Vibration transmission in helicopters is a significant problem, creating structural fatigue and substantial discomfort for passengers. Low frequency vibrations of the rotor gearbox are generated at the blade passing frequency of approximately 20Hz, and its harmonics. High frequency vibration is generated by the gear meshing in the rotor gearbox, in the range of 500 Hz to 2 kHz. Several active control approaches have been investigated for active isolation in helicopter gearbox support struts. In this paper, active isolation of the structure-borne noise transmission through a helicopter strut is presented. Vibration is generated in a helicopter by the rotor gearbox and propagates through rigid structural connections, resulting in significant noise and vibration levels in the passenger cabin. The struts that connect the gearbox to the helicopter cabin must be very stiff elements, and hence use of passive damping elements mounted at the structural joints is not practical due to safety concerns. Active control techniques are an ideal solution for attenuation of structural vibration transmission in a helicopter structure. A new active control system for the reduction of the vibration transmission through a connecting strut is presented. The system consists of a rigid block mass fixed halfway along the strut. Six inertial actuators are connected to the rigid mass in such a way as to generate control excitations in all six degrees of freedom. Also, six accelerometers are arranged on the mass in such a way as to measure the six degrees of freedom (6-DOF) vibration of the block mass. The vibration of the block mass can therefore be controlled by driving the inertial actuators in such a way as to cancel the six measured velocities. As a result, the vibration transmission beyond the mass is reduced. The presented model provides same initial physical insight info the dynamics of an integrated isolator system. Control actuators and error sensors were applied to the controller mass to actively attenuate all components related to its 6-DOF's. The orientation of the control forces and error sensors was shown to have a significant effect on the control performance.


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    Title :

    Active vibration isolation of a helicopter strut


    Additional title:

    Aktive Schwingungsisolierung bei Befestigungsstreben für Hubschraubergetriebe


    Contributors:


    Publication date :

    2002


    Size :

    16 Seiten, 9 Bilder, 3 Tabellen, 24 Quellen



    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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