Why are all closing pins not curved?

[dgw 8]

(Maybe better for gear and rigging, but it is a safety question)

Simple question, probably with a simple answer.

My understanding of the introduction of the curved pin is that it was introduced to 'throw away' deployment systems to prevent the pin 'locking' when the pilotchute pulled it at a 90 degrees to its stowed orientation, as could happen with a straight pin. The curved pin can rotate and slide through the closing loop.

A further advantage of the curved pin is that it can't be pushed out by pushing the tip of the pin. I've tried it, and the pin just rotates around the closing loop.

Reserve pins and pull out pins are straight. Would these pins not be more secure if they were curved? They would be better able to withstand an 'unseating' if pushed, and the curved pin would not, as I understand it, affect pull force.

Thanks!

[JohnRich 4]

I'm not a rigger.

A straight pin on a ripcord cable does the same thing as a curved pin on a pilot chute bridle. It allows the force to be applied to the pin in the direction of pull with the least resistance.

If you were to put a curved pin on a ripcord cable, it would be harder to extract from the closing loop. The cable housing also prevents the pin from being able to rotate to follow the path of a curved pin. And of course, a curved pin can't be withdrawn inside the cable housing, like a straight pin - it would jam at the opening. It would be the equivalent of a bent pin, which is a dangerous thing, that can cause a hang-up and a total malfunction.

[dgw 8]

Well, with respect, I don't agree.

The withdrawal force is mostly governed by the friction between the closing loop and the pin. This is largely independant of pin shape.

The bent pin argument is also weak. Every curved pin is 'bent'. They are not dangerous, and work routinely. They are 'bent' (curved) in a plane parallel to the grommet surface.

Bent straight pins are a different problem, because when they are bent, they can have tight bends.

In my view, a straight pin is far more likely to become 'bent', in the way that is dangerous, than a curved pin. Hence the question.

Thanks.

[Squeak 17]

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Well, with respect, I don't agree.

The withdrawal force is mostly governed by the friction between the closing loop and the pin. This is largely independant of pin shape.

The bent pin argument is also weak. Every curved pin is 'bent'. They are not dangerous, and work routinely. They are 'bent' (curved) in a plane parallel to the grommet surface.

Bent straight pins are a different problem, because when they are bent, they can have tight bends.

In my view, a straight pin is far more likely to become 'bent', in the way that is dangerous, than a curved pin. Hence the question.

Thanks.

The pin shape is governed by the DIRECTION of pull, if the pull is perpendicular to the pack (as in a Throw out PC) the pull for pin extraction id going to be at 90 degrees to the pack. A PULL OUT pin is straight because as the PC is extracted the pin is pull along the pack, not 90 degrees to it.
Same with reserve pins they get pull along not UP

As to pins being pushed out even curved pins can suffer this you may have tried to push the pin by hand but have you done it sitting in a loaded plane with a fair amount of force compressing the pack volume, and loosening the closing loop?

The configuration of pins is not an adhoc idea many years experience has gone into trying to design the most reliable and safe equipment possible for todays jumpers

You are not now, nor will you ever be, good enough to not die in this sport (Sparky)
My Life ROCKS!
How's yours doing?

[keithbar 1]

what squeak said. and the curved pin wouldn't fit thru the reserve ripcord cable housing would it? they did teach you to clear the cable all the way out of the housing when you were taught ep's didn't they?

i have on occasion been accused of pulling low . My response. Naw I wasn't low I'm just such a big guy I look closer than I really am .

[hackish 8]

As has already been mentioned the curved pin is designed to allow the pull in any direction. On a reserve the system is engineered so the pull is always in the same general direction. This is why you will find the guide rings on an RSL equipped rig - to make sure the pull is in that direction. This is the design and it's designed that way to work with a straight pin.

Pulling a curved pin in that same direction is ok as long as no obstruction exists to prevent it's rotation. Since you have a significantly higher amount of closing loop tension I believe the force that would need to contribute to the pin rotation would add to the pull force required.

What would we gain? Perhaps there would be less possibility of the pin being pushed out but if you look at the reserve pin covers rigs are designed to protect the pin.

-Michael

[Andy9o8 0]

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what squeak said. and the curved pin wouldn't fit thru the reserve ripcord cable housing would it? they did teach you to clear the cable all the way out of the housing when you were taught ep's didn't they?

Just to add to this, which also echoes what John Rich said above. As they said, a curved pin will act as a ripcord stop, preventing the ripcord from being pulled all the way thru and fully extracted from the housing. Historically, we've already been down this road a generation ago.

For a while back in the 60s & 70s, when all rigs had ripcords only (on the mains), some people put "ripcord stops" - lead sinkers, twisted stow bands, whatever - on the ends of their ripcords to avoid losing them if they dropped them. Problem with that is if they had a cutaway, the main ripcord, with its handle, was still dangling out of the housing. This caused a number of fatalities when reserves snagged and horseshoed on the dangling ripcord. (I suppose even a main canopy could hang up on it too.) If the ripcord is fully extracted, that takes care of that. Even if the ripcord is not fully extracted, if there is a canopy snag, the straight pin will increase the chance that a horseshoe can be prevented or cleared, either by the jumper pulling the cord out the rest of the way, or the force of the canopy extracting the cord. (That's why we were taught, back then, that Step #1 in a cutaway situation was THROW AWAY THE MAIN RIPCORD. I remember my FJC instructor teaching us to try hitting our foot with it - to get us throw it away hard, in order to clear it from the housing.) So anyhow, the word went out: RIPCORD STOPS KILL!!


http://www.parachutehistory.com/darwin/cablestops.html


Bottom line: anyone who's thinking of putting a curved pin on a reserve ripcord: DON'T DO IT! - it could easily kill whoever jumps the rig.

[freakflyer9999 1]

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what squeak said. and the curved pin wouldn't fit thru the reserve ripcord cable housing would it? they did teach you to clear the cable all the way out of the housing when you were taught ep's didn't they?

Not all reserve ripcord cables are designed to be cleared through the housing. My Vector's reserve ripcord actually pulls the pin that is directly attached to the RSL. The pin then blocks the cable from being cleared through the housing.

The first time I popped the reserve before a repack, it surprised the hell out of me that I pulled about 6 inches and couldn't pull any further. Tried 2 or 3 times before I realized that the reserve container had actually opened and the reserve pilot chute was laying on the ground behind me.

[Andy9o8 0]

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Not all reserve ripcord cables are designed to be cleared through the housing. My Vector's reserve ripcord actually pulls the pin that is directly attached to the RSL. The pin then blocks the cable from being cleared through the housing.

Ack!!
Bill??

[riggerrob 558]

Responding to the original poster ...

Maybe we should ask Hank Asquito (sp?).
You know ... the guy who's name is on the patent.
I did a couple of jumps with Hank in California City around the turn of the century. Last thing I heard Hank was still alive and helping Lockheed perfect the Joint Strike Fighter.

First of all, curved pins are only installed on throw-out, main pilot chutes. About 95 percent of sport containers use throw-out main pilot chutes and curved pins.
All other types of containers use straight pins.

Hank's logic for curving pins was to provide the same pull force at any angle the bridle decides to pull.
Previous to Hank's invention (circa 1980) we used bungee cord to close sport containers and just folded a little bridle into the bungee to hold the main container closed.

The first batch of curved pins were bent from straight, round rod and soldered/welded together.

The second batch of curved pins were stamped from sheet steel, then chrome plated. Since the chrome flaked off way too easily, the second batch quickly fell out of fashion.

Every since then, we have used curved pins stamped out of sheet stainless steel and tumbled until they have smooth edges. Curved pins are available from a dozen mills (Airolite, JCO Metals, RWS, Wichard, etc.).

[livendive 8]

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Not all reserve ripcord cables are designed to be cleared through the housing. My Vector's reserve ripcord actually pulls the pin that is directly attached to the RSL. The pin then blocks the cable from being cleared through the housing.

Ack!!
Bill??

He speaks the truth.

Blues,
Dave

"I AM A PROFESSIONAL EXTREME ATHLETE!"
(drink Mountain Dew)

[Andy9o8 0]

Well, you've got my attention. Now I'm hoping the boss will weigh in.
Bill, how's this issue addressed?

[billvon 2,400]

>Ack!!

He's been doing this for a while. Helps prevent kinked reserve cables among other things.

[indyz 1]

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Well, you've got my attention. Now I'm hoping the boss will weigh in.
Bill, how's this issue addressed?

I'm not sure why you think this is a big deal. The pin has been pulled, the reserve container is open, you just can't completely extract the ripcord from the housing.

[PhreeZone 15]

Nothing needs to be addressed in it. The design works out great. If the RSL pulls the pin then it pulls the pin to the right and the pin/RSL stays attached to the main canopy and the reserve rip cord can be pulled to full extention. If the reserve handle is pulled then the pin stays in the reserve ripcord and it stops at the housing.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[Andy9o8 0]

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>Ack!!

He's been doing this for a while. Helps prevent kinked reserve cables among other things.

OK. I'm trying to understand whether this represents a new approach (and/or new mindset) to the ripcord-stop issue the sport addressed a generation ago.

[Andy9o8 0]

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If the reserve handle is pulled then the pin stays in the reserve ripcord and it stops at the housing.

I understand it stops at the housing; that's my point: is this no longer considered an entanglement hazard? (I guess I mean particularly with a very unstable deployment.) (Sorry if I'm being dense, guys.)

[SethInMI 145]

bill weighs in:

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=1483959#1483959

It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

[PhreeZone 15]

What is there to entangle with? The pin is on the top of the flap that folds out of the way as the freebag moves past.

Its been this design on Vector3's and Sigma rigs for 6+ years with no issues.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[labrys 0]

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If the reserve handle is pulled then the pin stays in the reserve ripcord and it stops at the housing.

I've got this setup and I've pulled my reserve handle without a cutaway very recently for a repack.

The reserve cable came all the way through the housing. I wish I'd been looking at the pin when I pulled the handle, but just looking at it after closing, it seems to be designed so that the pin should rotate as the cable is pulled and allow the cable to release.

Owned by Remi #?

[dgw 8]

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Hank's logic for curving pins was to provide the same pull force at any angle the bridle decides to pull.

This bit is the reason why I don't see a disadvantage for curved pins, perhaps not on reserves (if it ain't broke etc..), but why not on pull-out deployment systems? Would the curved pin not offer better protection from unseating, without adding another problem? For any given closing closing loop tension, I would not expect the pull force to change significantly when using a curved pin versus a straight pin.

Not trying to reinvent the wheel....

Thanks!

[mjosparky 3]

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If the reserve handle is pulled then the pin stays in the reserve ripcord and it stops at the housing.

I understand it stops at the housing; that's my point: is this no longer considered an entanglement hazard? (I guess I mean particularly with a very unstable deployment.) (Sorry if I'm being dense, guys.)

Andy,

A ripcord stop was on the main ripcord. If you had a problem you would drop the main ripcord and go to the reserve. This left the handle and 8 or 10 inches of cable hanging in front of you where the reserve was in those days.

In the case of RWS rigs the one that may or may not make it through the housing is the reserve ripcord with the reserve coming off you back.

And Rob, Hank never bothered to patent the curved pin.

Sparky

My idea of a fair fight is clubbing baby seals

[Andy9o8 0]

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A ripcord stop was on the main ripcord. If you had a problem you would drop the main ripcord and go to the reserve. This left the handle and 8 or 10 inches of cable hanging in front of you where the reserve was in those days.

I know, but I remember they discouraged ripcord stops even with the new-fangled "piggyback" rigs - so I was wondering whether deploying a reserve, say, in a very unstable orientation might still produce an entanglement risk with a "stopped" reserve ripcord. Maybe I'm over-analyzing.

[Squeak 17]

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Not all reserve ripcord cables are designed to be cleared through the housing. My Vector's reserve ripcord actually pulls the pin that is directly attached to the RSL. The pin then blocks the cable from being cleared through the housing.

Ack!!
Bill??

That's a poor explanation Andy.
I too own a V3, the the set up is designed for the skyhook and colins lanyard. the pin is not attached to the ripcord, the pin runs through an eye on the end of the cord.


A mates ATOM also has a stop on the ripcord.

You are not now, nor will you ever be, good enough to not die in this sport (Sparky)
My Life ROCKS!
How's yours doing?

[brettski74 0]

With respect, I am going to disagree with you and agree with John.

Sure, the friction between between the closing loop and the pin determines what force is required perpendicular to the loop to move the pin, however, the shape of the pin affects the direction in which the force of your pull is applied. If you're applying a force perpendicular to the loop, such as is the case with a reserve pull, then a straight pin ensures that all of that force goes toward moving the pin through the loop. If the pin was curved, then as you move the pin further and further through the loop, the loop is rotated, and a progressively larger proportion of the force is now being applied along the plane of the loop, which is not moving the pin through the loop. With the arc length of a typical main pin, the difference might be relatively small, but it would be measurable.

If you're having trouble picturing what I'm talking about, keep the same radius of curvature and extend the length of the pin until it's now a full semi-circle. Iare you still sure that a straight pull will extract the pin?

Basically, it's different tools for different jobs. Applying a pull along or near to the the plane of the loop requires a curved pin. Pulling perpendicular to the plane of the loop is best served by a straight pin.