Abstract:
Bell Helicopter's 525 Relentless will be the world's first commercially certified fly-by-wire helicopter. As a fully computer controlled aircraft, the design aims at higher safety through reduced pilot workload, increased situational awareness, and improved handling qualities. The flight control system that achieves these results operates with numerous redundant sensors that provide flight data and feedback to the flight control logic. This paper describes the development of the Bell 525's redundant Pitot static airspeed system, showing how computational fluid dynamics (CFD) models were used to perform initial calibration of the triplex system far ahead of first flight. Since air data readings interact with the flight control logic, it was important to have a reasonable airspeed calibration available for first flight. The Bell 525 aerodynamics team developed an analytical approach to model the triplex airspeed system to account for position error across the flight envelope. The analysis developed calibration curves for forward flight, descent, and climbs to meet FAA rules for accuracy. The resulting process has allowed the 525 to conduct its first flight and full envelope expansion with an accurate and reliable production airspeed system.