why did kevlar lines go away?

[lyosha 46]

Just curious what about kevlar made it a poor choice and why the world went to dacron/spectra/vectran/hma.

[mark 102]

The line sequence was: 

1. sheath-and-core
2. dacron
3. kevlar
4. spectra
5. vectran/hma

Kevlar has poor abrasion resistance.  It is also skinnier than dacron, so less friction in slider grommets and harder openings.  Also, kevlar doesn't stretch much, so less shock absorption than dacron.  

[pchapman 261]

To humbly expand a bit on Mark's statement:

The wear & abrasion (to itself) issue was the big problem that people talked about. It was all a bit before my time, but Kevlar didn't work out on main canopies, while it was used on a few early ram air reserves, where the frequency of packing was less. (As the OP may know, but I'm just giving a bit of history.) It also was used for a while for high strength reinforcements -- Like reinforcement circumferential bands on lightweight National Phantom round reserves, or being used as reinforcement tapes in ram-air reserves, or being used as the reserve closing loop for the then-popular Racer rigs. I guess it was the first 'extra strength' material out there in use!

Kevlar is "an HMA", a high modulus aramid, but must be formulated & woven in a different manner than our current HMA lines which last better. (Although clearly they have their wear issues too, if made really skinny...)

So Kevlar had a real wear problem. While for the other things Mark mentions, it was more a case of "being ahead of its time" rather than being inherently deficient  -- We didn't all have stainless  grommets to resist abrasion, and canopy designs & packing techniques weren't ready either. Just like the early days of Microline / Spectra, where there were more problems with instant openings, broken risers, too small sliders, etc. 

Thus part of the whole problem was the changes in rigging technique & design needed, for the new material.  Here's an example from a 1980 [Edit: corrected. Not '85]  CSPA rigger's bulletin, where they quote GQ Security (which produced the Unit ram-air canopy, some of which had Kevlar lines) on some of the pitfalls for riggers to watch for:
 

Quote

 

 

We have received numerous telephone calls and written inquiries concerning field refit programs of canopies with Kevlar suspension lines. Kevlar, which is an ara­mid fibre such as Nomex, was primarily used up to this point for reinforcing cords in automobile tires.

Several things should be understood about Kevlar. Kev­lar has zero (0) elongation characteristics. Kevlar should NEVER be used for a round canopy suspension line set. Kevlar is also very strong and has a much higher breaking strength than a similar denier nylon braided or twisted cord. Kevlar has very, very little resis­tance to abrasion. We feel that local experimentation should be discouraged.

 

 

Ram Air canopy owners interested in having Kevlar line conversion should be urged to contact the manufacturer of their canopy for specific information. Some of the information that they must know is:

                 1.       Kevlar cannot be successfully finger trapped.

                 2.       Zigzag stitching of Kevlar is particularly tricky.

                 3.       Steering lines may be made of Kevlar down to the lower control line portion. Lower control lines should never be made of Kevlar because of the constant running through rings. Also, the constant daisy‑chaining of brakes would cause Kevlar used at that point to wear out very rapidly and possibly break.

                 4.       People owning canopies equipped with Kevlar lines must be constantly vigilant to inspect the entire metal surface of every grommet on their slider after every jump to insure that it is not nicked, pitted or roughed‑up in any way. Grommets found to be damaged in any way should immediately be smoothed off with a very fine grained emery paper. The same procedure would apply to Rapide links.

 

 

Local riggers must be discouraged from purchasing bulk Kevlar lines and attempting to design and install line sets on Ram Air Canopies using the normal techniques applied to coreless, braided lines made of nylon or dacron. We are fully aware that every holder of a Master Rigger's rating feels that he is qualified to make this type of alteration and the technical judgements required. We are stating, categorically, that we feel that this is not the case and that if this practice is allowed that it may have serious or even fatal conse­quences in some cases. We are enlisting the aid of the C.S.P.A., U.S.P.A., the Safety and Training Committee, the P.E.I.A., and all Conference Directors in assisting us in this effort.

G.Q. Security Parachutes, Inc. will not sell Kevlar line sets or bulk Kevlar to be used on any canopy but a Unit and only in cases where we know the qualifications of the individuals making the request.  We hope that other manufacturers of Ram Air canopies will take the same measures.

 

Edited April 9 by pchapman

[lyosha 46]

For context, I'm asking because these guys use kevlar for plane attachment straps (kind of like the "risers" of the system)

https://brsaerospace.com/

And when I asked them "why kevlar?" they mentioned it was more abrasion resistant... which I found odd.

Edited April 9 by lyosha

[pchapman 261]

Yeah, I don't know all the in's and out's of Kevlar abrasion resistance, in particular how old Kevlar lines got a poor reputation for degrading so quickly. Was it because of Kevlar on Kevlar between lines? Or a lot of flexing with say coarser weave lines? Or the formulation of Kevlar at the time?

Certainly Kevlar doesn't tend to get for example the same 'line burns' that spectra or nylon might, being more resistant to heat and that kind of abrasion. (E.g., in Kevlar reinforcement on some kill line bridles.) Kevlar is better in that way.

[JerryBaumchen 1,048]

3 hours ago, lyosha said:

For context, I'm asking because these guys use kevlar for plane attachment straps (kind of like the "risers" of the system)

https://brsaerospace.com/

And when I asked them "why kevlar?" they mentioned it was more abrasion resistant... which I found odd.

Hi Iyosha,

Re:   it was more abrasion resistant

Every day, all over the world, engineers are working on development/improvement of 'whatever.'

We do not live in a stagnant world.

Jerry Baumchen

Mech Engr, Ret'd

[fcajump 153]

On 4/9/2024 at 11:45 AM, pchapman said:

Yeah, I don't know all the in's and out's of Kevlar abrasion resistance, in particular how old Kevlar lines got a poor reputation for degrading so quickly. Was it because of Kevlar on Kevlar between lines? Or a lot of flexing with say coarser weave lines? Or the formulation of Kevlar at the time?

Certainly Kevlar doesn't tend to get for example the same 'line burns' that spectra or nylon might, being more resistant to heat and that kind of abrasion. (E.g., in Kevlar reinforcement on some kill line bridles.) Kevlar is better in that way.

While I've packed a couple reserves that had Kevlar lines, I don't know the ins/outs of the issue well...

What I was told at the time is that it was a two-stage issue:
 - Kevlar lines would abrade the metal components (brass slider grommets / steering guide rings) until there was a sharp area where it metal component has worn

 - that sharp area would then cut the Kevlar fibers.

Justification for use on the reserves was that they were strong/low-bulk and acceptable for low-use items where the abrasion issue would take much longer to present itself.

JW