The vibration suppression becomes very important for designing the helicopter blades to ensure the comfortability and safety. Now-a-day, the pendulum absorbers and others are adopted for the purposes to reduce the vibration of the rotor blades. But, the drawback is that the dimension of the pendulum absorbers is determined by the anti-resonance concept based on the linear theory, and also its characteristics are not analyzed completely. In a Helicopter, periodic forces act on the blades due to the influences of the air thrust. These periodic forces act on the blades with their integer multiple of the rotational speed of the rotor. We have proposed a two-degree-of-freedom model of the rotor blades and the pendulum absorbers, and it clarifys the vibration-proof effect of the pendulum absorbers on these forces.
