^Timeetyo is pretty much 100% correct in his post.
Roll is generated by the location of center of lift combined with gyroscopic precession. At high speeds and low angles of attack, the center of lift moves backward, behind the center of the disc. The gyroscope will move that force 90degrees in the direction of spin and roll the disc to the right (RHBH, clockwise spin). At lower speeds and higher angles of attack, the center of lift moves forward, ahead of the center of the disc. The gyroscope will move the force 90deg in the direction of spin and roll the disc to the left.
If the disc is spinning fast, it will be more resistant to the roll force and will change it's direction a little slower.
I keep reading that, but the aviation enthusiast in me is a bit puzzled about it. I would think that the spin creates increased airspeed over the left side of the disc compared to the right side of the disc. This increase in airspeed should lift the left side causing the disc to turn. Once the disc loses speed and spin the air friction of the disc spinning will overcome the lift forces causing the wing to lift and the disc starts to fade
Exactly what makes the disc fly more stable when it spins?
A disc is not a helicopter. They don't exhibit the same aerodynamic characteristics. In a helicopter, the advancing blade sees the aircraft forward speed
plus the blade's rotational speed. The retreating blade sees the aircraft forward speed
minus the blade's rotational speed. If the helicopter is traveling forward at 100mph and the tip of the blade is moving 400mph as it's spinning, the advancing blade will see the air at 500mph whereas the retreating blade will see the air at 300mph. The faster blade will generate more lift, causing an unbalanced lift distribution over the rotor. (Helicopters will change the angle of attack of the blade as it's spinning to balance out the lift distribution.)
Discs don't work like that. The disc is a solid body, and the entire body sees the air at the same speed. The left side of the disc is traveling 50mph, the right side of the disc is traveling at 50mph.
The only nuance here would be frictional effects. The "advancing" half of the disc would have more friction with the air than the "retreating" half, so the lift on the advancing side would be ever so slightly less than on the retreating side. This is opposite of how a helicopter sees it, but the effect is utterly negligible.
As a noob DGer and an old timer amateur physics nerd, I've researched this for a while now, and everything I've read physics/math-wise so far agrees with sumo21 et. al.
The paper at
http://www.odgc.ca/files/dg-flightphysics-mkIV.pdf gives a pretty good non-math overview of two of the 'sideways' forces involved due to spin (page 3 & pages 5-6).
That dude is almost 100% wrong about everything. His explanation of page 5-6 is making the helicopter mistake. (And even if the helicopter assumption were true, you'd still have to account for the precession of that force. The difference in speed of the advancing/retreating blade manifests itself as a pitch (nose up/down) moment, not a roll moment.)