Vibration Suppression of a Helicopter Using Pendulum Absorbers : First Elastic Mode of a Blade

Abstract

Centrifugal pendulum vibration absorbers are widely used as a vibration suppression device for helicopters. The vibration characteristics of this absorber have been investigated by utilizing linear anti-resonance theory. However, it has been noted that nonlinear characteristics appear when pendulums swing at large amplitudes. The authors investigated vibration suppression characteristics of pendulum absorbers considering nonlinear characteristics of pendulums. In the first report, we investigated a two-degree-of-freedom (2DOF) system composed of a rigid blade and a pendulum. In this system, the blade was excited by a harmonic deflection motion of the shaft. In the second report, we investigated a three-degree-of-freedom system composed of a fuselage, a rigid blade and a pendulum. In this third study, the model has 3DOF and is composed of a blade, a pendulum and a rotor mount. The blade is assumed to be flexible and only the first elastic mode is considered. An aerodynamic excitation force is applied to the blade. The vibration suppression characteristics of this system are investigated theoretically and experimentally.

Review of Research on Nonlinear Rotordynamics in Japan

“…Since these pendulums oscillate with large amplitude to suppress blade vibrations, the nonlinear analysis is necessary. Nagasaka et al studied this problem with a 2DOF rigid blade model (a blade and a pendulum) (122) , a 3DOF rigid blade model (a fuselage, a blade and a pendulum) (123) and a 3DOF flexible blade model (a mount, a blade and a pendulum) (124) .…”