Not being an engineer my arguments may well get shot down in flames, but I believe what Dave proposes will be impossible to implement in an efficient manner, simply because the strength and stiffness required is too great.. .. .As an illustration, compare Bell and Robinson rotor heads. Bells are pre-coned to a certain angle, a compromise between the ideal angle for a heavy, maneuvering ship, and that for sitting on the ground at 100% Nr at flat pitch. So in the first case the compromise pre-cone angle is too small, causing stresses in the rotor head and the blade roots, and in the second case the pre-cone angle is too large, causing different stresses in these same components. So the rotor heads and blade roots are built stoutly to accommodate said stresses, thus leading to the famous high inertia of Bell rotor systems.. .. .On the other hand, the coning hinges in the Robinson heads allow each blade to seek the ideal angle in any given situation, therefore no bending stresses in blade root and rotor head: these can be built more lightly. Thus leading to the famous low inertia of Robinson rotor systems.. .. .If one were to design as Dave proposes, a rotor system so stiff that it wouldn't cone at all, imagine how much more heavily built that system would have to be, even compared to the products of the Bell Ironworks. Not only that, for adequate stiffnes the blades would have to be pretty thick, probably too thick to be much good at producing lift.. .. .So for rotor systems light enough to get helicopters off the ground, coning is here to stay, and that means two-bladed systems will continue to be underslung.