Helicopter Tail Rotor Thrust and Main Rotor Wake Coupling in Crosswind Flight

摘要

The tail rotor of a helicopter with a singlemain rotor configuration can experience a significant reduction in thrustnwhen the aircraft operates in crosswind flight. Brown’s vorticity transport model has been used to simulate a mainnrotor and tail rotor system translating at a sideslip angle that causes the tail rotor to interact with the main rotor tipnvortices as they propagate downstream at the lateral extremities of the wake. The tail rotor is shown to exhibit andistinct directionally dependentmode duringwhich tail rotors that are configured so that the blades travel forward atnthe top of the disk develop less thrust than tail rotorswith the reverse sense of rotation. The range of flight speeds overnwhich this mode exists is shown to vary considerably with the vertical location of the tail rotor. At low flight speeds,nthe directionally dependent mode occurs because the tail rotor is immersed within not only the downwash from thenmain rotor but also the rotational flowassociatedwith clusters of largely disorganized vorticitywithin themain rotornwake. At higher flight speeds, however, the tail rotor is immersed within a coherent supervortex that stronglyninfluences the velocity field surrounding the tail rotor.