A propulsion unit with foldable propeller blades and a method for stopping the propeller at a division angle position.

Abstract

The present invention relates to a propulsion unit (22) for an aircraft (20) having a propeller (26), the propulsion unit comprising: - a nacelle (24); - a propeller (26) mounted in the nacelle (24) and rotatable about a longitudinal axis of rotation (X), the propeller (26) having blades (32) mounted through a root (34) and pivotable between an extended position and a folded position, wherein in the extended position the blades extend radially relative to the axis of rotation (X) and in the folded position the blades are longitudinally received against the nacelle (24); - a propulsion device that drives the propeller (26) to rotate; and an indexing device for stopping the propeller (26) relative to the nacelle (24) at at least one indexing angle position (θi); the propulsion unit (22) is characterized in that the indexing device includes a stepper motor (82) including a rotor (84) coupled to the propeller (26).

Description

Technical Field

[0001] This invention relates to a propeller propulsion unit for an aircraft, the propeller propulsion unit comprising:

[0002] - The cabin, which is designed to be assembled onto the structural components of the aircraft;

[0003] - A propeller, which is rotatably mounted in the nacelle about a longitudinal axis of rotation via a hub. The propeller includes blades evenly distributed around the hub. The blades are pivotally mounted on the hub between an extended position and a folded position via roots. In the extended position, the blades extend radially relative to the axis of rotation. In the folded position, the blades are longitudinally received against the nacelle.

[0004] - A propulsion device that drives the propeller to rotate;

[0005] - An indexing device for stopping the propeller relative to the nacelle at at least one indexing angle position. Background Technology

[0006] For example, this propeller propulsion unit is used in vertical takeoff and landing aircraft, also known as "VTOL (Vertical Take Off and Landing)". Of course, this propulsion unit can also be used in fixed-wing aircraft, also known as "CTOL (Classic Take Off and Landing)," which stands for "Classic Take Off and Landing." In this case, the aircraft can be equipped with multiple propeller propulsion units to distribute the thrust center and seek optimal propulsion efficiency on the aircraft.

[0007] These propeller propulsion units can be deactivated depending on the aircraft's flight configuration. When the propeller propulsion units are deactivated, the propellers may adversely affect the aircraft's aerodynamic performance, for example, by generating drag or by creating local disturbances in the airflow.

[0008] To address this issue, propulsion units equipped with foldable blade propellers have been proposed to remove these inactive blades from the local flow.

[0009] Typically, the blades are stopped by a brake that operates through friction with the rotor shaft of the propulsion unit. This device allows the propeller to stop at an angular position where the blades do not come into contact with structural components of the aircraft during folding. Such a device is described, for example, in document US 2019 / 016441 A1.

[0010] However, when the propeller unexpectedly stops at an angle incompatible with the propeller's folding, the propulsion motor must be restarted to turn the propeller again or the blade pitch must be modified to take advantage of the windmill effect caused by the aircraft's forward movement.

[0011] Furthermore, to reduce the drag of the propulsion unit when the blades fold, it is preferable to house the blades within a relevant compartment in the nacelle. However, such braking devices do not readily allow the propeller to stop at a precise angular position relative to the nacelle because they lack a mechanism for precisely indexing the propeller to the angular position. Summary of the Invention

[0012] This invention relates to a propulsion unit with a propeller for an aircraft, the propulsion unit comprising:

[0013] - The cabin, which is designed to be assembled onto the structural components of the aircraft;

[0014] - A propeller, which is rotatably mounted in the nacelle about a longitudinal axis of rotation via a hub. The propeller includes blades evenly distributed around the hub. The blades are pivotally mounted on the hub between an extended position and a folded position via roots. In the extended position, the blades extend radially relative to the axis of rotation. In the folded position, the blades are longitudinally received against the nacelle.

[0015] - A propulsion device that drives the propeller to rotate;

[0016] - An indexing device for stopping the propeller relative to the nacelle at at least one indexing angle position;

[0017] The indexing device is characterized by being formed by a stepper motor, which includes a rotor connected to the hub of a propeller.

[0018] The use of a stepper motor allows the propeller to be braked and stopped, but also allows the propeller to rotate again when it is not locked at the division angle position.

[0019] Another feature of the propulsion unit manufactured according to the teachings of the present invention is that the stepper motor is a variable reluctance motor.

[0020] Another feature of the propulsion unit manufactured according to the teachings of the present invention is that the stepper motor is a permanent magnet motor.

[0021] Another feature of the propulsion unit manufactured according to the teachings of the present invention is that the stepper motor is a hybrid motor.

[0022] Another feature of the propulsion unit manufactured according to the teachings of the present invention is that the propulsion unit includes means for mechanically locking the propeller at each of the propeller's angular positions. Advantageously, such locking means make it possible to prevent the propeller from rotating without requiring the stepper motor to be kept energized.

[0023] Another feature of the propulsion unit manufactured according to the teachings of the present invention is that the locking device includes a disc mounted to be fixed in rotation with respect to the propeller, the disc including at least one pawl capable of engaging a locking member mounted to be movable relative to the nacelle between an inactive position and an active position. In the inactive position, the disc can rotate freely, and in the active position, when the propeller occupies one of the angular positions of the propeller, the locking member can be received in the pawl to fix the propeller in rotation with respect to the nacelle.

[0024] In addition to the propulsion unit manufactured according to the teachings of the present invention, the pawl has a cam track shape that allows the propeller to rotate by cooperating with the locking member during the displacement of the locking member toward the movable position of the locking member, so as to precisely position the propeller at the propeller's pitch angle position. Therefore, the presence of this cam track enables the propeller to be positioned very precisely at the propeller's pitch angle position, even when the stepper motor prevents the propeller from moving with a small offset from the pitch angle position.

[0025] Another feature of the propulsion unit manufactured according to the teachings of the present invention is that the propulsion unit includes a sensing sensor for the angular position of the propeller about its axis of rotation. This sensor enables a stepper motor to be operated so that the propeller reaches the angular position of the propeller.

[0026] Another feature of the propulsion unit manufactured according to the teachings of the present invention is that a stepper motor forms the propulsion device. In this configuration, the propulsion unit is advantageously cheaper to manufacture and more compact.

[0027] Another feature of the propulsion unit manufactured according to the teachings of the present invention is that the propulsion device is formed by a propulsion motor separate from the stepper motor, which is inserted between the propeller hub and the propulsion motor in the motor torque transmission chain. In this configuration, the propeller can be propelled by the power of a dedicated motor.

[0028] Another feature of the propulsion unit manufactured according to the teachings of the present invention is that the propulsion motor is an electric motor.

[0029] Among the other features of the propulsion unit, the nacelle is fixedly mounted on the structural elements of the aircraft.

[0030] Among the other features of the propulsion unit, the cabin is pivotally mounted on the structural elements of the aircraft.

[0031] The present invention also relates to a method for stopping the rotation of a propeller at a graduated angular position according to any one of the preceding claims, characterized in that the method comprises:

[0032] - The initial step of stopping propulsion, during which the electric motor torque supplied by the propulsion motor is interrupted, allowing the propeller to rotate freely;

[0033] - The step of stopping the propeller at the division angle position using a stepper motor.

[0034] Another feature of the method implemented according to the teachings of the present invention is that when the propeller is rotating at a speed greater than the determined rotational speed at the end of the initial step of stopping propulsion, there is a braking step before the stopping step, during which a stepper motor is controlled to generate a resistance torque opposite to the free rotation of the propeller until the rotational speed of the propeller is less than or equal to the determined rotational speed.

[0035] Another feature of the method implemented according to the teachings of the present invention is that the method includes a step of checking the angular position of the propeller, which is triggered at the end of a blocking step, and during this step, the angular position of the propeller is measured by a sensing angle sensor.

[0036] Another feature of the method implemented according to the teachings of the present invention is that the method includes a step of adjusting the angular position of the propeller, which is triggered at the end of a check step, and the step includes controlling a stepper motor to provide a rotational torque that drives the propeller to rotate toward the angular position, and repeating a stop step at the end of the adjustment step to fix the propeller at the angular position of the propeller by means of the stepper motor.

[0037] Another feature of the method implemented according to the teachings of the present invention is that when the angular position of the propeller substantially coincides with the division angular position during the inspection step, a mechanical locking step of the propeller is triggered, during which the propeller is rotatably locked relative to the nacelle by a mechanical locking device. Attached Figure Description

[0038] Other features and advantages of the invention will become apparent from the following detailed description, and with reference to the accompanying drawings, in which:

[0039] Figure 1 This is a perspective view of an aircraft equipped with multiple propeller propulsion units, implemented according to the teachings of the present invention.

[0040] Figure 2 It is shown Figure 1 A side view of the propulsion unit of an aircraft, in which the propeller blades are deployed at a pitch angle position that enables increased thrust.

[0041] Figure 3 Is with Figure 2 A similar view, where the propeller blades are deployed at the folded pitch angle position.

[0042] Figure 4 Is with Figure 3 A similar view, in which the propeller blades are folded to the fold pitch angle position.

[0043] Figure 5 is based on Figure 10 The cross-sectional plane 5-5 shows an axial cross-sectional view of the rotating portion of the traction propulsion unit, wherein the propeller blades are deployed at a pitch angle position that enables increased thrust, and the traction propulsion unit is equipped with a folding device manufactured according to a first embodiment of the invention.

[0044] Figure 6 is based on Figure 12 Plane 6-6 shows an axial cross-sectional view of the rotating portion of the traction propulsion unit, wherein the propeller blades are deployed at the folding pitch angle position, and the traction propulsion unit is equipped with a folding device manufactured according to the first embodiment.

[0045] Figure 7 is based on Figure 13 The cross-sectional plane 7-7 shows an axial cross-sectional view of the rotating portion of the traction propulsion unit, wherein the propeller blades are folded, and the traction propulsion unit is equipped with a folding device manufactured according to the first embodiment.

[0046] Figure 8 It is a view similar to Figure 6, in which the traction propulsion unit is equipped with a folding device manufactured according to the second embodiment.

[0047] Figure 9 It is a view similar to Figure 7, wherein the traction propulsion unit is equipped with a folding device manufactured according to the second embodiment.

[0048] Figure 10 It shows Figure 1 A front view of the traction propulsion unit of an aircraft, wherein the propeller blades are deployed at a pitch angle position that enables increased thrust, and the propeller occupies any angular position about the axis of rotation of the propeller.

[0049] Figure 11 Is with Figure 10 A similar view shows the propeller blades deployed at the folded pitch angle position, with the propeller occupying any angular position around the propeller's axis of rotation.

[0050] Figure 12 Is with Figure 11A similar view shows the propeller blades deployed at the folded pitch angle position, with the propeller occupying the division angle position around the propeller's axis of rotation.

[0051] Figure 13 Is with Figure 12 A similar view shows the propeller blades folded into the nacelle housing.

[0052] Figure 14 It is shown schematically. Figure 1 A side view of the rotating portion of the propulsion unit of the aircraft in the first configuration, wherein the propeller is driven by an electric motor separate from the stepper motor.

[0053] Figure 15 Is with Figure 14 A similar view, in which the propulsion unit is manufactured according to the second configuration, wherein the propeller is driven by an internal combustion engine separate from the stepper motor.

[0054] Figure 16 Is with Figure 14 A similar view, in which the propulsion unit is manufactured according to the third configuration, wherein the propeller is driven by a stepper motor.

[0055] Figure 17 It is based on Figure 14 The cross-sectional plane 17-17 shows a radial cross-sectional view of the stepper motor according to the first embodiment.

[0056] Figure 18 Is with Figure 17 A similar view shows a stepper motor according to a second embodiment.

[0057] Figure 19 Is with Figure 17 A similar view shows a stepper motor according to a third embodiment.

[0058] Figure 20 It shows Figure 19 A perspective view of the rotor of a stepper motor.

[0059] Figure 21 This is a perspective view of a stepper motor according to a fourth embodiment.

[0060] Figure 22 It is shown schematically. Figure 1 A perspective view of the propeller of the propulsion unit, which includes a device for locking the propeller rotating relative to the nacelle, the locking device being in an inactive state.

[0061] Figure 23 Is with Figure 22 A similar view, where the locked device is active.

[0062] Figure 24 This is a circuit diagram showing the angular position of a sensor for the propeller about its axis of rotation relative to the nacelle.

[0063] Figure 25 It shows the method for... Figure 1 A block diagram illustrating the different steps involved in folding the blades of an aircraft's propulsion unit.

[0064] Figure 26 It shows the method for... Figure 1 A block diagram of the steps involved in the method of deploying the blades of the propulsion unit of an aircraft. Detailed Implementation

[0065] In the following description, elements with the same structure or similar function will be referred to by the same reference numerals.

[0066] In the remainder of the description, a longitudinal orientation will be used, as indicated by arrow "L" in the figure. This longitudinal orientation is locally associated with each propulsion unit within the propulsion unit. The longitudinal direction is oriented from front to back and is parallel to the axis of rotation of the propulsion unit's propeller.

[0067] A radial orientation should be used, which is orthogonal to the longitudinal direction and oriented from the inside out near the rotation axis of the propulsion unit. A tangential direction is also used, which is orthogonal to both the radial and longitudinal directions.

[0068] Figure 1 An aircraft 20 is shown, comprising a plurality of propeller propulsion units 22 manufactured according to the teachings of the present invention. This aircraft is a vertical takeoff and landing (VTOL) aircraft. In this respect, the aircraft 20 includes propulsion units 22 referred to as "lifting" units, which are designed to provide vertical thrust to the aircraft 20. These lifting propulsion units 22 are here arranged on the horizontal tail and fuselage of the aircraft 20. The aircraft 20 also includes propulsion units 22 referred to as traction units, which are designed to provide longitudinal thrust to enable the aircraft 20 to move forward. The traction propulsion units 22 are here arranged on the wings of the aircraft 20.

[0069] Alternatively, the invention applies to a typical aircraft, also referred to simply as "CTOL," meaning "Typical Takeoff and Landing." Therefore, the aircraft comprises only a traction propulsion unit.

[0070] The propulsion unit 22 has a similar design. Therefore, the following description of a single propulsion unit 22 applies to the other propulsion units 22. Figures 2 to 4As shown, the propulsion unit 22 includes a nacelle 24 designed for assembly to structural elements of the aircraft 20, such as wings or fuselage. The propulsion unit 22 is attached to the structural elements, for example, via struts (not shown). The nacelle 24 is equipped with an aerodynamic fairing.

[0071] The cabin 24 can be fixedly mounted on the structural element. When the structural element is fixed, the propulsion unit is fixed relative to the fuselage of the aircraft, thus forming a traction propulsion unit or a lifting propulsion unit. When the structural element is pivotally mounted relative to the fuselage of the aircraft, the propulsion unit alternately performs traction or lifting functions depending on the position of the structural element.

[0072] According to another variation of the invention, the nacelle is pivotally mounted on a structural element about a transverse axis, and the propulsion unit can alternately perform traction or lifting functions depending on the angular position of the nacelle on the structural element.

[0073] The propulsion unit 22 also includes a propeller 26, which is rotatably mounted in the nacelle 24 about a longitudinal axis of rotation “X” via a central hub 28. The front of the hub 28 typically covers the head 30 to improve the aerodynamic performance of the propulsion unit 22, particularly by reducing the drag of the propulsion unit.

[0074] The propeller 26 also includes a plurality of blades 32 extending along a main axis from a root 34 to a free end 36 called a blade tip, the blades 32 being linked to a hub 28 via the root. Each blade 32 has a profile extending from a leading edge to a trailing edge along the rotational orientation of the propeller. Each propeller 26 includes two blades 32. Of course, the invention is applicable to propellers comprising a large number of blades (e.g., three, four, or more blades).

[0075] The blades 32 are evenly distributed around the hub 28 at a defined angular pitch, such that the propeller 26 has rotational invariance about the given angular pitch about the axis of rotation “X”.

[0076] Each blade 32 can pivot relative to the hub 28 about a radial pitch axis “Y”, which, when the propeller 26 is deployed, substantially coincides with the main axis of the blade 32, as will be explained later. For this purpose, see Figures 5 to... Figure 9 As shown, the hub 28 includes as many blade tubes 38 as the propeller 26 includes blades 32. Each blade tube 38 is pivotally mounted on the hub 28 about a pitch axis “Y”. Each blade tube 38 is pivotally guided, for example, by rollers. Each blade tube 38 is in the form of a sleeve that receives the root 34 of the associated blade 32, such that the blade 32 is rotationally secured to the blade tube 38 about the pitch axis “Y”.

[0077] Therefore, blade 32 can be controlled at pitch angle position "β" around the pitch axis "Y" within a range extending between the first limiting pitch angle position "β1" and the second limiting pitch angle position "β2". The thrust generated by the rotation of propeller 26 is determined according to the propeller's pitch angle position "β". The range includes a folded pitch angle position "β0", for which blade 32 extends in a plane parallel to the displacement direction of aircraft 20 during cruise flight.

[0078] Therefore, as Figure 3 and Figure 4 As shown, for the lifting propulsion unit 22, the folding pitch angle position "β0" corresponds to the orientation of the blade 32 extending in a plane orthogonal to the rotation axis "X", also known as the zero load capacity pitch angle position.

[0079] On the contrary, such as Figures 11 to 13 and Figure 6 to Figure 9 As shown, for the traction propulsion unit 22, the fold pitch angle position "β0" corresponds to the orientation of the blade 32 extending in a plane parallel to the rotation axis "X", and the blade 32 is "feathered".

[0080] Furthermore, each propeller 26 in the propulsion unit 22 has the special feature of foldable blades 32. In particular, this makes it possible to improve the aerodynamic performance of the aircraft 20 under certain flight conditions, such as when the aircraft 20 is flying at a speed sufficient for the wings of the aircraft to provide load-bearing capacity alone, by folding the blades 32 of the propulsion unit 22.

[0081] Therefore, as shown in Figure 5 to... Figure 9 As shown, each blade 32 is pivotally mounted relative to its associated blade tube 38 about a folding axis “Z” that extends orthogonally to the radial pitch axis “Y” of the blade 32. Therefore, the folding axis “Z” rotates together with the blade tube 38 about the pitch axis “Y”. More specifically, the blade 32 is hinged to the blade tube 38 such that when the blade 32 occupies the folding pitch angle position “β0” of the blade, the folding axis “Z” is orthogonal to the rotation axis “X”.

[0082] Therefore, the blades 32 of the propeller 26 can be controlled between an extended position and a folded position. In the extended position, such as... Figure 2 , Figure 3 Figure 5, Figure 6 Figure 8 as well as Figures 10 to 12 As shown, the main axis of blade 32 extends approximately radially relative to the rotation axis "X", and in the folded position, as... Figure 4 Figure 7 Figure 9 as well as Figure 13As shown, the main axis of blade 32 extends approximately longitudinally parallel to the rotation axis "X". In the folded position, blade 32 is longitudinally received against nacelle 24.

[0083] Advantageously, such as Figures 2 to 4 as well as Figures 10 to 13 As shown, in order to reduce the drag of the propulsion unit 22 when the blades 32 are in the folded position, the nacelle 24 includes housings 39, each designed to accommodate a blade 32 of the propeller 26 at its folded pitch angle position "β0". Therefore, the blades 32 in the folded position are integrated into the fairing of the nacelle 24. For this purpose, the nacelle 24 includes as many housings 39 as the propeller 26 includes blades 32.

[0084] In order to control the pitch angle position "β" of the blade 32, the propulsion unit 22 includes a pitch device 40 (Figure 5 to 10). Figure 9 As can be seen in the image, the pitch device controls the pivoting of the blade tube 38 about the radial pitch axis "Y" relative to the hub 28 to determine the pitch angular position "β" of each blade 32. Here, the pitch device 40 enables all blades 32 of the propeller 26 to be controlled simultaneously to the same pitch angular position "β".

[0085] The pitch device 40 specifically includes a pitch actuator 42 comprising a control lever 44 that slides along a main axis coaxial with the rotation axis “X”. This pitch actuator 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 lever 44. Each blade 32 of the propeller 26 is connected to the plate 46 via a control link 48 having a first end hinged to the plate 46 and a second end hinged to the blade barrel 38 in an eccentric manner relative to the pitch axis “Y”, forming a link / crank connection between the plate 46 and the blade 32. Therefore, the pitch angular position “β” of the blade 32 varies with the axial position of the control lever 44.

[0086] Here, the pitch actuator 42 can be mounted in a fixed manner with respect to the propeller 26 in terms of rotation. The pitch actuator 42 is arranged, for example, inside the nose 30.

[0087] In a variant not shown in this invention, the pitch actuator is fixedly mounted relative to the nacelle, and only the control board 46 can be fixedly mounted to the propeller 26 in terms of rotation.

[0088] Advantageously, the propulsion unit 22 includes means for determining the pitch angular position "β". This means is, for example, a pitch sensor 45, which enables the detection of the longitudinal position of the rod 44. The pitch sensor 45 is, for example, an inductive sensor or any other known device, such as a mechanical copying device via a link.

[0089] Figure 5 to Figure 9 As shown, in order to control the blades 32 between their deployed and folded positions, the propulsion unit 22 includes a folding device 50, which includes an actuator 52 that controls the pivoting of each blade 32 relative to its blade barrel 38 between the deployed and folded positions. The folding actuator 52 is common to all blades 32, such that the blades 32 are controlled simultaneously between their deployed and folded positions. The folding actuator 52 is here formed by an electric actuator.

[0090] The folding device 50 includes a transmission 54 associated with each blade 32, which functions to transmit motion of the folding actuator 52 to the blade 32. Each transmission 54 includes a movable control member 56 mounted to be fixed in rotation with respect to the associated blade cylinder 38 and movable via the folding actuator 52. Each transmission 54 also includes a link 58 comprising a first end pivotally mounted eccentrically to the root 34 of the associated blade 32 relative to the folding axis "Z" and a second end pivotally mounted to the movable control member 56. The link 58 forms a link / crank connection with the blade root 34, which allows motion of the control member 56 to be converted into pivoting motion of the blade 32 about the folding axis "Z" of the blade. For this purpose, the two ends of the link 58 are mounted such that they can pivot about two axes parallel to the folding axis "Z".

[0091] according to Figure 8 and Figure 9 In the first embodiment of the folding device 50 shown, the control member 56 of each transmission device 54 is formed by a slider, which is mounted to slide radially in the associated blade cylinder 38 along the pitch axis "Y" between an inner limit position and an outer limit position, the inner limit position corresponding to one of the positions of the associated blade 32 and the outer limit position corresponding to another of the positions of the associated blade 32.

[0092] Figure 8 The external limit position of the control member 56 shown here corresponds to the deployed position of the associated blade 32, while Figure 9 The internal limit position of the control component shown corresponds to the folding position of the associated blade 32.

[0093] The sliding of the movable control member 56 is actuated here by a cam 60, which engages with the movable control member 56 via a cam follower 62. The cam follower 62 is mounted so that it is fixed in sliding relative to the control member 56 along the pitch axis "Y".

[0094] More specifically, the cam 60 is mounted to slide longitudinally along the axis of rotation “X” between a first forward longitudinal position and a second rearward longitudinal position, the first forward longitudinal position here corresponding to Figure 8 The unfolded position of the blade 32 shown here corresponds to the second rear longitudinal position. Figure 9 The folding position of the blade 32 is shown. For this purpose, the cam 60 has an inclined profile extending from a front end to a rear end, the front end being arranged radially close to the axis of rotation "X", and the rear end being arranged at a greater radial distance from the axis of rotation "X".

[0095] Cam 60 is mounted so that it is fixed in sliding relation to slide rod 64 of folding actuator 52. Since all blades 32 are simultaneously controlled by the same folding actuator 52, all cams 60 of each transmission in transmission 54 are attached to the same slide rod 64. Slide rod 64 is coaxial with the rotation axis "X".

[0096] The folding actuator 52 is mounted here so that it is fixed in rotation with the propeller 26 about the axis of rotation “X”.

[0097] Alternatively, the folding actuator is fixedly mounted relative to the nacelle. In this case, regardless of the angular position of the propeller about the axis of rotation, the cam can be formed by a truncated cone that allows the cam to work in conjunction with a cam follower, or the cam can be rotatably mounted relative to the nacelle about the axis of rotation to accompany the rotation of the propeller and remain coincident with the cam follower of the associated blade.

[0098] Furthermore, the cam follower 62 is formed here by rollers that rotate about an axis orthogonal to the rotation axis "X" and the pitch axis "Y". The rollers are, for example, diabolo-shaped rollers with two parallel rolling surfaces on the cam 60. Advantageously, the cam follower 62 is laterally guided relative to the cam 60 via a longitudinal guide 66, which is carried by the cam 60, during sliding. Regardless of the pitch angle position "β" of the associated blade 32, in order to keep the cam follower 62 engaged in the guide 66, the cam follower is rotatably mounted on the movable control member 56 about the pitch axis "Y". Therefore, the cam follower 62 is carried by a U-shaped clip 70, which is pivotally mounted, for example, on the inner end of the movable control member 56 via rolling bearings. Therefore, regardless of the pitch angle position "β" of the associated blade 32, the rotation axis of the cam follower 62 remains orthogonal to the rotation axis "X", while the movable control member 56 can freely and firmly pivot with the blade cylinder 28 about the pitch axis "Y".

[0099] According to a second embodiment of the folding device 50 shown in Figures 5 to 7, a movable control member 56 is formed by a crank that is pivotally mounted in the blade cylinder 38 about a control axis "Z1" parallel to the folding axis "Z" between a first limit angle position and a second limit angle position. The first limit angle position corresponds to one of the positions of the associated blades 32, and the second limit angle position corresponds to the other of the positions of the associated blades 32. The second end of the connecting rod 58 is eccentrically pivotally mounted on the control member 56 relative to the control axis "Z1" of the connecting rod.

[0100] The pivoting of the movable control member 58 is actuated here by a rack 68, which engages with the toothed section 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 and a second front longitudinal position, the first rear longitudinal position here corresponding to the unfolded position of the blade 32 as shown in Figures 5 and 6, and the second front longitudinal position here 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".

[0101] The rack 68 is mounted so as to be fixed in sliding relation to the sliding rod 64 of the folding actuator 52. Since all blades 32 are simultaneously controlled by the same folding actuator 52, all racks 68 of each transmission in the transmission 54 are attached to the same sliding rod 64. The sliding rod 64 is coaxial with the rotational axis "X". The folding actuator 52 is mounted so as to be fixed in rotational relation to the propeller 26 about the rotational axis "X".

[0102] Regardless of the embodiment of the folding device 50, it is advantageous to be able to check whether the blades 32 of the propeller 26 are in the deployed or folded position. Therefore, the folding device 50 is equipped with 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 arranged to detect that a movable element arranged on the transmission chain between the actuator 52 and the blades 32 occupies a specific position corresponding to the deployed position of the blades 32, while the second folding sensor 72B is arranged to detect that a movable element arranged on the transmission chain between the actuator 52 and the blades 32 occupies a specific position corresponding to the folded position of the blades 32. Here, the sensors 72A and 72B operate in an on / off manner, being activated only when the blades 32 occupy the associated deployed or folded position. These sensors are, for example, contact sensors 72A and 72B or sensing sensors 72A and 72B.

[0103] exist Figure 8 and Figure 9In the example shown, corresponding to the first embodiment of the folding device 50, the unfolding sensor 72A is activated by the free end of the control lever 64, while the folding sensor 72B is activated by the rear end of the cam 60.

[0104] In the example of the second embodiment corresponding to the folding device 50 shown in Figures 5 to 7, the unfolding sensor 72A is activated by the control member 56 at the angular position of the blade corresponding to the unfolded position of the blade 32, while the folding sensor 72B is activated by the front end of the control rod 64.

[0105] Furthermore, a mechanical locking device can be provided for the blade 32 in its deployed and folded positions. The locking device is, for example, formed by a latch 75 that engages with a movable element on a drive chain arranged between the actuator 52 and the blade 32. The latch 75 is arranged to prevent pivoting of the movable control member 56 when the blade 32 is in its deployed and folded positions. The latch 75 is operated by sliding of the rack 68.

[0106] On the other side of propulsion unit 22, such as Figures 14 to 16 As shown, the propulsion unit includes a rotor shaft 78, which is rotatably mounted in the nacelle 24 coaxial with the rotation axis "X" and is fixed to the propeller 26 in terms of rotation. The propulsion unit 22 also includes a propulsion device that drives the propeller 26 to rotate via the rotor shaft 78.

[0107] The propulsion unit 22 also includes an indexing device for stopping the propeller 26 about the axis of rotation "X" at at least one indexing angle position "θi", wherein the blades 32 in the deployed position coincide with the housing portion 34 of the nacelle 24. Due to the rotational invariance of the propeller 26, the propeller may have as many indexing angle positions "θi" as the blades 32.

[0108] The indexing device is formed by a stepper motor 82. In a known manner, this stepper motor 82 includes a rotor 84 rotatably mounted in a stator 86. The rotor 84 is coupled to the hub 28 of the propeller 26, while the stator 86 is fixed relative to the nacelle 24. The rotor 84 is mounted here such that it is rotationally fixed with respect to the rotor shaft 78 about the axis of rotation “X”.

[0109] The advantage of this stepper motor 82 is that it can slow down the propeller 26 by reversing its rotation using a resistance torque. Furthermore, the stepper motor enables the supply of motor torque to the propeller 26, allowing it to be driven with high precision to one of the propeller's angular resolutions "θi". Finally, the stator 86 of the stepper motor 82 is arranged such that each angular resolution "θi" of the propeller 26 is matched to a step of the stepper motor 82, which enables the propeller 26 to be prevented from rotating at each of the angular resolutions "θi".

[0110] exist Figure 14 In the example shown, the propulsion device includes an electric propulsion motor 80 separate from the stepper motor 82. In this case, the stepper motor 82 is inserted between the propulsion motor 80 and the propeller hub 28 in the drive train of the motor torque generated by the propulsion motor 80. The stepper motor 82 is here directly mounted on the rotor shaft 78, which is permanently coupled to the motor shaft of the propulsion motor 80.

[0111] exist Figure 15 In the example shown, the propulsion motor 80 is an internal combustion engine or heat engine, such as a turbine or alternating or rotary internal combustion engine. In this case, a stepper motor 82 is inserted between the propulsion motor 80 and the propeller hub 28 in the drive train of the motor torque generated by the propulsion motor 80. The stepper motor 82 is here directly mounted on the rotor shaft 78, which is controllably connected to the motor shaft of the propulsion motor 80 via a clutch 83.

[0112] exist Figure 16 In the example shown, the stepper motor 82 forms the propulsion device. Therefore, the propulsion device does not include any other electric motors besides the stepper motor 82.

[0113] according to Figure 17 In the first embodiment of the indexing device shown, the stepper motor 82 is a variable reluctance motor, also known as a "variable reluctance stepper motor" or "switched reluctance motor" (SRM). In this stepper motor 82, the rotor 84 is made of a ferromagnetic material. The rotor 84 is formed, for example, by a stack of soft iron sheets, or the rotor 84 is made of a single integral portion of magnets. The rotor 84 includes external teeth having an even number of teeth 88.

[0114] The stator 86 is typically made of a stack of ferromagnetic metal sheets. The stator 86 includes internal teeth with an even number of teeth 90. The stator includes multiple coils 92. The coils 92, arranged around two opposing teeth 90, are powered in series to form two electromagnets, the polarities of which are radially directed towards the rotor 84.

[0115] The number of teeth on the rotor 84 is different from the number of coils on the stator 86, which makes it possible to determine the number of pitches of the stepper motor 82, i.e. the number of angular positions, wherein the rotor 84 can be stably stopped by supplying power to the two opposing coils 92 of the rotor 86.

[0116] By sequentially supplying power to the opposing pairs of electric coils 92, the rotor 84 can be rotated by attracting the rotor teeth 88 that are closest to the alignment of the electric coils 92.

[0117] In the second embodiment of the indexing device, the stepper motor 82 is a permanent magnet motor, also known as a "permanent magnet stepper motor".

[0118] The stator 86 is substantially the same as the stator of the variable reluctance stepper motor described in the first embodiment. However, the rotor 84 includes at least one permanent magnet, rather than teeth, comprising a north pole "N" and a south pole "S", the polarity axis of the at least one permanent magnet being radially oriented. The polarities "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 arranged alternately around the rotation axis "X".

[0119] This stepper motor 82 typically has higher torque than a variable reluctance motor.

[0120] exist Figure 19 and Figure 20 In the third embodiment of the indexing device shown, the stepper motor 82 is a hybrid motor, also known as a "hybrid synchronous stepper motor".

[0121] The stator 86 is substantially the same as the stator of the variable reluctance stepper motor described in the first embodiment.

[0122] On the other hand, the rotor 84 is formed here by two gears 84A and 84B made of ferromagnetic material, both gears having external teeth equipped with the same even number of teeth 88A and 88B. The two gears 84A and 84B are coaxially mounted with an axially inserted permanent magnet 94, with the north pole contacting one gear 84A and the south pole contacting the other gear 84B.

[0123] Due to this configuration, tooth 88A of the first gear 84A forms the north pole, while tooth 88B of the second gear 88B forms the south pole. The teeth 88A of the first gear 84A and the teeth 88B of the second gear 84B are offset at an angle. Therefore, in an axial view, the tooth 88A forming the north pole is angled between the two teeth 88B forming the south pole.

[0124] The resulting rotor 84 can be rotatably received within the stator 86. Therefore, supplying power to some of the coils 92 of the stator 86 will attract the teeth 88A, 88B of the rotor 84, which are of opposite sign.

[0125] The advantage of this hybrid stepper motor 82 is that it has a large number of steps, similar to the variable reluctance motor 82 described in the first embodiment, while having high motor torque, similar to the permanent magnet motor 82 described in the second embodiment.

[0126] Alternatively, for this third embodiment, such as Figure 21 As shown, the stepper motor is an axial-flow stepper motor 82, wherein the rotor 84 is formed of a disk, and a magnet 94 with alternating polarities is provided on the outer periphery of the disk. The stator 86 also includes an electromagnet formed of an electric coil 92 wound around a core of ferromagnetic material to generate a magnetic field oriented parallel to the rotation axis "X" of the rotor 84 along the outer periphery of the rotor 84.

[0127] Regardless of the type of stepper motor 82 implemented, the propulsion unit 22 advantageously includes a device 96 for mechanically locking the propeller 26 about its axis of rotation "X" relative to the nacelle 24 at each of the propeller's angular positions "θi". Furthermore, the locking device 96 is designed such that the propeller 26 can only be locked at the angular positions "θi".

[0128] like Figure 22 and Figure 23 As shown, the locking device 96 includes a disc 98 mounted to be fixed in rotation with respect to the propeller 26. The disc 98 is mounted coaxially with the axis of rotation “X”. The disc 98 is radially defined by an annular outer peripheral edge 100 and axially defined by two circular surfaces.

[0129] The disk 98 includes at least one pawl 102, the at least one pawl corresponding to one of the division angle positions “θi”. The disk 98 here includes a single pawl 102.

[0130] Alternatively, disk 98 may include a plurality of pawls 102, each pawl corresponding to a division angular position “θi”. Therefore, disk 98 may include a plurality of pawls 102 equal to the number of division angular positions “θi”. In particular, this allows for faster access to the division angular position “θi” without requiring another full propeller rotation.

[0131] Pawl 102 can engage locking member 104, which is mounted to move relative to nacelle 24 between a non-active position and an active position. In the non-active position, disk 98 can rotate freely. In the active position, when propeller 26 occupies one of the propeller's angular positions "θi", locking member 98 can be received in pawl 102 to fix propeller 26 about the axis of rotation "X" relative to nacelle 24 in terms of rotation. Locking member 104 is moved, for example, by an electric actuator.

[0132] exist Figure 22 and Figure 23 In the illustrated embodiment, the pawl 102 is formed in the outer peripheral edge 100 of the disk 98. The locking member 104 is here mounted to slide radially relative to the cabin 24 between a non-active position and an active position. In the non-active position, such as... Figure 22 As shown, the locking member is spaced apart from the outer peripheral edge 100. In the movable position of the locking member, as... Figure 23 As shown, the locking member is radially displaced toward the rotation axis "X" to coincide with the pawl 102. When the propeller 26 does not occupy one of the pitch angle positions "θi" of the propeller, the locking member 104 cannot be controlled to the active position of the locking member because the locking member will abut against the outer peripheral edge 100 of the disk 98.

[0133] In a variant of the invention (not shown), the pawl is formed on an annular track on one of the circular surfaces of the disk. In this case, the locking member can be mounted to slide relative to the cabin in the longitudinal direction.

[0134] The locking sensor 105 is, for example, a contact sensor or a sensing sensor, which enables the detection of when the locking member 104 is in the active position of the locking member.

[0135] Advantageously, each pawl 102 has a cam track shape equipped with two ramps converging toward a bottom 106. The bottom 106 is arranged such that when the locking member 104 is received in the bottom of the pawl 102, the propeller 26 occupies exactly one of the angular positions “θi” of the propeller. The locking member 104 includes rollers 108 or sliding coatings at its free end, which can roll or slide against the ramps of the pawl 102. Thus, when the propeller 26 stops at an angular position defined within a tolerance range [θi-λ; θi+λ] on both sides of one of the angular positions “θi” of the propeller, the rollers 108 contact one of the ramps of the pawl 102 when the locking member 104 is controlled toward the moving position of the locking member. The locking member 104 provides sufficient force to rotate the propeller 26 by engaging with the ramp of the pawl 102, as the locking member moves toward the active position of the locking member until the roller 108 is at the bottom 106 of the pawl 102, so as to precisely position the propeller 26 at the propeller's pitch angle position "θi".

[0136] In order to perform such an operation, the propeller 26 is preferably not subjected to any electric motor torque or resistance torque, except for the torque caused by friction of the rotating guide member of the propeller 26.

[0137] In addition, such as Figures 14 to 16 As shown, in order to ensure that the propeller 26 occupies all the angular positions "θi" of the propeller, or at least occupies an angular position within a tolerance range [θi-λ; θi+λ] defined on both sides of one of the angular positions "θi" of the propeller, the propulsion unit 22 includes a sensor 110 for the angular position of the propeller 26 relative to the nacelle 24.

[0138] For example, the inductive sensor 110 enables the measurement of the propeller's angular position without contact. Thus, the first rotor element 111 is mounted to be fixed in rotation with respect to the propeller 26, while the second stator element 113 enables the detection of the rotor element's angular position via an electromagnetic device.

[0139] like Figure 24As shown, the sensing sensor 110 is a resolver, also known as an "RVDT" or "Rotary Variable Differential Transformer." As a known non-limiting example, this sensor 110 includes a main coil 112 carried by a stator element 113 and two secondary coils 114, 116. The main coil 112 is powered by an alternating voltage "Vr". The two secondary coils 114, 116 are offset by 90° about the rotation axis "X". The rotor element 111 includes a reference coil 118. The reference coil 118 and the main coil 112 form a resolver 120. The secondary coils 114, 116 are energized by the rotation of the reference coil 118 carried by the rotor element 111. The voltage value in each of the secondary coils 114, 116 uniquely enables the determination of the angular position of the rotor element 111 about the rotation axis "X".

[0140] Alternatively, the sensing sensor 110 is made of a product with the trade name "Inductosyn", which enables high angular accuracy.

[0141] Now refer to Figure 25 A method for folding the blades 32 of the propeller 26 of the propulsion unit 22 is described. This method is implemented by an electronic control unit (not shown). The method can be triggered automatically or by manual command from the pilot. At the start of the method, the blades 32 of the propeller 26 are as follows: Figure 2 , Figure 3 Figures 5 and 6 Figure 8 As shown in the diagram. Figure 2 As shown in Figure 5, blade 32 occupies a pitch angle position "β", which may differ from the folding pitch angle position "β0" of the blade. Furthermore, propeller 26 is typically driven to rotate by a propulsion device.

[0142] In the first step, “E1-1”, certain flight conditions of the aircraft are checked to obtain authorization to continue with the folding method of blade 32.

[0143] For example, when step "E1-1" is applied to the lifting propulsion unit 22, it checks whether the aircraft 20 has reached a speed sufficient to provide load-bearing capacity for the aircraft's wings without requiring lifting thrust from the lifting propulsion unit 22. For example, it checks whether the forward speed "V" of the aircraft 20 is significantly higher than a determined first threshold speed "V0". If the forward speed of the aircraft is significantly higher than the determined first threshold speed, step "E1-2" to stop the next propulsion is triggered; otherwise, the folding method is interrupted.

[0144] According to another example, when step "E1-1" is applied to the traction propulsion unit 22, it is checked whether the aircraft 20 has reached a sufficient speed for economical cruise flight without needing to use all traction propulsion units 22 simultaneously to provide thrust to the aircraft 20. For example, it is checked whether the forward velocity "V" of the aircraft 20 is significantly higher than a determined second threshold velocity "V1". The blades 32 of the traction propulsion unit 22 can also be folded when the aircraft 20 hovers, since the blades of the traction propulsion unit are no longer needed. Then it is checked whether the forward velocity of the aircraft 20 is zero. If one of these conditions is selected, the next step "E1-2" is triggered; otherwise, the folding method is interrupted.

[0145] During step “E1-2”, when propulsion is stopped, the electric motor torque supplied by the propulsion device is interrupted, allowing the propeller 26 to rotate freely, i.e., to rotate freely under the influence of the propeller’s inertia and any remaining aerodynamic forces that may be applied to the propeller blades.

[0146] When the propeller 26 is driven by the combustion propulsion motor 80, the clutch 83 is controlled to disengage, either at the start of step “E1-2” to stop the propulsion, or after a set time period determined for when the friction of the motor has begun to decelerate the propeller 26.

[0147] When the propeller 26 is driven by the electric propulsion motor 80, the propulsion motor 80 remains connected to the propeller 26 because the friction in such a motor is typically low.

[0148] At the end of step "E1-2" to stop propulsion, the pitch step "E1-3" is triggered. In this pitch step "E1-3", the blades 32 of the propeller 26 are controlled to the blade folding pitch angle position "β0", that is, controlled to the feathering position of the traction propulsion unit 22, as shown in Figure 6. Figure 8 and Figure 11 As shown, it may be controlled to the position where the lifting propulsion unit 22 has zero load-bearing capacity, such as... Figure 3 As shown.

[0149] Following pitch step "E1-3" is step "E1-4," during which the pitch angle position is checked. During this step, the pitch sensor 45 checks whether blade 32 occupies the folded pitch angle position "β0." A small offset "ε" of a few degrees from the folded pitch angle position "β0" along any orientation is generally tolerable. In this way, the pitch angle position "β" of blade 32 is checked more precisely to see if it falls within the pitch angle position range defined by the lower threshold "β0-ε" and the upper threshold "β0+ε". If the blade's pitch angle position falls within the range defined by the lower and upper thresholds, a method for stopping the rotation of propeller 26 at one of the propeller's division angle positions "θi" is triggered; otherwise, step "E1-3" is repeated.

[0150] The method for stopping the rotation of propeller 26 at one of the scaled angle positions "θi" of the propeller includes a step "E1-5" of checking the rotational speed "Nr", during which it is checked whether the rotational speed "Nr" of propeller 26 is less than or equal to a determined rotational speed "Nre".

[0151] If the rotational speed "Nr" of propeller 26 is higher than a certain rotational speed "Nre", braking step "E1-6" is triggered. During braking step "E1-6", stepper motor 82 is controlled to generate a resistance torque opposite to the free rotation of propeller 26 until the rotational speed "Nr" of propeller 26 is less than or equal to the predetermined rotational speed "Nre". The rotational speed "Nr" of propeller 26 is measured by a sensor (not shown), which is well-known and will not be described in detail below. At the end of braking step "E1-6", step "E1-5" of checking the rotational speed "Nr" is repeated.

[0152] If the rotational speed "Nr" of propeller 26 is less than or equal to a determined rotational speed "Nre", then step "E1-7" is triggered to stop the propeller at the division angle position. In this step, stepper motor 82 is controlled to stop propeller 26 at the division angle position "θi".

[0153] Following the blocking step "E1-7" is the step "E1-8" which checks the angular position "θ" of the propeller 26, measured by the sensing sensor 110. If the measured angular position "θ" of the propeller 26 is within the tolerance range [θi-λ; θi+λ] defined on both sides of the graduated angular position "θi", the locking step "E1-10" is triggered; otherwise, the adjustment step "E1-9" is triggered.

[0154] Adjustment step “E1-9” includes controlling stepper motor 82 to provide rotational torque that drives propeller 26 to rotate about the propeller’s rotation axis “X” toward one of the division angle positions “θi”.

[0155] During this adjustment step "E1-9", propeller 26 is driven to rotate only in one orientation. Therefore, when propeller 26 passes through the division angle position "θi", stepper motor 82 drives propeller 26 to rotate to the next division angle position "θi".

[0156] Alternatively, propeller 26 can be driven to rotate in two orientations by stepper motor 82, causing propeller 26 to rotate toward the nearest division angle position "θi".

[0157] After adjusting step "E1-9", repeat blocking step "E1-7".

[0158] Repeat adjustment steps “E1-9”, stop steps “E1-7”, and check steps “E1-8” until the angular position “θ” of propeller 26 is within the tolerance range [θi-λ; θi+λ] determined on both sides of one of the scale angle positions “θi”.

[0159] In the locking step "E1-10", as follows Figure 23 As shown, propeller 26 is rotatably locked relative to nacelle 24 at the propeller's angular resolution position "θi" by mechanical locking device 96. As previously explained, locking device 96 enables propeller 26 to be precisely brought into the propeller's angular resolution position "θi" by the engagement between locking member 104 and the ramp of pawl 102, the locking member being controlled to move toward the locking member.

[0160] At the end of locking step "E1-10", step "E1-11" for folding blade 32 is triggered. In this step, as previously described and as... Figure 4 Figure 7 Figure 9 and Figure 13 As shown, the blade 32 is folded into the corresponding receiving portion 39 of the blade by the folding device 50.

[0161] Then, in step "E1-12" of the folding inspection, sensor 72B is used to check whether blade 32 is folded correctly. Figure 25 As indicated by reference numeral "E1-14" in the attached diagram, if blade 32 is in the folded position, latch 75 is controlled in the final locking step "E1-13" to lock blade 32 in the folded position; otherwise, an incident is reported to the pilot of aircraft 20.

[0162] The aerodynamic design of the blades will take into account the requirement that the folded blades cannot be unintentionally deployed, that is, especially in the case that the blades are not effectively locked in the folded position. Under certain flight conditions that must be observed in such failure situations, the requirement that the folded blades cannot be unintentionally deployed will be taken into account.

[0163] Now refer to Figure 26 A method for deploying the blades 32 of the propulsion unit 22 is described. This method is implemented by an electronic control unit (not shown). The method can be triggered automatically or by manual command from the pilot.

[0164] In the first step “E2-1”, certain flight conditions of the aircraft 20 are checked, and these conditions must be met in order to obtain authorization for the continued deployment method of the blades 32.

[0165] For example, when step "E2-1" is applied to the lifting propulsion unit 22, it checks whether the speed of the aircraft 20 is decreasing and approaching a speed at which, without lifting thrust from the lifting propulsion unit 22, the aircraft's wings will no longer be sufficient to provide load-bearing capacity. For example, it checks whether the forward speed "V" of the aircraft 20 has decreased to a determined third threshold speed "V2". If the forward speed of the aircraft decreases to the determined third threshold speed, the subsequent deployment step "E2-2" is triggered; otherwise, the deployment method is not allowed.

[0166] According to another example, when step "E2-1" is applied to the traction propulsion unit 22, it is checked whether the speed of the aircraft 20 is below a sufficient economic cruise speed that requires all traction propulsion units 22 to be used simultaneously to provide thrust to the aircraft 20. For example, it is checked whether the forward velocity "V" of the aircraft 20 is significantly below a determined fourth threshold velocity "V3". The blades 32 of the traction propulsion unit 22 can also deploy as the aircraft 20 is about to leave hovering flight. If one of these conditions is selected, the next step "E2-2" is triggered; otherwise, the deployment method is interrupted.

[0167] In the unfolding step “E2-2”, the latch 75 is retracted and unlocked, and the folding actuator 50 is controlled to unfold the blade 32.

[0168] In the subsequent inspection step "E2-3" after deployment, the deployment sensor 72A checks whether the blade 32 is in the deployed position. If the blade is in the deployed position, the step "E2-4" to unlock the propeller 26 is triggered; otherwise, the deployment step "E2-2" is repeated.

[0169] In the unlocking step “E2-4”, the locking member 104 of the mechanical locking device 96 of the propeller 26 is controlled to the inactive position of the locking member to release the rotation of the propeller 26.

[0170] In step "E2-5" of the unlock check, the locking sensor 105 checks whether the propeller 26 is unlocked and rotating. If so, the deployment method is completed and the propulsion unit 22 is ready for use; otherwise, the unlock step "E2-4" is repeated.

Claims

1. A propulsion unit (22) having a propeller (26) and for use in an aircraft (20), the propulsion unit comprising: - Cabin (24), which is intended to be assembled onto the structural elements of the aircraft (20); - A propeller (26) rotatably mounted in the nacelle (24) about a longitudinal axis of rotation (X) via a hub (28), the propeller (26) comprising blades (32) evenly distributed around the hub (28), the blades (32) being pivotally mounted on the hub (28) between an extended position and a folded position via a root (34), in the extended position the blades extend radially relative to the longitudinal axis of rotation (X), and in the folded position the blades are longitudinally received against the nacelle (24); - A propulsion device that drives the propeller (26) to rotate; - Indexing device for stopping the propeller (26) relative to the nacelle (24) at at least one indexing angle position (θi). The indexing device is characterized by being formed by a stepper motor (82) including a rotor (84) connected to the hub (28) of the propeller (26).

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

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

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

5. The propulsion unit (22) according to any one of claims 1 to 4, characterized in that, The propulsion unit includes a mechanical locking device (96) for mechanically locking the propeller (26) at each of the angular positions (θi) of the propeller.

6. The propulsion unit (22) according to claim 5, characterized in that, The mechanical locking device (96) includes a disc (98) mounted to be fixed in rotation with respect to the propeller (26), the disc (98) including at least one pawl (102) capable of engaging a locking member (104) mounted to be movable relative to the nacelle (24) between an inactive position and an active position, in which the disc (98) is free to rotate, and in which the locking member (104) is received in the pawl (102) when the propeller (26) occupies at least one angular position (θi) so that the propeller (26) is fixed in rotation with respect to the nacelle (24).

7. The propulsion unit (22) according to claim 6, characterized in that, The pawl (102) has a cam track shape that allows the propeller (26) to rotate by cooperating with the locking member (104) as the locking member moves toward the movable position of the locking member, so as to precisely position the propeller (26) at the pitch angle position (θi) of the propeller.

8. The propulsion unit (22) according to any one of claims 1 to 4, characterized in that, The propulsion unit (22) includes a sensor (110) for sensing the angular position (θ) of the propeller (26) about its longitudinal axis of rotation (X).

9. The propulsion unit (22) according to any one of claims 1 to 4, characterized in that, The stepper motor (82) forms the propulsion device.

10. The propulsion unit (22) according to any one of claims 1 to 4, characterized in that, The propulsion device includes a propulsion motor (80) separate from the stepper motor (82), the stepper motor (82) being inserted between the hub (28) of the propeller (26) and the propulsion motor (80) in a motor torque transmission chain.

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

12. The propulsion unit (22) according to any one of claims 1 to 4, characterized in that, The cabin (24) is fixedly mounted on the structural element of the aircraft (20).

13. The propulsion unit (22) according to any one of claims 1 to 4, characterized in that, The cabin (24) is pivotally mounted on the structural element of the aircraft (20).

14. A method for stopping the rotation of a propeller (26) belonging to a propulsion unit (22) according to any one of claims 1 to 13 at a division angle position (θi), characterized in that, The method includes: - The initial step of stopping propulsion (E1-2), during which the electric motor torque supplied by the propulsion device is interrupted, allowing the propeller (26) to rotate freely; - The stopping step (E1-7) is to stop the propeller (26) at the division angle position (θi) by means of the stepper motor (82).

15. The method according to claim 14, characterized in that, When the propeller (26) rotates at a speed (Nr) greater than the determined speed (Nre) at the end of the preliminary step (E1-2) of stopping propulsion, the stopping step (E1-7) is preceded by a braking step (E1-6), during which the stepper motor (82) is controlled to generate a resistance torque opposite to the free rotation of the propeller (26) until the speed (Nr) of the propeller (26) is less than or equal to the determined speed (Nre).

16. The method according to claim 15, characterized in that, The propulsion unit (22) includes a sensing sensor (110) for the angular position (θ) of the propeller (26) about its longitudinal axis of rotation (X). The method includes an inspection step (E1-8) for checking the angular position (θ) of the propeller (26), which is triggered at the end of the blocking step (E1-7), and during the inspection step, the angular position (θ) of the propeller (26) is measured by the sensing sensor (110).

17. The method according to claim 16, characterized in that, The method includes an adjustment step (E1-9) to adjust the angular position (θ) of the propeller (26), the adjustment step being triggered at the end of the inspection step (E1-8), and the adjustment step including controlling the stepper motor (82) to provide rotational torque that drives the propeller (26) to rotate toward the division angular position (θi), and repeating the blocking step (E1-7) after the adjustment step (E1-9) to fix the propeller (26) at the division angular position (θi) of the propeller by means of the stepper motor (82).

18. The method according to claim 16, characterized in that, The propulsion unit includes a mechanical locking device (96) for mechanically locking the propeller (26) at each of the angular positions (θi) of the propeller. A locking step (E1-10) for mechanically locking the propeller (26) is triggered when the angular position (θ) of the propeller (26) substantially coincides with the angular position (θi) in the inspection step (E1-8). During the locking step, the propeller (26) is rotatably locked relative to the nacelle (24) by the mechanical locking device (96).

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