Abstract:
Aircraft fuselage frame in composite material with stabilising ribs which, in at least a first sector ( 31 ), comprises a frame ( 9 ) with an omega-shaped cross-section ( 11 ) formed by a top element ( 23 ), two webs ( 25, 25 ′), two feet ( 27, 27 ′) which includes at least one internal rib ( 41 ) formed by a top element ( 43 ) joined to the top element ( 23 ) of the frame ( 9 ), a web ( 45 ), two flanges ( 49, 49 ′) joined to the webs ( 25, 25 ′) of the frame ( 9 ) and a foot ( 47 ) aligned with the feet ( 27, 27 ′) of the frame ( 9 ). The invention also relates to a manufacturing procedure for the first sector ( 31 ) of the frame with stabilised web ( 10 ) comprising steps for: a) providing a frame ( 9 ) and at least one internal rib ( 41 ) with the configurations indicated; b) joining at least said internal rib ( 41 ) to the frame ( 9 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to aircraft fuselage frames made from composite material, in particular to frames with stabilised web. 
       BACKGROUND OF THE INVENTION 
       [0002]    Loading frames, in addition to shaping and stiffening the fuselage of an aircraft, are structural elements designed to withstand and transfer loads from other structural elements in the aircraft, such as the wings and stabilisers. 
         [0003]    Traditionally, loading frames have been made from metal material and have had various cross sections, with the most common being C-, I- and J-shaped, and which, by means of machining processes, form a framework of stiffeners which stabilise the webs in the frame. 
         [0004]    In today&#39;s aeronautical industry, the strength-weight ratio is of supreme importance which means that there is a demand for frames made from, or optimised using, composite materials, mainly carbon fibre, rather than metal frames. 
         [0005]    In the case of loading frames it is difficult to compete with machined metal frames since, due to the large amounts of different types of stress they have to withstand, alternative frames in composite materials usually pose diverse manufacturing problems due to their rather complex design. In any event, several solutions in this area are already known, such as those described in patent applications WO 2008/092970, US 2009/0026315 and WO 2009/030731. 
         [0006]    One of the aforementioned problems relates to attempting to produce a frame design with stabilised webs which would enable weight to be optimised. Although several solutions are already known for forming frames, none are available for loading frames in spite of the current demand for such frames in the aeronautical industry. 
         [0007]    The invention is aimed at meeting this demand. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the invention is to provide an aircraft fuselage frame with stabilised web made from composite material configured so that the strength-weight ratio is optimised not only in the frame itself but also in the skin. 
         [0009]    Another object of the invention is to provide an aircraft fuselage frame with stabilised web whose configuration facilitates its manufacture. 
         [0010]    In a first aspect, these and other objects are met by means of a frame with stabilised web in composite material which, in at least a first sector, comprises a frame with an omega-shaped cross-section formed by a top element, two webs and two feet and includes at least one internal rib formed by a top element joined to the top element of the frame, a web, two flanges joined to the webs of the frame and a foot aligned with the feet of the frame. 
         [0011]    In a preferred embodiment, the frame with stabilised web has the aforementioned configuration along its entire length. Optimised frames that require stabilised webs along their entire length are thus obtained. 
         [0012]    In another preferred embodiment, the frame with stabilised web can comprise a plurality of sectors with one of them having the aforementioned configuration and the others having a different configuration. Optimised frames for areas with differing requirements are thus obtained. 
         [0013]    In a second aspect, these and other objects are met by means of a manufacturing procedure for the aforementioned first sector in the frame with stabilised web which comprises steps for:
       providing a frame and at least one internal rib with the aforementioned configurations   joining at least said internal rib to the frame.       
 
         [0016]    In a preferred embodiment the manufacturing procedure for the aforementioned first sector in the frame with stabilised web comprises the following steps:
       manufacturing and curing, preferably using an RTM process, of one or more internal preforms of internal ribs (it is also possible to do this using a prepreg material and appropriate tooling)   manufacturing of a preform of the frame, preferably using a hot forming process and prepreg material.   co-bonding of said preforms in a curing cycle in an autoclave.       
 
         [0020]    A very efficient procedure is thus obtained for the manufacture of frames with stabilised web since, on the one hand, a high degree of dimensional accuracy can be obtained in the internal ribs which represents a major advantage particularly in the case of loading frames in which internal ribs have different dimensions in distinct zones and, on the other hand, it is an efficient procedure for manufacturing said loading frames (which are subject to large stresses) since, as the preform frame is made from prepreg material, it improves the mechanical characteristics of the frame because the mechanical characteristics of said material are better than those of RTM material. 
         [0021]    In another preferred embodiment, the manufacturing procedure for the aforementioned first sector of the frame with stabilised web comprises the following steps:
       manufacturing and curing of a preform of the frame preferably using an RTM process (it is also possible to do this using prepreg material and appropriate tooling)   manufacturing of one or more preforms of internal ribs, preferably using a hot forming process and prepreg material.   co-bonding of said preforms in a curing cycle in an autoclave.       
 
         [0025]    A very efficient procedure is thus obtained for the manufacture of frames with stabilised web since, on the one hand, a high degree of dimensional accuracy is obtained in the manufacture of the frame using RTM, which represents a major advantage particularly in the case of loading frames in which said frame has different dimensions in distinct zones and, on the other hand, bearing in mind the mechanical characteristics of RTM material, it is an efficient procedure for the manufacture of sectors of the frame that are subject to moderate loading stresses. 
         [0026]    In another preferred embodiment, the manufacturing procedure for the aforementioned first sector of the frame with stabilised web comprises the following steps:
       manufacturing of preforms of the frame and the internal ribs made from prepreg material.   co-curing of said preforms in a curing cycle in an autoclave.       
 
         [0029]    An efficient procedure is thus obtained for the manufacture of sectors of the frame with stabilised web that are subject to large loading stresses and free from any large dimensional variations. 
         [0030]    In another preferred embodiment, the manufacturing procedure for the aforementioned first sector of the frame with stabilised web comprises the following steps:
       manufacturing of dry preforms of the frame and the internal ribs.   co-curing of said preforms using an RTM process.       
 
         [0033]    An efficient procedure is thus obtained for the manufacture of sectors of the frame with stabilised web that are subject to moderate loading stresses and large dimensional variations. 
         [0034]    In another preferred embodiment, the manufacturing procedure for the aforementioned first sector of the frame with stabilised web comprises the following steps:
       manufacturing and separate curing of the frame and the internal ribs   joining of the ribs to the frame using adhesives.       
 
         [0037]    An efficient procedure is thus obtained for the manufacture of sectors of the frame with stabilised web that are subject to small loading stresses. 
         [0038]    In another preferred embodiment, the manufacturing procedure for the aforementioned first sector of the frame with stabilised web comprises the following steps:
       manufacturing and separate curing of the frame and the internal ribs.   joining of the ribs to the frame using rivets.       
 
         [0041]    An efficient procedure is thus obtained for the manufacture of sectors of the frame with stabilised web that are subject to small loading stresses. 
         [0042]    Further features and advantages of the invention will emerge from the detailed description which follows of an examplary embodiment of the object of the invention with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]      FIG. 1  shows the conventional solution for the stabilisation of the web of a frame made from composite material and with an omega-shaped cross section. 
           [0044]      FIG. 2  shows a schematic perspective view of a sector of a frame with stabilised web according to the invention. 
           [0045]      FIG. 3  shows a schematic perspective view of a sector of a frame with stabilised web according to the invention structured in a plurality of sectors of varying configurations. 
           [0046]      FIGS. 4   a  and  4   b  show sections of different sectors of the frame with stabilised web in  FIG. 3 . 
           [0047]      FIG. 5  schematically shows one of the manufacturing processes of a frame with stabilised web according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0048]    Patent application WO 2008/092970 describes a loading frame made from composite material with a closed cross-section which may be pi- or omega-shaped and which comprises three elements: two side elements and a base element each made using an appropriate laminate to withstand the loads to which they are going to be subjected. 
         [0049]    Whereas in a metal frame of similar configuration it would be easy to machine a plurality of stiffening elements, this is not the case in a frame made from composite material. In a frame  3  of this type, and as shown in  FIG. 1 , the conventional solution in composite material to stabilise its web and optimise its weight would be to join two L-shaped elements  5  to its web. 
         [0050]    The alternative according to the invention is a frame with stabilised web  10  which, in at least one of its sectors, and as shown in  FIG. 2 , comprises a frame  9  whose cross-section  11  is a closed omega-shaped cross section formed by a top element  23 , two webs  25 ,  25 ′ and two feet  27 ,  27 ′, and one or more internal stabilising ribs  41  formed by a top element  43 , a web  45 , a foot  47  and two flanges  49 ,  49 ′. 
         [0051]    The top element  43  and the flanges  49 ,  49 ′ of the rib are orientated in parallel and joined to the top element  23  and webs  25 ,  25 ′ of the frame  9  respectively and the foot  47  of ribs  41 , orientated in parallel to the feet  27 ,  27 ′ of the frame  9 , will be joined to the skin  17  of the fuselage. 
         [0052]    The rib  41  therefore has the dual function of stiffening both the web and the top element of the frame  9  and the skin  17  of the fuselage thus optimising the weight. The frame with stabilised web  10  according to the invention therefore provides an additional stabilising factor for the skin  17  of the fuselage which is not present in the known frames in the prior art. 
         [0053]    Similarly, ribs  41  can be used to be joined to and stabilise any T-shaped stringers of the fuselage  17  which intersect with the stabilised frame  10  in the vicinity of ribs  41 . 
         [0054]    The feet  27 ,  27 ′, top element  23  and webs  25 ,  25 ′ of the frame  9  and the foot  47 , top element  43 , web  45  and flanges  49 ,  49 ′ comprise layers of composite material arranged at 0°+/−45° and 90°. The composite material may be either carbon fibre or glass fibre with thermostable or thermoplastic resin. 
         [0055]    Unidirectional fibre reinforcements at 0° are also included in the feet  27 ,  27 ′ and in the top element  23  of the frame  9  in the same material or in a compatible material longitudinally and continuously extended along the entire frame. The material in the reinforcements has a high modulus of elasticity rendering the feet  27 ,  27 ′ and the top element  23  highly rigid. 
         [0056]    Webs  25 ,  25 ′ of the frame  9  may also comprise unidirectional fibre reinforcements in the same material or in a compatible material in any direction. The reinforcements of the webs  25 ,  25 ′ of the frame  9  may be continuous along the entire frame  9  or localised, in accordance with the stresses to which the frame is subjected. This means that webs  25 ,  25 ′ are thus capable of withstanding loads that are much larger than if it comprised exclusively fabrics at 0°+/−45° and 90°. 
         [0057]    By adding to the frame  9  the internal ribs  41 , the thicknesses of its webs  25 ,  25 ′ may be reduced to obtain a closed cross-section whose geometry and thickness can be varied, thus optimising its weight. Similarly, the skin  17  is also stiffened by the internal ribs  41  since these are also joined to it, so that its weight also can be optimised. 
         [0058]    The lengths of webs  25 ,  25 ′ of the frame  9  between internal ribs  41  must have holes, not shown in  FIG. 2 , which, on the one hand are necessary to ensure access to the inside of the stabilised frame  10  in order to be able to rivet the feet  47  of the internal ribs  41  to the skin  17 , and to be able to inspect said internal ribs  41  and which, on the other hand, if they are stamped, also contribute to weight reduction. 
         [0059]    In a preferred embodiment of the invention, the entire frame with stabilised web  10  joined to the skin  17  of the fuselage is a frame  9  with the cross-section  11  shown in  FIG. 2  with internal ribs  41 . 
         [0060]    In another preferred embodiment of the invention shown in  FIGS. 3 and 4 , the frame with stabilised web  10 , joined to the skin  17  of the fuselage, may have the aforementioned configurations in the first sector  31  (along plane B-B′), different cross-sections in other sectors, such as a cross-section  13  (along the plane A-A′) which is pi-shaped (shown in  FIG. 4   a ) without internal ribs in the second sector  33 , or a cross-section  15  (along the plane C-C′) in the shape of a single omega without any internal ribs (shown in  FIG. 4   b ) in the third sector  35 . 
         [0061]    The second sector  33  corresponds to a sector of the frame with stabilised web  10  with local loading inputs via fittings which are joined to the webs of the frame. A cross-section with a stiffening element in this sector is therefore not necessary and the frame can be simply formed using a pi-shaped element with a closed cross-section (it may also have the shape of a single omega) since the presence of the fittings in this area obviate the need for the webs to be stabilised. 
         [0062]    The third sector  35  corresponds to a sector in the frame which is subject to small stresses and hence a cross-section  15  in the shape of a single omega may be appropriate. 
         [0063]    Between the aforementioned sectors there are obviously transition areas between differently shaped cross-sections. 
         [0064]    In any of its embodiments, the frame with stabilised web  10  according to the invention can be used in cross sections of the fuselage which are circular, ellipsoid or rectangular in shape or have a different shape. 
         [0065]    We will now describe, in accordance with  FIG. 5 , a first variation embodiment for the procedure according to the invention to make a frame with stabilised web  10  with at least a first sector  31  with one or more stabilising ribs  41  as shown in  FIG. 2 . 
         [0066]    At a first stage  51  preforms  41 ′ of the internal ribs  41  would be made and then cured using an RTM, Resin Transfer Moulding, process (this can also be done using prepreg material and appropriate tooling). As is well known, in this process an enclosed flow and pressurised mould is used into which dry preforms are placed and then resin is injected. 
         [0067]    At a second stage a preform  9 ′ of the frame  9  would be made with the cross-section  11  using a hot forming process including a first step  55  comprising stacking prepreg material and a second stage  57  comprising hot forming. 
         [0068]    At a third stage  59  the preforms  41 ′ and  9 ′ would be co-bonded and the part would be consolidated in a curing cycle in an autoclave. As can be seen in FIG.  5 , this process requires on the one hand a first external device  61  on top of which the preform  9 ′ would be rested and on the other hand several internal devices (not shown in  FIG. 5 ) between the preforms  41 ′ and a second external device  65  to ensure suitable compacting of the preform  9 ′. 
         [0069]    In a second variation embodiment of a procedure according to the invention to make a frame with stabilised web  10  with at least a first sector  31  with one or more stabilising ribs  41 , a dry preform  9 ′ of the frame  9  with the cross-section  11  would be made which would be cured using an RTM (Resin Transfer Moulding) process (this can also be done using prepreg material and appropriate tooling). A plurality of preforms  41 ′ of the internal ribs  41  would then be made using a hot forming process and finally the preforms  41 ′ and  9 ′ would be co-bonded and the part would be consolidated in a curing cycle in an autoclave. 
         [0070]    In a third variation embodiment of a procedure according to the invention to make a frame with stabilised web  10  with at least a first sector  31  with one or more stabilising ribs  41 , preforms  9 ′,  41 ′ of the frame  9  and of the ribs  41  would be made separately from prepreg material which, following a hot forming process and after being duly arranged in appropriate tooling, would be co-cured in a curing cycle in an autoclave. 
         [0071]    In a fourth variation embodiment of a procedure according to the invention to make a frame with stabilised web  10  with at least a first sector  31  with one or more stabilising ribs  41 , dry preforms  9 ′,  41 ′ of the frame  9  and of the ribs  41  would be made separately and co-cured using an RTM process. 
         [0072]    In a fifth variation embodiment of a procedure according to the invention to make a frame with stabilised web  10  with at least a first sector  31  with one or more stabilising ribs  41 , the frame  9  and the ribs  41  would be made and cured separately and joined using adhesives. 
         [0073]    In a sixth variation embodiment of a procedure according to the invention to make a frame with stabilised web  10  with at least a first sector  31  with one or more stabilising ribs  41 , the frame  9  and the ribs  41  would be made and cured separately and joined using rivets. 
         [0074]    Although this invention has been described solely in relation to the preferred embodiments, these are non-limiting examples and it is obvious that modifications may be made without departing from the scope of the invention with the following claims taking precedence.