DEVELOPMENT AND FLIGHT TESTING OF A COMMAND VALIDATION ALGORITHM FOR A SIMPLEX FLY-BY-WIRE HELICOPTER

The National Research Council of Canada Flight Research Laboratory owns a Bell 412 HP helicopter that operates as the Advanced Systems Research Aircraft (ASRA). This aircraft is undergoing the final stages of an installation to incorporate a full-authority experimental fly-by-wire flight control system. This system will give the aircraft increased capability to perform handling qualities and control system research. An important element of the experimental fly-by-wire system is the Health Monitoring Unit including a Command Validation Algorithm (CVA). The purpose of the algorithm is to prevent the flight control computer (FCC) from commanding the system actuators to a position that would place the aircraft in a potentially dangerous situation. The CVA employs a simplified mathematical model of the aircraft and an assumed pilot response to predict the attitude and altitude of the ASRA Bell 412. This prediction is then compared to established envelope limits consisting of maximum rotational rates, attitudes and sink rates for a given altitude. These limits are based upon the attitudes for main or tail rotor strikes plus a factor of safety and a vertical velocity profile upon touchdown to prevent damage to the skid gear or dynamic roll-over. Extensive ground and flight testing has developed the algorithm, and demonstrated that the CVA accurately predicts aircraft attitudes up to ½ a second in the future. This prediction capability provides the necessary basis for the ASRA fly-by-wire safety system.