Thats really cool, researching frisbees and having your own wind tunnel and all that.
Can you talk a bit about what you learned about disc selection through your research?
What do you think about the characteristics of flat vs. domey discs? I have heard here and there that domey discs behave more squirrely.
And what is the difference between discs designed with flat vs. concave lower rims? Example would we a River (concave) vs. a Hawkeye/old FD which has a flat lower rim. Both discs fly fairly straight. I have noticed that Trilogy tends to design even their understable discs with a concave lower rim while Innova has chosen to make some discs with a flat lower rim and toyed with convex lower rim designs (for example the Innova IT).
Sure. About flat vs dome, it actually varies depending on the disc. Typically, we can say that dome increases glide (I don't like glide as a flight number, but that's a different discussion...). It also generally makes the disc more understable, as it pushes the parting line down compared to a flat disc. There are exceptions, though. I have a Wraith with a very pronounced dome in the center of the disc, but the parting line is still higher than a flatter Wraith. So it has more glide, but is also more overstable. From what I understand, this is an attractive feature in certain Destroyer runs (I don't throw hard enough to know
). I have simulated a comparison of different plastics, using the Alfa Discs Cosmic disc. These discs had a very pronounced difference in dome, and the parting line was a bit lower for the domey disc. You can see the result of this comparison below, both in terms of aerodynamic coefficients and typical flight shapes with low and high throwing speed ("beg"=beginner, and "pro"). You see that the domey disc has higher lift, and is also more understable (lower moment coefficient). This will make the disc more squirrely, as you say, as it will be more affected by the wind and also off-axis torque in your throw.
Same with concave/convex/flat lower rims, it is difficult to compare different discs since the overall design is different so you can't really isolate just the effect of the rim profile. For the River/FD, the River has a more pronounced curve on the shoulder of the disc, which together with the larger dome adds to the glide and understability. But I think this is a really interesting comparison, since it's two very different designs with the same goal of a glidey, straight disc. I will run it through my simulation setup and report back with more details.
For the convex rim, I do have an example in my article, comparing a Firebird against a Roadrunner. This was chosen as an extreme example on purpose to really highlight the differences. A different version of that comparison is shown below, with arrows indicating the wind pressure pushing on the disc. You see that for the concave rim, the disc is pushed up on the nose, making it more overstable. The convex rim is more neutral. There is also a big difference towards the back of the disc, where the air pushes more upwards on the Roadrunner, making it more understable. But again, this is the overall design, not just the rim shape.