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ramon

New HMA lines snapped !!!!!

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>Point is they are supposed to be tested at much..much greater weights..it is
> called "over design".
That is just one small part of how a canopy is loaded. Deploy it at a higher altitude, or in a track, or pack it with the slider not right up against the stops - and that margin you rely on goes away. Heck, that's why there's a margin to begin with - to deal with other than normal situations. Overloading a canopy cuts into that margin even before you take into account a poor pack job (for example) and is just not that great an idea.
>If they say 5 lines snapped because he was close to max suspended weight, I
>would never buy a canopy from that company...
Both PD and Precision have broken lines on canopies that have been overloaded, and both have stated that overloading the canopy might have contributed to the problem.
-bill von

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hook,
you are correct about why hma is not cascaded.
common paraglider construction technique was not to bartack hma but to glue using cyanoacrilate and sometines a ziz-zag stitch on a 2" side by side overlap.
also remember:
-a single fiber of hma loses up to 60% of its strength after only 4 hours of bright sunlight exposure.
-hma has 1/8 the elasticity of spectra.
sincerely,
dan
atair

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***
-a single fiber of hma loses up to 60% of its strength after only 4 hours of bright sunlight exposure.
-hma has 1/8 the elasticity of spectra.
***
Both of which can explain why a line snaps. 4 hours of sunlight exposure isn't too hard to get. Low elasticity means it won't tolerate shock loads too well. Spectra is already pretty inelastic...if HMA is less so, I would expect it to not like rogue hard openings much.

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>4 hours of sunlight exposure isn't too hard to get
It is hard to get - on every fibre in the bundle, and usually rope would get some UV absorbing stuff on it as well. Only outer ones would get the direct exposure.
PA claimed to have line sets with well above 1000 jumps on it. So probably UV is not an issue. Abrupt failure mode - with little visible defects, may be an issue.. Hm..
And somehow I doubt the 60% figure. Sources?
Why not to use kermantel construction, or some UV absorbing dye?

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It is hard to get - on every fibre in the bundle, and usually rope would get some UV absorbing stuff on it as well. Only outer ones would get
the direct exposure.


It doesn't have to be on every fiber in the bundle to reduce the strength of the line. Maybe the overall loss of strength in the line will be much less, say 20%, but remember we are dealing with lines that are 350-440 lb breaking strength. Lose 20 % of that, then subject it to a shock load (ie hard opening or uneven loading)...that low elasticity comes into play, and you have a broken line.
Maybe 60% is excessive, maybe not...cobaltdan gave that number. I'll let him supply a reference.

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>It doesn't have to be on every fiber in the bundle to reduce the strength of the line.
As I said - theoretical data is useful as long as it is backed up with experiment - and PA experiments show quite a good life span. I assume they test broke that 1000 jump linesets..
That would be a good reference - table of experimental breaking strength parameters, done at reline time - cobaltdan should have something like it, as he seems well informed.
Maybe manufacturers should just publish tested strength of linesets sent to him for relining - a good subset of them at least..
Climbing webbing was tested like that frequently, very educational (especially break strength of webbing left to rot for few winters - at the knot.. still god knows how often a failed to back it up.. ;))
And that for sure is not the only type of line to break.
Maybe people do not stove them too well? So thin and slippery? Like double fisherman not on spectra cord does not work..

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and PA experiments show quite a good life span. I assume
they test broke that 1000 jump linesets..


I am not familiar with PA's tests. I would guess that the line set that lasted 1000 jumps was taken well care of. I doubt they laid it in the sun for 4 hours before/during the 1000 jumps. Maybe they did.
Quote

Maybe people do not stove them too well? So thin and slippery? Like double fisherman not on spectra cord does not work..

I would believe this. Stows on HMA have got to be TIGHT...I would bet there are quite a few rigs out there with loose stows, which could contribute to a hard opening, which could contribute to a line breaking.
I mentioned elsewhere that testing done by a manufacturer is good, but may not be conclusive. The people who run those test know what they are doing, and if they don't intend to, might bias the results because they don't make stupid mistakes like the average jumper does. When you put it in the hands of the average consumer who is NOT and engineer, aerodynamicisit, rigger, canopy designer, etc., new problems are bound to come up.
Who knows? HMA is still new. As I said before, Time will tell.

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but with 30 second canopy ride (assuming all hop n pops on a highly loaded canopy which they probably were not).
1000 jumps is 30000 seconds exposure to UV light. 4 hours is only 14400 seconds so the PA test canopy got plenty of UV light and it can still be cloudy for UV to affect things. A paraglider gets much worse exposure to UV and from what I understand HMA was in use in paragliding in europe.
It is also in widespread use in sailing where there is plenty of UV and stress and strain from jibbing (turning the boat and switchig the sails through the pulleys and winches etc) although the strains and stress may not necessarilly be the same as a hard opening....but if a line breaks while your sailing...BFD :D
ramon
"wee girls on a skydive road trip on big bikes...... yikes, dykes and bikes kinda thing...... ", David McKelvie

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"It is also in widespread use in sailing where there is plenty of UV and stress and strain"
You need to compare apples with apples...the line construction for sailing and climping ropes is a completely different weave construction known as kernmantle.
The fibres in the kernel of the rope provide about 80% of the strength, then there is a woven sheath,or mantle on the outside to protect it. This design makes a very resilient rope.
Engovatov suggested manufacturing suspension lines like this earlier on in the thread....I think it would work if the technology could be mastered to keep the lines thin....
"but if a line breaks while your sailing...BFD" true if you are pootling about at the weekend regatta......OTO.....
If you are solo somewhere in the southern ocean, and you lose your mast because of it, you will probably die..... :(.....But point taken.....
"I might bend my hat in the process, but I'd still teach that guy a lesson or two" David Lund......

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I have the canopy at my house now. I plan on taking some pic’s and posting sometime.
My guess is line dump. I stopped counting after six broken lines. None of the breaks were at or close to the stitching, mostly directly in the middle of the line. Most of the broken lines are on left side, including all of the three sized lines. One of the left steering cascades broke, and the right steering line broke at the toggle loop. One line broke at the leading edge of one of the center cells then tearing the cell about three feet. One of the center line’s binding tape tore directly from the attachment point.
I would blame the lines until I noticed the steering lines, binding tape, and torn material. We plan on sending the canopy back to Precision soon.

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Holy $#!+!!! Who jumped that again? Is he okay? I haven't even had a hard opening in 200+ jumps on my 98.... Those larger sizes must be totally different animals.
If it broke that many lines, tore fabric, tape, and stitching, I'm sure that opening would have affected any canopy-- lined with Spectra, Vectran or aircraft cables!
If it was line dump, then I'm glad I've been using small super-bandz and skybands. Nothing else will hold the lines tightly.
Jason

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Kernmantel line .... Yeah, just like 400 lb type II and 550 type III nylon on T-10 and C-9 military rounds! :D This discussion probably could have taken place in the eighties when they first tried to use kevlar lines. (if the internet existed) I still service one hobbit reserve with them. They too started to break routinely and unexpectedly after use in the field and were withdrawn from mains. Maybe we should all go back to Pegasus's, 7 cells, F-111, and Dacron. ;)

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I've got 70 on my 98 with soft openings everytime... I also use small skybandz. single stow behind grommets and double stow up the bag 1" each. I also keep it the hell out of the sun as much as possible.
I get the impression something went real wrong with the way this canopy was packed and/or deployed if it blew out one side of the canopy... ie. one riser hanging up on the reserve tray or something so the thing was way assymetrical by time it got out of the bag...
Anyone know if there is something to coat HMA with to retard UV damage???
-Hixxx
"Woman... Wu -mon... Whoa - man! She stole my heart and my cat"

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