Eliminating rotor-blade vibration in helicopters has been a long-running target for rotorcraft manufacturers. Now Sikorsky, teamed with Lord Corp. and the U.S. Army, is poised for final flight tests of an active vibration control system that it believes will achieve the goal of a zero-vibration helicopter with “jet-smooth” operation throughout the entire flight envelope. Vibration occurs in helicopters because the loads on the main rotor blades constantly shift as they rotate.