A gas turbine engine fan blade assembly

Abstract: A stage of fan blades (12) in a ducted fan gas turbine engine (10) have the spaces between them filled by a rotary annulus wall filler (16), which has a leading portion (16 a ) made from metal and a trailing portion (16 b ) made from a composite material. The leading portion (16 a ) forming an integral part of the rotor disc (14). The metal portion (16 a ) resists the impact damage from the ingress of foreign bodies and the trailing portion (16 b ) provides a lighter structure.

Description: The present invention relates to a gas turbine engine fan blade assembly. More specifically, the invention relates to annulus wall fillers, these being members which are positioned one between each adjacent pair of fan blades. Until recent times it was the practice to produce rotary blades, both fan and first stage compressor blades, with integral platforms. The relevant art is well known and will not be enlarged upon hereinafter. The mode of manufacture meant that blade and platform were of common, integral material and moreover, necessitated considerable working to achieve the platform shape. Recent design trends have led to the obviation of integral blade/platform construction, at least in the design of ducted fans, and the inclusion of separate annulus fillers, which have their own features for removably locating them on the fan disc rim. Such and arrangement is disclosed in US-A-3393862. Advantages afforded by such design are relative simplicity of manufacture, use of metals or other materials, eg composites, which are lighter than the blade metal, and easy replacement of damaged fillers. As regards the latter, damage to the platform of an integral blade/platform construction often meant replacing the whole. Most damage incurred by the fan or first stage compressor structure immediately downstream of the fan is the result of the ingress of foreign objects, ie objects which range from birds to hailstones, and composite and lightweight metal parts tend to suffer more than heavier metal parts. An alternative approach is described in DE-A-2120470 in which the annulus fillers are an integral part of the fan disc. This can overcome the vulnerability of lightweight annulus fillers to foreign object damage. However, the drawback with this type of approach is that the overall disc/fan blade structure is often undesirably heavy. The present invention seeks to provide an improved rotary annulus wall filler for a gas turbine engine. According to the present invention, a gas turbine engine fan blade assembly comprises a rotary disc carrying an annular array of radially extending fan blades and a plurality of annulus wall fillers, one annular wall filler being interposed between adjacent fan blades, each annulus wall filler comprising a lightweight trailing portion attached to said disc and a leading portion which is integral with said disc so that said disc and said leading portion define a unitary structure. Such fan blade assembly combines the resistance to foreign object damage enjoyed by assemblies in which the annulus fillers are an integral part of the fan disc and the weight-saving advantages of assemblies in which the fan annulus fillers are formed from a lightweight material. The invention will now be described, by way of example and with reference to the accompanying drawings in which: Fig 1 is a diagrammatic view of a ducted fan gas turbine engine incorporating annulus fillers in accordance with the present invention. Fig 2 is an enlarged part cross sectional view of a fan blade, annulus filler and fan disc of the engine in Fig 1. Fig 3 is a view on line 3-3 in Fig 2 and Fig 4 is a view on line 4-4 in Fig 3. Referring to Fig 1. A ducted fan gas turbine engine 10 has a stage of fan blades 12 spaced about the rim of a fan disc 14. Each blade 12 is separated from the next by an annulus filler 16. A rotary spinner 18 is fixed to the disc 14 in a suitable manner (not shown) for co-rotation therewith. Referring now to Fig 2. The leading portion 16a of the annulus filler 16 is formed integrally with the disc 14. By leading is meant with respect to the flow of air through the fan duct during operation of the engine 10. The trailing portion 16 b of the annulus filler 16 is made from a composite material (a resin impregnated fibrous material) and is fixed via a flange 19 to an annular flange 20 formed as a radial extension to the rear face of the disc 14. The mode of fixing, which is merely by way of example, includes setscrews 22 which enables rapid disassembly of the structure. The leading edge of the portion 16 b locates under the trailing edge of the portion 16 a , and the trailing edge of the portion 16 b locates under the leading edge of structure immediately downstream thereof. Referring to Fig 3. Each blade 12 has a dovetail root 23 (Fig 4) the length of which is truly arcuate in form (Fig 3). This is known per se. Each blade root 23 is slid into a respective complimentary groove 24 (Fig 4) in the rim of the disc 14, and held there by any convenient, known means (not shown). Respective clearance 26,28 are provided between the blades 12 and adjacent leading and trailing annulus fillers 16 a , 16 b , so that either the blades 12 or the portions 16 a , 16 b , can be removed from the disc 14, in a direction generally axially of the engine 10. As illustrated in Fig 3, the trailing portions 16 b consist of a flanged cylinder which has appropriately shaped cut-outs 25 in it for the receipt of the trailing portions of the blades 12. However the trailing filler portions 16 b could consist of separate members, eg firstly produced as the flanged cylinder as described immediately hereinbefore, and then divided, preferably but not necessarily, along a line 30 which is an extension of the mean chord of the blade 12 at a position where it passes through the portion 16 b . The magnitude of the clearance 26,28 is determined partly by the path which the trailing edge of the blade 12 will follow, when the blade 12 is fitted to or removed from the disc 14, and will be such as to avoid fouling between the respective parts. Stub platforms 32, 34 are provided along the leading portion of the blade 12, so as to form a profile which being followed by the adjacent edges of the portion 16 a , provides a sealable gap in the portions 16a which gap is sufficiently wide as to enable withdrawal of the blade 12 per se from the disc 14. The stub platforms could be extended for the full lengths of the flanks of the blades 12, and their profile and extent of projection each side of their respective blades 10 would be governed by the paths traced by inter alia the extreme trailing edges of the respective blades 12 during the relative movement. This arrangement would allow smaller clearance gaps and would facilitate undersurface sealing between blades and fillers, a feature which again is known per se. It will be noted by referring to Figs 1, 2 and 4, that the annulus fillers 16 are arranged at an acute angle to the engine axis. It is when a fan stage or a first stage of compressor blade having annulus fillers arranged in this manner, for whatever technical or aerodynamic reasons, that most benefit is derived from use of the present invention. Thus, use of a metal for the leading filler portion 16 a and a composite material for the trailing portion 16 b provides both a lighter structure than one which is made from a single piece of heavy, impact resistant material and a leading portion which will better resist damage by bearing the brunt of foreign body ingestion. Where the annulus wall is substantially parallel with the engine axis, ie cylindrical, the advantage of light structure and easy replacement pertains. Protection against damage however is reduced, but not obviated, for when an aircraft powered by engines of the kind disclosed herein takes off, its attitude with respect to the ground is such as to effectively present the engine at a slope thereto and thus expose the outer surfaces of the lower leading portions 16 a of the annulus fillers 16 to any ingested foreign objects. The preferred embodiment of the present invention is described and illustrated herein and includes shaping the rim of the disc 14 so as to provide the leading annulus filler portion 16 a . However, individual portions (not shown) could be utilised and removably fixed in the same manner as the trailing portions 16 b . In Fig 4 the dovetail roots 22 of the blades 12 and their complimentary grooves in the disc 14 are clearly seen. Although the present invention has been described with reference to a rotary annulus wall filler in which an impact resistant metal leading portion and a trailing portion which is formed from a composite material, it will be appreciated that other material combinations could be employed. Thus the composite material trailing portion could be formed from a lightweight metal such as an aluminium alloy. The present invention therefore provides a rotary annulus wall filler which has several advantages over previous such wall fillers. Firstly it permits the use of lightweight materials in applications in which heavy, impact resistant materials have been used in the part. Secondly it provides a way of reducing the distance between the rim of the fan disc 14 and the annulus wall. This is desirable because it results in an overall weight reduction in the stage of fan blades 12. Thirdly it permits the easy removal of individual fan blades 12 whilst the annulus fillers 16 remain in position in the disc 14.

Claims: A gas turbine engine fan blade assembly comprising a rotary disc (14) carrying an annular array of radially extending fan blades (12) and a plurality of annulus wall fillers (16), one annulus wall filler (16) being interposed between adjacent fan blades (12) each annulus wall filler (16) comprising a lightweight trailing portion (16b) attached to said disc (14) characterised in that, each said annulus wall filler (16) additionally comprises a leading portion (16a) which is integral with said disc (14) so that said disc (14) and said leading portion (16 a ) define a unitary structure A gas turbine engine fan blade assembly as claimed in claim 1 characterised in that said trailing portion (16 b ) of each annulus wall filler (16) is formed from a composite material. A gas turbine engine fan blade assembly as claimed in claim 1 or claim 2 characterised in that said trailing portion (16 b ) is defined by a circular cross-section structure having axial length and including means (19) on its internal surface for fastening it to said fan disc (14) and a number of slots (25) equally spaced around the circular cross-section portion, the shapes of said slots (25) being complimentary to but larger than said fan blades (12). A gas turbine engine fan blade assembly as claimed in any previous claim characterised in that said annulus wall fillers (16) together define a frusto-cone. A gas turbine engine fan blade assembly as claimed in any of claims 1 to 4 characterised in that said annulus wall fillers (16) define a cylinder. A gas turbine engine fan blade assembly as claimed in any one preceding claim characterised in that each fan blade (12) has a stub platform (32) on at least one flank which stub platform (32) extends for at least part of the chordal length of the fan blade (12) and is in alignment with an opposing edge of the side of the annulus wall filler (16) adjacent thereto.

Inventors: KNOTT DAVID SYDNEY, RICHARDS MARTYN, KNOTT, DAVID SYDNEY, RICHARDS, MARTYN
Applicants: ROLLS ROYCE PLC, ROLLS-ROYCE PLC
Application year: 1995
Main classification: F01D11
IPC codes: F01D11