RU2532254C2 - Torsion box of wing from composite - Google Patents

Abstract

FIELD: transport.

SUBSTANCE: invention relates to structural elements of wings, particularly, to aircraft wing torsion box made of composites. Wing torsion box comprises top and bottom stringer panels. Front and rear spars and ribs of said panels divide torsion box inner space into compartments. Stringers are arranged in panel from the skin outer side and feature cross-section with the outrigger flange and set at spacing approximating to flange width. Stringers outer surfaces are coated with a thin layer of composite to make the panel outer skin. Stringer walls can plastically deform at impact loads.

EFFECT: higher safety of panels, simplified design and repair.

3 cl, 2 dwg

Description

The invention relates to the field of aviation, to structural elements of predominantly wings, in particular to the construction of a wing box of an aircraft made of composite materials.

Known designs of the wing box of an airplane made of composite material, for example, on a B-787 airplane (http://ru.wikipedia.org/wiki/Boeing_787_Dreamliner) or on an A-350 airplane (http://www.aex.ru/ news / 2011 / ll / 22/90489 /). These designs fundamentally do not differ from metal options, which can be taken as analogues of the proposed design option caisson. From the point of view of the structural scheme, both of these design options of the composite caisson are identical and any of them can be taken as a prototype. In these structures, the composite wing box includes upper and lower stringer panels, front and rear spars and ribs that divide the interior of the box into compartments. As with all traditional designs, panel stringers are located on the inside of the skin.

Common essential features of any of these prototypes that coincide with the essential features of the proposed technical solution are the following: a wing box made of composite material includes upper and lower stringer panels, front and rear spars and ribs, dividing the inner space of the box into compartments.

The main drawback of such a structural scheme in the case of using composite material is that when impacts on the wing (for example, during loading and unloading, when hitting large hailstones on the wing, in a collision with birds, etc.), the impact force directly falls on the vulnerable in relation to the impact, the casing is casing. This increases the risk of damage and is fraught with loss of tightness of the compartments containing fuel. As is known, the layered composite material used in aircraft construction, unlike metal, is prone to interlayer cracking provoked by shock, which leads to the destruction of the panel when it is subsequently loaded with the main operational load. This is especially noticeable on the upper panel of the wing, the main load for which is longitudinal compression, since the wing bends upward in flight. When the panel is compressed, the delamination in the skin that occurs as a result of the impact loses stability, which can lead to an avalanche-like development of fracture over the entire thickness of the skin with the resultant through crack in the entire width of the panel.

Another disadvantage of analogues and prototype is the inconvenience of ensuring the tightness of the internal volume of the caisson. The installation of special pressure fittings in places where stringers pass through the wall of the ribs complicates the design and increases labor costs during assembly operations and repair work. The structural nodes of the stringer tips (which are necessary due to the decrease in the number of stringers from section to section due to the narrowing of the caisson to the end of the wing) are also a weak point of the traditional design scheme. Since to ensure sufficient strength and reliability of the structure, the end of the stringer must be connected to the power belt of the ribs, the designer is forced to appropriately adjust the layout of the stringers and ribs, varying their pitch, which complicates the task of weight optimization of the design of the caisson.

Also, a significant disadvantage of the prototype is the lack of the ability to provide reliable control of the structural integrity after a possible impact through external inspection, since the laminated composite materials traditionally used in aircraft construction are stratified by impact without characteristic dents and through cracks that are easily detected in metal structures. Fundamentally, for a composite caisson, a situation is quite possible when the effects of impacts not detectable visually threaten the destruction of the wing in flight. In addition, repairing damaged areas in a traditional composite structure is challenging. Thus, the application of a patch after removal of the damaged area often entails the replacement of part of one or even several stringers, which requires complex refinement of the design, especially when stringer rebooting is necessary, which makes expensive disassembly of the entire caisson inevitable.

The proposed invention solves a set of technical problems:

- prevention (or a sharp decrease in the likelihood) of damage to the skin of the panels under the influence of shock operational loads;

- ensuring guaranteed detection of structural damage during impacts (visualization of critical impact damage);

- simplification of the structural ensuring the tightness of the caisson;

- simplification of repair work after local (for example, impact) structural damage.

To achieve the above technical results, in the wing box made of composite material, including the upper and lower stringer panels, front and rear spars and ribs, dividing the internal space of the box into compartments, unlike the prototype, the stringers are placed in panels on the outside of the skin, have a cross-section taken up (outward) by a shelf and installed with a step close to the width of the shelves of the stringers, on top of the stringers are covered with a thin layer of composite material, forming an additional outer skin of the panel, and the walls of the stringers are made with the possibility of elastic deformation under shock loads.

As a private option, the most preferred for implementation, we propose the design of the walls of the stringers with staggered racks and jumpers that form two rows of through slit-like grooves, so that the jumpers between them provide the necessary shock-absorbing effect in relation to the shock load.

As a possible option, to simplify assembly operations and increase the maintainability of the caisson, at least the shelf and jumpers of the stringers, as well as additional casing, can be made of composite material with a thermoplastic binder. This will allow, with relatively small damages, when only delamination of the material of structural elements takes place, to switch from replacing damaged parts with expensive technology for re-stringing stringers to restoring delaminated elements using the so-called “welding” technology.

Distinctive features of the proposed technical solution from the well-known prototype are the following: stringers are placed on the outer surfaces of the panels, have a cross section with a shelf raised up and installed with a step close to the width of the stringers shelves, outside the stringers are covered with a thin layer of composite, forming a continuous additional skin, and the walls of the stringers are made with the possibility of elastic deformation under shock loads. As the most preferred particular embodiment of the elastic stringers, it is proposed to design their walls with staggered racks and jumpers that form two rows of through slit-like grooves. As a possible option, at least the shelves and jumpers of the stringers, as well as additional casing, can be made of composite material with a thermoplastic binder.

Due to the presence of these distinguishing features in conjunction with the known achieved the following technical result:

Due to the presence of these essential features, the following technical effects are achieved:

- impacts in the area between the stringers are amortized due to the flexural flexibility of their shelves with stretching of the thin additional casing and their destruction during strong impacts, which in any case will significantly weaken the impact of the impact on the main casing, and impacts in the stringer's wall are amortized mainly due to its elastic compliance;

- since the protective cushioning coating of the caisson consists mainly of elements of longitudinal reinforcement, this allows to obtain high weight quality of the proposed design of the caisson. Only racks are not directly involved in the power reinforcement of the panels, the weight of which, according to calculations, is no more than 20% of the stringer's mass;

- the presence of effective impact protection in the proposed design gives an overall weight advantage, since in the traditional design, where the shock is perceived directly by the panel skin, in order to ensure the residual (impact) strength of the composite caisson, it is necessary to significantly increase the thickness of the skin. In addition, the proposed caisson design is free from a critical drawback - the impossibility of simple visual detection of traces of impacts critical to wing strength. Firstly, the depreciation effect itself is a factor significantly leveling the effects of an impact, since the impact force is proportional, as is known, to contact stiffness at the point of impact. In the presence of the proposed cushioning, impacts with relatively low energy will not cause any damage at all, and secondly, impacts with an energy level hazardous to wing strength will leave clearly visible traces of damage on the thin upper skin. Only in the case of high-intensity strikes, is it possible that the drummer, having overcome the defense, will still "get" to the main skin. But at the same time, a significant part of its destructive potential will already be lost;

- the manufacture of stringers using a thermoplastic binder can greatly simplify not only the manufacture of stringers and their installation on already installed panels, but also the repair of the caisson after destruction from shock and other influences. If the repair in the case of the traditional design of the caisson often requires its disassembly, in the proposed design in many cases (for damages that do not affect the main casing), it will not be necessary to dismantle the panels and carry out an expensive operation to replace damaged sections of the panels with re-stringers. The use of convenient and cheap technology of “welding” can make it possible to restore the integrity of stringer elements by simple local heating of the structure with melting of the binder. The presence of a protective coating in the form of stringer shelves and additional sheathing, as well as the very arrangement of the stringers on the outside of the panels, dramatically simplifies the repair of the composite caisson of the proposed design;

- the issue of strength and reliability of the nodes of the ends of the stringers is also solved in this design quite simply and efficiently. To do this, the more powerful extreme stringers (installed parallel to the edges of the panels) installed above the spar shelves, must have a wall height less than the rest of the stringer shelves. The breaking stringers with the free ends of their shelves go to the shelves of these extreme stringers and are fastened with them, for example, through the use of "welding" technology and, if necessary, additional mechanical fasteners.

The proposed constructive solution can be used in aviation - in the construction, mainly, of the wing box of the aircraft made of composite materials.

The proposed design is illustrated by the drawings of figures 1 and 2.

Figure 1 shows a General view of a section of the wing box.

Figure 2 shows the stringer (fragment and cross-section), the wall of which is made with alternating staggered racks and jumpers that form two rows of through slit-like grooves. At the same time (as an option) the shelves and jumpers of the stringers, as well as the additional casing, are made of composite material with a thermoplastic binder.

The wing box of composite material shown in FIG. 1 includes an upper 1 and a lower 2 stringer panels, in which stringers 3 are fixed to the skin 4, the front 5 and rear 6 spars and ribs 7 (fragmentary visible in FIG. 1), dividing the inner caisson space into compartments. Stringers 3 are placed on the outer side of the casing 4 and have a T-section with the shelf 8 extending upward (outward). The stringers 3 are installed with a step approximately equal to the width of the shelf 8. A small gap between the shelves makes it difficult for a potential impactor to penetrate (for example, gradients, stone from under the chassis wheel or a piece of torn pneumatic of this wheel). On the other hand, it is necessary to prevent the transverse propagation of local delaminations of the composite material after impact. The shelves 8 of the stringers 3 are covered with a layer of composite material, forming a continuous additional thin-walled sheathing 9 of the panel, and the walls 10 of the stringers 3 are made elastic in relation to the shock load. In this case (see Fig. 2), the walls 10 of the stringers 3 are made with staggered upper 11 and lower 12 uprights and jumpers 13, which form two rows of through slot-like grooves, so that the jumpers 13 between them provide the required shock-absorbing effect upon impacts . In this case, the jumpers 13 are sections of one part with a length equal to the length of the stringer 3. In addition to the ordinary stringers 3 on each panel 1 and 2, there are also two side stringers 14, which differ from ordinary stringers only in their sizes. Their height is less by the thickness of the shelves 8 of the ordinary stringers 3, and the remaining dimensions are determined based on strength requirements.

Shelves 8 and jumpers 13 of stringers 3, as well as additional thin-walled sheathing 9 can be made of composite material with a thermoplastic binder, which allows the use of "welding" technology, which greatly simplifies the assembly and repair of the caisson.

The assembly of the wing box is made in the following order. On panels that do not have stringers initially, lower racks 12 are fixed (for example, by mechanical fasteners), after which the caisson is assembled using traditional technology. The only difference is that now in ribs 7 there are no openings for stringers 3, which eliminates the need to install pressure fittings and greatly simplifies assembly. After installing the locking fastener, the stringers 3 are fastened to the box. Previously, the shelves 8 of the stringers 3 are connected (for example, using the technology of "welding" and / or mechanical fasteners) with the upper posts 11 and jumpers 13, which are sections of one part - in full the length of the stringers 3 and 14. First of all, the stingers 3 and 14 are installed at the edges of the panels 1 and 2. These side stringers 14 should be more powerful, because the ends of those ordinary stringers 3, which have to be cut off due to the narrowing of the caisson to the periphery, are attached to them. Accordingly, the height of the side stringers 14 should be less by the height of the shelves 8 of the ordinary stringers 3. Stringers 3 and 14 are fixed to the lower posts 12, for example, by means of mechanical fasteners, for which holes 15 are provided on the shelves 15. The edges of the shelves 8 breaking off due to the narrowing of the caisson stringers 3, can be fixed on the shelves 8 of the side stringers 14 by means of fasteners and technology of "welding". After installing the stringers 3 and 14 on their shelves impose an outer skin 9, which may be a composite on a thermoplastic binder. This makes it possible to use the technology of "welding", which simplifies this operation.

When repairing damage that does not affect the main skin of 4 panels 1 and 2, replace the damaged areas of thin external skin 9, shelves 8 and jumpers 13 of stringers 3 and 14. If damage led only to delamination of these parts, restoration of their integrity can be achieved using technology " welding ”, which makes repairs relatively simple and low cost. Such repairs can be made even in the field, which is not possible in the case of the traditional composite wing design.

Claims (3)

1. A wing box made of composite material, including the upper and lower stringer panels, in which the front and rear spars and ribs dividing the internal space of the box into compartments, characterized in that the stringers are placed in the panel on the outside of the skin, have a section with the top shelf and installed with a step close to the width of these shelves, on top of the stringers are covered with a thin layer of composite material forming an additional external paneling, and the walls of the stringers are made with the possibility of elastic deformation and under shock loads. 2. The wing box according to claim 1, characterized in that the walls of the stringers are formed by staggered racks and jumpers that form two rows of through slit-like grooves. 3. Wing box according to any one of claims 1 or 2, characterized in that at least the shelves and jumpers of the stringers, as well as additional casing, are made of composite material on a thermoplastic binder.

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