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Yoshi

why only 9

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ok so I am sitting here at work...bored out of my mind, and I was thinking (yeah it hurts a little)... why is it that we see 9 and 7 cell canopies (sure there are 21 and 27 cell tri cell crosbraced canopies, but essentially they are 7 or nine cells), but we dont see 11-13 or higher?? is the 9 cell really the most efficeint skydiving canopy design? would a 11 cell canopy change the aspect ratio and flight characteristics to a less desireable flying machine? I guess this question is kind of for the canopy manufacturers, but if you have any input please feel free to comment. has there been canopies with more than 9 cells? (not speaking of tricell canopies) I have seen 5 cell squares, and I realise that the less amount of cells may produce less desireable flight characteristics, but what about more?... I could understand the idea of having mroe drag due to the possibility of needing more lines as a con, but what are some other cons/ pros?
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I think you should ask Jim, Wyat, or Cobalt Dan this question. I remeber asking about this during my canopy course and as I remember, the inflation is longer and becomes more complex as you add cells thus the canopy manufacturers found nine cells to be most optimal for an inflated wing design.

G

"The edge ... there is no honest way to explain it because the only people who know where it is are those that have gone over"

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***how many cells do paragliders have? aren't they like super-efficient?
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They are, due in part to thier aspect ratios, which are extreme by skydiving standards. As a by product, they tend to fold their ends up under the canopy. Their sqaure footage allows them to keep flying, and the pilot can unfold things, but it might not work so well with a sub 100.

Thats one of the reasons canopies are 'limited' to 9 cells. To have an 11 cell canopy at the same sq. footage as a 9 cell, you have 11 smaller cells. If you maintain the cell dimension, you end up with a thinner wing. If you maintain the canopy thickness, you end up with a thinner cell. Either way I think you would lose rigidity, and see more collpasing and folding like paragliders (which are huge and have a million line groups).

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Some (but not all) of the reasons:

1) Openings. Make a canopy much wider span wise and your sliders are going to be less and less effective. There was a t one time a canopy produced by the OLD Aerodyne called the AR-11. 11 cells and an ice pack to take card of the opening pain.

1a) Openings. When you get asymetrical inflations your canopy WILL spin up big time.

2) Chord: as you make the Span wider, it makes sense to shorten the chord (front to back) to maintain the sizing. This makes the stability of the design difficult to manage. With a short chord it is a much more tricky prospect to suspend the load under the wing where you want it to have a good balance between dive, and glide, and riser pressures.

3) 9 cells work well enough.

There are 11 cell (33 when crossbraced) designs being tested by some of the top pilots, but they are really purpose built and event specific tools.
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You're not as good as you think you are. Seriously.

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There was an 11 cell canopy in production 7 or 8 years ago. Called the AR-11(I think). Never flew it so I have no input as to pro's or con's, but there should be someone out there who knows more. I would think that as you increase cells, that you increase drag with the extra lines and therefore decrease efficiency. Thats just a guess though

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You hit the heart of the issue, Line Drag. More lines means a less efficient wing at high speed.

For example, I built a tricell cross-braced airlock canopy with external cross-bracing in the form of triple spansize cascaded lines. It was rigid and had nice slow-slight characteristics, but the surf was incredibly short. Once I completed the turn for landing, it was as if I had hit some sort of airbrakes, the thing just slowed down instantly.

You see, efficiency is about drag reduction as much as it is a nice airfoild shape. Drag is the bottom of the fraction, and lift at the top. (L/D)

Hope this helps.
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and not everybody is ready to jump with lines as small as the ones the use on paragliders...
the smallest lines I saw were the one used by an italian guy on his Paradelta BullBall which were steel lines 0.03mm, approx 30kg resistance each... you could hear him from far away... and as soon as there was a sunshine on the lines... WAW what a visual effect with the reflection.B|B|
scissors beat paper, paper beat rock, rock beat wingsuit - KarlM

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thanks for the responses. I kinda figured the main reason was for the drag on the lines, but the opening characteristics make sense as well.. it still makes me wonder what kind of designs we arent thinking of (or maybe some are, but arent being used/made/implemented) that could take things yet another step beyond where we are now...
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this space for rent.

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From what I understand about aspect ratio, a larger AR negatively affects openings (spinning), but improves glide. While paragliders have an AR of like 4:1 and something like 30 cells(?), they make a nightmare to deploy at terminal velocity, I imagine. This is why you don't see people jumping out of planes with paraglider canopies. I hear John LeBlanc is/was testing a design that could be deployed at or near terminal. I suppose you can add more cells while retaining a smaller AR, but that'd be kind of pointless, you might as well use one of those 5-cell dealies.

I'd love to hop and pop from 14k and do a 30 mile cross-country :>

-Rory


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thanks for the responses. I kinda figured the main reason was for the drag on the lines, but the opening characteristics make sense as well.. it still makes me wonder what kind of designs we arent thinking of (or maybe some are, but arent being used/made/implemented) that could take things yet another step beyond where we are now...



You be the king and I'll overthrow your government. --KRS-ONE

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