REDUCTION OF BLADE-VORTEX INTERACTION (BVI) NOISE THROUGH X-FORCE CONTROL

Momentum theory and the longitudinal force balance equations of a sing le rotor helicopter are used to develop simple expressions to describe tip-path-plane tilt and uniform Inflow to the rotor. The uniform infl ow is adjusted to represent the inflow at certain azimuthal locations where strong Blade-Vortex Interaction (BVI) is likely to occur. This t heoretical model is then used to describe the flight conditions where BVI is likely to occur and to explore those flight variables that can be used to minimize BVI noise radiation. A separate X-force control is introduced to help minimize BVI noise. Several methods of generating the X-force are presented that can be used to alter the inflow to the rotor and thus increase the likelihood of avoiding BVI during approach es to a landing.