Jun 6, 2001, 5:03 AM
Post #1 of 11
7 cell vs 9 cell
There were couple of very interesting points made at the Diablo thread conserning 7 cell's performance compared to the 9 cell's. I found even more interesting comments when I surfed through manufacturers webpages. Aerodyne's page says (http://www.aerodyneusa.com/2thisisques2.html) "The Triathlon was the first truly high-performance ZP 7-cell and proved superior to the Sabre-class ZP 9-cells in every aspect." and icarus's page (http://www.icaruscanopies.com/canopies/EXTreme_VX/): "Jumpers have known for years that 9-cell canopy's out perform 7-cells" ??
Aerodyne specialises in 7 cells (Tria and Diablo), of course they will say their 7 cells outperform comparable 9 cells
And Icarus was positioning their VX as even more "fastester" then the FX, so of course they will say 9 cells outperform 7 cells...
Personnaly, I think the only rule that can be applied and is true 100% of the time: you will go faster with 0 cells then 7 or 9 cells! (whatch out, that Luigi with his 46 will prove me wrong by going more then 120 mph vertical speed!)
That VX 46 is just incredible. I didn't really realize how small the canopy actually was until I saw the picture of Jim Slaton kiting it in the June Parachutist. Then I realized that my current canopy is more than twice as large as my dormitory single last semester (single: 112 ft², canopy: 230 ft²) while that VX 46 is less than half the size of that room!!! For every square foot of canopy that Luigi Cani has, I have 5! I also did some rough estimations and figured that the VX 46 is about the same size as a king-sized bedspread!!
We all know that the Triathlon and Diablo aren't even in the same league as an Extreme as far as canopy performance. That is why you don't see anyone with a Diablo 46 over his head.. Because a Diablo 46 probably wouldn't fly very well? Extreme FX and VX canopies are without a doubt the best made for swooping. I don't believe it would be possible for a Diablo loaded at 2.0 to even think about flying in the same airspace as an Extreme loaded at 2.0. The 7 cell canopies are made with different performance characteristics in mind. 9 cell ellipticals are made for one or so things.. To impress all of us with their speed!! They are fast and very entertaining in the hands of a good pilot. That is exactly what it takes to fly one of those canopies highly loaded "A PILOT"! I think beginners "Low time canopy pilots with little time wrenching their canopies in and out of its flight envelope at both low speed and high speed" Have no business under an Extreme loaded at 2.0.. I've seen too many skydivers that downsized to fast for their skill level fly right into the ground, making the good swoopers look bad, driving potential skydivers away from the sport. On the other hand the Triathlon and Diablo are more forgiving in their low speed flight characteristics. You can STOP a Diablo or a Tri on a dime, if you stab the brakes on an Extreme my guess is you are going to go ballistic! OR back into the air. UP UP AND AWAY!! Maybe the issue here is canopy progression? Not what out performs what? For a low time canopy pilot a seven cell Tri or Diablo will probably keep you alive longer. Of my last 200 jumps at least one out of five was a hop and pop at altitude 13,000 ft+. I have ALL standup landings. The reason I do this is simple, I want to know EVERY aspect of the flight envelope of my canopy. Front risers, rear risers, weight shift in the harness, stalls, and recoveries. A couple of years ago I asked Charlie Mullins what it took to make a good canopy pilot? Since then I play around up high not down low.. I weigh 155 lbs, putting my first 150 jumps on a Triathlon 150 gave me a wing loading of 1.25. I learned EVERYTHING that my canopy could do. Which wasn’t a whole lot at 1.25. But I KNOW what it can do and I can pull myself out of anything with that thing. I demo’d a Diablo 120 as well as an Extreme FX114, I KNEW the Extreme for the moment was out of my league and I was not loading it enough to take advantage of what it is made for. The Diablo120 still had the low speed characteristics that I was comfortable with. And I could speed it up as fast as I was comfortable going. My point is this again, nothing can touch an Extreme with a good pilot… But until you are a good canopy pilot starting with a more solid, forgiving, yet high performance 7 cell like the Tri or Daiblo is a SAFE thing to do that could keep you in the sport longer. Safe being a relative term to your common sense. Blue Skies! I hope this helps someone.. Rhino
Do 7 cells out-perform 9-cells? It depends upon which corner of the envelope you want to fly in. Yes, tiny, elliptically tapered canopies like Icarus Extremely Extremes are the best things available for turf-surfing and blade running, but you won't catch me shooting accuracy, or flinging myself off a bridge, or docking on a stack with an Icarus Extremely Extreme. My point is that Icarus Extremely Extreme canopies sacrifice all other aspects of performance so they can become the best possible turf-surfers in this atmosphere! Other companies manufacture specialized 7 cells for other corners of the performance envelope. For example: all specialized BASE canopies are large, lightly loaded, low aspect ratio 7 cells. BASE jumpers prefer 7 cells for thier consistent, on heading openings. They prefer low wing loadings for softer landings between the boulders, trees and fast flowing rivers that surround their landing sites. For most of the same reasons, accuracy competitors prefer large, lightly loaded 7 cells for slow, steep predictable approaches on the edge of the stall. Almost all reserves are 7 cells because back in the early 1980s designers realised that 7 cells had the most predictable openings. CReW jumpers stick with 7 cells because they will survive rough docks and still stay inflated. In conclusion, yes Icarus Extreemly Extreem canopies out perform Triathlons, but only in one corner of the envelope. They are dangerous or useless in other corners. So when you say that one model out performs another model, please specify which corner of the envelope you are referring to.
As Rob has pointed out, when you talk about performance it depends on what aspect of it you are referring to. Typically 7 cell canopies have a lower aspect ratio (span/average chord) and 9 cell canopies have a higher aspect ratio. For a given area of wing and at lower airspeeds, one with a higher aspect ratio will generate more lift than one with a lower aspect ratio. An example of this is a sailplane or glider. They have very long wings and a short chord on the airfoil. Changing the planform to an elliptical shape also makes the wing more efficient, ie.faster and faster creates more lift.
This is partially why 9 cell ellipticals are said to "out perform" 7 cell canopies. The performance parameters they are referring to are speed and lift. A 150 sq. ft. 9 cell elliptical with a 170# pilot will fly farther and faster than a 150 sq. ft. 7 cell canopy with the same pilot. This also partially explains why we can load the 9 cell ellipticals more heavily and still land them. They are more efficient and have wider range of flight speed. Cross bracing simply adds to the effiency by making the wing more rigid and therefore having less distortion. Distortion reduces the amount of lift.
Yes, the small cross braced canopies are capable of very fast speeds, but the real beauty in them is that they can be flown slow enough to be landed safely by a good pilot. A 46 sq. ft. Diablo could be flown, but it would simply not provide enough lift at the lower airspeeds needed to land to be landed safely.
There are trade offs in perfromance. Rate of turn, glide angle, openings, etc. High aspect ratio 9 cell elliptical canopies typically are not as reliable for on heading openings, however; the newer designs using the latest advancements in technology have started to provide soft, on heading openings at a reliable rate. More speed means a longer runway is needed. Speed also magnifies the consequences of even small mistakes.
So, Rob is correct. The term "performance" can refer to a number of different aspects of flight. A VX does not make a very good choice for doing CRW, but it can do a barrel roll with very little effort. That 7 cell canopy is usually a pretty good choice for CRW, but would be difficult if not impossible to barrel roll.
Now, what about those 7 cell cross braced canopies? Actually they are 21 cells with the higher aspect ratios usually associated with 9 cell canopies. The VX? 27 cells with a slightly higher aspect ratio than the FX. More lines on the 9 (27) cell canopies create more drag than on the 7 (21) cell canopies, but that is more than offset by the additional lift provided by the higher aspect ratio, with less distortion.
As far as the manufacurers claims, someone else already said it best. Marketing. I hope this has helped you to better understand some of the aerodynamics of todays canopies. A full explanation would require a book (or more), so I hope this is sufficient.
<FONT SIZE=-1><EM>Edited by alan on 6/7/01 11:22 AM.</EM></FONT>