High-Speed Rotorcraft Pitch Axis Response Type Investigation

This paper presents a systematic investigation of high-speed rotorcraft pitch-axis response types, command models, and handling-qualities specifications. The investigation was done using two Future Vertical Lift-relevant rotorcraft configurations—a lift offset coaxial helicopter with a pusher propeller and a tiltrotor. Five response types were investigated, consisting of: a pitch rate-command/attitude-hold response type typically used for rotorcraft, a pitch ratecommand/attitude-hold response type using a higher-order command model based on the conventional airplane pitch rate transfer function, a normal acceleration/angle-of-attack hold response type, a flight path rate command/flight path hold response type, and a “blended” flight path rate command response type which varies the command model bandwidth based on stick input size. Designs of varying levels of pitch attitude bandwidth, flight path bandwidth, control anticipation parameter, and pitch attitude dropback were evaluated in a piloted simulation experiment conducted at the Penn State Flight Simulator facility using two high-speed Mission Task Elements. The results of the piloted simulation suggest that both the pitch attitude bandwidth and the pitch attitude dropback requirements must be met for Level 1 handling qualities. In addition, the current fixed-wing boundary for pitch attitude dropback appears to be too loose for high speed rotorcraft, and should be tightened to better match with pilot ratings. A set of recommended specifications and associated updated Level boundaries is provided in the Appendix.