Hi,

For what it's worth, I built a coaxial rotor gyro several years ago. Both top and bottom had 3 rotor blades, and both set of rotors had a fixed coning angle to ensure that they didn't get tangled up, and I didn't see any difference in the lift by adding the 2nd rotor. At the time I was using a Clark Y profile blade with a twist at the root end of the blade. However, it looks cool flying.

Phil