Forums: Skydiving: Gear and Rigging:
What causes end cell closures?

 


Dutchboy  (A 37004)

May 6, 2001, 6:25 AM
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What causes end cell closures? Can't Post

Did my first night jump last night. Also openned with both end cells closed. So I started thinking, what causes this anyway?



PalmettoTiger

May 6, 2001, 6:48 AM
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Re: What causes end cell closures? [In reply to] Can't Post

Not exactly sure why, but as aspect ratio increases, it's more and more difficult to keep the end cells pressurized. That's why the high aspect ratio canopies are elliptical - the shorter chord at the edges of the canopy makes it easier to keep the end cells filled.

Blues, squares,
PTiger


riggerrob  (D 14840)

May 6, 2001, 9:08 AM
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Re: What causes end cell closures? [In reply to] Can't Post

Basically the center cell inflates first and some time later the other cells catch air. Frequently as the center cell surges forward, the top skin wraps down over the nose, closing it and delaying inflation of the other cells. One other factor is that side loads during turns try to push the air out of end cells, collapsing them after a normal inflation.
Manufacturers have invented many cures for closed end cells, the most important cure being cross ports that allow pressure in the center cell to blow sideways and fill the end cells.
Small stabilizers also reduce side loads in turns, thereby reducing end cell closures after a normal opening.
If you want to see the latest tricks for inflating end cells, look at a new BASE canopy like a FOX.



Premier skybytch  (D License)

May 6, 2001, 9:44 AM
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Re: What causes end cell closures? [In reply to] Can't Post

When I was jumping an F111 7 cell loaded at about .75 I had end cell closure on just about every jump. I was told it was in part due to my light wingloading. Luckily it's an easy fix - I got into the habit of pumping the toggles as soon as I opened cuz I knew the end cells wouldn't be inflated yet.

pull and flare,
lisa


Dutchboy  (A 37004)

May 6, 2001, 5:58 PM
Post #5 of 8 (824 views)
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Re: What causes end cell closures? [In reply to] Can't Post

Thanks for the info.

I guess I've been having closed end cells a few times lately, and I was wondering if it had anything to do with me and how I might be packing or deploying.

I've never had the end cells deflate after opening. I'm loading my canopy at about 1.24 lbs/sq ft. With the two end cells closed the loading is effectively 1.6 and the canopy will dive a bit instead of having the normally flat glide with brakes still stowed. I just give the rear risers a couple of yanks and everything is good.

I'm curious if I'm doing something differently, because I never really saw this at all until recently.



PalmettoTiger

May 6, 2001, 7:53 PM
Post #6 of 8 (818 views)
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Re: What causes end cell closures? [In reply to] Can't Post

In reply to:
I'm curious if I'm doing something differently, because I never really saw this at all until recently.
Different humidity and temperature aloft may affect it. Or they might not, I'm just speculating wildly here. Smile If it's only started happening since the weather has improved, that might be a factor. Did you jump the same canopy last season?

Blues, squares,
PTiger


Dutchboy  (A 37004)

May 7, 2001, 5:38 AM
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Re: What causes end cell closures? [In reply to] Can't Post

I've been jumping this canopy since October. So, yes, the weather has changed since then. I don't think I've changed the way I pack or deploy.



riggerrob  (D 14840)

May 7, 2001, 11:14 AM
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Re: What causes end cell closures? [In reply to] Can't Post

End cells close more often as line sets wear out and the canopy gets out of trim. Dependign upon wing loading, etc. we only expect a line set to last 300 to 600 jumps.




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