This study deals with a new concept of active control to attenuate helicopter rotor noise and vibration using an actuator device called "smart spring". According to this concept, the "smart spring" replaces the usual flexbeam found in bearingless rotors. This particular smart structure device is able to adapt its cross-section stiffness following an electrical signal. Therefore, vibration generated along the blade and transmitted into the fuselage through the flexbeam can be controlled by actively changing the mechanical impedance of the blade attachment to the hub. The present paper presents the mathematical development of a control algorithm that can be used to achieve vibration reduction at the rotor critical frequency. The analysis is made in the frequency domain defined by the harmonics of the blade passage. It will be demonstrated that the problem may be cast into standard feedback control theory.
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