Innovative Systems to Reduce One per Rev Vibrations in Helicopters

Helicopter blade systems are constructed to tight tolerances, but slight manufacturing variations cause lift to vary from blade to blade at certain specific flight conditions. The resulting unbalanced lift forces cause undesirable 1/rev vibration. The current practice calls for adjustments to be made by ground crew maintenance personnel; pitch control rod, aluminum trim tabs, and rotor head mass balancing. The track and balance adjustments are costly in terms of labor and fuel costs because of the flight time needed to verify that the adjustments were made correctly. Under this Phase I SBIR funding from the US Army, Midé developed systems to make these adjustments automatically. Specifically, systems to change the length of the pitch rod and to adjust the rotor mass balance by translating a mass were demonstrated to be feasible. The ultimate capability of in-flight adjustments can be achieved by basing the feedback on information from a HUMS system. In Phase II, the system will be designed to minimize the impact of the added mass on the rotor hub and provide a valuable capability that is not currently available. Automating these adjustments eliminates significant downtime of the helicopter, saving a considerable amount of money for all helicopter operators.