Analysis of pilot workload in the helicopter/ship dynamic interface using time-accurate and stochastic ship airwake models

This paper describes a recent study in helicopter/ship dynamic interface simulation to examine pilot workload in the presence of a ship's airwake. The flight dynamics model represents a UH-60 helicopter and is based on the GENHEL software. This flight model has been updated to include high-order dynamic inflow model and gust penetration effects of the time-varying ship airwake. The airwake model is derived from time-accurate CFD solutions and provides an appropriately detailed level of fidelity to capture its effect on pilot workload. To simulate pilot control inputs for shipboard approach operations, an optimal control model of the human pilot is developed. The pilot model can be easily tuned to achieve different tracking performances based on a desired crossover frequency in each control axis and is designed to operate over a range of airspeeds using a simple gain scheduling algorithm. The pilot model is used to predict pilot workload for shipboard approaches in two different wind-over-deck conditions. Validation studies are conducted using both time and frequency domain analyses. The pilot control input autospectra predicted from the simulation model are compared to those of flight test data from the JSHIP program. The paper also discusses the application of a stochastic airwake model for more efficient simulation. This new airwake model is derived from the simulation with the full CFD airwake by extracting an equivalent six-dimensional gust vector. The spectral properties of the gust components are then analyzed, and shaping filters are designed to simulate the gusts when driven by white noise. It is proposed that the stochastic gust model can be used to optimize the automatic flight control system in order to improve disturbance rejection properties of the aircraft.