That's my theory too. In a very general way though. I also think that it has to do with the shape and depth of the bevel on the rim. Looking down my Discraft midranges. it looks like a more pronounced bevel mean more stability.
Take a bicycle whell in your hands (axis) and let it turn, now try to chage the position : it resist
a disc when spinning is the same and the aerodinamics tent to move the nose up.
if the spin is enought : it flight straight, if not : the nose's rising and with the gyroscopic effect it carves
The carving way is different because of the spinning direction because air/disc speed is not the same on right or left side (spinning adds speed on one side and retreive speed on the other) so the aerodynamic force is not centered.
Aerodynamics is fixed by the profile of the disc big dome : great for low speed, flat dome great for high speed.
Mixture of the rim design, weight distribution, disc diameter, how flat the top is and lotsa everything else. :) Some people that I know that have been around discs for many years can look at a disc and identify it with no stamp or markings.
I was watching some show on the Military Channel about ancient weapons and some guy uses todays tech to improve them. Well they had some weapon that looked like the Aerobie flying ring used by people in India. They threw the wepon and you got the classic RHBH fade to the left. They described that what caused this was the right hand side of the disc was producing more lift which caused the disc to turn left (when thrown RHBH). They even braught the guy out who designed the Aerobie flying ring and stated that somehow he designed it to have the lift on the rh side shifted to the front and also back, producing a disc that flies straight.
I agree with Birdie-Man, there are many factors, but the rim, the dome, and weight distribution, are the largest. A friend of mine has a theory about the factory stamp underside being the main factor of weight distribution. If you look at a new Katana there is only a stamp on one side, which would explain how it turns so fast.
I've heard that it is the rims edge and how it relates to the center of the disc. The closer the rims edge is to the flight plate the more overstable the disc is. The further the edge is from the flight plate typically makes a disc more understable. BH roller discs typically have an edge closest to center and thats why they roll so nice :) Hence Sidewinders/Road runners making good roller discs......Anyone?
There are manufacturers who are members of this site: Dave Dunipace of Innova and Dave McCormack of Gateway who could give an accurate and technical answer to this question. We also have Chuck Kennedy, who is a very smart guy and who knows a lot about most things and everything about everything else, and who could give scientific descriptions so involved you might get a headache just trying to pronounce the long words.
Me, being a lowly practitioner of the sport, and not scientifically minded at all, would suggest that the best way to figure out how stable a disc is, is to throw it.
Mr. Mark, surely to goodness you must have heard something about the recipe for making overstable, straight and or stable plastic. The molds and how they are weighted must have something to do with it too. Thickness of plastic here and there, high or low ?? Perhaps you have to be an alchemist to concoct these discs. Somebody has to know what they're talking about, or is it such a closely guarded secret they have to take the formulas out of the safe everytime they do a run.
Probably those alchemists start with a beveled edge and from there add weighting and rim configuration in top secret ways.
The real secret is not just how to make something overstable but how to make something overstable to a degree it is useful (the most overstable discs like the Extreme or a Whippet X are too overstable to be useful for mere mortals for anything more than an occasional trick shot) while maintaining a degree of glide that makes it functional.
Compare an Extreme to an average driver and you can see the obvious differences.
Shapes that effect the flow of air over and under the disc.
Edge thickness or edge height- thicker the edge = more overstable, XCal vs. Destroyer or Gator vs. Roc
Rim angle - more angled = more overstable, Valk vs. Sidewinder or Starfire vs. Sidewinder
Rim width - More weight in the rim generally makes the disc faster which can translate into being more stable depending on the shape.
Plastic type - More floppy usualy equates to less stable. Stiffer discs tend to be a little more stable.
There's more...Cooling temps, cooling time...