My next question is concerning rotor area.
I know that that R squared x pi = area, but what I'm not sure of is if I have two rotors spinning in opposite directions, do I add a certain percentage of the second rotor to total area or not. I know when you figure the area of a fixed wing bi-plane the area of the second wing is not 100% efficient so we normally say total area -25% to get effective area (something like that).

RW