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I have never had one ever release before line stretch.
Have you ever had or seen this happen? If YES then
please share the details regarding the occurrence.

I have had a few premature releases, but never with a Static Line.

not with static line using break cord.

 
180f bridge, nothing to use but masking tape good 10 plus wraps. tape broke as soon as it took tension of pins, 42pc. opened fine with short canapy ride.

same bridge, cold morning with 5 wraps of electrical tape same result this time with 48pc on.

is that classed as a free fall?

PS
electrical tape does work fine.

Have you looked at much video of your exits? I've only done maybe a couple dozen static line jumps, but of those I know at least one or two show the break cord going before the canopy hits line stretch -- usually either when the pins are popped or when the canopy is lifted off of the jumper's back.

None of these were something I noticed during the jump (usually around 160 feet), since the pins are popped in the first case, and (even better) the canopy is already largely brought to a stop in the second. But the frequency with which I saw it on a single loop of break cord led me to adopt the "two loops" approach.

from my experience with breakcord, you should notice it breaking.

if it yields before line stretch, no force really gets transferred to the jumper. it should feel like a go and throw.

if the breakcord maintains integrity, you will hit line stretch, and feel the tug that causes the material to break.

video of the breakcord itself should not be required. besides, who is there to video? on my jumps, the last jumper ties off, and PCA's everyone who prefers not to freefall.


but I have been wrong before...

I have done ~25 static line jumps, all of them with break cord,
some single strand, some loops, some with two loops, and
I always feel the exact moment when the cord breaks free
by that shock and first feeling of surging canopy flight.

A friend tied his break cord directly to the catwalk, specifically a square railing. The exit simultaneously pulled his pins and prematurely broke the cord putting him in essentially a freefall assist at 230'. That altitude is not normally a big deal but there were plenty of trees to clear which did not happen. The tree landing shredded two of his cells.

You certainly do when it breaks at line stretch, since the force is transmitted back to you. When it breaks lifting the canopy out of the container, I never have.


With respect to not feeling the break, yes. With respect to freefall time, not necessarily. As I say, my experience has been that often the cord breaks (when it breaks prematurely) as it lifts the canopy off of the jumper's back. While not as big a force as getting line stretch (and decelerating the jumper), decelerating the packed canopy puts a significant load on the break cord (something you can feel when you're PCAing someone, too).

Anyway, if the break cord snaps in the process of lifting the canopy off of your back, you can experience anything from a near go and throw (if it breaks very shortly after the pins are popped) to an opening that's only a little lower than you might expect (if it breaks when the packed canopy is largely slowed down).

Currently uploading a much higher res version as that one sucks donkey balls for clarity.........

http://www.youtube.com/watch?v=U8-dcw8Vy6o

While we could not see the break cord giving away early
your pack job rotating in space is a dead give away that
the static line let go right after pack opening.

Also I really liked your head high exit

You can see that the canopy is not at line stretch and that the static line has released. Head high? Not for a low static line......

Yeah, I totally agree with you and
I always exit head-high for PCA's,
Static-Lines, and Go & Throws!

Yeah, I launched hard from a lowish SL once. That sucked. Doesn't matter how ugly the structure is now, if it's SL, it's a head-high exit for me.

How far from the shrival flap was the sl attached? By how far the pc is hanging down it looks like he did shorten the bridle some, but it's hard to tell how much.

It's a dedicated SL bridle, with the attachment point maybe 3 or 3.5 feet from the shrivel flap, and the PC attached another foot from there. The break cord was tied with no slack (to prevent shock loading) but very little tension, from a loop in the bridle (made from accessory cord) to a biner attached to the rail.

would anyone care to explain why all the fuss? really?

I can explain the differences between static and dynamic loads, but who cares if there is any slack in the static line/breakcord?

once the container opens, there is a ton of slack. it might be in the bridle itself, the canopy s-folds, or the stowed lines. no matter where, the slack exists. the significant forces get transmitted when all lines are taunt and the slack has vanished. ANY slack will add to the dynamic (or shock) load. I fail to see where an inch or two of slack in the static line will make any difference. (shortening the bridle would be much more beneficial, from a technical standpoint.)

think of it, who climbs over the rail with NO slack in their bridle? any false move will pull pins or pull apart velcro. once the container is opened, the rest of the bridle must play out before the canopy gets extracted. eventually the lines must exit the tail pocket. this adds up to yards of slack, why worry about slack in the static line/breakcord?

as far as I can tell, avoiding breakcord slack seems to be either an urban myth, or started by folks too cheap to buy a roll of breakcord.

can anyone educate me?
please tell me where I'm wrong?

have you any prematures on pins?
because my one and only premature break was on my very first static line on a velcro rig.
i have a lot of static lines on pins, never broke early and i didn't use a backup loop.
nice video, thanks.

although it looks as if the break occurs when the canopy is loading the static line....

All the fuss? It was one sentence, in passing. I suspect it does nothing (though not for the reasons you state). But a person has to choose a way to tie their break cord, and since I've got no reason to tie it loose, and a questionable reason to tie it without slack, I tie it without slack. My mentioning it was intended more to head off anybody who thinks it's really important than anything, but I'm not sure I've ever met a jumper who thinks you'll die if you tie it loose.

cool.
sorry if I seemed to over-react, but I've seen people mention it aggressively before. (obviously, if someone uses 2 loops of breakcord, they must be different lengths!)

You do raise an interesting question, and I've been giving the physics of it some thought. I'm quite certain that tying the loop with a little slack or with none at all makes no difference. Static vs. dynamic loading works either (a) because if the same impulse is delivered over a longer time, it will result in a lower average force and presumably a lower peak force; or (b) because if the load is applied sufficiently slowly, the material has time to equilibrate as it goes. There's nothing of either of those here -- whether your break cord takes the load now or when you've fallen another centimeter, it'll still take very nearly the same load applied over the same time.

If anybody would care to share a reasoned explanation to the contrary, I'd love to hear it...

I have done very few SL's and have not to date had a problem at least not one that I'm aware of.

It seems that this thread indicates that premature breaks do occur although how frequently I'm not sure. If they do occur what is recommended to address them; double loops of differing lengths or what?

Can someone please advise if it is an unlikely possibility or a likely probability and the cure.

Thanks in advance

John

Assuming a 3.5 Kg canopy falls 3 m before SL system reaches full stretch, and assuming the whole system stretches additional 0.1 m during impact, the average impact force is ~ 1028 N which is 231 lbs. While these calculations are probably way off, it still seems that the force just to decelerate the canopy can be quite high. Though, it would be nice to test this under real life conditions.

Tools used to:
http://hyperphysics.phy-astr.gsu.edu/hbase/flobi.html
http://www.convertunits.com/from/newtons/to/lbs

Exactly. As you can see from the video Dave posted, it's not like this kind of premature break puts you scary-low or something. I suspect it happens much more frequently than people believe it does. In fact, if I recall correctly, Basic Research (or was it Apex at the time?) did some test jumps prior to the Superbowl jump, and it was the rate of premature breaks they saw there that led them to use the two-loop method.

That two-loop method (using two separate loops of break cord, one loop a centimeter or two longer than the other) is my preferred remedy for the problem.

I don't trust the calculations. the canopy does not just stop, it deploys (depending on how you pack).

it will unfold in a staged way. thus the full weight of the canopy does not hit the breakcord at once. it occurs over time. anyone who has jumped an original Sabre will appreciate how much softer a partial second delay feels!

IIRC
Apex found that shortening the bridle greatly reduced or eliminated premature breakage.

(I still prefer 2 loops. breakcord is too cheap.)




ps
people should want to find a balcony or similar platform, and drop test things for themselves. tie off a bagged canopy and give it a toss. then unbag the same canopy, tie it off, and check out the differences.

if you're bold, toss a packed BASE rig.

personal test should provide far more comfort than internet advice!

I think you might misunderstand. We're talking about the forces due the the canopy being pulled out of the container, not deploying. When the jumper hits the end of the bridle, the pins are very suddenly brought to a stop (because there's not much stretch in the bridle). Next, the canopy is brought to a stop and (because the jumper is not), the lines begin to deploy. Granted, the canopy isn't brought to a stop suddenly, since it unfolds as it comes out, but the forces are certainly not insignificant (again, one feels this force when PCA'ing), and it is brought to a stop, provided the break cord doesn't go prematurely.

agreed.

the force will depend on the pack method, how tight it fits into the container, if the container has dynamic or fixed corners, etc. fractions of a second can create huge variations in the dynamic load.

lifting the parachute generally is when a premature breakage will occur.

Exactly!

I have quite a few static lines done in exactly this same fashion and have never had any issues. I have seen numerous other people use this exact same method and never have any problems. Almost every premature break I have seen or heard of happened with a single loop of break cord and/or tying off at the PC.

Tie the break cord as close to your pins as is possible (giving yourself enough slack to maneuver on the exit point). Use two different length loops of 80lb break cord tied with a surgeon's knot.

I usually go one step further and attach a small quick link between the bridle and break cord to prevent the break cord from burning the bridle as it takes load. That does happen; take a look at your bridle next time you make a static line jump. Often, there will be small burn marks running across the bridle.

And remember, redundancy is your friend on low static lines!! :-)

fo sho.

where altitude is precious, i always use two loops.

also, IMO it is the fault of the velcro rig in that video. head high exits with velcro create a relatively high pull force at bridle stretch. then the system goes slack, then suddenly the weight and speed of the falling canopy. THAT is the dynamic force that causes the premature break.

in a pin rig with similar conditions, there is considerably less force at bridle stretch, therefore a smaller dynamic load at canopy extraction.

and thanks for the nice video.

I'd think the forces are equal. Because conditions are basically same (after pins are extracted): bridle reaches full stretch (between SL and canopy) and canopy is still going at the same speed as jumper. So extraction force will be the same. Unless I'm missing something...

I agree. The container is open by the time the canopy is being lifted off of the jumper's back. I don't see how the container used to be closed can be relevant.

That said, I agree with previous comments that container-opening forces (ie, pulling pins or peeling velcro) on head-high exits with velcro are higher than those with a pin rig, though I believe that the rapid rotation of the canopy suggests that a large force was applied to it, which suggests that the container was opened and the canopy being lifted before the static line broke.

if the opening force of the container is higher (i.e. velcro) the higher force i'm talking about is at bridle to shrivel flap. (before the container is open) that is where an initial dynamic load is placed on the SL and quite possibly severely weakening it. from that point, there is a very small amount of slack in the system between the flap and the canopy attachment point. when that comes under tension, it finishes the job.

Interesting video regarding forces generated in a fall and the effects of knotting a sling.
http://www.dmmclimbing.com/video.asp?id=5

had this happen early in my base career (earlier this year), soloing a 240 foot freestander but i had trees to worry about too. single loop, 80lb, tied to the metal structure (this is why it broke i believe). standard 9' bridle with 2 pin rig. backed up with a 48"PC. i ended up low facing the trees and had to slide in the landing after a hard toggle turn. Thank you PC for saving me, and everything worked out as good as i can expect. I now tie off to tubular webbing or other soft connection points.