Servo-actuator architecture with electromechanical-stability and control augmentation system

1. A Stability and Control Augmentation System (“SCAS”) module comprising one or more SCAS actuators, the or each SCAS actuator comprising:

a mechanical component that translates rotational motion to linear motion along a first axis of said SCAS;

one or more electric motors for driving linear movement of the mechanical component in response to a command signal;

one or more angular transducers to detect the position of the SCAS actuator along the first axis; and

first and second SCAS actuators, wherein the mechanical component of said first and second SCAS actuators are each operatively connected to a lever or balance beam to provide linear outputs thereto, and wherein said lever or balance beam is arranged to sum or otherwise combine the linear outputs provided by said first and second SCAS actuators;

wherein the mechanical component includes a nut connected to the lever or balance beam such that rotary motion of the one or more electric motors translates to linear motion of the nut to cause linear motion of the mechanical component.

2. The SCAS module of claim 1 , wherein the mechanical component comprises a roller screw.

3. The SCAS module of claim 1 , wherein the mechanical component comprises a ballscrew.

4. The SCAS module of claim 1 , further comprising:

a flight control system for providing electrical command signals to said one or more SCAS actuators,

wherein said motor controls the position of said piston along the first axis of the SCAS, in response to said electrical command signals.

5. An actuator system for a helicopter comprising:

a hydraulic actuator for providing an output to a main or tail rotor of the helicopter;

a SCAS” module as claimed in claim 1 ;

a control valve for controlling the flow of hydraulic fluid to said hydraulic actuator to vary said output provided to the main or tail rotor; and

a linkage mechanism connecting said control valve to said hydraulic actuator, said linkage mechanism comprising:

a plurality of interconnected levers including a first lever for receiving an input from a pilot, and a second input arranged to receive an output from said SCAS module,

wherein said linkage mechanism is configured to sum or otherwise combine the outputs from said first and second levers into a composite command and to transmit the composite command to the control valve to control the flow of hydraulic fluid to the hydraulic actuator.

6. The actuator system of claim 5 , further comprising a flight control system for providing electrical command signals to said one or more SCAS actuators, wherein said motor controls the position of said piston along the first axis of the SCAS, in response to said electrical command signals.

7. The actuator system of claim 5 , wherein the motion of the mechanical component along said first axis of said one or more SCAS actuator(s) is limited by one or more end stops provided within said SCAS module and/or within said linkage mechanism.

8. A helicopter comprising:

a main rotor;

a tail rotor; and

an actuator system as claimed in claim 5 , wherein said actuator system controls a position and/or orientation of the main rotor and/or of the tail rotor.