FAIL SAFETY ASPECTS OF THE V-22 PYLON CONVERSION ACTUATOR

The Bell-Boeing V-22 Osprey pylons are converted between helicopter and airplane modes by a linear actuator at each nacelle. The pylon conversion actuator is a telescoping ballscrew assembly powered to two hydraulic motors, with an electric motor backup mode. The actuator design is such that the ballscrew can be operated by driving the ball nut while grounding the screw, or driving the ballscrew while grounding the bail nut. This provides a totally separate backup drive system. Since the telescoping ballscrew is essentially two ballscrews in series, each providing half travel, the failure of one ballscrew will not preclude the other from providing at least one-half nacelle conversion. Partial conversion can position the rotors for a safe run-on landing. The primary power source is the two hydraulic motors, acting in parallel to rotate the ball nut located in the wing-mounted actuator housing. The backup electric power is applied to the ballscrew at the output end, or pylon attachment. Redundant load paths are used throughout the design.