tintrax, Im not planning on using hinges, at the moment its a ridgid system, but Im not sure whether the blades will rotate at the same speed or not. Ive got 2 layouts at the moment, one with a flapping head one without, after reading billf's post, I may skip the ridgid and go straight to the flapping.
As part of a design project Im working on a new rotorcraft design, part of the design requires the ship to be a coax, thats the main reason for the rotor layout.

billf, I would think that the top rotor would be slower than the bottom as its operating in the wash of the lower rotor.If you dont mind, whats the rotor diameter of yours, the space between the rotors, and did you have different blade incedence on the top and bottom rotors?
Thanx