Investigation of Performance, Loads, and Vibration of a Coaxial Helicopter in High-Speed Flight

A lift-offset coaxial helicopter is simulated using the Rotorcraft Comprehensive Analysis System (RCAS) at a speed of 230 kts. The XH-59 Advancing Blade Concept demonstrator aircraft is used for the simulation model. A variety of trim states are explored by varying vehicle pitch attitude and redundant controls, such as main rotor speed and differential lateral pitch. The performance, vibrations, and blade loads are compared for different trim states, notably, those states utilizing negative rotor power to drive the propulsor and states in which the rotor power is constrained to be non-negative. The optimal trim state for a system with a powered or free spinning rotor lies at about 3° pitch attitude, while the optimal trim state for a vehicle in which the rotor can extract power and direct it to the propulsor lies at 6-7° pitch attitude. With the aircraft operating at a high pitch attitude, the horizontal tail is able to provide a significant amount of the necessary aircraft lift, while the rotor can provide the longitudinal moment necessary for trim. The Blade loads and hub vibrations for the negative rotor power state are similar or less than for the marginally powered state.