Comparison of Different Approaches for Modeling Vortex – Rotor Wake Interference on Rotor Trim

Abstract

The flight of a helicopter within the wake of a preceding fixed-wing aircraft, for example during air-to-air refueling, is accompanied by vortex-rotor interactions. Prior studies made use of many simplifying assumptions such as ignor-ing any interactions of the rotor wake with the fixed-wing tip vortex, or assuming a vortex deflection into the rotor slipstream once the vortex reaches the rotor disk. The full mutuality of vortex and rotor wake interactions requires a free-wake solution to the problem. In the paper free-wake solutions are presented for different advance ratios and compared to existing simplified solutions. The results indicate that the simplified solutions are valid for higher ad-vance ratios whereas very small advance ratios require the use of a free-wake approach.