I discovered a peculiar kind of rotorcraft called the helicogyre, where the means to rotate the main rotor are built into the rotor blades. This is the kind of scattershot experimentation typical of the interwar period, before the stabilization of the helicopter format. One such machine was described as "like two small aeroplanes chasing each other" and I had a sudden though : why not two autogyros chasing each other ?
This gave me the idea to place freewheeling rotors at the tips of the driven rotor, in order to increase the swept area and thus the lift. The transmission of motive power to the rotor tips is similar to that of the Brennan Helicopter.