Abstract: An apparatus, for example for a pitch change mechanism, includes a cylinder having a magnetic portion defining an annular array of features extending parallel to the longitudinal axis of the cylinder, the cylinder rotating in use and able to translate longitudinally. There is a sensing arrangement including a stationary magnetised core and two coils connected in series and wound around the core. In use, the cylinder rotates and current is induced in the coils. Monitoring equipment is arranged to calculate rotational speed of the cylinder from the frequency of the current and to calculate longitudinal position from the relative amplitude of the current in each coil. Also a method.

Abstract: A mechanical arrangement for an engine having two propeller stages, including: a first epicyclic gear stage including a sun gear, a planet gear, a planet carrier and an annulus, wherein the sun gear is driven by a shaft of the engine, the planet carrier is stationary and thereby permits static structure to be located there through, and the annulus outputs torque and/or drive; a second epicyclic gear stage including a second sun gear, a second planet gear, a second planet carrier and a second annulus, wherein the second sun gear is driven by the annulus of the first epicyclic gear stage and is annular to accommodate the static structure, the second planet carrier includes the output to one of the propeller stages and the second annulus includes the output to the other of the propeller stages; wherein the static structure provides mounting for static components on one or both sides of each epicyclic gear stage.

Abstract: A mechanical arrangement for an engine having two propeller stages, including: a first epicyclic gear stage including a sun gear, a planet gear, a planet carrier and an annulus, wherein the sun gear is driven by a shaft of the engine, the planet carrier is stationary and thereby permits static structure to be located there through, and the annulus outputs torque and/or drive; a second epicyclic gear stage including a second sun gear, a second planet gear, a second planet carrier and a second annulus, wherein the second sun gear is driven by the annulus of the first epicyclic gear stage and is annular to accommodate the static structure, the second planet carrier includes the output to one of the propeller stages and the second annulus includes the output to the other of the propeller stages; wherein the static structure provides mounting for static components on one or both sides of each epicyclic gear stage.

Abstract: A hydraulic stepper motor comprising three hydraulic ports each coupled to a piston that is actuatable between pressurised and depressurised configurations; and a contoured cam surface having at least one peak and trough and arranged to react against the pistons, the cam surface coupled to an output shaft; whereby actuation of one of the pistons moves the cam surface until a trough reacts against one or more pressurised pistons.