Abstract:
A high lift system for an aircraft comprises a wing structure and a leading edge slat movably supported relative to a leading edge of the wing structure, the leading edge slat comprises a leading edge and a trailing edge, wherein the trailing edge is configured to take different positions to form a gap between the leading edge slat and the wing structure, a skin and enclosing an interior space of the leading edge slat, the skin having a flexible leading skin section facing away from the wing structure, a flexible trailing skin section facing towards the wing structure, at least one actuation arrangement arranged inside the interior space for selectively introducing a normal force onto at least one of the leading skin section and the trailing skin section.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to European Patent Application No. 14153177.8, filed 29 Jan. 2015, the disclosure of which application is herewith incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     This application pertains to a high lift system for an aircraft comprising a wing structure and a leading edge slat as well as an aircraft having a wing and such a high lift system. 
     BACKGROUND 
     Commercial aircraft for passenger transport usually comprise high-lift systems, which are able to drastically increase the lift of the respective aircraft, such that relatively low flight velocities are necessary during start and landing phases. However, high lift systems usually comprise one or more flow bodies that can be extended relative to a wing structure in order to increase the camber and active surface of the wing, but may also lead to an increased noise. 
     For meeting more and more stringent noise constraints, it is a constant desire to optimize the aero-acoustic profile of an aircraft. This is especially the case for congested air spaces in Europe and the United States of America, where a lower noise profile may be an enabler for early and late time slots, respectively, for landing and take-off. This may be realized inter alia by an active gap control for leading edge slats, which are able to adjust the gap size between a trailing edge of a leading edge slat and a wing structure, relative to which the leading edge slat is movably supported. 
     U.S. Pat. No. 8,383,044 shows a rotatable/tiltable trailing edge of a slat. 
     WO 2008/084260 A1 and WO2009/150446 A1 disclose a kinematic solution for an independent slat edge actuation. 
     In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     SUMMARY 
     A high lift system for an aircraft is provided, which allows an active gap control tier a leading edge slat, which is able to improve the noise reduction and the aerodynamic quality at the same time. 
     A high lift system for an aircraft is proposed comprising a wing structure and a leading edge slat movably supported relative to a leading edge of the wing structure. 
     According to an advantageous embodiment, a high lift system for an aircraft, comprises a wing structure and a leading edge slat movably supported relative to a leading edge of the wing structure, the leading edge slat comprising a leading edge and a trailing edge, wherein the trailing edge is configured to take different positions to form a gap between the leading edge slat and the wing structure, a skin enclosing an interior space of the slat, the skin having a flexible leading skin section facing away from the wing structure, a flexible trailing skin section facing towards the wing structure, and at least one actuation arrangement arranged inside the interior space tier selectively introducing a normal three onto at least one of the leading skin section and the trailing skin section, wherein the normal force changes the profile of the skin (and by this the whole shape of the slat) in such a way that the trailing edge changes its position relative to the wing structure to selectively close or open the gap between the leading edge slat and the wing structure. 
     A leading edge slat is a flow body or an aerodynamic surface situated on the leading edge of a wing structure which, when deployed, allows the wing to operate at a higher angle of attack. The deployment is conducted through extending the slat into a region upstream of a leading edge of the wing. In the context of this embodiment, the leading edge slat also creates a gap between a trailing edge of the slat and the wing structure for allowing air to pass through the gap for entering an upper surface of the wing in order to delay the stall point during high angles of attack. A leading edge of the slat is a region of the slat surface that directly faces into the flow that impinges on the slat. The trailing edge is a region in which the leading skin section and the trailing skin section run out and is a flat or wedge shaped section. 
     The slat comprises a flexible skin with a closed surface, which means that there are no prominent gaps in the surface, which may hinder the transfer of constraining forces. The skin encloses an interior space of the slat completely, which houses the actuation arrangement. 
     A core aspect of the embodiment is based on the actuation arrangement, which allows the introduction of a normal force onto at least one of the leading skin section and the trailing skin section, which means that a mechanical force is applied, which force comprises a force vector, that does not lie in a local extensional plane of the respective skin section, into which the force is introduced, but normal thereto, In distinction to the prior art, the embodiment proposes a mechanical actuation concept to achieve an active gap control through structural morphing of a slat body. 
     The flexible skin has a neutral profile shape, which is a predefined profile shape that is assumed by the slat in a completely unloaded or unaffected situation, i.e. when no load is introduced. 
     The high lift system according to the embodiment resultantly makes use of a morphing structure of the slat, leading to an adjustable profile shape of the slat depending on the normal force introduced by the actuation arrangement. Due to the closed surface of the skin and the resultant transfer of constraining forces, the slat does not provide a bulging motion, but leads to a change of camber leading to trailing edge being moved relative to the wing structure. 
     Consequently, no external elements are necessary for adjusting the gap between the trailing edge of the slat and the wing structure and the gap control does not lead to discontinuous aerodynamic characteristics. 
     In an advantageous embodiment, the at least one actuation arrangement is configured for introducing the normal force in a region distant from the trailing edge, such that due to the change in the profile, pulling forces act onto the trailing edge through the skin. The actuation arrangement may therefore be positioned in a region in which the largest installation space, i.e. possible installation height, is available. By transferring putting forces through the skin, the trailing edge may be moved despite the clear distance between the force introduction and the trailing edge. 
     In an advantageous embodiment, the actuation arrangement is configured for bending at least one of the leading skin section and the trailing skin section towards the interior space when the normal force is introduced. For example, the actuation arrangement may be supported in structural parts of the slat that allow bending of only one of the trailing skin section and the leading skin section, but may also allow bending of both surfaces. As commonly the leading skin section comprises a larger running length from the leading edge to the trailing edge than the trailing skin section, a change of the profile shape directly occurs when one of the leading skin section and the trailing skin section is bent, due to the transfer of constraining forces, i.e. pulling forces. 
     As a further embodiment, the actuation arrangement may be configured for bending the trailing skin section towards the leading skin section and the trailing edge of the skin is urged towards the leading edge of the wing structure upon bending the trailing skin section. By this measure, both skin sections are bent towards the interior space depending on their mechanical properties. 
     In an advantageous embodiment, the actuation arrangement comprises a release means, which is configured for abruptly releasing the normal force introduced by the actuation arrangement. Such a quick-release feature results in letting the slat revert to the neutral profile shape due to the deformation energy stored within the slat structure through its elastic deformation. For example, a formally closed or narrowed slot between the trailing edge of the slat and the fixed wing structure will be opened rapidly. This allows injecting additional mass flow into the flow boundary layer on the wing&#39;s upper side needed to avoid or recover an aerodynamic stall. For example, mechanical elements in the actuation arrangement may be disengaged to realize the release means, such as a clutch located between a motor and a driven element, such as a spindle, or alternatively a brake or a mechanical coupling between force introducing levers and a driving element may be used. 
     In a preferred embodiment, the actuation arrangement comprises a rotary actuator, which is coupled with a lever, pivotably attached to a joint on the inside of at least one of the trailing skin section and the leading skin section. The actuation arrangement may be supported in an interior structure of the slat. The rotary actuator is to be considered a device that provides a rotation about a rotational axis. For example, the rotary actuator may comprise a lever or a bracket having a borehole at a distance to the rotational axis, which is rotated around the rotational axis when the rotary actuator is operated. By simply pivotably coupling a lever with this borehole, the joint on the trailing skin section can be pulled towards the rotary actuator or pushed away. The main advantage of such a rotary actuator lies in a space effective design, which does not require a large installation space between the leading skin section and the trailing skin section, as the rotary actuator does not conduct a linear extension. Furthermore, the transferable torque may easily be adjusted to the expected force, by the integration of gearboxes or by adjusting the torque arm, respectively. 
     Preferably, the rotary actuator comprises a motor, a clutch and a gearbox, wherein the gearbox is selectively couplable to the motor through the clutch. The gearbox may, as mentioned above, be coupled with at least one lever pivotably, which may be coupled with one of the leading skin section and the trailing skin section. All components of the rotary actuator may be coupled through a transmission shaft, which may extend along a nose region of the slat. The gearbox may be realized as a planetary gear, which is rather compact and allows a high reduction of rotational speed and a clear increase of transferable torque. Also, the gearbox may be of a power hinge type having an output ring gear, to which at least one of the trailing skin section and the leading skin section of the slat is coupled through a rod or a different appropriate means. The motor may be hydraulically or electrically driven. Providing a clutch between the motor and the gearbox allows a rapid release of the applied force, in order to revert the profile shape of the slat to its neutral profile shape, i.e. the clutch may resemble the release means mentioned above. 
     As gear type also a continuously variable transmission gear may be utilised. With an increase of morphing the required torque increases as well. With a continuously transmission gear it is possible to drive the motor during morphing in the same operating point or the migration of the operating point on the torque-revolution characteristic diagram may be determined. A release of the profile shape of the slat to its neutral profile shape may be accomplished through rotation the rotary actuator backwards or through unpowering the rotary actuator, which should then not be of a self-locking type. The brake then supports maintaining a certain adjusted profile shape. 
     In a still further advantageous embodiment, a brake is coupled with the motor and the gearbox for selectively arresting the gearbox such that a profile shape is maintainable without the clutch coupling the motor and the gearbox, i.e. in a certain desired position with a certain morphing state of the slat body. Furthermore, the shaft brake may be configured such that it is released only when the motor is operated or in case the clutch is released. If the clutch is placed between brake and gear, for a rapid return of the profile to its original position, the brake may stay in its closed position. 
     Still further, the rotary actuator may comprise a motor, a brake and a gearbox, wherein the gearbox is permanently coupled with the motor, e.g. through a shaft. The gearbox may also be coupled with a lever and may be designed according to all of the above-mentioned features. Further, all components may be coupled through a transmission shaft, which may extend along a nose region of the slat. In this embodiment, release of the profile shape to a neutral profile shape is accomplished through rotating the rotary actuator backwards or, if the rotary actuator is not self-locking, through opening the brake and unpowering the motor. In the latter case, use of the brake is recommended for maintaining an adjusted profile shape and the brake may resemble the release means. 
     In a still further advantageous embodiment, the rotary actuator comprises a pair of bevel gears, couplable with a spindle screw, which engages with a screw nut couplable with a coupling element, e.g. a rod, lever or any other appropriate means, for coupling with at least one of the trailing skin section and the leading skin section of the slat. The main extension of the gear may follow the main extension of the motor and a rather high torque may be transferred by the bevel gear pair and an additional increase of transferable torque may be accomplished through the spindle. In this regard, the spindle screw should be designed in such a way that it is not self-locking. This allows to quickly release the introduced force without having to decouple the spindle from the gear, such that the shape reversion is conducted through rotation of the spindle automatically. 
     Especially for a self-locking spindle a cylindrical or friction ring clutch may be provided between screw nut and the coupling element coupled thereto, wherein the friction ring clutch may be engaged or disengaged, i.e. coupling the screw nut with the levers or uncoupling them. This leads to an abrupt return of the profile shape to its neutral shape. After conducting such a rapid return or release, the spindle screw may drive the screw nut to its start position, where it may be coupled with the levers again, as at the start position the screw nut and the inner ring of the clutch meet the outer part of the friction ring clutch to engage again. In such an embodiment the brake does not need to be released for rapidly opening of the gap between wing and slat and the friction ring clutch resembles the release means. 
     In a preferred embodiment, a plurality of actuation arrangements are located inside the slat. For example, this may be achieved through a multiplication of actuation arrangements, which may also include the use of a plurality of rotary actuators/motors for driving the components of the actuation arrangement. 
     Still further, the actuation arrangement may also be configured for introducing a normal force onto both of the leading skin section and the trailing skin section at the same time, such that their distance is decreased upon introducing the normal force. Through such an arrangement, the direction of the introduced force may be better adjusted and the compression effect is improved. 
     In a still further embodiment, a plurality of actuation arrangements is driven by a single shaft, which is extending along a nose region of the slat. A plurality of rather small actuation arrangements may be distributed along the nose region of the slat for introducing rather small individual compression forces, which increases the reliability and improves the stress distribution along the skin of the slat. 
     It goes without saying, that such an arrangement may also comprise brakes and clutches for being able to rapidly release the change in profile shape. 
     Further, if multiple spindle screw nuts are used, the flank angles of the spindle screws coupled therewith may differ, i.e. for providing different motion speeds for the individual spindle screw nuts, which leads to different normal forces onto the leading skin section and the trailing skin section at the same spanwise location or in a variable manner along the spanwise extension. This may allow different morphing requirements along the extension of the slat. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present embodiment will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: All the described and/or illustrated characteristics per se and in any combination form the subject of the embodiment, even irrespective of their composition in the individual claims or their interrelationships. Furthermore, identical or similar components in the figures have the same reference characters. 
         FIG. 1  illustrates a high lift system in a sectional view; 
         FIGS. 2 a  and 2 b    illustrate an actuation arrangement with and without a brake; 
         FIGS. 3 a  and 3 b    illustrate another actuation arrangement with and without clutches; 
         FIGS. 4 a  and 4 b    illustrate a still further actuation arrangement with and without clutches; 
         FIGS. 5 a  and 5 b    show another still further actuation arrangement with and without an integrated clutch; and 
         FIGS. 6 a  and 6 b    show another actuation arrangement with and without an integrated clutch. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature is not intended to limit the embodiment or the application and uses of the embodiment. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the embodiment or the following detailed description. 
       FIG. 1  shows a first exemplary embodiment of the high lift system  2  having a wing structure  4 , a leading edge slat  6  movably arranged relative to the wing structure  4 , wherein the slat comprises a flexible skin  8  having a leading skin section  10  and a trailing skin section  12 , which both extend from a leading edge  14  to a trailing edge  16 . Inside an interior space  18  of slat  6 , an actuation arrangement  20  is located, which comprises a rotary actuator  22  coupled with a lever  24  and a force introduction joint  26  on the interior side of the trailing skin section  12 . 
     The rotary actuator  22  comprises an axis of rotation  28 , about which a borehole  30  is rotated, to which the lever  24  is coupled in a pivotable manner. Hence, when the rotary actuator  22  in a clockwise direction, the borehole  30  pulls the lever  24  and, resultantly, the force introduction joint  26 . Hereby, the trailing skin section  12  is bent towards the interior space  18 , which leads to a deformation of the profile shape of slat  6 . 
     Due to the closed surface of skin  8 , constraining forces, i.e. pulling forces are transferred into the leading skin section  10 , altogether leading to a motion of the trailing edge  16  towards the wing structure  4 . Hence, by applying a normal force, i.e. a force that at least in part acts perpendicularly, onto the trailing skin section  12 , a gap between the slat  2  and the wing structure  4  can be controlled. 
       FIG. 2 a    shows an exemplary embodiment of the actuation arrangement  20 , comprising a motor  32 , which is coupled to a shaft  34 , extending at least through a clutch  36 , a gearbox  38  and a shaft brake  40 . The gearbox  38  provides a reduction of rotational speed and an increase in transferable torque and is coupled with the lever  24 , such that rotating the motor  32  leads to an introduction of normal force when the clutch  36  is engaged. By releasing the clutch  36  and the brake  40 , the profile shape reverts to is neutral shape. 
     It is preferred that the shaft brake  40  is only released, when motor  32  is operated. Furthermore, during the introduction of normal force into the force introduction joint  26 , deformation energy is built up, which may be released by simply releasing/disengaging the clutch  36 . 
     For example, in case of an aerodynamic stall, clutch  36  and brake  40  are opened by a control unit, which is not shown in  FIG. 1 or 2   a . Consequently, the deformation energy stored within the slat  6  through its elastic deformation reverts the slat  6  rapidly back to its neutral profile shape, yielding to opening the narrowed gap between the trailing edge  16  of the slat  6  and the wing structure  4  rapidly. Consequently, additional mass flow is injected into the flow boundary layer on the wings&#39; upper side needed to avoid or recover an aerodynamic stall. 
     Furthermore, the mentioned control unit or an additional control unit may be installed, which is coupled with a set of sensors to monitor the gap between the trailing edge  16  and the wing structure  4  through establishing a closed loop between the rotary actuator  20  and the deformation of slat  6 . In addition, it monitors for mechanical or electrical failures and may apply respective countermeasures. 
     However, as shown in  FIG. 2 b   , the actuation arrangement  20  may be modified to an actuation arrangement  21 , which does not comprise a brake  40 . Consequently, for rapidly releasing the actuation arrangement  21  only the clutch  36  needs to be opened. 
       FIG. 3 a    shows another exemplary embodiment with a slightly changed actuation arrangement  20  in form of an actuation arrangement  41 . Here, exemplarily two individual motors  42  are shown, which each are coupled to a transmission shaft  44 , which extends through a clutch  36 , a gear  46  and a brake  48  reaching a pair  50  of bevel gears  52  and  54 , for the purpose of changing the rotational axis about 90°, i.e. from a direction along a nose region or the leading edge  14  of the slat  6  to a direction vertical thereto. The pair of bevel gears  50  comprises a first bevel gear  52  and a second bevel gear  54 , wherein the second bevel gear  54  is coupled with a spindle  56 , which is preferably realized as a ball screw spindle. A screw nut  58  is engaging the spindle  56  and is further coupled to levers  60 , which in turn are pivotably coupled with a load introduction joint  26  or any other load introduction joint at the trailing skin section  12 . 
     Both actuation arrangements  41  individually deform a part of the slat  6 . It cannot be excluded that the slat  6  comprises even more actuation arrangements  41 . 
     Again, this exemplary embodiment may further be modified by removing the clutches  36 , which is shown in  FIG. 3 b    as an actuation arrangement  61 . Instead of clutch  36  cylindrical or friction ring clutch  37  may be placed between the screw nut  58  and the lever  60 . The inner part  38  of the friction ring clutch  37  is connected to the screw nut  58 , while the outer part  39  is connected to the levers  60 . The friction ring clutch  37  is to be understood as a device, which is able to provide a mechanical, force-transferring and releasable connection between the screw nut  58  and the levers  60 . If the friction ring clutch  37  is released, the levers  60  will not maintain their position adjusted by the screw nut  58  and will follow the trailing edge  16 , which will move as the profile shape reverts to the neutral shape. This is especially advantageous when the ball screw  56  is self-locking. After releasing the friction ring clutch  37  with the profile shape differing from the neutral shape, there may be a gap between the screw nut  58  and the outer part  39  of the friction ring clutch  37 . This gap may be eliminated by moving the screw nut  58  to the position of the outer part  39  of the friction ring clutch  37 , where the friction ring clutch  38  and  39  may be engaged again. 
     In a still further exemplary embodiment shown in  FIG. 4 a   , actuation arrangements  62  are shown, which act on the trailing skin section  12  and the leading skin section  10  at the same time. The actuation arrangement  62  may be a similar arrangement as shown in  FIGS. 3 a  and 3 b    with a motor  42 , a transmission shaft  44 , a clutch  36 , a gearbox  46 , a brake  48  and a pair of bevel gears  50  with a first bevel gear  52  and a second bevel gear  54 . However, a spindle  64  extends through the second bevel gear  54 , such that two screw nuts  58  may engage a single spindle  64 , which may comprise two opposed flank angles on two halves of the spindle  64  for allowing expansion and compression through both screw nuts  58 . It goes without saying that the flank angles of the two halves of the spindles  64  may differ in their absolute values, such that the trailing edge and the leading edge may be acted upon differently. 
       FIG. 4 b    shows modified actuation arrangements  63 , which are realized without the clutches  36 , but instead comprise cylindrical or friction ring clutches  37  between the screw nuts  58  and the levers  60 , as explained above referring to  FIG. 3 b   . It goes without saying that the friction ring clutches  37  may be used only for the trailing edge, only for the leading edge or for both of trailing edge and leading edge. Again, the flank angles of the two halves of the spindles  64  may differ in their absolute values, such that the trailing edge and the leading edge may be acted upon differently. 
     In  FIG. 5 a   , the actuation arrangements  41  of  FIG. 3 a    are still further modified in form of actuation arrangements  66  are provided, which instead of a single shaft  44  for each pair of bevel gears  50 , a single transmission shaft  68  for both or even more pairs of bevel gears  50  is used. This allows a synchronous rotation of all bevel gears. 
     In  FIG. 5 b   , actuation arrangements  67  are provided, which differ from the actuation arrangements  66  of  FIG. 5 a    in that the clutch  36  is removed. Again, they comprise a cylindrical or friction ring clutch  37  between the screw nut  58  and the lever  60 , as explained above. 
     Still further, in  FIG. 6 a   , the same modification is applied to the actuation arrangements  62  of  FIG. 4 a    to form an actuation arrangement  69 . This means, that a transmission shaft  70  extends through multiple pairs of bevel gears  50 , which in turn rotate individual spindle screws  56  couplable with the trailing edge and the leading edge. As explained regarding  FIG. 4 a    it is possible that the flank angles of the spindle screws  56  coupled with the trailing edge may differ from the flank angles of the spindle screws  56  coupled with the leading edge in their absolute values, such that the trailing edge and the leading edge may be acted upon differently. 
     Finally, in  FIG. 6 b   , actuation arrangements  71  are shown, which differ from the actuation arrangements  69  in  FIG. 6 a    in the lack of the clutch  36  and in the presence of a friction ring clutch  37 . Again, the friction ring clutches  37  may be used only for the trailing edge, only for the leading edge or for both of trailing edge and leading edge. Also, the flank angles of the spindle screws  56  coupled with the trailing edge may differ from the flank angles of the spindle screws  56  coupled with the leading edge in their absolute values, such that the trailing edge and the leading edge may be acted upon differently. 
     Regarding the actuation arrangements in all of the  FIGS. 2 a , 3 a , 4 a , 5 a  and 6 a    any of the (six) possible chains of clutch, brake and gearbox may be realized. However, if the gearbox is not the last element in the chain in view of the torque flow, the lever  24  may preferably be coupled to the respective shaft by means of a crank. As another alternative, the respective shaft may be designed as a crank shaft. 
     Regarding the actuation arrangements in all of the  FIGS. 2 b , 3 b , 4 b , 5 b  and 6 b    any of the two possible chains of brake and gearbox may be realized. 
     Finally, if in  FIGS. 3 a  to 6 b    self-locking spindle screws are used, the brake may be removed. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the embodiment in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the embodiment as set forth in the appended claims and their legal equivalents.