Correctly determining the length of closing loop

[PhreeZone 15]

After a near incident today its got me thinking about how most people determine their closing loop length. The event that triggered me thinking about this was a jumpers dbag fell out in the jump plane on the climb up. On investigation on the ground I was able to pull through all 4 grommets an additional 2 inches of the closing loop. The jumper leaned on their rig the entire flight up and compressed their main so there was now no tension on the closing loop and the pin just fell out. The jumper was unable to pull further on the loop when packing it themselves so they figured it was fine. I was able to pull additional length since I was using a packing tool and not a piece of pull up tape. After adjusting the loop towards a setting much closer to what I could pull it towards I was unable to replicate the issue.

This brought up the question though of what methods do you use to determine the correct length for a rig when you make and set a closing loop? Each person packing fills the volume differently so how can you best determine the correct length?

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[NWFlyer 2]

It's unscientific, but if I can close it with a pull-up cord it's too loose; if it requires my pack tool it's just right. If I can't get it closed with the pack tool, it's too tight.

Edit to add: I also pay attention to how the grommets on the flaps line up and try to get a length that allows them to line up on top of each other without slipping once I put the pin in place.

"There is only one basic human right, the right to do as you damn well please. And with it comes the only basic human duty, the duty to take the consequences." -P.J. O'Rourke

[Ronaldo 0]

Good question, I use trial and error until I can pull about ½” (12mm) out of the last grommet using a power tool and good strength. I tend to adjust it tight so it is usually difficult to close the container with a pull cord (but not tight enough to damage the grommets or stiffener). I also kneel on the bag for a while compressing the air and pull the flaps with my hands to help closing them.

Engineering Law #5: The most vital dimension on any plan drawing stands the most chance of being omitted

[Martini 0]

Lots of attention is given to closing loops that are too long, rightly so considering how dangerous this practice can be. But keep in mind that a container can be damaged by using too much tension especially with a packing tool. I onced owned a Vector-II that had damage from too short a closing loop that required excessive tension to close. The damage resulted in a grommet pulled away from the webbing and could have snagged a line on deployment. At about the same time I discovered the damage two jumpers went in as a result of lines snagged in improperly seated grommets. A closing loop that is too long or too short can be a serious problem. That's why we have riggers. People should use them for more than just repacks.

Sometimes you eat the bear..............

[FrogNog 1]

It's a tough one. I go with the metric "If I can barely close the container". However, I've found it depends on how neat my pack job is - if I fold everything at perfect widths and it goes in the bag like a ream of paper, I expect to feel like my closing loop could be shorter.

One thing I've never seen discussed is how much "range" a container has for bag volume vs. closing loop length and maintaining closing loop tension in two common scenarios: 1. packing then leaving it overnight, and 2. pressing the container against the cabin wall, as you (Phree) described.

I've noticed many times that a fresh pack job makes a tight closing loop but the next morning the loop tension is nowhere near as "safe". On the other hand, the manufacturer for my container specifies to determine the proper closing loop length based on "flap slack" (how far the flaps come to rest apart from each other) that is looser than I prefer, so when I see my overnight pack job is still at least as tight as the manufacturer's specifications, I assume it's "good enough".

And then I pray it really is.

I guess if I trust anyone, it's my rig manufacturer.

-=-=-=-=-
Pull.

[Icon134 0]

I go on the direction of the rigger who originally assembled my rig (and I believe he mentioned it was from my manual) suggestion of 1/2 inch to 1 inch maximum.

He also pointed out that the grommits on the container should be stacked on top of one another. (FWIW: I have a mirage G4)

Livin' on the Edge... sleeping with my rigger's wife...

[steve1 5]

I jumped with a guy at Lost Prairie last summer who had a bag lock. I'm trying to recall exactly what happened and what it looked like, but if memory serves there was a small piece of bridal that somehow worked it's way into the closing loop causing the main not to open. I wonder if a tighter closing loop would have prevented this. It was a really an unusual looking mal. Probably a one in a zillion chance.

I can also see how too short of a closing loop could mess up your grommets.....Steve1

[NWFlyer 2]

Quote

I jumped with a guy at Lost Prairie last summer who had a bag lock. I'm trying to recall exactly what happened and what it looked like, but if memory serves there was a small piece of bridal that somehow worked it's way into the closing loop causing the main not to open. I wonder if a tighter closing loop would have prevented this. It was a really an unusual looking mal. Probably a one in a zillion chance.

I can also see how too short of a closing loop could mess up your grommets.....Steve1

I was watching that one from the ground. From our viewpoint, it looked like it might be a PC in tow, so his whole ride down, we're watching him and saying "Stay in there, stay in there" ... came to find out later there was virtually no chance of that main coming out at any point during his reserve ride.

"There is only one basic human right, the right to do as you damn well please. And with it comes the only basic human duty, the duty to take the consequences." -P.J. O'Rourke

[riggerrob 558]

Several retorts ...

First of all, let's keep our terminology straight.
"Bag Lock" normally refers to a deployment bag that is outside the container, but not opening.
Your malfunction sounds more like a "container lock," or "pack closure," or "pilot chute in tow."

Secondly, if you can accidentally push some bridle through the closing loop, that loop is too long.

Finally, if too short a loop is damaging grommets, chances are, you have old-fashioned brass grommets. Most modern containers include stainless steel grommets to handle the additional pressure of the tighter pack volumes that are fashionable today.

[steve1 5]

I'm sorry for the mix up in terms. It was definitely a container lock, not a bag lock.

I'm not familiar with the new stainless steel grommets. They do sound a whole lot better than the old brass ones. (I went to rigger school about a 100 years ago)....Steve1

[phoenixlpr 0]

Quote

This brought up the question though of what methods do you use to determine the correct length for a rig when you make and set a closing loop? Each person packing fills the volume differently so how can you best determine the correct length?

There is one more factor: humidity. Canopies stored in dry place packs bigger than kept in more humid place.
The more I pack the smaller it packs.

By experience? If the loop is took loose I make it shorter. If I cannot open the knot I replace the loop.

[MakeItHappen 15]

Quote

After a near incident today its got me thinking about how most people determine their closing loop length. The event that triggered me thinking about this was a jumpers dbag fell out in the jump plane on the climb up. On investigation on the ground I was able to pull through all 4 grommets an additional 2 inches of the closing loop. The jumper leaned on their rig the entire flight up and compressed their main so there was now no tension on the closing loop and the pin just fell out. The jumper was unable to pull further on the loop when packing it themselves so they figured it was fine. I was able to pull additional length since I was using a packing tool and not a piece of pull up tape. After adjusting the loop towards a setting much closer to what I could pull it towards I was unable to replicate the issue.

This brought up the question though of what methods do you use to determine the correct length for a rig when you make and set a closing loop? Each person packing fills the volume differently so how can you best determine the correct length?

Some really unusual replies to this....?

Re: grommets lining up:
Most rigs do NOT want you to have the grommets stacked on top of each other.
The reason for this is that the edge or lip of a grommet may catch the lip or edge of the next grommet down or even the binding tape along the flap edge. This scenario could result in pack closure at deployment time. It was a common problem many years ago. RWS, aka their new name, manuals specifically mention this.
IOW, the ideal placement of the outside edge of a grommet is to the outside of the previous flap binding tape.
If your rig mfg says to line up all the grommets atop of each other, well, go look for a new rig.
If you can line up the grommets atop of each other then the pack tray is too large for the canopy.

Re: pressure on packed rig in various positions.
The best way to store a rig between jumps is to lay it on it's back.
Rig hangers are ok, too.
The worst way is to store it standing on it's end (bottom of main pack tray against a firm surface). That tends to put pressure on a loose loop and give you the impression that the loop is tight enough. Then while leaning back in an AC on the way to altitude, the pin pops.

Re: loop length:
I always go from the previous loop length. Sometimes I have to shorten it, when I jump in FL and then later lengthen it when back in the desert.
I usually have to re-shorten a new loop after a few pack jobs because it has been stretched.
I have even adjusted the loop length at the same DZ during the course of a year because of humidity effects.

Opening knots on the closing loop:
Use pliers to squish the knot in several directions. It will loosen up. Use pliers that do not have burrs to catch threads or some protective material.

Too long of a loop:
This is also an age-old malfunction. The loop should only be about 1/2 inch. Longer than that will tend to trap bridle lines.

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[jasonRose 0]

Quote

Quote

After a near incident today its got me thinking about how most people determine their closing loop length. The event that triggered me thinking about this was a jumpers dbag fell out in the jump plane on the climb up. On investigation on the ground I was able to pull through all 4 grommets an additional 2 inches of the closing loop. The jumper leaned on their rig the entire flight up and compressed their main so there was now no tension on the closing loop and the pin just fell out. The jumper was unable to pull further on the loop when packing it themselves so they figured it was fine. I was able to pull additional length since I was using a packing tool and not a piece of pull up tape. After adjusting the loop towards a setting much closer to what I could pull it towards I was unable to replicate the issue.

This brought up the question though of what methods do you use to determine the correct length for a rig when you make and set a closing loop? Each person packing fills the volume differently so how can you best determine the correct length?

Some really unusual replies to this....?

Re: grommets lining up:
Most rigs do NOT want you to have the grommets stacked on top of each other.
The reason for this is that the edge or lip of a grommet may catch the lip or edge of the next grommet down or even the binding tape along the flap edge. This scenario could result in pack closure at deployment time. It was a common problem many years ago. RWS, aka their new name, manuals specifically mention this.
IOW, the ideal placement of the outside edge of a grommet is to the outside of the previous flap binding tape.
If your rig mfg says to line up all the grommets atop of each other, well, go look for a new rig.
If you can line up the grommets atop of each other then the pack tray is too large for the canopy.

Re: pressure on packed rig in various positions.
The best way to store a rig between jumps is to lay it on it's back.
Rig hangers are ok, too.
The worst way is to store it standing on it's end (bottom of main pack tray against a firm surface). That tends to put pressure on a loose loop and give you the impression that the loop is tight enough. Then while leaning back in an AC on the way to altitude, the pin pops.

Re: loop length:
I always go from the previous loop length. Sometimes I have to shorten it, when I jump in FL and then later lengthen it when back in the desert.
I usually have to re-shorten a new loop after a few pack jobs because it has been stretched.
I have even adjusted the loop length at the same DZ during the course of a year because of humidity effects.

Opening knots on the closing loop:
Use pliers to squish the knot in several directions. It will loosen up. Use pliers that do not have burrs to catch threads or some protective material.

Too long of a loop:
This is also an age-old malfunction. The loop should only be about 1/2 inch. Longer than that will tend to trap bridle lines.

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I don't mean to be rude nor do I disagree with your advise. I would like to know more about the source i.e. profile.

Are your comments valid, how/why did you come up with your results?

Again, I am not intending for this to sound like your advise is not valid, just needs source clarification.

Some day I will have the best staff in the world!!!

[PhreeZone 15]

She's a national director with enough experience that people should listen to her

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[riggerrob 558]

Most of his comments are valid.

The only thing that I can add is that old sailors would tend to hammer on a tight knot to loosen it.

[MakeItHappen 15]

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I don't mean to be rude nor do I disagree with your advise. I would like to know more about the source i.e. profile.

Click on the MakeItHappen link in my sig block.

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Are your comments valid, how/why did you come up with your results?

My comments are my comments - take them as you see fit.
25 years of skydiving, reading lots of stuff, paying attention, yadda, yadda, yadda......
But I am not a rigger-----------yet.
but you don't believe me hardly anyone does....
go look at page58

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Make It Happen
Parachute History
DiveMaker

[jasonRose 0]

Your advise sounds good to me
I wasn't sure if a 200 jump wonder like myself was writing it or if was wisdom from a seasoned vet.

Thanks for the clarification. By the way I like the way you explained it!!

Some day I will have the best staff in the world!!!

[phoenixlpr 0]

Quote

Opening knots on the closing loop:
Use pliers to squish the knot in several directions. It will loosen up. Use pliers that do not have burrs to catch threads or some protective material.

It depends on what kind of knot you use. There are some strong, secure and even easy to open.

Try figure 8 or figure 9 knots. You may check it from here.

[fcajump 153]

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Your advise sounds good to me
I wasn't sure if a 200 jump wonder like myself was writing it or if was wisdom from a seasoned vet.

Thanks for the clarification. By the way I like the way you explained it!!

Always good to check your sources. In this case its a good source, but that is not always the case. Very reasonable to ask when you're not sure.
JW

Always remember that some clouds are harder than others...

[MakeItHappen 15]

Quote

Your advise sounds good to me
I wasn't sure if a 200 jump wonder like myself was writing it or if was wisdom from a seasoned vet.

Thanks for the clarification. By the way I like the way you explained it!!

Last night I awoke and realized that the 'grommets lining up thing is a historical legacy' thing.

When cones and pins were used, the grommets did line up over atop of each other.
This was ok because a spring loaded PC pushed the flaps off the cone. The flaps had angular motion that prevented (or reduced to near nil) chances of flaps hanging on each other. BTW cones are still used in limited military applications.

With the introduction of soft loops and hand deploys (c. 1970's), the overlapping grommets produced the unintended consequences of flaps hanging on each other.
There was no spring loaded PC pushing the grommets off a cone to separate them.
Instead, a PC or pud pulled a pin out of a soft loop and the flaps laid there until the tension from the bridle line pulled the bag out. The bag was saying 'Get out of my way' to the flaps.

In the earlier designs, the flaps said 'ok', but then appeared to be bumbling idiots of getting out of the way. But that was because the flaps were placed in each other's way.

The soft loop was a major improvement over cones, but it had the problem of not always working when the grommets were overlaid atop of each other with a hand deploy.

So it was found thru incidents and problems that if you offset the grommets, then the grommets would not hang up on each other. This was more important for hand deploys than spring loaded PCs.

On today's reserves, the grommets do tend to 'almost' line up. That is because they have the spring loaded PC pushing apart the flaps.
On today's mains with hand deploy systems, there is no spring loaded PC, so it is better to have the grommets offset.

I guess the ROT (rule of thumb) that you can take is that the grommets on hand deploy systems with soft loops should not overlap very much. And spring loaded/ripcord systems with soft loops can have a bit more overlap.

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DiveMaker

[riggerrob 558]

Remember that most early rigs used pack opening bands to pull flaps clear of cones.
POBs seemed like a silly solution until someone asked me to repack a faded, frayed and filthy Russian Air Force seat pack. Aside from a rusty KAP-3 (AAD) and weak rubber POBs, I also noticed that the pilot chute contained NO SPRING.
So POBs make sense if your pilot chute has a weak or non-existent spring.
Security tried to continue the POB concept by adding an extra spring to extract the closing loops, but as skydiving manufacturers conformed to the MIL SPEC of 18 pound springs, POBS faded into obscurity.

[ZigZagMarquis 8]

Hey! Maybe we ought to bring back POBs!!!

... oh... wait... Strong is already doing that on the reserve pack tray, errr... flaps... on the Quasair...