Aircraft landing gear

Abstract

Disclosed is a main landing gear 4a for an aircraft. The main landing gear comprises a strut 10 configured to attach to the aircraft at a first end; an axle 12 movably mounted to a second end of the strut 10, the second end opposite the first end; and a position adjusting mechanism 16 connected between the strut 10 and the axle 12. The axle is moveable in a lateral direction relative to the strut between a first position and a second position. The position adjusting mechanism is configured to control movement of the axle between the first position and the second position. The axle may move from the first position towards the second position based on aircraft weight.

Description

FIELD OF THE INVENTION [1] The present invention relates to an aircraft and a main landing gear for the aircraft. BACKGROUND OF THE INVENTION [2] On aircraft that have their main landing gear attached to the fuselage (or body) of the aircraft, it may be desirable to angle the main landing gear relative to the fuselage to increase the track width of the main main landing gear and improve stability of the aircraft on the ground. However, this may result in an increase in lateral forces experienced by the tyres of the main landing gear, which may in turn increase the wear rate of the tyres. The present invention seeks to address the above-mentioned problems and provide an improved main landing gear. SUMMARY OF THE INVENTION [3] According to a first aspect, there is provided a main landing gear for an aircraft, the main landing gear comprising: a strut configured to attach to the aircraft at a first end; an axle movably mounted to a second end of the strut, the second end opposite the first end, wherein the axle is moveable in a lateral direction relative to the strut between a first position and a second position; and a position adjusting mechanism connected between the strut and the axle, wherein the position adjusting mechanism is configured to control movement of the axle between the first position and the second position. [4] When the aircraft is being loaded, such that the total weight of the aircraft is increasing, there may be a sideways (i.e. lateral) force on the tyres of the main landing gear. This force may cause the tyres to try to slide sideways across the ground. This movement of the tyres may increase wear on the tyres and therefore reduce their lifetime and / or require the tyres to be replaced or inspected more often. By allowing the axle to move relative to the strut, this sideways (i.e. lateral) force may be taken up in the movement of the axle, rather than in the tyres. This may reduce the wear on the tyres, which may increase their lifetime and subsequently reduce costs by requiring fewer replacements. [5] The position adjusting mechanism may be configured to allow the axle to move towards the first position when the aircraft is at a first weight, and the position adjusting mechanism may be configured to allow the axle to move towards the second position when the aircraft is at a second weight, the second weight being less than the first weight. This may allow any lateral force being applied to the main landing gear to be accounted for by the movement of the axle, rather than by the tyre across the ground. This may reduce wear on the tyres and therefore increase the lifetime of the tyres. The first weight may be a fully-loaded weight (or maximum weight for the current mission) of the aircraft and the second weight may be an unloaded weight (or a minimum weight for the current mission) of the aircraft. [6] The position adjusting mechanism may be configured to restrict movement of the axle relative to strut during at least one of: taxi, take-off and landing of the aircraft. This may ensure that the main landing gear is stable during taxi and / or take-off. [7] The position adjusting mechanism may comprise a housing within which the axle is at least partly located. When the axle is located in the first position, the housing may be located at an outermost side of the axle relative to the aircraft. When the axle is located in the second position, the housing may be located at an innermost position on the axle relative to the aircraft [8] The main landing gear may be moveable between a retracted position and an extended position and the axle may be located at the first position when the main landing gear is in the retracted position. The main landing gear may be moveable between a retracted position and an extended position and the axle may be located at the second position when the main landing gear is in the retracted position. [9] The strut may comprise a shock absorber. The shock absorber may help to absorb shocks experienced by the main landing gear, to reduce the likelihood of the aircraft bouncing on landing. This may also increase the comfort to passengers during taxi may absorbing bumps in the taxiway / runway.

[10] The main landing gear may comprise a first and a second tyre, the first tyre may be located at a first end of the axle and the second tyre may be located at a second, opposite end of the axle.

[11] The position adjusting mechanism may comprise a piston and the position of the axle may be changed based on hydraulic pressure applied to the piston. The position adjusting mechanism may be operated by a flight crew within a cockpit of the aircraft. The position adjusting mechanism may be automatically operated without input from the flight crew. The position adjusting mechanism may be connected to a controller that is configured to control operation of the position adjusting mechanism based on one or more parameters. The position adjusting mechanism may be fluidically connected to a source of hydraulic fluid. The source of hydraulic fluid may be operated by the controller to change hydraulic pressure in the chamber of the position adjusting mechanism. The one or more parameters may comprise at least one of: a command received from an interface in the cockpit, an altitude of the aircraft, a climb rate of the aircraft, a weight of the aircraft. The axle may comprise the piston.

[12] According to a second aspect, there is provided a landing gear system comprising the main landing gear according to the first aspect; and a controller configured to control operation of the position adjusting mechanism.

[13] According to a third aspect, there is provided a method of operating a main landing gear according to the first aspect or the landing gear system according to the second aspect, the method comprising: receiving an indication to retract the main landing gear; causing the position adjusting mechanism to move the axle to the second position; and locking the axle in the second position.

[14] The method may comprise, while the aircraft is on the ground, receiving an indication to unlock the position adjusting mechanism; unlocking the position adjusting mechanism to allow the axle to move relative to the strut; receiving an indication to lock the position adjusting mechanism; and locking the position adjusting mechanism to restrict movement of the axle relative to the strut.

[15] The indication to lock the position adjusting mechanism may be received before the aircraft begins pushback and / or taxi. This may prevent the axle moving relative to the strut, which may help to ensure stability when the aircraft is taxiing. The indication to lock the position adjusting mechanism may be received after the aircraft has been loaded. This time may correspond to when the aircraft is at its heaviest.

[16] According to a fourth aspect, there is provided an aircraft comprising the main landing gear according to the first aspect, or the landing gear system according to the second aspect.

[17] 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. BRIEF DESCRIPTION OF THE DRAWINGS

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

[19] Figure 1 shows a schematic view of an aircraft;

[20] Figures 2 and 3 show a schematic views of a main landing gear of the aircraft of Figure 1 with an axle in a first position and a second position respectively; and

[21] Figure 4 and 5 show cross-sectional schematic views of a position adjusting mechanism of the main landing gear of Figures 2 and 3. DETAILED DESCRIPTION OF EMBODIMENT(S)

[22] Figure 1 shows a schematic view of an aircraft 1. The aircraft 1 comprises a pair of wings 2, a nose landing gear 3, a pair of main landing gear 4a, 4b and a controller 6 connected to the pair of main landing gear 4a, 4b. Each of the main landing gear 4a, 4b are attached to the fuselage 5 of the aircraft 1 (and may therefore also be referred to as body main landing gear), with a port side main landing gear 4a on a port side of the aircraft 1 and a starboard side main landing gear 4b on a starboard side of the aircraft 1. The port and starboard side main landing gear 4a, 4b are arranged symmetrically about a longitudinal axis of the aircraft 1, the longitudinal axis extending from a nose to a tail of the aircraft 1.

[23] As the main landing gear 4a, 4b are attached to the fuselage 5 of the aircraft 1, when in an extended position (as shown in Figure 1) an outermost part of the port side main landing gear 4a is spaced apart from an outermost part of the starboard side main landing gear 4b by a distance greater than a width of a fuselage 5 of the aircraft 1. This results in a strut 10 of each main landing gear 4a, 4b being at an oblique angle relative to the ground when the main landing gear 4a, 4b is extended and the aircraft 1 is on the ground. The main landing gear 4a, 4b is arranged in this way to improve stability of the aircraft 1 on the ground. However, this arrangement may also lead to tyres of opposing main landing gear 4a, 4b being forced further apart (such that they “splay”) as weight is added to the aircraft 1 (for example, when fuel, passengers and / or cargo are loaded onto the aircraft 1). This may put additional stress on the tyres as they are pushed sideways across the ground (as indicated by arrows 7 in Figure 1) when the aircraft 1 is stationary on the ground. This may reduce the lifetime of the tyres and increase servicing and maintenance costs. The present invention seeks to address these problems.

[24] The port side main landing gear 4a is shown in a front view in Figures 2 and 3. The brevity, the starboard side main landing gear 4b is not shown in more detail, as this is a mirror copy of the port side main landing gear 4b with the same features. The port side main landing gear 4a comprises a strut 10, an axle 12, an outer tyre 14, an inner tyre 15 and a position adjusting mechanism 16. The position adjusting mechanism 16 is located at a first end 18 of the strut 10. The first end 18 of the strut 10 is the end of the strut that is nearest the ground when the landing gear 4 is in an extended position and the aircraft 1 is on the ground. In Figure 2, the strut 10 is at the first position relative to the axle 12, such that the first end 18 of the strut 10 is at an outermost side of the axle 12. Figure 3 shows the strut 10 at a second position relative to the axle 12, wherein the first end 18 is at an innermost side of the axle 12. In use, the main landing gear 4 will be in the configuration shown in Figure 2 when the aircraft 1 is at maximum weight for the flight mission (for example, before take-off) and will be in the configuration shown in Figure 3 when the aircraft 1 is at a minimum weight for the flight mission (for example, when unloaded after landing).

[25] The position adjusting mechanism 16 is shown in more detail in Figures 4 and 5. Figure 4 shows a schematic cross-sectional view of the position adjusting mechanism 16 when the axle 12 is in the first position, while Figure 5 shows a schematic cross-sectional view of the position adjusting mechanism 16 when the axle 12 is at the second position. The position adjusting mechanism 16 comprises a housing 20, a chamber 22 within the housing 20, a fluid inlet 24 passing through the housing 20 into the chamber 22 and a piston 26 located within the housing 20. The axle 12 comprises a first part 12a extending from a first side 28 of the piston 26 (and protruding from a first side 30 of the housing 20), and a second part 12b extending from a second, opposite, side 32 of the piston 26 (and protruding from a second side 34 of the position adjusting mechanism 16). A seal 36 is provided between the radially outer surface 38 of the piston 26 and an inner surface 40 of the chamber 22. The seal 36 helps to prevent fluid (such as hydraulic fluid) leaking from the chamber 22 into other parts of the housing 20.

[26] The fluid inlet 24 is fluidically connected to a source of hydraulic fluid 42 such that hydraulic fluid can be supplied to, and removed from, the chamber 22 through the fluid inlet 24. The controller 6 is in communication with the source of hydraulic fluid 42 and is configured to control (either directly or indirectly) operation of the source of hydraulic fluid 42. In use, the controller 6 causes the source of hydraulic fluid 42 to supply hydraulic fluid through the fluid inlet 24 and into the chamber 22 within the housing 20. The fluid inlet 24 is located on an outermost side of the position adjusting mechanism 16, such that the fluid inlet 24 is closer to the outer tyre 14 of the main landing gear 4a than the inner tyre 15 of the main landing gear 4a. As hydraulic fluid is provided through the fluid inlet 24, the amount of fluid within the chamber 22 increases, causing the piston 26 to move with respect to the housing 20 of the position adjusting mechanism 16. This has the effect of changing the position of the axle 12 (and therefore the tyres 14, 15) relative to the strut 10. To move the axle 12 in the opposite direction, hydraulic fluid is removed from the chamber 22 through the fluid inlet 24.

[27] As the amount of hydraulic fluid (and therefore the hydraulic pressure) increases on the right hand side of the piston 26 shown in Figure 4 (as hydraulic fluid enters the chamber 22), the piston 26 moves to the left which causes the position adjusting mechanism 16 (and therefore the strut 10) to move towards the outer tyre 14 of the main landing gear 4a. The opposite then happens when hydraulic fluid is removed from the chamber 22 of the position adjusting mechanism 16 such that the piston 26 moves to the right causing the position adjusting mechanism 16 (and therefore the strut 10) to move towards the inner tyre 15 of the main landing gear 4a.

[28] As mentioned briefly above, operation of the position adjusting mechanism 16 is controlled by the controller 6. The controller 6 receives information indicative of various properties of the aircraft 1 (such as the weight of the aircraft 1, when landing gear retraction has been instructed and / or the altitude of the aircraft 1) to determine how to operate the position adjusting mechanism 16. This information is received from additional sensors on the aircraft 1, or from another input (such as an input into the flight management system by the flight crew).

[29] In the present example, the main landing gear 4 moves between an extended position (as shown in Figure 1) and a retracted position (not shown in the Figures) while in flight. For example, when on the ground, the main landing gear 4 is in the extended position. Shortly after take-off, when a positive rate of climb is observed, a member of the flight crew may request that the landing gear 4 is retracted. The controller 6 subsequently receives a signal indicative of the main landing gear 4 being retracted. In response, the controller 6 causes the position adjusting mechanism 16 to move the axle 12 to the first position and causes the position adjusting mechanism 16 to be locked in position in the first position (by maintaining hydraulic pressure in the chamber 22). As the aircraft 1 will be at its lightest on landing, when the main landing gear 4 is subsequently deployed for landing, the position adjusting mechanism 16 maintains the axle 12 in the first position until the aircraft 1 has taxied to the gate. After taxiing, the axle 12 is unlocked so that as the aircraft 1 is filled with passenger, cargo and / or fuel, the axle 12 can move towards the outermost position without the tyres 14, 15 changing position on the asphalt.

[30] While in the examples described above hydraulic fluid is used to operate the position adjusting mechanism 16, in other examples the position adjusting mechanism 16 may use pneumatic or electrically powered arrangements.

[31] While in the above embodiment the position adjusting mechanism 16 is automatically operated at different times of operation, in other examples the position adjusting mechanism 16 is manually controlled, for example, by the flight crew from the cockpit.

[32] 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. By way of example only, certain possible variations will now be described.

[33] The above embodiments are to be understood as illustrative examples of the invention. Equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

[34] It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments.

[35] 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.

[36] It should be noted that throughout this specification, “or” should be interpreted as “and / or”.

[37] Although the invention has been described above mainly in the context of a fixed-wing aircraft application, it may also be advantageously applied to various other applications, including but not limited to applications on vehicles such as helicopters, drones, trains, automobiles and spacecraft.

Claims

1. A main landing gear for an aircraft, the main landing gear comprising: a strut configured to attach to the aircraft at a first end;an axle movably mounted to a second end of the strut, the second end opposite the first end, wherein the axle is moveable in a lateral direction relative to the strut between a first position and a second position; anda position adjusting mechanism connected between the strut and the axle, wherein the position adjusting mechanism is configured to control movement of the axle between the first position and the second position.

2. The main landing gear according to claim 1, wherein the position adjusting mechanism is configured to allow the axle to move towards the first position when the aircraft is at a first weight, and wherein the position adjusting mechanism is configured to allow the axle to move towards the second position when the aircraft is at a second weight, the second weight being less than the first weight.

3. The main landing gear according to claim 1 or claim 2, wherein the position adjusting mechanism is configured to restrict movement of the axle relative to strut during at least one of: taxi, take-off and landing of the aircraft.

4. The main landing gear according to any one of claims 1 to 3, wherein the position adjusting mechanism comprises a housing within which the axle is at least partly located.

5. The main landing gear according to claim 4, wherein, when the axle is located in the first position, the housing is located at an outermost side of the axle relative to the aircraft.

6. The main landing gear according to claim 4 or claim 5, wherein, when the axle is located in the second position, the housing is located at an innermost position on the axle relative to the aircraft.

7. The main landing gear according to any one of claims 1 to 6, wherein the main landing gear is moveable between a retracted position and an extended position and wherein the axle is located at the first position when the main landing gear is in the retracted position.

8. The main landing gear according to any one of claims 1 to 6, wherein the main landing gear is moveable between a retracted position and an extended position and wherein the axle is located at the second position when the main landing gear is in the retracted position.

9. The main landing gear according to any one of claims 1 to 8, wherein the strut comprises a shock absorber.

10. The main landing gear according to any one of claims 1 to 9, comprising a first and a second tyre, the first tyre located at a first end of the axle and the second tyre located at a second, opposite end of the axle.

11. The main landing gear according to any one of claims 1 to 10, wherein the position adjusting mechanism comprises a piston and the position of the axle is changed based on hydraulic pressure applied to the piston.

12. The main landing gear according to claim 11, wherein the axle comprises the piston.

13. A landing gear system comprising:the main landing gear according to any one of claims 1 to 12; anda controller configured to control operation of the position adjusting mechanism.

14. A method of operating a main landing gear according to any one of claims 1 to 12 or the landing gear system of claim 13, the method comprising:receiving an indication to retract the main landing gear;causing the position adjusting mechanism to move the axle to the second position; and locking the axle in the second position.

15. The method according to claim 14, comprising:while the aircraft is on the ground, receiving an indication to unlock the position adjusting mechanism;unlocking the position adjusting mechanism to allow the axle to move relative to thestrut;receiving an indication to lock the position adjusting mechanism; andlocking the position adjusting mechanism to restrict movement of the axle relative to the strut.

16. An aircraft comprising the main landing gear according to any one of claims 1 to 12, or the landing gear system according to claim 13.12

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