GB2573155A

GB2573155A - Aerofoil Manufacture

Info

Publication number: GB2573155A
Application number: GB1806884.1A
Authority: GB
Inventors: Barnett Thomas; Proudler Lee; Scaife Andrew
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2018-04-27
Filing date: 2018-04-27
Publication date: 2019-10-30
Also published as: GB201806884D0

Abstract

A method of manufacturing a composite aerofoil, in particular a winglet, and a composite aerofoil are provided. A method of manufacturing an aerofoil comprises the steps of forming a stiffened first cover layup 33 in a first resin transfer mould tool (44, fig 6), the first cover layup comprising of plies of fibre reinforcing material and at least one stiffener preform 36, 37, 58, closing the first mould tool, filling the first mould cavity with liquid plastics matrix by injection, applying heat to cure the first cover layup, forming a second cover layup (43, fig 5) of plies of reinforcing fibre material on a second mould tool, introducing plastics matrix material to the second cover layup and curing, assembling the first and second covers. The matrix material may be introduced to the second cover layup by resin transfer moulding within a closed mould tool. The second cover layup may be combined with at least one stiffener preform. The at least one stiffener preform may include forming at least one preform from the group: ribs, spars and stringers. The method may include the step of forming a said preform around a rectangular mandrel by alternately wrapping sheets of fibre reinforcing material from opposing sides of the mandrel to extend across two adjoining sides thereof such that each sheet forms a C shape when wrapped around the mandrel. Each C shape sheet may overlap a sheet wrapped from an opposing side of the mandrel. A fibre reinforced composite comprises a stiffened first cover and a second cover attached to the first cover, the stiffened first cover being manufactured by RTM and having at least one stiffener for the cover selected from the group: ribs, spars, stringers formed integrally therewith.

Description

AEROFOIL MANUFACTURE

Field of Invention

The present invention relates to the manufacture of aircraft aerofoils from fibre reinforced composite material and in particular to the manufacture of such aerofoils in the form of winglets.

Background of the Invention

Winglets are attached to an aircraft wingtip and usually extend upwardly from the plane of the wing. Such winglets can be attached to the wingtip with a sharp angular transition or they can transition through a smooth curve. Winglets with a transition curve are known as blended winglets. Winglets can extend to several metres in length on large commercial aircraft and react large aerodynamic forces. Their purpose is generally to convert otherwise wasted energy in the wingtip vortex into thrust, to reduce vortex interference with laminar flow near the wingtip and to reduce the intensity of wake vortices.

It is known to manufacture aircraft wings and winglets from fibre reinforced composite material, in particular from carbon, glass or aramid fibre reinforced composite material in which a matrix material surrounding the fibres comprises a thermoset or thermoplastics material. Epoxy resin is the current matrix material and requires curing to set hard.

Currently, the manufacture of composite winglets comprises the steps of separately manufacturing covers (often known as “skins”), spars and ribs for the winglet and then assembling them together to form the completed winglet. This process is complex, involving many separate operations to manufacture each part. In addition, accurate assembly typically entails the use of complex jigs and skilled shimming and fettling of parts to ensure the required accuracy of fit. The use of fasteners is also required for many of the joints which adds weight and further complexity to the structure. The separate parts may typically be manufactured using pre-preg material, or dry fibre layup of single plies or unidirectional or multiaxial non-crimp fabrics. For dry fibre layup, matrix material may be applied by the use of resin films in the layup or the application of liquid resin by hand.

It is known to form both open and closed composite structures, using resin transfer moulding (RTM) techniques. RTM allows the fabrication of complex structures in a single shot process using removable blocks within the metal mould tool to support structural reinforcements. Heated liquid resin matrix material is introduced into the closed tool by a vacuum created within the tool and the vacuum may be assisted by positive pressure applied to force the liquid resin through an entry port into the tool cavity. The liquid resin then infuses the fibre reinforcing material, throughout the mould cavity, solidifies and cures to form a solid matrix surrounding and supporting the reinforcing fibres.

For such structural reinforcement in a closed composite structure, tapered mandrels may be used which may protrude from one end or one side of the structure and be withdrawn, after forming takes place, by pulling them from their cavity at the wider end thereof. For aerofoil construction, such tapered mandrels could be withdrawn from an open end of the aerofoil used to attach the aerofoil to a base structure. Such a method would be possible for spar and stringer reinforcement of the aerofoil. However, for aerofoils where ribs are required, mandrels used to support such ribs cannot be withdrawn as there is no adjacent open end to the structure through which the withdrawal may take place.

In addition, if it is necessary to apply an irregular curvature, lengthwise of a tapered mandrel, removal of the mandrel by sliding it out of its cavity will be made more difficult if not impossible.

Thus, to date, it has not been possible to form an aerofoil having either ribs or any significant spanwise curvature, as found for example in a blended winglet, using RTM techniques.

Summary of the Invention

According to a first aspect of the invention there is provided a method of manufacturing an aerofoil including the steps of forming in a mould cavity of a first resin transfer mould tool a stiffened first cover layup of plies of fibre reinforcing material, said stiffened first cover layup comprising a first cover layup from which a said first cover will be formed combined with at least one stiffener preform from which one or more stiffeners for the first cover will be formed, closing the mould cavity of the mould tool, filling the mould cavity with liquid plastics matrix material by injection, applying heat to the mould tool to cure the stiffened first cover layup and thereby form the stiffened first cover, cooling and opening the mould tool and removing the stiffened first cover from the mould; forming a second cover layup of plies of fibre reinforcing material on a second mould tool, said second cover layup comprising fibre layers from which said second cover will be formed, introducing plastics matrix material to the second cover layup, applying pressure and heat to the second cover layup to consolidate the layup and cure the matrix material and thereby form the second cover; removing the second cover from the second mould tool and assembling the stiffened first cover and second cover together to form the aerofoil.

The method of the invention therefore allows the whole stiffened first cover with spars, ribs and stringers, as required, to be formed with great accuracy in a single operation.

The second cover may also be formed by RTM in a closed mould tool and thus with the same speed and to the same level of accuracy as the first cover.

The method may include the step of combining the second cover layup with at least one stiffener preform from which one or more stiffeners for the second cover will be formed, whereby to manufacture the second cover as a stiffened second cover.

Any stiffeners or other aerofoil attachments, such as wiring, lights, pipework etc., not formed in the RTM operation, or indeed anything preferred to be made of a different material to the stiffened first cover, may be easily fitted to the stiffened cover, or indeed to the second cover, before the first and second covers are joined together.

The first and second covers may be joined together in any manner desired, for example, by adhesives, fasteners or any combination thereof.

The aerofoil may be manufactured in the form of a winglet which may be a blended winglet having a curved region which may conveniently be used for attaching the winglet to a wingtip.

The step of forming at least one stiffener preform for the aerofoil may include forming at least one preform selected from ribs, spars and stringers. A said preform may be formed around a rectangular mandrel by alternately wrapping sheets of fibre reinforcing material from opposing sides of the mandrel to extend across two adjoining sides thereof such that each sheet forms a C shape when wrapped around the mandrel.

Each C shape sheet may overlap a sheet wrapped from an opposing side of the mandrel.

According to a second aspect of the invention there is provided a fibre reinforced composite aerofoil comprising a stiffened first cover and a second cover attached to the first cover, the stiffened first cover being manufactured by RTM and having at least one stiffener for the cover selected from the group: ribs, spars, stringers formed integrally therewith.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:-

Figure 1 is a schematic illustration of the steps of an RTM process, according to the prior art;

Figure 2 is a schematic view of a ply cutting table;

Figures 3a to 31 show schematically the progressive forming of a preform around a rectangular mandrel, according to the invention;

Figure 4 is a perspective view of a stiffened lower cover of a blended winglet manufactured according to the invention;

Figure 5 is a perspective view of a completed winglet manufactured according to the invention;

Figure 6 is a ghosted perspective view of an angled RTM mould tool according to the invention containing a stiffened lower blended winglet cover similar to that shown in Figure 4, and

Figure 7 is a schematic perspective view of an RTM tool station for receiving the angled RTM mould of Figure 6.

Detailed Description of Preferred Embodiments of the Invention

Referring to Figure 1, there is shown, according to the prior art, a schematic layout of an RTM work area. Arrows show the direction of movement of goods and trolleys. A tool press station 1 comprises a tool press 2 having a pair of cranes 3, 4 attached thereto and an injection system (not separately shown) incorporated therein. Adjacent either end of the tool press 2 are tool trolleys 5, 6, each supporting an RTM tool 7, 8 with a respective lid 9, 10. Adjacent the tool press station 1 is a manned control module 11 for the tool press 2. Opposite the tool press station 1 is a layup station 12. At the layup station 12 is a tool support 13 having a lifting frame 14 and supporting a tool lid 15 and a trolley 16 supporting a tool 17.

Feeding into the layup station 12 are a braided and woven preform supply 18 and a mandrel preforming station 19. The preform supply 18 also feeds the mandrel preforming station 19. Approaching the layup station 12 is a returning trolley 20 carrying an empty mould tool.

Shown leaving the tool press station 1 is a completed aerofoil 21 from which mandrels 22 have been removed.

An example resin transfer moulding RTM process is as follows:- 1. Cleaning the mould and applying release agent; 2. Preforming wing covers and stiffeners; 3. Resin could be degassed in a dedicated degassing system; 4. Resin transferred to injection system by depression; 5. Assembly of the mould; 6. Clamping of the mould in the tool press; 7. Vacuum applied in tool and in injector; 8. Heating of tool and injector; 9. Resin injected into tool; 10. Tool vacuum port closed when resin witnessed emerging therefrom; 11. Tool heated to cure temperature; 12. Injector disconnected for cleaning a few minutes after gelation monitored in tool; 13. Demoulding.

Figure 2 shows a cutting table 23 on which plies of fibre reinforcing material 24, 25 lay.

Figures 3a to 1 show a draping, bagging and debulking sequence for plies of type 24, 25 as they are systematically applied to a mandrel 26, for use according to the invention. The shape of the mandrel 26 shown is for illustrative purposes only and can of course be of any shape required. The mandrel 26 has opposing sides 27, 28 and adjoining sides 29, 30. In Figure 3a, a ply 24 is draped over a first opposing side 27 of the mandrel 26 and extends, either side, over adjoining sides 29, 30. In Figure 3b, vacuum bag 31 is then sealed over the mandrel 26 and a room temperature debulk takes place. In Figure 3c, the mandrel, with ply 24 attached, is flipped over and in Figures 3d and 3e, the draping, bagging and debulking process is repeated for new ply 25. In Figure 3f, an overlap 32 of plies 24, 25 is seen. From Figures 3g to 31, the process is further repeated, with plies 24, 25 being cut and applied as shown to avoid stack up of overlaps 32, see Figure 31.

In an alternative arrangement, plies which extend substantially all around the mandrel could be used. Any overlaps of plies could be moved to different positions around the mandrel to avoid stacking of overlaps.

Figure 4 shows a stiffened lower cover 33 for a blended winglet, according to the invention. The lower cover has a tip 60 and an attachment end 61 with a transition curve region 59 adjacent to the attachment end 61. The cover 33 has been formed by RTM in a mould as illustrated in Figure 6. The cover 33 is fully composite in construction save for a metallic erosion shield 34 at a leading edge 63 thereof and a metal lug 35. The lower cover 33 is reinforced by C-section centre spars 36, 37 and front spar 58. It also has a number of ribs 38, 39, 40, 41 integrally formed with a lower cover 42.

Figure 5 shows the stiffened lower blended winglet cover 33 of Figure 4 with an upper cover 43 fitted. The upper cover 43 will be attached, here, by blind fasteners (not separately shown) passing through the upper cover 43 into the front, and two middle spars, 58, 36, 37, respectively and into a trailing edge 62 of the lower cover 33.

Figure 6 is a ghosted perspective view of an angled RTM mould tool 44 and lid 45, according to the invention, containing a stiffened lower blended winglet cover 46 similar to that shown in Figure 4. The tool 44 and lid 45 have been manufactured from tool billets 47, 48, and lid billets 49, 50 of aluminium, welded together at 51, 52, respectively. A mould tool of similar configuration to that shown could equally be used to manufacture an upper cover for the blended winglet.

The mould tool 44 and lid 45 shown are preferred versions of a suitable RTM mould tool for manufacture of blended winglets, according to the invention. However, other types of mould tool are envisaged. For example, a classic rectangular block mould with a multi-level cavity comprising a base and a number of frames, optionally with heating cartridges, could be used. Alternatively, a classic rectangular block mould with a base and welded frame, using inserts to support and form the winglet cover, could be used. A further alternative is a mould similar in shape to the mould illustrated in Figure 6 but having a stepped V form.

Figure 7 shows schematically an RTM tool station for injection moulding winglet lower and upper covers, according to the invention. The tool station 53 comprises a tool press 54 to receive a closed mould tool 55 and a rail arrangement 56 to transfer the mould tool 55 into the tool press. Operation of the tool press 54 is carried out at a control module 57.

While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of applicant’s general inventive concept.

Unless otherwise stated, the word “or” shall be taken to mean “and/or”.

Claims

1. A method of manufacturing an aerofoil including the steps of forming in a mould cavity of a first resin transfer mould tool a stiffened first cover layup of plies of fibre reinforcing material, said stiffened first cover layup comprising a first cover layup from which a said first cover will be formed combined with at least one stiffener preform from which one or more stiffeners for the first cover will be formed, closing the mould cavity of the mould tool, filling the mould cavity with liquid plastics matrix material by injection, applying heat to the mould tool to cure the stiffened first cover layup and thereby form the stiffened first cover, cooling and opening the mould tool and removing the stiffened first cover from the mould; forming a second cover layup of plies of fibre reinforcing material on a second mould tool, said second cover layup comprising fibre layers from which said second cover will be formed, introducing plastics matrix material to the second cover layup, applying pressure and heat to the second cover layup to consolidate the layup and cure the matrix material and thereby form the second cover; removing the second cover from the second mould tool, and assembling the stiffened first cover and second cover together to form the aerofoil.

2. A method according to claim 1, comprising manufacturing a said aerofoil in the form of a winglet.

3. A method according to claim 2, comprising manufacturing a said winglet in the form of a blended winglet having a transition curve region for attachment to a wingtip.

4. A method according to claim 1, 2 or 3, in which the matrix material is introduced to the second cover layup by resin transfer moulding within a closed mould tool.

5. A method according to any preceding claim, including the step of combining the second cover layup with at least one stiffener preform from which one or more stiffeners for the second cover will be formed, whereby to manufacture the second cover as a stiffened second cover.

6. A method according to any preceding claim, in which the step of forming at least one stiffener preform includes forming at least one preform from the group: ribs, spars and stringers.

7. A method according to any preceding claim, including the step of forming a said preform around a rectangular mandrel by alternately wrapping sheets of fibre reinforcing material from opposing sides of the mandrel to extend across two adjoining sides thereof such that each sheet forms a C shape when wrapped around the mandrel.

8. A method according to claim 7, in which each C shape sheet overlaps a sheet wrapped from an opposing side of the mandrel.

9. A fibre reinforced composite aerofoil comprising a stiffened first cover and a second cover attached to the first cover, the stiffened first cover being manufactured by RTM and having at least one stiffener for the cover selected from the group: ribs, spars, stringers formed integrally therewith.

10. A fibre reinforced composite aerofoil according to claim 9, in the form of a winglet.

11. A fibre reinforced composite aerofoil according to claim 10, in the form of a blended winglet having a transition curve region for attachment to a wingtip.

12. A fibre reinforced composite aerofoil according to claim 9, 10 or 11, in which the second cover is manufactured by RTM.