Abstract:
In a wing structure for an aircraft, a rib extends in a chord direction for connecting spars to each other with upper and lower stringer through holes through which stringers of skins pass being formed in upper and lower edges of the rib. A bead is formed on the rib so as to extend between the upper and lower stringer through holes. Upper and lower ends of the bead are formed into arcuate shapes so as to surround the upper and lower stringer through holes, respectively. Thus, it is possible to enhance the buckling strength of the rib against a shear load acting on the wing of the aircraft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2006-299008 filed on Nov. 2, 2006 the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wing structure of an aircraft, wherein a plurality of spars extend in a span direction; a plurality of stringers are arranged between the spars and extend in the span direction, a rib extends in a chord direction to connect the spars to each other and skins are provided for covering upper and lower surfaces of the spars, the stringers and the rib. 
     2. Description of Related Art 
     A wing structure of aircraft is known as described in Japanese Patent Application Laid-open No. 2002-302097 and Published Japanese Translation No. 2000-506816 of PCT Application No. PCT/US97/04550. 
     More specifically, a rib defining the airfoil of an aircraft wing is formed by press molding a thin plate-shaped material for weight reduction. Stringer through holes are formed on the upper and lower edges of the rib, and stringers are fixed on the inner surfaces of the skins of the wing and are passed through the stringer through holes with a gap therebetween. The wing has a box structure having a resistance against bending and torsion, and includes spars, stringers, ribs and skins connected to each other. However, when a lift or a drag acts on the wing, there is a possibility that the rib formed of a thin plate-shaped material is buckled by a shear load. To solve this problem, in the wing structure described in Japanese Patent Application Laid-open No. 2002-302097 or Published Japanese Translation No. 2000-506816, a bead extending in the vertical direction (wing thickness direction) is formed integrally on the rib when the rib is press-molded, thereby increasing the buckling strength of the rib against the shear load. 
     However, it is difficult to compensate for the reduction in strength of the rib due to stringer through holes formed therein, merely by forming the bead extending in the vertical direction (wing thickness direction) on the rib. In order to secure a sufficient strength, the wall thickness of the rib is required to be increased along with an increase in the weight. 
     SUMMARY OF THE INVENTION 
     The present invention has been achieved in view of the above-described circumstances, and has an object to increase the buckling strength of a rib against a shear load acting on the wing of an aircraft. 
     In order to achieve the above object, according to an embodiment of the present invention, there is provided a wing structure of an aircraft wherein a plurality of spars extend in a span direction with a plurality of stringers arranged between the spars and extending in the span direction. A rib extends in a chord direction to connect the spars to each other with skins that cover upper and lower surfaces of the spars, the stringers and the rib. Upper and lower stringer through holes through which the stringers pass are formed on upper and lower edges of the rib. A bead is formed on the rib so as to extend relative to each other in the vertical direction. Upper and lower ends of the bead are formed into arcuate shapes so as to surround the upper and lower stringer through holes, respectively. 
     A main spar  13  and a front spar  14  correspond to the spar in an embodiment of the present invention. An upper skin  19  and a lower skin  20  correspond to the skin in an embodiment of the present invention. A front rib  21  corresponds to the rib in an embodiment of the present invention. 
     In a conventional structure, if stringer through holes through which stringers of upper and lower skins pass are formed on an upper edge and a lower edge of a rib which connects spars to each other, the buckling strength of the rib against a shear load caused by a lift or a drag of the wing is decreased due to the stringer through holes formed in the rib. Thus, a box structure of the wing comprising the spars, the skins, and the ribs is deformed, leading to a possibility that the shape of the airfoil is changed. However, in the arrangement of an embodiment of the present invention, the bead extending between the upper and lower stringer through holes is formed on the rib, and the upper and lower ends of the bead are formed into arcuate shapes so as to surround the upper and lower stringer through holes. Therefore, the buckling strength of the rib against the shear load is effectively enhanced, thereby suppressing the deformation of the wing. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a top view of a left main wing of an aircraft including a wing structure according to an embodiment of the present invention; 
         FIG. 2  is an enlarged sectional view taken along line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a sectional view taken along line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is a partially cutaway perspective view of the main wing; and 
         FIG. 5  is a graph for explaining the effect of the embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in  FIGS. 1 and 2 , a main wing  12  is supported on a fuselage  11  of an aircraft, and includes a main spar  13  extending substantially in the span direction, a front spar  14  arranged in front of the main spar  13 , and a rear spar  15  arranged in the rear of the main spar  13 . A leading edge member  16  is fixed in front of the main spar  13 . A flap  7  is oscillatably supported on a trailing edge part of the main wings  12  on an inner side in the span direction. An aileron  16  is oscillatably supported on the trailing edge part of the main wings  12  on an outer side in the span direction. 
     An upper skin  19 , that defines the upper surface of the main wing  12 , includes a plurality of stringers  19   a  formed integrally on the lower surface thereof in the span direction. A lower skin  20  that defines the lower surface of the main wing  12  includes a plurality of stringers  20   a  formed integrally on the upper surface thereof in the span direction. 
     The main spar  13  comprises a member having an I-shaped cross section which includes a web  13   a  and a pair of upper and lower flanges  13   b  and  13   c . The front spar  14  comprises a member having a groove-shaped cross section which includes a web  14   a  and a pair of upper and lower flanges  14   b  and  14   c . Although not shown, also the rear spar  15  comprises a member having an I-shaped cross section similar to that of the main spar  13 . 
     The main spar  13  and the front spar  14  are connected to each other by a plurality of front ribs  21  arranged in the chord direction. The main spar  13  and the rear spar  15  are connected to each other by a plurality of rear ribs  22  arranged in the chord direction. Each of the front rib  21  and the rear rib  22  is a member formed by press molding a metallic plate, and has a shape for defining the shape of the airfoil of the main wing  12 . Because the front rib  21  and the rear rib  22  have substantially the same structure except for a minor difference in shape, the structure of the front rib  21  will be described below. 
     The front rib  21  is a substantially rectangular plate-shaped member having a slightly lower leading edge. Two lightening holes  21   a  and  21   b  are formed in the front and rear parts of the front rib  21  in order to reduce the weight. A vertically-extending bead  23  is integrally press-molded between the two lightening holes  21   a  and  21   b . The bead  23  integrally includes a vertically-extending straight part  23   a  and a pair of arcuate parts  23   b  and  23   c  formed at opposite ends in the vertical direction of the straight part  23   a . The bead  23  is formed so as to bulge inwardly in the span direction when the front rib  21  is press-molded. 
     Formed in the central portion of the upper edge of the front rib  21  is a stringer through hole  21   c  through which the stringer  19   a  formed on the lower surface of the upper skin  19  passes. Formed in the central portion of the lower edge of the front rib  21  is a stringer through hole  21   d  through which the stringer  20   a  formed on the upper surface of the lower skin  20  passes. A pair of front and rear flanges  21   e  and  21   f  bent inward in the span direction are formed on opposite sides in the front/rear direction of the stringer through hole  21   d  on the lower edge of the front rib  21 . 
     A mounting part  21   g  provided at the front end of the front rib  21  is fixed by rivets  24  to a plate-shaped mounting part  14   d  which connects the web  14   a  to the pair of upper and lower flanges  14   b  and  14   c  of the front spar  14 . A pair of front and rear mounting parts  21   h  and  21   i  provided at the upper edge of the front rib  21  are fixed by rivets  25  to mounting parts  19   b  and  19   c  which are formed on the lower surface of the upper skin  19 . 
     A mounting part  21   j  provided at the rear end of the front rib  21  is fixed by rivets  26  to a plate-shaped mounting part  13   d  which connects the web  13   a  to the pair of upper and lower flanges  13   b  and  13   c  of the main spar  13 . The pair of front and rear flanges  21   e  and  21   f  provided at the lower edge of the front rib  21  are fixed by rivets  27  to the lower skin  20 . 
     A bracket  20   b , integrally provided on the stringer  20   a  of the lower skin  20 , is fixed by rivets  28  to the front rib  21 . 
     Thus, even when a lift in the vertical direction or a drag in the front/rear direction acting on the main wing  12  during the flight makes an attempt to buckle the front rib  21  whose outer periphery is connected to the main spar  13 , the front spar  14 , the upper skin  19  and the lower skin  20 , the main wing  12  is prevented from being deformed because the buckling rigidity against a shear load is enhanced by the bead  23  formed on the front rib  21 . More specifically, although the buckling strength decreases because the front rib  21  has the stringer through holes  21   c  and  21   d  through which the stringers  19   a  and  20   a  of the upper skin  19  and the lower skin  20  pass, respectively, the buckling strength of the front rib  21  against the shear load is effectively enhanced because the arcuate parts  23   b  and  23   c  are formed at opposite ends in the vertical direction of the straight part  23   a  of the bead  23  so as to surround the stringer through holes  21   c  and  21   d.    
       FIG. 5  shows the relationship between allowable shear load and the thickness of the front rib  21  of the present embodiment and three comparative examples. Comparative Example (1) is the front rib  21  having no bead  23 , Comparative Example (2) is the front rib  21  having the straight part  23   a  only and no arcuate parts  23   b  and  23   c , and Comparative Example (3) is the front rib  21  having the arcuate parts  23   b  and  23   c  only and no straight part  23   a.    
     As is clearly shown in the graph of  FIG. 5 , in all the thicknesses, the shear stress acting on the front rib  21  are in the following decreasing order: the present embodiment&lt;Comparative Example (3)&lt;Comparative Example (2)&lt;Comparative Example (1). 
     Thus, the present embodiment could endure the largest allowable shear load, showing that the present embodiment has an increased strength. 
     The embodiment of the present invention has been described above, however various changes in design may be made without departing from the subject matter of the present invention. 
     For example, in this embodiment, a detailed description has been made on the front rib  21 , however, the present invention is also applicable to the rear rib  22  in the same way. Also, the rib according to the present invention may be a rib that is not divided and integrally continuous from the leading edge part to the trailing edge part. 
     Further, in this embodiment, the stringers  19   a  and  20   a  are integrally formed on the upper skin  19  and the lower skin  20 , however, the stringers  19   a  and  20   a  may be formed as members separate from the upper skin  19  and the lower skin  20  and connected to the skins  19  and  20  by rivets or the like. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.