The present invention relates to the field of propulsion systems for aircraft. It relates in particular to a propulsion system with a retractable nacelle fairing.

10 Technical background

The state of the art includes in particular documents CH-A2- 711721, US-A1 -2006/284007, US-A1 -2016/023754 and WO-A1 -2017/154552.

A propulsion system for an aircraft comprises at least one rotor or a propeller comprising a plurality of blades mounted on a rotating shaft.

15 There are aircraft, and in particular Take-off Aircraft and

Vertical Landing (ADAV or VTOL acronym for Vertical Take-Off and Landing in English), presenting propulsion systems with single rotors when they include only one rotor or contra-rotating when they include rotors grouped in pairs rotating in direction opposites.

20 These propulsion systems are either with shrouded rotors (the rotor is then surrounded by an annular nacelle shroud), or with free rotors, the propulsion systems and in particular the rotors (free or shrouded) being able to be mounted on a pivot shaft allowing the orientation of the propulsion systems and therefore of the rotors between a vertical position and a position

25 horizontal, for example the vertical orientation for vertical take-off or landing and the horizontal orientation for forward flight or airplane mode.

Ducted rotors have several interesting advantages, such as:

A significant reduction in the sound signature of the rotor in direct emission;

- protection of the rotor blades from surrounding obstacles;

an improvement in the performance of the rotor, in particular in hovering flight of the aircraft or at low forward speed.

In fact, the ducted nacelle provides the rotor with additional thrust in hovering flight, during take-off or at low forward speed linked to the effect of the ducted nacelle on an air flow downstream of the rotor, with reference to the direction of flow of this air flow on the faired nacelle, also called a current tube. More precisely, without the presence of the nacelle fairing, with a free rotor, the air flow downstream of the rotor exhibits a natural inward contraction. In other words, the diameter of the current tube decreases downstream until it reaches a diameter equal to half the section of the rotor.

On the other hand, for a ducted rotor, the outlet section of the nacelle fairing defines the shape of the air current tube, namely a cylindrical shape at the outlet of the nacelle fairing of substantially constant section, thus preventing its contraction. natural.

The propulsion balance depends on the outlet section of the nacelle fairing so that the larger the outlet section of the nacelle fairing, the more the propulsive balance increases. In fact, the thrust generated by the presence of the nacelle fairing is therefore generated at the leading edge of said fairing, via a local depression due to the bypassing of the nacelle fairing by the flow of air. flowing air. The more the air flow admitted into the propulsion system increases, in other words the more the outlet section of the nacelle fairing increases, the greater this depression and, consequently, the greater the thrust generated.

However, at high speed, the propulsive efficiency of a ducted rotor is lower. Indeed, when the forward speed of the aircraft increases, the performance of the ducted rotor decreases due to the rapid increase in drag induced by the presence of the fairing of the nacelle. In this way, depending on the speed of rotation and the size of the rotor, the propulsive efficiency decreases.

Thus, with a ducted rotor, the masking of the noise emission and the safety on the perimeter of the rotor are favored to the detriment of the propulsive efficiency in cruising of the aircraft, that is to say at high forward speed. .

On the other hand, for a free rotor propulsion system (without a nacelle fairing around the rotor), there is no drag induced by a possible fairing of the nacelle, so that when the forward speed of the aircraft is important, the propulsive efficiency is optimal allowing in particular higher flight operating altitudes, or even making it possible to have a higher flight endurance.

However, the absence of a fairing around the rotors induces higher noise emissions and consequently a significant noise nuisance. In addition, the rotor blades are then no longer protected, which increases the risk of hitting an obstacle and thus reduces the safety of the rotor, which is particularly risky or harmful during phases of flight close to the ground or to a structure. 'landing. Finally, without the presence of the nacelle fairing, the benefit of the thrust effect of the nacelle fairing while hovering or at low forward speed is also lost for a free rotor.

Thus, free rotors and shrouded rotors have additional advantages. In fact, it is advisable to be able to combine the benefit of the thrust effect of the nacelle fairing while reducing noise pollution during the phases of flight at low forward speed or in hovering flight by equipping the propulsion system with '' a nacelle fairing acting as a screen in line with the rotors and, the benefit of a free-rotor propulsion system exhibiting better efficiency for phases of flight at higher forward speed or when the environment flight does not present any rotor protection constraints or relating to noise pollution.

In the current art, there are turbomachines having an adjustable cover upstream of a nacelle fairing surrounding a rotor of the turbomachine (in the direction of flow of an air flow during operation of the turbomachine). This cowl is configured to slide axially relative to a longitudinal axis of the turbomachine in order to vary the inlet geometry of the nacelle fairing and thus provide a

increased thrust and reduced noise. The cowling comprises a plurality of segments which can be extended radially outwardly upstream of the fairing of the nacelle and retracted relative to the longitudinal axis of the turbomachine, so that at low speed, during take-offs or during landings of an aircraft equipped with such a turbomachine, the cowl is fully extended while at high speed, the cowl is fully retracted.

This arrangement, although it responds to the problem of optimizing the acoustics of a rotor and the aerodynamic performance in flight of an aircraft, does not make it possible to respond to all the aforementioned problems, a fairing nacelle always being present around it. of the rotor then inducing an additional drag at high forward speed.

There have also been proposed rotor nacelle fairings for aircraft partially retractable circumferentially around the rotor. Such a nacelle fairing comprises a fixed wall and a movable wall configured to move relative to the fixed wall so as to partially uncover the rotor, in particular during the landing phases of an aircraft, in order to limit a ground clearance of the rotor, the exposed rotor part being directed towards the ground. However, the angular nacelle fairing retraction portion remains minor compared to the angular nacelle fairing portion which remains fixed around the rotor so that this solution also fails to address the aforementioned problems.

There is therefore a need to provide a simple and effective solution to the problems mentioned above.

An aim of the present invention is to provide a solution making it possible to simply and quickly adapt the propulsion systems of aircraft in order to optimize their aeronautical and acoustic performance, according to the phases of flight and the environment in which they operate, while at the same time. ensuring the safety of the rotors.

Summary of the invention

To this end, the invention relates to a propulsion system for an aircraft, comprising at least one rotor and a nacelle having a fairing extending around said at least one rotor, this nacelle fairing being sectored and comprising at least one fixed sector and sectors 5 retractable in the circumferential direction with respect to an axis of rotation of the rotor, characterized in that the retractable sectors comprise at least a first series of sectors retractable telescopically in or on said at least one fixed sector, and at least one second series of telescopically retractable sectors in or over said at least one fixed sector, said at least one fixed sector having an angular extent about said axis which is less than or equal to 90 °.

The propulsion system according to the invention thus makes it possible to be able to benefit in a simple and rapid manner, depending on the needs of the aircraft, either from a ducted rotor or from a free rotor.

According to an exemplary embodiment, the retractable sectors of the first series of sectors are retractable telescopically one inside the other and inside said at least one fixed sector and the retractable sectors of the second series of sectors are telescopically retractable inside each other and inside said at least one fixed sector.

Advantageously, the retractable sectors are configured so that triggering of their retraction is slaved to predetermined flight conditions of the aircraft or to a voluntary command from a user.

Advantageously, the retractable sectors have a generally tubular shape and each have transverse dimensions which decrease from one circumferential end to an opposite circumferential end allowing their easy fitting into each other in the retracted position while ensuring their telescopic drive during their. 30 deployment or withdrawal. This frustoconical shape also ensures the seal between two adjacent sectors.

Advantageously, each of the series of sectors comprises:

- an end sector; and

- at least one intermediate sector;

the end sector of the first series of sectors comprising final guiding and locking means configured to cooperate with complementary final guiding and locking means with which the end sector of the second series of sectors is provided for a locking the platform fairing in the closed position.

Thus, the fairing of the nacelle is held in the deployed position in a secure manner.

Advantageously, at least some of the sectors include sealing means, for example at their circumferential ends, configured to provide sealing with one or more adjacent sector (s).

These sealing means, in addition to ensuring the tightness of the fairing of the nacelle, allow the supply of hot air inside the sectors 15 to ensure defrosting if necessary.

Advantageously, the propulsion system comprises a device for actuating the deployment and retraction of the sectors of each series, this device comprising a bidirectional sliding drive system for the deployment and retraction of said sectors in a telescopic manner, from or inside or on the fixed sector.

According to an advantageous embodiment, the bidirectional drive system comprises pinions and rack segments set in motion by the same electric motor, the bidirectional system being configured to drive a pinion on at least one rack of the end sector. , then, successively, to engage pinions on the racks of each intermediate sector, step by step, from the fixed sector in the case of the deployment of the nacelle fairing or to the fixed sector in the case of the retraction of the fairing of the basket.

Preferably and advantageously, the sectors comprise at least one slide segment having a U-shaped cross section.

Thus, they can deploy circumferentially ensuring proper deployment of the nacelle fairing also circumferentially.

The present invention also relates to a method of controlling a nacelle fairing of a propulsion system for an aircraft according to the invention, from an open, respectively closed position of the fairing of said nacelle, characterized in that the retractable sectors are deployed, respectively nested, in a circumferential direction, relative to an axis of rotation of the rotor, telescopically, from, respectively in or on, said / said at least one fixed sector.

According to an exemplary implementation of the control method according to the invention, the deployment of the nacelle fairing, from an open position of the nacelle fairing, comprises the following steps:

Detection of a predetermined flight condition in automatic control or of a manual control for closing the fairing of the nacelle;

- sending of a request for deployment of the sectors to a control and command box;

control of the bidirectional extension drive system to deploy the fairing of the nacelle in a circumferential direction around the rotor from the or each fixed sector;

- Locking of the nacelle fairing in the deployed position by the locking means of the or each end sector;

detection and warning to a user of the locking conditions 25 active in the deployed position.

Advantageously, the predetermined flight condition for automatic closing control of the fairing of the nacelle is a hover phase of the aircraft or a forward speed of the aircraft less than or equal to 180 km / h.

According to another exemplary implementation of the control method according to the invention, the retraction of the nacelle fairing, from a closed position of the nacelle fairing, comprises the following steps:

- detection of a predetermined flight condition in automatic control or of a manual opening control of the nacelle fairing;

- sending of a request for withdrawal of the sectors to a control and command box;

5 - control of the bidirectional contraction drive system to retract the fairing of the nacelle in a circumferential direction around the rotor until the sectors are completely overlapped in the or each fixed sector;

- locking of the nacelle fairing in the retracted position;

10 - detection and warning to a user of the active locking conditions in the retracted position.

Advantageously, the predetermined flight condition for automatic opening control of the fairing of the nacelle is a forward speed of the aircraft greater than 180 km / h.

As indicated previously, the changeover from a propulsion system with a free or ducted rotor is simple, rapid and secure.

The present invention finally relates to an aircraft characterized in that it comprises at least one propulsion system having any one of the aforementioned characteristics, the propulsion system being mounted.

20 pivoting on the aircraft by means of a pivot shaft offset or passing through with respect to the rotor.

Thus, the aircraft can easily switch from a conventional mode to a vertical take-off and landing mode, thus easily adapting to the environment in which it is intended to operate.

25

Brief description of the figures

Other characteristics and advantages of the invention will become apparent on reading the detailed description which follows, for the understanding of which reference is made to the accompanying drawings in

30 which:

[Fig. 1] Figure 1 is a schematic perspective view of a first embodiment of the propulsion system according to the invention, shown with a fairing nacelle in the deployed position, the propulsion system being in a horizontal position;

[Fig. 2] Figure 2 is a view similar to Figure 1, illustrating the propulsion system in a vertical position;

5 [Fig. 3] FIG. 3 is a view similar to FIG. 1, showing the fairing of the nacelle during retraction;

[Fig. 4] Figure 4 is a view similar to Figure 1 in which the fairing of the nacelle is almost completely retracted;

[Fig. 5] FIG. 5 is a schematic view of an aircraft equipped with propulsion systems according to the invention, the nacelles of which are shown with their fairings in the deployed position around the rotors;

[Fig. 6] FIG. 6 is a view similar to FIG. 5 in which certain nacelles are shown with their fairings in the retracted position and others are shown with their fairings in the deployed position;

15 [Fig. 7] FIG. 7 is a schematic perspective view of a second embodiment of the propulsion system according to the invention, shown with a nacelle with a fairing in the deployed position, the propulsion system being shown in a horizontal position;

[Fig. 8] Figure 8 is a view analogous to Figure 7 in which the nacelle fairing is almost completely retracted;

[Fig. 9a] FIG. 9a is a schematic view showing the interlocking of two adjacent sectors of the fairing of the nacelle;

[Fig. 9b] FIG. 9b is a detail view in section of a schematic character and not dimensioned showing the driving beads of two adjacent sectors of the fairing of the nacelle;

[Fig. 10] FIG. 10 is a detailed schematic view of an exemplary embodiment of the end sector;

[Fig. 11] FIG. 11 is a detailed view of a schematic nature showing a set of sectors of the fairing of the nacelle and their drive system according to the invention;

[Fig. 12] FIG. 12 is a perspective view showing a set of slide segments of the drive system according to the invention in the deployed position;

[Fig. 13] FIG. 13 is a partial detail view in section and from the front showing the slide segments of the drive system according to the invention in the retracted position;

[Fig. 14] FIG. 14 is a detail view illustrating the play take-up pinion system of the drive system illustrated in FIG. 11;

[Fig. 15] FIG. 15 is a detail view illustrating the device for adjusting the toothing offset of the pinion / rack system according to the invention.

îo Detailed description of the invention

In the present disclosure, the terms “distal” and “proximal” are used with reference to the positioning of the sectors of each series with respect to the fixed sector of this series. The terms “internal” and “external” are used in reference to the constituent elements of each sector.

15 A propulsion system generally consists of:

- a nacelle;

- an engine and its command and control system;

- and, in the case of propeller or rotor propulsion, its propeller or rotor (s).

The nacelle is the element which makes it possible to integrate the engine into the aircraft, 20 it consists of:

- fairings (making it possible to roll over the engine, to fair the rotors, to capture the flowing air in operation of the aircraft, to create a thrust effect, to reverse the thrust on the turbojets, etc.);

- equipment to be mounted on the engine (such as the engine casing comprising the 25 electrical, hydraulic and pneumatic networks known by the acronym

EBU from English Engine Build-up Unit); and

- aircraft attachment systems.

FIGS. 1 to 4 illustrate, in a simplified manner, a first embodiment of a propulsion system 100 for an aircraft according to the invention.

The propulsion system 100 here comprises at least one rotor 110 and a nacelle fairing 120 extending around said at least one rotor 110. The propulsion system 100 can be fixedly mounted on the aircraft 1. The propulsion system 100 can also be mounted. mounted on a pivot shaft 10, offset relative to an axis of rotation X of the rotor 110. The pivot shaft 10 is fixed by any means to the propulsion system 100, on the one hand, and to the aircraft 1, d 'on the other hand, and allows the orientation of the propulsion system 100 on the aircraft 1, allowing the tilting of the propulsion system 100 around a longitudinal axis L1 of the pivot shaft 10, according to the arrow F, by the intermediary of known actuators, between a horizontal position as illustrated in FIG. 1, and a vertical position as illustrated in FIG. 2.This changeover makes it possible to switch the aircraft 1 from a conventional mode as for an airplane, to a VTOL or helicopter mode.

The rotor 110 of the propulsion system 100 is connected to the aircraft 1 by a mast 111 supporting a motor 112, for example electric, driving the rotor 110 in rotation by means of a power shaft, in a manner known per se . According to the example illustrated in no way limiting, each rotor 110 comprises two blades 113.

The nacelle fairing 120 is sectored into a plurality of sectors. According to the example illustrated in Figures 1 to 4, the fairing 120 of the nacelle is sectored into eight sectors divided into two series, the sectors relating to a first series of sectors will be designated by the letter "a" and the sectors relating to one. second series of sectors will be designated by the letter "b".

Thus, the fairing 120 of the nacelle comprises:

- two fixed sectors 130a, 130b;

- four intermediate sectors 141 a, 142a, 141 b, 142b; and

- two end sectors 150a, 150b.

The sectors are thus grouped together by series, a first series comprising a fixed sector 130a, two intermediate sectors 141a, 142a and an end sector 150a and a second series comprising a fixed sector 130b, two intermediate sectors 141b, 142b and an end sector 150b. The first series and the second series are configured to cooperate together so as to constitute the fairing 120 of the nacelle.

The fairing 120 of the nacelle of the propulsion system 100 can be mounted directly on a wing section or a fuselage of the aircraft 1, or on the pivot shaft 10, via its fixed sectors 130a, 130b.

The intermediate sectors and the end sectors are retractable in the circumferential direction with respect to the axis of rotation X of the rotor 110. More precisely, according to a first exemplary embodiment, the end sector 150a is telescopically retractable to. within the distal intermediate sector 142a, which itself is telescopically retractable within the proximal intermediate sector 141a, which itself is telescopically retractable within the fixed sector 130a. Likewise, the end sector 150b is telescopically retractable inside the distal intermediate sector 142b, which itself is telescopically retractable inside the proximal intermediate sector 141b,

According to another exemplary embodiment (not shown), the sectors are retractable on one another and on the fixed sector. In other words, the end sector 150a is telescopically retractable over the distal mid-sector 142a, which itself is telescopically retractable over the proximal mid-sector 141a, which itself is telescopically retractable over the body. fixed sector 130a. Likewise, the end sector 150b is telescopically retractable over the distal intermediate sector 142b, which itself is telescopically retractable over the proximal intermediate sector 141b, which itself is telescopically retractable over the sector. fixed 130b.

In the remainder of the present disclosure, the retraction is presented (with reference to the drawings) according to the embodiment in which the retractable sectors are configured to be retracted, telescopically, one inside the other, from the most distal. towards the most proximal then in the fixed sector, without being limiting.

It could be envisaged to have only one fixed sector 130ab common to the “a” and “b” series, replacing the two fixed sectors 130a and 130b, the fairing 120 of the nacelle then being sectored into seven sectors.

Thus, the fairing 120 of the nacelle can go from a position fully deployed around the rotor as illustrated in Figures 1 and 2, to a fully retracted position as illustrated in Figure 4, the rotor 110 then being comparable to a rotor free. In fact, in this example, the sum of the angular extents of the fixed sectors 130a, 130b around the X axis of rotation of the rotor 110 is less than or equal to 90 ° so that in the retracted position of the fairing 120 of the nacelle , the rotor 110 of the propulsion system 100 is likened to a free rotor.

FIGS. 5 and 6 illustrate an aircraft 1 comprising four propulsion systems 100 with counter-rotating double rotors 110. Referring to Figure 5, propulsion systems 100 are all shown with a nacelle fairing 120 fully deployed around the rotors 110. Referring to Figure 6, two propulsion systems 100 are shown with a nacelle fairing 120 still fully deployed around. their respective 15 rotors 110, while two other propulsion systems 100 are presented with a nacelle fairing 120 whose retractable sectors are fully retracted inside the fixed sectors 130ab.

The aircraft 1 is illustrated here in conventional mode, in other words in translational flight mode or “airplane” mode. However, the pivot shaft 20 allows the aircraft 1 to switch to VTOL mode (vertical flight mode), thus ensuring the lift of the aircraft.

In the examples illustrated, some of the propulsion systems 100 are mounted on the upper surface of the wings of the aircraft 1. However, these propulsion systems could also be mounted on the lower surface of the wings of the aircraft 1.

FIGS. 7 and 8 illustrate a second embodiment of a propulsion system 200 for an aircraft according to the invention.

Similarly to the first embodiment, the propulsion system 200 here comprises at least one rotor 210 and a nacelle fairing 220 extending around said at least one rotor 210. The propulsion system 200 can be fixedly mounted on the aircraft. . The propulsion system 200 can still be mounted on a pivot shaft 20, passing through the

rotor 210 perpendicular to an axis of rotation X of rotor 210. The pivot shaft 20 is fixed by any means to the propulsion system 100, on the one hand, and to the aircraft, on the other hand, and allows the orientation of the propulsion system 200 on the aircraft, allowing the tilting of the propulsion system 200 around a longitudinal axis L2 of the pivot shaft 20, according to the arrow F, by means of known actuators, between a horizontal position as illustrated in Figures 7 or 8, and a vertical position (not shown). This changeover makes it possible to switch the aircraft from a classic mode as for an airplane, to a VTOL or helicopter mode.

The rotor 210 of the propulsion system 200 is connected to the aircraft by a mast 211 supporting a motor 212, for example electric, driving the rotor 210 in rotation by means of a power shaft, in a manner known per se. According to the exemplary embodiment shown, the mast 211 of the rotor 210 coincides with the pivot shaft 20. According to the example illustrated in no way limiting, each rotor 210 comprises two blades 213.

The fairing 220 of the nacelle is sectored into a plurality of sectors. According to the example illustrated in FIGS. 7 and 8, the fairing 220 of the nacelle is divided into ten sectors divided into four series, designated by the letters “a”, “b”, “c” and “d”.

20 Thus, the fairing 220 of the nacelle comprises:

- two fixed sectors 230ad, 230bc;

- four intermediate sectors 240a, 240b, 240c and 240d; and

- four end sectors 250a, 250b, 250c and 250d.

The sectors are thus grouped together by series, a first series 25 comprising a portion of the fixed sector 230ad, an intermediate sector 240a and an end sector 250a; a second series comprising a portion of the fixed sector 230bc, an intermediate sector 240b and an end sector 250b; a third series comprising a portion of the fixed sector 230bc, an intermediate sector 240c and an end sector 250c and a fourth series comprising a portion of the fixed sector 230ad, an intermediate sector 240d and an end sector 250d. The four series are configured to cooperate in pairs so as to constitute the fairing 220 of the nacelle.

In this embodiment, the fixed sector 230ad is common to the series of sectors "a" and "d" and the fixed sector 230bc is common to the series of sectors "b" and "c". It could be envisaged that each series have a fixed sector of its own, the fairing 220 of the nacelle then being sectorized into twelve sectors.

The fairing 220 of the nacelle of the propulsion system 200 can be mounted directly on a wing section or a fuselage of an aircraft, or on the pivot shaft 20, via its fixed sectors 230ad, 230bc.

The intermediate sectors and the end sectors are retractable in the circumferential direction relative to an axis of rotation X of the rotor 210. More specifically, according to a first non-limiting embodiment, the end sector 250a is retractable, so telescopic, inside the intermediate sector 240a which itself is telescopically retractable inside the fixed sector 230ad. Likewise, the end sector 250b is retractable, telescopically, inside the intermediate sector 240b which itself is retractable telescopically inside the fixed sector 230bc; the end sector 250c is telescopically retractable within the intermediate sector 240c which itself is telescopically retractable within the fixed sector 230bc;

As previously mentioned, another embodiment is envisioned, but not shown, in which the retractable sectors 250a-240a and 250d-240d, respectively 250b-240b and 250c-240c, are telescopically retracted over the fixed sectors 230ad, respectively 230bc.

Thus, the fairing 220 of the nacelle can go from a position 30 fully deployed around the rotor as illustrated in FIG. 7, to a fully retracted position as illustrated in FIG. 8, the rotor 210 then being comparable to a rotor. free. Indeed, in this example, the sum of the angular extents of the fixed sectors 230ad, 230bc around the axis X of

rotation of the rotor 210 is less than or equal to 90 ° so that in the retracted position of the fairing 220 of the nacelle, the rotor 210 of the propulsion system 200 is assimilated to a free rotor.

For ease of understanding, in the remainder of the present description common to the two above-mentioned embodiments, the fixed sectors will be designated by the reference 30, the intermediate sectors will be designated by the reference 40 and the end sectors will be designated by the reference number. reference 50.

The number of sectors constituting the fairing 120, 220 of the nacelle can be chosen as a function of aerodynamic and mechanical constraints.

Figures 9a, 9b and 10 illustrate retractable sectors. More specifically, Fig. 9a shows two intermediate sectors 40a, 40b, Fig. 9b is a detail view of Fig. 9a and Fig. 10 shows an end sector 50.

As already specified, the figures illustrate the embodiment in which the retractable sectors 50, 40a, 40c are configured to be retracted one inside the other, from the most distal to the most proximal, and 20 in the fixed sector 30. However, the characteristics detailed below can be adapted to the embodiment according to which the retractable sectors are configured to be retracted on one another, from the most distal to the most proximal, and on the fixed sector.

The intermediate retractable sectors 40a, 40b and end 50 25, as well as the fixed sector 30, have a generally tubular shape (thus presenting an internal cavity) having a longitudinal main axis and transverse sections.

The sectors 30, 40a, 40b and 50 each have transverse dimensions which decrease from a circumferential end called proximal 30 ', 40a', 40b ', 50', to an opposite circumferential end called distal 30 ”, 40a”, 40b ”, 50”. In other words, a section of the proximal circumferential end 30 ”, 40a”, 40b ”, 50”, of the sectors 30, 40a, 40b, 50, has larger dimensions than a section of the distal circumferential end 30 '. , 40a ', 40b', 50 'of sectors 30, 40a, 40b, 50, thus giving them a frustoconical shape allowing them to be easily fitted into each other in the retracted position. Respectively, in the embodiment where the retractable sectors 5 fit on each other and on the fixed sector, the sectors each have transverse dimensions which decrease from a circumferential end, called distal, to an opposite circumferential end, called proximal, thus giving them a frustoconical shape allowing them to be easily fitted together in the retracted position. , each sector has dimensions smaller than the dimensions of the sector in which it is to be nested. Respectively, each sector has dimensions greater than the dimensions of the sector on which it is to be nested. For example, according to the first embodiment, the distal intermediate sector 40b has dimensions smaller than those of the proximal intermediate sector 40a. The retractable sectors 40a, 40b, 50 being all intended to be nested in the fixed sector 30, this fixed sector 30 is therefore the one having the largest dimensions in order to contain all the other sectors in the retracted position. And the end sector 50 is therefore the sector which has the smallest dimensions.

The frustoconical shape of the sectors 30, 40a, 40b and 50 makes it possible to ensure their telescopic drive during their deployment or their retraction. By telescopic is meant the fact that each distal sector fits, respectively deploys, in a proximal adjacent sector, respectively from a proximal adjacent sector, by sliding of the distal sector in the proximal sector, respectively by sliding of the sector. distal from the proximal sector.

The circumferential ends of each sector have a bead (FIG. 9b) ensuring the joining of two adjacent sectors 30 to one another during the operations of deployment and retraction of the fairing 120, 220 of the nacelle. For example, the intermediate sector 40a has, on an internal surface, at its distal circumferential end 40a ”, an annular bead 41a and the sector

intermediate 40b has, on an outer surface, at its proximal circumferential end 40b ', an annular bead 41 b, the bead 41a of the sector 40a being able to cooperate with the bead 41 b of the sector 40b to ensure the securing of the sectors 40a , 40b between them 5 during operations of deployment and retraction of the fairing 120, 220 of the nacelle. This joining can be achieved by any other suitable means.

The retractable sectors 40a, 40b, 50 are configured so that the triggering of their deployment or their retraction is slaved to the flight conditions of the aircraft 1 or to a voluntary action by a user by command, as will be described. below.

The frustoconical shape of the sectors 30, 40a, 40b and 50 also ensures the seal between two adjacent sectors.

Advantageously, the sectors 30, 40a, 40b and 50 have an aerodynamic profile adapted to an air flow flow during operation of the propulsion system 100, 200.

The sectors 30, 40a, 40b and 50 constituting an angular portion of a fairing 120, 220 of an annular nacelle, they also have a curved shape.

The sectors 30, 40a, 40b and 50 are made of a structuring material having the necessary strength, such as, for example, an aluminum alloy or even a carbon fiber composite. Advantageously, the structure constituting the sectors 30, 40a, 40b and 50 can also have characteristics of absorption of acoustic emissions in order to reduce the noise of the rotor 110, 210 when the fairing 120, 220 of the nacelle is deployed.

The end sector 50 has, at a distal end, a plate 51 configured to bear against a plate of an end sector of another series of sectors in order to ensure the contact of two series of sectors. during the deployment of the fairing 120, 220 of the nacelle.

To guide the end sectors 50 of two series when they are brought into contact at the end of deployment, each end sector 50 can also include a terminal guide device 52. For example, this guide device 52 can include a pin. carried by the end sector 50 of one of the series, configured to cooperate with a notch carried by the end sector 50 of the other of the series.

The end sector 50 of the first series of sectors also comprises locking means 53 configured to cooperate with complementary locking means with which the end sector of the second series of sectors is provided, such as, for example, that an electrically controlled electromechanical latch, for locking the nacelle fairing in the closed position and also improving the tightness and aerodynamics of the nacelle fairing 120, 220.

However, this embodiment implies the presence of wire cabling inside the fairing 120, 220 of the nacelle, for which a winding or unwinding system must be provided at the same time as the movements of deployment and retraction of the fairing 120, 220 of the nacelle, or to provide an electric track set directly applied in the constituent elements of the fairing 120, 220 of the nacelle (such as for example the racks which will be described below).

In this way, another preferred embodiment of the locking means 53 is a mechanical latch for which the application of a first pressure allows the locking and the application of a second pressure allows the unlocking.

For obvious safety reasons, it is advisable to be able to ensure that the fairing 120, 220 of the nacelle is properly locked in the deployed position. In this way, the propulsion system 100, 200 can also include a device for monitoring the correct locking in the deployed position of the fairing 120, 220 of the nacelle such as, for example, an analog switch. This control device can also advantageously be configured to warn a user or a computer of the active locking of the fairing 120, 220 of the nacelle in the deployed position. Likewise, if the analog switch 30 detects improper locking of the fairing 120, 220 of the nacelle in the deployed position, an alert (for example by means of an audible device or an indicator light) could be sent to a

user of the aircraft, for example on an instrument panel in the cockpit of the aircraft.

To further improve the tightness of the nacelle fairing, and in particular the tightness between two adjacent sectors, at least some of the 5 sectors 30, 40a, 40b and 50 are still provided with sealing means (not shown), for example at their circumferential ends.

These sealing means are for example brush seals arranged on an outer surface of each sector 30, 40a, 40b and 50 at their circumferential ends and configured to cooperate with an inner surface of each sector 30, 40a, 40b. and 50 brought opposite these brush seals during the deployment or retraction of the fairing 120, 220 of the nacelle. This solution is preferred because, in addition to permitting sealing with one or more adjacent sectors, these brush seals do not prevent the supply of hot air to the internal cavity of the tubular sectors 30, 40a, 40b and 50, for allow them to be defrosted if necessary.

The tightness could also be ensured by any other means or by precise adjustment of the sectors 30, 40a, 40b and 50, this solution not being preferred.

In order to allow the telescopic deployment of the 20 sectors 30, 40a, 40b and 50 or the retraction by successive interlocking of the sectors 30, 40a, 40b and 50 two by two, each series of sectors 30, 40a, 40b and 50 is provided with an actuating device such as a bidirectional sliding drive system 2 of the rack cylinder type. FIGS. 11 to 15 illustrate the details of such a bidirectional drive system, for a fairing 120, 220 having eight sectors distributed in two series of four sectors 30, 40a, 40b, 50, in this example.

The bidirectional drive system 2 comprises a plurality of pinions 3a, 3b, 3c and a plurality of rack segments 4a, 4b, 4c integral, respectively, with slide segments 6a, 6b, 6c.

The rack and pinion pairs are set in motion by the same electric motor 5.

As can be seen in Figures 11 and 14, the rack 4a of the end sector 50 is single-toothed intended to cooperate with a single pinion 3a. On the other hand, the rack 4b of the distal intermediate sector 40a is double-toothed and is intended to cooperate with two pinions 3b. Likewise, the rack 4c of the proximal intermediate sector 40b has double teeth and is intended to cooperate with two pinions 3c.

The bidirectional drive system 2 is configured to extend into the internal cavities of the tubular sectors 30, 40a, 40b and 50. The slide segment 6a is associated with the end sector 50. The slide segment 6b is associated. at the distal end sector 40a. The slide segment 6c is associated with the proximal end sector 40b. A last slide segment 6d is associated with the fixed sector 30. However, several slide segments could be assigned to the same sector. As can be seen in Figure 11, the slide segments 6a, 6b, 6c, 6d are concentric. They have a U-shaped cross section and are curved so as to follow the curved shape of the sectors 30, 40a, 40b and 50. The slide segments 6a, 6b, 6c,

The slide segments 6a, 6b, 6c, 6d can advantageously be sized to ensure mechanical strength of the fairing 120, 220 in all its configurations when it is subjected to aerodynamic, gravitational and dynamic forces.

Advantageously, the surfaces of these slide segments in relative movement with respect to one another can be coated with a self-lubricating coating in order to prevent the risks of jamming or excessive wear.

The rack segments 4a, 4b, 4c are dimensioned and configured to be able to fit together two by two by sliding one into the other, like sectors 30, 40a, 40b and 50.

The bidirectional system 2 is dimensioned and configured to avoid any risk of contact with the rotors 110, 210 during the deployment or the retraction of the fairing 120, 220 of the nacelle.

The bidirectional system 2 is configured to actuate the 5 pinions 3a, 3b and 3c integral in rotation with the electric motor 5 by means of the same shaft. The pinion 3a of the end sector 50 engages on the rack segment 4a for driving the associated slide segment 6a, then, successively, the pinions of each intermediate sector 40a, 40b, step by step, from the most distal to the more proximal Io, from the fixed sector 30 in the case of deployment of the fairing 120, 220 of the nacelle or to the fixed sector 30 in the case of the retraction of the fairing 120, 220 of the nacelle. In other words, the pinion 3b of the distal intermediate sector 40b engages on the rack segment 4b for driving the associated slide segment 6b, then,

The slide segment 6d associated with the fixed sector 30, for its part not being coupled to any rack or pinion, remains stationary.

The bidirectional drive system 2 further comprises locking means 7b, 7c, 7d in the deployed position of the slide segments 6a, 6b, 6c and, consequently, retractable sectors 40a, 40b, 50. These locking means comprise for example mechanical means comprising two elements configured to cooperate (of the cam and pawl or pin and notch type) and are arranged, for one of the elements, at a proximal end of the rack segments 4a, 4b 4c and, for the 'Another of the elements, at a distal end of the slide segments 6b, 6c, 6d, thus making it possible to secure or mechanically unlock the rack segments associated with adjacent sectors. This locking means 7b, 7c, 7d can also be of the electromechanical type.

The deployment and retraction of the slide segments 6a, 6b, 6c and therefore of the sectors 30, 40a, 40b, 50 is carried out sequentially by successive locking of the adjacent segments by the locking devices 7b, 7c, 7d.

Thus, during the deployment of the sectors 30, 40a, 40b, 50 around the rotors 110, 210, the electric motor 5 rotates in a first direction and 5 drives all of the pinions 3a, 3b, 3c in rotation. Initially, the pinion 3a engages on the teeth of the rack segment 4a for driving the associated slide segment 6a out of the slide segment 6b until the slide segment 6a is secured to the slide segment 6b by the locking means 7b. Then, the pinions 3b engrain on the teeth of the rack segment 4b for driving the segments of slideways 6a and 6b joined together and in particular driving the slide segment 6b out of the slide segment 6c, until the segment of slide 6b is secured to the slide segment 6c by the locking means 7c. And finally,

Likewise, during the retraction of the sectors 30, 40a, 40b, 50 around the rotors 110, 210, the electric motor 5 rotates in a second direction opposite to the first direction and drives all the pinions 3a, 3b in rotation, 3c. Initially, the locking means 7d is unlocked and the pinions 3c engage on the teeth of the rack segment 4c for driving the slide segments 6a, 6b and 6c secured by the locking means 7b and 7c, until 'that the slide segment 6c is retracted into the slide segment 6d. Then, the locking means 7c is unlocked and the pinions 3b engage on the teeth of the rack segment 4b for the driving of the slide segments 6a and 6b secured by the locking means 7b, until the slide segment 6b is retracted into the slide segment 6c. And finally, the locking means 7b is unlocked and the pinion 3a engages on the teeth of the segment of

rack 4a for driving the slide segment 6a until the slide segment 6a is retracted into the slide segment 6b.

The pinions 3a, 3b, 3c can advantageously comprise a system for adjusting the toothing offset 8 known per se, which makes it possible to have only one rotation shaft for all the pinions 3a, 3b and 3c. For example, the toothing offset adjustment system 8 comprises pins in abutment in grooves with which the pinions 3a, 3b and 3c are provided.

The deployment and retraction of the sectors around the rotors 110, 210 could also be achieved by other methods, such as for example by means of dedicated pneumatic systems.

Thus, the deployment of the fairing 120, 220 of the nacelle of a propulsion system 100, 200 from an open position of the fairing 120, 220 of the nacelle (in other words when the retractable sectors 40a, 40b and 50 of the fairing 120, 220 of the nacelle are fully nested in the fixed sectors 30) can be done either on manual control or automatically, by detection of a predetermined flight condition requiring the propulsion system 100, 200 to pass through a free rotor configuration, a shrouded rotor configuration. Indeed, if the noise nuisance must be reduced because the aircraft 1 flies over a living area or an environment comprising obstacles that may present a risk for the rotors, a user can manually actuate the deployment of the fairing 120, 220 of Platform.

Thus, when such a manual command or when such a condition is detected, a request for the deployment of sectors 40a, 40b and 50 is sent to a control and command box which controls the bidirectional drive system 2 in extension for deploy the fairing 120, 220 of the nacelle.

The rack-pinion pairs 3a-4a, 3b-4b and 3c-4c are set in motion as previously described.

Consequently the sectors 40a, 40b, 50 are deployed in a circumferential direction around the rotor 110, 210 (in the direction of the arrows F1 in Figures 1 to 4 and 7 and 8) from the end sector 50 which slides out. the distal intermediate sector 40a, then the distal intermediate sector 40a slides out of the proximal intermediate sector 40b and finally the proximal intermediate sector 40b slides out of the fixed sector 30.

The retractable sectors thus deploy until they come into contact with the end sectors 50 of each series of sectors configured to cooperate in pairs. At the end of the deployment stroke, the guide means 52 of the end sectors 50 guide the latter to bring their respective plate 51 opposite one another. The locking means 53 of each end sector 50 are then actuated to lock the fairing 120, 220 of the nacelle in the closed position. The rotor 110, 210 then being a ducted rotor.

Likewise, the retraction of the fairing 120, 220 of the nacelle of a propulsion system 100, 200 from a closed position of the fairing 120, 220 of the nacelle (in other words when the fairing of the nacelle is fully deployed around rotor 110, 210) can be either manually or automatically, by detecting a predetermined flight condition requiring the propulsion system 100, 200 to be changed from a shrouded rotor configuration to a rotor configuration free, for example, when a high forward speed of the aircraft 1 is detected, meaning that a propulsive efficiency of the rotors must be privileged. According to an exemplary embodiment, the retraction or the opening of the fairing 120,

Thus, when such a manual control or when such a condition is detected, the locking means 53 of the end sectors 50 are unlocked to allow the separation of the series of sectors until then linked by their respective end sector 50. A request for retraction of the sectors 40a, 40b and 50 is then sent to a control and command box which controls the bidirectional drive system 2 in contraction to retract the fairing 120, 220 of the nacelle.

The rack-pinion pairs 3a-4a, 3b-4b and 3c-4c are set in motion as previously described.

Consequently the sectors 40a, 40b, 50 are retracted in a circumferential direction around the rotor 110, 210 (in the direction of the arrows F2 in Figures 1 to 4 and 7 and 8) from the end sector 50 which s' fits into the distal intermediate sector 40a, then the distal intermediate sector 40a fits into the proximal intermediate 40b and finally the proximal intermediate sector 40b fits into the fixed sector 30.

When the retractable sectors 40a, 40b and 50 of a series are all nested one inside the other and in the fixed sector 30 of this series, the rotor 110, 210 is then assimilated to a free rotor.

The propulsion system 100, 200 according to the invention also comprises means for locking in the open position of the fairing 120, 220 of the nacelle, in other words when the retractable sectors 40a, 40b and 50 of a series are all fitted together. one inside the other and in the fixed sector 30 of this series. These means are for example complementary mechanical means 25 carried by the fixed sector 30 and the end sector 50, these additional means then being configured to secure the end sector 50 to the fixed sector 30, and consequently also all the sectors. intermediaries. Another solution for locking the sectors in the retracted position would be to block the electric motor 5 from rotating.

There again, for obvious safety reasons, it is advisable to be able to ensure that the fairing 120, 220 of the nacelle is properly locked in the retracted position. In this way, a control device such as an analog switch can still advantageously equip the system.

propulsion 100, 200 and be configured to warn a user or a computer of the active locking of the fairing 120, 220 of the nacelle in the retracted position. Likewise, if the analog switch detects improper locking of the nacelle fairing 120, 220 in the retracted position, an alert (for example by means of an audible device or an indicator light) could be sent to a user of the nacelle. the aircraft, for example on an instrument panel in the cockpit of the aircraft.

The propulsion system 100, 200 according to the invention thus makes it possible to benefit in a simple and rapid manner, depending on the needs of the aircraft 1, either from faired rotors or from free rotors. When the fairing 120, 220 of the nacelle is deployed around the rotors 110, 210, there is a complete fairing of the rotor. The fairing 120, 220 of the nacelle, of the propulsion system 100, 200 according to the invention thus makes it possible, by its shape, its construction and the materials of which it is made, to act as an acoustic screen against the noise emanating from the vehicle. rotation of the rotors 110, 210, guaranteeing better attenuation of acoustic emissions but also increased safety of the rotors in relation to possible obstacles while benefiting from the thrust effect of the nacelle fairing useful in hovering flight or at low forward speed.

Thus, the aircraft according to the invention has the advantageous advantage of being able to have, as required, shrouded rotors or free rotors.

CLAIMS

1. Propulsion system (100, 200) for an aircraft (1), comprising at least one rotor (110, 210) and a nacelle having a fairing (120, 220)

5 extending around said at least one rotor (110, 210), this nacelle fairing (120, 220) being sectored and comprising at least one fixed sector (30, 130a, 130b, 130ab, 230ad, 230bc) ​​and sectors retractables (40a, 40b, 50, 141 a, 141 b, 142a, 142b, 150a, 150b, 240a, 240b, 240c, 240d, 250a, 250b, 250c, 250d) in the circumferential direction (F1, F2) with respect to a axis of rotation (X) of the rotor (110, 210), the retractable sectors (141 a, 141 b, 142a, 142b, 150a, 150b, 240a, 240b, 240c, 240d, 250a, 250b, 250c, 250d) comprising at least a first series of retractable sectors (141a, 142a, 150a; 240a, 250a; 240d, 250d) telescopically into or over said at least one fixed sector (130a; 130ab; 230ad), and characterized in that said retractable sectors (141 a, 141 b, 142a, 142b, 150a, 150b, 240a, 240b, 240c, 240d, 250a,250b, 250c, 250d) further comprise at least a second series of sectors (141 b, 142b, 150b; 240b, 250b; 240c, 250c) retractable in a telescopic manner in or on at least one fixed sector (130b; 130ab; 230bc ), said at least one fixed sector (30, 130a, 130b, 130ab, 20 230ad, 230bc) ​​having an angular extent around said axis (X) which is less than or equal to 90 °.

2. Propulsion system (100, 200) according to the preceding claim, wherein the retractable sectors (141a, 142a, 150a; 240a, 250a; 240d, 250d) of the first series of sectors are telescopically retractable.

25 within each other and within said at least one fixed sector (130a; 130ab; 230ad) and the retractable sectors (141b, 142b, 150b; 240b, 250b; 240c, 250c) of the second series of sectors are telescopically retractable inside one another and inside said at least one fixed sector (130b; 130ab; 230bc).

The propulsion system (100, 200) according to one of the preceding claims, wherein the retractable sectors (40a, 40b, 50) are configured so that an initiation of their retraction is subject to conditions.

aircraft flight predetermined (1) or a voluntary command from a user.

4. Propulsion system (100, 200) according to the preceding claim, wherein the retractable sectors (141 a, 141 b, 142a, 142b, 150a, 150b, 240a,

5 240b, 240c, 240d, 250a, 250b, 250c, 250d) are generally tubular in shape and each have transverse dimensions which decrease from one circumferential end to an opposite circumferential end.

5. The propulsion system (100, 200) according to any one of the preceding claims, in which each of the series of sectors comprises:

- an end sector (50; 150a, 150b; 250a, 250b, 250c, 250d); and

- at least one intermediate sector (40a, 40b; 141 a, 141 b, 142a, 142b; 240a, 240b, 240c, 240d);

the end sector (50; 150a, 150b; 250a, 250b, 250c, 250d) of the first series of sectors comprising final guide means (52) and locking (53) configured to cooperate with guide means final (52) and complementary locking (53) with which the end sector (50; 150a, 150b; 250a, 250b, 250c, 250d) of the second series of sectors for locking the fairing (120, 220) is provided platform in the closed position.

6. The propulsion system (100, 200) according to one of the preceding claims, wherein at least some of the sectors (30, 40a, 40b, 50) include sealing means, for example at their circumferential ends, configured to seal with adjacent sector (s).

7. The propulsion system (100, 200) according to one of the preceding claims, in which it comprises a device for actuating the deployment and retraction of the sectors (40a, 40b, 50, 141 a, 141 b, 142a, 142b, 150a, 150b, 240a, 240b, 240c, 240d, 250a, 250b, 250c, 250d) of each series, this device comprising a bidirectional drive system (2) slide 30 for the deployment and retraction of said sectors of telescopically, from or inside the or on the fixed sector (30, 130a, 130b, 130ab, 230ad, 230bc).

8. Propulsion system (100, 200) according to the preceding claim, wherein the bidirectional drive system (2) comprises pinions (3a, 3b, 3c) and rack segments (4a, 4b, 4c) set in motion. by a single electric motor (5), the bidirectional system (2)

5 being configured to engage a pinion (3a) on at least one rack (4a) of the end sector (50), then, successively to engage pinions (3b, 3c) on racks of each intermediate sector (40a, 40b ), step by step, from the fixed sector (30) in the case of the deployment of the fairing (120, 220) of the nacelle or to the fixed sector (30) in the case of the retraction of the fairing (120, 220) of the nacelle.

9. The propulsion system (100, 200) according to the preceding claim, wherein the sectors (30, 40a, 40b, 50) comprise at least one slide segment (6a, 6b, 6c, 6d) having a cross section in the form of U.

10. A method of controlling a nacelle fairing (120, 220) of a propulsion system (100, 200) for an aircraft (1) according to any one of claims 1 to 9, from a position. open, respectively closed of said fairing (120, 220) of the nacelle, characterized in that the retractable sectors (40a, 40b, 50, 141 a, 141 b, 142a, 142b, 150a, 150b, 240a, 240b, 20 240c, 240d, 250a, 250b, 250c, 250d) are deployed, respectively nested, in the circumferential direction (F1, respectively F2), with respect to an axis of rotation (X) of the rotor (110, 210), in a telescopic manner, from , respectively in or on, said / said at least one fixed sector (130a, 130b; 130ab; 230ad; 230bc).

11. The control method of claim 10, wherein the deployment of the nacelle fairing (120, 220) from an open position of the nacelle fairing (120, 220) comprises the following steps. :

- detection of a predetermined flight condition in automatic control 30 or of a manual control for closing the fairing (120, 220) of the nacelle;

- sending a request for deployment of the sectors (40a, 40b, 50) to a control and command box;

- Control of the bidirectional drive system (2) in extension to deploy the fairing (120, 220) of the nacelle in a circumferential direction (F1) around the rotor (110, 210) from the or each fixed sector (30);

5 - locking the fairing (120, 220) of the nacelle in the deployed position by the locking means (53) of the or each end sector (50);

- detection and warning to a user of active locking conditions in the deployed position.

12. The control method according to the preceding claim, wherein the predetermined flight condition for automatic closing control of the fairing (120, 220) of the nacelle is a hovering phase of the aircraft (1) or a speed of d. 'progress of the aircraft (1) less than or equal to 180 km / h.

13. The control method of claim 10, wherein the retraction of the nacelle fairing (120, 220) from a closed position of the nacelle fairing (120, 220) comprises the following steps:

- detection of a predetermined flight condition in automatic control or of a manual opening control of the fairing (120, 220) of the

20 pod;

- sending of a request for withdrawal of the sectors (40a, 40b, 50) to a control and command box;

- control of the bidirectional drive system (2) in contraction to retract the fairing (120, 220) of the nacelle in one direction

25 circumferential (F2) around the rotor (110, 210) until complete nesting of the sectors in the or each fixed sector (30);

- locking of the nacelle fairing in the retracted position;

- detection and warning to a user of active locking conditions in the retracted position.

14. The control method according to the preceding claim, in which the predetermined flight condition for automatically controlling the opening of the fairing (120, 220) of the nacelle is a forward speed of the aircraft (1) greater than 180. km / h.

15. Aircraft (1) characterized in that it comprises at least one propulsion system (100, 200) according to any one of claims 1 to 9, the propulsion system (100, 200) being pivotally mounted on the aircraft ( 1) by means of a pivot shaft (10, 20) offset or through with respect to the rotor (110, 210).