Hot slider grommets melting slinks and risers

[sundevil777 102]

I've noticed areas of slinks and the top of risers looking "polished".  At first I figured it was due to physical wear from long term contact with vibration from the slider flapping, but later realized it is from the grommets being hot due to line friction, and partial melting of the material. Now protection is provided with large link covers/slider stops similar to what you might see on a tandem rig.  

I use wide risers, do those using narrow risers not experience this so much because their slider comes farther down the riser before stopping, perhaps spreading out the transfer of the heat?  Do my Dacron lines perhaps generate more heat than the newfangled types? It seems the Dacron lines themselves do not suffer.

[riggerrob 643]

Dacron line will generate more friction and heat.

The short-term solution is vet-wrap around your Slinks and the upper ends of your main risers. Ask your local horse trainer where he/she buys their vet-warp.

The longer-term solution is closely inspecting your lines, slider and risers every 50 jumps.

[Veis 29]

It's still more interesting. The slider involves: aerodynamic drag, friction of the lines against rings or grommets, and friction of the lines among themselves. Some manufacturers compensate for the deficit of the first at the expense of the rest. Including by limiting the small diameter of the hole. Previously, the function of the slider was mainly to put in order the opening - and now it is mainly to regulate its dynamics. Therefore, friction began to be used more, and sometimes excessively. So, rommets made of brass, which have a greater thermal conductivity than stainless steel, are unsuitable. And stainless steel grommets, especially thin-walled ones and with an acute insufficient contact surface, manage to get very hot in local spot.

In my opinion, the grommets in the slider are a vestige from which it is high time to be in the main parachutes.

Edited May 20, 2024 by Veis

[parachutist 2]

I've experienced this (15 years ago) with a 120 canopy loaded 2.1. The field level was 4500'.  Openings were fast and the mini risers were getting shiny then eventually crunchy on the upper surfaces.   Lines were HMA

Edited May 23, 2024 by parachutist

[skydiverek 63]

On 5/7/2024 at 2:11 AM, sundevil777 said:

I've noticed areas of slinks and the top of risers looking "polished".  At first I figured it was due to physical wear from long term contact with vibration from the slider flapping, but later realized it is from the grommets being hot due to line friction, and partial melting of the material. Now protection is provided with large link covers/slider stops similar to what you might see on a tandem rig.  

I use wide risers, do those using narrow risers not experience this so much because their slider comes farther down the riser before stopping, perhaps spreading out the transfer of the heat?  Do my Dacron lines perhaps generate more heat than the newfangled types? It seems the Dacron lines themselves do not suffer.

 "Do my Dacron lines perhaps generate more heat than the newfangled types?"

Correct.

Also, PD says not to use Slinks on long lines (tandem canopies, student canopies) because of heat generation (regardless of line material).

 

.

[kleggo 145]

On 5/18/2024 at 2:16 PM, riggerrob said:

 

The short-term solution is vet-wrap around your Slinks and the upper ends of your main risers. Ask your local horse trainer where he/she buys their vet-warp.

 

or your local CReW enthusiast.

[Veis 29]

On 10/5/2024 at 7:41 PM, skydiverek said:

Also, PD says not to use Slinks on long lines (tandem canopies, student canopies) because of heat generation (regardless of line material).

PD are not looking for easy ways. It is enough to use monolithic stainless steel buckles that absorb heat well - instead of thin-walled grommets. This solves not only the heating problem, but also the lineset resource, the slider resource, and the opportunity to get more productivity from the slider for better openings.

Initially, grommets were used for slider rings because they were cheap, easy to install and did not carry a heavy load. This is not the case now. Grommets that serve well on tandems are expensive (like Rutgerson), and require a powerful press to install.

Edited October 9, 2024 by Veis

[skydiverek 63]

6 hours ago, Veis said:

PD are not looking for easy ways. It is enough to use monolithic stainless steel buckles that absorb heat well - instead of thin-walled grommets. This solves not only the heating problem, but also the lineset resource, the slider resource, and the opportunity to get more productivity from the slider for better openings.

Initially, grommets were used for slider rings because they were cheap, easy to install and did not carry a heavy load. This is not the case now. Grommets that serve well on tandems are expensive (like Rutgerson), and require a powerful press to install.

 

Would they be heavier?

 

 

.

[Veis 29]

1 hour ago, skydiverek said:

Would they be heavier?

HD-grommets are already comparable in weight to buckles. We have long switched to buckles for all uses, removable and non-removable, including tandems. And we do not see any use for grommets, except for reserves.

[SethInMI 173]

11 hours ago, Veis said:

HD-grommets are already comparable in weight to buckles. We have long switched to buckles for all uses, removable and non-removable, including tandems. And we do not see any use for grommets, except for reserves.

will you share an image of the buckle and slider?

[dudeman17 335]

17 hours ago, Veis said:

we do not see any use for grommets, except for reserves.

Is that because the TSO requires it, or is there a functional advantage?

[riggerrob 643]

Mains need those thick stainless steel grommets because they make a thousand or so jumps on the same slider and grommets. I expect a tandem main to last 1,000 jumps.

OTOH Tandem reserves rarely suffer 20 deployments during their service life, so can get by with thinner brass grommets. Thin brass grommets do not last 1,000 jumps in the gritty California desert. Sand and salt get imbedded in suspension lines and they act like sand-paper on the inner edges of grommets. When they wear completely through a single layer of brass, the sharp edge start to chew suspension lines. I have had to replace dozens of brass grommets after they developed sharp edges.

[Veis 29]

23 hours ago, SethInMI said:

will you share an image of the buckle and slider?

This is in the discussion about RDS:

We use unified buckles for removable and non-removable sliders.

[Veis 29]

17 hours ago, dudeman17 said:

Is that because the TSO requires it, or is there a functional advantage?

First of all, this is interference in someone else's product, on which people's lives depend. The manufacturer of the reserve will not assume safety  guarantees for such a product, just as we cannot.

The exception is for the main tandems, when it is impossible to prevent hard openings by other means. Are no good reason to interfere with reserves, as Rob wrote above.

Old: https://rutube.ru/video/private/72f7094ed91266ac99db0dfde15b7d34/?p=wIJx5DaGwW-xyQRo6P8TRg&r=plwd

New: https://rutube.ru/video/09356081ac863ee7eb5d667ef3251e88/?r=plwd

 

Edited October 11, 2024 by Veis

[kcaero 3]

So how hot do the grommets get??

[riggerrob 643]

20 hours ago, kcaero said:

So how hot do the grommets get??

Hot enough to melt the surface of nylon risers.

If you jump partially-melted risers long enough, they will eventually fail. Statistically they are most likely to fail during opening shock. In the worst case scenario, they fail during your last turn onto final approach.

No need to take a well-understood risk. Budget the money to replace tandem risers every 300 to 600 jumps.