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So let's say you're doing a static line on an object that is plenty high enough for you to go hand-held, or even stowed for all this point matters. You only use one strand of break cord for the static line (or, more importantly, your break cord is in direct contact with the object) and, per chance, your static line breaks early (I think on canopy extraction is the worst time for what I'm talking about). Look at the following screen shots and my idea of what's happening and let me know what you think!


pic 1 - jumper exits, pilot chute is clearly attached to object and blowing in the wind

pic 2 - canopy extraction begins and, just as this occurs, the break line breaks prematurely. This is how I think the physics breaks down:

instant before breaking - the bridle is fully stretched and under tension.

Instant after breaking - the bridle and everything else that was being pulled seeks equilibrium for any stretch outside of its rest length (these could be pretty small and add up quickly) and thus the pilot chute is jerked toward the jumper (it takes some distance for it to fully inflate, especially since it was a 46" PC, so the drag is low enough that it is pulled toward the jumper...this could be exasperated by the tailwind).

3- line breaks prematurely

4 - pilot chute is pulled to jumper and packjob floats just behind the jumper

5 - pilot chute and packjob come very close

6 - pilot chute has completely inflated and is already distanced from the packjob

7- canopy catches air and inflates

8- tailgate releases (albeit a bit early)


Picture 5 makes me wonder if the pilot chute could have been pulled around/under/through any manner of things that would cause a fatality / bad day / pants shiteing.

Thoughts? Maybe the static line should be rigged with backup / anchor even if it's a higher object...

Alternate possibility: the pilot chute and packjob dont come as close as it looks...it is just due to the angle the video was taken. (probably most likely)

So the elasticity of the bridle caused the PC to shoot down towards the jumper you mean? And a not-so-slow tailwind contributed? Using a 160 lb system with 2 loops of break cord might help maybe? Nice high quality pictures btw.

hi!

i dont think the pc came close to the packjob, more likely its because of the angle and the wave that goes through the whole system (lines, packjob, bridle, pc) as you can see in this video:
http://www.youtube.com/watch?v=U8-dcw8Vy6o

to prevent stuff like that (if even possible in 100% of the cases), lets say to make stuff like this less likely:
1. , and most important, dont tie the breakcord directly to the structure (rust, sharp edges, ... also a round railing will have the breakcord break later than on a triangular structure, and so on...)

2. if your life depends on the staticline, so lets say < 150 feet, or you really don't want to have it break early, set up a redundant staticline setup (2 pieces of breakcord, one just an inch longer than the other)

3. set up with 160lbs -> make a loop of 80lbs breakcord, im pretty sure that any modern base canopy (thats not an ultralight) will have a bridle attachment point that is built for taking that force without getting damaged

Ya sorry about quality. Past a certain level of dark, even decent video is hard to get.

Hahaha...well that was kinda funny, in a sick sort of way for me anyhow. That video clip you just posted the link for is a really familiar spot for me. Ironically I had what I think was a premature static line break there about 2 months ago...waiting for some snow before I go back out there again...I was there alone so I didn't have any video from the top or anything and have just a super short shot when I look up to see WTF was happening...my canopy wasn't fully inflated. I have about 20 jumps off of that object and the jump in question was approximately half the canopy time normally seen. Watching that clip you posted kind of confirms what I suspected happened to me.

I always use 2 loops but on the day in question I went out there and the first loop was a little short...couldn't tie and test the knot. Left it there anyway but I don't believe it did anything at all, just pulled away at the first tension on the system...the second one I believe broke on canopy extraction. (Somewhat like the video link you posted...) Was probably one of the shittiest moments when I realized I was going in somewhat hard...just cleared some rocks or it would have been a lot worse. I limped away from that jump but would have to say that any low static line jump must be approached with a lot of caution and a little redundancy is not so bad either. I would take a little more wear and tear on my gear rather than the alternative. I will continue to use two loops (being certain they are long enough...) and will also be shortening up my bridle tie-off point so it is a lot closer to the tie-off point used on the object. (No momentum built up...used to be very near my PC.) Anyhow just thought I would share that in the off chance it helped someone to avoid a mishap.

Enjoy your jumps out there!

I still feel like, if you tied off 2 break cords the same length, so they both had force applied to them at the same time, would still pull off at 80 pounds and not 160. I just use 2 different lengths of breakcord but ive heard the argument for the 160 lb of force with 2...Am I wrong?

electric tape. 3 wraps. Done.

Actually it doesn't matter how many break cords you have, they're all supposed to be of different lengths, so they break in a sequence one by one, at the same 160 lb (or 80 if you have an 80lb system) of weight.

Like if you tie 3 plain old break cord loops, they will be all have a different length. The force required to break each one of these loops will be no more than 160 lb.

The whole point of having more than one break cord, is that if the first one breaks prematurely(like in the video), the second one will do the rest of the job. But that's how I got it from reading the other threads about SL jumps (there are lots of them). But to be honest, I don't really understand your question.

I know about the different size break cords. Thats what I do as well. Maybe I misunderstood the post I replied to the first time, but I thought the dude was talking about tying 2 80 lb break cords the same length to make the pull force 160.

Oh, okai then I was talking about using a 160 lb system (i.e- a loop of break cord, but with a backup (another loop of bc).

I have no idea what was occuring from the photos, but from the description and in general i have a coulpe suggestions. If its a railing and not a "sensitive" object, JT's electrical tape system does work very well. Nevertheless I very often use a static line and break cord and I recommend redundancy in the break cord as others have suggested, no reason not to, I know of no disadvantages, maybe time and effort, but if its set up early it takes no more time, and if its too much effort well....

More importantly the suggestion of "elasticity" was brought up. I think its very important to carefully stage the application of force in SL systems, I never leave slack as I jusp that will just be taken up as I leave the object. To avoid premature breaks I think its important to slowly load the BC, andI do this by s-folding the bridle (and sometimes BC and SL depending on the object/setup) and holding this in my hand. As i exit I let it play out under the tension as I fall away. Some people will use a small rubber band on the sfolds to do the same. This stages the force so you don't get premature break at canopy extraction, and has the added advantage of keeping everything neat and tidy, which can be important on many objects.

I used to do this until I unintentionally free fell 160ft. Was not cool.

Try four wraps next time

Zebu, are you trying to learn how to base jump from the forum? fuck off for a while, i'm tired of reading your shit threads. read all you want, lurk and learn, but STFU. after you meet some real base jumpers and get mentored or attend an FJC, then you can finish filling out your profile and get back to posting questions (but with less stupidity involved)

Or are you just trolling?