Aircraft capable of vertical takeoff and landing, hovering, and efficient forward flight are described. An aircraft includes two side mounted tiltable proprotors and a central rotor disposed above the proprotors. The proprotors are tiltable between at least a horizontal position for forward flight and a vertical position for vertical or hovering flight. The central rotor may be powered for vertical and transitional flight modes and may turn by free autorotation during forward flight. The proprotors may be differentially tilted during vertical or hovering flight to counter torque effects of the central rotor. The central rotor may be foldable and/or easily detachable from the aircraft to facilitate storage and transportation. Left and right proprotors may provide both forward thrust and attitude control. Control inputs to left and right proprotors may be connected directly to an autopilot creating closed loop actuation using motor RPM feedback.

A pitch change actuation system for varying a propeller blade pitch includes: an actuator body defining an interior volume; and a chamber separator located within the interior volume of the actuator body and dividing the interior volume into a first chamber and a second chamber, the two chambers being fluidly separated by the chamber separator. The first and second chambers are configured to receive hydraulic fluid. The actuator body is configured to translate relative to the chamber separator in response to a difference in hydraulic pressure between the first chamber and second chamber; and the translation of the actuator body is configured to effect a change in propeller blade pitch.

A pitch change actuation system for varying a propeller blade pitch includes: an actuator body defining an interior volume; and a chamber separator located within the interior volume of the actuator body and dividing the interior volume into a first chamber and a second chamber, the two chambers being fluidly separated by the chamber separator. The first and second chambers are configured to receive hydraulic fluid. The actuator body is configured to translate relative to the chamber separator in response to a difference in hydraulic pressure between the first chamber and second chamber; and the translation of the actuator body is configured to effect a change in propeller blade pitch.

A control circuit for changing the angle of propeller blades includes a propeller control unit controlling a supply of oil to modify an angle of propeller blades, and a fixed-displacement pump providing the supply of oil from an engine oil return system to the propeller control unit. An oil cooling line extends between an outlet of the pump and the engine oil return system. The oil cooling line defines an oil leakage path leading to the engine oil return system for cooling the oil. A flow regulator between the pump and the propeller control unit is operable between an open position where oil is directed through the oil cooling line to the engine oil return system for cooling the oil, and a closed position blocking the oil cooling line and directing oil toward the propeller control unit to modify the angle of the propeller blades.

There is provided a control module for a hydraulic system. The module comprises a tank and a plurality of valves. The tank is configured to store hydraulic fluid and is substantially cylindrical. The plurality of valves fluidly connect with the tank and are configured to control distribution of hydraulic fluid from the tank to one or more components of the system. The plurality of valves are spaced around a circumference of the tank. One or more passages fluidly connect the tank with at least one of the plurality of valves and/or a first of the plurality of valves with a second of the plurality of valves.

A Stability and Control Augmentation System (“SCAS”) module includes a SCAS actuator. The SCAS actuator has a substantially cylindrical hydraulic chamber having a first and second regions. A piston is arranged for linear motion in first and second directions along an axis of the hydraulic chamber. The SCAS module also includes a valve system for controlling a flow of a hydraulic fluid into the hydraulic chamber. The valve system has: at least one supply line arranged to provide a first fluid flow path to the first region of the hydraulic chamber and/or a second fluid flow path to the second region of the hydraulic chamber, and a moveable valve member arranged to have a position between a first and second positions.

A Stability and Control Augmentation System (“SCAS”) module includes a SCAS actuator. The SCAS actuator has a substantially cylindrical hydraulic chamber having a first and second regions. A piston is arranged for linear motion in first and second directions along an axis of the hydraulic chamber. The SCAS module also includes a valve system for controlling a flow of a hydraulic fluid into the hydraulic chamber. The valve system has: at least one supply line arranged to provide a first fluid flow path to the first region of the hydraulic chamber and/or a second fluid flow path to the second region of the hydraulic chamber, and a moveable valve member arranged to have a position between a first and second positions.

An electromechanical system for a gas turbine engine includes a mechanical component located at a first side of a firewall of a gas turbine engine, and an electrical motor located at a second side of the firewall and configured to drive the mechanical component. The electrical motor mechanically connected to the mechanical component through a firewall opening in the firewall, the first side having a higher operating temperature than the second side. An electrical connection extends between the mechanical component and the electrical motor via the same firewall opening.

A control valve for a multi-stage hydraulic actuator includes a valve body defining a translation axis, a spool disposed within the valve body and movable along the translation axis, and a flange. The flange is fixed relative to the spool and has an aperture disposed externally of the valve body to removably fix the spool to a spool of a redundant control valve independently connected to the multi-stage hydraulic actuator for mitigating force fights between actuators coupled to the control valve.

A control valve for a multi-stage hydraulic actuator includes a valve body defining a translation axis, a spool disposed within the valve body and movable along the translation axis, and a flange. The flange is fixed relative to the spool and has an aperture disposed externally of the valve body to removably fix the spool to a spool of a redundant control valve independently connected to the multi-stage hydraulic actuator for mitigating force fights between actuators coupled to the control valve.