Aircraft control surface actuation and counterbalancing

In an aircraft,

• a frame structure;
• a flight control surface supported from the frame structure, for pivotal movement about a hinge axis, said surface being deployed against an aerodynamic load which is a function of surface deflection and imposes a torque on the flight control surface wanting to rotate it back to a neutral trimmed position;
• a source of hydraulic pressure;
• a counterbalancing hydraulic actuator, in the form of a single acting hydraulic cylinder which is connected to the source of hydraulic pressure by a valveless conduit means, said cylinder being connected between the frame structure and the flight control surface, and being oriented to impose a counterbalancing torque on the flight control surface acting in opposition to the torque imposed by the aerodynamic load;
• and
• controllable separate positioning actuator means connected between the frame structure and the flight control surface for positioning the flight control surface.