Propulsion unit having foldable propeller blades and method for stopping the propeller at an indexed angular position.

Abstract

The present invention provides a propeller propulsion unit equipped with indexing means for stopping the propeller at at least one indexed angular position relative to the nacelle. [Solution] An aircraft propulsion unit comprising: a nacelle 24; a propeller 26 mounted within the nacelle 24 and capable of rotating about a longitudinal axis of rotation X, wherein the propeller 26 has blades 32 attached to a root portion 34 so as to be pivotable between an extended position extending radially with respect to the axis of rotation X and a folded position longitudinally received relative to the nacelle 24; a drive means for rotating the propeller 26; and an indexing means for stopping the propeller 26 at at least one indexed angular position relative to the nacelle 24, wherein the propulsion unit is characterized in that the indexing means consists of a stepping electric motor having a rotor coupled to the propeller 26.

Description

Technical Field

[0001] The present invention relates to a propeller propulsion unit for an aircraft, a nacelle intended to be assembled to a structural element of the aircraft, a propeller rotatably mounted in the nacelle about a longitudinal axis of rotation by a hub, the propeller comprising blades evenly distributed around the hub, the blades being pivotably mounted by a root on the hub between a deployed position extending radially with respect to the axis of rotation and a folded position received longitudinally with respect to the nacelle, propulsion means for rotationally driving the propeller, indexing means for stopping the propeller at at least one indexed angular position with respect to the nacelle, and relates to a propeller propulsion unit comprising the same.

Background Art

[0002] Such propeller propulsion units are used, for example, in vertical take-off and landing aircraft, also referred to as "VTOL: vertical take-off and landing". Of course, it is also possible to use such a propulsion unit in a fixed-wing aircraft, also referred to as "CTOL: Classic Take Off and Landing", which represents "classical take-off and landing". In this context, it is possible to equip an aircraft with a plurality of propeller propulsion units so as to distribute the thrust center and seek the best propulsion efficiency for the aircraft.

[0003] These propeller propulsion units can be stopped according to the flight configuration of the aircraft. When the propeller propulsion units are stopped, their propellers may have an adverse effect on the aerodynamic performance of the aircraft, for example by generating drag or by generating local disturbances in the air flow.

[0004] To solve this problem, propulsion units with foldable blade propellers have already been proposed to remove these inactive blades from the local flow.

[0005] Generally, the blades are stopped by a brake that acts through friction with the rotor shaft of the propulsion unit. Such a device allows the propeller to be stopped at an angular position where the blades do not come into contact with the structural elements of the aircraft during folding. Such a device is described, for example, in U.S. Patent Application Publication No. 2019 / 016441. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2019 / 016441 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, if the propeller accidentally stops at an angle that does not fit its folding configuration, the propulsion motor must be restarted to make the propeller rotate again, or the blade pitch must be changed to take advantage of the windmill effect induced by the aircraft's forward movement.

[0008] Furthermore, to reduce the drag on the propulsion unit when the blades are folded, it is preferable to house the blades in the associated housing of the nacelle. However, such braking devices do not readily allow the propeller to be stopped at a precise angular position relative to the nacelle, as these braking devices do not have means to precisely index the propeller to an indexed angular position. [Means for solving the problem]

[0009] The present invention relates to a propulsion unit having a propeller for an aircraft, Nacelles intended to be incorporated into the structural elements of an aircraft, A propeller rotatably mounted within a nacelle by a hub about a longitudinal axis of rotation, the propeller comprising blades evenly distributed around the hub, the blades pivotably mounted by a root on the hub between an extended position extending radially with respect to the axis of rotation and a folded position receiving longitudinally with respect to the nacelle, A propulsion means that rotates the propeller, An indexing means for stopping the propeller at at least one indexed angular position relative to the nacelle, Equipped with, The indexing means is characterized by being formed by a stepping electric motor having a rotor coupled to the hub of the propeller. Regarding the propulsion unit.

[0010] The use of a stepping motor not only allows the propeller to be braked and stopped, but also allows the propeller to rotate again when it is not locked in an indexed angular position.

[0011] According to another feature of the propulsion unit manufactured in accordance with the teachings of the present invention, the stepping electric motor is a variable reluctance motor.

[0012] According to another feature of the propulsion unit manufactured in accordance with the teachings of the present invention, the stepping electric motor is a permanent magnet motor.

[0013] According to another feature of a propulsion unit manufactured in accordance with the teachings of the present invention, the stepping electric motor is a hybrid motor.

[0014] According to another feature of a propulsion unit manufactured in accordance with the teachings of the present invention, the propulsion unit comprises a device for mechanically locking the propeller to each of its indexed angular positions. Advantageously, such a locking device makes it possible to prevent the propeller from rotating without the need to keep the stepping motor energized.

[0015] According to another feature of a propulsion unit manufactured in accordance with the teachings of the present invention, the locking device comprises a disc fixedly mounted to rotate with a propeller, the disc comprising at least one stopper which can cooperate with a locking member, the locking member being movably mounted with respect to the nacelle between an inactive position in which the disc rotates freely and an active position in which the locking member can be received within the stopper when the propeller occupies one of its indexed angular positions in order to immobilize the propeller with respect to its rotation relative to the nacelle.

[0016] A further feature of a propulsion unit manufactured according to the teachings of the present invention is that the stopper has a cam track shape, such shape allows the propeller to rotate toward its active position by cooperating with a locking member during its displacement in order to precisely position the propeller toward its indexed angular position. Thus, the presence of this cam track makes it possible to position the propeller toward its indexed angular position with great precision, even if the stepping motor stops it slightly offset from the indexed angular position.

[0017] According to another feature of a propulsion unit manufactured in accordance with the teachings of the present invention, the propulsion unit comprises an induction sensor for the angular position of the propeller around its axis of rotation. Such a sensor enables a stepping motor to be operated so that the propeller reaches its indexed angular position.

[0018] According to another feature of the propulsion unit manufactured in accordance with the teachings of the present invention, a stepping electric motor forms the propulsion means. In this configuration, the propulsion unit is advantageously less costly to manufacture and more compact.

[0019] According to another feature of the propulsion unit manufactured in accordance with the teachings of the present invention, the propulsion means is formed by a propulsion motor different from the stepping electric motor, and the stepping motor is interposed between the propulsion motor and the hub of the propeller on the motor torque transmission chain. In this configuration, it is possible to benefit from the power of a dedicated motor for propelling the propeller.

[0020] According to another feature of the propulsion unit manufactured in accordance with the teachings of the present invention, the propulsion motor is an electric motor.

[0021] In a further feature of the propulsion unit, the nacelle is fixedly attached to a structural element of the aircraft.

[0022] In a further feature of the propulsion unit, the nacelle is pivotally attached to a structural element of the aircraft.

[0023] The present invention also relates to a method for stopping the rotation of a propeller at an indexed angular position according to any one of the above, a preliminary step of stopping propulsion in which the motor torque supplied by the propulsion motor is interrupted so that the propeller rotates freely, a step of stopping the propeller at the indexed angular position by a stepping electric motor, and a method comprising:

[0024] According to another feature of the method carried out in accordance with the teachings of the present invention, when the propeller rotates at a rotational speed greater than the rotational speed determined at the end of the preliminary step of stopping propulsion, the braking step precedes the stopping step, and during the braking step, the stepping motor is controlled to generate a resistive torque against the free rotation of the propeller until the rotational speed of the propeller is below the determined rotational speed.

[0025] According to another feature of the method performed in accordance with the teachings of the present invention, it comprises a step of determining the angular position of the propeller, which is triggered at the end of the stopping step, and the angular position of the propeller is measured by an induction angle sensor.

[0026] According to another feature of the method performed in accordance with the teachings of the present invention, the method comprises a step of adjusting the angular position of a propeller, which is triggered at the end of a confirmation step and involves controlling a stepping motor to provide rotational torque that drives the propeller toward an indexed angular position, wherein a stop step is repeated at the end of the adjustment step to immobilize the propeller by the stepping motor toward the indexed angular position.

[0027] According to another feature of the method performed in accordance with the teachings of the present invention, when the angular position of the propeller substantially coincides with the indexed angular position during the verification step, the mechanical locking step of the propeller is triggered, during which the propeller is rotatably locked relative to the nacelle by a mechanical locking device.

[0028] Further features and advantages of the present invention will become apparent from the following detailed description and refer to the accompanying drawings for their understanding. [Brief explanation of the drawing]

[0029] [Figure 1] This is a perspective view of an aircraft equipped with multiple propeller propulsion units that are executed according to the teachings of the present invention. [Figure 2] Figure 1 is a profile diagram showing the levitation propulsion unit of an aircraft, where the propeller blades are deployed at a pitch angle position that enables levitation. [Figure 3] This figure is similar to Figure 2, showing the propeller blades unfolded at the folded pitch angle position. [Figure 4]This figure is similar to Figure 3, showing the propeller blades folded to the aforementioned folding pitch angle position. [Figure 5] Figure 10 shows an axial cross-sectional view by cross-section 5-5, representing the rotating portion of a traction propulsion unit in which the propeller blades are deployed to a pitch angle position that enables levitation thrust. The traction propulsion unit is equipped with a folding device manufactured according to the first embodiment of the present invention. [Figure 6] Figure 12 shows an axial cross-sectional view by cross-section 6-6, illustrating the rotating portion of a traction propulsion unit in which the propeller blades are deployed at the folded pitch angle position. The traction propulsion unit is equipped with a folding device manufactured according to the first embodiment. [Figure 7] Figure 13 is an axial cross-sectional view by cross-section 7-7 showing the rotating portion of a traction propulsion unit with the propeller blades folded, and the traction propulsion unit is equipped with a folding device manufactured according to the first embodiment. [Figure 8] This figure is similar to Figure 6, in which the traction propulsion unit is equipped with a folding device manufactured according to the second embodiment. [Figure 9] This figure is similar to Figure 7, in which the traction propulsion unit is equipped with a folding device manufactured according to the second embodiment. [Figure 10] Figure 1 is a front view showing the traction propulsion unit of an aircraft, where the propeller blades are deployed in a pitch angle position that allows for lift thrust, and the propeller occupies any angular position around its axis of rotation. [Figure 11] This figure is similar to Figure 10, showing the propeller blades deployed to a folded pitch angular position where the propeller occupies any angular position around its axis of rotation. [Figure 12] This diagram is similar to Figure 11, showing the propeller blades deployed at the folded pitch angular position, with the propeller occupying an indexed angular position around its axis of rotation. [Figure 13] This diagram is similar to Figure 12, showing the propeller blades folded into the nacelle housing. [Figure 14]This is a schematic profile diagram showing the rotating portion of the propulsion unit of the aircraft in Figure 1 in a first configuration in which the propeller is driven by an electric motor separate from the stepping motor. [Figure 15] The propulsion unit is constructed according to a second configuration in which the propeller is driven by a combustion engine separate from the stepping motor, similar to the diagram in Figure 14. [Figure 16] The propulsion unit is constructed according to a third configuration in which the propeller is driven by a stepping motor, similar to the diagram in Figure 14. [Figure 17] This is a radial cross-sectional view taken along section 17-17 in Figure 14, showing a stepping motor according to the first embodiment. [Figure 18] This figure is similar to Figure 17, which shows a stepping motor according to the second embodiment. [Figure 19] This figure is similar to Figure 17, which shows a stepping motor according to the third embodiment. [Figure 20] Figure 19 is a perspective view showing the rotor of a stepping motor. [Figure 21] This is a perspective view showing a stepping motor according to a fourth embodiment. [Figure 22] Figure 1 is a schematic perspective view of the propeller of the propulsion unit, which is equipped with a device for locking the propeller to rotate relative to the nacelle, with the locking device in a deactivated state. [Figure 23] This diagram is similar to Figure 22, showing the locking device in the activated state. [Figure 24] This is an electrical diagram showing the sensor's angular position around the propeller's axis of rotation relative to the nacelle. [Figure 25] Figure 1 is a block diagram showing different steps for folding the blades of an aircraft's propulsion unit. [Figure 26] Figure 1 is a block diagram showing the various steps in the method for deploying the blades of the aircraft's propulsion unit. [Modes for carrying out the invention]

[0030] In the following description, elements having the same structure or similar function are referred to by the same reference numeral.

[0031] For the remainder of the explanation, the longitudinal orientation is adopted, as indicated by the arrow "L" in the diagram, which is locally associated with each propulsion unit. The longitudinal orientation is oriented from front to rear and is parallel to the axis of rotation of the propeller of the propulsion unit.

[0032] The radial orientation shall be used, oriented perpendicular to the longitudinal direction and directed from the inside out near the rotation axis of the propulsion unit. The tangential orientation, perpendicular to both the radial and longitudinal directions, shall also be used.

[0033] Figure 1 shows an aircraft 20 having a plurality of propeller propulsion units 22 manufactured in accordance with the teachings of the present invention. This is a vertical take-off and landing aircraft, also known by its acronym “VTOL”. In this regard, the aircraft 20 has propulsion units 22 called “lift” intended to provide the aircraft 20 with vertical thrust of lift. These lift propulsion units 22 are located here on the tail of the aircraft 20 and on the fuselage of the aircraft 20. The aircraft 20 also has propulsion units 22 called traction, intended to provide longitudinal thrust to allow the aircraft 20 to be displaced forward. The traction propulsion units 22 are located here on the wings of the aircraft 20.

[0034] Alternatively, the present invention is applicable to classic aircraft, also known as "CTOL," an acronym for "classical takeoff and landing." The aircraft then comprises only a traction propulsion unit.

[0035] The propulsion unit 22 has a similar design. Therefore, although a single propulsion unit 22 is described below, this description is also applicable to other propulsion units 22. As shown in Figures 2 to 4, the propulsion unit 22 comprises a nacelle 24 intended to be assembled to a structural element of the aircraft 20, such as a wing or fuselage. The propulsion unit 22 is attached to the structural element by, for example, a mast (not shown). The nacelle 24 is equipped with an aerodynamic fairing.

[0036] The nacelle 24 may be fixedly attached to a structural element. When the structural element is stationary, the propulsion unit is stationary relative to the aircraft's fuselage and forms either a traction propulsion unit or a buoyancy propulsion unit. When the structural element is pivotally attached to the aircraft's fuselage, the propulsion unit alternately performs traction or buoyancy functions depending on the position of the structural element.

[0037] According to another modification of the present invention, the nacelle is mounted so as to be rotatable around a transverse axis on a structural element, and the propulsion unit can alternately perform traction or buoyancy functions depending on the angular position of the nacelle on the structural element.

[0038] The propulsion unit 22 further comprises a propeller 26 rotatably mounted within the nacelle 24 about a longitudinal axis of rotation "X" by a central hub 28. The front of the hub 28 is generally capped with a nose 30 to improve the aerodynamic performance of the propulsion unit 22, particularly by reducing its drag.

[0039] The propeller 26 also comprises multiple blades 32, the blades 32 extending along the main axis from a root portion 34 connected to a hub 28 to a free end 36 called the blade tip. Each blade 32 has a profile that extends from the leading edge to the trailing edge in the direction of rotation of the propeller. Each propeller 26 comprises two blades 32. The present invention is, of course, applicable to propellers with a larger number of blades, for example, three, four, or more blades.

[0040] The blades 32 are evenly distributed around the hub 28 at a determined angular pitch such that the propeller 26 has rotational invariance of the given angular pitch around the axis of rotation "X".

[0041] Each blade 32 is pivotable relative to the hub 28 about a radial pitch axis "Y" which substantially coincides with the main axis of the blade 32 when the propeller 26 is deployed, as will be described later. For this purpose, the hub 28 has the same number of blade barrels 38 as the propeller 26 has blades 32, as shown in Figures 5 to 9. Each blade barrel 38 is pivotably mounted to the hub 28 about the pitch axis "Y". Each blade barrel 38 is pivotally guided, for example, by rolling. Each blade barrel 38 is in the form of a sleeve that receives the root portion 34 of the associated blade 32 so that the blade 32 is rotatably fixed to the blade barrel 38 about the pitch axis "Y".

[0042] Therefore, the blade 32 is controllable at a pitch angle position "β" around the pitch axis "Y" over a range extending between a first extreme pitch angle position "β1" and a second extreme pitch angle position "β2". The thrust generated by the rotation of the propeller 26 is determined according to the pitch angle position "β" of the propeller. The range includes a folded pitch angle position "β0" in which the blade 32 extends in a plane parallel to the displacement direction of the aircraft 20 during cruising flight.

[0043] Therefore, in the case of the lift propulsion unit 22, the folded pitch angle position "β0" corresponds to the direction in which the blade 32 extends in a plane perpendicular to the rotation axis "X", also known as the zero-support force pitch angle position, as shown in Figures 3 and 4.

[0044] In contrast, in the case of the traction propulsion unit 22, the folded pitch angle position "β0" corresponds to the orientation in which the blade 32 extends in a plane parallel to the rotation axis "X", and the blade 32 is feathered as shown in Figures 11-13 and 6-9.

[0045] Furthermore, each propeller 26 of the propulsion unit 22 has the special feature of having a foldable blade 32. In particular, this makes it possible to improve the aerodynamic performance of the aircraft 20 under certain flight conditions by folding the blades 32 of the propulsion unit 22 when the aircraft 20 is flying at a speed sufficient to provide support with its wings alone.

[0046] For this purpose, each blade 32 is pivotably mounted to the associated blade barrel 38 about a folding axis "Z" that extends perpendicular to the radial pitch axis "Y" of the blade 32, as shown in Figures 5 to 9. Thus, the folding axis "Z" rotates with the blade barrel 38 around the pitch axis "Y". More specifically, the blade 32 is hinged to the blade barrel 38 such that the folding axis "Z" is perpendicular to the rotation axis "X" when the blade 32 occupies its folded pitch angular position "β0".

[0047] Therefore, the blades 32 of the propeller 26 are controllable between an extended position, where the main axis of the blade 32 extends substantially radially with respect to the axis of rotation "X", as shown in Figures 2, 3, 5, 6, 8, and 10-12, and a folded position, where the main axis of the blade 32 extends substantially longitudinally parallel to the axis of rotation "X", as shown in Figures 4, 7, 9, and 13. In the folded position, the blade 32 is received longitudinally with respect to the nacelle 24.

[0048] Advantageously, in order to reduce the drag of the propulsion unit 22 when the blades 32 are in the folded position, the nacelle 24 is provided with housings 39, each intended to house the blades 32 of the propeller 26 in their folded pitch angular position "β0", as shown in Figures 2-4 and 10-13. Thus, the blades 32 in the folded position are integrated with the fairing of the nacelle 24. For this purpose, the nacelle 24 is provided with the same number of housings 39 as the propeller 26 houses its blades 32.

[0049] To control the pitch angle position "β" of the blades 32, the propulsion unit 22 is equipped with a pitch device 40, as shown in Figures 5 to 9. The pitch device 40 controls the pivot of the blade barrel 38 around the radial pitch axis "Y" relative to the hub 28 to determine the pitch angle position "β" of each blade 32. Here, the pitch device 40 makes it possible to control all the blades 32 of the propeller 26 to the same pitch angle position "β" at the same time.

[0050] The pitch device 40 includes a pitch actuator 42, in particular, which has a control rod 44 that slides along its main axis, coaxial with the rotation axis "X". This is a linear electric actuator 42. Alternatively, the pitch actuator is a hydraulic actuator or an electro-hydraulic actuator. A radial plate 46 is attached to the free end of the control rod 44. Each blade 32 of the propeller 26 is connected to the plate 46 by a control link 48, which has a first end articulated on the plate 46 and a second end articulated on the blade 32, eccentrically mounted with respect to the pitch axis "Y", so as to form a link / crank connection between the plate 46 and the blade barrel 38. Thus, the pitch angular position "β" of the blade 32 changes with the axial position of the control rod 44.

[0051] Here, the pitch actuator 42 is fixedly and rotatably mounted to the propeller 26. The pitch actuator 42 is located, for example, inside the nose 30.

[0052] In modifications not shown in the present invention, the pitch actuator is mounted stationarily to the nacelle, and only the control plate 46 is rotatably mounted in a manner fixed to the propeller 26.

[0053] Advantageously, the propulsion unit 22 includes means for determining the pitch angular position "β". This is, for example, a pitch sensor 45 capable of detecting the longitudinal position of the rod 44. The pitch sensor 45 is, for example, an induction sensor, or any other known means such as a mechanical copy means by link.

[0054] To control the blades 32 between their deployed and folded positions, the propulsion unit 22 includes a folding device 50, as shown in Figures 5 to 9, which comprises actuators 52 that control the pivoting of each blade 32 relative to its blade barrel 38 between its deployed and folded positions. The folding actuators 52 are common to all blades 32 so that the blades 32 are controlled simultaneously between their deployed and folded positions. The folding actuators 52 are here formed by electric actuators.

[0055] The folding device 50 includes a gearbox 54 associated with each blade 32, which functions to transmit the movement of the folding actuator 52 to the blades 32. Each gearbox 54 includes a movable control member 56, which is rotatably fixed and mounted to the associated blade barrel 38 and is moved by the folding actuator 52. Each gearbox 54 further includes a link 58, which has a first end pivotably mounted eccentrically with respect to the folding axis "Z" to the root portion 34 of the associated blade 32, and a second end pivotably mounted to the movable control member 56. The link 58 forms a link / crank connection with the blade root portion 34, thereby converting the movement of the control member 56 into pivotal motion of the blade 32 about its folding axis "Z". For this purpose, both ends of the link 58 are mounted to pivot about two axes "Z" parallel to the folding axis.

[0056] According to the first embodiment of the folding device 50 shown in Figures 8 and 9, each transmission 54 control member 56 is formed by a slider, which is mounted to slide radially along the pitch axis "Y" of the associated blade barrel 38 between an extreme internal position corresponding to one of the positions of the associated blade 32 and an extreme external position corresponding to the other of the positions of the associated blade 32.

[0057] The external limit position of the control member 56 shown in Figure 8 corresponds to the deployed position of the associated blade 32, while its internal limit position shown in Figure 9 corresponds to the folded position of the associated blade 32.

[0058] Here, the sliding of the movable control member 56 is actuated by a cam 60 that cooperates with the movable control member 56 via a cam follower 62. The cam follower 62 is mounted to the control member 56 in a fixed position, sliding along the pitch axis "Y".

[0059] More specifically, the cam 60 is mounted to slide longitudinally along the rotation axis "X" between a first forward longitudinal position corresponding to the extended position of the blade 32 shown in Figure 8 and a second rearward longitudinal position corresponding to the folded position of the blade 32 shown in Figure 9. For this purpose, the cam 60 has an inclined profile that extends from a front end radially positioned near the rotation axis "X" to a rear end located at a greater radial distance from the rotation axis "X".

[0060] The cam 60 is slidably fixed and mounted to the sliding rod 64 of the folding actuator 52. Since all blades 32 are controlled simultaneously by the same folding actuator 52, all cams 60 in each transmission 54 are mounted here to the same sliding rod 64. The sliding rod 64 is coaxial with the rotation axis "X".

[0061] The folding actuator 52 is mounted here in a fixed, rotatable manner with the propeller 26 around the rotation axis "X".

[0062] Alternatively, the folding actuator may be mounted stationarily to the nacelle. In this case, the cam may be formed by a frustum that allows it to cooperate with the cam follower regardless of the angular position of the propeller around the axis of rotation, or the cam may be mounted rotatably to the nacelle around the axis of rotation so that it remains aligned with the cam follower of the associated blade as the propeller rotates.

[0063] Furthermore, the cam follower 62 is formed here by a roller that rotates about an axis perpendicular to the rotation axis "X" and perpendicular to the pitch axis "Y". This is, for example, a diabolo-shaped roller having two parallel running surfaces on the cam 60. Advantageously, the cam follower 62 is guided laterally relative to the cam 60 as it slides along the longitudinal rail 66 supported by the cam 60. Regardless of the pitch angular position "β" of the associated blade 32, the cam follower 62 remains engaged with the rail 66, so it is mounted to rotate about the pitch axis "Y" on the movable control member 56. Thus, the cam follower 62 is supported by a clevis 70 pivotably mounted to the inner end of the movable control member 56, for example by a rolling bearing. Therefore, the rotation axis of the cam follower 62 remains perpendicular to the rotation axis "X" regardless of the pitch angular position "β" of the associated blade 32, while the movable control member 56 pivots reliably and freely together with the blade barrel 28 around the pitch axis "Y".

[0064] According to the second embodiment of the folding device 50 shown in Figures 5 to 7, the movable control member 56 is formed by a crank, which is pivotably mounted within the blade barrel 38 about a control axis "Z1" parallel to the folding axis "Z" between a first extreme angular position corresponding to one of the positions of the associated blade 32 and a second extreme angular position corresponding to the other of the positions of the associated blade 32. The second end of the link 58 is pivotably mounted to the control member 56 eccentrically with respect to its control axis "Z1".

[0065] The pivot of the movable control member 58 is actuated here by a rack 68 that meshes with the toothed sector 71 of the movable control member 58. More specifically, the rack 68 is mounted to slide longitudinally along the axis of rotation "X" between a first rear longitudinal position corresponding to the extended position of the blade 32, as shown in Figures 5 and 6, and a second front longitudinal position corresponding to the folded position of the blade 32, as shown in Figure 7. The rack 68 extends parallel to the axis of rotation "X".

[0066] The rack 68 is mounted in a sliding and fixed manner to the sliding rod 64 of the folding actuator 52. Since all the blades 32 are controlled simultaneously by the same folding actuator 52, all the racks 68 of each transmission 54 are mounted here to the same sliding rod 64. The sliding rod 64 is coaxial with the rotation axis "X". The folding actuator 52 is mounted here in a rotating and fixed manner together with the propeller 26 around the rotation axis "X".

[0067] Regardless of the embodiment of the folding device 50, it is advantageous to be able to determine whether the blades 32 of the propeller 26 are in their deployed or folded positions. Therefore, the folding device 50 hereby includes a device for detecting the position of the blades 32. The detection device is formed, for example, by a first deployment sensor 72A and a second folding sensor 72B. The first deployment sensor 72A is configured to detect when a movable element located on a transmission chain between the actuator 52 and the blade 32 occupies a specific position corresponding to the deployed position of the blade 32, and the second folding sensor 72B is configured to detect when a movable element located on a transmission chain between the actuator 52 and the blade 32 occupies a specific position corresponding to the folded position of the blade 32. Here, the sensors 72A, 72B operate in an on / off manner and are activated only when the blade 32 occupies the relevant deployed or folded position. These are, for example, contact sensors 72A, 72B or induction sensors 72A, 72B.

[0068] In the example shown in Figures 8 and 9, which corresponds to the first embodiment of the folding device 50, the unfolding sensor 72A is actuated by the free end of the control rod 64, and the folding sensor 72B is actuated by the rear end of the cam 60.

[0069] In the example shown in Figures 5 to 7, which corresponds to the second embodiment of the folding device 50, the deployment sensor 72A is activated by the control member 56 at its angular position corresponding to the deployed position of the blade 32, and the folding sensor 72B is activated by the front end of the control rod 64.

[0070] Furthermore, a mechanical locking device can be provided on the blade 32 in its deployed and folded positions. The locking device is formed, for example, by a latch 75 that cooperates with a movable element located on a transmission chain between the actuator 52 and the blade 32. The latch 75 is positioned here to stop the pivoting of the movable control member 56 when the blade 32 is in its deployed and folded positions. The latch 75 is operated here by the sliding of a rack 68.

[0071] In another embodiment of the propulsion unit 22, as shown in Figures 14 to 16, it includes a rotor shaft 78 that is rotatably mounted within the nacelle 24 coaxially with the rotation axis "X" and rotatably fixed to the propeller 26. The propulsion unit 22 further includes propulsion means that rotate the propeller 26 by the rotor shaft 78.

[0072] The propulsion unit 22 further comprises indexing means for stopping the propeller 26 at at least one indexed angular position "θi" around a rotation axis "X" that coincides with the housing 34 of the nacelle 24 when the blades 32 are in the deployed position. Due to the rotational invariance of the propeller 26, the propeller is likely to have as many indexed angular positions "θi" as the blades 32.

[0073] The indexing means is formed by a stepping electric motor 82. In known methods, such a stepping motor 82 comprises a rotor 84 rotatably mounted on a stator 86. While the stator 86 is stationary relative to the nacelle 24, the rotor 84 is coupled to the hub 28 of the propeller 26. The rotor 84 is here mounted to rotate and fix together with the rotor shaft 78 about the axis of rotation "X".

[0074] Such a stepping motor 82 has the advantage of being able to decelerate the propeller 26 by counteracting its rotation with resistive torque. Furthermore, it also makes it possible to provide motor torque to the propeller 26 and bring it very precisely to one of its indexed angular positions "θi". Finally, the stator 86 of the stepping motor 82 is configured to match each of the indexed angular positions "θi" of the propeller 26 with a step of the stepping motor 82 that can stop the propeller 26 in relation to the rotation at each of those indexed angular positions "θi".

[0075] In the example shown in Figure 14, the propulsion system includes an electric propulsion motor 80 separate from the stepping motor 82. In this case, the stepping motor 82 is interposed between the propulsion motor 80 and the propeller hub 28 on a transmission chain for the motor torque generated by the propulsion motor 80. Here, the stepping motor 82 is directly mounted on the rotor shaft 78, which is permanently coupled to the motor shaft of the propulsion motor 80.

[0076] In the example shown in Figure 15, the propulsion motor 80 is a combustion or heat engine such as a turbine or an alternating or rotary internal combustion engine. In this case, the stepping motor 82 is interposed between the propulsion motor 80 and the propeller hub 28 on a transmission chain for the motor torque generated by the propulsion motor 80. The stepping motor 82 is here positioned directly on the rotor shaft 78, which is controllably coupled to the motor shaft of the propulsion motor 80 by a clutch 83.

[0077] In the example shown in Figure 16, the stepping electric motor 82 forms the propulsion means. Therefore, the propulsion means does not include any motors other than the stepping electric motor 82.

[0078] According to the first embodiment of the indexing means shown in Figure 17, the stepping electric motor 82 is a variable reluctance motor also called a "variable reluctance stepping motor" or "switched reluctance motor" (SRM). In such a stepping motor 82, the rotor 84 is made of a ferromagnetic material. The rotor 84 is formed, for example, by lamination of soft iron sheet metal, or the rotor 84 is manufactured from a monolithic component of electromagnetic steel. The rotor 84 has an outer tooth section having an even number of teeth 88.

[0079] The stator 86 is generally manufactured from a lamination of ferromagnetic sheet metal. The stator 86 has an inner tooth section having an even number of teeth 90. This section comprises several electric coils 92. The coils 92, arranged around two opposing teeth 90, are powered in series to form two electromagnets with poles of opposite signs radially oriented toward the rotor 84.

[0080] Unlike the number of teeth on the rotor 84 and the number of coils on the stator 86, the number of pitches on the stepping motor 82, i.e., the number of angular positions at which the rotor 84 can be stably stopped by supplying power to the two opposing electric coils 92 of the rotor 86, can be determined.

[0081] By sequentially supplying power to the opposing pair of electric coils 92, and thus attracting the rotor teeth 88 closest to the alignment of the electric coils 92, it is possible to rotate the rotor 84.

[0082] In a second embodiment of the indexing means, the stepping electric motor 82 is a permanent magnet motor, also known as a "permanent magnet stepping motor".

[0083] The stator 86 is substantially the same as that of the variable reluctance stepping motor described in the first embodiment. However, instead of teeth, the rotor 84 comprises at least one permanent magnet having a north pole "N" and a south pole "S", the pole axis of which is oriented radially. The magnetic poles "N" and "S" of the permanent magnet are arranged symmetrically with respect to the rotation axis "X" such that the north pole "N" and the south pole "S" are alternately arranged around the rotation axis "X".

[0084] Such a stepping motor 82 generally has higher torque than a variable reluctance motor.

[0085] In the third embodiment of the indexing means shown in Figures 19 and 20, the stepping electric motor 82 is a hybrid motor, also known as a "hybrid synchronous stepping motor".

[0086] The stator 86 is substantially identical in this case to the variable reluctance stepping motor described in the first embodiment.

[0087] Meanwhile, the rotor 84 is formed by two toothed wheels 84A and 84B made of ferromagnetic material, each having an outer toothed portion with the same even number of teeth 88A and 88B. The two toothed wheels 84A and 84B are mounted coaxially with a permanent magnet 94 interposed in the axial direction, with the north pole of one toothed wheel 84A in contact and the south pole of the other toothed wheel 84B in contact.

[0088] In this configuration, the teeth 88A of the first toothed wheel 84A form the north pole, and the teeth 88B of the second toothed wheel 88B form the south pole. The teeth 88A of the first toothed wheel 84A are angularly offset from the teeth 88B of the second toothed wheel 84B. Therefore, in an axial view, the teeth 88A forming the north pole are angularly sandwiched between the two teeth 88B forming the south pole.

[0089] The rotor 84 thus formed is rotatably housed within the stator 86. Therefore, supplying power to multiple coils 92 of the stator 86 attracts the teeth 88A, 88B closest to the rotor 84 with the opposite sign.

[0090] Such a hybrid stepping motor 82 has the advantage of having a large number of steps, like the variable reluctance motor 82 described in the first embodiment, and high motor torque, like the permanent magnet motor 82 described in the second embodiment.

[0091] Instead of this third embodiment, as shown in Figure 21, this is an axial flow stepping motor 82 in which the rotor 84 is formed by a disk with magnets 94 having alternating signs of poles around it. The stator 86 also includes an electromagnet formed by electric coils 92 wound around a core of ferromagnetic material, which generates a magnetic field directed parallel to the rotation axis "X" of the rotor 84 in the direction around the rotor 84.

[0092] Regardless of the type of stepping motor 82 implemented, the propulsion unit 22 is advantageously equipped with a device 96 for mechanically locking the propeller 26 relative to the nacelle 24 around its axis of rotation "X" at each of its indexed angular positions "θi". Furthermore, the locking device 96 is designed so that the propeller 26 can only be locked at the indexed angular positions "θi".

[0093] As shown in Figures 22 and 23, the locking device 96 here comprises a propeller 26 and a rotating and fixedly mounted disk 98. The disk 98 here is mounted coaxially with the axis of rotation "X". The disk 98 is defined radially by an annular periphery 100 and axially by two circular surfaces 101.

[0094] The disk 98 includes at least one stopper 102 corresponding to one of the indexed angular positions "θi". Here, the disk 98 includes a single stopper 102.

[0095] Alternatively, the disk 98 may have a plurality of stoppers 102, each corresponding to an indexed angular position "θi". Thus, the disk 98 may have a number of stoppers 102 equal to the number of indexed angular positions "θi". In particular, this makes it possible to reach the indexed angular position "θi" more quickly without having to rotate the propeller completely again.

[0096] The retaining arm 102 can cooperate with the locking member 104, which is mounted to be movable relative to the nacelle 24 between an inactive position in which the disk 98 rotates freely and an active position in which the locking member 98 is received by the retaining arm 102 when the propeller 26 occupies one of its indexed angular positions "θi", thereby fixing the propeller 26 so as not to rotate relative to the nacelle 24 around the axis of rotation "X". The locking member 104 is moved, for example, by an electric actuator.

[0097] In the embodiments shown in Figures 22 and 23, the retaining element 102 is generated on the peripheral edge 100 of the disk 98. The locking member 104 is mounted to slide radially relative to the nacelle 24 between its inactive position, where it is spaced away from the peripheral edge 100, as shown in Figure 22, and its active position, where it is radially displaced toward the axis of rotation "X" to coincide with and enter the retaining element 102, as shown in Figure 23. When the propeller 26 does not occupy one of its indexed angular positions "θi", the locking member 104 cannot be controlled to its active position because it is in contact with the peripheral edge 100 of the disk 98.

[0098] In a modified version of the present invention not shown, the stopper is generated on an annular track on one of the circular surfaces of the disc. In this case, the locking member can be mounted to slide longitudinally relative to the nacelle.

[0099] For example, a lock sensor 105, such as a contact sensor or induction sensor, can detect when the lock member 104 is in its active position.

[0100] Advantageously, each stopper 102 has a cam track shape with two inclined sections converging toward a bottom 106. The bottom 106 is positioned such that when the locking member 104 is received by the bottom of the stopper 102, the propeller 26 occupies exactly one of its indexed angular positions "θi". The locking member 104 has a roller 108 or sliding coating at its free end, which can rotate or slide against the inclined section of the stopper 102. Thus, when the propeller 26 stops at an angular position located within the tolerance range [θi-λ, θi+λ] determined on either side of its indexed angular position "θi", the roller 108 contacts one of the inclined sections of the stopper 102 as the locking member 104 is controlled toward its active position. The locking member 104 works in cooperation with the inclined portion of the retaining arm 102 to rotate the propeller 26 as the roller 108 is displaced toward its active position until it is at the bottom 106 of the retaining arm 102, providing sufficient force to precisely position the propeller 26 at its indexed angular position "θi".

[0101] To perform this operation, it is preferable that the propeller 26 does not receive motor or resistance torque other than that caused by friction of the rotation guide member of the propeller 26.

[0102] Furthermore, to ensure that the propeller 26 occupies its overall indexed angular position "θi", or at least an angular position within a determined tolerance range [θi-λ, θi+λ] on either side of its indexed angular position "θi", the propulsion unit 22 is equipped with a sensor 110 for the angular position of the propeller 26 relative to the nacelle 24, as shown in Figures 14 to 16.

[0103] For example, the induction sensor 110 enables the measurement of the propeller's angular position without contact. Thus, the first rotor element 111 is mounted to rotate and fix with the propeller 26, while the second stator element 113 enables the angular position of the rotor element to be detected by electromagnetic means.

[0104] As shown in Figure 24, the induction sensor 110 is a resolver also known here as “RVDT: Rotary Variable Differential Transformer” or “rotationally variable differential transformer”. As a known non-limiting example, such a sensor 110 comprises a primary coil 112 and two secondary coils 114, 116 supported by a stator element 113. The primary coil 112 is powered by an AC voltage “Vr”. The two secondary coils 114, 116 are offset by 90° around the rotation axis “X”. The rotor element 111 comprises a reference coil 118. The reference coil 118 and the primary coil 112 form a rotary transformer 120. The secondary coils 114, 116 are excited by the rotation of the reference coil 118 supported by the rotor element 111. The voltage values ​​in each secondary coil 114, 116 allow for the unique determination of the angular position of the rotor element 111 around the rotation axis “X”.

[0105] Alternatively, the induction sensor 110 is formed from a product known by the trade name "Inductosin," which can achieve high angular accuracy.

[0106] A method for folding the blades 32 of the propeller 26 of the propulsion unit 22 will be described with reference to Figure 25. Such a method is carried out by an electronically controlled unit (not shown). This method can be triggered automatically or by a manual command from the pilot. At the start of the method, the blades 32 of the propeller 26 are unfolded as shown in Figures 2, 3, 5, 6, and 8. The blades 32 occupy a pitch angle position "β" which can be different from their folded pitch angle position "β0", as shown in Figures 2 and 5. Furthermore, the propeller 26 is generally rotationally driven by the propulsion means.

[0107] In the first step, "E1-1," specific flight conditions for the aircraft are confirmed in order to obtain approval for continuing the folding method of the blade 32.

[0108] For example, when step "E1-1" is applied to the levitation propulsion unit 22, it is confirmed that the aircraft 20 has reached a speed sufficient to allow its wings to provide support without requiring lift from the levitation propulsion unit 22. For example, it is confirmed that the forward speed "V" of the aircraft 20 is considerably above the first determined threshold speed "V0". In this case, step "E1-2" is triggered to stop the next propulsion; otherwise, the folding method is interrupted.

[0109] In another example, when step "E1-1" is applied to the traction propulsion units 22, it is confirmed that the aircraft 20 has reached a speed sufficient for economical cruising flight, where it is not necessary to use all traction propulsion units 22 simultaneously to provide thrust to the aircraft 20. For example, it is confirmed that the forward speed "V" of the aircraft 20 is considerably above a second determined threshold speed "V1". The blades 32 of the traction propulsion units 22 can also be folded while the aircraft 20 is hovering, as they are no longer needed. Next, it is confirmed that the forward speed of the aircraft 20 is zero. If any of these conditions are confirmed, the next step "E1-2" is triggered; otherwise, the folding process is interrupted.

[0110] During step E1-2, in which propulsion is stopped, the motor torque supplied by the propulsion means is interrupted so that the propeller 26 can rotate freely, that is, under the influence of its inertia and, if applicable, residual aerodynamic forces acting on the propeller blades.

[0111] When the propeller 26 is driven by the combustion propulsion motor 80, the clutch 83 is controlled to the disengaged position at the start of step "E1-2" which stops propulsion, or after a set period determined to allow the motor friction to begin decelerating the propeller 26.

[0112] When the propeller 26 is driven by the electric propulsion motor 80, the propulsion motor 80 remains coupled to the propeller 26 because the friction of such motors is generally low.

[0113] At the end of step "E1-2" which stops propulsion, pitch step "E1-3" is triggered. In this pitch step "E1-3", the blades 32 of the propeller 26 are controlled to their folded pitch angle position "β0", i.e., the feather position of the traction propulsion unit 22 as shown in Figures 6, 8 and 11, or the zero support position of the lift propulsion unit 22 as shown in Figure 3.

[0114] Following the pitch steps "E1-3", a step "E1-4" is taken to confirm the pitch angular position, in which the pitch sensor 45 confirms that the blades 32 occupy their folded pitch angular position "β0". A slight offset of a few degrees "ε" from the folded pitch angular position "β0" in either direction is usually acceptable. In this way, it is more precisely confirmed that the pitch angular position "β" of the blades 32 falls within the pitch angular position range delimited by the lower threshold "β0-ε" and the upper limit "β0+ε". If this is the case, a method for stopping the rotation of the propeller 26 at one of its indexed angular positions "θi" is triggered; otherwise, step "E1-3" is repeated.

[0115] A method for stopping the rotation of propeller 26 at one of its indexed angular positions "θi" comprises step "E1-5" of checking the rotation speed "Nr", during which it is confirmed that the rotation speed "Nr" of propeller 26 is less than or equal to a determined rotation speed "Nre".

[0116] If the rotational speed "Nr" of the propeller 26 is higher than a certain rotational speed "Nre", the braking step "E1-6" is triggered. During the braking step "E1-6", the stepping motor 82 is controlled to generate a resistive torque to counteract the free rotation of the propeller 26 until the rotational speed "Nr" of the propeller 26 falls below a predetermined rotational speed "Nre". The rotational speed of "Nr" of the propeller 26 is measured by a well-known sensor (not shown), which will not be described in detail later. At the end of this braking step "E1-6", step "E1-5", which verifies the rotational speed "Nr", is repeated.

[0117] If the rotational speed "Nr" of the propeller 26 is less than or equal to the determined rotational speed "Nre", step "E1-7" is triggered to stop the propeller at the indexed angular position. In this step, the stepping motor 82 is controlled to stop the propeller 26 at the indexed angular position "θi".

[0118] Following the stop step "E1-7", there is a step "E1-8" to check the angular position "θ" of the propeller 26, which is measured by the induction sensor 110. If the measured angular position "θ" of the propeller 26 is within the tolerance interval [θi-λ, θi+λ] determined on both sides of the indexed angular position "θi", the lock step "E1-10" is triggered; otherwise, the adjustment step "E1-9" is triggered.

[0119] The adjustment step "E1-9" consists of controlling the stepping motor 82 to provide rotational torque that drives the propeller 26 to rotate around its axis of rotation "X" toward one of the indexed angular positions "θi".

[0120] During this adjustment step "E1-9", the propeller 26 is driven to rotate in only one direction. Therefore, when the propeller 26 passes an indexed angular position "θi", the stepping motor 82 drives the propeller 26 to rotate to the next indexed angular position "θi".

[0121] Alternatively, the propeller 26 may be rotated in both directions by the stepping motor 82 so that the propeller 26 rotates toward the nearest indexed angular position "θi".

[0122] After this adjustment step "E1-9", the stop step "E1-7" is repeated.

[0123] The adjustment step "E1-9", the stopping step "E1-7", and the verification step "E1-8" are repeated until the angular position "θ" of the propeller 26 falls within the tolerance interval [θi-λ, θi+λ] determined on either side of the indexed angular position "θi".

[0124] In lock step "E1-10", the propeller 26 is rotatably locked to the nacelle 24 at its indexed angular position "θi" by a mechanical locking device 96, as shown in Figure 23. As previously mentioned, the locking device 96 enables the propeller 26 to be precisely positioned at its indexed angular position "θi" through the cooperation between the locking member 104, which is controlled toward its active position, and the inclined portion of the retaining arm 102.

[0125] At the end of lock step "E1-10", step "E1-11" is triggered, which folds the blade 32. In this step, the blade 32 is folded into its respective housing 39 by the folding device 50, as described above and as shown in Figures 4, 7, 9, and 13.

[0126] Then, in step E1-12, which verifies that the blade 32 is properly folded, sensor 72B verifies that the blade 32 is properly folded. If the blade 32 is in the folded position, latch 75 is controlled to lock the blade 32 in the folded position in the final lock step E1-13; otherwise, an incident is reported to the pilot of the aircraft 20, as shown by reference numeral E1-14 in Figure 25.

[0127] The aerodynamic design of the blade should take into account the requirement that the folded blades not unintentionally deploy, especially when the blades are not effectively locked in the folded position, under specific flight conditions that should be considered in the event of this failure.

[0128] Here, the method for deploying the blades 32 of the propulsion unit 22 will be described with reference to Figure 26. Such a method is carried out by an electronic control unit (not shown). This method can be triggered automatically or by a manual command from the pilot.

[0129] The first step, "E2-1," involves verifying specific flight conditions for aircraft 20 that must be met to obtain authorization for continuing the deployment method of blade 32.

[0130] For example, when step "E2-1" is applied to the levitation propulsion unit 22, it is confirmed that the speed of the aircraft 20 has decreased and is approaching a speed at which its wings are no longer sufficient to provide support without lift from the levitation propulsion unit 22. For example, it is confirmed that the forward speed "V" of the aircraft 20 has decreased to a determined third threshold speed "V2". In this case, the subsequent deployment step "E2-2" is triggered; otherwise, the deployment method is not permitted.

[0131] In another example, when step "E2-1" is applied to the traction propulsion units 22, it is confirmed that the speed of the aircraft 20 is below a sufficiently economical cruising speed that all traction propulsion units 22 must be used simultaneously to provide thrust to the aircraft 20. For example, it is confirmed that the forward speed "V" of the aircraft 20 is well below a fourth determined threshold speed "V3". The blades 32 of the traction propulsion units 22 may also be deployed when the aircraft 20 is about to leave hovering flight. If any one of these conditions is confirmed, the next step "E2-2" is triggered; otherwise, the deployment method is interrupted.

[0132] In deployment step "E2-2", the latch 75 is retracted and unlocked, and the folding actuator 50 is controlled to deploy the blade 32.

[0133] In the subsequent confirmation step "E2-3" following deployment, the deployment sensor 72A is used to confirm that the blades 32 are in their deployed positions. If this is the case, step "E2-4" to unlock the propellers 26 is triggered; otherwise, the deployment step "E2-2" is repeated.

[0134] In the unlocking step "E2-4", the locking member 104 of the mechanical locking device 96 for the propeller 26 is controlled to its inactive position, thereby releasing the rotation of the propeller 26.

[0135] In step E2-5, which verifies the unlocking, it is confirmed that the propeller 26 has been unlocked by the lock sensor 105. If so, the deployment process is complete and the propulsion unit 22 is ready for use; otherwise, the unlocking step E2-4 is repeated.

Claims

1. A propulsion unit (22) having a propeller (26) for an aircraft (20), A nacelle (24) intended to be assembled to a structural element of an aircraft (20), A propeller (26) is rotatably mounted within a nacelle (24) by a hub (28) about a longitudinal axis of rotation (X), the propeller (26) comprises blades (32) evenly distributed around the hub (28), and the blades (32) are pivotally mounted to the hub (28) by a root (34) between an extended position extending radially with respect to the axis of rotation (X) and a folded position receiving longitudinally with respect to the nacelle (24), the propeller (26) A propulsion means for rotating the propeller (26), An indexing means for stopping the propeller (26) at at least one indexed angular position (θi) relative to the nacelle (24), Equipped with, The propulsion unit (22) is characterized in that the indexing means is formed by a stepping electric motor (82) having a rotor (84) coupled to a hub (28) of a propeller (26).

2. The propeller propulsion unit (22) according to claim 1, characterized in that the stepping electric motor (82) is a variable reluctance motor.

3. The propeller propulsion unit (22) according to claim 1, characterized in that the stepping electric motor (82) is a permanent magnet motor.

4. The propeller propulsion unit (22) according to claim 1, characterized in that the stepping electric motor (82) is a hybrid motor.

5. A propeller propulsion unit (22) according to any one of claims 1 to 4, characterized by comprising a device (96) for mechanically locking the propeller (26) at each of its indexed angular positions (θi).

6. The propulsion unit (22) according to claim 5, wherein the locking device (96) comprises a disk (98) fixedly mounted to rotate with the propeller (26), the disk (98) comprising at least one stopper (102) which can cooperate with a locking member (104), and the locking member (104) is movably mounted with respect to the nacelle (24) between an inactive position in which the disk (98) rotates freely and an active position in which the locking member (104) can be received in the stopper (102) when the propeller (26) occupies at least one indexed angular position (θi) to immobilize the propeller (26) so as to rotate with respect to the nacelle (24).

7. The propulsion unit (22) according to claim 6, characterized in that the stopper (102) has a cam track shape, and such shape allows the locking member (104) to cooperate with the locking member to rotate the propeller (26) in order to precisely position the propeller (26) at its indexed angular position (θi).

8. The propulsion unit (22) is characterized by comprising a guidance sensor (110) for the angular position of the propeller (26) about its rotation axis (X), as described in any one of claims 1 to 7.

9. The propulsion unit (22) according to any one of claims 1 to 8, characterized in that the stepping electric motor (82) forms a propulsion means.

10. The propulsion means comprises a motor (80) different from the stepping electric motor (82), and the stepping motor (82) is interposed between the propulsion motor (80) and the hub (28) of the propeller (26) on a motor torque transmission chain, characterized in that the propulsion unit (22) is according to any one of claims 1 to 8.

11. The propulsion unit (22) according to claim 10, characterized in that the propulsion motor (80) is an electric motor.

12. The propulsion unit (22) according to any one of claims 1 to 11, characterized in that the nacelle (24) is fixedly attached to a structural element of the aircraft (20).

13. The propulsion unit (22) according to any one of claims 1 to 11, characterized in that the nacelle (24) is pivotably attached to a structural element of the aircraft (20).

14. A method for stopping the rotation of a propeller (26) at an indexed angular position (θi) as described in any one of claims 1 to 13, A preliminary step (E1-2) to stop propulsion is performed, in which the motor torque supplied by the propulsion means is interrupted so that the propeller (26) can rotate freely. Step (E1-7) involves stopping the propeller (26) at an indexed angular position (θi) using a stepping electric motor (82), A method characterized by comprising:

15. The method according to claim 14, characterized in that when the propeller (26) is rotating at a rotational speed (Nr) greater than a determined rotational speed (Nre) at the end of a preliminary step (E1-2) to stop propulsion, a braking step (E1-6) is performed before the stopping step (E1-7), during which the stepping motor (82) is controlled to generate a resistive torque to counteract the free rotation of the propeller (26) until the rotational speed (Nr) of the propeller (26) becomes less than or equal to the determined rotational speed (Nre).

16. The method of claim 15, as interpreted in combination with claim 8, comprising a step (E1-8) to confirm the angular position (θ) of a propeller (26), the confirmation step (E1-8) being triggered at the end of a stop step (E1-7), during which the angular position (θ) of the propeller (26) is measured by an induction angle sensor (110).

17. The method according to claim 16, comprising an angle position (θ) adjustment step (E1-9) of a propeller (26), the adjustment step (E1-9) being triggered at the end of the confirmation step (E1-8) and controlling a stepping motor (82) to provide rotational torque to rotate the propeller (26) toward an indexed angle position (θi), and a stop step (E1-7) being repeated after the adjustment step (E1-9) to immobilize the propeller (26) toward its indexed angle position (θi) by the stepping motor (82).

18. The method according to any one of claims 14 or 15, as interpreted in combination with any one of claims 5 to 7, characterized in that when the angular position (θ) of the propeller (26) substantially coincides with the indexed angular position (θi) in the verification step (E1-8), a step of mechanically locking the propeller (26) (E1-10) is triggered, during which the propeller (26) is locked by a mechanical locking device (96) to rotate relative to the nacelle (24).

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