Hard Reserve Pull

[Broke 0]

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?do=post_attachment;postatt_id=54615;

Divot your source for all things Hillbilly.
Anvil Brother 84
SCR 14192

[erdnarob 1]

Training? What kind of training? That makes the whole difference...a realistic training. To be repeated at the beginning of each season at the safety day or any suitable time. I think the best training is from a suspended harness with an actual fall in a matress for instance and under the supervision of an instructor (when beginner) who believes in that. People on training have to be very aggressive on that ripcord.
In the air, under a parachute with a malfunction, everything seems to be harder than on the ground especially when people have not lived a real experience about pulling a rip cord. As a rigger I whish the owner of a rig to be repacked put first his rig on his back and while in a horizontal position, pulls his reserve rip cord. His brain will "remember" the feeling. I think it is good also to train the people to pull their reserve ripcord with the left hand accompanied by the right hand. A person can generate like that way more force. The direction of the pull obviously should be in the same direction than the cable housing but if there is an small angle (10-30 degrees) that shouldn't make a big difference.

Learn from others mistakes, you will never live long enough to make them all.

[hackish 8]

Quote

Quote

The sealing thread about 4.75lb and there are generally 2 strands so you're looking at a total maximum of 31.5lbs pull force.

Please tell me where you get these #'s and your extrapolated theory? If the sealing thread is a part of the friction load holding the pin in place in the 1st place, then it is not installed correctly. Otherwise, the snatch/break force "fail point" of the sealing thread is not linearly cumulative (ie does not add to) the overall pull force required to move the pin from the reserve closing loop, in deploying a reserve.

Fact: Thread is approx 4.75lb breaking strength.
Fact: Thread in most cases is doubled over.

It is fairly simple to multiply these. I'm working toward a worst case which is that each thread is under tension at the same time.

If the thread does not contribute to the overall pull force required to pull the pin then take a 22lb pull and apply 22.1lbs. Tell me if it stops at the sealing thread or not?

Although nitpicking this is not just a theory I pulled out of my ass. I tested it. A rig I was to repack took 16lbs to move the pin. I saw at least 22lbs indicated before it activated. My testing method wasn't 100% accurate but it seems to agree with what I'm saying.

I've had this discussion with several other riggers and they've all shrugged and said "suppose so..." Who really cares? I only brought it up as it was relevant to this discussion.

We must ensure the pin's pull force is within the specs. I would not certify a rig that isn't. I further ensure that for the apparently less "strong" clients it is at the lower part of the spectrum but still within specs.

-Michael

[hackish 8]

Quote

Agreed. However, the original poster to this point we are now responding to (post #16) does seem to think so, and has further continued on the logic indicating that he apparently accounts for and COMPENSATES for the sealing-thread added pull-force, as part of his standard routine.

To save you the trouble of scrolling up to re-read...

Quote

I will redo the loop if it's at 22lbs and I generally aim for about 10-12 if the owner is a a small woman. A few more if she's feisty and has red hair.

22lbs is the max. I will loosen the loop if it is within a pound or two of the maximum to ensure it is 100% within specs. Completing a small woman rig with 10-12lbs force is also within specs. I am more comfortable delivering this than a 21.99lb pull force even though both are 100% legal.

I don't know how you would be led to believe anything is being COMPENSATED for. It's done as per the specs and the testing procedure.

-Michael

[mjosparky 3]

Quote

Although nitpicking this is not just a theory I pulled out of my ass. I tested it. A rig I was to repack took 16lbs to move the pin. I saw at least 22lbs indicated before it activated. My testing method wasn't 100% accurate but it seems to agree with what I'm saying.

Almost all “pull testing” is done with some type of spring scale like a fish scale. It is hooked to the ripcord handle and pressure is slowly applied, during which time the tester is concentrating on watching the pin. When he sees it move he stops the pressure and looks at the scale to check the reading. This in no way reflects the way a ripcord is used in real life. In real life you have a skydiver whose pulse just went over the top and looking to save his life. That is why in addition to the “22 lb” test the following tests are required during TSO testing.

---

AS8015-B

4.3.2 Human Factors and Actuation Force Tests: An anthropometrically diverse group of individuals from the intended user group shall be employed for all human factors tests in 4.3.2.

4.3.2.1 Primary Actuation Device/Ripcord, Human Factors Tests: The primary actuation device/ripcord shall be ground tested by a representative user group of no less than 6 male and 6 female subjects. They shall be able to operate the actuation device without difficulty. The ripcord, or equivalent, shall be sealed in accordance with FAR 65.133 for these tests.

4.3.2.1.1 Single harness reserve parachute assemblies shall be tested with the main compartment(s) both full and empty. The tests shall be conducted by the user in a suspended harness1 (3 male/3female), and while standing upright (3 male/3 female); (24 tests total).

4.3.2.1.2 Emergency parachute assemblies shall be tested while standing upright only (6 male/6 female); (12 tests total).

4.3.2.1.3 Dual harness reserve parachute assemblies shall be tested with the passenger attached as follows: Main compartment(s) both full and empty; with the user in a suspended harness1 (3 male/3 female), with the user suspended by the drogue bridle (3 male/3 female) and while standing upright (3 male/3 female). These tests shall be repeated without the passenger attached; (72 tests total)2.

4.3.2.2 Main Canopy Release, Human Factors Tests: The main canopy release, if used, shall be ground tested in a suspended harness1 by a representative group of no less than 6 male and 6 female subjects; (12 tests total). They shall be able to operate the release device without any undue difficulty. Dual harness reserve parachute assemblies shall be tested while in a suspended harness1 and while suspended by the drogue bridle with and without a passenger attached by a representative group of no less than 6 male and 6 female subjects; (48 tests total). They shall be able to operate the release device without any undue difficulty.2

4.3.2.3 Drogue Release, Human Factors Tests: The drogue release (if used) shall be ground tested by a representative group of no less than 6 male and 6 female subjects. They shall be able to operate the release device without any undue difficulty. The drogue release shall be tested with the test subject(s) suspended by the drogue bridle (6 male/6 female), and with an additional test subject, if used, in the passenger harness (6 male/6 female); (24 tests total)2.

Sparky

My idea of a fair fight is clubbing baby seals

[Scrumpot 1]

Quote

Although nitpicking this is not just a theory I pulled out of my ass. I tested it....

Then, further:

Quote

My testing method wasn't 100% accurate but it seems to agree with what I'm saying.

Okay, so then - what was your testing method? Just to help me understand, what you are saying then - is you tested once first pre-riggers thread seal, then again immediately thereafter POST riggers-thread seal (applied by you, presumably) being installed, and you came up with a linear INCREASE in pull-force being needed, relatively equal to the thread's rated tensile strength? With no other factors contributing other than you just simply installed the riggers seal to that same rig just tested, and it resulted in increased pull force then being required to move the pin?

coitus non circum - Moab Stone

[hackish 8]

I took a rig that was up for repack. There was about 1/2" of slack in the seal. I did a pull test as I normally would with my finger on the pin to see when it starts to move.

I held the number of pounds that allowed the pin to move and it stopped when the sealing thread became taunt. I then applied more force until the thread broke and it popped. This happened very fast but the second number was the last place I saw indicated before the pilot chute was in the air.

There will probably be a few repacks to do before people head off to winter boogies so when I get those I can repeat the tests as well.

The results make sense to me. If you consider that it takes 16lbs of overcome the resistance of the pin/closing look and grommet. You apply 16.5 lbs then stopping the pin from moving should require 0.5lbs in the other direction. The sealing thread is therefore applying it's breaking strength worth of additional resistance.

-Michael

[riggerrob 558]

Another factor is that sealing thread frays, so that it is often half-strength before you get around to pulling.
Ergo, sealing thread often has no effect on ripcord pull force.

What is the scientific basis for my conclusion??????

24 years as a rigger, full-time for the last 16 years, repacking more than 200 reserves per year ....
I used to seal student reserves with lead and thread, but after far too many threads broke halfway through the repack cycle and far too many people ran around in a panic, I quit sealing student and tandem reserves (in accordance with CSPA's Technical policy).

[erdnarob 1]

I don't like the idea to not seal a tandem or student packed reserve even if CSPA does not require it. I know that those equipments have a rough life and that the seal breaks easily but it is a bit like not washing the hands of a kid because he plays too often in the sand.
The seal is the visible trace of a job done properly and not sealing a student or tandem reserve is maybe an invitation for some people to not take the repack cycle seriously. I have seen DZO pen repack their tandem reserves, a very sad approach.

Learn from others mistakes, you will never live long enough to make them all.

[erdnarob 1]

About the direction of the reserve handle pull, I am really looking forward to see the reserve rip cord made of 1000 lbs Sectra line (with a bungee inside) get TSOed. Bill Booth made a presentaion of this ripcord at the last Reno Symposium. Bill explained that using a Spectra line decreases the friction a lot especially when the pull is as much as 40 degrees off the direction of the housing. The fact that that kind of ripcord is equiped with a bungee making sure the handle cannot be floating doesn't hurt either.

Learn from others mistakes, you will never live long enough to make them all.

[mjosparky 3]

Jim Handbury had one made of kevlar over 20 years ago. TSO'ing it was not a problem

Sparky

My idea of a fair fight is clubbing baby seals

[JohnMitchell 14]

Quote

Jim Handbury had one made of kevlar over 20 years ago. TSO'ing it was not a problem

Oh yeah, I remember those rigs.

Back to the original post, could he have grabbed a handful of jumpsuit along with his soft handle? I've seen this done before. Also, I think one of the biggest factors is pulling at a large angle to the ripcord housing. This is the result of poor training. You should always pull any ripcord in the direction the housing runs, period.

Reference the blast handle comment made earlier, my first piggyback reserve pull was a BH with the center post still in. I pulled straight down, no problems. We didn't know those were unsafe at the time.

[hackish 8]

Quote

Another factor is that sealing thread frays, so that it is often half-strength before you get around to pulling.
Ergo, sealing thread often has no effect on ripcord pull force.

A good point and probably an explanation as to why my test measurement did not work out to closer to the theoretical result.

I think I remember having this discussion with you in the past about the thread and we both agreed that they have a history of working. As long as everything is within the specs it has a history of working as expected.

Poynter details a test done (I think in Australia) where they sampled the strength of a number of male and female subjects and found that 22lbs was well within their ability.

-Michael

[erdnarob 1]

Hi John, glad to hear about somebody who knows what is a blast handle. I got one with my first Wonderhog in 1977 but its center post was drilled off. I made 2 flawless cut aways with it. Don't start laughing too much you and your girlfriend but the picture of myself in attachment was taken in 1979. You can see on it the blast handle and the belly band for the pilot chute.

Learn from others mistakes, you will never live long enough to make them all.

[erdnarob 1]

Hi John, glad to hear about somebody who knows what is a blast handle. I got one with my first Wonderhog in 1977 but its center post was drilled off. I made 2 flawless cut aways with it. Don't start laughing too much you and your girlfriend but the picture of myself in attachment was taken in 1979. You can see on it the blast handle and the belly band for the pilot chute.

Learn from others mistakes, you will never live long enough to make them all.

[JohnMitchell 14]

Quote

Don't start laughing too much you and your girlfriend but the picture of myself in attachment was taken in 1979. You can see on it the blast handle and the belly band for the pilot chute.

I better not laugh. That's the same rig I was jumping about the same time, except mine had tapewells instead of a 3 ring.

BTW, that's my wife of 24+ years in the pic. Used to be my girlfriend, but I was smart enough to marry her.

[Piece 0]

OK, I'll bite. Could you enlighten us young'uns about why such a handle is unsafe? It looks like it might need a weird angle to pull at, though the pull seems like it would be better aligned with the housing. I can't see anything else, maybe I'm blind.

http://icanhascheezburger.com/2008/02/28/funny-pictures-i-come-with-sarcasm/
Proudly uncool since 1982.

[JohnMitchell 14]

Blast handles were used for years. Then one member of the USPA board of directors had a hard pull on one. That started the movement to ban them. Were they dangerous? I don't know. They worked for me. But the campaign against them was too strong. Regular D-rings seem to do a good job anyway.

[erdnarob 1]

The blast handle with the center post on necessitates a hard pull when done at angle with respect to the housing direction. Mine had the center post removed and only the semi circular metal snaps at the top of the handle were holding on the circular groove of the cable housing ending. It worked fine for me (2 cut away) but the acquired "bad reputation" of the blast handle was going on and on. When I was showing up at DZs people were scarred until I told them that my blast handle had the center post removed and it was easy to show them. The advantage of the blast handle was that there was no need for a ripcord pocket since it was just holding tightly on the housing ending.

Learn from others mistakes, you will never live long enough to make them all.

[BrianM 1]

Two points that I haven't seen mentioned yet:

- The coefficient of static friction is higher than the coefficient of kinetic friction, which means it takes more force to start moving the pin than it does to keep it moving. You can verify this yourself with a rig and a scale. If the pull force remains the same after the pin starts moving, you already have at least some of the force required to break the thread.

- If there is slack in the thread, by the time the thread goes taught the pin/cable/handle/hand has gained some momentum, which I think would help to break the thread.

"It's amazing what you can learn while you're not talking." - Skydivesg

[Scrumpot 1]

Quote

- The coefficient of static friction is higher than the coefficient of kinetic friction, which means it takes more force to start moving the pin than it does to keep it moving. You can verify this yourself with a rig and a scale. If the pull force remains the same after the pin starts moving, you already have at least some of the force required to break the thread.

- If there is slack in the thread, by the time the thread goes taught the pin/cable/handle/hand has gained some momentum, which I think would help to break the thread.

THANK YOU for (someone) finally saying/realizing that!

Again - bottom line, so long as the seal is installed correctly it should be of relative little issue to increased over-all pull force being required.

As the pull force already being exerted (extremely slow pulls aside) to get the pin moving, clearly exceeds the tensile strength/breaking force rating of the thread (using proper thread as well) - the thread will rather EASILY break, as the pin simply KEEPS ON MOVING past the thread reaching its tension point. Only if the thread is attached with no slack at all to it, ie: INCORRECTLY (or alternately in BillVon's WCS of an already moved pin in post #19) THEN is it any part at all, of the initial static friction that (in any significance anyway) contributes to pull force, overall.

This is exactly what I have really, all along in this thread (pun intended ) been actually referring to!

Finally! Someone "wins the prize"!
Blues,
-Grant

coitus non circum - Moab Stone

[hackish 8]

If you read back to the posts I made you will see that I clearly state many times that the worst case is 22+the breaking strength of 2 strands of thread.

I am however interested in seeing what the thread actually contributes. Maybe when things slow down this winter I will build a test fixture and apply weights to see what the real pull force is with a moving pin.

Is the kinetic friction like 5% or 40% lower? I'll bet it's more like 5%.

-Michael

[JohnMitchell 14]

All I know is this: in all my reserve rides (13-ish, I think), I've never felt any resistance from velcro, pins, or threads.

Amazing what adrenaline does.

Oh yeah, and pull the direction of the housing every time. It's the right thing to do.

[hackish 8]

On my last one I think I remember feeling the thread but it could just be all up in my head. I'm going to ask an aerospace engineer what they think about the kinetic friction thing tomorrow. Since it peeks my curiosity I'm sure I'll do some more study and see what I find.

-Michael

[mjosparky 3]

Quote

On my last one I think I remember feeling the thread but it could just be all up in my head. I'm going to ask an aerospace engineer what they think about the kinetic friction thing tomorrow. Since it peeks my curiosity I'm sure I'll do some more study and see what I find.

-Michael

If you felt the resistance for the seal thread you must hate it when there is a pea under your mattress.
As for an aerospace engineer just what is it you are going to ask him, how mush force does it take to break a double wrap of 4+ lb seal thread?

Sparky

My idea of a fair fight is clubbing baby seals