Hollow parametric spar blade with double tapered bearing

Abstract

The present invention relates to a fan blade of a turbomachine (1) configured to be pivotally mounted about a pivot axis (17) relative to a hub (43) of a fan (4), comprising: - a skin (9) forming a lower surface (16) and an upper surface (15) of the blade, the skin delimiting an internal cavity, the skin being able to comprise a composite material comprising a fibrous reinforcement embedded in a matrix; - a spar (7) housed at least partially in the internal cavity of the skin (9), the spar (7) comprising a root (41) extending outside the cavity and configured to be mounted in a hub of the fan (4) and a retaining structure (11) housed at least partially in the cavity and extending from the root (41);the retaining structure (11) comprising a base (13) connected to the root and a single branch (12) extending radially from the base (13) at a distance from the root (41), this retaining structure (11) having a width of the base (E2) greater than a width of the branch (E3) and these widths being curvilinear distances measured along a first skeleton (SQ1) of the blade, the first skeleton corresponding to a line passing through a point located at the intersection between the upstream edge (121) of the branch and the upstream edge (131) of the base, the first skeleton (SQ1) extending midway between the intrados (16) and the extrados (15) of the blade in a plane normal to the pivot axis (17) Figure for the abstract: Fig. 1;

Description

Title of the invention: Hollow parametric spar blade with double conical bearing Technical field

[0001] The invention relates generally to the field of turbomachines, and more particularly to the field of fan blades for aeronautical turbomachines. STATE OF THE ART

[0002] A turbomachine has a main direction extending along a longitudinal axis, and typically comprises, from upstream to downstream in the direction of gas flow, a fan, a compression section which may comprise a low pressure compressor and a high pressure compressor, a combustion chamber, a turbine section which may comprise a high pressure turbine and a low pressure turbine.

[0003] The fan comprises at least one fan rotor adapted to be rotated relative to a stator portion of the turbomachine by the turbine section. The fan rotor comprises a hub and blades extending radially from the hub. A fan blade comprises a root configured to be mounted in a cell of the hub, an aerodynamically profiled blade adapted to extend in an airflow passing through the fan, and may comprise a stilt connecting the root and the blade.

[0004] The blades of the fan rotor may be fixed relative to the hub or have a variable pitch. In this case, the root of the rotor blades is pivotally mounted along a pitch axis and is connected to a pitch change mechanism mounted in the turbomachine, the pitch being adjusted according to the flight phases by the pitch change mechanism.

[0005] It is desirable to make the fan blades as light as possible, because the weight of many components (such as blade retaining means, pitch angle changing mechanisms, discs, shafts and bearings) depends directly on the centrifugal forces to which the blades are subjected in operation.

[0006] Thus, fan blades are traditionally manufactured from a ductile metal alloy, typically titanium due to the good weight / strength ratio and the ductility of this material which makes it possible to avoid sudden breakage of the blades, in particular in the event of a bird being ingested by the turbomachine. More recently, it has been proposed to produce fan blades from a composite material comprising a fiber reinforcement embedded in a matrix (generally a polymer matrix), due to their lightness and mechanical strength. Some blades made from a composite material are composed of a spar covered with a skin, the spar and the skin being able to be made of composite material.

[0007] In operation, the stilt may be subjected to significant forces generated by the pressure difference between the intrados and the extrados of the blade. In addition, in polycyclic fatigue (in English, high-cycle fatigue or HCF), that is to say when the blade is subjected to moderate stresses in a cyclic manner, with a large number of cycles - such as flight missions - the cyclic forces to which the blade is subjected in flight are likely to have a frequency close to the natural frequency of the first bending mode of the blade. This can lead to vibrations of very high amplitude, by resonance phenomenon.

[0008] The invention is based on several publications by the Applicant. In particular, mention may be made of patent FR3121474 which relates to an unducted fan rotor blade structure, with an aerodynamic profile structure comprising two skins made of composite material and a spar. Mention may also be made of international application WO 2022 018357 relating to a variable-pitch blade provided with a root comprising a solid body, the solid body comprising a free end, a bulb and a stilt. Statement of the invention

[0009] An objective of the present application is to propose a turbomachine fan which is both light, mechanically resistant and which has an improved service life, despite possible resonance phenomena.

[0010] To this end, according to a first aspect of the invention, there is provided a fan blade of a turbomachine configured to be mounted pivoting about a pivot axis relative to a hub of a fan, and comprising: - a skin forming an intrados and an extrados of the blade, the skin delimiting an internal cavity, the skin being able to comprise a composite material comprising a fibrous reinforcement embedded in a matrix; - a spar housed at least partially in the internal cavity of the skin, the spar comprising a foot extending outside the cavity and configured to be mounted in a hub of the fan and a retaining structure housed at least partially in the cavity and extending from the foot; the retaining structure comprising a base connected to the foot and a single branch extending radially from the base at a distance from the foot, this retaining structure having a width of the base greater than a width of the branch and these widths being curvilinear distances measured along a first skeleton of the blade, the first skeleton corresponding to a line passing through a point located at the intersection between the upstream edge of the branch and the upstream edge of the base, the first skeleton extending midway between the intrados and the extrados of the blade in a plane normal to the pivot axis.

[0011] According to one embodiment, the base and the branch have an upstream edge and a downstream edge, the upstream edge facing a leading edge of the blade and the downstream edge facing the trailing edge of the blade, the upstream edge of the branch extending in the extension of the upstream edge of the base and the downstream edge of the branch being at a distance from the downstream edge of the base.

[0012] According to one embodiment, the width of the branch is less than a curvilinear distance between the upstream edge of the branch and the pivot axis, this distance being measured along the first skeleton of the blade.

[0013] According to one embodiment, the first skeleton has a first total curvilinear length between the leading edge and the trailing edge, a curvilinear length between the upstream edge of the branch and the leading edge of the blade along the first skeleton being between 20% and 40% of the first total curvilinear length of the first skeleton.

[0014] According to one embodiment, the blade has a second skeleton corresponding to a line passing through a point located at the intersection between the upstream edge of the branch and a radially external limit of the branch, the second skeleton extending midway between the intrados and the extrados of the blade in a plane normal to the pivot axis and having a second total curvilinear length between the leading edge and the trailing edge, a curvilinear length between the upstream edge of the branch and the leading edge of the blade along the second skeleton being between 20% and 60% of the second total curvilinear length of the second skeleton.

[0015] According to one embodiment, the width of the branch is between 10% and 30% of a first total curvilinear length of the first skeleton, between the leading edge and the trailing edge of the blade.

[0016] According to one embodiment, a distance between a radially inner limit of the skin and a radially outer limit of the base is between 4% and 14% of a blade height, the radially inner limit of the skin corresponding to a face of the skin configured to extend facing the hub, the radially outer limit of the base corresponding to a face of the base closest to a tip of the blade, and the height of the blade corresponds to a distance, along the pivot axis, between the radially inner limit of the skin and the tip of the blade.

[0017] According to one embodiment, a distance between a radially internal limit of the skin and a radially external limit of the branch is between 10% and 30% of a blade height, the radially internal limit of the skin corresponding to a face of the skin configured to extend facing the hub, the radially external limit of the branch corresponding to a face of the branch closest to a tip of the blade, and the height of the blade corresponds to a distance, along the pivot axis, between the radially internal limit of the skin and the tip of the blade.

[0018] According to one embodiment, the upstream edge of the branch is substantially parallel to the pivot axis.

[0019] According to one embodiment, the spar has an upstream edge and a downstream edge, the upstream edge facing a leading edge of the blade and the downstream edge facing the trailing edge of the blade, the spar further comprising a connecting portion extending between the base and the root, the connecting portion having a flared shape from the root and in the direction of the base, at least one of an upstream edge and a downstream edge of the connecting portion forming an angle of between 70° and 90° with a plane normal to the pivot axis.

[0020] According to one embodiment, the blade has a third skeleton corresponding to a line passing through the intersection between an internal radial limit of the skin and the connecting portion which extends midway between the intrados and the extrados of the blade in a plane normal to the pivot axis and has a third total curvilinear length between the leading edge and the trailing edge, where the radially internal limit of the skin corresponds to a face of the skin configured to extend facing the hub, the connecting portion comprising a recess centered on the pivot axis, a thickness of the recess measuring approximately 2% of the third total curvilinear length, a thickness between the upstream edge of the connecting portion and the pivot axis measuring approximately 18% of the third total curvilinear length and a thickness between the downstream edge of the connecting portion and the pivot axis measuring approximately 7% of the third total curvilinear length,where the thicknesses are curvilinear distances measured along the third skeleton of the blade.

[0021] According to a second aspect of the invention, there is provided a fan rotor, comprising a hub, a variable pitch mechanism and at least one blade as described above, the variable pitch mechanism being configured to allow pivoting of the blade relative to the hub around the pivot axis.

[0022] According to a third aspect of the invention, there is provided a turbomachine provided with a fan comprising a fan rotor as described in the preceding paragraph, the fan being of the unducted type. DESCRIPTION OF FIGURES

[0023] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0024] [Fig.l] schematically illustrates an example of fan blade architecture of turbomachine.

[0025] [Fig. 2] is a sectional view of an example of a blade according to one embodiment, on which a skeleton of the blade has been shown.

[0026] [Fig.3] schematically illustrates a cross-section of the blade in the part corresponding to its aerodynamic blade.

[0027] [Fig.4] illustrates an example of a turbomachine which may comprise a blade according to one embodiment.

[0028] [Fig.5] illustrates an example of an aircraft which may comprise at least one turbomachine comprising a blade according to one embodiment.

[0029] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION

[0030] As described above, a turbomachine 1 has a main or axial direction XI extending along a longitudinal axis, and typically comprises, from upstream to downstream in the direction of gas flow, a fan 4, a compression section which may comprise a low-pressure compressor and a high-pressure compressor, a combustion chamber, a turbine section which may comprise a high-pressure turbine and a low-pressure turbine.

[0031] In the present application, upstream and downstream are defined with respect to the normal flow direction of the gas in the fan 4. Furthermore, the axial direction X1 corresponds to the direction of the axis of the fan rotor and a radial direction X2 is a direction perpendicular to this axis and passing through it. Furthermore, the circumferential direction X3 corresponds to a direction perpendicular to the axis of the fan rotor and not passing through it. Unless otherwise specified, internal (respectively, inside) and external (respectively, outside), respectively, are used with reference to a radial direction so that the internal part or face of an element is closer to the axis of the fan rotor than the external part or face of the same element.

[0032] The fan 4 comprises at least one rotor provided with a hub 43 and blades 44 extending radially from the hub 43. Each blade 44 comprises a root 41 which will be mounted in a cell of the hub 43. In a radially external direction relative to the root 41, each blade 44 comprises a blade 42 with an aerodynamic profile, which extends into the air flow of the fan 4. A stilt 40 makes it possible to connect the root 41 to the blade 42, the stilt not extending into the air flow.

[0033] The blade 44 is pivotally mounted around a pivot axis 17 relative to the hub 43, a setting mechanism 19 making it possible to adjust a setting angle of the blade 44 relative to the hub 43.

[0034] The blade 44 comprises a skin 9 and a spar 7.

[0035] The skin 9 forms an extrados 15 and a intrados 16 of the aerodynamic blade 42 of the vane 44 and is shaped so as to delimit an internal cavity in which the spar 7 is housed at least partially. The skin 9 can in particular be made of a composite material comprising a fibrous reinforcement embedded in a matrix, typically a polymer matrix.

[0036] The spar 7 may be metallic, in particular comprising titanium.

[0037] When the spar is metallic and the skin is made of composite material, the blade obtained is light due to the low density of the composite materials, while being capable of withstanding high bending forces without breaking, due to the mechanical strength and high ductility of metals such as titanium.

[0038] Alternatively, it may be provided that the spar 7 also comprises a composite material with a fibrous reinforcement embedded in a matrix.

[0039] The spar 7 comprises a retaining structure 11 radially external relative to the root 41, when the blade 44 is in position in the hub 43. An internal part of the retaining structure 11 forms the Péchasse 40 of the blade, radially connecting the root 41 to the aerodynamic blade 42. An external part of the retaining structure 11 extends into the internal cavity of the skin 9. The external part of the retaining structure 11 comprises a base 13 as well as a single branch 12.

[0040] The pivot axis 17 of the blade extends in the radial direction when the blade 44 is mounted in the hub 43. The proposed blade architecture is characterized by dimensions, in this radial direction or in a plane normal to it.

[0041] The blade defines a tip 54, a radially inner limit 51 of the skin 9 which is a face of the skin configured to extend opposite the hub 43, a radially outer limit 52 of the base which corresponds to the area of ​​the base 13 closest to the tip 54 of the blade, and a radially outer limit 53 of the branch which is a face of the branch closest to the tip 54 of the blade. The blade 44 also has a blade height h, corresponding to a distance along the pivot axis 17 between the radially inner limit 51 of the skin 9 and the tip 54 of the blade 44, and a blade height H, which corresponds to a distance along the pivot axis 17 between a radially inner limit of the root and the tip 54 of the blade 44.

[0042] In the following, and with reference to [Fig. 2], skeleton SQn will be understood to mean the curve extending from the leading edge 5 of the blade to its trailing edge 6, midway between the intrados 16 and the extrados 15 of the blade, in a plane normal to the pivot axis 17, called the radial plane, at a given percentage of height of the height of the blade H. Thus, a first skeleton SQ1 extends in the radial plane comprising a point located at the intersection between an upstream edge 121 of the branch and an upstream edge 131 of the base, these upstream edges facing the leading edge 5 of the blade. A second skeleton SQ2 extends in the radial plane comprising a point located at the intersection between the upstream edge 121 of the branch and the radially external limit 53 of the branch. Each skeleton SQn defines a total curvilinear length LTn corresponding to the distance traveled between the leading edge 5 and the trailing edge 6 of the blade along the skeleton SQn.

[0043] At the level of the first skeleton SQ1, the base 13 defines a width E2 and the branch 12 defines a width E3 so that E3 is less than E2. Such a geometry of the spar 7 advantageously makes it possible to obtain a light blade, while taking into account the natural frequency of its first bending mode, so that this frequency is sufficiently far from the vibration frequency of the cyclic forces to which the blade will be subjected in flight. This ensures that the structural integrity of the blade will not be compromised by possible dynamic resonance effects. Such effects can in particular be caused by vibrations due to asymmetric forces in the climb phase, during which the influence of the ground and the fuselage on the flow seen by the blades has the consequence that this flow is not parallel to the axis of the engine.Furthermore, such a spar geometry reduces the propagation of cracks in polycyclic fatigue and therefore allows to increase the life of the blade. The proposed blade also allows sufficient strength to meet the bird ingestion constraints imposed by the certification authorities.

[0044] In one embodiment, the root 41 may have a biconical shape. Reference may in particular be made to document WO 2022 / 018357 for further details on this blade root shape. For a variable-pitch blade, such an attachment geometry allows for better resistance of the attachment to the asymmetrical forces imposed on the blade during certain flight phases such as the climb phases, as described above.

[0045] According to one embodiment, the blade further comprises a filling portion 8 placed in the internal cavity, between the spar 7 and the skin 9. The filling portion 8 may comprise several separate parts, typically a first part placed along an upstream edge 71 of the spar and a second part placed along a downstream edge 72 of the spar 7, located respectively opposite the leading edge 5 and the trailing edge 6 of the blade. The two parts of the filling portion 8 may optionally be separate, so that the spar 7 has between these two parts contact interfaces with the skin 9. This filling portion 8 may for example comprise a foam, for example an expanded foam. It is thus possible to further reduce the total mass of the blade, the mechanical strength being ensured by the spar 7 and the skin 9 made of composite material.

[0046] The spar 7 and the filling portion 8 may have a continuity of tangency, so that the internal cavity 9 of the skin has a continuous internal surface.

[0047] According to one embodiment, the base 13 and the branch 12 respectively have downstream edges 132 and 122 facing the trailing edge 6 of the blade, the upstream edge 121 of the branch 12 extends in the extension of the upstream edge 131 of the base, and the downstream edge 122 of the branch is at a distance from the downstream edge 132 of the base. An external part of the retaining structure 11 of the spar 7 then has an “L” shape, the branch 12 forming the external part of the L and the base 13 forming the internal part. This L shape allows both a thickness of the base 13 which ensures adequate absorption of the static and dynamic bending forces imposed on the root 41 and the internal part of the retaining structure 11, and a lesser thickness of the branch 12 which makes it possible to stiffen the blade, in particular so as to distance the natural frequency of the blade from the excitation frequencies of the forces to which it is likely to be subjected.Furthermore, providing a branch 12 closer to the leading edge 5 than to the trailing edge 6 of the blade makes it possible to increase the stiffness of the blade at the leading edge 5, where the aerodynamic pressure field is highest. Finally, the reduced thickness of the branch 12 compared to the base 13 lightens the blade and contributes to the aforementioned distance of its natural frequency from the excitation frequencies.

[0048] According to one embodiment, the width of the branch E3, measured along the first skeleton SQ1, is less than the curvilinear distance between the upstream edge 121 of the branch 12 and the pivot axis 17 along the first skeleton SQL. In other words, the entire branch 12 is located upstream of the pivot axis 17 in the axial direction XL. This embodiment aims to further increase the stiffness of the blade near the leading edge 5 of the blade.

[0049] According to one embodiment, a curvilinear length L2 between the upstream edge 121 of the branch 12 and the leading edge 5 of the blade along the first skeleton SQ1 is between 20 and 40% of the first total curvilinear length LT1 corresponding to the first skeleton SQL

[0050] According to one embodiment, a curvilinear length L3 between the upstream edge 121 of the branch and the leading edge 5 of the blade along the second skeleton SQ2 is between 20% and 60% of the second total curvilinear length LT2 corresponding to the second skeleton SQ2.

[0051] According to one embodiment, the width E3 of the branch 12 evaluated at the level of the first skeleton SQ1 is between 10% and 30% of the total curvilinear length LT1 of the first skeleton. The width of the branch 12 may in particular be constant between the radially external limit 52 of the base and the radially external limit 53 of the branch 12. Alternatively, this width may vary with the pivot axis 17, always being between 10% and 30% of the total curvilinear length LT1. These dimensions make it possible to minimize the total volume and therefore the mass of the branch, without compromising its structural integrity.

[0052] According to one embodiment, a distance H2 between the radially internal limit 51 of the skin and the radially external limit 52 of the base is between 4% and 14% of the blade height.

[0053] According to one embodiment, a distance H3 between the radially internal limit 51 of the skin and the radially external limit 53 of the branch is between 10% and 30% of the blade height.

[0054] These values ​​of the two distances H2, H3 define a height of the branch 12 and a height of the part of the spar 7 between the radially internal limit 51 of the skin and the radially external limit 52 which makes it possible to maximize the volume of material in the spar 7 where the forces due to the asymmetry of the flow on the blade are significant, while reducing the volume of material on a part of the spar 7 subjected to lesser forces, thus ensuring a good compromise between strength and weight of the blade.

[0055] According to one embodiment, the upstream edge 121 of the branch 12 is substantially parallel to the pivot axis 17.

[0056] According to one embodiment, the spar 7 has an upstream edge 71 and a downstream edge 72, the upstream edge 71 facing the leading edge 5 of the blade and the downstream edge 72 facing the trailing edge 6 of the blade, and the spar 7 further comprises a connecting portion 14 extending between the base 13 and the root 41, the connecting portion 14 having a flared shape starting from the root 41 in the direction of the base 13. This flared shape allows the connecting portion 14 to retain the skin made of composite material on the spar, by opposing a movement thereof away from the hub due to the centrifugal forces which are exerted on the blade in flight. The stilt 40, which extends outside the aerodynamic flow in the example shown - that is to say between the foot 41 and the radially internal limit 51 of the skin - then forms an internal part of the connecting portion 14, the remainder of the connecting portion 14 forming an external part housed in the internal cavity of the skin 9.Thus, according to this embodiment, the base 13 is indirectly connected to the foot 41 via the connecting portion 14.

[0057] Advantageously, at least one of the upstream edge 141 and the downstream edge 142 of the connecting portion 14 forms an angle α of between 70° and 90° with a plane normal to the pivot axis 17. Such an angle α makes it possible to have a connecting portion 14 that is flared enough to ensure the retention of the skin 9 on the spar 7 while minimizing the contribution of this connecting portion 14 to the total mass of the blade.

[0058] When the spar 7 comprises such a connecting portion 14, a third skeleton SQ3 can be defined, corresponding to the skeleton passing through a point located at the intersection of the internal radial limit 51 of the skin with the connecting portion 14.

[0059] According to one embodiment, the connecting portion 14 comprises a recess 18 centered on the pivot axis 17, a thickness LE of the recess 18 along the third skeleton measuring approximately 2% of a third total curvilinear length LT3 defined by the third skeleton SQ3 between the leading edge 5 of the blade and its trailing edge 6. For example, a thickness LIA between the upstream edge 141 of the connecting portion and the pivot axis 17 measures approximately 18% of the third total curvilinear length, and a thickness L1F between the downstream edge 142 of the connecting portion and the pivot axis measures approximately 7% of the third total length LT3.

[0060] The thickness of the recess 18 may in particular be constant along the direction defined by the pivot axis 17.

[0061] Other embodiment variants are conceivable, including:

[0062] - the thickness of the skin 9, evaluated along a fourth skeleton SQ4 passing through the intersection between the foot 41 and the connecting portion 14, can be 20mm;

[0063] - The spar 7 can be solid in its internal part relative to the limit ra- internal dialy 51 of the skin 9;

[0064] - the thickness of the skin 9 between a radially internal limit of the base, cor corresponding to a face of the base 13 located closest to the hub 43, and the radially external limit 53 of the branch can be between 2 and 5 mm.

[0065] An aircraft 100 may comprise at least one turbomachine 1 as described above. According to one embodiment, the aircraft is an airplane comprising a fuselage 101 and two wings 102, and also comprising two turbomachines 1 as described above. Each turbomachine 1 is attached to a respective wing 102 of the airplane 100 via a pylon. In another embodiment, the aircraft could comprise one or more turbomachine(s) attached to the fuselage 101.

[0066] A fan rotor may comprise a hub 43, a variable pitch mechanism 19 and one or more blades 44 as described previously. The variable pitch mechanism 19 makes it possible to adjust a pitch angle of the blades 44 around the pivot axis 17. A turbomachine 1 may comprise a fan 4 provided with such a fan rotor.

[0067] According to one embodiment of the fan rotor, the fan 4 is of the unducted type.

[0068] According to one embodiment of the fan rotor, the fan 4 comprises from 12 to 18 blades, preferably from 12 to 16 blades.

[0069] According to one embodiment, the rotor diameter is between 2 and 6 meters, preferably between 2.5 and 5 meters, even more preferably between 3 and 4 meters.

[0070] Depending on the number of blades and the diameter of the fan rotor, the spar and its retaining structure are particularly effective in resisting both centrifugal stresses and stresses resulting from aerodynamic forces on the blades, in particular during changes in operating phases including differences in variable pitch of the blades. In relation to these stresses, the chord of the blades is generally larger for a smaller number of blades and then the blade chord is generally smaller for a larger number of blades, weighting with the blade height h according to the desired thrust.

Claims

Claims

1. Fan blade of a turbomachine (1) configured to be pivotally mounted about a pivot axis (17) relative to a hub (43) of a fan (4), comprising: - a skin (9) forming a lower surface (16) and an upper surface (15) of the blade, the skin delimiting an internal cavity, the skin being able to comprise a composite material comprising a fibrous reinforcement embedded in a matrix; - a spar (7) housed at least partially in the internal cavity of the skin (9), the spar (7) comprising a root (41) extending outside the cavity and configured to be mounted in a hub of the fan (4) and a retaining structure (11) housed at least partially in the cavity and extending from the root (41); the retaining structure (11) comprising a base (13) connected to the foot and a single branch (12) extending radially from the base (13) at a distance from the foot (41), in which the base (13) and the branch (12) have an upstream edge (131,121) and a downstream edge (132, 122), the upstream edge facing a leading edge (5) of the blade and the downstream edge facing the trailing edge (6) of the blade, the upstream edge (121) of the branch extending in the extension of the upstream edge (131) of the base and the downstream edge (122) of the branch being at a distance from the downstream edge (132) of the base, the retaining structure (11) having a width of the base (E2) greater than a width of the branch (E3) and these widths being curvilinear distances measured along a first skeleton (SQ1) of the blade, the first skeleton corresponding to a line passing through a point located at the intersection between the upstream edge (121) of the branch and the upstream edge (131) of the base, the first skeleton (SQ1) extending halfway between the intrados (16) and the extrados (15) of the blade in a plane normal to the pivot axis (17).,

2. A blade according to claim 1, wherein the width of the branch (E3) is less than a curvilinear distance between the upstream edge (121) of the branch and the pivot axis (17), this distance being measured along the first skeleton (SQ1) of the blade.

3. Blade according to one of claims 1 or 2, in which the first skeleton (SQ1) has a first total curvilinear length (LT1) between the leading edge (5) and the trailing edge (6), a length curvilinear length (L2) between the upstream edge (121) of the branch and the leading edge (5) of the blade along the first skeleton (SQ1) being between 20% and 40% of the first total curvilinear length (LT1) of the first skeleton (SQ1).

4. A blade according to one of claims 1 to 3, wherein the blade has a second skeleton (SQ2) corresponding to a line passing through a point located at the intersection between the upstream edge (121) of the branch (12) and a radially external limit (53) of the branch, the second skeleton (SQ2) extending midway between the intrados (16) and the extrados (15) of the blade in a plane normal to the pivot axis (17) and having a second total curvilinear length (LT2) between the leading edge (5) and the trailing edge (6), a curvilinear length (L3) between the upstream edge (121) of the branch and the leading edge (5) of the blade along the second skeleton (SQ2) being between 20% and 60% of the second total curvilinear length (LT2) of the second skeleton (SQ2).

5. Blade according to one of claims 1 to 4, in which the width (E3) of the branch is between 10% and 30% of a first total curvilinear length (LT1) of the first skeleton (SQ1), between the leading edge (5) and the trailing edge (6) of the blade.

6. A blade according to one of claims 1 to 5, wherein a distance (H2) between a radially inner limit (51) of the skin and a radially outer limit (52) of the base (13) is between 4% and 14% of a blade height (h), the radially inner limit of the skin (51) corresponding to a face of the skin configured to extend facing the hub (43), the radially outer limit of the base (52) corresponding to a face of the base closest to a tip (54) of the blade, and the height of the blade corresponds to a distance, along the pivot axis, between the radially inner limit (51) of the skin and the tip (54) of the blade.

7. A blade according to one of claims 1 to 6, wherein a distance (H3) between a radially inner limit (51) of the skin and a radially outer limit (53) of the branch (12) is between 10% and 30% of a blade height (h), the radially inner limit (51) of the skin corresponding to a face of the skin configured to extend facing the hub (43), the radially outer limit (53) of the branch corresponding to a face of the branch closest to a tip (54) of the blade, and the blade height (h) corresponds to a distance, along the axis pivoting (17), between the radially internal limit (51) of the skin and the tip (54) of the blade.

8. Blade according to one of claims 1 to 7, in which the upstream edge (121) of the branch (12) is substantially parallel to the pivot axis (17).

9. Blade according to one of claims 1 to 8, in which the spar comprises a connecting portion (14) extending between the base (13) and the root (41), the connecting portion (14) having a flared shape from the root (41) and in the direction of the base (13), at least one of an upstream edge (141) and a downstream edge (142) of the connecting portion (14) forming an angle of between 70° and 90° with a plane normal to the pivot axis (17).

10. A blade according to claim 9, having a third skeleton (SQ3) corresponding to a line passing through the intersection between an internal radial limit (51) of the skin and the connecting portion (14) which extends midway between the intrados (16) and the extrados (15) of the blade in a plane normal to the pivot axis (17) and has a third total curvilinear length (LT3) between the leading edge (5) and the trailing edge (6), where the radially internal limit (51) of the skin corresponds to a face of the skin configured to extend facing the hub (43), the connecting portion (14) comprising a recess (18) centered on the pivot axis (17), a thickness (LE) of the recess (18) measuring approximately 2% of the third total curvilinear length (LT3),a thickness between the upstream edge (141) of the connecting portion (14) and the pivot axis (17) measuring approximately 18% of the third total curvilinear length (LT3) and a thickness between the downstream edge (142) of the connecting portion and the pivot axis (17) measuring approximately 7% of the third total curvilinear length (LT3), where the thicknesses are curvilinear distances measured along the third skeleton (SQ3) of the blade.,

11. A fan rotor, comprising a hub (43), a variable pitch mechanism (19) and at least one blade according to any one of claims 1 to 10, the variable pitch mechanism (19) being configured to allow pivoting of the blade relative to the hub (43) about the pivot axis (17).

12. Turbomachine (1) provided with a fan (4) comprising a rotor of blower according to claim 11, the blower being of the unducted type.

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