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CoolBeans

Shock absorbing risers - with crumple zones - to soften hard openings

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Posted (edited)

I've been thinking of simple riser design to absorb some of the hard opening energy. In a similar way that crumple zones work in the car. Those zones could be for example: 7G, 7.5G, 8G, 8.5G, 9G, 9.5G, 10G etc. Below is my simple prototype, in real world, using modern technology, those zones could be integrated into the riser (webbing) itself. I believe professional name for that is tear webbing or shock absorbing webbing.

Disadvantages?

  • crumple zones could break unevenly which would result in uneven lengths of risers
  • crumple zones could break when not desired, for example during high performance low turn
  • after hard opening crumple zones would leave jumper with extra long risers which, depending on design, might not be landable anymore and may require cutaway
  • crumple zones will have tolerance that will change over time; ones that initially were designed to tear at 7G after years may tear at 6G which could happen unexpectedly during high performance maneuver
  • in order to operate properly, those risers would have to be rated for very limited body weights, e.g. 150-155 lbs only
  • torn risers would have to be replaced which is extra cost for jumper

Advantages

  • crumple zones should not affect base riser strength
  • crumple zones would absorb some of the hard opening energy
  • risers with crumple zones should be very similar to regular risers and wouldn't require any other equipment modifications
  • risers with crumple zones should behave exactly like regular risers in < 7G conditions; no extra flex should be observed
  • risers with crumple zones could potentially be beneficial in fast spinning malfunctions as they would lengthen the risers making the spin slower

What do you think? I think some other industries already use similar approach, e.g. Petzl ASAP`SORBER https://www.petzl.com/US/en/Professional/Mobile-fall-arresters/ASAP-SORBER

_________
Assumptions

  • hard opening that would require extra shock absorption is above 7G
  • any regular canopy maneuvers are below 6G
  • crumple zones should preferably be numerous and short, as short as possible ; that way if 1 zone tears at undesired moment, it shouldn't cause too much damage

IMG_4449.JPG

IMG_4448.JPG

Edited by CoolBeans

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That's a very interesting concept. I'm hoping some engineers (in addition to riggers) have a look at this. However, it would not surprise me to learn that BB investigated this years ago. IMO linear dissipation of kinetic energy would be kind of what the parachute itself does, only more focused and functioning in a catastrophic scenario (killer hard opening), where the risers would fail, but only enough to take some of the G-shock off the wearer's body.

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Just now, Deyan said:

Here's why this is not going to work.

7G on someone 110 pounds will require completely different strength than 7G on someone 220 pounds.

Just a my thought

 

The author addressed that by specifying a weight range. This could also possibly be compensated for. Like I said, I'm sure someone like Bill Booth has looked at this and done the research. I'm thinking the added bulk and expense (and other limits as you mentioned) make it impractical, but perhaps only due to the lack of a particular substance; something with the right combination of rigidity and elasticity to do the job. Got to admit it's a great idea and could save lives which might otherwise be lost to things like torn aortas induced by hard openings.

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(edited)

Some ejection seats use tear-strip bridles to even out surges in opening sequences. Tear-strips function the same way as the cotton break-cord used to stage openings on military static-line mains. Lazy skydivers switched to Velcro, then rubber bands, than sili-stows, then tuck tabs, then magnets, then  ... quick! invent another gadget ....!

Once airspeeds exceed 200 knots, even the slightest pause in opening shock is quickly followed by a massively harder load surge as different components struggle to match speeds. Those surges tear parachutes and pilots.

The simplest tear-strips involve a piece of (full strength) webbing folded over on itself and zig-zag sewn with E-thread. Tearing E-thread is more consistent than the rubber bands suggested above. Since the E-thread consistently fails at 8.5 pounds, it is easy to calculate when it will tear.

The problem is protecting that tear-strip until it is needed. Protection is easy inside a sealed ejection seat or reserve container, but more difficult on main risers that are expose during every jump.

Perhaps you add a tear-strip just below the 3-Rings and protect it with a fabric cover. ???? Mind you, the most painful openings tend to force all the opening shock onto one side of the harness.

This challenge requires a brighter mind than mine.

Edited by riggerrob
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(edited)
8 hours ago, riggerrob said:

The problem is protecting that tear-strip until it is needed. Protection is easy inside a sealed ejection seat or reserve container, but more difficult on main risers that are expose during every jump.

Perhaps you add a tear-strip just below the 3-Rings and protect it with a fabric cover. ???? Mind you, the most painful openings tend to force all the opening shock onto one side of the harness.

This challenge requires a brighter mind than mine.

Hi Rob,

Some fall protection for industrial workers has the shock dissipating device encased in a heavy plastic shrink wrap.

It sounds like you are suggesting it be below the three ring on the harness, that raises TSO problems, but maybe I am misreading what you wrote.

 

To the OP

I see few problems myself.

The main one is balancing the risk of a fatal hard opening, against the risk of a fatality cause by uneven activation from a hard opening that still manages to incapacitate the jumper but would have be survivable without the device. If you tear one side only the canopy is going to dive the rest of the way to the ground in a turn.

 

This is going to be a bulky device.

 

Also the potential need to have it vary by weight it problematic from a cost perspective. Now you need risers of different lengths, and different weights. There is going to be no economy of scale here, and what happens when the fat guy grabs the skinny guy's rig? 

 

 

 

Edited by DougH

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Besides attempting to solve a problem that doesn't exist, except on  " one in a million"  jumps - Consider: (What Doug H said)  One rips to full length or, at least very unevenly.   The other one doesn't. =  result - dangling by one riser.  Ram air parachute is now in a spiral from 3000+  feet to the ground, spiral tightening and becoming more forceful as time elapses.(as Doug H said).  Jumper probably quickly passes out from the G's  then fatally impacts the ground in a hard spiral..

No reason to assume each side will rip the same. In fact, in my opinion it would be unlikely to have both risers ever rip the same. 

My opinion:  Very bad idea..

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Add another pair of 3-rings to "extend" the riser on demand. If one breaks it will extend the other one as well. Obviously this would all be a lot smaller and shorter and protected by a cover which also limits the distance between the risers. ^.^

image.png.8d8cae71a827e4c95a0609c59fea4b9f.png

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17 hours ago, dpreguy said:

Besides attempting to solve a problem that doesn't exist, except on  " one in a million"  jumps - Consider: (What Doug H said)  One rips to full length or, at least very unevenly.   The other one doesn't. =  result - dangling by one riser.  Ram air parachute is now in a spiral from 3000+  feet to the ground, spiral tightening and becoming more forceful as time elapses.(as Doug H said).  Jumper probably quickly passes out from the G's  then fatally impacts the ground in a hard spiral..

No reason to assume each side will rip the same. In fact, in my opinion it would be unlikely to have both risers ever rip the same. 

My opinion:  Very bad idea..

it does exist and i am getting near the age where a hard opening could kill me.  i rather like the idea of someone looking into it.  it does not make a difference if it rips unevenly or even one side and not the other.  it prevents your torn aorta and allows a cutaway and reserve deployment, even if the canopy starts spinning wildly right away.  it may induce one to pass out very quickly, but i like that idea much more than just dying right off the bat without getting a chance at all.  of course, all this depends on whether it would work or not.  even if it weren't cost effective, it would be nice to have the option if i want to pay for it.  like an aad.

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(edited)

Uneven risers in case of hard opening are pretty much guaranteed. However, I bet anybody who went through serious hard opening would have traded that for uneven risers.

Uneven risers leave pilot with two options, either pull one riser to make them even or cutaway. I suspect one could also correct uneven risers with toggle input, obviously that depends on how badly uneven the risers would be. 

Small improvement to help with uneven risers would be to put flexible element inside the folds so that way after stitches are torn, the flexible part would still maintain original riser length. The outcome would be same or very similar length risers but flexible. Although, they wouldn't flex all that much as normal canopy flying wouldn't put 7G+ forces. 

I've done some simple calculations:

a = 6G

m = 200 lbs ; F = 5339 N
m = 180 lbs ; F = 4805 N
m = 160 lbs ; F = 4271 N
m = 140 lbs ; F = 3737 N
m = 120 lbs ; F = 3203 N
m = 100 lbs ; F = 2669 N

____

a = 8G

m = 200 lbs ; F = 7119 N
m = 180 lbs ; F = 6407 N
m = 160 lbs ; F = 5695 N
m = 140 lbs ; F = 4983 N
m = 120 lbs ; F = 4271 N
m = 100 lbs ; F = 3559 N

____

a = 10G

m = 200 lbs ; F = 8899N
m = 180 lbs ; F = 8009N
m = 160 lbs ; F = 7119N
m = 140 lbs ; F = 6229N
m = 120 lbs ; F = 5339N
m = 100 lbs ; F = 4449N

____

a = 12G

m = 200 lbs ; F = 10679N
m = 180 lbs ; F = 9611N
m = 160 lbs ; F = 8543N
m = 140 lbs ; F = 7475N
m = 120 lbs ; F = 6407N
m = 100 lbs ; F = 5339N

As you can see, the forces are all over and because of that shock absorbing risers would have to be rated for very limited weights.

Shock absorbing riser rated at 5339 N would tear for 100 lbs jumper at 12G and for 200 lbs jumper at only 6G.

The important data points are around how many Gs does hard opening vs normal canopy operation put on the risers.

shock-absorbing-risers.png

Edited by CoolBeans

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2 hours ago, CoolBeans said:

Uneven risers in case of hard opening are pretty much guaranteed. However, I bet anybody who went through serious hard opening would have traded that for uneven risers.

Uneven risers leave pilot with two options, either pull one riser to make them even or cutaway. I suspect one could also correct uneven risers with toggle input, obviously that depends on how badly uneven the risers would be. 

Small improvement to help with uneven risers would be to put flexible element inside the folds so that way after stitches are torn, the flexible part would still maintain original riser length. The outcome would be same or very similar length risers but flexible. Although, they wouldn't flex all that much as normal canopy flying wouldn't put 7G+ forces. 

I've done some simple calculations:

a = 6G

m = 200 lbs ; F = 5339 N
m = 180 lbs ; F = 4805 N
m = 160 lbs ; F = 4271 N
m = 140 lbs ; F = 3737 N
m = 120 lbs ; F = 3203 N
m = 100 lbs ; F = 2669 N

____

a = 8G

m = 200 lbs ; F = 7119 N
m = 180 lbs ; F = 6407 N
m = 160 lbs ; F = 5695 N
m = 140 lbs ; F = 4983 N
m = 120 lbs ; F = 4271 N
m = 100 lbs ; F = 3559 N

____

a = 10G

m = 200 lbs ; F = 8899N
m = 180 lbs ; F = 8009N
m = 160 lbs ; F = 7119N
m = 140 lbs ; F = 6229N
m = 120 lbs ; F = 5339N
m = 100 lbs ; F = 4449N

____

a = 12G

m = 200 lbs ; F = 10679N
m = 180 lbs ; F = 9611N
m = 160 lbs ; F = 8543N
m = 140 lbs ; F = 7475N
m = 120 lbs ; F = 6407N
m = 100 lbs ; F = 5339N

As you can see, the forces are all over and because of that shock absorbing risers would have to be rated for very limited weights.

Shock absorbing riser rated at 5339 N would tear for 100 lbs jumper at 12G and for 200 lbs jumper at only 6G.

The important data points are around how many Gs does hard opening vs normal canopy operation put on the risers.

shock-absorbing-risers.png

Hi Beans,

As a retired Mech Engr, I applaud your efforts.  I do not know if your concepts will work out successfully.  But, just kicking ideas around is a big step in the right direction.

Keep at it; Bill Booth did not develop the WonderHog on his first attempt.

Jerry Baumchen

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It seems a more reliable solution would be something like a urethane bumper in maybe a metal sleeve (think shock absorber) the urethane is available in different hardness / compression would make it tunable and reusable and wouldn't cause uneven risers. With stitching it would degrade with jumps and be difficult to know it's strength was degraded.

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The location of the shock absorber could be moved from the riser to the attachment to the largest of the 3 rings or the main lift web of the container, which might be easier from an engineering perspective.

Agreed about the point above about stitching - over time it would grow weaker, and "trip" at a much lower load, like a normal opening.

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58 minutes ago, accumack said:

It seems a more reliable solution would be something like a urethane bumper in maybe a metal sleeve (think shock absorber) the urethane is available in different hardness / compression would make it tunable and reusable and wouldn't cause uneven risers. With stitching it would degrade with jumps and be difficult to know it's strength was degraded.

They have that technology already. They are called dacron lines. xD

 

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19 hours ago, sfzombie13 said:

it does exist and i am getting near the age where a hard opening could kill me.  i rather like the idea of someone looking into it.  it does not make a difference if it rips unevenly or even one side and not the other.  it prevents your torn aorta and allows a cutaway and reserve deployment, even if the canopy starts spinning wildly right away.  it may induce one to pass out very quickly, but i like that idea much more than just dying right off the bat without getting a chance at all.  of course, all this depends on whether it would work or not.  even if it weren't cost effective, it would be nice to have the option if i want to pay for it.  like an aad.

So I assume that right now you are jumping a slow opening canopy like a pilot, with an oversized slider, and dacron lines?

If you aren't, why aren't you first gathering up all of the low hanging fruit that will reduce your risk.

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actually, it's a pd 210 at a 0.9 wl with a regular slider and dacron lines.  i haven't heard of the oversized slider, thanx for the tip.  i will ask about it when i go to the dz this weekend.  it opens pretty smoothly though, i don't think i want to mess with it.  the shock risers was for when and if i decide to downsize.  i just got this one so it will be at least the rest of the year with it to get comfortable. 

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(edited)

I jump a Pilot with Dacron lines.

I wonder if this talk of stretching risers might all be pointless. What we first should be figuring out is how much of a "crumple/stretch" zone is needed to significantly reduce a hard opening.

Edited by sundevil777

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(edited)
43 minutes ago, sundevil777 said:

 I am quite  skeptical that a few inches would be enough to matter much.

 

I agree. I tried doing the math, and fail to see how this solution would work. It sounds nice, as a concept, but there is no way I can make it work on paper. On a climbing harness this solution makes sense; a rope stretches maybe half a meter, adding 20 cm to that helps. But unlike a climbing rope that is anchored into a mountain, a canopy moves with the skydiver and simply excerts a force through the lines, which mainly depends on air speed. Unlike a climbing rope, the force is independent on distance travelled; it just depends on the speed.

A canopy opening at  7G has a "braking distance"  of about 26 meters (thats ~86 ft, ouch!) , adding a few inches to that is insignificant. Or is this too much of a simplification? If so, how should you calculate this?

 

 

 

Edited by evh

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(edited)

All it has to do is change the amount of time the spike hits. During test jumps at Para-Flite I had several openings above 15g's documented The duration of the spike was very important. The majority of those were with Dacron lines.

 

 

Edited by accumack

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(edited)
5 hours ago, evh said:

A canopy opening at  7G has a "braking distance"  of about 26 meters (thats ~86 ft, ouch!) , adding a few inches to that is insignificant. Or is this too much of a simplification? If so, how should you calculate this?

Let's start from the basics, the source of the problem is how many Gs are experienced by the jumper. Simply let's say, <6G the opening is ok, 7G - 12G would be pretty hard, 13G+ would be life threatening. That's just rough guidance. 

In any case, we are dealing with abrupt slowing from approx 120mph down to approx 20mph, that's a difference of 100mph that needs to be dissipated. If the parachute opening completes within 0.3 sec it will put 15Gs on the jumper. If we can do anything to extend that process to e.g. 0.6 sec it will put 7.5Gs on the jumper. That's what's most important here.

If shock absorbing risers can maintain the process of tearing for the duration of only 0.3 sec they will eat up 7.5Gs that jumper won't experience. Or in other words, they will make jumper experience 7.5Gs over 0.6 sec instead of 15Gs over 0.3 sec.

As a side note, 0.1s opening would take 45Gs and 0.2s opening would take 22.5Gs. 22.5 is better than 45, ain't it? Dacron lines do pretty much the same thing, they flex extending the opening duration and eat up Gs. Advantage of the shock absorbing risers is that during normal operation they don't flex like Dacron lines do, they only flex on super high Gs

Edited by CoolBeans

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#1 - I commend you for recognizing a problem and searching for answers. Really. 

I fully agree with Jerry's comments in post 11.

However, this has been discussed before. 

This thread was spun off of an "Incidents" thread, when it got too far off the actual incident:
 



But it covers what you are thinking about.

There are a few posts from 'RiggerLee'. He's probably the smartest and most experienced guy on here when it comes to stuff like this. Last I heard, he was designing and building recovery parachutes for rockets. 
 

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(edited)

I figured I could do some basic testing in garage conditions. I would need to get a hold of some old 3-ring system and some old risers that I could reuse to make a prototype. Does anybody know what's the easiest/cheapest way to go about obtaining old/used risers and 3-ring systems? I'm in California / Bay Area. 

Edited by CoolBeans

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i've got an old container i could send you but it didn't come with risers.  i'll look and see if we have any sitting around the attic at the dz when i go down today.  i was talking with a rigger this weekend about this.  i asked about a 2d set of slinks to use for this.  have one set like the normally go that are designed to break away at 7 g's and another set that has slack in them to catch when the others break, like maybe double or triple the size but strong enough to handle the extra force.  it would bulk up the risers though, maybe that can be worked out.

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"Well, in all my years I ain't never heard, seen nor smelled an issue that was so dangerous it couldn't be talked about. Hell yeah! I'm for debating anything. " - Stephen Hopkins (RI)  "1776"

As others have said before, don't let our nay-saying discourage you from trying (carefully) to find a new way... but also look at what has been tried before so as to not relearn lessons (especially those we've paid blood to learn).

That having been said, I'm thinking that the simplest solutions usually are the best... how about this:

Learn from the:

                         Type 17 risers pre-reinforcing strap. 

                         Collin's Lanyards.

Solution concept:  Dual Collin's Lanyards with main risers designed to fail on overload, where the Collin's lanyard connection point is above the weak-link on each riser.  If either riser experiences an overload, it fails, releases both risers and the reserve is free to be deployed (if not all ready by RSL/MARD).  (notice, I said dual Collin's lanyards, NOT a single dual-connected strap like the Racer RSL)

Hang-on ...let me get my kevlar on and adjusted...

OK, FLAME ON!! ;-)  Debate!

 

JW

 

 

 

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