605,063. Semi-rotary engines. UNITED AIRCRAFT CORPORATION. Oct. 26, 1943, No. 31973/45. Convention date, Feb. 4, 1943. Divided out of 605,045, [Group XXXIII]. [Class 110 (ii)] A hydraulically operated engine used in the propellerpitch-changing mechanism described in Specification 605,045, comprises radial pistons 56, 58, secured to a member 54, and abutments 62, 64. An external pump 136 pumps fluid from a reservoir 138 through passages 142, 150, 154 to connectors such as 108 leading fluid to between a piston and an abutment. A speed-responsive governor 140 is included in the line. Pistons and abutments are packed as shown. An inner part 60 has a lower flange 61, Fig. 1, provided with a sealing ring 72 bearing on the inner face of the outer member 54. A similar sealing ring 69 is provided in an end cap 68. Specification 560,522, [Group XXXIII], describing an alternative hydraulic system of supply, and Specification 594,396, [Group XXXIII], describing vernier adjustments between the hubs of the blades, are referred to in the Specification.