METHOD FOR SIZING A PROPULSION SYSTEM COMPRISING A MAIN ENGINE AND AN AUXILIARY ENGINE

Abstract

The invention relates to the dimensioning (S) of a propulsion system (2) comprising a main engine (3) providing primary thrust assisted by an auxiliary engine (4) providing auxiliary thrust, according to the following steps: (i) determine (S1) a distribution between the main thrust and the auxiliary thrust to obtain the takeoff thrust of the propulsion system, the auxiliary thrust contributing from 5% to 65% of the takeoff thrust, (ii) depending on the distribution determined for the takeoff condition, determine (S2) a distribution between the main thrust and the auxiliary thrust to obtain the peak climb thrust of the propulsion system, the auxiliary thrust contributing at most 70% of the peak climb thrust.and (iii) dimension (S3) the propulsion assembly (2) so that the main thrust of the main engine (3) determined for the takeoff condition corresponds to the maximum thrust that can be achieved by the main engine (3).

Description

1. SCOPE OF THE INVENTION The invention relates to the general field of aircraft, and more particularly to the sizing of engines for such aircraft with a view to improving, among other things, their specific fuel consumption. The invention is applicable to all types of aircraft intended to perform missions involving diverse operating conditions. TECHNOLOGICAL BACKGROUND In operation, a given engine is subjected to different stresses depending on the aircraft's flight phases. Indeed, each flight phase is associated with an engine operating condition, including idle, takeoff, climb, top of climb (or maximum climb), and cruise. During the aforementioned operating conditions, the engine is held for a relatively long time (between about thirty seconds for takeoff andseveral hours for cruising) at predefined speed spectra, which depend on the engine's redlines (i.e., the absolute maximums encountered by engine operating parameters such as shaft speed or the temperature of the various hot engine parts throughout the flight). The most demanding engine operating condition in terms of thrust is generally takeoff. Therefore, aircraft engines are usually sized according to this operating condition to guarantee their ability to get the aircraft airborne. To this end, engines are designed to operate at maximum combustion chamber inlet and outlet temperatures during the takeoff phase, so that the efficiency of the engine's thermodynamic (and therefore energy) cycle is optimal during this phase. These combustion chamber inlet and outlet temperatures will directly determineThe size of the high-pressure engine components (high-pressure compressor, combustion chamber, and high-pressure turbine) and their constituent materials are crucial to ensure they can provide the thrust necessary for aircraft takeoff. However, the takeoff phase is very short (between one and five minutes approximately, depending on the aircraft type and its mission) compared to the other flight phases. Consequently, for most of the flight, the engine requires less thrust and therefore exhibits lower thermodynamic (and thus energy) efficiency. This is particularly true during cruise, which typically lasts at least thirty minutes. Indeed, during cruise, the power required by the engine is lower than during takeoff. This reduction in engine power is achieved by lowering the temperature at the combustion chamber outlet and therefore at the inlet of the engine's high-pressure turbine.This implies a reduction in the overall compression ratio. As a result, during this phase of flight, the engine's specific fuel consumption is higher than its optimum. Currently, in order to comply with increasing regulatory constraints (particularly regarding acoustics and pollutant emissions) and to reduce engine operating costs, especially those related to specific fuel consumption, engine manufacturers tend to increase the combustion chamber inlet and outlet temperatures in order to reduce the size of the high-pressure core and increase the size of the low-pressure core, while maintaining fan diameters acceptable to aircraft manufacturers. Such an increase in combustion chamber inlet and outlet temperatures does indeed improve the efficiency of the engine's thermodynamic cycle, insofar as the overall compression ratio and the turbine inlet temperature are reduced.High pressure increases. This effectively improves thermodynamic efficiency during takeoff, which is the critical phase. However, thermodynamic efficiency in other flight phases is not optimal, particularly during cruise. Engine manufacturers therefore seek to find a compromise between engine requirements under different operating conditions and the impact of these constraints in terms of specific fuel consumption, mass, noise levels, etc. SUMMARY OF THE INVENTION One objective of the invention is therefore to provide a solution in the field of aircraft propulsion that addresses this problem of reconciling operational constraints, such as the ability of the propulsion system to take off, with ambitious fuel consumption targets typical of civil commercial aviation. To this end, the invention proposes a method for sizing a propulsion system.propulsion system for an aircraft, said propulsion system being configured to operate under at least two distinct operating conditions and comprising: - at least one main engine, configured to provide main thrust, and - at least one auxiliary engine, separate from the main engine and configured to provide auxiliary thrust, the sizing method being characterized in that it comprises the following steps: (i) for a first operating condition corresponding to a first thrust of the propulsion system, determining a first distribution between main thrust and auxiliary thrust to obtain said first thrust, the auxiliary thrust contributing at least 5% and at most 65% of the first thrust, (ii) for a second operating condition corresponding to a second thrust of the propulsion system and as a function of the first distribution determined for the first operating condition, determininga second distribution between the main thrust and the auxiliary thrust to obtain said second thrust, the auxiliary thrust contributing at most 70% of the second thrust, and (iii) size said propulsion system so that the main thrust of the main engine determined for the first operating condition corresponds to the maximum thrust that can be achieved by the main engine regardless of the operating condition of the propulsion system. Some preferred but non-limiting features of the sizing method described above are the following, taken individually or in combination: - the first and second distributions between the main thrust and the secondary thrust are determined, to within 2%, from the following operating ranges: the auxiliary thrust contributes at least 15% plus 45% of the first thrust for the first operating condition and the thrustthe main thrust contributes 100% to the second thrust for the second operating condition; or the auxiliary thrust contributes 45% to 48% to the first thrust for the first operating condition and 0% to 20% to the second thrust for the second operating condition; or the auxiliary thrust contributes 48% to 55% to the first thrust for the first operating condition and 20% to 35% to the second thrust for the second operating condition; or the auxiliary thrust contributes 55% to 63% to the first thrust for the first operating condition and 35% to 50% to the second thrust for the second operating condition; or the auxiliary thrust contributes 63% to 70% to the first thrust for the first operating condition and 50% to 60% to the second thrust for the second operating condition.operation; - the first and second distributions between the main thrust and the secondary thrust are determined, to within 2%, from the following operating ranges: the auxiliary thrust contributes 38% to 42% of the first thrust for the first operating condition and the main thrust contributes 100% of the second thrust for the second operating condition; or the auxiliary thrust contributes 47% to 49% of the first thrust for the first operating condition and 18% to 21% of the second thrust for the second operating condition; or the auxiliary thrust contributes 52% to 55% of the first thrust for the first operating condition and 33% to 36% of the second thrust for the second operating condition; or the auxiliary thrust contributes 60% to 63% of the first thrust for the first conditionof operation and at 49% to 52% of the second thrust for the second operating condition, 15 - the first operating condition corresponds to takeoff and the second operating condition corresponds to the peak of climb. According to a second aspect, the invention also proposes a propulsion system for an aircraft configured to operate in at least one distinct first and second operating condition and comprising: - at least one main engine, configured to provide main thrust, and 25 - at least one auxiliary engine, separate from the main engine and configured to provide auxiliary thrust, said propulsion system being sized in accordance with a sizing method as described above, so that the main thrust of the main engine during the first operating condition corresponds to the maximum thrust that can be achieved by the main engine regardless of the condition.of operation. 3043724 6 Some preferred but non-limiting features of the propulsion system described above are the following, taken individually or in combination: - the main engine comprises one or more turbojets or one or more turboprops, - the auxiliary engine comprises one or more turbojets and / or one or more turboprops and / or one or more electrically powered thrust effectors, and / or - the auxiliary engine is retractable. 10 According to a third aspect, the invention provides an aircraft comprising a propulsion system as described above. Optionally, the aircraft may include at least two auxiliary engines, the thrust of said auxiliary engines contributing up to 100% of the auxiliary thrust. BRIEF DESCRIPTION OF DRAWINGS Other features, objects, and advantages of the present invention will become more apparent from the detailed description that follows, and from the 20th drawings.The accompanying drawings are given by way of non-limiting examples and in which: Figure 1 is a graph illustrating examples of sizing points for operating conditions corresponding to takeoff and peak climb of a propulsion system according to the invention, in which the y-axis represents the percentage of the total thrust of the propulsion system produced by the main engine at takeoff and the x-axis represents the percentage of the total thrust of the propulsion system produced by the auxiliary engine of the propulsion system at peak climb. Figure 2 illustrates an example of an embodiment of an aircraft that may include a propulsion system according to the invention. Figure 3 is a flowchart illustrating steps in an example of a method for sizing a propulsion system according to the invention. 5 DETAILED DESCRIPTION OF AN EMBODIMENT In order to improve specific fuel consumptionIn a propulsion system 2 for an aircraft 1 comprising a main engine 3, the invention proposes to free the main engine 3 from the constraint of being able to provide sufficient thrust to take off the aircraft 1 and to add to the propulsion system 2 an auxiliary engine 4, separate from the main engine 3, in order to compensate for the loss of thrust related to this modification of the main engine 3. It then becomes possible to size the main engine 3 by significantly improving its specific fuel consumption during long flight phases, such as cruise, while ensuring that the propulsion system 2 is capable of taking off the aircraft 1. To this end, the propulsion system 2 is configured to operate under at least two distinct operating conditions and comprises at least one main engine 3 configured to provide primary thrust and at least one auxiliary engine 4, separate from the main engine 3, and configured toto provide auxiliary thrust. This propulsion unit 2 is dimensioned according to the following steps: (i) for a first operating condition corresponding to a first thrust of the propulsion unit 2, determine (step 51) a first distribution between the main thrust and the auxiliary thrust to obtain said first thrust, the auxiliary thrust contributing at least 5% and at most 65% of the first thrust, (ii) for a second operating condition corresponding to a second thrust of the propulsion unit 2 and depending on the first distribution determined for the first operating condition, determine (step S2) a second distribution between the main thrust and the auxiliary thrust to obtain said second thrust, the auxiliary thrust contributing at most 70% of the second thrust, and (iii) dimension (step S3) said propulsion unit 2 so that the main thrust of the engineThe main engine 3, determined for the first operating condition 5, corresponds to the maximum thrust that can be achieved by the main engine 3 regardless of the operating condition. The auxiliary engine 4 can provide continuous thrust 10 between the first and second operating conditions, or alternatively, be shut down during at least one of said operating conditions. In the remainder of this description, the first operating condition 15 of the propulsion assembly 2 corresponds to takeoff, while the second operating condition corresponds to the peak of climb. Typically, for an engine with a low-pressure shaft rotation speed redline between 3000 rpm and 4000 rpm, takeoff corresponds to a low-pressure shaft rotation speed between 2500 and 3000 rpm, while the peak of climb corresponds to a low-pressure shaft rotation speedpressure between 3000 rpm and 3500 rpm. Furthermore, the propulsion system 2 may exhibit additional operating conditions, such as, among others, cruise, idle (on the ground and in flight), etc. However, the choice of these operating conditions for sizing the propulsion system is not limiting; the method of the invention can be applied to a propulsion system 2 based on other operating conditions of said propulsion system 2. Figure 1 is a graph illustrating, on the y-axis, the proportion (percentage) of the total thrust of the propulsion system 2 produced by a main engine 3 at takeoff and, on the x-axis, the proportion (percentage) of this total thrust produced by the auxiliary engine 4 at the peak of climb. All the points on the curve shown correspond to possible dimensioning points 5 for the propulsion system assembly 2 andallowing for an improvement in the specific fuel consumption of said propulsion system 2. It should be noted that Figure 1 illustrates thrust ratios at maximum design conditions but in no way prejudges how the main engines 3 and auxiliary engines 4 will be used subsequently. Indeed, once the main engine 3 and auxiliary engine 4 of propulsion system 2 have been designed, it is possible to use these engines 3 and 4 at thrusts lower than these maximum thrusts. The choice of a point on the curve, and therefore the design of a given propulsion system 2, can be determined according to the type of aircraft 1 and the type of associated mission (short, medium, long-haul, etc.). Typically, for an aircraft 1 configured to perform a long-haul mission, the proportion of auxiliary thrust in the second distribution is preferably greater than in the case of an aircraft 1 configured to perform a mission of the typeshort-haul. Indeed, the cruise flight time is shorter on a short-haul flight than on a long-haul flight, so it may be preferable to improve the thermodynamic efficiency of the propulsion system 2 at the peak of climb and limit the size and weight of the auxiliary engine 4 rather than improve its thermodynamic efficiency in cruise and increase the size and weight of the auxiliary engine 4. In what follows, the thrust distribution shares during a given operating condition provided by the main engine 3 and the auxiliary engine 4 are indicated to the nearest 2%, this tolerance corresponding to the possible variations for the choice of the sizing compression ratio of the main engine 3's fan. Typically, the compression ratio of the main engine 3's fan can be between 1.2 and 1.7, preferably between 1.3 and 1.6, for example, on the order of 1.45 to 1.5. OnNote that the fan compression ratio is determined here when the main engine 3 is stationary in a standard atmosphere (as defined by the International Civil Aviation Organization (ICAO) Manual, Doc 7488 / 3, 3rd edition) and at sea level. The propulsion system 2 can be sized so that the thrust provided by said propulsion system 2 during the takeoff operating condition is obtained up to a maximum of 45% by the auxiliary engine 4, the remainder being provided by the main engine 3, while only the main engine 3 provides the necessary thrust during the peak climb operating condition. This configuration 15 corresponds to the segment of the curve extending between points A (corresponding to 95% main thrust, 5% auxiliary thrust at takeoff and 100% main thrust at peak climb) and B (corresponding to 58% main thrust, 42% auxiliary thrust)at takeoff and 100% of main thrust at the peak of climb) of the curve illustrated in Figure 1. In this configuration, the auxiliary engine 4 therefore only contributes to thrust during the takeoff operating condition. Such a sizing of the propulsion system 2 improves the specific fuel consumption of the main engine 3 compared to a conventional engine (i.e., an engine sized based on the takeoff operating condition and which lacks an auxiliary engine), particularly during the peak of climb and cruise operating conditions, since the main engine 3 is sized based on a lower maximum main thrust (at takeoff). Alternatively, the propulsion system 2 can be sized so that 45% to 48% of the thrust provided by said propulsion system 2 is obtained from the auxiliary engine 4 during the operating condition oftakeoff and at a rate of 0% to 20% during the peak climb operating condition, the remainder in each operating condition being provided by the main engine 3. This configuration corresponds to the section extending between points B and C (corresponding to 52% main thrust and 48% auxiliary thrust at takeoff, and 80% main thrust and 20% auxiliary thrust at the peak climb) of the curve illustrated in Figure 1. In this configuration, the auxiliary engine 4 therefore contributes to the thrust both during the takeoff operating condition and during the peak climb operating condition. Alternatively, the propulsion system 2 can be sized so that the thrust provided by said propulsion system 2 is obtained at a rate of 48% to 55% by the auxiliary engine 4 during the takeoff operating condition and at a rate of 20% to 35% during the peak climb operating condition.The remaining thrust in each operating condition is provided by the main engine 3. This configuration corresponds to the section extending between points C and D (corresponding to 45% main thrust and 55% auxiliary thrust at takeoff, and 65% main thrust and 35% auxiliary thrust at the peak of climb) of the curve illustrated in Figure 1. In this configuration, the auxiliary engine 4 therefore contributes to the thrust both during the takeoff operating condition and during the peak of climb operating condition. Alternatively, the propulsion system 2 can be sized so that the thrust provided by said propulsion system 2 is obtained at a rate of 55% to 63% by the auxiliary engine 4 during the takeoff operating condition and at a rate of 35% to 50% during the peak of climb operating condition, the remaining thrust in each operating condition being provided by the engineMain engine 3. This configuration corresponds to the section extending between points D and E (corresponding to 37% main thrust and 63% auxiliary thrust 5 at takeoff, and 50% main thrust and 50% auxiliary thrust at the peak of climb) of the curve illustrated in Figure 1. In this configuration, the auxiliary engine 4 therefore contributes to the thrust both during the takeoff operating condition and during the peak of climb operating condition. Alternatively, the propulsion system 2 can be sized so that the thrust supplied by said propulsion system 2 is obtained at a rate of 63% to 70% by the auxiliary engine 4 during the takeoff operating condition and at a rate of 50% to 60% during the peak of climb operating condition, the remainder in each operating condition being provided by the main engine 3. This configuration corresponds to the section extending between points E and F(corresponding to 30% main thrust and 70% auxiliary thrust at takeoff, and 40% main thrust and 60% auxiliary thrust at the peak of climb) of the curve illustrated in Figure 1. In this configuration, the auxiliary engine 4 therefore contributes to the thrust both during the takeoff operating condition and during the peak of climb operating condition. 25 In a first embodiment, the propulsion system 2 can be sized so that, during the takeoff operating condition, the thrust supplied by the propulsion system 2 is obtained at a rate of 38% to 42% by the auxiliary engine 4 during the takeoff operating condition (the remainder being supplied by the main engine 3) and at a rate of 100% by the main engine 3 during the peak of climb operating condition. 3043724 13 This first embodiment is particularly suitable for aircraft 1 having a mission ofshort-haul type. Indeed, the thermodynamic cycle of the main engine 3 is optimized at the peak of climb, which improves its specific fuel consumption compared to a conventional engine, particularly under peak climb and cruise operating conditions, without requiring a large auxiliary engine 4. This reduces the overall size of the propulsion system 2 and the additional weight resulting from the addition of an auxiliary engine 4. In a second embodiment, the propulsion system 2 can be sized so that the thrust provided by the propulsion system 2 is obtained 47% to 49% by the auxiliary engine 4 during takeoff and 18% to 15% by the auxiliary engine 4 during peak climb, with the remainder of the thrust being provided by the main engine 3. This second embodiment is particularly suitablefor aircraft 1 with a short-haul to medium-haul mission. 20 Indeed, the thermodynamic cycle of the main engine 3 is improved at the peak of climb and optimized at the maximum corrected fan speed point (N1 K), which corresponds to an intermediate operating condition between the peak climb operating condition and the cruise operating condition, which is representative of 25 the average use of the aircraft on this type of mission. Typically, the specific fuel consumption of a propulsion system 2 sized according to this embodiment is further reduced compared to that of the propulsion system 2 conforming to the first embodiment. The diameter of the auxiliary engine 4 is, however, more 30 important. 3043724 14 In a third embodiment, the propulsion system 2 can be sized so that the thrust provided by the propulsion system 2 is obtained at a rate of 52% to 55% by theauxiliary engine 4 during takeoff operating conditions and 33% to 36% by auxiliary engine 5 during peak climb operating conditions, the remainder of the thrust being provided by the main engine 3. This third embodiment is particularly suitable for aircraft 1 with medium- to long-range missions. Indeed, the thermodynamic cycle of the main engine 3 is improved at the peak climb and optimized at the fan speed corresponding to 95% of its maximum corrected speed, which corresponds to a medium-duration initial cruise operating condition, representative of the average aircraft use on this type of mission. Typically, the specific fuel consumption of a propulsion system 2 sized according to this third embodiment is further reduced compared to that of the propulsion system 2 conforming to the second embodiment.implementation. The diameter of the auxiliary engine 4 is, however, larger. 20 In a fourth embodiment, the propulsion system 2 can be sized so that the thrust provided by the propulsion system 2 is obtained by the auxiliary engine 4 at a rate of 60% to 63% during the takeoff operating condition and at a rate of 49% to 52% during the peak climb operating condition, the remainder of the thrust being provided by the main engine 3. This fourth embodiment is particularly suitable for aircraft with a long-range mission. Indeed, the thermodynamic cycle of the main engine 3 is improved at the peak climb and optimized at the fan speed point corresponding to 90% of its maximum corrected speed, which corresponds to a long-duration mid-cruise operating condition, representative of the average use of the aircraft on this type of mission.Typically, the specific fuel consumption of a propulsion system 2 sized according to this fourth embodiment is 5 further reduced compared to that of the propulsion system 2 conforming to the third embodiment. The diameter of the auxiliary engine 4 is, however, larger. The propulsion system 2 may comprise one or more main engines 3 and one or more auxiliary engines 4. In this case, the main engine(s) 3 participate together in providing the main thrust, while the auxiliary engine(s) 4 participate together in providing the auxiliary thrust. The main engine(s) 3 may comprise one or more turbojets and / or one or more turboprops, said main engines 3 being able to include at least one fan / propeller, ducted or unducted. The auxiliary engine(s) 4 may comprise one or more turbojets and / or one or moreturboprop engines and / or one or more electric propulsion effectors. Where applicable, the auxiliary engine(s) 4 may be retractable, i.e., their position may be changed during certain phases of flight of the aircraft 1 in order to minimize their drag. For example, the auxiliary engines 4 25 can be retracted by being moved into a specific compartment formed in the wings of aircraft 1. For example, the propulsion system 2 may include a main engine 3 and two auxiliary engines 4. The auxiliary engines 4 may, for example, be mounted under the wings of an aircraft 1 while the main engine 3 may be placed at the rear of the fuselage of aircraft 1, as illustrated in Figure 2. Typically, the propulsion system 2 may include a turboprop engine with an unfaired propeller and two auxiliary engines 4, each comprising one or more propulsive effectors (such as a fan) driven by an electric motor. 5

Claims

DEMANDS 1. Method for sizing (S) a propulsion system (2) for an aircraft (1), said propulsion system (2) being configured to operate under at least two distinct operating conditions and comprising: - at least one main engine (3), configured to provide main thrust, and - at least one auxiliary engine (4), separate from the main engine (3) and configured to provide auxiliary thrust at least during a first operating condition corresponding to the takeoff phase, the dimensioning process (S) being characterized in that it comprises the following steps: (i) for the first operating condition corresponding to the takeoff phase and a first thrust of the propulsion system (2), determine (S1) a first distribution between the main thrust and the auxiliary thrust to obtain said first thrust, the auxiliary thrust contributing at least 5% and at most 65% of the first thrust, (ii) for a second operating condition corresponding to the peak of climb and a second thrust of the propulsion system (2), determine (S2) a second distribution between the main thrust and the auxiliary thrust to obtain said second thrust, this second distribution being a function of the first distribution determined, the auxiliary thrust contributing at most 70% of the second thrust, (iii) dimension (S3) said propulsion assembly (2) so that the main thrust of the main engine (3) determined for the first operating condition corresponds to the maximum thrust that can be achieved by the main engine (3) regardless of the operating condition of the propulsion assembly (2), this dimensioning being carried out with the thrust distributions determined for the first and second operating conditions as constraints.

2. Sizing method (S) according to claim 1, wherein the first and second distribution between the main thrust and the secondary thrust are determined, to within 2%, from the following operating ranges: - the auxiliary thrust contributes at most 45% of the first thrust for the first operating condition and the main thrust contributes 100% of the second thrust for the second operating condition, or - the auxiliary thrust contributes 45% to 48% of the first thrust for the first operating condition and 0% to 20% of the second thrust for the second operating condition, or - the auxiliary thrust contributes 48% to 55% of the first thrust for the first operating condition and 20% to 35% of the second thrust for the second operating condition, or - the auxiliary thrust contributes 55% to 63% of the first thrust for the first operating condition and 35% to 50% of the second thrust for the second operating condition, or - the auxiliary thrust contributes 63% to 70% of the first thrust for the first operating condition and 50% to 60% of the second thrust for the second operating condition.

3. Sizing method (S) according to claim 2, wherein the first and second distribution between the main thrust and the secondary thrust are determined, to within 2%, from the following operating ranges: - the auxiliary thrust contributes 38% to 42% of the initial thrust for the first operating condition and the the main thrust contributes 100% of the second thrust for the second operating condition, or - the auxiliary thrust contributes 47% to 49% of the first thrust for the first operating condition and 18% to 21% of the second thrust for the second operating condition, or - the auxiliary thrust contributes 52% to 55% of the first thrust for the first operating condition and 33% to 36% of the second thrust for the second operating condition, or - the auxiliary thrust contributes 60% to 63% of the first thrust for the first operating condition and 49% to 52% of the second thrust for the second operating condition.

4. Propulsion system (2) for an aircraft (1) configured to operate at least under a first operating condition corresponding to the takeoff phase and a second operating condition corresponding to the peak of climb, and comprising: - at least one main engine (3), configured to provide main thrust, and - at least one auxiliary engine (4), separate from the main engine (3) and configured to provide auxiliary thrust during the takeoff phase and up to the peak of climb, said propulsion assembly (2) being characterized in that it is dimensioned in accordance with a dimensioning method (S) according to any one of claims 1 to 3, so that the main thrust of the main engine (3) during the first operating condition corresponds to the maximum thrust that can be achieved by the main engine (3) regardless of the operating condition.

5. Propulsion assembly (2) according to claim 4, wherein the main engine (3) comprises one or more turbojets and / or one or more turboprops. 5 6. Propulsive assembly (2) according to any one of claims 4 or 5, in which the auxiliary engine (4) comprises one or more turbojets and / or one or more turboprops and / or one or more electrically powered propulsive effectors. 10 7. Propulsive assembly (2) according to any one of claims 4 to 6, in in which the auxiliary motor (4) is retractable.

8. Aircraft (1) characterized in that it comprises a propulsion assembly (2) according to any one of claims 4 to 7. 15 9. Aircraft (1) according to claim 8, wherein the propulsion assembly (2) comprises at least two auxiliary engines (4), the thrust of said auxiliary engines (4) contributing 100% of the auxiliary thrust.

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