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kkeenan

Severe Opening Shock Protection

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With the severe opening shock incident at DeLand recently, I'm wondering if anyone has looked into designs to mitigate an "extreme" event like this. I'm thinking of something like the fall-protection lanyards with built-in section of sacrificial stitching that gives way during a super-severe load. This would not come loose during normal use, but only give way to mitigate an extreme opening shock.

I'm sure there are other approaches to the problem. Clearly, an opening like this can have devastating consequences. If there could be something in the force line between canopy and jumper which could mechanically intervene and spread out the impulse somewhat.

Just curious to hear if anyone has seen any work in this area.

Kevin K.

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This idea has been considered before, but the problems outweighed the benefits. If the 'fail safe' let go when it wasn't wanted, you just opened yourself up to the risks of a cutaway when one wasn't needed. If the 'fail safe' let's go under canopy at a low altitude, you just rendered your canopy un-landable below your do-not-cutaway altitude.

I think what it comes down to is some very basic preventative measures that most people will be too busy, too lazy, or too cheap to implement.

Note: I'm not suggesting that any of these factors played a role in the recent incident in Deland. Hard openings can happen anytime for any reason, these are just some steps you can take to minimize that risk.

1. Packing - this is a no-brainer. Learn to pack. Learn to pack your rig neatly and correctly, even if it means practicing at home and taking your time at the DZ. Bagging the canopy is, for most, the hardest part of packing and it's also the time where the flaking/organizing you did can come undone as you try to shove the canopy in the bag. Keeping the slider up at the stops, the line tension even, and the nose/tail preparations intact are key to getting good openings, and if you lose them bagging the canopy, the whole pack job is a waste of time. The other side to this is properly sizing your container for your main canopy, because if you're trying to squeeze your main into a tiny rig, your chances for success go down.

2. Maintenance - keep your rig in good shape. Worn closing loops and BOC pouches can lead to premature deployments, and if you're not in a good body position, it can lead to a hard opening. Likewise, keep your lines in trim can also go a long way toward keeping your openings good and consistent. This isn't a mystery, you can measure your lines against the factory trim chart, and see how far out they are. Since nobody wants to be without their canopy in the middle of the season, this where sometimes you have to look 'into the future' and bite the bullet for an early reline. If you lines are 'close' to being out of whack in January, but still 'ok', what are they going to look like in 50 or 100 jumps in the middle of the season? At that point, it's either send it in mid-season, or jump the rest of the season with 'questionable' lines. The solution is to send it in for the reline in Jan, and do the preventative maintenance. This is skydiving, it costs money, just get it done.

3. Body position - first off, let's remember our pull priorities in order, 1. PULL, 2. Pull at the correct altitude, 3. Pull while stable. You can see that pulling while stable is last on the list, it does contribute toward getting a good opening. You want to be level on all axis (not head low, or leaning to one side) and going at a 'slower' speed in the flattest position that you can still be comfortable and in control. The trick is that getting to that position at pull time takes planning and sticking to that plan. If you bust your break-off altitude from a jump, and end up low and trying to get away from the group, it becomes tough to meet all of the pull priorities. The way to prevent this is with conservative break off altitudes where you have time to track sufficiently, slow down, and get into an 'optimal' pull position by the time you reach your pull altitude. This is where, again, you have to bite the bullet and sacrifice 500 or 1000ft of freefall and move your break-off up enough to allow time for you to be careful on the bottom end.

Those three areas are where you can do your best to prevent hard openings, but sadly it's probably a lost cause. I'm willing to bet that if you went to the average DZ and watched the proceedings, you would see more people than not who either use a packer or rush through a sloppy pack job, put off gear maintenance/relines based on the cost, and plan skydives with lower break-offs adding pressure to the bottom end maybe making them choose between a 'clean' pull or an 'on time' pull.

Sad, but true.

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That's not a bad idea. The risers themselves could have a rip-through energy absorbing section like found in climbing equipment, but then i guess it's the question if the occurrence is frequent enough for the manufacturers to take action and to justify the extra complication with our gear.

http://www.petzl.com/en/pro/verticality/lanyards-and-energy-absorbers/energy-absorbing-lanyards/asapsorber

P.S. To avoid 'misunderstandings', even a single occurrence would be enough in my book, as this is a devastating situation. The whole 'use Dacron', 'take care packing', etc. arguments apply, but some extra mitigating just-in-case's wouldn't go amiss.

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The risers themselves could have a rip-through energy absorbing section like found in climbing equipment,



As mentioned when this same issue was brought up earlier, and the same piece of equipment was cited as an example, those fall protectors are designed to take one fall and 'fail' in order to save the person falling. In daily use, those devices take no load until there is a 'fall', with the fall being the time when the device goes to work.

In skydiving, daily use involves repeated opening shocks, and even a 'good' opening will impart more load than a short fall while climbing. The problem is making something that can last for 100's of openings without failing, but still fail when you want it to.

That's there the issue of 'calibration' comes in, and how you make something that holds through 100's of openings without failing or weakening, but then still fails only when you want it to. In that sense, it's way different than climbing.

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davelepka

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The risers themselves could have a rip-through energy absorbing section like found in climbing equipment,



As mentioned when this same issue was brought up earlier, and the same piece of equipment was cited as an example,



Yep, sorry, there were no replies when i started writing my post.

There was a study a while ago that involved parachute opening shocks using soldiers as guinea pigs that surmised the highest shock that the human body can take without injury is 6kn and 12g or so. A later study focusing in fall arrest systems referencing these past tests can be found here http://www.hse.gov.uk/research/hsl_pdf/2003/hsl03-09.pdf

It is possible to 'calibrate' the absorber to start ripping at a particular load of, let's say 8kn (most models are set to start deploying at between 2/4kn), and there are re-setable systems that could be adapted http://www.e-climb.net/en/12-schock-absorbers, but since as you said manufacturers already looked into it and i'm just a punter i'll default to them knowing more than me on the issue. :)

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With the severe opening shock incident at DeLand recently, I'm wondering if anyone has looked into designs to mitigate an "extreme" event like this.



Absolutely, this has been done. The SPEED bag would have prevented it. There has never been a line strip or dump from a SPEED bag.
Riggers are too lazy to pack it and the packers bitch every time they see one. What a sport, our equipment is dictated by packers who condemn safety improvements because it’s too much work.
The SPEED Bag was used by the USAFA for 3 years I know of and it reduced their malfunctions to 1 in 3 years from 54 in 3 years.
It has been available for 10 years now as a main and for the last 5 or so years on reserves.

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The speed bag Does work. I can testify to this. I blatently stole the idea for another project. It's about the best staging you can hope to get with out getting radical.

Con is that they are a bit of a pain to pack. Perticuarly if the canopy is too big for the bag or you are not competent enough to get it into the bag. They are not tolerant of the big blob hanging out technique of packing which is bull to begen with. And for the record. As good as it is. You can still have a line dump. I know because I managed it. It was an extream enough situation that I doubt any one here could reproduice it. But just saying. Yes, there has been a line dump on a speed bag.

I work with screamers. You have to keep in mind that the amount of energy absorbed is a product of force over elongation. So to really be meaningfull they have to extend a lot or be really stiff. Do the math on the percentage of energy absorbed. Dacron lines as an example just don't have that much give. I think the benefit is more from improved staging, the rubber bands held them, as opposed to specter, where the rubber bands and tube stowes did not. It might also tame the slider a bit. I don't think you will see a tecnilogical fix to this. And you wouldn't want it if we had one. Most hard openings are radically asimetric. You would create a malfunction extending one side with out the other. I think the focas should be on prevention. Improving the staging. Dome slider, pockets around the edges of the slider, magnets on the slider, Dacron or hma lines, better stows, better bags, canopy design.

Lee
Lee
lee@velocitysportswear.com
www.velocitysportswear.com

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JohnSherman

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With the severe opening shock incident at DeLand recently, I'm wondering if anyone has looked into designs to mitigate an "extreme" event like this.



Absolutely, this has been done. The SPEED bag would have prevented it. There has never been a line strip or dump from a SPEED bag.
Riggers are too lazy to pack it and the packers bitch every time they see one. What a sport, our equipment is dictated by packers who condemn safety improvements because it’s too much work.
The SPEED Bag was used by the USAFA for 3 years I know of and it reduced their malfunctions to 1 in 3 years from 54 in 3 years.
It has been available for 10 years now as a main and for the last 5 or so years on reserves.



................................................................................

John,

Packers also whine loudly about the bungee cords on Strong's Anti-Line Slump Bag. I know (the hard way) what happens when you extend the bungee cords long enough to quiet the packers.
Hah!
Hah!
IOW I have learned - the hard way - that there are two possible lengths for ALS bungees: Strong's recommendation and the wrong length.

Face it John, packers will whine about any system.

Tape over your ears if you don't like the whining.

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And for the record. As good as it is. You can still have a line dump. I know because I managed it. It was an extream enough situation that



Lee,

I think it is important to explaine that your line dump did not occur on a personal deployment. I would love to see the video if there is one and there must be as you identified it as "Line Dump"

To the poster who said "if I don't like the whinning cover your ears". I say the whinning doesn't bother me because I understand the ignorance. But it sure bothers the customers when they will not buy it because their packer doesn't like it.

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In fairness to Sherman I will clarify.

I was referring to a recovery system. It's for a suborbital sounding rocket rated for reentry from 350,000 feet. We're trying to do it with a two stage system going directly from the reentry ballute, think drogue, to the main. We had a problem when we had an early abort do to a guideance failure. So it was a low altitude, high speed, heavy abort. We had over 2500 lb of snatch force on the bag rather then the expected 1000 lb of force lifting the bag. The real problem was the connecter links. We have eight 15,000 lb drag chute links that hold the lines on the risers. They weigh about 10 lb. They were tied to the bottom of the bag with 80 lb break cord along with bites of the ten foot long risers. But with the 33 g acceleration of the bag that was not enough to lift them and the stayed behind stripping the risers and lines off of the bag with out leaving the pack tray. The canopy deployed and then the rocket fell the remaining ten feet to riser streatch. Ka bam. blew out several cells bottom skin and top skin. There was just a grid work of reinforcing tapes on that part of the canopy. Cool thing was WayMores AGU compensated and flew it back to withen 50 meters of the target.

So unless you are working with hypersonic deceleraters at over mach 4 with 2,500 lb of snatch force (and I don't think even Sherman will claim that on his pilot chute) and have 15,000 lb drag chute links on your risers... you should be fine. I hope this clarifies what I mean by an extreame situation.

In short I fell fully confident endorsing Mr. Shermans Speed Bag for all normal deployment regimes that even the fastest free flyer or speed diver will face.

It was just that one oppsy. We fixed it by spiting the two riser groups and tieing them seperetly with muttible wraps of 80 break cord to lift the links along with the bag to riser streatch. Problem solved. Just a minor hiccup in the learning curve.

Lee
Lee
lee@velocitysportswear.com
www.velocitysportswear.com

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