pin tension

[guest]

Hey, I have a serious question regarding pin rigs.

I often see disclaimers and warnings from manufacturers and experienced jumpers about having too tight a pin tension on pin rigs. My question is:

why?

I admit my sole pin experience is with skydiving rigs. As a rigger and experienced skydiver, I know for a fact that the adage that "if you can close it with your hands without assistance, and if your PC is in good shape, the container WILL open" is 100% true. Ignoring misrouted bridles of course.

Of course I understand that we are talking about subterminal versus terminal. However, I have a hard time seeing how after a 1-2 second delay a 42" PC is not going to pull the pins on a pin rig, following the same adage. The old test for determining if your skydiving rig was tight enough was to put the rig on the floor, pull on the bridle, and if the rig stated to lift off the floor a bit before the pin pulled, you were good to go. Assuming your average skydiving rigged weighed about 22 lbs (sheer guestimate), that equates to a pull force of about 22 lbs. Are we saying that after a 1-2 second delay 42" is not giving us 22lb of pull force?

It seems that if 42" will pull brand spankin new velcro in a head down shrivel flap situation without too much trouble, it would easily deal with a pin in any situation.

I guess I am asking because I would feel pretty nervous taking a pin rig off some off an object with some of the pin tensions I have seen in the field, and discussed on the board, especially terminal. It seems like at 4 to 6lbs pull force, the only thing standing between you and a nasty horseshoe mess is the pin flap. I would guess that the designers did not intend the flap to take such an important role in keeping the pins in place....

So..... what am I missing?


Standard Disclaimer:
Now before I get a bunch of flamage, please understand I am asking for purposes of enlightenment, not to stir up crap or call the 4-6 pounders stupid. I fully understand that these guidelines are based on experience and best practices, so please let me know why the pin tensions are supposed to be so low....

[346]

See this thread:

http://www.blincmagazine.com/forum/board/3766.html

The delay was 1 to 1-1/2 and the jumper trailed the fully inflated PC for around 1-1/2 to 2 seconds. I didn't inspect the gear or anything, but the jumper commented to me that the pin tensions were high.

Your "lift the rig off the floor" test is a good start but it is missing a very important, tension-increasing variable: the jumper. The only way to test it properly is to have the jumper put the rig on and tighten the leg straps and chest strap as if that person was actually jumping the rig. Then lay down on the floor and have a friend pull the bridle with a scale. The increase in pin tensions is usually quite noticeable.

Mark &-)

[guest]

At the risk of sounding like a little kid....

So what is considered a high pull force in the subterminal environment?

Do you guys all have faith in your pin flaps when jumping terminal with low tension loops?

Or do you bump up the tension when going terminal.

What are large size PCs producing in terms of drag after a couple seconds? Or is that even measurable with all the variables such as PC packing, throw style, etc, that probably come into play in short delays?

[imported_Tom Aiello]

Disclaimer: Please do not attempt free fall parachute deployment below 200'. Even the best modern BASE gear is neither designed nor tested for deployment under these conditions.

>Are we saying that after a 1-2 second delay 42" is not giving us 22lb of pull force?

My three rigs (velcro, one pin, two pin) topped out under 20 pounds of pull to open (18, as I recall) in even the worst possible configuration (head up tuck).

I've never measured pull forces of PC's in the field, but BASE689 (did I get that number right?) did a nifty spreadsheet showing theoretical maximum pull forces for different sizes at different delays, which was also niftily adjustable for various degrees of realism/safety factor. (Unfortunately, I appear to have lost it--anyone want to email me a copy?)

As I recall, all the pull forces he calculated were way over my measured container opening forces. Still, evidence from the field suggests that black death can still govern container opening (I think Huckin' Idiot towed a 42" PC for an estimated 1.5 seconds on a rig that probably had a maximum of around 20 pounds of pressure).

>I guess I am asking because I would feel pretty
>nervous taking a pin rig off some off an object
>with some of the pin tensions I have seen in the
>field, and discussed on the board, especially
>terminal.

Me too. I always use the standard closing loops, which yield at least 12 pounds of pull to open, on any jump over 200'. I made one (rather poorly received) 150' free fall last year with the standard loop. Although there was a slight PC hesitation, I was still open at least 20' off the water.

>It seems like at 4 to 6lbs pull force,
>the only thing standing between you and a nasty
>horseshoe mess is the pin flap.

I concur. In my opinion, jumps with any significant delay (not just terminal) ought to be made with the standard 12 pounds of pull force.

>so please let me know why the pin tensions are supposed to be so low....

They're not. I believe the manufacturers pretty much all recommend something like 12-15 pounds of pull force (anyone know the real numbers for certain?). I was sternly lectured by one responsible manufacturer, when I announced my intention to substitute a spectra loop (4 pounds by my measurement). He grudgingly gave me some spectra when I assured him I would never use it above 200'.

As always, we all have our personal preferences and opinions. Here's mine:

Minimizing opening force by changing loop material (or other means) is a trick that ought ONLY to be used for ultra low (sub 200') free falls.

This is an advanced trick for the truly silly. We ought to discourage it's spread to general use.

--Tom Aiello
tbaiello@mac.com