GB2268461A

GB2268461A - Aircraft manufacture.

Info

Publication number: GB2268461A
Application number: GB9312621A
Authority: GB
Inventors: Paul Charnock; Keith Rowlandson; Terence Carter
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1992-06-20
Filing date: 1993-06-18
Publication date: 1994-01-12
Anticipated expiration: 2013-06-18
Also published as: GB2268461B; GB9213211D0; GB9312621D0

Abstract

A method of manufacturing flying surface and fuselage portions for an aircraft includes the steps of forming respective upper (44) and lower (46, 48) flying surface and fuselage skins at least one of which is an integrated i.e. unitary or one-piece flying surface and fuselage skin; forming a frame (24) including a plurality of transverse integrated fuselage and wing spar elements linked in longitudinal spaced apart relationship by longitudinal support members for supporting the respective upper and lower flying surface fuselage skins; machining the frame so as to match the contours required for the inner surfaces of the upper and lower flying surface skins; and attaching the respective upper and lower flying surface and fuselage skins to said frame. In this way the flying surfaces (wings, for example) and fuselage are both formed from the same structure (frame 24). Thus, the requirement for wing to fuselage attachment points is obviated, therefore saving weight and improving aerodynamic efficiency of the aircraft Frame 24 is of metal. Skins (44, 46, 48) may be of fibre-reinforced composites. <IMAGE>

Description

AIRCRAFT MANUFACTURE This invention relates to aircraft structural components and methods of manufacture thereof. More particularly the invention relates to flying surface and fuselage portions for an aircraft and to methods of manufacturing the same.

Conventional aircraft have an airframe comprising a central fuselage to which various flying surfaces (for example wings, tails, fins and canards) are attached.

Obviously it is vital that the flying surfaces are securely attached to the aircraft fuselage sufficiently well so that there is no danger of them becoming detached due to the various stresses encountered during flight. Further, in addition to the various devices for facilitating this attachment, fairings must be provided in the areas where the flying surfaces and fuselage join to avoid unnecessary drag.

However, the requirements for strong and safe attachment and low drag inevitably lead to increased aircraft mass and volume. As is well known to those skilled in the art, increased mass and volume is incompatible with requirements for fuel efficiency, manoeuvrability and space for occupants.

In GB patents no's 734,532 and 774,688 Fairey Aviation describe a delta winged aircraft structure in which the wing spars are at right angles to the fore and aft axis of the aircraft, a conventional arrangement with most aircraft but difficult at that time to achieve with a delta winged aircraft. The constructions described comprise either fuselage frames in the shape of rings with wing spars pinned to the rings on either side, or wing spars integral with left or right hand fuselage ring segments, the ring segments being pinned together during construction to form a complete fuselage skeleton. Some of the ring frame members have pivoting, part circumferential, portions to act as access doors to the engine or other internal aircraft elements. The fuselage and wing skins are applied separately to the ring frame members and the spars respectively.In all the constructions shown by Fairey Aviation a joint is required be it between wing spar and fuselage frame or opposite hands of a split fuselage frame.

A problem with the construction shown by Fairey Aviation in GB 734,532 in which fuselage rings are pinned to wing spar elements and then skins are applied separately to the fuselage and to the wings is that there is no continuous load path through either the spars, fuselage frames or the skins, leading to weight, complexity and cost penalties.

The construction shown in GB744,688 also needs two joints completed in a vertical centre line for the two piece version or three joints for the three piece version.

This gives rise to a fatigue critical area again with cost and weight penalties.

At the time of Fairey Aviation's inventions large scale forging of parts was not possible and the various elements of their construction were machined from plate metal. Consequently grain flow around the combined fuselage/wing spar elements is not controllable, as it would be with forging, for optimum strength.

It is an object of the invention to provide flying surfaces and a fuselage for an aircraft and a method of manufacture thereof which substantially eliminates, or at least reduces, the mass and volume penalties associated with the conventional design and the Fairey Aviation designs described above.

It is another object of the invention to provide a method of manufacturing an aircraft which is more efficient than the methods currently employed and which takes advantage of advances in forging technology.

According to one aspect of the present invention there is provided a method of. manufacturing flying surface and fuselage portions for aircraft, the method including the steps of: (i) forming respective upper and lower flying surface and fuselage skins at least one of which is an integrated flying surface and fuselage skin; (ii) forming a plurality of integrated transverse fuselage and wing spar elements; (iii) linking said elements in longitudinally spaced relationship to form a frame for supporting said respective upper and lower flying surface and fuselage skins; (iv) machining the frame so as to match the contours required for the inner surfaces of the upper and lower flying surface and fuselage skins; and (v) attaching said respective upper and lower flying surface and fuselage skins to said frame.

The term 'integrated' is used herein to mean unitary, or one-piece. Our frame may be a made in essentially one manufacturing operation and is designed to accept integrated fuselage and flying surface skins. In prior art methods of manufacture fuselage frames and wing frames were made and covered in separate operations and subsequently connected together.

By forming one frame which supports the upper and lower flying surface and fuselage skins, the need to attach the flying surfaces to the fuselage in separate operations is obviated, thus reducing weight and increasing rigidity.

Additionally, because the transverse fuselage and wing spar elements are integrated, it is a simple matter of design to make the area where the flying surface and fuselage meet aerodynamically efficient without the need for resorting to the use of wing-root fairings.

Conveniently, each integrated transverse fuselage and wing spar element is manufactured by forging it from metal, for example zinc or aluminium alloy.

Preferably, the machining of each fuselage and wing spar element or the assembly of these into a frame to the required contours is performed automatically using predetermined surface contour information. Advantageously the predetermined surface contour information may also be used in the forming of said respective upper and lower flying surface and fuselage skins. By using the same contour information to manufacture both the frame and the skins, the matching of the contours of the frame to the inner surfaces of the skins should be relatively precise.

Optionally the respective upper and lower flying surface and fuselage skins comprise composite materials, such as carbon fibre composites. The skins may be formed by mould tools, in which case the predetermined surface contour information may advantageously be used to define the surface contours of the mould tools.

Advantageously, a fuel tank may be formed in said flying surface and fuselage portion, and which extends from within said flying surface to within said fuselage. Such an arrangement is not possible with conventional aircraft flying surface and fuselage arrangements because they are separate components, and therefore often each incorporate a separate fuel tank. By having one fuel tank formed in the flying surface and fuselage, fuel may be stored more efficiently (because only one tank is required), and there is more freedom of choice as to where the tank should be located and what shape it should take, thereby allowing for greater capacity, battle damage tolerance and aircraft centre of gravity control.

According to another aspect of the invention there is provided an aircraft incorporating a frame comprising a plurality of integrated fuselage and wing spar elements manufactured according to the methods described above.

According to a further aspect of the invention there is provided a combined flying surface and fuselage portion for an aircraft including a frame comprising a plurality of transverse integrated fuselage and wing spar elements linked in longitudinal spaced relationship with longitudinal support elements and respective upper and lower flying surface and fuselage skins at least one of which comprises an integrated fuselage and flying surface skin said skins being attached to the frame, the frame having been machined to match the contours required for the inner surfaces of said skins.

For a better understanding of the invention, an embodiment of it will now be described by way of example only, and with reference to the accompanying drawings, of which: Figure 1 shows integrated fuselage and wing spar elements of a flying surface and fuselage portion of an aircraft ready for assembly into a frame; Figures 2 - 4 show a fuselage and flying surface frame, comprising the elements of Figure 1, at various stages of its manufacture; Figure 5 shows the assembly of an integrated fuselage and flying surface upper skin with the frame of Figure 4; Figure 6 shows the assembly of lower flying surface skins with the frame of Figure 4; Figure 7 shows the formation of the integrated fuselage flying surface upper skin of Figure 5; and Figure 8 shows an aircraft incorporating a flying surface and fuselage portion manufactured as shown in the previous Figures.

To improve understanding of the drawings, like elements which appear in more than one figure are designated by the same reference numbers.

Referring to the drawings, four integrated fuselage and wing spar elements 2, 4, 6 and 8 are forged in a known manner from a suitable material such as zinc alloy or aluminium alloy. As can be seen, the elements are transverse components of an aircraft frame each comprising a central body 10 from which two arms 12 extend by varying amounts. The central body 10 will form part of the fuselage of an assembled aircraft, and the pair of arms 12 extending therefrom will form a whole or part of respective flying surfaces of the aircraft. These flying surfaces could be wings, tail planes or canards, for example.In the embodiment described the arms 12 will form part of respective aircraft wings, the wings being of the folding variety and therefore comprising two sections: an inner section adjacent to the fuselage and an outer wingtip section hingedly attached to the inner section; although clearly it will be understood that the invention is equally applicable to aircraft with non-folding wings.

Each of the elements 2, 4, 6 and 8 are strengthened by relatively thick strengthening members 14 formed thereon which extend around the periphery of and across the elements. The strengthening members 14 may be formed by forging each of the elements so that they are thicker than required in use, and subsequently machining the surfaces selectively so as to define the relatively thick strengthening members 14. Additionally, the elements may be further modified as required in any particular application. For example, elements 2 and 4 each include two duct apertures 16 and intake apertures 18, while element 4 also includes undercarriage mountings 20.

Elements 6 and 8 each include an engine bay aperture 21 which, in element 8, opens out to the periphery thus forming a U-shaped recess therein. Link attachment points 22 are provided on the two re-entrant parts of the U-shaped recess in element 8. The link attachment points 22 allow a bracing member 23 to be attached there across after the aircraft engine has been fitted.

Further modification and assembly of other components on each of the elements 2, 4, 6 and 8 may then follow depending on the particular application. It should be appreciated that as much assembly work as possible should be done at this stage when accessibility to the elements is relatively easy.

When each of the elements has been prepared they are then located in an assembly jig (not shown) which supports each of the elements in their relative longitudinally spaced apart positions with respect to one another as required by a frame which is formed therefrom. Various connecting and longitudinal strengthening members are then positioned between the frame elements 2, 4, 6 and 8. These members may be attached by welding or any other suitable method.

Figures 2 - 4 show the assembly process of the frame 24 from the elements 2, 4, 6 and 8, shown in its finished state in figure 4. The strengthening and support members comprise wing leading edge spars 26, connecting elements 2 and 4, and which will provide support for the leading edge surface of the wings of the finished aircraft; outer ribs 28 connecting the outermost part of the arms 12 of elements 4, 6 and 8; intermediate rib sets 30 and 32 positioned at respective different points midway along the arms 12 and forming a connection between each of the elements 2, 4, 6 and 8 and leading edge spars 26; and sheer webs 34 and 36 connecting the inner part of the arms 12 of each of the elements 2, 4, 6 and 8, and the central body parts of the elements 4, 6 and 8 respectively.

The frame 24 is now formed and the fitting of various components required in the frame 24 of the aircraft can now be undertaken advantageously at this time while there is good accessibility.

The surfaces 38, 40 and 42 of the frame 24 to which the wing upper and lower skins will be attached are machined using a milling facility - preferably of the high-speed variety. The machining is robotically controlled using predetermined surface contour information which accurately defines the required shape for the outer surfaces of the frame 24.

Figures 5 and 6 show the assembly of upper skin 44, which is of integrated fuselage and flying surface construction to reduce weight, and lower skins 46 and 48 to the frame 24. When correctly located various holes are drilled for attachment of the skins 44, 46 and 48 to the frame 24 with the skins in situ. The skins are then again removed to facilitate attachment of the frame 24 to the other parts of the aircraft structure.

The upper and lower wing skins 44, 46 and 48 may be manufactured from composite materials, such as carbon fibre composite, in a well known manner. Figure 7 shows one example of such a forming process for forming the upper wing skin 44. A mould tool 50 includes a recessed portion 52 having the desired contours required for the inner surface of the upper wing skin. An appropriately shaped sheet of uncured composite material 54 (which will form the upper fuselage and wing skin 44) is positioned in the mould recess 52. Heat and pressure are then applied in an autoclave (not shown) to cure the material 54, which may then be removed from the mould tool 50 and attached to the frame 24. Lower wing skins 46 and 48 could be formed in a similar manner.

To ensure that the upper and lower wing skins 44, 46 and 48 fit precisely to the frame 24, the same predetermined surface contour information that was used to machine the outer surfaces 38, 40 and 42 of the frame 24 is also used to define the mould surface contours in the recess 52 of the mould 50, and likewise for the mould tools (not shown) for the lower wing skins. For example, the contour information could be utilised by a computer-controlled robot arm assembly to which a suitable tool for machining the mould tool 50 is attached.

The assembled frame 24 may then be attached to the front and rear fuselage sections 56 and 58 as shown in figure 8. Wingtip sections 60 and 62 are then hingedly attached to the outermost part of the arms 12 of the frame 24, and finally upper and lower wing skins 44, 46 and 48 are securely attached to the frame 24 by any suitable method using the attachment holes previously formed, thus completing aircraft assembly as shown in Figure 8. As an alternative to using attachment holes, the wing skins could be bonded to the frame or attached in many other ways known to those skilled in the art. After fitting of an engine to the fuselage, a central lower skin panel (not shown) will be fitted in the space between lower wing skins 46 and 48.

The combined flying surface and fuselage construction described above allows fuel to be housed therein between the skins - thereby forming a fuel tank which extends from within the flying surface to within the fuselage. Fuel flow is facilitated by forming holes in the inner frame elements 4, 6 and the intermediate rib sets 30, 32. The fuel may be simply contained by the skins, or may be contained in a flexible bag or by any other means.

Baffles may be incorporated into the tank to enable the regulation of fuel flow and hence control of the aircraft's centre of gravity.

It should be understood that the invention could equally well be applied to the manufacture of parts of aircraft other than the central fuselage portion incorporating the wings, for example a combined tail plane and rear fuselage unit could be made in a similar manner.

Claims

1. A method of manufacturing flying surface and fuselage portions for aircraft, the method including the steps of: (i) forming respective upper and lower flying surface and fuselage skins at least one of which is an integrated flying surface and fuselage skin; (ii) forming a plurality of integrated transverse fuselage and wing spar elements; (iii) linking said elements in longitudinally spaced relationship with longitudinal support elements to form a frame for supporting said respective upper and lower flying surface and fuselage skins; (iv) machining the frame so as to match the contours required for the inner surfaces of the upper and lower flying surface and fuselage skins; and (v) attaching said respective upper and lower flying surface and fuselage skins to said frame.

2. A method according to claim 1 wherein said integrated transverse fuselage and wing spar elements are manufactured by forging from metal.

3. A method according to claim 2 wherein said elements are manufactured from zinc or aluminium alloy.

4. A method according to any preceding claim, wherein said machining of the frame to the required contours is performed automatically using predetermined surface contour information.

5. A method according to claim 4, wherein said predetermined surface contour information is also used in the forming of said respective upper and lower flying surface and fuselage skins.

6. A method according to any preceding claim, wherein said respective upper and lower flying surface and fuselage skins comprise composite materials.

7. A method according to claim 6, wherein said materials are carbon fibre composite.

8. A method according to any preceding claim, wherein said respective upper and lower flying surface and fuselage skins are formed by mould tools.

9. A method according to claim 8 when dependent on claim 5, wherein said predetermined surface contour information is used to define the surface contours of said mould tools.

10. A method according to any preceding claim, wherein a fuel tank is formed in said flying surface and fuselage portion, and which extends from within said flying surface to within said fuselage.

11. An aircraft incorporating a flying surface and fuselage portion manufactured in accordance with a method as claimed in any preceding claim.

12. A flying surface and fuselage portion for an aircraft, including respective upper and lower flying surface and fuselage skins at least one of which is an integrated fuselage and flying surface skin; and a frame to which said skins are attached, the frame having been machined to match the contours required for the inner surfaces of said skins.

13. A method of manufacturing a flying surface and fuselage portion for an aircraft substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

14. A flying surface and fuselage portion for an aircraft substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.