Aircraft landing gear assembly

Abstract

An aircraft landing gear assembly (36) comprising a wheel and brake assembly and a shock absorbing strut (37), the strut including a mounting bearing for movably coupling the aircraft landing gear assembly to an aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing, the aircraft landing gear assembly further comprising: a noise-inducing region (37); a first perforated sheet fairing (1n); and a second perforated sheet fairing (3n) arranged downstream of the first perforated sheet fairing when the landing gear is in the deployed condition.

Description

[0001] Aircraft Landing Gear Assembly

[0002] 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.

[0003] 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. However, the present inventors have identified that known noise reducing devices, such as fairings, can undesirably increase the weight of the landing gear.

[0004] Surface pressure fluctuations on the landing gear due to turbulent flow and unsteady aerodynamic forces further exacerbate the challenges for effective noise mitigation. While perforated sheet fairings have been proposed for reducing aero-acoustic noise, they can be ineffective in addressing the issues of flow-induced noise, turbulence, and surface pressure fluctuations. Moreover, known perforated sheet fairings can offer limited adaptability to different aircraft configurations and operating conditions, making it difficult to achieve noise reduction performance in a range of situations.

[0005] In accordance with a first aspect of the present invention, there is provided an aircraft landing gear assembly comprising a wheel and brake assembly and a shock absorbing strut, the strut including a mounting bearing for movably coupling the aircraft landing gear assembly to an aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing, the aircraft landing gear assembly further comprising: a noise-inducing region; a first perforated sheet fairing arranged upstream with respect to the noiseinducing region when the landing gear is in the deployed condition and positioned to affect airflow approaching the noise-inducing region in use; and a second perforated sheet fairing arranged downstream of the first perforated sheet fairing when the landing gear is in the deployed condition.

[0006] In accordance with a second aspect of the present invention, there is provided an aircraft landing gear assembly comprising a wheel and brake assembly and a shock absorbing strut, the strut including a mounting bearing for movably coupling the aircraft landing gear assembly to an aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing, the aircraft landing gear assembly further comprising: a noise-inducing region; a first perforated sheet fairing arranged downstream with respect to the noiseinducing region when the landing gear is in the deployed condition and positioned to affect airflow leaving the noise-inducing region in use; and a second perforated sheet fairing arranged downstream of the first perforated sheet fairing when the landing gear is in the deployed condition.

[0007] Thus, the claimed invention relates to a noise reduction system for landing gear, utilizing a staggered, double perforated fairing configuration which work in series to affect airflow negotiating the noise inducing region to achieve enhanced turbulence reduction and broadband noise reduction across various frequency ranges. The double perforated fairing can offer significant advantages over a single perforated sheet fairing, as it exploits multiple noise reduction mechanisms, including aerodynamic and flow-related effects. The double perforated fairing arrangement can effectively control the velocity and turbulent kinetic energy of the imping flow and also the boundary layer, reducing vortex shedding and dissipating turbulent kinetic energy to minimize flow-induced noise generation. Advantageously, the double perforated fairing arrangement enables the distance between the front and back perforated fairings to be optimised for a given landing gear and / or operational use. This enables better flow control in terms of velocity and turbulent kinetic energy which can result in improved noise reduction performance. Thus, the landing gear assembly according to the first and second aspects can effectively address limitations of single perforated sheet fairings by offering enhanced broadband noise reduction, effective turbulence reduction, reduced surface pressure fluctuations, and adaptability to different aircraft configurations and operating conditions, improving landing gear noise reduction performance, and contributing to the development of environmentally friendly and acoustically optimized aviation solutions.

[0008] For the first aspect, the downstream fairing can be arranged upstream of the noiseinducing region when the landing gear is in the deployed condition. Thus, the staggered fairing system can be used in front of the region being treated.

[0009] Alternatively, the downstream fairing can be arranged downstream of the noiseinducing region when the landing gear is in the deployed condition. Thus, the staggered fairing system can be used in front and in the aft of the region being treated.

[0010] The following statements apply to both of the first and second aspects.

[0011] The landing gear assembly can comprise an intermediate perforated sheet fairing arranged downstream with respect to the upstream fairing and upstream with respect to the downstream fairing when the landing gear is in the deployed condition.

[0012] The porosity of the upstream fairing can be different than the porosity of the downstream fairing. Where an intermediate fairing is provided, the porosity of each faring can be different to each of the other fairings. Thus, the self-noise of the fairings can be at different frequencies, thereby reducing the overall noise generated by the staggered fairing system.

[0013] The upstream fairing can for example have a higher porosity than the downstream fairing. Thus, the upstream fairing can have a higher porosity, designed to address lower-frequency noise, while the downstream fairing can have a lower porosity, targeting higher-frequency noise. This combination can result in enhanced broadband noise reduction across various frequency ranges. Alternatively, the upstream fairing can have a lower porosity than the downstream fairing.

[0014] In embodiments where the fairings have different porosities, the upstream and downstream fairings can be positioned to tread distinct noise generating regions of the landing gear assembly. Thus, different parts of the landing gear can be treated using different porosity so that noise generated by the fairings are in different frequencies for different parts of the landing gear, which can lead to improved acoustic performance.

[0015] The shape or shapes of the perforations in the upstream fairing can be different with respect to the shape or shapes of the perforations in the downstream fairing. By using two perforated sheets with different porosities, different pore sizes and / or shapes, the fairing assembly can offer broadband noise reduction across different frequencies, providing a more effective solution for a wider range of noise sources. Where an intermediate fairing is provided, the shape or shapes of the perforations of each faring can be different to each of the other fairings. This can improve self-noise generated by the staggered fairing system.

[0016] One of the fairings can be positioned to cover only a partial region of another one of the fairings, which can lead to better performance. The side edges and corners of a porous fairing has been found to cause additional noise due to the shear layer generated at these regions. Special treatment of these regions of interest with the staggered arrangement of another porous fairing can lead to better acoustic performance. This partial staggering could also be used only in the regions of the stagnation point region. This approach can also result in an effective noise reducing fairing which has less weight than two fairings of the same size and shape.

[0017] The porosity level of each fairing can be between 30% and 70%.

[0018] One or more of the fairings can include one or more regions which are not perforated in order to provide regions with mechanical strength to maintain structural integrity of the faring and via which the faring can be mounted on the landing gear. In such cases, the defined porosity can relate only to the region of the fairing that is configured to treat noise inducing regions, rather than any solid, structural regions provided for mechanical strength.

[0019] One or more of the perforated sheet fairings can each include a plurality of perforations of a first size and a plurality of perforations of a second size which is different to the first size and optionally a plurality of perforations of a third size which is different to the first size and the second size. Thus, a fairing can include perforation holes of different sizes, which can provide improved noise reduction in comparison to a fairing with perforations of a single size. The perforations can be uniformly distributed or non-uniformly distributed. The perforation holes can be circular, with the axes of the circles defining the uniform or non-uniform distribution. One or more or each fairing can be constructed of a plurality of discrete perforated sheet elements joined together. Thus, the modular design approach can allow for greater adaptability and flexibility when fitting the fairings to various landing gear configurations, ensuring efficient noise reduction without compromising the ease of installation and maintenance. The downstream fairing can be used to deflect flows away from areas such as the brakes for example.

[0020] The upstream and downstream fairings can be arranged in a parallel arrangement with respect to one another.

[0021] Alternatively, the upstream and downstream fairings can be arranged in a non-parallel arrangement with respect to one another, for example for strategic flow deflection.

[0022] In either case, where an intermediate fairing is provided, the intermediate fairing can be arranged so as to be parallel or non-parallel with respect to the upstream and / or downstream fairing.

[0023] The upstream fairing, downstream fairing and / or intermediate fairing can be distinct, discrete components.

[0024] The upstream fairing can be mounted at a first distance from a centre point of the noise inducing region and the downstream fairing can be mounted at a second distance from the centre point of the noise inducing region, wherein the first and second distances are different to one another; for example, at least 10% different. Thus, the fairings can be positioned at different distances from the noise inducing region.

[0025] In accordance with a third aspect of the invention, there is provided an aircraft landing gear assembly comprising a wheel and brake assembly and a shock absorbing strut, the strut including a mounting bearing for movably coupling the aircraft landing gear assembly to an aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing, the aircraft landing gear assembly further comprising: a noise-inducing region; a perforated sheet fairing arranged either: upstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow approaching the noise-inducing region in use; or downstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow leaving the noise-inducing region in use, wherein the perforated sheet fairing has a sinusoidal cross section defining a plurality of upstream peaks and plurality of downstream troughs.

[0026] The fairing can have sinusoidal cross section in orthogonal planes. Thus, the fairing can have an egg-box like shape, defining a 3D wave profile.

[0027] In accordance with a fourth aspect of the invention, there is provided an aircraft landing gear assembly comprising a wheel and brake assembly and a shock absorbing strut, the strut including a mounting bearing for movably coupling the aircraft landing gear assembly to an aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing, the aircraft landing gear assembly further comprising: a noise-inducing region; a perforated sheet fairing arranged either: upstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow approaching the noise-inducing region in use; or downstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow leaving the noise-inducing region in use, wherein the perforated sheet fairing includes a plurality of perforations of a first size and a plurality of perforations of a second size which is different to the first size.

[0028] The fairing can include a plurality of perforations of a third size which is different to the first size and the second size.

[0029] The perforations can be uniformly distributed or non-uniformly distributed. The perforation holes can be circular, with the axes of the circles defining the uniform or non-uniform distribution.

[0030] Optional features of the first and second aspects can be applied to the third and fourth aspects. Brief of the

[0031] By way of example only, certain embodiments of the invention will now be described by reference of the accompanying drawings, in which:

[0032] Figures 1 to 13 are schematic diagrams of aircraft landing gear assemblies according to respective embodiments of the inventions, each illustrating a staggered fairing arrangement relative to incident airflow and a noise inducing region;

[0033] Figure 14 is a schematic diagram of a side view of an aircraft landing gear assembly according to an embodiment of the invention;

[0034] Figures 15 to 18 are diagrams of perforated sheet fairings for use in aircraft landing gear assemblies according to embodiments of the invention; and

[0035] Figures 19a and 19b are diagrams of a 3D wave profiled perforated fairing according to an embodiment of the invention; and

[0036] Figure 20 is a diagram of a known aircraft landing gear assembly.

[0037] Detailed

[0038] Figure 20 shows a known aircraft landing gear assembly generally at 100.

[0039] It has been observed that specific regions comprising one or more components of the landing gear predominantly generate noise as they move through the air. The landing gear 100 includes a noise-inducing region 12, which in the illustrated example is in the form of a pin joint of a torque link but could be any noise inducing region or component of the landing gear assembly 100. The landing gear 100 is shown in a deployed condition, for take-off and landing, but is movably mounted to an aircraft (not shown) for movement between the deployed condition and a stowed condition, for flight.

[0040] Due to the motion of the aircraft to which the landing gear assembly 100 is coupled, the landing gear assembly 100 generally moves in the direction of arrow M, which will be referred to as the landing gear motion direction M. Consequently, airflow moves relative to the landing gear 100 in the direction of arrow A, which will be referred to as airflow A. Airflow A can be considered to be a primary or resultant airflow from the forward and vertical velocity of the aircraft and will usually also include a cross wind component.

[0041] It is known to place a single perforated sheet fairing (not shown) in front of a noise inducing region 12. However, the present inventors have recognised that known landing gear including a perforated sheet fairing can suffer from one or more of the following disadvantages:

[0042] • Inadequate noise reduction across a wide range of frequencies; conventional single perforated sheet fairings offer limited effectiveness in reducing noise across a wide range of frequencies, particularly in addressing flow-induced noise sources.

[0043] • Self-noise of perforated sheets; although perforated sheets and meshes have been shown to reduce noise in landing gears, the self-noise of the porous materials remain a problem.

[0044] • Aerodynamically and flow-induced noise generation; the interaction between the landing gear and high velocity flow field can result in turbulent wake flow, vortex shedding, and boundary layer separation, leading to increased noise generation.

[0045] • Surface pressure fluctuations on landing gear; surface pressure fluctuations due to turbulent flow impingement and unsteady aerodynamic forces contribute to noise generation, posing challenges for effective noise mitigation using traditional methods.

[0046] • Limited adaptability to different aircraft configurations and operating conditions; conventional noise reduction solutions may not offer the flexibility to optimize performance across various aircraft configurations and operating conditions, and different types of landing gears making it difficult to achieve maximum noise reduction performance in all situations.

[0047] By way of a non-limiting overview, embodiments of the invention solve one or more of the above-identified technical problems by introducing a staggered perforated sheet fairing assembly for landing gear noise reduction. The fairing assembly combines at least two discrete perforated sheets which each affect airflow that would in their absence negotiate the noise inducing region and relative to one another can have different porosities, pore sizes and / or shapes to target a wider range of noise sources and frequencies effectively. Embodiments of the invention also include single fairing systems in which the perforated sheet fairing either has a wavy cross section or includes perforation holes of different sizes.

[0048] Before describing illustrated embodiments of the invention, we will first provide some general statements which apply to embodiments of the invention.

[0049] Staggered perforated sheet fairing

[0050] Embodiments of the invention can include two or three or more perforated fairings acting as one system, which can have either the same porosity or different levels of porosity for each fairing. The front perforated fairing can possess a relatively high porosity, while the rear perforated fairing can have a relatively a lower porosity, or vice versa. This combination facilitates enhanced broadband noise reduction across diverse freguency ranges, addressing the limitations of single perforated sheet fairings.

[0051] Directing air away from these components or allowing only partial incoming flow to interact with the landing gear can mitigate the noise they produce. The staggered perforated sheet fairing arrangement can achieve this by the reduction of flow velocity and turbulent intensity that interacts with these landing gear components. The staggered perforated sheet fairing assembly employs perforated sheets arranged in a step-by-step configuration, enabling a gradual reduction of flow velocity and turbulence in the front and around the landing gear components. This methodical arrangement can not only minimize the generation of noise due to the interaction of turbulent airflows and large coherent structures but can also enhance the overall effectiveness of noise reduction in comparison to a single fairing system. The staggered perforated sheet configuration can be designed to provide a controlled, gradual process of reducing airflow and turbulence around crucial noise-generating areas, contributing to a significant decrease in landing gear noise.

[0052] The staggered perforated sheet fairing assembly can be arranged in a standalone configuration or can be interconnected. The interconnection of the perforated sheet can be achieved using various fairing shapes.

[0053] The upstream and downstream fairings may be held in position by being mechanically coupled to the component they are intended to treat, or they can be supported independently by different components of the landing gear assembly. This flexibility in design and configuration allows for optimal customization and adaptation to various scenarios and specific noise reduction requirements. Additionally, the upstream and downstream fairings can be constructed from multiple discrete parts to facilitate easy mounting on the landing gear. For example, the front fairing can be composed of three discrete sections, while the rear fairing can be composed of four discrete parts. This modular design approach allows for greater adaptability and flexibility when fitting the fairings to various landing gear configurations, ensuring efficient noise reduction without compromising the ease of installation and maintenance. The downstream fairing can be used to deflect flows away from areas such as the brakes.

[0054] Porositv / Perfo ration

[0055] Porosity can be defined as the percentage of openings in a solid fairing sheet used for deflecting the flow. The porosity level of each perforated fairing can be between 30% and 70%. The shapes of the holes used for perforations can be geometrical (e.g., circle / ellipse, square / rectangle, rectangle with rounded corners, triangle, star, hexagon etc.) or non-geometrical shape (e.g. deformed geometrical shapes). The size of each hole can be the same throughout the fairing or can vary between a certain range to improve the noise reduction properties. The arrangement of the perforations can be staggered uniformly or in a non-uniform distribution. A varying level of porosity can be be used in the fairing, i.e., the stagnation region might have a different porosity, pore distribution pattern for both the front and back fairings compared to the pore distribution and pattern on the edges of the fairing.

[0056] Fairing distance optimization

[0057] Embodiments of the invention allow for optimizing the distance between the front and back perforated fairings during the design phase based on operational flow velocity and landing gear configurations. This optimization can ensure that a downstream fairing is placed in the most optimal wake location of an upstream fairing for effective noise reduction, addressing the surface pressure fluctuations on the landing gear and the wake flow. The wake distance can be based on the size of the holes used in the upstream fairing.

[0058] Fairing shape optimization

[0059] The shape of the upstream fairing can be optimised based on the regions and the type of landing gear component that is to be treated for acoustic purposes. For example, an upstream fairing can be curved toward the flow and a downstream fairing can be planar or have shapes with several other permutations and combinations where the shape of the upstream and downstream fairings are the same or different. The shape and size of a downstream, wake fairing can therefore be different to that of an upstream fairing.

[0060] Area of fairing and porosity

[0061] The size or area of the perforated sheets used to make the upstream and downstream fairings can be the same or different to one another. The fairing arrangement can be such that one of the fairings is placed to cover only a partial region of the other fairing for better performance. For instances the side edges and corners of a porous fairing has been found to cause additional noise due to the shear layer generated at these regions. Special treatment of these regions of interest with the staggered arrangement of an upstream or downstream fairing can lead to better acoustic performance. The staggering arrangement can therefore be used only in the regions of the stagnation point region. A perforated sheet fairing can be supported by non-perforated, structural regions which impart mechanical strength to the fairing and can be used to mount the fairing to the landing gear.

[0062] Fairing Positions

[0063] The staggered fairing arrangement can be used in front of the components being treated or in the aft of the components being treated or a combination of both. The staggered fairing arrangement can be used around the component being treated. This is so that the use of fairing not only reduces the flow impingement on the landing gear component but also the supresses the vortex shedding from a large landing gear structure that is being treated, such as the main strut. The boundary layer on the bluff body of the landing gear can also be controlled by enclosing the component using a staggered perforated fairing system.

[0064] Aerodynamic and flow-related noise reduction

[0065] The staggered perforated sheet fairing is designed to control the flow velocity and turbulent kinetic energy impinging on the landing gear.

[0066] Perforated sheet fairings according to embodiments of the invention can be used on both nose landing gear and main landing gear and any landing gear component. The present invention offers adaptability to different aircraft types and operational conditions, with the ability to optimize the fairing distances based on operational flow velocity during the design phase. This can ensure maximum noise reduction performance across various configurations and requirements.

[0067] With reference to Figure 1, an aircraft landing gear according to an embodiment of the invention is shown generally at 10 with the upstream and downstream perforated sheet fairings employed ahead of the bluff body. A indicates the direction of fluid flow, while B highlights the presence of large-scale structures in the flow. The incorporation of upstream perforated fairing la disrupts these extensive structures, transforming them into smaller scales C and concurrently reducing both flow velocity and turbulent kinetic energy. The application of a subsequent, downstream perforated fairing 2b, in this embodiment featuring distinct porosity, is designed to further diminish velocity, turbulent kinetic energy, and the size of turbulent structures D prior to their interaction with the landing gear components 3a which define a noise inducing region.

[0068] With reference to Figure 2, an aircraft landing gear according to an embodiment of the invention is shown generally at 12 with the fairings surrounding a noise inducing bluff body. A signifies the direction of fluid flow, while B underscores the presence of large- scale structures within the flow. The upstream perforated fairing lb disrupts these substantial structures, converting them into smaller scales C and simultaneously reducing flow velocity and turbulent kinetic energy before their encounter with the landing gear components 4b. An additional, intermediate perforated fairing 2b, at the sides of the bluff body with a unique porosity, regulates the boundary layer over the bluff body, thereby controlling the vortex shedding behaviour. To further mitigate vortex shedding, flow velocity, and turbulent kinetic energy, a downstream perforated fairing 3b is provided in the wake of the bluff body, resulting in small-scale turbulent structures D.

[0069] Figures 3, 4, and 5 show further aircraft landing gear assemblies according to embodiments of the invention generally at 14, 16 and 18 respectively. These embodiments comprise staggered perforated fairings employed ahead of the bluff body, showcasing several possible generic shapes for the staggered fairing system. Figure 3 presents an example where the fairing profile aligns with the shape of the structure it aims to shield, with both the upstream fairing 1c and downstream fairing 2c having a curved shape which generally matches the outer shape of the bluff body 3c and also conform to one another. Figure 4 depicts a different configuration in which the perforated sheets Id, 2d do not conform with the bluff body 3d, but conform to one another, while Figure 5 shows an embodiment in which two perforated sheets le, 2e can be arranged to create an enclosure, enhancing structural rigidity between the fairings le, 2e, and do not conform to one another. A indicates the direction of fluid flow, and B emphasizes the presence of large-scale structures in the flow. The upstream perforated fairing 1c, Id, le disrupts these extensive structures, converting them into smaller scales C and simultaneously reducing both flow velocity and turbulent kinetic energy. The downstream perforated fairing 2c, 2d, 2e, with distinct porosity, further decreases velocity, turbulent kinetic energy, and the size of turbulent structures D before they interact with the landing gear components 3c, 3d, 3e.

[0070] Figures 6, 7, 8, and 9 show further aircraft landing gear assemblies according to embodiments of the invention generally at 20, 22, 24 and 26 respectively. In each embodiment the staggered perforated fairing system is positioned in front of the bluff body. These figures demonstrate the potential for employing the second perforated sheets selectively in regions of interest, which can provide weight reduction in comparison to earlier embodiment. Figure 6 shows the use of a downstream perforated fairing 2f only at the outer edges of the upstream perforated fairing If, which can modify the shear layer generated at the edges and corners of the upstream perforated sheet If. Figure 7 shows a variant of the partially staggered fairing with a curved downstream perforated fairing 2g attached only at the outer edges of the upstream perforated fairing 1g. Figure 8 shows a variant of the partially staggered fairing with a curved upstream perforated fairing 2h attached only at the outer edges of the downstream perforated fairing Ih, rather than in its wake. Figure 9 shows a curved partial downstream fairing 2i mounted to only cover a central region of the upstream perforated fairing li, which can be the stagnation point of the primary, upstream fairing li. Although these embodiments depict a curved elliptical structure, it should be noted that the shape of the partial fairing can take any suitable form, which can be based on the structural rigidity and properties of the perforated sheets used. A indicates the direction of fluid flow, and B emphasizes the presence of large- scale structures in the flow. The integration of perforated fairing If, 1g, Ih, li disrupts these extensive structures, converting them into smaller scales C, reducing both flow velocity and turbulent kinetic energy. Perforated fairing 2f, 2g, 2h, 2i, with distinct porosity, is designed to further decrease velocity, turbulent kinetic energy, and the size of turbulent structures D before they interact with the landing gear components 3f, 3g, 3h, 3i. In such embodiments, the partial fairing can be a distinct component with respect to the larger faring or can be formed by bending one or more regions of the larger fairing over on itself to provide the partial fairing portions. The partial fairing portion(s) can be parallel or non-parallel with respect to the larger fairing and / or can have the same or different shape, conforming or not conforming to the larger fairing, and can be positioned upstream or downstream with respect to the larger fairing.

[0071] Figures 10 and 11 show further aircraft landing gear assemblies according to embodiments of the invention generally at 28 and 30 respectively. In each embodiment the staggered perforated fairing at least partially encloses the component being treated. In Figure 10, the upstream perforated fairing li is in front of the landing gear component 3j and the downstream perforated fairing 2j is positioned after the landing gear component 3j and is designed to suppress vortex shedding and reduce turbulence generated by the bluff body. Figure 11 shows an intermediate fairing 2k placed ahead of the bluff body 4k to further decrease velocity and turbulent kinetic energy following upstream fairing Ik before interaction with the landing gear component 4k. Additionally, downstream fairing 3k is placed after the landing gear component 4k, providing comprehensive treatment for the component 4k. A indicates the direction of fluid flow, and B emphasizes the presence of large-scale structures in the flow. The integration of perforated fairing Ik disrupts these extensive structures, converting them into smaller scales C and simultaneously reducing both flow velocity and turbulent kinetic energy.

[0072] Figures 12 and 13 show further aircraft landing gear assemblies according to embodiments of the invention generally at 32 and 34 respectively. Figure 12 demonstrates the use of the staggered perforated fairing while using a staggered fairing arrangement II, 21 with wavy shape. Thus, each perforated sheet fairing II, 21 has a two-dimensional sinusoidal cross section defining a plurality of upstream peaks P and plurality of downstream troughs T, with a set amplitude and a set wavelength throughout the fairing. The perforated sheet fairing II, 21 can each have a sinusoidal cross section in orthogonal planes X, Y as illustrated in Figures 19a and 19b. Thus, the fairings can have an egg-box like shape, defining three-dimensional wave profile. In Figure 13, intermediate perforated fairing 2m, wavy in shape and is positioned in between the flat upstream fairing Im and downstream fairing 3m. A indicates the direction of fluid flow, and B emphasizes the presence of large-scale structures in the flow. The integration of the perforated fairing II, Im disrupts these extensive structures, converting them into smaller scales C and simultaneously reducing both flow velocity and turbulent kinetic energy.

[0073] In other embodiments, a wavy perforated sheet fairing can be used as a single fairing system, with the fairing arranged either upstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow approaching the noise-inducing region in use or downstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow leaving the noise-inducing region in use. The use of a single wavy fairing can provide better performance than a single planar fairing because it can imitate a staggered fairing setup due to the upstream peaks and downstream troughs. The wavy fairing can be shaped to conform to the component that it is treating or can have a planar overall shape.

[0074] Figure 14 shows a further aircraft landing gear assembly according to an embodiment of the invention generally at 36, showing a side view of the fairing system applied to a landing gear. Intermediate fairing 2n is used as a partial fairing for the primary, upstream fairing In. This figure illustrates the versatility of mounting options, including attachment to different parts of the landing gear such as the main strut and wheel axle, not solely to the fairing itself. Additionally, this configuration demonstrates the implementation of downstream fairing 3n in the wake of the main strut 37 to address wake flow treatment.

[0075] Figure 15 shows a uniformly perforated sheet which can form a perforated sheet fairing, where P represents the pitch of the holes and D denotes the diameter of the holes. The diameter D can for example be between 0.1mm and 20mm and the pitch P can for example be between 0.1mm to 20mm based on the component that it is being treated on the landing gear component. A variety of D and P could be used in a single perforated fairing. The staggering angle can for example be between 1 to 90 degrees.

[0076] Figure 16 shows a variant of the perforated sheet that uses uniformly distributed holes with different diameters to alter the self-noise of the porous plates. In this example, first holes Hl have a first diameter, second holes H2 have a smaller diameter than first holes Hl and third holes H3 have a smaller diameter than second holes H2. The perforated sheet fairing can have holes of two or more different sizes. Thus, the perforated sheet fairing includes a plurality of perforations of a first size and a plurality of perforations of a second size which is different to the first size and the fairing can include a plurality of perforations of a third size which is different to the first size and the second size and likewise can include pluralities of holes of further sizes which are distinct. The perforations can be uniformly distributed or non-uniformly distributed. The perforation holes can be circular, with the axes of the circles defining the uniform or non-uniform distribution. In other embodiments, perforated sheet fairing having holes of different sizes can be used as a single fairing system, with the fairing arranged either upstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow approaching the noise-inducing region in use or downstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow leaving the noise-inducing region in use. The use of a single fairing having holes of different sizes can provide better performance than a single planar fairing.

[0077] Figure 17 shows a perforated sheet with non-uniform hole distribution and hole sizes, which is a preferred approach, as perforation with identical holes with similar shape and diameter may result in additional noise due to constructive interference.

[0078] Figure 18 illustrates a staggered perforated configuration using only two perforated sheets, with the front perforated sheet US featuring a larger porosity than the rear perforated sheet DS.

[0079] The distance DI between the front and back perforated fairings US, DS can be determined with routine testing. The distance DI can be based on the type of perforation used, the diameter of the perforation holes and the operational condition of the landing gear. In one example, the smallest distance DI can be 5 times the pore diameter of the sheets used and the largest distance DI can be the wheelbase of the landing gear for multi axle gear employing a bogie beam and for single axle landing gear the largest separation distance can be the diameter of the wheels. This optimization process can result in placement of the second fairing in an optimal wake location for improved noise reduction effects. By altering the flow around the landing gear, the staggered fairing system can significantly reduce surface pressure fluctuations on the landing gear, leading to improved overall noise reduction performance. The acoustic effects of the fairing such as resonant cavity effects, impedance mismatch, and interference can also be altered due to the distance optimisation.

[0080] Perforated sheet fairings used in embodiments of the invention can be formed from conventional landing gear fairings materials, such as aluminium, steel, stainless steel, titanium, a plastics material or a composite material.

[0081] 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" can mean "including" or "consisting of" and therefore does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The word "coupled" can mean "attached" or "connected". The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In an apparatus claim enumerating several parts, several of these parts may 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 wheel and brake assembly and a shock absorbing strut, the strut including a mounting bearing for movably coupling the aircraft landing gear assembly to an aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing, the aircraft landing gear assembly further comprising: a noise-inducing region; a first perforated sheet fairing arranged upstream with respect to the noiseinducing region when the landing gear is in the deployed condition and positioned to affect airflow approaching the noise-inducing region in use; and a second perforated sheet fairing arranged downstream of the first perforated sheet fairing when the landing gear is in the deployed condition.

2. An aircraft landing gear assembly comprising a wheel and brake assembly and a shock absorbing strut, the strut including a mounting bearing for movably coupling the aircraft landing gear assembly to an aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing, the aircraft landing gear assembly further comprising: a noise-inducing region; a first perforated sheet fairing arranged downstream with respect to the noiseinducing region when the landing gear is in the deployed condition and positioned to affect airflow leaving the noise-inducing region in use; and a second perforated sheet fairing arranged downstream of the first perforated sheet fairing when the landing gear is in the deployed condition.

3. The aircraft landing gear assembly according to claim 1, wherein the downstream fairing is arranged upstream of the noise-inducing region when the landing gear is in the deployed condition.

4. The aircraft landing gear assembly according to claim 1, wherein the downstream fairing is arranged downstream of the noise-inducing region when the landing gear is in the deployed condition.

5. The aircraft landing gear assembly according to any preceding claim, further comprising an intermediate perforated sheet fairing arranged downstream with respect to the upstream fairing and upstream with respect to the downstream fairing when the landing gear is in the deployed condition.

6. The aircraft landing gear assembly according to any preceding claim, wherein the porosity of the upstream fairing is different than the porosity of the downstream fairing.

7. The aircraft landing gear assembly according to claim 6, wherein the upstream fairing has a higher porosity than the downstream fairing.

8. The aircraft landing gear assembly according to any preceding claim, wherein the shape or shapes of the perforations in the upstream fairing are different with respect to the shape or shapes of the perforations in the downstream fairing.

9. The aircraft landing gear assembly according to any preceding claim, wherein one of the fairings is sized, shaped and positioned to cover only a partial region of another one of the fairings.

10. The aircraft landing gear assembly according to any preceding claim, wherein the porosity level of each fairing is between 30% and 70%.

11. The aircraft landing gear assembly according to any preceding claim, wherein one or more of the perforated sheet fairings each includes a plurality of perforations of a first size and a plurality of perforations of a second size which is different to the first size and optionally a plurality of perforations of a third size which is different to the first size and the second size, and / or the perforations are uniformly distributed.

12. The aircraft landing gear assembly according to any preceding claim, wherein one or more or each fairing is constructed of a plurality of discrete perforated sheet elements joined together.

13. The aircraft landing gear assembly according to any preceding claim, wherein the upstream and downstream fairings are arranged in a parallel arrangement with respect to one another.

14. The aircraft landing gear assembly according to any of claims 1 to 12, wherein the upstream and downstream fairings are arranged in a non-parallel arrangement with respect to one another.

15. The aircraft landing gear assembly according to any preceding claim, wherein the upstream fairing is mounted at a first distance from the noise inducing region andthe downstream fairing is mounted at a second distance from the noise inducing region, wherein the first and second distances are different.

16. An aircraft landing gear assembly comprising a wheel and brake assembly and a shock absorbing strut, the strut including a mounting bearing for movably coupling the aircraft landing gear assembly to an aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing, the aircraft landing gear assembly further comprising: a noise-inducing region; a perforated sheet fairing arranged either: upstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow approaching the noise-inducing region in use; or downstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow leaving the noise-inducing region in use, wherein the perforated sheet fairing has a sinusoidal cross section defining a plurality of peaks and plurality of troughs.

17. The aircraft landing gear assembly according to claim 16, wherein the perforated sheet fairing has a sinusoidal cross section in orthogonal planes.

18. An aircraft landing gear assembly comprising a wheel and brake assembly and a shock absorbing strut, the strut including a mounting bearing for movably coupling the aircraft landing gear assembly to an aircraft for movement between a stowed condition for flight and a deployed condition for take-off and landing, the aircraft landing gear assembly further comprising: a noise-inducing region; a perforated sheet fairing arranged either: upstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow approaching the noise-inducing region in use; or downstream with respect to the noise-inducing region when the landing gear is in the deployed condition and positioned to affect airflow leaving the noise-inducing region in use, wherein the perforated sheet fairing includes a plurality of perforations of a first size and a plurality of perforations of a second size which is different to the first size.

19. The aircraft landing gear assembly according to claim 18, wherein the perforated sheet fairing includes a plurality of perforations of a third size which is different to the first size and the second size.

20. The aircraft landing gear assembly according to claim 18 or claim 19, wherein the perforations of the perforated sheet fairing are uniformly distributed.

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