Basejumper.com - archive

How did that happen??

This has already happened a few times at Bridge Day. I believe the last time was in 2007.

It happens because the bridle is incorrectly attached to the PC; the bridle gets routed outside or around the attachment point loop, rather than through the attachment point loop. This gives the impression of a correct attachment, but in reality all the opening force is loaded onto just one stitching point. This stitch tears, and the PC detaches from the bridle. This happens just as the canopy hits line stretch, which is when maximum force is applied to the bridle. I don't know of any cases of the PC detaching earlier in the deployment sequence. Detachment prior to line stretch would probably be fatal.

I watched that pink PC float away.

Also chatted with that guy's crew which were a nice
bunch of fellas who kept offering me beers every
time I walked by their camp on the way to my cabin.

It was the guy's birthday so I told his buddies that the
next day they should all line up and take turns
punching him in the nuts...

You know, for his own sake

If anyone wants to see video of this, thank God,
non-event, then be sure to order the official DVD
from jump-Cuts

The last time it happened, they figured it out after recovering and examining the pc.

I do not know if anyone collected the recent free floating pc.

It felt odd at the gear check when Moe told me how to correctly attach my pc. Initially, I thought he had found an oops on my part. Nope, he was just trying to prevent a repeat.

 

my buddy said there was a pop sound, like breakcord... so unless it was actually that, I don't think it was a joke.


not sure if this link will work, if you aren't his "friend"...

http://www.facebook.com/video/video.php?v=1183325515235&ref=nf

I think that there was 2 different events. The first was very early into jumping, where a guy went handheld and the pc separated from the bridal.

The second was a joke but i didnt see that one so im not sure what it looked like. I dont know how you could get a pc in your hand AND in your BOC past gear check though.

For anyone curious, there's video of the 2007 incident in Jimmy Halliday's trailer for the 2007 DVD:

http://www.youtube.com/watch?v=xalXYrrE2iM

Fast forward to 03:40 and keep an eye on the lower jumper with the bright yellow canopy.

 
not sure if this link will work, if you aren't his "friend"...

Andrew...Your my only friend....proof my life sucks.
;-)

I'll post the PC cutaway on youtube when I get home.

they were indeed two separate events. i was working the ramp during both.

the first was an old crappy velcro rig where the PC did in fact break off during deployment. it was scary, but obviously the canopy deployed safely after.

the second, was (IIRC) some of the Ill Vision guys. had a PC hand held with a short bridle just tucked in the rig, then a normally stowed PC. funny trick that has not been done for a few years.

all in all, some good jumps and a great day.

thanks!

myself and a really gay shuttle van driver watched it from the corner of the packing area. it was at 9:12 and it was a pink PC. The handheld fake PC was black, so definitely two separate incidents.

One of the gear checkers caught a PC hooked up identical to the 2007 incident during setting someone up for handheld on top. (bridle routed by bringing both sides of the centerline up from the inside and thus held on by just the bartacking that holds that center line to the load tape hub.

get your heads out of your asses people ! Talk to Sangi, and learn what not do in BASE !

So are you saying that you can use break cord to attach your PC to the bridle? Ive never heard of this. Must be something new, huh?

JUST KIDDING

I don't see why not. If it's good enough for static line, it should be good enough for a pilot chute. Would make for some very expensive jumps though, losing the PC every time.

P.S. I'm not actually suggesting using break cord. I'm just saying that physically it is feasible.

Not necessarily...

It can be seen from a lot of unpacked jumps that even at short delays the canopy has a high enough drag-to-weight ratio that it will make it's own way to linestretch.

All the PC would have to do is get the container open and the packjob out of the jumper's burble.

I'm picturing funny like, "Hey I have cancer. Just kidding! Haha"

With break cord, you still have your PC attached. If the break cord breaks before the canopy is at line stretch, it still has done most of it's job, putting the PC into the wind at the highest spot possible and perhaps even opening the container and starting the canopy extraction. You will be open lower than you wanted because the PC has to finish the deployment, keeping the lines tight, etc...

A good static line will put the PC in the proper orientation to keep working until the canopy is out or you are dead.

If you use break cord to attach your PC - then the whole scenario is different. There is nothing to finish the job should the break cord break early.

I have three videos I could show people in person that help prove my point. 1) A PCA where the person was "dropped". The PC finishes the deployment as the PC was let go when the canopy was about half way to line stretch. The deployment was just a bit lower than what you would have seen in a pure PCA.

2) A closeup of a bridle snapping in half leaving the break cord AND PC on the object. That is a break cord that worked too good, but it proves the canopy has to be to line stretch to give that much tension on the line. In that case two break cords were used with a bit of slack between the two attachments on the bridle. The theory - both have to break in succession so the system has redundancy, but without cumulative force required to break if the break cords were attached at the same spot. In reality, the moment of slack between the first break cord breaking and the second break cord getting hit with the load - caused enough shock load to snap the bridle. Moral to the story - the break cord should be under constant tension thru the entire jump (the least amount of "bridle dump" to hit it with sudden force).

Using a break cord on a PC violates this rule (keeping a SL taught thru the deployment process) as we all have heard of "snatch force", which is essentially the sudden force the PC gives the rig the moment the PC hits bridle extension and the jumper is still accelerating while the PC has been decelerating or at least not accelerating as much as the jumper. Especially if the PC has inflated and got a bite of the wind, the moment it is loaded it will have a sudden force as it accelerates to the speed of the canopy coming off the jumper's back.

3) A video of a bridle "Whip-lashing the object" so hard before/as the canopy gets to line stretch that it puts a great deal of tension on the break cord and friction burns the bridle. It would not be too far fetched for the bridle to get snagged half way thru the deployment causing the deployment to occur, followed by a snag-release. The sudden force that would "hit" the break cord when the bridle went taught again could cause a break before full extraction. The PC is crucial to keep the deployment occurring as best as possible.

So, I disagree with your analysis that break cord COULD be used for PC attachment... With any PCA/Staticline you need a PC solidly attached to backup the system, a PC you would trust to open your gear quickly if you are near the ground in the first place.

Just posted the vid on Youtube.


http://www.youtube.com/watch?v=naNxJ1JL6p4

clicky
http://www.youtube.com/watch?v=naNxJ1JL6p4

I guess I'm confused about what you are saying...

simple statics means:
- a single strand of break cord is rated ~80 lbs.
- loop of break cord is rated ~160 lbs.

if two loops are used, and they break sequentially, then the system is still rated ~160 lbs. this will only occur if the load only gets applied to one loop at a time. i.e. there is slack in the system to the 2nd loop.

if there is NO slack in either loop, they should be loaded at the same time. this will increase the system rating to ~320 lbs since the loops must break essentially simultaneously.

slack can't be the uber-evil culprit. once the container opens, there is plenty of slack in the system. the canopy must unfold, riser covers must pop, lines must play out, etc. heck, if there is no slack in the bridle between the attachment point and the first pin, that pin may not pull!



ps
on one s/l gone bad, my parachute tore open before the break cord finally gave out. the bridle remained fine. night, no video, not sure what cause the hangup.

Dynamic loads vs Static Loads.

Imagine taking a bucket and suspending it a few feet over the railing at a bridge by a rope tied in a knot around your wrist. In the rope is a link designed to break at say 100 pounds.


Slowly add one grain of salt, one at a time to the bucket. Your wrist will feel the weight be added, and eventually the link will break when 100.1 pounds of salt is added. What you feel is suspended static weight and at no time does your wrist get subjected to the forces of more than 100.1 pounds of suspended weight. A mortal human could hold that rope for a long time without damage to their body.

Take the same bucket. Fill it with 100 pounds of salt you held under the static load moments ago, put a lid on it... Get a Ryder moving truck to park on the bridge and have a friend hold the bucket as high as possible above your head. Your friend lets go of the bucket while the rope is tied around your wrist.

What forces do you feel as the bucket hits line extension and the link breaks? If you are lucky your bones won't snap and you won't fall over the railing and your hand will be still attached to you.

The link's breaking strength is the same - however energy transfers thru the system and loads the entire system as the weakest links break. Other components in the same system (your wrist) might receive energy equal to their breaking strength too. Heck, some materials in the system might respond differently to static vs dynamic loads due to their elasticity, material makeup, and general characteristics - thus the components that break might change.


Its not slack alone - its the amount of slack and the difference in velocity and mass between the objects on each end of the slack... In the system you just described, every time slack is added, it is taken back and goes under tension before the next slack is added - so each bit of slack is minor and the velocities and mass between the objects is small.

The whole design of a well packed/designed parachute is to pay out the lines and components with the least slack possible, the opposite of "line dump"... The parachute, which is going the same velocity as you initially, slowly decelerates as it comes off your back so by the time it is ready to apply decelerating forces to you all the components are under tension with no slack.

How much slack is bad? Any... In the same example above, drop a bucket a few inches vs a few feet. What drop height do you think your wrist would take before breaking?

Line dump = slack = slammer of an opening.

Bill Booth at PIA this year described the forces involved with riser covers. Traditional riser covers on skydiving rigs release after the canopy is out of the bag and at line tension and in the middle of deployment. This leaves 6"+ of line dump on every jump as six inches of slack is added to the system after the canopy is grabbing air and opening up. The magnetic riser covers he designed open with less force, so they open as the bag is decelerating above you, effectively paying out the lines from both ends at the same time. Once the canopy comes out of the bag - there is no more slack in the system. His theory - this should prevent the infrequent slammer openings that have been breaking leg bones, which have increased in frequency with the exact same canopy models with the only change in the system being stronger "freefly friendly" riser covers.

Going back to the subject at hand... Slack in a system and break cord. My theory - keep the break cord and bridle at tension at all times thru the deployment as best as possible so it "feels" less shock until the end. Unfortunately, at the end of the deployment it will recieve a shock load any way you look at it, but if it is under tension just before the shock load is the least possible.

The idea being - every component in the system "feels" the shock load, from the canopy attachment point to the bridle... Why load it with forces you don't need?

Thus, rig the static line high (above you, not below you). Rig it a few feet away from the PC so you don't fall far before the bridle starts taking load (Jumping away from the object will put you at bridle extension before you even start falling).

And to reiterate... I have a close up video of an 80 pound break cord snapping a bridle when the attachment was slammed with 6 inches of slack. Bad luck or physics... It happened.

wow.
first off, I have taken courses in dynamics. I well understand the difference between static dynamic loading.

second, you did not explain how to avoid having any slack between the primary loop of break cord and the second, back-up loop. at least without doubling the break force.

third, no matter how loosely you tie the first, primary loop of breakcord, it will be taunt. make it 2 foot long, flapping in the breeze. so what? (other than entanglement. note, most carry-with-you set-ups contain significant slack.) for the bridle to generate the force to pull the pins, all slack will be gone. now as the break cord and bridle continue to "pull" the parachute off your back, it must remain under tension. the tension will be momentarily released as the excess bridal between attachment point and the first pin is played out. also, a "cornerless" rig is more likely to "dump" the entire folded canopy into the slipstream, adding slack, and dropping the tension. the tension will build to pop the primary stow (if used).

still, if there is tension in the system, there is no slack. simple physics.

feel free to disagree. only you can decide if a set-up is right for you to jump. only you can make that call. every jumper must choose for themselves.





oh, and I wish my bridle HAD broken. instead my canopy suffered amazing damage which led to a brutal landing. plus it would have been a whole lot cheaper to replace a bridle...

Well, this whole thing started as a reason why a breakcord would be a poor choice for PC attachments and has moved quite far... But oh well...

I am open for suggestions... Do you have any ideas? I have plenty of ways to keep the slack to a bare minimum, but no ways to not dynamically load the 2nd loop with all the force...

BTW, I also have video of electric tape static line... I might say I prefer this method. The bridle, when shown in slowmo, actually slips for a while under the tape before the tape breaks. If you wrap the object once or twice before you incorporate the bridle, what the bridle slips against is smooth. I think this transfers less load to the system in the same way an elastic rope is used for loads that can fall. But it leaves garbage on the object. Give and take.

correct, we have drifted this thread probably too much.


I don't fear dynamic loading like you, but maybe I need to see your video! I believe minimizing sharp edges, eliminate snag points, keep any rigging as simple as possible, and consider shortening the bridle. (Apex conducted test on the later. They concluded it can help reduce premature breakage.) Not all objects may let you shorten the bridle and climb out.


I would agree as well. Any abrupt loading means a very small delta T (how long it takes to fully load the system). Tape, bungees, etc. will always lengthen the delta T. I bet the softest "break" would come if you spiral wrapped tape around several feet of bridle to secure your set-up to a rail. Make the bridle detach like a zipper.

That just violates the KISS principle too much for my tastes...




so does anyone have any news on the separated pc at BD?

anyone have any news on the separated pc at BD?

Yes, a homeless man was found
using it as a make-shift hat

I know the pc pop off guy. He said he did not rig the pc correctly. The scary part is it was not even larks headed to the load tapes alone, or the center line alone. ie no damage to either area of the pc. I did not get to inspect the gear, so this is second hand from him. He has several base jumps, but was not current. I wish I would have asked him to look at the gear myself. Oh yeah, it was his birthday. So his present was life!

AMEN Brudda

Check BASE fatality #73. It was super gross up close and personal, and it was a fucking big mistake.

That's what I thought. Disclaimer: My physics training stopped at like 7th grade

say my pin(s) are insane loose, I would simply compare the break strength of my static line to the break strength of my bridle (or any other part of the system) Common sense tells me that with a clean exit the 80lb breakcord will extract pins/packjob then 'pop' at line stretch

The last thing I would expect is a broken bridal. ??

the guy was with us....he is an old'in.......couple thousand skydives and 49 base jumps...he just got a new nick name SBD....should be dead!

new nick name SBD....should be dead!

That is good!!

ha i also belive sombody from that crew drank the poo freshener that came in the gift bag thinking it was breath freshener hmm....

that shit should be illegal........glad i didn't think it wash eye drops

didn't that dude spend like $10k on drugs for personal use that month and that was part of his brain fart?