A Methodology for Rotorcraft Brownout Mitigation Through Flight Path Optimization

A methodology is presented for the selection of approach-to-landing maneuvers that result in improved brownout characteristics. The methodology is based upon a brownout metric that assesses the relative brownout cloud densities in critical regions of the pilot's field of view. The metric becomes the objective function of a procedure in which a typical visual approach profile is parameterized and optimized to minimize brownout in a representative landing maneuver. The optimization is constrained to avoid maneuvers that would be conducive to the onset of vortex ring state or would result in flight within the "avoid" regions of a typical helicopter height-velocity diagram. The analysis uses a free-vortex wake model and simulates the dynamics of the dust particles immersed in the rotor downwash. The results show that the optimal approach trajectories affect the resulting flow field, particularly the development of a ground vortex ahead of the rotor disk, which influences the rate of development, size, and intensity of the brownout cloud. The results are compared with prior experimental results, and potential operational interpretations of the outcomes are examined.