It's VERY generic, but IN GENERAL, the 7-cell will open more reliably and on heading, have a steeper glide, and require a quicker flare. IN GENERAL the 9-cell will have "sportier" turns, a longer glide, and a more powerful 2-stage-ish flare with more "swoop" to the landing.
But there are exceptions. Compare a Falcon 150 to a Diablo 150 ...
Traditionally, nine cells and seven cells do have the characteristics described above. Compare the original PD 7 and 9 cells, for example. Nowadays, different design techniques mean canopies are very varied. The PD Spectre, for example, a 7 cell, has a flatter glide than the PD Sabre 2, a 9 cell.
There are very few difference between them, aside from the physical number of cells, that cannot be designed in or out of the canopy.
'Glide angle' is simply a matter of line trim, and has nothing to do with the number of cells.
Aspect ratio is also simply a matter of design choices, you can cut up any apect ratio into either 7 or 9 slices.
Look back in history, and you'll see where the 'myths' about these differences come from. Back in the day, most canopies were 7-cell F-111. When squares frist came out there were even 5-cell designs, but those fell by the wayside with 7 being the popular number.
Then they started to produce 9-cell canopies, and in an effort to increase 'performance', they bumped up the aspect ratio. The added number of cells allowed them to make a stable canopy with a higher aspect ratio. Those wings would turn faster, and were more efficient to allow for a flatter trimmed line set, and still be able to get a good flare from the slower trimmed airspeed.
Early on in performance, the goals were fast turns and flat glide, with the Stiletto being the 'end game' of that trend. What they found (eventually) is that the Stiletto didn't dive very well due to the flat trim, and was tough to control the roll axis on the flare because of how much it liked to turn. In time, swooping became the goal, so they went to steep trims for longer dives, less turn response to make those canopies easier to fly at (much) high wingloadings.
Anyway, back in the day, there were some 'universal' differences between 7 and 9 cells besides the number of cells, but most of that was due to the idea that the 9 cells were the 'new' designs and the 7 cells were the old designs. However, that was a long time ago, and since then they have discovered that you can simply design those differences in or out by building the canopy the way you want.
Now if you want to know the differences between specific canopies, then list the models and we can go from there, but what you're asking is like saying 'what's the differences between a car with a 4-cylinder engine or one with a 6-cylinder engine'? Twenty-five years ago, it would have been that the 4-banger was the slower, base level car, and the 6 was the faster, upgraded machine, but today it's not always the case. There are 4-cylinder cars that can out-perform 6-cylinder cars by a mile, and it's all based on the design choices when you build the car itself.
(This post was edited by davelepka on Oct 12, 2012, 5:14 AM)