ABSTRACT Title of dissertation: CONTRIBUTIONS TO THE CHARACTERIZATION AND MITIGATION

Rotorcraft brownout, the condition in which the flow field of a rotorcraft mobi-lizes sediment from the ground to generate a cloud that obscures the pilot’s field of view, continues to be a significant hazard to civil and military rotorcraft operations. This dis-sertation presents methodologies for: (i) the systematic mitigation of rotorcraft brownout through operational and design strategies and (ii) the quantitative characterization of the visual degradation caused by a brownout cloud. In Part I of the dissertation, brownout mitigation strategies are developed through simulation-based brownout studies that are mathematically formulated within a numerical optimization framework. Two optimization studies are presented. The first study involves the determination of approach-to-landing maneuvers that result in reduced brownout sever-ity. The second study presents a potential methodology for the design of helicopter rotors with improved brownout characteristics. The results of both studies indicate that the fun-damental mechanisms underlying brownout mitigation are aerodynamic in nature, and the evolution of a ground vortex ahead of the rotor disk is seen to be a key element in the development of a brownout cloud