Hi,
Usually I donīt talk in English about aerodynamic aspects of a helicopter, so iīm sorry when I donīt always use the right terms. I hope it will still be clear what I mean.
Maybe itīs not all about the angle of attack to the mainrotor and/or the energy, i think we should talk about the forces which decelerate the helicopter.
The aerodynamic drag, parasite drag, and so on stay always the same at a particular airspeed. We all know the formula
F = m * a , F = const. , m = mass, a = acceleration
m1 = light heli
m2 = heavy heli
a1 = F/m1 > a2 = F/m2
As you can see, a1 is bigger than a2, so in case 1 the helicopter will be more decelerated than in case 2. But as we want to have a constant speed in the autorotation, we have to take down the nose of the helicopter so the acceleration by gravity will work against the deceleration produced by the drag.
But if we do so, we will have an higher ROD because of the nose down attitude.
Itīs just a consideration, so maybe itīs all bull**** i wrote
Bye!