Design and testing of an active vibration absorber for a helicopter rotor

Abstract

This article presents the design and the experimental tests on a prototype of an active vibration absorber for helicopter rotors. The main disturbance forces are those transferred by the blades to the rotor, which are harmonic with a frequency multiple of the rotor angular speed times the number of blades, and the device aims to counteract the two main frequencies of the disturbance. This device is composed of two identical subsystems, one for each frequency, which are put in rotation by a mechanical transmission connected to the rotor hub guaranteeing that the generated force always has the correct frequency for any angular velocity of the rotor. On each subsystem, there are two eccentric masses actuated by electric motors, which are used to modulate the amplitude and the phase of the generated force. The control algorithm of the device is based on the EPLL harmonic tracking to identify the amplitude and the phase of the disturbance, and the positioning algorithm allows to place the masses in the correct position avoiding collisions between them. The device has been built and tested on a dedicated test bench, measuring the generated forces. The results of the experiments are promising since the eccentric masses follow the reference positions, indicating that the device would significantly suppress the vibrations.