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Why Your Canopy Is Slapping You Around

By adminon - Read 11430 times
Image by Lukasz Szymanski

Ah, your canopy.

When you first got together, everything was great. A few tussles over crispy, slippery fabric were the biggest issues you two had. You packed carefully -- lovingly, even -- or you were at least habitually spying on your packer. And after freefall, it was a joy to reach for that pilot chute.

Now, things are horribly, horribly different.

What happened?

Maybe it’s because you stopped paying attention -- or maybe because you’re both getting older -- but something has changed. There have been some bad moments. Violent moments, even. There was that time that you landed from a jump with a three-ring mark and a stunned expression on your face. Your friends asked what happened to you. You started to wonder if it’s time to say goodbye for good.

Don’t thumbtack that “for sale” sign to the corkboard too quickly, friend. You can save this relationship. Here’s how.

1. Wrap your head around the dynamics involved.

When a ram-air canopy opens in freefall, the dynamics of that opening are controlled by two processes: cell inflation (air pressurizing the airfoil through the nose inlets) and bottom-skin spreading (the side-to-side spreading action that takes place as relative wind rushes against the bottom of the canopy). You might not be aware of how separate these processes are, but they are quite distinct.

Even without cell inflation, bottom-skin spreading is such an efficient phenomenon that a canopy can open entirely by this method, before the cells have a chance to inflate and pressurize. Since the force of that kind of opening is brutal enough to be quite literally fatal, square skydiving canopy designers invented a system to put on the all-important brakes -- the humble slider.

That funny little square has a single function: to sync up bottom-skin spreading with cell inflation. A correctly packed slider stays at the very top of the lines during the early part of inflation, kept there by the same forces that would smack the canopy open with bottom-skin inflation.

2. Help your slider help you.

Make quartering your slider the most important part of your pack job. Be thorough about it. Draw the folds evenly between each of the four line groups, then tug the center of the slider straight down to settle the grommets snugly against the stops. A slider that’s sorted out in this way is a slider that is most likely to present itself correctly to the relative wind (and therefore do its job optimally).

3. Avoid getting dumped.

Optimizing your slider is only the first step in the process. The second, as you might imagine, has to do with your tangled handfuls of marionette strings. Incorrect line stows can release prematurely -- or, colloquially, “dump” -- resulting in a configuration wherein the canopy inflates before line stretch. When the lines catch up to the nylon, the jumper gets one heckuva headbanger. (Picture a Great Dane running at full tilt to the end of a long, long leash.)

4. Keep the right amount of pressure on.

It should take roughly 8 to 12 pounds of pressure to pull your lines from the stows. If you’ve gotten complacent (or too tired to be trusted), you’re probably going to pay for it.

5. Use the rule of thumb.

The loops of line on the outside of each rubber band stow (technically called “bights”) should be approximately two inches long. If that’s longer than you’re used to, that’s normal -- but know that right-sized bights keep about a quarter of the stowed line on the outside of the stow, minimizing the lines’ ability to dump. Luckily, two inches is about the size of the average human thumb, so you have a ready reference when you’re on the packing mat.

If you happen to have stowless gear, your line dump issues are probably related to uneven folding of the lines (or lazy bag closure). The same pressure principle applies to the closing bands on your system: close the bag with 8-12 pounds of pressure, equal on each side.

6. Get professional help.

If you go through all those steps and you’re still not on good terms with your canopy, look elsewhere for guidance. Take your canopy to a rigger for inspection. You may discover a deeper problem -- and he/she might just be able to fix it right up. (There’s no shame in a little counseling, after all. Love is worth it.)



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Thank you very much for the continued excellence in articles Ms. O'Neil. Previous to your frequent contributions, my interest in the random assortment of articles on this site had been . . . fair-to-middling.
No disrespect to other authors, more of a function of my own ADD than anything else.
That said, I have read about 6 of your articles, and appreciate each one whole-heartedly.
Thank you m'am.

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Good read, enjoy your posts.
To add...Dump stable, and not too quick after a track etc. Also makes for a good banger.

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Thank you for this article!

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If, as you say, 8-10 lbs of line stow extraction force is necessary to prevent a hard opening, why do the thousands of semi-stowless bags open softly and beautifully? It seems to me that the issue is bag dump. In my experience, elastics that are too tight (other than the closing stows), cause off heading openings and line twists.
From what I understand, out of sequence line deployment is the focus of the "double stow" religion, as the belief is that lines that come off the bag out of sequence will cause tension knots. I have not seen this in the field very often, and the risks posed by double stowing seem to out weight the need for this paranoia-driven panic to double stow everything.

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Brian, thank you. I would *love* for you to write that up in an extended format. I can think of no one who would make the point more clearly and intelligently than you, and it would be my pleasure to read and share it.

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