Optimization of a helicopter stability augmentation system for operation in a ship airwake

A stability augmentation system is optimized for a UH-60 helicopter operating in a turbulent ship airwake. The system is demonstrated using a flight dynamic model based on the GENHEL software integrated with CFD solutions of the airwake of a LHA ship. A stochastic airwake model was developed for more efficient simulation and analysis. The stochastic model uses an equivalent six-component gust vector and shaping filters based on the von Karman turbulence model. The filters were derived from simulations of the helicopter with full time-varying CFD airwake solutions. The proposed stochastic airwake model can be easily integrated with off-line analysis or real-time applications. For disturbance rejection, a new performance specification is designed based on the power spectrum density of the transfer function between the gust inputs and aircraft rate responses. The baseline limited authority SAS is modified and optimized using CONDUIT® (Control Designer's Unified Interface) in order to improve handling-qualities and stability, and to minimize a weighted objective of gust responses. The optimized SAS are tested using the non-linear simulation model with time-varying airwake. Time domain and frequency domain analyses of the simulation show that the modified SAS resulted in reduction of pilot workload in the longitudinal and directional axes, with modest improvements in the lateral axis.