Patent Publication Number: US-2022228414-A1

Title: Door arrangement for use on an aircraft

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to European Patent Application No. 21275005.3 filed Jan. 15, 2021, the entire contents of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure relates to a door arrangement for use on an aircraft, and to an aircraft comprising such a door arrangement. 
     BACKGROUND ART 
     Aircraft typically comprise a number of external doors which allow access to parts of the aircraft or allow deployment of in air equipment. Particularly when the aircraft is in flight, the doors experience significant external forces which try to move the doors into an open position. The external forces acting to move the doors towards an open position may be any relevant force and may, for example, be the result of pressure differences between an inside and an outside of the door or the result of passing airflow which can act to pull the door towards an open position. In prior art systems, in order to resist the external forces, and hold the doors in a closed position, the doors typically comprise locks which act on an end of the door to hold it in place. The locks typically latch onto the door to hold it in the closed position. As will be appreciated, the locks may have to resist significant forces and thus may become worn over time. The replacement of the locks may be costly and time consuming. Additionally, in prior art systems, the external forces are often at least partially transferred through the door directly to the actuator which controls movement of the door. As a result, over time, the actuator may become damaged as a result of these forces, and may also require replacement. Again, this may be costly and time consuming. 
     It would be advantageous to provide a door arrangement for use on an aircraft which addresses the problems outlined above. 
     SUMMARY OF THE DISCLOSURE 
     In accordance with a first aspect, the present disclosure provides a door arrangement, for use on an aircraft. The arrangement includes: a door and an actuation arrangement, configured to move the door between an open position and a closed position. The actuation arrangement includes: a first member coupled to the door such that movement of the first member moves the door and a second member pivotally coupled to the first member and arranged to drive movement of the first member. The the second member is movable between a first position which corresponds to the door being in an open position and a second position which corresponds to the door being in a closed position. The actuation arrangement also includes: an actuator arranged to rotate the second member between the first position and second positions; and a fixed stop arranged such that when the second member is in the second position, an external force acting on the door acting to move the door towards its open position causes at least one of the first member and second member to contact the fixed stop and thereby prevent movement of the door towards the open position. 
     Thus it will be appreciated that aspects of the present disclosure provide an improved door arrangement which prevents the opening of the door by the external force. In accordance with the present disclosure, the fixed stop acts to stop the external force from moving the door into the open position. The use of a fixed stop may remove the need to provide a lock and may also minimise the amount of force which is transferred to the actuator. In the door arrangement of the present disclosure, the external force is transferred, via the first member and/or second member, to the fixed stop, rather than being transferred to an actuator or a lock as is the case in the prior art. The fixed stop may be purpose designed to withstand the external forces which the door arrangement experiences. The fixed stop may be considered to prevent back driving of the door arrangement. 
     The external force may be any force other than the force provided by the actuation arrangement. For example, the external force may be a force provided by the weight of the doors themselves, the aerodynamic effects of door surfaces or edges which protrude into an airflow passing over the door and/or a force applied as a result of a pressure difference between two sides of the door. 
     In a set of examples, the first member and second member form an over centre arrangement, and wherein when the second member is in the second position, the first member and second member are in an over centre position such that the external force acts to drive the first member towards the fixed stop. The first member being driven towards the fixed stop may simultaneously drive the second member to be driven towards the fixed stop. 
     Which of the first and second members ends up in contact with the fixed stop may depend on the relative position of the fixed stop and the particular arrangement of the first and second members. Of course, if one of the first and second members is already in contact with the fixed stop when the second member is in the second position, the external force may not actually move the first member and/or the second member but may instead act to increase the force holding the first member and/or second member against the fixed stop. Alternatively, when the second member is in the second position corresponding to the door being in the closed position, the first member and/or the second member may be separated from the fixed stop, and thus the external force may cause the first member and/or the second member to move slightly before coming into contact with the fixed stop. It will be appreciated that the external force acts through the door, and through the first member which is coupled to the door. 
     Contact between the first member and/or the second member and the fixed stop may not require direct physical contact. For example, an intermediate member, arranged between the first member, and/or the second member, and the fixed stop may come into contact with the fixed stop. The first member and/or second member may thus indirectly contact the fixed stop. Alternatively, the first member and/or second member may come into direct contact with the fixed stop. 
     The fixed stop and the first and second members may be arranged such that one or both of the first and second members come into contact with the fixed stop when an external force acts on the door acting to move the door towards its open position. Contact of both of the first and second members with the fixed stop may advantageously distribute the external force through each of the first and second members which may minimise the wear of the first and second members and potentially increase the amount of contact between the first and second members and the fixed stop. However, in another set of examples, the fixed stop is positioned such that only the first member comes into contact with the fixed stop. Positioning the fixed stop in this manner may advantageously prevent or minimise the amount of force transferred to the second member, and thus prevent or minimise the amount of force which is transferred to the actuator. This may advantageously minimise any damage caused to the actuator by the external force and mean that the actuator does not have to be designed to be capable of accounting for such forces. 
     The door may be any door which can be moved between open and closed positions by the actuation arrangement. For example, the door may translate, e.g. by sliding. Of course, the actuation arrangement, specifically the first and second members, may be designed to control suitable movement of the door. In a set of examples, the door is pivotally mounted to a support structure at a first pivot point. The door may thus be a rotatable door. The support structure may be a support structure of the door arrangement itself, or the structure to which the door arrangement is mounted. In examples in which the door is pivotally mounted, the first member and second member may be arranged in any suitable manner such that movement of the second member drives movement of the first member which causes rotation of the door about the first pivot point. The first member may be fixedly coupled to the door, such that rotation of the first member causes rotation of the door. In this case, the first member may be fixedly coupled at the first pivot point. In another set of examples, the first member is pivotally coupled to the door at a second pivot point. The second pivot point may have any suitable position on the door. In a set of examples, the second pivot point is spaced from the first pivot point. Spacing the second pivot point from the first pivot point may advantageously reduce the force which is transferred via the first member to the fixed stop and thus reduce the force which the fixed stop needs to be capable of withstanding. 
     The fixed stop may be a permanent, i.e. irreplaceable, component of the door arrangement. For example, the fixed stop may be an integrally formed part of the door arrangement. In such examples, the fixed stop may be designed to last the expected lifetime of the door arrangement. In an alternative a set of examples, the fixed stop is detachably mounted. Accordingly, the fixed stop may be detached, and replaced with a replacement fixed stop when the fixed stop becomes worn. The provision of a detachably mounted fixed stop may therefore facilitate easy maintenance of the door arrangement and potentially increase its life span. 
     As will be appreciated by those skilled in the art, as the fixed stop prevents an external force from driving the door towards the open position, when the second member is in the second position, the fixed stop may also act to define the second position of the second member and thus the closed position of the door. For example, the second position may be defined as the position of the second member when it comes into contact with the fixed stop. In a set of examples, a position of fixed stop is adjustable. Adjustment of the position of the fixed stop may therefore allow adjustment as to the degree of movement of the second member which may therefore define the second position of the second member, which may at least partially define the closed position of the door. Accordingly, the position of the fixed stop may be adjusted to adjust the closed position of the door. This may facilitate simple maintenance of the door arrangement. For example, if, for some reason, the door is not closing fully or is closing too much, the position of the fixed stop may be adjusted so that it redefines the second position such that the closed position of the door is adjusted as desired. 
     Providing a fixed stop having an adjustable position may be achieved by any suitable means. For example, the fixed stop may be fixed in place by at least one fixing element, e.g. a bolt. It may be possible to release the fixing element, reposition the fixed stop, and reaffix the fixing element. For example, the fixed stop may be arranged to move within a slot which provides a plurality of positions which the fixed stop can be moved into, and the fixing element may secure the fixed stop in place, i.e. hold it in a fixed position, in the slot. 
     The fixed stop may be made from any material which can suitably withstand the first or second member repeatedly coming into contact with it without imparting wear or damage to the first and second members. The fixed stop, or indeed a coating applied thereto, may be made from any material which is suitable to withstand the force and contact of the first and/or second members which may be experienced during operation. For example, the fixed stop may be made from any one of: a copper alloy, e.g. phosphor bronze, aluminium bronze, copper nickel tin alloys, rubber or plastic. The entire of the fixed stop may be made from the materials described above. Of course, in some examples, only a portion of the fixed stop which the first and/or second members comes into contact with may be made from a material suitable for repeated contact, and the rest of the fixed stop may be made from any other suitable material. As the door arrangement may experience significant temperature fluctuations in use, it may be advantageous for the fixed stop to be capable of withstanding such temperature variations. Thus, in a set of examples the fixed stop is made from a soft metal, e.g. a copper alloy. 
     The first member and/or the second member may be made from any suitable material. In a set of examples, the first member and/or the second member is made from a material with a higher wear resistance than the fixed stop. This may advantageously mean that the fixed stop wears as a result of the interaction between the first member and/or the second member and the fixed stop, rather than the first member and/or second member. The fixed stop may be easier to replace than the first and/or second members and so this may facilitate simpler maintenance of the door arrangement. The first member and/or the second member may, for example, be made from at least one of: hardened steel, steel, titanium and aluminium. 
     The degree of contact between the first member and/or second member and the fixed block may impact how securely the door is held in the closed position. The degree of contact may also impact the level of wear on the first member and/or second member and/or the fixed block. In a set of examples, the fixed stop comprises a rounded surface against which the first member and/or second member comes into contact with. In another set of examples, the first member and/or the second member comprises a respective rounded surface arranged to come into contact with the fixed stop. The rounded surface of the fixed stop and/or the first member and/or the second member may be curved in a single direction, i.e. such that the surface is at least partially cylindrically shaped, or be curved in multiple directions such that it forms an at least partially spherical surface. The use of a rounded surface may ensure that irrespective of the point at which the first member and/or the second member comes into contact with the fixed stop, there is a predictable degree of contact. The rounded surface may also ensure that there is sufficient contact even as the fixed stop and/or the first member and/or the second member becomes worn through repeated contact. In a set of examples, the rounded surface has a radius which is as large as possible, whilst maintaining appropriate geometric contact between the rounded surface and the point of contact between the fixed stop and first and/or second members under all potential positions of the first and/or second members relative to the fixed stop. A radius which is as large as possible may ensure appropriate contact between the first member and/or the second member and the fixed stop irrespective of any misalignment which may occur. 
     Depending on the size of the door, some examples may comprise a plurality actuation arrangements. Each actuation arrangement may comprise any of the features of the examples described above and function in an identical manner. Each of the actuation arrangements may be spaced along the length of the door and thus the force acting to drive the door between the open and closed positions may be distributed along the length of the door. The actuation arrangement may comprise any suitable actuator capable of driving the second member between the first and second positions. The actuator may, for example, comprise a motor which drives movement of the second member. The motor may, for example, comprise an electric, hydraulic or pneumatic motor. The actuator may further comprise a gearbox coupled to the motor and the second member. The gearbox may be capable of creating the torques necessary to drive movement of the second member and thus the door. The gearbox may be a high ratio gearbox and may, for example, have a ratio of at least 100:1. 
     For certain openings, it may be desirable to have multiple doors. For example, for larger openings, a single door may otherwise be too large and cumbersome to control. Thus, in a set of examples, the door arrangement comprises a further door, and wherein the actuation arrangement comprises: a third member coupled to the further door such that movement of the third member moves the further door between an open position and a closed position; a fourth member pivotally coupled to the third member and arranged to drive movement of the third member, wherein the fourth member is movable between a respective first position which corresponds to the further door being in the open position and a respective second position which corresponds to the further door being in the closed position; and a further fixed stop arranged such that when the fourth member is in the second position, an external force acting on the further door acting to move the further door towards its open position causes at least one of the third member and fourth member to contact the fixed stop and thereby prevent movement of the further door towards the open position. 
     Accordingly, the further door may also be prevented from moving towards an open position by the external forces. The fourth member may be rotatable between the first position and second position. The fourth member may be moved, e.g. rotated, by a further actuator, which is different to the actuator which rotates the second member. However, this may require suitable synchronisation of the actuator and further actuator in order to open and close the door and further door simultaneously. Thus, in a set of examples, the actuator is further arranged to drive the fourth member between the first position and second position. The actuator may comprise a rotary geared actuator. Through the use of the same actuator, movement of the door and further door may by synchronised more easily. 
     The actuator may comprise any suitable arrangement for moving the second member and the fourth member. For example, the actuator may comprise a motor and at least one gearbox coupled to the motor and arranged to drive each of the second member and fourth member. The motor may be any suitable motor and may, for example, comprise an electric, hydraulic or pneumatic motor. Any suitable gearbox may be used. The ratio of the gearbox may depend on the motor being used and the size of the doors being moved. In order to achieve the torques necessary to move the door and the further door between the open and closed positions, the gearbox may have a high ratio. For example, the gearbox may have a ratio of at least 100:1. 
     In a further set of examples, the actuator comprises a dual output gearbox which comprises a first output and a second output, and wherein the first output is arranged to rotate the second member and the second output is arranged to rotate the fourth member. The dual output gearbox may be in the form of a T-gearbox. The use of a dual output gearbox may simplify the synchronization of movement of the door and further door. For example, each of the first output and second output of the dual output gearbox may be synchronized and thus movement of the door and further door may be synchronized. This mechanical synchronization provided by the dual output gearbox may be simpler and easier to implement when compared to the alternative examples whereby separate actuators are provided for each of the second member and fourth member. 
     The third member may comprise any of the features of the first member described above, and may also be configured in a similar manner to the first member described above. Similarly, the fourth member may comprise any of the features of the second member described above, and may also be configured in a similar manner to the second member described above. Additionally, each of the door and further door may comprise a plurality of actuation arrangements. 
     As will be appreciated, the external forces may generally act to move the door towards the open position in one direction. For example, the external forces may generally act to pull the door outwards or push the door inwards. However, in some instances, external forces may act to force the door in a different direction. For example, the external force may act to push the door in an inward direction, against its normal direction of movement towards the open position. In a set of examples, the actuator is arranged to actively drive the first and/or second member into contact with the fixed stop when the door is in the closed position. As such, the actuator may continuously act to hold the first member and/or second member in contact with the fixed stop when the door is in the closed position. In such examples, an external force acting to move the door towards its open position in one direction will cause the first member and/or second member to pull against the fixed stop and thus the door will be prevented from opening. An external force acting to move the door in a different direction, e.g. pushing the door inwards against its normal movement direction, may act to drive the first member and/or second member away from the fixed stop. However, in examples as described above, movement of the first and/or second members away from the fixed stop may be resisted by the actuator which is actively driving the first member and/or second member into contact with the fixed stop. Movement of the door may thus be prevented irrespective of the action of the external force. As external forces acting to drive the first and/or second member away from the fixed stop may be significantly less than the forces tending to move the door towards its open position, the motor may be capable of resisting this motion without experiencing significant wear. Such an arrangement may advantageously prevent movement of the door irrespective of the external force without requiring the use of additional locks. In examples comprising a further door, the actuator may also be arranged to actively drive the third and/or fourth member into contact with the further fixed stop when the further door is in the closed position. 
     In another set of examples, the fixed stop may be arranged to stop movement of the door in a first direction, i.e. when moving towards an open position, and the door arrangement may comprise a separate holding means for preventing movement of the door in a second, different direction. The holding means may, for example, comprise a locking arrangement which may be provided to prevent the door and optionally the further door from moving in the second direction. The external forces may be larger in the first direction, when compared to the second direction, and thus the holding means may not have to be capable of withstanding forces as large as those experience by the fixed stop. 
     According to a further aspect of the present disclosure there is provided an aircraft comprising a door arrangement according to any of the examples described above. 
     The door arrangement may be any suitable door arrangement on the aircraft. For example, the door arrangement may be an undercarriage door arrangement, a door arrangement which provides access to an auxiliary power unit, a door arrangement which provides access to a refueling arm bay, a door arrangement which allows access to a Ram Air Turbine or a payload-bay door arrangement. 
     According to another aspect of the present disclosure there is disclosed an actuation arrangement, for moving a door on an aircraft between an open position and a closed position includes: a first member configured to be coupled to the door such that movement of the first member moves the door; a second member pivotally coupled to the first member and arranged to drive movement of the first member, wherein the second member is movable between a first position which corresponds to the door being in an open position and a second position which corresponds to the door being in a closed position; and an actuator arranged to rotate the second member between the first position and second position; and a fixed stop arranged such that when the second member is in the second position, an external force acting on the first member causes at least one of the first member and second member to contact the fixed stop and thereby prevent movement of the first member. 
     The actuation arrangement of this aspect of the disclosure may comprise any of the features related to the actuation arrangement described above with respect to the door arrangement. In accordance with this aspect of the disclosure, the door does not form part of the actuation arrangement. However, when installed, the actuation arrangement may be suitably coupled to a door, e.g. through the coupling of the first member to the door. When coupled to a door, any external forces acting on the door will act through, i.e. on, the first member. Further, as will be appreciated, as the first member is configured to be coupled to the door, by preventing movement of the first member, this will consequently prevent movement of the coupled door. According to a further aspect of the present disclosure there is provided an aircraft comprising an actuation arrangement as described above. The aircraft may comprise a door to which the first member is coupled. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain examples of the present disclosure will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a door arrangement, in accordance with an example of the present disclosure, with the doors in a closed position; 
         FIG. 2A  is an end-on view of the door arrangement shown in  FIG. 1 ; 
         FIG. 2B  is a sectional view of the door arrangement through the line B-B shown in  FIG. 2A ; 
         FIG. 3  is a perspective view of the door arrangement shown in  FIG. 1  with the second member and fourth member in a first intermediate position; 
         FIG. 4  is an end-on view of the door arrangement shown in  FIG. 3 ; 
         FIG. 5  is a perspective view of the door arrangement shown in  FIG. 1  with the second member and fourth member in a second intermediate position in which the doors are partially opened; 
         FIG. 6  is an end-on view of the door arrangement shown in  FIG. 5 ; 
         FIG. 7  is a perspective view of the door arrangement shown in  FIG. 1  with the second and fourth members in a first position corresponding to the doors being in a fully open position; 
         FIG. 8  is an end-on view of the door arrangement shown in  FIG. 7 ; 
         FIG. 9  is a sectional view through the section A-A indicated in  FIG. 2A ; 
         FIGS. 10A-10B  show the door arrangement shown in  FIG. 1  in an aircraft body in accordance with an example of the present disclosure; and 
         FIGS. 11A-11B  illustrate a fixed stop which has an adjustable position in accordance with another example of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a perspective view of a door arrangement  2 , for use on an aircraft, in accordance with an example of the present disclosure. Part of the structural wall  30  of the door arrangement  2  is removed to reveal the internal components of the door arrangement  2 . As is visible, the door arrangement  2  comprises a door  4 A and a further door  4 B. The door  4 A and further door  4 B are pivotally mounted doors. The door arrangement  2  further comprises an actuation arrangement  6  which is configured to move the door  4 A and the further door  4 B between an open position and a closed position. In  FIG. 1 , the door  4 A and further door  4 B are shown in the closed position. 
     The actuation arrangement  6  comprises a first member  8  which is pivotally coupled to the door  4 A at a second pivot point  10 . The second pivot point  10  is spaced from a first pivot point  12  about which the door  4 A is mounted to the structure  13  of the door arrangement  2 . A second member  14  is pivotally coupled to the first member  8  at a respective pivot point  16  and is arranged to drive movement of the first member  8 . The second member  14  is arranged to rotate between first and second positions. The actuation arrangement  6  comprises an actuator  18  which comprises a motor  20  which drives a dual output gearbox  22 . The motor  20  may be an electric, hydraulic or pneumatic motor. A first output  24  of the dual output gearbox  22  is operatively coupled to the second member  14  and acts to rotate the second member  14 . In the example depicted, the dual output gearbox  22  also acts to drive a fourth member  38  as will be described in more detail below. However, in examples in which the door arrangement  2  only comprises a single door  4 A, it will be appreciated that the dual output gearbox  22  may be replaced by a single output gearbox. 
     The door arrangement  2  further comprises a fixed stop  26 . In the example depicted, the fixed stop  26  is fixedly mounted to a beam  28  which is fixedly coupled to a structural wall  30 . The structural wall  30  may be a wall of the door arrangement  2  itself, or a wall of the component to which the door arrangement  2  is affixed, e.g. a structural wall of the aircraft itself. The fixed stop  26  is held in a fixed position relative to the other components of the door arrangement  2 . As depicted, the fixed stop  26  has a rounded outer surface  32 . 
     In order to move the further door  4 B between the open and closed positions, the door arrangement  2  comprises a third member  34  which is coupled to the further door  4 B. As depicted, the third member  34  is pivotally coupled to the further door  4 B at a respective second pivot point  36  which is spaced from a respective first pivot point  37  at which the further door  4 B is mounted to the structure  13  of the door arrangement  2 . The actuation arrangement  6  further comprises a fourth member  38  which is pivotally coupled to the third member  34  at a respective pivot point  40 . In the example depicted, the fourth member  38  is coupled to a second output  42  of the dual output gearbox  22 . The second output  42  drives the fourth member  38  to rotate between first and second positions. 
     The door arrangement  2  comprises a further fixed stop  44  which is fixedly mounted to a beam  46 . The beam  46  is fixedly coupled to a structural wall (not visible in this Figure). The further fixed stop  44  comprises a rounded surface  48 . 
     As depicted, the first member  8  and third member  34  are coupled to the door  4 A and further door  4 B at a first end thereof. In the example depicted, the door arrangement  2  comprises a further actuation arrangement  6 A. The actuation arrangement  6 A is identical to the actuation arrangement  6  described above, except that its members are coupled to a second end of the door  4 A and further door  4 B. The actuation arrangement  6 A operates in an identical manner to the actuation arrangement  6  and thus description of its operation will not be repeated. The use of multiple actuation arrangements  6 ,  6 A as depicted may ensure that the door  4 A and further door  4 B can be opened in an appropriate manner. Of course, any number of actuation arrangements may be included and the number and distribution may depend on the size of the door  4 A and further door  4 B. 
     Operation of the door arrangement  2  will be now be described, first with reference to  FIG. 1 . As depicted in  FIG. 1 , the second member  14  and the fourth member  38  are in a second position which corresponds to the door  4 A and further door  4 B being in the closed position. In the example depicted, the fixed stop  26  and further fixed stop  44  is arranged such that when an external force  50  (depicted by the arrow) acts to pull the door  4 A and further door  4 B towards an open position, the first member  8  and the third member  34  come into contact with the fixed stop  26  and further fixed stop  44 , respectively. The contact between the first member  8  and the fixed stop  26  prevents the first member  8  from moving any further than the fixed stop  26  and thereby prevents the door  4 A from moving towards an open position. Similarly, the contact between the third member  34  and the further fixed stop  44  prevents the third member  34  from moving any further than the further fixed stop  44  and thereby prevents the further door  4 B from moving towards an open position. Accordingly, the fixed stop  26  and the further fixed stop  44  act to stop the door  4 A and further door  4 B from being opened when arranged appropriately as depicted. Of course, the fixed stop  26  and further fixed stop  44  may have any suitable arrangement such that an external force  50  acting to open the door  4 A and further door  4 B causes the first member  8  and/or second member  14  to abut against the fixed stop  26  and third member  34  and/or fourth member  38  to abut against the further fixed stop  44 . 
       FIG. 2A  shows an end-on view when looking at the end face  52  of the fixed stop  26  of the door arrangement  2  in the configuration shown in  FIG. 1 . The further fixed stop  44  is not visible in this Figure and so discussion will be focused on the first member  8  and second member  14  and their interaction with the fixed stop  26 . However, the same may apply to the third member  34  and the fourth member  38 . As depicted, when an external force  50  acts to try and move the door  4 A towards an open position, the first member  8  comes into contact with the fixed stop  26 . As will be appreciated, due to the constraints of the first member  8 , for example because it is pivotally coupled to the second member  14  and pivotally coupled to the door  4 A, when the first member  8  is in contact with the fixed stop  26 , the first member  8  cannot move any further under the external force  50 . Accordingly, this acts to prevent the door  4 A from moving towards an open position. The fixed stop  26  comprises a rounded surface  32  which contacts the first member  8 . The rounded surface  32  ensures consistent contact between the first member  8  and the fixed stop  26  irrespective of the relative position of the first member  8  and the fixed stop  26 . 
       FIG. 2B  shows a sectional view of the door arrangement  2  through the line B-B, shown in  FIG. 2A , when viewed from the direction indicated by arrows  35 . This sectional view illustrates the dual output gearbox  22  with the first output  24  coupled to the second member  14 , which is coupled to the first member  8 . In the sectional view shown, the cross sections of the first member  8  and second member  14  are visible. The second output  42  of the dual output gearbox  22  is coupled to the fourth member  38  which is coupled to the third member  34 . 
     In the position shown, the first member  8  abuts against the fixed stop  26  and the third member  34  abuts against the further fixed stop  44 . As shown in this Figure, the first member  8  comprises a rounded surface  9  which comes into contact with the fixed stop  26 . This rounded surface  9  may help to ensure that the first member  8  achieves a consistent amount of contact with the fixed stop  26 , even if the first member  8  becomes partially misaligned with respect to the fixed stop  8 . Whilst not visible in this sectional view, the third member  34  also has a similar rounded surface arranged to contact the further fixed stop  44 . Additionally, whilst not depicted, in embodiments wherein the second member  14  and fourth member  38  contact the fixed stop  26  and further fixed stop  44 , respectively, each of the second member  14  and fourth member  38  may comprise respective rounded surfaces. 
     In the example depicted in  FIGS. 2A and 2B , the first member  8  comes into contact with the fixed stop  26  and the second member  14  does not. This may advantageously transfer at least a significant portion the external force to the fixed stop  26  and minimise the amount of force which is transferred to the actuator  18 . However, in other examples, in addition or alternatively, the second member  14  may come into contact with the fixed stop  26 . Additionally, whilst it is depicted that that first member  8  comes into direct contact with the fixed stop  26 , the first member  8 , or indeed the second member  14 , may indirectly contact the fixed stop  26 . For example, the first member  8  may comprise a member which extends therefrom which contacts the fixed stop  26 . In the position depicted in  FIGS. 2A and 2B , the first member  8  and second member  14  form an over centre mechanism and the first member  8  may be considered to be in an over-centre position with respect to the second member  14  and the pivot point  16 . When in this over-centre position, the external force  50  pulls the first member  8  in a clockwise direction in the view shown, which brings the first member  8  into contact with the suitably arranged fixed stop  26 . 
     Whilst in the example described above the fixed stop  26  is coupled to a beam  28  which is attached to the structural wall  30 , the fixed stop  26  and indeed the further fixed stop  44  may have any suitable form. For example, the beam  28  may be omitted and the fixed stop  26  may be integrally provided with the structural wall  30 . In this regard, the fixed stop  26  may be part of the structural wall  30 . The same applies to the further fixed stop  44 . Similarly, depending on the specific arrangement of the first, second, third and fourth members  8 ,  14 ,  34 ,  38 , the fixed stop  26  and further fixed stop  44  may be integrally provided by a single component. 
       FIGS. 1, 2A and 2B  show the second member  14  and fourth member  38  each in a second position which corresponds to the door  4 A and the further door  4 B being in a closed position, and when in this position the further force  50  causes the first member  8  to contact the fixed stop and the third member  34  to contact the further fixed stop  44 . As will be appreciated, when in their respective second positions, the first member  8  and third member  34  may already be in contact with their respective fixed stops  26 ,  44  and thus the external force  50  may simply act pull the first member  8  and third member  34  against the fixed stops  26 ,  44  with an increased force. The first member  8  and third member  34  may be made from a material having a higher wear resistance than that of the fixed stop  26  and further fixed stop  44 . 
     The second member  14  and fourth member  38  may be rotated towards a first position in which the door  4 A and further door  4 B is in an open position when it is desired to open the door  4 A and further door  4 B. Movement of the door  4 A and further door  4 B into this open position will now be described with reference to  FIGS. 3 to 8 . 
       FIG. 3  shows the door arrangement  2  in which second member  14  and fourth member  38 , of the actuation arrangement  6 , have been driven, i.e. rotated, by the motor  20  into a first intermediate position, between the second position shown in  FIG. 1  and the first position shown later in  FIGS. 7 and 8 . As shown in  FIG. 3 , in the first intermediate position, the first member  8  has been driven by movement of the second member  14  to the point at which the first member  8  is aligned with the second member  14  such that they are on-centre. The same is the case for the third member  34  which has been driven by movement of the fourth member  38  and which is aligned with the fourth member  38  and therefore also on-centre. When in this first intermediate position, the first, second, third and fourth members  8 ,  14 ,  34 ,  38  have been rotated away from the fixed stop  26  and further fixed stop  44 . 
     The dual output gearbox  22 , in which the first output  24  and second output  42  are synchronized, advantageously means that the second member  14  and fourth member  38  have rotated by the same amount, and thus the door  4 A and further door  4 B are in the same positions. 
       FIG. 4  shows an end-on view of the door arrangement  2  in the configuration shown in  FIG. 3 , focusing on the actuation arrangement  6 . As can be seen more clearly in this Figure, the first member  8  is aligned with the second member  14  and the third member  34  is aligned with the fourth member  38 , and the second member  14  and fourth member  38  cannot be seen in this end-on view due to the alignment. Additionally, it can more clearly be seen how the first member  8 , and therefore also the second member  14  (although not visible in the Figure), have rotated away from the fixed stop  26 . As the second member  14  and fourth member  38  are moved into this first intermediate position, the door  4 A and further door  4 B are pulled inwards slightly, and may be pulled into a more closed position, or even just past the closed position to an inverted position. 
       FIG. 5  shows a perspective view of the door arrangement  2  with the second member  14  and fourth member  38  in a second intermediate position. The motor  20  and dual output gearbox  22  advantageously drive the second and fourth members  14 ,  38  simultaneously. Accordingly, the second and fourth members  14 ,  38  have been driven by the same rotational amount, thereby driving each of the first member  8  and third member  34  by the same amount, and thus the door  4 A and further door  4 B have been opened by the same amount. As depicted, in this second intermediate position, the door  4 A and further door  4 B are partially opened. As will be appreciated, when moving towards the second intermediate position shown, the first, second, third and fourth member  8 ,  14 ,  34  and  38  move further away from the respective fixed stop  26  and further fixed stop  44 . 
       FIG. 6  shows an end-on view of the door arrangement  2  in the configuration shown in  FIG. 5 . As shown, as the second member  14  rotates, the second member  14  moves the first member  8  which causes the door  4 A to move towards an open position. The movement of the first member  8  is constrained by the pivotal connection between the first member  8 , the door  4 A and the second member  14 , and thus the rotation of the second member  14  acts to drive the first pivot point  10  downwards. The same applies to the further door  4 B, with the third member  34  and the fourth member  38  (not visible in this Figure). 
       FIG. 7  shows a perspective view of the door arrangement  2  with the second member  14  and fourth member  38  in a first position which corresponds to the door  4 A and further door  4 B being in an open position. The actuator  18 , specifically the motor  20  and the dual output gearbox  22  may drive the second member  14  and fourth member  38  into the first position as shown, which thereby act to drive the first member  8  and third member  34  accordingly. As mentioned previously, the first output  24  and second output  42  may be synchronized such that the second member  14  and fourth member  38  move by the same amount. As the second member  14  and fourth member  38  move into the first position, the second member  14  and fourth member  38  move the first member  8 , and third member  34 , respectively, which each move the door  4 A and further door  4 B into the open position as depicted. 
       FIG. 8  shows an end-on view of the door arrangement  2  shown in  FIG. 7 , focusing on the actuation arrangement  6 , the door  4 A and further door  4 B. This Figure more clearly shows how when the second member  14  and fourth member  38  are moved into the first position, the first member  8  and third member  34  are driven downwards. Due to the pivotal coupling of the first member  8  to the door  4 A at the pivot point  10  and the pivotal coupling of the third member to the door  4 B at the pivot point  36 , and due to each of the door  4 A and the further door  4 B being pivotally mounted, the downward movement of the first member  8  and third member  34  causes the door  4 A and further door  4 B to rotate out into an open position as depicted. 
     As will be appreciated by those skilled in the art, the door  4 A and further door  4 B may be moved from the open position shown in  FIGS. 7 and 8 , back into the closed position shown in  FIGS. 1 and 2 , by rotating the second member  14  and fourth member  38  in the opposite direction. This may be achieved by operating the motor  20  in the opposite direction. The second member  14  and fourth member  38  may rotate from the first position shown in  FIGS. 7 and 8 , through the second intermediate position shown in  FIGS. 5 and 6 , through the first intermediate position shown in  FIGS. 3 and 4 , until they are back in the second position shown in  FIGS. 1 and 2 . Additionally, whilst operation of the actuation arrangement  6  has been described above in relation to the opening of the door  4 A and further door  4 B, it will be appreciated that the further actuation arrangement  6 A may operate simultaneously with the actuation arrangement  6  to drive the second end of the door  4 A and further door  4 B into the open position. 
       FIG. 9  shows a sectional view through the door arrangement  2  through the line A-A shown in  FIG. 2A , when viewed from left to right in the direction indicated by arrows  33 . This view more clearly shows the actuation arrangement  6 , specifically the dual output gearbox  22  thereof. The motor  20  drives a single input  21  which results in rotation of the first output  24  and rotation of the second output  42 . As depicted, the dual output gearbox  22  is in the form of a T-shaped gearbox. The second member  14  is coupled to the first output  24  such that rotation of the first output  24  drives rotation of the second member  14 , which drives movement of the first member  8 . The third member  34  and fourth member  38  cannot be seen in this Figure due to the position of the cross-section, but the fourth member  38  is driven to rotate by the second output  42  in a similar manner as the second member  14 . The further actuation arrangement  6 A operates in an identical manner to the actuation arrangement  6 . 
       FIG. 10A  illustrates an aircraft  54  comprising the door arrangement  2  shown in earlier Figures. For clarity, only a portion of the body of the aircraft  54  is shown. In  FIG. 10A , the door arrangement  2  is in a closed configuration whereby the door  4 A and further door  4 B are in closed positions. This corresponds to the configuration of the door arrangement shown in  FIGS. 1 and 2 .  FIG. 10B  shows the aircraft  54  with the door arrangement  2  in an open configuration whereby the door  4 A and further door  4 B are in open positions. This corresponds to the configuration of the door arrangement  2  shown in  FIGS. 7 and 8 . 
       FIGS. 11A and 11B  show an example of a fixed stop  126  in accordance with an example of the present disclosure whereby the position of the fixed stop  126  is adjustable. In the example depicted, similarly to the examples discussed above, the fixed stop  126  is attached to a beam  128 . The fixed stop  126  comprises a rod  156  which extends from an end face  162  of the fixed stop  126 . At least a portion of the rod  156  comprises an external thread. The rod  156  is dimensioned to extend through an elongate slot  158  in the beam  128 . As will be appreciated, the position of the fixed stop  126  relative to the beam  128  may be adjusted by sliding the rod  156  along the elongate slot  158  until at a desired position, or inserting the rod  156  into the elongate slot  158  at the desired position. 
     The fixed stop further comprises a series of holes  160  which extend into the end face  162  of the fixed stop  126 . The beam  128  comprises a series of through holes  164  which are arranged either side of the elongate slot  158 . In the example depicted the through holes  164  are equally spaced, however it will be appreciated that the through holes  164  may have any appropriate spacing. The depicted arrangement further comprises two dowels  166  which are dimensioned to pass through the through holes  164  and extend into the holes  160  on the fixed stop  126 . A dowel retention plate  168  is provided to hold the dowels  166  in position, and a threaded nut  170  is provided to engage the external thread on the rod  156 , and thereby hold the fixed stop  126  in a fixed position relative to the beam  128 . 
     Adjustment and fixing of the position of the fixed stop  126  will now be described with reference to  FIG. 11A  and  FIG. 11B . The rod  156 , on the fixed stop  126 , is first passed into the elongate slot  158 . The rod  156  may be inserted at the desired position, or alternatively the rod  156  may be inserted and may subsequently be moved within the elongate slot  158  into the desired position. Once in position, the dowels  166  may be inserted through the through holes  164  into the respective holes  160  in the fixed stop  126 . The holes  160  on the fixed stop  126  may be arranged in a spiral configuration. As will be appreciated, such an arrangement of holes  160  may allow for fine adjustment of the fixed stop  126  relative to the beam  128 . For example, the fixed stop  126  may be moved slightly within the elongate slot  158 , and rotated accordingly, until an appropriate hole  160  aligns with a suitable through hole  164 . 
     With the fixed stop  126  in the desired position, and the dowels  166  inserted through the through holes  164  and received by the respective holes  160 , the fixed stop  126  will be held in a fixed position relative to the beam  128 . In order to secure the fixed stop  126  in this position, the dowel retention plate  168  is placed onto the rod  156  and the threaded nut  170  is rotated onto the rod  156 , engaging with the external thread thereon, until the plate  168  is firmly held against the beam  128 . This fully assembled configuration is depicted in  FIG. 11B . 
     As discussed previously, as the fixed stop  126  may at least partially define the position of the doors when in their closed position, adjustment of the position of the fixed stop  126  may permit adjustment of the closed positions of the doors. Adjustment of the fixed stop  126  as a means for adjusting the closed position of the doors may provide a convenient means for adjusting the closed position of the doors. The adjustable fixed stop  126  described above with respect to  FIGS. 11A and 11B  may be employed in any of the examples described above. The adjustable fixed stop  126  illustrated and described is just one example of how adjustment of the fixed stop  126  may be achieved and it will be appreciated that any other suitable arrangement which allows for the position of the fixed stop  126  to be adjusted may be employed. 
     In the example described above, the door arrangement  2  comprises two doors  4 A,  4 B. However, it will be appreciated that this is just for explanatory purposes and the door arrangement  2  may comprise only a single door, or indeed a larger number of doors. The actuation arrangement  6  may be adapted to suitably control an appropriate number of doors. 
     It will be appreciated by those skilled in the art that examples of the present disclosure provide an improved door arrangement which resists external forces that act to try and open the door. While specific examples of the disclosure have been described in detail, it will be appreciated by those skilled in the art that the examples described in detail are not limiting on the scope of the disclosure.