Unducted aeronautical propulsion unit for aircraft

Abstract

The invention relates to a propulsion unit which comprises: - an outer casing (102); - a hub; - a pusher propeller; and - a fixed flow straightener comprising at least one stator blade (114) with variable pitch about a pitch axis (Y'), each variable-pitch stator blade (114) having a pitch angle defined as the angle between any plane perpendicular to the main axis (X) and a chord line (706) connecting a leading edge of the stator blade (114) to a trailing edge of the stator blade (114), this chord line (706) being taken at 75% of an outer radius of the stator blade (114) with respect to the main axis (X). The leading edge of at least one stator blade (114) has a dihedral angle (D'BA') at 95% of the outer radius with an absolute value greater than 1°, preferably greater than 3°, more preferably greater than 10°, for at least one value of the pitch angle within the range [70°; 90°].

Description

Description TITLE: UNCOUPELED AERONAUTICAL PROPELLER FOR AIRCRAFT Technical field of the invention

[0001] The present invention relates to an unducted aeronautical propeller for an aircraft, for example such as a turbomachine or a turbojet or a turboshaft engine, as well as to an aircraft comprising such an aeronautical propeller. Technological background

[0002] Known from the state of the art is an unducted aeronautical propeller for an aircraft, comprising: - an outer casing; - a hub mounted to pivot relative to the outer casing about a main axis extending in an upstream-downstream direction of the aircraft; - a propulsive propeller mounted on the hub so as to pivot relative to the outer casing; and - a fixed rectifier mounted on the outer casing downstream of the propulsive propeller along the main axis, the fixed rectifier extending around the main axis and comprising at least one variable-pitch stator blade about a pitch axis, each variable-pitch stator blade having a pitch angle defined as the angle between, on the one hand, any plane perpendicular to the main axis and, on the other hand, a chord line connecting a leading edge of the stator blade to a trailing edge of the stator blade.

[0003] Typically, the propeller has variable-pitch rotor blades. Variable-pitch systems are known as Fan Pitch Actuation Systems (FPAS) and / or Pitch Change Mechanisms (PCM). To achieve a target thrust, several combinations of propeller rotational speeds and rotor and stator blade pitches are possible.

[0004] One of the challenges of such an aeronautical propeller is the certification of noise levels during takeoff and landing operations. The noise levels emitted by aircraft are subject to increasingly strict international regulations in order to limit the acoustic footprint around airports. Currently, the regulations in force are mentioned in Chapter 14 of Annex 16, Volume 1 of the ICAO (International Civil Aviation Organization), which gives the maximum sound levels in EPNL (“Effective Perceived Noise Level”) depending on the phase of flight and the weight of the aircraft.

[0005] The main sources of noise on unducted aircraft propellers are as follows.

[0006] A first source of noise is the interaction noise of the vortex generated at the tip of the rotor blades and the propeller wake upstream which interacts with the leading edge of the rectifier downstream. This source of noise contributes to the increase in broadband noise, because the turbulence rate on the wake is often very high at the tip of the rotor blade, and to the increase in tonal noise, linked to the periodic nature of this vortex during rotation of the rotor blades.

[0007] A second source of noise is the self-noise of the rotor and stator blades. This self-noise is related to the stationary load of the rotor blades (a source of tonal noise) and the development of the boundary layer on the rotor and stator blades. Thus, a broadband noise source is generated when the turbulent boundary layer passes over the trailing edge of the rotor and stator blades. The increase in the chord of the rotor and / or stator blades on unducted aeronautical propellers increases the surface area over which the boundary layer develops and consequently the broadband noise.

[0008] The aim of the invention is to improve the acoustic performance of the rectifier downstream of the propeller without degrading the aerodynamic performance and while respecting certain mechanical constraints.

[0009] Furthermore, patent applications US 20170284304 A1 and FR 3124832 A1, as well as the article “Cruise noise of an advanced propeller with swirl recovery vanes”, Dittmar et al., 2012, describe unducted aeronautical propellers for aircraft. Summary of the invention

[0010] There is therefore proposed an unducted aeronautical propeller for an aircraft, comprising: - an external casing; - a hub mounted to pivot relative to the external casing around a main axis extending in an upstream-downstream direction of the aircraft; - a propeller mounted on the hub so as to be pivotable relative to the outer casing; and - a fixed rectifier mounted on the outer casing downstream of the propeller along the main axis, the fixed rectifier extending around the main axis and comprising at least one variable-pitch stator blade around a pitch axis, each variable-pitch stator blade having a pitch angle defined as the angle between, on the one hand, any plane perpendicular to the main axis and, on the other hand, a chord line connecting a leading edge of the stator blade to a trailing edge of the stator blade;characterized in that the chord line is taken at 75% of an external radius of the stator blade relative to the main axis and in that the leading edge of at least one stator blade has a dihedral angle at 95% of the external radius with an absolute value greater than 1°, preferably 3°, more preferably 10°, for at least one value of the pitch angle included in the interval [70°; 90°].;

[0011] The invention may further comprise one or more of the following optional features, in any technically possible combination.

[0012] Optionally, the absolute value of the dihedral angle at 95% of the outer radius is greater by at least 1°, preferably by at least 3°, or even more preferably by at least 10°, than the absolute value of the dihedral angle of the leading edge of the stator blade at 50% of the outer radius, for at least one value of the pitch angle included in the interval [70°; 90°].

[0013] Also optionally, the absolute value of the dihedral angle on the leading edge of the stator blade is strictly monotonic for radial positions greater than 90% of the external radius, for at least one value of the pitch angle included in the interval [70°; 90°].

[0014] Also optionally, a projection of the leading edge of the stator blade onto a plane perpendicular to the main axis has a so-called transverse deviation along a so-called transverse direction perpendicular to the main axis and to the radial component of the pitch axis, the transverse deviation of the leading edge of the stator blade being greater than 1% and less than 10% of an external radius of said stator blade, for at least one value of the pitch angle included in the interval [70°; 90°].

[0015] Also optionally, a projection of the leading edge of the stator blade onto a plane perpendicular to the main axis has at least one local maximum and / or minimum, for at least one value of the pitch angle within the interval [70°; 90°].

[0016] Also optionally, a projection of the leading edge of the stator blade onto a plane perpendicular to the main axis has at least one point of inflection, for at least one value of the pitch angle within the interval [70°; 90°].

[0017] Also optionally, the propulsion propeller comprises at least one rotor blade with variable pitch around a pitch axis crossing the main axis and having a non-zero radial component relative to the main axis, each variable pitch rotor blade having a pitch angle defined as the angle between, on the one hand, any plane perpendicular to the main axis and, on the other hand, a chord line connecting a leading edge of the rotor blade to a trailing edge of the rotor blade, this chord line being taken in a plane perpendicular to the radial component of the pitch axis and crossing the rotor blade at 75% of an external radius of the rotor blade relative to the main axis.

[0018] Also optionally, a trailing edge of a rotor blade and the leading edge of a stator blade have dihedral angles such that the absolute value of the dihedral angle on the trailing edge of the rotor blade is greater than the absolute value of the dihedral angle on the leading edge of the stator blade at 95% of an external radius of the stator blade, for at least one value of the pitch angle of the rotor blade lying in the interval [50°; 80°] and for at least one value of the pitch angle of the stator blade lying in the interval [70°; 90°].

[0019] Also optionally, the trailing edge of a rotor blade and the leading edge of a stator blade have dihedral angles such that the absolute value of the dihedral angle on the trailing edge of the rotor blade is at least 10° greater than the absolute value of the dihedral angle on the leading edge of the stator blade at 75% of the external radius of the stator blade, for at least one value of the pitch angle of the rotor blade lying in the interval [50°; 80°] and for at least one value of the pitch angle of the stator blade lying in the interval [70°; 90°].

[0020] Also optionally, the trailing edge of a rotor blade and the leading edge of a stator blade have dihedral angles of opposite signs at 95% of an external radius of the stator blade, for at least one value of the pitch angle of the rotor blade included in the interval [50°; 80°] and for at least one value of the pitch angle of the stator blade included in the interval [70°; 90°].

[0021] Optionally also, at any height from the main axis, the absolute value of the dihedral angle of the leading edge of the stator blade is at least 2°, preferably at least 10°, greater than the absolute value of the dihedral angle of the trailing edge of the rotor blade, for at least one value of the pitch angle of the rotor blade included in the interval [50°; 80°] and for at least one value of the pitch angle of the stator blade included in the interval [70°; 90°].

[0022] Also optionally, a projection of the trailing edge of the rotor blade onto a plane perpendicular to the main axis has a so-called transverse deviation along a so-called transverse direction perpendicular to the main axis and to the radial component of the pitch axis of the rotor blade, a projection of the leading edge of the stator blade onto a plane perpendicular to the main axis has a so-called transverse deviation along a so-called transverse direction perpendicular to the main axis and to the radial component of the pitch axis of the stator blade, the transverse deviation of the leading edge of the stator blade being less than the transverse deviation of the trailing edge of the rotor blade, for at least one value of the pitch angle of the rotor blade included in the interval [50°; 80°] and for at least one value of the pitch angle of the stator blade included in the interval [70°; 90°].

[0023] Also optionally, the leading edge of at least one variable-pitch stator blade has a head located downstream of the radial component of the pitch axis, for at least one value of the pitch angle within the interval [70°; 90°].

[0024] Also optionally, at least one variable pitch stator blade has an activity factor of between 50 and 200, preferably between 90 and 150.

[0025] An aircraft comprising an aeronautical propeller according to the invention is also proposed. Brief description of the figures

[0026] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings in which: - Figure 1 is a sectional view of an aeronautical propeller according to the invention, - Figure 2 is a side view of a rotor blade of a propeller of the aeronautical propeller of Figure 1, - Figure 3 is a sectional view of the rotor blade of Figure 2, - Figure 4 is a view similar to that of Figure 2, illustrating a sweep angle of the rotor blade, - Figure 5 is a front view of the rotor blade of Figure 2, illustrating a dihedral angle of the rotor blade, - Figure 6 is a side view of a stator blade of a fixed rectifier of the aeronautical propeller of Figure 1, - Figure 7 is a sectional view of the stator blade of Figure 6, - Figure 8 is a view similar to that of Figure 2, illustrating a sweep angle of the rotor blade, - Figure 9 is a side view of a stator blade of a fixed rectifier of the aeronautical propeller of Figure 1, - Figure 10 is a sectional view of the stator blade of Figure 1, - Figure 11 is a side view of a stator blade of a fixed rectifier of the aeronautical propeller of Figure 1, - Figure 12 is a side view of a stator blade of a fixed rectifier of the aeronautical propeller of Figure 1, - Figure 13 is a sectional view of the stator blade of Figure 1, - Figure 14 is a side view of a stator blade of a fixed rectifier of the aeronautical propeller of Figure 1, - Figure 15 is a sectional view of the stator blade of Figure 1, - Figure 16 is a side view of a stator blade of a fixed rectifier of the aeronautical propeller of Figure 1, - Figure 17 is a sectional view of the stator blade of Figure 1, - Figure 18 is a side view of a stator blade of a fixed rectifier of the aeronautical propeller of Figure 1 that of figure 6, illustrating an angle of arrow of the stator blade,- Figure 9 is a front view of the stator blade of Figure 6, illustrating a dihedral angle of the stator blade, - Figure 10 is a view similar to that of Figure 6, illustrating a stator blade with a rounded tip, - Figure 11 is a graph illustrating the evolution of a chord of the stator blade as a function of a blade height, - Figure 12 is a sectional view of another aeronautical propeller according to the invention, illustrating the spacing between the propulsive propeller and the fixed rectifier, - Figure 13 is a sectional view of the stator blade of Figure 6, and - Figure 14 is a front view of a trailing edge of the rotor blade and a leading edge of the stator blade., Detailed description of the invention

[0027] In the following description, when a characteristic applies to at least one element, it can also apply to all of these elements. Similarly, when a characteristic applies for at least one value within an interval, it can also apply for all values ​​within that interval.

[0028] With reference to Figure 1, an aeronautical propeller 100 in which the invention is implemented will now be described. The aeronautical propeller 100 is for example a turbomachine or a turbojet or a turboshaft engine, since the type of aeronautical propeller is not decisive here.

[0029] The 100 aircraft propeller is unducted (from the English “Unducted Single Fan”, also designated by the acronym USF) and is designed to participate in the propulsion of an aircraft.

[0030] The aeronautical propeller 100 firstly comprises an external casing 102 and a hub 104 pivotally mounted relative to the external casing 102 around a main axis X.

[0031] Subsequently, the terms “upstream” and “downstream” will be used to specify the relative position of the elements of the aeronautical propeller 100 along the main axis X in a direction of flow of an air flow PHI when the aircraft is propelled by the aeronautical propeller 100. For example, the aircraft can be propelled by the aeronautical propeller 100 in cruising mode at a flight Mach number greater than 0.7.

[0032] The hub 104 is thus, for example, located upstream of the external casing 102.

[0033] The aeronautical thruster 100 further comprises an unducted propulsive propeller 106 mounted on the hub 104 so as to be pivotable relative to the external casing 102 around the main axis X. The propeller 106 is designed to drive the air flow PHI downstream to propel the aircraft in flight. For this purpose, the propeller 106 comprises rotor blades 108 (for example between 3 and 25, preferably between 10 and 16) organized for example in a single annular row around the main axis X. The rotor blades 108 may for example all be identical and angularly spaced regularly around the main axis X.

[0034] At least one rotor blade 108 is for example variable pitch, around a respective pitch axis Y. The pitch axis Y may pass through the main axis X or be slightly offset from the main axis X, for example by an offset of at most 10 cm, for example still at most 5 cm, for example still at most 2 cm, for example still at most 1 cm. The pitch axis Y may be perpendicular to the main axis X or may make a slightly different angle, due to manufacturing tolerances or intentionally. The pitch axis Y may thus be for example perpendicular to within 5°, for example still within 2°, for example still within 1°, for example still within 0.1°. In all cases, the pitch axis Y makes a non-zero angle with the main axis X and thus has a non-zero radial component. As illustrated in the figures, the Y axis can thus be radial, that is to say it makes an angle of 90° with the main X axis.The pitch of each variable-pitch rotor blade 108 is defined by a pitch angle C which will be detailed later. In a preferred embodiment, all the rotor blades 108 are variable-pitch.

[0035] The aeronautical thruster 100 further comprises a motor 110 for driving the hub 104, and therefore the propeller 106 via the hub 104. The motor 110 extends for example into the external casing 102. The motor 110 is for example located downstream of the propeller 106. Such an arrangement is known as a “tractor” (from the English “puller”). The motor 110 is for example a gas generator conventionally comprising, from upstream to downstream, at least one compressor, at least one combustion chamber and at least one power turbine intended to drive the propeller 106.

[0036] The aeronautical thruster 100 further comprises a fixed rectifier 112 which is not shrouded and mounted on the external casing 102 downstream of the propeller 106. The rectifier 112 forms a stator located on the external casing 102 extending around the main axis X, but which cannot rotate around the latter. The rectifier 112 comprises stator blades 114 organized for example in a single annular row around the main axis X. For example, between 3 and 25 stator blades, preferably between 8 and 14 stator blades 114, are provided. Preferably, the number of stator blades 114 is different from the number of rotor blades 108, in order to reduce the noise of the aeronautical propeller 100. In particular, the number of rotor blades 108 is greater than the number of stator blades 114. Indeed, in the case where the number of rotor blades 108 and the number of stator blades 114 were equal, the rotor blades 108 would be followed by wakes which would interact simultaneously with the stator blades 114, which would increase the sound levels. The stator blades 114 may for example all be identical or different and spaced angularly in a regular manner or in a heterogeneous manner around the main axis X, so that at least two stator blades 114 have a different angular spacing around the main axis X.In particular, in the case of an aeronautical propeller installed in the aircraft, the stator blades 114: - may have an external radius smaller than that of the rotor blades 108 to reduce the interaction noise of the tip vortex of the rotor blades 108 with the stator blades 114; this external radius of the stator blades 114 may be different for each stator blade 114 in order to limit the interaction during the phases of flight at incidence, such as landing and takeoff; - may have different geometric characteristics (pitch angles, thicknesses, chord, etc.) to optimize their operation according to the local properties of the flow; and - may have heterogeneous angular spacings around the main axis X, in particular near the mast or pylon; this makes it possible to optimize the operation of the stator blades 114 according to its installation in the aircraft.

[0037] The rectifier 112 is designed to straighten at least a portion of the airflow PHI passing through the propeller 106, in order to improve the performance of the aeronautical thruster 100. More specifically, the rectifier 112 aims to take up the gyration of the flow induced by the propulsive propeller 106 in order to improve the performance of the unducted configuration. However, its presence induces a dominant noise source resulting from the interaction with the wake of the propeller 106 (and the blade tip vortex when the truncation of the stator blades 114 is not sufficient). It is therefore appropriate to reduce the noise generated by the rectifier 112 and its interaction with the wake of the propeller 106 while preserving good aerodynamic performance, because the reduction of noise emissions and consumption is a major issue for unducted engine architectures.

[0038] For example, at least one stator blade 114 has variable pitch about a respective Y' axis. The pitch axis Y' may pass through the main axis X or be slightly offset from the main axis X, for example by an offset of at most 10 cm, for example still at most 5 cm, for example still at most 2 cm, for example still at most 1 cm. The pitch axis Y' may be perpendicular to the main axis X or may be at a slightly different angle, due to manufacturing tolerances or intentionally. The pitch axis Y' may thus be, for example, perpendicular to within 5°, for example still to within 2°, for example still to within 1°, for example still to within 0.1°. In all cases, the pitch axis Y makes a non-zero angle with the main axis X and thus has a non-zero radial component. As illustrated in the figures, the axis Y' may thus be radial, i.e. it makes an angle of 90° with the main axis X. The pitch of each stator blade 114 with variable pitch is defined by a pitch angle C' which will be detailed later. In a preferred embodiment, all of the stator blades 114 are variable pitch.

[0039] In the case where one of the stator blades is fixed (for example for integration constraints, such as if there is insufficient space under the hub to integrate the pitch change system or to reduce weight), the Y' axis of the blade can be defined by the line perpendicular to the main X axis passing through the leading edge BA' at the blade root. In this case, the blade has a fixed pitch angle C'.

[0040] The aeronautical propeller 100 further comprises, for example, an air inlet 116 for supplying primary flow to the engine 110. This air inlet 116 is, for example, provided between the propeller 106 and the rectifier 112.

[0041] With reference to FIG. 2, the rotor blade 108 firstly comprises a leading edge BA where the air flow PHI arrives, i.e. the front part of the rotor blade 108 facing the fluid (or coming into contact first with the fluid), and a trailing edge BF from which the air flow PHI moves away, i.e. the rear part of the rotor blade 108 in the direction of flow.

[0042] The leading edge BA extends from a root BA_P which is the point of the leading edge BA closest to the hub 104 to a head BA_T which is the point of the leading edge BA which is highest or has a maximum radius relative to the main axis X on the upstream part of the rotor blade 108. Between the root BA_P and the head BA_T, the leading edge BA has a curvature of constant direction, that is to say without an inflection point (in other words, the second derivative of the axial position xBA of the leading edge as a function of h BAis not zero, ≠ 0, along the leading edge BA as a function of the height hBA of rotor blade 108 and hBA is the height from the root BA_P), for at least one value of the pitch angle C included in the interval [50°; 80°]. The curvature of the leading edge BA is furthermore regular, i.e. without discontinuity. The leading edge BA furthermore comprises an antinode BA_V which is the point of the leading edge BA furthest upstream (min{xBA}), in particular for at least one value of the pitch angle C included in the interval [50°; 80°].

[0043] Similarly, the trailing edge BF extends from a root BF_P which is the point of the trailing edge BF closest to the hub 104 to a head BF_T which is the point of the trailing edge BF which is highest or has a maximum radius relative to the main axis X on the rear part of the rotor blade 108. Between the root BF_P and the head BF_T, the trailing edge BF has a curvature of constant direction, that is to say without an inflection point (in other words, the second derivative of the axial position x BF of the trailing edge BF as a function of h BF is not zero, % # ! ' ≠ 0, along the trailing edge BF as a function of the height h BF of rotor blade 108 and h BFis the height from the foot BF_P), for at least one value of the setting angle C included in the interval [50°; 80°]. The curvature of the trailing edge BF is also regular, i.e. without discontinuity. The trailing edge BF also has an antinode BF_V which is the point of the trailing edge BF furthest upstream (min{x BF}), in particular for at least one value of the setting angle C included in the interval [50°; 80°].

[0044] The rotor blade 108 may further be truncated at its free end, as in the example illustrated, i.e. there is a truncated section 202, for example straight, connecting the heads BA_T, BF_T. In this case, there is a discontinuity of curvature at the head BA_T between the leading edge BA and the truncated section 202 and another discontinuity of curvature at the head BF_T between the truncated section 202 and the trailing edge BF. Alternatively, the propeller blade could be non-truncated, in which case the heads BA_T and BF_T would be merged.

[0045] Subsequently, when applied in the context of the rotor blade 108, the term "height" will refer to the distance between two points along the radial component of the pitch axis Y, i.e., between the orthogonal projections of these points onto the radial component of the pitch axis Y.

[0046] It is thus possible to define an upstream blading height Hamont to position oneself on the leading edge BA. The upstream blading height Hamont is thus the ratio between a height hBA from the root BA_P and a total height HBA of the edge attack BA between the foot BA_P and the head BA_T: = hBA / HBA. The upstream blading height Hamont can thus be expressed in percentages and varies between 0% (position at the foot BA_P) and 100% (position at the head BA_T). Similarly, it is possible to define a downstream blading height H aval to position itself on the trailing edge BF. The Haval downstream blade height is thus the ratio between a height hBF from the root BF_P and a total height H BF of the trailing edge BF between the foot BF_P and the head BF_T: H aval = h BF / H BF . The downstream blade height H aval can thus be expressed in percentages and varies between 0% (position at the foot BF_P) and 100% (position at the head BF_T).

[0047] Furthermore, the propeller 106 has an external radius Re equal by definition to the height or distance between the main axis X and the point of the rotor blade 108 furthest from the main axis X, in particular for at least one value of the pitch angle C included in the interval [50°; 80°]. This furthest point is the head BA_T of the leading edge BA in the illustrated example.

[0048] Figure 3 is a section (also called an aerodynamic profile) of the rotor blade 108 perpendicular to the radial component of the pitch axis Y at a certain height.

[0049] As can be seen, the rotor blade 108 has a lower surface face 302 and an upper surface face 304, respectively concave and convex, connected to each other by the leading edge BA and the trailing edge BF. The leading edge BA therefore makes it possible to separate the lower surface face 302 from the upper surface face 304 in the upstream part of the rotor blade 108, while the trailing edge BF makes it possible to separate the lower surface face 302 from the upper surface face 304 in its rear part.

[0050] The leading edge BA is for example the point of the cut in the upstream part of the rotor blade 108, having a local minimum radius of curvature. Similarly, when the downstream part of the rotor blade is rounded, the trailing edge BF is for example the point of the cut in this downstream part, having a local minimum on the radius of curvature. To simplify the manufacturing method of the rotor blade 108, its downstream part could be truncated. In the latter case, the trailing edge BF is for example the middle of this truncated part.

[0051] When the leading edge BA and the trailing edge BF are present in the section considered (that is to say for example at a height not too close to the foot BA_P and below the truncated section 202), the leading edge BA and the trailing edge BF can be connected by a chord line 306 whose orientation changes according to the height considered. The leading edge BA and the trailing edge BF are separated, on the chord line 306, by a distance, called chord L, which can change depending on the height considered.

[0052] There is thus an angle A between any plane P perpendicular to the main axis X and the chord line 306 at a height. This angle A can therefore change depending on the height considered. To unambiguously identify the pitch, the pitch angle C is chosen as the previous angle A at a height of 75% of the external radius Re of the rotor blade 108 (see Figure 2). The pitch angle C is for example measured on the upstream side of the plane P, positively in a direction going from the plane P to the chord line 306. This direction coincides with the direction going from the intrados 302 to the extrados 304.

[0053] With reference to Figure 4, it is also possible to define a sweep angle F for the rotor blade 108, varying according to the blade height H amont. By definition, the sweep angle F is the angle between the radial component of the pitch axis Y and the projection, in the plane of the radial component of the pitch axis Y and the main axis X (plane of the sheet for figure 4), of the line 402 connecting the point 404 of the leading edge BA to the blade height H amont considered and point 406 of the leading edge BA at the Hamont blade height considered plus 1% of the total height HBA.

[0054] With reference to Figure 5, it is also possible to define a rotor blade angle 108 at the leading edge BA, varying according to the height By definition, the dihedral angle DBA at the leading edge BA is the angle between the pitch axis Y (or more generally the radial component of the pitch axis Y) and the projection, in the plane (plane of the sheet for figure 5) perpendicular to the main axis X containing the pitch axis Y (or more generally the radial component of the pitch axis Y), of the line 402. As explained above, the latter connects the point 404 of the leading edge BA to the considered Hamont blade height and the point 406 of the leading edge BA to the considered Hamont blade height plus 1% of the total height HBA. Similarly, it is possible to define a dihedral angle DBF at the trailing edge BF.

[0055] With reference to Figure 6, the stator blade 114 firstly comprises a leading edge BA' where the air flow PHI arrives from the propeller 106, that is to say the front part of the stator blade 114 facing the fluid (or coming into contact first with the fluid), and a trailing edge BF' from which the air flow moves away. PHI, that is to say the rear part of the stator blade 114 in the direction of flow.

[0056] The leading edge BA' extends from a root BA'_P which is the point of the leading edge BA' closest to the external casing 102 to a head BA'_T which is the point of the leading edge BA' which is the highest or has a maximum radius relative to the main axis X on the upstream part of the stator blade 114. Between the root BA'_P and the head BA'_T, the leading edge BA' has a curvature of constant direction, that is to say without an inflection point (in other words, the second derivative of the axial position x' BAof the leading edge BA' as a function of h'Ba is not zero, 0, along the edge leading edge BA as a function of the height h'BA of the stator blade 114 and h'BA is the height from the root BA'_P), in particular for at least one value of the pitch angle C' included in the interval [70°; 90°]. The curvature of the leading edge BA' is also regular, i.e. without discontinuity. The leading edge BA' also has an antinode BA'_V which is the point of the leading edge BA' furthest upstream (min{x' BA}), in particular for at least one value of the setting angle C' included in the interval [70°; 90°].

[0057] Similarly, the trailing edge BF' extends from a root BF'_P which is the point of the trailing edge BF' closest to the outer casing 102 to a head BF'_T which is the point of the trailing edge BF' which is the highest or has a maximum radius relative to the main axis X on the rear part of the stator blade 114. Between the root BF'_P and the head BF'_T, the trailing edge BF' has a curvature of constant direction, that is to say without an inflection point (in other words, the second derivative of the axial position x'BF of the trailing edge BF' as a function of h'BF is not zero, 0, along the trailing edge BF' as a function of the height h' BF of stator blade 114 and h' BFis the height from the foot BF'_P), in particular for at least one value of the setting angle C' taken in the interval [70°; 90°]. The curvature of the trailing edge BF' is also regular, i.e. without discontinuity. The trailing edge BF' also has an antinode BF'_V which is the point of the trailing edge BF' furthest upstream (min{x'BF}), in particular for at least one value of the setting angle C' included in the interval [70°; 90°].

[0058] The stator blade 114 may further be truncated, as in the example illustrated, that is to say that there is a truncated section 602, for example straight, connecting the heads BA'_T, BF'_T. In this case, there is a discontinuity of curvature at the level of the head BA'_T between the leading edge BA' and the truncated section 602 and a curvature discontinuity at the head BF'_T between the truncated section 602 and the trailing edge BF'. Alternatively, the stator blade could be non-truncated, in which case the heads BA'_T, BF'_T would be merged.

[0059] Subsequently, when applied in the context of the stator blade 114, the term "height" will refer to the distance between two points along the radial component of the pitch axis Y', i.e. between the orthogonal projections of these points onto the radial component of the pitch axis Y'.

[0060] It is thus possible to define an upstream blade height H' amont to position itself on the leading edge BA'. The upstream blade height H' amont is thus the ratio between a height h' BA from the foot BA'_P and a total height H' BAof the leading edge BA' between the foot BA'_P and the head BA'_T: H' amont = h' BA / H' BA . The upstream blade height H' amont can thus be expressed in percentages and varies between 0% (position at the foot BA'_P) and 100% (position at the head BA'_T). Similarly, it is possible to define a downstream blading height H' aval to position itself on the trailing edge BF'. The downstream blade height H' aval is thus the ratio between a height h' BF from the BF'_P root and a total height H'BF of the trailing edge BF' between the BF'_P root and the BF'_T head: H'aval = h'BF / H'BF. The downstream blade height H'aval can thus be expressed in percentages and varies between 0% (position at the BF'_P root) and 100% (position at the BF'_T head).

[0061] Furthermore, each variable-pitch stator blade 114 of the rectifier 112 has an external radius Re' equal by definition to the height or distance between the main axis X and the point of the stator blade 114 furthest from the main axis X, in particular for at least one value of the pitch angle C' included in the interval [70°; 90°]. This furthest point is the head BF'_T of the trailing edge BF' in the illustrated example. Alternatively, this furthest point could be the head BA'_T of the leading edge BA'.

[0062] Each variable-pitch stator blade 114 also has an internal radius Ri'BA at the leading edge BA' which is the distance between the main axis X and the root BA'_P of the leading edge BA, as well as an internal radius Ri'BF at the trailing edge BF' which is the distance between the main axis X and the root BF'_P of the trailing edge BF'.

[0063] Figure 7 and Figure 13 are sections of the stator blade 114 perpendicular to the radial component of the pitch axis Y' at different heights.

[0064] As can be seen, the stator blade 114 has a lower surface face 702 and an upper surface face 704, respectively concave and convex, connected to each other by the leading edge BA' and the trailing edge BF'. The leading edge BA' therefore makes it possible to separate the lower surface face 702 from the upper surface face 704 in the upstream part of the stator blade 114, while the trailing edge BF' makes it possible to separate the lower surface face 702 from the upper surface face 704 in its rear part.

[0065] The leading edge BA' is for example the point of the cut in the upstream part of the stator blade 114, having a local minimum radius of curvature. Similarly, when the downstream part of the stator blade is rounded, the trailing edge BF' is for example the point of the cut in this downstream part, having a local minimum on the radius of curvature. To simplify the manufacturing method of the stator blade 114, its downstream part could be truncated. In the latter case, the trailing edge BF' is for example the middle of this truncated part.

[0066] When the leading edge BA' and the trailing edge BF' are present in the section considered (i.e., for example, in the illustrated example, below the truncated section 602), the leading edge BA' and the trailing edge BF' may be connected by a chord line 706 whose orientation changes depending on the height considered. The leading edge BA' and the trailing edge BF' are separated, on the chord line 706, by a distance, called chord L', which may change depending on the height considered.

[0067] There is thus an angle A' between any plane P' perpendicular to the main axis X and the chord line 706 at a height. This angle A' can therefore change depending on the height considered. To unambiguously identify the pitch, the pitch angle C' is chosen as the previous angle A' at a height of 75% of the external radius Re' of the stator blade 114 (see Figure 6). The pitch angle C' is for example measured on the upstream side of the plane P', positively in a direction going from the plane P' to the chord line 706. This direction coincides with the direction going from the intrados 702 to the extrados 704.

[0068] With reference to Figure 8, it is also possible to define a sweep angle F' of the stator blade 114, varying according to the upstream blade height H'. By definition, the sweep angle F' is the angle between the radial component of the pitch axis Y' and the projection in the plane of the radial component of the pitch axis Y' and the main axis X of the line 802 connecting the point 804 of the leading edge BA' to the upstream blade height H' considered and the point 806 of the leading edge BA' to the blade height H' amont considered plus 1% of the total height H' BA .

[0069] With reference to figure 9, it is also possible to define a dihedral angle D'BA' of the stator blade 114 at the leading edge BA', varying according to the blade height H' amont . By definition, the dihedral angle D' BA’at the leading edge BA' is the angle between the radial component of the setting axis Y' and the projection in the plane perpendicular to the main axis X containing the radial component of the setting axis Y' of the line 802. Similarly, it is possible to define a dihedral angle D' BF’ at the trailing edge BF'.

[0070] The shape of the stator blades 114 of the rectifier 112 is designed to reduce noise pollution while ensuring good aerodynamic performance.

[0071] Thus, the head BA'_T of the leading edge BA' is downstream of the pitch axis Y' along a straight line parallel to the main axis X and passing through the head BA'_T, for at least one value of the pitch angle C' in the interval [70°; 90°]. In this way, the free end of the stator blade 114 is distant from the propeller 106, which makes it possible to reduce the noise, for a large range of pitch angle C'. Indeed, the downstream positioning of the free end of the stator blade 114 makes it possible to reduce the interaction noise between the wake of the propeller 106 and the leading edge BA' of the stator blades by a decorrelation effect of the noise sources along the leading edge BA' and a dissipation effect of the wake of the propeller 106 thanks to the increase in the distance between the trailing edge BF of the rotor blades 108 and the leading edge BA' of the stator blades 114.

[0072] Preferably, in order to promote the downstream positioning of the free end of the stator blade 114, the belly BA'_V, the root BA'_P and the pitch axis Y' follow one another in this order from upstream to downstream along the main axis X for at least one value of the pitch angle C' included in the interval [70°; 90°]. In other words, xBA'_V < xBA'_P < xY' for at least one value of the pitch angle C' in the interval [70°; 90°]. Thus, it is possible to increase the sweep angle F' in the upper part of the stator blade 114, in particular near the free end of the stator blade 114. When the pitch axis Y' is inclined or is not perpendicular to the main axis X, xY' corresponds to the axial position of the pitch axis Y' of the stator blade at the level of the external casing 102.Furthermore, the belly BA'_V, the foot BA'_P and the head BA'_T preferably follow one another in this order along the main axis X from upstream to downstream, for at least one value of the setting angle C' included in the interval [70°; 90°].

[0073] Preferably again, in order to promote the downstream positioning of the free end of the stator blade 114, the belly BA'_V is located between 20% and 70% of the total blading height H' BA , preferably between 25% and 55% of the total blade height H' BA. This makes it possible to position the belly BA'_V close to the outer casing 102, and thus to start increasing the sweep angle F' from a relatively low radial position, which reduces the interaction noise. Thus, it is possible to achieve a significant sweep angle F' in the upper part of the stator blade 114, in particular near the free end of the stator blade 114. In addition, this positioning of the belly BA'_V moves mass in the lower part of the stator blade 114 upstream, which makes it possible to move mass in the upper part of the stator blade 114 downstream (and therefore the free end), without significantly changing the center of mass of the stator blade 114 and with a low impact on the moment of the aerodynamic forces around the pitch change axis. This promotes dimensioning and mechanical balance of the stator blade 114.

[0074] With such positioning of the belly BA'_V of the leading edge BA', the belly BF'_V of the trailing edge BF' is preferably located between 20% and 70% of the total blade height H'BF of the trailing edge, preferably between 30% and 60%. This ensures that the belly BF'_V of the trailing edge BF' is located at a height relatively close to that of the belly BA'_V of the leading edge BA', which can be useful for the mechanical strength of the stator blade 114. This position of the belly BF'_V of the trailing edge BF', like that of the belly BA'_V of the leading edge BA', moves mass in the lower part of the stator blade 114 upstream, which makes it possible to move mass in the upper part of the stator blade 114 downstream (and therefore the free end), without greatly changing the center of mass of the stator blade 114.

[0075] In one embodiment, the height or radius (height or distance from the main axis X) of the belly BA'_V of the leading edge BA' is less than the height or radius (height or distance from the main axis X) of the belly BF'_V of the trailing edge BF'. This makes it possible to improve the mechanical strength of the blade and to better distribute the chord law L' along the span (see figure 11).

[0076] Furthermore, with such a positioning of the belly BA'_V of the leading edge BA', it is possible to obtain a stator blade 114 satisfying one or more of the three criteria below, for at least one value of the pitch angle C' included in the interval [70°; 90°], allowing an acceptable aero-acoustic and mechanical compromise to be obtained.

[0077] According to the first criterion, the belly BA'_V of the leading edge BA' and the head BF'_T of the trailing edge BF' are separated along the main axis X by a distance greater than or equal to a coefficient K multiplied by the maximum chord L' (max{L'}), with K between 1 and 2, preferably between 1.2 and 1.6. The following equation summarizes this first criterion: x BF’_T – x BA’_V ≥ K * max{L'}, where x M is the axial position of point M along the principal axis X.

[0078] According to the second criterion, the belly BA'_V and the head BA'_T of the leading edge BA' are separated along the main axis X by a distance less than or equal to a coefficient B multiplied by the maximum chord L' (max{L'}), with B between 0.5 and 1.2. The following equation summarizes this second criterion: x BA’_T – x BA’_V ≤ B * max{L'}.

[0079] According to the third criterion, the foot BF'_P and the head BF'_T of the trailing edge BF' are separated along the main axis X by a distance greater than or equal to a coefficient E multiplied by the maximum chord L' (max{L'}), with E between 0.05 and 0.7, preferably between 0.25 and 0.6. The following equation summarizes this third criterion: xBF'_T – xBF'_P ≤ E * max{L'}.

[0080] More preferably, in order to promote the downstream positioning of the free end of the stator blade 114, the chord L' of the cut closest to the head BA'_T of the leading edge BA' is smaller than the chord L' at the root BA'_P of the leading edge BA' and / or at the root BF'_P of the trailing edge BF' which is itself smaller than the chord L' of the cut at the belly BA'_V of the leading edge BA' ("smaller" means "has a shorter length"). Increasing the chord L' at the belly BA'_V and reducing the chord L' at the head BA'_T makes it possible to increase the sweep angle F' in the upper part of the stator blade 114, and therefore to move the free end of the stator blade 114 back downstream, which is advantageous for noise reduction. Furthermore, with the chord L' at the foot BA'_P greater than that at the head BA'_T, the mechanical strength of the blades (following, for example, the ingestion of a bird) is improved.Furthermore, the smaller the chord L' at the head BA'_T, the lighter the free end of the stator blade 114 is, and therefore the more it is possible to place this free end downstream without moving the center of mass of the stator blade 114 too much.

[0081] Thus, the sweep angle F' at the leading edge BA' of the stator blade 114 is for example greater than 20°, preferably greater than 35°, above 80% of the upstream blade height H' amont , preferably still greater than 45° above 90% of the upstream blade height H'amont, preferably still greater than 50° above 95% of the upstream blade height H'amont. This makes it possible to reduce the component of the flow velocity which is perpendicular to the trace of the leading edge BA' of the sections, which makes it possible to reduce the interaction noise.

[0082] More preferably, in order to promote the downstream positioning of the free end of the stator blade 114, the belly BF'_V is upstream of the root BF'_P which itself is upstream of the head BF'_T, for at least one value of the pitch angle C' included in the interval [70°; 90°]. In other words, x BF’_V < x BF’_P < x BF’_T for at least one value of the setting angle C' included in the interval [70°; 90°].

[0083] Referring to Figure 10, a non-truncated, rounded-tip stator blade 114 is illustrated.

[0084] With reference to Figure 11, the chord L' is preferably strictly decreasing from 40% to 100%, preferably from 50% to 100%, of the upstream blade height H' amont and / or downstream H' aval (in figure 11, the reference H' can thus represent H' amont or H' aval). This makes it possible, on the one hand, to increase the distance between the trailing edge BF of the rotor blades 108 and the leading edge BA' of the stator blades 114, and, on the other hand, to increase the sweep angle F' towards the free end of the stator blade 114, in particular when there are integration constraints or mechanical constraints which prevent the trailing edge BF' of the stator blade 114 from being modified or offset. Indeed, offsetting the trailing edge BF' in the upper part of the blading, for example on the tip section 602, can increase the moment of the aerodynamic forces around the pitch axis Y' and therefore have a significant impact on the mechanical dimensioning of the pitch change system.

[0085] A parameter that allows to give a first estimate of the chord distribution along the span of a stator blade 114 is its Activity Factor (AF), which is defined as follows: )* = +,,,,, + - ∫ where Ri' corresponds to the internal radius Ri' BA from the stator blade 114 to the leading edge BA', or to the internal radius Ri' BF of the stator blade 114 to the trailing edge BF' (see figure 6); Re' corresponds either to the external radius Re' BA from the stator blade 114 to the leading edge BA', or to the external radius Re' BF of the stator blade 114 to the trailing edge BF'; 8 represents a radial distance from the main axis X, divided by the outer radius Re'; L'(8) represents a chord between the leading edge BA' and the trailing edge BF' of a section (or aerodynamic profile) of the stator blade 114 in the plane perpendicular to the radial component of the setting axis Y' at said radial distance 8.

[0086] The activity factor of the stator blade 114 is preferably between 50 and 200, more preferably between 90 and 150. With such values, this makes it possible to ensure that the chord L' is sufficient in the lower part of the stator blade 114, which helps with the mechanical strength of the blading, as well as to reduce the chord L' in the upper part of the stator blade 114, which makes it possible to increase the sweep angle in the upper part of the blading and therefore to reduce the noise.

[0087] More preferably, the chord L' at an upstream blade height H'amont and / or downstream H'aval of 95% is less than or equal to half the maximum chord L' max{L'} of the stator blade 114: L'(H'=95%) ≤ 0.5 * max{L'}, with H' = H'amont or H'aval. This makes it possible to increase the sweep angle F' relative to a position at mid-span and close to the belly of the blade, which is beneficial from an aeroacoustic point of view, as well as to reduce the mass of the blade in the upper part, which is beneficial from a mechanical point of view, as well as to reduce the inertia in the event of a possible loss of blade tip (for example, in the event of bird ingestion) or a blade loss event (from the English "Fan Blade Out", FBO).

[0088] More preferably, the chord L' has an upstream blade height H' amont and / or downstream H' aval of 95% is less than or equal to half of the chord L' at an upstream height H' amont and / or downstream H' avalof 10%: L'(H'=95%) ≤ 0.5 * L'(H'=10%), with H' = H' amont or H' aval This helps reduce inertia in the event of a blade tip loss (e.g., bird ingestion) or blade loss event.

[0089] With reference to Figure 12, the downstream positioning of the free end of the stator blades 114 makes it possible to obtain a significant distance between the trailing edge BF of the rotor blades 108 and the leading edge BA' of the stator blades 114, reducing the noise of the aeronautical propeller 100. In particular, the axial distance s (along the main axis X) between the trailing edge BF of the rotor blades 108 and the leading edge BA' of the stator blades 114, taken at an upstream blade height H'amont and / or downstream H'aval of 95% is preferably thus greater than 0.35*Re, or even preferably greater than 0.5*Re, of the propeller 106 for at least one value of the pitch angle C included in the interval [50°; 80°] and for at least one value of the setting angle C' included in the interval [70°; 90°].

[0090] Figure 14 illustrates a projection yBF of the trailing edge BF of the rotor blade 108 and a projection yBA' of the leading edge BA' of the stator blade 114 on a plane perpendicular to the main axis X (the plane of the sheet for Figure 14).

[0091] As can be seen, the leading edge BA' of at least one stator blade 114 has a dihedral angle D' BA’ at 95% of the external radius Re' with an absolute value greater than 1°, preferably 3°, more preferably 10°, for at least one value of the setting angle C' included in the interval [70°; 90°].

[0092] Preferably, the absolute value of the dihedral angle D' BA’ at 95% of the external radius Re' is greater by at least 1°, preferably by at least 3°, or even preferably by at least 10°, than the dihedral angle D BA’of the leading edge BA' of the stator blade 114 at 50% of the external radius Re', for at least one value of the pitch angle C' included in the interval [70°; 90°].

[0093] More preferably, the absolute value of the dihedral angle D BA’ on the leading edge BA' of the stator blade 114 is strictly monotonous for radial positions greater than 90% of the external radius Re', for at least one value of the pitch angle C' included in the interval [70°; 90°].

[0094] More preferably, the projection yBA' of the leading edge BA' of the stator blade 114 on a plane perpendicular to the main axis X has at least one local maximum and / or minimum, for at least one value of the pitch angle C' included in the interval [70°; 90°].

[0095] More preferably, the projection yBA' of the leading edge BA' of the stator blade 114 on a plane perpendicular to the main axis X has at least one inflection point PI, for at least one value of the pitch angle C' included in the interval [70°; 90°]

[0096] Furthermore, the projection yBF of the trailing edge BF of the rotor blade 108 and the projection yBA' of the leading edge BA' of the stator blade 114 go in opposite directions as they approach their free ends. This is obtained by providing that the dihedral angle DBA' of the leading edge BA' of the stator blade 114 is of opposite sign to the dihedral angle DBF of the trailing edge BF of the rotor blade 108, at least for the upstream blade heights H' of the stator blade 114 greater than 80%, for at least one value of the pitch angle C of the rotor blade 108 included in the interval [50°; 80°] and for at least one value of the pitch angle C' of the stator blade 114 included in the interval [70°; 90°]. Thus, the leading edge BA' of the stator blade 114 is no longer aligned from this height (80%) with the trailing edge BF of the rotor blade 108 and therefore with the wake of the propeller 106. In this way, the propeller 106 and the rectifier 112 forming noise sources are decorrelated from each other, which makes it possible to reduce the interaction noise between the propeller 106 and the rectifier 112 from this height.

[0097] Preferably, the absolute value of the dihedral angle D' BA’ of the leading edge BA' of the stator blade 114 is greater than 20% of the absolute value of the dihedral angle D BF of the trailing edge BF of the rotor blade 108, i.e. |D' BA’ | > 0.2 *|D BF |, for at least one value of the pitch angle C of the rotor blade 108 included in the interval [50°; 80°] and for at least one value of the pitch angle C' of the stator blade 114 included in the interval [70°; 90°].

[0098] More preferably, the dihedral angle D' BA’ of the leading edge BA' of the stator blade 114 is different from the dihedral angle D BF of the trailing edge of the rotor blade 108: that is, at any radius (height or distance from the main axis X), the absolute value of the dihedral angle D' BA’ of the leading edge BA' of the stator blade 114 is greater than 130% of the dihedral angle D BFof the trailing edge BF of the rotor blade 108, for at least one value of the pitch angle C of the rotor blade 108 included in the interval [50°; 80°] and for at least one value of the pitch angle C' of the stator blade 114 included in the interval [70°; 90°], i.e., at any radius, the dihedral angle DBA' of the leading edge BA' of the stator blade 114 is less than 50% of the dihedral angle DBF of the trailing edge BF of the rotor blade 108, for at least one value of the pitch angle C of the rotor blade 108 included in the interval [50°; 80°] and for at least one value of the pitch angle C' of the stator blade 114 included in the interval [70°; 90°].

[0099] Indeed, the optimal value of the dihedral angle D'BA' of the leading edge BA' of the stator blade 114 depends on the dihedral angle DBF of the trailing edge BF of the rotor blade 108. This makes it possible to maximize the phase shift during the interaction of the wake of a rotor blade 108 with a stator blade 114. This is particularly important on the upper part of the blades near their free end, where the noise sources are more intense.

[0100] More preferably, the absolute value of the dihedral angle D' BA’ of the leading edge BA' of the stator blade 114 is greater than 15° at the upstream blade height H'amont of 95%, preferably still greater than 30° at the upstream blade height H' amont of 95%. The fact that the dihedral angle D BA’ of the leading edge BA' of the stator blade 114 is relatively large at the blade head is useful for reducing acoustic levels by increasing the phase shift of the noise sources, for at least one value of the pitch angle C of the rotor blade 108 included in the interval [50°; 80°] and for at least one value of the pitch angle (C') of the stator blade (114) included in the interval [70°; 90°].

[0101] As can be further seen, the projection y BF of the trailing edge BF of the rotor blade 108 on the plane perpendicular to the main axis X, has a transverse deviation Δy BF along a transverse direction T, perpendicular to the main axis X and / or to the radial component of the pitch axis Y. Similarly, the projection of the leading edge BA' of the stator blade 114 onto the plane perpendicular to the main axis X, has a transverse deviation Δy BA’, along a transverse direction T' perpendicular to the main axis X and / or to the radial component of the setting axis Y'.

[0102] Preferably, the transverse deviation Δy BA’ of the leading edge BA' of the stator blade 114 is greater than 1% and less than 10% of the external radius Re' of the stator blade 114, for at least one value of the pitch angle C' included in the interval [70°; 90°]. This ensures that the stator blade 114 is not too inclined in the transverse direction T', which can be beneficial for the balancing and / or mechanical strength of the blade.

[0103] Preferably, the deviation ΔyBA' of the leading edge BA' of the stator blade 114 is less than the deviation ΔyBF for all operating points, for at least one value of the pitch angle C of the rotor blade 108 included in the interval [50°; 80°] and for at least one value of the pitch angle C' of the stator blade 114 included in the interval [70°; 90°]. This makes it possible to maximize the phase shift and / or the interaction between the wake of the propeller 106 (generated at the trailing edge BF of the rotor blades 108) and the leading edge BA' of the stator blades 114 downstream. Indeed, the greater the deviation ΔyBA', the greater the dihedral angle can be on the blading, in particular at the blade tip.

[0104] In conclusion, it will also be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching which has just been disclosed to them.

[0105] In the detailed presentation of the invention given above, the terms used should not be interpreted as limiting the invention to the embodiments set forth in this description, but should be interpreted to include all equivalents which can be predicted by a person skilled in the art by applying his general knowledge to the implementation of the teaching which has just been disclosed to him.

Claims

Claims [1] Unducted aeronautical propeller (100) for an aircraft, comprising: - an external casing (102); - a hub (104) pivotally mounted relative to the external casing (102) around a main axis (X) extending in an upstream-downstream direction of the aircraft; - a propulsive propeller (106) mounted on the hub (104) so ​​as to pivot relative to the external casing (102);and - a fixed rectifier (112) mounted on the outer casing (102) downstream of the propulsion propeller (106) along the main axis (X), the fixed rectifier (112) extending around the main axis (X) and comprising at least one stator blade (114) with variable pitch around a pitch axis (Y'), each stator blade (114) with variable pitch having a pitch angle (C') defined as the angle between, on the one hand, any plane (P') perpendicular to the main axis (X) and, on the other hand, a chord line (706) connecting a leading edge (BA') of the stator blade (114) to a trailing edge (BF') of the stator blade (114);characterized in that the chord line (706) is taken at 75% of an external radius (Re') of the stator blade (114) relative to the main axis (X), in that the leading edge (BA') of at least one stator blade (114) has a dihedral angle (D'BA') at 95% of the external radius (Re') with an absolute value greater than 1°, preferably 3°, more preferably 10°, for at least one value of the pitch angle (C') included in the interval [70°; 90°], and in that a projection of the leading edge (BA') of the stator blade (114) on a plane perpendicular to the main axis (X) has at least one local maximum and / or minimum, for at least one value of the pitch angle (C') included in the interval [70°;90°]. [2] Aeronautical thruster (100) according to claim 1, in which the absolute value of the dihedral angle (D'BA') at 95% of the external radius (Re') is greater by at least 1°, preferably by at least 3°, or even more preferably by at least 10°, than the absolute value of the dihedral angle (D'BA') of the leading edge (BA') of the stator blade (114) at 50% of the external radius (Re'), for at least one value of the pitch angle (C') included in the interval [70°; 90°].; [3] Aeronautical thruster (100) according to claim 1 or 2, wherein the absolute value of the dihedral angle (D'BA') on the leading edge (BA') of the stator blade (114) is strictly monotonic for radial positions greater than 90% of the external radius (Re'), for at least one value of the pitch angle (C') included in the interval [70°; 90°]. [4] Aeronautical thruster (100) according to any one of claims 1 to 3, wherein a projection (y BA’) of the leading edge (BA') of the stator blade (114) on a plane perpendicular to the main axis (X), presents a so-called transverse deviation (Δy BA’ ) along a so-called transverse direction (T') perpendicular to the main axis (X) and to the radial component of the setting axis (Y'), the transverse deviation (Δy BA’) of the leading edge (BA') of the stator blade (114) being greater than 1% and less than 10% of an external radius (Re') of said stator blade (114), for at least one value of the pitch angle (C') included in the interval [70°; 90°]. [5] Aeronautical thruster (100) according to any one of claims 1 to 4, wherein a projection of the leading edge (BA') of the stator blade (114) on a plane perpendicular to the main axis (X) has at least one point of inflection (PI), for at least one value of the pitch angle (C') included in the interval [70°; 90°].[6] Aeronautical thruster (100) according to any one of claims 1 to 5, in which the propulsive propeller (114) comprises at least one rotor blade (108) with variable pitch about a pitch axis (Y) crossing the main axis (X) and having a non-zero radial component with respect to the main axis (X), each rotor blade (108) with variable pitch having a pitch angle (C) defined as the angle between, on the one hand, any plane (P) perpendicular to the main axis (X) and, on the other hand, a chord line (306) connecting a leading edge (BA) of the rotor blade (108) to a trailing edge (BF) of the rotor blade (108), this chord line (306) being taken in a plane perpendicular to the radial component of the pitch axis (Y) and crossing the rotor blade (108) at 75% of an external radius (Re) of the rotor blade (108) relative to the main axis (X).[7] Aeronautical thruster (100) according to claim 6, in which a trailing edge (BF) of a rotor blade (108) and the leading edge (BA') of a stator blade (114) have dihedral angles (DBF, D'BA') such that the absolute value of the dihedral angle (D. BF ) on the trailing edge (BF) of the rotor blade (108) is greater than the absolute value of the dihedral angle (DBA') on the leading edge (BA') of the stator blade (114) at 95% of an external radius (Re') of the stator blade (114), for at least one value of the pitch angle (C) of the rotor blade (108) included in the interval [50°; 80°] and for at least one value of the pitch angle (C') of the stator blade (114) included in the interval [70°; 90°]. [8] Aeronautical thruster (100) according to claim 6 or 7, wherein the trailing edge (BF) of a rotor blade (108) and the leading edge (BA') of a stator blade (114) have dihedral angles (D BF, D' BA’ ) such that the absolute value of the dihedral angle (D BF ) on the trailing edge (BF) of the rotor blade (108) is at least 10° greater than the absolute value of the dihedral angle (D' BA’) on the leading edge (BA') of the stator blade (114) at 75% of the external radius (Re') of the stator blade (114), for at least one value of the pitch angle (C) of the rotor blade (108) included in the interval [50°; 80°] and for at least one value of the pitch angle (C') of the stator blade (114) included in the interval [70°; 90°]. [9] Aeronautical thruster (100) according to any one of claims 6 to 8, in which the trailing edge (BF) of a rotor blade (108) and the leading edge (BA') of a stator blade (114) have dihedral angles (DBF, D'BA') of opposite signs at 95% of an external radius (Re') of the stator blade (114), for at least one value of the pitch angle (C) of the rotor blade (108) included in the interval [50°; 80°] and for at least one value of the pitch angle (C') of the stator blade (114) included in the interval [70°; 90°].[10] Aeronautical thruster (100) according to any one of claims 6 to 9, wherein, at any height from the main axis (X), the absolute value of the dihedral angle (DBA') of the leading edge (BA') of the stator blade (114) is greater by at least 2°, preferably by at least 10°, than the absolute value of the dihedral angle (DBF) of the trailing edge (BF) of the rotor blade (108), for at least one value of the pitch angle (C) of the rotor blade (108) included in the interval [50°; 80°] and for at least one value of the pitch angle (C') of the stator blade (114) included in the interval [70°; 90°]. [11] Aeronautical thruster (100) according to any one of claims 6 to 10, in which a projection of the trailing edge (BF) of the rotor blade (108) on a plane perpendicular to the main axis (X) has a so-called transverse deviation (Δy. BF ) THE along a so-called transverse direction (T) perpendicular to the main axis (X) and to the radial component of the pitch axis (Y) of the rotor blade (108), in which a projection of the leading edge (BA') of the stator blade (114) on a plane perpendicular to the main axis X, has a so-called transverse deviation (Δy BA’ ) along a so-called transverse direction (T') perpendicular to the main axis (X) and to the radial component of the pitch axis (Y') of the stator blade, the transverse deviation (Δy BA’ ) of the leading edge (BA') of the stator blade (114) being less than the transverse deviation (Δy BF) of the trailing edge (BF) of the rotor blade (108), for at least one value of the pitch angle (C) of the rotor blade (108) included in the interval [50°; 80°] and for at least one value of the pitch angle (C') of the stator blade (114) included in the interval [70°; 90°]. [12] Aeronautical thruster (100) according to any one of claims 1 to 11, in which the leading edge (BA') of at least one stator blade (114) with variable pitch has a head (BA'_T) located downstream of the radial component of the pitch axis (Y'), for at least one value of the pitch angle (C') included in the interval [70°; 90°]. [13] Aeronautical propeller (100) according to any one of claims 1 to 12, in which at least one variable-pitch stator blade (114) has an activity factor of between 50 and 200, preferably between 90 and 150. [14] Aircraft comprising an aeronautical propeller (100) according to any one of claims 1 to 13.

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