Abstract: An apparatus and method for automatic balancing and inertial damping of vibrations in a rotor are disclosed. According to one embodiment, a rotor drive shaft is adapted to mount a rotor and rotate the rotor. A lower drive shaft connects to a source of rotation. A flexible coupling attaches the rotor drive shaft to the lower drive shaft and transfers a rotational force applied by the source of rotation to the rotor while permitting relative lateral motion between the rotor drive shaft and the lower drive shaft. An inertial coupling is coupled to the rotor drive shaft and provides inertial resistance to the relative lateral motion. A clamping collar is coupled to the inertial coupling to couple the inertial coupling to a chassis and permit the relative lateral motion between the rotor drive shaft and the lower drive shaft.