DESIGN AND DEVELOPMENT OF A PYLON CONVERSION ACTUATION SYSTEM FOR A CIVIL TILTROTOR AIRCRAFT

The BA 609 will be the world’s first civilian tiltrotor aircraft, and the pylon conversion system is a key technology that will make this unique aircraft possible. The pylon conversion system is used to convert the BA 609 aircraft between vertical lift and fixed-wing flight. This hydromechanical actuation system rotates the aircraft nacelles (pylons) between vertical (helicopter mode) to horizontal (airplane mode) by extending and retracting the pylon conversion actuators. The system consists of two pylon conversion actuators and a mechanical cross shaft connecting the actuators. The primary influence in the design of the pylon conversion system was system reliability. For the BA 609 to perform either a vertical or run-on landing, the pylon conversion system must rotate the pylons to a nacelle angle of at least 45 degrees. Based on this requirement, FAA regulations state that any failure or combination of failures that results in total loss of the capability to convert the nacelles to a minimum of 45 deg in flight must be extremely improbable. This paper reviews the BA 609 pylon conversion system requirements, design, and development test results.