View Full Version : Why do some discs fly differently from the same mold?

Jungle Tim
06-16-2009, 06:19 PM
Was thinking about the reasons behind the different flights from the same mold and got a little carried away. apologies in advance for the essay.

Any thoughts to improve my understanding of these effects?

And what is special about the discs that act exactly the same way regardless?

Whatever your view is on Star, ESP, Champ, elite z, Pro, elite x, DX, Pro D etc, the reason for this shift in flight characteristics is the shrinkage of the disc when it cools.
The injection temperature of Polypropelene, a common base plastic, is above 160 Celcius, so freeking hot! (I have a hunch that champ, esp star have a PP or similar base) The liquid cools inside the mould and becomes solid and contracts, however it is still mega hot and will further cool and contract. The thin flight plate and the thick rim cool at different rates, this cooling and contraction is consistent in a will mixed plastic, but can be inconsistent run to run, plastic to plastic, and is the source of the varied flight properties. It’s hard to control the shrinkage, you can maintain the strictest of environments, temperature, humidity etc, often parts (and I assume discs) are placed in temperature controlled baths and yet there still will be variations.
Basically the ingredients all act differently, their quantity, inherent humidity etc. are different so how they shrink will be different too. Keeping the ingredients the exactly the same can be good for discs like the 2nd first run buzz. But it seems that its hard to do. This is even acknowledged with disc such as the Pro Starfire being the origin of the SL. I guess the seed of the ‘yellow is the most overstable boss’ forum posts is most likely a happy coincidence, but still possible influencial.

It’s hard to perfectly tell with heavy vs. light discs as the human arm can get light discs a bit faster generally speaking, faster meaning more hss turn. Lighter discs are also require less lifting force from the flight plate, as they are lighter… so at 70mph a the lifting force of 2 identically shaped discs is the same but the lighter disc will have less resistance to the lift. Resulting in the common rule of thumb that lighter is more under stable. No to mention effect of wind.
As the discs all come from the same mould, they all require the same volume of plastic injected to fill that mould. However at different weights that constitutes different density. From a manufacturing point of view though with a heavier disc, denser / more filler agent is used, sometimes this can affect shrinkage. but i think that maybe its more flight based here.
Dave Dunipace posted on the pdga forums that the filler used to make the light star boss's actually affected the disc shrinkage in such a way that the lighter ones became the more over stable ones...

Basic flight theory says that the dome should increase the lift, and there for glide of a disc. Glide is very commonly associated with under stability. So domey = understable…And it appears it does, in some moulds. The famous roc mould for example, the ‘ching flat top’ is highly prized for its over stability. And the poppy top dx is the floaty dependable fade that most of us throw. Perhaps the buzz is a better example, domey buzz’s turn more that flat tops but they are all mostly straight. So its only a minor effect at normal wind speeds. This is cool for the blunt nosed discs, and even holds true up to speed 10 drivers?
This is all cool until you think about the latest drivers that are completely the opposite. Super flippy flat top forces and mega stable domey bosses. For the sake of my argument im gonna assume that discs don’t get more domey once they come out of the mould. So a domey disc is how the mould has been cut, the nose is at the perfect position.
When the discs dome become flattened, the disc become more under stable. Why? Because the flight plate radius increases slightly as the dome is flattened, pushing the nose down slightly, enough to put these super high speed drivers into a under stable nose position? Im looking at it like this, if you throw a disc nose down, it acts more under stable and if you throw the disc nose up it acts over stable.

What do you think?

06-16-2009, 11:26 PM

06-16-2009, 11:35 PM
Umm, elves make it so.

06-16-2009, 11:44 PM
All your points seem very sound and make a lot of sense.

Omega SuperSloth
06-17-2009, 12:25 AM
I WOULD EMAIL THAT TO THE DISC MANUFACTURERS, INNOVA SEEMS TO HAVE A HARDER TIME BEING AS CONSISTENT AS DISCRAFT?...I COULD BE WRONGi wonder if the sheer volume innova makes wears out the molds and the older molds change slowly or the new ones arent the same , i dont know j.s. about any of that process but ive noticed they are consistent within the same run but do change from run to run .

The most noticably ive seen is the 11x to 12x teebirds , im not sure if they really throw any different but the 12x is less domey. The omega supersofts seem to change alot but i think thats on purpose as theyve tried to make them more durable over the years , the new ones(1.25) seem to have alot more plastic in them where the older ones are more rubberey , alot of people are saying theyve sucked for years but i think the 1.24 are some of the best while the 1.25 look not very well constructed and are almost identical to the dx aviars now as far as stiffness goes.

Three Putt
06-17-2009, 01:10 AM
This is jacked from the PDGA site. I thought it might be on topic, although I'm not even sure if I know what "on-topic" means.

Hey Dave, does a dome really make a disc more stable? Or does it have something to do with the wing? I prefer flat discs because they feel better in my hand and don't seem to get pushed around in the wind as much. But I have heard a lot of people say that domes make discs stable, but have not noticed it myself. thanks!

The dome doesn't have much to do with high speed stability, but does help with low speed stability. The position of the wing has much more to do with hss. That being said, cooling can have a lot to do with both of these and one can influence the other with respect to final shape.

The confounding variable is the shrink rate of the flight plate vs the shrink rate of the rim vis a vis different plastic. Flat discs are made when the rim shrinks relatively less or the plate shrinks relatively more. Flat discs tend to shrink with nose up attitudes on the wind. Domey tend to shrink with nose down, but as we have seen with the longer wing discs, that doesn't hold true any more.