Multicyclic Control for Vibration Reduction of Lift-Offset Coaxial Rotorcraft

This study explores the best vibration reduction using a multicyclic controller through an individual blade control (IBC) actuation scheme for a lift-offset coaxial helicopter in high-speed flight. The rotorcraft dynamics model consists of coaxial, three-bladed counter-rotating rotors and a finite element fuselage stick model constructed based on the measured data of the XH-59A helicopter. The two-way coupled rotor-body vibration analysis results exhibit excellent correlations with the test data for rotor hub loads and airframe vibrations. The best actuation scenarios are sought for the minimum vibration of the vehicle using either open- or closed-loop control scheme. It is shown that the IBC actuation effectively reduces the vibrations at both locations of the rotorcraft. The co-reduction of 3P (per rotor revolution) and 6P vibration of the rotorcraft is achieved using the multicyclic control with offline system identification. A multicyclic harmonic IBC actuation enables to suppress the rotorcraft vibration by 81.4% and 3P pilot seat vibration by 92%, respectively, as compared to the uncontrolled case, leading to a significantly reduced vibration level (below 0.05g) of the rotorcraft. The closed-loop multicyclic control using the identified system and the aircraft model shows a good correlation ensuring the suitability of the present optimal control simulations.