Individual Blade Pitch Control (IBC) for Vibration Reduction of Lift-Offset Coaxial Rotor Vehicles with Auxiliary Propulsion

The present study investigates the vibration reduction potential of single harmonic individual blade pitch control (IBC) applied to a lift-offset coaxial main rotor. An open-loop phase sweep is conducted using comprehensive aeroelastic simulations of the XH-59A rotor to quantify the effects of IBC on the hub vibration index and the rotor effective lift-to-drag ratio. Applying 4/rev, 1° amplitude IBC at 0° phase to both rotors decreased the hub vibration index by 64% at 200 knots and only decreased the rotor lift-to-drag ratio by 2%. Single harmonic IBC retained effective hub vibration index reduction with varying flight speed, including a 56% decrease at 160 knots and a 69% decrease at 240 knots. Higher amplitude IBC inputs were more effective at higher forward flight speeds. The vibration reduction of single harmonic IBC with 2° pitch amplitude increased from 24% to 69% when the forward flight speed increased from 160 to 240 knots. Application of a closed-loop control algorithm using multiple-harmonic IBC achieved an 84% decrease in the hub vibration index with only a 2% decrease in the rotor effective lift-to-drag ratio.