ROTOR BLADE FOR AN AIRCRAFT TURBOMACHINE PROPELLER AND ITS MANUFACTURING METHOD

Abstract

Rotor blade (14) for a propeller (10) of an aircraft turbomachine, this blade (14) comprising a blade (20) connected to a root (40) which is housed in a platform (22), the blade (20) and the root (40) being made of a composite material comprising a fibrous body (50) embedded in a polymer matrix, the root (40) having a generally elongated shape, the platform (22) comprising a housing (38) for receiving said root (40), this housing (38) having a shape complementary to this root (40), the platform (22) being configured to define a setting axis (Y) of the blade (10) which extends along an elongation axis of the blade (20), characterized in that the root (40) comprises an internal cavity (60) comprising an expanded material. Figure for the abstract: Figure 2

Description

Title of the invention: ROTOR BLADE FOR AN AIRCRAFT TURBOMACHINE PROPELLER AND METHOD FOR MAKING SAME BRICATION Technical field of the invention

[0001] The present invention relates to the field of aircraft turbomachines and in particular to the propulsion propellers of these turbomachines which comprise variable-pitch blades. Technical background

[0002] The state of the art includes in particular documents FR-A1-3 017 163 and FR-Al-3 080 322.

[0003] An aircraft turbomachine propeller may be shrouded, as is the case with a fan for example, or unshrouded as is the case with an open-rotor type architecture for example.

[0004] A propeller comprises blades which can be variable pitch. The turbomachine then comprises a mechanism for modifying the pitch angle of the blades in order to adapt the thrust generated by the propeller according to the different phases of flight.

[0005] The design of a propeller blade involves several disciplines whose objectives are generally antagonistic. It must allow optimal aerodynamic performance (i.e. provide thrust while maximizing efficiency), guarantee mechanical strength of the blade (i.e. withstand the mechanical constraints resulting from static and dynamic loadings) while limiting the mass as well as the acoustic signature. In particular, the improvement of the aerodynamic performance of the propeller tends towards an increase in the BPR (By Pass Ratio), which results in an increase in its external diameter and therefore in the span of the blades.

[0006] In current technology, it is common to fix a blade to its support by a so-called broached fastener. The blade comprises a foot which has a general dovetail shape and which is intended to be engaged by complementary shapes in a housing of a support platform, this housing being conventionally produced by broaching.

[0007] The support platform is housed in an orifice of a hub of the propeller and defines the pitch axis of the blade. The platform is therefore movable in rotation around the pitch axis inside this orifice of the hub.

[0008] For a blade with a pinned attachment, the aerodynamic force is so intense that it can cause rigid solid movements of the blade root in its housing which are similar to swiveling. Indeed, during a feather start, the reduced speed of the fan does not generate sufficient centrifugal force to prevent these movements induced by the aerodynamic force. This results in frictional damage to the blade and the shim inserted between the root and the bottom of its housing, in just a few cycles. This shim is intended to take up the assembly clearances in the broaching between the blade and its mounting housing, and must also perfectly position the blade perpendicular to the propeller's rotation axis. For the same reasons, this problem may arise in a freewheeling situation (or "windmilling") following an engine failure because variable pitch blades are generally equipped with a feathering system.

[0009] In addition, intense vibration excitation can also occur at much higher rotational speeds on unducted architectures due to the effects of engine installation on the aircraft and the direction of the upstream infinite flow. Indeed, an unducted engine is subject to the influence of the ground and the fuselage, which causes a distortion in the supply of the propeller, in flow speed, according to the engine azimuths. This results in a vibration response of the propeller blades on the first engine orders IN, 2N and 3N (possibly more). On the other hand, in the absence of an air intake sleeve, the direction of the air flowing through the blades is not parallel to the engine axis. This sideslip angle results in so-called "IP" forces which cause a vibration response of the propeller blades on the engine order IN.Similarly, these IP forces can also occur during the aircraft's climb or approach phases because the air flows through the blades at an angle of incidence. These high rotational speed vibration excitations can cause the same friction damage discussed above if the blade attachment is not suitable.

[0010] For all of these reasons, there is a need to improve the existing technology for fixing and securing the blade root to its support platform. Summary of the invention

[0011] The invention relates to a rotor blade for an aircraft turbomachine propeller, this blade comprising a blade connected to a root which is housed in a platform,

[0012] the blade and the root being made of a composite material comprising a fibrous body embedded in a polymer matrix, the blade comprising a lower surface and an upper surface connected together at a leading edge and a trailing edge of the blade, the root having a generally elongated shape,

[0013] the platform comprising a housing for receiving said root, this housing having a shape complementary to this root, the platform being configured to define a blade setting axis which extends along an axis of elongation of the blade,

[0014] characterized in that the foot comprises an internal cavity comprising a material expanded.

[0015] In the present application, an expandable material is understood to mean a material capable of expanding, and an expanded material is understood to mean a material (originally expandable) already expanded.

[0016] In the present invention, an expandable material is present or injected into the internal cavity of the foot and is intended to expand so as to occupy the volume of this cavity and to exert pressure on the side walls of the cavity. The foot will then itself expand and increase in volume so that its foot bears on the walls of the housing. In practice, the housing comprises a bottom extending between two lateral bearing surfaces and connected to these lateral bearing surfaces. The expansion of the foot allows it to bear on the lateral bearing surfaces, which limits or reduces the risk of play in these areas and guarantees optimal support of the foot by the platform.

[0017] The blade according to the invention may comprise one or more of the following characteristics, taken in isolation from one another, or in combination with one another:

[0018] — the foot has a dovetail shape in section;

[0019] — the housing has a dovetail shape in section;

[0020] — the foot and the housing cooperate with each other by broached attachment and complementarity of shapes; • the foot comprises at one end a filling orifice which opens into said internal cavity; • the orifice has a cross-section smaller than that of the internal cavity; • the orifice has a generally circular cross-section; • the internal cavity has a general triangular or trapezoidal cross-sectional shape; • which the internal cavity has the general shape of a right prism with pentagonal bases, the two bases of the right prism being located respectively at the level of the longitudinal ends of the foot; • the foot comprises two lateral flanks inclined relative to each other and an end surface situated between these lateral flanks, the internal cavity comprising two lateral walls which are inclined relative to each other and which are parallel to said lateral flanks and a bottom wall which extends between the two lateral walls and which is parallel to said end surface, this bottom wall being situated on the side opposite the blade; • the foot has a wall thickness between one of the side walls and the parallel side flank, which is different from the wall thickness between the other of the side walls and the parallel side flank;

[0021] — the foot has a wall thickness between the bottom wall and the end surface, which is different from the aforementioned wall thicknesses of the foot; • the internal cavity comprises a ceiling wall which is located on the blade side, this ceiling wall forming a dihedral with two inclined faces extending along the root and forming an acute angle on the blade side, and an edge common to these two faces which extends along the root; • the two inclined faces comprise different angles of inclination;

[0022] — the expanded material is alveolar or cellular; • the expanded material is a foam;

[0023] — the foot is housed without any play in said housing and is secured to the platform thanks to said polymer matrix; this is made possible by the fact that the platform of the blade is used to mold the root. It is therefore understood that the root of the blade will take up all the space available in the platform housing. There is therefore no play between the root and the walls of the housing because the polymer matrix at the root will occupy all the space in the housing. Furthermore, the polymer matrix will harden upon contact with the walls of the housing and thus allows the blade to be further secured to the platform and therefore participate in the retention of the blade by the platform;

[0024] — the platform comprises a first aerodynamic surface located on the side of said intrados, and a second aerodynamic surface located on the side of said extrados, said first and second aerodynamic surfaces being capable of being swept by an air flow when the propeller is operating;

[0025] — said housing has an elongated shape and opens at its two long ends tudinal, said foot occupying the entire volume of this housing, the longitudinal ends of the foot being aligned with the longitudinal ends of the housing;

[0026] — the longitudinal ends of the housing open onto a cylindrical surface of the platform which extends around said wedging axis, the longitudinal ends of the foot comprising portions of cylindrical surface which extend in the extension of the cylindrical surface of the platform and which complete this cylindrical surface at the level of the outlets of the housing;

[0027] — the dawn further comprises two locks fixed on the platform, on either side of the foot, and configured to cover the longitudinal ends of the foot respectively; the locks thus make it possible to block the foot in its housing;

[0028] — a first of the locks comprises a first aerodynamic surface located on the side of said leading edge, and a second of said locks comprises a second aerodynamic surface located on the side of said trailing edge, said first and second aerodynamic surfaces of the first and second locks being capable of being swept by an air flow when the propeller is operating; the locks thus make it possible to reconstitute part of the aerodynamic vein of the propeller,

[0029] — the platform comprises a cylindrical body which extends under the foot along said timing axis;

[0030] — the platform comprises a disc centered on the wedging axis and comprising the foot reception housing.

[0031] The present invention also relates to a propeller for an aircraft turbomachine, comprising an annular hub which extends around an axis of rotation and which comprises a series of orifices which are regularly distributed around the axis of rotation and which are oriented radially relative to the axis of rotation, and blades as described above, the platforms of which are mounted respectively in these orifices so that the blades extend radially outwards from the hub, each of the platforms being able to rotate around its pitch axis inside the orifice of the hub.

[0032] The present invention also relates to a turbomachine, in particular for an aircraft, comprising a propeller as described above.

[0033] The invention further provides a method of manufacturing a blade as described above, comprising the following steps:

[0034] a) preparation of the fibrous body of the blade,

[0035] b) insertion of the foot into the platform housing,

[0036] c) injection of an expandable material into the internal cavity of the foot.

[0037] The method according to the invention may comprise one or more of the following characteristics, taken in isolation from one another, or in combination with one another:

[0038] - the expandable material is a foam;

[0039] — the method comprises a following step d) of injecting a resin into the housing the platform so as to give it the function of an injection mold, or molding of the foot previously impregnated with resin in the housing of the platform, the resin being intended to form said polymer matrix, to eliminate any play between the foot and the housing, and to secure the foot to the platform; it is therefore understood that the resin is injected into the platform forming the injection-molding mold, which is advantageous because it is not necessary to provide for a foot demolding operation in this case;

[0040] — the resin injected or which impregnates the foot or the fibrous body is liquid or pasty; • between steps b) and c) or in step c), molding shells are placed on the platform; • the shells compress the foot and / or the resin in the platform housing, the foot preferably having a volume greater than that of the housing; the molding shells are thus shells for compressing the foot and / or the resin in the platform housing; the in compression of the foot is advantageous to guarantee the molding without play of the foot and the stressing of the foot in the housing of the platform after polymerization; • the foot has a longitudinal length or extent greater than that of the housing and includes projecting longitudinal portions at the end of step b);

[0041] — after step c), the process comprises a step d) of cooking with a view to polymerizing resinization; the difference in thermal expansion intrinsic to each material allows, during cooling, the platform to exert a constant and homogeneous pressure force on the blade root; the clearances are not only consumed, but a retention force between the parts is naturally applied;

[0042] — after step c) or d), the method comprises a cooling step e) controlled and homogeneous resin to control thermal expansion forces between the platform and the foot; • for example after step c), d) or e), the method comprises a step f) of removing, for example by machining, said longitudinal portions; • the method further comprises a following step g) of fixing two locks on the platform, on either side of the foot, these locks respectively covering the longitudinal ends of the foot. Brief description of the figures

[0043] Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which:

[0044] [Fig-1] [Fig.l] is a schematic perspective view of a propeller for a tur- aircraft engine,

[0045] [Fig.2] [Fig.2] is a schematic perspective view of a rotor blade for a propeller such as that of [Fig.l],

[0046] [Fig.3] [Fig.3] is another schematic perspective view of the rotor blade of [Fig.2],

[0047] [Fig.4] [Fig.4] is a schematic perspective view of a blade of the vane of [Fig.l], and illustrates a step in a method of manufacturing a vane,

[0048] [Fig.5] [Fig.5] is another schematic perspective view of another step of the method, in particular of mounting the blade of [Fig.4] in a platform,

[0049] [Fig.6] [Fig.6] is a schematic perspective view of the blade and platform assembled after the step of [Fig.5],

[0050] [Fig.7] [Fig.7] is a schematic sectional view of the assembled blade and platform of [Fig.6],

[0051] [Fig-8] [Fig.8] is a schematic perspective view of the assembled blade and platform of [Fig.6] with additional schematic representation of molding and compression shells, and illustrates another step in the manufacturing process,

[0052] [Fig.9] [Fig.9] is a view similar to that of [Fig.6] and illustrates a removal step of the manufacturing process,

[0053] [Fig. 10] [Fig. 10] is a view similar to that of [Fig.6] and illustrates the end of the removal step of the manufacturing process,

[0054] [Fig. 11] [Fig. 11] is a partial schematic perspective view of the rotor blade platform and locks, and illustrates another step in the manufacturing process,

[0055] [Fig. 12] [Fig. 12] is a partial schematic perspective view of a propeller and the blade platform housed in an orifice of a hub of this propeller;

[0056] [Fig. 13] [Fig. 13] is a partial schematic perspective view of a blade according to the invention; and

[0057] [Fig. 14] [Fig. 14] is an enlarged view of a portion of the blade of [Fig.13]. Detailed description of the invention

[0058] [Fig.l] shows a propeller 10 for an aircraft turbomachine, this propeller 10 being able to be shrouded or unshrouded, that is to say surrounded or not by an annular casing of the turbomachine.

[0059] The propeller 10 is rotatable about an axis X and comprises a hub 12 and blades 14 carried by the hub 12. The hub 12 has an annular shape about the axis X and comprises a series of orifices 16 regularly distributed about the axis X. These orifices 16 have substantially radial orientations relative to the axis X and generally open in a radial direction inside the hub 12, and outside the hub 12. The orifices 16 open for example onto an external annular surface 12a of the hub 12, which may be cylindrical or frustoconical.

[0060] Each of the blades 14 comprises a blade 20 and a platform 22 secured to a root of the blade 20. Conventionally, the blade 20 comprises a lower surface face 21, an upper surface face 24, a leading edge 26, and a trailing edge 28. The blade 20 comprises a free end opposite its root, called the apex 29. The root and the platform 22 are located at the end opposite the apex 29.

[0061] The orifices 16 are intended to receive the platforms 22 of the blades 14 which make it possible to guide the blades 14 in rotation around radial axes Y and to wedge them angularly around these radial axes Y, called wedge axes.

[0062] Figures 2 and 3 show a rotor blade 14 which can equip a propeller 10 such as that illustrated in [Fig.l].

[0063] The platform 22 has a particular shape in the example shown. It essentially comprises two parts, namely a cylindrical body 30 and a disc 32. The cylindrical body 30 forms a pivot for setting the blade 14. The disc 32 can have a function of holding the blade and ensuring an aerodynamic junction between the vein and the body / pivot.

[0064] The body 30 is centered on the setting axis Y and has a generally elongated shape along this axis Y. The upper or radially external end of the body 30, relative to the axis X, is connected to the disk 32 and located on the side of the blade 20. The lower or radially internal end of the body 30, relative to the axis X, is intended to be connected to a mechanism for actuating the setting of the blade 14 which is generally located inside the hub 12 of the propeller 10 and which is not shown in the drawings.

[0065] The platform 22, and in particular the disc 32, comprises an aerodynamic surface 34 intended to be aligned with the surface 12a of the hub 12 and therefore to be swept by a flow of gas in operation.

[0066] In the example shown, the disc 32 comprises a first aerodynamic surface 34a located on the side of the intrados face 21, and a second aerodynamic surface 34b located on the side of the extrados face 24.

[0067] The platform 22, and in particular the body 30, comprises a cylindrical surface 36 which extends around the Y axis.

[0068] The platform 22 comprises a housing 38 for receiving the root 40 of the blade 20. In the example shown, the housing 38 is of the broached type and the root 40 of the blade 20 has a generally elongated shape, preferably with a dovetail section.

[0069] Alternatively, other types of pinned attachment are conceivable. Instead of a dovetail section, the foot 40 and the housing 38 could have another sectional shape and for example a fir tree, C, Z shape, etc.

[0070] The housing 38 has an elongated shape along an elongation axis Z substantially perpendicular to the setting axis Y and opens at its two longitudinal ends at the surface 36 in the example shown. There are therefore two outlets of the housing 38, on the surface 36, diametrically opposite relative to the axis Y.

[0071] The foot 40 of the blade 20 also has an elongated shape along the aforementioned elongation axis Z, and has a shape complementary to that of the housing 38

[0072] It can be seen in Figures 2 and 3 that the longitudinal ends of the foot 40 have convex curved shapes which extend at the level of the aforementioned outlets and which reproduce the missing portions of the surface 36 by extending in the extension thereof.

[0073] The blade 20 and the foot 40 are made from a composite material comprising a fibrous body embedded in a polymer matrix. The fibrous body is made by three-dimensional weaving of fibers, for example carbon, or by draping of folds or canvases (woven or non-woven) which are superimposed on each other.

[0074] The polymer matrix is ​​generally obtained by polymerization of a resin, which can be thermosetting and which is for example an epoxy resin.

[0075] The foot 40 of the blade 20 is preferably housed without any play in the housing 38 of the platform 22 and is secured to the platform 22 by means of the polymer matrix.

[0076] For this, a method of manufacturing the blade 12 is proposed which will be described below with reference to Figures 4 and following. Figures 4 and following illustrate several steps of this method.

[0077] [Fig. 4] illustrates a first step a) of the method in which the fibrous body 50 of the blade 20 and the root 40 of the vane 14 is prepared. As mentioned above, the fibrous body can be prepared by three-dimensional weaving of fibers or draping of folds. A three-dimensional shape is thus obtained comprising a (part of) blade and a / a (part of) root, the blade and the root being integral. The root 40 of the fibrous body 50 has a generally elongated and preferably dovetailed shape with a length along its elongation axis Z which is denoted LL

[0078] [Fig. 5] illustrates another step b) of the method in which the foot 40 is inserted into the housing 38 of the platform 22. As mentioned above, the housing 38 is obtained by broaching and the foot 40 is intended to be inserted into the housing 38 by translation along the elongation axis Z. The foot 40 is thus intended to slide or slide into the housing 38. It can be seen in [Fig. 6], after mounting the foot 40 in the housing 38 of the platform 22, that the length L1 of the foot 40 is greater than the length L2 of the housing 38. [Fig. 7] shows that the foot 40 has a complementary shape with the housing 38 of the platform 22, mounting clearances being able to exist between them after step b).

[0079] [Fig.8] illustrates another step c) of the method in which a resin is injected into the housing 38 of the platform 22 so as to give it an injection mold function. Alternatively, the fibrous body or only the foot could be impregnated or pre-impregnated with a resin. Step c) would then consist of molding the foot previously impregnated with resin in the housing of the platform.

[0080] The resin is intended to form the aforementioned polymer matrix, to eliminate any play between the foot 40 and the housing 38, and to secure the foot 40 to the platform 22.

[0081] In practice, the platform 22 may constitute a part of the injection mold and additional elements, such as molding shells 52, may be added to the platform 22 in order to constitute the molding cavity all around the platform 22.

[0082] [Fig. 8] very schematically represents two molding shells 52 which are arranged on two diametrically opposite sides of the platform 22, with respect to the Y axis. In particular, these two shells 52 can make it possible to cover the portions of foot 40 which protrude from housing 38.

[0083] The molding shells 52 may have the function of compressing these portions of the foot 40 radially inwards, with respect to the setting axis Y (see arrows F). The molding shells 52 are then shells for compressing the foot and / or the resin. This solution has the advantage of filling the assembly clearances to create a fitting connection.

[0084] To facilitate or allow compression of the foot into the platform housing, the foot may initially have a volume greater than that of the platform housing.

[0085] During compression (and preferably also during polymerization of the resin), the blade 20 and the platform 22 are perfectly positioned to guarantee the repeatability of each blade 14 of the propeller 10.

[0086] [Fig. 8] thus also represents an optional step of the process in which, between steps b) and c) or after step c), molding shells 52 are attached to the platform 22.

[0087] After step c), the method may include a step d) of curing for the polymerization of the resin. The difference in thermal expansion intrinsic to each material allows, during cooling, the platform to exert a constant and homogeneous pressure force on the blade root. The clearances are not only consumed, but a retention force between the parts is naturally applied.

[0088] After step c) or d), the method comprises a cooling step e). During cooling of the blade, the material (generally metallic) of the platform 22 generally has a coefficient of expansion greater than the composite material of the blade, which allows the cold clearance to become negative between the parts. The cooling of the resin is preferably controlled and homogeneous to control the thermal expansion forces between the platform and the root.

[0089] The method may further comprise an optional step f) illustrated in [Fig.9], in which the projecting longitudinal portions of the foot 40 are removed, for example by machining.

[0090] At the end of step f) or directly after step c), a blade is obtained as illustrated in [Fig. 10] in which the longitudinal ends of the foot 40 comprise cylindrical surface portions which extend in the extension of the cylindrical surface 36 of the platform 22 and complete this cylindrical surface 36 at the level of the outlets of the housing 36.

[0091] The method may further comprise a following step g) of fixing two locks 54 on the platform 22, on either side of the foot 40 ([Fig. 11]). The locks 54 may be fixed by elements of the screw-nut type or the like.

[0092] These locks 54 are intended to cover the longitudinal ends respectively of foot 40.

[0093] A first of the locks 54 comprises a first aerodynamic surface 54a located on the side of the leading edge 26, and a second of the locks 54 comprises a second aerodynamic surface 54b located on the side of the trailing edge 28.

[0094] These aerodynamic surfaces 54a, 54b are aligned on the one hand with the surface 34 of the platform 22, and are further intended to be aligned with the surface 12a of the hub (cf. [Fig. 12]).

[0095] Figures 13 and 14 represent an embodiment of a rotor blade 14 according to the invention.

[0096] The blade 14 includes all the features of those illustrated in Figures 2 to 12 to the extent that these features do not contradict the following.

[0097] The housing 38 of the platform 22 is preferably dovetail-shaped and comprises a bottom 38a which extends between two lateral bearing surfaces 38b and which is connected to these lateral bearing surfaces 38b.

[0098] As mentioned above, the root 40 of the blade has a generally elongated shape, preferably dovetail-shaped, and comprises two lateral flanks 40a inclined relative to each other, and an end surface 40b located between these lateral flanks 40a.

[0099] The lateral flanks 40a of the foot 40 respectively face the lateral bearing surfaces 38b of the housing 40 and are capable of coming to bear against these bearing surfaces 38b, or are directly in bear against these bearing surfaces 38b.

[0100] The end surface 40b of the foot 40 faces the bottom 38a of the housing 40. A shim can be inserted between the end surface 40b of the foot and the bottom 38a of the housing 40. Alternatively, in the aforementioned case where there is no play between the foot 40 and the housing 38, the end surface 40b bears against the bottom 38a.

[0101] According to the invention, the foot 40 comprises an internal cavity 60 comprising an expanded material (not visible).

[0102] The expanded material is preferably a foam. It may, for example, be a polyurethane foam.

[0103] Advantageously, the foot 40 comprises at one end a filling orifice 62 which opens into the internal cavity 60 in order to be able to insert and preferably inject the filling material (expandable) into the cavity 60.

[0104] The orifice 62 may have a cross-section smaller than that of the internal cavity 60.

[0105] In the example shown, the orifice 62 has a generally circular cross-section.

[0106] The internal cavity 60 may have a generally triangular or trapezoidal cross-sectional shape.

[0107] In the example shown, the internal cavity 60 has the general shape of a right prism with pentagonal bases 60a. A right prism is a three-dimensional geometric figure which comprises two superimposable (i.e., of the same shape and dimensions) and parallel bases. The two bases 60a of the right prism are here located respectively at the longitudinal ends of the foot 40. These bases 60a may be parallel or substantially parallel to the surfaces of the longitudinal ends of the foot 40.

[0108] The internal cavity 60 may comprise two side walls 60b which are inclined relative to each other and which are parallel to the lateral flanks 40a of the foot, and a bottom wall 60c which extends between the two side walls 60b and which is parallel to the end surface 40b of the foot.

[0109] As seen in [Fig. 14], the foot 40 has a wall thickness E1 between one of the side walls 60b and the parallel side flank 40a, which is different from the wall thickness E2 between the other of the side walls 60b and the parallel side flank 40a.

[0110] The foot 40 may have a wall thickness E3 between the bottom wall 60c and the end surface 40b which is different from the wall thicknesses E1 and E2.

[0111] The internal cavity 60 further comprises a ceiling wall 60d located on the blade side, which preferably forms a dihedron 64. This dihedron 64 comprises two inclined faces 64a, 64b extending along the root 40 and forming an obtuse angle γ on the blade side, and an edge 64c common to these two faces 64a, 64b which extends along the root 40.

[0112] The two inclined faces 64a, 64b comprise different inclination angles a, [3. These angles a, [3 can be measured relative to the same plane parallel to the ceiling wall 60d or to the end surface 40b.

[0113] The particular shape of the cavity 60 and in particular of the ceiling wall 60d allows the expandable material to apply its pressure forces perpendicular to the spans, and to orient itself as best as possible during its expansion and the need for the walls of the foot to be deformed.

[0114] The invention further provides a method of manufacturing a blade as described above, comprising the following steps:

[0115] a) preparation of the fibrous body of the blade,

[0116] b) insertion of the foot into the platform housing,

[0117] c) injection of an expandable material into the internal cavity of the foot.

[0118] During the expansion of the material of the root, the blade is preferably held so that the lateral flanks 40a of the root are supported on the lateral bearing surfaces 38b of the housing so that the consumption of the clearances is optimal without impacting the orientation of the blade.

[0119] The expandable material is intended to push the walls of the foot to deform preference at critical locations (maximum aerodynamic forces), i.e. at the level of the lateral spans 38b.

[0120] The shape of the cavity 60 is optimized to direct these thrust forces in preferred directions.

[0121] This method may include all or part of the steps of the method described above and therefore be combined with one or more of the steps of manufacturing the blade in which the platform 22 is used as a mold for manufacturing the root of the blade.

[0122] For example, the method may comprise a following step d):

[0123] - injecting resin into the platform housing so as to give it a injection mold function, or

[0124] - molding the foot previously impregnated with resin in the housing of the platform.

[0125] The resin is intended to form the polymer matrix, to eliminate any play between the foot and the housing, and to secure the foot to the platform. At the foot, the resin will be present all around the expanded material, between this material and the walls of the housing 38.

Claims

Claims

1. Rotor blade (14) for a propeller (10) of an aircraft turbomachine, this blade (14) comprising a blade (20) connected to a root (40) which is housed in a platform (22), the blade (20) and the root (40) being made of a composite material comprising a fibrous body (50) embedded in a polymer matrix, the blade (20) comprising a lower surface (21) and an upper surface (24) connected together at a leading edge (26) and a trailing edge (28) of the blade (20), the root (40) having a generally elongated shape, the platform (22) comprising a housing (38) for receiving said root (40), this housing (38) having a shape complementary to this root (40), the platform (22) being configured to define an axis (Y) for setting the blade (14) which extends along a elongation axis of the blade (20), characterized in that the foot (40) comprises an internal cavity (60) comprising an expanded material.

2. Blade (14) according to claim 1, in which the foot (40) comprises at one end a filling orifice (62) which opens into said internal cavity (60).

3. A blade (14) according to claim 2, wherein the orifice (62) has a smaller cross-section than the internal cavity (60).

4. A blade (14) according to claim 2 or 3, wherein the orifice (62) has a generally circular cross-sectional shape.

5. Blade (14) according to one of the preceding claims, in which the internal cavity (60) has a generally triangular or trapezoidal cross-sectional shape.

6. Blade (14) according to one of claims 1 to 4, in which the internal cavity (60) has the general shape of a right prism with pentagonal bases, the two bases (60a) of the right prism being located respectively at the level of the longitudinal ends of the foot (40).

7. Blade (14) according to one of the preceding claims, in which the foot (40) comprises two lateral flanks (40a) inclined relative to each other and an end surface (40b) located between these lateral flanks (40a), the internal cavity (60) comprising two lateral walls (60b) which are inclined relative to each other and which are parallel to said lateral flanks (40a) and a bottom wall (60c) which extends between the two lateral walls (60b) and which is parallel to said end surface (40b), this bottom wall (60c) being located on the side opposite to the blade (20).

8. Blade (14) according to one of the preceding claims, in which the root (40) has a wall thickness (El) between one of the side walls (60b) and the parallel side flank (40a), which is different from the wall thickness (E2) between the other of the side walls (60b) and the parallel side flank (40a).

9. Blade (14) according to one of the preceding claims, in which the internal cavity (60) comprises a ceiling wall (60d) which is located on the side of the blade, this ceiling wall (60d) forming a dihedral (64) with two inclined faces (64a, 64b) extending along the root (40) and forming an acute angle (y) on the side of the blade, and an edge (64c) common to these two faces (64a, 64b) which extends along the root (40).

10. Blade according to the preceding claim, in which the two inclined faces (64a, 64b) comprise different inclination angles (a, |3).

11. A blade according to the preceding claim, wherein the expanded material is a foam.

12. Propeller (10) for an aircraft turbomachine, comprising an annular hub (12) which extends around an axis of rotation (X) and which comprises a series of orifices (16) which are regularly distributed around the axis of rotation (X) and which are oriented radially relative to the axis of rotation (X), and blades (14) according to one of the preceding claims, the platforms (22) of which are mounted respectively in these orifices (16) so that the blades (20) extend radially outwards from the hub (12), each of the platforms (22) being able to rotate around its pitch axis (Y) inside the orifice (16) of the hub (12).

13. Aircraft turbomachine, comprising a propeller (10) according to the preceding claim.

14. Method for manufacturing a blade (14) according to one of claims 1 to 11, comprising the following steps: a) preparation of the fibrous body (50) of the blade (14), b) insertion of the root (40) into the housing (38) of the platform (22), c) injection of an expandable material into the internal cavity (60) of the root (40).

15. The method of claim 14, wherein the expandable material is a foam.

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