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Abstract
The Bell 525 is the world’s first commercial helicopter to incorporate fly-by-wire flight controls. Fly-by-wire features will allow unparalleled safely and decreased pilot workload - especially for operation in austere environments. To support the unique requirements of a commercial fly-by-wire flight control system, the 525 design needed to incorporate three functionally identical, separate and continuously operating hydraulic systems. Any one system is independently capable of sustaining continued safe flight in the unlikely event that two systems become inoperative. The hydraulic system architecture incorporates complete system separation so that a hydraulic failure in one hydraulic system can not affect the other systems. To ensure that the flight control systems operate within required tolerances, thermal aspects of the three hydraulic systems are closely regulated. This unique Fly-by-wire architecture was optimized for weight, ease of aircraft manufacture/assembly, reliability, and field maintenance by using a technical approach that integrates system components to create rugged individual line replaceable units (LRU’s). The integration concept was validated early in the 525 program by development testing of the components. This approach ensured that the aircraft build schedule would not be impacted by the hydraulic system design. Thermal design of the hydraulic system was optimized using Dynamic Physics based Amesim Hydraulic Systems Models to achieve weight targets of the hydraulic fluid conveyance system, and to fully validate the functional performance of the system. The sum total of these efforts led to an elegant 525 hydraulic system design which is successfully supporting 525 flight test activities.

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