Propulsion systems for aircraft

Abstract

The invention relates to a propulsion system (1, 1') for an aircraft, comprising a rotor (2) and a nacelle fairing (3), the nacelle fairing extending around the rotor relative to an axis (X) and comprising an upstream portion (10) forming an inlet section (BA) of the nacelle fairing (3) and a downstream end (21) of the downstream section forming an outlet section (BF) of the nacelle fairing (3); characterized in that the downstream portion (20) has a radial inner wall (20a) and a radial outer wall (20b) both made of deformable shape memory material, and the downstream end (21) comprises pneumatic or hydraulic actuators (23, 23') extending around the axis (X) in different consecutive angular sectors, each actuator being independently actuatable and configured to deform, under a predetermined command pressure, in a direction extending radially relative to the axis (X) and angularly centered relative to the angular sector.

Description

Technical Field

[0001] The present invention relates to the field of propulsion systems for aircraft. In particular, the present invention relates to a propulsion system capable of providing a lateral thrust component.

[0002] The invention also relates to an aircraft comprising such a propulsion system. Background Art

[0003] The background art includes in particular documents US 2011 / 030380 A1, EP 2184481 A2, US 5328098 A1 and FR 2310471 A1.

[0004] A propulsion system for an aircraft includes at least one rotor or propeller including a plurality of blades mounted on a rotating shaft.

[0005] There are aircraft, and in particular Vertical Take-Off and Landing (VTOL) aircraft, having a single rotor when the propulsion system of the aircraft comprises only one rotor, or having counter-rotating rotors when the propulsion system of the aircraft comprises a paired combination of rotors that rotate in opposite directions.

[0006] These propulsion systems have either a shrouded rotor (which is then surrounded by an annular nacelle fairing) or a free rotor, the propulsion system and in particular the rotor (free or shrouded) being mountable on a pivot axis, allowing the propulsion system and therefore the rotor to be oriented between a vertical position and a horizontal position, for example a vertical orientation for vertical take-off or vertical landing and a horizontal orientation for forward flight or airplane flight mode.

[0007] Shrouded rotors offer several attractive advantages, such as:

[0008] - The rotor's acoustic signature is significantly reduced at direct exhaust;

[0009] - Protect the rotor blades from surrounding obstacles;

[0010] - Improved rotor performance, especially when the vehicle is in mid-air or moving forward at low speeds.

[0011] However, VTOL aircraft with shrouded rotors do not have the same maneuverability as conventional helicopters, particularly when airborne.

[0012] For conventional helicopters, in the X, Y, Z aviation standard reference trihedron, altitude correction and position correction can be performed in the following ways:

[0013] - correction around the roll axis X (the axis of rotation of the helicopter around its longitudinal axis) by the action of the cyclic pitch to the left or right (here the orientation of the thrust acting on the rotor in a plane perpendicular to the axis X);

[0014] - correction about the pitch axis Y (the axis of the helicopter about its transverse axis) by the action of the cyclic pitch forwards (nose down) or backwards (nose up) (here the orientation of the thrust acting on the rotor in a plane perpendicular to the Y axis);

[0015] - by correcting the action of the rudder (thrust acting on the anti-torque rotor of the helicopter) about the yaw axis Z (the axis of rotation of the helicopter in a horizontal plane around its vertical axis);

[0016] - correction of the longitudinal translation along the axis X of the reference trihedron of aviation standards (longitudinal axis) by command of the cyclic / collective pitch (orientation of the thrust acting on the rotor in this case forward or backward);

[0017] - correction of the lateral translation according to the axis Y of the reference trihedron of aviation standards (transverse axis) by command of the cyclic / collective pitch (orientation of the thrust acting on the rotor to the right or to the left);

[0018] - Correction of the vertical translation along the reference axis Z by means of the command of the collective pitch up and down (thrust acting on the rotor, setting the pitch: command to pull upward).

[0019] Of course, coordinated corrections to collective pitch and rudder, known to the pilot, are needed to counter the induced effects of the loss of lift component as well as the induced effects of torque effects.

[0020] For VTOL aircraft with shrouded rotors, positioning corrections in airborne flight or corrections to enable gusts to be counteracted are often complicated and make the passengers in the aircraft uncomfortable during flight.

[0021] For example, in the case of a quadrotor aircraft (i.e., an aircraft with four rotors), in order to make a correction in the direction of a reference axis X, it is necessary to tilt the aircraft forward about a reference axis Y (along the pitch axis), then make corrections to the position reached (e.g., to counteract gusts of wind), and quickly return to a neutral position (referred to as a "flat position"). Similarly, in order to make a correction in the direction of the reference axis Y, it is necessary to tilt (i.e., roll) the aircraft toward and about the reference axis X (along the roll axis), then make corrections to the position reached, and quickly return to a neutral position. Using such a quadrotor aircraft, when transporting passengers, passengers may experience forward / backward sway and / or right / left sway.

[0022] A gas turbine engine is proposed comprising a two-dimensional nozzle comprising a flexible panel adapted to change position under the action of a cylinder in order to condition the exhaust gas of the engine.

[0023] Gas turbine engines comprising variable geometry nozzles have also been proposed, such that the exit surface area of ​​the nozzle can be varied.

[0024] These proposed solutions therefore propose nozzles implementing two-dimensional vector thrust technology.

[0025] However, none of these proposed solutions proposes implementing three-dimensional thrust vectoring technology in the nacelle fairing of the propulsion system, in particular in VTOL mode with a rotor, so as to guide the airflow generated by said rotor.

[0026] Therefore, a simple and effective solution is needed to address the above problems.

[0027] One object of the present invention is to provide a solution making it possible to improve the maneuverability of a VTOL aircraft while reducing the impact of the weight and aerodynamic penalties associated with flight commands.

[0028] In particular, the present invention proposes to improve the maneuverability of a VTOL aircraft by providing a propulsion system capable of providing a thrust component lateral to the rotor axis. Summary of the invention

[0029] To this end, the present invention relates to a propulsion system for an aircraft, the propulsion system comprising at least one rotor and a nacelle fairing, the nacelle fairing extending around the at least one rotor relative to the rotation axis of the rotor, the nacelle fairing comprising an upstream section and a downstream section, the upstream section forming an inlet cross section of the nacelle fairing, the downstream end of the downstream section forming an outlet cross section of the nacelle fairing; characterized in that the downstream section comprises a radial inner wall and a radial outer wall made of a deformable shape memory material, and the downstream end forming the outlet cross section comprises a plurality of pneumatic or hydraulic actuators, the actuators extending around the rotation axis in different continuous angular sectors, each actuator being actuable independently of the other actuators and being configured to deform under the action of a predetermined command pressure in a direction radial to the rotation axis and angularly centered with respect to the angular sector over which the actuator extends.

[0030] The propulsion system according to the invention may have a single rotor or counter-rotating rotors mounted in a fixed or pivoting nacelle with a through or offset pivot axis.

[0031] According to the invention, a fairing is made of a semi-deformable shape memory material and a plurality of pneumatic or hydraulic actuators at the air outlet of the fairing, which are configured to automatically change the shape of the nacelle and thus the orientation of the airflow at the outlet of the nacelle in order to maneuver the aircraft on which said nacelle is installed.

[0032] Advantageously, the profile of the fairing has a semi-rigid downstream portion, the size and shape of the outlet cross-section of the trailing edge of which can be modified so that the outlet cross-section of the trailing edge can be laterally oriented under the action of a controlled device to form a current tube that generates a thrust with a lateral component (known as vector thrust or directional thrust).

[0033] The propulsion system according to the invention thus makes it possible to improve the maneuverability of the aircraft on which it is installed, in particular during maneuvers at low forward speeds, such as during take-off and landing, while minimizing the noise pollution caused by the rotor of the propulsion system and ensuring the safety of this rotor through the presence of the nacelle fairing.

[0034] In fact, the shape of the fairing is constantly adjusted according to the deflection of the controlled thrust to obtain the precise position of the aircraft. Therefore, the profile of the fairing can be oriented laterally according to the mechanical constraints of the flight sought in VTOL mode, so as to generate a thrust component perpendicular to the rotor axis.

[0035] Advantageously, the pneumatic actuator system can be locked, for example by means of a controlled opening / closing valve, once the command pressure has been established, and thus the pneumatic actuator system does not consume energy once actuated.

[0036] During the flight phase in airplane mode, the actuator systems useful during the forward phase at low speed can be deactivated.

[0037] Each actuator may have a substantially ring segment shape.The actuators may extend in different consecutive angular sectors around said axis of rotation such that the group of actuators has a substantially torus shape.

[0038] According to one embodiment, each actuator is made of a radially reinforced elastic material comprising fibers.

[0039] According to another embodiment, each actuator comprises a bladder in the form of a generally annular segment made of a flexible material, the bladder being wrapped in a coil spring. Each actuator may be embedded in a rigid support at one end. In particular, each coil spring may be embedded in a rigid support at one end, and each bladder may be embedded in a rigid support at one end. Each bladder may include an inlet valve configured to receive a predetermined command pressure. The inlet valve may be a solenoid valve.

[0040] The plurality of actuators may include two actuators having a substantially semi-annular shape.

[0041] Advantageously, the propulsion system further comprises a reinforcing bridge connecting the radially inner wall and the radially outer wall of the downstream section and making it possible to ensure that the distance between the radially inner wall and the radially outer wall of the downstream section is substantially constant.

[0042] The nacelle fairing may include an upstream section forming an inlet cross section of the nacelle fairing and a middle section connecting the upstream section and the downstream section.

[0043] Advantageously, the middle section is rigid and connected to the engine of the propulsion system by at least one rod. This provides a rigid structure for the nacelle fairing of the propulsion system which ensures a shielding function.

[0044] The invention also relates to an aircraft, characterized in that it comprises at least one propulsion system having at least one of the above-mentioned characteristics, which is mounted so as to be pivoted on the aircraft by means of a pivot axis offset from or passing through the rotor. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The invention will be better understood and other details, features and advantages of the invention will become more apparent by reading the following description of non-limiting examples with reference to the accompanying drawings, in which:

[0046] [ Figure 1A ] Figure 1A is a schematic perspective view of a first embodiment of a propulsion system having a nacelle mounted on an offset pivot axis, the propulsion system being in a horizontal position;

[0047] [ Figure 1B ] Figure 1B is similar to Figure 1A , showing the propulsion system in a vertical position;

[0048] [ Figure 1C ] Figure 1C is a schematic perspective view of a second embodiment of a propulsion system having a nacelle mounted on a through-pivot axis, the propulsion system being in a horizontal position;

[0049] [ Figure 2 ] Figure 2 is a schematic view in longitudinal cross section of a propulsion system according to the invention, the downstream section of the nacelle fairing of the propulsion system being in a symmetrical thrust mode, i.e. an axial thrust mode;

[0050] [ Figure 3-Figure 4 ] Figure 3 and Figure 4 is a propulsion system according to the invention similar to Figure 2 A view of the propulsion system with a downstream section of the nacelle fairing in an asymmetric thrust mode;

[0051] [ Figure 5A-Figure 5B ] Figure 5A and Figure 5B are respectively a schematic rear view and a side view of an embodiment of a semi-annular actuator according to the present invention in an axial thrust mode;

[0052] [ Figure 6A-6B ] Fig. 6A and Figure 6B are respectively a schematic rear view and a side view of an embodiment of a semi-annular actuator according to the present invention in an asymmetric thrust mode;

[0053] [ Figure 7A-7B ] Fig. 7A and Figure 7B Schematic rear and side views of another embodiment of the semi-annular actuator according to the present invention in an asymmetric thrust mode, respectively.

[0054] Elements having the same function in different exemplary embodiments are provided with the same reference numerals in the figures. DETAILED DESCRIPTION

[0055] In the present disclosure, the terms "axial", "inner" and "outer" are used with reference to the axis of rotation of the propulsion system according to the present invention.

[0056] The propulsion system typically includes:

[0057] - Engine room;

[0058] - engines and command and control systems for such engines; and

[0059] - in the case of propeller or rotor propulsion, the propeller or one or more rotors of the propulsion system.

[0060] The nacelle is the element that integrates the engine with the aircraft and consists of the following parts:

[0061] - nacelle fairing (making it possible to cover the engine, cover the rotor, capture the airflow during the operation of the aircraft, generate thrust effect, reverse the thrust on the propulsion system, etc.);

[0062] - Equipment installed on the engine (such as the Engine Build-Up (EBU) unit, including the electrical network, hydraulic network and pneumatic network); and

[0063] - Systems for attachment to aircraft.

[0064] Figure 1A and Figure 1B A first embodiment of a propulsion system 1 for an aircraft according to the invention is shown in a simplified manner.

[0065] Here, the propulsion system 1 comprises at least one rotor 2 and a nacelle fairing 3, which extends around the at least one rotor 2 relative to the rotation axis X of the rotor 2. The fairing 3 advantageously acts as a sound barrier due to its shape and material. The propulsion system can be fixedly mounted on the aircraft. The propulsion system 1 can also be mounted on a pivot axis 4, offset from the rotation axis X of the rotor 2. The pivot axis 4 is attached to the propulsion system 1 on the one hand and to the aircraft on the other hand by any means and enables the propulsion system to be oriented on the aircraft so that the propulsion system can be moved according to arrow F1 by known actuators such as Figure 1A The horizontal position shown and Figure 1B Between the vertical positions shown there is a tilt about the pivot axis 4. This tilt enables the aircraft to switch from a conventional aircraft mode to a VTOL mode or a helicopter mode.

[0066] The rotors 2 of the propulsion system 1 are connected to the aircraft by means of a rod 5 supporting an engine 6, for example an electric motor, which drives the rotors 2 in rotation in a manner known per se via a power shaft. According to the example illustrated in a non-limiting manner, each rotor 2 comprises two blades 7.

[0067] Figure 1C A second embodiment of a propulsion system 1 ' for an aircraft according to the invention is shown, in which the propulsion system 1 ' can be mounted on a pivot axis 4' which passes through the rotor 2 perpendicularly to the axis of rotation X of the rotor 2. The rotor 2 of the propulsion system 1 ' is connected to the aircraft via a rod 5 supporting an engine 6 (for example an electric motor) which drives the rotor 2 in rotation in a manner known per se via a power shaft. According to this embodiment, the rod 5 of the rotor 2 coincides with the pivot axis 4'.

[0068] Reference Figures 2 to 4 According to the present invention, the nacelle fairing 3 of the propulsion system 1, 1' comprises:

[0069] - an upstream section 10;

[0070] - a downstream section 20; and

[0071] An intermediate section 30 , which connects the upstream section 10 and the downstream section 20 .

[0072] The upstream section 10 forms an inlet cross section (or in other words, a leading edge) BA or an air inlet of the nacelle fairing 3 .

[0073] The upstream section 10 is made of a material that can withstand temperatures that make it suitable for anti-icing when supplied with hot air.

[0074] The middle section 30 is rigid. For example, it is made of an aluminum alloy, a titanium alloy filled with 6% aluminum and 4% vanadium (TA6V) or a carbon fiber composite material with an organic matrix. Advantageously, the middle section 30 is connected to the engine 6 of the propulsion system 1, 1 ' by at least one rod 5, preferably by two rods 5, to mechanically assemble the nacelle fairing 3 to the engine 6 of the propulsion system 1, 1 '. Thus, the middle section 30 confers a shielding function to the propulsion system 1, 1 ' by its material and configuration.

[0075] The downstream end 21 of the downstream section 20 forms the outlet cross section (or in other words the trailing edge) BF or the air outlet of the nacelle fairing 3 .

[0076] The downstream section 20 comprises a radially inner wall 20a and a radially outer wall 20b. The radially inner wall 20a and the radially outer wall 20b of the downstream section 20 provide not only a structural function of the downstream section 20 but also an aerodynamic function.

[0077] The radial inner wall 20a and the radial outer wall 20b of the downstream section 20 are made of a semi-rigid deformable shape memory material. In other words, the material constituting the radial inner wall 20a and the radial outer wall 20b of the downstream section 20 is both rigid so that the downstream section 20 has a structural shape, and flexible so that the downstream section 20 has deformability. Therefore, the radial inner wall 20a and the radial outer wall 20b of the downstream section 20 are made of a material that can react under the action of an actuator as described below. When the radial inner wall 20a and the radial outer wall 20b of the downstream section 20 are excited by one or more actuators, the wall is deformed, and when the excitation stress of the one or more actuators stops, the wall returns to its original shape. For example, the radial inner wall 20a and the radial outer wall 20b are made of a composite material or a nickel-titanium alloy (also known as "KiOkAlloy") such as NiTiNol or NiTiCu.

[0078] The shape memory material constituting the radially inner wall 20a and the radially outer wall 20b is fail-safe, i.e. its rest position (in other words, when no actuator acts on the shape memory material to deform it) corresponds to the natural storage geometry of said material or a longer period of use. Thus, in the event of a failure of an actuator, the shape memory material will return to its natural rest shape and the nacelle fairing 3 will return to a safe geometry ensuring axial thrust, in order to ensure the correct operation of the propulsion system 1, 1' of the aircraft.

[0079] The radially inner wall 20a and the radially outer wall 20b may also have a thickness that varies in the axial direction and in the azimuth in the vicinity of the reinforcing bridge 22, so as to locally modify the elasticity of the structure. The mechanical properties of the shape memory material constituting the radially inner wall 20a and the radially outer wall 20b may also be locally optimized according to the desired local properties along the downstream section 20. Thus, it is conceivable that the downstream section 20 is composed of a plurality of sections of different materials.

[0080] The downstream section 20 is made of a deformable semi-rigid material which guarantees a rigid structural shape to avoid collapse of the deformable semi-rigid material at rest and under the effect of the airflow during operation of the propulsion system 1, 1', thus enabling the nacelle fairing 3 to maintain a uniform aerodynamic profile of its outlet cross section BF. Advantageously, the downstream end 21 of the downstream section 20 can be made of an orthotropic material having a suitable elastic modulus.

[0081] The local elasticity of the radially inner wall 20a and the radially outer wall 20b of the downstream section 20 may vary according to the thickness or the mechanical properties of the shape memory material, depending on the desired local deflection.

[0082] Furthermore, in order to ensure that the distance between the radially inner wall 20a and the radially outer wall 20b of the downstream section 20 is substantially constant, reinforcing bridges 22 are provided at regular angular intervals between these walls.

[0083] One object of the present invention is to be able to benefit from a nacelle fairing 3 of a propulsion system 1 , 1 ′, the outlet cross section BF of which and the shape of this outlet cross section can be varied in order to direct the thrust of said propulsion system.

[0084] The downstream section 20 therefore comprises means making it possible to vary the shape of the outlet cross section BF.

[0085] To this end, the downstream end 21 of the downstream section 20, which forms the outlet cross section BF of the nacelle fairing 3, comprises a plurality of pneumatic or hydraulic actuators 23, 23'. Each actuator 23, 23' has a substantially annular segment shape. The actuators 23, 23' extend in different consecutive angular sectors around the axis of rotation X, so that the group of actuators 23, 23' has a substantially torus shape. Thus, the downstream end 21 of the downstream section 20 is divided into annular segments, each of which is associated with an actuator of substantially annular segment shape.

[0086] Each actuator 23, 23' is actuatable independently of the other actuators and is configured to deform, under a predetermined command pressure, in a direction radial to the axis of rotation X and angularly centered with respect to the angular sector over which it extends. Thus, each actuator 23, 23' is configured to deform radially with respect to the axis X the annular segment of the downstream end of the downstream segment with which it is associated.

[0087] To this end, each actuator 23, 23' is connected to an automatic pneumatic or hydraulic device (not shown) known per se, which enables fluid to be introduced into or extracted from this actuator 23, 23', in order to obtain the desired lateral thrust component, by applying a command pressure adjusted according to the desired configuration of the nacelle fairing 3. In particular, the automatic pneumatic or hydraulic device sends or extracts fluid in an actuator 23, 23' independently of the other actuators.

[0088] Preferably and advantageously, each actuator 23, 23' is made of a radially reinforced elastic material, for example containing fibers.For example, each actuator is made of a polymer material incorporating external devices or inclusions that reinforce the actuator in radial direction.

[0089] according to FIG. 5A to FIG. 7B In the embodiment shown, the propulsion system 1, 1 ' comprises two actuators 23, 23' of semi-annular shape: a first actuator extending in a first part (upper part in the figure) of the downstream end 21 of the downstream section 20, and a second actuator extending in a second part (lower part in the figure) of the downstream end 21 of the downstream section 20. In the figure, the actuators are shown in the upper (top) part and in the lower (bottom) part of the downstream section, but the actuators can of course be integrated in different angular sectors (for example on the right and on the left in the figure), depending on the orientation of the propulsion system when it is installed on the aircraft. The actuators 23, 23' are arranged to form a torus. Of course, the invention is not limited to this embodiment, and the propulsion system 1, 1 'can comprise more actuators.

[0090] In these FIG. 5A to FIG. 7B In the embodiment, each actuator 23, 23' includes a bladder 23a, 23a' of a roughly semi-annular shape made of a flexible material, and the bladder is wrapped in a coil spring 23b, 23b'. Each coil spring 23b, 23b' is embedded in a rigid support 25 having a structural function at one end. Therefore, each coil spring 23b, 23b' is kept integral with the rigid support 25. The function of the coil spring 23b, 23b' is to limit the radial expansion amount of the cross section of the bladder 23a, 23a'. Each bladder 23a, 23a' is connected to the rigid support 25 at each of its ends. Therefore, the actuator 23, 23' is firmly assembled to the rigid support 25. Another embodiment may be to use an orthotropic material, the elastic modulus of which in the radial direction is greater than the elastic modulus in the azimuthal direction.

[0091] Each bladder 23a, 23a' comprises an inlet valve 27, 27' configured to receive a predetermined command pressure. The inlet valve 27, 27' may be, for example, a solenoid valve.

[0092] Each actuator 23, 23' is configured so that when the pressure to which it is subjected increases, this causes a local deformation of the annulus formed by the group of actuators, i.e. a radial and local expansion E. The outlet cross section of the fairing is therefore asymmetrical, the shape of which is determined by the mechanical characteristics of the structure subjected to the thrust of the bladders 23a, 23a'. When the actuators 23, 23' are actuated, the dimension of the annular cross section of the actuated actuator along the axis X varies very little compared to the radial expansion, with the result that a local deflection of the structure is produced on one side of the actuated actuator.

[0093] Figure 2 A propulsion system 1 , 1 ′ according to the invention is shown, wherein the nacelle fairing 3 is shown in a neutral position, ie with pure axial thrust. Figure 5A and Figure 5B The actuators 23, 23' are shown in this neutral position. Each actuator 23, 23' is subjected to a command pressure substantially equal to the ambient pressure between the radially inner wall 20a and the radially outer wall 20b of the downstream section 20 of the nacelle fairing 3. The local deformation of the actuators 23, 23' is then zero. The group of actuators 23, 23' forms an annulus centered on the axis X.

[0094] Figure 3 A propulsion system 1 , 1 ′ according to the invention is shown, wherein the nacelle fairing 3 is shown in a position in which the airflow is turned upwards. Fig. 6A and Figure 6B The actuators 23, 23' are shown in this asymmetric downward thrust position. The command to produce a lateral downward displacement of the nacelle requires that the outlet cross section of the nacelle be deformed upward to produce a force directed downward from the top. The actuator 23 is operated to deform the bladder 23a radially. A pressure set point is calculated based on the flight command input and then sent to the bladder inlet through valve 27. The bladder 23a is radially centered in a radial direction ( ) relative to the axis of rotation X and relative to the angular sector α. Figure 3 and Fig. 6A The actuator 23 is deformed on the angular sector, i.e., on the arrow F2 in FIG. Fig. 6A20 and 23 '. The actuator 23 is thus subjected to a command pressure which is greater than the ambient pressure between the radial inner wall 20a and the radial outer wall 20b of the downstream section 20 of the nacelle fairing 3. On the other hand, the actuator 23' is subjected to a command pressure which is substantially equal to the ambient pressure between the radial inner wall 20a and the radial outer wall 20b of the downstream section 20 of the nacelle fairing 3. In other words, the actuator 23' is in a stationary position. Therefore, the outer radius R23' of the semi-annular surface formed by the actuator 23' is equal to half of the radial dimension D23 of the group of actuators 23, 23' at rest. However, the radial dimension of the semi-annular surface formed by the actuator 23 is equal to the sum of the outer radius R23 of the actuator 23 at rest and the expansion amount E. The actuator 23' maintains its semi-annular shape when stationary, whereas the actuator 23 deforms when actuated (e.g., as Fig. 6A The group of actuators 23, 23' forms a non-axisymmetric ring, a part of which (here the upper part) has a radial deformation.

[0095] Figure 4 A propulsion system 1 , 1 ′ according to the invention is shown, wherein the nacelle fairing 3 is shown in a position where the airflow is deflected downwards. Fig. 7A and Figure 7B The actuators 23, 23' are shown in this asymmetric upward thrust position. The command to produce a lateral upward displacement of the nacelle requires a downward deformation of the nacelle outlet cross section to produce a force directed upward from the bottom. The actuator 23' is operated to deform the bladder 23a' radially. A pressure set point is calculated based on the flight command input and then sent to the bladder inlet through the valve 27'. The bladder 23a' is radially centered in a radial direction ( ) with respect to the axis of rotation X and with respect to the angular sector β. Figure 4 and Fig. 7A The actuator 23' extends on the angular sector, that is, on the arrow F3 in FIG. Fig. 7A 23' extends vertically downward. Therefore, the command pressure to which the actuator 23' is subjected is greater than the ambient pressure between the radial inner wall 20a and the radial outer wall 20b of the downstream section 20 of the nacelle fairing 3. Furthermore, the command pressure to which the actuator 23 is subjected is substantially equal to the ambient pressure between the radial inner wall 20a and the radial outer wall 20b of the downstream section 20 of the nacelle fairing 3. In other words, the actuator 23 is in a stationary position. Therefore, the outer radius R23 of the semi-annular surface formed by the actuator 23 is equal to half of the radial dimension D23 of the group of actuators 23, 23' at rest. However, the radial dimension of the semi-annular surface formed by the actuator 23' is equal to the sum of the outer radius R23' of the actuator 23' at rest and the expansion amount E. The actuator 23 maintains its semi-annular shape when stationary, while the actuator 23' deforms when actuated (for example, as Fig. 7AThe group of actuators 23, 23' forms a non-axisymmetric ring, a part of which (here the lower part) has a radial deformation.

[0096] The gradual increase of the command pressure caused by the automatic pneumatic or hydraulic device gradually changes the shape and size of the outlet cross section BF. In particular, the radial inner wall 20a and the radial outer wall 20b made of deformable shape memory material of the downstream section 20 associated with the actuator are deformed radially and locally relative to the axis X. This, in turn, changes the size and shape of the outlet cross section BF, which therefore changes from as follows: Figure 2 The minimum radial dimension D23 and the circular shape in the axial thrust mode configuration shown in FIG. 1 are changed to a radial dimension D23+E greater than the minimum radial dimension D23, as shown in FIG. Figure 3 and Figure 4 In the asymmetric thrust mode configuration shown, the outlet cross section BF is deformed in at least one radial direction.

[0097] Similarly, a gradual reduction in command pressure caused by an automatic pneumatic or hydraulic device moves the nacelle fairing 3 from Figure 3 and Figure 4 The asymmetric thrust mode configuration shown gradually shifts to Figure 2 Axial thrust mode configuration shown.

[0098] The downstream section 20 of the nacelle fairing 3 is Figure 5A Configuration to Fig. 6A or Fig. 7A The transition of configuration (and vice versa) is carried out continuously according to the command pressure caused by automatic pneumatic or hydraulic equipment, and during the change of configuration (size and shape) of the outlet cross section BF (in other words, the outlet cross section) of the nacelle fairing 3, the reinforcing bridge 22 ensures that the distance between the radially inner wall 20a and the radially outer wall 20b of the downstream section 20 is approximately constant.

[0099] The invention has been described primarily with respect to a propulsion system comprising two actuators in the shape of semi-rings, but the propulsion system may of course comprise a greater number of actuators in the shape of ring segments when at rest.

Claims

1. A propulsion system (1, 1') for an aircraft, comprising at least one rotor (2) and a nacelle fairing (3), the nacelle fairing extending around the at least one rotor (2) relative to the axis of rotation (X) of the rotor (2), the nacelle fairing (3) comprising an upstream section (10) and a downstream section (20), the upstream section forming an inlet cross section (BA) of the nacelle fairing (3), and a downstream end (21) of the downstream section forming an outlet cross section (BF) of the nacelle fairing (3); characterized in that The downstream section (20) comprises a radial inner wall (20a) and a radial outer wall (20b) made of a deformable shape memory material, and the downstream end (21) forming the outlet cross section (BF) comprises a plurality of pneumatic or hydraulic actuators (23, 23'), the actuators (23, 23') extending around the rotation axis (X) in different continuous angular sectors, each actuator (23, 23') being actuable independently of the other actuators and being configured to deform, under a predetermined command pressure, in a direction radial to the rotation axis (X) and angularly centered with respect to the angular sector over which the actuator extends.

2. The propulsion system (1, 1') according to claim 1, wherein: Each actuator (23, 23') has a substantially annular segment shape, the actuators (23, 23') extending around the rotation axis (X) in different consecutive angular sectors, so that the group of actuators (23, 23') has a substantially toroidal shape.

3. The propulsion system (1, 1') according to claim 1 or 2, wherein: Each actuator (23, 23') is made of a radially reinforced elastic material including fibers.

4. The propulsion system (1, 1') according to claim 1 or 2, wherein: Each actuator (23, 23') comprises a bladder (23a, 23a') in the form of a substantially annular segment made of flexible material, which is enclosed in a helical spring (23b, 23b').

5. The propulsion system (1, 1') according to claim 4, wherein: Each actuator (23, 23') is embedded at one end in a rigid support (25).

6. The propulsion system (1, 1') according to claim 4, wherein: Each bladder (23a, 23a') includes an inlet valve (27, 27') configured to receive a predetermined command pressure.

7. The propulsion system (1, 1') according to claim 6, wherein: The inlet valve (27, 27') is a solenoid valve.

8. The propulsion system (1, 1') according to claim 1 or 2, wherein: The plurality of actuators (23, 23') include at least two actuators having a substantially semi-annular shape.

9. The propulsion system (1, 1') according to claim 1 or 2, further comprising a reinforcing bridge (22) connecting the radially inner wall (20a) and the radially outer wall (20b) of the downstream section (20).

10. The propulsion system (1, 1') according to claim 1 or 2, wherein: The nacelle fairing further comprises an upstream section (10) forming an inlet cross section of the nacelle fairing, and an intermediate section (30) connecting the upstream section (10) and the downstream section (20), wherein the intermediate section (30) is rigid and connected to an engine (6) of the propulsion system (1, 1') via at least one rod (5).

11. An aircraft, characterized in that: The aircraft comprises at least one propulsion system (1, 1') according to any one of claims 1 to 10, mounted to pivot on the aircraft by means of a pivot axis (4, 4') offset from or passing through the rotor (2).

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