Aeronautics and astronautics – Landing gear
Reexamination Certificate
2000-09-05
2003-09-16
Dinh, Tien (Department: 3644)
Aeronautics and astronautics
Landing gear
C244S00100R
Reexamination Certificate
active
06619587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to aircraft noise reduction apparatus, in particular to apparatus to reduce noise emanating from landing gear of the aircraft when deployed on approach to landing.
2. Discussion of Prior Art
The invention has particular application to commercial aircraft when landing at airports in or near to built up areas where aircraft approach noise is an increasing nuisance with increasing frequency of use of airports and ever larger aircraft. Noise emanating from commercial aircraft, whether cargo aircraft and/or passenger carrying aircraft, is now an important environmental issue. The increasing frequency of use of airports has led to aircraft of increasing size being used. This in turn has led to greater noise being generated by each aircraft in its approaches to the airport. Modem high bypass ratio turbofan engines are now extremely quiet on approach to landing and dominant noise on some aircraft types, perceived at ground level, is starting to become the noise generated by landing gear and by high lift devices on the wings.
This invention addresses the problem of aircraft noise, as perceived at ground level, generated by landing gear. Although noise is likely to be induced by any element which creates turbulence in the airflow past the landing gear, those elements which have been found particularly likely to create high noise levels are as follows: elements which act as Helmholz resonators such as hollow axles, apertures, fastener fittings, spindles, etc; also elements likely to create small vortices such as small protuberances, sharp edges; dresssings such as small pipes, tubes, cables, and coil springs, etc. All such features are to be found aplenty on modern landing gear and tend to be more prevalent in the region of steering gear and wheel axles.
Although wind tunnel tests have been carried out on landing gear fully enclosed by fairings to determine noise levels in the far field, such full enclosure fairings are normally completely impractical for everyday use on an aircraft. This is because articulation of the landing gear during deployment and retraction movement is prevented by the fairings and because very limited stowage space in the landing gear bay in most aircraft will not accommodate full enclosures owing to the space which they take up. Additionally, full enclosure fairings render daily visual inspection regimes and maintenance of the landing gear almost impossible. Firstly, this is because visible inspection through such fairings is generally impossible and secondly because regular removal of such fairings for inspection or maintenance is far too time consuming and difficult. To date therefore no practical solution to the problem of landing gear induced airframe noise has been found.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided aircraft noise reduction apparatus including at least one noise-reducing attachment for landing gear of the aircraft shaped for positioning on the landing gear to deflect air away from noise inducing components of the landing gear and to permit deflection, articulation movement and stowage of the landing gear with the attachment installed.
The attachments may comprise deflector screens adapted not to completely surround noise inducing components on the landing gear. The said lack of a complete surrounding being for the purposes of allowing the said access and foldability of the landing gear.
Induced noise is proportional to the sixth power of the relative velocity of the airflow and component around which the air flows, and attachments of the invention are positionable to deflect incident air away from noise inducing components, preferably into the free stream.
The attachments must withstand all aerodynamic loads and foreign object damage, and it will be appreciated that the use of attachments according to the invention may increase landing gear drag.
Preferably a said attachment is shaped such that when positioned on the landing gear, airflow over the attachment during flight leaves the attachment substantially in the free stream direction.
Preferably a said attachment is shaped to avoid or minimise an air stagnation region forming in front thereof when positioned on the landing gear and in use. Such stagnation regions tend to increase both drag and noise emanating downstream of the stagnation region. The term “in front of” as used herein refers to a position upstream in the airflow, during flight.
In regions of the landing gear where incident air is accelerated between components of the landing gear, such as struts, stays and actuators, at least one said attachment is preferably positioned to deflect incident air away from the said air-accelerating region. In this way any noise-inducing components of the landing gear positioned in the said air-accelerating region will not be subject to the passage of such accelerated high speed air past them.
The apparatus may include an axle attachment positionable in front of an axle for nose gear of the aircraft to deflect air away from noise inducing components such as landing gear dressings in the region of the axle.
The axle attachment may be shaped to shield items such as a towbar fitting on the nose gear and the said shaped portion is desirably separately removable or pivotable out of the way in order to provide access to such a towbar fitting without disturbing the remainder of the axle attachment. Cam fasteners or other quick release fittings are suitable for fastening the shaped portion.
The axle attachment may extend laterally into close proximity with the wheels and may include generally cylindrical wheel extensions extending between a central portion thereof and each wheel whereby to deflect air away from noise inducing components on the axle and at the same time to deflect air away from a cavity formed within each wheel.
The wheel extensions preferably extend into close proximity with a rim of each wheel. Alternatively the wheels may be fitted with inner hub caps or wheel fillers. Such fillers may be of say foam material formed in two opposing sections with wedge-shaped elements driven into position therebetween. The foam or like material is preferably covered on the outside with a weatherproof material.
The axle attachment may include upper extension portions for positioning on either side of a main leg of the nose gear to deflect air away from torque link attachments usually sited on the axle.
The apparatus may include a said attachment positionable in front of a steering mechanism for the landing gear. Such a steering mechanism has been found to be prone to noise inducement including, as it usually does, many sharp edges, apertures and sundry pipe and cable work.
Similarly, the axle attachment deflects air away from another region of the landing gear particularly prone to noise inducement, i.e. the joint between the main leg and the axle, again liable to include sundry sharp edged fittings and pipe and cable work.
For circular landing gear components such as main legs or actuators positioned immediately in front of noise inducing components, transition strips of tape may be attached to the circular component on either side thereof to encourage clean detachment of airflow therefrom and to encourage airflow away from a region immediately behind the circular component.
Where articulation and stowage permits it, components such as circular legs or actuators may be fitted with trailing extensions from either side thereof. Such extensions, in combination with the component, may then act as an attachment according to the invention to deflect air away from noise inducing components behind the said component with trailing extensions.
The said apparatus may include at least one said attachment positionable in front of an apertured landing gear strut or stay to deflect air away from edges of the aperture.
For a said strut or stay having surfaces extending approximately streamwise in the airflow a said attachment may be shaped to blend in airflow leaving the attachment with airflow pass
Chow Leung C
Foot David A
Wood Christopher N
Airbus UK Limited
Dinh Tien
Nixon & Vanderhye P.C.
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