The paper describes a methodology for the design of helicopter rotors with improved brownout characteristics. A brownout metric is introduced, based on the density of the sediment cloud in the field of view of the pilot. The metric becomes the objective function of a procedure in which blade chord, rotor radius, and blade twist rate are optimized to minimize brownout in a representative landing maneuver. The analysis includes a free-vortex wake model and simulates the dynamics of the sediment particles immersed in the rotor downwash. The results show that the optimized configurations have improved visibility within 2—3 rotor radii from the pilot, as desired, because the rotor generates increased groundwash that pushes the dust cloud away from the pilot. The clouds, however, do not necessarily become smaller or less dense further away from the pilot's field of view. Simple polynomial expressions are provided that quantify brownout mitigation in terms of rotor design parameters, within the assumptions used in the derivation, and can be used in preliminary design applications.
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