Abstract:
A lifting structure for aircraft is essentially applicable to a horizontal stabilizer that includes two side symmetrical boxes that converge at one end (its root) thereof in a shared center area in order to connect integrally in the central area. Both boxes connect by a single part that constitutes a center rib with a double T-shaped profile. The root of the side boxes overlap converging on the inside surfaces of the wings of the center rib. The connection is ensured with rivets (lap joint). The proposed connection simplifies the assembly process (single part) and lead to a weight reduction since a carbon fiber connecting rib can be used.

Description:
OBJECTIVE OF THE INVENTION 
     The present invention, as described in the heading of this descriptive report, refers to a lifting structure for aircraft that is used essentially as a horizontal stabilizer situated in the rear area of the aircraft. The stabilizer consists in principal of two symmetrical, lateral boxes that remain solid due to certain characteristic joining methods that enable us to use a single, lighter material, such as carbon fibre. 
     Furthermore, the structure of the invention has a characteristic design that enables us to achieve a higher level of performance and effectiveness. 
     BACKGROUND TO THE INVENTION 
     At present, the union of lateral boxes for lifting structures for aircraft consists of a central metallic box that provides wings for inserting and riveting the lateral boxes. These in all cases have a flat structure, normally sloping upwards towards their free extremities. 
     Another known solution is a joint that incorporates upper or lower formers in titanium, with a central ribbing made of carbon fibre. 
     A third solution consists of a double shear joint. 
     This consists of upper and lower partial formers installed in the interior of the box, with exterior plates and central ribbing in composite material, creating a double shear joint. 
     Another known solution is a joint that includes a former in several sections. 
     In this case it consists of partial upper and lower formers installed from the outside of the box with a central ribbing in composite material. 
     Another solution incorporates formers in several places together with lattice ribbing. In this case it consists of partial upper and lower formers installed from the outside of the box with a central ribbing formed by bars in a latticed structure made from composite material. 
     DESCRIPTION OF THE INVENTION 
     The lifting structures for aircraft that constitutes the object of the invention is characterised by a single, central, integral component which acts as the nexus for joining a number of symmetrical lateral boxes to form a horizontal stabilizer. 
     The joint between the integral component and the side boxes is complemented by some strong rivets that are inserted from inside, into aligned holes made previously in superimposed laminated sections belonging to the three parts of the structure previously mentioned. 
     The central piece consists of a configuration in the form of a double “T”, the extremities of which incorporate a number of flaps, at the rear and front, positioned perpendicularly at the extremities from the core of this central piece, which make their union to the rear and front lifting possible. 
     In addition, the lifting structure assembly has a characteristic, curved configuration when seen from the front. This is such that in the areas where they meet the integral central component, the lateral boxes have extremities that make further contact with the internal faces of the profile&#39;s wings in the form of a double “T”, incorporating the rivets precisely in these contact areas. 
     In this way, then, the incorporation of a single one-piece part to join the two lateral boxes together makes the following possible:
         Joining the materials involved (carbon fibre), increasing the percentage of composite material as much as possible   Improving the processes of drilling and riveting by eliminating different materials, achieving improvements in tolerances and saving time making holes, as well as reducing non-conformities.   Significant improvement for the client in terms of inspection and maintenance, by not incorporating metallic materials.       

     A substantial improvement in the joint is also achieved, simplifying the assembly process. 
     Finally it should be pointed out that internal drilling and riveting of the box is practically eliminated, leaving only the insertion of a few rivets from inside, into previously made holes, and deforming the collars from outside. 
     To provide a better understanding of this descriptive report and as an integral part of the report, some drawings are provided below in which the invention is described for illustrative purposes. The drawings are not definitive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 . Shows a view of the structure for aircraft from the front, the structure being the object of the invention. Its application is essentially as a horizontal stabiliser. 
         FIG. 2 . Shows a view in perspective of a part of the lifting structure of the invention. The view shows an arrangement for joining the two lateral boxes of the stabiliser by means of a characteristic single central piece, in the manner of an integral rib. 
         FIG. 3 . Shows a view of the mounting of the integral rib onto the lateral boxes. 
     
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     Using the numbering in the diagrams, the structure for aircraft serves essentially as a horizontal stabilizer and consists of two symmetrical lateral boxes ( 1 ) that are joined together by a single, central piece ( 2 ) constituting a rib in the form of a double “T”, in such a way that the extremities ( 3 ) of the boxes ( 1 ) overlap the internal faces of the wings ( 4 ) of the rib ( 2 ), close to the core ( 5 ) of the central piece ( 2 ). 
     By being in this position, the three pieces [( 1 ) and ( 2 )] are joined together by means of four areas of rivets ( 6 ) that are inserted in pairs in aligned holes made previously in the wings ( 4 ) of the central rib ( 2 ) and the extremities ( 3 ) of the boxes ( 1 ). 
     The central rib ( 2 ) incorporates a number of flaps ( 7 ) for joining to a number of supports, at the front and at the rear (not shown in the diagrams). The flaps are situated perpendicularly at the extremities of the core ( 5 ) of the central rib ( 2 ) forming an integral part of it. 
     In addition, the central rib ( 2 ) gradually increases in height from the rear extremity to the front extremity, this variation in height being complemented by the extreme portions ( 3 ) of the lateral boxes ( 1 ). 
     The horizontal stabilizer consists of symmetrical boxes ( 1 ) that have a characteristic arch that increases in height as it goes outwards, in such a way that in this case the sections at the extremities ( 3 ) that overlap with the wings ( 4 ) of the central rib ( 2 ) are prepared in advance so as to be fitted to the wings ( 4 ) of the central rib ( 2 ). This preparation consists simply of flattening these end sections ( 3 ) so that they sit perfectly on the flat wings ( 4 ) of the central rib ( 2 ), thereby creating a flat transition. 
     This transition between the two boxes ( 1 ) is made on a surface that is not wet, and does not affect the aerodynamics of the aircraft. 
     As a result, when the application is used as a horizontal stabilizer with the arched boxes ( 1 ) as described, a transition of the surface skin is created that is curved and smooth within the fuselage area, in such a way that it has no effect on the aerodynamics of the aircraft. In this way we achieve a surface ready for a flat joint in the central area. 
     The rib wing interface angle must be sufficient to ensure union with the rib and ensure that the work of sealing and supplementing can be carried out without pulling on the sealant used. In the front area, this angle must be such that it is possible to install the front part correctly. The central rib will vary in thickness towards the exterior, taking into account the rows of rivets with the skin. 
     Another detail to be pointed out is that the front opening must be sufficiently large to allow access and the insertion of the rivets in the aligned holes, deforming the rivet collars from outside. 
     A further detail to be pointed out is that the rib can incorporate the rear and front section stiffeners and angle pieces. 
     Finally, we must also point out that the assembly system must be compatible with a box assembly system “to aerodynamic tolerances” that locally (in the area of the joint) ensures exterior tolerances that are compatible with the rib. This can be achieved either by means of adding material to the assembly, having designed the sections to be compatible with it, or applying extra material to the support elements of the skin which can be removed if necessary.