Line Dump cause

[FOF 6]

Your experience jumping the FX without brakes stowed certainly gives you reason to be skeptical of manufacturers' recommendations, or at least that particular recommendation. Did you really follow it without question, though? Or did you think it over beforehand and decide to follow the recommendation anyway?

I'm not saying we should follow anyone's advice without question. I've given careful consideration to PD's recommendations regarding line stow tension and length, and believe they are based on sound theory, supported by thorough testing, and reinforced by feedback from jumpers in the field.

I might not be concerned if this was simply a discussion about the benefits vs. risks of double-wrapping. As you pointed out, there are other ways to make tight stows and if someone prefers one of those alternate methods that's fine. I just question how some people can be so thoroughly convinced that the original poster did not experience line dump / bag strip. I also wonder why only one other person addressed the issue of short line stows.

A bag lock is a serious malfunction, but hard openings seem far more common. Even the exceptionally hard openings that result in equipment damage or injury seem to occur more frequently than bag locks of any sort. There are some convincing arguments supporting the idea that hard openings can be caused by bag strip, and I'd rather risk a slim chance of having to chop a bag lock compared to the risk of being knocked out under a damaged canopy.

[Hooknswoop 19]

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Did you really follow it without question, though?

Yep, that was back when I thought the manufacturers knew everything.

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I just question how some people can be so thoroughly convinced that the original poster did not experience line dump / bag strip.

Because I have seen a lot of video of deployments and seen a lot of hard openings and I have never seen the canopy come out of the d-bag before line stretch.

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A bag lock is a serious malfunction, but hard openings seem far more common.

Yep, and I believe 90%+ of hard openings are caused by either not slowuing down after a diving (not flat) track or not keeping the slider against the stops while packing. I do not believe that bag strip or line dump is the cause of very many hard openings. That sort of thing tends to result in an extremely hard, even catostrauphic opening.

If loose stows cause hard openings, why does using 2 locking stows and a pouch for the lines (no stows) not result in 100% hard openings?

Derek

[phoenixlpr 0]

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a diving (not flat) track

Why do you think that? Some manufacturer even states their canopy open better from track/dive.

[Hooknswoop 19]

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Why do you think that?

I think that for 2 reasons. 1) physics; slowing down from 100 to 5 mph vs. 140 to 5 mph over the same amount of time results in more 'G' forces. 2) personal experience. Pitching up to slow my foward speed and pitching before my vertical speed increased back to normal belly speeds would result in a noticable softer opening than simply deploying on my belly without tracking first.

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Some manufacturer even states their canopy open better from track/dive.

And they also think an elliptical 170 makes a good student canopy They are also known for hit or miss quality control.

Derek

[phoenixlpr 0]

Let me rephrase it. How come tracking yields to higher deployment speed?

Dive is out of question due to higher deployment speed.

[Hooknswoop 19]

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Let me rephrase it. How come tracking yields to higher deployment speed?

I think I am misunderstanding the question, but let me see if I can get it. Most people do not flat track. They either stay at the same fall rate or greater than normal belly fly speeds. Flat tracking will yield a softer opening. When I would hear someone complain about a hard opening canopy, I would try and jump with them and follow them on their track and watch them deploy, almost 100% of them were diving in their track and not flat tracking. I would teach them to flat track and amazingly their canopy would open much nicer.

So, flat tracking makes for better openings and diving tracks make for harder openings.

Derek

[riggerrob 558]

Agreed!

Few kydivers know how to flat track.

The other problem - with deploying in a track - is the angular change ... far greater than if you deploy while flat and stable.

[elias123 0]

Will do, I have lots of small tube stoes. Thanks for the advice! :)

"In a mad world, only the mad are sane"

[phoenixlpr 0]

Agreed. That makes sense.

[FOF 6]

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If loose stows cause hard openings, why does using 2 locking stows and a pouch for the lines (no stows) not result in 100% hard openings?

As long as the locking stows remain in place the canopy will stay in the bag until line stretch even if the other stows "dump" prematurely or are free-stowed. You already completely agreed with VTmotoMike08 about this point, didn't you? I believe you also addressed this in your first post:

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Line dump is when line stows release pre-maturely, but the canopy remains inside the deployment bag until line stretch. This will have almost no impact on how the canopy opens

Bag strip is when the locking stows release pre-maturely and the canopy comes out of the deployment bag prior to line stretch. This can cause extremely hard opening, injury and/or canopy damage.

That's why I've specifically been using the term "bag strip" during this discussion rather than "line dump."

[Hooknswoop 19]

Right, and to prevent bag strip, you do not need to double wrap your line stows, nor should very tight, double wrapped stows be used as as fix for a hard opening canopy.

That is why I would question a manufacturer's recommendation to double wrap rubber bands.

Bag strip is very rare and is easy to prevent. Line dump and bag strip are often blamed for a hard opening when again bag strip is rare and line dump doesn't create a hard opening.

I have offered good reasons not to double wrap. I have not heard any good reasons to double wrap rubber bands.

Derek

[peek 20]

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But I've often heard people describe an "instant opening," where the canopy seems to open hard and fast immediately after releasing the pilot chute. Doesn't bag strip seem the most likely explanation for these cases where there's a dramatically reduced time between P/C release and snatch force?

No.

[peek 20]

Well, Derek, this manufacturer not only thinks a person need not double stow their lines, but even thinks the last few don't even need to be stowed:

http://www.basik.fr/en/index.php?page=shop.product_details&flypage=shop.flypage&product_id=189&category_id=6&manufacturer_id=0&option=com_virtuemart&Itemid=28&vmcchk=1
"Anti-Line Twist Main D-Bag"
(I saw this link posted by someone else related to another thread.)

Maybe one of these days we will be able to put to rest this double stow nonsense!

[relyon 0]

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Maybe one of these days we will be able to put to rest this double stow nonsense!

Yup, some myths die hard ... but I'll try and help.

I've never bought the line dump arguments. For the last 900 or so jumps, I haven't used any bag at all, preferring a tail pocket instead. Before that it was freestow bag. I also demoed a popular ZP 7-cell freefall canopy once for couple jumps (to terminal, no less). I didn't have a bag, so I used a single "sacrificial" rubber band for the locking stow and freepacked (*) the main.

For each method there is a single locking stow and they've all open smoothly.

Bob

* - highly discouraged because of the malfunction possibilities. If you don't know what freepacking is, don't ask.