Rotary actuator for controlling a flight control surface

1. A rotary actuator for controlling a flight control surface, the actuator comprising:

a rotary output shaft for driving a flight control surface;

a locking mechanism for selectively preventing rotation of the rotary output shaft; and

a torque limiter for allowing the locking mechanism to be bypassed upon the locking mechanism experiencing a torque above a predetermined limit, wherein the torque limiter comprises a ball detent torque limiter;

wherein the locking mechanism is configured, when in a first operating state, to allow rotation of the output shaft in both first and second rotational directions, and, when in a second operating state, to prevent rotation of the output shaft in the first rotational direction and to allow rotation of the output shaft in the second rotational direction;

wherein the locking mechanism comprises a locking actuator for switching the locking mechanism between the first and second operating states and optionally, the locking mechanism is configured such that upon deactivation of the locking actuator, the locking mechanism is switched from the first operating state to the second operating state;

wherein the locking mechanism further comprises:

a ratchet wheel operatively connected to the output shaft and rotatable therewith; and

a pawl operatively connected to the locking actuator and being operable between a first position in the first operating state to a second position in the second operating state, the pawl being out of contact with the ratchet wheel in its first position to allow rotation of the output shaft in the first rotational direction and in contact with the ratchet wheel in the second position of the pawl to prohibit rotation of the output shaft in the first rotational direction; and

wherein the ball detent torque limiter comprises a plurality of ball bearings located in holes in the ratchet wheel and a respective ball biasing member associated with each ball bearing.

2. The rotary actuator of claim 1 , wherein the locking mechanism further comprises a pawl biasing member arranged to bias the pawl into the second position of the pawl.

3. The rotary actuator of claim 2 , wherein the pawl biasing member is a pawl spring.

4. The rotary actuator of claim 2 , wherein, the locking actuator is configured to switch the locking mechanism into its first operating state by overcoming the bias force of the pawl biasing member and moving the pawl into the first position of the pawl.

5. The rotary actuator of claim 1 , wherein, upon the locking mechanism experiencing a torque above the predetermined limit in the second operating state of the locking mechanism, the torque limiter allows the output shaft to rotate relative to the ratchet wheel.

6. The rotary actuator of claim 1 , wherein the locking actuator comprises a linear actuator, optionally comprising a solenoid and a push-rod.

7. The rotary actuator of claim 1 , wherein each ball biasing member comprises a spring.

8. A flight control surface actuation assembly comprising:

an actuator as claimed in claim 1 ; and

a flight control surface being operatively connected to the rotary output shaft.

9. The assembly of claim 8 , wherein rotating the rotary output shaft in a or the first direction causes the flight control surface to be extended into a deployed position and rotating the rotary output shaft in a or the second direction causes the flight control surface to be moved into a stowed position.

10. The assembly of claim 8 , wherein the flight control surface is a spoiler.