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PrairieDoug

Dacron vs. No-Stretch Lines

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The thread in Incidents about the recent hard opening at Skydive Dallas got me thinking again about the wisdom of using dacron lines to protect against hard openings.

Bill Booth had this to say:

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Again, I ask the question: Is the small amount of extra speed you get from jumping with "no-stretch" lines worth all the injuries, and fatalities, we are getting from hard openings nowadays?



So I was wondering how many jumpers use dacron vs. non-stretch lines.

In my case, I ordered spectra without being aware of safety issues. Will probably switch to dacron for next line set.

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My Sabre2 came with Spectra. Put 75 to 100 jumps on it, did some research, learned some details, cut the Spectra off and installed Dacron.

Made a difference.
"America will never be destroyed from the outside,
if we falter and lose our freedoms,
it will be because we destroyed ourselves."
Abraham Lincoln

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My Sabre2 came with Spectra. Put 75 to 100 jumps on it, did some research, learned some details, cut the Spectra off and installed Dacron.

Made a difference.



Did you notice any different in glide/forward speed?


No, but I do not do HP landings and I have it loaded enough that I am really moving anyway.
"America will never be destroyed from the outside,
if we falter and lose our freedoms,
it will be because we destroyed ourselves."
Abraham Lincoln

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Will probably switch to dacron for next line set.



Unfortunately pack volume is significantly larger also.
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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Unfortunately pack volume is significantly larger also.



IMHO, in occurance of tension knots is higher (w/ dacron) as well.

A q. for Bill Booth: If, as you claim, people used to get knocked out from hard openings, why do they now get injured instead of knocked out? It seems to me like openings in the old days were harder with dacron than we have now with no stretch lines.

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A q. for Bill Booth: If, as you claim, people used to get knocked out from hard openings, why do they now get injured instead of knocked out? It seems to me like openings in the old days were harder with dacron than we have now with no stretch lines.



Better canopy design. Better opening trims. It's also easier to make a small canopy open slower/softer than a larger canopy.


Cheers,
Travis

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Spectra is no-stretch now?
When did that happen? I know it stretches less than dacron but no-stretch? Are you sur you're not thinking of Kevlar line?
Spectra's low stretch attributes are the reason the lines stay in trim longer.
If the high stretch attributes are why you want dacron, then why not nylon line? They can stretch up to 20%!

The fact is there are many things that can be done to reduce opening forces. Going to a line that is less robust and bulkier seems odd to me.
I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet.

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Spectra is no-stretch now?
When did that happen? I know it stretches less than dacron but no-stretch? Are you sur you're not thinking of Kevlar line?
Spectra's low stretch attributes are the reason the lines stay in trim longer.
If the high stretch attributes are why you want dacron, then why not nylon line? They can stretch up to 20%!

The fact is there are many things that can be done to reduce opening forces. Going to a line that is less robust and bulkier seems odd to me.



Correct, spectra has more stretch than vectran/hma etc. But spectra goes out of trim almost as quickly as dacron, but dacron stretches permanently over time and spectra shrinks over time due to heat created by friction from the slider. Spectra IS nylon line. Dacron is polyester.


Cheers,
Travis

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Correct, spectra has more stretch than vectran/hma etc. But spectra goes out of trim almost as quickly as dacron, but dacron stretches permanently over time and spectra shrinks over time due to heat created by friction from the slider. Spectra IS nylon line. Dacron is polyester.




Mostly correct!

The one part that is not correct is Spectra goes out of trim FASTER than Dacron.

Dacron is also more consistent in regards to how much stretch vs number of jumps.

With Spectra, you just never know when it is out of trim unless you measure the lines regularly.


MEL
Skyworks Parachute Service, LLC
www.Skyworksparachuteservice.com

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I used to get "knocked out" quite often (but never "injured") jumping early ram airs without sliders. But they had NYLON lines which are very stretchy. I think the difference is the "speed of onset" of the opening force on the jumpers body. Think of falling on a bare wood gym floor. Then take the same fall with a 2" mat on the floor. The same force is applied, but the compression of the mat spreads it out a little, so the fall on the mat is less likely to injure you. Nylon, and to a lesser extent, Dacron lines work the same way to spread out the force a little. Because the force builds up more gradually, your body has more time to "get ready" for the peak, which is never as high anyway.

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With Spectra, you just never know when it is out of trim unless you measure the lines regularly.




very true indeed. I for myself don't like spectra except for closing loops.
;)
but it all depends on what you expect from your canopy. if you want performance I like vectran the best. it isn'tas bridle as HMA and doesn't go out of trim like spectra. for wingsuits I prefer dacron because I like fast openings.... i don;t mind the extra pack volume there. if you keep having hard openings it might be worth to pay a good packer to show you some tricks as well :$

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Spectra IS nylon line.



Buzzzzzzzzz. Incorect
Cored nylon line predates spectra. It is mostly seen coreless and used as closing loops. Nylon line had a very high elongation propertyof about 20%. This made it an ideal line in the days of old.

Spectra is an ultra high strength polyethylene fiber

Polyethylene Fiber — (Spectra currently produced in the U.S. by Honeywell) is one of the world's strongest and lightest fibers. A bright white polyethylene, Polyethylene fiber is, pound-for-pound, 10 times stronger than steel and up to 40 percent stronger than aramids. It floats, resists chemicals and water, and exhibits superior fiber-to-fiber abrasion.

Basically, nylon is a familly of synthetics not a specific material but when we talk about Nylon line in skydiving we are talking about type II or type V, not spectra.

Spectra is Olefin.
I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet.

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I just had two real points; first in skydiving nylon line is usually type II or V. Secondly, Spectra is olefin not nylon.

Now unless we have those in the textile field out there, the specific type of nylon will probably be useless. I know of about 75. There is a good chance that type II line is made from TypeII nylon!)

All you need to know is this;
1.)Type II & V are a nylon 6/6 line which is a poly amide base with an elongation of about 20%
2.)Kevlar is an aramid with very low resistance to abrasion. It's also a bitch to fingertrap and has very low elongation. It also breaks down quickly in UV light
3.)Dacron is a polyester base with an elongation of about 12-16%.
4.)Vectran is a a liquid crystal aromatic polyester noted for its thermal and chemical stability, moisture resistance, and high strength and modulus.
5.) Spectra is an olefin polyethylene fibre with an elongation of about 5% if memory serves. It is 40% stronger than kevlar and 4 time stronger than nylon.
In tests, nylon line fails after 550,000cycles
Polyester fails after 150,000 cycles
Kevlar after 25,000 cycles
And the big winner (you guessed it) Spectra with 675,000 Cycles!

And by the way, you can also make fabric out of Dacron, Nylon, Spectra and kevlar. Just a fun fact;);)
I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet.

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Teason,

Pure Cycles of the different fibers are not all that we are looking for in line material.

Also, as you may already know, changing the fiber, carrier and bundle count changes the strength of each material

In the case of Spectra,it may have lasted longer, but the desired length of it will have diminished well beyond the other fibers. So, In the parachute world it would not be the winner.

You remind me of my friend who is a chemist. This is his exact field.


MEL
Skyworks Parachute Service, LLC
www.Skyworksparachuteservice.com

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You remind me of my friend who is a chemist. This is his exact field.



Excactly. It's kind of absurd to go beyond the basic definitions of the different types of line. After a while it just becomes noise.
My real point was that Spectra isn't nylon and the lines all have different make up and properties. Strengths an weaknesses, if you will. I was replying to a "stump the wizard" question about the "type of nylon" in nylon line. Just trying to post a point.
I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet.

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I think you know what I mean. But just for the sake of answering the question, I Actually mean MIL-C-5040 type IIa (or just core Type, same thing) It is most commonly used for closing loops. I've also seen Type II used on handgliding reserves quite extensively (as well as spectra). Many other canopies used nylon line ranging from type I in pilot chutes, Type III on military mains, Type IV in early para foils and Type V in early paraplanes. Generally, "nylon line" cover all these types as well as the Mil specs you have mentioned.
Type IIa and V seem to be main ones I see, type V also being used in closing loops on Racers.

By the way when you say Dacron, do you mean flat braided......?:P
I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet.

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I had my Spectre relined with dacron about a year ago because the microlines I had had previously had shrunk so much that the brake lines were 8 inches too short and the canopy was no longer flaring adequately.

The dacron lines have improved the openings with only a very small increase in pack volume (hardly noticeable).

The dacron lines were cheaper than microline too!

It's an absolute no-brainer in my opinion! ;)

Vicki

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