Abstract: A linear hydraulic actuator of small size having limited clearance between the inside of the cylindrical housing and the outside of the piston rod is provided with a deformable or frangible piston of an engineered plastic material which is sufficiently strong to survive normal operation of the actuator but which will break or deform if the cylinder is punched through or "petalled" causing inward projections tending to block movement of the piston. Another embodiment discloses a plastic end gland which is frangible, or deformable in the event of an impact deforming the rod such that it would not pass through the end gland except for such deformation. Because of the relative weakness of the plastic material, the width of the land on the piston acting against the inside of the cylinder is maximized by placing the dynamic seals at or near its outside circumferential edges.

Abstract: A linear hydraulic motor includes a piston rod of conventional steel carrying a fragible piston head movable in a cylinder, the head being designed to break away in the event the cylinder wall is punctured and deformed such that a portion of the cylinder wall becomes an obstacle in the path of the piston. Two or more such motors are frequently connected redundantly to one control surface such that if one motor is damaged, the other can continue to perform its function. The piston head is of a brittle metallic matrix material and includes a conventional seal groove formed on its cylindrical surface.

Abstract: A ballistic tolerant linear actuator incorporates a piston (16, 46, 76) and piston rod (38, 42 or 48, 50 or 90, 92) within a cylindrical housing (58, 60 or 81, 88) connected at each end (14, 22 or 42, 54 or 74, 82) to a source of fluid. A sleeve (18, 62 or 88) of a metal matrix or composite material which will break or puncture but which will not bend or petal on impact is incorporated as part of the barrel within which the piston is translated. The piston rod which extends through at least one end of the cylindrical housing is formed with an external sleeve of the metal matrix or composite material (38, 50 or 92) spaced from an internal load carrying metal rod (42, 48 or 96).