GB2585075A - Landing gear assembly - Google Patents

Abstract

A landing gear assembly 1 comprising a main strut 8 moveable between an extended position and a retracted position; an actuator 12 connected to the main strut and configured to move the main strut from the extended position to the retracted position; and an accumulator 24. The accumulator may comprise a spring or a pneumatic or hydraulic accumulator, for example an air spring or spring type hydraulic accumulator and be moveable between a lower stress configuration and a higher stress configuration in which the store of potential energy in the accumulator is increased relative to the lower stress configuration. Potential energy stored in the accumulator acts on the main strut to move the main strut away from the extended position towards the retracted position thereby reducing the energy that would otherwise be required by the actuator to move the main strut from the extended position to the retracted position. The accumulator may also provide a damping function when lowering the landing gear. Further disclosed is a system in which the energy in the accumulator is derived from the power system which drives the main strut during periods of low power demand. Methods of retracting the landing gear using sorted potential energy are also disclosed.

Description

LANDING GEAR ASSEMBLY

BACKGROUND OF THE INVENTION

100011 The present invention relates to aircraft landing gear.

[0002] The present invention concerns a landing gear assembly. More particularly, but not exclusively, this invention concerns a landing gear assembly including an accumulator arranged to accumulate potential energy during period of lower demand and to use the energy so accumulated to reduce the energy required to raise the landing gear during retraction. The invention also concerns an aircraft comprising such a landing gear, a kit of parts for such a landing gear and a method of using such a landing gear.

100031 It is advantageous to retract the landing gear of an aircraft quickly on take-off to reduce drag. This may increase the fuel efficiency of the aircraft and/or allow for an increase in the maximum take-off weight allowable for a given size of engine.

[0004] Typically the landing gear is retracted using an actuator. The actuator may be powered by a hydraulic system. Alternatively, pneumatic, electric or other power systems may be used. The power system often provides power for a number of aircraft systems including primary and secondary flight controls, braking, cargo doors and others. It would be advantageous to reduce the size of the power system thereby reducing the weight of the power system and increasing the efficiency of the aircraft.

100051 Typically, in normal operation a landing gear is extended under the action of gravity, with the motion being controlled by the actuator. However, the landing gear and the aircraft structure supporting it are sized to resist the increased loads generated in the unlikely event that the actuator fails to control the motion of the landing gear -an event referred to as an undamped extension. If the loads generated during such an undamped extension could be reduced then it may be possible to reduce the strength (and therefore weight) of the supporting structure thereby increasing the efficiency of the aircraft.

100061 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

[0007] The present invention provides a landing gear assembly comprising one or more of: a main strut moveable between an extended position and a retracted position; an actuator connected to the main strut and configured to move the main strut from the extended position to the retracted position; an accumulator (for example a spring) connected to the main strut. The accumulator may be connected to the main strut such that potential energy stored in the accumulator acts on the main strut to move the main strut away from the extended position towards the retracted position thereby using at least part of said potential energy to reduce the energy that would otherwise be required by the actuator to move the main strut from the extended position to the retracted position.

100081 It may be that the accumulator is moveable between a lower stress configuration and a higher stress configuration in which the store of potential energy in the accumulator is increased relative to the lower stress configuration. For example, an application of force to the accumulator may cause it to deform and store energy as elastic potential energy. The accumulator may be connected to the main strut such that movement of the main strut away from the retracted position towards the extended position causes an increase in the energy of the accumulator (for example deformation of the spring). Additionally or alternatively, the accumulator may be connected to the actuator such that movement of the actuator, for example movement of the actuator independently of the main strut, causes an increase in the energy of the accumulator (for example deformation of the spring). The accumulator may be connected to the main strut such that the accumulator exerts a force on the main strut that acts to move the main strut away from the extended position towards the retracted position, for example when the main strut is out of the retracted position. -3 -

X00091 Extension of the landing gear and/or the action of the actuator may be used to increase the energy stored in the accumulator for use during the subsequent retraction of the landing gear. For example, deformation of the accumulator, for example the spring, from its original shape during extension of the landing gear assembly and/or under the action of the actuator may cause an increase in the potential energy of the accumulator, for example the spring. This potential energy may be used during retraction of the landing gear assembly to assist the actuator in returning the landing gear to the retracted position thereby reducing the power required from the actuator. It is often the case that the landing gear retraction load represents the maximum load case for the power system and the need to achieve this loading places a lower limit on the size of the power system. So, for example, a hydraulic system may be sized for an operation that lasts about 20 seconds of a 17 hour flight. Once in flight, much of the weight of the hydraulic system is then dead weight. Use of an accumulator as described above may facilitate a reduction in the size of the power system required to retract the landing gear, for example by reducing the maximum load required from the power system. Additionally or alternatively, the accumulator may damp the motion of the landing gear during extension, thereby reducing the loads generated in the event of an undamped extension and facilitating a reduction in the weight of the structure that must accommodate such loads. Additionally or alternatively, use of the energy from the accumulator may increase the speed of retraction of the landing gear for a given actuator and/or power system.

[0010] For the purposes of the present application, an accumulator may be defined as a device that stores mechanical energy. It may be that the accumulator is configured to store mechanical energy when under stress. Thus, the store of potential energy in the accumulator may be increased by moving the accumulator from a lower stress configuration to a higher stress configuration, for example through deformation of the device from its original shape. The potential energy stored in the accumulator may be released by movement of the accumulator away from the higher stress configuration to a lower stress configuration. The accumulator may comprise, for example be, a spring. A spring may be defined as a device that stores mechanical energy through elastic deformation of the device from its original shape. The energy may be stored as elastic potential energy. A spring may be a mechanically simple, efficient and/or reliable way of providing an accumulator for use in the present invention. Alternatively, the accumulator may comprise a pneumatic or hydraulic accumulator, for example an air spring or spring type hydraulic accumulator, or other type of accumulator in which energy may be stored. The accumulator may be said to be in a lower stress configuration when it is extended and a higher stress configuration when it is compressed.

[0011] The connection between the main strut and the accumulator may be configured to transmit force from the main strut to the accumulator in a first direction that causes the amount of energy stored in the accumulator to increase, for example that causes the accumulator to move away from the lower stress configuration towards the higher stress configuration. Thus, the movement of the main strut during extension of the landing gear may be used to increase the energy of the accumulator. The connection between the main strut and the accumulator may be configured to transmit force from the accumulator to the main strut in a second direction that causes the main strut to move away from the extended position towards the retracted position. "f he first direction may be opposite to the second direction. The accumulator may be connected to the main strut such that the force exerted on the main strut by the accumulator as it releases said energy, for example as it moves away from the higher stress configuration towards the lower stress configuration, causes the main strut to move away from the extended position towards the retracted position. It will of course be appreciated that the force from the accumulator may, in and of itself, not be sufficient to move the main strut towards the retracted position but will, in any case, reduce the effort required by the actuator to do so.

[0012] The connection between the accumulator and the actuator may be configured to transmit force from the actuator to the accumulator in a first direction that causes an increase in the energy stored in the accumulator. Thus, the actuator may be connected to the accumulator such that movement of the actuator, for example in a first direction, causes an increase in the energy stored in the accumulator. The connection between the actuator and the main strut may be configured to prevent the transmission of force in the first direction from the actuator to the main strut such that the actuator may be used to increase the energy of the accumulator without moving the main strut. Thus, the actuator may be connected to the main strut and accumulator such that the energy of the accumulator can be increased by the actuator independently of any movement of the main strut. This may allow the actuator to increase the energy of the accumulator during periods of low demand, that additional energy then being available to assist in retracting the main strut at a later time.

[0013] The landing gear may be configured such that the energy of the accumulator increased by the movement of the main strut, the action of the actuator or both.

[0014] The step of moving the main strut from the retracted position to the extended position may be referred to as extending the landing gear. The step of moving the main strut from the extended position to the retracted position may be referred to as retracting the landing gear.

100151 Movement of the accumulator between the lower and higher stress configurations may comprise a translation and/or rotation of one part of the accumulator relative to another. For example, the accumulator may deform axially, rotationally and/or a combination of the two as it moves between the lower and higher stress configurations. The accumulator may comprise an extension spring (i.e. a spring configured to store mechanical energy when extended), a compression spring (i.e. a spring configured to store mechanical energy when compressed), a torsion spring (i.e. a spring configured to store mechanical energy when twisted) or any other type of spring. The spring may be a linear spring (i.e. a spring configured such that the degree of elastic deformation for a given increase in force remains constant) or a non-linear spring (i.e. a spring configured such that the degree of elastic deformation for a given increase in force varies depending on the amount of force applied).

[0016] The spring may be connected to the main strut such that movement of the main strut away from the retracted position towards the extended position causes a deformation of the spring, for example extension, compression and/or twisting of the spring, thereby increasing the potential energy of the spring. The spring may be connected to the actuator such that movement of the actuator, for example in the first direction, causes a deformation of the spring, for example extension, compression and/or twisting of the accumulator, thereby increasing the potential energy of the spring. The spring may be -6 -connected to the main strut such that when the spring is deformed, for example extended, compressed and/or twisted, force exerted by the spring on the main strut acts in a direction towards the retracted position and away from the extended position. Thus, the spring may be configured to do work on the main strut, transforming the potential energy into kinetic energy to move the main strut towards the retracted position. The spring may be connected to the main strut such that as the spring returns to its original shape, for example contracts, expands and/or untwists, the potential energy released acts to move the main strut away from the extended position towards the retracted position.

[0017] The actuator may be a hydraulic, pneumatic, electrical or other type of actuator. The actuator may be configured for connection to a power system, for example a hydraulic, pneumatic, electrical or other power system.

100181 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. 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.

[0019] The actuator, for example a first end of the actuator, may be connected to the main strut in the region of the first (upper) end of the main strut. The actuator may be connected to the main strut at a point adjacent to the pintle. The actuator, for example a second end of the actuator, may be suitable for connection to an aircraft on which the landing gear assembly is mounted. The actuator may comprise an actuator body and an arm mounted for movement relative to the actuator body. A distal end of the arm may comprise one or more attachment features configured for connection to the main strut.

100201 The accumulator, for example a first end of the accumulator, may be connected to the main strut in the region of the first (upper) end of the main strut. The accumulator may be connected to the main strut at a point adjacent to the pintle and/or the point at which the actuator is connected to the main strut. The accumulator, for example a second -7 -end of the accumulator, may be suitable for connection to an aircraft on which the landing gear assembly is mounted. The first and/or second ends of the accumulator may comprise one or more attachment features configured for connection to the main strut and the aircraft respectively.

100211 The accumulator may be directly connected to the main strut. Alternatively, the accumulator may be indirectly connected to the main strut, for example via a main linkage. Using a main linkage may provide more control over when during extension and retraction of the landing gear assembly energy is transferred to or from the accumulator. [0022] The main linkage may comprise one or more members connecting the first end of the accumulator to the main strut. Said members may be connected, for example pivotally, slidably, rotatably or otherwise moveably connected, to each other such that force can be transmitted between the accumulator and the main strut via the main linkage. It will be appreciated that by varying the design of the linkage, the point in the extension and/or retraction cycle at which energy is extracted to and/or returned by the accumulator can be adjusted to enable optimisation for a given geometry.

[0023] The accumulator, for example the first or second end of the accumulator, may be connected to the actuator. Thus the first or second end of the accumulator may comprise one or more attachment features configured for connection to the actuator. The accumulator may be indirectly connected to the actuator, for example via an actuator linkage. The actuator linkage may be configured to transmit force from the actuator to the accumulator in a first direction that causes an increase in the amount of energy stored in the accumulator. The actuator linkage may be configured to prevent the transmission of force in the first direction from the actuator to the main strut such that the actuator may be used to increase the energy of the accumulator without moving the main strut. Thus, the actuator linkage may be configured to allow the actuator to increase the energy of the accumulator, for example deform the accumulator, without moving the main strut.

100241 The actuator may have a longitudinal axis, for example the axis along which the actuator acts, for example along which the arm moves. The accumulator may have a longitudinal axis, for example the axis along which the accumulator (for example the spring) extends and/or contracts, or the axis around which the accumulator twists (for -8 example the axis around which a torsion spring twists). The longitudinal axis of the accumulator may be parallel to the longitudinal axis of the actuator when the main strut is in the extended position.

100251 The landing gear assembly may be configured to extend at least in part under the action of gravity. That is to say, the landing gear assembly may be configured such that the main strut moves away from the retracted position towards the extended position, for example from the retracted position to the extended position, under the action of gravity. It may be that the landing gear does not comprise a mechanism arranged to accelerate the main strut away from the retracted position towards the extended position. The actuator may be connected to the main strut and configured to control, for example damp, the movement of the main strut away from the retracted position towards the extended position. Thus, the actuator may be connected to the main strut and configured to act against (i.e. resist) the movement of the main strut away from the refracted position towards the extended position.

[0026] The actuator may be an actuator that uses a fluid containing magnetic particles, for example a magnetorheological fluid or a ferrofluid (with smaller magnetic particles) to vary the ability of the actuator to transmit force. Such an actuator is described and claimed in GB 2,538,746. The contents of that application are fully incorporated herein by reference. The claims of the present application may incorporate any of the features disclosed in that patent application.

[0027] The landing gear assembly may comprise one or more wheels, for example a plurality of wheels, mounted to the main strut in the region of a second (lower) end of the strut. The main strut may be configured to transmit loads from the wheels to the aircraft. The main strut may be substantially vertical when in the extended position. The main strut may be substantially horizontal when in the retracted position. The main strut may comprise one or more attachment features configured for connection to the actuator and/or the accumulator.

[0028] The accumulator, for example the spring, may have an original shape defined as the configuration of the accumulator when the main strut is in the retracted position. The original shape may be the lower stress configuration. It may be that there is no load on -9 -the accumulator when the main strut is in the retracted position. Thus, the original shape may be the unstressed shape of the accumulator. Alternatively, the accumulator may be deformed to some extent when the main strut is in the refracted position. The accumulator may have a number of configurations (or shapes), each configuration corresponding to a different degree of stressing of the accumulator (and/or distance of the main strut from the retracted position) and therefore a different level of potential energy stored by the accumulator.

[0029] It may be that the accumulator has a series of different configurations (or shapes) as the main strut moves away from and/or towards the retracted position. The accumulator may have a first configuration when the main strut is in the extended position. The first configuration may be the higher stress configuration. The amount of potential energy stored in the accumulator may be greater when the accumulator is in its first configuration than when the accumulator is in its original shape (or lower stress configuration). The potential energy of the accumulator may be highest when the accumulator is in its first configuration (e.g. when the strut is in the extended position) as compared to any other configuration taken by the accumulator as the main strut moves from the retracted position to the extended position or vice versa.

[0030] 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.

[0031] In a second aspect of the invention, there is provided an aircraft comprising a landing gear assembly in accordance with the first or fifth aspects.

[0032] The aircraft may comprise a power system, for example a hydraulic, pneumatic, electrical or other power system. The actuator may be connected to the power system to receive power therefrom. The power system may be connected to other aircraft systems for example one or more of the primary flight controls, secondary flight controls, braking system, cargo doors and others. In the case of a hydraulic or pneumatic power system, the system may comprise a liquid (for a hydraulic system) or gas (for a pneumatic -10 -system) reservoir, one or more pumps, a manifold for distributing the liquid or gas and a plurality of distribution lines connected to aircraft systems requiring hydraulic or pneumatic power. It may be that the accumulator does not form part of, for example is not in fluid communication with, the power system. It may be that the accumulator does not form part of, for example is not in fluid communication with, the actuator. It may be that the accumulator is separate to, for example physically and/or functionally separate to, the power system and the accumulator.

[0033] The actuator, for example the second end of the actuator, may be connected to the aircraft, for example to at a mounting point, for example to a pin, located on the aircraft (i.e. not forming part of the landing gear assembly), for example located in a landing gear bay of the aircraft. Thus, a first end of the actuator may be connected to the main strut and a second end of the actuator may be connected to the aircraft such that extension and/or retraction of the actuator causes the landing gear assembly to extend and/or retract. Movement, for example retraction, of the actuator may cause the main strut to move away from the extended position towards the retracted position. Controlling the movement, for example the extension, of the actuator may limit the speed at which the main strut moves away from the retracted position towards the extended position.

[0034] The accumulator, for example the second end of the accumulator, may be connected to the aircraft, for example to at a mounting point, for example to a pin, located on the aircraft (i.e. not forming part of the landing gear assembly), for example located in a landing gear bay of the aircraft. The accumulator may be connected to the aircraft in the region of, for example at, the same mounting point as, for example the same pin as, the actuator. Thus, a first end of the accumulator may be connected to the main strut and a second end of the accumulator may be connected to the aircraft such that movement of the main strut away from the retracted position towards the extended position causes the accumulator to deform.

1003511n a third aspect of the invention, there is provided a method of operating a retractable landing gear comprising a main strut, an actuator, for example driven by a power system, connected to the main strut and/or an accumulator (for example a spring) connected to the main strut. The power system may experience periods of higher demand and periods of lower demand. The method may comprise one or more of the following steps. The method may comprise increasing the potential energy of the accumulator during a period of lower demand, for example during extension of the landing gear and/or while the landing gear is locked in the extended position. The method may comprise extending the landing gear. Said extension of the landing gear may comprise movement of the main strut from a retracted position to an extended position, said movement of the main strut increasing the potential energy of the accumulator, for example by moving the accumulator away from a lower stress configuration towards a higher stress configuration. Additionally or alternatively, the method may comprise using the actuator to increase the potential energy of the accumulator, for example to move the accumulator away from a lower stress configuration towards a higher stress configuration. The method may comprise retracting the landing gear by moving the main strut from the extended position to the retracted position using the actuator and at least part of said potential energy stored in the accumulator, for example stored in the accumulator during extension of the landing gear.

[0036] Increasing the potential energy of the accumulator during a period of lower demand and then using that energy during retraction (a period of higher demand) may allow the maximum load on the power system (and therefore the size of the power system) during retraction to be reduced Increasing the potential energy of the accumulator may comprise moving the accumulator away from a lower stress configuration towards a higher stress configuration, for example deforming the accumulator.

[0037] Periods of higher demand may occur when the power system supplies power to the actuator (or any other system if present) during a high power event, for example during retraction of the landing gear. Periods of lower demand may occur when no high power event is taking place, for example while the main strut remains in the extended and/or retracted positions and/or while the main strut is moving from the retracted position to the extended position. Thus, the method may comprise increasing the potential energy of the accumulator using the movement of the main strut during extension of the landing gear (a period of lower demand). Additionally or alternatively, -12 -the method may comprise increasing the potential energy of the accumulator using the actuator while the main strut remains in the extended or retracted positions (both periods of lower demand), for example before or after retraction of the landing gear, for example during or immediately prior to the take-off run.

[0038] The movement of the main strut from a retracted position to an extended position may occur (at least in part) under the action of gravity, for example with the movement of the main strut being controlled (i.e. damped) by the actuator. Thus, the actuator may act against the movement of the main strut from a retracted position to an extended position. The method may comprise releasing the main strut, for example unlocking an uplock mechanism, and allowing the main strut to rotate under the action of gravity. The speed of rotation of the main strut may be controlled, for example limited, by the actuator. It will be appreciated that the accumulator may also act to slow the extension of the landing gear as gravitational potential energy becomes potential energy in the accumulator instead of kinetic energy of the main strut When the main strut is in the extended position, the method may comprise locking the landing gear, for example the main strut, in position, for example using a downlock mechanism, for example a locking actuator. The method may comprise using the actuator to increase the potential energy of the accumulator, for example to do mechanical work on the accumulator, for example to deform the accumulator, when the landing gear is in the extended position.

[0039] The method may comprise unlocking the landing gear, for example the main strut, for example the downlock mechanism, to allow the landing gear to retract. The method may comprise providing power to the actuator and operating the actuator to move the main strut from the extended position to the retracted position. It may be that as the main strut moves from the extended position to the contracted position the accumulator moves away from the higher stress configuration towards the lower stress configuration, for example contracts, expands and/or untwists, causing potential energy in the accumulator to be transformed into kinetic energy that acts to return the main strut towards, for example to, the retracted position. Thus, potential energy from the accumulator may be used to reduce the work required by the actuator.

-13 - 100401 The method may comprise a load alleviation step carried out during unlocking of the landing gear and/or main strut from the extended position. Use of a load alleviation step may reduce the risk of an explosive movement of the main strut under the action of the loaded accumulator. The load alleviation step may comprise exerting a force on the main strut using the actuator to substantially balance the force exerted on the main strut by the accumulator, for example immediately prior to unlocking the landing gear. The force exerted on the main strut by the actuator may act to over-extend the landing gear, for example to move the main strut away from the retracted position and beyond the extended position. It will be appreciated that the force is balanced by the action of the accumulator and accordingly it may be that no such over-extension occurs in practice. The method may then comprise unlocking the landing gear, for example the main strut. The method may then comprise switching the direction in which the actuator acts, for example reducing the force exerted by the actuator in the first direction and then increasing the force exerted by the actuator in the second direction.

[0041] In a fourth aspect of the invention there is provided a kit of parts for forming the landing gear assembly of the first or fifth aspects. The kit of parts may comprise one or more of an actuator, an accumulator, a main strut, a main linkage, an actuator linkage and one or more wheels, all of which may have any of the features described above with reference to first aspect.

[0042] In a fifth aspect of the invention there is provided a landing gear assembly comprising: an actuator for retracting the landing gear assembly; and/or an accumulator connected to the landing gear assembly. The accumulator may be connected to the landing gear to (i) oppose extension of the landing gear such that the potential energy of the accumulator is increased during extension of the landing gear and/or (ii) assist the actuator in retracting the landing gear assembly such that at least part of said potential energy is used in retracting the landing gear assembly.

100431 In a sixth aspect of the invention there is provided a method of operating a retractable landing gear comprising a main strut moveable by an actuator between an extended position and a retracted position. The method may comprise the step of converting kinetic energy of the main strut as it moves from the retracted position to the -14 -extended position into captured potential energy. The method may comprise the step of the actuator with the assistance of at least some of the captured potential energy then moving the main strut from the extended position to the retracted position.

100441 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

[0045] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: [0046] Figure I shows a perspective view of an aircraft including a landing gear according to an example embodiment of the invention; [0047] Figures 2(a) and (b) show the landing gear of Figure I in the extended and retracted configurations respectively; and 100481 Figure 3 shows an example method in accordance with the method of the invention.

DETAILED DESCRIPTION

100491 Figure 1 shows an aircraft 1 including two main landing gear 4 in accordance with an example embodiment. 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.

[0050] Figure 2a shows a close up of a schematic view of a main landing gear 4 in the extended configuration. For comparison, the position of some elements of the landing gear when the landing gear is retracted is indicated using dashed lines in Fig. 2a. Main landing gear 4 is mounted on aircraft I via a pintle 6 located at the upper end of a main strut 8. A pair of wheels 10 are mounted at the lower end of main strut 8. in Figure 2 two wheels 10 are shown in a diablo type arrangement, but in other embodiments further wheels may be included and/or bogies may be used. An actuator 12 is attached at one -15 -end to the main strut 8 and at the other end to the aircraft 1 at a point located within landing gear bay 13 (shown in Figure 2b). A spring 14 lies parallel to the actuator 12 and is attached at one end to the main strut 8 and at the other end to the aircraft 1. A foldable support strut 16 is attached at one end to the main strut 8 and at the other end to the aircraft 1. The foldable support strut 16 comprises two support members 16a, lob. The first support member 16a is pivotally connected at one end to the aircraft 1 and at the other end to the second support member 16b. The second support member 16b is pivotally connected at one end to the first support member 16a and at the other end to the main strut 8. The foldable support strut 16 is straight in Fig. 2a. In other embodiments a telescopic support strut may be used. Actuator 12 is connected to hydraulic system 18 via hydraulic supply lines 20.

100511 In some embodiments, spring 14 may be a tension/extension spring, for example a coil spring. In other embodiments spring 14 may be a compression spring, a torsion spring or any other type of structure that stores mechanical energy through elastic deformation. In yet other embodiments, a different type of accumulator may be used in place of spring 14, for example an air spring or spring-type hydraulic accumulator.

100521 While the system in Fig. 2a includes a hydraulic system to provide hydraulic power to actuator 12, other power systems may be used. In other embodiments a pneumatic or electric system may be used to provide power to actuator 12.

[0053] Figure 2b shows a close up of a schematic view of a main landing gear 4 in the retracted configuration. For comparison, the position of some elements of the landing gear when the landing gear is extended is indicated using dashed lines in Fig. 2b. In Fig. 2b, the main strut 8 is rotated by about 90 degrees relative to its position in Fig. 2a. In Fig. 2b, foldable support strut 16 is folded and actuator 12 and spring 14 are shorter relative to their lengths in Fig. 2a. Wheels 10 are located within landing gear bay 13 when the landing gear is in the retracted configuration.

100541 In use, the landing gear 1 is released from the retracted position by unlocking a locking mechanism (not shown), for example prior to landing. The main strut 8 and the wheels 10 attached thereto drop under the action of gravity with the motion being damped by actuator 12. Movement of the main strut 8 from the retracted to the extended -16 -position causes spring 14 to stretch, stressing the spring and increasing the potential energy of the spring and further damping the movement of the main strut 8. The landing gear 1 is then locked in the extended position in a conventional way, for example using a locking actuator (not shown). The landing gear remains in the extended position during landing, taxiing and take-off. Following take-off the landing gear is unlocked and the actuator 12 moves the main strut from the extended position to the retracted position using force generated from pressure provided by hydraulic system 18. During retraction spring 14 seeks to return to its original shape and therefore exerts a force on the main strut 8 in the direction of the retracted position. Accordingly, in landing gear in accordance with the present example embodiment, energy harvested by the spring during extension is used to assist the actuator in retracting the landing gear thereby reducing the demand on the actuator and its associated power system. Further, the spring damps the motion of the main strut during extension, thereby limiting the loads generated in the case of an undamped extension and facilitating optimisation of the structure designed to react those loads. The additional energy provided by the spring may also increase the speed with which the landing gear retracts.

100551 Figure 3 shows a flow chart of an example method in accordance with the method of the invention. The method may be carried out using the landing gear of the first embodiment. The first step 50 in Fig. 3 corresponds to the landing gear being in the retracted position. The landing gear then moves towards the extended position 52. Movement of the landing gear towards the extended position 52 moves the accumulator from a lower stress configuration towards a higher stress configuration 54 thereby increasing its potential energy. In sonic embodiments, said movement may comprise one part of the accumulator moving relative to another part of the accumulator. The landing gear continues to move 52 until it is in the extended position 56. While the landing gear is in the extended position 56 the actuator moves the accumulator further away from the lower stress configuration towards the higher stress configuration 58. Later, the actuator moves the landing gear towards the retracted position 60 until it reaches the retracted position 64. While the actuator is moving the landing gear 60 the accumulator acts on the landing gear 62 to assist the actuator in moving the landing gear towards the retracted -17 -position and in doing so moves away from the higher stress configuration towards the lower stress configuration. It will be appreciated that in some embodiments, step 54 is not carried out, and movement of the accumulator occurs only in step 62 under the action of the actuator. In other embodiments, step 62 is not carried out and movement of the accumulator occurs only in step 54 as a result of the movement of the landing gear.

100561 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.

100571 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 (18)

1. -18 -CLAIMS1. A landing gear assembly comprising: a main strut moveable between an extended position and a retracted position; an actuator connected to the main strut and configured to move the main strut from the extended position to the retracted position; and an accumulator moveable between a lower stress configuration and a higher stress configuration in which the store of potential energy in the accumulator is increased relative to the lower stress configuration, and connected to the main strut such that potential energy stored in the accumulator acts on the main strut to move the main strut away from the extended position towards the retracted position thereby using at least part of said potential energy to reduce the energy that would otherwise be required by the actuator to move the main strut from the extended position to the retracted position.
2. 2. A landing gear assembly according to claim 1, wherein the accumulator is connected to the main strut such that movement of the main strut away from the retracted position towards the extended position causes movement of the accumulator towards the higher stress configuration thereby increasing the potential energy of the accumulator.
3. 3 A landing gear assembly according claim I or claim 2, wherein the accumulator is connected to the actuator such that movement of the actuator independently of the main strut causes movement of the accumulator towards the higher stress configuration thereby increasing the potential energy of the accumulator.
4. 4. A landing gear assembly according to any previous claim, wherein the accumulator comprises a spring.
5. 5. A landing gear assembly according to claim 4, wherein the spring is connected to the main strut such that movement of the main strut away from the retracted position towards the extended position causes extension, compression and/or twisting of the spring, thereby increasing the potential energy of the spring.
6. -19 - 6. A landing gear assembly according to claim 4 or claim 5, wherein the spring is connected to the main strut such that movement of the main strut away from the extended position towards the retracted position allows the spring to contract, expand and/or untwist, thereby releasing potential energy to assist the actuator in moving the main strut.
7. 7. A landing gear assembly according to any previous claim, further comprising a pintle for mounting the landing gear assembly on an aircraft for movement relative to the aircraft.
8. 8. A landing gear assembly according to any previous claim, wherein the landing gear is configured to extend at least in part under the action of gravity and the actuator is connected to the main strut to resist the movement of the main strut away from the refracted position towards the extended position.
9. 9. An aircraft having a landing gear assembly according to any previous claim mounted thereon, and wherein the accumulator is connected to a mounting point located in a landing gear bay of the aircraft.
10. 10. An aircraft according to claim 9, wherein the actuator is connected to the aircraft at a mounting point located in a landing gear bay of the aircraft.
11. 11. An aircraft according to claim 10, wherein the actuator and accumulator are connected to the aircraft at the same mounting point.
12. 12. A method of operating a retractable landing gear comprising a main strut, an actuator driven by a power system and connected to the main strut and an accumulator connected to the main strut, and wherein the power system experiences periods of higher demand and periods of lower demand, the method comprising the steps of: increasing the potential energy of the accumulator during a period of lower demand by moving the accumulator from a lower stress configuration to a higher stress configuration; and retracting the landing gear by moving the main strut from the extended position to the retracted position using the actuator and at least part of said potential energy stored by the accumulator.
13. -2 0 - 13. A method according to claim 12, further comprising extending the landing gear, said extension of the landing gear comprising movement of the main strut from a retracted position to an extended position, said movement of the main strut causing the accumulator to move away from the lower stress configuration towards the higher stress configuration and increasing the potential energy of the accumulator.
14. 14. A method according to claim 13, wherein the movement of the main strut from the retracted position to the extended position occurs at least in part under the action of gravity and with the movement of the main strut being controlled by the actuator.
15. 15. A method according to any of claims 12 to 14, further comprising moving the actuator while the main strut remains stationary, said movement of the actuator causing the accumulator to move away from the lower stress configuration towards the higher stress configuration and increasing the potential energy of the accumulator.
16. 16. A kit of parts for forming a landing gear assembly in accordance with any of claims I to 11 and 17, the kit comprising an actuator, an accumulator and a main strut.
17. 17. A landing gear assembly comprising: - an actuator for retracting the landing gear assembly; and - an accumulator connected to the landing gear assembly to (i) oppose extension of the landing gear such that the potential energy of the accumulator is increased during extension of the landing gear and (ii) assist the actuator in retracting the landing gear assembly such that at least part of said potential energy is used in retracting the landing gear assembly.
18. 18. A method of operating a retractable landing gear comprising a main strut moveable by an actuator between an extended position and a retracted position, the method comprising the steps of: converting kinetic energy of the main strut as it moves from the retracted position to the extended position into captured potential energy, - the actuator with the assistance of at least some of the captured potential energy then moving the main strut from the extended position to the retracted position.