CA2575332C - Improved composite structure for aircraft - Google Patents

Abstract

An aircraft (1) structure (2) including transverse partitions (3-8) connected to longitudinal partitions (9-12); the partitions (3-12, 18, 18B) each include two composite material envelopes (19) placed on each side of an intermediate arrangement (20); the structure includes a cruciform shaped bar (21) connecting a transverse partition to a longitudinal partition. The aircraft structure therefore allows material damage to be limited in the case of aircraft impact (crash).

Description

Improved composite structure for aeretlef The invention aims at a composite anti-crash structure for an aircraft, as well as such an aircraft comprising such a structure.
The invention applies in particular to rotorcraft, particularly to helicopters.
The structure of such devices must be compatible with functional, normative, and certification constraints, especially.
In particular during an impact (crash) of the aircraft with the ground, the property damage must be limited or even annihilated, proximity to the cabin and vital components of the aircraft. Indeed, all Unacceptable human damage must then be avoided.
At present, compliance with certain specifications is antinomic to obtaining desired functions for one or another constituting an aircraft, which requires compromises that are not always acceptable in practice. This is particularly relevant for rotary wing aircraft.
The search for increased absorption capacity of Penergic due to a shock (accident) by the structure of an aircraft, has resulted in various proposals.
Patent FR-2632604 describes a helicopter structure comprising a frame consisting essentially of a portico whose ends are connected by a cross; the transom consists mainly of a panel having a sandwich structure and consisting of two thin vertical souls delimiting a space filled with a material deformable (nest of aliaille or moss) on which they adhere; the souls of panel have horizontal undulations in the lower part; a particular structure makes it possible to obtain a controlled deformation of the crosses by initiation of buckling in case of shock.

2 Patents US 4084029, US-4734146 and FR-2817608 relate to beams having a sinusoidal composite corrugated friend;
the beam according to FR-2817608 is designed to absorb in a controlled manner an intense and brutal compression effort applied in the direction of its height, under the effect of the kinetic energy produced by a violent shock such than the crash of an aircraft. The ime has several layers of carbon and stacked aramid fabrics; cutouts formed on an edge adjacent to the sole of each fiber web serve as the initiator of rupture, so as to load and progressively degrade the water table during the application of a compressive force capable of causing the rupture of the beam.
The present invention applies in particular to rotorcraft whose structure has several frames such as those described in FR-2632604, as well as beams connecting these frames two by two.
Various other energy absorption structures in case of impact of fuselage of an aircraft against the ground have also been proposed.
US-6620484 discloses an absorption structure comprising vertical composite panels through which a thread is sewn according to an increasing density from the base of the structure to its part higher.
US-4593870 relates to a shock absorber extending under the floor of the cabin of a helicopter and having a network of interlocking beams comprising a laminate or two laminates covering a core with honeycomb structure; breakthroughs are planned at the base of the laminate.
US-4941767 discloses a brace and bonds by ring section pieces. Patent FR-2763313 describes a plant of suspension of a tank.
US-5069318 discloses a reinforcement surrounding a thin wall to stabilize its hold in case of crash. US-5451015 discloses a =

3 installation of protection of a tank in case of crash. US Patent discloses a preformed member with an insertion channel of a planar partition. The document VVO 03018295 describes a preformed organ in the form of a letter "Pi", for the assembly of composite parts.
Despite this research, there remains a need for an improved structure aircraft for force recovery and energy absorption resulting from a shock.
In particular, it is appropriate to secure such a structure in case of crash, that the necessary adaptations do not entail the environment of the recovery structure (existing or design); he agrees that the additional embarked mass and congestion be reduced or negligible, and that the generated kinematics (buckling, displacement of on-board equipment) do not penalize the functioning normal of the device; it is also desirable that the costs installation and maintenance are low, and that the means used are simple, robust and durable.
In particular, it is desirable to obtain a compatible aircraft structure with an impact speed of the order of 7 to 9 m / s, for example of approximately 8.2 metre per second (noted m / s). It is also desirable that the impact forces maximum on the aircraft structure (eg cabin floor) in end crash, are compatible with the resistance of the surrounding structure, to not to degrade it.
An object of the invention is to overcome the problems and respect the most great possible number of criteria mentioned above.
For this purpose, according to one aspect of the invention, there is provided a structure (2) aircraft (1) having transverse walls (3-8, 18B) connected to walls longitudinal (9-12.18)

4 characterized in that the walls (3-12, 18, 18B) each comprise two envelopes (19) in composite material arranged on either side of an arrangement (20) intermediate, it comprises a cross-section link bar (21) connecting a wall transverse to a longitudinal wall; and it further comprises an insert (26) for damaging the connecting bar (21) then impact along the longitudinal axis (21B, Z) thereof, said insert having a shape lying along the longitudinal axis, and being engaged in a hole made in a base (21A) of the link bar.
According to preferred embodiments of the invention:
the structure may comprise a floor, transverse walls in the form of frame, and longitudinal walls in the form of a beam whose soul extends according to substantially vertical direction (Z), and said longitudinal walls and said Link bar extend under the floor;
a first blade of the bar can be inserted into a slot formed in a first wall of the structure, and a second blade of the bar can extend against an envelope of a second wall connected to the first wall by said bar;
said bar may be made of a composite material;
the insert can be engaged in an orifice extending from the base of the closed off;
the insert may have an elongated shape along the longitudinal axis of the closed off, in particular a cylindrical shape provided with a pointed end and / or a frustoconical head;
at least one of the walls may comprise a corrugated core having undulations extending in a direction (Z) substantially parallel to the envelopes, so that the energy absorption capacity through the wall when a shock in this direction is increased;

4a at least one of the walls may have a weakening favoring initiating a controlled degradation of the wall during an impact, both envelopes of a wall each preferably comprising at least one weakening to promote symmetrical degradation of the wall corresponding during a shock;

- losses can be in the form of interruption (s) localized with a layer of at least one envelope; stiffeners may be shaped concavity (s) formed in a envelope;

5 - the bar, an envelope, and if necessary a wavy soul of a wall, may comprise one or more layers of fibers or carbon or aramid fabrics, or obtained from poly-para-phenylene terephthalamide, -the fibers or tissues being impregnated with an epoxy resin, and the intermediate arrangement can contain a cellular material such as a synthetic foam or a honeycomb structure;
a wall of the structure may comprise a corrugated core with flattened portions of skin areas at the climax of corrugations, to provide a flat assembly surface.
Another object of the invention is a rotary wing aircraft, which has at least one anti-crash composite structure according to the invention.
The invention makes it possible to integrate into an effort recovery structure essentially composite, means capable of ensuring a -------------------------------------------------- --------------- sbse, tpt; e, n remarkable energy during a crash, s.ns a1.é1 resistance static of this structure.
Other aspects, features, and advantages of the invention appear in the following description, which refers to the drawings annexed and illustrating, without any limiting character, preferred modes embodiment of the invention.
FIG. 1 is a schematic view of longitudinal elevation of a helicopter according to the invention, shown from the side with its end before said nose to the left and its rear end said tail towards the right ;

6 FIG. 2 is an exploded perspective view (from the side and from above) of a helicopter structure according to the invention, with its components illustrated before assembly;
FIG. 3 is a cross-sectional view of a first wall of a structure according to the invention, on which is also illustrated a second wall of the structure, which is connected to the first wall by via a cross section bar (or section) interconnection) four branches;
FIG. 4 is a view in partial section along IV-IV of FIG.
structure of Figure 3, which illustrates the position of a delamination insert of cruciform section profile.
In the drawings, where identical or similar elements are designated by the same reference numbers, are shown:
orthogonal directions to each other.
A so-called elevation or vertical direction Z, corresponds to the height cc thickness of structures described: the terms up / down or inferior / superior refer to it.
Another direction X said longitudinal or horizontal, corresponds to the main length or dimension of the structures described. Terms forward / backward refer to it.
Another direction Y said transverse or horizontal, corresponds the width or lateral dimension of the structures described. The term side refers.
The X and Y directions define a horizontal X, Y plane. The X and Z directions define an X, Z longitudinal (and vertical) plane. The directions Y and Z define a plane Y, Z transverse (and vertical).
In FIGS. 1 and 2, the aircraft 1 is a helicopter comprising a fuselage 2B, a main rotor 15, and an and-couple rotor 16. This aircraft 1 is sometimes called device. The invention can be implemented in

7 other types of aircraft, both fixed wing and lighter than air by example.
In FIGS. 1 or 2, a recovery structure 2 can be noted This type of structure 2 brings in particular the fuselage 2B
the apparatus 1, the rigidity required for its operation, as well as safe behavior in case of crash.
This structure 2 of recovery efforts comprises, in Figure 2 in particular, carrier walls 18 in the form of: i) frames 3 to 8 transversal marked from the back (left) to the front (right); ii) longitudinal beams 9 to 12; iii) a floor 13; iv) a floor technical 14 adapted to support a main gearbox coupled to the main drive and lift rotor as well as to the rotor back 16; v) walls in the form of partitions, connected only those identified 17 and 17B which serve to clad the structure 2 and form parts lateral and ventral fuselage 2B_ The structure 2 of recovery of efforts is of the composite type (stratified).
With reference to FIGS. 3 and 4 in particular, each wall 18 of the structure 2 has outer envelopes 19 generally flat and arranged on either side of an intermediate arrangement.
In FIGS. 3 and 4, the structure 2 comprises two walls 18 and 18B, each with an envelope assembly 19 and an arrangement 20. The skins or wraps 19 are made from a fiber fabric impregnated with a resin. Composite parts can be formed by hot molding, for example at a molding temperature of the order of 180 C. The arrangement 20 consists of a honeycomb to which the envelopes adhere 19.
Each envelope 19 may comprise several stacked layers, for example :
an outer ply layer of composite fabric made of carbon impregnated extended substantially at an angle of

8 the order of 45 (degrees) from the main direction Z energy absorption;
a folded middle layer of composite aramid fiber fabric impregnated extend substantially at an angle of the order of 450 in relation to the Z direction; and an intermediate layer made of folded fiber composite fabric carbon impregnated extended substantially at an angle dc the order of 00 or 90 with respect to the Z direction.
Other layers may be provided whose fibers are oriented following a zero angle (00) with respect to the Z direction; in such a stacking, we can distinguish odd layers including the layer outer envelope 19 say "first fold", and layers pairs may include an inner layer called last fold.
Certain layers of the wall may comprise arranged fibers internally in cross, that is to say in under layers of fibers extending in intersecting directions at a predetermined angle (900 per example), from one under layer to another. These underlays can be together impregnated within one. resin substrate.
In other layers, the fibers are arranged in layers uniform orientation, that is to say substantially in parallel.
The walls 18 and 183 illustrated in FIGS. 3 and 4 are assembled by via a cross-shaped bar ¨ or profiled or cross-shaped - 21 interconnection and are filled with a honeycomb-like material bee 20.
The wall 18B has conformations 25 ¨ called external - of energy control, including reinforcing concavities formed within two envelopes 19.
A 26 cylindrical insert 26A axis (parallel to Z) having a 26B frustoconical head is housed at the base 21A of the 21 axis 21B, for

9 cause degradation of the material of the profile 21 surrounding the insert during shock in the Z direction.
The profile 21 and the insert 26 extend substantially according to the Z direction of energy absorption in case of crash; the insert allows in this case, by partial degradation of at least section 21, to reduce the resistance of the profile to the forces according to Z and make it close to that of walls 18, 18E, thereby promoting a balanced contribution of components of the structure at the absorption of energy shock.
The inserr or 41 Cl011 promotes in case of shock tearing, bursting, or delamination, of the material of the profile 21, by drilling a channel inside the base at least of this profile.
The insert 26 thus makes it possible to create a fracture initiation by bursting of the connecting part or assembly which surrounds it at the section 21 which serves as connecting member between the walls 18 and 18E.
Such a profile or spider 21 can for example be obtained by winding fibers and / or placing tissue around a core.
In normal situation, the blades of the spider 21 ensure the structural continuity between the walls 18 and 18B, and the insert 26 has no function.
In case of a crash, the stiffness (along the Z axis) of the cross and the The link with which it cooperates is detrimental to the absorption of energy. Thanks to the presence of the delamination insert, the spider is in these conditions degraded or partially destroyed, allowing for the separation of elements of structure (frame or beam in particular) that it connected, these elements that can contribute to the absorption of crash energy.
The assembly of the two walls, 18 and 183 (Figures 3 and 4) is performed during the manufacture of the constituent of structure 2 that incorporates these walls molding. This manufacture can include the main steps following.

The wall 18B extends along a first plane (Y, Z), while the wall 18 extends along a second plane (X, Z) perpendicular to the first plan. Each wall has the energy absorption conformations and a filling 20, 23 honeycomb.
5 For the assembly of these walls, we use a shell mold multiple delimiting an interior cavity.
A shell is covered with layers or layers of fibers, the case appropriate pre-impregnated. Honeycomb fills and brace 21 connected with the delamination insert 26, are then placed

10 in the mold, a wool (21C Figure 4) of the section 21 being engaged in a slot provided in the filling 23 of the wall 18. The cross 21 provides additional rigidity to the structure 2 to be manufactured.
Additional layers are stacked, and resin impregnation is added and / or integrated into the layers.
Following stacking of an external series of layers, a counter-shell which may include an inflatable containment element, shall be placed above all the layers and constituents arranged in the mold.
A hot compression (for example at 1500 kg / mml and 180 C) is then operated. The subsequent opening of the mold by removal of the shell and counter-shell allows the release of the structure 2 where the two walls 18, 18B are connected by the profile 21.
Such an integration limits the risks of positioning error and / or mounting when grouping the constituents of structure 2.
The walls 18 carrying structure 2 have anti crash plastically deformable, especially in the form of conformations contributing to energy absorption controlled by localized buckling.
These deformable anti-crash means can be calculated for a impact speed of the apparatus 1 of the order of 8 m / s. From then on, the forces maximum impact on structure 2 at the end of the crash, must thanks to

11 the intervention of these anti-crash means, participate in the resistance of the structure 2 so that it does not degrade unacceptably. Until an acceptable value of crash impact forces, these forces are not transmitted to the part of the structure 2 extending above the beams, and their energy is absorbed by these anti-crash means in particular.
In order to initiate in case of crash the rupture of the wall 18, it is equipped with conformations or areas 45 (Figure 3) weakening under form of composite layer stops within the envelope 19 of the wall 18.
Moreover, in order to prevent in the event of a crash the lateral deflection of the wall 18B, such a deflection may disrupt the vertical crushing of the wall and therefore the process of energy absorption, the wall can be equipped with conformations 25 whose role is to reinforce the wall 18B in lateral flexion.
These concave zones are generally extended according to the direction of elevation Z, and draw parallel oblong grooves and regularly spaced in the transverse direction Y.
At the location of these conformations 25, the wall 18 has a reduced thickness. Guiding the propagation of buckling of the wall 18 according to the direction Z can be obtained thanks to this network of throats.
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Claims (12)

1. Structure (2) of aircraft (1) having transverse walls (3-8, 18B) connected to longitudinal walls (9-12,18), characterized in that the walls (3-12, 18, 18B) each comprise two envelopes (19) in composite material arranged on either side of an arrangement (20) intermediate, it comprises a connecting rod (21) of cruciform cross section connecting a wall transverse to a longitudinal wall; and it further comprises an insert (26) for damaging the connecting bar (21) then a shock along the longitudinal axis (21B, Z) thereof, said insert (26) having a elongate shape along the longitudinal axis, and being engaged in an orifice convenient in a base (21A) of the link bar. 2. Structure (2) according to claim 1, which comprises a floor (13), said walls comprising said transverse walls (3-8) shaped like frame, and said beam-like longitudinal walls (9-12) whose core extends in a substantially vertical direction (Z), and in which said walls longitudinal and said connecting bar (21) extend under the floor. 3. Structure (2) according to claim 1 or 2, wherein a first blade (21C) of the bar is inserted into a slot formed in a first wall (18) of the structure (2), and wherein a second blade (21D) of the closed off extends against an envelope (19) of a second wall (18B) connected to the first wall by said bar. 4. Structure (2) according to any one of claims 1 to 3, in which said bar is made of a composite material. 5. Structure (2) according to any one of claims 1 to 4, in which said insert (26) is provided with a pointed end, or a head frustoconical (26B), or both. 6. Structure (2) according to claim 5, wherein said insert (26) to one cylindrical shape. 7. Structure (2) according to any one of claims 1 to 6, in which at least one of the walls has a corrugated core (70) having undulations extending in a direction (Z) substantially parallel to the envelopes, so that the energy absorption capacity through the wall when a shock in this direction is increased, and in that at least one of the walls has a weakening (45) promoting a controlled degradation of the wall during such an impact, the two envelopes of a wall preferably comprising each at least one weakening (45) to promote deformation symmetrical of the corresponding wall during a shock. 8. Structure (2) according to any one of claims 1 to 7, in which attenuations (45) are in the form of an interruption (s) localized (s) a layer of at least one envelope (19), and in which reinforcements (25) are shaped concavity (s) formed in an envelope (19). 9. Structure (2) according to any one of claims 1 to 8, in which the bar (21) and an envelope (19) comprise one or more layers fibers or fabrics impregnated with a resin, and in which the arrangement (20) intermediate contains a cellular material. 10. Structure according to claim 7, characterized in that said soul corrugated fabric has one or more layers of impregnated fabric fibers resin, and wherein the intermediate arrangement (20) contains a cellular material. 11. Structure (2) according to any one of claims 1 to 10, in a wall comprises a corrugated core having flattened portions of areas of skin at the peak of ripples, to provide a flat surface assembly. 12. Aircraft (1) with rotary wing characterized in that it comprises a structure (2) according to any one of claims 1 to 11.