Regarding the original question posed:
"Are there any other advantages / disadvantages of this system in autorotation?"
I don't have any stick time in a contra-rotating aircraft, but there are a couple of notable differences in the coaxial (Kamov) type system during autorotation that I'm aware of. Most notably in the how the aircraft behaves about the yaw axis.
Obviously, in a conventional helicopter, yaw is controlled by the application of pitch to the antitorque rotor - in the coaxial system, however, yaw is controlled by the application of differential torque to each rotor system. This allows helicopters with coaxial rotor systems to dispense with the long tailboom common to almost all other configurations and results in all of the Kamovs looking sort of like a fat goldfish. This config reduces the aerodynamic moment of the tail - i.e. the fuselage does not "weathervane" into the relative wind as easily as a conventional helicopter. What this necessitates on most coaxials is a large set of vertical tailplanes on the horizontal stabilizer, usually equipped with a set of rudders....
In short, since yaw control in a coaxial system is based on engine torque being applied to the system, when that torque is removed during a freewheeling autorotation, the only yaw axis control remaining is that provided by the aerodynamic surfaces, resulting in the aircraft being sort of squirrelly, heading-wise, on the way down through the auto.
To quote from Shawn Coyle, "Maintaining directional control [in a coaxial system] is difficult, as the amount of differential lift between the two rotors is not high, and may in fact, reverse. The rigging that produces a left pedal turn in powered flight may produce a different effect in autorotation."
On a different note, I've heard nothing but rave reviews from my friends who used to fly HH
-43s and some dudes who are flying K-MAXs now. Apparently with the intermeshing (eggbeater) config, autorotational performance is pretty impressive. You've still got the yaw control problems requiring extensive stabilizer set-ups, but apparently they are some of the most forgiving rotor systems out there. I've heard the old HH
-43 guys talk about autos in which, after rolling the throttle off, you could take the aircraft all the way to the ground without raising the collective from the floor. Some of 'em have even said you could do an auto without even lowering the collective....pretty amazing.
I'm all ears if anybody has any contradicting info or thinks I'm off-base....
Hope this helps......
PAVE LOW LEADS!