Active Balancing for Lift Fan Drive Shaft

The F-35 VSTOL configuration includes a lift fan driven by a long, slender hollow shaft that operates at high speeds. The shaft spins whenever the aircraft's engine runs, and transmits considerable horsepower when the lift fan is activated. In additionto being a key element in the aircraft's drive train, shaft maintenance will require engine removal. A device that observes and automatically adjusts imbalance in this shaft to eliminate its vibration would result in significant O&M savings. To addressthis need, an on-the-fly, self-adjusting balancing device is proposed that utilizes measured vibration to position shaft-mounted balancing disks to minimize shaft imbalance. This active balancing system will reduce or eliminate drive shaft vibrationscaused by rotational dynamics to preclude undue maintenance of shaft system components. Based on influence coefficient (IC) methods, feasibility of the rotating balance disk concept will be demonstrated in Phase I by experiment. A system will be designedto perform multiplane balancing on a spinning shaft by properly positioning shaft-mounted adjustable weights. A test rig will be built to demonstrate the system in a single balance plane, and initial on-board mechanical and electronic hardware capable ofwithstanding the centrifugal loads without contributing to imbalance will be implemented. Performance of a single-plane balance on the test rig will demonstrate feasibility of the proposed approach.