Forums: Skydiving: Gear and Rigging:
Three Rings Grommet

 


Alvitz  (B 1596)

May 29, 2001, 5:24 AM
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Three Rings Grommet Can't Post

Question for riggers (and whoever has an opinion about the problem!!!!):

Lately I've been thinking a lot about a fatality happened about 1 year ago at a dropzone near where I lived: a highly loaded Stiletto deployed with a serious line twist. The guy tried to cut away, but the 3 rings sys was wrongly set up (2nd and 3rd both passing through the first, PULLING THE YELLOW CABLE THROUGH THE GROMMET). He deployed his reserve, that didn't entangle with his main but went immediately in downplane and hit the ground at about 50 mph.....

Now, my question is (besides all the obvious considerations that it is something to think about that somebody can get on an airplane with a rig in that conditions...) why the three rings grommet is so big to allow the yellow cable to be sucked in? Why isn't it half (or even less) of the diameter it is? There would still be room enough for the loop to pass through it without any hesitation and release the risers but not for the yellow cable to fold and get in.

Well, just a though. LET ME KNOW YOUR OPINIONS!

Deep Blue Skies

A.




DBTECH  (B 21186)

May 29, 2001, 9:11 AM
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Re: Three Rings Grommet [In reply to] Can't Post

With the rings assembled properly there is about a 25 to 1 "ring" mechanical advantage. (not considering the loop mechanical advantage of a nominal 2 X 25=50) If the small riser ring is passed through the harness ring, then the ring mechanical advantage is less than five, or less than ten at the release cable, as apposed to fifty with the rings assembled properly.

Dave Brownell



Craig

May 29, 2001, 2:01 PM
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Re: Three Rings Grommet [In reply to] Can't Post

In my opinion, why fix it if it isn't broken? The reason for the non-functioning release system was due to incorrect assembly. If this was happening to properly maintained riser/release systems then it would be important to look into the design and see how it could be fixed. Somewhat going along the lines of DB's post, if I remember correctly the white loop on the risers that retains the ring sees in the area of 5 pounds. In other words it requires about 5 pounds to hold the smaller ring in place when the system is loaded due to the mechanical advantage the 3 ring release system provides. Point being...make sure your rig is assembled properly and is in good working order. Always follow manufacturers instructions! If you choose not to you have just become a test jumper. Not a rigger, just my opinion.

Safe Skies,
Craig



PalmettoTiger

May 29, 2001, 2:37 PM
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Re: Three Rings Grommet [In reply to] Can't Post

In reply to:
In my opinion, why fix it if it isn't broken?
Well, it's more of an issue of "is it broken?" There are lots of ways to assemble and design parachute gear. Some of them are less idiot-proof than others. Example:
Some rigs allow the harness ring to fall down after the 2 riser rings have been released. This shouldn't be a problem because everyone is supposed to LOOK at their reserve handle before they yank on it. However, that's not always how it happens; a post here a while back mentioned that during suspended harness training, people were hauling on that harness ring as if their life depended on it. Just because people didn't follow instructions doesn't mean we shouldn't modify gear to reduce the possibility of that mistake.

I'm not saying you're wrong or that riser grommets need to be modified (I can't quite visualize the issue at hand), it's just that any modification that reduces the possibility/catastrophic potential of human error is worth looking into.

Blues, squares,
PTiger

*insert witty sig here*


Craig

May 29, 2001, 3:29 PM
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Re: Three Rings Grommet [In reply to] Can't Post

While I agree that making gear safer and less "idiot proof" is good for everyone sometimes I feel as if it can be "overdone", for lack of a better word. A couple examples...

Integrity (reversed) risers were manufactured because there was supposedly more webbing strength without adding a hole through the riser and installing a grommet. While this part may have been true, the change made to the release system on the risers could cause hard or in some cases impossible pulls, or in some cases the rings would fail to "tumble" and release the risers in a low drag belly to earth position.

The two sided RSL system was invented to prevent main/reserve entanglement in case of standard RSL Ty 17 riser breakage IIRC. Later it was found that with the dual RSL's could somehow result in a snag up and entanglement themselves, not allowing a cutaway main to fully release...fixed one problem, but created another.

Lastly there is Reflex's "Catapult" system. While I am not real keen on the specifics, the system used to aid the reserve in deploying in a situation where you have a reserve PC or bridle horseshoe actually caused some problems. Like I said, I am not real sure on the specifics, but recall that jumpers had their "catapult" removed due to some problems with them.

As our gear progresses and we get more innovative there will likely be problems to come. Look at your example of the harness ring flopping down, or microline and container grommet snags. Sadly enough jumpers will likely die due to the progressing of our sport skydiving gear for one reason or another. While new designs can be tested and re-tested, add in the human factor and flaws will surface and the cycle continues.

Blues,
Craig



Premier slotperfect  (D 13014)

May 29, 2001, 5:10 PM
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Re: Three Rings Grommet [In reply to] Can't Post

Anything that is designed well and put through a significant testing process will consequently perform well if used correctly. "Idiot proof" connotes that NOBODY can screw it up. That's nearly impossible in most cases. As Bill Booth says, "the idiots are smarter than I am."

Use the piece of equipment as it was designed, and it will work as it was designed. An incorrectly assembled 3-ring assembly that caused the cable to be sucked through the grommet does not warrant a redesign. Rather, it warrants better education for the person using it.

As far as the lad who was spied getting ready to board the plane with the misrouted 3-ring - that's a strong case for spending some time with your Rigger to gain a basic education of how gear functions and why. Even if you never want to be a Rigger, it might save your life or someone else's. Of course if it was his Rigger that hooked it up, he has other issues to overcome first!

As for me, I hope you are looking at my gear as well, because I will be looking at yours. Let's take care of each other!

Check your gear before you put it on - every jump. Get a gear check before you get on the plane. Check your gear before you exit.

Respectfully,
SP


Alvitz  (B 1596)

May 30, 2001, 1:11 AM
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Re: Three Rings Grommet [In reply to] Can't Post

PalmettoT.,

You got exactly what I was thinking about when I started this thread.

Yes, the three rings system is fine as it is and, analizing that accident, the FIRST point is really not why the yellow cable was sucked in the grommet but how/why somebody can, not only board, but dive out of an airplane with his rig so badly assembled.

However, the point I was trying to focus is exactly "idiot proofness": IMO we should never, ever, stop working on that! Even if it could look like a lost battle...

(Always) respectfully

A.



riggerrob  (D 14840)

May 30, 2001, 7:52 AM
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Re: Three Rings Grommet [In reply to] Can't Post

The price of freedom is eternal vigilance.




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