A commercial airliner

Abstract

A commercial airliner (2, figure 1) comprising a trailing-link type main landing gear 24 is disclosed. The landing gear has a rigid support arm 20 and a pivotable trailing arm 32 coupled thereto. The

Description

BACKGROUND OF THE INVENTION

[0001] The present disclosure relates to the field of commercial airliners. It relates particularly, but not exclusively, to a commercial airliner, a commercial airliner trailing-link type main landing gear, and a method of absorbing shocks in a trailing-link type main landing gear of a commercial airliner.

[0002] In the field of commercial airliners, rather than other technical fields such as military aircraft, UAVs and aircraft for general aviation, most main landing gear use an oleo-pneumatic shock absorber or “Oleo strut”. These are well known in the art. In brief, these shock absorbers have a piston which is reciprocally movable within a chamber or (often referred to as a cylinder). The cylinder is filled with both a liquid (such as hydraulic fluid) and a gas (such as nitrogen or air). When the shock absorber is loaded, its two ends are urged towards one another, which pushes the piston further into the cylinder. This movement of the piston compresses the gas within the cylinder, and the compressed gas in turn acts on the piston and urges it back out of the cylinder, providing a restorative force. The Oleo strut therefore acts as a gas spring. Equally, movement of the piston within the cylinder also displaces the liquid in the cylinder, for instance forcing it through ducts in the cylinder and / or the piston, which dissipates energy through viscous friction. The Oleo strut therefore acts as a damper or dashpot, as well as a gas spring.

[0003] Generally speaking, in commercial airliners the Oleo struts extends downward from the aircraft and directly support an axle or bogey on which wheels are provided. The Oleo struts are sometimes positioned at a slight angle to the vertical, but beyond a limit a few degrees from vertical the internal friction within the struts obstructs their function. When the aircraft rests on its landing gear, its weight and the resulting ground reaction force load the Oleo strut as described above. Any shocks the aircraft experiences, such as when touching down or when hitting a bump while taxiing, are absorbed by the Oleo strut - the strut compresses and the wheels move upward towards the body of the aircraft, while the Oleo strut dissipates energy, then the restorative force from the compressed gas returns the wheels to their default position.

[0004] In a few military aircraft, the nose landing gear does not use an Oleo strut but rather uses a liquid spring assembly. Liquid springs share some similarity with Oleo struts in that they utilise a piston reciprocally movable within a chamber. However, whereas Oleo struts utilise compression of a gas to provide the restorative force, in liquid springs the chamber does not contain any gas and the restorative force is provided by compression of liquid within the chamber. In many cases liquid spring assemblies are also configured to act as shock absorbers, with movement of the piston moving some of the liquid in the chamber and dissipating energy in similar fashion to Oleo struts.

[0005] The reason liquid springs have seen successful use only in military aircraft is due to their short stroke length and considerably greater stiffness. In essence, the “ride quality” they offer is generally excessively harsh. Some military aircraft are built sufficiently robustly and / or are sufficiently light to be able to tolerate the shocks involved, particularly for nose landing gear which generally support less of an aircraft’s weight. Also, military aircraft often have a very short service interval so fatigue from excessive shock loading has a shorter time-frame in which to propagate. Commercial airliners, however, weigh considerably more, are designed with the focus on efficiency rather than absolute strength, and work with long service intervals. Thus, Oleo struts have remained the sole choice for commercial airliners.

[0006] In aircraft manufacture there is a drive towards using wings which have a higher aspect ratio (i.e. wings with a longer span and a shorter chord), since all else being equal they are more efficient. Such wings are usually vertically thinner as well, so as to keep the thickness to chord ratio of the wing within a desired range. Further, there is often a desire to move towards proportionally thinner wings (i.e. those of a lower thickness to chord ratio), since this too can provide aerodynamic benefits. However, due to their reduced chord and / or thickness such wings have less space available into which landing gear can be stowed.

[0007] Also, there are several conflicting requirements for use of such wings. For example, for swept wings a higher aspect ratio results in the centre of gravity of the wings, and thus the aircraft as a whole, being further aft. In aircraft where the main landing gear are attached to the wings, there is a limit on how far aft the centre of gravity can be located (since the centre of gravity must be forward of the ground contact point of the main landing gear). Exacerbating this is the fact that the main landing gear are often attached to the rear spar of the wing. Shortening the chord of a wing often requires its rear spar, and thus landing gear attached thereto, to be brought further forward. Another consideration is the fact that increasing the aspect ratio of a swept wing moves the centre of lift aft. Since the centre of lift should be positioned close to the centre of gravity, the wings may need to be moved (which in turn would move the centre of gravity and the position of the landing gear, and so on). With factors such as these at play, it is often necessary for aircraft to use nonoptimum wing shapes and / or locations so as to provide an acceptable compromise between design constraints.

[0008] One attempt to address the problem of the contrasting requirements between the position of the centre of gravity and the position of the ground contact point of the main landing gear is the use of “trailing link” landing gear, where the wheels are provided on a trailing arm which extends downwardly and rearwardly from a support arm. In such landing gear, the Oleo strut extends diagonally downward from the trailing arm to the support arm. With the trailing arm extending rearwardly the wheels can be positioned further back relative to the attachment point of the landing gear, in comparison to designs where the wheels are located beneath the attachment point on the end of a vertical Oleo strut. The wheels located further back means that the centre of gravity of the aircraft can also be located further back as well.

[0009] However, the designs of conventional trailing link landing gear exert a greater force on the shock absorber, due to the trailing link acting as a lever and providing a mechanical advantage to the ground reaction force acting through the wheels. A shock absorber capable of withstanding a greater force must generally be larger and heavier, which is usually undesirable in aviation but is particularly so where (as discussed above) stowage space for the landing gear is particularly limited.

[0010] It can therefore be seen that there are many mutually-contrasting requirements and objectives in landing gear design for commercial airliners.

[0011] The present invention seeks to mitigate one or more of the above-mentioned problems and / or provide a more beneficial compromise. Alternatively or additionally, the present invention seeks to provide an improved or alternative commercial airliner, commercial airliner trailing-link type main landing gear, or method of absorbing shocks. SUMMARY OF THE INVENTION

[0012] According to a first aspect of the present invention there is provided a commercial airliner comprising a trailing-link type main landing gear which comprises: a rigid support arm with a proximal end attached to the body of the commercial airliner, and a distal end; a trailing arm rotatably coupled to the distal end of the support arm, the trailing arm having a proximal end, and distal end configured to support one or more wheels; and a shock absorber having a proximal end connected to the support arm and a distal end connected to the trailing arm, the ends of the shock absorber being resiliently movable towards one another so as to resiliently oppose pivoting of the trailing arm relative to the support arm, wherein the shock absorber is a liquid spring shock absorber which has a sealed chamber containing a liquid and substantially no gas, movement of the ends of the shock absorber towards one another reducing the volume of the sealed chamber and thereby pressurising and compressing the liquid therein, compression of the liquid producing a restorative force which urges the ends of the shock absorber apart and movement of the liquid within the sealed chamber dissipating energy through viscous friction.

[0013] The landing gear being of the trailing link type, having the wheels supported by a trailing arm, allows the wheels to be placed further back as described above. This in turn may allow the centre of gravity of the airliner to be positioned further rearward, for instance due to the use of high aspect ratio wings.

[0014] A liquid spring shock absorber is generally capable of withstanding higher loads than an Oleo strut of similar size, or put another way a liquid spring shock absorber for a particular service load can be smaller than the equivalent Oleo strut. The landing gear using a liquid spring shock absorber can therefore allow the shock absorber (and by extension the whole landing gear) to be smaller. This may be beneficial in terms of aerodynamics, and in terms of stowing the landing gear into a smaller space (for instance in a wing).

[0015] It is to be understood that the landing gear being of trailing-link type, and the shock absorber being a liquid spring shock absorber, are synergistic in nature. The shorter stroke and stiffer response of a liquid spring shock absorber can be compensated for using the mechanical advantage of trailing-link type landing gear, allowing it to be used in the field of commercial airliners. Equally, the greater load placed on shock absorbers when a trailing-link landing gear is used can be withstood more easily, and with improved compactness, when a liquid spring shock absorber is used.

[0016] For the avoidance of doubt, reference to the sealed chamber containing a liquid and substantially no gas is not intended to mean that the liquid can have a gas dissolved therein. Rather, it is intended to mean that substantially no material in the gaseous phase (with the exception, perhaps, of one or two small bubbles due to slight leakage of a seal or the like) is present in the sealed chamber.

[0017] The support arm, the trailing arm and the shock absorber may be positioned substantially in the same plane.

[0018] This may position said components in a manner which is more aerodynamic and / or more compact (for instance for easier stowage into a smaller space).

[0019] The landing gear may be movable between a stowed configuration and a deployed configuration.

[0020] In the stowed configuration, the landing gear may be received at least partly within a wing of the commercial airliner.

[0021] The landing gear may be movable between the deployed and stowed configurations by rotating the support arm, trailing arm and shock absorber together.

[0022] This may be an advantageously straightforward and / or lightweight mechanism for retraction, and / or an arrangement which can fit into the space available inside a wing advantageously easily.

[0023] The landing gear may be movable between said configurations by pivoting the support arm, trailing arm and shock absorber together about an axis which is positioned within or substantially parallel to said plane.

[0024] Optionally: the trailing arm extends along a length of the trailing arm; a wheel support, for supporting the one or more wheels, is provided on the trailing arm at a point along the length of the trailing arm; and the shock absorber is connected to the trailing arm at substantially the same point along the length of the trailing arm as the wheel support is provided.

[0025] This may provide the best balance of leverage, with neither moments exerted on the trailing arm by the shock absorber, nor moments exerted on the trailing arm by the wheels, having significant mechanical advantage in terms of lever length.

[0026] That being said, in other embodiments the shock absorber may be connected at a point further towards the support arm than the wheel support (at which point the moment exerted by the wheels may have a mechanical advantage in terms of lever length), or the wheel support may be provided at a point further towards the support arm than the shock absorber (at which point the moment exerted by the shock absorber may have the mechanical advantage in terms of lever length).

[0027] The wheel support may for example be an axle, or a hole for an axle.

[0028] The support arm may be attached to a wing of the aircraft.

[0029] For example, the support arm may be attached to a rear spar of said wing.

[0030] This may position the landing gear beneficially far backward in the airliner (thereby allowing the centre of gravity to be positioned further back due to the use of higher aspect ratio wings), without the need for the landing gear to be mounted to the fuselage.

[0031] The trailing arm and the support arm may be pivotally connected by a pivot joint.

[0032] This may make the kinematics of the landing gear beneficially simple and / or reliable.

[0033] As an alternative, the trailing arm and the support arm may be connected to one another by an intermediate member, the intermediate member being movably attached to both the trailing arm and the support arm.

[0034] This may allow the kinematics of the landing gear to be adjusted or customised after assembly of the landing gear.

[0035] The intermediate member may be pivotally attached to both the trailing arm and the support arm.

[0036] The distal end of the shock absorber and the trailing arm may be pivotally connected to one another.

[0037] This may make the kinematics of the landing gear beneficially simple and / or reliable.

[0038] As an alternative, the distal end of the shock absorber and the trailing arm may be connected to one another via an intermediate member.

[0039] This may allow the kinematics of the landing gear to be adjusted or customised after assembly of the landing gear.

[0040] The intermediate member may be pivotally attached to both the shock absorber and the trailing arm.

[0041] With the commercial airliner resting on the ground via the landing gear, the support arm may be positioned generally upright, for instance substantially vertical.

[0042] Optionally: the landing gear has a length direction which extends generally from the proximal end of the support arm to the distal end of the trailing arm, and a thickness direction which is perpendicular to the length direction and perpendicular to a roll axis of the aircraft; the support arm, the trailing arm and the shock absorber each define a thickness in the thickness direction; and the thickness of the shock absorber is no larger than the thickness of the support arm and / or no larger than the thickness of the trailing arm.

[0043] With the shock absorber being no thicker than the support arm and / or the trailing arm may reduce the extent to which the shock absorber is the limiting factor in whether or not the landing gear can be stowed into a particular space (for instance a space within a wing).

[0044] The commercial airliner may have a pair of wings, each wing having an aspect ratio of at least 10, for instance at least 12 or at least 14.

[0045] One or more of the advantages discussed above may be particularly applicable for such airliners, due to the effect that high aspect ratio wings has on other design considerations as discussed above.

[0046] The commercial airliner may have a maximum take off weight of at least 50 tonnes, for instance at least 70, at least 100 or at least 200 tonnes.

[0047] One or more of the advantages discussed above may be particularly applicable for such airliners, due to the larger loads which the landing gear of such airliners must withstand.

[0048] The commercial airliner may be configured to carry at least 50 passengers, for instance at least 100 or at least 150 passengers. For example, the airliner may comprise at least 50, at least 100 or at least 150 passenger seats.

[0049] One or more of the advantages discussed above may be particularly applicable for such airliners, for instance due to the weight which such airliners must carry (and thus the loading that their landing gear must operate under) and / or due to the importance of ride comfort for such airliners.

[0050] Optionally: one of the ends of the shock absorber is connected to the sealed chamber and the other of the ends is connected to a piston rod which extends along a longitudinal axis into the sealed chamber through an aperture therein, the piston rod being movable along the longitudinal axis within the aperture while in sealing engagement therewith; and the shock absorber is configured whereby movement of the ends of the shock absorber towards one another inserts the piston rod further into the sealed chamber, thereby reducing the volume of the sealed chamber and thus pressurising and compressing the liquid, and moving some of the liquid within the sealed chamber and thus dissipating energy through viscous friction.

[0051] According to a second aspect of the present invention there is provided a commercial airliner trailing-link type main landing gear for a commercial airliner according to any preceding claim.

[0052] Such a landing gear may provide one or more of the advantages discussed above.

[0053] According to a third aspect of the present invention there is provided a method of absorbing shocks in a trailing-link type main landing gear of a commercial airliner, the landing gear comprising: a rigid support arm with a proximal end attached to the body of the commercial airliner, and a distal end; a trailing arm rotatably coupled to the distal end of the support arm, the trailing arm having a proximal end, and distal end configured to support one or more wheels; and a shock absorber having a proximal end connected to the support arm and a distal end connected to the trailing arm, the method comprising: supporting some of the weight of the airliner using the landing gear, while the airliner is in motion; and allowing a shock loading of the landing gear to move the ends of the shock absorber towards one another, said movement of the ends of the shock absorber reducing the volume of the sealed chamber and thereby pressurising and compressing the liquid, and moving some of the liquid inside the sealed chamber, wherein compression of the liquid produces a restorative force which urges the ends of the shock absorber apart, and movement of the liquid within the sealed chamber dissipates energy through viscous friction.

[0054] A method according to the third aspect of the invention may provide one or more of the advantages discussed above in respect of the first aspect of the invention in terms of position of centre of gravity of the airliner, compactness of landing gear, or synergy between the use of trailing-link landing gear and the use of a liquid spring shock absorber.

[0055] The step of supporting some of the weight of the airliner using the landing gear while the airliner is in motion may begin at the same time as said shock loading. For example, the step of supporting some of the weight of the airliner using the landing gear while the airliner is in motion may comprise touching down of the landing gear onto a runway during landing, with said touching down also providing said shock loading.

[0056] As an alternative, the step of supporting some of the weight of the airliner using the landing gear while the airliner is in motion may begin before said shock loading. For example, the step of supporting some of the weight of the airliner using the landing gear while the airliner is in motion may comprise taxiing the airliner in advance of takeoff, and said shock loading may be provided by the airliner hitting a bump after starting to taxi.

[0057] 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. Further, it is to be understood that different steps of a method described herein need not necessarily be performed in the order in which they are recited. DESCRIPTION OF THE DRAWINGS

[0058] 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 a front view of a commercial airliner according to a first embodiment of the invention; Figure 2 shows a schematic side view of a main landing gear of the commercial airliner of Figure 1; Figure 3 shows a schematic cross-sectional side view of a liquid spring assembly, more particularly a liquid spring shock absorber, of the landing gear of Figure 2; Figure 4 shows a kinematic diagram of the landing gear of Figure 2; Figure 5 shows a flow-chart of a method according to the first embodiment of the invention; Figure 6 is a kinematic diagram of a landing gear according to a second embodiment of the invention; and Figure 7 is a kinematic diagram of a landing gear according to a third embodiment of the invention. DETAILED DESCRIPTION

[0059] Figure 1 shows an aircraft, more particularly a commercial airliner 2, according to an embodiment of the invention. It has a body 4 made up of a fuselage 6, a tail 8 and two wings 10. Within the fuselage 6 is a cockpit and room for around 200 passengers seated in conventional fashion. Each wing 10 has a skin which envelops a substructure (not visible) made up of a front spar, a rear spar and a set of ribs, as is known in the art. Though only the length and thickness of the wings 10 is shown in Figure 1, it is noteworthy that each wing 10 has an aspect ratio of around 14.

[0060] The airliner 2 also has a nose landing gear 12 and two main landing gear 14, each of which is shown in a deployed configuration in Figure 1. The nose landing gear 12 depends from the fuselage 6 beneath the nose of the aircraft. Each main landing gear 14 is attached to a respective wing 10, more particularly the rear spar (not visible) of that wing 10. In known fashion, the landing gear 12, 14 are movable to a stowed configuration in which the nose landing gear is received within the fuselage 6 and each main landing gear 14 is received in its respective wing 10. In the present embodiment the airliner 2 has a maximum take off weight of around 250 tonnes.

[0061] Figure 2 shows one of the main landing gear 14, schematically, from the side. Figure 2 will now be referred to in combination with Figure 1. The landing gear 14 has a rigid supports arm 20 which extends from a proximal end 22 to a distal end 24. With the landing gear 14 in the deployed configuration with the airliner 2 resting on the ground, the support arm 20 is positioned substantially vertically. The proximal end 22 of the support arm has a pair of flanges 26 which receive an axle 27 therethrough so as to attach the support arm 20, and thus the landing gear 14 as a whole, to the rear spar (not visible) of one of the wings 10. The distal end 24 of the support arm 20 also has a pair of flanges 28 (one of which is visible from the perspective of Figure 2). Flanges 28, which are oriented generally perpendicularly to flanges 26, support a pivot pin 30. The support arm 20 also has a pair of fins 29 (one of which is visible from the perspective of Figure 2) projecting generally rearwardly therefrom. The fins 29 support a pivot pm 31.

[0062] The landing gear 14 also has a trailing arm 32 which extends along a length 34 thereof from a proximal end 36 to a distal end 38. The trailing arm 32 is rotatably coupled to the support arm 20. More particularly, the trailing arm 32 and the support arm 20 are pivotally connected to one another by the pivot pin 30, which forms a pivot joint. The trailing arm 32 can therefore pivot about the pivot pin 30 relative to the support arm 20.

[0063] The distal end 38 of the trailing arm 32 has a wheel support in the form of an axle 40 which supports a pair of wheels 42 either side of the trailing arm 32, only one of which is shown in Figure 2. The trailing arm 32 also has a pair of fins 44 (one of which is visible from the perspective of Figure 2) which support a pivot pin 46 at substantially the same position along the length 34 of the trailing arm as the axle 40.

[0064] The landing gear 14 also comprises a liquid spring assembly 50 which is configured as a liquid spring shock absorber. The liquid spring shock absorber 50 has a first end in the form of a proximal end 52 and a second end in the form of a distal end 54. The proximal end 52 is connected to the support arm 20. More particularly, the proximal end 52 of the liquid spring shock absorber 50 is pivotally connected to the support arm by the pivot pin 31, which forms a pivot joint. The shock absorber 50 can therefore pivot relative to the support arm 20 about the pivot pin 31.

[0065] The distal end 54 of the shock absorber 50 is connected to the trailing arm 32. More particularly, the distal end 54 is pivotally attached to the trailing arm 32 by the pivot pin 46, which forms a pivot joint. The shock absorber 50 and trailing arm 32 can thus pivot relative to one another about the pivot pin 46.

[0066] The proximal end 52 of the shock absorber 50 is connected to, and in this embodiment integrally formed with, a sealed chamber 56. The distal end 54 of the shock absorber is connected to, and in this case integrally former with, a piston rod 58 which extends along a longitudinal axis 60 into the sealed chamber 56.

[0067] It is noteworthy that in this embodiment the support arm 20, the trailing arm 32 and the shock absorber 50 are all positioned in the same plane, namely a plane which is normal to the pitch axis of the aircraft (parallel to the page from the perspective of Figure 2). The axle 27 which passes through the flanges 26 of the support arm 20 also lies within this plane. The axle 27 provides an axis about which the support arm 20, trailing arm 32 and shock absorber 50 pivot together when the landing gear 14 moves between the stowed and deployed configurations.

[0068] The landing gear 14 defines a length direction 64 which runs between the proximal end 22 of the support arm 20 and the wheels 42. The landing gear 14 also defines a thickness direction which is perpendicular to the length direction 64 and also to the roll axis of the airliner 2. The thickness direction runs through the page from the perspective of Figure 2. It is noteworthy that the thickness of the shock absorber 50, in the thickness direction, is no larger than that of the support arm 20 or that of the trailing arm 32. Indeed, in this case the shock absorber 50 has a thickness which is slightly smaller than that of the support arm 20 and that of the trailing arm 32.

[0069] For the sake of completeness, the landing gear 14 also has a foldable inboard sidestay which braces the landing gear against lateral loads. However, the foldable inboard sidestay is not material to the present invention. It has therefore been omitted from the drawings for the sake of simplicity, and will not be described here.

[0070] The shock absorber 50 will now be described in more detail with reference to Figure 3, which shows the shock absorber 50 in schematic cross section, in combination with Figures 1 and 2. As noted above, the proximal end 52 of the shock absorber 50 is connected to a sealed chamber 56 and the distal end 54 is connected to a piston rod 58. The sealed chamber 56 is generally cylindrical in shape and contains a liquid 70 in the form of hydraulic oil. Unlike the cylinder / chamber of an Oleo strut, the sealed chamber 56 of the shock absorber contains substantially no gas. The chamber 56 has an aperture 72 through which the piston rod 58 is slidingly received.

[0071] The piston rod 58 extends into the chamber 56 through the aperture 72, and is movable along the longitudinal axis 60 within the aperture 72 while remaining in sealing engagement with the aperture 72 (thereby maintaining the seal of the sealed chamber 56). The piston rod 58 terminates in a piston head 74 which is located within the liquid 70 inside the chamber 56. The piston head 74 is generally hollow. It has a solid front wall 76, a solid peripheral wall 77 and a porous rear wall 78 by which the piston head 74 is attached to the piston rod 58. The peripheral wall 77 is a close fit to the interior of the sealed chamber, minimising the potential for leakage of liquid therebetween while allowing the piston head 74 to move within the chamber 56.

[0072] The piston head 74 has a conduit 80 which extends generally along the longitudinal axis 60. The conduit 80 runs through a hole 82 in the front wall 76 and into the piston head 74, then out to behind the piston head 74 through the porous rear wall 78. Some of the liquid 70 in the sealed chamber 56 can flow through the conduit 80 during movement of the piston head 74 within the chamber 56, as described in more detail later.

[0073] The shock absorber 50 is configured whereby movement of its ends 52, 54 towards one another inserts the piston rod 58 further into the sealed chamber 56. With more of the piston rod 58 received in the chamber 56, the volume of the chamber is reduced. Being forced to occupy a smaller volume, the liquid 70 within the chamber 56 is pressurised and compressed. Compression of the liquid 70 creates a restorative force which urges the piston rod out of the chamber 56. Accordingly, when the ends 52, 54 of the shock absorber 50 are moved towards one another the shock absorber 50 resiliently biases them apart again.

[0074] When the piston rod 58 is inserted further into the sealed chamber 56, the piston head 74 moves along the chamber 56. This has the effect of pushing some of the liquid 70 through the conduit 80 in the piston head 74, from in front of the piston head to behind it. The liquid being forced through the conduit 80, in particular the hole 82 in the front wall 76, acts to dissipate energy through viscous friction in the liquid 70, thereby exerting a damping action on relative movement of the ends 52, 54 of the shock absorber 50. It is noteworthy that this damping action is also provided when the piston rod moves further out of the sealed chamber 56 under action of the restorative force from the compressed liquid 70 (i.e. when the ends 52, 54 are moved apart), with some of the liquid passing through the conduit 80 from behind the piston to in front of it.

[0075] A method of using the liquid spring assembly 50, more particularly a method of absorbing shocks in the landing gear 14, according to the present embodiment will now be described with reference to Figures 4 and 5 (which show a kinematic diagram of the landing gear 14 and a flow-chart of the method respectively) along with continued reference to Figures 1 to 3.

[0076] In a first step 210 the airliner 2 is rested on the ground with the landing gear 12, 14 in the deployed configuration. When the airliner 2 rests on the ground, a portion of its weight W acts downwards through the support arm 20. The ground reaction force R acts upwards through the wheels 42. With the support arm 20 being urged downwards and the distal end 38 of the trailing arm 32 being urged upwards by the wheels, the trailing arm 32 is urged anticlockwise from the perspective of Figure 3, about the pivot pin 30, relative to the support arm 20. This acts to push the ends 52, 54 of the shock absorber 50 together, pressurising and compressing the liquid 70 in the chamber 56. The landing gear 14 reaches an equilibrium point when the ends 52, 54 of the shock absorber 50 have moved together sufficiently (i.e. the liquid 70 in the chamber 56 has been compressed sufficiently) for the restorative force exerted by the liquid 70 to exert a moment on the trailing arm 32 which counteract the moment exerted by the ground reaction force R.

[0077] In step 220 a shock loading is applied to the landing gear 14, for instance from the aircraft 2 hitting a bump in the runway when taxiing. The bump temporarily increases the ground reaction force R, applying a moment (anticlockwise from the perspective of Figures 2 and 4) which exceeds the moment (clockwise from the perspective of Figures 2 and 4) which is exerted by the shock absorber 50 (due to the restorative force from the compressed liquid 70). As a result of these imbalanced moments, the trailing arm 32 pivots upwards (anticlockwise from the perspective of Figures 2 and 4) relative to the support arm 20 about pivot pin 30. This pivoting motion is accompanied by slight pivoting of the shock absorber 50, both anticlockwise (from the perspective of Figures 2 and 4) relative to the support arm 20 about pivot pin 31, and clockwise (from the perspective of Figures 2 and 4) relative to the trailing arm 32 about pivot pin 46.

[0078] Upward pivoting of the trailing arm 32 moves the ends 52, 54 of the shock absorber 50 further together, which inserts the piston rod 58 further into the sealed chamber 56. This further reduces the volume within the chamber 56, further compressing the liquid 70 and increasing the restorative force generated thereby. Also as the piston rod 58 is further inserted into the chamber 56, the piston head 74 moves forward within the chamber 56. This forces some of the liquid 70 in front of the piston head 74 through the conduit 80 and to the rear of the piston head 74, dissipating energy through viscous friction and thereby damping the movement of the ends 52, 54 of the shock absorber 50 (and thus the movement of the trailing arm 32).

[0079] In some cases, in step 230 the trailing arm 32 pivots and the restorative force from the shock absorber 50 increases until the trailing arm reaches a position in which the moment exerted by the shock absorber 50 again counteracts the moment exerted by the (increased) ground reaction force R. The landing gear 14 then reaches equilibrium again. In other cases the shock loading may be removed before the landing gear reaches the new equilibrium state.

[0080] In either case, in step 240 the shock loading is removed (for instance due to the airliner 2 passing over the bump in the runway. The ground reaction force R therefore drops to a lower level. At this point the moment exerted on the trailing arm 32 by the restorative force applied by the shock absorber 50 more than counteracts the moment exerted by the ground reaction force R, and the trailing arm 32 pivots downward (clockwise from the perspective of Figures 2 and 4) relative to the main arm 20 about the pivot pin 30. This pivoting motion is accompanied by slight pivoting of the shock absorber 50, both anticlockwise (from the perspective of Figures 2 and 4) relative to the support arm 20 about pivot pin 31, and clockwise (from the perspective of Figures 2 and 4) relative to the trailing arm 32 about pivot pin 46.

[0081] As the trailing arm 32 pivots downward, the ends 52, 54 of the shock absorber are permitted to move apart from one another, withdrawing the piston rod 58 from the sealed chamber 56 to some extent. This has the effect of increasing the volume of the chamber 56, allowing the liquid to expand and become a little less pressurised. Also, this movement of the piston rod 58 moves the piston head 74 rearwards, forcing some of the liquid 70 back through the conduit 80 and dissipating energy as discussed above.

[0082] As the trailing arm 32 pivots, the shock absorber 50 lengthens and the liquid 70 in the sealed chamber 56 becomes less compressed. The restorative force provided by the liquid 70 therefore decreases. In step 250 the trailing arm 32 reaches a position where moment applied to it by the restorative force of the shock absorber 50 is counteracted by the moment applied by the (reduced) ground reaction force R, and the landing gear 14 again reaches an equilibrium position.

[0083] Figure 6 shows a kinematic diagram of a landing gear 14 according to a second embodiment of the invention. The second embodiment is generally the same as the first embodiment, so only the differences will be described.

[0084] Whereas in the first embodiment the trailing arm 32 was directly attached to the support arm 20 (by the pivot pin 30), in this embodiment the trailing arm 32 and the support arm 20 are connected to one another by an intermediate member 84. The intermediate member 84 is movably attached, more particularly pivotally attached, to both the trailing arm 32 and the support arm 20. Pivot pin 30 pivotally connects the intermediate member 84 to the support arm 20, and an additional pivot pin 86 pivotally connects the intermediate member 84 to the trailing arm 32.

[0085] Figure 7 shows a kinematic diagram of a landing gear 14 according to a third embodiment of the invention. The third embodiment is generally the same as the first embodiment, so only the differences will be described.

[0086] Whereas m the first embodiment the trailing arm 32 was directly attached to the shock absorber 50 (by the pivot pin 46), in this embodiment the trailing arm 32 and the shock absorber 50 are connected to one another by an intermediate member 88. The intermediate member 88 is movably attached, more particularly pivotally attached, to both the trailing arm 32 and the shock absorber 50. Pivot pin 46 pivotally connects the intermediate member 84 to shock absorber 50, and an additional pivot pin 90 pivotally connects the intermediate member 88 to the trailing arm 32.

[0087] The second and third embodiments function in generally the same way as the first embodiment. However, in each case the presence of the intermediate member 84, 88 gives the mechanism an additional degree of freedom, which could cause instability or unpredictability of the landing gear 14 if left unchecked. For this reason, in each embodiment the pivoting movement of the trailing arm 32, the shock absorber 50 and / or the intermediate member 84, 88 may be limited or controlled so as to fine-tune the behaviour of the landing gear. Indeed, in some cases one of the above described pivot joints may be replaced with a fixed joint, for example the shock absorber 50 may be prevented from rotating relative to the support arm 20 about pin 31.

[0088] 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.

[0089] The term ‘or’ shall be interpreted as ‘and / or’ unless the context requires otherwise.

Claims

1. A commercial airliner comprising a trailing-link type main landing gear which comprises:a rigid support arm with a proximal end attached to the body of the commercial airliner, and a distal end;a trailing arm rotatably coupled to the distal end of the support arm, the trailing arm having a proximal end, and distal end configured to support one or more wheels; anda shock absorber having a proximal end connected to the support arm and a distal end connected to the trailing arm, the ends of the shock absorber being resiliently movable towards one another so as to resiliently oppose pivoting of the trailing arm relative to the support arm,wherein the shock absorber is a liquid spring shock absorber which has a sealed chamber containing a liquid and substantially no gas, movement of the ends of the shock absorber towards one another reducing the volume of the sealed chamber and thereby pressurising and compressing the liquid therein, compression of the liquid producing a restorative force which urges the ends of the shock absorber apart and movement of the liquid within the sealed chamber dissipating energy through viscous friction.

2. A commercial airliner according to claim 1 wherein the support arm, the trailing arm and the shock absorber are positioned substantially in the same plane.

3. A commercial airliner according to claim 1 or 2 wherein the landing gear is movable between a stowed configuration and a deployed configuration.

4. A commercial airliner according to claim 3 wherein in the stowed configuration, the landing gear is received at least partly within a wing of the commercial airliner.

5. A commercial airliner according to claim 3 or 4 wherein the landing gear is movable between the deployed and stowed configurations by rotating the support arm, trailing arm and shock absorber together.

6. A commercial airliner according to claim 5, incorporating claim 2, wherein the landing gear is movable between said configurations by pivoting the support arm, trailing arm and shock absorber together about an axis which is positioned within or substantially parallel to said plane.

7. A commercial airliner according to any preceding claim wherein: the trailing arm extends along a length of the trailing arm;a wheel support, for supporting the one or more wheels, is provided on the trailing arm at a point along the length of the trailing arm; andthe shock absorber is connected to the trailing arm at substantially the same point along the length of the trailing arm as the wheel support is provided.

8. A commercial airliner according to any preceding claim wherein the support arm is attached to a wing of the aircraft.

9. A commercial airliner according to claim 8 wherein the support arm is attached to a rear spar of said wing.

10. A commercial airliner according to any preceding claim wherein the trailing arm and the support arm are pivotally connected by a pivot joint.

11. A commercial airliner according to any one of claims 1 to 9 wherein the trailing arm and the support arm are connected to one another by an intermediate member, the intermediate member being movably attached to both the trailing arm and the supportarm.

12. A commercial airliner according to claim 11 wherein the intermediate member is pivotally attached to both the trailing arm and the support arm.

13. A commercial airliner according to any preceding claim wherein the distal end of the shock absorber and the trailing arm are pivotally connected to one another.

14. A commercial airliner according to any one of claims 1 to 12 wherein the distal end of the shock absorber and the trailing arm are connected to one another via an intermediate member.

15. A commercial airliner according to claim 14 wherein the intermediate member is pivotally attached to both the shock absorber and the trailing arm.

16. A commercial airliner according to any preceding claim wherein with the commercial airliner resting on the ground via the landing gear, the support arm is positioned generally upright.

17. A commercial airliner according to claim 16 wherein with the commercial airliner resting on the ground via the landing gear, the support arm is positioned substantially vertical.

18. A commercial airliner according to any preceding claim wherein:the landing gear has a length direction which extends generally from the proximal end of the support arm to the distal end of the trailing arm, and a thickness direction which is perpendicular to the length direction and perpendicular to a roll axis of the aircraft;the support arm, the trailing arm and the shock absorber each define a thickness in the thickness direction; andthe thickness of the shock absorber is no larger than the thickness of the support arm and / or no larger than the thickness of the trailing arm.

19. A commercial airliner according to any preceding claim wherein the airliner has a pair of wings, each wing having an aspect ratio of at least 12.

20. A commercial airliner according to any preceding claim wherein the airliner has a maximum take off weight of at least 50 tonnes.

21. A commercial airliner according to any preceding claim wherein the airliner is configured to carry at least 100 passengers.

22. A commercial airliner according to any preceding claim wherein:one of the ends of the shock absorber is connected to the sealed chamber and the other of the ends is connected to a piston rod which extends along a longitudinal axis into the sealed chamber through an aperture therein, the piston rod being movable along the longitudinal axis within the aperture while in sealing engagement therewith; andthe shock absorber is configured whereby movement of the ends of the shock absorber towards one another inserts the piston rod further into the sealed chamber, thereby reducing the volume of the sealed chamber and thus pressurising and compressing the liquid, and moving some of the liquid within the sealed chamber and thus dissipating energy through viscous friction.

23. A commercial airliner trailing-link type main landing gear for a commercial airliner according to any preceding claim.

24. A method of absorbing shocks in a trailing-link type main landing gear of a commercial airliner, the landing gear comprising:a rigid support arm with a proximal end attached to the body of the commercial airliner, and a distal end;a trailing arm rotatably coupled to the distal end of the support arm, the trailing arm having a proximal end, and distal end configured to support one or more wheels; anda shock absorber having a proximal end connected to the support arm and a distal end connected to the trailing arm,the method comprising:supporting some of the weight of the airliner using the landing gear, while the airliner is in motion; andallowing a shock loading of the landing gear to move the ends of the shock absorber towards one another, said movement of the ends of the shock absorber reducing the volume of the sealed chamber and thereby pressurising and compressing the liquid, and moving some of the liquid inside the sealed chamber,wherein compression of the liquid produces a restorative force which urges the ends of the shock absorber apart, and movement of the liquid within the sealed chamber dissipates energy through viscous friction.

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