Continuous control lines and tension knots

[A-73988 4]

Hey guys,

Just wanted to get different opinions on the link between continuous control lines and decreased tension knot risk (both frequency and severity from what little I read). Atair, squirrel and adrenalin all use these lines and specifically mention that it is for the express purpose of lowering tension knot risk. Apex, on the other hand , say they have no evidence continuous control lines reduce tension knots. As someone who jumps apex containers and canopy, this is something I wanted to understand better. 

Edited February 14, 2022 by A-73988

[TomAiello 25]

I have no evidence that they reduce tension knot risk.  I have clear photos and video of a canopy with this style of control lines experiencing a tension knot.

I have also seen some evidence that the use of a different line weight in the 'trunk' line focuses the force of opening more on the 'trunk' line attachment.  I have seen three different canopies with this style of control line that experienced structural failures (tearing) at the line attachment point of the 'trunk' line.

Basically, on this one I agree with Apex.  I have no problem with personally jumping lines of either style though.

 

Also be aware that the 'trunk and branch' style control line creates the possibility for a new problem with discontinuity of the control line.  If you drop your toggle at landing and do not clear the control lines from canopy to toggle on each pack job, it's possible to have the toggle flip through an upper cascade and compress the canopy tail in flight, resulting in an apparent 'built in turn' until you correct the discontinuity.  I have seen multiple jumpers who did not perform this check and complained of out of trim canopies until someone else corrected the problem for them and explained what to look for.

[A-73988 4]

Thanks for the response Tom! Any theories as to why squirrel, adrenalin and atair all decided to go down the "trunk and branch" route? 

[dudeman17 267]

2 hours ago, TomAiello said:

If you...  do not clear the control lines from canopy to toggle on each pack job

Then you need to rethink what you're doing.

 

2 hours ago, TomAiello said:

I have seen multiple jumpers who did not perform this check

Complacency kills.

[A-73988 4]

Hey dudeman17, with all due respect, lets keep it on point. This is not a post about who should be base jumping and who shouldnt, or whether complacency kills. If you would like to address those things, please create your own post. Lets not go off topic please. This post is about the link between continuous break lines and tension knots. Thats it.

[TomAiello 25]

1 hour ago, A-73988 said:

Thanks for the response Tom! Any theories as to why squirrel, adrenalin and atair all decided to go down the "trunk and branch" route? 

 

Basically, we're all grasping at straws trying to find a fix.  Anything promising gets tried, and anything that you customers think might work will get added in, in an effort to keep the customers happy.

Tension knots are the last great unsolved malfunction in BASE.  I know tons of people who would love to find an answer for them.  I know good, knowledgeable, experienced jumpers and riggers who think that;

Thinner lines tension knot more often

Thicker lines tension knot more often

New lines tension know more often (because they are stiffer)

Old lines tension knot more often (because they are fuzzier)

I know a master rigger who squeezes beeswax into his lines so that if they tension knot they will 'slip out'.  I know a leading European jumper who sprays his lines with food grade silicon lubricant, for the same reason.  I even know a jumper who replaced his upper control lines with a giant triangle of mesh (no lines = no tension knots).

The 'trunk and branch' system was created by Simon Perriard for the prototype that became the Squirrel Outlaw, and then added to and refined as it was replicated by other manufacturers.  I think there is some good thinking there--I just haven't seen any evidence that it is actually effective in reducing the malfunction rate.  I think everyone is still working on the problem, though, which is good.

Edited February 15, 2022 by TomAiello

[mark 102]

42 minutes ago, TomAiello said:

The 'trunk and branch' system was created by Simon Perriard . . .

An MC-4 canopy control line has one line continuous from toggle to canopy, and other control lines branch off from this one continuous line. Is this the same thing as "trunk and branch"?  If not, how are they different?  From the MC-4 manual, a close-up of the branching off from the continuous control line:

Edited February 15, 2022 by mark

[TomAiello 25]

That looks basically the same to me.  There are variations within the manufacturers, having to do with line type and junction location.  Simon put his junctions at fairly wide intervals, where Atair has placed their junctions all within a fairly close spacing.

Virtually all BASE gear involves adopting ideas from other fields.  Slats came from aircraft wings, loop style brake settings were first used on tandem rigs...the list goes on.

Edited February 15, 2022 by TomAiello

[dudeman17 267]

23 hours ago, A-73988 said:

with all due respect, lets keep it on point

I'm sorry, I just have a hard time letting elementary stuff like that pass. To tie it to your topic, if people are overlooking that point, what else are they overlooking? Keeping twists out of the brake lines? Keeping proper and symmetrical line tension? Things that can contribute to tension knots, while they wait for someone to engineer them out of existence?

But I get your point. You're asking a specific question.  So I'll leave it at that.

 

Oh, except

9 hours ago, TomAiello said:

loop style brake settings were first used on tandem rigs

If you're referring to what I think you are, loop style brake settings preceded tandem rigs by a long shot.

[AntoineLaporte 2]

Of what I know at Brento the ground crew noticed that there are more tension knots with 'trunk and branch', but the fact that most of the canopies have now 'trunk and branch' does not help to know if tension knots happen more with a configuration than with the other.

[A-73988 4]

On 2/20/2022 at 8:24 AM, AntoineLaporte said:

Of what I know at Brento the ground crew noticed that there are more tension knots with 'trunk and branch', but the fact that most of the canopies have now 'trunk and branch' does not help to know if tension knots happen more with a configuration than with the other.

Thanks for the answer Antoine. I think from speaking with BASE jumpers with way more experience than me, the consensus seems to be that there is no definitive solution, or even an indication as to what a solution looks like, with respect to tension knots and canopy design. I just thought it interesting that 3 of the biggest BASE canopy manufacturers use this approach. I was thinking about putting together a slider up specific rig and while going over the various options, this pattern emerged. 

[TomAiello 25]

If you prefer the old standard line cascade, I know that Atair has made them that way on request for several of my students.

[A-73988 4]

On 2/21/2022 at 2:43 PM, TomAiello said:

If you prefer the old standard line cascade, I know that Atair has made them that way on request for several of my students.

What made them opt for that design? The reasons you mentioned above? About the different line weights triggering more opening shock on those lines etc? 

I have an apex container and canopy(Summit and Flik2), but I was wondering if maybe getting a different canopy would be better for slider up openings and slider up jumping in general. Continuous lines and ZP on the nose seem to be the main differences, and Im not sure whether its worth making a change. Apex has a blog post on why it doesnt have ZP and it made sense. But once again, they seem to be the exception as Atair, squirrel and adrenalin all use ZP on the nose.  

I know the spectra lines are another point of difference but nobody really talks shit about dacron so thats not really an issue for me. 

Edited February 23, 2022 by A-73988

[TomAiello 25]

1 hour ago, A-73988 said:

What made them opt for that design?

Ease of maintenance and use mostly.  If you need to replace lower control lines at home (or in the field) it's substantially easier with the traditional style cascades.  It's also somewhat easier to find a customized deep brake setting with the traditional cascades.

That might be one reason that Apex has stayed with them.  Apex canopies have old style (two pieces of Dacron finger trapped in and out) brake settings, where everyone else has gone to the new loop style (loop of spectra brought back around) settings.  The loop style settings appear to have a much greater service life (approaching infinite, in our use--we have yet to need to replace a loop style setting at the school).

[TomAiello 25]

1 hour ago, A-73988 said:

I have an apex container and canopy(Summit and Flik2), but I was wondering if maybe getting a different canopy would be better for slider up openings and slider up jumping in general.

I don't think so.  You have a great set up for slider up (and generally all) BASE.  The reason to get a slider up specific rig would be to reduce weight and size, not to improve performance.  You already have the smallest/lightest general purpose setup on the market though, so I'm not sure you'll really gain much in terms of weight and size by going to a slider up specific rig.

The same is true of spectra lines.  They aren't going to make your openings any better--they're just going to reduce pack volume.  They'll make the canopy fly marginally better, but even the highest performance BASE canopies are basically boats, so I don't know that you'll notice much difference.  I have spent a lot of time under a pair of Atair Visions, one with spectra and one with Dacron lines, and if you put me under one of them without me knowing which one it was, I don't think I'd be able to tell the difference from the flight characteristics.  And that's the the highest performance general purpose BASE canopy ever made.

I do think the ZP is worthwhile, but mostly as the canopy ages.  If you're looking at buying a new rig for a slider up trip, it's going to increase the pack volume, and probably isn't worth the extra expenditure on a new rig.  I also vastly prefer the loop style brake settings, but I can easily change out the brake settings on my Apex canopies, so that's not a big deal to me either.

[A-73988 4]

Thanks a lot Tom. Your advise really helped clear some stuff up. Really appreciate it.

[ChrisHoward 8]

On 2/14/2022 at 9:31 PM, mark said:

An MC-4 canopy control line has one line continuous from toggle to canopy, and other control lines branch off from this one continuous line. Is this the same thing as "trunk and branch"?  If not, how are they different?  From the MC-4 manual, a close-up of the branching off from the continuous control line:

They are the same.  The one difference that comes to mind is that on the MC-4s I have seen (DOM 84ish) they used Flat Braid Dacron and the "Cascade" was simply sewn to the side of the continuous line. On the BASE canopies that are finger trapped into the line.

[flite 0]

Check out Squirrels 6 grommet slider, could be the answer to tension knots.

[A-73988 4]

On 4/23/2022 at 10:22 AM, flite said:

Check out Squirrels 6 grommet slider, could be the answer to tension knots.

Was that the reason they did that? In their newsletter they mentioned something about a reliability study containing data of about 40000 jumps that led to the Hayduke 2. When I was in Brazil in Jan, some people were saying a disproportionate number of tension knots were linked to the Hayduke, and that squirrel was planning an upgrade. Of course I dont know how much of it is true or what evidence it was based on , but if there is something to it, it would be interesting to know which new features on the Hayduke 2 were added with the express purpose of reducing tension knot occurrence and/or severity. 

[BMAC615 205]

5 hours ago, A-73988 said:

Was that the reason they did that? In their newsletter they mentioned something about a reliability study containing data of about 40000 jumps that led to the Hayduke 2. When I was in Brazil in Jan, some people were saying a disproportionate number of tension knots were linked to the Hayduke, and that squirrel was planning an upgrade. Of course I dont know how much of it is true or what evidence it was based on , but if there is something to it, it would be interesting to know which new features on the Hayduke 2 were added with the express purpose of reducing tension knot occurrence and/or severity. 

The thought that the Hayduke had a disproportionate number of tension knots led to a survey and year long study that resulted in a change in brake line design for the Hayduke, the Hayduke 2 and a 6-grommet slider to reduce the propensity of tension knots. A fairly comprehensive white paper should be released, soon, that outlines the work and findings.

Edited April 30, 2022 by BMAC615

[TomAiello 25]

Was there any data to support the thought that the Hayduke had more tension knots?

I saw a tension knot on an Outlaw here last week, and on inspection it was found that there was a pretty good set of twists (probably three full twists) sewn into the control line that tension knotted.  It was factory original, so I'm pretty sure that the twists and been there the entire time the canopy had been in service.  The 'Trunk and Branch' cascade system made it so that it was impossible to untwist the control line during normal packing or inspection, and we had to remove the bar tacks to the branches to untwist the trunk line, then re-attach the branches once we were done.

It's possible that if there is a higher incidence of tension knots on those canopies, the cause is not the design, but rather the quality control at Parapex, in Vietnam.  I haven't inspected any other Haydukes or Outlaws for the same quality control issue but I would be interested in hearing from anyone else who has one and can inspect both control lines for twists, to see if the problem we saw here is relatively rare or relatively common.

[sundevil777 93]

7 hours ago, TomAiello said:

Was there any data to support the thought that the Hayduke had more tension knots?

I saw a tension knot on an Outlaw here last week, and on inspection it was found that there was a pretty good set of twists (probably three full twists) sewn into the control line that tension knotted.  It was factory original, so I'm pretty sure that the twists and been there the entire time the canopy had been in service.  The 'Trunk and Branch' cascade system made it so that it was impossible to untwist the control line during normal packing or inspection, and we had to remove the bar tacks to the branches to untwist the trunk line, then re-attach the branches once we were done.

It's possible that if there is a higher incidence of tension knots on those canopies, the cause is not the design, but rather the quality control at Parapex, in Vietnam.  I haven't inspected any other Haydukes or Outlaws for the same quality control issue but I would be interested in hearing from anyone else who has one and can inspect both control lines for twists, to see if the problem we saw here is relatively rare or relatively common.

This makes me wonder if any mfgs control this - the twist sewn into any of the lines on a canopy.  Seems like it would be a great idea.  Has this been recognized as a source of malfunctions before? Is this a new "discovery" perhaps?

 

[TomAiello 25]

It's a well understood risk, and something you should check for during assembly of the rig, and any time you open the links.  If the canopy is assembled to the links properly, the lines will not twist unless you open the links.  I don't think I've ever seen a suspension line with a sewn in twist.  With traditional control line cascades, there is no risk of improper assembly, but the lines can twist during the jumping process (usually after landing), which is one of the reasons you should check your control lines for twists (and continuity) regularly--preferably on every pack job.

So, no, definitely not a new idea.  I think the first time I heard that twisted lines could cause tension knots was in the 90s, but I'm sure it was understood even before that--I just wasn't jumping in the 80s to hear about it.

Edited May 6, 2022 by TomAiello

[A-73988 4]

On 5/5/2022 at 7:16 PM, TomAiello said:

Was there any data to support the thought that the Hayduke had more tension knots?

I saw a tension knot on an Outlaw here last week, and on inspection it was found that there was a pretty good set of twists (probably three full twists) sewn into the control line that tension knotted.  It was factory original, so I'm pretty sure that the twists and been there the entire time the canopy had been in service.  The 'Trunk and Branch' cascade system made it so that it was impossible to untwist the control line during normal packing or inspection, and we had to remove the bar tacks to the branches to untwist the trunk line, then re-attach the branches once we were done.

It's possible that if there is a higher incidence of tension knots on those canopies, the cause is not the design, but rather the quality control at Parapex, in Vietnam.  I haven't inspected any other Haydukes or Outlaws for the same quality control issue but I would be interested in hearing from anyone else who has one and can inspect both control lines for twists, to see if the problem we saw here is relatively rare or relatively common.

I always thought people made too much of the "Made in Vietnam" angle, but from what you say it could potentially be a big deal. Like "life or death" big deal. Would also be interested to know and understand the evidence linking the Hayduke to tension knots, because all I have so far are discussions between some BASE jumpers I met in Brazil. Look forward to that white paper, but the whole idea so far has been that this is a design issue. If there is a design issue, and on top of that improper rigging , that's not a good look for squirrel at all. Did you report this issue with the Outlaw to Squirrel?

Edited May 7, 2022 by A-73988

[TomAiello 25]

9 hours ago, A-73988 said:

I always thought people made too much of the "Made in Vietnam" angle, but from what you say it could potentially be a big deal.

I don't think that the location of manufacture creates quality issues.  I know lots of Americans who think that 'Slovenia' is some kind of third world sweatshop (it's not--I've been there) and yet some of the world's best canopies are made there.

Parapex is a huge operation, and is very good at following instructions.  I think that 'check that the trunk line isn't twisted before sewing in the branch lines' just wasn't on the instruction sheet when that canopy was made.  I'm not sure if it is now or not.  The major issues with Asian manufacturing are about communication, not quality.  You have to be incredibly explicit about every single step in the process, to make sure they follow your exact procedures.  I've spent many hours writing up spec sheets and then had products made that found every single possible way to screw something up that I hadn't explicitly specified.  We tend to have this weird view that you can just send things off to Asia and get them made for nothing.  But there is actually quite a lot of work involved with setting up that supply chain and maintaining it.  The back and forth prototyping on a new product, especially if you aren't physically flying to the factory, is insanely tedious.