Rotor-Wake Modeling for Simulation of Helicopter Flight Mechanics in Autorotation

Abstract

Rotorcrafte ightmechanicssimulationstypicallyusee nite-stateinducedvelocitymodelstomimictheeffectofthe rotorwakeon bladeloads. However, with recent developmentsin computational methods coupled e ight mechanics and comprehensive rotor-wake analyses have become more tractable. This paper compares results from a e nitestate induced velocity model with a vorticity transport wakemodel that computes thee owe eld in a domain around the aircraft. The study focuses on e ight mechanics in autorotation. Simple parameter estimation using three- and e ve-state induced velocity model structures facilitates interpretation of the vorticity transport induced velocity e eld as well as providing a direct comparison with the e nite-state model. Comparisons of performance, trim, and control response indicate that there is little difference between the two models where the autorotative descent is shallow. However, as airspeed reduces the descent angle steepens, and clear discrepancies become apparent. These are directly related to a single parameter in the e nite-state model. It is concluded that e nite-state models are adequate for much of the autorotation regime, but for low speeds in steep descents the improved resolution of the rotor ine ow provided by more comprehensive rotor-wake models might be essential.