dioxide) atmosphere which compresses easily and gets out of the way fast. There is no freakin' way we can deliver much of a shock load to our suspension.

And - as Janni pointed out - we're using all that stuff to lift a water balloon.

We've got way more elasticity than we're ever gonna want or use and need not deliberately add to it.

The elasticity of the stitching is just plain microscopic. I test loaded a few overlaps to the point of failure and found I could get about 1400 pounds out of a square inch. The two segments of webbing don't start moving with respect to each other as you're approaching failure - they stay put until they instantly explode.

On my harness I've got two (count 'em - two) 3500 pound overlaps to keep me connected to an eighteen hundred pound glider. I'm sleeping just fine, thank you. If anything is going to suddenly fail it's gonna be the same spar that would've snapped anyway.

[Flying Lobster]

Rope elongation in a climbing rope is essential--this is what limits the ultimate impact force to the fixed protection--not to mention the climber. Protection is almost never the solid piton in granite that Tad cites. More often, it is a small nut or cam fitted into a crack or weakness in sandstone or limestone which is vulnerable to directional shock loads. If the protection pulls--climber go splat.

Stretch characteristics among/between synthetic webbing materials is so negligible that there is no statistically significant difference between the materials other than their ultimate shear/breaking strength. In other words, there is no benefit in terms of shock/impact force absorbtion through elongation.

Webbing is also vulnerable to abrasion and cutting when loaded--this is almost entirely independant of it's ultimate load failure strength. It also generates heat rapidly when rubbed against another surface--easily attaining a melt temperature which can accelerate failure.

If you feel the odds are that your suspension will remain unfettered in an upside down spinning wreckage--then by all means make your hang strap out of dental floss.

marc

[Tad Eareckson]

Marc,

Yes - that's my point.

Because climbers are anchoring to a totally inelastic medium and are engineering to absorb the energy of long falls they wanna use nylon between themselves and their little steel doohickeys.

Because we are anchoring ourselves to fairly elastic gliders supported in an extremely elastic medium and are desperately trying not to dissipate energy - we don't.

If you believe that there is negligible difference in stretch characteristics between synthetic webbing materials try this little experiment...

Use fifty feet of nylon webbing to bungee jump off the bridge.

Repeat using an equal length of Spectra. If you were still conscious after you stopped you'd probably be able to watch your fillings disappearing into the New River Gorge.

I'm not sure what the relevance of Paragraph 3 is. Abrasion is not an issue in hang gliding suspension.

I have very little interest in remaining attached to upside down spinning wreckage - so I have no idea what point you're trying to make there.

"Dental floss" is another way of saying "nylon thread". My suspension isn't made of dental floss - yours and everybody else's is.

My suspension is made of polyester. It is - however - stitched with dental floss 'cause:

it lends itself well to hand sewing; and
I've got a theory that - because of its elasticity - the loads end up better equalized between stitches.

Brian,

You wanna talk elasticity in glider tension bearing elements? Let's look at the sidewires.

Ever hear the expression "wire slap"? We don't need elasticity in those wound strands of stainless steel 'cause the rest of the glider takes care of it just fine. Those things - by the way - are good for no more than a thousand pounds and are typically not the first parts to blow when the Gs start going way out of specs.

[brianvh]

You're right Tad, it's not correct to compare the effects of pulling ropes against solid rock surfaces versus unfixed moorings. But the strength arguments still apply, even if not mathematically precise. If suitably overstrength though I guess it wouldn't matter.