Abstract: A plurality of propeller blades are mounted to an axially elongated tubular propeller hub (H1). Each blade is rotatable in position about a radial axis. An electromechanical linear actuator (A1) is housed within the hub for rotating the blades to change their pitch. The actuator includes a rod member (R1) fixed in position relative to the hub, a casing (C1) which can extend and retract relative to the rod member, a rotary electric motor (M1), and a planetary screw drive (SD1). The screw drive (SD1) drivingly interconnects the electric motor (M1) with the casing (C1) for causing the casing to move axially in response to operation of the motor. The actuator (A1) is connected to the propeller (P1) by a linkage (L1) so that movement of the casing causes the propellers to change their pitch. A second actuator (A2) may be housed within the hub (H1) and connected to the first actuator (A1) for providing redundancy in the event of failure of the first actuator.