To provide the government with independent control-system design, handling qualities analysis, and simulation research capabilities in support of Future Vertical Lift, the U.S. Army Combat Capabilities Development Command Aviation & Missile Center has developed generic high-fidelity flight-dynamics models of several advanced high-speed rotorcraft configurations including a tiltrotor. Full-flight envelope explicit model following control laws were designed for the generic tiltrotor using a multiobjective optimization approach to meet a comprehensive set of stability, handling qualities, and performance specifications. Helicopter response types were used for hover/low-speed, while typical fixed-wing response types (normal acceleration and sideslip command) were used at high speed. The control laws were evaluated in a piloted simulation experiment at the NASA Ames Vertical Motion Simulator using a series of previously developed high-speed handling qualities demonstration maneuvers. This paper discusses the control laws and the results of the piloted handling qualities assessment which show overall assigned Level 1 handling qualities in high-speed and Level 2 in transition.
BackgroundThe force-feel system characteristics of the cyclic inceptors of most helicopters are set based on the characteristics of the mechanical components in the control system (mass, springs, friction dampers, etc.). For these helicopters, the force-feel characteristics typically remain constant over the entire flight envelope, with perhaps a trim release to minimize control forces while maneuvering. With the advent of fly-by-wire control systems and active inceptors in helicopters, the force-feel characteristics are now determined by the closed-loop response of the active inceptor itself as defined by the inertia, force/displacement gradient, damping, breakout force and detent shape configuration parameters in the inceptor control laws. These systems give the flexibility to dynamically prescribe different feel characteristics for different control modes or flight conditions, and the ability to provide tactile cueing to the pilot through the actively controlled side-stick or center-stick cyclic inceptor.
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