Abstract:
The invention relates to nose parts of the fairing of vertical and horizontal tails and wings of an aircraft with a skin and a support structure, the skin ( 2 ) being disposed on the support structure ( 4, 6 ). The support structure is provided with a plurality of ribs ( 6 ) and a plurality of stringers ( 4 ), the plurality of stringers being arranged on the plurality of ribs to support the skin. Advantageously, an improved deformation behavior can be obtained, e.g. in the event of an impact of a bird, while the weight and cost are minimized by providing the stringers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of International Application No. PCT/EP2005/004097, filed Apr. 18, 2005 and published as WO 2005/100152, which international application claims the benefit of the filing date of German Patent Application No. 10 2004 018 579.4, filed Apr. 16, 2004 and of U.S. Provisional Patent Application No. 60/598,256 filed Aug. 3, 2004, the disclosure of which applications is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a fairing or cover for an aircraft structure, in particular for the formation of nose parts of vertical and horizontal tails and wings. In particular, the present invention relates to a cover for an aircraft structure and to an aircraft with a corresponding fairing.  
         [0003]     In aircraft, nose parts of the fairing of vertical tails and horizontal tails as well as of wings are exposed to the danger of impact by objects, for example bird strike. In any case, these fairings must ensure that the support structure of the aircraft, which support structure is located below said fairing, is fully protected against damage as a result, for example, of such a bird strike. At present, this is achieved by carbon-fibre reinforced plastic (CFP) sandwich constructions or aluminium constructions. Corresponding metal constructions usually comprise sheet metal that has been drawn in an aerodynamic form and that has been stiffened by ribs.  
         [0004]     In a disadvantageous manner, a large number of ribs and relatively thick sheet metal have usually to be provided in order to, for example, avoid crack formation in the sheet metal which, for example, forms the skin of the aircraft. Consequently, such metal constructions are heavy.  
         [0005]     Known CFP constructions require expensive erosion protection paint or correspondingly expensive corrosion protection.  
       SUMMARY OF THE INVENTION  
       [0006]     It is an object of the present invention to state a light-weight and economical cover of fairing for an aircraft structure.  
         [0007]     According to an exemplary embodiment of the present invention a cover or fairing for an aircraft structure is provided, which cover can in particular be used for nose parts of vertical and horizontal tails or wings. The cover comprises a skin and a support structure. The skin is arranged on the support structure. The support structure comprises a plurality of ribs and a plurality of stringers. The plurality of stringers are arranged on the plurality of ribs to support the skin.  
         [0008]     Advantageously, this exemplary embodiment of the present invention makes it possible to distribute the impact energy, for example from a bird strike, to a larger region. In other words the stringers that are arranged underneath the skin deflect the impact energy to a larger region, as a result of which the energy introduced following the bird strike is distributed to a larger area as a result of plastic deformation of the skin, the stringers and the ribs. In this context the term “large area” refers to the area that is deformed by the impacted object being larger, preferably significantly larger, than the dimensions of the impacted object.  
         [0009]     In contrast to prior art, discussed above, in the case of the present invention the energy that has been introduced, for example by a bird strike, is distributed, by the stringers, to a large region of the cover, as a result of which, for example, a thinner skin and a significantly reduced number of ribs can be provided so that the weight of the cover can be reduced.  
         [0010]     According to a further exemplary embodiment of the present invention the skin forms a curvature around the structure of the aircraft. The form of the plurality of ribs is fastened at least to a cross section of the curvature, and the plurality of stringers essentially extend parallel to each other on the plurality of ribs. As a result of the parallel arrangement of the stringers at defined spacing, a situation can be achieved in which at a defined size of the impacting object a defined number of stringers undergo plastic deformation along a considerable length, thus absorbing a large part of the introduced energy. Only a small part of the introduced energy is absorbed by plastic deformation of the sheet metal, which is in contrast to prior art as discussed above where the aircraft skin as a result of deformation absorbs a significant part of the energy introduced.  
         [0011]     According to a further exemplary embodiment of the present invention the skin, the plurality of stringers and the plurality of ribs are designed, i.e., arranged such that the impact energy is deflected to a region that is significantly larger than the dimensions of the impacting object. This embodiment essentially relates to a thickness and a material of the skin, to dimensions and spacing of the stringers, as well as to dimensions of the ribs. In particular this also relates to the spacing of the arranged ribs, which spacing can be significantly increased when compared to the spacing in prior art as discussed above. For example in the case of various structures the spacing between the ribs can be doubled, trebled or even quadrupled, as a result of which, overall, the weight of the cover can be reduced, i.e., kept low.  
         [0012]     According to a further exemplary embodiment of the present invention the skin forms a nose part of the vertical tail, horizontal tail or of wings of the aircraft. The nose part then comprises an edge, for example the tail unit edge or wing edge, which extends essentially in one direction. The plurality of ribs are essentially arranged at right angles to this direction, and the plurality of stringers are arranged essentially parallel to the direction. For example by a parallel arrangement of the plurality of stringers parallel to the tail unit edge or wing edge, in this way it is possible, if an object impacts, to deflect deformation to regions that are arranged along this direction. In other words, transfer of the impact energy or deformation along the tail unit edge or wing edge is achieved, wherein deformation into the tail unit or into the wing, i.e., at a right angle to the direction, can be kept relatively small, so that good protection of the aircraft structure can be achieved.  
         [0013]     According to another advantageous exemplary embodiment of the present invention the plurality of stringers are connected to the skin. For example, stringer installation can be carried out by means of a laser welding process.  
         [0014]     According to a further advantageous exemplary embodiment of the present invention in contact regions where the plurality of stringers touch the skin or are connected to the skin, the skin comprises thickened parts or regions. This makes in possible in an advantageous manner to design the aircraft&#39;s skin so that it is even thinner, because certain minimum thicknesses of the skin, which are for example necessary for welding of the stringers to the skin, are only required in the immediate surroundings of the welding regions rather than having to extend over the entire region of the skin.  
         [0015]     According to a further exemplary embodiment of the present invention the stringers may have a T-, L-, Z-, U- or J-shaped cross section, which makes possible a simple and structurally stable design and arrangement of the stringers.  
         [0016]     According to a further advantageous exemplary embodiment of the present invention each of the plurality of stringers comprises a stringer base that is designed to contact the skin. The stringer base can comprise recesses. These recesses can, for example for further weight reduction, be evenly distributed over all the stringers, but also be distributed so as to be accumulated in regions where less stability of the stringers is required. In this way it is, for example, possible to achieve a further reduction in weight.  
         [0017]     According to a further advantageous exemplary embodiment of the present invention the recesses, which are for example designed as cut-outs, towards the skin comprise an opening that opens towards the skin of the aircraft. These recesses can then advantageously serve as expansion compensation regions in the case of deformation that is caused by an object impacting the skin. In this manner compression forces or expansion forces that occur in the case of such an impact can be controlled.  
         [0018]     According to a further exemplary embodiment of the present invention the support structure and the skin are designed or arranged such that, when a spherical body impacts the skin, deformation of the skin occurs that does not have a rotationally symmetrical cross section. This means for example that a direction of the greatest deformation of the skin can advantageously be set by the direction and design of the stringers underneath the skin, and in this manner, for example, deformation can be designed such that regions where a support structure is arranged just under the surface of the skin deform only a little and that the essential deformation energy is transferred to other regions.  
         [0019]     According to a further advantageous exemplary embodiment of the present invention the skin is made of sheet metal, for example of aluminium sheet metal.  
         [0020]     Claim  12  of the present invention relates to an aircraft with a fairing as described in claims  1  to  11 . 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     Below, exemplary embodiments of the present invention are described in more detail with reference to the following figures.  
         [0022]      FIG. 1  shows a three-dimensional diagram of a fairing according to a first exemplary embodiment of the present invention.  
         [0023]      FIGS. 2   a  to  2   c  show deformation due to the impact of a spherical body on the fairing of  FIG. 1 .  
         [0024]      FIG. 3  shows a three-dimensional view of a further advantageous exemplary embodiment of the present invention.  
         [0025]      FIG. 4  shows a cross section of a stringer and its affixation to the skin according to an advantageous exemplary embodiment of the present invention.  
         [0026]      FIG. 5  shows a lateral view of a stringer according to a further advantageous exemplary embodiment of the present invention.  
         [0027]      FIG. 6  shows the stringer of  FIG. 5  in its deformed state.  
         [0028]      FIG. 7  shows an aircraft with an exemplary embodiment of the fairing according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0029]     In the following description of FIGS.  1  to  7  the same reference characters are used for identical or corresponding elements.  
         [0030]      FIG. 1  shows a three-dimensional view of a cover according to an exemplary embodiment of the present invention. The fairing shown in  FIG. 1  can, for example, be a nose part of a vertical tail, of a horizontal tail or of a wing of the aircraft. As shown in  FIG. 1 , a skin  2  is bent such that it forms a certain radius, which, for example, forms the nose part of an aircraft&#39;s tail unit or wing or tail unit edge or wing edge. The nose part essentially extends along a direction indicated in the diagram by a dot-dash line. Below the skin, essentially in the region of the tail unit edge or wing edge or the back of the nose part, a plurality of stringers  4  are arranged essentially parallel in relation to the direction of extension of the fairing. In order to prevent deformation of the skin by air loads, at large distances small ribs  6  are arranged. The ribs can, for example, comprise holes  30  so as to save weight. Furthermore, it is possible, for example, to use crescent-shaped or boomerang-shaped ribs  6 . The ribs can be arranged at an equidistant spacing a or b. However, it is also possible, as shown in  FIG. 1 , to vary the spacing between the ribs, for example such that two ribs are arranged at a spacing a, while two further ribs are arranged at a spacing b. The spacing between the ribs can be varied in accordance with the loads that will occur.  
         [0031]     In contrast to the state of the art discussed above, where for example in the case of a bird strike the introduced energy is not adequately distributed or essentially converted to deformation of the skin and thus a substantial material thickness of the skin or of the arranged ribs is necessary, according to this exemplary embodiment, as a result of plastic deformation of the stringers, said energy is absorbed along a substantial length, as a result of which the stringers absorb the largest part of the introduced energy. Only a small part of the introduced energy is absorbed by plastic deformation of the skin or of the sheet metal of the skin. The precise course of deformation can be variably matched by the frequency of the ribs, by the dimensions and arrangement of the stringers, as well as by the material, the thickness or the design of the skin. In this way, the structure of the fairing can be matched by simulation such that desired deformation is achieved.  
         [0032]     For example, the stringers  4  can be affixed to the skin  2  by means of a laser welding process, as a result of which a simple and economical production process can be stated.  
         [0033]     The following  FIGS. 2   a  to  2   c  show the effect of an impact of a spherical body on the nose of the fairing according to the exemplary embodiment shown in  FIG. 1 . As shown in  FIG. 2   a,  an impact of a spherical body  10  on the skin  2  of the fairing is shown. In particular,  FIG. 2   a  shows that, although a spherical body  10  has impacted the nose, no rotationally symmetrical deformation of the skin and of the underlying support structure has been caused. The direction of impact of the body  10  is shown by arrow  12  in  FIG. 2   a.    
         [0034]     Deformation is greatest in the region  14  of the immediate surrounding of the impacted body  10 . However, as shown in  FIG. 2   a,  deformation along the stringers  4  that are arranged underneath the skin  2  is distributed over a large area to the regions  16  that extend essentially along the nose direction.  
         [0035]     The above is also shown in  FIGS. 2   b  and  2   c,  which show a lateral view and a direct top view of the deformation. As shown in  FIGS. 2   a  to  2   c,  essentially a lenticular deformation is achieved or a deformation which corresponds to a buckled circle. The deformation extends significantly further along the direction of deformation of the nose than it does in a direction at a right angle to it. In other words, when the fairing is a tail unit edge or a wing edge, deformation extends essentially along the tail unit edge or wing edge, rather than into the tail unit or into the wing.  
         [0036]     Consequently the introduced kinetic energy that is predefined by the mass velocity of the impacted body is converted to forming-work of the material involved. Since according to the present invention the adjoining regions  16  are included in the deformation, the metal volume required for energy conversion is distributed over a larger surface so that a lesser wall thickness can be used, for example for the skin  2 . As a result of the geometry of the nose parts, in an advantageous manner, for example in the case of a vertical tail, the regions above and below the impact point are available to this effect.  
         [0037]      FIG. 3  shows a further three-dimensional view of a further advantageous exemplary embodiment of the cover according to the present invention. As  FIG. 3  shows, the deformation depth and the size of the deformation into adjacent regions  16  can be defined by dimensioning the stringers and by setting the spacing d between the stringers. It is possible to arrange the stringers with equidistant spacing. However, the frequency of stringers can be greater where less deformation depth is required. In  FIG. 3  the stringers  4  are arranged essentially parallel in relation to each other in the direction of extension of the nose part.  
         [0038]     The design of the cover shown in  FIG. 3  essentially corresponds to that of the cover shown in  FIG. 1 . However, each of the stringers  4  is arranged on a thickened part  20  of the skin  2 . In an advantageous manner, at contact points the thickened parts  20  of the stringers  4  are welded to the skin  2 . In an advantageous manner this can be carried out by means of a laser welding process.  
         [0039]      FIG. 4  shows a section view of a stringer  4  of the skin  2  and of the thickened part  20  of  FIG. 3 .  
         [0040]     As shown in  FIG. 4 , the stringer  4  is essentially T-, L-, Z-, U- or J-shaped, wherein a stringer base  22  is connected to a thickened part  20  in the skin  2 . As shown in  FIG. 4 , the thickened part  20  in the skin  2 , which can for example be made of aluminium sheeting, can merely be a rectangular thickened part in the regions of the stringer base  20 . However, it is also possible to achieve continuous transitions between the thickened part and normal regions of the sheet metal, as is, for example, shown in  FIG. 4  by means of the dashed line.  
         [0041]     As shown in  FIG. 4 , the stringer  4  can also comprise a reinforcement  24  in the head region of the stringer  4 , as a result of which the T-, L-, Z-, U- or J-shaped cross sectional structure can be achieved. This makes it possible to produce the stringer in a simple manner with light weight yet good stability.  
         [0042]      FIG. 5  shows a lateral view of an exemplary embodiment of a stringer according to the present invention. As shown in  FIG. 5 , the stringer base  22  comprises interruptions, recesses or cut-outs which, as shown in  FIG. 5 , can open towards the skin. In  FIG. 5  these recesses are designated  26 . These recesses  26  can be provided at any desired constant or varied frequency along the stringer base  22 .  
         [0043]      FIG. 6  shows the effect of these recesses  26  during deformation of the stringer. As shown in  FIG. 6 , the recesses  28  are closed in regions in which the surface of the stringer  4  buckles, wherein in regions where expansion of the surface of the stringer base occurs recesses  40  are widened. In other words the recesses act as expansion compensation regions during deformation as a result of impact of an object on the skin, such that buckling or expansion can be compensated for by means of the recesses  26 . Furthermore, it is possible by designing the recesses  26  to control the forces that occur during an impact in such a way that deformation can be controlled. Advantageously the recesses  26  can also be used to prevent cracks in expansion regions.  
         [0044]     According to the present invention, a cover, for example for nose parts of the fairings, of vertical tail units and horizontal tail units as well as wings of an aircraft, is thus stated, in which cover stringers are provided that in the case of impact of an object plastically deform along considerable length and that absorb a large part of the introduced energy. In this manner it becomes possible for only a small part of the introduced plastic energy to be absorbed by the plastic deformation of the skin of the aircraft. As a result of the measures described above, the precise course of deformation can be set. This can, for example, be determined by means of crash simulations. In order to prevent deformation as a result of air loads, small crescent-shaped ribs can be provided at corresponding spacings. In particular, the present invention can make it possible to save weight and costs. Furthermore, improved deformation behaviour, for example in the case of a bird strike, can be made possible.  
         [0045]      FIG. 7  shows an aircraft with a fairing according to an exemplary embodiment of the present invention. The aircraft shown in  FIG. 7  comprises a vertical tail  36  as well as a horizontal tail  32  with the fairing according to the invention. Likewise, the wing noses  34  can be designed according to the fairing of the present invention.  
         [0046]     In addition it should be pointed out that “comprising” does not exclude other elements or steps, and “a” or “one” does not exclude a plural number. Furthermore, it should be pointed out that characteristics or steps which have been described with reference to one of the above embodiments can also be used in combination with other characteristics or steps of other embodiments described above. Reference characters in the claims are not to be interpreted as limitations.