Abstract:
A rudder system for an aircraft includes a center box, a rudder and actuators, wherein the rudder is pivoted around a hinge line relative to the center box. The actuators are arranged at an acute angle relative to the hinge line, and connected with at least one pivoted pivot lever, wherein the pivot lever is fastened to the rudder by way of a first push rod. This provides considerably more installation space in a vertical stabilizer of an aircraft for a center box, so that the latter can comprise a distinctly smaller wall thickness than usual in prior art to absorb air load-induced torsion and bending stresses.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of International Application No. PCT/EP2011/069163, filed Oct. 31, 2011, which claims priority from German Patent Application No. 10 2010 051 216.8 filed Nov. 12, 2010 and U.S. Provisional Patent Application No. 61/412,944 filed Nov. 12, 2010, the disclosures of which are hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates to a rudder system on an aircraft, an aircraft as well as the use of a pivot lever with an actuator movably arranged on the pivot lever for moving a rudder of an aircraft. 
     BACKGROUND OF THE INVENTION 
     A vertical stabilizer in prior art usually consists of a centre box, a nose edge that is arranged on the centre box and aligned in the flow, and a rudder that is arranged on the opposing side of the centre box and pivoted around a hinge axis. Given a deflection of the rudder, the vertical stabilizer is exposed to air loads independently of the rudder angle, which lead to a torsion moment and bending moment. In order to roughly determine these moments on the centre box, a pressure point is assumed for the centre box, at which all air loads converge to exert a point force. Based on this assumption, it becomes clear that the magnitudes of the torsion and bending moments depend on an aerodynamically predetermined sweep angle of the vertical stabilizer, since as the sweep angle grows, so too does the distance between the pressure point and a midpoint on a centre box surface directed toward the aircraft fuselage. In transonic aircraft, the sweep angle is especially pronounced, and very high torsion and bending moments may arise in particular in larger commercial aircraft with very large rudder areas, which have to be completely absorbed by the centre box from a mechanical standpoint. 
     The centre box is dimensioned subject to several boundary conditions, which encompass not only aerodynamic, but also mechanical and geometric limitations, resulting from the arrangement of rudder actuators in the vertical stabilizer. In particular given large rudders with a prescribed hinge axis, actuators arranged perpendicular to the hinge axis, and the necessary actuator size, this may place tangible limitations on the space available for a centre box. 
     US 2010/0096497 A1 depicts several variations of drive kinematics for rudders, which reveal claddings for rudder actuators that are effective in terms of structural mechanics, and may mechanically shift as the rudder moves. 
     In addition, EP 763 465 B1 and U.S. Pat. No. 6,206,329 B1 show a typical arrangement of three actuators, which together move a rudder pivoted around a hinge axis. 
     BRIEF SUMMARY OF THE INVENTION 
     In the usual configuration for the centre box of a vertical stabilizer, which has limited available space due to aerodynamic and mechanical boundary conditions, a rather small cross section necessitates the use of relatively thick sheet metal, so that these centre boxes may comprise a considerable weight. While the arrangement of a cladding active in terms of structural mechanics and able to follow a rudder motion could relieve the load on a centre box or other components in the vertical stabilizer, it is mechanically complicated, and thus production and cost-intensive, and when combined with the thicker design of the sheet metal in a cladding would not economize on weight in a major way. 
     Therefore, an aspect of the invention proposes a rudder system that permits as lightweight a centre box as possible, while simultaneously providing for a sufficiently high stiffness and stability, which preferably is at least on a par with those of a conventionally configured centre box. Such a rudder system preferably has a simple mechanical design, and in particular comprises the fewest possible additional components, which are also preferably immovable. 
     An aspect of the invention involves arranging the rudder-moving actuators at an acute angle relative to the hinge line, and not perpendicular to the hinge line, as is usually the case. This acute angle is preferably 0°, so that the actuators are arranged parallel to the hinge line. This is enabled by a pivot lever, which is attached to the rudder, pivoted to the centre box, and set up to redirect a force exerted by the actuators toward the rudder. As a consequence, the installation space required for the actuators is not excessively expanded by a component running perpendicular to the hinge line. Since vertical stabilizers usually comprise a relatively flat shape, clearly extending from one aircraft fuselage with a component running toward the vertical axis of the aircraft, the vertical, i.e., having a directional component parallel to the vertical axis of the aircraft, has enough space to accommodate an actuator arranged essentially perpendicular, upright and roughly parallel to the hinge axis. Given an unchanged position and alignment of the hinge line of the rudder, this actuator arrangement helps to again free up some of the space between the centre box and hinge line that is unusable in prior art, which may then be utilized according to an aspect of the invention for a larger geometric extension of the centre box along the longitudinal axis of the aircraft. In light of the clearly increased space available for a centre box, its wall thickness may be tangibly reduced, while maintaining a constant polar section modulus. 
     This finally results in a clear reduction in weight by comparison to the conventional centre boxes of vertical stabilizers known from prior art. 
     The components necessary for fabricating the rudder system according to an embodiment of the invention are very simple in nature, with only the pivot lever being incorporated into the rudder system as an additional, moving element. Since such pivot levers are mechanically mature and sufficiently reliable, practically no additional measures are needed to ensure the usual reliability of a rudder system. 
     The weight reduction effect may be estimated with the following calculation. For this purpose, we proceed from a simplified centre box having a rectangular profile with thin walls exposed to a bending and torsion load. The torsion stress essential to dimensioning may be calculated with 
                 τ   t     =       M   t       W   t         ,         
wherein M t  stands for the acting torsion moment, and W t  for the polar section modulus of the centre box. The simplification to a thin-walled rectangular profile makes it possible to calculate the polar section modulus W t  with the following equation:
 
                 W   t     =         2   ·     t   1       ⁢     t   2     ⁢     l   1   2     ⁢     l   2   2             l   1     ·     t   1       +       l   2     ·     t   2             ,         
wherein l 1  and l 2  are edge lengths of the rectangular profile, and t 1  and t 2  are the respective accompanying thickness of the walls with edge lengths l 1  and l 2 .
 
     If l 2  is increased by a factor f, and the accompanying thickness t 2  of the edge with edge length l 2  is simultaneously decreased by the same factor, and the cross sectional area is held constant, an enlarged section modulus is obtained: 
     
       
         
           
             
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     Conversely, t 1  and t 2  may also be reduced while keeping the section modulus W t  unchanged and reducing the torsion stress owing to the larger possible edge length l 1, new  achieved through the perpendicular arrangement of the actuators. This doubles the effect in terms of economizing on weight. 
     In an advantageous embodiment, the actuators extend parallel to the hinge axis, the spatial position of which depends on the sweep angle of the vertical stabilizer. The fact that the latter is usually greater than 0° provides an installation space for the actuators that extends in the form of the hypotenuse of a right-angled triangle over a greater distance than the adjacent side associated with the sweep angle in the form of the height of the vertical stabilizer. 
     In an advantageous embodiment of the invention, the pivot lever comprises two legs standing at an angle in relation to each other, as well as a pivot point arranged in the vertex, on which the pivot lever is mounted so that it may pivot relative to the centre box. Each end of the actuator is rotatably connected with a leg of the pivot lever, while the other leg is joined with a first push rod that is fastened to the rudder. This mechanical construction is very simple and reliable, the pivot lever-push rod combination making it resemble a relatively large rudder lever, and enables the reliable operation of the perpendicularly arranged actuator. Although the angle between the two legs may measure 90° in the simplest case, this is not necessary as long as the function according to the invention may also be satisfied with pivot levers having alternative leg angles. 
     In another, equally advantageous embodiment of the invention, each actuator is positioned so that it cannot rotate or pivot relative to the centre box, wherein the movable end of each actuator comprises a second push rod situated on the leg of the pivot lever facing the actuator. This makes it possible to achieve a balance between the linear motion of the actuator and rotational motion of the allocated leg of the pivot lever, reached by deflecting the thrust lever. As a result, the actuator may be mounted in a very reliable manner, with no swivel bearing exposed to a strong load being provided for an actuator, and the installation space required for the actuator receives a more compact configuration. 
     In an advantageous embodiment, the movable ends of two actuators are aligned toward each other, and engage a shared pivot lever. This makes it possible to economize on one pivot lever, so that the weight of the rudder system according to an embodiment of the invention may be reduced even further in comparison to prior art. 
     In an advantageous embodiment, the two movable ends of the actuators aligned toward each other engage the shared pivot lever by way of a second push rod. As a result, the two actuators aligned toward each other may also be immovably arranged inside the vertical stabilizer, thereby potentially economizing on space. 
     In another, equally advantageous embodiment, a first end of the actuator may be connected by means of a push rod to the structure of an aircraft to resemble a pendulum support, while its other end uses a pivot lever to move the end of a flange, which may be pivoted in the structure and is connected with the rudder. The end of the actuator mounted via a push rod is further joined by way of another push rod with a pivot lever, which may be rotatably mounted on the structure, and moves the other end of the flange. The rotational axis of the flange lies in a plane that runs at an angle to the plane in which the rotational axes of the pivot levers lie. The angle between these planes depends on the configuration of the vertical stabilizer, in particular its sweep angle, and preferably ranges from 60° to 90°. This arrangement makes it possible to economize significantly on installation space not just in the longitudinal direction, but also in the transverse direction. 
     Other embodiments of the invention include an aircraft equipped with such a rudder system, as well as actuators arranged parallel to a hinge line of a rudder for moving the rudders in combination with pivot levers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Additional features, advantages and possible applications of the present invention may be gleaned from the following description of the exemplary embodiments and figures. All described and/or graphically depicted features here constitute the subject matter of the invention, both separately and in any combination desired, even independently of their composition in the individual claims or back references thereto. The same reference numbers in the figures stand for the same or similar objects. 
         FIGS. 1   a  and  1   b  show a vertical stabilizer according to prior art. 
         FIGS. 2   a ,  2   b  and  2   c  show a rudder system according to an embodiment of the invention as contrasted with prior art. 
         FIG. 3  shows a detailed view of an actuator arrangement in a rudder system according to an embodiment of the invention. 
         FIG. 4  shows a variation of the rudder system according to an embodiment of the invention. 
         FIG. 5  shows another variation of the rudder system according to an embodiment of the invention. 
         FIG. 6  shows another variation of the rudder system according to an embodiment of the invention. 
         FIG. 7  shows a detailed view of another variation of the rudder system according to an embodiment of the invention. 
         FIGS. 8   a  and  8   b  show another variation of the rudder system according to an embodiment of the invention. 
         FIG. 9  shows an aircraft that comprises a rudder system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1   a  and  1   b  show a vertical stabilizer arrangement  2  according to prior art, with a nose edge  4 , a centre box  6  and a rudder  8 , which is mounted on a spar  12  of the centre box  8  so that it may pivot around a hinge line  10 . The rudder  8  is deflected using several actuators  14 , which are essentially arranged perpendicular to the hinge line  10 . By moving the axis of the actuators  14  in and out, an eye of the rudder  8  may be pulled or pushed, thereby pivoting the rudder  8  around the rudder hinge line  10 . 
     With the rudder  8  deployed, air loads arise that may be viewed as concentrated in an imagined pressure point  16  within the centre box  6 . The distance marked “a” from a midpoint  18  to an area  22  of the centre box  6  directed toward an aircraft fuselage  20  to the pressure point  16  determines the torsion moment on the centre box  6 . If this centre box  6  is designed as a thin-walled hollow body with a rectangular cross sectional area, its area moment of inertia or section modulus must be dimensioned in such a way that the torsion stresses in the centre box  6  do not exceed a permissible value. 
     As evident from  FIG. 1   b , an area  24  of the vertical stabilizer  2  prescribed by the arrangement of the actuator  14  is for the most part practically unused space, which is not utilized for accommodating air loads. As a consequence, the centre box  6  shown on  FIGS. 1   a  and  1   b  comprises a relatively pronounced wall thickness, so that it may provide a sufficient polar section modulus given the available cross sectional area. 
       FIGS. 2   a ,  2   b  and  2   c  contrast a rudder system  21  according to an embodiment of the invention and a rudder system  2  according to prior art. As may be gleaned from  FIG. 2   a , the actuator  14  according to the invention is arranged parallel to the rudder hinge line  10  configured as prescribed by the flight mechanics, and diverts the movement of the actuator  14  by way of a pivot lever  26  mounted on a hinge point  28  so that it may move relative to the centre box  30 , so that the rudder  8  may execute a desired rudder motion. Since the actuator  14  depicted on  FIG. 2   a  is parallel to the hinge line  10 , virtually none of the previously unused installation space in front of the hinge line  10  in the vertical stabilizer  32  is occupied, so that the centre box  30  may extend considerably more in the direction of the hinge line than the centre box  6  from  FIGS. 1   a  and  1   b . This is made evident by the direct comparison on  FIG. 2   b  and  FIG. 2   c , in which the leading edge strip and respective front end of the centre box  6  and  30  of a rudder from prior art and the invention align with each other. 
     In addition to the size of the centre box  30 ,  FIG. 2   a  also reveals that the distance between the midpoint  19  of an area  36  directed toward the aircraft fuselage  20  and a pressure point  17  for the arising air loads on the centre box  30  is smaller than the distance between the midpoint  18  and pressure point  16  of the centre box  6  from  FIG. 2   a . At a constant section modulus, this makes it possible to considerably diminish the wall thickness of the centre box  30 , so that a centre box  30  at the same section modulus may comprise a lower weight than the centre box  6  from  FIGS. 1   a  and  1   b.    
       FIG. 3  shows a section of the rudder system  21  according to an embodiment of the invention, in which the actuator  14  comprises a bearing point  38  that is mounted on a flange  40  connected with the centre box  30 . The pivot lever  26  is arranged at an end  42  lying opposite the bearing point  38 , and its bearing point  28  is also pivoted to the flange  40 . A rudder brace  44  on the rudder  8  is hinged with the pivot lever  26 , so that the rudder  8  swivels around the hinge line  10  when the actuator  14  is deflected  14  in a direction parallel to the rudder hinge line  10 . 
       FIG. 4  shows a possible further development involving the use of two or more groups each having two actuators  14 , which engage shared pivot levers  26 , wherein the two actuators  14  of one group are mirror inverted relative to each other. The use of two actuators  14  on one pivot lever  26  could make it possible to give the actuators a smaller piston cross section than a single actuator  14 . In addition, should one actuator  14  in a group of two actuators  14  be defective, the other, still intact actuator  14  could at least partially compensate for any misalignment, jamming, or the like. Within the framework of the usual configuration of flight control systems, it also makes sense to hook up at least two of the depicted actuators  14  to different hydraulic systems, so that one of the actuators  14  remains functional given a failure of a hydraulic system. Similarly to the above, this may also be achieved with the individual groups of actuators  14 , so that the groups of actuators  14  are interconnected with different hydraulic systems. 
       FIG. 5  shows an actuator  48  that engages the pivot lever  26  by way of a second push rod  50 . The advantage to the above is that the actuator  48  need not be suspended on a single bearing point, but rather may be completely rigidly and immovably mounted relative to the centre box  30 . The second push rod  50  may bring about a balance between the exclusively linear movement of the end  42  of the actuator  48  and the accompanying rotating end of the pivot lever  26 . 
     As shown on  FIG. 6 , this may also be performed with an arrangement from  FIG. 4  with two actuators  14  from a group of actuators  14  that are aligned toward each other, and each act on a shared pivot lever  26  by way of a second push rod  50 . 
     The spatial, simplified depiction on  FIG. 7  reveals another solution to shorten the lever arm necessary for moving the rudder  8 . An actuator  14  is pivoted to a hinge  54 , and presses on another hinge  52 , to which are secured two push rods  56  and  58 , which in turn are joined with a bearing point  60  and hinge  62 . A pivot lever  64  is pivoted around a fixed bearing by way of a hinge  66  and hinge  62 , and uses another push rod  68  and hinge  70  to move one end of a flange  72 , which imparts its rotation to a rudder (not shown). The actuator  14  uses the hinge  54  to actuate a second pivot lever  73 , which moves the other end of the flange  72  by way of a hinge  75 , another push rod  76  and an additional hinge  77 . As evident from  FIG. 7 , the pivot levers  64  and  73  are movably mounted on a structure of the aircraft, like the flange  72 . The actuator  14  and flange  72  lie in two planes situated at an angle to each other, for example offset by 90° to each other. The kinematic chain of this arrangement may reduce the space required in both the transverse and longitudinal direction within the structure of a vertical stabilizer. 
       FIGS. 8   a  and  8   b  show an additional variant in which a shaft  78  joined with the rudder extends into the aircraft fuselage, to there be driven by actuators  14  with pivot levers  80 . As a result, nearly no installation space in the vertical stabilizer is occupied, so that its centre box  16  may be given especially large dimensions, and may comprise a very small sheet thickness, and hence a low weight, at a constant polar section modulus. 
     A combination comprised of a shaft  78  and a hollow shaft enveloping this shaft  78  could lend itself to driving a two-part rudder, separately moving the individual rudder segments. 
     Finally,  FIG. 9  shows an aircraft comprising a vertical stabilizer  52  with a rudder  8  that is pivoted around a hinge line  10  and comprises several actuators  14 , which are aligned at an acute angle to the hinge line, and in particular parallel thereto. 
     Let it be noted in addition that “comprising” does not preclude any other elements or steps, and “a” or “an” do not rule out a plurality. Let it further be noted that features described with reference to one of the above exemplary embodiments may also be used in combination with other features from other exemplary embodiments described above. Reference numbers in the claims are not to be construed as a limitation.