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

[dgw 8]

1 hour ago, olofscience said:

How about some magnets to hold the slider corners against the start of the line groups until the canopy inflates more? It could help solve sliders coming down too fast. Would also keep the canopy size constrained to the sliders until inflation overcomes the magnets.

Just throwing some thinking out there...

I expect that they would all just coalesce into one group of magnets in the pack job. That might hinder the slider opening correctly, and therefore hinder proper opening. 
My $0.02

[sfzombie13 307]

15 hours ago, CoolBeans said:

You guys are talking about completely different solutions to hard openings that are not related to adding shock absorbing component to risers or harness. They are all valuable but please keep them in separate topics. Otherwise it gets difficult to follow the discussion. 

Also, remember that multiple solutions can exist at once, they are not competing against each other.

you are correct in that statement but it doesn't apply to this i would think.  now, i have been wrong before, so please correct me if i am this time.  the reason for the tread was to prevent hard openings from killing the jumper by using some type of break away system with the risers.  i started with that in person with a rigger and told her the ideas we were talking about.  she brought up a very good point:  why introduce a weakness into the system designed to save your life?  since this made sense, and it came up when we talked about possibly using a tailgate like in a base canopy.

i am not saying that the original idea of having a break away riser is a bad idea, i am just agreeing with someone who has a lot more knowledge about this crap than i do.  i'm not an inventor or engineer, but a hacker.  most of the time that works much to my advantage, as in a case like this.  i can modify or improve something a hell of a lot easier than i could ever design it.  having done shit like this for almost 50 years, i can say for a fact that it will be safer to move an existing drogue system to a container than trying to design break away risers from scratch.  making a working system do the same thing in another environment is a lot easier than making a working system do something it is not designed to do.  hell, i have an old container lying around and may be able to install a drogue system on it myself.

since you are correct though, i will refrain from mentioning the system and apologize for hijacking the thread.

[dgw 8]

On 6/18/2020 at 8:28 PM, olofscience said:

Someone posted something similar earlier this thread, but I thought it was still viable until I did some calculations.

Assuming that freefall speed is 120 mph (54 m/s), and canopy speed is 14 m/s (30 mph - still pretty fast), if the opening takes 1 second (pretty hard opening) you'll get about 4 Gs.

That doesn't sound very high until you realise the upright position is quite bad for this kind of acceleration.

Let's assume it's even worse, say your canopy opens in 0.5 s, giving an 8G acceleration.

If we were to completely absorb 0.5 seconds with an elastic stretching to bring it back to 4 G's, you'll need 10 metres of stretching since you're trying to get rid of 40 m/s (from 54 to 14 m/s).

Even if you're just trying to mitigate the very worst case, say 0.25-second opening which causes 16 G's, you'll need 5 metres of stretching to bring it down to 8 G's.

If your risers are stiffer and don't stretch 5 metres, they won't relieve the acceleration anyway. It would be like trying to use water to break a terminal freefall - it will feel hard as concrete when you get a hard opening.

So as much as I wanted this elastic stretching idea to work, unfortunately it probably won't. However, what might work is if the risers break completely at a certain load - if the RSL or a MARD is connected, then the reserve might give you a second chance of not opening so hard.

 

I might have missed the point entirely here, but it seems to me that Mr Beans had an idea that ‘fall arrest’ type risers might ameliorate opening acceleration, not by stretching of the risers, but by failure of the thread in the stitching in the sewn parallel ‘accordion’ of webbing. So, I don’t think his idea needs metres of webbing, but it might need meters of thread. 
$0.02 

[olofscience 420]

31 minutes ago, dgw said:

not by stretching of the risers, but by failure of the thread

Yes I know that. However, I did study fracture mechanics in university and the energy absorbed by failure of the thread is:

total energy = energy absorbed by stretching + surface energy of new fracture surface created + kinetic energy released by the fracture + remaining strain energy

Of these, the surface energy of the new fracture surface created is tiny - because threads are tiny. You can also assume that the remaining strain energy is zero or very close to zero as after failure there is nothing to constrain the risers. So most of the energy goes to the remaining 2 terms. Now, you want the kinetic energy released by the fracture to be low, too. I mean that was the point, right? Meaning, most of the energy has to go into stretching (or permanent deformation) before failure.

And since acceleration is a function of time and distance, it can be calculated independently of any material elastic properties, resulting in the lengths I came up with in the post you quoted.

[CoolBeans 11]

olofscience has good ideas and understanding of the problem.

Let's say 5 m stretch is the value that makes real difference. I'm an engineer. I'm asking if 0.5 m makes a difference? What about 5 cm, does that make any difference?

Many glorify Dacron lines. I read different values for how much Dacron stretches, but let's say Dacron can stretch up to 10% and average line length is 120 inch. That gives us 12 inch of stretch. 

If shock absorbing risers could stretch by 12 inch and you used Dacron lines, you would end up getting 2x benefit of Dacron lines. Now, any of you tell me if that's worth the hassle or not.

 

There are many other aspects one could look at. Have a look at these diagrams of soft / hard openings: https://www.pcprg.com/g-forces.htm . Let's think out loud, if one was to use shock absorbing risers + Dacron lines and had a hard opening. At around 6Gs mark the chart would be flat (absorption of energy into lines/risers) for maybe 100 or 200 miliseconds. Then once lines and risers reach full stretch, Gs would keep growing and get absorbed into the jumper's body.

My question is, would you rather get hit with 12 Gs in belly to earth orientation (left picture) or hit with 11 Gs in potentially straight up position (right picture)? Would that extra 100 - 200 milisecons delay at 6G be enough to put jumper into upright position without braking their neck immediately and better prepare them for incoming stronger hit? Would it make a difference between broken spine vs sore neck? Those are all of the questions I'm asking myself to understand if it's worth pursuing this idea. 

Edited August 13, 2020 by CoolBeans

[olofscience 420]

5 hours ago, CoolBeans said:

ave a look at these diagrams of soft / hard openings:

Thanks for the link!

The overall Gs and lengths I calculated assumed average accelerations, but obviously that's oversimplifying and the charts show it's not uniform. So a mechanism could still reduce the peak force.

Actually, this means that you don't need to do jump testing - if you have a machine that can apply the loads like the graph in the link, then you can apply different risers into that machine and find which one reduces the peak.

[dgw 8]

On 6/2/2020 at 9:55 AM, CoolBeans said:

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

You might want to have a look at some of the injury tolerance research. It might help with understanding the relevance of the opening deceleration and impulse to risk of injury. 
 

https://humanresearchroadmap.nasa.gov/evidence/reports/Occupant Protection.pdf

Here’s an extract setting out some relationships between deceleration, impulse, and injury:

 

[dgw 8]

Here is a study on fall arrest harnesses / acceleration / impulse published by the UK Government’s Health and Safety Laboratory. I think it touches on your idea, and might help.

https://www.hse.gov.uk/research/hsl_pdf/2003/hsl03-09.pdf

[olofscience 420]

43 minutes ago, dgw said:

Here is a study on fall arrest harnesses / acceleration / impulse published by the UK Government’s Health and Safety Laboratory. I think it touches on your idea, and might help.

https://www.hse.gov.uk/research/hsl_pdf/2003/hsl03-09.pdf

Very informative link! Following their sources actually leads to a NASA design:

https://ntrs.nasa.gov/citations/19730010159

Edit: it seems rock climbers already have something that we could theoretically repurpose:

Edited August 13, 2020 by olofscience

[dgw 8]

25 minutes ago, olofscience said:

Very informative link! Following their sources actually leads to a NASA design:

https://ntrs.nasa.gov/citations/19730010159

Edit: it seems rock climbers already have something that we could theoretically repurpose:

Yes. That is what I thought Coolbeans more or less had in mind. I noted your comment responding to me but I couldn’t reply earlier. My thoughts were that, for this sort of idea, more thread  / stitches = less riser stretch over a bit longer time than in a normal deployment. That was it. The injury risk is not just acceleration related, but duration related. 

[JerryBaumchen 1,046]

19 hours ago, olofscience said:

Edit: it seems rock climbers already have something that we could theoretically repurpose:

Hi olof,

Some thoughts on those.  I would sew that portion  that is sticking out ( at about 3 o'clock & pointing to the right in the photo ) in with that now-broken stitching to keep things tidy.  Also, I would consider some stitching that would take a pretty good force initially, prior to going to the long sacrificial stitching shown, that is destroyed.  Possibly, use a bartack or zig-zag at the top of the stitching.  Then you would have to have experience that 'pretty good force' before anything comes undone.

Just some random thoughts,

Jerry Baumchen

[CoolBeans 11]

Does anybody have old, unused risers, preferably 23 - 25 inch long that they would be willing to donate for the project? I'm building a prototype. 

[sfzombie13 307]

4 hours ago, CoolBeans said:

Does anybody have old, unused risers, preferably 23 - 25 inch long that they would be willing to donate for the project? I'm building a prototype. 

i may have a set.  let me look around if i still have it or if it went with the last rig.

[councilman24 36]

On 6/6/2020 at 12:28 PM, CoolBeans said:

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. 

Build your own. Reuse hardware.

[councilman24 36]

Radom comments.

For information there are two currently marketed civilian parachute systems that include sacrificial bartack lazy leg systems, not to protect the jumper so much as the parachute components. Butler includes a bartack lazy leg on the bridle of their higher rated pilot parachutes and Free Flight Enterprises also uses a bartack lazy leg on their higher rated Preserve V between bag and the PC.

Rock climbers depend on the elastic nature of climbing rope to soften their falls. Shock absorbing sacrificial shock absorbers are more to protect sketchy hardware anchor placement from the fall load. Rescue rope or repelling rope is designed to have very limited stretch. With such rope and with fall arresting safety systems shock absorbing systems are required in case of an unintended fall. This is where the commercial safety system and rescue shock absorbers are used.  (I am trained in high angle rope rescue)

Perhaps we need to bring back Softer Man!!  Those who were at PIA symposiums in the late 90's or early 00's remember a jumper who had an invention to soften openings. It was essentially a large domed slider attached to the four main connector links. Essentially the theory was it acted as a  drogue when the risers came out before the canopy started deploying. He had an ad in Parachutist and or Skydiving for about a year or two. I don't know anyone that took him seriously, especially since he ran into the seminar room in a super hero outfit. I don't know anyone who thought that it was a good idea.

Anyone who knows me knows I'm the resident sceptic. A mildly amusing discussion that comes up every few years.

PIA used UPT's wireless load sensing and data accumulation system for the reserve PC and extraction force data. 

It seems that controlling force instead of a breakable "fuse" is more acceptable to jumpers and eliminates the issues with two suspension points.