GB2552216A - Stiffened aerospace structure and method of manufacture - Google Patents
Stiffened aerospace structure and method of manufacture Download PDFInfo
- Publication number
- GB2552216A GB2552216A GB1612276.4A GB201612276A GB2552216A GB 2552216 A GB2552216 A GB 2552216A GB 201612276 A GB201612276 A GB 201612276A GB 2552216 A GB2552216 A GB 2552216A
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- stiffener
- stiffened
- layer
- foot
- web
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- 238000004519 manufacturing process Methods 0.000 title claims description 15
- 238000000034 method Methods 0.000 title claims description 13
- 239000003351 stiffener Substances 0.000 claims abstract description 166
- 239000000463 material Substances 0.000 claims abstract description 151
- 239000002131 composite material Substances 0.000 claims abstract description 14
- 239000011347 resin Substances 0.000 abstract description 17
- 229920005989 resin Polymers 0.000 abstract description 17
- 239000010410 layer Substances 0.000 description 130
- 239000000835 fiber Substances 0.000 description 13
- 239000002184 metal Substances 0.000 description 9
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 239000002648 laminated material Substances 0.000 description 3
- 230000007704 transition Effects 0.000 description 3
- 239000000853 adhesive Substances 0.000 description 2
- 230000001070 adhesive effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 229920002430 Fibre-reinforced plastic Polymers 0.000 description 1
- 229920000914 Metallic fiber Polymers 0.000 description 1
- 238000004026 adhesive bonding Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 239000011151 fibre-reinforced plastic Substances 0.000 description 1
- 238000001802 infusion Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
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- 239000002356 single layer Substances 0.000 description 1
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
- B29D99/00—Subject matter not provided for in other groups of this subclass
- B29D99/0003—Producing profiled members, e.g. beams
- B29D99/0007—Producing profiled members, e.g. beams having a variable cross-section
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C1/00—Fuselages; Constructional features common to fuselages, wings, stabilising surfaces or the like
- B64C1/06—Frames; Stringers; Longerons ; Fuselage sections
- B64C1/064—Stringers; Longerons
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C1/00—Fuselages; Constructional features common to fuselages, wings, stabilising surfaces or the like
- B64C1/06—Frames; Stringers; Longerons ; Fuselage sections
- B64C1/12—Construction or attachment of skin panels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C3/00—Wings
- B64C3/18—Spars; Ribs; Stringers
- B64C3/182—Stringers, longerons
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C3/00—Wings
- B64C3/26—Construction, shape, or attachment of separate skins, e.g. panels
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Aviation & Aerospace Engineering (AREA)
- Moulding By Coating Moulds (AREA)
- Laminated Bodies (AREA)
Abstract
A stiffened aerospace structure comprise a stiffener, for example a stringer 4, bonded to a member to be stiffened, for example an aircraft wing panel 2. The stiffener has a foot 6 and a web 7, each extending along the length of the stiffener. A further layer of material 20 covering an end of the stiffener is bonded both to the member and to the foot, and includes a slot 22 through which the web of the stiffener extends. The further layer of material is bonded, for example, by co-cured resin, and acts to resist or prevent peel-off loads that would otherwise cause the stiffener at its termination to peel off from the member to which it is attached. The stiffener, member and further layer of material may be composite materials and may be bonded together by means of a co-infused co-cured resin material.
Description
(54) Title ofthe Invention: Stiffened aerospace structure and method of manufacture Abstract Title: Stiffened aerospace component and method of manufacture (57) A stiffened aerospace structure comprise a stiffener, for example a stringer 4, bonded to a member to be stiffened, for example an aircraft wing panel 2. The stiffener has a foot 6 and a web 7, each extending along the length of the stiffener. A further layer of material 20 covering an end of the stiffener is bonded both to the member and to the foot, and includes a slot 22 through which the web of the stiffener extends. The further layer of material is bonded, for example, by co-cured resin, and acts to resist or prevent peel-off loads that would otherwise cause the stiffener at its termination to peel off from the member to which it is attached. The stiffener, member and further layer of material may be composite materials and may be bonded together by means of a co-infused co-cured resin material.
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STIFFENED AEROSPACE STRUCTURE AND METHOD OF MANUFACTURE
BACKGROUND OF THE INVENTION [0001] The present disclosure concerns a stiffened aerospace structure and a method of manufacturing such a structure.
[0002] Embodiments of this invention relate to an aerospace structure, that may for example form, or be intended for forming, part of an aerospace component. In this context, such an aerospace component includes one that forms part of a fixed-wing aircraft, a helicopter, a missile, a satellite, a space structure or the like. The invention relates however particularly, but not exclusively, to aircraft panels, such as wing skins, stiffened by one or more stiffeners, for example in the form of stringers. A stringer is typically provided in the form of a stiffening member which extends in a lengthwise direction, has a foot which is glued to, cocured with, or otherwise bonded to, the surface of a panel being stiffened, and a has web (for example a “vertical web”) which extends from the foot and away from the surface of the panel.
[0003] In an aerospace component, where a flat or curved panel is reinforced with one or more stiffening members, the location where that stiffener terminates is often subject to significant stress. For example, in the case where stringers are used to stiffen the internal surface of the skin of an aircraft wing, flexing of the wing during operation of the aircraft may cause high stresses particularly in the region of the stringer run-outs. Extra support and/or protection to the stiffener termination location is therefore often required.
[0004] The stiffener termination design can be a challenge due to the high stress occurring at the termination of the stiffener. The primary stress comes principally from two modes:
- a first mode due to the transfer of in-plane load from the stiffener to the panel causing a shear stress and
- a second mode due to the out-of-plane deflection of the termination of the stiffener, for example arising from the offset of the stiffener from the panel and/or the out-of-plane deflection of the panel/stiffener, either of which causing “peel stress”.
[0005] There have been proposed several ways in which to deal with such issues.
[0006] Firstly, it has been proposed to reduce the stiffness of the stiffener at the termination. This may be achieved by modifying the cross sectional area of the stiffener (i.e. reduced vertical web height, thinning of stiffener web and/or foot) and/or changing the layup (i.e. in the case where the materials are composite laminate materials).
[0007] Secondly, it has been proposed to increase the area of load diffusion at the termination of the stiffener. This may be achieved by running out the vertical web and continuing on the stiffener foot and splaying/fanning out the stiffener foot, in a widthwise direction, to cover a larger area.
[0008] Thirdly, it has been proposed to apply one or more through-thickness attachments, such as one or more bolts, rivets or the like, directly between the stiffener foot and panel to give additional structural support to the stiffener-panel attachment region. This acts to constrain the substrates against peel, and to arrest any cracks which may form if in the connection between the stiffener and panel.
[0009] Lastly, it has been proposed to bolt an additional structural element, such as a strap or plate, to enable transfer of load from the stiffener to the panel (to stabilise the termination location) and/or to prevent the peel failure (e.g. by adding a scarf plate).
[0010] All of the aforementioned solutions suffer from one or more disadvantages. Some add complexity in manufacturing. All add extra mass. Some may suffer from similar peel-off problems in time and therefore only defer the problem or require additional measures to be taken. It may be that a combination of two or more of the solutions described above is required to reduce the risk of peel-off to a level that is sufficient for long-term commercial use in an aircraft. Such a solution is proposed by US 2013/0313391 (Airbus), which discloses the use of a metal plate for mechanically clamping the end of a stringer to a wing skin. US 2013/0313391 proposes a combination of the following features: (a) a stringer foot comprising multiple plies of composite material and having a thickness which decreases towards the end of the stringer foot by means of a progressive reduction in the number of plies, and (b) attaching a metal plate over the end of the foot, wherein the plate has a shape that complements the reducing thickness of the stringer foot and is mechanically secured with bolts to both the stringer foot and the skin the plate. The use of bolts or other mechanical fixings provides a mechanical solution which substantially prevents peel-off but may suffer from other disadvantages such as for example bringing undesirable additional complexity at the assembly stage and/or an increased part count.
[0011] The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved or alternative stiffened aerospace structure and/or a method of making the same.
SUMMARY OF THE INVENTION [0012] The present invention provides, according to a first aspect, a stiffened aerospace structure comprising a member to be stiffened and a stiffener having a length, wherein the stiffener has a foot from which a web extends, the web extending along the length of the stiffener, the member has a first surface onto which a first surface of the foot of the stiffener is bonded, there being a second surface of the foot of the stiffener, which is on the opposite side of the foot to the first surface of the foot, the stiffened aerospace structure includes a further layer of material covering an end of the stiffener, the further layer of material is bonded both to the first surface of the member and the second surface of the foot, and the further layer of material includes a slot through which the web of the stiffener extends.
[0013] According to a second aspect of the invention there is also provided a method of manufacturing a stiffened aerospace structure comprising arranging a layer of material, a member to be stiffened and a stiffener so that the member to be stiffened and the stiffener are positioned against each other, the layer of material lies over a foot of the stiffener extending to either side of a web of the stiffener, the layer of material also extends to cover a portion of the member to be stiffened, and bonding the layer of material to both the foot and to the member to be stiffened, whereby the layer of material is, in use of the stiffened aerospace structure so made, thus arranged to resist peel-off loads which might otherwise urge the end of the stiffener to peel off from the member to be stiffened.
[0014] According to other aspects of the invention there is also provided an aircraft panel stiffened with multiple stringers, wherein the aircraft panel is in accordance with the stiffened aerospace structure of the invention as described or claimed herein and an aircraft including multiple such panels.
[0015] There is also provided an anti-peel product for use in protecting the end of a stringer from peeling off from an aircraft panel, wherein the anti-peel product is in the form of a layer of material configured and adapted in accordance with the present invention as described or claimed herein.
[0016] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.
DESCRIPTION OF THE DRAWINGS [0017] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:
Figure 1 is a cut-away perspective view showing an end of a panel and three stringers bonded to the panel;
Figure 2 is a cut-away perspective view showing an end of a single stringer on a portion of a panel;
Figure 3 is a cut-away perspective view showing an additional layer of material being added to the arrangement of Figure 2 thus illustrating a first embodiment of the invention;
Figure 4 shows the arrangement of Figure 3 after the additional layer has been bonded to the panel and stringer;
Figure 5 is a cut-away perspective view showing an end of a panel and three stringers bonded to the panel in accordance with a second embodiment of the invention;
Figure 6 is a cut-away perspective view showing an end of a panel and three stringers bonded to the panel in accordance with a third embodiment of the invention;
Figure 7 shows a cross-section of a stringer used in the first embodiment;
Figures 8 to 11 show alternative cross-sections of stringers that may be used in other embodiments;
Figure 12 is a cut-away perspective view showing additional layers of material being added to the arrangement of Figure 2; illustrating a fourth embodiment of the invention;
Figure 13 shows the arrangement of Figure 12 after the additional layers have been bonded to the panel and stringer;
Figure 14 is a plan view of an aircraft incorporating a wing cover which includes a panel according to that shown in Figure 4; and
Figure 15 is a flow diagram illustrating a method according to a fifth embodiment of the invention.
DETAILED DESCRIPTION [0018] Certain embodiments of the present invention relate to a stiffened aerospace structure comprising a member to be stiffened, such as an aircraft wing panel for example, and a stiffener, such as a stringer for example, for stiffening that member. The stiffener will typically have a discernible length, width and height. The width and length will typically be in a plane that is generally aligned with the local surface of the member to be stiffened. (The length, width and height of other parts of the stiffened aerospace structure will typically be assumed to be in the same direction as the length, width and height of the stiffener, unless the context suggests otherwise). The stiffener has a foot from which a web extends, the web extending along the length of the stiffener. The foot of the stiffener is bonded to the member. The surface of the foot which is bonded to the member will be referred to as the first surface of the foot. Likewise, the surface of the member which is bonded to the foot will be referred to as the first surface of the member. It will be appreciated that the foot also has a second surface, which is on the opposite side of the foot to the first surface of the foot.
[0019] The stiffened aerospace structure includes a further layer of material covering an end of the stiffener, for the purposes of resisting peel-off loads, which might in time otherwise cause the end of the stiffener to peel-off- i.e. partially detach from - the member. The further layer of material is bonded to the first surface of the member. The further layer of material is also bonded to the second surface of the foot. The further layer of material includes a slot through which the web of the stiffener extends. Thus, it may be that the further layer of material is able to cover a relatively large surface area of the second surface of the foot, extending to regions significantly inward of the end of the stringer, whilst also being bonded to the member in the regions immediately surrounding the end of the stringer. Loads that might otherwise contribute a risk of peel-off may be spread out and/or resisted by the further layer of material in an effective manner. The bonding of the further layer of material may be effected without the need for bolts, rivets of the like. The use of run-off plates, extra straps or the like may be avoided. Part-count may thus be reduced. Assembly time, and in-tank work, may be lower than the case where bolts, rivets or other fixings are used to prevent/reduce the risk of peel-off [0020] As will be clear from the contents of this patent specification, the term “bonded” as used in the context of the present invention covers the fixing/securing of one thing to another by means of an adhesive, by means of cured resin, and/or by means of being formed together as a unitary structure as in the case for example when co-curing composite material parts of a larger component. Objects that are secured only by mechanical means, such as bolts, rivets or the like, are not considered to be bonded together.
[0021] The height of the web of the stiffener may be constant for the majority of its length. It may be that the height of the web of the stiffener tapers down towards the end of the stiffener. The height of the web at any given cross-section may for convenience’s sake be taken as the greatest height of the stiffener as measured in a perpendicular direction from the plane of the second surface of the foot. It may be that the web terminates, lengthwise, at a position spaced apart from and inward of the end of the stiffener. The further layer of material may terminate, lengthwise, at a position inward, along the length of the stiffener, of the position at which the web terminates. The further layer of material may cover substantially all of the second surface along the length of the portion of the foot which extends between the end of the foot and the inward position at which the web terminates. In the case where the web tapers down, the further layer of material may terminate at a position inward, along the length of the stiffener, of the position at which the web starts to taper. The further layer of material may terminate at a position inward, along the length of the stiffener, of the position at which the web is at a height greater than 90% of its average height along its length (which in the case where the web tapers may be at lengthwise position where the web is tapering). The foot of the stiffener may have a run-out portion towards the end of the stiffener, for example including a region where the web-height tapers down and an adjacent region where no discernible web is provided on the foot. The further layer of material may extend beyond (for example, in the outward direction, away from the stiffener, but parallel to its length) the end of the stiffener by a significant distance. For example, the further layer of material may extend beyond the end of the stiffener by a distance which is at least twice the average width of the foot of the stiffener in the region covered by the further layer of material. The further layer of material may extend beyond the end of the stiffener by a distance which is at least 50mm.
[0022] The further layer of material may have an average width which is greater than twice the average width of the foot of the stiffener in the region covered by the further layer of material. The further layer of material may have a length (measured in the same direction as the length of the stiffener), which is greater than three times the average width of the foot of the stiffener in the region covered by the further layer of material. The further layer of material may, in certain embodiments, have a length (measured in the same direction as the length of the stiffener) greater than its width.
[0023] It may be that the slot of the further layer of material has a length which is greater than twice the average width of the foot of the stiffener in the region covered by the further layer of material. It may be that the slot of the further layer of material has a length which is greater than half of the length of the further layer of material. It may be that the slot of the further layer of material has an average width which is less than half the average width of the foot of the stiffener in the region along the length of the slot. The slot may be long and thin in shape. For example, the aspect ratio may be longer/thinner than 5:1, and possibly longer/thinner than 10:1. The lengthwise edges of the further layer of material which define the slot may be positioned directly adjacent to the portion of the stiffener at the same height. The web may fit snugly within the slot. Each lengthwise edge of the slot may be positioned such that there is contact, or only a negligible gap, between the edge of the slot and the stiffener in the region of the base of the web.
[0024] It may be the case that the junction between the web and the foot of a stiffener is in the form of a smooth transition from foot to web. There may be a curved section at the junction between the web and the foot. Where there is such a curved section/smooth transition and in the case where the exact location of the junction at which the foot ends and the web begins is not readily apparent to the skilled person, the junction may be deemed as being at the location at which the line defining the shape of the outwardly-facing surface of the stiffener when viewed in cross-section is closer to being perpendicular to the surface of the member to be stiffened than it is to being parallel.
[0025] The further layer of material may have the general shape of a rectangle in which a slot is formed. The further layer of material may thus have a footprint in the general form of a flat-bottomed U-shape. The slot may have a generally rectangular shape. The slot will typically have an open end, inward of the end of the stiffener and a closed end outward (beyond) the end of the stiffener.
[0026] The foot of the stiffener may have a width which is approximately constant along its length. If the foot has a varying width, the average width along a given length may be calculated by discounting the narrowest widths for 10% of the length, discounting the widest widths for 10% of the length, and taking the mean average width for the remaining 80% of the length. Other average widths, lengths and the like, as mentioned herein, may be similarly calculated.
- 8 [0027] The further layer of material may have an average width of greater than 100mm, preferably greater than 200mm. The further layer of material may have an average length of greater than its average width. The further layer of material may have a length of greater than 200mm, preferably greater than 400mm. The further layer of material may have a maximum thickness of greater than 0.5mm. The further layer of material may have a maximum thickness of 1mm or greater. The further layer of material may have a maximum thickness of less than 3mm.
[0028] The member to be stiffened may have an average thickness of greater than 5mm. The member to be stiffened may have an average thickness of less than 50mm, and may have a thickness of less than 20mm in certain embodiments.
[0029] The further layer of material may be one of many such further layers that are arranged one on top of the other.
[0030] One or more of the layer of material, the member to be stiffened and the stiffener may comprise laminated material, for example composite material. The composite material may, at least in part, be fibre-metal laminate material. The composite material may, at least in part, be carbon fibre reinforced polymer (“CFRP”) material. The further layer of material may itself be formed of multiple sub-layers. In the case where the further layer of material is a layer of composite fibre material, the further layer of material may comprise multiple plies of fibre material. Each ply may have fibres aligned in a particular direction. There may be a ply aligned with the length of the stiffener (the 0° direction). There may be a ply with fibres aligned with the width of the stiffener (the 90° direction). There may be two plies with fibres aligned with the 45° direction and the 135° direction, respectively. There may be at least four plies all having different directions of alignment. The multiple plies may be woven. Alternatively, the multiple plies may be non-woven but nevertheless held together as a single fibre mat (a non-crimp blanket for example). The multiple plies may, for example, be stitched together optionally by means of one or more non-structural stitches. Each ply may have a thickness of between 0.01mm and 2.5mm, optionally between 0.1mm and 0.5mm. In certain embodiments, each ply may have a thickness of about 0.25mm [0031] The average height of the web of the stiffener may be greater than 10mm, and may be 20mm or greater. The web may have a thickness of greater than 1mm, and may be 2.5mm or greater.
[0032] The member to be stiffened may be sheet-like in form, for example being in the form of a panel.
[0033] ] The member may be stiffened by means of multiple stiffeners. Not all such stiffeners need to be configured in accordance with the present invention.
[0034] The member is typically sheet-like in shape, for example having a length and width significantly greater than its thickness. The member may be substantially flat in shape, but will typically have some curvature. The member may have a substantially constant thickness, but there may be embodiments in which the member has some regions that are thicker than others.
[0035] The stiffener may have a cross-sectional shape that is generally the same along its length. It will be appreciated that the cross-section may vary along the length, but nevertheless have a shape that is readily discernible to the skilled person. The stiffener may have a cross-sectional shape in the form of an inverted T. The stiffener may have a crosssectional shape which is L-shaped. The stiffener may have a cross-sectional shape which is Ishaped. The stiffener may have a cross-sectional shape in the general form of the crosssection of a top-hat. The stiffener may have a cross-sectional shape which is Ω-shaped (taking the general form of the Greek letter omega). The web of the stiffener may extend generally vertically from the foot. The shape of the web, in cross-section, may include some sections which are inclined closer to the horizontal than the vertical. The web of the stiffener need not extend perpendicularly from the foot, nor does the web need to be straight in crosssection, and may in some embodiments be curved. If the second surface of the foot is nonplanar then, for a given cross-section along the length of the stiffener, the plane may be taken as coinciding with the line of best fit of the second surface of the foot.
[0036] Certain embodiments of the present invention relate to a method of manufacturing a stiffened aerospace structure. Such a method may comprise a step of arranging a layer of material, a member to be stiffened and a stiffener (a) so that the member to be stiffened and the stiffener are positioned against each other (for example in contact, preferably direct contact, with other), (b) so that the layer of material lies over a foot of the stiffener extending to either side of a web of the stiffener, and (c) so that the layer of material also extends to cover a portion of the member to be stiffened. The method then includes a step of bonding the layer of material to both the foot and to the member to be stiffened. The method may thus be so performed that the layer of material is, in use of the stiffened aerospace structure so made, arranged to resist peel-off loads which might otherwise urge the end of the stiffener to peel off from the member to be stiffened. It may be that the layer of material includes a slot through which the web of the stiffener extends. It may be that the layer of material covers an end of the stiffener.
[0037] The layer of material may be over-engineered (for example being bigger, more massive, stronger and/or have enhanced mechanical properties) so that it contributes to the structural and mechanical properties and performance of the stiffened aerospace structure so made. For example, the layer of material may be configured (e.g. may be designed to have a size, shape, mechanical properties) such that it not only resists peel-off loads, but also contributes to the structural strength of the member to be stiffened, preferably to the extent that the layer of material is larger than required for the purpose of only resisting peel-off loads, thereby allowing the combination of the member and the stiffener to be smaller than would be required absent the layer of material. As such it may then be possible to design the member to be stiffened and/or the stiffener taking into account the beneficial properties that will be provided by the layer of material. The combination of the member to be stiffened and the stiffener may be designed to be smaller than would otherwise be required absent the layer of material. By designing the properties (for example, the size, shape, material/mechanical properties) of the layer of material such that it not only resists peel-off loads, but also contributes to the structural strength of the member to be stiffened, the performance of the stiffened aerospace structure so made may be improved with little or no significant increase in overall mass. It may for example be that the further layer of material adds to the thickness to provide a level of strength to the structure that is required and which would not be provided without the extra layer.
[0038] It may be advantageous effectively to embed the foot of the stiffener within the stiffened aerospace structure manufactured. The method may be so performed that the layer of material lies over the foot of the stiffener and extends along the entire length of the stiffener. It may be that the layer of material extends along either side of the web of the stiffener for the entire length of the web. It may be that the layer of material extends over a sufficient proportion of the second surface of the foot (substantially the entire surface) that the foot of the stiffener may be considered as being embedded in the stiffened aerospace structure so manufactured.
[0039] There may be multiple stiffeners. Each stiffener may be covered with a respective layer of material for resisting peel-off loads. In some embodiments, a single layer of material lies over a foot of each of two or more stiffeners. In such a case, it may be that the layer of material has a length (measured in the same direction as the length of a stiffener) which is less than its width. The stiffeners may be arranged so that adjacent pairs are separated by a distance of between 150mm and 400mm, preferably between 180mm and 300mm.
[0040] It may be, at least once the stiffened aerospace structure has been produced, that one, preferably two or optionally all three of (i) the layer of material, (ii) the member to be stiffened and (iii) the stiffener is in the form of composite material. It may be that at least two of the layer of material, the member to be stiffened and the stiffener are initially provided in the form of uncured material and the step of bonding the layer of material includes co-curing said at least two of the layer of material, the member to be stiffened and the stiffener. It may be that all of the layer of material, the member and the stiffener are initially provided in the uncured form and all are co-cured together.
[0041] At a stage, before the step of bonding the layer of material to the foot and the member to be stiffened, one or both of the foot and the member to be stiffened may comprise cured resin. At this stage, it may be that one or both of the foot and the member to be stiffened comprises “pre-preg” (i.e. one or more fibre layers pre-impregnated with resin). At this stage, it may be that one or both of the foot and the member to be stiffened comprises dry fibre layers (i.e. one or more fibre layers which are not pre-impregnated with resin).
[0042] The step of bonding the layer of material to both the foot and to the member to be stiffened may comprise co-curing the layer of material and the foot (optionally with the member to be stiffened having already, previously, been partially or fully cured). The step of bonding the layer of material to both the foot and to the member to be stiffened may comprise co-curing the layer of material and the member to be stiffened (optionally with the stiffener having already, previously, been partially or fully cured). The step of bonding the layer of material to both the foot and to the member to be stiffened may comprise co-curing all of the layer of material, the member to be stiffened and the foot. The step of bonding may include a step of curing resin. The step of bonding the layer of material to both the foot and to the member to be stiffened may comprise adding a quantity of resin to the assembled layer of material, member to be stiffened and stiffener. There may be a step of causing resin to infuse into fibre material as part of the bonding step. The step of bonding the layer of material to both the foot and to the member to be stiffened may comprise co-infusing, with resin, at least two of (and optionally all of) the layer of material, the member to be stiffened and the foot. The step of bonding the layer of material to both the foot and to the member to be stiffened may comprise providing at least one of the layer of material, the member to be stiffened and the foot in a form that comprises material pre-impregnated with resin (e.g. as “pre-preg”).
[0043] The step of bonding the layer of material to both the foot and to the member to be stiffened may comprise gluing, at least in part, the layer of material to either or both the foot and the member to be stiffened. One or more layers of adhesive may be added.
[0044] One or more of the layer of material, the member to be stiffened and the stiffener may comprise non-metallic fibres. One or more of the layer of material, the member to be stiffened and the stiffener may comprise a layer of metal. The layer of metal may be in the form of a sheet. The layer of metal may have a thickness of less than 1mm. For example, the layer of metal may form a fibre metal laminate structure.
[0045] Certain embodiments of the present invention relate to an aircraft panel stiffened with multiple stringers, wherein the aircraft panel is in accordance with the stiffened aerospace structure as described or claimed herein. Such an aircraft panel may include one or preferably more stringers embedded within the panel. Certain embodiments of the present invention relate to an aircraft including multiple such panels, each panel being in accordance with the panel of the present invention as described or claimed herein.
[0046] Certain embodiments of the present invention relate to an anti-peel product for use in protecting the end of a stringer from peeling off from an aircraft panel. The anti-peel product may be provided separately from the stringer and/or the aircraft panel. The anti-peel product will typically be in the form of a layer of material configured and adapted for use as the further layer of material of the present invention as described or claimed herein.
[0047] There now follows a description of specific embodiments, including the embodiments illustrated by the accompanying Figures.
[0048] Figure 1 shows an aircraft wing panel 102 on which are mounted three stringers 104. The stringers 104 and panel 102 are all made from CFRP composite material. The panel 102 has a thickness, ζ of about 10mm. Only part of the length of the stringers and of the panel are shown in Figure 1. In the remaining Figures, sections of panel s/stringers are shown for the ease of illustration. Figure 2, shows a section of one of the stringers 104 and a section of the panel 102 shown in Figure 1. (It will be appreciated that only part of the panel is shown and that the stringer extends to the right of Figure 2, and that only a small portion is shown near one end of the stringer.) [0049] With reference to Figure 2, the stringer 104 has a foot 106 bonded to the panel and a vertical web 107 which extends vertically from the foot. Thus, a first surface (hidden from view) of the foot (the underside of the foot in the view shown in Figure 2) is bonded to a first surface (the uppermost surface 108) of the panel 102. The foot has a second (uppermost) surface 110. The foot 106 of the stringer 104 has portions (not shown) which are wider at regions where the stringer intersects with a rib (rib grow-outs). At such wider portions the stringer has a width of about 150mm. At the regions between such rib grow-outs, which account for less than 10% of the length of the stringer typically, the foot has a substantially constant width of about 80mm. The web 107 of the stringer has a height, at its tallest, of about 120mm, and an average height of about 80mm. Figure 2 shows one end 112 of the stringer, at which the stringer terminates. At the termination there is a run-off portion, including a first portion 114 where the height of the vertical web tapers down to zero and a second portion 116 where the foot has no significant web. During use the panel may be subject to flexure and there is a risk, unless preventative measures are taken, of “peel-off’ loads causing debonding of the end of the stringer from the panel. As such, it is known to provide some extra mechanical fixings in the region of the termination of the stringer. As shown in Figure 3, the present embodiment instead uses a layer 20 of additional surface material, which is laid over and bonded to the stiffener 4 and panel 2, to enable a smoother transition of load, to add local stiffening and to reduce the peak peel-stress loads. The layer 20 of additional material includes a slot 22 through which the web 7 of the stringer 4 protrudes, as shown in Figure 4, which illustrates the panel 2 stiffened with the stringer 4 and the layer 20 of additional material bonded thereto to reduce the risk of peel-off.
[0050] The layer 20 of surface material has a width W of about 250mm and is in the form of a 4-ply non-crimp blanket of carbon fibre, with plies in the 0, 45, 90 and 135 degree directions. The thickness of the layer of surface material is about 1mm. Such blankets may be supplied in widths of about 1.2m and may therefore need to be cut to size. The length L of the layer 20 is about 400mm.
[0051] Figure 4 shows the outline of the foot 6 of the stringer in broken line 26. There is a slight incline in the region of the outline of the foot as the layer 20 of additional material overlies the slight step (see Figure 3) from the first surface 8 of the panel to the second surface 10 of the foot 6. It is possible in other embodiments for the shape of the foot to taper or to have a chamfer so that there is less of a step between the foot and the panel.
[0052] Figure 5 shows how multiple stringers 204 on a single panel 202 may be treated using multiple additional layers 220, one layer per stringer termination, in accordance with a second embodiment. The stringers are regularly spaced apart, with a pitch of 250mm. In a variation of Figure 5, the multiple additional layers 220 may be wider so that they abut one another.
[0053] Figure 6 shows how multiple stringers 304 on a single panel 302 may be treated using a single additional layer 320, there being one layer for all three stringer terminations, in accordance with a third embodiment. Foads may be spread further using such an arrangement. There needs however to be adjustment to the design of the panel, stringer feet or panel thickness, if overall mass is not to be increased.
[0054] It will be appreciated that the advantages of the embodiments described and illustrated herein may be of benefit in relation to stringers, or other stiffeners, having a profile with a shape that is different in cross-section from that of the stringer shown in Figure 2. The stringer of Figure 2 has an inverted T-shape, as shown schematically in Figure 7. Other possible shapes are shown, by way of example only (there may be others) in Figure 8 (backto-back F-shapes, which together form an inverted T-shape), Figure 9 (F-shape), Figure 10 (top-hat), and Figure 11 (omega-shape). The junction between web and foot of the stringer cross-section shown in Figure 11 is shown by the reference j, whereas the height of the web is indicated as h.
[0055] Figure 12 illustrates a fourth embodiment, which is in the form of a variation on the first embodiment shown in Figure 3. In the embodiment of Figure 3, there is a slight incline in the region of the outline of the foot as the layer of additional material overlies the slight step from the first surface of the panel to the second surface of the foot. The fourth embodiment includes a step of adding an intermediate layer 430 which reduces or removes that step. The intermediate layer 430 thus has the same overall width and length as the upper additional layer 420, but has a wider slot 432. The wider slot 432 (as compared to slot 422) of the intermediate layer 430 accommodates the foot 406 of the stringer 404, and is substantially the same width or very slightly wider than the width of the foot.
[0056] Figure 13 shows the arrangement 440 of Figure 12 after the additional layers 420, 430 have been bonded to the panel 402 and stringer 404. There is substantially no step or change in incline in the uppermost additional layer 420 of material in region of the outline of the foot of the stringer 404.
[0057] Figure 14 is a plan view of an aircraft 500, according to a further embodiment, incorporating a wing cover 550 which includes a panel 502 according to the first embodiment (for example that shown in Figure 4). The section of the panel which includes a stiffener termination is shown in broken line 552 in Figure 14.
[0058] Figure 15 is a flow diagram 600 illustrating a method according to a fifth embodiment of the invention.
[0059] As a first step, represented by box 601, a CFRP stringer is positioned on a wing skin panel. Both the wing skin panel and stringer are pre-formed dry fibre awaiting resin infusion. The arrangement may look like that shown in Figure 2 for example.
[0060] The next step (box 602) includes laying (see Figure 3 for example) one or more additional (fry-fibre) plies of CFRP, which have a cut out to allow for the stiffener vertical web, over the top of the stiffener and panel.
[0061] Once the additional ply or plies are in place, the complete component is then coinfused with resin and cured (the step represented by box 603), under vacuum and/or pressure, to produce a fully integral component. The component may look like that shown in Figures 4 or 13 for example. Various finishing steps are then performed (represented by box 604) such that the component if ready for use.
[0062] Once in place the additional ply/plies will serve the purpose of diffusing the load more gradually from the stiffener into the panel as well as supporting the stiffener termination in the out of plane sense and reducing the peel stress. This therefore acts as an integrated stiffener diffusion device without the need for additional mechanical fastening or additional structural elements.
[0063] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.
[0064] Embodiments could additionally employ different stringer termination geometries to lessen peel-off loads (stress, for example) by tapering the thickness of the stringer foot, splaying out the footprint of the stringer foot, and/or reducing the stiffness of the stiffener by varying the layup (in terms of a CFRP) and/or geometry.
[0065] Embodiments of the invention may concern any metallic or composite materials on any aerospace structure. Certain processes described above use carbon fibre composite (CFRP) materials co-infused with resin. Embodiments of the invention may alternatively/additionally use pre-preg or other formats of CFRP. Embodiments could also potentially be applied to metallic stiffeners, for example for stiffening fibre metal laminate panels. Resin may be cured in an autoclave in certain embodiments.
[0066] The number of plies may be different than described above and different orientations can be considered depending on the requirements.
[0067] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.
Claims (20)
1. A stiffened aerospace structure comprising a member to be stiffened and a stiffener having a length, wherein the stiffener has a foot from which a web extends, the web extending along the length of the stiffener, the member has a first surface onto which a first surface of the foot of the stiffener is bonded, there being a second surface of the foot of the stiffener, which is on the opposite side of the foot to the first surface of the foot, the stiffened aerospace structure includes a further layer of material covering an end of the stiffener, the further layer of material is bonded both to the first surface of the member and the second surface of the foot, and the further layer of material includes a slot through which the web of the stiffener extends.
2. A stiffened aerospace structure according to claim 1, wherein the height of the web tapers down towards said end of the stiffener.
3. A stiffened aerospace structure according to claim 1 or claim 2, wherein the web terminates at a position spaced apart from and inward of said end of the stiffener.
4. A stiffened aerospace structure according to claim 3, wherein the further layer of material terminates at a position inward, along the length of the stiffener, of the position at which the web terminates.
5. A stiffened aerospace structure according to the combination of claims 2 to 4, wherein the further layer of material terminates at a position inward, along the length of the stiffener, of the position at which the web is at a height greater than 90% of its average height along its length.
6. A stiffened aerospace structure according to claim 5, wherein the further layer of material extends beyond the end of the stiffener by a distance which is at least twice the average width of the foot of the stiffener in the region covered by the further layer of material.
7. A stiffened aerospace structure according to any preceding claim, wherein the further layer of material has an average width which is greater than twice the average width of the foot of the stiffener in the region covered by the further layer of material, the further layer of material has a length greater than its width and the slot of the further layer of material has a length which is greater than twice the average width of the foot of the stiffener in the region covered by the further layer of material.
8. A stiffened aerospace structure according to any preceding claim, wherein the slot of the further layer of material has an average width which is less than half the average width of the foot of the stiffener in the region along the length of the slot.
9. A stiffened aerospace structure according to any preceding claim, wherein the lengthwise edges of the further layer of material which define the slot are positioned directly adjacent to the lengthwise edges of the base of the web.
10. A stiffened aerospace structure according to any preceding claim, wherein the member to be stiffened is sheet-like in form and is stiffened by means of multiple stiffeners.
11. A method of manufacturing a stiffened aerospace structure comprising arranging a layer of material, a member to be stiffened and a stiffener so that the member to be stiffened and the stiffener are positioned against each other, the layer of material lies over a foot of the stiffener extending to either side of a web of the stiffener, the layer of material also extends to cover a portion of the member to be stiffened, and bonding the layer of material to both the foot and to the member to be stiffened, whereby the layer of material is, in use of the stiffened aerospace structure so made, thus arranged to resist peel-off loads which might otherwise urge the end of the stiffener to peel off from the member to be stiffened.
12. A method of manufacturing a stiffened aerospace structure according to claim 11, wherein the layer of material is configured such that it not only resists peel-off loads, but also contributes to the structural strength of the member to be stiffened to the extent that the layer of material is larger than required for the purpose of only resisting peel-off loads but the combination of the member to be stiffened and the stiffener is smaller than would be required absent the layer of material.
13. A method of manufacturing a stiffened aerospace structure according to claim 11 or claim 12, wherein the layer of material lies over the foot of the stiffener and extends along the entire length of the stiffener and along either side of the web of the stiffener for the entire length of the web such that the foot of the stiffener is embedded in the stiffened aerospace structure so manufactured.
14. A method of manufacturing a stiffened aerospace structure according to any of claims 11 to 13, wherein there are multiple stiffeners and the layer of material lies over a foot of each stiffener.
15. A method of manufacturing a stiffened aerospace structure according to any of claims 11 to 14, wherein each of at least two of the layer of material, the member to be stiffened and the stiffener is in the form of composite material in the stiffened aerospace structure so produced.
16. A method of manufacturing a stiffened aerospace structure according to any of claims 11 to 15, wherein at least two of the layer of material, the member to be stiffened and the stiffener are initially provided in the form of uncured material and the step of bonding the layer of material includes co-curing said at least two of the layer of material, the member to be stiffened and the stiffener.
17. An aircraft panel stiffened with multiple stringers, wherein the aircraft panel is in accordance with the stiffened aerospace structure as claimed in any of claims 1 to 10 or is made in accordance with method as claimed in any of claims 11 to 16.
18. An aircraft panel according to claim 17, where the stringers are embedded within the panel.
19. An aircraft including multiple panels, each panel being as claimed in claim 17 or claim 18.
20. An anti-peel product for use in protecting the end of a stringer from peeling off from an aircraft panel, wherein the anti-peel product is in the form of a layer of material configured and adapted for use as said further layer of material of any preceding claim.
Intellectual
Property
Office
Application No: Claims searched:
GB1612276.4
1-20
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1612276.4A GB2552216A (en) | 2016-07-14 | 2016-07-14 | Stiffened aerospace structure and method of manufacture |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1612276.4A GB2552216A (en) | 2016-07-14 | 2016-07-14 | Stiffened aerospace structure and method of manufacture |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB201612276D0 GB201612276D0 (en) | 2016-08-31 |
| GB2552216A true GB2552216A (en) | 2018-01-17 |
Family
ID=56890493
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB1612276.4A Withdrawn GB2552216A (en) | 2016-07-14 | 2016-07-14 | Stiffened aerospace structure and method of manufacture |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2552216A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110329519A (en) * | 2019-07-05 | 2019-10-15 | 酷黑科技（北京）有限公司 | A kind of engine room structure of aircraft, aircraft and hovercar |
| US12077289B2 (en) * | 2019-05-31 | 2024-09-03 | Airbus Operations Limited | Aircraft assembly having an integral spar-cover |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011003844A2 (en) * | 2009-07-10 | 2011-01-13 | Airbus Operations Limited | Stringer |
| EP2799220A1 (en) * | 2013-04-30 | 2014-11-05 | Airbus Operations S.L. | Composite structure for an aircraft and manufacturing method thereof |
-
2016
- 2016-07-14 GB GB1612276.4A patent/GB2552216A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011003844A2 (en) * | 2009-07-10 | 2011-01-13 | Airbus Operations Limited | Stringer |
| EP2799220A1 (en) * | 2013-04-30 | 2014-11-05 | Airbus Operations S.L. | Composite structure for an aircraft and manufacturing method thereof |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US12077289B2 (en) * | 2019-05-31 | 2024-09-03 | Airbus Operations Limited | Aircraft assembly having an integral spar-cover |
| CN110329519A (en) * | 2019-07-05 | 2019-10-15 | 酷黑科技（北京）有限公司 | A kind of engine room structure of aircraft, aircraft and hovercar |
| CN110329519B (en) * | 2019-07-05 | 2023-09-22 | 酷黑科技（北京）有限公司 | Cabin structure of aircraft, aircraft and aerocar |
Also Published As
| Publication number | Publication date |
|---|---|
| GB201612276D0 (en) | 2016-08-31 |
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| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |