Aircraft turbomachine provided with an unducted propeller with blades having a composite-material insert bonded to their leading edges

Abstract

An aviation turbine engine having at least one unducted rotary propeller having a plurality of blades, each blade including: a blade body made of composite material including fiber reinforcement densified by a matrix, the fiber reinforcement of the blade body presenting three-dimensional weaving, the body extending between a leading edge and a trailing edge, and a protective fitting for protecting the leading edge and made of composite material having fiber reinforcement densified by a matrix, the fitting being adhesively bonded onto the leading edge of the blade body, the fitting being formed from a dry fiber preform injection molded with a densifying resin, and a polyurethane film for providing protection against erosion covering the blade body and the fitting.

Claims

1. An aviation turbine engine having at least one unducted rotary propeller having a plurality of blades, each blade comprising: a blade body made of composite material comprising fiber reinforcement and a first matrix, the fiber reinforcement of the blade body presenting three-dimensional weaving, said blade body extending transversally in a transverse direction between a leading edge and a trailing edge and longitudinally in a longitudinal direction between a root and a tip; a protective fitting for protecting the leading edge and made of composite material having fiber reinforcement and a second matrix, said fitting being bonded onto the leading edge of the blade body after densification of the blade body and solely using adhesive, said fitting extending longitudinally from the tip of said blade body and over the entire length of the leading edge and extending along the transverse direction between a first end and a second end, said fitting being formed from a dry fiber preform that is injection molded and solidified prior to being bonded onto the leading edge of the blade body; and a polyurethane film for providing protection against erosion covering the blade body, the adhesive, and the fitting, wherein, in a transverse cross section of the blade: a thickness of the adhesive provided between a forward transverse end of the leading edge and the second end of protective fitting along a transverse direction is greater than a thickness of the adhesive provided between the blade body and the first end of the protective fitting, and the adhesive is provided between the blade body and the first end of the protective fitting and has a transverse thickness between an edge of the blade body and an edge of the first end of the fitting that is covered by the polyurethane film.

2. The turbine engine according to claim 1, wherein the dry fiber preform comprises at least one fiber layer presenting two-dimensional weaving.

3. The turbine engine according to claim 1, wherein the dry fiber preform presents three-dimensional weaving.

4. The turbine engine according to claim 1, wherein the leading edge of the blade body presents a tenon shape in cross-section, and the fitting presents a U-shape in cross-section so that the fitting restores the aerodynamic profile to the leading edge.

5. The turbine engine according to claim 1, wherein a cross-section of the fitting presents a constant thickness around the leading edge.

6. A method of fabricating a blade for an unducted rotary propeller of an aviation turbine engine, the method comprising: fabricating a blade body out of composite material having fiber reinforcement densified by a first matrix, said blade body extending transversally in a transverse direction between a leading edge and a trailing edge and longitudinally in a longitudinal direction between a root and a tip, the fiber reinforcement of the blade body presenting three-dimensional weaving; fabricating a protective fitting for protecting the leading edge out of composite material having fiber reinforcement densified by a second matrix, said fitting extending longitudinally from the tip of said blade body and over the entire length of the leading edge and extending along the transverse direction between a first end and a second end and the fitting being fabricated from a dry fiber preform that is injection molded and solidified; bonding the fitting that is solidified onto the leading edge of the blade body solely using adhesive and after densification of the blade body, said fitting extending longitudinally from the tip of said blade body and over the entire length of the leading edge; and forming a polyurethane film on the blade body and the fitting so as to cover the blade body, the adhesive, and the fitting with said polyurethane film, wherein, in a transverse cross section of the blade: a thickness of the adhesive provided between a forward transverse end of the leading edge and the second end of protective fitting along a transverse direction is greater than a thickness of the adhesive provided between the blade body and the first end of the protective fitting, and the adhesive is provided between the blade body and the first end of the protective fitting and has a transverse thickness between an edge of the blade body and an edge of the first end of the fitting that is covered by the polyurethane film.

7. The method according to claim 6, wherein the dry fiber preform comprises at least one fiber layer presenting two-dimensional weaving.

8. The method according to claim 6, wherein the dry fiber preform presents three-dimensional weaving.

9. The method according to claim 6, wherein the leading edge of the blade body presents a tenon shape in cross-section and the fitting presents a U-shape in cross-section so that the fitting restores the aerodynamic profile of the leading edge, the method including, prior to adhesively bonding the fitting on the leading edge of the blade body, a step of machining the leading edge of the blade body so as to impart a tenon-shaped cross-section thereto.

10. The method according to claim 9, wherein the cross-section of the fitting presents a constant thickness around the leading edge.

11. The turbine engine according to claim 4, wherein the cross-section of the fitting presents a constant thickness around the leading edge.

12. The turbine engine according to claim 1, wherein the leading edge of the blade body has a transverse cross-section that is different from a transverse cross-section of the protective fitting.

13. The turbine engine according to claim 12, wherein the leading edge of the blade body presents a tenon shape in cross-section, and the fitting presents a U-shape in cross-section with a constant thickness around the leading edge so that the fitting restores the aerodynamic profile to the leading edge.

14. The method according to claim 6, wherein the leading edge of the blade body has a transverse cross-section that is different from a transverse cross-section of the protective fitting.

15. The method according to claim 14, wherein the leading edge of the blade body presents a tenon shape in cross-section and the fitting presents a U-shape in cross-section with a constant thickness around the leading edge so that the fitting restores the aerodynamic profile of the leading edge, the method including, prior to adhesively bonding the fitting on the leading edge of the blade body, a step of machining the leading edge of the blade body so as to impart a tenon-shaped cross-section thereto.

16. The turbine engine according to claim 1, wherein the protective fitting is spaced apart entirely in said transverse cross section of the blade from the blade body using said adhesive so that no contact exists in said transverse cross section of the blade between the protective fitting and the blade body.

17. The turbine engine according to claim 16, wherein, in said transverse cross section of the blade, an entire region extending from the forward transverse end of the leading edge and the second end of protective fitting is filled with said adhesive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawings, which show an embodiment having no limiting character. In the figures:

(2) FIG. 1 shows a turboprop having an unducted fan;

(3) FIG. 2 shows a turbojet having an unducted fan;

(4) FIG. 3 shows a fan for a turbojet or a turboprop in an embodiment of the invention;

(5) FIG. 4 is a section view of the FIG. 3 blade showing its leading edge; and

(6) FIG. 5 is a flow chart showing the various steps of a method of fabricating a blade for an aviation turbine engine in an implementation of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(7) The invention applies to making unducted propeller blades for aviation turbine engines, e.g. for a turboprop or a turbojet. More generally, the invention applies to making unducted propeller blades having requirements concerning impact resistance that are less severe than for ducted propeller blades. The unducted propellers in question may be characterized by having a speed of rotation that is lower than the speed of rotation of ducted propellers. For example, the maximum peripheral speed of rotation of the blades of an unducted propeller of a turboprop or a turbojet is less than 260 meters per second (m/s), whereas in a turbojet having a ducted fan, that speed may be as great at 460 m/s.

(8) FIG. 1 is a diagrammatic view of a turboprop 1 having an unducted propulsive propeller 2 with a plurality of blades 3. FIG. 2 is a diagrammatic view of a turbojet 4 having an unducted fan provided with two unducted propellers 5a and 5b that are propulsive and contrarotating, each propeller having a plurality of blades 6. The invention applies equally well to the blades 3, 6 both of the above-described turboprop 1 and of the turbojet 4, providing the blades form part of a propeller 3, 5a, 5b that is unducted.

(9) FIGS. 3 and 4 show respectively a blade 6 in an embodiment of the invention, and a section view of a portion of the FIG. 3 blade 6. In known manner, such a blade 6 has a blade body 8 with a pressure side face 9 (FIG. 4) and a section side face 10, the body extending transversely between a leading edge 12 and a trailing edge 14. The blade 6 shown also has a root 15 for mounting the blade on a rotor.

(10) The blade body 8 is made of composite material comprising fiber reinforcement densified by a matrix. The fiber reinforcement of the body is preferably obtained from a fiber preform made by three-dimensional weaving. By way of example, the matrix of the body 8 may be ceramic or organic, and it may be obtained from a densification resin, for example.

(11) In accordance with the invention, the leading edge 12 of the blade 6 is protected by a protective fitting 16 for protecting the leading edge 12, which fitting is made of composite material having fiber reinforcement densified by a matrix. In this example, the fitting 16 is adhesively bonded directly onto the leading edge 12 of the blade 6. In the example shown, the fitting 16 extends on either side of the body 8 and overlies parts of both the pressure side face 9 and the suction side face 10 of the body 8. In this example, the body 8 in the vicinity of the leading edge 12 is in the shape of a tenon so as to enable the fitting 16 to be fitted closely to the leading edge 12, while avoiding the presence of any discontinuities between the body 8 and the fitting 16. In this example, the fitting 16 presents a U-shaped cross-section so that the fitting 16 restores the aerodynamic profile of the leading edge 12. In this example, the fitting 16 holds the leading edge 12 of the body 8 like a vice. The fitting 16 and the body 8 can thus be assembled together using a tenon-and-mortise type connection. The fitting 16 co-operates with the leading edge 12 of the blade so as to provide continuity between the faces 8 and 9 and the outside surface of the fitting 16. In the example shown, the fitting 16 extends longitudinally over the entire length of the leading edge 12, but, in a variant, it may be observed that it could extend longitudinally over only a portion of said edge 12.

(12) FIG. 5 is a flow chart showing the steps of a method of fabricating a blade in an embodiment of the invention.

(13) In a first step E1, a fitting 16 is fabricated out of composite material.

(14) The fitting 16 may be fabricated in several ways. In one method of fabrication of the invention, the fitting 16 is fabricated by injecting a resin into a dry fiber preform by means of a technique known as resin transfer molding (RTM). For that purpose, an injection mold having the shape of the fitting 16 is made available and the dry fiber preform is positioned therein, after which a resin is injected under pressure into the inside of the mold, the resin is solidified, and the fitting 16 as fabricated in this way is extracted from the mold.

(15) In another method of fabrication that does not form part of the present invention, the fitting 16 is made from a stack of plies of two-dimensional fabric that are pre-impregnated with resin (known as “prepregs”) that are shaped and compacted in appropriate compression tooling. Thereafter, the resin is solidified in order to obtain the fitting 16.

(16) In yet another method of fabrication that does not form part of the present invention, it is also possible to fabricate the fitting 16 using known automatic draping or filament deposition techniques.

(17) In a second step E2, the body 8 that is to receive the fitting 16 is fabricated.

(18) The step E1 and the step E2 may equally well be performed simultaneously or one after the other.

(19) The fiber reinforcement of the body 8 and of the protective fitting 16 may comprise carbon fibers, or more generally ceramic fibers. A fiber preform for fabricating the fitting 16 may comprise fabric obtained by two-dimensional weaving, e.g. of the plain, twill, or satin type. For the body 8, a fiber preform made by three-dimensional weaving is used.

(20) The densification resin used in the RTM method or in the pre-impregnated plies may be a thermosetting resin belonging to the family of epoxies, bismaleimides, polyimides, polyesters, vinyl esters, cyanate esters, phenolics, etc. Alternatively, the resin may be a thermoplastic resin of any of the following types: polyphenylene sulfide (PPS), polysulfone (PS), polyether sulfone (PES), polyamide-imide (PAI), polyetherimide (PEI), or indeed the family of polyaryletherketones (PAEK): PEK, PEKK, PEEK, PEKKEK, etc.

(21) The resin is solidified or hardened by curing for a thermosetting resin or by cooling for a thermoplastic resin. The temperature of the injection mold or of the compression tooling may be regulated by any known regulation means, e.g. by using heating cartridges, by regulation in water or oil, by an induction heater system, etc.

(22) Once the body 8 has been fabricated, it can be machined roughly at its leading edge 12 (step E3) so that the fitting 16 can fit closely to the leading edge 12. Such prior machining also serves to avoid the fitting 16 modifying the aerodynamic profile of the blade, while ensuring continuity between the body 8 and the fitting 16 over the pressure side and suction side faces 9 and 10. In other words, the machining enables the surface of the fitting 16 on the outside, i.e. its surface opposite from its surface in contact with the adhesive, lies at the same level as the faces 9 and 10 of the body 8.

(23) In a fourth step E4, a layer of adhesive 18 is spread on the leading edge 12 and on the portions of the faces 9 and 10 of the body 9 that are to receive the fitting 16. Thereafter, the fitting 16 is placed on the adhesively coated zones in order to be bonded thereto (step E5). Depending on the type of adhesive 18 used, it may possibly be necessary to solidify it. By way of example, the adhesive forming the adhesive layer 18 may be selected from among epoxy adhesives.

(24) In the example shown, the fitting 16 presents a thickness e that is constant, thereby making it easier to fabricate.

(25) In a variant, it is possible to make a fitting 16 that presents varying thickness, e.g. greater thickness at the leading edge 12. In order to vary the thickness of the fitting 16, it is possible, by way of example, to make use of yarns of different sizes within the above-mentioned fabrics while they are being woven, or else to have recourse to a fiber preform that is woven three-dimensionally.

(26) By way of example, the thickness e of the fitting may lie in the range 0.5 millimeters (mm) to 2 mm, and preferably in the range 0.5 mm to 1.5 mm. The inside radius of curvature of the fitting 16 at the leading edge 12 may be 1 mm, for example.

(27) In order to provide the composite material blade 6 with better protection against erosion, the body 8 and the fitting 16 are covered in an anti-erosion film 20. In this example, such an anti-erosion film is a polyurethane film. By way of example, the anti-erosion film 20 may be deposited by spraying liquid polyurethane onto the blade 6, with the polyurethane then being solidified, e.g. by being polymerized, so as to form the film 20. In a variant, the anti-erosion film 20 may be deposited directly in the form of a prefabricated film. Advantageously, the film 20 may also enhance the mechanical strength of the fitting 16 on the leading edge 12, and also the cohesion of the assembly, in particular in the event of impacts, by minimizing the probability of any yarns or strands of the weaving projecting externally. In particular, cohesion may be optimized concerning strands or yarns of the fiber preform of the fitting that protects the leading edge.