Patent Document

This application is the U.S. national phase of International Application No. PCT/GB2009/051078, filed 27 Aug. 2009, which designated the U.S. and claims priority to GB Application No. 0816022.8, filed 3 Sep. 2008, the entire contents of each of which are hereby incorporated by reference. 
     INTRODUCTION 
     The present invention relates to a support assembly for supporting the slats on the leading edge of an aircraft wing. The invention also relates to an aircraft wing comprising at least one slat attached to a leading edge of the wing using the support assembly of the invention. 
     BACKGROUND 
     Aircraft need to produce varying levels of lift for take-off, landing and cruise. A combination of wing leading and trailing edge devices are used to control the wing coefficient of lift. The leading edge device is known as a slat. On larger aircraft there may be several slats spaced along the wing edge. During normal flight the slats are retracted against the leading edge of the wing. However, during take-off and landing they are deployed forwardly of the wing so as to vary the airflow across and under the wing surfaces. The slats usually follow an arcuate or curved path between their stowed and deployed positions. By varying the extent to which the slat is deployed along said path, the lift provided by the wing can be controlled. 
     An assembly is required to support and guide movement of a slat between stowed and deployed positions and a typical arrangement showing a cross-section through part of a wing  1  and a slat  2  in its stowed position is illustrated in  FIG. 1 . As can be seen from  FIG. 1 , the slat  2  is provided with an arcuate support arm or slat track  3  one end  4  of which is rigidly attached to the rear of the slat  2  and extends into the wing  1 . The slat track  3  penetrates machined rib  5  and wing spar  6  forming the wing structure. The slat track  3  defines an arc having an axis and is mounted within the wing so that it can rotate about that axis (in the direction indicated by arrows “A” and “B” in  FIG. 1 ) to deploy and retract the slat  2  attached to one end of the slat track  3 . 
     To drive the slat rack  3  so as to deploy or retract the slat  2 , a toothed slat rack  7  having an arcuate shape corresponding to the arcuate shape of the slat track  3  is mounted within a recess  3   a  on the slat track  3  and a correspondingly toothed drive pinion  8  is in engagement with the teeth  7   a  on the slat rack  7  so that when the drive pinion  8  rotates, the teeth  8   a  on the drive pinion  8  and the teeth  7   a  on the rack  7  cooperate to pivot or drive the slat rack  7  and the slat attached thereto, into a deployed position, i.e. in the direction of arrow “A” in  FIG. 1 . Typically, the slat track  3  rotates through an angle of 27 degrees between its fully stowed and fully deployed positions. Rotation of the pinion  8  in the opposite direction also drives the slat track  3 , in the direction of arrow “B”, back into its stowed position, as shown in  FIG. 1 . 
     The drive pinion  8  is mounted on a shaft  9  that extends along, and within, the leading edge of the wing  1 . Several gears  8  may be rotatably mounted on the shaft  8 , one for driving each slat  2  so that when the shaft  9  is rotated by a slat deployment motor close to the inboard end of the wing  1 , all the slats are deployed together. 
     The slat track  3  has a generally square cross-sectional profile such that its upper and lower surfaces  3   b ,  3   c  each define a portion of a curved surface of a cylinder each having its axis coaxial with the axis of rotation of the slat track  3 . 
     The slat track  3  is supported between roller bearings  10   a ,  10   b  both above and below the slat track  3  and the axis of rotation of each bearing  10   a ,  10   b  is parallel to the axis of rotation of each of the other bearings  10   a ,  10   b  and to the axis about which the slat track  3  rotates in the direction of arrows “A” and “B” between its stowed and deployed positions. The upper bearings  10   a  lie in contact with the upper surface  3   b  of the slat track  3  and the lower bearings  10   b  lie in contact with the lower surface  3   c  so that they support the slat track  3  and guide it during deployment and retraction. The bearings  10   a ,  10   b  resist vertical loads applied to the slat  2  during flight both in stowed and deployed positions and also guide movement of the slat track  2  during slat deployment and retraction. 
     It will be appreciated that the bearings  10   a ,  10   b  resist loads that are applied in the vertical direction only. By vertical loads are meant loads that act in a direction extending in the plane of the drawing or, in a direction acting at right-angles to the axis of rotation of each bearing. 
     It will be appreciated that there can be significant side loads acting on a slat  2  in addition to loads acting in a vertical direction during flight, especially as the slats  2  generally do not extend along the leading edge of the wing  1  exactly square to the direction of airflow. By side-loads is meant loads that act in a direction other than in a direction that extends in the plane of the drawing or, in other words, those loads that act in a direction other than at right-angles to the rotational axis of each bearing  10   a ,  10   b.    
     To counteract side-loads, the slat track  3  is also supported by further bearings  11  disposed on either side of the slat track  3  as opposed to the vertical load bearings  10  mounted above and below the slat track  3 . These side-load bearings  11  may not be rotational and may just comprise bearing surfaces, pads or cushions against which the side walls of the slat track  3  may bear when side loads are applied to the slat  2 . 
     It is also conventional to provide at least one failsafe shaft  12 , commonly referred to as a “funk pin” between each of the upper bearings  10   a  and which are positioned so as to support the slat track  3  in the event that one or more of the vertical load bearings  10  fail. The funk pins  12  may be non-rotatable shafts against which the slat track  3  slides or skids in the event of failure of a bearing  10 . During normal operation the funk pins perform no function and a clearance gap exists between each pin and the surface of the slat track  3  so that the slat track  3  does not contact the funk pins except in the event of a bearing failure. 
     It will be appreciated that space for components within the wing structure close to the leading edge of the wing  1  is very limited, especially once the slat track  3  together with its vertical and side load bearings  10   a ,  10   b , 11 , the drive pinion  8  and the funk pins  12  have all been installed. The requirement to house all these components places considerable design restrictions on the shape of the wing  1  in addition to increasing weight, manufacturing costs and complexities. 
     As the additional side-load bearings  11  and funk pins  12  are disposed between each of the upper and lower bearings  10   a ,  10   b , these bearings must be spaced from each other in the circumferential direction about the axis of the slat track  3  by a distance which provides sufficient space between the bearings  10   a ,  10   b  to receive the side-load bearings  10   a ,  10   b  and the funk pins  12 . As a consequence of this, a further disadvantage with the conventional assembly is that the slat track  3  must be relatively long to accommodate the desired maximum deployment angle for the slat  2  whilst ensuring that the slat track  3  is adequately supported by two vertical load bearings  10   a  above the slat track  3  and two vertical load bearings  10   b  below the slat track  3 , even at maximum deployment. As a result of its extended length, the slat track  3  penetrates the spar  6  and so the free end of the slat track  3  must be received within a track can  13  that separates the slat track  3  from the fuel stored within the wing  1  behind the spar  6 . However, it is undesirable to have openings in the spar  6  as this can weaken the wing structure. It will also be appreciated that the requirement for a track can  13  also presents additional problems and assembly issues with the need to provide an adequate seal where the track can  13  is attached to the spar  6  so as to prevent fuel leakage. 
     Embodiments of the invention seek to provide an aircraft slat support assembly that overcomes or substantially alleviates the problems referred to above. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a slat support assembly comprising a slat support arm having a plurality of bearing surfaces extending along its length, the slat support arm being movable to deploy a slat attached to one end of said slat support arm from a leading edge of an aircraft wing, and a plurality of bearings mountable within the wing, each bearing being in rolling contact with an associated bearing surface to support the slat support arm and guide it during deployment and retraction of the slat, wherein at least some of the bearing surfaces and associated bearings are configured so that each bearing counteracts load applied to the slat support arm in more than one direction. 
     As each of the bearings is able to withstand loading applied to the slat support arm in multiple directions, additional side-load bearings or cushions are no longer required reducing the number of components required and the weight of the assembly. The reduction in components also provides more space within the leading edge of the wing and enables the bearings to be positioned closer together in the deployment direction, thereby allowing a shorter slat support arm to be used than is normally the case. 
     In one preferred embodiment, the slat support arm has a pair of adjacent upper bearing surfaces, each upper bearing surface being arranged at an angle relative to its adjacent upper bearing surface such that a bearing associated with one upper bearing surface does not share a common axis with the bearing associated with the other upper bearing surface. 
     The axis of rotation of each bearing may intersect at right angles to each other, although it is envisaged that the axis of rotation of each bearing may also intersect at an angle less, or more, than 90 degrees. 
     In one embodiment, the slat support arm has a lower pair of adjacent bearing surfaces, each lower bearing surface being arranged so that the axis of rotation of a bearing associated with one lower bearing surface is coaxial with the axis of rotation of a bearing associated with the other lower bearing surface. 
     In another embodiment, wherein the slat support arm has a second pair of lower adjacent bearing surfaces, each bearing surface of said second pair being arranged at an angle relative to its adjacent lower bearing surface such that a bearing associated with one lower bearing surface does not share a common axis with the bearing associated with its adjacent lower bearing surface. 
     In said other embodiment, the axis of rotation of each bearing associated with each lower bearing surface may intersect at right angles to each other, although other angles are also envisaged. 
     In another embodiment, the slat support arm is curved and rotatable about an axis that corresponds to its axis of curvature, at least the upper bearing surfaces having a width extending in the axial direction and the radial distance from the axis of the slat support arm to each of the upper bearing surfaces changing across the width of each of the upper bearing surfaces. 
     As the radial distance from the axis to the bearing surface varies across the width of the bearing surface, the bearings in rolling contact with the bearing surface are able to withstand loading in all directions including side-loads as well as vertical loads. By radial distance is meant the shortest distance from the axis of the slat support arm to the bearing face, i.e. the length of a line extending perpendicular from the axis of the slat support arm to the bearing face. 
     Typically, the radial distance changes linearly in a direction across the width of the bearing surface. 
     In a preferred embodiment, the bearing surface includes a pair of upper bearing faces. 
     Most preferably, the radial distance from the axis of the slat support arm to one upper bearing face increases in a direction across its width and the distance from the axis of the slat support arm to the other upper bearing face decreases in the same direction across its width. 
     In one embodiment, each upper bearing face is separated by a region having a width extending in the axial direction and the distance from the axis to said region is constant in a direction across its width. 
     In a preferred embodiment, the bearing surface also includes a pair of lower bearing faces. 
     Preferably, the lower bearing faces each have a width extending in the axial direction and the radial distance from the axis to each of said lower bearing faces is constant in a direction across the width of each lower bearing face. 
     A distance from the axis of the slat support arm to one lower bearing face may increase in a radial direction across its width and the distance from the axis to the other lower bearing face may decrease in the same direction across its width. 
     Conveniently, each lower bearing face may be separated by a region having a width extending in the axial direction and the radial distance from the axis to said region is constant in a direction across the width of each lower bearing face. 
     In a preferred embodiment, each upper bearing face is spaced from a lower bearing face in a radial direction. 
     The radial distance from the axis of the slat support arm to one bearing face may increase in a direction across its width whereas the distance from the axis to the other bearing face spaced from said one bearing face in a radial direction may decrease in the same direction across its width. 
     Typically, at least one bearing is in rolling contact with each bearing face. Ideally, there are two or even three bearings in rolling contact with each face. 
     In a preferred embodiment, the axis of rotation of each bearing is parallel to the bearing face with which the bearing is in contact, although it also envisaged that the axis of rotation of the bearings could be parallel to the axis of the slat support arm, in which case the surfaces of the bearing are angled so as to make rolling contact with their corresponding bearing faces. 
     The bearings may, advantageously, be mounted in a bearing yoke, the yoke being configured for attachment to the wing structure of an aircraft. 
     The bearing yoke preferably comprises a frame having an aperture to receive the slat support arm, and means to mount the bearings in the yoke such that they lie in rolling contact with the bearing surface. 
     In one embodiment, each bearing may be rotatably mounted on a shaft having a cap at one end. The other end of the shaft remote from the cap can be threaded to engage a corresponding threaded hole in the yoke and the yoke may have an opening to receive and support the cap when said threaded end of the shaft is in threaded engagement with the threaded hole in the yoke. 
     In one embodiment, a seal may be formed between the cap and the yoke with ‘o’ ring seals to prevent the ingress of dirt into the bearing between the cap and the yoke. 
     Conveniently, tool engagement means are provided on the cap to enable the shaft to be rotated so as to couple the threaded portion of the shaft to the yoke. 
     In one embodiment, a plurality of yokes are spaced from each other by an angle about the axis of the slat support arm, each yoke housing a pair of upper and a pair of lower bearings. 
     In one embodiment, the free end of the slat support arm remote from the slat is chamfered. 
     The slat support assembly preferably comprises a groove in the slat support arm and a slat rack mounted to the slat support arm in the groove for cooperation with a drive pinion configured to rotate the slat track about its axis for deployment and retraction of the slat. 
     According to another aspect of the invention, there is provided an aircraft wing having a slat and a slat support assembly according to the invention, the slat support arm being configured such that it disengages the yoke spaced furthest away from the leading edge of the wing when the slat has reached its fully deployed position. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, and with reference to  FIGS. 2 to 7  of the accompanying drawings, in which: 
         FIG. 1  is a prior art side sectional view through a portion of a leading-edge of a wing of an aircraft with a slat shown in its stowed position; 
         FIG. 2  is a schematic cross-sectional view through a slat support arm, and bearings to illustrate the principle of the present invention; 
         FIG. 3  is a schematic cross-sectional view of a modification of the slat support arm configuration shown in  FIG. 2 ; 
         FIG. 4  is a schematic side sectional view through the leading edge of a wing and slat with the slat in its retracted position; 
         FIG. 5  is a schematic side sectional view through the leading edge of a wing and slat as shown in  FIG. 4 , but with the slat in its maximum deployed position; 
         FIG. 6  is a perspective view of a more practical application of the embodiment of  FIG. 3 , and 
         FIG. 7  is a perspective view similar to that of  FIG. 6 , but with the bearing yokes removed for clarity. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  represents a prior art view of a portion of a leading edge of a wing and slat and has already been described above. 
     Referring now to  FIGS. 2 and 3 , there is shown a simplified cross-sectional view through a slat track support assembly  20  according to an embodiment of the invention. This cross-section is taken through the curved slat support arm or slat track  21  viewed from the front, i.e. looking towards the leading edge of the wing, and so the slat itself, which is attached to the front end of the slat support arm  21  is not visible in these drawings and the slat support arm rotates  21  about its theoretical centre or axis (not shown in the Figures), in a direction out of the sheet towards the viewer, when a slat  2  attached to the slat support arm  21  is deployed. 
     As in the prior art view of  FIG. 1 , the curved slat support arm  21  has an arcuate groove or recess  22  along its length in which is received a slat rack  23  attached to the slat support arm  21 . The slat rack  23  has teeth  23   a  extending along its lower exposed surface for engagement with a drive pinion (not shown but similar to drive pinion  8  shown in  FIG. 1 ), to drive the slat support arm  21  between slat deployed and slat retracted positions, as is conventional. 
     The slat support arm  21  extends within a space formed between two ribs  24  forming part of the structure of the aircraft wing and an upper bearing yoke  25  is rigidly attached to and extends between the ribs  24 . A shaft  26  is also rigidly mounted and extends between the ribs  24  below the slat support arm  21 . Two bearings  27   a , 27   b  are rotatably mounted on the shaft  26  and lie in rolling contact with corresponding bearing surfaces  28   a , 28   b  on the slat support arm  21 . It will be appreciated that the axis of rotation (A-A—see  FIG. 2 ) of the bearings  27   a ,  27   b , and corresponding bearing surfaces  28   a , 28   b  are both parallel to the axis of rotation (X-X) of the slat support arm  21  as it moves between its deployed and retracted positions. These bearings are therefore only able to resist loads applied to the slat support arm  21  in a vertical direction, i.e. in the direction of arrow “F” in  FIG. 2 , but cannot support any side loading of the slat support arm  21 . However, the upper side of the slat support arm  21  is divided into two bearing surfaces  29   a , 29   b  that each extend upwardly from the side of the slat support arm  21  at an angle towards a tip  30 . In effect, the upper edge of the slat support arm  21  has a triangular profile in cross-section, although it is envisaged that the bearing surfaces  29   a , 29   b  need not meet at a tip and there could be a region between the two bearing surfaces that extends parallel to the axis of the slat support arm  21 . 
     A pair of upper bearings  31   a ,  31   b  are rotatably mounted on separately angled shafts  32   a ,  32   b , received within the upper bearing yoke  25  and bearing  31   a  lies in rolling contact with angled bearing surface  29   a  whilst bearing  31   b  lies in rolling contact with angled bearing surface  29   b . The shafts  32   a , 32   b  are angled such that the axis of rotation (B-B and C-C) of each bearing  31   a , 31   b  is parallel to its corresponding bearing surface  29   a , 29   b . It will be appreciated that, as a result of orientating the upper bearings  31   a , 31   b  so that the contact face between the bearings  31   a , 31   b  and their corresponding bearing surfaces  29   a ,  29   b , are no longer parallel to the axis of rotation of the slat support arm  21 , the upper bearings  31   a , 31   b  are now able to counteract side-loading forces applied to the slat support arm  21 , i.e. forces applied in the direction of arrows “L” in  FIG. 2 , in addition to vertical loads. Therefore, the additional side-load bearings conventionally used in the prior art slat support assemblies are no longer required, thereby reducing weight and saving space and cost. 
     It will be appreciated that as the bearing surfaces  29   a , 29   b  are not parallel to the axis of rotation of the slat support arm, the radial distance from the axis X-X of the slat support arm changes in a direction along the axis between a maximum distance D 1  and a minimum distance D 2 , as indicated in  FIG. 2 . It will be noted that the radial distance decreases in a first direction (right to left, as shown in  FIG. 2 ) for the lefthand bearing surface  29   a  and that the radial distance decreases in a second direction (left to right, as shown in  FIG. 2 ) for the righthand bearing surface  29   b.    
       FIG. 3  shows a similar arrangement to that shown in  FIG. 2 , except that the lower bearings  27   a ,  27   b  are arranged in the same way as the upper bearings  31   a ,  31   b  (and now have separate axes A 1 -A 1  and A 2 -A 2 ) and the lower bearing surfaces  28   a ,  28   b  of the slat support arm  21  are also angled relative to the axis of rotation of the slat support arm  21 . Each of the lower bearings  27   a ,  27   b  are also rotatably mounted on individual shafts  32   a ,  32   b  received in a lower yoke  33  that extends between ribs  24  of the aircraft wing. In this embodiment, both the lower and upper bearings  27   a , 27   b ;  31   a ,  31   b  are able to counteract both side and vertical loads applied to the slat support arm  21 . 
     Although the lower and/or upper bearing surfaces  28   a , 28   b ;  29   a , 29   b  are shown as being angled at 45 degrees relative to the axis about which the slat support arm  21  rotates, it will be appreciated that the bearing surfaces  28   a , 28   b ; 29   a , 29   b  could assume any angle between 0 and 90 degrees depending on the loading that the bearings need to withstand. For example, the side-loading forces will be substantially less than the vertical loading forces and so the bearing surfaces will be angled so that their associated bearings are positioned so as to counteract a greater vertical loading force than a side-loading force. 
     A generalised side view of the arrangement shown in  FIG. 2  is illustrated in  FIG. 4 , and in which the slat  2  can be seen in its retracted position in which it sits against the leading edge of the wing  1 . In this embodiment, there are three upper yokes  25  arranged spaced by an angle about the theoretical centre or axis of rotation “X” of the slat support arm  21  above the slat support arm  21 , each of which receive two bearings  31   a ,  31   b , as shown and described with reference to  FIG. 2 . Also shown is three lower bearings  27   a  spaced from each other by an angle about the axis “X” of rotation of the slat support arm  21  and corresponding to each of the upper sets of bearings  31   a ,  31   b . A drive pinion  33  in engagement with the teeth  23   a  on the slat rack  23  is also shown positioned between two of the lower bearings  27   a  to drive the slat support arm  21  between its deployed and retracted positions. 
     The same generalised side view is shown in  FIG. 5 , except that in this view, the slat  2  is shown in its maximum deployed position. To achieve this position, the slat support arm  21  has rotated about its axis “X” by an angle of approximately 24 degrees (indicated by angle α in  FIGS. 4 and 5 ). It can be seen that, in this position, the trailing set of bearings  27   a , 27   b ;  31   a , 31   b , i.e. those furthest from the leading edge of the wing or the slat  2 , are redundant because the slat support arm  21  is no longer engaged with these bearings and is entirely supported by the remaining two sets of bearings closer to the leading edge of the wing  1 . It is envisaged that this trailing set of bearings could be omitted altogether, although it may be advantageous to provide the trailing set of bearings to provide additional support for the slat during cruise, when the slat  2  is retracted. To guide the free end of the slat support arm  21  back into engagement with the trailing set of bearings when the slat support arm  21  is retracted, the free end of the slat support arm  21  may have a slight chamfer or beveled surface  35 . 
     As there is no longer any requirement to provide additional side-load bearings between the vertical load bearings, the bearing sets can be placed much closer together, thereby saving space within the wing structure and allowing for a consequential reduction in the length of the slat support arm  21  because the slat support arm  21  can still be supported by two bearing sets even at full deployment of the slat  2 . As a consequence of the reduction in the length of the slat support arm  21 , there is no longer any need to penetrate the spar  6  and a track can is also no longer required. As an additional advantage, it is also possible to arrange corresponding upper and lower bearings so that a line extending from the theoretical centre or axis of rotation of the slat support arm  21  extends through the axis of both the lower and upper bearings because the bearings can be placed on the true radial centre lines that pass through the theoretical centre of rotation of the slat support arm, thereby improving load carrying capability. In the prior art configuration, this is not possible due to the shortage of space and the requirement to provide additional side-load bearings between the vertical load bearings. 
     Reference will now be made to  FIGS. 6 and 7  which illustrate a more practical configuration of the generalised embodiment of  FIG. 3  and in which can be seen the slat support arm  21  having upper bearing faces  29   a ,  29   b  and lower bearing faces  28   a ,  28   b . The slat rack  23  is received in groove  22  and has teeth  23   a  for engagement with a drive pinion (not shown). 
     The bearings  27   a , 27   b ;  31   a , 31   b  of each set are mounted within a unitary yoke  40  which has an opening  41  shaped to receive the slat support arm  21  therethrough. The yoke  41  has recesses  42  in its end faces  43  to facilitate insertion and removal of the bearings  27   a , 27   b ;  31   a ,  31   b , which can be seen more clearly in  FIG. 7 , which shows the same view as  FIG. 6 , but with the yokes  40  omitted for clarity. Each bearing  27   a ,  27   b ;  31   a ,  31   b  comprises a bearing element  43  (see  FIG. 7 ) which is rotatably mounted on a shaft  44 . The shaft  44  has an end cap or head portion  45  and the end of the shaft  44  remote from the cap  45  is part-threaded at  46  for threaded engagement with a corresponding threaded aperture (not shown) in the yoke  40 , when the shaft  44 , together with the bearing element  43  mounted thereon, is inserted through the aperture  42  in the end faces of the yoke  40 . The cap  45  is supported within the recess  42  in the yoke and may be provided with a sealing element to seal any gap between the cap  45  and the wall of the recess  42  to prevent ingress of dirt. The upper face  47  of the cap  45  may be provided with holes  48  for engagement with a tool for inserting it into and mounting it to the yoke  40 . The yoke  40  may also be provided with drainage holes  40   a  to allow egress of water out of the yokes  40 . 
     The end faces  43  of the yoke  40  are provided with shoulders  49 . It is envisaged that these will be shaped to enable each yoke  40 , complete with its internally mounted bearings  27   a , 27   b ,  31   a ,  31   b , to be inserted into the aircraft wing  1  during assembly so that the shoulders  49  engage between corresponding ribs  5 , thereby locating respective yokes  40  in the correct position to receive the slat support arm  21 . 
     Embodiments of the invention essentially reduce the number of bearings required over a conventional slat support assembly by up to 50%, because the side-loads are now counteracted by the same bearings that counteract the vertical loads and so there is no longer any need to provide separate side-load bearings. This may enable a significant weight reduction and/or greatly reduce the design space constraints in the densely populated leading edge of the wing. 
     It will be appreciated that the foregoing description is given by way of example only and that modifications may be made to the slat support assembly of the present invention without departing from the scope of the appended claims. For example, it should be noted that, in the above described embodiment of the invention, the slat support arm is curved about an axis and rotates about said axis between its stowed and deployed positions. However, it is envisaged that the slat support arm could follow a non-circular path such as an elliptical or linear path and/or that the slat support arm may not be curved.

Technology Category: 7