Patent Publication Number: US-2022227473-A1

Title: Pin joint assembly

Description:
FIELD OF THE INVENTION 
     The present invention relates to a pin joint assembly, an aircraft assembly comprising the pin joint assembly, and an aircraft comprising the aircraft assembly. 
     BACKGROUND OF THE INVENTION 
     The internal space available for components and systems within an aircraft is typically restricted, particularly in the wings where structural and aerodynamic considerations are paramount. 
     Pin joints are often required within wing structures, for example to actuate control surfaces or folding wing tip mechanisms. A pin joint typically requires various bushing arrangements to reduce the friction between respective rotating surfaces, however the design of these bushing arrangements can dictate the positioning of the pin joint due to the restricted space within the aircraft structure. This can have a knock-on effect to the choice and positioning of other adjacent components within the aircraft structure. 
     SUMMARY OF THE INVENTION 
     A first aspect of the invention provides a pin joint assembly, comprising: a first lug and a second lug; a pin extending through the first and second lugs; a U-shaped bushing between the first lug and the pin, wherein the U-shaped bushing comprises a first end flange and a second end flange that extend radially outwards and retain the U-shaped bushing to the first lug; wherein the U-shaped bushing comprises a bearing surface between the first and second end flanges on which the first lug is slidable. 
     The float provided to a pin joint assembly may be relatively large for ease of assembly and then subsequently require reduction prior to operation of the pin joint. With the arrangement of the present invention, the U-shaped bushing is able to reduce the amount of float provided to a pin joint assembly, whilst allowing movement of the second bushing, as well as being positionable on any of the lugs of the pin joint. 
     Preferably, the pin comprises a head end, a tail end, and a body portion between the head end and tail end, wherein the head end has a diameter greater than a diameter of the body portion. 
     Preferably, the U-shaped bushing is adjacent the head end of the pin. The U-shaped bushing can be particularly advantageous in combination with a headed pin, as the U-shaped bushing can be placed anywhere along the length of the pin, including adjacent the head end. 
     Preferably, the U-shaped bushing bears against the second lug. With this arrangement, relative movement between the U-shaped bushing and the second lug can be prevented. 
     Preferably, the pin assembly comprises a first bushing between the first lug and the pin and/or a second bushing between the second lug and the U-shaped bushing. 
     Preferably, the first bushing is a fixed bushing fixedly attached to the first lug and/or the second bushing is a fixed bushing fixedly attached to the second lug. 
     Preferably, the U-shaped bushing is a two-part bushing comprising: a first bushing component having a first body portion and a first flanged portion extending from the first body portion; a second bushing component having a second body portion and a second flanged portion extending from the second body portion; wherein the first body portion is arranged to overlap the second body portion to fasten the first and second bushing components together. 
     With this arrangement, the second bushing is easier to position on the bearing surface of the U-shaped bushing. 
     Preferably, the first body portion overlaps the second flanged portion and terminates substantially flush with an outer-most face of the second flanged portion. 
     With this arrangement, the join between the first and second bushing components is not at the inner bearing surface of the U-shaped bushing. 
     Preferably, the outer-most face of the second flanged portion is arranged adjacent the head end of the pin. 
     With this arrangement, the join between the first and second bushing components is not adjacent to a lug or bushing. This can be particularly advantageous when the relative rotation between U-shaped bushing and the second lug is expected to be greater than the relative rotation between the U-shaped bushing and the pin. 
     Preferably, the first body portion and second body portion are fastened together via an interference fit. 
     Preferably, the first body portion or second body portion comprises a protrusion, and the other of the first body portion or second body portion comprises a depression sized to correspond to the protrusion; and wherein the first and second bushing components are fastened together by lodging the protrusion into the depression. 
     Preferably, the U-shaped bushing is rotatable with respect to the pin. This provides a dual-slip path, thereby providing a redundant slip path in the event that a slip path becomes damaged or otherwise unusable. 
     A second aspect of the invention provides an aircraft assembly comprising the pin joint assembly of any preceding claim, a first aircraft component, and a second aircraft component, wherein the first end lug extends from one of the first or second aircraft components and the second lug extends from one of the first or second aircraft components, such that the first aircraft component is arranged to rotate relative to the second aircraft component about an axis of the pin joint assembly. 
     Preferably, the first aircraft component is a main wing portion of a wing and the second aircraft component is a wing tip device. 
     Preferably, the first aircraft component is a main wing portion of a wing and the second aircraft component is a flight control surface. 
     Preferably, the flight control surface is one of: an aileron, a slat, a spoiler, and a flap. 
     Preferably, the aircraft assembly further comprises an obstruction arranged at an obstructed end of the pin hole. 
     Preferably, the obstruction is an actuator for rotating the second aircraft component relative to the first aircraft component. 
     Preferably, the head end of the pin is arranged adjacent the obstruction. With this arrangement, the tail end and associated locking features may be positioned on an opposite end of the pin assembly, away from the obstruction, thereby providing additional space for the obstruction. This can be useful when the obstruction is, e.g., an actuator for actuating the first aircraft component and second aircraft component about the axis of the pin joint assembly. The obstruction may be positioned in a better position, or allow a bigger obstruction (e.g. actuator) to be installed, or even more room for maintenance. 
     Preferably, the pin joint assembly is a first pin joint assembly, and the aircraft assembly further comprises a second pin joint assembly, wherein the obstruction is arranged at the obstructed end of the first pin joint assembly and at an obstructed end of the second pin joint assembly. 
     Preferably, the head end of the pin of the second pin joint assembly is arranged adjacent the obstruction. 
     Preferably, the first aircraft component and/or second aircraft component comprises an outer shell, and wherein a clearance distance between the pin and the outer shell in a direction parallel to an axis of the pin varies along the pin. The pin assembly can be particularly advantageous in an aircraft assembly with an outer shell (e.g. an aerodynamic shell) that causes the clearance distance between the pin assembly and outer shell to vary, as the U-shaped bushing is suitable for positioning anywhere along the pin, such that the increased stack height caused by the U-shaped bushing can be positioned where there is most clearance room. 
     A third aspect of the invention provides an aircraft comprising the aircraft assembly of the second aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  shows a perspective view of a typical fixed wing aircraft; 
         FIG. 2  shows a planform view of a port side wing; 
         FIG. 3  shows a pin joint assembly of the prior art; 
         FIG. 4  shows a z-shaped bushing of the prior art; 
         FIG. 5  shows a close-up view of the pin joint assembly of  FIG. 3 ; 
         FIG. 6  shows an aircraft assembly including a pair of pin joint assemblies of the prior art; 
         FIG. 7  shows an example of a pin joint assembly of the present invention; 
         FIG. 8  shows a U-shaped bushing according to an example of the present invention; 
         FIG. 9A  shows a first bushing component of the U-shaped bushing of  FIG. 8 ; 
         FIG. 9B  shows a second bushing component of the U-shaped bushing of  FIG. 8 ; 
         FIG. 10  shows a close-up view of the pin joint assembly of  FIG. 7 ; 
         FIG. 11  shows the pin joint assembly in a first, rear-most, position; 
         FIG. 12  shows the pin joint assembly in a second, forward-most, position; 
         FIG. 13  shows an aircraft assembly including a pair of pin joint assemblies according to the present invention; 
         FIG. 14  shows an example of a pin joint assembly comprising a headless pin; 
         FIG. 15A  shows a pin joint assembly between a wing and a slat; 
         FIG. 15B  shows a pin joint assembly between a wing and an aileron; 
         FIG. 15C  shows a pin joint assembly between a wing and a spoiler; 
         FIG. 15D  shows a pin joint assembly between a wing and a flap. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT(S) 
       FIG. 1  illustrates a typical fixed wing aircraft  1 . The aircraft  1  may have a port wing  2  and a starboard wing  3  that extend from a fuselage  4 . Each wing  2 ,  3  may carry wing mounted engines  9 . The fuselage  4  has a nose  5  and a tail  6 . The tail  6  may have horizontal and vertical stabiliser surfaces  7 ,  8 . The aircraft  1  may be a typical jet passenger transport aircraft although the invention is applicable to a wide variety of fixed wing aircraft types, including commercial, military, passenger, cargo, jet, propeller, general aviation, etc. with any number of engines attached to the wings or fuselage. 
     Each wing  2 ,  3  of the aircraft  1  may have a main wing portion  10  that is a cantilevered structure with a length extending in a span-wise direction from a wing root to a wing tip, the root being joined to the aircraft fuselage  4 . A wing tip device  20  may be provided on the tip end of each wing  2 ,  3 . The wings  2 ,  3  are similar in construction so only the starboard wing  3  will be described in detail with reference to  FIG. 2 . 
     The wing  3  may have a plurality of flight control surfaces. The wing  3  may include slats  12 .  FIG. 2  shows slats  12  adjacent to the leading edge of the wing  3 . A plurality of slats  12  may be distributed along the span of the wing  3 . The wing  3  may include an aileron  13 .  FIG. 2  shows an aileron  13  provided on an outboard section of the trailing edge of the wing  3 . The wing  3  may include air brakes/spoilers  14 .  FIG. 2  shows air brakes/spoilers  14  provided across the upper surface of the wing  3  towards the trailing edge of the wing  3 . The wing  3  may include a flap  15 .  FIG. 2  shows an inner flap  15   a  adjacent to the wing root, and an outer flap  15   b  outboard of the inner flap towards the aileron  13 . 
     Whilst the aircraft  1  is shown with a particular quantity and configuration of control surfaces, it will be understood that the wings  2 ,  3  may comprise a different number and/or arrangement of control surfaces. 
     The wing tip device  20  may be a folding wing tip device  20  configured to rotate relative to the wing  3  about a fold axis  11 . The fold axis  11  may extend from a leading edge to a trailing edge of the wing  3 . The folding wing tip device  20  may be rotated relative to the wing  3  by an actuator  50 . 
       FIG. 3  shows an existing folding wing tip mechanism according to an example of the prior art. The mechanism includes a pin joint assembly  30 . 
     The pin joint assembly  30  includes a first set of lugs, first lug  41   a , third lug  41   c , and fifth lug  41   e  extending from the tip end of the wing  3  and a second set of lugs, second lug  41   b , and fourth lug  41   d , extending from a root end of the wing tip device  20 . The first and fifth lugs  41   a ,  41   e  are end lugs positioned at opposing ends of the pin joint assembly  30 . The lugs  41   a - e  may be aluminium lugs. 
     The lugs  41   a ,  41   b ,  41   c ,  41   d ,  41   e  include a pin hole  31  extending therethrough, and through which a headed pin  62  is inserted. The headed pin  62  may be a steel pin. The headed pin  62  is inserted into a pin sleeve  61 . A set of bushings, first bushing  63   a , second bushing  63   b , third bushing  63   c , fourth bushing  63   d  and fifth bushing  63   e , are arranged between the pin sleeve  61  and each lug  41   a ,  42   a ,  43   a ,  43   b  to reduce the friction between the relative parts when the wing tip device  20  folds relative to the wing  3 , and for example to protect the relatively soft aluminium of the lugs  41   a - e  from the steel pin  62  or pin sleeve  61 . The bushings  63   a - e  may be fixed bushings, fixedly attached to each of the respective lugs  41   a - e.    
     The bushings  63   a - e  may be integral with their respective lugs  41   a - e . For example, if the lugs  41   a - e  and pin  62  are made of the same material, such as steel. Alternatively, any of the bushings  63   a - e  may be rotatable with respect to their respective lugs  43   a - e.    
     The headed pin  62  has a head end  65  and a tail end  66 . The head end  65  has a diameter larger than the pin hole  31  and headed pin  62 , such that the headed pin  62  is prevented from being fully inserted into the pin hole  31 . The tail end  66  includes a set of locking features  67  (for example locking nuts) that tighten towards the head end  65 , thereby pressing the headed pin  62  against the pin sleeve  61 .  FIG. 3  shows the headed pin  62  pressing against the end bushings  63   a ,  63   e  of the end wing lugs  41   a ,  41   e , although alternatively the end lugs may be wing tip lugs. 
     The end bushing  63   a  adjacent the tail end  66  is located on the bearing surface  71  of a substantially z-shaped bushing  70 , for example as shown in cross-section in  FIG. 4 . The z-shaped bushing  70  comprises a first end flange  72  that is an inwardly extending flange, such that the flange extends towards an axis of the bushing  63   a , and a second end flange  73  that is an outwardly extending flange, such that the flange extends away from the axis of the bushing  63   a . The bearing surface  71  is defined as being between the first and second end flanges  72 ,  73 , on which the fixed bushing  63   a  of the end lug  41   a  is positioned. 
     As shown in  FIG. 3 , and in an expanded view shown in  FIG. 5 , the z-shaped end bushing  70  is clamped to a shoulder  61   a  of the pin sleeve  61  by a set of locking features  68 . Specifically, the inwardly extending end flange  72  is clamped to the pin sleeve  61 . 
     The locking features  68  may comprise one or more of a locking ring  69   a , tab washer  69   b  or thrust washer  69   c.    
     The z-shaped bushing  70  has a length greater than the length of the fixed bushing  63   a  in a direction parallel to the axis  38  of the pin  62 , such that the z-shaped bushing  70  reduces the gap to the fixed bushing  63   b  of the adjacent lug  41   b  of the wing tip device  20  whilst allowing the fixed bushing  63   a  on its bearing surface  71  to move along the bearing surface  71 . 
     Consequently, the axial movement of the first set of lugs  41   a ,  41   c ,  41   e  with respect to the second set of lugs  41   b ,  41   d  is limited by the addition of the z-shaped bushing  70 , as the axial movement of the second set of lugs  41   b ,  41   d  is prevented in one direction by the z-shaped bushing  70  and in the opposite direction by the third lug  41   c . This third lug  41   c  is itself limited in its axial movement towards the head end  65 , as the third lug  41   c  is connected to the first (end) lug  41   a  and fifth (end) lug  41   e  via the structure of the wing  3 , and the axial movement of the third lug  41   c  is thereby restricted by the fifth lug  41   e  contacting the head end  65  or by the first lug  41   a  contacting the outwardly extending end flange  73  of the z-shaped bushing  70 . 
     The movement prior to the installation of the z-shaped bushing  70  may be 3 mm, 5 mm, or more so as to provide additional clearance (i.e. float) for assembling the wing  3  to the wing tip device  20 . Installation of the z-shaped bushing  70  reduces this float to a value that is acceptable in the assembled state for actuation of the pin joint, for example, the float may be 1 mm or less after assembly of the z-shaped bushing  70 . 
     There may be limited space within a structure to house the pin joint assembly  3 , for example due to the aerodynamic profile of the airframe or wing structure  80  in which the mechanism may be housed. 
       FIG. 6  schematically shows an actuator  50  positioned between a pair of pin assemblies  30 : a first pin joint assembly  30   a  adjacent a leading edge of the wing  3  and a second pin joint assembly  30   b  adjacent the trailing edge of the wing  3 . The axes  38  of the headed pins  62  of each assembly  30   a ,  30   b  are aligned with each other to define a hinge axis of the folding assembly, for example a hinge axis  11  of the wing  3  and wing tip device  20 . 
     Due to the limited space within the wing structure  80 , the actuator  50  fills a substantial amount of the space between the two pin joint assemblies  30   a ,  30   b , such that the first and second pin joint assemblies  30   a ,  30   b  need to be housed close to the leading edge and trailing edge of the wing  3 , respectively. 
     As a result, the vertical clearance distance between the pin  62  and the wing structure  80  (e.g. the outer shell of the wing box) in a direction parallel to the axis  38  of the pin  62  varies along the length of the pin  62 . For example,  FIG. 6  shows the vertical clearance distance Y 1  of the first pin joint assembly  30   a  and the wing structure  80  at a first end of the pin  62  adjacent the tail end  66  is smaller than the vertical clearance distance Y 2  of the first pin joint assembly  30   a  and the wing structure  80  at a second end of the pin  62  adjacent the head end  65 . This may be due to the aerodynamic profiling of the wing structure  80 . This can limit the possible arrangement and orientation of the first and second pin joint assemblies  30   a ,  30   b.    
     In  FIG. 6 , the first pin joint assembly  30   a  is oriented with the tail end  66  facing towards the leading edge and the head end  65  facing towards the trailing edge. This provides additional space for the actuator  50  positioned between the first and second pin joint assemblies  30   a ,  30   b , as the locking features  67  of the pin joint assembly  30   a  take up a large amount of axial space (with respect to the axial space taken by the arrangement at the head end). 
     In contrast, there is limited vertical clearance towards the trailing edge of the wing structure  80 . Due to the increased stack height resulting from use of the z-shaped bushing  70  (i.e. the combined height of the z-shaped bushing  70  and the fixed bushing  63   a ), which is positioned against the tail end  66  of the pin  62 , it is not possible to position the tail end  66  towards the trailing edge. As a result, the tail end  66  is positioned so as to face the leading edge, and thereby occupies space between the two pin joint assemblies  30   a ,  30   b . This limits the size and position of the actuator  50 . 
       FIG. 7  shows an example of a pin joint assembly  130  according to the present invention. The pin assembly  130  of the present example is substantially similar to the examples of the pin assemblies  30 ,  30   a ,  30   b  described in relation to  FIGS. 3 to 6 , with like numerals used to denote like parts. The pin joint assembly  130  may be used in a folding wing tip mechanism, as described in relation to  FIG. 3 , or any other type of hinge assembly, for example a pin joint assembly between a wing  3  and an aileron, slat, spoiler, flap or other control surface. 
     The pin joint assembly  130  comprises a U-shaped bushing  90  having features that allow it to be positioned against a lug, for example any of the lugs  41   a ,  41   b ,  41   c ,  41   d ,  41   e  shown in  FIG. 7 , such that the U-shaped bushing  90  may be positioned on a lug  41   a ,  42   a ,  43   a ,  43   b  adjacent the head end  65  or tail end  66  of a pin  62 , or anywhere in between, as will be made clear below. 
     The pin joint assembly  130  may include a set of lugs, first lug  41   a , third lug  41   c , and fifth lug  41   e  extending from a first structure (for example the tip end of a wing  3 ) and a set of lugs, second lug  41   b , and fourth lug  41   d , extending from a second structure (for example the root end of a wing tip device  20 ). The first and fifth lugs  41   a ,  41   e  may be end lugs positioned at opposing ends of the pin joint assembly  130 , as shown in  FIG. 7 . 
     The lugs  41   a ,  41   b ,  41   c ,  41   d ,  41   e  include a pin hole  31  extending therethrough, and through which a headed pin  62  may be inserted. The headed pin  62  may be inserted into a pin sleeve  61 . A set of bushings  63   a ,  63   b ,  63   c ,  63   d ,  63   e ,  90  may be arranged between the pin sleeve  61  and each lug  41   a ,  42   a ,  43   a ,  43   b  to reduce the friction between the relative parts when the first structure  20  folds relative to the second structure  3 , with two of the bushings  63   e ,  90  stacked on top of each other, as will be explained below. 
     The headed pin  62  has a head end  65  and a tail end  66 , and a pin body  64  between the head end  65  and the tail end  66 . The head end  65  may have a diameter larger than the pin hole  31  and headed pin  62 , such that the headed pin  62  is prevented from being fully inserted into the pin hole  31 . The head end  65  may be integral with the pin body  64 , or separate to the pin body  64  such that the head end  65  may be attachable and/or detachable from the pin body  64 . 
     The tail end  66  may include a set of locking features  67  (for example locking nuts) that tighten towards the pin sleeve  61 , thereby pressing the headed pin  62  against the pin sleeve  61 .  FIG. 7  shows a pair of wing tip lugs  41   b ,  41   d  positioned between three wing lugs  41   a ,  41   c ,  41   e , although any number and arrangement of lugs  41   a - e  may be provided. 
     The U-shaped bushing  90  adjacent the head end  65  of the pin  62  comprises end flanges  92   a ,  92   b  arranged to extend outwardly from a central axis of the U-shaped bushing  90 , and an outer bearing surface  95   a  between the flanges  92   a,b . The U-shaped bushing  90  may be positioned adjacent the head end  65  of the pin, with the bushing  63   e  of the end lug  41   e  located between the flanges  92   a,b  and slidable along the outer bearing surface  95   a , as shown in  FIG. 7 . The U-shaped bushing  90  may be rotatable with respect to the pin  62  via an inner bearing surface  95   b  (See  FIG. 12A ). 
     An example of a U-shaped bushing  90  is described in more detail in relation to  FIGS. 8, 9A, and 9B . 
     The U-shaped bushing  90  may be a two-part bushing, for example as shown in  FIG. 8 . 
     The U-shaped bushing  90  may include a first bushing component  91   a  having a first body portion  93   a  and a first flanged portion  92   a  extending from the first body portion  93   a . The first flanged portion  92   a  may extend substantially perpendicular from the first body portion  93   a.    
     The U-shaped bushing  90  may include a second bushing component  91   b  having a second body portion  93   b  and a second flanged portion  92   b  extending from the second body portion  93   b . The second flanged portion  92   b  may extend substantially perpendicular from the second body portion  93   b.    
     The first body portion  93   a  may comprise a protrusion  96 . The second body portion  93   b  may comprise a depression  97  sized to correspond to the protrusion  96 . The protrusion  96  and depression  97  may be arranged such that the protrusion  96  is lodged in the depression  97 , thereby fastening the first and second bushing components  91   a,b  together when the first body portion  91   a  overlaps the second body portion  91   b . This prevents the first and second bushing components  91   a ,  91   b  from being separated easily. 
     In an alternative example, the first body portion  93   a  may comprise a depression  97  and the second body portion  93   b  may comprise a protrusion  96 . 
     The height of the protrusion  96  and depth of the depression  97  may be partially dictated by the thickness of the first and second body portions  93   a,b , for example the height of the protrusion  96  and depth of the depression  97  may be approximately half of the thickness of the first or second body portions  93   a ,  93   b.    
     The protrusion  96  and depression  97  may have a smoothly curved cross-section when viewed in a direction perpendicular to the axis of the bushing  90 . The cross-section may be continuously circular or ovalised, and may smoothly taper towards the body portion  93   a ,  93   b.    
     The first body portion  93   a  may overlap the second flanged portion  92   b  and terminate substantially flush with an outer-most face  98  of the second flanged portion  92   b , for example as shown in  FIG. 8 . This provides a join between the first and second bushing components  91   a,b  adjacent a side of the bushing  90 , i.e. away from the inner bearing surface  95   b.    
     The first body portion  93   a  and second body portion  93   b  may be fastened together via an interference fit, such that the overlapping faces of the first and second body portions  93  a,b may be held together by friction. The interference fit may be formed by freeze-fitting or shrink-fitting, wherein the relative size of one of the first or second body portions  93   a,b  is changed under temperature prior to assembly such that a return to room temperature forces the portions  93   a,b  tightly together. 
     The outer bearing surface  95   a  of the U-shaped bushing  90  has a length greater than a length of the bushing  63   e  located between the flanges  92   a,b , for example as shown in  FIG. 10 , such that the bushing  63   e  may slide along the outer bearing surface  95   a . The bushing  63   e  may slide by a distance defined by the difference between the length of the bearing surface  95   a  and the length of the bushing  63   e . The length of the bushing  63   e  may correspond substantially to the contact distance of the bushing  63   e  with the bearing surface  95   a  in a direction parallel to the axis of the U-shaped bushing  90 . 
       FIG. 10  shows an example in which the outer-most face  98  of the second flanged portion  92   b  is arranged adjacent the bushing  63   d  of the fourth lug  41   d . In an alternative example, it may be preferable to position the outer-most face  98  of the second flanged portion  92   b  adjacent the head end  65  of the pin  62  due to the increased relative rotation expected between the first and second sets of lugs  41   a - e.    
     The bushing  63   e  is slidable along the outer bearing surface  95   a  with respect to the outer bearing surface  95   a  in a direction parallel to the axis  38  of the pin  62 . The bushing  63   e  of the lug  41   e  may be a fixed bushing fixedly attached to the lug  41   e . The bushing  63   e  may be integral with the lug  41   e . Alternatively, the bushing  63   e  may be rotatable with respect to the lug  43   e.    
     The movement of the bushing  63   e  along a direction parallel to the axis  38  of the pin  62 , with respect to the outer bearing surface  95   a , is limited by the flanges  92   a,b  on either end of the outer bearing surface  95   a.    
     Each of the bushings  63   a - d ,  90  positioned against the pin sleeve  61  is moveable along the direction of the pin axis  38  with respect to the pin sleeve  61 , such that relative movement is provided between the set of lugs  41   a ,  41   c ,  41   e  extending from the tip end of the wing  3  and the set of lugs  41   b ,  41   d  extending from the root end of the wing tip device  20 . 
     The set of lugs  41   a,c,e  extending from a first structure (for example the tip end of a wing  3 ) are fixedly attached to each other such that each of the lugs  41   a,c,e  are fixed in position relative to each of the other lugs  41   a,c,e . Similarly, the set of lugs  41   b,d  extending from a second structure (for example the root end of a wing tip device  20 ) are fixedly attached to each other such that each of the lugs  41   b,d  are fixed in position relative to each of the other lugs  41   b,d.    
       FIG. 11  shows the pin joint assembly  130  in a first, rear-most, position in which the first set of lugs  41   a,c,e  are positioned towards the head end  65  of the pin  62 , as close to the head end  65  of the pin  62  as the arrangement will allow in this example. 
     In this configuration, a gap X 1  is provided between the fixed bushing  63   a  of the first lug  41   a  and the locking features  68  that clamp against the shoulder  61   a  of the pin sleeve  61 . The gap X 1  is prevented from increasing in size, as the third lug  41   c  bears against the fourth lug  41   d , which bears against the U-shaped bushing  90 , which itself bears against the shoulder  61   b  of the pin sleeve  61 . Gap X 2  between the fifth bushing  63   e  of the fifth lug  41   e  is therefore prevented from decreasing in size. 
       FIG. 12  shows the pin joint assembly  130  in a second, forward-most, position in which the first set of lugs  41   a,c,e  are positioned towards the tail end  66  of the pin  62 , such that there is no gap (i.e. gap X 1  has closed up) between the fixed bushing  63   a  of the first lug  41   a  and the locking features  68  that clamp against the shoulder  61   a  of the pin sleeve  61 , as the first lug  41   a  has moved forward towards the tail end  66  of the pin  62 . 
     As the first lug  41   a  is connected to the third and fifth lugs  41   c ,  41   e , via the first structure  3 , the third and fifth lugs  41   c ,  41   e  move forward towards the tail end  66  of the pin  62  with the first lug  41   a . The gap X 2  has therefore increased in size. The increase in size of X 2  corresponds to the decrease in size of X 1  with respect to the arrangement shown in  FIG. 11 . 
     The gap X 1  therefore defines an allowable amount of float between the first set of lugs  41   a,c,e  and the second set of lugs  41   b,d . The float allows relative fore and aft movement between the first set of lugs  41   a,c,e , the second set of lugs  41   b,d , and the pin  61 . The float may be 2 mm, 1 mm, or 0.5 mm, although the amount of float will typically depend on the size of the pin joint assembly and the particular application. 
     The first set of lugs  41   a,c,e , second set of lugs  41   b,d , and pin sleeve  61  (and pin  62  attached to the pin sleeve  61 ) are moveable relative to each other, i.e. the first set of lugs  41   a,c,e  are movable with respect to the second set of lugs  41   b,d , the first set of lugs  41   a,c,e , are moveable with respect to the pin sleeve  61 , and the second set of lugs  41   b,d  are movable with respect to the pin sleeve  61 . Each of the bushings  63   a - e ,  90  of the pin joint assembly  130  is unclamped, such that they are rotatable with respect to the pin  62  and pin sleeve  61 . 
     The U-shaped bushing  90  reduces the amount of float without having to modify the width of the lugs, and unlike the z-shaped bushing  70  described in relation to  FIGS. 3 to 6 , the U-shaped bushing  90  of the present invention does not need to be clamped to the pin sleeve  61 . This may allow a dual slip-path between the end lug  40   e  of the U-shaped bushing  90  and the pin sleeve  61  (and pin  62 ), thereby providing a reserve slip-path in the event that one of the slip-paths is damaged or otherwise unusable. 
     As the U-shaped bushing  90  does not need to be clamped, it will be apparent that the U-shaped bushing  90  is suitable for positioning under any of the fixed bushings  63   a - e  of the lugs  41   a - e , not just the fifth bushing  63   e  or the fifth lug  41   e.    
     This allows more design freedom in the arrangement of the pin joint assembly  130 , which can have beneficial knock-on effects to other features and systems. 
       FIG. 13  schematically shows an obstruction  49  positioned between a pair of pin assemblies  130 : a first pin joint assembly  130   a  adjacent a leading edge of the wing  3  and a second pin joint assembly  130   b  adjacent the trailing edge of the wing  3 . The obstruction may be an actuator  50 . The axes  38  of the pins  62  of each pin assembly  130   a ,  130   b  are aligned with each other to define a hinge axis of the folding assembly, for example a hinge axis  11  of the wing  3  and wing tip device  20 . 
     The vertical clearance distance Y 1  of the first pin joint assembly  130   a  and the wing structure  80  at a first end of the pin  62  adjacent the tail end  66  is smaller than the vertical clearance distance Y 2  of the first pin joint assembly  130   a  and the wing structure  80  at a second end of the pin  62  adjacent the head end  65 . This may be due to the aerodynamic profiling of the wing structure  80 , for example the wing structure  80  may be aerofoil shaped. 
     The position of the U-shaped bushing  90  is not dictated by the position of the tail end  66  of the pin  62 , in contrast to the z-shaped bushing  70 , and so can be positioned adjacent the head end  65  of the pin  62 , as shown in  FIG. 13 . This allows the second pin joint assembly  130   b  to be reversed, with respect to the arrangement shown in  FIG. 6 , so that the head end  65  is positionable towards the middle of the structure. This increases the available space for fitting and positioning the actuator  50  between the pin joint assemblies  130   a ,  130   b.    
     The pin  62  described in relation to  FIGS. 7 to 13  is shown to have a head end  65  and a tail end  66 , wherein the head end  65  has a diameter larger than the pin hole  31  and headed pin  62 , such that the headed pin  62  is prevented from being fully inserted into the pin hole  31 . However, it will be appreciated that in alternative examples a headless pin  162  may be provided, in which the headless pin  162  includes a first tail end  166   a  with a corresponding set of locking features  167   a  (for example locking nuts) and a second tail end  166   b  with a corresponding set of locking features  167   b  (for example locking nuts), wherein the locking features of the first tail end  166   a  tighten towards the second tail end  166   b  and the locking features of the second tail end  166   b  tighten towards the first tail end  166   a , thereby clamping the headed pin  162  against the pin sleeve  161 . 
     The pin joint assemblies  130 ,  130   a ,  130   b  described in relation to  FIGS. 7 to 14  are part of a folding wing tip mechanism, between a wing  2 , 3  and a wing tip device  20 . In alternative examples, a pin joint assembly  230  may be part of a flight control surface mechanism, for example between a wing  2 , 3  and one of a slat  12 , aileron  13 , spoiler  14 , flap  15  or other control surface. 
       FIG. 15A  shows a pin joint assembly  230   a  comprising a first set of lugs  141   a,c,e  extending from a wing  2  and a second set of lugs  141   b,d  extending from a slat  12 . 
       FIG. 15B  shows a pin joint assembly  230   b  comprising a first set of lugs  241   a,c,e  extending from a wing  2  and a second set of lugs  241   b,d  extending from an aileron  13 . 
       FIG. 15C  shows a pin joint assembly  230   c  comprising a first set of lugs  341   a,c,e  extending from a wing  2  and a second set of lugs  341   b,d  extending from a spoiler  14 . 
       FIG. 15D  shows a pin joint assembly  230   d  comprising a first set of lugs  441   a,c,e  extending from a wing  2  and a second set of lugs  441   b,d  extending from a flap  15 . 
     The U-shaped bushing  90  is particularly applicable in the pin joint assembly  130  shown in  FIGS. 7 to 15 , however it will be clear that the U-shaped bushing  90  will be suitable to a wide range of pin joint assemblies. 
     The described examples refer to a first set of lugs comprising three lugs and a second set of lugs comprising two lugs, however it will be clear that the first and second sets may have any number of lugs, including one lug. 
     Where the word or appears this is to be construed to mean ‘and/or’ such that items referred to are not necessarily mutually exclusive and may be used in any appropriate combination. 
     Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.