Flight Control Design for the Systematic Improvement of Ride Qualities

Abstract

The reduction of rotor-induced vibrations has been a major concern in the history of helicopter engineering. This has led to the development of numerous countermeasures, which cause the vibration levels to decrease considerably. Recent findings have shown that the reduced level of rotor vibrations highlights the importance of turbulence for the ride qualities. The rejection of atmospheric disturbances is a key task of the flight control system (FCS). However, the FCS design is currently focused on stability and handling qualities rather than ride qualities. This work addresses this shortcoming by the introduction of a systematic control design procedure. The improvement of ride qualities is achieved by linking an existing discomfort criterion to parameters of the sensitivity function. This allows the systematic modification of these parameters according to their contribution to discomfort. The approach is embedded into a design framework for systematic compliance with stability and handling quality specifications. The procedure is applied to the control design of a light helicopter resulting in considerably improved ride qualities, while compliance with stability and handling quality specifications is maintained. This represents an important step towards a more comprehensive ride quality engineering for rotorcraft that goes beyond the reduction of rotor-induced vibrations.