New Safety Video: "Pilot Chute Kill Line Maintenance"

[BrianSGermain 1]

This one came out great, please watch and share:

https://www.youtube.com/watch?v=GA0Wqs8c7-8

Wishing you many happy landings,
-Bri

New Instructional Video: "Navigation and Accuracy Secrets":
http://bit.ly/1MWONby

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[TEB6363 0]

Nice information about Kill Line Maintenance Brian..

For those of us who don't keep Cypres Silicone in our back pocket; do you have another recommendation..?

I have used several different types of silicone for automotive window seals, belt drives on RC helicopters, etc. But, would not want to just start trying stuff on my bridle..

Thanks..

Once the plane takes off, you're gonna have to land - Might as well jump out!!

[BrianSGermain 1]

That is a great question. It is likely that any food grade silicone lubricant will work, but I have only tested it with the product furnished by our friends at Airtec. It is readily available from any dropzone rigger, gear dealer or directly from Airtec.

Keep in mind, you only need a bit...

-Bri

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[jerolim 7]

Once again great advice from you.

I just wanted to add that you don't have to use gun cleaning rod, you can use small fingertrapping fid to reinsert a new kill line. You have to bunch bridle "skin" over fid and to remove some "skin" from end of the fid. This way fid with new kill line travels from end to another,...

Together with sewless fingertrap method http://www.jumpshack.com/default.asp?CategoryID=TECH&PageID=Nosewtrap&SortBy=TITLE_A you can replace kill line in field (if you have a spool of spectra with you).

[BrianSGermain 1]

This is true. I am in favor of methods that do not require and new tools. A power tool also works for re-threading the bridle. Best yet, lubricate the kill line and yo wont have to replace it for a long, long time.

Bri

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[peek 20]

BrianSGermain

... It is likely that any food grade silicone lubricant will work ...

Brian, the idea of using the same silicone lubricant that we use on reserve closing loops is very good. That stuff is thick and sticky, so it should last longer than the thinner silicone sprays.

I have noticed that a lot of people refer to using "food grade" silicone, but the only difference in that and any other kind of silicone spray is that it is less toxic if some of it is ingested. (I verified this with a chemist.)

Folks, don't lick your kill line!

[BrianSGermain 1]

The CYPRES silicone is used on spectra every day, so I figure it is the right stuff. Just make sure that stuff stays far away from your closing loop and pin. A horseshoe may ensue.

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[Hooknswoop 19]

I replace my spectra kill line with vectran day 1. I use vectran for my kill line the same reason we use it for canopy lines. I don't ever have to worry about it shrinking and my PC not fully inflating.

Derek V

[BrianSGermain 1]

I have done the same with good success, however the friction in the bridle is higher and can damage the bridle itself, so silicone is just as important in that case.

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[mathrick 2]

Why not something like dacron? It seems to have the properties we want, and since kill line shouldn't (?) experience significant loads (plus dacron's stretchy), its lower strength for the same bulk compared to spectra wouldn't matter that much.

"Skydivers are highly emotional people. They get all excited about their magical black box full of mysterious life saving forces."

[uer16 1]

While we're on topic, what recommendations are there regarding the material? (I.e. what kind of Spectra is it by default, and what can it be substituted with).

Specific example: I have 400lb Dacron and 725lb Spectra, would either of these work? Both seem to be around 2x the bulk of whatever is in the PC.

[gowlerk 1,904]

Quote

Specific example: I have 400lb Dacron and 725lb Spectra, would either of these work? Both seem to be around 2x the bulk of whatever is in the PC.

And that is why neither of there are appropriate. Bridles with kill lines are already bulkier than the ideal. That's why we keep making them out of lighter and lighter materials over the years. The current commonly used materials offer a balance between bulk, strength, and longevity. The bridle/pc system is a high wear item that needs periodic replacement. Yes, you could use a stronger, more durable kill line. But they already often outlast other parts of the system. If you were to lubricate it periodically it would almost certainly outlast the p/c.

Always remember the brave children who died defending your right to bear arms. Freedom is not free.

[mathrick 2]

I meant more specifically the shrinkage aspect, rather than more general "longevity". If a kill line is worn out and breaks on deployment, that is a bummer, but you still have a functional deployment system. If it shrinks too much and you fail to catch that, it will look normal but the deployment won't be, and will lead to a potentially very serious malfunction. If both types last the same number of jumps, the one that breaks visibly but works correctly up until that point is the safer one.

What kind of strength does a kill line need to have? If we were to halve the bulk of the Dacron line to match typical spectra, we have ~200lbs left, which is still 2.5x the pull force of a PC. My naive understanding certainly would believe that to be sufficient.

And related, why is a thinner bridle better? Is it only about the lifting weight the PC has to contend with, or are the physical dimensions also important? If the latter, I'm rather surprised, as reserve bridles are purposefully made wide (not, as the urban legend has it, to replace a failed lift by the PC, but to stabilise it once the PC has caught air).

"Skydivers are highly emotional people. They get all excited about their magical black box full of mysterious life saving forces."

[gowlerk 1,904]

Usually the Spectra kill line is constructed about 1.5 inches longer than needed to allow for later shrinkage. This means that the pc is slightly less collapsed when new than it will be after it's broken in. That is a design compromise. Design is always a series of compromises. Your kill line can not shrink so much that it will cause deployment failure. If it did shrink that much you would notice that your pc no longer can be fully cocked. The use of Vectran would eliminate the shrinkage problem, but would wear the bridle quickly. Dacron is bulky and that bulk would cause the BOC pouch to stretch more. The strength needed for the kill line is not generally considered to be a limiting factor. But Dacron in thin sizes, although probably available from the mill, is not commonly used in rigging as it is not strong enough for canopy lines. There is a strong tendency to use materials that are already commonly used because they are familiar.

The physical dimensions of the bridle are only important for bulk considerations and for drag in canopy flight. CRW bridles are usually 1000 lb Dacron, the pc does not collapse but instead is retracted to lie on top of the canopy.

Always remember the brave children who died defending your right to bear arms. Freedom is not free.

[uer16 1]

gowlerk

The current commonly used materials

Specifically, what kind of material is the standard kill line made of and where can one get some?

[mathrick 2]

gowlerk

Usually the Spectra kill line is constructed about 1.5 inches longer than needed to allow for later shrinkage. This means that the pc is slightly less collapsed when new than it will be after it's broken in. That is a design compromise. Design is always a series of compromises. Your kill line can not shrink so much that it will cause deployment failure. If it did shrink that much you would notice that your pc no longer can be fully cocked.

It has another failure mode, however, where the line hasn't shrunk enough to be impossible to cock, but it will uncock very easily during the course of normal packing. Of course, you can and should spot this, but we're talking about skydivers here. "Guaranteed to develop problems which can be spotted if the owner is diligent" is always worse than "unlikely to develop problems in the lifetime of the system, and if it does, it will be obviously but harmlessly broken". Maintenance burden would be similar (or possibly less, if Dacron lives long enough to outlive the PC fabric, which it should because I expect the actual loads on a kill line to be way lower than the design pull force of the PC), but the failure to maintain & operate properly would lead to much less dangerous outcomes.

Additionally, kill line shrinkage has the even more insidious and dangerous property of being a creeping change on top of the already creeping PC wear. So a fairly worn out (but still mostly cockable) kill line will exacerbate a fairly worn out (but not yet cheesecloth) PC, possibly resulting in PC in tow or nasty line twists, whereas a non-shrinking one will keep the problem to worn out PC fabric only.

gowlerk

The use of Vectran would eliminate the shrinkage problem, but would wear the bridle quickly. Dacron is bulky and that bulk would cause the BOC pouch to stretch more. The strength needed for the kill line is not generally considered to be a limiting factor. But Dacron in thin sizes, although probably available from the mill, is not commonly used in rigging as it is not strong enough for canopy lines. There is a strong tendency to use materials that are already commonly used because they are familiar.

So, to make sure I'm perfectly clear on this, the reason is not so much "it can't be done with 200lb Dacron", but rather "nobody has done it with 200lb Dacron before, so everyone is going to be very cautious about even trying"? Understandable, but in that case, why wasn't it tried back when kill lines were being introduced (and manufacturers warned about mounting a kill line system of any kind), when all materials were a novelty by definition? The shrinkage is a well-known property of Spectra, and surely if you're willing to invent and try completely new materials like Spectra or Vectran for structural lines, you could consider using a slightly different variety of the already well-known and widely-used material like Dacron for non-structural applications where Spectra has obvious downsides.

I'm not saying that it definitely can be done, but if we're spending time and effort educating people about the dangers of shrinkage and manufacturing slightly out-of-specs components to offset it, then it'd be really nice to know that somebody smart has investigated the possibility and rejected it for reasons that I failed to consider, and not "it's the way it's always been done".

"Skydivers are highly emotional people. They get all excited about their magical black box full of mysterious life saving forces."

[gowlerk 1,904]

uer16

***The current commonly used materials

Specifically, what kind of material is the standard kill line made of and where can one get some?

500lb Spectra, Paragear.

Always remember the brave children who died defending your right to bear arms. Freedom is not free.

[gowlerk 1,904]

Those could all be considerations. If you don't maintain your equipment you can have failures. But I think you don't really understand the degree to which a pc needs to be collapsed before it will fail to be effective. A pc is never "mostly cockable". If you can cock it to the point that the limiting tapes are stretched out, it is good. If you can not do that, it is not good and needs repair or replacement.

Basically, there has not been a problem in this area, so no one is searching for a solution. Like I said, design is a series of compromises. What you propose could be tried. If you like you could try it yourself. But really, this is mostly a winter day thought exercise.

A pc will generally not become cheesecloth as a wear mode. If it's made from ZP material it will never fail in that way. If it's made from f-111 type material it should be large enough to allow it to still be effective after hundreds of uses. Usually the limiting tapes fail, or the handle attachment, or the mesh gets torn, or the bridle wears at the other end, or the kill line breaks or the tape the bridle is made from wears from the kill line. Some of these problems can be fixed, but usually when one of them shows up, the others are near. At that point the overall condition of the system indicates the best solution is replacement.

Always remember the brave children who died defending your right to bear arms. Freedom is not free.

[mathrick 2]

Somewhat tangential, but I've heard that ZP is not commonly chosen for PCs because it tends to be significantly less forgiving of inexact PC geometry. Is that (still?) true?

"Skydivers are highly emotional people. They get all excited about their magical black box full of mysterious life saving forces."

[Hooknswoop 19]

Quote

The use of Vectran would eliminate the shrinkage problem, but would wear the bridle quickly.

I have not experienced this.

Derek V

[gowlerk 1,904]

mathrick

Somewhat tangential, but I've heard that ZP is not commonly chosen for PCs because it tends to be significantly less forgiving of inexact PC geometry. Is that (still?) true?

Some OEMs will not use ZP, some will only use ZP. You would have to ask them what the reasons are. Generic replacement ones are available in both, and in several sizes. You need to use some care in choosing what is appropriate for your rig. Most people will rely on their riggers judgement for this. Which sometimes will result in a less than ideal choice depending what the rigger has in available stock.

Always remember the brave children who died defending your right to bear arms. Freedom is not free.

[gowlerk 1,904]

Hooknswoop

Quote

The use of Vectran would eliminate the shrinkage problem, but would wear the bridle quickly.

I have not experienced this.

Derek V

There we have an observation from the field. Vectran is not as slippery as Spectra. So I would assume that it would cause faster wear. But I have never seen or installed a Vectran kill line, so I don't know for sure.

Always remember the brave children who died defending your right to bear arms. Freedom is not free.

[Remster 24]

Considering that the PC gets on the ground on every single jump, I'd be hesitant to use any kind of lube on it in the desert.

Remster

[BrianSGermain 1]

I have tested Vectran on a kill line and it seems to work fine. I didn't notice any bridle damage, and it slides well enough to collapse every time. That said, I still think silicone couldn't hurt.

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[gowlerk 1,904]

BrianSGermain

I have tested Vectran on a kill line and it seems to work fine. I didn't notice any bridle damage, and it slides well enough to collapse every time. That said, I still think silicone couldn't hurt.

There you go. More experience from the field. Perhaps Vectran is not as abrasive as I assumed. That brings up the next potential problem. Will it it wear faster than the Spectra? In other words, will it fail in less uses than Spectra? If it does break it is replaceable. But if you have to pay a rigger to do it you may decide on just replacing it depending on the overall condition. If you are a rigger, or even just comfortable with that kind of tinkering, it would be a cheap fix. Again lubricating it is a good idea.

Always remember the brave children who died defending your right to bear arms. Freedom is not free.