Abstract:
The invention provides a deployment mechanism  60  for deploying an auxiliary wing surface device  30  from an aircraft wing body  20,  the deployment mechanism providing a first connector portion  75, 576  for connecting the deployment mechanism to the aircraft wing body, a second connector portion  65  for connecting the deployment mechanism to the auxiliary wing surface device, and a telescopic rod  61  linking the first and second connector portions, the telescopic rod comprising an inner rod  64  extendable from inside of an outer rod  63  to increase the length of the telescopic rod, such that the distance between the first and second connector portions can be increased. The invention also provides an aircraft wing  10, 510,  an aircraft and a method of operating an aircraft.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention concerns deployment mechanisms for use on aircraft wings. More particularly, but not exclusively, this invention concerns deployment mechanisms for deploying an auxiliary wing surface device from an aircraft wing body. The invention also concerns aircraft wings, an aircraft and methods of operating aircraft. 
         [0002]    Modern aircraft wings are designed to maximise the angle of attack during take-off and landing operations. This often involves the wing having high-lift devices, with air-profiled surfaces, that can be extended and retracted along a predefined path in relation to the main wing body. These devices can be extended from the leading edge or from the trailing edge of the main wing body. 
         [0003]    Prior art methods of deploying the high-lift devices generally comprise a power drive unit, gears, rotary (or possibly linear) actuators, a drive shaft, rotation control sensors and a set of linkages. This makes them bulky, heavy and complicated. An alternative method that has been used to deploy a trailing edge flap comprises a flap track beam with a mechanical gear and ball screw spindle attached to it. A ball nut is attached to the flap using a gimble arrangement. Movement of the nut along the stationary spindle deploys the flap and the gimble arrangement allows the flap to rotate into the desired orientation. 
         [0004]    There are three main types of high-lift device; slats, drooped noses and Krueger flaps. Krueger flaps are generally used on a leading edge of a main wing body which is designed to maximise laminar flow along the upper wing surface. A typical Krueger flap, in its retracted position, forms at least part of the leading edge of the main wing body. This means that the profile of the Krueger flap is blended with the lower profile of the leading edge. This means that laminar flow when the flap is stowed (i.e. during cruise) is not disturbed. 
         [0005]    However, as Krueger flaps are often used with narrow profiled wings designed for laminar flow, and because the Krueger flap stows within the profile of the wing, the deployment mechanisms needed to extend and retract the Krueger flaps need to be small. A small size of deployment mechanism is also needed so that a minimum required clearance to other systems in the wing (for example in the leading edge of the wing) and to other structures (e.g. a fuel tank) in the wing can be achieved. 
         [0006]    The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved deployment mechanism, especially for a Krueger flap. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides, according to a first aspect, a deployment mechanism for deploying an auxiliary wing surface device from an aircraft wing body, the deployment mechanism providing a first connector portion for connecting the deployment mechanism to the aircraft wing body, a second connector portion for connecting the deployment mechanism to the auxiliary wing surface device, and a telescopic rod linking the first and second connector portions, the telescopic rod comprising an inner rod extendable from inside of an outer rod to increase the length of the telescopic rod, such that the distance between the first and second connector portions can be increased. 
         [0008]    Having a telescopic rod allows the deployment mechanism to have a large stroke length (to deploy the device) whilst still taking up less space in the aircraft wing body than prior art deployment mechanisms, which are much more bulky, heavy and complicated. The deployment mechanism is usually housed completely inside the profile of the aircraft wing when it is stowed. The deployment mechanism can even be used in narrow profile wings, where space is limited, and still leave enough room for other systems and structures to be installed. 
         [0009]    Also, the deployment mechanism only needs a single connection point to the aircraft wing body and a single connection point to the auxiliary wing surface device. This gives a further weight and space saving. 
         [0010]    When the deployment mechanism deploys the auxiliary wing surface device, it causes only a small drag effect. 
         [0011]    The deployment mechanism has less failure paths than prior art mechanisms due to the smaller number of parts and simpler mechanism. This increases the service life of the deployment mechanism. The small size of the deployment mechanism also means that access for maintenance and inspection is easier. 
         [0012]    In addition, the deployment mechanism may be attached to a spar of the aircraft wing body, and also may be attached near an upper cover of the aircraft wing body, both of which are advantageous in terms of the structural support required for the mechanism. 
         [0013]    The deployment mechanism may be designed to take high loads from the auxiliary wing surface device and thus allow the device to be used during high-speed operations (such as being used as an additional air brake during cruise) as well as low-speed operations (such as during landing and take-off). 
         [0014]    Preferably, the outer rod has an internally threaded portion corresponding to an externally threaded portion of the inner rod, such that the inner rod is extendable from inside the outer rod by a screw action of the threaded portions. 
         [0015]    Preferably, the telescopic rod comprises an innermost rod, an outermost rod and a number of intermediate rods, each inner rod in each pair of adjacent rods being extendable from inside of an outer rod in the pair of adjacent rods. The number/length of rods can be chosen to give the desired stroke length of the mechanism. 
         [0016]    Preferably, the telescopic rod is able to extend to a length that is at least 150% of its fully retracted configuration. More preferably, the telescopic rod is able to extend approximately double the length (200%) of its fully retracted configuration. For example, the telescopic rod may be able to extend from a length of approximately 300 mm to a length of approximately 700 mm. It may be possible for the telescopic rod to extend to significantly more than double the length of its fully retracted configuration. This allows the deployment mechanism to deploy the device to a position where it can shield a leading edge of a wing, for example from debris. Such a position may be at 120 degrees to the wing. 
         [0017]    Preferably, the mechanism further comprises a ball screw actuator and ball bearings in the threaded portions of either of the inner and outer rods and wherein movement of the inner rod with respect to the outer rod of the telescopic rod is actuated by the ball screw actuator. Using a ball screw actuator allows precise control of the position of the auxiliary wing surface device. A ball screw actuator can be efficient, generate low levels of heat and be able to actuate the mechanism to deploy (and retract) quickly. In addition, a ball screw actuator can be designed to incorporate a brake (or brakes) so that the mechanism can hold high loads. The use of ball bearings in precisely manufactured threads (preferably, semi-circular threads) of the threaded portions improves the service life of the deployment mechanism. 
         [0018]    Preferably, the ball screw actuator is provided with a brake for locking in the event of a failure. 
         [0019]    Preferably, the mechanism comprises two ball screw actuators. 
         [0020]    The mechanism may comprise a rotating shaft and gearing for powering the ball screw actuator. Rotational power can be efficiently delivered from the rotating shaft to the gearing. It is also possible to use gearing, for example a worm gear, which is able to lock in the event of a failure. Preferably, the deployment mechanism comprises a sensor for monitoring the rotation of the shaft. 
         [0021]    Alternatively and preferably, the mechanism comprises an electric motor for powering the ball screw actuator. This eliminates the need for a rotational shaft and gearing. Hence, an electrical actuation system has a lower weight than a mechanical actuation system. An electrical actuation system also has a lower number of parts, giving an improved service life. Preferably, the deployment mechanism comprises a sensor, for example, a potentiometer, for monitoring the function of the electric motor. 
         [0022]    Preferably, at least one of the first and second connector portions comprises a pivotable joint and a bracket. This allows the deployment mechanism to rotate to accommodate the changing position of the auxiliary wing surface device as it deploys. 
         [0023]    According to a second aspect of the invention there is also provided an aircraft wing comprising a wing body, an auxiliary wing surface device and the deployment mechanism of any preceding claim, wherein the first connector portion is connected to the aircraft wing body, the second connector portion is connected to the auxiliary wing surface device and wherein the inner rod is extendable from inside of the outer rod to increase the length of the telescopic rod, such that the distance between the aircraft wing body and the auxiliary wing surface device can be increased. 
         [0024]    Preferably, the auxiliary wing surface device is located at the leading edge of the aircraft wing. 
         [0025]    Preferably, the auxiliary wing surface device is stowable within the aircraft wing to form part of the profile of the aircraft wing. 
         [0026]    The auxiliary wing surface device may be a slat. Alternatively, the auxiliary wing surface device is a drooped nose device. Alternatively and preferably, the auxiliary wing surface device is a Krueger flap. 
         [0027]    Preferably, a bracket of the first connector portion is attached to a spar, preferably a front spar, of the aircraft wing. This provides a load path from the auxiliary wing surface device directly to a significant structural component of the aircraft wing body. 
         [0028]    Preferably, the bracket of the first connector portion is attached near to an upper cover of a wing box of the aircraft wing body. This is advantageous in terms of the structural support required for the mechanism. 
         [0029]    Preferably, the aircraft wing further comprises a number of linkages between the auxiliary wing surface device and the aircraft wing body, the linkages defining the travel path of the auxiliary wing surface device in relation to the aircraft wing body when the length of the telescopic rod is increased. 
         [0030]    Preferably, the linkages are connected to one or more ribs of the aircraft wing body. This is advantageous as the ribs are a significant structural component of the aircraft wing body. 
         [0031]    Preferably, there is a first linkage for reacting lateral loads from the auxiliary wing surface device and a second linkage for reacting shear loads. 
         [0032]    Preferably, the aircraft wing comprises a support structure attached to the auxiliary wing surface device, and wherein each of the two linkages is pivotally connected to the support structure. 
         [0033]    Preferably, the two linkages are connected to the support structure at different positions such that their axes of rotation with respect to the auxiliary wing surface device are spaced apart. This allows both the position and the angle of the auxiliary wing surface device to be controlled by the linkages. 
         [0034]    Preferably, the aircraft wing body comprises a pivot pin attached to one or more ribs of the aircraft wing body and wherein one of the linkages, preferably the first linkage, is connected so as to be pivotable around the pivot pin. 
         [0035]    Preferably, the aircraft wing body comprises a support bracket attached to one or more ribs of the aircraft wing body and wherein one of the linkages, preferably the second linkage, is connected so as to be pivotably connected to the support bracket. 
         [0036]    Preferably, the two linkages are pivotally connected to the aircraft wing body at different positions such that their axes of rotation with respect to the aircraft wing body are spaced apart. 
         [0037]    According to a third aspect of the invention there is also provided an aircraft comprising the aircraft wing or deployment mechanism as described above. 
         [0038]    According to a fourth aspect of the invention there is also provided a method of operating an aircraft, wherein the method comprises the steps of actuating a telescopic rod so that an inner rod of the telescopic rod extends from inside of an outer rod of the telescopic rod to increase the length of the telescopic rod, thereby increasing the distance between a first connector portion at a first end of the telescopic rod and a second connector portion at a second end of the telescopic rod, wherein the first connector portion is connected to the auxiliary wing surface device, and the second connector portion is connected to the aircraft wing body, and thereby deploying the auxiliary wing surface device from the aircraft wing body. 
         [0039]    According to a fifth aspect of the invention there is also provided a method of operating an aircraft, wherein the method comprises the steps of actuating a telescopic rod so that an inner rod of the telescopic rod retracts inside of an outer rod of the telescopic rod to decrease the length of the telescopic rod, thereby decreasing the distance between a first connector portion at a first end of the telescopic rod and a second connector portion at a second end of the telescopic rod, wherein the first connector portion is connected to the auxiliary wing surface device, and the second connector portion is connected to the aircraft wing body, and thereby retracting the auxiliary wing surface device towards the aircraft wing body. 
         [0040]    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 method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0041]    Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: 
           [0042]      FIG. 1   a  shows a partially cut-away perspective view of part of an aircraft wing according to a first embodiment of the invention; 
           [0043]      FIG. 1   b  shows an enlarged view of the deployment mechanism in  FIG. 1   a;    
           [0044]      FIG. 2   a  shows a partially cut-away perspective view of part of an aircraft wing according to a second embodiment of the invention; 
           [0045]      FIG. 2   b  shows an enlarged view of the deployment mechanism in  FIG. 2   a;    
           [0046]      FIG. 3  shows a partially cut-away side view of the ball screw actuator in either the first or second embodiments; 
           [0047]      FIG. 4  shows a perspective view of the linkage system in either the first or second embodiments; 
           [0048]      FIG. 5   a  shows a side view of part of the aircraft wing of  FIGS. 2   a  and  2   b , with the Krueger flap in a fully stowed position; 
           [0049]      FIG. 5   b  shows a side view of part of the aircraft wing of  FIGS. 2   a  and  2   b , with the Krueger flap in a partially deployed position; and 
           [0050]      FIG. 5   c  shows a side view of part of the aircraft wing of  FIGS. 2   a  and  2   b , with the Krueger flap in a fully deployed position. 
       
    
    
     DETAILED DESCRIPTION 
       [0051]      FIG. 1   a  shows a partially cut-away perspective view of part of an aircraft wing  10  according to a first embodiment of the invention. The aircraft wing  10  comprises an aircraft wing body  20  and a number of Krueger flaps  30  forming the lower leading edge of the aircraft wing  10 . 
         [0052]    The aircraft wing body comprises a front spar  21 , an upper cover  23  and a lower cover ( 24 , not shown in  FIG. 1   a ). The aircraft wing body  20  also comprises a number of ribs  22 , arranged in adjacent pairs, extending forwards from the front spar  21 . 
         [0053]    The aircraft wing  10  comprises a number of linkage systems  80 ,  90 ,  100  which will be described in more detail in relation to  FIG. 4 . Each linkage system  80 ,  90 ,  100  is located between a pair of adjacent ribs  22  and is used to control the movement path of one of the Krueger flaps  30 . 
         [0054]    The aircraft wing  10  also comprises a deployment mechanism  60  and actuation system for each Krueger flap  30 . One of these is shown enlarged in  FIG. 1   b.    
         [0055]    The deployment mechanism  60  comprises a telescopic rod  61 , which is attached at a first end to a ball screw actuator  70  and at a second end to the Krueger flap  30 . 
         [0056]    The telescopic rod  61  comprises three sections; an outermost rod section  62 , an intermediate rod section  63  and an innermost rod section  64 . The outermost rod section  62  is attached to the ball screw actuator  70  at the first end of the telescopic rod  61 . The outermost rod section  62  has an internally threaded portion ( 67   a,  not shown in  FIG. 1   b ). The intermediate rod section  63  has a smaller diameter than the outermost rod section with an externally threaded portion  67   b  corresponding to the internally threaded portion  67   a  of the outermost rod section  62 . The intermediate rod section  63  can be screwed in and out of the outermost rod section  62 . The intermediate rod section  63  also has an internally threaded portion ( 68   a,  not shown in  FIG. 1   b ). The innermost rod section  64  has a smaller diameter than the intermediate rod section with an externally threaded portion  68   b  corresponding to the internally threaded portion  68   a  of the intermediate rod section  63 . The innermost rod section  64  can be screwed in and out of the intermediate rod section  63 . 
         [0057]    The innermost rod section  64  comprises a flat bulbous portion  65  at the second end of the telescopic rod  61 . This bulbous portion  65  has a spherical bearing installed in a hole through it and is attached to a bracket  40  by a pin extending through the bulbous portion  65  and also through bushes installed in holes  43 ,  44  in two lugs  41 ,  42  of the bracket  40 . Each lug  41 ,  42  is located either side of the bulbous portion  65  so that the bulbous portion  65  is pivotally mounted between the lugs  41 ,  42  of the bracket  40 . The bracket  40  also comprises a flat base portion  46  that is attached to an interior surface  33  of the Krueger flap  30 . 
         [0058]    The ball screw actuator  70  (which will be described in more detail in relation to  FIG. 3 ) is attached at its other end to a universal joint  73 . The universal joint  73  is also attached to a gear housing  74 . The gear housing is attached to the front spar  21  of the aircraft wing  10  by a bracket  75 . Underneath the gear housing  74  is a worm gear  76  mounted on a rotational shaft  77 . The rotational shaft  77  is mounted on the front spar  21  by brackets  78  and extends along in front of the front spar  21  and provides a rotational movement to the worm gear  76  for each deployment mechanism  60  in the wing  10 . In addition, there is an optical sensor (not shown) at each end of the rotational shaft  77 . The sensors monitor the function and position of the rotational shaft  77 . 
         [0059]      FIG. 2   a  shows a partially cut-away perspective view of part of an aircraft wing  510  according to a second embodiment of the invention. This second embodiment is similar to the first embodiment with the exception that the actuation system is different; while the first embodiment has a mechanical shaft  77  actuation system for actuating the ball screw actuator  70 , the second embodiment uses an electrical motor  573  for doing so. In the figures and in the following description, like numerals will be used for like elements between the embodiments. Elements unique to or different in the second embodiment will be prefixed with “5”. 
         [0060]    The different elements of the actuation system of the second embodiment aircraft wing  510  will now be described in relation to  FIG. 2   b.    
         [0061]    The ball screw actuator  70  is attached to a plate  575 . The plate  575  is attached to a bracket  576 , secured to the front spar  21 . In addition, an electrical motor  573  is attached to the plate  575  and is electrically connected to the ball screw actuator  70 . An electrical harness  574  connects the electric motor  573  to an electricity supply in the aircraft. In addition, there is a potentiometer (not shown) attached to the electrical motor  573  to monitor the function of the electrical motor  573  and/or ball screw actuator  70 . 
         [0062]    The deployment mechanism  60  shown in  FIG. 2   b  is almost identical to that in  FIG. 1   a.  However, the deployment mechanism  60  as shown in  FIG. 2   b  has a longer outermost rod section  62  and so, for the same position of the Krueger flap  30 , the intermediate  63  and innermost  64  rod sections have less length protruding from the outermost rod section  62 . The outermost rod section  62  can be longer than in the first embodiment due to the electrical actuation system of the second embodiment being smaller than the mechanical actuation system of the first embodiment. 
         [0063]      FIG. 3  shows a partially cut-away side view of one ball screw actuator  70  in either the first or second embodiments. In each embodiment, there will actually be a second identical ball screw actuator present for each flap  30  in order to have a back-up actuator in case the first should fail. The ball screw actuator  70  comprises ball bearings  71  which fit into two sets of channels  72  formed between two internally threaded portions  67   a  of the outermost rod section  62  and the externally threaded portion  67   b  of the intermediate rod section  63 . The ball bearings  71  fill up the two sets of channels and cause the intermediate rod section  63  to move in relation to the outermost rod section  62 . 
         [0064]      FIG. 4  shows a perspective view of the linkage system  80 ,  90 ,  100  in either the first or second embodiments. The linkage system comprises three components; an A-link  80 , a support bracket  90  and an I-link  100 . 
         [0065]    The A-link  80  comprises an A-frame  81 . The A-frame  81  is provided with two foot portions  82 ,  83  extending behind the “A” shape from the bottom of the two legs of the “A” shape. Each foot portion  82 ,  83  is provided with a hole  84 ,  85 . A pin  88  is located through bushes in the two holes  84 ,  85  so that the pin  88  is parallel to but behind the bottom of the “A” shape. The pin  88  is fixed between a pair of adjacent ribs  22   a,    22   b  at the leading edge of the aircraft wing  510 . The A-frame  81  can pivot around the pin  88  and so can pivot with respect to the aircraft wing body  20 . Adjacent to the top apex of the A-frame  81  is another bush installed in a hole  86  that is parallel to the bottom of the “A” shape. This hole  86  accommodates another pin  87 . This pin  87  is attached to a supporting structure  50  of the Krueger flap  30 , as will be described later. The A-link  80  is designed to react lateral loads from the Krueger flap  30 . 
         [0066]    The supporting bracket  90  comprises two side flanges  91 ,  92 , each one being riveted  93  to an inner facing side of each of the adjacent pair of ribs  22   a,    22   b.  The supporting bracket  90  has a top portion  94  with a central gap  95  in the top portion. The supporting bracket  90  also has a downwards facing foot portion  96  at the bottom centre of the supporting bracket  90 . This foot portion  96  has two lugs  97 , each with a hole  98  in. These two holes  98  accommodate the pin  88  so that the supporting bracket  90  helps to secure the pin  88  to the ribs  22 . Adjacent to the holes  98  and slightly above them is another set of holes  99  through the foot portion  96 . These holes  99  connect the I-link  100 . 
         [0067]    The I-link  100  comprises an I-beam  101  with a tail portion  102  that is slightly angled. At the end of the tail portion  102  is a hole  103 . The I-link  100  is connected to the supporting bracket  90  by a pin  104  extending through a spherical bearing installed in the hole  103  in the I-link  100  and bushed installed in holes  99  in the supporting bracket  90 . The I-beam can pivot about pin  104 . At the non-tail end of the I-beam  101  is another hole  105  with a bearing installed in it. The hole  105  has an axis that is parallel to the pin  104 . This hole  105  accommodates another pin  106 . This pin  106  is attached to a supporting structure  50  of the Krueger flap  30 , as will be described later. The I-link  100  is designed to react shear loads from the Krueger flap  30 . 
         [0068]      FIG. 5   a  shows a side view of part of the aircraft wing of  FIGS. 2   a  and  2   b , showing one Krueger flap  30  in a fully stowed position.  FIG. 5   b  shows the Krueger flap  30  in a partially deployed position, and  FIG. 5   c  shows the Krueger flap  30  in a fully deployed position. 
         [0069]    In the partially deployed position of  FIG. 5   b , the Krueger flap is at approximately 90 degrees to the wing. Here, the Krueger flap can act as a brake. 
         [0070]    The Krueger flap  30  and its supporting structure  50  will now be described in relation to these figures. Importantly, the Krueger flap  30  and its supporting structure  50  are the same as in the first embodiment and so the following description applies to the first embodiment too. 
         [0071]    The Krueger flap  30  is in the shape of a cambered aerofoil with a bluff rounded end  31  and a tapered narrow end  32 . As can be seen in  FIG. 5   a , when stowed, the flap  30  is stowed with its bluff end  31  towards the rear of the wing  510  and the tapered end  32  at the leading edge of the wing  510 . An interior surface  33  of the flap  30  sits adjacent to the underside of the main wing body  20  with an exterior surface  34  forming the underside leading edge profile of the wing  510 . 
         [0072]    A supporting structure  50  for the Krueger flap  30  is in the form of a right-angled triangle beam. A short side  51  of the beam is placed inside the flap  30  so that it is abutting the inside of the exterior surface  34  of the flap  30 . A longer side  52  of the beam that is at right angles to the short side  51  extends outwards from the flap  30  to the apex of the beam. A sloping side  53  of the beam extends from the apex in the direction of the tapered end  32  of the Krueger flap  30 . At the apex of the beam is a hole  54  for accommodating pin  106  of the I-link  100  to allow the I-link to pivot with respect to the supporting structure  50  and Krueger flap  30 . Approximately one third of the distance along the sloping side  53  from the apex is another hole  55  for accommodating pin  87  of the A-link  80  to allow the A-link to pivot with respect to the supporting structure  50  and Krueger flap  30 . 
         [0073]    In use, the Krueger flap  30  is moved in relation to the aircraft wing body  20  from a stowed position (in  FIG. 5   a ), for example during cruise, to a fully deployed position (in  FIG. 5   c ), for example for take-off and landing operations. In the stowed position, the Krueger flap  30  profile is blended with the leading edge lower profile of the aircraft wing  510  and so laminar flow along the wing is not disturbed. In the fully deployed position, the Krueger flap  30  provides an auxiliary wing surface in front of the leading edge of the aircraft wing body  20 . This increases the lift co-efficient of the wing  510 . In this fully deployed position, the Krueger flap is at approximately 120 degrees to the wing. Here, the Krueger flap can act as a shield for protecting the leading edge of the wing from debris, for example during take-off. 
         [0074]    During take-off and landing, the Krueger flap  30  is in its fully deployed position ( FIG. 5   c ). Once the aircraft has taken off and its speed has increased so that the auxiliary wing surface is no longer required, the Krueger flap  30  can be retracted into its stowed position. This is done by actuating either the electric motor  573  (in the second embodiment) or the rotational shaft  77  (in the first embodiment). 
         [0075]    In the case of the first embodiment, the rotational shaft  77  causes the worm gear  76  to rotate and this causes the gear in the gear housing  74  to also rotate. This actuates the ball screw actuator  70 . 
         [0076]    In the second embodiment, the electric motor  573  actuates the ball screw actuator  70  directly. 
         [0077]    In both embodiments, with the ball screw actuator  70  activated, the intermediate rod section  63  is retracted into the outermost rod section  62  and also the innermost rod section  64  is retracted into the intermediate rod section  63 . This causes the Krueger flap  30  to be pulled backwards towards the front spar  21 . This causes the linkages  80 ,  100  to pivot clockwise (as seen in  FIGS. 5   a  to  5   c ) and thereby define the retraction travel path of the Krueger flap  30 . 
         [0078]    When the aircraft is approaching landing, the Krueger flap  30  can be re-extended into its deployed position. This is done by actuating either the electric motor  573  (in the second embodiment) or the rotational shaft  77  (in the first embodiment). 
         [0079]    In the case of the first embodiment, the rotational shaft  77  is rotated in the opposite direction to during retraction, which causes the worm gear  76  to rotate in the opposite direction and this causes the gear in the gear housing  74  to also rotate in the opposite direction to before. This actuates the ball screw actuator  70  to deploy the flap  30 . 
         [0080]    In the second embodiment, the electric motor  573  actuates the ball screw actuator  70  to deploy the flap  30  directly. 
         [0081]    In both embodiments, with the ball screw actuator  70  activated, the intermediate rod section  63  is extended out of the outermost rod section  62  and also the innermost rod section  64  is extended out of the intermediate rod section  63 . This causes the Krueger flap  30  to be pushed forwards away from the front spar  21 . This causes the linkages  80 ,  100  to pivot anti-clockwise (as seen in  FIGS. 5   a  to  5   c ) and thereby define the extension travel path of the flap  30 . 
         [0082]    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. 
         [0083]    As a variation to the first embodiment, there may be more than one rotational shaft  77 . For example, there may be one rotational shaft  77  for each Krueger flap  30  or one rotational shaft for each deployment mechanism  60 . 
         [0084]    Also, instead of having an optical sensor at each end of the rotational shaft  77  for monitoring the function and position of the rotational shaft  77 , a magnetic sensor at each end of the rotational shaft  77  may be used. 
         [0085]    As a variation to both embodiments, the Krueger flap  30  may also be deployed (or at least partially deployed) during cruise flight of the aircraft to act as an air brake. 
         [0086]    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.