Simulation and Experiments for the Study of a Fault-Tolerant Hydraulic Actuator for Fly-By-Wire Helicopters

The availability of accurate equipment models plays a key role in the project of fly-by-wire flight control systems, since crucial activities as closed-loop controls’ design, performance analysis, integration studies, and the development of monitoring algorithms can be strongly enhanced if a high-fidelity simulation is used. This paper deals with the development and the validation of the model of a hydraulic actuator for fly-by-wire helicopter controls. The model provides a detailed simulation of the main actuator parts, and is capable to simulate the system dynamics with electrical and hydraulic failures. Simulation results are validated via experiments, by performing an extensive test campaign in terms of frequency and time responses. The validation, obtained in both normal and fail-operative conditions at servovalve as well as actuator level, allowed to highlight the importance of some model details for simulating relevant system nonlinearities, such as the actuator limit cycle oscillations.