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Methods and apparatus are provided for an actively variable shock absorbing system for actively controlling the load response characteristics of a shock absorbing strut. In one embodiment the shock absorbing system comprises a controllable valve adapted for actively varying a load response character

Methods and apparatus are provided for an actively variable shock absorbing system for actively controlling the load response characteristics of a shock absorbing strut. In one embodiment the shock absorbing system comprises a controllable valve adapted for actively varying a load response characteristic of the shock absorbing strut. The shock absorbing system further comprises an electronic control system comprising an input for receiving a signal from a sensor, an algorithm adapted to determine an optimal position for the controllable valve in view of the sensor signal, and an output for sending a control signal to the controllable valve to place the valve in the optimal position.

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1. A system for actively controlling the load response characteristics of a shock absorbing aircraft landing gear assembly, comprising: a shock absorbing strut disposed between a displaceable, ground contacting portion of the landing gear assembly and the airframe of the aircraft;a passage from a fi

1. A system for actively controlling the load response characteristics of a shock absorbing aircraft landing gear assembly, comprising: a shock absorbing strut disposed between a displaceable, ground contacting portion of the landing gear assembly and the airframe of the aircraft;a passage from a first fluid chamber in the strut to a second fluid chamber in the strut;a controllable valve adapted for actively varying a load response characteristic of the shock absorbing strut by controlling the rate at which fluid may flow through the passage from the first fluid chamber to the second fluid chamber;a sensor onboard the aircraft providing a signal representative of an aircraft landing parameter; anda control system comprising an input for receiving the sensor signal, an algorithm adapted to calculate the rate at which the aircraft is closing with the ground using sink rate and height above ground data, and determine an associated optimal position for the controllable valve, and an output for sending a control signal to the controllable valve to place the valve in the optimal position prior to the aircraft touching down. 2. The system of claim 1, wherein in addition to sink rate and height above ground data, the algorithm uses any one of, or any combination of the group comprising: rate of change in aircraft sink rate; aircraft linear velocity; aircraft angular velocity; ambient temperature; aircraft gross weight, and ground surface conditions. 3. The system of claim 2, wherein the sensor onboard the aircraft comprises a short range radar system capable of instantaneously measuring aircraft height above ground. 4. The system of claim 3, wherein the short range radar system is further capable of instantaneously determining aircraft sink rate. 5. The system of claim 3, wherein the short range radar system is of a type used in automotive collision avoidance systems. 6. The system of claim 2, wherein the algorithm further calculates predicted aircraft vertical velocity at impact. 7. The system of claim 6, wherein the algorithm incorporates a look-up table relating selected aircraft landing parameters to predicted aircraft vertical velocity at impact. 8. The system of claim 2, wherein the algorithm comprises a curve that delineates a first landing condition and associated first control valve signal, from a second landing condition and associated second control valve signal, the first landing condition comprising combinations of aircraft sink rate and height above ground falling on one side of the curve, and the second landing condition comprising combinations of aircraft sink rate and height above ground falling on the other side of the curve. 9. The system of claim 8, wherein the first landing condition and associated first control valve signal correspond to a normal landing. 10. The system of claim 1, further comprising a gas valve adapted to actively vary the pressure in a gas spring portion of the strut. 11. The system of claim 1, wherein the algorithm is adapted to substantially continuously update the optimal position for the controllable valve, and the control system is adapted to substantially continuously transmit updated control signals to the controllable valve. 12. An actively variable aircraft shock absorbing system adapted for controlling the load response characteristics of a shock absorbing aircraft landing gear assembly, comprising: a shock absorbing strut disposed within a load path between a displaceable, ground contacting portion of the landing gear assembly and the aircraft airframe;a passage from a first fluid chamber in the strut to a second fluid chamber in the strut;a strut adjustment mechanism for actively varying a load response characteristic of the shock absorbing strut by controlling the rate at which fluid may flow through the passage from the first fluid chamber to the second fluid chamber;a sensor adapted for instantaneous measurement of aircraft height above ground; anda controller comprising an input for receiving a signal from the sensor, an algorithm adapted to calculate the rate at which the aircraft is closing with the ground using aircraft sink rate and height above ground data, and determine a corresponding strut adjustment signal, and an output for sending the strut adjustment signal to the strut adjustment mechanism prior to the aircraft touching down. 13. The actively variable aircraft shock absorbing system of claim 12, wherein the algorithm further takes into account any of the group comprising: rate of change in aircraft sink rate; aircraft linear velocity; aircraft rotational velocity; ambient temperature; aircraft gross weight; and ground surface conditions. 14. The actively variable aircraft shock absorbing system of claim 12, wherein the height above ground sensor is a downward looking radar based system. 15. The actively variable aircraft shock absorbing system of claim 14, wherein the downward looking radar based system is selected from the group comprising: aircraft terrain avoidance radar systems; and automotive collision avoidance radar systems. 16. The actively variable aircraft shock absorbing system of claim 12, wherein the strut adjustment mechanism is any one of or any combination of the group comprising: a flow control valve to vary the amount of viscous damping in the strut; a source of pressurized gas to vary the pressure in a gas spring portion of the strut; and a pressure relief valve to vary the maximum allowable gas pressure. 17. The actively variable aircraft shock absorbing system of claim 12, wherein the algorithm incorporates a look-up table assigning a first landing condition and associated first strut adjustment signal to a first array of aircraft sink rates and heights above ground; and a second landing condition and associated second strut adjustment signal to a second array of aircraft sink rates and heights above ground. 18. The actively variable aircraft shock absorbing system of claim 17, wherein the look-up table comprises a curve separating the first array of aircraft sink rates and heights above ground on one side of the curve from the second array of aircraft sink rates and heights above ground on the other side of the curve. 19. The actively variable aircraft shock absorbing system of claim 18, wherein the first array of aircraft sink rates and heights above ground corresponds to a normal landing. 20. The actively variable aircraft shock absorbing system of claim 12, wherein the algorithm is adapted to substantially continuously update the strut adjustment signal, and the controller is adapted to substantially continuously transmit updated strut adjustment signals to the strut adjustment mechanism. 21. A method for actively varying the load response characteristics of an aircraft landing gear assembly, comprising: mounting a shock absorbing strut between a displaceable, ground contacting portion of the landing gear assembly and the aircraft structure;monitoring aircraft sink rate and height above ground;calculating the rate at which the aircraft is closing with the ground using the aircraft sink rate and height above ground data; andprior to the aircraft touching down adjusting a characteristic of the shock absorbing strut calculated to minimize the peak load imparted to the aircraft structure by operating a controllable valve to control the rate at which a fluid may flow through a bypass from a first fluid chamber in the strut to a second fluid chamber in the strut. 22. The method of claim 21, wherein monitoring aircraft height above ground comprises use of a radar system. 23. The method of claim 22, wherein monitoring aircraft sink rate also comprises use of a radar system. 24. The method of claim 22, wherein the radar system is of a type used in automotive collision avoidance systems. 25. The method of claim 21, wherein the act of adjusting a characteristic of the shock absorbing strut calculated to minimize the peak load imparted to the aircraft comprises any of the following: adjusting the degree of damping in a viscous fluid damping portion of the strut; varying the gas pressure in a gas spring portion of the strut; and varying a gas pressure relief setting. 26. The method of claim 21, wherein calculating the rate at which the aircraft is closing with the ground comprises assigning a first landing condition and associated first strut adjustment signal to a first array of aircraft sink rates and heights above ground; and assigning a second landing condition and associated second strut adjustment signal to a second array of aircraft sink rates and heights above ground. 27. The method of claim 26, wherein a look-up table comprises a curve delineating the first array of aircraft sink rates and heights above ground on one side of the curve from the second array of aircraft sink rates and heights above ground on the other side of the curve. 28. The method of claim 27, wherein the first array of aircraft sink rates and heights above ground corresponds to a harder than normal landing. 29. The method of claim 21, further comprising monitoring a strut parameter after initial contact of the landing gear with the ground, and actively adjusting a load response characteristic of the shock absorbing strut as the strut strokes to absorb the landing load. 30. The method of claim 29, further comprising monitoring a strut parameter after the landing stroke of the strut, and adjusting a load response characteristic of the shock absorbing strut accordingly. 31. An actively variable shock absorbing system for actively controlling the load response characteristics of a shock absorbing aircraft landing gear strut, comprising: a bypass connecting a first fluid chamber in the strut to a second fluid chamber in the strut;a first controllable valve adapted for controlling the rate at which fluid may flow through the bypass from the first fluid chamber to the second fluid chamber;a second controllable valve selected from the group comprising an actively variable gas valve to vary the pressure in a gas spring portion of the strut and an actively variable pressure relief valve to vary the relief pressure in a gas spring portion of the strut; andan electronic control system comprising an input for receiving sink rate and height above ground data, an algorithm that calculates the rate at which the aircraft is closing with the ground using the sink rate and height above ground data, and determines a corresponding optimal position for at least one of the first and second controllable valves, and an output for sending a control signal to the respective controllable valve or valves to place the valve or valves in the optimal position. 32. The actively variable shock absorbing system of claim 31, further comprising a strut internal pressure sensor. 33. The actively variable shock absorbing system of claim 31, further comprising a strut load sensor.