Ballistic tolerant dual load path ballscrew and ballscrew actuator

Abstract

Ballscrew actuators are well known for use as a primary flight control actuator for operating a flight control surface. The operation of the ballscrew actuator is critical to the success of an aircraft mission; however, when the actuator is subject to ballistic fire, a projectile hit which is not totally destructive can still render the actuator inoperable. Increasing the potential for operability of the ballscrew actuator after a projectile hit which is not totally destructive will increase the number of successful returns from aircraft missions. The ballistic tolerant dual load path ballscrew actuator has a selectively-driven ballnut and a ballscrew drivingly connected to the ballnut. The ballscrew has an outer tubular member with an external helical ball groove providing a primary load path. An inner tubular member fits closely within and is fixed to the outer tubular member to provide a secondary load path upon cracking of the outer tubular member by a projectile passing through the outer tubular member. The inner tubular member is formed of ballistic tolerant composite material to maintain its structural integrity when contacted by a projectile which has passed through and cause cracking of the outer tubular member. In one embodiment, the inner tubular member has an outer energy absorbing layer of a ceramic material. In another embodiment, the inner tubular member is preloaded in tension to prevent propagation of a circumferential crack in the outer tubular member and is constructed of wound fibers providing ballistic tolerance and strength in torsion and tension.