Active Solutions for Reduction of the Transmission of Structure-Borne Noise to the Cabin Structure on a A109 Mockup

The paper presents some preliminary results of active control strategies aimed at reducing the transmission of structure-borne noise to the cabin structure on a AgustaWestland A109 helicopter mockup. The experiments were performed on a full-scale mockup consisting of a gearbox housing connected to the fuselage via two front and two rear struts and an anti-torque plate. The mockup is provided with two electric motors that appropriately drive the gearbox at the nominal rotating speed. A suitable aerodynamic brake is attached to the rotor must in order to reproduce the load effect of the rotor blades. Peaks at the gear meshing frequencies reveal amplitudes very close to those acquired during in-flight measurements. Rear gearbox struts and the anti-torque plate were equipped with piezoelectric actuators and some control algorithms were designed and implemented to change the transfer function at the connection between the gearbox and the cabin. Vibration and acoustic results inside the cabin are presented and critical issues of the adopted solutions are discussed.