Aircraft structure made of composite material

Abstract

An aircraft structure made of composite material, comprising a skin reinforced longitudinally with stringers, and frames perpendicular to the stringers, each stringer comprising a head and two webs, and each frame having recesses in its web for the passage of the longitudinal stringers, such that an internal preform is provided in the gap existing between each stringer and the skin, filling the gap.

Claims

1. An aircraft structure made of composite material, comprising: a skin reinforced longitudinally with stringers, and frames perpendicular to the stringers, each stringer comprising a head and two webs, and each frame having recesses in a web thereof for the passage of the longitudinal stringers, and an internal preform located in a gap existing between each stringer and the skin, filling the gap, the stringers and the internal preforms being omega shaped, wherein a distance x between the feet of a stringer is greater than a distance y between the foot of one stringer and the feet of an adjacent stringer.

2. The aircraft structure made of composite material, according to claim 1, wherein the stringers and the frames are joined to the skin by means of mechanical joints.

3. The aircraft structure made of composite material, according to claim 1, comprising a highly integrated structure, in which the stringers and the frames are not joined to the skin with mechanical joints.

4. The aircraft structure made of composite material, according to claim 3, wherein an angle of the webs of the stringers and the angle of webs of the internal preforms with respect to the skin is between 35 and 47.

5. The aircraft structure made of composite material, according to claim 1, wherein the frames are J-shaped.

6. A method for manufacturing aircraft structures made of composite material according to claim 1, comprising the following steps: a) curing or semicuring the internal preforms; b) laying up and forming the fresh stringers, including the internal preforms inside the stringers, the stringers and the preforms being omega shaped; c) subassembling the skin and the stringers, including the internal preforms inside such that the distance x between the feet of a stringer is greater than the distance y between the feet of adjacent stringers; d) laying up and forming the frames; e) placing the frames in direct contact with the subassembly comprising the skin and the stringers; f) finally curing the assembly comprising the skin, the stringers and the frames in a single process.

7. An aircraft structure made of composite material, comprising: a skin reinforced longitudinally with stringers, and frames perpendicular to the stringers, each stringer comprising a head, two webs, and two feet, the two feet being separated by a distance x, and each frame having recesses in a web thereof for the passage of the longitudinal stringers, and an internal preform located in a gap existing between each stringer and the skin, filling the gap, the stringers and the internal preforms being omega shaped and both being joined to the skin, wherein a distance between adjacent stringers is defined by a distance y between the foot of one stringer and the foot of an adjacent stringer, and wherein the x is greater than y.

8. An aircraft structure made of composite material, comprising: a skin reinforced longitudinally with stringers, and frames perpendicular to the stringers, each stringer comprising a head and two webs, and each frame having recesses in a web thereof for the passage of the longitudinal stringers, and an internal preform located in a gap existing between each stringer and the skin, filling the gap, the stringers and the internal preforms being omega shaped, wherein a distance x between the feet of a stringer is greater than a distance y between the foot of one stringer and the foot of an adjacent stringer, wherein an angle of the webs of the stringers and the angle of webs of the internal preforms with respect to the skin is between 35 and 47.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an aircraft structure made of composite material.

(2) FIG. 2 shows a front view of a stringer with an internal preform.

(3) FIG. 3 shows a view of a frame.

(4) FIG. 4 shows a cross section of the frame of FIG. 3 at a point where there is not a recess for the passage of a stringer (A-A).

(5) FIG. 5 shows a cross section of the frame of FIG. 3 at a point where there is a recess for the passage of a stringer (B-B).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) FIG. 1 illustrates an aircraft structure 1 made of composite material.

(7) These structures in general comprise a skin 2, longitudinal stringers 3 and transverse frames 4.

(8) The structure according to the invention is an aircraft structure 1 made of composite material, which comprises a skin 2 reinforced longitudinally with stringers 3, and frames 4 perpendicular to the stringers 3. Each stringer 3 comprises a head 6 and two webs 7, and each frame 4 has recesses 10 in its web 9 for the passage of the longitudinal stringers 3.

(9) As can be seen in FIG. 2, there is an internal preform 5 in the gap existing between each stringer 3 and the skin 2, filling said gap. FIG. 2 shows that the internal preform 5 inside the stringers 3 makes it possible to reduce the angle between the stringers web 7 and the skin 2 in order to facilitate the final integration.

(10) Besides that, the existence of the internal preform 5 allows a more continuous contact between the stringer 3 and the skin 2, and the load transfer is improved: not only the feet 8 of the stringer 3 are joined to the skin 2, but the preform 5 is also joined to the skin 2.

(11) The distance x between the feet 8 of a stringer 3 is greater than the distance y between the feet 8 of adjacent stringers 3.

(12) In an embodiment of the invention, the stringers 3 and the frames 4 are joined to the skin 2 by means of mechanical joints.

(13) In another embodiment of the invention, the aircraft structure 1 is a highly integrated structure, in which the stringers 3 and the frames 4 are not joined to the skin 2 by means of mechanical joints.

(14) FIG. 3 shows that each frame 4 comprises a lower flange 11 extending also along the contour of the recesses 10. FIG. 4 shows a cross section of a frame 4 at a point where there is not a recess 10 for the passage of a stringer 3 (A-A cross section at FIG. 3) and FIG. 5 shows a cross section of a frame 4 at a point where there is a recess 10 for the passage of a stringer 3 (B-B cross section at FIG. 3). In a preferred embodiment, the stringers 3 and the internal preforms 5 are omega shaped.

(15) In the embodiment corresponding to a highly integrated structure, the angle of the webs 7 of the omega-shaped stringers 3 with respect to the skin 2 and the angle of the webs of the internal preforms 5 with respect to the skin 2 is preferably between 35 and 47.

(16) Additionally, to improve the bonded interface between stringers 3 and frames 4, two preforms, one with C and the other with Z section, may be used to make the frames 4. When these two preforms are joined together with one caping, a J-shaped frame 4 is obtained. FIG. 4 shows a cross-section of a frame 4, in which the C shape and the Z shape can be seen.

(17) The frames 4 of FIGS. 4 and 5 are J-shaped. The reason for that shape is that it allows the frame 4 to rest on the skin 2 (FIG. 4) or on the head 6 of the stringer 3 (FIG. 5) in a symmetrical manner Besides that, the bonded area is increased, because there are flanges 11 on both sides of the web 9 of the frame 4.

(18) The method proposed by the invention to manufacture aircraft structures 1 made of composite material according to the invention comprises the following steps:

(19) a) the internal preforms 5 are cured or semicured;

(20) b) lay up of the fresh stringers 3 and forming, including the internal preforms 5 inside the stringers 3, the stringers 3 and the preforms 5 being omega shaped;

(21) c) subassembly comprising the skin 2 and the stringers 3, including the internal preforms 5 inside, such that the distance x between the feet 8 of a stringer 3 is greater than the distance y between the feet 8 of adjacent stringers 3;

(22) d) lay up of the frames 4 and forming;

(23) e) the frames 4 are placed in direct contact with the subassembly comprising the skin 2 and the stringers 3;

(24) f) final curing of the assembly comprising the skin 2, the stringers 3 and the frames 4 in a single process.

(25) As the internal preform 5 is cured or semicured, tooling currently needed during the cycle in autoclave to maintain the radius and inner shape can be removed, since the inner preform 5 itself can do this role.

(26) In the embodiments that we have just described, it is possible to introduce the modifications within the scope defined by the following claims.

(27) As is apparent from the foregoing specification, the invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. It should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of my contribution to the art.