Abstract:
The invention provides a landing gear  120  for an aircraft  110,  the landing gear comprising a main strut  121  having a first upper end arranged to be moveably mounted to a structure of the aircraft, a landing gear wheel assembly  131, 132  connected to a second lower end of the main strut, the landing gear wheel assembly comprising at least one landing gear wheel arranged to roll in a fore-aft direction with respect to the main strut, and a stay  122  having a first upper end arranged to be connected to a structure of the aircraft, and a second lower end pivotally mounted to a mounting element  140  on the main strut, wherein the mounting element on the main strut is positioned substantially in line with the main strut in the fore-aft direction. The invention also provides a main strut, an aircraft and a kit of parts.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention concerns landing gear for an aircraft. 
         [0002]    More particularly, but not exclusively, this invention concerns landing gear comprising a main strut having a first upper end arranged to be moveably mounted to a structure of the aircraft, a landing gear wheel assembly connected to a second lower end of the main strut, the landing gear wheel assembly comprising at least one landing gear wheel arranged to roll in a fore-aft direction with respect to the main strut, and a stay having a first upper end arranged to be connected to a structure of the aircraft, and a second lower end pivotally mounted to a mounting element on the main strut. 
         [0003]    The invention also concerns a main strut for an aircraft landing gear, an aircraft and a kit of parts. 
         [0004]    It is known that landing gear on aircraft produce noise when deployed, and the aircraft manufacturing industry tries to reduce this noise as much as possible, especially during approach and landing of the aircraft. A typical prior art main, wing landing gear comprises a main strut and a side stay attached to the side of the main strut in order to aid in the deployment of the landing gear and its retraction into a landing gear bay on the aircraft. 
         [0005]    Two typical prior art wing landing gears  20  are shown in  FIGS. 1 and 2 . 
         [0006]    Looking at  FIG. 1 , the landing gear  20  extends below a wing of an aircraft  10 . An aircraft landing gear bay door  11  can be seen in its open position to allow the landing gear  20  to be deployed. The landing gear  20  comprises a main strut  21  extending substantially vertically below the aircraft wing. The upper end of the main strut  21  is attached inside the aircraft landing gear bay in the aircraft wing. 
         [0007]    At the lower end of the main strut  21  is a landing gear wheel assembly  30  with two landing gear wheels  31 ,  32 . The wheels  31 ,  32  are mounted to the main strut  21  via a wheel axle (not shown) so that they can roll in a fore-aft direction (i.e. towards and away from the position where the figure is taken). This allows the aircraft to move in a fore or aft direction (i.e. forwards or backwards). 
         [0008]    An upper end of a side stay  22  is attached inside the aircraft landing gear bay in the aircraft wing at a position to the side of the main strut  21 . The side stay extends down below the aircraft and towards the main strut  21  and a lower end of a side stay  22  is attached to the main strut  21  in a middle region of the main strut. The side stay  22  comprises an upper section  22   a  and a lower section  22   b.  The upper  22   a  and lower  22   b  sections of the side stay are pivotally connected by a hinge  22   c.    
         [0009]    At the lower end of the side stay  22 , a cardan pin  41  is pivotally connected to a second hinge  22   d.  The cardan pin  41  is part of a cardan pin joint  40 , also comprising a cardan pin frame  42 . The cardan pin frame  42  contains the cardan pin  41  and allows it to rotate within the frame  42 . There are also bearings (not shown) in between the cardan pin  41  and the cardan pin frame  42  to aid rotation. The cardan pin frame  42  forms part of the main strut  21  and is positioned on a side surface  21   a  of the main strut  21 . 
         [0010]    On the upper section  22   a  of the side stay  22 , just above the hinge  22   c,  a first end of a lock stay  23  is pivotally connected to the side stay  22 . A second end of the lock stay extends towards the main strut  21  and is pivotally connected to the main strut  21  towards its upper end. 
         [0011]    A first end of a downlock actuator  24  is pivotally connected towards the upper end of the side stay  22 . A second end of the downlock actuator  24  is pivotally connected towards the first end of the lock stay  23 . 
         [0012]    The pivotal connections of the cardan pin joint  40 , downlock actuator  24 , lock stay  23 , two sections of the side stay  22  and the main strut  21  allow the landing gear  20  to be deployed and retracted from the landing gear bay of the aircraft  10 . 
         [0013]    Looking at  FIG. 2 , the landing gear  20  is similar to that shown in  FIG. 1 , with more detail shown. This additional detail will now be described. Any reference numerals used for  FIG. 2  that are also used for  FIG. 1  refer to similar elements. 
         [0014]    In  FIG. 2 , the landing gear  20  is shown attached to a wing rear spar  15  of the wing of the aircraft  10 . The upper end of the main strut  21  is attached to a rib  14  that is attached to the spar  15 . 
         [0015]    The landing gear wheel assembly  30  has four landing gear wheels  31 ,  32 ,  33 ,  34 . Front wheels  31 ,  32  are mounted on a first wheel axle  35  and rear wheels  33 ,  34  are mounted on a second wheel axle  35 . The two wheel axles  35  are connected to each other and also to the lower end of the main strut  21 . All four wheels  31 ,  32 ,  33 ,  34  can roll in a fore-aft direction. 
         [0016]    The landing gear wheel assembly  30  also comprises a bogie alignment pitch trimmer  37  and associated articulated links  38 , a brake rod  39  and torque links  36 . 
         [0017]    An upper end of the side stay  22  is attached to the wing rear spar  15  by a side stay attachment  12 , including a side stay attachment pivotable pin  13 . 
         [0018]    The lower end of the side stay  22  is connected to the main strut  21  by a cardan pin joint  40  mounted on a mounting element sleeve  43 , which is an integral part of the main strut  21 . The cardan pin joint  40  is mounted on a side surface of the main strut  21 . 
         [0019]    A drag arm  26  extends out from the fore side of the main strut  21 . The lower end of the drag arm  26  is fixedly attached to the main strut  21  approximately halfway along the length of the main strut  21 . The upper end of the drag arm  26  is pivotally attached to the wing rear spar  15 . The drag arm  26  forms a third leg of an upside down tripod, also comprising the main strut  21  and the side stay  22 . The drag arm  26  and main strut  21  (collectively known as the main fitting) are aligned in the fore-aft direction. 
         [0020]    A retraction actuator  27  is also connected to the fore side of the main strut  21  with its lower end attached to the main strut  21  a short distance above the lower end of the drag arm  26 . The upper end of the retraction actuator  27  is connected to a retraction link  29  via a retraction lever  28 . The retraction link is attached to the wing rear spar  15 . 
         [0021]    On the upper section  22   a  of the side stay  22 , just above the hinge  22   c,  a first end of a lock stay  23  is pivotally connected to the side stay  22 . A second end of the lock stay extends towards the drag arm  26  and is pivotally connected to the drag arm  26  towards its upper end, near its connection to the wing rear spar  15 . 
         [0022]    Either of the landing gear may also include passive noise reduction devices (not shown), such as solid or porous fairings over some of the components of the landing gear. 
         [0023]    The present invention seeks to provide an improved landing gear, with improved noise reduction. 
       SUMMARY OF THE INVENTION 
       [0024]    The present invention provides, according to a first aspect, a landing gear for an aircraft, the landing gear comprising a main strut having a first upper end arranged to be moveably mounted to a structure of the aircraft, a landing gear wheel assembly being connected to a second lower end of the main strut, the landing gear wheel assembly comprising at least one landing gear wheel arranged to roll in a fore-aft direction with respect to the main strut, and a stay having a first upper end arranged to be connected to a structure of the aircraft, and a second lower end pivotally mounted to a mounting element on the main strut, wherein the mounting element on the main strut is positioned substantially in line with the main strut in the fore-aft direction. 
         [0025]    The inventors have found that having the mounting element substantially in line with the main strut in the fore-aft direction reduces the noise produced. 
         [0026]    One reason for this is that the noise produced when air flows past a landing gear is proportional to the velocity of the airflow to the power of six. It has been found that the local air speed in line with the main strut in the fore-aft direction is lower than the air speed at the side of the main strut. 
         [0027]    As the stay extends from the aircraft to the front or aft of the main strut, the side stay is longer that it would have been if it was mounted to the side of the main strut. 
         [0028]    In addition, with the stay mounted at the fore or aft of the main strut, the mounting experiences a greater force and so the pivotal mounting to the main strut must be designed to take a larger force. This results in an increased size and weight of the pivotal mounting and possibly the side stay. Also, the kinematic design of the landing gear has to be changed. 
         [0029]    It has been found that, despite these extra considerations, noise can still be reduced by the new arrangement. 
         [0030]    Here, main strut refers to the strut of the landing gear that extends down substantially vertically from the aircraft when deployed. The main strut takes the majority of the load on the landing gear through mainly axial loading and therefore has a large axial strength. 
         [0031]    Here, stay refers to an element used to support the main strut and provide strength to the landing gear in a direction that is not aligned with the axis of the main strut. 
         [0032]    Here, the landing gear wheel may be pivotally mounted to allow the aircraft to be steered on the ground. However, the neutral or central position of the wheel in its pivotal mounting will be such that the wheel rolls in the fore-aft direction. 
         [0033]    Preferably, the stay extends laterally away from the main strut with a substantial sideways component perpendicular to the fore-aft direction. Here, the stay provides strength to the landing gear in a sideways direction. 
         [0034]    Preferably, the landing gear is arranged such that when it is retracted, the main strut extends sideways, with a substantial component perpendicular to the fore-aft direction from its mounting to the aircraft structure. More preferably, the main strut extends to the same side as the sideways component of the stay. 
         [0035]    The stay may also extend away from the main strut with a fore-aft component. Here, the stay provides strength to the landing gear in the fore-aft direction. Preferably, the stay extends away from the main strut in the fore direction. 
         [0036]    The landing gear may also comprise a drag arm to form a third leg of an upside down tripod, also comprising the main strut and the stay. The drag arm and main strut are preferably aligned in the fore-aft direction. 
         [0037]    Preferably, the mounting element on the main strut is on the fore side of the main strut. More preferably, the mounting element is near a flow stagnation point (or line) on the fore side of the main strut. It is less complicated to have the mounting element at the fore side of the main strut as there are not so many other components present, compared to the aft side. 
         [0038]    Preferably, the stay is pivotally mounted to the main strut by a cardan pin joint, the cardan pin joint comprising a cardan pin frame and a cardan pin rotatably mounted inside the frame. 
         [0039]    Here, cardan pin joint refers to a joint that allows pivotal movement in order to allow a landing gear to be retracted and deployed. The cardan pin joint must be able to take very strong loads experienced during landing and ground manoeuvres of an aircraft. 
         [0040]    More preferably, the cardan pin is attached to the second lower end of the stay and the cardan pin frame is the mounting element on the main strut or is attached to the mounting element on the main strut. 
         [0041]    Preferably, the stay is pivotally mounted to the cardan pin joint. 
         [0042]    Even more preferably, the cardan pin frame is attached to the main strut such that its longitudinal axis is orientated away from the longitudinal axis of the main strut such that the upper end of the cardan pin frame is at a different lateral position with respect to the main strut than the lower end. Even more preferably, the orientation of the cardan pin frame with respect to the longitudinal axis of the main strut is in the opposite direction to the orientation of the stay with respect to the longitudinal axis of the main strut. 
         [0043]    Preferably, the landing gear is a main landing gear, preferably for mounting to a wing of an aircraft. 
         [0044]    According to a second aspect of the invention there is also provided a main strut for an aircraft landing gear, the main strut comprising a landing gear wheel connector for connecting a landing gear wheel assembly such that a wheel of the assembly is arranged to roll in a fore-aft direction with respect to the main strut, and a mounting element for pivotally mounting a stay to the main strut, wherein the mounting element on the main strut is positioned substantially in line with the main strut in the fore-aft direction. 
         [0045]    According to a third aspect of the invention there is also provided an aircraft comprising the landing gear or main strut of any preceding claim, wherein the main strut is attached at its first upper end to a structure of the aircraft such that the fore side of the main strut faces towards the front of the aircraft and the aft side of the main strut faces the rear of the aircraft. 
         [0046]    The present invention is of greater application to larger aircraft although the present invention may also be applied to smaller aircraft. The aircraft is preferably heavier than 10 tonnes dry weight, more preferably heavier than 50 tonnes dry weight, and even more preferably heavier than 200 tonnes dry weight. The aircraft is preferably of a size equivalent to an aircraft designed to carry more than 40 passengers, and more preferably more than 100 passengers. 
         [0047]    According to a fourth aspect of the invention there is also provided a kit of parts for an aircraft landing gear comprising a main strut, a landing gear wheel assembly for connecting to an end of the main strut such that a wheel of the assembly is arranged to roll in a fore-aft direction with respect to the main strut, and a stay for pivotally mounting to a mounting element on the main strut positioned substantially in line with the main strut in the fore-aft direction. 
         [0048]    It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the main strut, aircraft and kit of parts of the invention may incorporate any of the features described with reference to the landing gear of the invention and vice versa. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0049]    Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: 
           [0050]      FIG. 1  shows a front view of a landing gear according to the prior art; 
           [0051]      FIG. 2  shows a perspective view of a landing gear according to the prior art, similar to that shown in  FIG. 1 ; 
           [0052]      FIG. 3  shows a front view of a landing gear according to a first embodiment of the invention; 
           [0053]      FIG. 4   a  shows a front view of a landing gear according to a second embodiment of the invention; and 
           [0054]      FIG. 4   b  shows a rear view of the landing gear of  FIG. 4   a ; and 
           [0055]      FIG. 5  shows a rear view of a landing gear according to a third embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0056]      FIG. 3  shows a front view of a wing landing gear  120  according to a first embodiment of the invention. The landing gear  120  is similar to that shown in  FIGS. 1 and 2 , except where differences are described below. 
         [0057]    The landing gear  120  extends below a wing of an aircraft  110 . An aircraft landing gear bay door  111  can be seen in its open position to allow the landing gear  120  to be deployed. The landing gear  120  comprises a main strut  121  extending substantially vertically below the aircraft wing. The upper end of the main strut  121  is attached inside the aircraft landing gear bay in the aircraft wing. 
         [0058]    At the lower end of the main strut  121  is a landing gear assembly  130  with two landing gear wheels  131 ,  132  on a wheel axle  135 . The wheels  131 ,  132  are mounted to the main strut  121  so that they can roll in a fore-aft direction (i.e. towards and away from the position where the figure is taken). This allows the aircraft to move in a fore or aft direction (i.e. forwards or backwards). 
         [0059]    An upper end of a side stay  122  is attached inside the aircraft landing gear bay in the aircraft wing at a position to the side of the main strut  121 . The side stay extends down below the aircraft and towards the main strut  121  and a lower end of a side stay  122  is attached to the main strut  121  in a middle region of the main strut. The side stay  122  comprises an upper section  122   a  and a lower section  122   b . The upper  122   a  and lower  122   b  sections of the side stay are pivotally connected by a hinge  122   c.    
         [0060]    At the lower end of the side stay  122 , a cardan pin  141  is pivotally connected to a second hinge  122   d.  The cardan pin  141  is part of a cardan pin joint  140 , also comprising a cardan pin frame  142 . The cardan pin frame  142  contains the cardan pin  141  and allows it to rotate within the cardan pin frame  142 . There are also bearings (not shown) in between the cardan pin  141  and the cardan pin frame  142  to aid rotation. 
         [0061]    The cardan pin frame  142  is mounted on a fore surface  121   b  of the main strut  21 . This is different to the landing gear  20  of  FIG. 1 , where the cardan pin frame  42  is mounted to the side  21   a  of the main strut  21 . The cardan pin frame  142  of  FIG. 3  is mounted on the surface of the main strut that faces the direction of travel of the aircraft  110  during flight. 
         [0062]    The axis of the cardan pin frame  142  is angled on the main strut  121  such that it is angled away from the side stay  122 . 
         [0063]    A drag arm (not shown) extends out from the fore side of the main strut  121 . The lower end of the drag arm is fixedly attached to the main strut  121  approximately halfway along the length of the main strut  121 . The upper end of the drag arm is pivotally attached to the aircraft wing. The drag arm forms a third leg of an upside down tripod, also comprising the main strut  121  and the side stay  122 . The drag arm and main strut  121  (collectively known as the main fitting) are aligned in the fore-aft direction. 
         [0064]    On the upper section  122   a  of the side stay  122 , just above the hinge  122   c,  a first end of a lock stay  123  is pivotally connected to the side stay  122 . A second end of the lock stay extends towards the main strut  121  and is pivotally connected to the main strut  121  towards its upper end. 
         [0065]    A first end of a downlock actuator  124  is pivotally connected towards the upper end of the side stay  122 . A second end of the downlock actuator  124  is pivotally connected towards the first end of the lock stay  123 . 
         [0066]    The pivotal connections of the cardan pin joint  140 , downlock actuator  124 , lock stay  123 , two sections of the side stay  122 , drag arm and the main strut  121  allow the landing gear  120  to be deployed and retracted from the landing gear bay of the aircraft  110 . 
         [0067]      FIGS. 4   a  and  4   b  shows front and rear views of a wing landing gear  220  according to a second embodiment of the invention. The landing gear  220  extends below a wing of an aircraft  210 . An aircraft landing gear bay door  211  can be seen in its open position to allow the landing gear  220  to be deployed. 
         [0068]    The landing gear  220  comprises a main strut  221  extending substantially vertically below the aircraft wing. The upper end of the main strut  221  is attached inside the aircraft landing gear bay in the aircraft wing. At the lower end of the main strut  221  is a landing gear wheel assembly  230  with two landing gear wheels  231 ,  232  on a wheel axle  235 . The wheels  231 ,  232  are mounted to the main strut  221  so that they can roll in a fore-aft direction (i.e. towards and away from the position where the figures are taken). This allows the aircraft to move in a fore or aft direction (i.e. forwards or backwards). 
         [0069]    An upper end of a side stay  222  is pivotally attached, at pivotal joint  213  to a downwardly extending strut  212 , which is attached inside the landing gear bay of the aircraft  210  at a position to the side of the main strut  221 . The side stay  222  extends down below the aircraft  210  and towards the main strut  221  and a lower end of a side stay  222  is attached to the main strut  221  in a middle region of the main strut. The side stay  222  comprises an upper section  222   a  and a lower section  222   b.  The upper  222   a  and lower  222   b  sections of the side stay are pivotally connected by a hinge  222   c.    
         [0070]    At the lower end of the side stay  222 , a cardan pin  241  is pivotally connected to a second hinge (not shown). The cardan pin  241  is part of a cardan pin joint  240 , also comprising a cardan pin frame  242 . The cardan pin frame  242  contains the cardan pin  241  and allows it to rotate within the cardan pin frame  242 . The cardan pin frame  242  is mounted on a fore surface  221   b  of the main strut  221 . The cardan pin frame  242  of  FIG. 4   a  is mounted on the surface of the main strut that faces the direction of travel of the aircraft  210  during flight. 
         [0071]    The axis of the cardan pin frame  242  is angled on the main strut  221  such that it is angled away from the side stay  222 . 
         [0072]    A drag arm (not shown) extends out from the fore side of the main strut  221 . The lower end of the drag arm is fixedly attached to the main strut  221  approximately halfway along the length of the main strut  221 . The upper end of the drag arm is pivotally attached to the aircraft wing. The drag arm forms a third leg of an upside down tripod, also comprising the main strut  221  and the side stay  222 . The drag arm and main strut  221  (collectively known as the main fitting) are aligned in the fore-aft direction. 
         [0073]    On the upper section  222   a  of the side stay  222 , just above the hinge (not shown), a first end of a lock stay  223  is pivotally connected to the side stay  222 . A second end of the lock stay extends towards the main strut  221  and is pivotally connected to the main strut  221  towards its upper end. 
         [0074]    A first end of a downlock actuator  224  is pivotally connected towards the upper end of the side stay  222 . A second end of the downlock actuator  224  is pivotally connected towards the first end of the lock stay  223 . 
         [0075]    The pivotal connections of the cardan pin joint  240 , downlock actuator  224 , lock stay  223 , two sections of the side stay  222 , the pivotal joint  213 , the drag arm and the main strut  221  allow the landing gear  220  to be deployed and retracted from the landing gear bay of the aircraft  210 . 
         [0076]      FIG. 5  shows a rear views of a wing landing gear  320  according to a third embodiment of the invention. The landing gear  320  extends below a wing of an aircraft  310 . 
         [0077]    The landing gear  320  comprises a main strut  321  extending substantially vertically below the aircraft wing. The upper end of the main strut  321  is attached inside the aircraft landing gear bay in the aircraft wing. At the lower end of the main strut  321  is a landing gear wheel assembly  330  with two landing gear wheels  331 ,  332  on a wheel axle  335 . The wheels  331 ,  332  are mounted to the main strut  321  so that they can roll in a fore-aft direction (i.e. towards and away from the position where the figures are taken). This allows the aircraft to move in a fore or aft direction (i.e. forwards or backwards). 
         [0078]    An upper end of a side stay  322  is pivotally attached, at pivotal joint  313  to a downwardly extending strut  312 , which is attached inside the landing gear bay of the aircraft  310  at a position to the side of the main strut  321 . The side stay  322  extends down below the aircraft  310  and towards the main strut  321  and a lower end of a side stay  322  is attached to the main strut  321  in a middle region of the main strut. The side stay  322  comprises an upper section  322   a  and a lower section  322   b.  The upper  322   a  and lower  322   b  sections of the side stay are pivotally connected by a hinge  322   c.    
         [0079]    At the lower end of the side stay  322 , a cardan pin  341  is pivotally connected to a second hinge (not shown). The cardan pin  341  is part of a cardan pin joint (not labelled), also comprising a cardan pin frame (not labelled). The cardan pin frame contains the cardan pin  341  and allows it to rotate within the cardan pin frame. The cardan pin frame is mounted on an aft surface  321   c  of the main strut  321 . The cardan pin frame of  FIG. 5  is mounted on the surface of the main strut that faces away from the direction of travel of the aircraft  310  during flight. 
         [0080]    This is different to the cardan pin frame of  FIGS. 4   a  and  4   b  where the cardan pin frame is mounted on the surface of the main strut that faces the direction of travel of the aircraft  210  during flight. As a result, the kinematic design of the landing gear is also different as a result. 
         [0081]    The axis of the cardan pin frame is angled on the main strut  321  such that it is angled away from the side stay  322 . 
         [0082]    A drag arm (not shown) extends out from the fore side of the main strut  321 . The lower end of the drag arm is fixedly attached to the main strut  321  approximately halfway along the length of the main strut  321 . The upper end of the drag arm is pivotally attached to the aircraft wing. The drag arm forms a third leg of an upside down tripod, also comprising the main strut  321  and the side stay  322 . The drag arm and main strut  321  (collectively known as the main fitting) are aligned in the fore-aft direction. 
         [0083]    On the upper section  322   a  of the side stay  322 , just above the hinge (not shown), a first end of a lock stay  323  is pivotally connected to the side stay  322 . A second end of the lock stay extends towards the main strut  321  and is pivotally connected to the main strut  321  towards its upper end. 
         [0084]    A first end of a downlock actuator  324  is pivotally connected towards the upper end of the side stay  322 . A second end of the downlock actuator  324  is pivotally connected towards the first end of the lock stay  323 . 
         [0085]    The pivotal connections of the cardan pin joint, downlock actuator  324 , lock stay  323 , two sections of the side stay  322 , the pivotal joint  313 , the drag arm and the main strut  321  allow the landing gear  220  to be deployed and retracted from the landing gear bay of the aircraft  310 . 
         [0086]    Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described. 
         [0087]    The landing gear may also include passive noise reduction devices (not shown), such as solid or porous fairings over some of the components of the landing gear. In particular, the side stay may be provided with a mesh fairing. The landing gear may have a cylindrical shape side stay component. 
         [0088]    The landing gear may have any suitable number of wheels; for example, 2, 4 or 6 wheels. 
         [0089]    The arrangement of the various parts of the landing gear can vary. For example, whether or not the stay is pivotally mounted to the main strut in a middle region of the main strut, or the arrangement of the torque link, pitch trimmer, articulation link etc., depend on the landing gear design chosen. Also, the length of the landing gear on touchdown will be compressed, compared to its fully stretched length on approach to landing. Of course, the landing gear design will be different for different aircraft. 
         [0090]    Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.