A SIMULATION SURVEY ON THE EFFECTS OF PROGRESSING FAULTS WITHIN THE SCAS OF A FLIGHT CONTROL ACTUATOR FOR HELICOPTERS

Stability Control Augmentation Systems (SCAS) are widely adopted to enhance the flight stability of rotary-wing aircraft operating in difficult aerodynamic conditions, such as low altitude missions, stationary flight nearby vertical walls or in presence of heavy gusts. Such systems are based upon small electro-hydraulic servosystems controlled in position through a dedicated servovalve. The SCAS operates with limited authority over the main control linkage translating the pilot input in the movement of the main flight control actuator. Being critical for the operability of the helicopter, the definition of a Prognostics and Health Management (PHM) framework for the SCAS systems would provide significant advantages, such as better risk mitigation, improved availability, and a reduction in the occurrences of unpredicted failures which still represent one of the most known downsides of helicopters. This paper provides the results of a preliminary analysis on the effects of the inception and progression of several degradation types within a simulated SCAS system. Signals usually available within such devices are hence combined with measurements provided by additional sensors to check the feasibility of a PHM system with and without dedicated sensors. The resulting features selection process shows that although the dedicated measurements are required to design a complete PHM system, it appears nonetheless possible to obtain valuable information on the health status of the SCAS system without resorting to additional sensors.