GB343653A - Improvements in variable pitch airscrews - Google Patents

Abstract

343,653. Airscrews. SHAW, H. S. HELE- and BEACHAM, T. E., 64, Victoria Street, London. Dec. 19, 1929, No. 38935. [Class 114.] In hydraulically controlled variable pitch screw propellers wherein a hydraulic ram movable axially with respect to the propeller shaft is employed the pitch of the blades is adjustable to two or more predetermined positions. The limits of the stroke of the ram can be adjusted to correspond to the two or more pitch positions of the blade. Coaxial with the main shaft A and within the hollow spigots a<1>, a2 is mounted a ram cylinder d which is adjustable as to its stroke axially by means of screws x<2>, x<1> and stops d<6>. Inside the cylinder is a ram c<2> which is fixedly carried by a sleeve c mounted on a main boss a<3> ; passages are provided between the two sides of the ram and central supply ducts t<1>, t<2>, t<3>, ml which are in turn coupled by pipes s<1>, s<2>, through a controlling valve v<9> with a hydraulic pressure pump p. The valve v<9> is coupled by a bell-crank lever v<3> with a control rod v<4> having notches v<6>, v<7> adapted to be held by a spring detent v<8>. According to the position of this control, the valve v<9> is positioned relative to the pipes s<3>, s<2> to supply pressure fluid to the required side of the ram c<2>. The other pipe s<1> then acts as an exhaust and the liquid from the other side of the ram flows back to the common tank w. To avoid strains in the stop position, passages become open just before the end of the stroke having a safety valve set to open at a minimum pressure sufficient to prevent blade flutter. The main sliding cylinder d has lugs which are coupled by pins to the roots of the blade for the purpose of angularly adjusting them. Specification, 295,248, [Class 114, Ships &c., Propelling &c.], is referred to.