Aircraft landing gear assembly

Abstract

An aircraft landing gear assembly comprising: a ground contacting assembly (10); a main strut (8); a mounting bearing arranged for coupling the landing gear assembly to an aircraft such that the main strut supports the aircraft on the ground when the ground contacting assembly is in contact with the ground; a noise-inducing component; and a perforated sheet fairing (6a, 6b) comprising a body having a first surface and a second surface and plurality of holes (64) extending from the first surface to the second surface, each hole having an axis, wherein the perforated sheet fairing further comprises a plurality of airflow disruption elements (66) each extending towards the axis of a hole at an angle between 5° and 185° relative to the axis of the hole.

Description

[0001] Aircraft Landing Gear Assembly

[0002] Background

[0003] An aircraft can generate considerable noise during a landing approach. A significant portion of this noise is attributable to air flowing around the deployed landing gear. Although the aircraft may be travelling at around 80m / s during a landing sequence, localised airflow around a noise-inducing region of the landing gear may reach speeds of around 300m / s. The interaction between the landing gear and the airflow can lead to the generation of turbulent flow, vortex shedding, and boundary layer separation, all of which contribute to increased noise generation. This is known in the art, and will be referred to herein, as aero-acoustic noise. Aero-acoustic noise is particularly undesirable because airports are often located close to cities, or other densely populated areas.

[0004] Attempts have been made to address aero-acoustic noise problems. For example, it is known to provide an aircraft landing gear with a fairing. A fairing is a generally rigid structure, usually made from metal or composite materials, arranged to shield a noiseinducing region of an aircraft landing gear from airflow during landing.

[0005] The present inventors have devised a new type of aircraft landing gear fairing which can have improved self-noise properties in comparison to known aircraft landing gear fairings.

[0006] Summary

[0007] In accordance with a first aspect of the invention, there is provided an aircraft landing gear assembly according to claim 1.

[0008] According to a second aspect of the invention, there is provided an aircraft landing gear assembly according to claim 10.

[0009] Thus, the aircraft landing gear assembly according to the first and second aspects of the invention provide alternative solutions to the technical problem of reducing selfnoise generated by the perforates sheet fairing. The landing gear assembly of the first aspect includes airflow disruption elements arranged to induce streamwise vortices in the holes, which can result in enhanced turbulence mixing and velocity reduction. Likewise, the landing gear assembly of the second aspect includes secondary holes directed toward the exit axis of the primary holes. The interaction of these secondary flows with the jet shear layer of the primary hole can lead to improved mixing, resulting in the disintegration of the large-scale turbulence structure.

[0010] Optional features of the first and second aspects are set out in the dependent claims.

[0011] The noise inducing component can for example comprise some or all of the main strut, side stay, lock link, torque link, an axle, wheel assembly, brake assembly, hydraulic pipe, or the like.

[0012] In accordance with a third aspect of the present invention, there is provided an aircraft including one or more aircraft landing gear assemblies according to the first aspect.

[0013] Brief Description of the Drawings

[0014] By way of example only, certain embodiments of the invention will now be described by reference to the accompanying drawings, in which:

[0015] Figure 1 is a diagram of an aircraft;

[0016] Figures 2 and 3 are diagrams of a known aircraft landing gear assembly;

[0017] Figure 4 is a diagram showing a cross section through a perforated sheet fairing, illustrating the axial column of each hole;

[0018] Figure 5 is a diagram showing a cross section through the perforated sheet fairing of Figure 4, illustrating airflow though the holes;

[0019] Figures 6a and 6b are diagrams of part of a landing gear assembly according to an embodiment of the invention, including a perforated sheet fairing including airflow disruption elements;

[0020] Figure 7 is a diagram of part of a fairing according to an embodiment of the invention, including airflow disruption elements; Figure 8 is a diagram indicating angles for airflow disruption elements;

[0021] Figures 9a and 9b are diagrams of part of a landing gear assembly according to an embodiment of the invention, including a perforated sheet fairing including microjets; and

[0022] Figure 10 is a diagram showing a cross section through the fairing of Figures 9a and 9b.

[0023] Detailed Description

[0024] By way of a non-limiting overview, embodiments of the invention relate to an aircraft landing gear assembly which include a perforated sheet fairing for reducing aeroacoustic noise, the fairing being provided with either protrusions or microjets arranged to generate streamwise vortices and improve turbulence mixing in the wake of the holes in the perforated fairing to reduce self-noise generated by the perforated sheet fairing.

[0025] Figure 1 is a diagram of an aircraft 2. The aircraft includes assemblies such as a nose landing gear 4 and a pair of main landing gear 6. The landing gear 4, 6 each includes a shock absorber strut for damping landing loads and supporting the weight of the aircraft 2 when it is on the ground. The term aircraft as used herein can include aeroplanes, helicopters and the like having mass in excess of 450kg.

[0026] Figure 2 is an example of an aircraft landing gear assembly 6 which can include a flow deflector system according to an embodiment of the invention. It will however be appreciated that a flow deflector system according to embodiments of the invention can be used in a range of types of aircraft landing gear including main landing gear and nose landing gear, with one or more axles and include wheels or other ground contacting means.

[0027] The aircraft landing gear assembly 6 is movable between a deployed condition, for take-off and landing, and a stowed condition for flight. The landing gear assembly includes a main shock absorber strut 8, comprising an outer cylinder and a sliding tube, a foldable stay 14, and a lock link 20. An upper end of the strut 8 is provided with a bearing 9 via which the strut 8 is pivotally coupled to the airframe of the aircraft 2. A lower end of the strut 8 is provided with a wheel and brake assembly 30. A retraction actuator 12 is provided for moving the landing gear between the deployed condition and the stowed condition. The retraction actuator can have one end coupled to the airframe 11 and another end coupled to the strut 8.

[0028] The stay 16 serves to support the orientation of the strut 8 when the landing gear is in the deployed condition. The stay 18 generally includes a two-bar linkage 16, 18 that can be unfolded to assume a generally straight or aligned, over centre condition in which the stay 18 is locked to inhibit movement of the outer cylinder, as shown in Figure 2. When the stay is broken, it no longer inhibits pivotal movement of the strut 8 about the mounting bearing and strut 8 can be moved by the retraction actuator 12 towards the stowed condition.

[0029] The lock link 20 has an elongate upper link arm having a lower end pivotally coupled to an upper end of an elongate lower link arm via a pivot pin. The link arms can therefore pivotally move relative to one another about the pivot pin. The lock link is pivotally coupled to the strut 8 and one of the stay arms 16. When the lock link 20 is in the locked condition, as illustrated in Figure 2, the upper and lower link arms are generally longitudinally aligned or coaxial, and can be 'over-centre', such that the lock link 20 is arranged to oppose a force attempting to break or fold the stay 14. The lock link 20 must be broken to enable the stay 14 to be broken and folded, thereby permitting the strut 6 to be moved by the retraction actuator 12 towards the stowed condition.

[0030] The down lock assists in moving the landing gear assembly to the deployed condition and locking it in that state by making the lock link 20. Down lock springs also inhibit the lock link 20 accidentally being broken / unlocked.

[0031] A lock stay actuator 22 is coupled between the stay 14 and lock link 20 and arranged to pivotally move the link arms so as to make and break the lock link 20. The lock stay actuator 22 can break the lock link 20 against the down lock spring bias, allowing the landing gear assembly to be folded and stowed as described previously.

[0032] Referring additionally to Figure 3, the outer cylinder 24 and sliding tube 26 of the strut 8 can be coupled via a set of torque links 28 which permit relative axial movement but inhibit relative rotational movement between the outer cylinder 24 and sliding tube 26.

[0033] Wheel and brake assemblies 10 can be mounted on axles 30 which in turn are mounted at end regions of a bogie beam 32. The bogie beam 32 is pivotally coupled near its centre to the sliding tube 26 via a bogie pivot pin 34. Brake rods 36 can be provided to anchor the brake packs to the sliding tube 26 to react brake torque.

[0034] As will be appreciated by the skilled person, the above-mentioned landing gear components can, in use, result in generation of aeroacoustic noise.

[0035] It is known to position a perforated sheet fairing relative to a noise inducting component on an aircraft landing gear to reduce aeroacoustic noise. A perforated sheet fairing can for example comprise a planar or non-planar sheet of metal or composite material which has a plurality of through-holes extending between major surfaces of the sheet.

[0036] Referring to Figure 4, a cross sectional view of a perforated sheet fairing is shown generally at 40. The fairing 40 has a body 42 defining major surfaces 42a, 42b separated by the thickness TH of the body 42. A plurality of holes 44 extend through the body 42 and are arranged with regular or irregular spacing and allow some incident airflow to pass through the body 42. The holes 44 can for example be circular in cross section. The bore of each hole 44 has an axis AX and each bore can be considered to define an axial column of free space 44a.

[0037] Referring additionally to Figure 5, as incident airflow A passes through a hole 44, it enters the first end of the hole 44, which opens onto major surface 42a, passes through the bore of the hole 44 and then exits the second end of the hole 44, which opens onto major surface 42b. The airflow existing the second end of the hole 44 is relatively turbulent. The present inventors have found that airflow exiting the second end of the holes 44 can constructively build to generate self-noise from the faring 40.

[0038] Referring to Figures 6a and 6b, a perforated sheet fairing according to an embodiment of the invention is shown generally at 60. The fairing 60 can be positioned relative to a noise inducting component on an aircraft landing gear such as the landing gear of Figure 3 to reduce aeroacoustic noise generated by the noise-inducting component.

[0039] The fairing 60 is similar to the fairing 40 of Figure 4, with first and second major surfaces 62a, 62b and holes 64 formed though the body. The fairing 60 differs from the fairing 40 in that the fairing 60 of this embodiment is provided with airflow disruption elements 66 arranged to induce streamwise vortices in the holes, which can result in enhanced turbulence mixing and velocity reduction. This can contribute to the reduction of self-noise from the fairing 60 as well as overall noise from the landing gear. The airflow disruption elements 66 can also disrupt large-scale structures that would otherwise be produced by unobstructed holes in a perforated sheet fairing.

[0040] More specifically, and referring additionally to Figure 7, each hole has a perimeter surface P which terminates at the bore of the hole. In this embodiment the perimeter is circular due to the cylindrical bore with a diameter ranging from 0.2mm to 10mm, but in other embodiments holes can have any regular or irregular shape; for example, holes can be of geometric shapes including elliptical, square, rectangular, triangular, diamond, pentagonal, or hexagonal. The area of these alternate shapes can correspond to that of a circle with a diameter within the range of 0.2mm to 10mm. This flexibility in hole shape can enhance the versatility and adaptability of the noisereduction treatment.

[0041] As illustrated, the airflow disruption elements 66 extend from the front surface 62a of the fairing 60 across the perimeter P of the hole 64 and into the axial column of free space of the hole 64 such that the airflow disruption elements 66 disrupt incident airflow approaching the hole 64.

[0042] Referring additionally to Figure 8, the airflow disruption elements 66 can extend from the perimeter of a respective hole 64 towards the axis AX of the hole 64 at an angle p between 5° and 185° relative to the axis AX of the hole 64. In the embodiment of Figures 6a and 6b, the airflow disruption elements 66 extend from the front face 62a at an angle P of about 60°, so as to extend forward relative to the front face 62a such that the airflow disruption elements 66 do not enter the bore. As will be appreciated, in other embodiments where the airflow disruption elements 66 extend from the front face 62a at an angle P greater than 90° the airflow disruption elements 66 will extend backwards and into the bore of the hole 64. Likewise, although the airflow disruption elements 66 are illustrated as extending from the front face 62a, in other embodiments the airflow disruption elements 66 can extend from the back face 62b at an angle P between 5° and 185° relative to the axis AX of the hole 64. This flexibility in angulation provides enhanced capability to tailor the noise reduction solution to the specific aerodynamic conditions encountered. In some embodiments two or more of the airflow disruption elements 66 around a hole 64 can have different angles P with respect to one another and / or the airflow disruption elements 66 around a first hole 64 can have different angles P with respect to the airflow disruption elements 66 around a second hole 64. The airflow disruption elements 66 can be arranged in an equiangular arrangement around the perimeter P or can be arranged with unequal spacings around the perimeter.

[0043] The airflow disruption elements 66 around a hole 64 can each have the same size and shape as one another or can have different sizes and shapes relative to one another.

[0044] In the illustrated embodiment, the airflow disruption elements 66 are chevrons, which are triangular in shape. However in other embodiments the airflow disruption elements 66 can for example be formed as tabs, having a rectangular shape.

[0045] In any embodiment the airflow disruption elements 66 can extend towards the hole axis AX by any amount that results in some overlap with the hole 64 without completely blocking the hole 64, such that the airflow disruption elements 66 permit airflow to enter the hole 64 when the landing gear assembly is deployed but also generate streamwise vortices in the holes which, in turn, facilitate improved turbulence mixing.

[0046] In any embodiment, the airflow disruption elements 66 can be rigid, formed from metal, composite, or a hard plastics material for example. Alternatively, the airflow disruption elements 66 can be formed from a resiliently deformable material such as rubber. Thus, airflow disruption elements 66 can possess different degrees of rigidity, ranging from solid and rigid to flexible structures. When airflow disruption elements 66 are flexible, they can function akin to trailing-edge brushes, interacting with the boundary layer of air moving over the aircraft surface. This interaction introduces controlled disturbances into the airflow, reducing large-scale turbulence structures that are significant contributors to noise. This flexible feature can enhance the overall noise reduction capability of the system, allowing it to adapt effectively to varied operational conditions and aerodynamic demands. Moreover, airflow disruption elements 66 on a fairing 60 can have different properties with respect to one another in terms of rigidity.

[0047] Referring now to Figures 9a and 9b, a perforated sheet fairing according to an embodiment of the invention is shown generally at 70. The fairing 70 of this embodiment is similar to the fairing 60 of Figures 6a and 6b and for brevity the following description will focus on the differences. In the illustrated embodiment, rather than being provided with airflow disruption elements 66, the perforated sheet fairing 70 is provided with secondary holes which define microjets 76.

[0048] More specifically, the relatively large primary holes 74 are each surrounded with several smaller holes 76 that are angled towards the jet plume of the primary hole 74. The interaction of these secondary flows with the jet shear layer of the principal hole 74 can lead to improved mixing, resulting in the disintegration of the large-scale turbulence structure in a manner similar to the airflow disruption elements 66 approach.

[0049] As illustrates in Figure 10, the primary hole 74 has a diameter DI and the secondary holes 76 each has a diameter D2 which is smaller than DI; for example, D2 can be half DI.

[0050] Each secondary hole 76 has an axis AX2 orientated at an angle a of between 20° and 70° relative to the axis AX of the primary hole 74, such as between 25° and 65° relative to the axis AX of the primary hole 74.

[0051] In any embodiment, the number of airflow disruption elements 66 secondary holes can vary, without any specific restriction to odd or even numbers. Their count can range from a minimum of one to a maximum of 12 for example. This flexibility allows for diverse configurations to optimize noise reduction performance under varying conditions.

[0052] The treatments provided by embodiments of the invention are designed to focus on both the flow impingement side of the sheet and wake regions of the perforated sheets utilised as fairings for landing gear.

[0053] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parenthesis shall not be construed as limiting the claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. Parts of the invention can be implemented by means of hardware comprising several distinct elements. In a device claim enumerating several parts, several of these parts can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

Claims1. An aircraft landing gear assembly comprising: a ground contacting assembly; a main strut; a mounting bearing arranged for coupling the landing gear assembly to an aircraft such that the main strut supports the aircraft on the ground when the ground contacting assembly is in contact with the ground; a noise-inducing component; and a perforated sheet fairing comprising a body having a first surface and a second surface and plurality of through holes extending from the first surface to the second surface, each hole having an axis, wherein the perforated sheet fairing further comprises a plurality of airflow disruption elements, each airflow disruption element being located adjacent to a respective hole and extending from the first surface or second surface of the body towards the axis of the hole at an angle between 5° and 185° relative to the axis of the hole.

2. The aircraft landing gear assembly according to claim 1, wherein a plurality of the holes are each provided with a plurality of airflow disruption elements arranged around the respective hole and defining a set of airflow disruption elements each extending from the first surface or second surface of the body towards the axis of the hole at an angle between 5° and 185° relative to the axis of the hole.

3. The aircraft landing gear assembly according to claim 2, wherein the airflow disruption elements of each set are arranged around the hole in an equiangular arrangement.

4. The aircraft landing gear assembly according to claim 2 or claim 3, wherein the airflow disruption elements of each set extend from the same one of the first surface and the second surface.

5. The aircraft landing gear assembly according to any preceding claim, wherein one or more of the airflow disruption elements are rigid.

6. The aircraft landing gear assembly according to any preceding claim, wherein one or more of the airflow disruption elements are formed from a resiliently deformable material.

7. The aircraft landing gear assembly according to any preceding claim, wherein one or more of the airflow disruption elements are generally triangular in shape, tapering towards the axis of the hole.

8. The aircraft landing gear assembly according to any preceding claim, wherein one or more of the airflow disruption elements are rectangular in shape.

9. The aircraft landing gear assembly according to any preceding claim, wherein one or more or all of the airflow disruption elements extend away from the perforated sheet fairing.

10. An aircraft landing gear assembly comprising: a ground contacting assembly; a main strut; a mounting bearing arranged for coupling the landing gear assembly to an aircraft such that the main strut supports the aircraft on the ground when the ground contacting assembly is in contact with the ground; a noise-inducing component; and a perforated sheet fairing comprising a body having a first surface and a second surface and plurality of first holes extending from the first surface to the second surface, each first hole having a first axis, wherein the perforated sheet fairing further comprises a plurality of secondary holes, each secondary hole extending from the first surface to the second surface adjacent to one of the first holes, wherein each secondary hole has a second axis which is non-parallel with respect to the first axis of the respective first hole such that airflow passing through each secondary hole is directed towards airflow exiting the respective first hole and wherein the diameter of each secondary hole is less than the diameter of the respective first hole.

11. The aircraft landing gear assembly according to claim 10, wherein a plurality of the first holes are each provided with a plurality of secondary holes arranged around a perimeter of the respective first hole and defining a set of secondary holes.

12. The aircraft landing gear assembly according to claim 11, wherein the secondary holes of each set are arranged around the respective first hole in an equiangular arrangement.

13. The aircraft landing gear assembly according to claim 11 or claim 12, wherein the axis of the secondary holes are each arranged at an angle of 20 to 70 degrees with respect to the axis of the adjacent first hole.

14. An aircraft including one or more aircraft landing gear assemblies according to any preceding claim.

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