3 rings AGAIN....

[BenW 0]

Hi all,
This has been asked before and I'm sure it will be again. I've also read through the previous posts on this subject.
I am in the process of ordering a new container/harness system and am debating the pros and cons of the standard 3 ring release (Bill Booth type) vs the now ubiquitous mini-ring set.
I understand the physics of it relating to the mechanical advantage differences (200:1 vs 30:1). The Relative Workshop and Jump Shack have written some informative articles on Type 17, Type 8 risers and the 3 ring system.
The breaking point for Type 17 is neither here nor there in comparison to Type 8. What concerns me is the opportunity for a high speed spinning malfunction causing a no-pull/hard-pull situation.
I've cutaway from a spinning mal on my previous rig which had Type 17 and mini-rings with no problem. That was my first rig (2nd hand), so didn't have a choice in what the rig came. Now I do.
I'm interested in what the riggers or larger guys on the forum (I'm 210lbs out the door), who HAVE cutaway from a spinning mal with the mini-rings, have to say about them. Would you go for the standard 3 rings next time?
Here are the figures I've been pushing around in my head:
210lb jumper in a 3G spin = 630lbs of force being exerted on risers.
Assume 75% of that force is being exerted on one side of the harness due to the spin. Also assume that the weight distribution between front and rear is 50/50.
This gives a force on the highest loaded front riser of (630*0.75)/2=236.25lbs.
So, 236lbs of force at the riser will equate to a load on the smallest ring of 236/200=1.181lbs for the large ring set. Using the same figures for the mini-rings @ 30:1 gives 7.86lbs. This force is acting upon the teflon cable.
The load on the other riser is going to be 78.75lbs. At the cable we're going to see 0.39lbs for Large and 2.625 for mini.
A load of 10.485lbs (mini) on the teflon cables doesn't seem that large. Granted, I've worked this out in a very simple way and to get the teflon cables moving you will require a force significantly greater than the 10.485lbs, plus you need to add in friction for the rest of the system. Maybe we're looking at 25 or so lbs (arbitrary figure).
Is 25lbs a reasonable figure to expect?
So, to finalise (I've bored loads of you shitless), has anyone been in a situation where they couldn't cutaway from a spinning mal using mini-rings?
Thanks for bearing with me.....
Ben.

[PhillyKev 0]

That's a damn good question....I'm 220 exit weight and was wondering the same thing. My plan was to go for large rings just b/c i'll take all the advantage I can get. But if it really is a non-issue regarding a high spin cutaway, then I'll have to go back and consider the mini rings again.
In making that determination, is their any other advantage to the mini-rings besides narrower risers that allows you to pull a collapsible slider down over the risers?
cielos azules y cerveza fría
-Kevin

[BenW 0]

Kev,
The narrower risers allow for less drag, if you're a super swooper this might be of importance to you. I'm just wondering if everybody who uses mini-rings knows what the issues are for them...
Before I buy, I want my ideas to be confirmed or denied!
Someone got any reliable info on this?
B.

[jumpervali 2]

Sorry I'm not including any math on this reply, but I have recently had a malfunction on mini risers. It was a sabre with bad line twist and violent spin. My javelin still has soft housings for the Teflon cables. All that was required was a single right hand only pull. It zipped right out, and I was spit out from under it like a watermelon seed. One thing I must say though is lube your cables at every reserve repack, and check for cracks in the laminate. Now as an instructor and S&TA no one should ever exit an airplane without. #1 the intention and confidence to cutaway a malfunction main and deploy their reserve. #2 the skill to calmly perform this task.
be safe, have fun, look cool for the camera!
jumpervali

[cobaltdan 0]

as you assume the brunt of the force will be taken up on one side, but the distribution between front and rear makes no difference as the sum will be applied to the ring.
the issue is not steady state force on your cable but the peak force. the peak force applied can be enough to kink the cable into the relatively wide gromet. once that is done it forms a 'detent mechanism' which has a huge mecanical advantage.
a pull force on a non kinked cable of 25# can become 10 times higher with a kink.
sincerely,
dan
atair

[alan 1]

I've had a violent spinning mal with type 17 risers and mini rings. All of the load was on one riser since the mal was the result of an improperly manufactured locking loop on the riser. My weight was about 215# out the door on an 89 VX. I had hybrid riser housings meaning they are hard where they pass through the yoke and soft on the external loop to the grommet. I was able to cutaway. I used the two hand method and I had to get serious about it.
Proper inspection and maintenance of your three ring release is critical, yet largely overlooked by most skydivers. I base that on my inspections of rigs that I get in for reserve repacks. I would also encourage you to look into the hard inserts for your risers that protect the cutaway cable ends. I still use type 17 and mini rings with the hard housings and the inserts.
alan

[BenW 0]

Dan,
You are right, a kink formed by a transient load may prevent a cutaway in this type of situation. So, does this mean that you advocate the larger ring mechanism? What type do you jump?
Thanks
Ben

[Kris 0]

This is definitely a subject that I can speak about. I am about 245# out the door and both my cutaways were spinning mals.
Cutaway #1 was my Sabre 210 in my old Talon with large risers / large rings. It was a spinning mal and was an easy one-handed pull.
Cutaway #2 was weekend before last on my new Heatwave 190 elliptical in a Mirage G3 with mini risers / mini rings. It was a violently spinning mal with several line-twists above the risers, but was still an easy one-handed pull. Even if it had been down to the risers it still should have been just as easy since the Mirage has armored risers just like the Vectors do.
I thought long and hard about getting mini-risers at my weight because of the spinning mal issue but now I know my new Mirage can handle it.
The only other down-side to mini-risers is that you will have to inspect them every so often and they will need to be replaced every few hundred jumps as they will not wear as well as large risers will.
Just my 2 peso's...
Kris

[Aviatrr 0]

Quote

So, to finalise (I've bored loads of you shitless), has anyone been in a situation where they couldn't cutaway from a spinning mal using mini-rings?

Well, if they weren't able to cutaway from a spinning mal because of the forces on the 3 rings, I don't think they would be around to tell you about it. I had a spinning mal on a Stiletto 150, at 215lbs out the door. I dumped high, so I tried to remedy the situation for longer than most people would be able to. I finally chopped it when I burned 1500+ft fighting it and made no progress. I had an easy, one handed cutaway with mini rings and mini risers. There were hard riser inserts on that rig.
Mike

[BenW 0]

Thanks for the replies everyone,
Dan, you were talking about a transient load kinking the cutaway cable. I take it this is in the situation of a slamming opening where the transient could be much higher than 3G transmitted through the 3 ring to the cutaway cables. How much of a likelyhood is this?
I understand that my previous scenario only covered a normal opening and a subsequent spinning mal which would produce the sustained load on the cable.
Is no-one worried about their cutaway cables being damaged during a v.hard opening? Would this hard an opening leave you unconscious anyway?
Does anybody know who has done any research on this?
Many thanks
Ben

[BenW 0]

Sorry to bother you all again!
I've been bandying a few more numbers around in my head, I won't bore you with the maths (I've taken into account what Dan said about the total load on one side being applied to the 3 rings on that side) but I've worked out the following:
This is assuming a reduction ratio of 30:1 for the mini-ring set, rather than the 50:1 some talk of. Also assuming the opening shock is 75% asymmetrical between the two riser sides.
Taking an arbitrary 6G (with a 210lb jumper) transient during the opening shock of a v.hard opening, approx 31.5lbs of force trys to pull the teflon cable through the grommet.
Bearing in mind that this is a transient (very sharp) load, is this enough to kink the cable and make cutting away difficult, if not impossible on that side?
Thanks
Ben

[RemiAndKaren 0]

Ben,
I've seen Tear Drops with large rings mounted on mini risers. Lisa had not seen that config coming through Square 1, so it was news to her, but I'm almost sure I'veen it in Ccanada too on a US made rig...
Remi
Muff 914

[BenW 0]

Remi!
How's things? The more I look into this subject the more it interests me!
You jump Spinetto 150? What ring system do you have? I know you've had a reserve ride you didn't pull, but what about a self initiated one? Easy, difficult?
Ta
B

[RemiAndKaren 0]

Quote

I know you've had a reserve ride you didn't pull

Pulling is in deed for wusses........ I let either my Cypress or my plane take care of that for me.. eheheh (JUST KIDDING folks)
I jump a Stiletto 170, and when the toggles dont fly off during opening, the openings are fine.... not much twists... the rig I have has mini rings and risers.
Never had to cut it way (the only real reverve ride I had was a tension knot in a Sabre 210.. cant remember what rings I had on that rig anymore.. its true what they say, the minds is the 2nd thing to go)...
Take care Ben, and see ya around (if the freaking weather decides to stop crapping!)
Remi
Muff 914

[Spectrejumper 0]

Well, I haven't had a cutaway yet (knock on wood), but I jump Type 8 risers with large rings. I believe one of the Jump Shack articles recommends Type 8 risers for jumpers over 200 lbs. I'm about 250 out the door, so Type 8 seemed like the way to go. The other thing I found is that I have a harder time getting a decent grip on Type 17 risers when making riser turns or hanging on em to get back from a long spot. But I only made 30 jumps on the demo canopy with the small risers, so maybe I'd get used to it.
Mike D-23312
"It's such a shame to spend your time away like this...existing." JMH

[cobaltdan 0]

a note on your 6 g estimate. this is not a worst case assumption....
i have recorded a force vs time graph with the peak force spike exceeding 50 g's on a sabre 135 canopy....
a quick 6 g's spike would not be very noticable as a hard opening. it depends on the width of the spike. remember to the jumper it is all about force vs time. ie how long that force is applied to your body.
a hard opening canopy will typically spike you in the 6-11g range and a dangerously hard canopy can spike over that.
to your cable a short high spike may kink it whereas a longer more moderate spike may not.
another point to consider. the 3 ring system does not have fixed fulcrums, it is a flexible structure and the pivot points can move considerably. therefore its mecanical advantage can vary, in particular if it is twisted.
sincerely,
dan
atair

[DBTECH 0]

Ben said-->
Here are the figures I've been pushing around in my head:
210lb jumper in a 3G spin = 630lbs of force being exerted on risers.
DB: I agree
Ben: Assume 75% of that force is being exerted on one side of the harness due to the spin. Also assume that the weight distribution between front and rear is 50/50.
DB: OK--although 75-25 seems way to high. (60-40 seems more likely
Ben: This gives a force on the highest loaded front riser of (630*0.75)/2=236.25lbs.
DB: This is incorrect, as the force on the three ring assembly is the combined total of the front and rear risers
Ben: So, 236lbs of force at the riser will equate to a load on the smallest ring of 236/200=1.181lbs for the large ring set. Using the same figures for the mini-rings @ 30:1 gives 7.86lbs. This force is acting upon the Teflon cable.
DB: This is incorrect, as the force on the three ring assembly is the combined total of the front and rear risers.
Ben: The load on the other riser is going to be 78.75lbs. At the cable we're going to see 0.39lbs for Large and 2.625 for mini.
DB: This is incorrect, as the load on the riser/three ring assembly is the combined total of both the front and rear risers. 75% on one side would be 472 lbs. three ring load, not 235. But, as I said before, I believe that 60% is a more realistic figure--not 75%
Ben: A load of 10.485lbs (mini) on the Teflon cables doesn't seem that large. Granted, I've worked this out in a very simple way and to get the Teflon cables moving you will require a force significantly greater than the 10.485lbs, plus you need to add in friction for the rest of the system. Maybe we're looking at 25 or so lbs (arbitrary figure). Is 25lbs a reasonable figure to expect?
DB: If we go with my numbers of 60% for the highest loaded riser, that would translate to 60% of 630 lbs, or 378 lbs for the highest three ring/riser load. With a 30-1 reduction, that would result in 12.6 lbs at the loop end with a mini ring set-up at 30-1.
Dave Brownell