A magazine ad from 1967 showing a concept for a “Hot Cycle” helicopter. The “hot cycle” was a way to spin the rotors without imparting a massive torque to the fuselage as usually happens with helicopters, requiring a tail rotor to counter. here, instead of mechanically linking the engine to the rotor via drive shafts and gears, the engine exhaust was ducted up through the central rotor shaft, then out to the tips of the rotors, and then ejected through thrust-generating nozzles. This would impart only a trivial amount of torque to the fuselage, largely from friction with the shaft bearings. it was a great idea, but there were some issues with leakage around the bearings as well as being impressively loud and fuel-hungry.
Note that while the “hot cycle” eliminated the great majority of the need for an anti-torque tail rotor, this and similar designs still had one. This tail rotor would be used to swing the tail back and forth, yawing the aircraft at low speed.. This woudl require that the rotor be able to provide thrust in either direction on demand.
