Abstract:
The invention pertains to a connecting device for connecting a first structural component and a second structural component that can be moved relative to the first structural component in an articulated fashion such that three rotatory degrees of freedom are provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT/EP2011/000442 filed Feb. 1, 2011 which claims the benefit of and priority to U.S. Provisional Application No. 61/300,091, filed Feb. 1, 2010 and German Patent Application No. 10 2010 006 447.5, filed Feb. 1, 2010 the entire disclosures of which are herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates to a connecting device for connecting a first structural component and a second structural component that can be moved relative to the first structural component in an articulated fashion such that three rotational degrees of freedom are provided. Further, invention relates to a flap system and aircraft having such a connecting device. 
     BACKGROUND 
     For example, regulating flaps of an aircraft are connected to a main wing by means of an actuator, wherein the actuator serves for moving the regulating flap relative to the main wing. In known systems, a connection with a pivot bearing is normally used as connecting device between such an actuator on the one hand and a regulating flap on the other hand. However, their rotational degrees of freedom are very limited, particularly to permissible pivoting angles of no more than 16°. Some special designs make it possible to achieve slightly larger pivoting angles, but only with a high constructive effort. This constructive effort not only increases the required space, but also the weight of the connecting device. Bolt bearings may also be used as connecting devices. In this case, it is common practice to provide bolts that extend through bearing bores in both structural components, i.e., in the actuator as well as in the regulating flap. These bolts make it possible to realize a rotative movement of the two structural components relative to one another about the rotational axis of the bolt. However, the disadvantage of such an arrangement can be seen in that only a single degree of freedom of the relative movement can be realized. 
     It is the objective of the present invention to eliminate the disadvantages of known connecting devices and, in particular, to provide a connecting device that makes it possible to realize three rotative degrees of freedom, as well as the corresponding failure safety. 
     The aforementioned objective is attained with the features of the independents claims. Further embodiments are defined in the subclaims referred thereto. 
     SUMMARY 
     With a connecting device according to the invention, loads are transmitted with allowing three rotational degrees of freedom and with a high reliability. If the connecting device is used for connecting structural components of a high-lift system of an aircraft, this concerns, for example, the transmission of the aerodynamic loads created by the air acting upon the regulating flaps. The load transmission according to the invention is in particular fail-safe in many applications, primarily in the field of aviation. This means that the failure of a supporting part due to a defect is avoided. 
     According to the invention, a connecting device is provided for connecting a first structural component and a second structural component that can be moved relative to the first structural component in an articulated manner such that three rotational degrees of freedom are provided, the connecting device featuring: 
     a joint head joint part with a joint head for being accommodated by a receiver of the first structural component and a joint head support with a joint head endpiece for the mounting thereof on the second structural component such that a first load path between the two structural components is formed due to the accommodation of the joint head in the receiver, with the joint head joint part featuring a cavity with an inner cavity surface, wherein the cavity extends through the joint head and the joint head support,
         a securing arm with a securing arm endpiece for the mounting thereof on the second structural component, with said securing arm extending into the cavity of the joint head joint part,
 
wherein the securing arm respectively is sectionally extending along an inner cavity surface of the joint head support such that the securing arm makes available a second load path between the first and the second structural component in case of a mechanical defect that involves a weakening of the joint head joint part and an accommodation of a section of the securing arm by the inner cavity surface of the joint head support.
       

     An inventive connecting device for connecting a first structural component and a second structural component that can be moved relative to the first structural component such that three rotatory degrees of freedom are provided. In particular, it features a joint head joint part with a joint head that is accommodated in a receiver like a bearing shell or a retainer being accommodated by or fixed to the first structural component and a joint head support with a joint part endpiece or joint head endpiece for the mounting thereof on the second structural component such that a first load path between the two structural components is formed due to the accommodation of the joint head in the receiver. In this case, the joint head joint part features a cavity that extends through the joint head and the joint head support. In addition, a securing arm with a securing arm endpiece for the mounting thereof on the second structural component is provided and extends in the cavity of the joint head joint part. The securing arm respectively can be sectionally positioned adjacent to an inner cavity surface of the joint head support and an inner cavity surface of the joint head such that the support arm provides a second load path between the first and the second structural component in case of a mechanical defect that involves weakening of the joint head joint part. 
     According to an embodiment of the invention, the securing arm respectively is sectionally extending adjacent to an inner cavity surface of the joint head support such that the securing arm makes available a second load path between the first and the second structural component in case of a mechanical defect that involves a weakening or rupture of the joint head joint part and an accommodation of a section of the securing arm by the inner cavity surface of the joint head support. 
     According to an embodiment of the invention, the securing arm is sectionally extending adjacent to an inner cavity surface of the joint head support such that the securing arm makes available a second load path between the first and the second structural component in case of a mechanical defect that involves a weakening of the joint head joint part and an accommodation of a section of the securing arm by the inner cavity surface of the joint head support. In particular, the cavity is formed such that it enlarges behind the joint head support when seen from the securing arm endpiece. 
     In the present invention, one essentially distinguishes between two operating modes of the connecting device. The first mode is the “normal mode,” in which the joint head joint part is intact with respect to its supporting and load transmitting functions. The other mode is the “defect mode,” in which a mechanical defect has occurred that involves weakening of the joint head joint part. Such a defect may consist, for example, of a fracture of the joint head joint part or of a material weakening caused by temperature effects or mechanical influences such as stoning. Due to the mechanical defect in the joint head joint part, the load transmission for supporting the load in the joint head joint part is impeded or even interrupted. Such a defect therefore would lead to the failure of the connecting device which, in the worst-case scenario, would correspond to the two connected structural components breaking up. 
     Due to the inventive connecting device, the aforementioned disadvantages of the state of the art are eliminated and, in particular, a failure safety with respect to the connecting function in the defect mode is realized. A bearing connection consisting of a receiver and a joint head joint part makes it possible to achieve the load transmission for supporting the loads on the one hand and the rotatability with three degrees of freedom on the other hand. This simple and, in particular, compact design is combined with the advantage that the securing arm provides a second load path that only transmits part of the load in case of a defect in the joint head joint part. In this case, the securing arm is not subjected to a load in the normal mode, but rather situated in the interior of the joint head joint part in a load-free fashion. Such a second, securing load path is also referred to as a dormant load path. In this context, it needs to be noted that no load is respectively transmitted between the securing arm and the inner cavity surface of the joint head support and the inner cavity surface of the joint head that are sectionally situated adjacent thereto in the normal mode, but rather only in the defect mode. It furthermore needs to be noted that deformations of the joint head joint part in the elastic range may also occur in the normal mode without activating the second load path. In other words, the securing arm also remains load-free during such elastic deformations of the joint head joint part. The advantage of this embodiment can be seen in that the securing arm is not subjected to any loads in the normal mode and therefore also not subjected to any wear caused by loads. Consequently, the securing arm is, in a manner of speaking, essentially unused at the time it is needed, i.e., in case of a defect. 
     The scope of the present invention also includes embodiments, in which the securing arm transmits a load in the normal mode. However, the securing arm does not serve as the primary load path in this normal mode, but rather merely contributes to the load transmission. In case of a defect, such a second effective load path transmits the entire load. The advantage of such an embodiment can be seen in that practically no relative movement between the joint head joint part and the securing arm needs to take place in case of a defect in order to activate the second load path. A brief interruption of the load transmission and an ensuing shock during the absorption of the load by the second load path do not occur in such an embodiment. 
     The inventive mode of operation can be achieved, for example, in that a certain clearance respectively exists between the securing arm and the inner cavity surface of the joint head support and the inner cavity surface of the joint head that are sectionally situated adjacent thereto in the normal mode, wherein this clearance prevents a load transmission between these parts in this normal mode, as well as during elastic deformations of the joint head joint part. 
     If a defect occurs in the joint head joint part, the load transmission in the first load path is impeded or even interrupted. In this case, the lacking load transmission causes the joint head joint part to begin moving in such a way that it exceeds the radius of action of the joint head joint part in the normal mode. During this movement, the securing arm, in particular, at least partially adjoins the inner cavity surface of the joint head support and the inner cavity surface of the joint head that are sectionally situated adjacent thereto such that they can support one another. In this way, the second load path is activated and the mechanical defect is, in a manner of speaking, bypassed. 
     According to one exemplary embodiment of the present invention, the joint head joint part is composed of several parts, namely of the joint head support and the joint head accommodated thereby. Among other things, this multipart design provides the advantage that more complex shapes of the joint head joint part can also be assembled of simpler individual parts. In this way, the manufacturing costs for the individual parts, as well as for the entire joint head joint part, are reduced. This also makes it possible, in particular, to decouple the shaping of the joint head from the shaping of the mounting on the second structural component. In addition to the superior geometric adaptability, this decoupling also makes it possible to use different materials for the individual parts of the joint head joint part. Such material differences may be adapted to different manufacturing techniques or optimally withstand the different influences during the operation of the connecting device. It would be conceivable, for example, to utilize high-quality and/or coated joint heads that are optimized with respect to the movement within the receiver while the joint head support is made of a material with superior torsional rigidity. In this way, the exchange of wearing parts such as, for example, the joint head is also simplified because it is no longer necessary to exchange the entire joint head joint part. 
     The joint head joint part may alternatively also be manufactured in one piece. The one-piece design is particularly advantageous with respect to the fatigue strength of the joint head joint part because connections of any type frequently form weak points. A one-piece design of the joint head joint part consequently provides the advantage of reducing the required connections between individual components of the connecting device to a minimum. This also automatically reduces the susceptibility to defects of the entire connecting device. 
     It may be advantageous to sectionally provide a clearance between the outside contour of the securing arm and the inside contours of the inner cavity surface of the joint head support and an inner cavity surface of the joint head such that the securing arm is not subjected to a load when the joint head joint part is mechanically intact. As already mentioned above, this embodiment of the present invention concerns the design with a dormant second load path that is only activated for the load transmission in case of a defect. This means that the loads, to which the second load path and, in particular, the securing arm are subjected in the normal mode, are reduced to a minimum such that the functionality of the securing arm is preserved over a long period of time. Since practically no wear of the securing arm takes place due to mechanical loads in such a construction, a securing arm of this type can be used much longer and also remain in the connecting device after the exchange of wearing parts such as, for example, the joint head. 
     According to another exemplary embodiment of the present invention, the respective clearance between the securing arm and an inner cavity surface of the joint head support and an inner cavity surface of the joint head amounts to no more than 5% of the maximum diameter of the joint head joint part. With respect to the creation of the second load path in case of a defect, a clearance between 0.5% and 5% of the maximum diameter of the joint head joint part may be particularly advantageous for the functionality of the securing arm. The reference of the clearance to the maximum diameter is advantageous because connecting devices with different dimensions can be designed in this way. In this case, the maximum diameter of the hollow joint head provides a correlation to the elastic deformations of the joint head joint part to be expected in the normal mode. In relatively small connecting devices, a relatively small clearance between the securing arm and an inner cavity surface of the joint head support and an inner cavity surface of the joint head accordingly suffices while a correspondingly larger clearance may be advantageous for a relatively large joint head. 
     It may be advantageous if the joint head of an inventive connecting device is realized spherically and at least partially accommodated in the receiver in a form-fitting fashion. In this case, the spherical design is not only ideal with respect to the desired rotative degrees of freedom, but also with respect to the load transmission. The ball with a receiver that accordingly is at least partially realized in the form of a hollow sphere is able to carry out tilting movements in all directions, as well as rotational movements about the main axis referred to the opening of the receiver. The corresponding spherical surfaces of the joint head and the receiver also provide an optimal load transmission. The load to be transmitted is evenly distributed over these spherical surfaces such that load peaks that could lead to undesirable plastic deformations within the receiver or the joint head are prevented. In this context, it should be noted that the terms “spherical” and “form-fitting” naturally not only refer to the geometrically ideal shapes, but also to shapes with tolerances that can be realized with the respective production technology. 
     Another option for dimensioning the clearance between the securing arm and an inner cavity surface of the joint head support and an inner cavity surface of the joint head consists of this clearance amounting to no more than 20% of the minimum material thickness at the respective inner cavity surface. In this case, the clearance lies, in particular, between 1 and 20% of the minimum material thickness at the respective inner cavity surface. The material thickness at the respective inner cavity surface also provides a correlation to the elastic deformations to be expected and to be tolerated in the normal mode. In this context, it needs to be observed that the clearance between the securing arm and an inner cavity surface of the joint head support and an inner cavity surface of the joint head does not have to be constant along the components, but may also vary. This variation may be dependent on or also independent of the correlation to the material thickness. 
     In order to secure the largest possible portion of the joint head joint part, it may be advantageous if the securing arm extends through the joint head joint part. The securing arm, in a manner of speaking, penetrates the joint head joint part, particularly the joint head. In this way, it is possible to realize the maximal securing of the joint head joint part. The opening may be realized, for example, relatively small in the form of a round bore, wherein the inner bore surface in the form of an inner cavity surface of the joint head may form a supporting surface of the joint head joint part. In this case, a supporting surface would be adjacently positioned on the outer side of the securing arm that extends through this bore. The two supporting surfaces consist of generated surfaces of a cylinder that can be supported on one another in case of a defect. 
     In order to also quantitatively adapt the freedom of motion of the two structural components in all three rotative degrees of freedom to complex relative movements, it may be advantageous if the pivoting range with respect to the rotatory degrees of freedom is as large as 60°. A pivoting range of up to 60° allows a multitude of complex movements, particularly with respect to a combination of the individual rotative degrees of freedom. However, it would also be conceivable to realize smaller pivoting ranges depending on the intended use of the connecting device. In the connection of structural components of an airframe, for example, it may be sensible if the pivoting range is as large as 20°. In order to ensure a certain safety with respect to the freedom of motion, it may furthermore be sensible to additionally provide another 8° pivoting range in each rotational degree of freedom so as to prevent an overrotation and possibly associated damages to the receiver and/or the joint head joint part. 
     It may furthermore be advantageous to provide a receiver safety for being mounted on the first structural component, wherein said receiver safety prevents the joint head from being removed from the receiver in case of a mechanical defect that involves weakening in the receiver. Such a receiver safety therefore forms a failure safety for the area of the receiver analogous to the failure safety for the area of the joint head joint part formed by the securing arm. Mechanical defects that involve a weakening in the receiver may be created, for example, by abrasion over the service life and, for example, jamming of the joint head. Material defects in the receiver or shocks transmitted from the joint head to the receiver also may lead to plastic deformations, cracks or even fractures in the receiver. In case of such a defect, the receiver may still be able to transmit compressive forces and shearing forces due to its accommodation in the first structural component, but the transmission of tensile forces may no longer be ensured. Consequently, the receiver safety prevents the joint head from being pulled out of the receiver and therefore a separation of the connection between the two structural components. 
     In order to further improve the simplicity of the present invention, it may be advantageous to at least partially mount the securing arm and the joint head joint part on the second structural component with the same mounting means. Such mounting means could consist, for example, of threaded bolts that are used for screwing the connecting device to the second structural component. In this case, such bolts may extend through a part of the joint head endpiece that is shaped similar to a flange and interact with corresponding bores in the second structural component. At least some of the bolts may also serve for mounting the securing arm such that the securing arm and the joint head joint part are mounted on the second structural component by means of the same bolts. However, it would also be conceivable to use mounting means in the form of separate bolts that exclusively serve for mounting the securing arm on the second structural component. In this way, the securing arm may also be decoupled from the first load path with respect to its connection to the second structural component. This decoupling serves for additionally improving the safety because impairments that leads to a mechanical defect involving a weakening in the joint head joint part also are not transmitted to the mounting means of the securing arm. This connection therefore also forms part of the failure safety realized with the securing arm. 
     It may also be advantageous if the joint head and/or the receiver feature/features a coating for improving the relative sliding movements at least in the contact regions of the two parts. Such a coating serves for reducing the coefficient of sliding friction between the two parts. This reduction on the one hand makes it possible to reduce the forces required for the relative movement between the two structural components by at least the frictional forces to be overcome. On the other hand, a coating of this type minimizes the risk of a “bearing seizure,” in which both the joint head and the receiver are plastically deformed and the relative moveability of the connecting device is lost. 
     In order to ensure that the safety path also has a sufficient surface with respect to the loads to be transmitted, it may be advantageous if the sections, in which the securing arm respectively is situated adjacent to an inner cavity surface of the joint head support and an inner cavity surface of the joint head, amount to at least 25% of the inside contour of the joint head joint part. In other words, at least 25% of the inside contour of the joint head joint part are secured by the securing arm in this way and serve as supporting surfaces in case of a defect. The loads can be transmitted along the second load path via these surfaces. 
     Another object of the present invention is a flap system of an aircraft that features at least a structural component of an airframe component and at least a structural component of a flap component. The structural component of an airframe component can be the first component and structural component of a flap component can be the second component, and vice versa. The two structural components are at least partially connected to one another by means of one or more connecting devices according to the present invention. Particularly in the connection of regulating flaps to the main wing of an aircraft, the flap system requires, according to aerodynamic aspects, a complex movement in order to ideally position the regulating flap relative to the main wing. This ideal positioning is based on the direction, in which the relative wind acts upon the main wing, and not on the orientation in the wingspread direction. 
     A complex movement of the regulating flap relative to the main wing therefore is required for the ideal positioning. An inventive connecting device makes it possible to attach the regulating flap to the main wing in a compact fashion without preventing the complex movement due to this attachment. 
     Consequently, only the utilization of the inventive connecting device makes it possible to realize a compact design despite ideal aerodynamic positioning. 
     In an inventive flap system, it may be advantageous if the connecting device is provided between an actuator arranged on an airframe component and a regulating flap. In this case, the connection to an actuator is particularly important because relatively large relative movements between the actuator and the regulating flap take place at this location when the complex relative movement is carried out. In the connection to an actuator, the available structural space is also limited because the actuator is a moving apart, the movements of which require a corresponding clearance zone. The utilization of an inventive connecting device therefore makes it possible to realize a compact connection despite the failure safety and the complex movement. 
     Another object of the present invention is an aircraft that features an inventive flap system. The failure safety of components is of decisive importance, particularly in aircraft, such that the combination of the fail-safe design of the connecting device and the three rotational degrees of freedom is a decisive advantage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in greater detail with reference to the attached drawings. In this context, the terms “left,” “right,” “top,” and “bottom” refer to an orientation of the drawings with normally readable reference symbols. In these drawings: 
         FIG. 1  shows an exemplary embodiment of a connecting device in a flap system of an aircraft, 
         FIG. 2  shows a detail of the connecting device according to the exemplary embodiment illustrated in  FIG. 1 , 
         FIG. 3  shows an individual illustration of the first structural component according to the exemplary embodiment illustrated in  FIG. 1 , 
         FIG. 4  shows a detail of a dismounted joint head joint part according to the exemplary embodiment illustrated in  FIG. 1 , 
         FIG. 5  shows an exemplary embodiment of a connecting device in the form of a cross section, 
         FIG. 6  shows the joint head joint part according to the exemplary embodiment illustrated in  FIG. 5  in the form of a cross section, 
         FIG. 7  shows the exemplary embodiment according to  FIG. 6  in the normal mode, wherein the first load path is also illustrated in this figure, 
         FIG. 8  shows the exemplary embodiment according to  FIG. 6  in case of a defect, wherein the second load path is also illustrated in this figure, and 
         FIG. 9  shows another exemplary embodiment of a connecting device with separate joint head support. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a first exemplary embodiment of a connecting device  10  that connects two structural components  110  and  120  of a flap system  100  to one another. The first structural component  110  consists of an actuator in the form of a lever, wherein said lever forms part of a lever linkage that in turn is connected to the airframe  130  and able to move the second structural component  120  relative to the first structural component  110 . The second structural component  120  consists of a regulating flap of a flap component  140  that can be arranged in different positions relative to the first structural component  110  depending on the flight situation. In this exemplary embodiment, the relative positioning is realized with the actuator, i.e., with the first structural component  110 . However, it would also be possible to realize exemplary embodiments, in which the first structural component is not a relatively movable part, but rather merely represents a bearing point for the relative movement of the second structural component  120 . 
     In addition to an essentially triangular lever that serves as first support of the flap component  140 , this flap component is connected to the first structural component  110  by means of a second structural component  120  and a connecting device  10 . Since the positioning of the second structural component  120  relative to the first structural component  110  takes place in a complex fashion, i.e., is realized with more than one rotational degree of freedom, a connecting device  10  is provided that serves as a bearing for the load transmission between the two structural components  110  and  120  despite this complex movement. The connecting device  10  in the exemplary embodiment illustrated in  FIG. 1  is essentially realized in the form of a ball-and-socket joint that is designed in a fail-safe fashion with respect to mechanical defects. For example, a connecting device  10  of the type described in greater detail below, particularly with reference to  FIGS. 5 to 9 , is used in this exemplary embodiment. 
       FIG. 2  shows a detail of the exemplary embodiment according to  FIG. 1 . The region of the connecting device  10  is illustrated in an enlarged fashion in this detail. The first structural component  110  that forms part of a lever actuator for moving the second structural component  120  is shown on the left side of this illustration. The second structural component  120  forms part of a flap system  140  and is situated on the right side in  FIG. 2 . The connecting device  10  is arranged in between. This connecting device features a joint head joint part  30  that is at least partially illustrated between the two structural components  110  and  120  in  FIG. 2 . This joint head joint part  30  is provided with three regions, wherein the joint head  20  according to  FIG. 2  partially protrudes from a receiver  20  accommodated in the first structural component  110 , and wherein a joint head support  34  is also illustrated in this figure. 
     The mounting between the second structural component  120  and the joint head joint part  30  is ensured with mounting means  90  in the form of several bolts. The joint head joint part  30  therefore is connected to the second structural component  120  in a motionally rigid fashion while the receiver  20  is connected to the structural component  110  in a motionally rigid fashion due to its accommodation therein. In this exemplary embodiment, the relative movement between both structural components  110  and  120  takes place in the form of a relative movement between the receiver  20  and the joint head joint part  30 . 
       FIG. 2  furthermore shows a receiver safety that serves as failure safety in case mechanical defects occur that involve a weakening of the receiver  20 . The concrete function of this receiver safety is described in greater detail further below. This receiver safety  60  is also mounted on the first structural component  110  with mounting means in the form of bolts. In order to simplify the installation, the receiver safety  60  consists of two parts such that it can also be installed or even exchanged after the installation of the connecting device is completed. 
       FIG. 3  shows a dismounted first structural component  110  in the form of an actuator. This first structural component already features a receiver  20  or bearing shell that is accommodated therein and ready to accommodate a joint head joint part  30 . In this case, the receiver is essentially realized in the form of a hollow sphere and designed for cooperating with a joint head  32  of a joint head joint part  30 . The joint head  32  essentially has the shape of a ball, i.e. a major part of the outer surface of the joint head  32  forms a ball. The receiver safeties  60  are already installed in the illustration according to  FIG. 3 . These two receiver safeties  60  need to be removed for the installation of the joint head joint part  30  and can be reattached after the joint head  32  has been installed. 
       FIG. 4  shows the counterpart of the first structural component  110  according to  FIG. 3 . The dismounted joint head joint part  30  is illustrated in  FIG. 4 . This joint head joint part  30  is connected to the second structural component  120 . This connection is produced with mounting means  90  in the form of bolts. The joint head joint part  30  is equipped with three functional regions. One of these regions is a joint head  32  that has an essentially spherical shape and therefore is suitable for being accommodated in and cooperating with the receiver  20  according to  FIG. 3 . The joint head joint part  30  furthermore features a joint head support that bridges the distance between the joint head  32  and the second structural component  20 . In addition, a joint head endpiece  36  is provided and mounted on the second structural component  120 . In this case, the joint head endpiece is essentially realized in the form of a flange such that the joint head endpiece  36  and therefore also the entire joint head joint part  30  is mounted on the structural component  120  with mounting means  90  in the form of bolts. The four mounting means  90  illustrated in this figure should be interpreted as an example only. Depending on the operating situation and the safety requirements, it is also possible to use a much larger number of bolts as mounting means  90 . In  FIG. 4, 12  bores suitable for accommodating bolts are already machined into the joint head endpiece  36  in the form of a flange. 
     The spherical shape of the joint head  32  is interrupted on the outermost end (in  FIG. 7  the left end) of the joint head joint part  30  that is positioned farthest within the receiver  20  after the installation in this receiver  20 . The end of a securing arm  50  is visible through the thusly created opening or a through hole in the joint head. This region of the opening is not intended for the load transmission between the two structural components  110  and  120  and therefore also not intended for the load transmission between the receiver  20  and the joint head joint part  30 . The load rather is exclusively transmitted from the spherical surface of the joint head  32  to the hollow spherical surface of the receiver  20 . The opening in the joint head  32  serves for the installation of the securing arm  50 , particularly for mounting the securing arm  50  with the aid of a screw. 
     According to an embodiment of the invention, the outermost part of the securing arm  50 , which is located opposite to the securing arm endpiece  56 , extends over a flange  33   a  which is formed in the through hole and extends in circumferential direction around the through hole. A first face or abutment face of the flange  33   a  is directed away from the securing arm endpiece  56 . As can be seen in  FIG. 7 , the securing arm  50  comprises an abutment piece  33   b  which can be a separate part like a retainer which can be connected to the securing arm  50  for example at the end of the same. Alternatively, the abutment piece  33   b  and the securing arm  50  are formed or manufactured as one piece. The abutment piece  33   b  extends in radial direction over the circumferential surface of the securing arm  50  which extends from the abutment piece  33   b  in direction to the securing arm endpiece  56 . In this section of the abutment piece  33   b  extending radially over the surface of the securing arm  50 , a second face or abutment face  33   c  is formed which is directed to the securing arm endpiece  56  and is facing the first face of the flange  33   a . Preferably, in the normal operation of the connecting device, the first and the second face are positioned such that there is a predetermined clearance between the first and the second face. Further, there can be clearance between the outer circumferential section of the surface of the securing arm  50  lying opposed to the respective inner surface of the through hole. In the case of a defect that involves a predetermined weakening or a predetermined rupture of the joint head joint part  30 , the first and the second face are transferring a load path, as can be seen in  FIG. 8 . In the embodiment in which a clearance is between the surfaces of the securing arm  50  and the inner surface of the through hole which are facing each other, by such a predetermined weakening or a predetermined rupture of the joint head joint part  30  ( FIG. 8 ) the first and the second face are getting in an abutment to each other. 
       FIGS. 5 and 6  show cross sections of an exemplary embodiment of a connecting device  10 . This exemplary embodiment represents one optional design suitable for use in a flap system according to  FIGS. 1 to 4 . According to the exemplary embodiment illustrated in  FIG. 5 , the connecting device  10  features a receiver  20  and a joint head joint part  30  as central elements. The receiver  20  is accommodated in the first structural component  110  and practically recessed therein in its entirety. The receiver is furthermore secured from sliding out of the receptacle in the first structural component  110  by means of the receiver safety  60 . This receiver safety  60  is in turn mounted on the first structural component  110  with mounting means  90  in the form of bolts. In this way, the position of the receiver  20  relative to the first structural component  110  is defined. 
     The joint head joint part  31  once again features three functional regions and is manufactured in one piece. The three regions consist of the joint head  32  itself, the joint head support  34  and the joint head endpiece as they are identified in  FIG. 6 . The joint head joint part  30  is mounted on the second structural component  120  by means of the joint head endpiece  36  and with mounting means  90  in the form of bolts. 
     The concrete design of the securing arm  50  is elucidated further below with reference to the cross section illustrated in  FIG. 6 . In this figure, the joint head joint part  30  is removed from the receiver  20 . The securing arm  50  protrudes into the interior of the cavity  38  of the joint head joint part  30 . This cavity extends through the joint head joint part  30 , particularly through joint head  32  and the joint head support  34 . In this case, the securing arm  50  is realized in a slightly conical fashion such that it can be easily inserted into the cavity  38  of the joint head joint part  30  during the installation. In addition, the securing arm  50  respectively is sectionally positioned adjacent to an inner cavity surface  40  of the joint head support  34  and an inner cavity surface  40  of the joint head  32 . A clearance that can also be referred to as play exists between the securing arm  50  and the respective inner cavity surface  40 . This clearance is so large that the securing arm  50  does not come in contact with the inner cavity surfaces  40 , namely not even during elastic deformations of the joint head joint part  30 . Due to its geometric extent into the cavity  38  of the joint head joint part  30  and the above-described clearance, the securing arm  50  forms a dormant second load path that does not transmit a load in the normal mode. 
     The securing arm  50  is positioned between the joint head endpiece  36  and the second structural component  120  and mounted on this second structural component  120  analogous to the joint head joint part  30  with the same mounting means in the form of bolts. A compensating ring that exactly positions the joint head joint part  30  relative to the second structural component is arranged between the securing arm  50  and the second structural component  120 . 
       FIGS. 7 and 8  show the two operating situations with respect to possible mechanical defects that involve a weakening in the joint head joint part  30 .  FIG. 7  shows the normal mode, i.e., the operating situation without a mechanical defect. In this normal mode, the load is transmitted from the first structural component  120  to the second structural component  110  along a first load path  70 . In this context, it should be noted that the load is by no means transmitted along a line only, but that this first load path  70  merely represents the basic path of a three-dimensional load transmission from the first structural component  120  to the first structural component  110 . 
     The first load path  70  extends from the second structural component  120  into the joint head joint part  30  and from there into the first structural component  110  via the receiver  20 . In this case, the first load path  70  refers to compressive forces, as well as to tensile forces and shearing forces. Consequently, the entire intact joint head joint part  30  forms part of the first load path. 
     In the event of damages, a mechanical defect that involves a weakening in the joint head joint part  30  may occur, for example, as illustrated in  FIG. 8 . This figure shows a fracture of the joint head joint part  30  in the region of the transition from the joint head support  34  to the joint head  32 . This fracture interrupts the first load path  70  illustrated in  FIG. 7 . Due to the interrupted first load path  70 , the load can at least no longer be diverted from the second structural component  120  such that it unintentionally moves relative to the first structural component  110 . In this case, no movement or hardly any movement of the joint head joint part  30 , particularly of the joint head  32 , relative to the receiver takes place. However, a relative movement takes place between the joint head joint part  30  and the securing arm  50 . 
     The result of the relative movement between the joint head joint part  30  and the securing arm  50  is illustrated in  FIG. 8 . This relative movement stops as soon as the securing arm  50  comes in contact with the inner cavity surfaces  40  of the joint head  32  and of the joint head support  34 . This means that the securing arm  50  is supported on these inner cavity surfaces  40 . This support creates a second load path  80  that is also schematically illustrated in the form of two lines in  FIG. 8 . However, the second load path  80  also represents a three-dimensional load transmission, wherein the load is now transmitted from the second structural component  120  to the securing arm  50  and from there into the receiver and therefore into the first structural component  110  via part of the joint head. The second load path  80 , in a manner of speaking, bypasses the mechanical defect  200 . 
       FIG. 9  shows another exemplary embodiment of a connecting device  10 . The connecting device  10  illustrated in this figure is realized very similar to the exemplary embodiment according to  FIGS. 5 to 7 , but the joint head joint part  30  has a multipart design in this exemplary embodiment. In this case, the multipart design refers to a separation of the functional regions of the joint head joint part  30 . The joint head  32  is manufactured separately of the joint head support and rigidly connected thereto. The joint head endpiece  36  is realized integrally with the joint head support in this exemplary embodiment. This made it possible to create a shape that allows a much simpler and, in particular, more cost-effective manufacture of the joint head joint part  30 . If a mechanical defect occurs in the joint head joint part  30 , it furthermore is merely required to exchange the corresponding defective component, i.e., either the joint head  32  or the joint head support  34 . This also makes it possible to reduce the costs for maintenance and repair procedures. In the exemplary embodiment according to  FIG. 9 , the functionality of the securing arm  50  is identical to that described in detail above with reference to the exemplary embodiment illustrated in  FIGS. 5 to 8 . 
     REFERENCE SYMBOLS 
     
         
           10  Connecting device 
           20  Receiver 
           30  Joint head joint part 
           32  Joint head 
           33   a  flange 
           33   b  abutment face 
           33   c  first surface 
           34  Joint head support 
           36  Joint part endpiece or joint head endpiece 
           38  Cavity 
           40  Inner cavity surface 
           50  Securing arm 
           56  Securing arm endpiece 
           60  Receiver safety 
           70  First load path 
           80  Second load path 
           90  Mounting means 
           100  Flap system of an aircraft 
           110  First structural component 
           120  Second structural component 
           130  Airframe component 
           140  Flap component 
           200  Mechanical defect