AEROFOIL, AN AEROFOIL SUB-ASSEMBLY AND A METHOD OF MAKING THE SAME
An aerofoil sub-assembly of a blade, in particular an aerofoil blade for a gas turbine engine. A multi-layer construction including first and second skin panels which together define the external surfaces of the aerofoil and aerofoil leading and trailing edges. Between the skin panels at least there is at least one web-forming membrane which has a multiplicity of fingers trapped between the first and second panels at one of the edges and which extend away from the edge region. The fingers each have “dog-leg” shapes which are overlaid immediately behind the blade leading edge to form a transition zone providing additional support to resist crumpling of the hollow blade in the event of an external foreign object striking the leading edge.
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The invention relates to an aerofoil sub-assembly for use in the formation of a hollow aerofoil, particularly an aerofoil for use as a fan blades in a jet engine. The invention also relates to an aerofoil made from the sub-assembly and a method of making such an aerofoil.
The invention concerns hollow aerofoil blades manufactured by a diffusion bonding and blow forming process and especially concerns an aerofoil, an aerofoil sub-assembly and a method of manufacturing the same.
In the simplest form of a blow forming manufacturing process a hollow component is formed of two thin metal skins joined along their peripheral edges, which are then heated in a die to a temperature at which they can be blow formed to the shape of the cavity of the die by internal gas pressure. To give the component strength an internal structure may be provided made up of one or more membranes sandwiched between the metal skins and selectively bonded to their inner faces and each other. In the blow forming step the inner membranes deform into the shape of a chosen support structure. In more complex blow forming processes alloys may be used which have super plastic characteristics within a given temperature range. The articles are heated to the within the superplastic range before pressurising to superplastically deform the article. The use of superplastic materials affords greater control to internal structures as the article is inflated.
Hollow aerofoil blades made in this way, that is with this kind of internal structure, are found to have regions of high rigidity interspersed with regions of lower rigidity. For example, under impact in the chordal direction of a blade the leading and trailing edge regions behave as fundamentally solid regions. Where internal spars, or other support, is bonded to the inner surface the skin exhibits higher strength than other intermediate regions. Therefore if the aerofoil is struck by a foreign object, e.g. during a bird strike, the relatively weaker regions can tend to crumple. As a counter and to increase strength the thickness of the outer panels is increased at a penalty of increased mass and weight.
It is an objective of the present invention to provide an improved internal structure, and in particular to provide a structure located between regions of higher strength capable of resisting buckling under impact loads without a penalty of increased weight.
A method for forming an aerofoil can comprise the steps of: providing a first skin panel, providing a first web-forming membrane adjacent the first panel, selectively bonding part of the web-forming membrane to parts of the first panel, providing a second skin panel, providing a second web-forming membrane, selectively bonding parts of the second web-forming membrane to parts of the second skin panel, selectively bonding parts of the first web forming membrane to parts of the second structure-forming membrane, arranging the panels together so that the first skin panel overlays the second skin panel with the first and second web-forming membranes arranged therebetween to define an aerofoil sub-assembly, heating the aerofoil sub-assembly to a temperature and inflating the aerofoil sub-assembly to draw the first and second skin panels apart and to cause the first and second web-forming membranes to form webs internally of the aerofoil.
According to the present invention there is provided an aerofoil sub-assembly of a multi-layer construction comprising first and second skin panels which together define the external surfaces of the aerofoil and aerofoil leading and trailing edges, and lying between the skin panels and two or more web-forming membranes which comprise a multiplicity of fingers trapped between the first and second panels at one of the edges and which extend away from the edge region.
Preferably the web-forming membrane comprises a comb-like structure in which the multiplicity of fingers project from a spine portion at a panel edge and the fingers extend from the spine portion and have a proximal portion and a distal portion angled thereto in the shape of a dog-leg, and wherein the proximal portions of the fingers of a web-forming membrane subtend an oblique angle relative to the spine of the web.
Furthermore it is preferred that the distal portion of the fingers lie in a direction perpendicular to the spine of the web-forming membrane and alternate ones of the fingers are bonded to opposite skin panels.
These and further features of the invention will be described in greater detail below, in which reference by way of example will be made to the accompanying drawings illustrating the invention, in which:
Referring now to the drawings,
The blade illustrated in
Although the blade structure described thus far is light and strong, at the limit, as for example under foreign object impact loads, e.g. a bird strike, the leading edge region of the blade is liable to crumple. It is thought this occurs due to a lack of chordal support immediately behind the leading edge 10. The trailing edge 12 can exhibit the same characteristics, but is less likely to receive a direct impact. The present invention is intended to provide additional support to these regions, in particular to the leading edge 10 as shown at 14.
The second web-forming membrane 18 also comprises a spine or base part 28 of rectangular outline and has a multiplicity of fingers 30 extending from the edge of part 28 and spaced apart at regular intervals. In this case, however, the proximal part 32 of each finger is inclined in the opposite direction to the fingers 22 of the first membrane 16. The proximal portions 32 of fingers 30 are formed at an angle (180°-α) relative to the edge of the base portion. Therefore the proximal portions 24, 32 of the web membrane fingers 22, 30 are angled in opposite directions.
In a preferred method of manufacture the skin panels 2, 4 and web-forming membranes 16, 18 are placed in a stack between tooling pieces (not shown). In accordance with the present invention the membranes 16, 18 are placed face to face with the base parts 20, 28 in register and the distal parts 26, 34 of the fingers 22, 30 overlying one another. In this position the proximal parts 24, 32 of the fingers are interdigitated and of sufficient length so that the fingers cross-over each other. In order to produce the reinforcing parts of the invention, as illustrated in
During a later phase of the process, that is after the bonding phase but while the metal remains at temperature, an inert gas at high pressure is introduced into the interior of the assembly and causes plastic deformation of the panels and membranes within the limits set by exterior tooling or mould. Bonded interfaces remain attached but other parts placed under tension expand up to the limits set by the tooling.
Thus, in the arrangement illustrated in
The invention provides a region of graded strength between the edge being reinforced and the nearest adjacent spar, or load carrying member, in order to reduce the chance of buckling occurring upon foreign object impact on the edge. Thus, the invention may be employed to reinforce an aerofoil leading or trailing edge or both. Alternatively, where inflation of the blade occurs through an aperture in the blade tip the edge against which the intertwining occurs may be the blade tip. The thickness of a skin panel may be reduced, thus reducing weight while maintaining the strength of the structure. In one embodiment of the invention a preferred structure is formed of two outer panels, of approximately 10 mm thickness, and two internal membranes, typically each having a selected thickness of between 0.5 mm and 2.0 mm. It is possible, therefore, to adapt an existing aerofoil design to incorporate the invention without increasing the overall thickness of the reinforced edge, that is the distance between the aerofoil surfaces on the pressure and suction sides of the aerofoil blade. For example, the invention may be employed in the structure disclosed in our co-pending GB Patent Application No 0813539.4 but it may also be employed in other aerofoil structures of hollow construction.
Although each finger has been shown to have a single dog-leg it is conceivable that each distal portion of the fingers of the membranes may be divided into multiple regions having one or more dog-legs which cross over the dog-legs of the other membrane. In this way the inflation of the blade may be further improved.
Claims
1. An aerofoil sub-assembly of multi-layer construction comprising first and second skin panels which together define the external surfaces of the aerofoil and aerofoil leading and trailing edges, and lying between the skin panels two or more web-forming membranes which comprise a multiplicity of fingers trapped between the first and second panels at one of the edges and which extend away from the edge region, wherein each web-forming membrane comprises a comb-like structure in which the multiplicity of fingers project from a spine portion at a panel edge, wherein the fingers of the web-forming membranes extend from a spine portion and have a proximal portion and a distal portion angled thereto in the shape of a dog-leg.
2. An aerofoil sub-assembly of multi-layer construction comprising first and second skin panels which together define the external surfaces of the aerofoil and aerofoil leading and trailing edges, and lying between the skin panels two or more web-forming membranes which comprise a multiplicity of fingers trapped between the first and second panels at one of the edges and which extend away from the edge region.
3. An aerofoil sub-assembly according to claim 2, comprising first and second web-forming membranes wherein each web-forming membrane comprises a comb-like structure in which the multiplicity of fingers project from a spine portion at a panel edge.
4. An aerofoil sub-assembly according to claim 1, wherein part of the first web-forming membrane is bonded to part of the first panel and part of the second web-forming membrane is bonded to part of the second panel.
5. An aerofoil sub-assembly according to claim 4 in which the fingers of the first and second membranes are overlaid.
6. An aerofoil sub-assembly according to claim 3, wherein the fingers of the web-forming membranes extend from a spine portion and have a proximal portion and a distal portion angled thereto in the shape of a dog-leg.
7. An aerofoil sub-assembly according to claim 1, wherein the proximal portions of the fingers of a web-forming membrane subtend an oblique angle relative to the spine of the web.
8. An aerofoil sub-assembly according to claim 1, wherein the proximal portions of the fingers of the first and second web-forming members are angled in opposite directions.
9. An aerofoil sub-assembly according to claim 1, wherein the distal portion of the fingers lie in a direction perpendicular to the spine of the web-forming membrane.
10. An aerofoil sub-assembly according to claim 1, wherein the web-forming membranes are assembled such that the distal portions of the fingers of one membrane overlap those of the other membrane and are diffusion bonded together and to a skin panel.
11. An aerofoil sub-assembly according to claim 10, wherein alternate fingers are bonded to opposite skin panels.
12. An aerofoil sub-assembly according to claim 1, wherein the distal portion comprises a first distal portion immediately adjoining the proximal portion and a second distal portion comprising one or more further dog-legs.
13. An aerofoil sub-assembly of multi-layer construction comprising first and second skin panels which together define the external surfaces of the aerofoil and aerofoil leading and trailing edges, and lying between the skin panels two or more web-forming membranes which comprise a multiplicity of fingers trapped between the first and second panels at one of the edges and which extend away from the edge region, wherein each web-forming membrane comprises a comb-like structure in which the multiplicity of fingers project from a spine portion at a panel edge, wherein the fingers of the web-forming membranes subtend an oblique angle relative to the spine of the web.
14. An aerofoil sub-assembly according to claim 2, wherein part of the first web-forming membrane is bonded to part of the first panel and part of the second web-forming membrane is bonded to part of the second panel.
15. An aerofoil sub-assembly according to claim 6, wherein the proximal portions of the fingers of a web-forming membrane subtend an oblique angle relative to the spine of the web.
16. An aerofoil sub-assembly according to claim 6, wherein the proximal portions of the fingers of the first and second web-forming members are angled in opposite directions.
17. An aerofoil sub-assembly according to claim 6, wherein the distal portion of the fingers lie in a direction perpendicular to the spine of the web-forming membrane.
18. An aerofoil sub-assembly according to claim 6, wherein the web-forming membranes are assembled such that the distal portions of the fingers of one membrane overlap those of the other membrane and are diffusion bonded together and to a skin panel.
19. An aerofoil sub-assembly according to claim 6, wherein the distal portion comprises a first distal portion immediately adjoining the proximal portion and a second distal portion comprising one or more further dog-legs.
Type: Application
Filed: Jul 20, 2011
Publication Date: Feb 9, 2012
Applicant: ROLLS-ROYCE PLC (London)
Inventors: Keith C. GOLDFINCH (Bristol), Oliver M. STROTHER (Leeds)
Application Number: 13/186,850
International Classification: F01D 5/14 (20060101);