Vibration attenuator

A vibration attenuator for a rotor rotatable about a mast axis, the attenuator comprising:

• a shaft having an axis perpendicular to the mast axis and configured for rotation about the mast axis relative to the rotor;
• a first mass carried by the shaft, the first mass being axially translatable along the associated shaft from a first-mass rest position in a first direction and in an opposing second direction, a first biasing force urging the first mass toward the first-mass rest position for opposing motion of the first mass in the first direction and a second biasing force urging the first mass toward the first-mass rest position for opposing motion in the second direction;
• and
• a second mass axially carried by the shaft, the second mass being translatable along the shaft only in the second direction together with the first mass from a second-mass rest position, the second biasing force also urging the second mass toward the second-mass rest position for opposing motion of the second mass in the second direction;
• wherein the masses are configured for moving radially outward from the rest position to oppose vibrations caused by operation of the rotor.