Simulation Testing of Advanced Response Types for Ship-Based Rotorcraft

Piloted simulation tests were conducted to develop and evaluate advanced control laws and optimal response types for ship-based rotorcraft. Simulations used the GENHEL-PSU model integrated with the Penn State rotorcraft flight simulator. The simulation includes ship motion, a visual model of a FFG-7 frigate, and the Control Equivalent Turbulence Input (CETI) model for airwake turbulence. The controller uses a Non-Linear Dynamic Inversion scheme to accurately track a variety of response types. An Attitude Command / Attitude Hold (ACAH) control mode was used as the baseline control law. Different variants of Acceleration Command / Velocity Hold (ACVH) and Translational Rate Command / Position Hold (TRC/PH) response types were designed to make use of ship deck motion measurements. Filtered deck states are fed into the control laws to command velocity and position relative to the landing spot. Piloted simulation tests were performed for a variety of control configurations with and without ship motion and airwake turbulence effects using a maritime MTE. Pilot comments and preliminary handling qualities ratings indicated that the best performance was achieved using an ACVH response type for the pitch axis on approach, which then automatically transitions to TRC/PH over the ship deck. A 3.5 HQR improvement over the baseline ACAH control mode was achieved when using the optimized ship-relative ACVH/TRC/PH control mode. Simulation results indicated that it is best to filter out most of the dynamic ship deck motion (primarily ship roll) and to maximize the lateral axis TRC bandwidth.