Shock absorber

1. An aircraft weight and balance measurement system including a landing gear shock absorber comprising:

an inner housing portion slidably coupled within an outer housing portion, the shock absorber including a chamber which defines a sealed fluid volume for containing shock absorber fluid within the shock absorber;

a moveable wall portion located in the chamber and arranged to be moved by a motive force between a first position and a second position, wherein in the second position an effective volume of the chamber is decreased relative to when the moveable wall portion is in the first position such that the shock absorber fluid pressure increases to extend the shock absorber;

an aircraft weight and balance measurement unit including a pressure sensor located in the shock absorber to measure the pressure of the shock absorber fluid; and

a motive force provider configured to generate the motive force to move the moveable wall from the first position to the second position to cause the inner portion to slide relative to the outer portion to extend the shock absorber and subsequently remove the motive force to move the moveable wall from the second position to the first position to cause the inner portion to slide relative to the outer portion to shorten the shock absorber;

wherein the shock absorber comprises first and second stops, positionally fixed relative to the inner or outer housing portion, the first stop being positioned to contact and hold the moveable wall at the first position when the motive force is not being generated, and the second stop being positioned to contact and hold the movable wall at the second position when the motive force is being generated.

2. The aircraft weight and balance measurement system according to claim 1 , further comprising a control port in fluid communication with a distal side of the moveable wall portion with respect to the chamber, the control port being arranged to be coupled to a source of control fluid for providing the motive force to move the moveable wall portion from the first position to the second position, wherein the control port is isolated from the sealed fluid volume by the moveable wall portion.

3. The aircraft weight and balance measurement system according to claim 2 wherein the control port is a hydraulic control port.

4. The aircraft weight and balance measurement system according to claim 2 wherein the moveable wall portion is moveable from the second position to the first position by shock absorber fluid pressure within the chamber.

5. The aircraft weight and balance measurement system according to claim 4 wherein the moveable wall portion is a floating piston.

6. The aircraft weight and balance measurement system according to claim 1 wherein the moveable wall portion is moveable from the second position to the first position by an electrical actuator.

7. The aircraft weight and balance measurement system according to claim 1 wherein the chamber is housed completely within an internal cavity defined by the inner and outer housing portions.

8. The aircraft weight and balance measurement system according to claim 1 wherein the shock absorber includes an orifice support tube and the chamber is partially defined by side walls of the orifice support tube.

9. The aircraft weight and balance measurement system according to claim 1 wherein the chamber is partially located in an internal cavity defined by the inner and outer housing portions and partially located in a chamber extension unit which is directly fixed to a port in the outer housing portion so that the chamber extension unit is in direct fluid communication with the internal cavity.

10. The aircraft weight and balance measurement system according to claim 1 , wherein the movable wall portion is in the first position during normal operation of the shock absorber.

11. An aircraft landing gear including a weight and balance measurement system according to claim 1 .