Abstract:
A control surface element skew and/or loss detection system ( 100 ) is provided which combines a cable ( 168, 178 ) system linked to movement transducers ( 120 ) via mechanical links ( 114, 116 ) connecting the fixed wing structure ( 102 ) to the control surface elements ( 106, 112 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is concerned with a control surface element skew and/or loss detection system. More specifically, the present invention is concerned with a cable-type skew and/or loss detection system for use with slats and flaps of aircraft wings. 
       BACKGROUND OF THE INVENTION 
       [0002]    Aircraft wings typically comprise a series of actuable control surface elements. These control surface elements define control surfaces (also known as auxiliary aerofoils) which are moveable relative to the fixed wing structure in order to alter the aerodynamic characteristics of the wing. Such control surface elements include leading edge devices such as slats, and trailing edge devices such as flaps. 
         [0003]    Typically, control surface elements are actuated at either span-wise end by two separate actuators. It is conceivable that if either of these actuators malfunctions, inconsistent actuation and skew or loss of the relevant control surface could occur. It is important that if skew or loss is detected, the relevant systems are shut down and the pilot of the aircraft is notified. 
         [0004]    Various methods have been proposed in the prior art for providing detection of skew and/or loss of control surface elements. One such system described in U.S. Pat. No. 5,680,124 proposes a cable which is coupled to each of a series of control surface elements. The cable is put in tension in the event of skew or loss. A movement detector with a proximity sensor is provided coupled to the cable such that any movement of the cable resulting from skew and/or loss can be detected. This detector is mounted on the endmost flap or slat. It is coupled to the flap/slat electronics unit (FSEU) in the aircraft fuselage via electric cables running from the moveable control surface element through the fixed wing structure into the fuselage and to the FSEU. 
         [0005]    This system detects skew by differential motion of adjacent surface elements which acts to pull the cable. A first problem with this system is that because the cable must be anchored at the endmost control surface elements, skew of those elements cannot be easily detected by this system. For example, if the endmost surface drive mechanism fails to move, this will not necessarily result in differential motion between the endmost surface and the next surface. 
         [0006]    A further problem with this prior art system is that wiring needs to be routed between the moveable control surface element on which the detector is mounted to and the fixed wing structure. Translating wiring between a moveable structure and a fixed structure is undesirable as wear and fatigue can occur. Furthermore, such wiring will be exposed to, and subject to, damage by external elements. 
         [0007]    In addition, leading edge control surface elements such as slats need to have anti-icing features. Such features generate a range of adverse temperature conditions which can affect the performance and reliability of the cable pull detector mounted on these control surface elements. 
         [0008]    A further problem with the prior art system is that the moveable control surface element is usually an enclosed panel, making access to the sensor difficult for maintenance. 
         [0009]    A still further problem with the prior art system is that a broken cable can not be detected. If the cable is broken then the skew or loss can no longer be detected which compromises the safety of the system. A check is therefore required at regular intervals to verify the cable is intact. This is a manual operation which adds maintenance time, cost and administration effort. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an aim of the present invention to overcome or at least mitigate one or more of the above problems. 
         [0011]    According to the invention there is provided an aircraft control surface element skew and/or loss detection system comprising an aircraft wing structure comprising a fixed part, a first control surface element and a second control surface element, the elements configured to be movable relative to the fixed part, a cable coupled to each of the first and second control surface elements such that a tensile force is applied to the cable upon skew and/or loss of one of the control surface elements, a mechanical link having a first end connected to the fixed wing structure, and a second end movably mounted to the first control surface element, a movement transducer configured to detect articulation of the mechanical link, wherein a first end of the cable is connected to the second end of the mechanical link such that skew and/or loss of one of the control surface elements causes articulation of the mechanical link by movement of the second end of the link relative to the first control surface element. 
         [0012]    The aircraft control surface elements may be any type of controls surface, preferably high lift surfaces such as slats or flaps. 
         [0013]    By “mechanical link” we mean a structure capable of being articulated such as a multi-bar linkage, telescopic rod, strut or the like. Because the mechanical link is mounted between the fixed wing structure and a control surface element (usually one of the end control surface elements), unexpected movement of that element can be directly detected via the link and, as such, none of the control surface elements will be exempt from skew and/or loss detection. 
         [0014]    In addition, because only a mechanical link is required between the first control surface element and the fixed part, no electronics or wiring is required to span the control surface element and the fixed wing structure. As such, the above mentioned disadvantages of such wiring can be avoided. 
         [0015]    Because the movement transducer is situated on a fixed wing structure it can be appropriately shielded and/or shrouded. It can also be made easily accessible for service and/or repair. Because the movement transducer is situated on a fixed wing structure it can be located away from the anti-icing area with its associated temperature extremes. 
         [0016]    Preferably the detection system comprises a cable loss detection system configured to detect a cable tension less than a predetermined amount. More preferably the cable loss detection system is configured to cause articulation of the mechanical link upon detection of a cable tension less than the predetermined amount. In this way the same transducer can be used to detect loss in cable tension. 
         [0017]    Preferably the cable loss detection system comprises a resilient element disposed between the second end of the link and the first control surface element, which resilient element acts in opposition to cable tension such that in the event that the cable tension drops below the force of the resilient element the second of the link moves relative to the first control surface element. 
         [0018]    Preferably the cable loss detection system is arranged to articulate the mechanical link in a direction opposite to the direction of articulation in the event of loss or skew of one of the control surface elements. 
         [0019]    BRIEF DESCRIPTION OF THE DRAWING VIEWS 
         [0020]    An example skew and/or loss detection system according to the present invention will now be described with reference to the accompanying drawings in which: 
         [0021]      FIG. 1  is a schematic plan view of a first skew and/or loss detection system according to the present invention installed on the leading edge of an aircraft wing; 
         [0022]      FIG. 2  is a side schematic view of the system of  FIG. 1  in direction II; 
         [0023]      FIG. 3  is a close-up section view of a part of the skew and/or loss detection system shown in  FIGS. 1 and 2 ; 
         [0024]      FIG. 4  is a partially cut-away view of the part of the skew and/or loss detection system shown in  FIG. 3 , 
         [0025]      FIG. 5  is a side schematic view of a second skew and/or loss detection system according to the present invention installed on the leading edge of an aircraft wing; 
         [0026]      FIG. 6  is a close-up section view of a part of a third skew and/or loss detection system according to the present invention from an underside of a slat; and; 
         [0027]      FIG. 7  is a close-up section view of a part of a fourth skew and/or loss detection system according to the present invention from an underside of a slat. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    Referring to  FIG. 1 , a control surface element skew and/or loss detection system  100  is shown schematically. The system is shown installed on a fixed wing structure  102  having a leading edge  104 . A plurality of control surface elements in the form of first slat  106 , a second slat  108 , a third slat  110  and a fourth slat  112  are independently moveably mounted to the fixed wing structure  102 . The method of attachment and actuation of the slats  106 ,  108 ,  110 ,  112  is well known in the art and will not be described further here. The overall position of the slat system is indicated by a system movement transducer, typically located at the endmost position one each wing. 
         [0029]    The skew and/or loss detection system  100  comprises a first link assembly  114 , a second link assembly  116  and a cable assembly  118 . The first link assembly  114  and the second link assembly  116  are substantially identical and connect the outermost part of the first slat  106  (distal to the fuselage) and the innermost part of fourth slat  112  (proximal to the fuselage) respectively to the fixed wing structure. Only the second link assembly  116  will be described in detail here although it will be understood that the first link assembly  114  operates in the same manner. 
         [0030]    Turning to  FIG. 2 , the second link assembly  116  is shown in detail. A rotary movement transducer  120  such as a rotary variable differential transformer (RVDT) is attached to the fixed wing structure  102 . A rotary input shaft  122  to the transducer  120  is connected to the first end  124  of a first link arm  126 . As such, the first link arm  126  can rotate about its first end  124  on the input shaft  122  of the transducer  120 . The rotary movement transducer  120  can therefore detect any rotational movement of the first link arm  126 . A second end  128  of the first link arm  126  is pivotably connected to a first end  130  of a second link arm  132  such that the second link arm  132  can rotate about its first end  130  relative to the first link arm  126 . A second end  134  of the second link arm  132  is pivotably attached to a slider element as will be described below. 
         [0031]    The second link assembly  116  further comprises a slider track  138  mounted to the fourth slat  112 . Referring to  FIGS. 3 and 4 , the slider track  138  is a hollow, generally rectangular prism defining a hollow cavity and a lower slot  140 , the function of which will be described below. The slot  140  extends substantially all the way along the length of the track  138  and has a width W substantially less than the width of the cavity of the track  138 . A first side wall  142  of the track  138  comprises a first detent  144  and a second detent  146  longitudinally spaced along the track  138 . At the end of the track  138 , a cable guide slot  148  is formed in the end wall. 
         [0032]    The slider element  136  comprises a rectangular body  150  which is slidable within the cavity of the track  138 . The rectangular body  150  comprises a blind bore  152  extending from a side wall  154 . The blind bore  152  contains a ball bearing  156  which is resiliently biased outwardly by a compression spring  158  within the blind bore  152 . In the position shown in  FIG. 3 , the ball bearing  156  is urged into the first detent  144  such that the slider element  136  is held stationary relative to the track  138 . 
         [0033]    The slider element  136  further comprises a cable attachment formation  160 , the function of which will be described below. 
         [0034]    The slider element  136  further comprises a first extending plate  162  and a second parallel link arm mounting plate  164 . The plates  162 ,  164  extend through the slot  140  in the track  138 . The plates  162 ,  164  define concentric through bores  166  through which a pin is passed in order to pivotably connect the second end  134  of the second link arm  132  therebetween. As such, the second link arm  132  is pivotably mounted to the slider element  136 . 
         [0035]    It will be noted that upon movement of the fourth slat  112  relative to the fixed wing structure  102 , the second link assembly  116  will articulate causing the link arms  126 ,  132  to rotate relative to each other and relative to the rotary movement transducer  120 . As such, during normal motion of the fourth slat  112 , detection of a movement at the rotary movement transducer  120  is to be expected. The motion recorded at the system movement transducer can be compared to the movement detected by the rotary movement transducer. Any discrepancy (e.g. excessive movement) will indicate skew or loss as will be described below. 
         [0036]    Turning to the cable assembly  118 , a substantially inextensible first cable portion  168  is provided and is attached to the cable attachment formation  160  of the slider element  136 . The first cable portion  168  passes through the cable slot  148  to a cable turn guide  170  in the fourth slat  112 . The first cable portion  168  is thereby turned through  90  degrees to extend parallel to the leading edge  104 . The first cable portion  168  then passes through the third slat  110  to the second slat  108 . It will be noted that the first cable portion  168  is coupled to the slats so as to be axially moveable relative thereto and in such a way that it can be tensioned by movement caused by skew or loss of the slat. For example, the first cable portion  168  could be encased within a guide sleeve passing through the slat structure. 
         [0037]    When the first cable portion  168  reaches the second slat  108  it is coupled to a lost motion device  172 . The lost motion device  172  comprises a cylinder  174  in which a piston  176  is slidably moveable. The first cable portion  168  is connected to the cylinder  174 . The piston  176  is connected to a second cable portion  178  such that relative movement between the first cable portion  168  and the second cable portion  178  is permitted by sliding motion of the piston  176  in the cylinder  174 . The piston  176  is biased by a compression spring  180  such that the ends of the cable portions  168 ,  178  are urged together. The lost motion device  172  accounts for any acceptable motion of the cable due to known factors in normal use such as expansion and contraction due to changes in ambient temperature and normal wing deflection during use. A rigging window is provided in the lost motion device such that it can be easily set during assembly. 
         [0038]    The second cable portion  178  continues through a second cable guide  182  mounted on the first slat  106 . The second cable guide  182  turns the cable  178  through 90 degrees such that it is perpendicular to the leading edge  104 . The second part of the cable  178  terminates at a cable attachment formation in the first link assembly  114  which will not be described here in detail. 
         [0039]    In use, the system operates as follows: 
         [0040]    Normal variations in the length of the cable between the first and second link assemblies  114 ,  116  is accounted for by the lost motion device  172 . As such, any tension on the cable due to normal thermal and/or wing deflection effects will be accounted for by the lost motion device. 
         [0041]    For more severe events such as flap skew or loss, the lost motion device  172  will “bottom out”. Specifically, the compression spring  180  will be fully compressed and the piston  176  will reach the end of the cylinder  174 . When this occurs, a tensile force is applied to the cable attachment formations  160  of the slider elements  136  in the link assemblies  114 ,  116 . Turning to  FIG. 3 , such a force will cause the ball bearing  156  to exit the first detent  144  by compressing the spring  158 . The slider element  136  will then be free to move relative to the fourth slat  112 . It will be understood that this may also occur at the first link assembly  114  depending on the nature of the skew and/or loss event. 
         [0042]    This causes the link arms  126 ,  132  to rotate relative to one another and such articulation to be detected at the rotary movement transducer  120 . As such, by comparing the expected output of the rotary movement transducer  120  (e.g. from the slat actuation system) and the actual output, any skew or loss can be detected as unexpected or excessive movement and articulation of the first link assembly  114  has occurred. 
         [0043]    Once the slider element  136  has reached the end of the track  138  proximate the cable guide slot  148 , the ball bearing  156  will enter the second detent  146  under the resilient force of the spring  158 . This ensures that should the skew and/or loss be sufficient to break the cable  168 ,  178  the slider element  136  will remain in the skew and/or loss detection position without returning back to its normal position. The skew and/or loss therefore remains detectable until the system is reset by maintenance personnel. 
         [0044]    It will be noted that advantageously the skew and/or loss is detected at two positions in the wing assembly, notably the first and last slats in the plurality. As such, skew and/or loss is reliably detected with redundancy. 
         [0045]    Turning to  FIG. 5 , a second skew and/or loss detection system  200  is shown. Reference numerals of common features are identical to the system  100 . 
         [0046]    In the system  200 , the rotary movement transducer  120  has been replaced by a linear movement transducer (e.g. an LVDT)  202 . The linear movement transducer determines changed in it&#39;s length and is configured to report these changes to the aircraft control systems (not shown). 
         [0047]    The transducer  202  is in the form of an extensible strut which is pivotably mounted to the fixed wing structure  102  at a first end  204  and pivotably mounted to the slider element  136  at a second end  206 . Upon regular movement of the fourth slat  112  during use, the length of the transducer  202  changes. The length change reported by the transducer  202  is compared with an expected change in length given the expected movement of the fourth flap  112  following actuation. A significant difference between the reported change in length and the expected value is indicative of a skew or loss event. 
         [0048]    Turning to  FIG. 6 , a part of the third skew and/or loss detection system  300  is shown. The system is viewed from underneath the slat panel (not shown), and is in section. Forward (FD) and rearward (RD) directions of the wing are labelled. Reference numerals of common features are identical to the system  100 . In particular a part of the second link assembly including the slider element  136  and track  138  is shown. 
         [0049]    In the skew and/or loss detection system  300 , the lost motion device  172  is incorporated attaching the first cable portion  168  to the slider element  136 . The lost motion device  172  works in substantially the same manner as in system  100  having a compression spring  302  disposed between a shoulder  304  at the end of the first cable portion  168  and a shoulder  306  defined on the slider  136 . 
         [0050]    Turning to  FIG. 7 , a part of a fourth skew and/or loss detection system  400  is shown. The system is viewed from underneath the slat panel (not shown), and is in section. Forward (FD) and rearward (RD) directions of the wing are labelled. 
         [0051]    Reference numerals of common features are identical to the system  300 . The system  400  is similar to the system  300  with the exception of the construction of the track  138 . 
         [0052]    In the fourth system  400 , the track  138  comprises an outer track component  138   a  and an inner track component  138   b.  The outer track component  138   a  comprises a rearward facing shoulder  402  which faces rearward to the leading edge of the wing where the slat is attached. The inner track component  138   b  is slidably engaged within the outer track component  138   a  and comprises a first forward facing shoulder  404  and a second forward facing shoulder  405  both of which face the rearward facing shoulder  402 . 
         [0053]    A compression spring  406  is disposed between the shoulders  402 ,  404  which act as spring abutments, the spring  406  acting to urge the track components  138   a,    138   b  (and the shoulders  402 ,  405 ) apart. In normal use, the spring  406  is compressed and the rearward facing shoulder  402  is in contact with the second forward facing shoulder  405 . 
         [0054]    The spring  302  is selected to have a higher preload than the spring  406 , and as such as long as a pull force is applied to the cable  168  (as is the case in normal use), the spring  406  will be compressed first (to its minimum length) to urge shoulders  402 ,  405  together. 
         [0055]    The system  400  is designed to provide an alert if any part of the cable snaps, thus removing all tensile force. In this instance, the springs  302  and  406  will extend, and out-of-range motion will be detected by the associated displacement transducer because the slider  136  will move relative to the slat to which the outer track component  138   a  is attached (carried by the inner track component  138   b ). 
         [0056]    Because a flap skew events always acts to increase the tension on the cable (not decrease it), cable tension loss may be differentiated from a skew event because the slider (and hence the movement transducer) will be moved in the opposite direction. In the embodiment of  FIG. 2 , a skew event will act to rotate the link  126  counter clockwise about the shaft  122 . On the other hand, if the system  400  is employed with cable loss detection, loss in cable tension (due to the cable snapping or failing) will act to rotate the link  126  clockwise. Such movements can be differentiated to determine whether the out-of-range reading by the RVDT  120  is due to flap skew or cable tension loss, which may be a result of flap loss or mechanical failure in the cable. It will be noted that in either given situation, the system will have to be shut down. The main benefit is in diagnosis of the failure mode. 
         [0057]    Variations fall within the scope of the present invention. 
         [0058]    Skew and/or loss of one of any number of surfaces can be detected with the aforementioned invention. 
         [0059]    The lost motion device can be positioned in any of the surfaces or (per system  300 ) within the slider element/track mechanism. 
         [0060]    Alternative slider and detent mechanisms may be employed, providing a certain degree of linear motion is permitted between the mechanical link, which motion is initiated at a predetermined cable tension load. 
         [0061]    A lost motion device may be incorporated into the slider mechanism at each end- i.e. half of the lost motion of the system can be accounted for by two arrangements, one at the track of the first link and one at the track of the second link. Installation of the cable through the surfaces is simplified and inspection and checking of the system is made easier. 
         [0062]    The RVDT may be replaced with any suitable rotary sensor such as but not limited to a potentiometer or resolver. 
         [0063]    As an alternative to the output from the RVDT being compared to the expected output due to motion of the flaps in use, the left wing RVDT output may be compared to the right wing PVDT output. Because aircraft flaps are actuated symmetrically, any undesired skew on one of the wings compared to the other will be detected by a significant difference in RVDT output. 
         [0064]    The invention is equally applicable to flaps (trailing edge) as well as slats (leading edge).