Shipboard launch and recovery of helicopters continue to pose operational challenges even for experienced pilots. The factors affecting pilot workload include unsteady ship motion, the influence of ship air wakes on helicopters, insufficient visual cues, and adverse weather conditions. The goal of the current research is to investigate novel visual and control augmentation techniques and evaluate their impact on pilot workload and handling qualities for shipboard recovery operations. This paper first outlines a helicopter-ship dynamic interface model developed and integrated into our existing rotorcraft simulation environment (ROSIE). It then describes a visual augmentation concept using a see-through helmet-mounted display (HMD) system for enhancing the pilot's visual cueing environment during the shipboard approach and landing tasks. Next, it describes the synthesis of robust nonlinear control laws for achieving advanced helicopter response types with predicted Level 1 handling qualities. Lastly, the paper reports the results of simulation tests of maritime mission task elements by four experimental test pilots with different levels of augmentation and under different environmental conditions. Results on navigation performance, workload indices, and handling quality ratings indicate a decreased workload and improved handling qualities to almost Level 1 with the assistance of the visual and control augmentation system. Moreover, all piltos stated a higher situational awareness while operating in degraded visual environment conditions using visual and control augmentation.
Sliding mode control (SMC) is a promising technique for robust control synthesis with desirable properties. This paper describes the synthesis and piloted evaluation of advanced helicopter response types using the SMC technique. The required closed-loop response characteristics are specified as ideal, lower order, axial transfer functions that conform to predicted level 1 handling qualities. Two-loop, full-authority, output-tracking SMC laws are then synthesized to enforce the closed-loop performance and accurately track pilot commands. Analytical proofs for SMC gain tuning are given for the closed-loop performance to remain robust to unknown but bounded uncertainties in the input channels and the effects of rotor modes on closed-loop stability. The closed-loop eigenstructure is nearly identical to the specified closed-loop performance and has good modal decoupling. Furthermore, a frequency domain analysis with a nonlinear helicopter model shows good stability margins and disturbance rejection characteristics. Finally, the paper reports on simulation testing conducted with four experimental test pilots in a rotorcraft simulation environment. The simulation results indicate improved mission task performance and handling qualities ratings and a substantial reduction in pilot workload for the SMC-based advanced response types compared to the bare-airframe responses.
Sliding mode control (SMC) is a promising technique for robust control synthesis with desirable properties. This paper describes the synthesis and piloted evaluation of advanced helicopter response-types using the SMC technique. The required closed-loop response characteristics are specified as ideal, lower-order, axial transfer functions that conform to predicted level 1 handling qualities. Two-loop, full-authority, output-tracking SMC laws are then synthesized to enforce the closed-loop performance and accurately track pilot commands. Analytical proofs for SMC gain tuning are given for the closed-loop performance to remain robust to unknown but bounded uncertainties in the input channels and the effects of rotor modes on closed-loop stability. The closed-loop eigenstructure is nearly identical to the specified closed-loop performance and has good modal decoupling. Furthermore, a frequency domain analysis with a nonlinear helicopter model shows good stability margins and disturbance rejection characteristics. Finally, the paper reports on simulation testing conducted with four experimental test pilots in a rotorcraft simulation environment. The simulation results indicate improved mission task performance and handling qualities ratings, and a substantial reduction in pilot workload for the SMC-based advanced response-types compared to the bare-airframe responses.
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