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Stretching lineset back to trim

 

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EOCS  (C License)

Dec 28, 2012, 3:30 AM
Post #1 of 73 (4349 views)
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Stretching lineset back to trim Can't Post

Has anyone heard of taking a Spectra lineset and stretching it back into trim? this is something ive heard about and have a friend who is jumping a canopy with the lineset stretched and he said it was like a new canopy.

Does anyone have experiences with this good or bad?


phoenixlpr  (D 3049)

Dec 28, 2012, 3:59 AM
Post #2 of 73 (4286 views)
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Re: [EOCS] Stretching lineset back to trim [In reply to] Can't Post

I have seen seen this kung-foo once done.
I can't remember any difference in flight.
There is a better trick out there: get a new Dacron or Vectran line-set instead.


EOCS  (C License)

Dec 28, 2012, 4:06 AM
Post #3 of 73 (4277 views)
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Re: [phoenixlpr] Stretching lineset back to trim [In reply to] Can't Post

I totally agree, just the idea of the practice seems kind of radical. i would think it could decrease the strength of the lines. I did ask PD about it and they had this to say.

''What little you may gain will then be lost again right away as the lines continue to heat shrink. My best guess is that he is not going to accomplish anything beneficial.''

I asked about it possibly weakening the lines but there was no comment on that. makes sense as its not something they recommend doing at all...


GLIDEANGLE  (D 30292)

Dec 28, 2012, 9:27 AM
Post #4 of 73 (4158 views)
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Re: [EOCS] Stretching lineset back to trim [In reply to] Can't Post

i was taught how to do it by Brian Germain.

When I tried it on my Spectra line set, the results were unimpressive. i suspect that my technique was poor.

I suggest that you ask him for more info.


adumbelk  (C 39695)

Dec 28, 2012, 10:49 AM
Post #5 of 73 (4094 views)
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Re: [EOCS] Stretching lineset back to trim [In reply to] Can't Post

The amount of noticeable change will depend on how many jumps your lines have, and how fast the openings are.

I jump a monarch 155 and it can spank like the girl next door. After about 4-500 jumps on the lines I was getting way too many rough openings and was told stretching the lines might help. After I did that she opened like a dream again (well, as soft as she can open).

At the club I jump at, 7hills, we have a hook screwed into one of the wall support beams. I unhooked the risers and linked them to the hook and was able to pull on the lines with my entire body. The whole process took me about 1.5-2 hours, and I was dripping sweat by the end, but it made a big difference. Before I stretched them, they were uneven by as much as 1.5 inches in some areas, and afterwards they were all the same length. I have some pictures of the before and after that I will try to find later today.

The way I did it was to put a metal bar through the end of the lines where it attaches to the canopy and pull on it for a good minute. After a couple of lines were stretched, I realized I could lean my entire body back to stretch them without fear of the lines breaking.

If you are uncomfortable doing it, talk to your rigger, but if you are up to the task it can really make a difference for the last hundred or so on the lineset.

Edit: Attached the picture. I can't remember which lines these were and unfortunately I don't have an after shot (I wanted to make the first load) but you can see how out of trim they are. Honestly, if you have the money on hand it will probably be easier to get it relined, and if you are looking for improved flight characteristics you might not find much by doing this. But, if you are feeling ambitious and are comfortable with the idea, then give it a try.


(This post was edited by adumbelk on Dec 28, 2012, 11:01 AM)
Attachments: 2012-07-04_08-52-28_982.jpg (177 KB)


Premier ianmdrennan  (D 25821)
Moderator
Dec 28, 2012, 10:49 AM
Post #6 of 73 (4092 views)
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Re: [GLIDEANGLE] Stretching lineset back to trim [In reply to] Can't Post

In reply to:
i was taught how to do it by Brian Germain.

When I tried it on my Spectra line set, the results were unimpressive. i suspect that my technique was poor.

I suggest that you ask him for more info.

Reline the canopy.

If your car needed an oil change would you try and 'fix' the oil, or would you just do what needs to be done and change it.

I'm constantly fascinated as to how some people are looking for ways to cut corners on an article designed to save your life. I'd imagine you would frown on aircraft operators doing the same thing - why do it to yourself intentionally.

Ian


(This post was edited by ianmdrennan on Dec 28, 2012, 10:52 AM)


sundevil777  (D License)

Dec 28, 2012, 11:00 AM
Post #7 of 73 (4077 views)
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Re: [ianmdrennan] Stretching lineset back to trim [In reply to] Can't Post

In reply to:
In reply to:
i was taught how to do it by Brian Germain.

When I tried it on my Spectra line set, the results were unimpressive. i suspect that my technique was poor.

I suggest that you ask him for more info.

Reline the canopy.

If your car needed an oil change would you try and 'fix' the oil, or would you just do what needs to be done and change it.

I'm constantly fascinated as to how some people are looking for ways to cut corners on an article designed to save your life. I'd imagine you would frown on aircraft operators doing the same thing - why do it to yourself intentionally.

Ian

The use of crappy analogies is not needed. What would be useful is a study of the result of stretching. Does it affect the strength or some other property? Perhaps it is a very reasonable thing to do and the fear of some ill effect is unfounded. I'm not saying that I'd try it, but if others are willing to do some experiments, I'm open to the possibility of good results.


Premier ianmdrennan  (D 25821)
Moderator
Dec 28, 2012, 11:46 AM
Post #8 of 73 (4029 views)
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Re: [sundevil777] Stretching lineset back to trim [In reply to] Can't Post

Whatever blows your hair back.


(This post was edited by ianmdrennan on Dec 28, 2012, 11:48 AM)


dragon2  (D 101989)

Dec 28, 2012, 11:48 AM
Post #9 of 73 (4022 views)
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Re: [EOCS] Stretching lineset back to trim [In reply to] Can't Post

Well Brian Germain stretched the lines on my vengeance once, and it def improved the canopy for a bit (eventually I had to reline it of course).


Deyan  (D 322)

Dec 28, 2012, 12:49 PM
Post #10 of 73 (3988 views)
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Re: [EOCS] Stretching lineset back to trim [In reply to] Can't Post

In reply to:
Has anyone heard of taking a Spectra lineset and stretching it back into trim? this is something ive heard about and have a friend who is jumping a canopy with the lineset stretched and he said it was like a new canopy.

Does anyone have experiences with this good or bad?

This trick it's working only if you start stretching the lines from day one. What I mean is that if you have a new canopy and you stretch the lines every 30-50 jumps, you will have a good result. If you have a canopy with 4-500 jumps and you stretch the lines the trick would work for 5-10 jumps only.

My canopy has about 300 jumps ( Spectra 725 lines). Right now it's off trim by 2/3 inch. I'm stretching the lines twice per season ( which I found useless because the time I need for that is 45 min. to an hour and that mean I've spent 6 hours to keep the lines in trim. For the same time I can build my own lineset)

I can't comment on the strength of the lines. So far so good . I'll let you all know if I break a line .

After all, it's not worth the trouble. It takes time and if done wrong, it will give you funny openings or the canopy will not fly straight ( depend of the size of the canopy of course).
If your line set is new and you know how to do it , and you are willing to spend the time....go ahead. In any other case, reline is the answer .


Martini  (D 23756)

Dec 28, 2012, 4:29 PM
Post #11 of 73 (3890 views)
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Re: [EOCS] Stretching lineset back to trim [In reply to] Can't Post

I was also shown how to do this by Brian Germain. The difference it made on that canopy was remarkable. I've done it on several canopies, the results depend on how out of trim the canopy is. (more out of trim shows more benefit from stretching) The effect lasts remarkably long and the lines can be stretched more than once. Paraglider lines lose trim for a different reason but many pilots stretch their lines routinely 1-2 times per season.

Personally I believe that stretching Spectra parachute and paraglider lines 1-2 times per season is a good idea, keeping the lines tuned up between changes due to wear makes perfect sense as a maintenance routine. Parachute lines take me 30-45 minutes depending on condition. I don't worry about trim charts, the lines won't stretch past their original length. I'm primarily trying to attain symmetry, also working to stretch outside lines the most since they shrink the most due to slider heat.

Note that stretching does not work on HMA and Vectran. As always YMMV.


popsjumper  (D 999999999)

Dec 28, 2012, 6:08 PM
Post #12 of 73 (3846 views)
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Re: [sundevil777] Stretching lineset back to trim [In reply to] Can't Post

In reply to:
What would be useful is a study of the result of stretching. Does it affect the strength or some other property? Perhaps it is a very reasonable thing to do and the fear of some ill effect is unfounded. I'm not saying that I'd try it, but if others are willing to do some experiments, I'm open to the possibility of good results.

I'm with Ian on this. Everyone get off your cheap ass and do the right thing. You are seeing worst case here. People doing stuff with no factual back-up other than somebody's opinion. And no, just because it was Germaine doesn't make opinion any more valid without factual back-up.

We hammer students to never get involved in that flaky business and here we go doing it ourselves. Great example for them, eh?

And I am also with you in this: Leave it for the test jumpers. They will provide the answers whether or not the practice is safe enough and provides any value-added.


EOCS  (C License)

Dec 28, 2012, 6:30 PM
Post #13 of 73 (3837 views)
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Re: [EOCS] Stretching lineset back to trim [In reply to] Can't Post

Quite a few replies here with different opinions. Ive personally no need for new lines or stretching but am interested in the topic more then ever now.. I too would like to see some tests done to see if it actually changes the strength of the line. i personally dont have the equipment for it. Interesting idea and im hoping someone comes along with some data. Does anyone know if this is an old practice or something more recent. i would think the longer its been in use without problems the more reliable it is.

Thanks


Martini  (D 23756)

Dec 28, 2012, 7:31 PM
Post #14 of 73 (3818 views)
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Re: [popsjumper] Stretching lineset back to trim [In reply to] Can't Post

Here's a little fact: My lines are vastly closer to stock trim after I stretch them than before. This particularly applies to symmetry.

Safety-wise I am not aware of an increase in line breakage due to this practice. Broken Spectra lines seem uncommon even on badly worn linesets. If line breakage isn't a problem and openings, flight and landings are improved by better line trim then I would say safety is improved by using this technique. The only potential issue I see is brake lines snapping during a swoop, that would merit some study to see if there might be some vulnerability.

Value added? For 30 minutes of free labor (you can do this during a weather hold or whatever) your lines are in far better trim.

You're right about one thing, people are mostly too lazy to do this.

(edited to correct "break" to "brake" Wink )


(This post was edited by Martini on Dec 28, 2012, 9:20 PM)


talon2

Dec 28, 2012, 9:58 PM
Post #15 of 73 (3774 views)
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Re: [Martini] Stretching lineset back to trim [In reply to] Can't Post

yep ,when my tires go bald I rotate them .....what a crock


Martini  (D 23756)

Dec 28, 2012, 10:01 PM
Post #16 of 73 (3773 views)
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Re: [talon2] Stretching lineset back to trim [In reply to] Can't Post

Terrific analogy Crazy


pnuwin  (D 112233)

Dec 29, 2012, 1:47 AM
Post #17 of 73 (3715 views)
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Re: [Martini] Stretching lineset back to trim [In reply to] Can't Post

Are there any videos or tutorials for stretching spectra back into trim? How did you hang onto the end of the line and how much weight did you put on it?


Martini  (D 23756)

Dec 29, 2012, 9:49 AM
Post #18 of 73 (3613 views)
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Re: [pnuwin] Stretching lineset back to trim [In reply to] Can't Post

No tutorials that I know of. It would be nice if Brian spoke up here, he has by far the most knowledge on this technique. This subject isn't new, there are posts going back several years. I use as much weight as I can by sitting or kneeling on a carpeted floor and leaning back. I am careful not to stress the attachment point at the canopy fabric. I found that I could hold on better without pulling on canopy fabric by inserting a rod through the finger trapped line loop so the rod rested on the attachment material. I don't know if this is "recommended" practice but it seemed the best solution to hanging on to the line.

I use a different method on my paragliders, using a 40 lb weight suspended by a pulley I stretch each line to the same pressure for the same count (like 10 seconds). There seems to be less controversy in the PG world about this, not everyone does it but its pretty common.


timgaines  (C 107228)

Dec 29, 2012, 10:33 AM
Post #19 of 73 (3588 views)
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Re: [EOCS] Stretching lineset back to trim [In reply to] Can't Post

Not a rigger, but Spectra is basically a form of polyethylene. To make it into a line it gets drawn out into long thin fibres. During this process the long polymer chains that make it up essentially get 'untangled' and get arrange neatly in order (think more like uncooked spaghetti compared to cooked spaghetti).

When it gets heated (due to friction of the slider running down the lines) this gives these polymer chains energy to start tangling themselves back up. These tangled polymers take up less space than untangled polymers making your line shrink.

Once this has happened the quoted tensile strengths for the spectra has dropped along with its limits for elastic and plastic deformation.
Will stretching this new material will make the line substantially weaker than the original line? Yes.
Will this new, stretched line be within the tolerances of skydiving? Well it seems like people have done it and it works... there are comments that people in the PG community have done it but the big stresses for a parachute (opening shock) don't really happen much for a PG...


Martini  (D 23756)

Dec 29, 2012, 10:47 AM
Post #20 of 73 (3586 views)
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Re: [timgaines] Stretching lineset back to trim [In reply to] Can't Post

Quote:
Will stretching this new material will make the line substantially weaker than the original line? Yes.

Good to have info on this. What is your source? How much is Spectra weakened by heat shrinkage? How much further weakening is caused by stretching the shrunken line?


hookitt  (D License)

Dec 29, 2012, 10:49 AM
Post #21 of 73 (3591 views)
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Re: [Martini] Stretching lineset back to trim [In reply to] Can't Post

Personally, if I had known about rotating bald tires, I would have rotated them my entire skydiving career.I used to put a lot of jumps on Spectra and just dealt with the crummy trim. I believe it would have helped me. I would say the reason few people knows about it, is that many people will damage their own equipment so its not even brought up.

Edit. plus I'm sure there are rules that people do not want to break about the manufacturer's recommendations.


(This post was edited by hookitt on Dec 29, 2012, 11:02 AM)


phoenixlpr  (D 3049)

Dec 29, 2012, 11:41 AM
Post #22 of 73 (3558 views)
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Re: [hookitt] Stretching lineset back to trim [In reply to] Can't Post

In reply to:
I would say the reason few people knows about it, is that many people will damage their own equipment so its not even brought up.
I'd rather say Spectra is going out of fashion, HMA and Vectran are used on more and more canopies.


Martini  (D 23756)

Dec 29, 2012, 12:54 PM
Post #23 of 73 (3539 views)
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Re: [phoenixlpr] Stretching lineset back to trim [In reply to] Can't Post

Are you implying that my Sabres lined with Spectra aren't fashionable? Shocked


Martini  (D 23756)

Dec 29, 2012, 1:07 PM
Post #24 of 73 (3530 views)
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Re: [ianmdrennan] Stretching lineset back to trim [In reply to] Can't Post

Quote:
If your car needed an oil change would you try and 'fix' the oil, or would you just do what needs to be done and change it.

If your guitar was out of tune would you change the strings? More than likely you would tune the guitar by adjusting the strings many times before deciding to replace them.

In any event canopy suspension lines are a unique case, awkward analogies don't mean much.


popsjumper  (D 999999999)

Dec 29, 2012, 1:09 PM
Post #25 of 73 (3530 views)
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Re: [hookitt] Stretching lineset back to trim [In reply to] Can't Post

In reply to:
....I used to put a lot of jumps on Spectra and just dealt with the crummy trim...
Funny you should mention that.
I had a new line set put on and the rigger told me that the old set had so many jumps on it and was so far out of trim that I would have to re-learn flying and landing.
LaughLaughLaugh


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