Optimal coaxial spacing between rotors

[Skytrek]

I need a simple method of determining the optimal vertical spacing between the upper and lower rotors of a fixed pitch coaxial system. What is the most efficient angle of pitch (incidence?) for fixed blades?

 

[Intermesher]

Skytrek

The greater the vertical gap, within reason, the greater the efficiency. The greater the pitch, within reason, the greater the efficiency.

A couple of homebuilt coaxials have fixed pitch, but IMHO, the rotor gap is going to be 'zero' a few seconds after a loss of power.

One small improvement over fixed pitch is to have a very simple 2-position pitch. Engine torque puts the setting at the upper limit [+/- 9-degrees] and lack of torque (autorotation) puts the pitch at its lower limit [+/- 1-degree].

For a slightly more sophisticated rotor RPM thrust control, you might consider.

http://www.unicopter.com/0575.html

Dave Jackson