GB2586824A

GB2586824A - Landing gear assembly

Info

Publication number: GB2586824A
Application number: GB1912718.2A
Authority: GB
Inventors: White Nick
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2019-09-04
Filing date: 2019-09-04
Publication date: 2021-03-10
Also published as: GB201912718D0

Abstract

A trailing-arm landing gear assembly 4, that shortens during retraction is disclosed and comprises a main strut 6, a trailing arm 10, and a rigid linkage 14 connected to the trailing arm 10 and acts to shorten the landing gear 4. ln the second embodiment first and second linkages (150, 152, figures 5a-c) are provided. Movement of the second linkage (152) from the extended to the retracted configuration causes movement of the first linkage (150) from the retracted to the extended configuration. That movement of the first linkage (150) causes a rotation of the trailing arm (110) that shortens the landing gear (104).

Description

LANDING GEAR ASSEMBLY

BACKGROUND OF THE INVENTION

100011 The present invention relates to aircraft landing gear. More particularly, but not exclusively, this invention concerns a landing gear assembly comprising a linkage arranged to move the wheel of a landing gear upwards (i.e. shorten the landing gear) as the landing gear retracts. The invention further concerns a method of operating such a landing gear and an aircraft including such a landing gear.

[0002] In some circumstances, it is desirable to increase the length of a wing-mounted landing gear, for example to accommodate larger engines under the wing and/or to enable more aircraft rotation at take-off and landing. Wing-mounted landing gear typically retract by rotating the landing gear about an axis lying substantially parallel to the longitudinal axis of the aircraft. The length of a landing gear that is retracted is limited by the need to accommodate the landing gear within the distance between the point at which the landing gear is mounted to the wing and the centre-line of the aircraft. The ability to shift the spanwise location of a wing-mounted landing gear outboard is limited by the need to meet airport span limits and/or the ability of the wing structure at outboard locations to support the loads associated with the landing gear. It would therefore be advantageous to provide a landing gear that is more compact when retracted than extended.

100031 Alternatively, it may be desirable to move a landing gear of a given length further inboard to meet airport span limits or to a location where the structure of the wing is better able to accommodate landing gear loads. Again the ability to do so is limited by the need to accommodate the landing gear within the distance between the point at which the landing gear is mounted to the wing and the centre-line of the aircraft and a landing gear that is more compact when retracted than extended would be advantageous.

100041 US 2018/0208298 discloses a landing gear comprising a truck lever (or trailing arm) and a tension link assembly configured to rotate the trailing arm as the landing gear retracts thereby shortening the landing gear for stowage. The arrangement of US -2 - 2018/0208298 comprises a number of moving elements and it would be advantageous to provide a mechanically simpler arrangement for shortening the landing gear for stowage. Additionally or alternatively it would be advantageous to provide an arrangement for shortening the landing gear for stowage that provides an improved load distribution as between the main strut of the landing gear and the rest of the aircraft.

[0005] The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved landing gear assembly.

SUMMARY OF THE INVENTION

[0006] In a first aspect of the invention there is provided a landing gear assembly for mounting to an aircraft. The landing gear assembly may comprise a main strut. The landing gear assembly may comprise a trailing arm rotatably mounted to the main strut. The trailing arm may be mounted to the main strut at a point located partway along the length of the trailing arm, thereby dividing the trailing arm into a first portion located on one side of the main strut and a second portion located on the other side of the main strut. The second portion of the trailing arm may be configured for connection to at least one wheel. The landing gear assembly may comprise a first linkage connected to the first portion of the trailing arm and to the main strut. The first linkage may be configured for movement between an extended and a retracted configuration. The landing gear assembly may comprise a second linkage connected to the first linkage and to the main strut. The second linkage may be configured for movement between an extended and a retracted configuration. The landing gear assembly may be configured, for example the first linkage and second linkage may be connected and arranged, such that movement of the second linkage from the extended to the retracted configuration causes movement of the first linkage from the retracted to the extended configuration. It may be that said movement of the first linkage from the retracted to the extended configuration causes a rotation of the trailing arm that moves a distal and/or free end of the second portion -3 - (and/or a wheel when mounted on the second portion of the trailing arm) upwards and shortens the landing gear.

[0007] The use of a first linkage and a second linkage configured such that movement of the second linkage from the extended to the retracted configuration causes movement of the first linkage from the retracted to the extended configuration may provide for an improved load distribution in the main strut, particularly in comparison to the arrangement of US 2018/0208298.

100081 The length of a linkage (for example the straight-line distance between the first end and the second end of a linkage) in its extended configuration may be greater than the length of the same linkage in its retracted configuration, for example at least 10% greater, for example at least 20% greater, for example at least 50% greater. Thus, the length of a linkage may vary as it moves between its extended and retracted configurations. A linkage may be configured to fold such that its length can vary. Alternatively, a linkage may be telescopic such that its length can vary. It will be apparent that the linkage can be configured in a number of different ways in order to provide a linkage the length of which can vary. It may be that in the extended configuration a linkage is substantially straight and in the retracted configuration a linkage is folded. Alternatively, it may be that in the extended configuration a linkage is folded and in the retracted configuration a linkage is folded to a greater degree.

[0009] It may be that, in use, the second linkage is in its retracted configuration and the first linkage is in its extended configuration when the landing gear is in the extended position. It may be that, in use, the second linkage is its extended configuration and the first linkage is in its retracted configuration when, in use, the landing gear is in the retracted position.

[0010] The trailing arm may comprise an elongate body. The first portion may comprise a first end of the trailing arm. The second portion may comprise a second end of the trailing arm. The trailing arm may be mounted to the main strut in the region of a second end of the main strut, for example the end of the main strut located farthest from the aircraft when, in use, the landing gear is in the extended position. The trailing arm may be mounted to the main strut for rotation about an axis lying substantially parallel to the -4 -axis about which the wheels of the landing gear rotate and/or lying substantially parallel to the spanwise axis of the aircraft. The trailing arm may be mounted to the main stmt at a point located midway between the first and second ends of the trailing arms. Each portion of the trailing arm may comprise a distal and/or free end, the distal and/or free end being the end of the trailing arm furthest from the point at which the trailing arm is mounted to the main strut.

[0011] Each linkage (for example the first linkage, the second linkage, a control linkage (if present) and/or a rigid linkage (as discussed below, if present) may comprise at least one link member. Each link member may comprise an elongate body, for example an elongate body of fixed length. The first and/or second linkage may comprise two or more link members, for example a plurality of link members, connected to move relative to each other and thereby change the length of the linkage. Said two or more link members may be connected, for example directly connected, to rotate, pivot, slide or any combination thereof relative to each other. Each link member may be pivotally connected to at least one other link member of the linkage. The pivotal connection may allow for rotation about at least one axis of rotation, for example an axis of rotation that is substantially perpendicular to the longitudinal axis of each link member and/or an axis lying substantially parallel to the axis about which the wheels of the landing gear rotate and/or lying substantially parallel to the spanwise axis of the aircraft. The pivotal connection may allow for movement in a single degree of freedom, for example rotation around a single axis, for example said at least one axis of rotation.

[0012] A first end of the second linkage may be connected, for example pivotally connected, to the first linkage, for example to a point located partway between the first and second ends of the first linkage. The first end of the second linkage may be connected to the first linkage such that the action of the first end of the second linkage on the first linkage as the second linkage moves from the extended to the refracted configuration causes movement of the first linkage from the retracted to the extended configuration, for example causes the first linkage to unfold (and/or vice versa for movement of the second linkage from the retracted to the extended configuration). The first end of the second linkage may be connected to the first linkage at a point located -5 -partway between the first and second ends of the second linkage. A second end of the second linkage may be connected, for example pivotally connected, to the main strut. Movement of the second linkage from the extended to the retracted configuration may comprise movement of the first end of the second linkage closer to the main strut. The first and/or second end of the second linkage may be connected to the first linkage and/or the main strut respectively for rotation relative to the first linkage and/or the main strut about an axis lying substantially parallel to the axis about which the wheels of the landing gear rotate and/or lying substantially parallel to the spanwise axis of the aircraft.

[0013] The second linkage may comprise two link members, a first link member connected at a first end to the first linkage (said first link member therefore comprising the first end of the second linkage) and at a second end to a second link member of the second linkage. The second link member of the second linkage may be connected at a first end to the first link member of the second linkage and at a second end to the main strut (said second link member therefore comprising the second end of the second linkage) 'The first and second link members may be pivotally connected.

[0014] A first end of the first linkage may be connected, for example pivotally connected to the trailing arm, for example to the first portion of the trailing arm, for example in the region of a first end of the trailing arm. The first end of the first linkage may be connected to the trailing arm such that the action of the first end of the first linkage on the trailing arm as the first linkage moves from the retracted to the extended configuration causes rotation of the trailing arm relative to the main strut, for example causes the first end of the trailing arm to move downwards and consequently the wheels to move upwards (and/or vice versa for movement of the first linkage from the extended to the retracted configuration). A second end of the first linkage may be connected, for example pivotally connected, to the main strut. The second ends of the first and second linkages may be connected to the main strut at points spaced apart from each other along the longitudinal axis of the strut. For example, the second linkage may be connected to the main strut at a point below that at which the first linkage is connected to the main strut. This may assist in better distributing landing gear loads in the main strut. The first and/or second end of the first linkage may be connected to the second linkage and/or the -6 -main strut respectively for rotation relative to the second linkage and/or the main strut about an axis lying substantially parallel to the axis about which the wheels of the landing gear rotate and/or lying substantially parallel to the spanwise axis of the aircraft.

[0015] The first linkage may comprise two link members, a first link member connected at a first end to the trailing arm (said first link member therefore comprising the first end of the first linkage) and at a second end to a second link member of the first linkage. The second link member of the first linkage may be connected at a first end to the first link member of the first linkage and at a second end to the main strut (said second link member therefore comprising the second end of the first linkage). The first and second link members may be pivotally connected. The second linkage may be connected to the first linkage in the region of, for example at, the point at which the first and second link members of the first linkage are connected.

[0016] The main strut may comprise an elongate body configured to transfer landing gear loads from one or more wheels mounted to one end of the main strut to the aircraft. The main strut may comprise a shock absorber configured to damp movement of said one or more wheels mounted on the main strut. For example, the main strut may comprise a cylinder and an arm mounted therein for movement relative to the cylinder. The main strut may be an oleo strut. The landing gear assembly may comprise a conventional set of torque links connecting the arm to the cylinder to prevent rotation of the arm relative to the cylinder about the longitudinal axis of the strut. The landing gear assembly may be configured such that the trailing arm rotates relative to the main strut during compression of the main strut.

[0017] The landing gear assembly may be configured for mounting on an aircraft, for example wherein the landing gear assembly is moveable, for example rotatable and/or pivotable, relative to the aircraft. The landing gear assembly may comprise a pintle for mounting the landing gear assembly on an aircraft. The pintle may define the axis about which the main strut rotates and/or pivots as it moves between the extended and retracted positions (hereafter 'the pintle axis'). The pintle may be mounted on, for example integrally formed with, the main strut. The pintle may be mounted on the main strut in the region of a first (upper) end of the main strut. The main strut may comprise a main fitting, for example integrally formed with or mounted to the main strut, for example the cylinder. The main fitting may comprise the pintle.

[0018] The landing gear assembly may comprise a control linkage (which may be a rigid linkage as discussed further below), for example a control linkage having a first end and a second end. It may be that the first end of the control linkage is connected to the second linkage, for example in the region of the connection between two of the link members of the second linkage, for example in the region of the connection between the first and second link members of the second linkage. It may be that a second end of the control linkage is configured for connection to the aircraft proximate the upper end of the main strut, for example proximate the pintle (if present). The landing gear assembly may be configured such that, in use, rotation of the main strut from the extended to the refracted position results in movement of the second end of the control linkage relative to the main strut, for example along the length of the main strut. In the case that the control linkage is connected to the second linkage, said movement may cause the second linkage to move from the extended to the retracted configuration. Thus, the landing gear may be configured such that the action of the control linkage results in the landing gear being shortened automatically as the landing gear retracts. The control linkage may be connected to the landing gear assembly such that rotation of the landing gear assembly from the extended to the retracted position causes rotation of the control linkage. As the main strut rotates between its extended and retracted positions (i.e. the positions it occupies when the landing gear assembly is in the extended and retracted positions respectively) a point on the main strut may pass through a series of points lying along a main-strut locus. Likewise, as the control linkage rotates between its extended and retracted positions, a point on the control linkage, for example the first end of the control linkage, may pass through a series of points lying along a second, different, locus, which may be referred to as a control-linkage locus and/or in the case that the control linkage is rigid, a rigid-linkage locus. The landing gear assembly may be configured such that the locus of the first end of the control linkage differs from the locus of the main strut (or a given point thereon) and/or the second linkage (or a given point thereon) such that, in use, rotation of the main strut from the extended to the retracted position results in movement -8 -of the second end of the control linkage relative to the main strut, for example along the length of the main strut, for example downwards along the main strut. The landing gear assembly may be configured such that the control linkage rotates about a centre of rotation offset from the centre of rotation of the main strut. It may be that the main strut and the control linkage move from their respective extended positions to their retracted positions by rotating about a main-strut centre of rotation and a rigid-linkage centre of rotation respectively, the rigid-linkage centre of rotation being offset from the main-strut centre of rotation such that the main-strut locus and the control-linkage (or rigid-linkage) locus differ (particularly if the length of the control-linkage is fixed).

[0019] The landing gear assembly may be configured such that movement of the main strut from its extended position to its retracted position causes movement of the control linkage from its extended position to its retracted position. It may be that the control linkage is connected to the second linkage such that as the main strut (to which the second linkage is mounted) rotates about its axis of rotation from the extended position to the retracted position the second end of the control linkage moves with it about the same axis of rotation, for example the rotational position (but not the radial position) about the main-strut axis of rotation of the first end of the control linkage is fixed relative to the rotational position of the second linkage arm. It will be appreciated that the rotational position of the point at which the second (and first) linkage is mounted to the main strut is similarly fixed relative to the rotational position of the main strut. The connection between the control linkage and the second linkage (and/or the first linkage and the trailing arm and/or the first and/or second linkage and the main strut) may prevent movement of the control linkage relative to the second linkage arm (and/or the first linkage relative to the trailing arm and/or the first and/or second linkage relative to the main strut) about the axis of rotation of the main strut, e.g. the pintle axis.

100201 The control linkage may comprise one or more link members. The length of the control linkage, for example the distance between a first end of the linkage and a second end of the linkage, may be fixed. Thus, the control linkage may be said to be rigid. The control linkage may comprise a single link member, for example a control rod. -9 -

[0021] The landing gear assembly may comprise a mount. The second end of the control linkage may be pivotally connected to the mount in the region of a first end of the mount. The first end of the mount may be spaced apart from upper end of the main strut (for example the pintle) such that the rigid-linkage centre of rotation is offset from the main-strut centre of rotation. The mount may be connected to the aircraft in the region of, for example at, a second end of the mount. The mount may be mounted on the pintle, for example for rotation thereabout.

100221 The landing gear may be mounted for movement between an extended and retracted position. In normal operation, the landing gear is in the extended position for landing and taxiing and the retracted position during flight, for example during cruise. The main strut may be substantially vertical when the landing gear is in the extended position. The main strut may be substantially horizontal when the landing gear is in the retracted position. The position of each element of the landing gear, for example the main strut, first linkage, second linkage, control linkage and/or wheels, when the landing gear is in the extended and retracted positions may be referred to as the extended and the retracted positions respectively.

100231 The landing gear assembly may comprise at least one wheel, for example two wheels. The landing gear assembly may comprise no more than two wheels. The landing gear may comprise two wheels mounted to the main strut, for example the lower end of the main strut. It may be that the landing gear assembly does not include a landing gear bogie. The landing gear assembly may comprise an axle, for example a single axle, for example configured to connect a pair of wheels to the main strut.

[0024] The landing gear assembly may be suitable for use on a commercial passenger aircraft, for example an aircraft suitable for transporting at least 50, for example at least 100, for example at least 200 passengers. For the purposes of the present specification the term commercial passenger aircraft also covers aircraft of an equivalent size configured for cargo and/or used on a non-commercial basis.

[0025] It will be appreciated that as used herein the terms 'down' and 'downwards' refer to movement in a direction away from the aircraft and towards the wheels of the landing -10 -gear. The terms 'up' and 'upwards' refer to movement in a direction towards the aircraft and away from the wheels of the landing gear.

[0026] In a second aspect of the invention there is provided a landing gear assembly comprising one or more of a main strut, a trailing arm and a rigid linkage. The landing gear assembly may have a first end for mounting to an aircraft for movement of the main strut between a first (extended) position (i.e. the position occupied by the main strut when the landing gear is extended, e.g. for landing, take-off and taxiing) and a second (retracted) position (i.e. the position occupied by the main strut when the landing gear is retracted, e.g. during flight). It may be that the main strut, for example the lower end of the main strut, moves between a plurality of points located along a main-strut locus as it moves between its first position and its second position. The trailing arm may be rotatably mounted to the main strut, for example at a point located partway along the length of the trailing arm, thereby dividing the trailing arm into a first portion located on one side of the main strut and a second portion located on the other side of the main stmt. The second portion of the trailing arm may configured for connection to at least one wheel. The rigid linkage may be connected in the region of a first end to the first portion of the trailing arm and/or may be configured to be pivotally connected in the region of a second end to the aircraft, for example in the region of an upper end of the main strut. The rigid linkage may be configured for movement between a first (extended) position occupied by the rigid linkage when the landing gear is extended and a second (retracted) position occupied by the rigid linkage when the landing gear is retracted. It may be that the rigid linkage, for example the first end of the rigid linkage, moves between a plurality of points located along a rigid-linkage locus as it moves between its first position and its second position. It may be that the main-strut locus differs from the rigid-linkage locus, such that the first end of the rigid linkage moves relative to the main strut as the main strut and rigid linkage move from their respective first positions to their respective second positions thereby moving the first portion of the trailing arm downwards and a wheel mounted on the second portion of the trailing arm upwards and shortening the landing gear.

[0027] Providing a rigid linkage having a different locus to the main strut may allow for a mechanically simple solution to the problem of providing a landing gear that is shorter when retracted than extended.

[0028] It will be appreciated that, as used herein, the term 'rigid linkage' refers to a linkage in which the length of the linkage is fixed (i.e. the straight-line distance between the first end and the second end of the linkage remains constant). The rigid linkage may have any features of the control linkage as described above except where such features are incompatible with its being a rigid linkage.

[0029] The length of the rigid linkage may be greater than or equal to the length of the main strut (when the main strut is compressed to its fullest extent in the case that the main strut is compressible). The rigid linkage may be pivotally connected in the region of a second end to the aircraft, for example to the main fitting, in the region of an upper end of the main strut, and to a trailing arm mounted to the lower end of the main strut, thus the rigid linkage may extend along the majority, for example substantially all, of the length of the main strut.

[0030] The radius of curvature of the main strut-locus and rigid-link locus may differ. Additionally, or alternatively, the main strut-locus and rigid-link locus may comprise curves having the same radius but an offset centre of rotation. Such a differing locus may be provided by a fixed length rigid linkage having a centre of rotation offset from the centre of rotation of the main strut.

[0031] The landing gear assembly may be configured such that movement of the main strut from its first position to its second position causes movement of the rigid linkage from its first position to its second position. It may be that the rigid linkage is connected to the trailing arm such that as the main strut (upon which the trailing ann is mounted) rotates about its axis of rotation from the first position to the second position the second end of the rigid linkage moves with it about the same axis of rotation, for example the rotational position (but not the radial position) about the main-strut axis of rotation of the first end of the rigid linkage is fixed relative to the rotational position of the trailing arm. It will be appreciated that the rotational position of the point at which the trailing arm is mounted to the main strut is similarly fixed relative to the rotational position of the main -12 -strut. The connection between the rigid linkage and the trailing arm (and/or the trailing arm and the main strut) may prevent movement of the rigid linkage relative to the trailing arm (and/or the trailing arm relative to the main strut) about the axis of rotation of the main strut, e.g. the pintle axis.

[0032] It will of course be appreciated that features described in relation to the first aspect of the present invention may be incorporated into the second aspect of the present invention (and vice versa). For example, the landing gear assembly of the second aspect may incorporate features of the main strut, trailing arm, first linkage, second linkage, and/or control linkage etc. described above.

[0033] In a third aspect of the invention, there is provided an aircraft comprising a landing gear assembly in accordance with the first or second aspects.

100341 In a fourth aspect of the invention, there is provided a method of operating a landing gear assembly comprising one or more of a main strut, a trailing arm mounted on the main strut, a first linkage connected to the main strut and the trailing arm, a second linkage connected to the first linkage and the main strut, and at least one wheel mounted on the trailing arm. The method may comprise one or more of the following steps; while the landing gear assembly is in an extended position and the second linkage in an extended configuration, the first linkage moves from a retracted configuration towards an extended configuration in response to a landing gear load on the at least one wheel; as the landing gear assembly moves from the extended position to a retracted position, the second linkage moves from an extended configuration to a retracted configuration thereby causing the first linkage to move from a retracted configuration to an extended configuration and the trailing arm to rotate relative to the main strut such that the at least one wheel moves upwards.

100351 Methods in accordance with the present aspect of the invention may facilitate reaction of landing gear loads, for example by a compressible main strut, while also allowing the length of the landing gear to reduce when the landing gear is retracted.

-13 - [0036] It may be that when the second linkage is in the extended configuration, the second linkage limits the movement of a portion, for example a first link, of the first linkage It may be that a second link of the first linkage is free to pivot relative to the first linkage when the second linkage is the extended configuration. Thus, it may be that the first linkage moves from a retracted configuration towards an extended configuration in response to a landing gear load on the at least one wheel. That is to say, rotation of the trailing arm as a consequence of a landing gear load, for example a portion of the weight of the aircraft on the wheel, for example during taxiing and/or landing, may cause the first linkage to move from the retracted configuration towards the extended configuration, for example to an intermediate (or 'on-ground') configuration. The length of the first linkage in the intermediate configuration may be greater than the length of the first linkage in the retracted configuration but less than the length of the first linkage in the extended configuration.

[0037] In a fifth aspect of the invention, there is provided a method of operating a landing gear assembly comprising one or more of a main strut; a trailing arm mounted on the main strut; a rigid linkage connected at one end to the trailing arm at the other end to the aircraft in the region of an upper end of the main strut; and at least one wheel mounted on the trailing arm. The method may comprise one or more of the following steps; retracting the landing gear by moving the main strut (or a given point thereon, for example the lower end thereof) along a main-strut locus from an extended position to a retracted position; allowing the rigid linkage (or a given point thereon, for example the second end thereof) to move along a rigid-linkage locus in response to the movement of the main strut; and wherein the main-strut locus differs from the rigid-linkage locus such that the movement of the rigid linkage relative to the main strut causes the trailing arm to -14 -rotate relative to the main strut thereby moving the at least one wheel upwards and shortening the landing gear assembly.

[0038] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

100391 Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 shows an aircraft comprising a landing gear in accordance with first or second embodiments of the invention; Figure 2 shows a perspective view of a landing gear in accordance with a first example embodiment in (a) the extended configuration and (b) the retracted configuration; Figure 3 shows a side view of a landing gear in accordance with the first example embodiment in (a) the extended configuration, (b) the on-ground configuration and (c) the retracted configuration; Figure 4 shows a perspective view of a landing gear in accordance with a second example embodiment in (a) the extended configuration and (b) the retracted configuration; Figure 5 shows a side view of a landing gear in accordance with the second example embodiment in (a) the extended configuration, (b) the on-ground configuration and (c) the retracted configuration; -15 -Figure 6 shows a close up view of a portion of a landing gear in accordance with the second example embodiment in (a) the extended configuration and (b) the retracted configuration; Figure 7 shows a flow chart of a method of using a landing gear in accordance with the first embodiment; and Figure 8 shows a flow chart of a method of using a landing gear in accordance with the second embodiment.

DETAILED DESCRIPTION

[0040] Figure 1 shows an aircraft 1 including two main landing gear 4 in accordance with either example embodiment discussed hereafter. The aircraft comprises fuselage 3 and wings 5, a nose landing gear 2 is mounted on fuselage 3 and a main landing gear 4 is mounted to each wing 5.

[0041] Figure 2 shows a close up view of a main landing gear 4 in accordance with a first example embodiment in (a) the extended and (b) the retracted positions. The arrow A in Fig. 2(a) indicates the forward direction. Landing gear 4 comprises a main strut 6 connected to the aircraft 1 via a pintle (not shown) for rotation about a pintle axis labelled B in Fig 2(a) via a main fitting 8 located at an upper end of the main strut 6. In the present embodiment the main strut 6 is an oleo or shock strut comprising a cylinder 6a and an arm 6b mounted for longitudinal movement relative to the cylinder 6a. It will be appreciated that some standard elements of the structure, for example main fitting 8, of the landing gear 4 have been simplified in these Figures. A trailing arm 10 is pivotally mounted to a lower end of the main strut 6. A pair of wheels 12 are mounted to one end of the trailing arm 10 (the lower end of the trailing arm 10 in Fig. 3(a)). A first end 14a (see Fig. 3) of a rigid linkage 14 is pivotally connected to the other end of the trailing arm 10 (the upper end I Ob of the trailing arm in Fig. 3(a)). The connection between the first end 14a of rigid linkage 14 and the trailing arm 10 provides two degrees of freedom; rotation of the trailing arm 10 relative to the rigid linkage 14 about a first axis lying -16 -substantially parallel to the pintle axis B and a second axis lying substantially perpendicular to the pintle axis B. A second end 14b (see Fig. 2(b)) of the rigid linkage 14 is connected to a first end 16a of a mount 16 for rotation about a point laterally offset from the pintle axis B. Mount 16 (sometimes referred to as a 'pork chop') takes the form of an elongate member connected at a second end 16b to the aircraft structure 18, for example a wing spar (not shown), and is also mounted on the pintle such that the main strut 6 rotates relative to the mount 16 about the pintle axis B. In other embodiments, mount 16 is absent and the second end 14b of the rigid linkage 14 is connected directly to the aircraft structure 18, again at a point spaced apart from the pintle axis B and proximate the upper end of the main strut 6. A foldable side-stay 20 extends inboard and upwards from main strut 6 and is connected at one end to the main strut 6 and at the other end to a pair of reaction bars 22. Reaction bars 22 extend in a spanwise direction from the end of second side-stay member 20b to the pintle. A side-stay lock linkage 24 extends between main fitting 8 and side-stay 20 and is connected to a locking actuator 26 mounted on the side-stay 20. In other embodiments the side-stay 20 and/or reaction bars 22 may be absent. A conventional pair of torque links 28 connects the cylinder 6a and arm 6b. In the extended position shown in Fig. 2(a) the lower end of main strut 6 and wheel 12 are located outside a landing gear bay 30 formed in aircraft 1. Dashed line Ci shows the locus of a point on the main strut 6 as it moves between the extended position shown in Fig. 2(a) and the retracted position as shown in Fig. 2(b). Dashed line C2 shows the locus of a point located in the region of the first end 14a of the rigid linkage 14 as it moves between the extended position shown in Fig. 2(a) and the retracted position as shown in Fig. 2(b). The distance between the lines CI and C, increases as they approach the retracted position.

100421 In the retracted position as shown in Fig. 2(b), the main strut 6 and rigid linkage 14 are rotated by approximately 90 degrees about the pintle axis B in comparison with their positions in Fig. 2(a) so that the main stmt 6 and wheels 12 are contained within landing gear bay 30.

100431 Figure 3 shows the landing gear 4 of the first embodiment in the (a) extended, (b) on-ground and (c) retracted configurations. It will be appreciated that while (a) and (b) -17 -are side views of the landing gear 4, (c) is a top-down view, the purpose of Fig. 3 being to allow a comparison in the arrangement of rigid linkage 14 and trailing arm 10. Fig. 3(a) shows the configuration of the landing gear 4 when the landing gear is extended and prior to landing. In Fig. 3(b) which shows the configuration of the landing gear 4 when the aircraft is on the ground (i.e. when there is weight on the wheels 12) the main strut 6 is compressed in comparison to its position in Fig. 3(a). The wheels 12 are therefore closer to the cylinder 6a and the landing gear is shorter overall. In comparison to its position in Fig. 3(a) the first end of the rigid linkage 14 has moved forwards away from the main strut 6, and the upper end I Ob of the trailing arm 10 has moved downwards. In Fig. 3(c) which shows the configuration of the landing gear 4 when the landing gear is retracted, the first end of the first end of the rigid linkage 14 has moved further forward away from the main strut 6, and the upper end 10b of the trailing arm 10 has moved further downwards in comparison to their positions in Fig. 3(a), and the wheels 12 are therefore closer to the cylinder 6a and the cylinder 6 is shorter overall in comparison to Fig. 3(a). 100441 In landing gear in accordance with the first example embodiment, the offset between the centre of rotation of the rigid linkage 14 and the centre of rotation of the main strut results in the locus CI differing from the locus C, such that movement of the landing gear from the extended position (as shown in Fig. 2(a)) to the retracted position (as shown in Fig. 2(b)) causes the first end 14a of the rigid linkage 14 to move from a first position relative to the main strut 6 (and in particular the cylinder 6a) to a second position relative to the main stmt 6, the first position being spaced apart from the second position along the longitudinal axis of the main strut. This in turn causes the first end 14a of the rigid linkage 14 to exert a force on the upper end 10b of the trailing arm 10 which causes the trailing arm 10 to rotate about the end of the main strut 6. As the rigid linkage acts to push the upper end 10b of the trailing arm 10 away from the main fitting 8 the lower end of the trailing arm 10 moves closer to the main fitting 8 thereby moving wheels 12 closer to the main fitting 8 and shortening the length of the landing gear 4.

[0045] As described above, landing gear in accordance with the first embodiment provide a mechanically simple way of automatically shortening a trailing arm landing gear during retraction of the landing gear. The mechanical simplicity of the solution of the first -18 -embodiment may increase reliability and/or reduce the additional weight added by the linkage. Additionally or alternatively, the connection between the linkage 14 and trailing arm 10 is located closer to the wheel 12 than some prior art solutions and accordingly inspection of the mechanism is facilitated.

[0046] Figure 4 shows a close up view of a main landing gear 4 in accordance with a second example embodiment in (a) the extended and (b) the retracted positions. The arrow A in Fig. 4(a) indicates the forward direction, elements that are similar as between the first and second embodiments have been indicated in the second embodiment using their reference numeral from the first embodiment incremented by 100 (i.e. landing gear 4 in the first embodiment is referred to as landing gear 104 in the second embodiment). The arrangement of the main strut 106, pintle axis B, main fitting 108, side-stay 120 and associated side-stay lock linkage 124 and side-stay locking actuator 126, reaction bars 122 and torque links 128 is substantially as described above for the first embodiment. As in the first embodiment a trailing arm 110 is pivotally mounted to a lower end of the main strut 106. A pair of wheels 112 are mounted to one end of the trailing arm 110 (the lower end of the trailing arm 110 in Fig. 4(a)). In contrast to the first embodiment, a drop-link 150 connects the trailing arm 110 to the main strut 106. The drop-link 150 comprises two drop-link members 150a, 1506; a first drop-link member 150a pivotally connected at one end to an upper end 110b of the trailing arm 110 and at the other end to a second drop-link member 150b; a second drop-link member 15013 pivotally connected at one end to the a first drop-link member 150a and at the other end to the main strut 106 (see also Fig. 5(a) which shows this more clearly). A lock linkage 152 extends between the drop-link 150 and the main strut 106. The lock linkage 152 comprises two lock members I52a, 152b; a first lock member I52a pivotally connected at one end to the drop-link 150 and at the other end to a second lock member 152b: a second lock member 152b pivotally connected at one end to the a first lock member 152a and at the other end to the main strut 106. The second lock member 152b is pivotally connected to the main strut 106 at a point spaced apart along the length of the main strut 106 from the point at which the second drop-link member 150b is connected to the main strut. In other embodiments the degree of spacing between these two points may be different from that -19 -shown in the present embodiment. In the present embodiment the first lock member 152a is pivotally connected to the drop-link 150 at the point at which the first drop-link member 150a and the second drop-link member 150b are connected. In other embodiments the lock linkage 152 may be connected to the drop-link 150 at a different location. A drop-link spring 154 (shown in close up in Fig. 6) extends between the second drop-link member 150b and the second lock member I52b. A first end 114a of a rigid linkage 114 is pivotally connected to the lock linkage 152 at the point where the first lock member 152a and the second lock member 152b are connected. Where the first lock member I 52a connects to the second lock member I52b the end of the second lock member I52b extends beyond the point of connection with the first lock member 152a to form a stop 153 (see Fig. 6(b)). A second end 114b of the rigid linkage 114 is pivotally connected to a mount 116 for rotation of the rigid linkage 114 relative to the mount 116 about a point offset from the pintle axis B. The mount 116 is substantially as described with reference to the first embodiment. In other embodiments, mount 116 is absent and the second end 1146 of the rigid linkage 114 is connected directly to the aircraft structure 118. In the extended position shown in Fig. 4(a) the lower end of main strut 106 and wheels 112 are located outside a landing gear bay 130 formed in aircraft 1.

[0047] In the retracted position as shown in Fig. 4(b), the main strut 106 is rotated by approximately 90 degrees about the pintle axis B in comparison with its position in Fig. 4(a) so that the main strut 106 and wheels 112 are contained within landing gear bay 130. [0048] Figure 5 shows the landing gear 104 of the second embodiment in the (a) extended, (b) on-ground and (c) retracted configurations. It will be appreciated that while (a) and (b) are side views of the landing gear 104, (c) is a top-down view, the purpose of Fig. 5 being to allow a comparison in the arrangement of drop-link 150, lock linkage 152, rigid linkage 114 and trailing arm 110. Fig. 5(a) shows the configuration of the landing gear 104 when the landing gear is extended and prior to landing. In the Fig. 5(a) configuration the angle between the longitudinal axis of first lock member 152a and second lock member 152b is slightly less than 180 degrees when measured clockwise from the second lock member152b to the first lock member 152a) thus lock linkage 152 is almost straight. In Fig. 5(b) which shows the configuration of the landing gear 104 -20 -when the aircraft is on the ground (i.e. when there is weight on the wheels 112) the main strut 106 is compressed in comparison to its position in Fig. 5(a). The wheels 112 are therefore closer to the cylinder 106a and the landing gear is shorter overall. The angle between the longitudinal axis of first lock member 152a and second lock member 152b remains unchanged (and accordingly the position of second drop-link member 150b remains unchanged) in comparison to its Fig. 5(a) position. The end of the first drop-link member 150a which is attached to the trailing arm 110 has moved away from the main strut and the upper end 110b of the trailing arm 110 has moved downwards. The angle between the longitudinal axis of the first drop-link member I 50a and the second drop-link member I 50b, when measured clockwise from the second drop-link member I 50b is increased in comparison with Fig. 5(a) but remains acute (i.e. less than 90 degrees). In Fig. 5(c) which shows the configuration of the landing gear 104 when the landing gear is retracted, the lower end of rigid linkage 114 has moved closer to the trailing arm 1 I 0 relative to its position in Figs. 5(a) and (b). The angle between the longitudinal axis of first lock member 152a and second lock member 152b has increased as is now reflex (i.e. greater than 180 degrees). Thus drop-link linkage is no longer almost straight but is now folded. The end of the first drop-link member 150a which is attached to the trailing arm 110 has moved further away from the main strut 106 and the upper end 1106 of the trailing arm 110 has moved downwards in comparison to their positions in Fig. 5(a), and the wheels 112 are therefore closer to the cylinder 106a and the cylinder 106a is shorter overall in comparison to Fig. 5(a). The angle between the longitudinal axis of the first drop-link member 150a and the second drop-link member I 50b, when measured clockwise from the second drop-link member 150b is increased in comparison with Fig. 5(a), and has become obtuse i.e. greater than 90 degrees but less than 180 degrees).

100491 In landing gear in accordance with the second example embodiment, the offset between the centre of rotation of the rigid linkage 114 and the centre of rotation of the main strut 106 means that movement of the landing gear 104 from the extended position (as shown in Fig. 4(a)) to the retracted position (as shown in Fig. 4(b)) causes the first end 114a of the rigid linkage 114 to move from a first position relative to the main strut 106 (and in particular the cylinder 106a) to a second position relative to the main strut -21 - 106, the first position being spaced apart from the second position along the longitudinal axis of the main strut 106. This in turn causes the first end 114a of the rigid linkage 114 to exert a force on the lock linkage 152 pushing the point at which rigid linkage 114 is attached to the lock linkage 152 (i.e. the intersection between the first lock member 152a and the second lock member 152b) downwards causing the lock linkage 152 to fold and consequently the length of the lock linkage 152 to reduce. As the lock linkage 152 folds, drop link spring 154 is stretched thereby increasing its elastic potential energy. The lock linkage 152 (in particular first lock member 152a) in turn exerts a force on the drop linkage 150 and in particular the point at which lock linkage 152 is attached to drop linkage 150 (i.e. the intersection between the first drop-link member I 52a and the second drop-link member 152b) thereby causing the first drop-link member 152a to exert a force on the upper end 110b of the trailing arm 110 which causes the trailing arm 110 to rotate about the end of the main strut 106. As the drop-link 150 acts to push the upper end 110a of the trailing arm 110 away from the main fitting 108 the lower end 110b of the trailing arm 110 moves closer to the main fitting 108 thereby moving wheels 112 closer to the main fitting 108 and shortening the length of the landing gear 104. During extension of the landing gear, as the wheels 112 drop down, the trailing arm 110 rotates to fold the drop link 150 which in turn unfolds the lock linkage 152. The energy stored in drop link spring 154 brings lock linkage 152 over-centre into a straight configuration and stop 152 prevents further movement of the first lock member 152a and second lock member 152b. [0050] The arrangement of the first and second linkages, and in particular their separate connection to the main strut may provide an improved load distribution in the strut as compared to prior art arrangements.

[0051] Figure 6 shows a flow chart of a method of operating a landing gear in accordance with the first example embodiment. The method comprises rotating 80 the main strut 6 from an extended position to a retracted position by moving a point on the main strut 6 along a main-strut locus CI. As a consequence of rotating 80 the main strut 6, the first end of the rigid linkage moves 82 along a rigid-linkage locus C2, thereby rotating 84 trailing arm 10 to move 86 wheel 12 upwards thereby shortening the landing gear 4.

-22 - [0052] Figure 7 shows a flow chart of a method of operating a landing gear in accordance with the second example embodiment. Upon landing or taxiing 190 (i.e. while the landing gear is in the on-ground configuration) the method comprises maintaining 192 the lock linkage 152 in an extended configuration and allowing 194 the drop linkage 150 to move between 196 (i.e. fold and unfold) an intermediate position and the refracted configuration so that main strut 106 can compress and/or extend 198. To retract 199 the landing gear following take-off the method comprises rotating 180 the main strut 106 from an extended position to a retracted position by moving a point on the main strut 106 along a main-strut locus CI. As a consequence of rotating 180 the main strut 106, the first end 114a of the rigid linkage moves 182 along a rigid-linkage locus C2, thereby folding 183 the lock linkage 152 which in turn unfolds/extends 185 the drop linkage 150 thereby rotating 184 trailing arm 110 to move 186 wheel 112 upwards thereby shortening the landing gear 104.

[0053] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.

100541 Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

-23 -CLAIMSI. A landing gear assembly for mounting to an aircraft, the landing gear assembly comprising; - a main strut - a trailing arm rotatably mounted to the main strut, the trailing arm being mounted to the main stmt at a point located partway along the length of the trailing arm, thereby dividing the trailing arm into a first portion located on one side of the main strut and a second portion located on the other side of the main strut; the second portion of the trailing arm being configured for connection to at least one wheel; - a first linkage being connected to the first portion of the trailing arm and to the main strut and configured for movement between an extended and a retracted configuration; a second linkage being connected to the first linkage and to the main strut and configured for movement between an extended and a retracted configuration; and wherein movement of the second linkage from the extended to the retracted configuration causes movement of the first linkage from the retracted to the extended configuration, said movement of the first linkage causing a rotation of the trailing arm that moves a free end of the second portion upwards and thereby shortens the landing gear.
2. A landing gear assembly according to claim 1, wherein the first and/or second linkage is configured to move from the extended to the retracted configuration by folding and from the retracted to the extended configuration by unfolding.
3. A landing gear assembly according to claim 1 or claim 2, wherein the first and/or second linkage each comprises two pivotally connected link members.
-24 - 4. A landing gear assembly according to claim 3, wherein the first linkage comprise two pivotally connected link members and the second linkage connects to the first linkage in the region of, for example at, a connection point between said two link members.
5. A landing gear assembly according to any previous claim, wherein the main strut is configured for mounting to the aircraft for rotation between an extended position and a retracted position, the landing gear assembly further comprising a control linkage, a first end of the control linkage being connected to the second linkage, the landing gear assembly being configured such that rotation of the main strut from the extended to the retracted position results in movement of the second end of the control linkage relative to the main strut thereby moving the second linkage from the extended to the retracted configuration.
6. A landing gear assembly according to claim 5, wherein the landing gear assembly is configured such that, in use, a second end of the control linkage is connected to the aircraft proximate an upper end of the main strut.
7. A landing gear assembly according to claim 6, further comprising a pintle and a mount, the main strut being pivotally connected to the pintle at an upper end for rotation thereabout and the second end of the rigid linkage being pivotally connected to the mount in the region of a first end of the mount, the first end of the mount being spaced apart from the pintle such that a rigid-linkage centre of rotation is offset from a main-strut centre of rotation.
8. A landing gear assembly according to claim 6, wherein the control linkage is a rigid linkage.
9. A method of operating a landing gear assembly comprising a main strut, a trailing arm mounted on the main strut, a first linkage connected to the main strut and the trailing arm, a second linkage connected to the first linkage and the main strut, and at least one wheel mounted on the trailing arm, the method comprising the following steps; -25 - - while the landing gear assembly is in an extended position and the second linkage in an extended configuration, the first linkage moves from a retracted configuration towards an extended configuration in response to a landing gear load on the at least one wheel; as the landing gear assembly moves from the extended position to a retracted position, the second linkage moves from an extended configuration to a retracted configuration thereby causing the first linkage to move from a retracted configuration to an extended configuration and the trailing arm to rotate relative to the main stmt such that the at least one wheel moves upwards.
10. A landing gear assembly comprising; - a main strut, comprising a first end for mounting to an aircraft for movement of the main strut between a first position occupied by the main strut when the landing gear is extended and a second position occupied by the main strut when the landing gear is retracted, the main strut moving between a plurality of points located along a main-strut locus as it moves between its first position and its second position; a trailing arm rotatably mounted to the main strut, the trailing arm being mounted to the main strut at a point located partway along the length of the trailing arm, thereby dividing the trailing arm into a first portion located on one side of the main strut and a second portion located on the other side of the main strut; the second portion of the trailing arm being configured for connection to at least one wheel; - a rigid linkage connected in the region of a first end to the first portion of the trailing arm and configured to be pivotally connected in the region of a second end to the aircraft in the region of an upper end of the main strut, the rigid linkage being configured for movement between a first position occupied by the rigid linkage when the landing gear is extended and a second position occupied by the rigid linkage when the landing gear is retracted, the first end of the rigid linkage -26 -moving between a plurality of points located along a rigid-linkage locus as it moves between its first position and its second position, and wherein the main-strut locus differs from the rigid-linkage locus such that the first end of the rigid linkage moves relative to the main strut as the main strut and rigid linkage move from their respective first positions to their respective second positions thereby moving the first portion of the trailing arm downwards and a wheel mounted on the second portion of the trailing arm upwards and shortening the landing gear.
I I. A landing gear assembly according to claim 10, wherein the rigid linkage is connected to the trailing arm such that movement of the main strut from its extended position to its retracted position causes movement of the rigid linkage from its extended position to its retracted position.
12. A landing gear according to claim 11, wherein the main strut-locus and rigid-link locus comprise curves having the same radius and an offset centre of rotation.
13. A landing gear assembly according to any of claims 10 to 12, wherein the rigid linkage comprises a single member.
14. A landing gear according to any of claims 10 to 13 wherein the length of the rigid linkage is be greater than or equal to the length of the main strut
15. An aircraft comprising a landing gear assembly according to any of claims 1 to 8 or I 0 to 14.