Reversible flight control systems

1. A control system for an aircraft comprising:

a control input member for receiving control input from a pilot of the aircraft, the control input member pivotally attached to the aircraft at a control member mount point;

a spring;

a spring arm having a first end and a second end, the first end of the spring arm pivotally attached to the control input member at a spring arm mount point, and the second end of the spring arm attached to the first end of the spring;

an extendable and retractable preload actuator having a first end and a second end, the first end of the preload actuator attached to the second end of the spring and the second end of the preload actuator pivotally attached to the aircraft at a preload actuator mount point;

wherein the tension or compression of the spring is adjusted by extending or retracting the preload actuator; and

wherein at a neutral position the spring arm mount point is substantially in line with the preload actuator mount point and the control member mount point.

2. The control system of claim 1 further comprising a trim control member pivotally attached to the aircraft at the preload actuator mount point; wherein the second end of the preload actuator is pivotally attached to the trim control member at a trim mount point so that the spring does not substantially exert a rotational force on the control member.

3. The control system of claim 2 wherein the spring arm mount point at a trim position is substantially between the control input mount point and the trim mount point.

4. The control system of claim 3 wherein the control input mount point at a trim position is substantially between the spring arm mount point and the trim mount point.

5. The control system of claim 2 further comprising a centering device for exerting a force on the spring arm towards the neutral position.

6. The control system of claim 5 wherein the centering device comprises a pair of opposed low stiffness springs attached to the preload actuator.

7. The control system of claim 5 wherein the centering device comprises:

a second pair of cams pivotally attached to the aircraft, wherein the cams are attached to each other by a spring; and

a pin attached to the control input member and disposed between the cams.

8. The control system of claim 2 wherein the extension of the preload actuator is scheduled based on aircraft performance parameters.

9. The control system of claim 2 wherein the extension of the preload actuator is scheduled based on aircraft control surface settings.

10. The improvement of claim 1 further comprising a damper cartridge attached to the spring arm assembly in parallel with the spring.

11. The improvement of claim 1 further comprising a trim member slidably attached to the aircraft;

wherein the linear actuator is pivotally attached to the trim member at the third point; and

wherein the trim member may be moved generally perpendicular to the linear actuator to move the third point so that when the aircraft is in a trimmed position the spring does not substantially exert a rotational force on the control member.

12. The improvement of claim 1 further comprising a monitoring system for determining a failure of the spring arm.

13. The improvement of claim 12 further comprising a mechanical disconnect operated by the monitoring system for disconnecting the spring arm from the control input member.

14. The improvement of claim 1 further comprising a second linear actuator attached between the preload actuator and the spring.

15. The improvement of claim 12 wherein the monitoring system compares a measured augmentation force to a measured control surface deflection to determine a failure of the spring arm assembly.

16. The improvement of claim 12 wherein the monitoring system measures the position of the linear actuator to determine a failure of the spring arm assembly.

17. An improvement to the control system for an aircraft, the aircraft having a control member pivotally mounted at a first point to the aircraft for receiving input from a pilot of the aircraft and translating the input to a control surface of the aircraft, the improvement comprising:

a spring having a first end and a second end, wherein the first end of the spring is pivotally attached to the control member at a second point radially separated from the first point;

a linear actuator fixedly attached to the second end of the spring and pivotally attached to the aircraft at a third point, wherein the extension or retraction of the linear actuator alters the tension or compression of the spring;

wherein when the control surface of the aircraft is in a neutral position, the second point is substantially in a line with the first and third points so that the spring does not substantially exert a rotational force on the control member.

18. The improvement of claim 17 wherein when the control member rotates in response to input received from the pilot the second point is not in a line with the first and third points and the spring exerts a rotational force on the control member.

19. The improvement of claim 18 wherein the rotational force exerted by the spring is adjusted by extending or retracting the linear actuator.

20. The improvement of claim 19 wherein the extension or retraction of the linear actuator is scheduled based on performance parameters of the aircraft or on control surface settings of the aircraft.

21. The improvement of claim 17 further comprising a centering device for exerting a force on the spring arm towards the neutral position.

22. The improvement of claim 21 wherein the centering device comprises a pair of opposed low stiffness springs attached to the linear actuator.

23. The improvement of claim 21 wherein the centering device comprises a pair of cams pivotally attached to the aircraft, wherein the cams are attached to each other by a second spring; and

a follower attached to the control input member and disposed between the cams.

24. The improvement of claim 17 wherein when the control surface is in a neutral position, the second point is disposed between the first and third points and the spring is a compression spring.

25. The improvement of claim 17 wherein when the control surface is in a neutral position, the first point is disposed between the second and third points and the spring is a tension spring.

26. The improvement of claim 17 wherein when the control surface is in a neutral position, the second point is disposed between the first and third points and the spring is a tension spring.

27. The improvement of claim 17 wherein when the control surface is in a neutral position, the first point is disposed between the second and third points and the spring is a compression spring.

28. The improvement of claim 17 further comprising a trim member pivotally attached to the aircraft at the third point, wherein the linear actuator is pivotally attached to the trim member at a fourth point radially separated from the third point; and

wherein the trim member may be rotated to maintain the fourth point substantially in a line with the first and second points when the aircraft is in a trimmed position, so that the spring does not substantially exert a rotational force on the control member.