Dynamic Interactions in an Electromechanical Main Gearbox of a High-Speed Coaxial Compound Helicopter

To further increase the speed of conventional helicopters, several new concepts and technology demonstrators have been developed. This paper proposes an electromechanical main gearbox for a compound, coaxial helicopter. The speed and power variation of the main rotor between hover and high-speed cruise is realised by two brushless permanent magnet (BPM) machines and a differential planetary gear set that act as a continuously variable transmission (CVT). To assess such highly integrated hybrid applications, a novel analysis method is proposed that captures the influences of electrical motor and gear excitations in a full system approach. Alternative gear and motor designs are explored by completing speed sweeps through different operating conditions in the frequency domain. System responses are shown and indicate that motor and gear excitations can interact if their parameters are not selected carefully. This can lead to critical situations when hitting resonances and demonstrates the importance of considering electromechanical interactions from early design stages.