Why Full Scale Helicopters are not using Electric Motor Tail Rotor Unit?

Just been re reading this thread.

One poster mentioned that an electric tail rotor would probably be 400Hz. From memory this frequency removes the necessity for iron core to the motor which would dramatically reduce the weight for a given power. The higher rpm would need a reduction gearbox, adding weight.

Voltage/frequency control would enable rotor thrust variation to be by speed control rather than pitch, again reducing weight and simplifying mechanical design. There may be some lag in response compared to pitch variation which could make flying more difficult but probably no worse than the turbine lag that pilots have learned to deal with.

Thrust would increase roughly linearly with rpm.

Efficiency of generator probably about the same as the rotor motor - say 88% and a gearbox of about 98% giving total efficiency of around 76% which should be comparable to a shaft drive with it's flexible couplings, universal joints, bearings, gearboxes etc.

A homopolar motor would probably be even lighter but would need a higher ratio gearbox.

Seems the mechanical and electrical would be comparable in weight and the electrical perhaps lighter, but the mechanical weight is distributed from above the cockpit to the tail while the electrical would be entirely in the tail - a definite disadvantage.

The safety aspect of the mechanical being linked to the main rotor during auto rotation is important but in an electric system the tail rotor could be driven by the APU. The overload of the APU wouldn't matter as it only needs to operate for a very short time. Normally the electric rotor would be driven by the main motor generator.