Simultaneous Vibration Reduction and Performance Improvement of Helicopter Rotor Using Individual Blade Pitch Control with Multiple Harmonic Inputs

This study attempts to minimize vibrations while improving the aerodynamic performance of a UH-60A helicopter rotor using individual blade pitch control (IBC) with multiple harmonic inputs. A nonlinear flexible multibody dynamics analysis code, DYMORE II, integrated with a free-wake model, is used for rotor aeromechanics modeling and analyses. The rotor vibration index (VI) at advance ratios of 0.40 and 0.35 are minimized by 20% and 31%, respectively, when 2P and 3P actuation frequencies are applied, respectively; however, the IBC inputs for minimization of rotor vibration increase the rotor power by 2.66% and 2.34%, respectively. Therefore, IBC using combined 2P and 3P actuations is applied to achieve simultaneous vibration minimization and performance improvement (power reduction) of the UH-60A rotor at an advance ratio of 0.35. The best IBC pitch amplitudes and control phase angles for the combined 2P and 3P actuations are determined from the design optimization using a gradient-based optimizer, fmincon, based on the sequential quadratic programming in the MATLAB Optimization ToolBox. When 2P actuation with an amplitude of 2.15° and a control phase angle of 198° (2P/2.15°/198°) and 3P actuation with an amplitude of 1.21° and a control phase angle of 69.93° (3P/1.21°/69.93°) are applied in combination with the IBC input, the rotor VI decreases by 38.72%, whereas the rotor power slightly decreases by 0.11%. This study shows that an IBC with optimized multiple harmonic inputs can simultaneously minimize rotor vibration and improve rotor performance at a high-speed flight.