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Meeting	ACGS Committee Meeting 117 - Napa, CA - March 2016
Agenda Location	7 SUBCOMMITTEE D – DYNAMICS, COMPUTATIONS, AND ANALYSIS 7.2 Control Law Design of the Bell 525 Fly by Wire Helicopter
Title	Control Law Design of the Bell 525 Fly by Wire Helicopter
Presenter	Jillian Alfred
Affiliation	Bell Helicopter
Available Downloads*	presentation
	Downloads are available to members who are logged in and either Active* or attended this meeting.
Abstract	The Bell 525 will be the world’s first commercially certified fly by wire helicopter. The fly by wire control law system (CLAW) has been engineered for safety. The design achieves improved handling qualities, reduced pilot workload and increased pilot situational awareness through intuitive and automatic transitioning between flight regimes. Increased situational awareness is driven by a displacement trim control strategy for the main rotor controls (collective and cyclic) relating control margin awareness to the pilot. Tactile cueing in the collective control stick provides power margin awareness. Additional safety features, driven by fly-by-wire control, include one engine inoperative compensation, automatic autorotation entry assist, consistent CAT A performance, and high rate of descent protection. The control laws consist of a three loop design comprised of an inner loop for stabilization, a rate loop for controllability, and an outer loop for high-level augmentation. The inner and rate loops are always active. However the outer loops are turned off in certain sensor or equipment failure scenarios. To manage such failures, the CLAWS have two modes of augmentation: AUG OFF and AUG ON. AUG OFF refers to switching the outer loops off while maintaining rate and inner loop augmentation. AUG ON is the full augmentation system. The CLAWS have been extensively tested via desktop simulation, an engineering simulator, and a specific 525 Systems Integration Lab that permits simultaneous pilot, software, and hardware in the loop testing at Bell Helicopter. Engineers at the Systems Integration Lab thoroughly test all elements of the CLAW code on the real flight control computers with real control surface actuators before the software is ever installed on the helicopter. The thoroughness of SIL testing greatly reduces integration development time on the aircraft and achieves the confidence needed to proceed with fly-by-wire testing and certification on the Bell 525. From its first flight on July 1, 2015, the 525 has completed major portions of its envelope expansion, including tests at maximum gross weight and attaining its top speed of 200 knots on February 25, 2016. With over 130 flight hours completed, it is clear that the high level of integrated testing ahead of first flight has produced a robust CLAW design that continues meet or exceed the pilot expectations for the 525.