A survey of research in the area of helicopter vibration reduction through the use of higher harmonic bade pitch control is presented. Higher Harmonic Control (HHC) is an active vibration suppression system for helicopters. Vibration is reduced through feathering of helicopter rotor blades at (b-1)omega, bomega, and (b+1)omega harmonic relationships to reduce airframe vibrations at the blade passage frequency bomega where b is the number of blades and omega is the main rotor rotational speed. Research has been in the areas of blade stresses, vibrations, control systems HHC algorithms, and methods of actuation. HHC has also been reported to affect helicopter performance and main rotor noise. Also presented are preliminary plans for performance testing testing of a Higher Harmonic Control system by the Naval Postgraduate School on the U.S. Naval Academy whirl tower at Annapolis.
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