Electric Tail Rotor Drives for Helicopter Applications

Most helicopters in use and in production today carry tail rotors that are mechanically driven from the main turboshaft powerplant through a complex system of shafts, transmissions, and couplings. The configuration requires intensive maintenance and continuous monitoring for signs of possible failures. Two key technologies have been identified that would, together or separately, improve performance safety, and maintainability of the next generation of military and commercial helicopters. They are 1) the elimination of the conventional tail rotor, and 2) replacement of tail rotor shafts and gearboxes with electrical power transfer and rotor drives. Elimination of the conventional tail rotor is already underway with fan-in-fin (fenestron) designs and the NOTAR (fan-in-boom) system. In contrast, functional electric drives for tail rotors have not been demonstrated. Studies at McDonnell Douglas in the late 1980s showed the feasibility of electric tail rotors for military aircraft. Concurrently, beginning in 1989, a development program was undertaken at SatCon to develop and build a lightweight Direct Electric Tail Rotor Integrated Drive (DETRID) Motor. Satcon proposes to continue development of the DETRID motor system by fabricating a lightweight rotor to DETRID specifications using production methods developed only recently at Satcon. By completing the rotor during the proposed Phase I, a major technical issue is addressed, and all motor components are available to begin testing immediately in Phase II. Testing would be followed by the design, production, and test of a flight-worthy Advanced Electric Tail Rotor Drive (AETRD) motor, resulting in the construction and analysis of two "generations" of electric tail rotor motors during the Phase II program. It has been shown that with existing technology, the AETRD system is especially applicable to lighter commercial helicopters. The lower parts count and improved reliability will make these Systems attractive to helicopter manufacturers that are aggressively marketing to corporations, municipalities and foreign militaries.