Basejumper.com - archive

Hi Guys,

Does anyone have any specifics on the typical location of tension knots? For example,

1) where on the lines do they typically occur, above or below the slider stops?

2) Which line groups, control lines, inner or outer?

I'm trying to think of ways to prevent them.

Thanks

I would think that they would be more common on slider up jumps. Has anyone heard of or experienced tension knots on a slider off jump? As far as prevention goes, when I pack I always ensure that the red lines are to the inside of all the black lines. I run them up from the risers to the pack job & ensure none of the outer lines are wrapped around them. I am referring to slider off jumps, as I have not used my slider since 2 bridge days ago....

The slider stops on your stabilizer? Below that and above the cascades.

Usually control lines into D lines sometimes into C lines if it's a good one.

Pack neatly.

I took some high speed video of a terminal opening of my ace260 w/ a 32'' vented zp pilot chute. i did a very neat flat pack on the thing, and it still looked like shit when it came out. Control lines were flopping around everywhere.

That's cos you are throwing a ball of nylon and lines into the wind.
Just don't look at it next time

Aren't tension knots typically on the steering lines? the way i see it is the toggles spin around after they they are released from your grip and they are not immediately stowed. they are then repacked with a twist in them. same for a situation where you released your toggles or the toggles were lost on an opening.

i was taught to walk the steering lines back from the canopy to the risers to untwist them during all pack jobs.

+1
That's it! I was told to untwist the steering lines on each and every packjob!

Yes. Usually when the become knotted amongst the D lines.


Twisted control lines will tension knot more readily than twist free lines. So untwisting them helps to prevent tension knots but won't eliminate them.

if your not already doing it... lay your canopy on its side. when its on its left side... pick up your furthest most right lines. (right steering and the line far most right on the rear riser and the line far most right on the front riser) walk them up to make sure they are in order.

next... grab all the steering lines and flake them out pulling back against the risers. make sure the tail section you are holding has the steering line attachment points in order and walk the line back to the risers untwisting the line.

i do this by squeezing tight on the steering line after the cascading lines with my fingers and walking it up to the risers. set the breaks and shaaazame... no tension knots in the steering lines.

repeat with the other side of the canopy.

wait what? how will lines have tension knots if all lines are straight?

Tension knots are not fully understood. They can certainly develop even in straightened lines.

Most documented BASE tension knots have occured between the control line cascade and the D line cascade.

I have good video of a slider down tension knot--it's on one of the early Will Forshay Bridge Day segments.

In my opinion, the most likely cause of tension knots is slack lines moving past each other prior to line stretch (i.e. canopy inflating out of sequence). The best remedy to this that we currently have available (and it's by no means certain) is to use the primary stow (locking stow) under the tail pocket, to help stage deployment such that the canopy reaches line stretch before it begins to expand.

Ecoli: Was your canopy free packed, or put in a bag? Skydiving rig or BASE rig? Did you use the locking stow? Did you use the tailgate with your slider for the terminal pack job?

Hi Tom,

It was put in a perigee pro with the primary locking stow under the tail pocket, with no tail gate.

So this would occur below the slider stops?

Yes.

Pardon me if this is a dumb question, but why are cascades necessary? why not just have more lines?

While it is possible to get a single line to tension knot on it self that is very rare. They usually occur when the D lines tension while the control lines are still amongst them trappping them in place. The reason it usually involves the control line and the D line cascade is because of the amount of lines present in that area (tandem canopies are prone to tension knots due to them havin 8 control lines). The reason you should untwist the brake lines is because neater control lines are less likely to hang up in the cascade for it to knot there.

Cascades aren't necessary. Many canopies are designed with continuous line sets. Not sure it would be a practical application for BASE as your line bulk would increase drastically. For the record every continuous line set i have ever seen still featured cascaded brake lines.

Also, this will not stop tension knots as continuous line sets still have their fair share of tension knots.
While tension knots occur around the D line cascade the cascade is not a defining factor just a convenient location. The D lines are significantly longer than the other lines and are left slack until it's their turn to tension. I believe it is this slack that allows them to get all messy and tangle with shit before they are tensioned.
For the record I have only witnessed BASE tension knots and have not experienced one my self. I have how ever chopped like 9 skydive canopies because of them so have had a good view of them from the drivers seat. But seeing as we are talking terminal jumps here it's all the same shit really. Once the canopy hits the wind and before the slider starts to move D lines can get messy.

Are the thin slippery spectra lines of some slider up only base canopies less likely to have tension knots?

In theory yes.

I've been pondering if the tailgate or tape gate on slider up jumps could help to prevent tension knots. In theory if tension knots are caused by slack in the brake lines sliding past the d lines then a tailgate should remove the slack for at least the first stage of the opening.

Those that have experience with sl up tension knots, do you know if a tailgate or tapegate was used?

If the tailgate/tapegate is above the locking stow, how is it going to change anything? The cascades where the tension knot is most likely to appear are below the locking stow already, and I can't see adding the tailgate above the locking stow really doing much that the stow itself does not.

As a somewhat bizarre thought experiment, have you considered the idea of taping around the entire line bundle somewhere (or several places) along the length of the lines? Picture wrapping the lines with a loop of masking tape every 24" or something. Do you think that would change the incidence of tension knots?

I had thought and sorta tried it,
on a Falcon 300, TARD, Perrine.
Worked well but too few jumps
to recommend it to anyone...

 
I had a thought the other day (yes I really did), when thinking about this tension knot business. Could the brake lines be made so that the final bits, everything above the cascades was made of a different, very slippery material?

I was thinking something unlike a regular line, but more like approx 1-2mm diameter synthetic material, kinda like super-heavy duty fishing line? And because of its slippery monofil structure it could be less prone to twist and turn on itself and its fellow brake lines?

The forces on the upper brake lines are not too great and the slider doesn't wear them down, so theoretically it would probably work. I sure don't know if it would help to avoid tension knots, but it might. What do you think?

Like I said this was a thought I had a few days ago. I don't get those very often and most of the time they suck.

Kerkko
BASE1184

you should simply forget that you ever had that thought.

 
Probably, Chuckster. I think I brainfarted a little there, I just re-read what I wrote. Why wouldn't the slider rings burn the shit out of them?? Dumbass me. Ok, I'll give you that, but other than that I believe my future design categorically eliminates tension knots! There can't be anything else wrong with it! I'll make a fortune!

So obviously the next evolution must be that the chosen material is so space-age that its immune to all effects of friction.

I need a name for it though, help me out buddy!


Kerkko
BASE1184

This part of your thought is actually already applied for example in Atair Trango where the steering lines are made out of dacron up to the cascade and the upper (cascading) parts are made out of spectra.

I remember from your FJC that the primary stow helps to prevent tension knots, and I agree with your logic.

I was thinking that perhaps a tension could form in the microsecond between when the locking stow releases and the lines spread. Do you know that this is not the case?

It seems that there is a consensus that tension knots are more common in sl up. I also know that a lot of jumpers don't use the tailgate sl up. It would be interesting to know how many tension knots have occurred where the primary stow was used but the tailgate was not vs how many when both were used. Does anyone know if tension knots were more common sl down before the tailgate was widely used?

I have thought about this a lot, and about putting some sort of weak sheathing around and down the full length of the lines or maybe separate sheathing for the control lines and the rest of the lines. I came to the conclusion that it would be almost impossible to test these ideas, given how small of a statistical anomaly tension knots are and how many unknown or uncontrollable variables there are in an opening. Also, the more I thought about it the more it seemed that the cure could be worse than the disease.

I believe that tension knots are caused due to the time difference between tension being applied to each line group. When the locking stow releases we immediately load up the A lines as those are the ones we are hanging from but the D lines aren't fully tensioned until the canopy pressurizes. That is why they become more common on slider up jumps due to the longer pressurization phase (even more common on skydives with sail sliders), also the same reason for them occurring above the slider. So while the locking stow controls the lines until line stretch it doesn't have any influence while the canopy is pressurizing like a tape gate possibly could. I would be interested to know the ratio of tension knots with and without a tape gate.


I don't believe so. But that is working on my principle that tension knots occur during inflation before the slider starts to descend not on the way to line stretch. I also recall reading that tail gate/tape gates are placed in a position that guarantees its release (due to forces exerted by the canopy)and that the lower down the lines the more likely a hang up will be (due to less forces being exerted on the tape gate).

Have you tried a differential stow?

If your theory is correct, that old technique should reduce the incidence of tension knots. I'm not sure if anyone has really done any substantial number of jumps with both the differential stow and the tailgate, though, as the tailgate largely pushed the differential stow aside in the development of the gear.

No, that's well before my time so the most I ever did with that was read about it :-)
However I believe that the differential stow was CRs solution to tail inversions before the tail gate became mainstream. The differential stow is also stowed with the locking stow so therefore it would be released at line stretch and therefore have no effect on the inflation from that point on, it could even have an adverse effect. I know the CR article repeatedly states that the differential stow is not to be used on slider up jumps.
What I do for Terminal jumps is place my control lines into the centre of my slider and wrap the slider around them before placing it into the slider stow band. I think this should help keep the control lines and D lines separate until the slider starts to move down the lines. We know that the slider is pushed down by the inflating canopy therefore I believe I am effectively keeping the offending lines separate until pressurization has been achieved. Again this is based on my theory that tension knots are usually caused above the slider before full inflation.
Also note that I only do this on terminal jumps not low slider up jumps. I have had some erratic openings (headings) on low SU jumps that I believe were caused by this technique. For terminal though it works a charm.

I don't know how relevant this is, but I had a skydiving main that had four "tension knot mals." BITD. We called them "Steering Line Entanglements," because it was almost always the steering line. Was for me, anyway. Right at the cascades on the steering line. Wrapped around the outside D line.

There is a lot going on during inflation, and steering lines have always been trouble, either with line overs or tension knots. Those things obviously can whip around like crazy.

I was never able to clear them, and pulling hard on the other steering line to straighten out the spin always put me in a stall, so I cut them all away. I know others who had them on certain canopies and they cleared.

Never happened on a BASE jump, but if you were to be dumb enough to route your steering lines outside the slider, the slider would hang up at the entanglement and you would have a half inflated spinning mess. If all the lines are through the grommets, at least the slider would come down and you would have an inflated spinning mess. You can slow down the spinning, but you may stall. Maybe you could correct for it with a big docile canopy.

The spin rate on mine was nowhere near what a line over does.

I was videoing a tandem once, and the three ring popped on one of the risers. Now that was some scary ass video.

Tom, by the time you have reached the primary stow below the TP the lines are stretched out. I personally do not use the PS on SD jumps but I DO on SU.

One of the BASE manufactures doesn't even use the PS on SD jumps. But he does for staging on SU.

People use to make comments that the PS prevents line dump, B.S.(bullshite). Good velcro and proper opening at the TP does that. Again, by the time the lines are stretched out does the PS engage.

The purpose of the primary stow is not to constrain the lines--it is to constrain the canopy. The primary stow prevents the canopy from beginning to expand prior to line stretch.

In theory, if the primary stow holds the canopy together, the lines move to line stretch in a single bundle. If the primary stow does not hold the canopy together, by the time the lines achieve full extension, they are already spreading out away from each other. In so doing, they are moving past each other before they are fully tensioned. If they are then tensioned as they move past each other (in that fraction of a second), two newly tightened cascades could be trying to move past each other, forming a tension knot.

The primary stow can't prevent line dump. The line dump would occur below the primary stow. For the stow to prevent it, the dumping would have to occur above the stow.

I think this is a flawed theory. If this was the cause of tension knots then there would be a lot less of them occuring, they would appear in any cascade a lot more randomly and there would be zero tension knots in skydiving due to the D bag eliminating the potential for all the caos you just described.

OK. Like I said, I have had them four times, but on a skydiving canopy. It always had them on the right side, and it was always the right steering line around the outside D line.

Never had a problem with newer skydiving mains. This only happened on the most caveman gear of the time.

What they look like is a mess of slack steering line wrapped at least once around the D line, creating a sort of messy slip knot. I believe that they were all a little below the cascade.

That tells me that there must have been a ton of slack in the steering line.

I never had one, or even saw one, after ZP and Spectra showed up. I will say this for Spectra, it is slippery and doesn't burn as easily.

I see no real problem with the D line. It was really obvious that there had been a ton of slack in the steering line during inflation.

Line overs were a huge problem in the olden days. You NEVER saw them at the DZ, but you saw them in slider down BASE often enough to eventually take notice. That should tell you something right there, and led Mark Hewitt to the line release mod and eventually the tail pocket.

Solving the problem of slack in the steering lines should put this to rest. Steering lines cause all sorts of problems. In my mind, they are the #1 problem slider down. The fact that this thread is up in 2011 tells me that steering lines aren't well understood to this day.

Factory shallow brake settings on most of the canopies I've seen are usually in almost full flight. I imagine they could be much deeper and help some of this. I had tension knots on a slider up jumps that I attribute to this, and it was the first and last time I will let anyone else pack a BASE canopy of mine.

Not necessarily true. Deeper brake settings will also cause a greater difference in tensions between the slack D lines and the now even shorter control lines possibly making the problem worse. But that is just speculation. There is also one well known tandem canopy that uses no brake setting whatsoever with absolutely no increase in tension knots. Which sinks your deep brake theory.

BASE 104, did your old canopies have flat lines? Those entangle pretty easily.

I know of a master rigger who occasionally would apply vegetable grade silicone spray to his lines. The lines repelled water and dirt and became slippery as hell. He said the openings were noticeably harder slider up, I assume due to reduced friction between the slider and the lines.

Another help might be a better staged release of the lines. For example, instead of just a figure 8 coil with the lines all interacting, perhaps using the line separator flaps.

I'm personally too lazy to do these things at the moment due to other more pressing concerns in my life outside of jumping. But for those who are exceptionally paranoid about their gear and the risk of a tension know may want to consider such remedies.

But in real life, no. I just had one(in your words a good one, including C) on trango with spectra lines. Unable to undo, when trying to stop turning into stall. crash landed in slow turn.
I have been looking at some of my openings when filming backwards and feel like you that it might happen between release locking stow and inflation.
I used direct slider control, no tailgate but brake lines behind the indirect slider control rubberbands. All terminal wingsuit openings.
In the past I used direct slider control and used to tape brake lines together against line overs.
I will do this again and film some openings and see how this looks. Since putting behind the rubberbands does not keep tension on the lines and I feel when you tape them together it might be better.

Tension knots seem to happen on all kind of canopies and all type of lines. I did not have a single twist in my brake line, and a good tight locking stow.

haha, man that is some scary shit. I can't even imagine.

can you describe what you tried for solutions and were you injured. Also, how high were you on opening and how long till impact. thanks for sharing. scary !!!

Well, I tried pulling the riser as far as possible and letting it go to try to get a moment without tension but after three times and spinning pretty hard I gave up.
I then pulled the riser on the other side trying to stop the spinning, this worked till the canopy stalled. I let up the riser a bit and got a nice slow turn but at the end it got a bit faster and I crashed in between boulders on a patch of sand. Only hurted my knee, nothing damaged just 2 weeks no jumping/working.

I did not release the brakes as I was afraid to increase the spinning. I have been thinking of this afterwards and not sure what would be better.

The opening was high, I just pulled because I reached the landing of a 1700m flight. I pulled between 300 and 400m I think. I timed and my canopy time was just over 30sec.

Thing to think of, I kind of landed where I pulled (half over ski slope, half over little creek). This because of spinning/stalling. It is not controllable where to land, perhaps vented canopy flying backwards? But, if not necessery you might not want to pull really above stuff like power lines, highways or other scary stuff.

Thanks for sharing :)