WO2024028571A1

WO2024028571A1 - Aircraft landing gear assembly

Info

Publication number: WO2024028571A1
Application number: PCT/GB2023/051959
Authority: WO
Inventors: Ian Bennett
Original assignee: Safran Landing Systems UK Limited
Priority date: 2022-08-04
Filing date: 2023-07-25
Publication date: 2024-02-08
Also published as: GB202211390D0; GB2621160A

Abstract

An aircraft landing gear assembly comprising an oleo-pneumatic shock absorber (50) comprising an outer cylinder (52) and sliding tube (54) movable between a compressed position and an extended position, further comprising a sprung element coupled to the shock absorber, movable between a spaced position and an engaged position, and further comprising a weight-on-wheels sensor (62, 64, 66) arranged to monitor movement of the sprung element from the spaced position to the engaged position.

Description

AIRCRAFT LANDING GEAR ASSEMBLY

Background to the Invention

It is common for an aircraft landing gear assembly to include a main hydraulic shock absorber strut having an upper end arranged to be pivotally coupled to the underside of the aircraft and a lower end coupled to a wheel and brake assembly.

Such shock absorber struts can comprise an outer cylinder and a sliding tube arranged to telescope relative to the outer cylinder. The shock absorber strut can be compressed and extended as the sliding tube moves relative to the outer cylinder. The two portions are coupled together to define a chamber containing oil and in some cases a gas. As the shock absorber is compressed, oil within the chamber is forced through damping orifices and, where gas is also provided, the gas is compressed, in order to absorb landing loads. The compressed gas serves as a spring to lengthen the shock absorber as applied external load decreases. Recoil damping orifices can be provided to restrict the flow of oil to the annulus as the shock absorber extends.

"Weight-on-wheels" is a term used in the art to refer to an operational phase of an aircraft when the weight of the aircraft is being support by its landing gear. Weight-on-wheels switches or sensors, also known in the art as "squat switches", are commonly used to indicate to aircraft systems via an electronic signal that the aircraft has transitioned from air to ground mode or vice-versa. This signal, which will be referred to as a "weight-on- wheels signal", can be used to enable lift dumpers or brakes to operate on fixed wing aircraft or can be used in the case of rotorcraft to indicate a change of control laws once in ground contact.

It is desirable to transmit the weight-on-wheels signal as soon as possible (consistent with reliability) so that lift dumpers for example can be deployed as early as possible to shorten landing distance.

A weight-on-wheels signal is typically triggered by proximity sensors or proximity switches, or by microswitches on older aircraft, driven by a mechanism related to strut closure i.e. extension state. Various mechanisms exist for the operation of the switch, but it is common to sense an initial angular movement of the upper torque link i.e. the upper link of the pivotable linkage which inhibits axial rotation of the lower cylinder or "sliding tube" of the shock absorber strut relative to the outer cylinder of the shock absorber strut. Microswitches can be set to trigger at consistent movement but have several disadvantages. As such, microswitches largely been replaced by proximity sensors. However, proximity sensors have a tolerance range on their sensing i.e. variation in position between guaranteed activation and guaranteed deactivation. For commercial wide body aircraft it is common for the weight-on-wheels switch to not be guaranteed to trigger before about 25 to 30 mm of shock absorber closure has occurred.

Due to the inflation pressure of a shock absorber there is a minimum "breakout load" below which the shock absorber will not move. Thus, a weight-on-wheels transition can occur before it is sensed and the weight-on-wheels signal is transmitted to the aircraft systems.

EP3069994B1 and WO2021/019422 describe aircraft landing gear assemblies.

The present inventor has devised a new type of aircraft landing gear assembly that can have one of more of the following advantages relative to known aircraft landing gear assemblies:

• faster and/or more reliable sensing of a weight-on-wheels condition upon landing

• a reduction in mass of the aircraft landing gear shock absorber strut

• a reduction in complexity of the aircraft landing gear shock absorber strut

Summary of Invention

According to a first aspect of the invention, there is provided an aircraft landing gear assembly comprising: an oleo-pneumatic shock absorber comprising: an outer cylinder having an inner surface defining a cylinder bore extending into the outer cylinder from a first axial face of the outer cylinder, the cylinder bore defining an oleo chamber for containing pressurised oleo-pneumatic shock absorber fluid; a sliding tube including a tube member coupled to first piston head, the first piston head being movably mounted within the cylinder bore so as to be movable along an axis of the cylinder bore between: a compressed position in which a free end portion of the tube member disposed outside of the cylinder bore is relatively close to the first axial face of the outer cylinder; and an extended position in which the free end portion of the tube member is relatively far from the first axial face of the outer cylinder, wherein the first piston head includes a first axial surface upon which pressurised oleo-pneumatic shock absorber fluid within the oleo chamber acts to apply a first spring force to force the sliding tube to move from the compressed position to the extended position; a ground contacting assembly arranged to contact the ground upon landing to support the weight of an aircraft through the oleo-pneumatic shock absorber, the ground contacting assembly comprising a mounting member; a spring arrangement; a set of torque links arranged to inhibit relative rotation between the outer cylinder and the ground contacting assembly about the axis of the cylinder bore, the torque links comprising a first link and a second link pivotally coupled to one another, the first link being pivotally coupled to the outer cylinder and the second link being pivotally coupled to the ground contacting assembly; and a weight-on-wheels sensor; wherein the sliding tube is movably coupled to the mounting member of the ground contacting assembly such that the mounting member and the ground contacting assembly can move relative to the sliding tube along the axis of the cylinder bore between a spaced position and an engaged position, wherein the spring arrangement is arranged to exert a second spring force on the mounting member to bias the mounting member to the spaced position, the second spring force being less than the first spring force, and wherein the weight-on-wheels sensor is arranged to detect movement of a component of the aircraft landing gear assembly which moves as the mounting member moves from the spaced position to the engaged position.

Thus, the aircraft landing gear assembly according to the first aspect has sprung element at the bottom of the shock absorber leg, to which ground contacting assembly and lower torque link are attached. In the spaced position, there is no ground contact and hence no counterforce against the second spring force which is large enough to compress the spring arrangement. This results in a force transfer surface of the mounting member being spaced from the free end portion of the tube member. Upon landing, initial ground contact has only to overcome the second spring force, not the first spring force (full shock absorber out-stop force), until there is enough travel to trip the weight on wheels sensor, by means of torque link closure motion for example. In the engaged position, ground contact provides a counterforce against the second spring force which can compress the spring. This reduces the spacing between the force transfer surface of the mounting member and the free end of the tube member. In the engaged position, the spring arrangement is compressed to enable the force transfer surface of the mounting member to transfer landing loads to the sliding tube, for example by way of the force transfer surface abutting and axial end surface, flange and/or other counter surface of the tube member. Once landing load has moved the mounting member from the spaced position to the engaged position, the landing load is therefore transmitted to the sliding tube such that the oleo- pneumatic shock absorber behaves in a conventional manner. As such, the aircraft landing gear assembly according to the first aspect can increase the likelihood of compressing sufficiently to trigger a weight-on-wheels sensor upon a light landing without altering the static spring curve for the oleo-pneumatic shock absorber. The spring arrangement is provided for improved weight-on-wheels detection and can therefore absorb negligible energy in comparison to the oleo-pneumatic shock absorber.

The weight-on-wheels sensor can be mounted on the sliding tube and the component can be part of the ground contacting assembly, the sensor being orientated to detect a proximity condition of the part of the ground contacting assembly. Alternatively, the weight-on-wheels sensor can be mounted on the ground contacting assembly and the component can be part of the sliding tube, the sensor being orientated to detect a proximity condition of the part of the sliding tube. In another variant the sensor or the sensor target could be mounted on the torque links in order to detect relative motion. In all cases, the sensor is arranged to monitor parts of the assembly which will experience significant relative motion as the mounting member moves from the spaced position to the engaged position, which can provide improved weight-on-wheels sensing. By directly monitoring the relative motion of the sliding tube and ground contacting assembly, the reliance on this relative motion being translated through other components to be observed is reduced.

The spring arrangement can comprise a mechanical spring located between the sliding tube and the mounting member. The mechanical spring can for example comprise a coil spring or a disc spring. The mechanical spring can be arranged in coaxial manner with respect to the bore.

As the mechanical spring can provide a significantly smaller spring force than that provided by the shock absorber pressure, initial motion can be detected even at low-sink rates. While the lost motion using a mechanical spring would absorb very little energy during its 'lost motion' stroke of up to some 30 mm, the shock absorber can have approximately the same stroke as previously, for example approximately 500 mm to 700 mm. The mounting member can define an opening arranged to slidably receive the free end portion of the tube member, one of the mounting member and the tube member including an elongate slot oriented parallel with respect to the bore axis and the other one of the mounting member and the tube member including a key member positioned in the slot to engage an end of the slot when the mounting member is in the spaced position to hold the mounting member at the spaced position. The key member can also prevent rotation of the tube member relative to the ground contacting assembly.

The sliding tube can include a radial flange abutment arranged to engage an axial face of the mounting member when the mounting member is in the engaged position. Alternatively or additionally, an axial face of the free end of the tube member can be arranged to engage a base of the opening in the mounting member the mounting member is in the engaged position.

The free end of the tube member can define an opening arranged to slidably receive a head member of the mounting member, the head member including an opening which houses the mechanical spring, wherein an out-stop member is located within the opening and the head member includes a radially enlarged portion which engages the out-stop member when the mounting member is in the spaced position to hold the mounting member at the spaced position.

Alternatively, the spring arrangement can comprise the gas of the oleo-pneumatic shock absorber. The tube member can be hollow to define bore in fluid communication with the oleo chamber and arranged to slidably receive a head member of the mounting member, wherein an out-stop member is located within the opening and the head member includes a radially enlarged portion which engages the out-stop member when the mounting member is in the spaced position to hold the mounting member at the spaced position. The first piston of the sliding tube having a first axial surface having a first surface area and the radially enlarged portion of the head member defining a second piston head slidably mounted within the tube bore in sealing engagement to inhibit pressurised oleo- pneumatic shock absorber fluid passing from the oleo chamber beyond the second piston head, wherein the second piston head includes a second axial surface upon which pressurised oleo-pneumatic shock absorber fluid within the oleo chamber acts to force the sliding tube to move from the compressed position to the extended position, the second axial surface having a second surface area which is less than the first surface area. An advantage of a spring arrangement comprising the gas of the oleo-pneumatic shock absorber is that the shock absorber can have increased resistance at higher sink rates due to increased damping pressure within the shock absorber, as the lost motion piston can be connected to the damping pressure side of the shock absorber. This can therefore give a contribution to energy absorption at high sink rates (when energy absorption is more important) but still provide early weight on wheels indication at low sink rates (lower damping pressure increment) when energy absorption is of less importance. Such embodiments can also result in a shorter landing gear in comparison to embodiments utilising a mechanical spring.

The distance between the spaced position and an engaged position along the axis of the bore can be at least 25mm, preferably at least 30mm and/or preferably no more than 50mm.

The landing gear assembly can comprise a side stay, drag stay or plunger lock arrangement coupled to the shock absorber strut and arranged to enable the shock absorber strut to be maintained in a deployed condition relative to an aircraft to which the landing gear assembly is movably coupled.

Brief Description of the Drawings

Embodiments of the invention will now be described, strictly by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is a diagram of an aircraft;

Figures 2a to 2e are diagrams of an aircraft landing gear assembly;

Figure 3 is a diagram of an aircraft landing gear assembly shock absorber strut according to an embodiment of the invention;

Figure 4 is a diagram of an example of a typical aircraft landing gear assembly shock absorber spring curve;

Figure 5 is a diagram of an aircraft landing gear assembly shock absorber strut according to an embodiment of the invention; and Figure 6 is a diagram of an aircraft landing gear assembly shock absorber strut according to a further embodiment of the invention.

Description of Embodiments

By way of a non-limiting overview, the embodiments of the invention relate to an aircraft landing gear assembly comprising an oleo-pneumatic shock absorber comprising an outer cylinder and sliding tube movable between a compressed position and an extended position, further comprising a sprung element coupled to the shock absorber, movable between a spaced position and an engaged position, further comprising torque links between the aforesaid sprung element and the outer cylinder and further comprising a weight-on-wheels sensor arranged to monitor movement of the sprung element from the spaced position to the engaged position. The assemblies are configured such that the force required to move the sprung element from the spaced position to the engaged position is less than the force required to move the sliding tube movable from the extended position towards the compressed condition against the pressurised fluid within the shock absorber.

Figure 1 is a diagram of an aircraft 10. The aircraft 10 includes assemblies such as a nose landing gear 12, main landing gear 14 and engines 16. The landing gear 12, 14 each includes a shock absorber strut for damping landing loads and supporting the weight of the aircraft 10 when it is on the ground. The term aircraft as used herein can include aeroplanes, helicopters and the like having mass in excess of 450Kg.

Referring now to Figures 2a to 2e, an aircraft assembly, namely an aircraft landing gear assembly, is shown generally at 14. Figures 2a to 2e are an example of an aircraft landing gear assembly which can include a shock absorber strut according to an embodiment of the invention. It will however be appreciated that shock absorber struts according to embodiments of the invention can be used in a range of types of aircraft landing gear.

The landing gear assembly 14 includes a foldable stay 18, a lock link 20 and a down lock spring arrangement 22 mounted to the stay 18 and arranged to urge the lock link 20 to assume a locked state. The landing gear assembly also includes a main shock absorber strut 24, comprising an outer cylinder 26 and a sliding tube 28, as well as a wheel and brake assembly 30.

The aircraft landing gear assembly is movable between a deployed condition, for take-off and landing, and a stowed condition for flight. An actuator (not shown) is provided for moving the landing gear between the deployed condition and the stowed condition. This actuator is known in the art as a retraction actuator, and more than one can be provided. A retraction actuator can have one end coupled to the airframe and another end coupled to the outer cylinder such that extension and retraction of the actuator results in movement of the outer cylinder between deployed and stowed conditions.

The stay 18 serves to support the orientation of the outer cylinder 26 when the landing gear is in the deployed condition. The stay 18 generally includes a two-bar linkage that can be unfolded to assume a generally straight or aligned, over centre condition in which the stay 18 is locked to inhibit movement of the outer cylinder, as shown in Figures 2c and 2e. When the stay is broken, it no longer prevents pivotal movement of the outer cylinder 26 and the outer cylinder 26 can be moved by the retraction actuator towards the stowed condition, as shown in Figure 2a. During flight the stay 18 is arranged in the folded condition, while during take-off and landing the stay 18 is arranged in the generally straight or aligned condition. Some main landing gear assemblies include a pair of stays coupled to a common shock absorber strut.

The stay 18 has an elongate upper stay arm 18a having a lower end defining a pair of lugs pivotally coupled via a pivot pin 32 to a pair of lugs defined at an upper end of an elongate lower stay arm 18b. The stay arms 18a and 18b can therefore pivotally move relative to one another about the pivot pin 32. The upper end of the upper stay arm 18a defines a pair of lugs that are pivotally coupled to a lug of a connector 34 which in turn is pivotally coupled to the airframe 11. The lower end of the lower stay arm 18b defines a pair of lugs pivotally coupled to a lug of a connector 36 which in turn is pivotally coupled to the outer cylinder 26.

The lock link 20 has an elongate upper link arm 20a having a lower end pivotally coupled to an upper end of an elongate lower link arm 20b via a pivot pin 38. The link arms 20a, 20b can therefore pivotally move relative to one another about the pivot pin 38. An upper end of the upper link arm 20a defines a pair of lugs that are pivotally coupled to a lug of a connector 40 which in turn is pivotally coupled to the outer cylinder 26. A lower end of the lower link arm 20b defines a lug that is pivotally coupled to lugs of the stay arms 18a, 18b via the pivot pin 32. Lugs of the upper stay arm 18a are in this example disposed between the lugs of the lower stay arm 18b and the lugs of the lower link arm 20b.

When the lock link 20 is in the locked condition, as illustrated in Figures 2d and 2e, the upper and lower link arms 20a, 20b are generally longitudinally aligned or coaxial, and can be 'over-centre', such that the lock link 20 is arranged to oppose a force attempting to fold the stay 18, so as to move the landing gear assembly from the deployed condition towards the stowed condition. The lock link 20 must be broken to enable the stay 18 to be folded, thereby permitting the outer cylinder 26 to be moved by the retraction actuator towards the stowed condition.

One or more down lock springs 22 are generally provided to assist in moving the landing gear assembly to the deployed condition and locking it in that state by making the lock link. Down lock springs 22 also inhibit the lock link accidentally being unlocked. Down lock springs 22 are generally metal coil springs, which can be coupled between the lock link and another part of the landing gear assembly, such as an arm of the stay assembly, as shown in Figures 2b and 2e.

The spring arrangement 22 is arranged to bias the lock link 20 towards the locked condition by way of spring tension. A distal end of the spring 22a is coupled to the lower stay arm 18b via a lower engagement formation 22b which in turn is coupled to an anchor point defined by the lower connector 22c.

The coil spring of the spring arrangement 26 is at its shortest when the landing gear assembly is in the deployed condition, as shown in Figure 2e, and at its longest when the landing gear assembly approaches the stowed condition, as shown in Figure 2b. As the landing gear assembly is retracted towards the stowed condition, the spring of each spring arrangement extends, resulting in increased spring load and torsional stress.

Referring to Figure 2e, a lock stay actuator 42 is coupled between the upper stay arm 18a and lower link arm 20b and arranged to pivotally move the link arms 20a, b so as to 'lock' and 'unlock' the lock link 20, as illustrated in Figure 2c. The actuator 42 can break the lock link 20 against the down lock spring bias, allowing the landing gear assembly to be folded and stowed as described previously.

Figure 3 is a diagram of an aircraft landing gear assembly 50 according to an embodiment of the invention.

The shock absorber strut 50 comprises an outer cylinder 52 having an inner surface 52a defining a cylinder bore B extending into the outer cylinder from a first axial face 52b of the outer cylinder 52. The cylinder 52 is elongate and in this embodiment is of circular cross section. A sliding tube 54 is movably mounted within the cylinder bore B so as to be movable along the cylinder bore B between a compressed position in which a first free end portion 54a of the sliding tube 54 disposed outside of the bore B is relatively close to the first axial face 52b of the outer cylinder 52 and an extended position in which the first free end portion 54a of the sliding tube 54 is relatively far from the first axial face 52b of the outer cylinder 52.

A piston head 56 is located at the inner end 54b of the sliding tube 54 to slide against the inner surface 52a defining the bore B. The lower end of the cylinder 52 can be provided with a lower bearing assembly sleeve insert (not shown) to define a lower bearing arranged to act on the outer surface of the sliding tube 54 as it moves between the compressed and extended positions. A gland nut (not shown) can be screwed into the end of the bore to retain the lower bearing assembly. However, in other embodiments, any suitable bearing assembly can be utilised.

The outer cylinder 52 can be provided with a mounting bearing (not shown) by which the shock absorber strut is arranged to be pivotally coupled to an aircraft to move between stowed and deployed conditions.

The cylinder bore defines an oleo (e.g. oil and gas) chamber O. A space within the bore B between the cylinder 52 and sliding tube 54 defines an annular chamber which varies in size (length) as the sliding tube 54 moves between the compressed and extended positions. The annulus can include an out-stop member 60. The out-stop member 60 provides an abutment surface for the piston head 56 at full extension of the shock absorber. The oil can comprise any suitable hydraulic liquid and the gas can comprise nitrogen for example.

One or more dynamic seals (not shown) are arranged within the cylinder bore B between the inner surface of the outer cylinder 52 and an outer surface of the sliding tube 54 to inhibit oil within the oil chamber O passing the dynamic seals as the sliding tube 54 moves between the extended and compressed positions. In this embodiment, the dynamic seals are mounted on the lower bearing sleeve assembly 58.

The piston head 56 can be provided with plurality of damping orifices at least some, but not all, of which are provided with one-way valves such that oil can flow relative easily through them as the shock absorber is compressed but flow is relatively difficult in the reverse direction, in order to provided recoil damping as oil flows from the annulus back into the main region of the oil chamber O. Weight-on-wheels signal is typically sensed by proximity sensors or proximity switches, or by microswitches on older aircraft, driven by a mechanism related to leg closure. There are a number of different mechanisms for the operation of the switch, but they usually relate to shock absorber closure and typically by sensing an initial angular movement of the upper torque link.

Figure 3 shows an example of such typical weight-on-wheels sensor 62 arranged to monitor the initial angular motion of the upper torque link 34a with respect to the outer cylinder 52 during initial compression of the shock absorber.

The sliding tube 54 is slidably coupled to a ground contacting assembly 71 via a mounting member 72. The ground contacting assembly 71 comprises the mounting member and at least one axle and wheel assembly. In the embodiment shown in Figure 3, the sliding tube 54 defines a recessed portion 78 arranged at the first free end portion of the sliding tube 54a. The portion of the sliding tube 54 which houses the recessed portion 78 is at least partially arranged within the mounting member 72. Therefore, the mounting member 72 axially surrounds a portion of the recessed portion 78 of the sliding tube 54. The mounting member 72 can be a cylindrical tube with an open end for receiving the first free end portion of the sliding tube 54a and an opposing substantially closed end.

A sprung element comprises a spring arrangement 68 and the mounting element 72. The spring arrangement 68 is arranged within the recessed portion 78 and couples the sliding tube 54 to the mounting member 72. The sprung element can therefore be sleeved over the first free end of the sliding tube 54. The spring arrangement 68 is biased to exert a force which acts to increase the longitudinal separation between the sliding tube 54 and mounting member 72. Specifically, in the embodiment shown in Figure 3, the spring arrangement exerts a force to increase the separation between the axial face of the first free end portion of the sliding tube 54a and the substantially closed end of the mounting member 72. The spring arrangement 68 provides a lower spring force than that of the full shock absorber strut.

When the landing gear is fully extended, without ground contact, the sliding tube 54 is fully extended within the outer cylinder 52 and the mounting member 72 is at a maximum longitudinal distance from the sliding tube 54. Upon landing, the ground contacting assembly 71 makes contact with the ground which results in a counterforce being exerted on the mounting member 72, against the spring arrangement 68. The spring arrangement 68 compresses due to the counterforce and continues to compress as the counterforce due to the ground contact becomes larger than the force exerted on the mounting member 72 by the spring arrangement 68. The compression of the spring arrangement 68 results in the longitudinal distance between the first free end portion of the sliding tube 54a and the mounting member 72 to reduce. Increased counterforce on the spring arrangement 68 due to increased ground contact will result in the mounting member 72 and sliding tube 54 moving into an engaged position in which spring arrangement 68 is at maximum compression and/or the mounting member 72 contacts the sliding tube 54.

If the spring arrangement 68 reaches maximum compression, any further counterforce due to ground contact will travel through the spring arrangement 68 and be exerted on the sliding tube 54, against the internal pressure within the bore B. This would result in typical operation of the oleo-pneumatic shock absorber as the ground force increases to overcome the internal pressure within the bore B and the shock absorber compresses. Alternatively, the sliding tube 54 can be arranged with a feature which limits the travel of the spring arrangement 68 relative to the sliding tube 54. For example, the sliding tube 54 can be arranged with an abutment surface 70 which is arranged to engage with a force transfer surface of the mounting member 72, for example the open end of the cylindrical tube of the mounting member 72. The inner base surface of the mounting member 72 can also serve as part of the force transfer surface to contact the free axial end of the tube 54a. After the sliding tube 54 and mounting member 72 have made contact, further ground contact will result in the counterforce being applied to the sliding tube 54, against the internal pressure of the bore B. Again, this results in the typical operation of an oleo- pneumatic shock absorber as the shock absorber begins to compress. The abutment surface 70 can be on an external surface of the sliding tube 54 or on an internal surface of the mounting member 72 to engage with an aperture in the sidewall of the sliding tube 54 at the recessed portion.

The torque link assembly and more specifically the lower torque link 34b is coupled to the ground contacting assembly 71, for example via the mounting member 72, rather than the sliding tube 54. This allows torsional loads about the shock absorber axis BA to be passed from the ground contacting assembly 71 to the outer cylinder 52.

The torque link assembly may be at any angle around the vertical axis BA of the shock absorber.

The weight-on-wheels sensor 62 can be arranged to observe the initial rotational movement of the upper torque link 34a with respect to the outer cylinder 52. This arrangement allows the use of typical weight-on-wheels sensors. Alternatively, the weight- on-wheels sensor 64, 66 can be arranged to observe the relative motion of the sliding tube 54 and mounting member 72. To this end, the weight-on-wheels sensor 64 can be arranged on the sliding tube 54, for example on the abutment surface 70, and monitor the proximity of the axial face of the free end of the mounting member 72. Alternatively, the weight-on-wheels sensor 66 can be arranged on the mounting member 72, for example on the substantially closed end of the mounting member 72 and monitor the proximity of the axial face of the free end of the sliding tube 54. The weight-on-wheels sensor 62, 64, 66 can thus detect the movement of the mounting member 72 as a result of the ground contact overcoming the spring force of the spring arrangement 68, which is less than that of the oleo-pneumatic shock absorber.

The spring arrangement can be any suitable sprung element which provides a resilient means. For example, the spring arrangement could be a coil spring or disc spring.

Figure 4 shows a typical shock absorber spring curve, demonstrating the amount of compression due to the load on the shock absorber. The solid curve demonstrates a typical spring curve at a temperature of 20°C. Typically, the shock absorber travel (compression) is low until the load begins to approach the maximum static load of the shock absorber (as shown by the dashed line). In low-sink rate landings, the initial load on the shock absorber can be low and slow to increase meaning that the shock absorber travel is low. In such landing events, the weight-on-wheels sensor may not be triggered until a higher load is experienced. A delay in triggering the weight-on-wheels senor can cause a delay in automated landing systems being triggered. The present inventor has noted that by arranging a spring arrangement at the base of the shock absorber leg, initial ground contact has only to overcome the spring force of the spring arrangement, not the full shock absorber out-stop force, until there is enough travel to trip the weight-on-wheels switch, for example, by means of torque link closure motion.

Figure 5 shows an aircraft landing gear assembly 80 according to a further embodiment. The assembly 80 is similar to the assembly 50 of Figure 3 and for brevity the following description will focus on the differences.

A sliding tube 84 is movably mounted within the cylinder bore B2 so as to be movable along the cylinder bore B2 between a compressed position in which a first free end portion 84a of the sliding tube 84 disposed outside of the bore B is relatively close to the first axial face 92b of the outer cylinder 92 and an extended position in which the first free end portion 84a of the sliding tube 84 is relatively far from the first axial face 92b of the outer cylinder 92. The sliding tube 84 defines a cylindrical bore split into an upper B3 and lower B4 portion by an internal portion 86 arranged within the cylindrical bore. The upper sliding tube bore B3 is exposed to the oil and gas chamber 02 such that the internal pressure of the chamber 02 applies a force to an axial face of the internal portion. The internal portion 86 can be arranged closer to the first free end portion 84a of the sliding tube 84 than the piston head 96. The lower sliding tube bore B4 defines an inner surface 84b. The ground contacting assembly 81 comprises a mounting member 82. The mounting member 82 is movably mounted within the lower sliding tube bore B4 and arranged with a mounting member piston head 82a located at the inner end of the lower sliding tube bore B4 to slide against the lower sliding tube bore inner surface 84b. The mounting member 82 is moveable along the cylindrical bore B4 between a compressed position in which a first end portion of the mounting member 82 coupled to the ground contacting assembly 81 is relatively closer to the first free end portion 84a of the sliding tube 84 and an extended position in which the first end portion of the mounting member 82 coupled to the ground contacting assembly 81 is relatively far from the first free end portion 84a of the sliding tube 84.

A space within the lower sliding tube bore B4 between the sliding tube 84 and mounting member 82 defines an annular chamber which varies in size (length) as the mounting member 82 moves between the compressed and extended positions. The annulus can include an abutment surface for the mounting member piston head 82a at full extension of the mounting member.

The lower sliding tube bore B4 comprises a spring arrangement 88 arranged to bias the mounting member 82 into the extended position. Suitable spring arrangements can include a resilient member such as a coil spring or disc spring. A first end of the spring arrangement can be coupled to the internal portion 86 and a second end of the spring arrangement 88 can be coupled to the mounting member 82. The mounting member 82 can be arranged with a recessed portion 82b which extends into the mounting member 82 from an axial face of the mounting member piston head 82a. The spring arrangement can be coupled to the mounting member 82 at an inner face of the recessed portion 82b such that the spring arrangement 88 is located partially within the recessed portion 82b. Such arrangement allows for a spring arrangement 88 without a large increase in the overall shock absorber length. The mounting member 82 extends partially out of the sliding tube 84, the external portion of the mounting member 82 having a diameter greater than that of the internal portion such that the external portion provides an abutment surface 90 which can engage with the first free end portion of the sliding tube 84a. The mounting member 82 and spring arrangement 88 together form a sprung element of the shock absorber strut.

Whilst rotational motion about a vertical axis BA between the axle of the ground contacting assembly and the sliding tube 84 is restrained via toque links, additional rotational restraints can be provided. Such additional rotational restraints can be via a key or splines located in the mounting member piston head 82a or annulus between the mounting member 102 and sliding tube inner surface 84b.

When the shock absorber strut is fully extended, with no ground contact, the mounting member 82 is extended into the spaced position. Upon ground contact, the ground contacting assembly 81 applies an upwards force to the mounting member 82 which acts as a counterforce against the spring force of the spring arrangement 88. This counterforce can compress the spring arrangement 88 such that the distance between the abutment surface 90 of mounting member 82 and the first free end portion 84a of the sliding tube reduces. As the ground contact increases, the mounting member 82 continues to compress, reducing the length of the spring arrangement 88, thus allowing the mounting member 82 to move into an engaged position. The engaged position can be achieved when the first free end portion 84a of the sliding tube contacts an axial face of the external portion of the mounting member 82, such as the abutment surface 90. Thus, the counterforce due to ground contact is transferred through the mounting member to the base of the sliding tube. Alternatively, the engaged position can be achieved by the mounting member piston head 82a contacting the internal portion 86 of the sliding tube 84. In another alternative arrangement, the engaged position can be achieved by the spring arrangement 88 reaching full compression and transferring the counterforce to the internal portion 86 of the sliding tube 84.

A weight-on-wheels sensor 62, 66, 68 (illustrated in Figure 3) monitors the mounting member 82 moving from the spaced position towards the engaged position. The weighton-wheels sensor can monitor the upper torque link initial rotation with respect to the outer cylinder 92 or monitor the proximity of the sliding tube 84 and the mounting member 82, for example via the movement of the abutment surface 90 with respect to the first free end portion of the sliding tube 84a.

Figure 6 shows an aircraft landing gear assembly 100 according to a further embodiment. The assembly 100 is similar to the assembly 80 of Figure 5 and 50 of Figure 3 and for brevity the following description will focus on the differences. The sliding tube 104 defines a cylindrical bore B5 which extends through the sliding tube length and defines an inner surface 104a. A ground contacting assembly 101 comprises a mounting member 102. The mounting member 102 is movably mounted within the cylindrical bore B5 and arranged with a mounting member piston head 102a located at the inner end of the cylindrical bore B5 to slide against the sliding tube inner surface 104a. The mounting member 102 is moveable along the cylindrical bore B5 between a compressed position in which a first end portion coupled to the ground contacting assembly 101 is relatively closer to the first free end portion 104b of the sliding tube 104 and an extended position in which the first end portion coupled to the ground contacting assembly

101 is relatively far from the first free end portion 104b of the sliding tube 104.

A space within the lower sliding tube bore B5 between the sliding tube 104 and mounting member 102 defines an annular chamber which varies in size (length) as the mounting member 102 moves between the compressed and extended positions. The annulus can include an abutment surface for the mounting member piston head 102a at full extension of the mounting member. The mounting member 102 extends partially out of the sliding tube 104, the external portion of the mounting member having a diameter greater than that of the internal portion such that the external portion provides an abutment surface which can engage with the first free end portion of the sliding tube.

As the cylindrical bore B5 extends through the sliding tube 104, the internal pressure within the oil and gas chamber 02 exerts a force on the axial face of the sliding tube piston head 106 and the axial face of the mounting member piston head 102a. A form of piston head or diaphragm containing orifices or valve (not shown) may obstruct the top of bore B5. The internal pressure within the chamber 02 therefore biases the mounting member

102 into a spaced position in which the mounting member is extended. Thus, the internal shock absorber pressure provides a spring arrangement. When initial ground contact occurs, the mounting member 102 travels towards a compressed position which results in the abutment surface 110 of the mounting member 102 engaging with the first free end portion 104a of the sliding tube. As the ground contact increases and with the mounting member in the engaged position, the counterforce due to the ground contact will also act on the sliding tube, against the internal pressure within the chamber 02. The shock absorber 100 then acts as a traditional oleo-pneumatic shock absorber with the sliding tube 104 moving into a compressed position. As the surface area of the mounting member piston 102a over which the pressure acts is substantially smaller than the full sliding tube 106 surface area, the initial closure load will be substantially smaller (in the same ratio). In low-sink rate landings, a substantially smaller initial closure load allows earlier detection of weight-on-wheels.

A weight-on-wheels sensor 62, 66, 68 (illustrated in Figure 3) monitors the mounting member 102 moving from the spaced position towards the engaged position. The weighton-wheels sensor can monitor the upper torque link initial rotation with respect to the outer cylinder or monitor the proximity of the sliding tube 104 and the mounting member 102, for example via the movement of the abutment surface 110 with respect to the first free end portion of the sliding tube 104b.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parenthesis shall not be construed as limiting the claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. Parts of the invention can be implemented by means of hardware comprising several distinct elements. In a device claim enumerating several parts, several of these parts can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. An aircraft landing gear assembly comprising: an oleo-pneumatic shock absorber comprising: an outer cylinder having an inner surface defining a cylinder bore extending into the outer cylinder from a first axial face of the outer cylinder, the cylinder bore defining an oleo chamber for containing pressurised oleo-pneumatic shock absorber fluid; a sliding tube including a tube member coupled to first piston head, the first piston head being movably mounted within the cylinder bore so as to be movable along an axis of the cylinder bore between: a compressed position in which a free end portion of the tube member disposed outside of the cylinder bore is relatively close to the first axial face of the outer cylinder; and an extended position in which the free end portion of the tube member is relatively far from the first axial face of the outer cylinder, wherein the first piston head includes a first axial surface upon which pressurised oleo-pneumatic shock absorber fluid within the oleo chamber acts to apply a first spring force to force the sliding tube to move from the compressed position to the extended position; a ground contacting assembly arranged to contact the ground upon landing to support the weight of an aircraft through the oleo-pneumatic shock absorber, the ground contacting assembly comprising a mounting member; a spring arrangement; a set of torque links arranged to inhibit relative rotation between the outer cylinder and the ground contacting assembly about the axis of the cylinder bore, the torque links comprising a first link and a second link pivotally coupled to one another, the first link being pivotally coupled to the outer cylinder and the second link being pivotally coupled to the ground contacting assembly; and a weight-on-wheels sensor; wherein the sliding tube is movably coupled to the mounting member of the ground contacting assembly such that the mounting member can move relative to the sliding tube along the axis of the cylinder bore between a spaced position and an engaged position, wherein the spring arrangement is arranged to exert a second spring force on the mounting member to bias the mounting member to the spaced position, the second spring force being less than the first spring force, and wherein the weight-on-wheels sensor is arranged to detect movement of a component of the aircraft landing gear assembly which moves as the mounting member moves from the spaced position to the engaged position.

2. The aircraft landing gear assembly according to claim 1, wherein the weight-on- wheels sensor is mounted on the sliding tube and the component is part of the ground contacting assembly, the sensor being orientated to detect a proximity condition of the part of the ground contacting assembly.

3. The aircraft landing gear assembly according to claim 1, wherein the weight-on- wheels sensor is mounted on the ground contacting assembly and the component is part of the sliding tube, the sensor being orientated to detect a proximity condition of the part of the sliding tube.

4. The aircraft landing gear assembly according to any preceding claim, wherein the spring arrangement comprises a mechanical spring located between the sliding tube and the mounting member.

5. The aircraft landing gear assembly according to claim 4, wherein the mechanical spring comprises a coil spring or a disc spring.

6. The aircraft landing gear assembly according to claim 4 or 5, wherein, the mechanical spring is arranged in coaxial manner with respect to the bore.

7. The aircraft landing gear assembly according to any preceding claim, wherein the mounting member defines an opening arranged to slidably receive the free end portion of the tube member, one of the mounting member and the tube member including an elongate slot oriented parallel with respect to the bore axis and the other one of the mounting member and the tube member including a key member positioned in the slot to engage an end of the slot when the mounting member is in the spaced position to hold the mounting member at the spaced position and/or inhibit relative rotation between the sliding tube and the mounting member about the bore axis.

8. The aircraft landing gear assembly according to any preceding claim, wherein the sliding tube includes a radial flange abutment arranged to engage an axial face of the mounting member when the mounting member is in the engaged position.

9. The aircraft landing gear assembly according to any preceding claim, wherein an axial face of the free end of the tube member is arranged to engage a base of the opening in the mounting member when the mounting member is in the engaged position.

10. The aircraft landing gear assembly according to claim 4, wherein the free end of the tube member defines an opening arranged to slidably receive a head member of the mounting member, the head member including an opening which houses the mechanical spring, wherein an out-stop member is located within the opening and the head member includes a radially enlarged portion which engages the out-stop member when the mounting member is in the spaced position to hold the mounting member at the spaced position.

11. The aircraft landing gear assembly according to any preceding claim, wherein the spring arrangement comprises gas of the oleo-pneumatic shock absorber.

12. The aircraft landing gear assembly according to claim 11, wherein the tube member is hollow to define a bore in fluid communication with the oleo chamber and arranged to slidably receive a head member of the mounting member, wherein an out-stop member is located within the opening and the head member includes a radially enlarged portion which engages the out-stop member when the mounting member is in the spaced position to hold the mounting member at the spaced position.

13. The aircraft landing gear assembly according to claim 12, wherein the first piston of the sliding tube having a first axial surface having a first surface area and the radially enlarged portion of the head member defining a second piston head slidably mounted within the tube bore in sealing engagement to inhibit pressurised oleo-pneumatic shock absorber fluid passing from the oleo chamber beyond the second piston head, wherein the second piston head includes a second axial surface upon which pressurised oleo-pneumatic shock absorber fluid within the oleo chamber acts to force the sliding tube to move from the compressed position to the extended position, the second axial surface having a second surface area which is less than the first surface area.

14. The aircraft landing gear assembly according to any preceding claim, wherein the distance between the spaced position and an engaged position is at least 25mm, preferably at least 30mm and/or preferably no more than 50mm.

15. The aircraft landing gear assembly according to any preceding claim, comprising a side stay, drag stay or plunger lock arrangement coupled to the shock absorber strut and arranged to enable the shock absorber strut to be maintained in a deployed condition relative to an aircraft to which the landing gear assembly is movably coupled.