Vibration Reduction on Servo Flap Controlling Rotor Using HHC

Vibration reduction on the servo flap controlled rotor using higher harmonic control (HHC) inputs has been investigated. Three different types of transfer functions were utilized to predict the HHC requirements during high speed flight: (a) bending moment transfer functions; (b) hub shear transfer functions; and (c) regression equation transfer functions based on blade bending moments. The SH-2F helicopter was reconfigured to 12,500 lbs gross weight and 30 ft 2 flat plate drag area. This configuration was used to acquire the HHC effectiveness on the servo flap controlled main rotor. Both generalized inverse and exact solution techniques were used to compute the required HHC so that the helicopter vibration levels were close to no vibration or a vibration level equivalent to that of a desired airspeed. Fixed system and rotating system airloads were investigated in the study. Results show that the HHC significantly reduces the blade vibration level using both rotating and fixed system parameters. This approach can be a viable technique to reduce helicopter vibration on the servo flap controlled rotor for future flight test programs.