Thanks Dave, Nick an others.
Nick, thanks for the detailed explanation.
I see the inertia reserve and low disk load is, as you confirm it, the most important factors.
But these factors, assuming the rotor is correctly designed to endorse CF efforts, have not the same efficiency if coupled to bad/uneffective blades.. am i wrong ?
Behind these mechanical factors, what are the aerodynamic factors ?
for example does a 3 bladed rotor autorotates better than a 2 bladed ? are the asymetrical airfoils better for autorotation ?
Is an enstrom or a ecureuil better than a B47 or a B206 in autorotation ?
I must say that by "good autorotation capabilities" , i mean a low Rate of descent and a good inertia reserve.
Thanks for helping me to understand.