Why do sliders have different size grommets (related to "A first look at a no pull cypres save")

[riggerrob 561]

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councilman24

... There is a number 10 brass grommet that might have been used. I haven't done much with tandems so don't remember.

"

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I have replaced a "whole hockey sock's" worth of brass #8 slider grommets on Strong-built F-111 tandem mains.
ZP tandem mains tend to use the similar-sized stainless steel grommets.

[skydiverek 58]

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That being said soft links do provide some advantages and SOME tandem system / parachutes allow slinks to be installed. These are different from the normal sport versions (I believe they use a stronger line in there manufacture).

Check out this whole thread for more info on Slinks nad tandem:

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?do=post_view_flat;post=3326440;page=1;mh=-1;;sb=post_latest_reply;so=ASC

[Deyan 31]

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In fact I'm looking at the PD slink instructions which make no reference to tacking down. Simply states "Tuck tab away"

That said, with the slink being approved under a TSO C23d. The installation should be done in accordance with manufacturer's instructions. Whether container, parachute or slink. The PD instructions do not then require it to be tacked and I may have reservations about doing some of these modifications without manufacturer explicitly stating this.

The fact that its not stated by the manufacturers in there installation instructions is probably a good indication that tacking is not required.

Look further in the manual
PD res.manual rev.F page 35

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The first 15-20 deployments will cause the Slink to take a more permanent “set”. It is important to ensure that the tab is located
between the risers during this period so as to insure this set occurs with the tab in the proper position. Once this has occured, the
Slink will have a tendency to remain in this position. If this procedure is not followed, the tab may rotate out of position. Allowing
the tab to remain outside of the risers during deployment and flight will result in excessive wear of the Slink, potentially leading to
structural failure.
Note: Should you find that the tab does not remain in place, PD recommends tacking the tab to insure it stays locked between the risers

It's not mandatory, just recommended in case they don't stay in place.

"My belief is that once the doctor whacks you on the butt, all guarantees are off" Jerry Baumchen

[skytribe 16]

My personal thought that there are few advantages for tandems especially mains. I don't need to pull the slider down and the standard metal links supplied by the tandem manufacturer seem to work fine and be easily maintainable.

How main metal links have failed which have that were not found to have been overtightened or worked loose(not tightened) ?. Something that can be made more visually obvious with some Loctite and a visible mark to make it easier to determine if they are starting to loosen up.

For tandems this make things easy to inspect each time. I think slinks are more difficult for packers to do a thorough inspect each time. I wonder if use of vectran as lines would effect heating issue (ie is there less friction) or the material used for slink being made or something with a higher melting point.



I'm wondering if the issue is less with vectran lines.

[skytribe 16]

Thanks for the confirmation that tandems use #8 grommets.

I also to a look at Paragear, the largest grommet / die that they sell (or at least list in the catalogue is a #8). Which leads me to believe that it is probably unlikely any common use of grommets bigger than this on current skydiving gear.

[pchapman 262]

skytribe

Which leads me to believe that it is probably unlikely any common use of grommets bigger than this on current skydiving gear.

While rare in general, there have been some accuracy canopies that at times have used large D-ring shaped slider rings, sewn to the corners of the slider.

These are some sort of custom welded assemblies that are slider rings but not acutally grommets.

They allow pulling a large slider down behind one's head, even with full width risers. This is in place of having the old split slider system to allow the canopy to spread out. I don't have any good photo handy, but I've seen in on a number of ParaFoils including my own.

[Deyan 31]

Hi Peter,

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I don't have any good photo handy, but I've seen in on a number of ParaFoils including my own

Hint: Check PD's Zero manual

"My belief is that once the doctor whacks you on the butt, all guarantees are off" Jerry Baumchen

[skytribe 16]

I'd seen these Rings on some old accuracy canopies. But not so much these days - perhaps split sliders or RDS are a different solution, to allow for wider riser spread.

Technically these are not grommets but are used in place of.

I'm sure there are other old/strange setups as well but the reality is these are not particularly common (you may see at DZ's that have a accuracy community - Do you know if these were these supplied from factory with these slider rings or was it a jumper modification and if you order one now how do they come equipped.)

[skytribe 16]

PD obviously still use the Slider rings.

That's one unusual setup but its probably fairly familiar to the accuracy crowd. ;-)

[Beatnik 2]

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When sliders were invented, ram air canopies became much more practical.

The slider was invented in 1948 long before ramair canopies were on the market. It was originally used on rounds and later adapted for use on square canopies. They weren't invented for ramairs, they were adapted to them. Just wanted to make sure the correct historical information is presented.

[3mpire 0]

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Is it rotating and coming out ?. If it has, have you rotated it back in and it occurred again. If its not coming out then I would question whether you need it.

Sorry for the delay -- it is not coming out every jump but I would say every five jumps or so when I'm repacking I see that it is peeking out (maybe 1/2 the tab visible) so I tuck it back in. The slink is fairly set, probably just a hair off of where it should be. So it isn't a situation where the slink is rotated 90 degrees from where it should be, however it does annoy me that I still can see it from time to time.

The thought of the hand tack was that it would just prevent it from coming out at all

[masterrigger1 2]

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Two soft links have failed in the USA.
The first failure occurred shortly after soft-links hit the American market, during the last 1990s. It was blamed on a brass slider grommet that had a sharp edge. The slider grommet had been damaged by hitting a metal link too many times. When they installed soft-links, they did not bother to inspect the brass slider grommets and ignored a rough edge that eventually cut the tab off the soft-link.

Koji's accident occurred a decade - or so - later. Koji did a thousand or so jumps on a main canopy, without inspecting it. A frayed soft-link failed when he was too low to deploy his reserve.

Rob,
Koji's accident was due to the fact that he was re-using his slinks after ever canopy reline.

He had two Crossfires that he alternated in and out of the shop about every 3-4 months.

Yes, That is right. He was doing some serious jump numbers with those canopies.

He would send them in with the lines cut just above the risers.
We would then reline them and send them back to him where evidently he was re-using the same worn out slinks.

This is what bit him; lack of slink inspection, not canopy inspection!

Cheers,
MEL

Skyworks Parachute Service, LLC
www.Skyworksparachuteservice.com

[riggerrob 561]

Which is why I always insisted on new SLinks every time I re-lined a canopy.

[skytribe 16]

When you think about it the link and the lines are made of similar material (Yes I know slinks are spectra and the lines could be vectran or HMA) and therefore it sounds pretty logical that if one is worn out and need replacing the other probably does as well.

[3mpire 0]

I would guess slinks would wear even faster given the fact that all the energy is focused on such small area where as individual lines probably individually have much less energy (more distributed).

Is that an accurate assumption?

[skytribe 16]

Every line wears - some more than others. The outside lines tend to wear quicker than some of the others. This may be evident with spectra lines going out of trim due to the heating effect of slider. BUT when a lineset needs replacing then you generally replace the whole lineset rather than just a line or two. Generally all the lines will be showing signs of wear.

I haven't seen wear on slinks any faster than on other lines, but the tandem issue identifies a potential problem which means slinks should be periodically inspected for signs of wear.

So I would guess the additional 30 bucks on a new set of slinks should just be considered as part of the cost of a reline for jumpers. RiggerRob's advice to change slinks at time of reline sounds extremely sensible.

[riggerrob 561]

Beatnik

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When sliders were invented, ram air canopies became much more practical.

The slider was invented in 1948 long before ram-air canopies were on the market. It was originally used on rounds and later adapted for use on square canopies. They weren't invented for ramairs, they were adapted to them. Just wanted to make sure the correct historical information is presented.

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Yes, Floyd Smith got a patent in 1945, but it was several more decades before anyone figured out how to make a slider work on a round. The problem is that rounds do not inflate well with solid sliders.
The only old rounds - that I can remember - with sliders were a few Para-Commander class canopies (e.g. Sparrow) that had "X" sliders.
Yarbenet re-invented to slider - for squares - during the mid-1970s.
After that, Ballistic Recovery Systems invented a donut-shaped slider, with mesh in the middle and a ring of fabric.
BRS sells ring sliders on their heavier and faster all-airplane recovery systems.
Circa 1998 Butler invented his "Sombrero Slider" with a small, domed canopy in the middle, surrounded by a ring of mesh. Butler had the same idea as BRD, just reversed the mesh and fabric. Butler sells Sombrero Sliders on Pilot Emergency Parachutes and a variety of military cargo chutes.

[wmw999 2,165]

Actually it was the Starlite that had the X slider -- I don't believe the Sparrow did. I had (and loved) a Starlite for years, and learned to love definitive openings with it.

Wendy P.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)