Vibration Reduction and Rotor Performance Analyses of Lift-offset Rotors using Individual Blade Pitch Controls with Multiple Harmonic Inputs

This study using IBC (Individual Blade pitch Control) attempts to reduce the hub vibratory loads of a lift-offset rotor in high-speed forward flight while the rotor performance is maintained or improved. The rigid coaxial rotor of XH- 59A compound helicopter is considered as a lift-offset rotor for the present work and CAMRAD II is used to calculate the hub vibration and performance of a rotor. The single harmonic input the using 3/rev actuation frequency, amplitude of 1°, and control phase angle of 270° (3P/1°/270°) for the IBC minimizes the vibration index of the XH-59A rotor at 200 knots by about 62%, but it reduces the rotor effective lift-to-drag ratio by 3.43%. When the 2/rev actuation frequency with the amplitude of 2° and control phase angle of 270° (2P/2°/270°) and the 3/rev actuation frequency using the magnitude of 1° and control phase angle of 210° (3P/1°/210°) are used in combination for the IBC with multiple harmonic inputs, the rotor vibration is reduced by about 62%;, while the rotor performance increases by 0.37% at 200 knots. This study shows that the hub vibration of the lift-offset rotor in high-speed flight can be reduced significantly (by above 50%) but the rotor performance is maintained or improved moderately, using the IBC with multiple harmonic inputs.