Pilot chute twists

[PhreeZone 15]

I'm going to see if anyone has any ideas on what might be causing my collapsible pilot chute to spin up to the point that the 9 foot bridle has 60-75 twists in it by the time I land. I've checked to see if the center lines in the pilot chute were equal still and they are. The issue started appearing about 20 jumps ago with 15-20 twists and now its twisting so much that its became a real pain to sit and untwist them all on the ground.

Anyone have any other spots that could be causing the balance of it to be off enough that it would spin up like this?

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[likestojump 3]

how about center line elongation ? That would cause the PC to stay inflated, and in turn it would have to orbit causing it to spin. Simple thing to do if that's the case is to put a knot or two in the kill line at the canopy attachment point, which would reduce it's length.

[erdnarob 1]

I doubt the problem comes from the center line elongation since it is likely made from Spectra which shrinks due the heat caused by friction. Could it be caused by the POD ? Twisting of the PC bridle is due to uneven shape of the POD or PC or both or an uneven flight. If for any reason the POD is not symetrical after deployment, that can be the problem. Do you do a lot of spirals after opening ? Yet another cause. Otherwise have a rigger inspecting the whole assembly.

Learn from others mistakes, you will never live long enough to make them all.

[ast4711 0]

I jump an atom container, with original bag and pilot chute.

Of maybe 10 jumps there are 2 where the bridle is twisted up as you described, on the other 8 there are no twists at all to only a few twists in the bridle. I always wonder what the magic acround this is...
Maybe it has to do with some weired issues around the coriolis force or the ugly bridle twisting wizzard... :-)

alex

--
www.tandemmaster.net
www.skydivegear.de

[DrewEckhardt 0]

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how about center line elongation ? That would cause the PC to stay inflated, and in turn it would have to orbit causing it to spin. Simple thing to do if that's the case is to put a knot or two in the kill line at the canopy attachment point, which would reduce it's length.

.

1) With symetric construction and attachment pilot chutes don't spin.

2) The traditional spectra center line shrinks with age. It can get bad enough that your pilot chute doesn't have much drag and when you're stupid enough to jump it you should probably dump your reserve although reaching around and pulling the pin by hand will get you a canopy. I haven't been that daft but have loaned D-bags and pilot chutes to people who were. I think one is still out on now permanant loan.

Have it inspected.

[hookitt 0]

Asymmetry is nearly guaranteed on all pilot chutes due to construction. No reinforcement on the canopy material and only 4 tapes on the mesh. It's not much of a concern.

Try this.

Collapse it. Look in the bag and see how much line remains or if there is no line showing. Remember that as a reference.

While collapsed, hang it by the bridle. Is there canopy material showing or just mesh? How much canopy material is showing? If the line is slightly long, canopy material will show meaning the edge of the pilot chute can inflate. If it inflates the edges of the pilot chute, it will spin up. Some do it more than others and it sounds like you're one of the lucky ones.

This is why I asked for the kill line in the bag reference. If there is a few inches of line, you can shorten the kill-line to make the pilot chute collapse more.

Make sure the center lines will fully extend when you cock it.


Tip: Tie the PC in a knot, it's easier to unspin.

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto

[Acoisa 0]

Is your rig new?

Mine did that for the first 40 jumps or so... then it stopped twisting all of a sudden..

Mike

[Nutz 0]

I have always wondered that too. Mine doesn't have all those twists in it every jump. I said out loud why does this do this sometimes in Sebastion and some guy sitting there said, "Maybe you are putting spin on it when you throw it." I thought about that and tried to throw it really straight the next time and it wasn't all twisted up. I don't know if there is anything to that or not.

"Don't! Get! Eliminated!"

[captain_stan 0]

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I'm going to see if anyone has any ideas on what might be causing my collapsible pilot chute to spin up to the point that the 9 foot bridle has 60-75 twists in it by the time I land. I've checked to see if the center lines in the pilot chute were equal still and they are. The issue started appearing about 20 jumps ago with 15-20 twists and now its twisting so much that its became a real pain to sit and untwist them all on the ground.

Anyone have any other spots that could be causing the balance of it to be off enough that it would spin up like this?

We just test-jumped 2 PCs that I successfully altered/repaired because of this same problem. I first thought that these might be slightly non-symetrical/non-concentric, but it's really hard to measure that accurately. However, both of these were not quite fully retracting, so I corrected that issue first, and it did indeed solve the problem.

With each of these I ended up replacing the kill-line and the lanyard that connects the bag-end of the bridle to the main canopy. This was necessary because the kill lines couldn't be shortened any farther without creating other problems. By first lengthening the bag-canopy lanyard, I increased the retract "stroke" of the entire assambly. Then I was able to make a new kill-line of the appropriate length (actually longer than original) to permit full inflation and full retraction.

I suspect that the mfrs of these PCs failed to maintain good tollerance, hence the need for correcting these dimensions.

Caution: The lengths of the kill line, the bag-canopy lanyard, and the apex pull-down line(s) all affect the PCs function. If you change the dimensions of any one of these, the dimensions of the others may require adjustment also.

[captain_stan 0]

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2) The traditional spectra center line shrinks with age.

Some of these are mfr'd w/ Vectran or HMA, which may permanently stretch over time.

[captain_stan 0]

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Simple thing to do if that's the case is to put a knot or two in the kill line at the canopy attachment point, which would reduce it's length.

... and which may also prevent it from fully inflating and/or tear the top skin of the main by sucking fabric into the bag grommet when cocking. I've seen both of these conditions occurr from a too-short kill line. I would encourage the average jumper to get help from a (competent) rigger.

[riggerpaul 1]

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I'm going to see if anyone has any ideas on what might be causing my collapsible pilot chute to spin up to the point that the 9 foot bridle has 60-75 twists in it by the time I land. I've checked to see if the center lines in the pilot chute were equal still and they are. The issue started appearing about 20 jumps ago with 15-20 twists and now its twisting so much that its became a real pain to sit and untwist them all on the ground.

Anyone have any other spots that could be causing the balance of it to be off enough that it would spin up like this?

We just test-jumped 2 PCs that I successfully altered/repaired because of this same problem. I first thought that these might be slightly non-symetrical/non-concentric, but it's really hard to measure that accurately. However, both of these were not quite fully retracting, so I corrected that issue first, and it did indeed solve the problem.

With each of these I ended up replacing the kill-line and the lanyard that connects the bag-end of the bridle to the main canopy. This was necessary because the kill lines couldn't be shortened any farther without creating other problems. By first lengthening the bag-canopy lanyard, I increased the retract "stroke" of the entire assambly. Then I was able to make a new kill-line of the appropriate length (actually longer than original) to permit full inflation and full retraction.

I suspect that the mfrs of these PCs failed to maintain good tollerance, hence the need for correcting these dimensions.

Caution: The lengths of the kill line, the bag-canopy lanyard, and the apex pull-down line(s) all affect the PCs function. If you change the dimensions of any one of these, the dimensions of the others may require adjustment also.

I have seen a number of instances recently where a too short kill line was taking the load when the pilot chute was collapsed, and this resulted in wear to the point of failure of the two "wings" of bridle material inside the bag that have the quick link through them to anchor the base of the outer bridle to the bag.

(Recently, one of the manufacturers went back to putting kevlar loops in this area which do not seem to wear out.)

Anyway, after much thought, I have come to some ideas regarding how a kill line pilot chute should be constructed.

One thought is that the bag-canopy lanyard should be approximately the same length as the apex tapes inside the pilot chute. As you mentioned, the length of this lanyard determines the overall limit on the "stroke" of the collapsing operation. If the lanyard is appreciably longer than the apex tapes, then I can imagine the situation where the kill line shrinks and the kill line than takes the load instead of the lanyard. This can happen because the stroke of the collapse is going to be limited by the shorter of the lanyard length, and the length of the apex tapes. If the apes tapes are shorter than the lanyard, you will jam the inside of the apes into the end of the bridle, and if the kill line is short enough, it will begin taking the load instead of the lanyard. Of course, the previously mentioned kevlar loops might mitigate some of all of this problem.

So I am wondering how you chose the length of the bag-canopy lanyard.

The other thought, which follows from the first, is that the kill line should be long enough that it is never under tension once the pilot chute is collapsed. This can certainly lead to a partially collapsed pilot chute when taken to the extreme.

So I am wondering how you determine what is a fully collapsed pilot chute as opposed to a partially collapsed pilot chute.

Thanks very much for giving me the chance to discuss this! You seem to have thought about this more than most of the people I talk to.

[captain_stan 0]

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So I am wondering how you determine what is a fully collapsed pilot chute as opposed to a partially collapsed pilot chute.

Hookitt described this very well. He refers to whether mesh or fabric is showing at the skirt, which will be at the bottom as the collapsed PC is hung upside-down:

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While collapsed, hang it by the bridle. Is there canopy material showing or just mesh? How much canopy material is showing? If the line is slightly long, canopy material will show meaning the edge of the pilot chute can inflate. If it inflates the edges of the pilot chute, it will spin up. Some do it more than others

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So I am wondering how you chose the length of the bag-canopy lanyard.

The priority for establishing the length of these three components is:

1) The length of the apex lines must be established first to permit the PC to inflate to a degree that creates the most amount of drag.

2) The bag-canopy lanyard then must be slightly longer than the apex lines to permit enough stroke to cock/deflate the PC. Excess length here doesn't create a dimensional problem. It just means that the kill line will have to be made longer to corrrespond. However at some point, excess lanyard length coiled up in the bag may be undesireable because it may snag the top skin of the main or entangle w/ the kill-line during cocking. I mfr lanyards 2-3" longer than the apex lines, thus leaving a corresponding 2-3" of excess, slack kill-line in the bottom of the bag after cocking.

3) Finally, the kill-line is fit. I make it long enough that the apex lines are drawn tight during cocking, but short enough that it will fully rectact the PC. If all other dimensiona are correct, there will be 2-3" of slack kill-line left inside the bag when cocked.

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I have seen a number of instances recently where a too short kill line was taking the load when the pilot chute was collapsed,

There is very minimal tension on any of these components once the PC is retracted, because it's drag is then greatly reduced.

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this resulted in wear to the point of failure of the two "wings" of bridle material inside the bag that have the quick link through them to anchor the base of the outer bridle to the bag.

(Recently, one of the manufacturers went back to putting kevlar loops in this area which do not seem to wear out.)

I believe this wear is the result of kill-line abrasion across the bag attachment point during retraction, which coincidentally reaches a critical degree of damage about the same time the kill-line is worn-out and/or excessively shrunk in length.

Again, the requirement for kill-line length is very simple if the other components are correctly in trim:

1) If it is too short, the PC may not fully inflate when cocked, and the resulting pinching/binding inside the bag may damage the top skin of the main, not the bridle.

2) If it is too long, it may not fully retract the PC, a condition that is only likely to cause that annoying bridle spin-up.

Sorry for any spelling/grammar errors. Will edit as needed.

[riggerpaul 1]

First off, thanks to hookit for the details of collapsing the pilot chute. I missed that one.

you said

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***this resulted in wear to the point of failure of the two "wings" of bridle material inside the bag that have the quick link through them to anchor the base of the outer bridle to the bag.

(Recently, one of the manufacturers went back to putting kevlar loops in this area which do not seem to wear out.)

I believe this wear is the result of kill-line abrasion across the bag attachment point during retraction, which coincidentally reaches a critical degree of damage about the same time the kill-line is worn-out and/or excessively shrunk in length.



My own personal pilot chute has many times the number of jumps than the ones that had the unusual wear, and it shows no sign of this wear. The ones with what I consider unusual wear were nearly new, likely between 50 and 100 jumps. This is not the result of normal wear at this age.

The gear in question had the lanyard several inches longer than the apex lines in the pilot chute, and the kill line was carrying all the load when the pilot chute was collapsed.

The moment of retraction lasts a fraction of a second, whereas the pilot chute is dragged behind the main for several minutes on each jump. In addition, the moment of retraction will have everything basically stretched out in a line, so I think the side loading on the loops inside the bag will be minimal.

So, I am afraid that in the cases to which I refer with wear to the point of failure in 100 jumps, I must conclude that dragging by the kill line is the problem. The kill line is thin and "sharp" when under tension. I still believe that this combination of tension and the random motions of the pilot chute behind the main canopy for several minutes is when the damage was done to the loops, not the moment of retraction.

Now, you call for the lanyard to be "slightly longer than the apex lines", and this was certainly not the case in the gear I mention. The difference was more like 3 to 4 inches.

So, clearly, the pilot chutes I am thinking of did not conform to what either of us consider correct configurations.

At this point, the difference between our thinking seems to be whether the lanyard is "not longer than the apex lines" or "slightly longer than the apex lines".

Maybe this is not to big a difference after all.

Clearly we both agree that the lanyard that was 3 or 4 inches longer than the apes lines is not the way we think it should be.

I still think that "not longer" is better because as you said, the lanyard sets the length of the collapsing stroke. If that stroke exceends the length of the apex lines, you will slam the inside of the apex into the pilot chute end of the bridle. Also, if the lanyard is not longer than the apex lines, it is easy to see how long the kill line must be in order to not cause problems after some shrink.

Now, I just had a thought, and it might resolve all our differences. And maybe I will change my position. See if you agree with what I am thinking.

At the pilot chute end of the bridle there are usually 2 loops formed from the two sides of the bridle. The pilot chute skirt and apex lines are attached to these loops. I had been thinking that the retraction stroke should be equal to the length of the apex lines so that they would be retracted to where they are attached to the loops at the end of the bridle.

If the lanyard is longer than the apex lines, but only longer by an amount not to exceed the length of the loops at the pilot chute end of the bridle, then I guess I will agree with your method of configuring the length of the lanyard.

This way, the kill line can ensure maximum retraction, while still not putting undue stresses on the components involved, because the loops at the pilot chute end of the bridle can squash a bit when the retraction stroke exceeds the length of the apex lines.

So if the length of the loops is the limit to the "slightly longer", then I'm okay with that.

Maybe you hadn't thought about what limits the "slightly longer than the apex lines" measurement. Or maybe you knew, but didn't state it in your discussion. Either way, it is a benefit to be able to write it down clearly for all to see.

Thanks again for the opportunity to refine my thinking here.

[linestretch 0]

I've had it happen w/ new and old PC's that I replaced the kill line on and everytime.....shortening the kill line fixed it. I didn't believe it when someone told....even said he was full of shit until he tied a knot in the kill line and then what do you know...it fixed it.

my pics & stuff!

[captain_stan 0]

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Clearly we both agree that the lanyard that was 3 or 4 inches longer than the apes lines is not the way we think it should be.

Nah, I think I'll let you disagree w/ me on that one. I consider the greater priority of having a kill-line that's of adequate length to match the lanyard. If everything else is in trim, a longer lanyard just requires a longer kill-line.

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as you said, the lanyard sets the length of the collapsing stroke.

Yes, it determines the maximum length of retract stroke, but the stop-point at the "retracted" end of that stroke is also limited by the length of the kill-line.

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If that stroke exceends the length of the apex lines, you will slam the inside of the apex into the pilot chute end of the bridle.

Unless you just make the kill-line longer so it can't utilize the full stroke and retract that far. BTW, this won't affect the "cocked" end of the stroke because the apex lines will act as the stop-point to limit that.

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Also, if the lanyard is not longer than the apex lines, it is easy to see how long the kill line must be in order to not cause problems after some shrink.

??? If your lanyard is the same length as the apex lines and you have excess kill-line slack in the bag after cocking, this assembly will stop short of full retraction by an amount equal to that slack. Try it and see for yourself. I have retrimmed these by lengthening the lanyard.

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Now, I just had a thought, and it might resolve all our differences. And maybe I will change my position.

God forbid! Where the fun in that?

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Yada yada

I'll say it again and apologize to our many bored readers. Extra lanyard length is not problematic as long as the kill-line is trimmed to correspond to it. In a perfectly trimmed retractable PC, you could add an equal amount of length to both the lanyard and the kill-line without affecting function. Longer lanyard requires longer kill-line. However at some point in extra length, you're gonna end up with a bunch of unnecessary kill-line & lanyard wadded up in the bottom of the bag with the packed canopy, and this can lead to entanglement inside the bag. I allow only a token amout of extra length so these materials can stretch or shrink a little but still stow neatly and continue to function.

I don't mean to be argumentive, but that's as well as I can explain it. Sorry for the repetitioin.

[PhreeZone 15]

I am actually enjoying this conversation! What are the thoughts on the bridles that go all around the kill line all the way to the attachment point on top of the canopy?

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[riggerpaul 1]

Now we're talking about very fine points indeed.

Excess lanyard and kill line length to match just puts more stuff in the bag to catch on fabric and cause burns, so I try to avoid it.

But sure, extra length on the kill line to match extra length on the lanyard will prevent the kill line from coming under tension when the bag is trailing behind the open parachute.

We are in agreement that the lanyard must be at least the length of the apex lines, or there's no chance for a complete collapse.

You didn't tell us how much is "a little longer than the apex lines". You think it should be 3 or 4 inches or more? Why, when you've already said that the retract stroke can't be longer than the apex lines? Do you think that 1 inch longer than the apex lines is too short? Why?

You didn't said anything about the pilot chutes that I saw with damage in 50 to 100 jumps. I'd really like to hear more of what you think about that. Really.

On the other hand, if you think this is beating a dead horse, you can let it drop.

Still, your posts have made me think more about it, and result my changing some of how I think about it.

That's a successful discussion in my book.

[captain_stan 0]

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I am actually enjoying this conversation! What are the thoughts on the bridles that go all around the kill line all the way to the attachment point on top of the canopy?

Some smart guy invented that & solved 2 problems:

1) Eliminated entanglement possibility inside the bag for those of us who cock the PC after we bag the canopy. Even those who cock the PC first no longer need to separate/dress the lanyard & kill-line inside the bag before cocking.

2) Eliminated the possibility of pinching/tearing the main top skin when the kill-line shrinks and draws the attachment point down tight against the grommet every time the PC is cocked. If the kill-line shrinks excessively, it can only reduce performance by not allowing PC to fully inflate. Wake-up call from slower deployments, but no damage to gear.

[riggerpaul 1]

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I am actually enjoying this conversation! What are the thoughts on the bridles that go all around the kill line all the way to the attachment point on top of the canopy?

Some smart guy invented that & solved 2 problems:

1) Eliminated entanglement possibility inside the bag for those of us who cock the PC after we bag the canopy. Even those who cock the PC first no longer need to separate/dress the lanyard & kill-line inside the bag before cocking.

2) Eliminated the possibility of pinching/tearing the main top skin when the kill-line shrinks and draws the attachment point down tight against the grommet every time the PC is cocked. If the kill-line shrinks excessively, it can only reduce performance by not allowing PC to fully inflate. Wake-up call from slower deployments, but no damage to gear.

But everything has good and bad points.

I had one like this for a while, and, especially when new, it tried to un-cock itself. The crunched up tube between the canopy and the bag would try to act a bit like a spring.

I could get it completely cocked again after bagging the canopy. Except when I had a really tight canopy/bag combination. Then it was harder to correct after bagging the canopy.

But, as captain_stan said, it solves some other problems that are probably more serious then the things I mentioned here.

[captain_stan 0]

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Now we're talking about very fine points indeed.

I'm hoping these fine points may result in more service life from a PC and maybe even prevent damage to a canopy or a PC in tow.

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You didn't tell us how much is "a little longer than the apex lines".

Didn't I mention I design my PCs to have 2-3" of slack kill line in the bag when cocked? This corresponds to a lanyard being aprox 2-3" longer than the apex lines.

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Why, when you've already said that the retract stroke can't be longer than the apex lines?

During cocking, the maximum stroke permitted by the lanyard is stopped short by the length of the apex lines. The length by which the lanyard exceeds the apex lines is equal to the amout of slack kill-line that will appear in the bottom of the bag when cocked. Call this excess a safety factor. If you have no extra lanyard length, there can be no extra kill-line length. If that's the case, then any stretch or shrink of these components can put the PC out of trim. Kill line and bridle are made from different materials that stretch or shrink by different amounts over time and under load. During lab-testing, I notice that my PCs undergo dimensional changes as I apply tension to the assembly. By providing extra length to these components as mentioned, I ensure that the PC will perform well not only during static testing and measuring, but during varying loads and varying conditions, and after undergoing normal service over extended periods. Again there is much more potential for harm if the kill-line and lanyard are made to minimum lengths for service in a dynamic environment.

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You didn't said anything about the pilot chutes that I saw with damage in 50 to 100 jumps. I'd really like to hear more of what you think about that. Really.

Without actually seeing the PCs in question, and just from your description I'd expect that your solution may be as simple as lengthening the kill-line. That would prevent your expected case of "excessive-retraction" and yet would still permit full inflation. Of course any increase in length must be limited by the need to still retract fully. Excess kill-line length may result in bridle spin-up as some of us here have experineced. The Lanyard would be the last thing I'd alter, but I have done so in some cases.

[captain_stan 0]

BTW, if you want a bullet-proof kill-line material for repairing these PCs, try some 400 lb, flat-braided Dacron available from Para-Gear. It's plenty strong doesn't shrink like Specta, wears better than HMA, isn't too bulky, and only costs about 40c/yd.

[hookitt 0]

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I am actually enjoying this conversation! What are the thoughts on the bridles that go all around the kill line all the way to the attachment point on top of the canopy?

The sheath inside the D-Bag must be long enough to allow an easy compression. If it's hard to cock, the design is poor. I don't like them. After they wear out I make the other kind of bridle to replace it.

Stan is absolutely correct.

The lanyard can be an inch or several longer inside the bag. Match the length of the kill line to allow full collapse of the pilot chute.

Wear on the canopy isn't a concern unless you actually shove material between the lanyard and kill line. Otherwise the extra length just sits on top until the bag comes off.

If you use spectra you WANT the added length of the lanyard to compensate for shrinkage of the spectra.

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto