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peek

Double-stowing lines in rubber bands - another data point

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Please allow me to add to the controversy of whether to double stow your suspension lines in the rubber bands.

I often jump a fully zero-porosity Manta (288). It is the best opening "stock" canopy that I have ever experienced. A good initial snivel, just the right amount to slow me down before canopy spreading. Never off-heading more than 10-15 degrees.

It has Dacron lines and I use "regular" rubber bands, in other words, not small ones like many people use for small lines. I had a very, very experienced rigger pack for me. He told me later that he double stowed the lines. He did this because some of the rubber bands did not seem that tight. (Actually, for this canopy they don't need to be because it opens so well regardless.)

On the opening that he packed, there was a relatively long delay before I felt snatch force, enough to startle me, and when it opened, it had about one full line twist. It never does this when I pack and single stow.

I think there is plenty of evidence to suggest that the double stowing of the lines makes the bag "rock" and rotate.

With the increased use of "stowless" deployment bags that have only 2 "locking stows", I have to believe that double stowing the rest of the stows is not necessary, and sometimes counterproductive at least on some canopies.

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I think most of the double-stow advice is based on the assumption that the majority of people are using Spectra/Vectran/HMA lines, and those who aren't can think for themselves B|

I have a Spectre 230 with Dacron lines and use large bands for locking stows, small ones for non-locking, and single-wrap everywhere. This gives me 8-10 lbs of extraction force on every stow (just measured it this weekend), which is exactly what PD recommends (8-12 lbs). If your packer double-wrapped locking stows on a 9-cell Dacron-lined canopy, those were probably too tight. I tried double-wrapping large bands when I first assembled my rig, but the extraction force was too high.

The other thing to consider is bulk distribution. With single stows, I use ~3" bights to equally distribute the mass of the lines about each band. If I double-stowed, each bight would need to be ~1.5", so I would need an extra stow. Depending on how your canopy fits into the container that could be a good or a bad thing.

It's well-known that bad things will happen if the canopy comes out of the d-bag before line stretch. In that sense, the only stows that really matter are the locking stows. Those need to hold until the lower lines and risers are stretched. However, the force required to extract the non-locking stows affects the difference in the speed between the d-bag and the jumper, which probably influences the snatch force. I'd be curious to find out what that relationship is, given that the stowless pouches probably allow the d-bag to decelerate more than rubber band stows. Since people seem to prefer the openings on (semi-)stowless d-bags, that would be an argument against tight non-locking stows.

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Nope. The double stow advice is based on the snatch force when the pilot chute pulls the d-bag out of the container. When the bag is pulled it actually elongates the entire bag momentarily including the single stow. This leaves an open gap between your bite and the d-bag in the rubber band where the bite can come out. But when you double stow the same elongating effect cause the rubber band to tighten down harder on the bit greatly eliminating the chance of it coming out.
(insert philosophical quote here)

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rtroup

You've come to this conclusion after one jump with double stowed bands?



No, it is just one data point for this configuration. It is a rather convincing data point to me due to the conditions. Some of the significance of this is the many openings I have had that are good without double stowing and with stows that are not all that tight, similar to "stowless" bags.

Quote

Do you normally pack for yourself? Does your rigger normally pack for you?



I normally pack for myself. He on occasion packs for me at events.

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rtroup

Nope. The double stow advice is based on the snatch force when the pilot chute pulls the d-bag out of the container. When the bag is pulled it actually elongates the entire bag momentarily including the single stow. This leaves an open gap between your bite and the d-bag in the rubber band where the bite can come out. But when you double stow the same elongating effect cause the rubber band to tighten down harder on the bit greatly eliminating the chance of it coming out.



I'm not sure what you're contradicting in my post. Elongation of the band is why you need a longer bight when single-stowing. Nothing will slip out prematurely as long as the mass of the line is equally distributed (think of how a suspension bridge is constructed). The release behavior is, indeed, different, but since you do want the stow to come out eventually at the right time, the question is whether double-stowing helps in all cases, or whether there are some configurations where single-stowing is the better option.

To put it another way, an ideal d-bag will hold all stows in place until the lines prior to each stow are stretched out. At that point, you want the stow to release without inducing any sort of instability in the d-bag.

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AndreLapointe

When using large rubber bands, PD recommends double wrapping all line stows.



This was the point of my post with regard to different line types. PD actually recommends 8-12 lbs to release the stow. With Spectra (I don't have first-hand experience with Vectran or HMA), small bands will be too loose if single-stowed, and probably too tight if double-stowed, so PD came up with the simplistic recommendation of double-stowing using large bands. It's a good rule of thumb, but it's not applicable to all cases.

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AndreLapointe

some riser covers will require close to 5 lbs pull force to peel off, so the line stows should require more than 5 lbs pull force to release them in order to have the right deployment sequence.



That is an interesting point. What if all of the stows except the locking stows release from the bag before the risers covers open. Is that a problem? Does this usually happen with "stowless" bags anyway due to their design?

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peek

***some riser covers will require close to 5 lbs pull force to peel off, so the line stows should require more than 5 lbs pull force to release them in order to have the right deployment sequence.



That is an interesting point. What if all of the stows except the locking stows release from the bag before the risers covers open. Is that a problem? Does this usually happen with "stowless" bags anyway due to their design?

Yep: https://www.youtube.com/watch?v=CiACEdS_Zmk

I don't think it actually matters whether the risers release at the start or the end of the sequence, as long as they are out before the canopy is released from the bag.

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As Max said, as long as the riser covers peel off before the last two bights, we're good!
On a Vector III for instance, the shoulder riser covers are very secure with the long tuck tabs that wrap around the top of the shoulder, especially with the harness cinched down. I'd be worried to wait for the last two bights of semi-stowless bag to find out if the riser covers are coming off.

https://www.youtube.com/watch?v=GSVRSIicQDk

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Hi Gary, I agree with you completely. Rubber bands come in all sizes therefore it's better to find the size which fits your lines.

I use for the past 4 years, Jerry Baumchen early Magbag, there is only two rubber bands to close the D-bag flap. I use tandem tube stoes. This D-bag line pouch is similar to the line pouch of a reserve and is held shut by magnets instead of Velcro. That means the lines unstow from the middle of the pouch avoiding any D-bag rocking. Several videos shot from behind show that the line extraction is straight and very orderly unlike D-bag using rubber bands on the sides.
That being said, you shouldn't never double rubber bands (if any) on a reserve. If it's good for a reserve, the same can apply for the main.
Learn from others mistakes, you will never live long enough to make them all.

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Quote

That being said, you shouldn't never double rubber bands (if any) on a reserve. If it's good for a reserve, the same can apply for the main.



A lot of the things we do when we pack reserves are because that's the way it's always been done. And newer methods haven't been fully tested. Like a lot of things in aviation, it's best to take a conservative approach. That does not mean that the way we do it is the best way. Even if that's what the instructions say to do.

We don't pack mains the same as we pack reserves, because we don't have to.
Always remember the brave children who died defending your right to bear arms. Freedom is not free.

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Hi Ken,

Quote

We don't pack mains the same as we pack reserves



And most people should be thankful.

I have been modifying gear since the mid-60's. I've been building d-bags for mains/reserves since the 80's.

Things evolve; that which is the 'best' is lousy in 10 yrs.

I think each person should do as they wish; and I hope that is the best decision for them.

Jerry Baumchen

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Backing erdnarob.

I have never double-stowed rubber bands on a reserve. That includes a thousand-or-so round reserves along with a few diapered squares (Hobbit an Security X-210R) and some Racers that had free-bags closed with rubber bands. When packing newer Speed=Bags, I use smaller MIL SPEC rubber bands when the lines are thin.

OTOH the I have double-stowed thousands of rubber bands on main d-bags. .. partly because the Strong manual says to double-stow bands on Dual Hawk tandems and partly because I was too lazy to search for small rubber bands when I broke one half-way through packing my own main.

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Your decision but...if any of you single stow just be sure that locking stow ruber bands are not worn or close to break. If you single stow with a worn ruber band on a locking stow, this can break and beging the secuence from there while the other secuence from the pilot chute has begin too, this 2 secuences meet in the middle of the lines and Boom!!! Thats an out of secuence deployment that can lead to a injury, equipment damage or even death by a very hard opening. Be sure before of take any decision about this and dont be complacient about locking stows ruber bands condition. "I want to be like you because he wants to be like me"

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On ‎2‎/‎9‎/‎2019 at 9:06 PM, dluque said:

Your decision but...if any of you single stow just be sure that locking stow ruber bands are not worn or close to break. If you single stow with a worn ruber band on a locking stow, this can break and beging the secuence from there while the other secuence from the pilot chute has begin too, this 2 secuences meet in the middle of the lines and Boom!!! Thats an out of secuence deployment that can lead to a injury, equipment damage or even death by a very hard opening. Be sure before of take any decision about this and dont be complacient about locking stows ruber bands condition. "I want to be like you because he wants to be like me"

3+ year old post, make sure you check this when using search.

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8 hours ago, dluque said:

Who cares? people keep talking about this in multiple forums, personally i have been discusing this even with Brian Germain 2 or 3 months ago and he is against doble stow, the way he explain the theme is very convincent.

 

Can you explain what Brian Germain said and why he is against double-stowing?

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I don't know why this is still a debate. The manufacturers are nearly in universal agreement--double stow. Virtually every manufacturer out there says this. By contrast, I don't know of even one major manufacturer who currently recommends against double stowing rubber bands.

Bag strip is a very serious malfunction and if it happens to you there is a legitimate chance you could die from the resulting hard opening. Double stowing is explicitly intended to prevent a bag strip malfunction and it is more effective at doing it than other forms of stowing. At the bare minimum, if you dont double stow you should be able to easily lift your bag off the ground by the lines without them falling off. If you cannot do that, you need to use a different stow method that provides greater stow tension.

One of the problems that makes single stowing seem attractive is that the problem that is created with single stowing does not immediately manifest itself. You could go thousands of jumps without ever having a problem. But one day out of nowhere the physics align and you get slammed like you just got into a car accident at 120 MPH. That would be the bag stripping off the parachute causing premature inflation because your locking stows were too lose.

Edited by 20kN
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11 hours ago, Timxx said:

Can you explain what Brian Germain said and why he is against double-stowing?

Try "Parachute Rigging for Dummies" group in facebook" personally i just doble stow my lines and thats all even though my lines are dacron and this are bulky and some times i just single stow on the locking stow groomets, some times i wish larger ruber bands but there is not in the market.

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