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OK this has probably asked loads of times b4 but i am a low time (60 jump) skydiver with BASE strongley in mind. Why 7 cell? Also, anyone who can help get me get started in UK N. London would be appreciated PM me on paul.jcooper@btinternet.co.uk cheers.

The short answer is: because BASE manufacturers are only making 7 cells.

In theory, it ought to be possible to build a 5 cell BASE canopy (should have great openings, but poor flare) or a 9 cell (which would be tougher to get good openings on, but would fly more efficiently), or heck, a 36 cell, or a 3 cell. I've made BASE jumps on 5 cells and on 9, and I know of jumps on much higher and lower performance canopies, as well as single surface canopies, triangular canopies--heck almost anything you can imagine.

For now, the canopies that are manufactured for BASE, and perform the best over a range of BASE conditions, are all 7 cells. Will it always be that way? Who knows.

My first few base jumps were on 5 cells and I had not so much as a 1 degree off-heading in the lot. Landings were less than desireable for todays standards and my older body.

jon

So is there a relationship between Cell No's and 'reliability of on heading opening'
But also a relationship of increasing cell no. and decreasing efficiency of flare?
Can somebody explain this?

It's much more complex than that.

In _very_ general, more cells are used in higher performance canopies, which _generally_ tend to open more erratically, fly more efficiently, and flare better.

But everything changes depending on aspect ratio, shape, wing planform, trim, etc, etc, etc...

Why would 5 cell would open more on heading? Is it because they are less chances that the sides cells inflate before the center cell Why not creating a 7 cell with the two external (outside) cells closed. They would only inflate with vents and/or pressurized from the 5 center cells.
Does it make sense? Would this kind of design worked?

There is also less total fabric to flap around, and bigger cells that inflate cleaner.

There are many, many variables to this equation. I'd love to see some re-examination of these things, but I'd want to see lots of test jumping in (relatively) safe conditions.

For example, why not create a ZP 5 cell, with closed nose inlets on the outboard cells and a big bottom skin vent on the center cell?

Sound's like a good design but don't want ot be the test jumper

now that sounds interesting!

I'd really like to see that canopy, but with the added features of airlocks (so it will stay inflated and hopefully somewhat pressurized while flying backwards) and an airfoil section that's designed to fly backwards fairly well, while on the rear risers with the brakes stowed.....

  I Heard that the new troll or a proto canopie from atair was very good under this condition

A my right? or just heard a bad rumor

Shit, send it to me. I'll jump it.

So Why aren't canopies made in a 6 cell, or 8? Maybe two center cells would inflate more evenly and balance each other out?

You wouldn't *have* a center cell anymore.
-Josh

Hey Tom, I posted another post a long time ago about jumping a 5 cell reserve canopy. And I believe you had said what has been already posted.

added link http://www.dropzone.com/...i?post=916865#916865

Goodthing, it postponed me starting to BASE, untill I bought real gear.

But as soon as get rid (trash) the rig the 5 cell is in, I can see about getting it modded' and test jump the bridge... what'da'ya'think?

Thanks for all the info, I suppose what I was getting at is can you use a big docile 9 cell (silhouette 210) or do you need a specific base canaopy. Anyone who e-mailed, I put my address down wrong, should be paul.jcooper@btinternet.com (not .co.uk). Thanks for p.m. Darren, good points. I'll be in touch soon!

sent email and sent PM......................

contact me

You need a BASE specific canopy for BASE jumps, it's that simple.

get hold of the Bridge Day 2003 DVD ( http://www.bridgeday.info if you don't know anyone who has a copy)

watch that a few times (all 6 hours) and you'll see why you want a BASE specific canopy over anything that skydiving has to offer...

edited to add clicky, and while you are at it, get the 'Official Bridge Day Safety and Malfunctions' video - it's really worth it and will give you an idea of what can and does happen, even off a relatively easy object.

Silhouette would be a bad choice for a BASE canopy. The openings would likely be very scary.

I can't recomend a BASE specific canopy strongly enough.

The Silhouette would be a very poor choice, though it *could* be done on some objects. Slow, off heading openings aren't fun in the BASE world.

Theoretically, a 9 cell canopy could be designed and built with desirable traits for BASE jumping.

In practice, the only non-base canopies that even come close to having appropriate traits are modified seven cell skydiving reserves.
Even those aren't all that good.

For BASE canopies you want:
Rapid, consistent openings.
Heavily reinforced/overbuilt stitching and seams.
Very light wingloadings (around .7lbs/ft2)
Stable flight in deep brakes.
Tailpockets as opposed to d-bags.
An assortment of different sized, usually BIG pilot chutes.
A longer bridle.
Sliders are either not used or usually made of mesh as opposed to solid fabric.

This is a list off the top of my head. It' not complete.
BASE specific gear and quality training are essential for minimizing the already high risk of injury or death.
-Josh

So why does there have to be one "center" cell?

makes packing easier, lol

8 cell canopies have been made in the past(not for BASE). They were not popular.

Center cell inflation first, is ideal. Fill the middle cell, then the outers, it aids in heading performance. Without a center cell, the air can fill one side or the other first.

Once filled with air, it doesn't matter all that much.

I do not know the answer. But does the centre cell have any structural properties. As if you had a seem in the middle it would be more likely to fold here if not fully inflated etc.. ? Also if you had two centre cells, what would happen if one was not inflated as quickly as the other. Could this cause one side of the canopy to inflate and cause a turn? Anyone got any good books on fluid dynamics etc.. Btw I will be looking through the forum to see if someone has already discussed books etc.. I am just figuring if someone knows off the top of their head.

Not so much specifically fluid dynamics, but if you can understand it MIT's OpenCourseWare is an amazing resource. It's essentially all of MIT's textbooks and courses online and free to use. You should be able to find a wealth of information on almost anything that you'd learn in a college environment.

http://ocw.mit.edu/index.html

http://ocw.mit.edu/...CourseHome/index.htm - Aerodynamics of Viscous Fluids

Has anyone done any studies with a larger or smaller volume center cell opposed to the other cells? Maybe something like a large 5 cell type center cell with 3 7-cell types cells on either side. Might make for a funny flying canopy Or maybe not???

Jason
570

Thanks for that. If I'm gonna do this I'll definately get a BASE specific rig now that I understand the importance a bit more!

another reason: simplicity.
one center cell implies an odd number of cells.

for example:
a seven cell canopy has 8 sets of lines.
4 sets of lines to each riser.

to have 2 center cells, you'd have a parachute with an even number of cells, and an odd number of lines (or some novel configuration).
while I'm sure it's possible, is it worth the extra headaches?

hence easier packing

true.
but don't overlook easier design, development, and manufacture as well. (i.e. cheaper)

oh yes, by no means am I saying hamper future design

The 6 and 8 cell mains I've seen had line groups meeting at the center, like this.

Makes sense. What about what the other suggestion of having a larger center cell? maybe just wider than the rest.?

I have no opinion on that since I don't design canopies.

how about a combo.. 7 cell canopy
larger center cell with larger vent.. and closed end cells..
might help it to presurize evenly. and if you watch alot of video looks like end cells presurize from inside. the leading edge of the end cells are shut on alot of openings..