A methodology is presented for the design of helicopter rotors with 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 the number of blades, blade chord,rotor radius,and blade twist rate are optimized to minimize brownout in a representative landing maneuver. The inclusion of number of blades makes the optimization a Mixed Integer Non-Linear Programming problem, requiring special algorithmic considerations. In particular, a Genetic Algorithms-based approach is examined in parallel with an assessment of the efficacy of applying the Branch-and-Bound algorithm. The analysis includes a free- vortex wake model and simulates the dynamics of the dust particles immersed in the rotor downwash. The results show that the optimum rotor design affects the resulting flow field, particularly the development of a ground vortex ahead of the rotor disk, which influences the rate of development and overall geometry of the brownout cloud. A methodology is presented for deriving preliminary design guidelines from the data generated during the optimization procedures.
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