Closed-loop feedback control system for landing gear load alleviation

1. A method comprising:

receiving, at a flight control computer of a vehicle, pitch angle sensor information indicative of a pitch angle of the vehicle, wherein the vehicle comprises a main landing gear having a strut and a pitch control surface configured to control the pitch angle of the vehicle;

determining, by the flight control computer, a trailing-edge-up limit for upward movement of the pitch control surface to control a de-rotation rate of the vehicle as the vehicle lands;

receiving, at the flight control computer, load sensor information indicative of a load on the strut of the main landing gear of the vehicle;

based on the pitch angle of the vehicle being below a pitch angle threshold, determining, by the flight control computer, an updated trailing-edge-up limit based on the load on the strut; and

controlling, by the flight control computer, the pitch control surface based on the updated trailing-edge-up limit.

2. The method of claim 1 , wherein determining the updated trailing-edge-up limit based on the load on the strut comprises:

determining a load error comprising a difference between the load on the strut and a target strut load; and

providing the load error to a closed-loop feedback controller that determines the updated trailing-edge-up limit.

3. The method of claim 1 , wherein the main landing gear is a right main landing gear, wherein the vehicle further comprises a left main landing gear, wherein receiving the load sensor information indicative of the load on the strut comprises:

receiving information indicative of a respective deflection of a right strut of the right main landing gear;

receiving information indicative of a respective deflection of a left strut of the left main landing gear; and

determining the load on the strut having a greater deflection.

4. The method of claim 1 , wherein the main landing gear comprises a torque linkage coupled to the strut and having a first link rotatably coupled to a second link at a joint, wherein relative rotation between the first link and the second link about the joint correlates with deflection of the strut after landing of the vehicle, wherein the main landing gear further comprises an angle sensor at the joint, and wherein receiving the load sensor information indicative of the load on the strut comprises:

receiving angle sensor information from the angle sensor; and

determining the load on the strut based on the angle sensor information.

5. The method of claim 1 , wherein the main landing gear is a right main landing gear, wherein the vehicle further comprises a left main landing gear, wherein receiving the load sensor information indicative of the load on the strut comprises:

receiving information indicative of a respective deflection of a right strut of the right main landing gear;

receiving information indicative of a respective deflection of a left strut of the left main landing gear;

determining a difference between the respective deflection of the right strut and the respective deflection of the left strut; and

determining a load differential based on the difference, wherein determining the updated trailing-edge-up limit based on the load on the strut comprises determining the updated trailing-edge-up limit based on the load differential.

6. The method of claim 1 , further comprising:

controlling a rate of change of the updated trailing-edge-up limit to be less than a threshold rate of change.

7. The method of claim 1 , further comprising:

determining, by the flight control computer, a trailing-edge-down limit for downward movement of the pitch control surface to control the de-rotation rate of the vehicle as the vehicle lands; and

controlling, by the flight control computer, the pitch control surface further based on the trailing-edge-down limit.

8. The method of claim 1 , further comprising:

providing an enable load relief signal, wherein controlling the pitch control surface based on the updated trailing-edge-up limit comprises: controlling the pitch control surface based on the updated trailing-edge-up limit based on the enable load relief signal meeting an enable load relief threshold.

9. A non-transitory computer readable medium having stored therein instructions that, in response to execution by a flight control computer of a vehicle, cause the flight control computer to perform operations comprising:

receiving pitch angle sensor information indicative of a pitch angle of the vehicle, wherein the vehicle comprises a main landing gear having a strut and a pitch control surface configured to control the pitch angle of the vehicle;

determining a trailing-edge-up limit for upward movement of the pitch control surface to control a de-rotation rate of the vehicle as the vehicle lands;

receiving load sensor information indicative of a load on the strut of the main landing gear of the vehicle;

based on the pitch angle of the vehicle being below a pitch angle threshold, determining an updated trailing-edge-up limit based on the load on the strut; and

controlling the pitch control surface based on the updated trailing-edge-up limit.

10. The non-transitory computer readable medium of claim 9 , wherein determining the updated trailing-edge-up limit based on the load on the strut comprises:

determining a load error comprising a difference between the load on the strut and a target strut load; and

providing the load error to a closed-loop feedback controller that determines the updated trailing-edge-up limit.

11. The non-transitory computer readable medium of claim 9 , wherein the main landing gear is a right main landing gear, wherein the vehicle further comprises a left main landing gear, wherein receiving the load sensor information indicative of the load on the strut comprises:

receiving information indicative of a respective deflection of a right strut of the right main landing gear;

receiving information indicative of a respective deflection of a left strut of the left main landing gear; and

determining the load on the strut having a greater deflection.

12. The non-transitory computer readable medium of claim 9 , wherein the main landing gear is a right main landing gear, wherein the vehicle further comprises a left main landing gear, wherein receiving the load sensor information indicative of the load on the strut comprises:

receiving information indicative of a respective deflection of a right strut of the right main landing gear;

receiving information indicative of a respective deflection of a left strut of the left main landing gear;

determining a difference between the respective deflection of the right strut and the respective deflection of the left strut; and

determining a load differential based on the difference, wherein determining the updated trailing-edge-up limit based on the load on the strut comprises determining the updated trailing-edge-up limit based on the load differential.

13. The non-transitory computer readable medium of claim 9 , wherein the operations further comprise:

controlling a rate of change of the updated trailing-edge-up limit to be less than a threshold rate of change.

14. The non-transitory computer readable medium of claim 9 , wherein the operations further comprise:

determining a trailing-edge-down limit for downward movement of the pitch control surface to control the de-rotation rate of the vehicle as the vehicle lands; and

controlling the pitch control surface further based on the trailing-edge-down limit.

15. The non-transitory computer readable medium of claim 9 , wherein the operations further comprise:

providing an enable load relief signal, wherein controlling the pitch control surface based on the updated trailing-edge-up limit comprises: controlling the pitch control surface based on the updated trailing-edge-up limit based on the enable load relief signal meeting an enable load relief threshold.

16. A flight control computer of a vehicle, the flight control computer comprising:

one or more processors; and

data storage storing thereon instructions, that when executed by the one or more processors, cause the flight control computer to perform operations comprising:

receiving pitch angle sensor information indicative of a pitch angle of the vehicle, wherein the vehicle comprises a main landing gear having a strut and a pitch control surface configured to control the pitch angle of the vehicle,

determining a trailing-edge-up limit for upward movement of the pitch control surface to control a de-rotation rate of the vehicle as the vehicle lands,

receiving load sensor information indicative of a load on the strut of the main landing gear of the vehicle,

based on pitch angle of the vehicle being below a pitch angle threshold, determining an updated trailing-edge-up limit based on the load on the strut, and

controlling the pitch control surface based on the updated trailing-edge-up limit.

17. The flight control computer of claim 16 , wherein determining the updated trailing-edge-up limit based on the load on the strut comprises:

determining a load error comprising a difference between the load on the strut and a target strut load; and

providing the load error to a closed-loop feedback controller that determines the updated trailing-edge-up limit.

18. The flight control computer of claim 16 , wherein the main landing gear is a right main landing gear, wherein the vehicle further comprises a left main landing gear, wherein receiving the load sensor information indicative of the load on the strut comprises:

receiving information indicative of a respective deflection of a right strut of the right main landing gear;

receiving information indicative of a respective deflection of a left strut of the left main landing gear; and

determining the load on the strut having a greater deflection.

19. The flight control computer of claim 16 , wherein the main landing gear is a right main landing gear, wherein the vehicle further comprises a left main landing gear, wherein receiving the load sensor information indicative of the load on the strut comprises:

receiving information indicative of a respective deflection of a right strut of the right main landing gear;

receiving information indicative of a respective deflection of a left strut of the left main landing gear;

determining a difference between the respective deflection of the right strut and the respective deflection of the left strut; and

determining a load differential based on the difference, wherein determining the updated trailing-edge-up limit based on the load on the strut comprises determining the updated trailing-edge-up limit based on the load differential.

20. The flight control computer of claim 16 , wherein the operations further comprise:

determining a trailing-edge-down limit for downward movement of the pitch control surface to control the de-rotation rate of the vehicle as the vehicle lands;

controlling the pitch control surface further based on the trailing-edge-down limit;

providing an enable load relief signal, wherein controlling the pitch control surface based on the updated trailing-edge-up limit comprises: controlling the pitch control surface based on the updated trailing-edge-up limit based on the enable load relief signal meeting an enable load relief threshold; and

controlling the pitch control surface based on the determining the trailing-edge-up limit to control the de-rotation rate of the vehicle based on the enable load relief signal not meeting the enable load relief threshold.