LANDING GEAR ASSEMBLEY

The present invention relates to reducing noise caused by an aircraft landing gear. In particular, the invention relates to landing gear designed to reduce the noise generated by the interaction of the wheel of a landing gear and the air flowing past it during the approach of the aircraft when landing.

It is desirous to reduce the noise generated by aircraft, for example, to lessen disruption or inconvenience, resulting from aircraft noise, caused to the public on the ground near airports. A significant amount of noise is generated by the interaction of the aircraft and the air flowing past it, which results in turbulent flows and consequently noise. It is particularly important to reduce noise created during approach of the aircraft on landing. During approach, a significant contribution to the amount of noise that the aircraft makes is made by the landing gear, which is typically deployed early for landing for safety reasons. The deployment of landing gear will increase drag and assist deceleration of the aircraft. One source of noise is the wheel of the landing gear. During take-off, noise from the landing gear is a less significant factor because engine noise is generally greater and because the landing gear is generally stowed at the earliest opportunity to reduce drag and aid take-off. During normal flight, the landing gear of an aircraft is typically stowed in a landing gear bay, the bay being closed off by doors so that no part of the landing gear is subjected to the air flow.

It is an aim of the present invention to provide a landing gear that generates less noise compared to a landing gear of the same size that has not been adapted, designed or manufactured in accordance with the present invention.

According to the invention there is provided an aircraft landing gear including a wheel having a rim around which there is mounted a tyre, and a part located at the junction between the tyre and the rim, the part being shaped such that on one side of the wheel, during use of the landing gear on an aircraft when airborne and the landing gear is in a position ready for landing of the aircraft, the surface of said part interfaces smoothly with the surfaces, presented to the airflow, of both the tyre and the wheel, whereby noise resulting from the interaction of the landing gear and the airflow during approach of the aircraft on landing may be reduced as a result of the gap, which would otherwise exist between the tyre and the rim, being closed, characterised in that said part is configured to be movable so that the tyre may be inspected, whilst the aircraft is on the ground and the tyre is mounted on the rim, without requiring said part to be separated from the wheel.

It has previously been proposed to provide a landing gear including a wheel comprising a wheel rim, a tyre, and a hub cap that covers various voids. However, in that proposal the hub cap has not covered all such voids and in particular there may be a significant gap defined between the wheel rim and tyre. Such a landing gear could create significant noise as a result of the interaction of the parts of the wheel defining that gap and the air flowing past the wheel. Thus the noise caused by the interaction of the air and the wheel, caused during the approach when landing, may be reduced by means of providing a wheel according to the present invention.

British Patent Application published under number 395,150 describes a fairing for an aircraft wheel, the fairing comprising a metal disc portion and a removable rubber ring, the fairing extending from the hub of the wheel to the tyre. The rubber part of the fairing needs to be removed to allow inspection of the tyre. The fairing described in that patent specification has been designed for the purpose of streamlining the airflow over the wheel for the purpose of reducing drag and not for the purpose of noise reduction. For an aircraft that has a landing gear that is fixed in position, the landing gear should ideally be designed to minimise drag. If however, the landing gear is able to be moved to a stowed position, out of the airflow, there is no similar motivation to reduce drag. Moreover, in such cases there are advantages in having a landing gear that has a relatively high drag, because the landing gear may, when deployed, improve the rate of deceleration of the aircraft during the approach on landing. Even though there is no disclosure of any aircraft landing gear in GB 395,150, it might therefore be concluded that the wheel of GB 395,150 was designed for use on a fixed landing gear, which is thus not able to be moved out of the airflow.

Other tyre wheel assemblies are disclosed in the prior art. US, 4434,830 for example discloses a pneumatic tyre for a road vehicle, wherein the wheel comprises a hub and rim on which there is mounted a tyre, there also being a wheel cover which interfaces smoothly with the surfaces presented to the airflow of both the tyre and the wheel rim. Also, US 1,969,088 discloses an aircraft wheel having a rim around which there is mounted a tyre, the tyre including an overhanging shoulder portion that meets the rim of the wheel, thereby presenting a streamlined smooth surface to the airflow.

DE4301778 is a further example of a road vehicle wheel and tyre assembly including a flexible cover plate for absorbing sound radiated from the tyre side wall.

It will be appreciated that the noise generated by an aircraft wheel during approach on landing is generally as a result of the airflow interacting with the wheel and that the wheel will typically not be rotating during approach on landing.

Advantageously, the wheel including the rim, tyre and said part, is designed, modified and/or configured to reduce, in use, the amount of turbulent air flow generated in the region of the junction between the tyre and the rim. Advantageously, the wheel including the rim, tyre and said part, is designed, modified and/or configured to streamline, in use, the flow of air past the wheel. Said part is preferably so shaped that it does not include any substantial portion that is concave (when viewed from outside of the wheel) when the aircraft is airborne. Said part is preferably so shaped that it is substantially flat and/or convex (when viewed from outside of the wheel) when the aircraft is airborne. Thus, there need be no gap between the wheel rim and the tyre, when the part is shaped in accordance with these preferred features of the invention. Having no such gap reduces the noise created by the wheel when compared with otherwise identical wheels having such gaps. Such gaps are generally concave in shape and have edges where different surfaces meet, such edges also contributing to unwanted noise.

Said part may be defined by a separate component part of the wheel. Said part may be defined by a sealing element, which bridges a gap between the wheel rim and the tyre. The sealing element may for example be provided in the form of a separate component. The sealing element may for example be in the form of a soft rubber pad. The sealing element may be formed from liquid sealant material that has been solidified. The term liquid is intended to cover sealant in a plastic and/or malleable state as well as sealant in a less viscous state. The sealing element may comprise an adhesive, a silicone based material or similar sealing material. The sealing element may be moulded before being assembled. Alternatively, the sealing element may be moulded into shape in situ. For example, a liquid sealant material may be deposited into a gap between the wheel rim and the tyre and then allowed to solidify (or set). The sealing element may be in the form of an elastomeric element, such as, for example, a rubber seal. The sealing element may be generally annular in shape and tapering in cross-section so that the thickness of the element reduces with radial distance from its centre.

Preferably, said part (the part that interfaces smoothly between the tyre and the wheel) is defined by a multiplicity of flexible elements extending radially across the junction between the tyre and the rim. For example, brushes may be provided, which bridge a gap between the wheel rim and the tyre. Said part may be defined by such brushes.

The shape of said part (the part that interfaces smoothly between the tyre and the wheel) is advantageously maintained throughout the approach of the aircraft when landing. On touching down, the aircraft generates a significant amount of noise and reducing the noise generated by air flowing past the wheels may no longer be important. Thus, the part between the wheel rim and the tyre may change shape significantly after touchdown. The part is preferably stiff enough not to change shape significantly during normal flight, but flexible enough that the shape of the part changes on touchdown (and preferably so flexible that the shape of the part when the aircraft is at a standstill on the ground is significantly different from when the aircraft is airborne). The tyre and the wheel rim may for example be so shaped that there is a need for a gap to be present between the tyre and the wheel rim when landing to allow for deformation of the tyre without causing undesirable local wear of the tyre at a position between the wheel rim and the periphery of the tyre. It may for that reason be advantageous for at least a portion of said part to be so configured to be deflected from, or otherwise forced out of, a gap that said part bridges when the aircraft lands. The part if configured to be so movable in that way, is advantageously also configured such that once the aircraft is airborne again said at least a portion moves back to the position in which it bridges the gap.

At least a portion of said part may be so configured that, once the force between the wheels and the ground exceeds a given threshold force, for example on touchdown, it moves out of a gap that said part bridges when the aircraft is airborne. The threshold force may be less than or equal to the weight supported by the wheel when the aircraft is unloaded and stationary on the ground.

Said at least a portion of said part may also be so configured that, once the force between the wheels and the ground drops to or below a given threshold force, for example after the aircraft has lifted off the ground during take-off, said at least a portion of said part moves back to the position in which it bridges the gap. Said threshold force may be the same as the threshold force first mentioned above. The threshold force is preferably greater than zero, but could be close to or equal to zero. The threshold force may be between 0.01 and 0.5 times the weight supported by the wheel when the aircraft is unloaded and stationary on the ground.

Said part is preferably defined at least partly by an elastically deformable material. The material is preferably chosen such that the deforming of such material during normal usage is reversible (i.e. substantially elastic deformation) so that the part does not deteriorate after only a few series of take-offs and landings.

As mentioned above, said part is so arranged and configured that the tyre may be inspected whilst the aircraft is on the ground and the tyre is mounted on the wheel. It is particularly important, insofar as this feature is concerned, that the side wall portion of the tyre immediately adjacent to the wheel rim may be inspected for wear and/or damage. Only a portion of said part may be configured to be movable for this purpose. For example, a portion of the part bridging a gap between the wheel rim and the tyre, thereby hiding the portion of the wheel behind said part, is advantageously flexible, and preferably resiliently flexible, and is so arranged that said part may be moved manually to reveal the portion of the tyre that is otherwise hidden from view. Said part may be moved by lifting the periphery of the part thereby bending the part. Such an action may for example be considered as peeling back the part to reveal the tyre underneath.

The wheel may include a hub cap. The hub cap may extend to the junction between the wheel rim and the tyre. The surface, presented to the airflow, of the rim may be defined by the hub cap. Said part may be defined at least in part by a part of the hub cap. For example the hub cap may have an outer portion in the form of a flexible sealing member that extends radially outwardly from the periphery of an inner portion of the hub cap.

Said part may extend significantly beyond the immediate vicinity of the junction between the tyre and the rim. For example, said part may cover an area of greater than 5% of the wheel area (equal to πR² where R is the radius of the tyre when in the air). Preferably, said part covers more than 10% of the wheel area and more preferably more than 20% of the wheel area and yet more preferably more than 40% of the wheel area.

It is stated above that at least one side of the wheel includes said part. Preferably, said at least one side is the side of the wheel opposite to the side which is configured to receive the axle. Both sides of the wheel may be arranged in accordance with the present invention. Thus, the wheel may include a further part shaped such that on the other side of the wheel, during use of the landing gear on an aircraft when airborne and the landing gear is in a position ready for landing of the aircraft, the surface of said further part interfaces smoothly with the surfaces, presented to the airflow, of both the tyre and the wheel, whereby noise resulting from the interaction of the landing gear and the airflow during approach of the aircraft on landing may be reduced as a result of the gap, which would otherwise exist between the tyre and the rim, being closed.

According to a further aspect of the invention there is provided an aircraft including an aircraft landing gear according to the present invention. The aircraft landing gear of the aircraft may be fixed in position. Alternatively, the landing gear is movable from a stored position to an operative position. The present invention has particular application to aircraft wherein the landing gear is moveable between a stowed (stored) position and a deployed (operative) position. Aircraft having landing gear that are fixed in position are generally not designed with noise reduction in mind. The invention is of greater application to larger aircraft, particularly passenger-carrying aircraft, where noise reduction on landing of the aircraft is of greater relevance. The landing gear is preferably of a size suitable for use on an aircraft designed to carry more than 50 passengers, and more preferably more than 100 passengers. Such aircraft generally have retractable landing gear assemblies. Other features of the invention described herein may of course be incorporated into this aspect of the present invention.

The present invention also provides a method of reducing noise caused by landing gear on an aircraft, for example during approach of the aircraft on landing, including a step of manufacturing an aircraft according to any aspect of the above-described invention. Such a method advantageously includes a step of modifying an existing design in order to reduce noise caused by the landing gear.

There is further provided a component, such as a sealing element for example, for use in the landing gear according to the present invention, the component advantageously being in the form of a separate component as described herein.

Embodiments of the present invention will now be described by way of example with reference to the following schematic drawings of which:

Figure 1a

shows a cross-section of a wheel and tyre according to a first embodiment of the invention;

Figure 1b

is an enlarged portion of Figure 1a illustrating more clearly the parts of the wheel at the junction between the rim of the wheel and the tyre;

Figure 2

shows an aircraft having a landing gear including a wheel as shown in Figures 1a and 1b.

Figure 3a

shows a cross section of a wheel according to a second embodiment of the invention; and

Figure 3b

is an enlarged portion of Figure 3a illustrating more clearly the parts of the wheel at the junction between the rim of the wheel and the tyre.

Figure 1a shows a cross-section of a wheel 1 according to a first embodiment. The wheel 1 comprises a hub 2 and a wheel rim 3. A tyre 4 is held in place on the wheel rim 3 by means of circumferential flanges 5. The tyre 4 is generally toroidal in shape and has a cross-sectional profile that is generally U-shaped. The arms of the U-shaped cross-section are defined by the sides 4a of the tyre 4 and the base from which the arms extend are defined by the portion 4b of the tyre that contacts the ground. The cross-sectional shape of the wheel rim 3, and in particular of the flanges 5, is such that the innermost part of the tyre 4 (the innermost portion of the tyre defined by the free end of the sides 4a of the tyre 4) is held between opposing flanges 5 by means of the opposing innermost portions of the tyre 4 being resiliently urged apart as a result of the shape of the tyre 4 when in a relaxed state. The gap 6 defined between the innermost portion of the tyre 4 and the wheel rim 3 is filled by means of an annular resilient rubber sealing element 7. Figure 1b shows a portion 10 of Figure 1a magnified for the sake of illustrating the shape of the sealing element 7 (which is not shown in Figure 1a for the sake of clarity). The sealing element 7 has a generally triangular cross-section. A first side 7a of the generally triangular shape follows the shape of the tyre 4. A second side 7b of the generally triangular shape follows the shape of the wheel rim 3. The third side 7c of the triangle follows the notional surface that smoothly envelopes the wheel 1 in the part of the junction between the tyre 4 and the wheel rim 3. The sealing element 7 thus bridges the gap 6.

The wheel 1 includes a hub cap 2a (seen most clearly in Figure 1b) that covers the hub 2 and extends just up to the outermost part of the wheel rim 3 (defined by flanges 5). The shape of the wheel hub cap 2a is such that the whole side 1a of the wheel 1 is substantially smooth, generally flat and has substantially no unnecessary discontinuities or gaps.

Figure 2 shows an aircraft 8 including a landing gear 9 including wheels 1 being configured as described with reference to Figure 1. When the aircraft is airborne, the sealing element 7 is in the position shown in Figure 1. When landing the smooth surface resulting from the provision of the sealing element 7 generates less noise than would be generated if no sealing element 7 were provided. It is believed that this reduction in noise is achieved because the wheel generates less turbulent airflows and because air flows relatively smoothly across the side 1a of the wheel 1. On touchdown, the tyre 4 deforms significantly by virtue of the increased pressure within the tyre 4 resulting from the increased weight supported by the wheel 1 and therefore the tyre 4. The sealing element 7, being resilient, deforms with the tyre 4, and therefore does not cause any damage to the tyre 4 when the aircraft 8 is on the ground. The sealing element 7 is removable to allow inspection of the portion of the tyre 4 that would otherwise be hidden from view. After the tyre has been inspected the sealing element 7 can simply be pushed back into position.

Figure 3a shows a cross section of a wheel 1 according to a second embodiment, the wheel being generally of the same construction as that illustrated in Figure 1a (such that the same reference numerals are used in Figure 3a to represent the parts that are common to Figures 1a and 3a). Thus the wheel 1 comprises a hub 2, hub cap 2a, which has a substantially flat outer face, and wheel rim 3. A tyre 4 is held in place by means of flanges 5 of the wheel 1. Figure 3a also shows an axle 14 on which the wheel 1 is mounted (there being a single hub cap 2a). A flexible annular rubber sealing member 13 extends radially from, and substantially in the same plane as, the rigid hub-cap 2a. A magnified view of a portion 11 of Figure 3a is shown in Figure 3b, to illustrate more clearly the shape of the sealing member 13. The sealing member 13 tapers radially outwardly from an inner thick root 13a to its thin free end 13b. The hub cap 2a and the sealing member 13 define a smooth and flat surface having a normal generally parallel to the axis of the tyre 4, the surface covering the portions of the wheel 1 and tyre 4 within the area defined by the tyre 4 at its widest. The surface of the wheel/tyre assembly, on the side opposite to the axle 14, presented to the airflow on landing is therefore substantially planar. Moreover, the hub cap 2a and sealing member 13 cover the voids 12 that would otherwise be presented to the airflow. In a manner similar to the sealing element 7 of the first embodiment, the sealing member 13 is flexible enough that it does not interfere with the tyre/wheel assembly on landing and also is moveable (by lifting the thin end 13b of the sealing member 13 away from the tyre 4) to facilitate inspection of the tyre 4.

It will be appreciated that various modifications may be made to the above-described embodiments of the invention. For example, the function of the sealing element 7 of the first embodiment (or of the sealing member 13 of the second embodiment) could be achieved by means of brushes having resiliently deformable bristles aligned radially with respect to the axis of the tyre 1 (i.e. in a radial direction from the axis). The rubber sealing element 7 of the first embodiment could alternatively be replaced with flexible adhesive or gel or other suitable sealing material.

Whilst the side 1a of the wheel 1 in the embodiments described above has substantially no discontinuities, the wheel 1 may include certain features requiring such discontinuities to be provided, for example in the form of small apertures or protrusions. Such discontinuities may contribute to the noise generated by the wheel 1 travelling through the air, but the reasons for providing such features may outweigh the benefits of the greater reduction in noise that might be achieved if such features were not provided. It is however envisaged that the provision of such features would not interfere with the benefits provided by the above-described embodiment in terms of noise reduction gained by the provision of the sealing element (or by means of the smoothing of the junction between the wheel rim and the tyre).