Method for controlling an aircraft propulsion system having turbine engines operating in parallel and capable of being placed on standby. Corresponding aircraft.

Abstract

Method for controlling an aircraft propulsion system (S) according to claim 1. FIGURE OF THE ABSTRACT: Fig. 1

Description

Title of the invention: Method for controlling an aircraft propulsion system having turbine engines operating in parallel and capable of being placed on standby. Corresponding aircraft.

[0001] The present invention relates to the propulsion of aircraft.

[0002] BACKGROUND OF THE INVENTION

[0003] A helicopter is an aircraft conventionally equipped with a main rotor driving a rotating wing to provide its lift and propulsion. In order to rotate the main rotor, it is known to equip the helicopter with two turboshaft engines operating in parallel at generally similar speeds. Each of the turboshaft engines is designed to be oversized so as to be able to provide, in the event of failure of the other of the turboshaft engines, sufficient power to allow the helicopter to continue its flight and land in safe conditions.

[0004] When the helicopter is in cruising flight, the turboshaft engines operate at low power levels, which results in a particularly high specific consumption CS (defined as the ratio between the hourly fuel consumption by the combustion chamber of the turboshaft engine and the power supplied by this turboshaft engine) and therefore excess fuel consumption.

[0005] In order to reduce the fuel consumption of the helicopter, it has been proposed, in a cruising flight situation, to put one of the turboshaft engines on standby and to operate this flight phase with the other of the turboshaft engines which then operates at a higher speed and therefore benefits from a lower specific consumption CS.

[0006] Such a mode of operation of the turboshaft engines is called for this “economic mode” or “eco mode”.

[0007] SUBJECT OF THE INVENTION

[0008] The invention therefore aims to propose a method for controlling the propulsion system of an aircraft, which is more fuel-efficient while operating safely. Summary of the invention

[0009] The use of eco mode must not weaken the operational safety of the helicopter but it is also necessary to be able to return the propulsion system to nominal mode reliably. According to the invention, the use of eco mode is based on an automatic control system which assists the crew and implements a verification strategy to, before putting one of the turbine engines on standby, detect latent failures of the propulsion system on the one hand and guarantee the subsequent restart of the dormant turbine engine on the other hand.

[0010] For this purpose, a method according to claim 1 is proposed.

[0011] Thus, the method of the invention makes it possible not only to determine whether the transition of the propulsion system from nominal mode to eco mode can be done without endangering the aircraft but also whether the propulsion system can be returned to nominal mode.

[0012] The invention also relates to an aircraft implementing this method.

[0013] Other characteristics and advantages of the invention will emerge on reading the following description of particular non-limiting embodiments of the invention. Brief description of the drawings

[0014] Reference will be made to the accompanying drawings, among which:

[0015] [Fig-1] [Fig.l] is a schematic view of a propulsion system of a helicopter twin-engine;

[0016] [Fig.2] [Fig.2] is a schematic view of one of the engines of the propulsion system illustrated in [Fig.l];

[0017] [Fig.3] [Fig.3] is a flowchart illustrating the steps of the control method of the propulsion system illustrated in [Fig.l];

[0018] [Fig.4] [Fig.4] is a block diagram illustrating the sequence of steps of vé verification of this process. DETAILED DESCRIPTION OF THE INVENTION

[0019] With reference to [Fig.l], a helicopter comprises a propulsion system S comprising a main rotor R on which blades P are fixed, ensuring the lift and propulsion of the helicopter. The rotor R is rotated by a first turbine engine Mi and a second turbine engine M2, each having an output shaft XSb XS2 connected to said rotor R via a main gearbox MGB. The first turbine engine Mi and the second turbine engine M2 operate in parallel and are respectively controlled by a first regulation computer Ci and a second regulation computer C2. Such regulation computers are commonly called FADEC (from the English acronym "Full Authority Digital Engine Control") and have a structure known per se.The first computer Ci and the second computer C2 communicate with each other via a digital link called intercomputer L and are connected to avionics A of the helicopter to ensure in particular the control of the turboshaft engines and in particular the functions of automatic start, protection against overheating, protection against overtorque, protection against surge, protection against flameout, and management of the life of the first turboshaft engine Mi and the second turboshaft engine M2.

[0020] Each of the first turbine engine Mi and the second turbine engine M2 is designed to be oversized so as to be able to provide, in the event of failure of the other of the first Mi turboshaft engine and the second M2 turboshaft engine, sufficient power to allow the helicopter to continue its flight and land in safe conditions.

[0021] The first turbine engine Mi and the second turbine engine M2 are here gas turbines and comprise, as illustrated in [Fig.2], a gas generator G and a free turbine TBP (called low pressure) capable of being driven in rotation by a gas flow F generated by the gas generator G. In a manner known per se, the free turbine TBP is mounted on the output shaft XSb XS2 which transmits the rotational movement to the rotor R via the main gearbox MGB. The rotational speed NR of the rotor R depends on the rotational speed Nb N2 of the output shafts XSb XS2.

[0022] The gas generator G comprises a drive shaft XEb XE2 on which are mounted a centrifugal compressor CP and a high-pressure turbine THP, as well as a combustion chamber Cc arranged axially between the compressor CP and the high-pressure turbine THP. The combustion chamber Cc is connected to a fuel supply device Daiim controlled by the computer Ci, C2 of the turbine engine Mb M2 concerned. The supply device Daiim comprises a metering device Do connected to the outlet of a fuel pump Pc via a solenoid valve Ev with an on-off flap.

[0023] The first turboshaft engine M1 and the second turboshaft engine M2 are provided with an air inlet (not shown) through which fresh air enters the gas generator G. The air inlet is provided with one or more surfaces movable between two extreme positions in order to form an intake valve (here of the IGV or “inlet guide vane” type) arranged to optimize the operation of the compressor CP.

[0024] After its admission into the gas generator G, the fresh air is compressed by the compressor CP which delivers it towards the inlet of the combustion chamber Cc in which it is mixed with fuel via the feed device DaUm. The combustion which takes place in the combustion chamber Cc causes a high-speed evacuation of burnt gases towards the high-pressure turbine THP which rotates the drive shaft XEb XE2 of the gas generator G and therefore the compressor CP. The high-pressure turbine THP does not absorb all the kinetic energy of the burnt gases and the excess energy constitutes the gas flow F generated by the gas generator G. This gas flow F is directed towards the free turbine TBP, which has the effect of causing an expansion in said free turbine TBP leading to the rotation of the output shaft Xsi, XS2.The rotation speed Ni, N2 of the output shaft XSi, XS2 is a function of the fuel flow entering the combustion chamber Cc.

[0025] In a manner known per se, air is taken from the first turbine engine Mi and the second turbine engine M2 in order in particular to cool the combustion chambers Cc, the high pressure turbines THP and the free turbines TBP of said first turbine engine. Mi and said second M2 turboshaft engine.

[0026] The drive shaft XEb XE2 of the gas generator G is coupled to an electric motor / generator SG via an accessory box (not shown). The motor / generator SG is arranged to supply or take a quantity of rotational kinetic energy from said drive shaft XEb XE2 in order in particular to start the gas generator G or to supply electrical energy to the computers C1, C2, the avionics A and / or other electronic equipment of the helicopter. The motor / generator SG is here controlled by the computer Ci, C2.

[0027] In nominal mode, the two turboshaft engines Mb M2 operate in parallel and provide the necessary power to the rotor R. The nominal mode is preferred for the landing and takeoff phases and possibly used for cruise phases. When the flight conditions (speed, altitude, etc.) of the helicopter are substantially stable, the first turboshaft engine Mi and the second turboshaft engine M2 can operate asymmetrically, with, for example, the first turboshaft engine Mi operating, in a so-called "active" mode, at a relatively high power output, and the second turboshaft engine M2 operating, in a so-called "standby" mode, at a lower (or even zero) power output. Such operation of the first turboshaft engine Mi and the second turboshaft engine M2 allows for better fuel efficiency and therefore better specific consumption CS. This operating mode of the propulsion system is for this reason called "eco mode".

[0028] It will be noted that here, by "speed" we mean the "rotation speed / torque" pair at the output shaft XSb XS2 of the Mb M2 turboshaft engine concerned.

[0029] In certain circumstances, operating parameters (flow rate, temperature, speed, etc.) of the first turbine engine Mi and / or of the second turbine engine M2 (measurements of which are captured and transmitted to the first computer Ci and to the second computer C2) may not be conducive to the operation of said first turbine engine Mi and of said second turbine engine M2 in eco mode.

[0030] Thus, the avionics A of the helicopter is, according to the invention, configured to implement a method for verifying the correct operation of the propulsion system of the helicopter before putting the first turbine engine Mi or the second turbine engine M2 on standby to operate in eco mode.

[0031] In the remainder of the description, with reference to FIGS. 3 and 4, the transition from the nominal (or symmetrical) mode, in which the first turboshaft engine Mi and the second turboshaft engine M2 operate in parallel at a substantially identical power regime, to the eco (or asymmetrical) mode in which the turboshaft engine M1 operates in active mode and the turboshaft engine M2 operates in standby mode, is described.

[0032] As shown in [Fig.3], the method according to the invention comprises the steps of: - while the propulsion system is in nommai mode, check the compatibility of aircraft operating parameters with eco mode (step 10); - if so and if a command to switch to eco mode is received, stop the air / electricity samples taken from the second turbo-engine and check the compatibility of the operating parameters of the first turbo-engine with eco mode (step 40); - if so, idle the second turbine engine so that its output shaft has a lower speed than that of the rotor (step 70); - check the correct operation of the starter of the second turboshaft engine (step 90); - if so, put the second turboshaft engine on standby by interrupting a fuel supply to the second turboshaft engine to switch to eco mode (step 100).

[0033] More specifically, also with reference to [Fig.4], during step 10 of the method of the invention, occurring while the first turbine engine Mi and the second turbine engine M2 are operating in parallel at a substantially identical power regime, a first series of checks is carried out continuously by the first computer Ci and the second computer C2 to determine availability of the eco mode, and a second series of checks is carried out continuously by the avionics A to determine a capacity of the helicopter to use the eco mode.

[0034] The first series of checks includes the following checks: • no critical level failure at the level of the first turbine engine Mi and the second turbine engine M2 is detected by the first computer Ci and the second computer C2; • no overspeed of the output shafts XSb XS2 and or of the drive shafts XEb XE2 of the first and second turboshaft engines Mb M2 is detected by the first computer Ci and the second computer C2; • the first turboshaft engine Mi and the second turboshaft engine M2 operate in parallel at a substantially identical speed to drive the rotor R in rotation (operating speed called AEO, from the English acronym “AU Engines operative”); • the SG motor / generator is operating correctly; • an electrical power source external to the second turbine engine M2 is available to electrically power the second computer C2 (when the second turbine engine M2 is in active mode, it is powered by the engine / generator SG coupled to the gas generator G of said second turbine engine M2); and • the temperature of the fuel injected into the combustion chambers Cc is within a determined range recorded in a memory of the first and second computers Ch C2.

[0035] The results of this first series of checks are transmitted to avionics A.

[0036] The second series of checks includes the following checks: • the Ml turboshaft engine has sufficient operating margins in relation to current flight conditions (i.e. its operating parameters have values ​​within an operating range relatively far from its lower and upper operating limits); • the first turbine engine Mi is capable of operating at a power speed high enough to guarantee on its own the rotation of the rotor R at a speed NR equal to a set speed, this power speed being lower than a predetermined threshold power speed; • no critical level failure is detected by avionics A; and • atmospheric conditions (temperature, pressure, humidity, etc.) are favorable for putting the second M2 turboshaft engine on standby.

[0037] During a second step 20 of the method of the invention, the avionics A analyzes the results of the first and second series of checks. More precisely, if at least one of the conditions listed in the first and second series of checks is not verified, the avionics A is configured to inform the pilot via a human-machine interface of the unavailability of the eco mode.

[0038] Otherwise, if all the conditions listed in the first and second series of checks are verified, the avionics A is configured to inform the pilot via the human-machine interface of the availability of the eco mode.

[0039] When the pilot requests activation of the eco mode via a selector of the avionics A, a third series of checks is carried out by the avionics A during a third step 30 of the method of the invention to determine the correct reception of the request for activation in eco mode. The third series of checks comprises the following checks: • the selector is in the eco mode position; • eco mode is requested by avionics A; • the rotor R operates at a power speed greater than a predetermined threshold power speed which is for example greater than 90% of a maximum power speed; and • the first computer Ci and the second computer C2 received from the avionics A the request to put the second turboshaft engine M2 on standby (verification for example carried out via the intercomputer L).

[0040] If at least one of the conditions listed in the third series of checks is not verified, the avionics A is configured to inform the pilot via the human-machine interface of the unavailability of the eco mode.

[0041] Otherwise, if all the conditions listed in the third series of checks are verified, the air sampling and the kinetic energy sampling carried out on the second turbine engine M2 are stopped, so that: • the combustion chambers Cc, the high pressure turbines THP and the free turbines TBP of the first and second turboshaft engines Mb M2 are no longer cooled by means of the air bleed normally carried out on the second turboshaft engine M2, and • the first computer Cb, the second computer C2, the avionics A and the electronic equipment of the helicopter are no longer electrically powered by the motor / generator SG of the second turbine engine M2.

[0042] During a fourth step 40 of the method of the invention, a fourth series of checks is carried out by the avionics A to determine whether the air sampling and the kinetic energy sampling carried out on the first turbine engine Mi will be sufficient to provide the air and electrical energy needs of the helicopter when the second turbine engine M2 is on standby.

[0043] The fourth series of checks includes the following checks: • the air sampling carried out on the turbine engine Mi is greater than a predetermined threshold air sampling which is recorded in the memory of the first computer Ci; and • the kinetic energy extraction carried out on the first turbine engine Mi by means of the engine / generator SG is greater than a predetermined threshold kinetic energy extraction which is recorded in the memory of the first computer Cb

[0044] If at least one of the two conditions listed in the fourth series of checks is not verified, the avionics A is configured to inform the pilot via the human-machine interface of the unavailability of the eco mode.

[0045] Otherwise, if all the conditions listed in the fourth series of checks are verified, the avionics A proceeds to a misalignment of the first turbine engine Mi and the second turbine engine M2 to bring each of said first and second turbine engines Mb M2 to a power regime close to that which it will deliver in eco mode (step 50; it will be noted that this step is optional). The misalignment will for example be carried out: • by slowly reducing the torque delivered by the second turbine engine M2 to a low value, while regulating the speed of the first turbine engine Mi so as to maintain the speed NR of the rotor R at the set speed; Or • by imposing, via a balancing module of the first and second turboshaft engines Mb M2, a torque ratio between said first and second turboshaft engines Mb M2 (for example, the torque delivered by the second turboshaft engine M2 is substantially equal to 20% of the torque delivered by the first turboshaft engine Mi), while regulating the speed of the first turboshaft engine Mi and of the second turboshaft engine M2 so as to maintain the speed NR of the rotor R at the set speed.

[0046] In order to minimize the variation in the speed NR of the rotor R during the misalignment of the first and second turboshaft engines Mb M2, the avionics A can advantageously warn the first computer Ci of the imminent change in the power regime of the second turboshaft engine M2 so that the first turboshaft engine Mi anticipates the fact that it will have to accelerate the speed of its output shaft XSb

[0047] During a sixth step 60 of the method of the invention, a fifth series of checks is carried out by the avionics A to determine whether the misalignment of the first turbine engine Mi and the second turbine engine M2 has been correctly carried out and whether the first turbine engine Mi is operating correctly to compensate for the standby of the second turbine engine M2.

[0048] The fifth series of checks includes the following checks: • at the end of the misalignment of the first turbine engine Mi and the second turbine engine M2, the speed NR of the rotor R is still equal to the set speed; and • operating parameters (temperature, pressure, speed, torque, power, etc.) of the first Mi turboshaft engine are included in value ranges compatible with eco mode.

[0049] If at least one of the two conditions listed in the fifth series of checks is not verified, the avionics A is configured to inform the pilot via the human-machine interface of the unavailability of the eco mode and carries out a realignment of the first turbine engine Mi and the second turbine engine M2.

[0050] Otherwise, if all the conditions listed in the fifth series of checks are verified, the second turbine engine M2 is idled (step 70) so as to deliver at the output shaft XS2 a substantially zero torque, the power speed of the gas generator G or of the free turbine TBP of said second turbine engine M2 being regulated so that the power delivered by the output shaft XS2 is less than that delivered by the rotor R. Idling the second turbine engine M2 makes it possible to thermally stabilize said turbine engine M2 and thus to avoid coking the fuel and the oil in the bearings on which the free and low pressure turbines THp, TBp are mounted.

[0051] During an eighth step 80 of the method of the invention, a sixth series of checks is carried out by the avionics A to determine in particular whether the first turbo-engine Mi has sufficient power reserve to ensure flight safety.

[0052] The sixth series of checks includes the following checks: • the intake valve equipping the air inlet of the second M2 turboshaft engine is capable of moving between its two extreme positions; and • the power delivered by the first turbine engine Mi is less than a maximum power available from said first turbine engine Mi (for example, the power delivered by the first turbine engine Mi is less than 80% of the maximum power available from said first turbine engine Mi).

[0053] Maximum power means the maximum power for particular operating conditions. There are thus several maximum powers and for example the maximum power at take-off for different temperatures and pressures, the power in hovering flight out of ground effect, etc.

[0054] If at least one of the two conditions listed in the sixth series of checks is not verified, the avionics A is configured to inform the pilot via the human-machine interface of the unavailability of the eco mode and carries out a realignment of the first turbine engine M1 and the second turbine engine M2.

[0055] Otherwise, if all the conditions listed in the sixth series of checks are verified, the avionics A proceeds, during a ninth step 90 of the method of the invention, to a seventh series of checks to verify the correct operation of the engine / generator to restart the gas generator G of the second turbine engine M2 in flight.

[0056] The seventh series of checks includes the following checks: • in the case where the SG engine / generator of the second M2 turboshaft engine is with freewheel, activate the SG engine / generator of the second M2 turboshaft engine up to a given speed then regulate the speed of the SG engine / generator of the second M2 turboshaft engine up to the standby mode speed (standby mode is also called turning mode) or approximately 10% of the nominal speed of the gas generator of the second M2 turboshaft engine. • in the case where the SG engine / generator of the second turbine engine M2 is in direct drive (i.e. coupled to the second turbine engine without freewheel), activate the SG engine / generator of the second turbine engine M2 to rotate the drive shaft XE2 and check that the operating parameters of the second turbine engine (rotation speed of the output shaft XS2, air flow rate F, temperature T45 at the inlet of the free turbine TBp, etc.) show a change representative of power generation by said SG engine / generator.

[0057] If the conditions listed in the seventh series of checks are not verified, the avionics A is configured to inform the pilot via the human-machine interface of the unavailability of the eco mode and carries out a realignment of the first turbo-engine Mi and the second turbo-engine M2.

[0058] Otherwise, the avionics A cuts off the fuel supply to the combustion chamber Cc of the second turbine engine M2 via the solenoid valve E v and / or the metering valve Do of the supply device D.,|im so as to put said second turbine engine M2 on standby (step 100)

[0059] During an eleventh step 110 of the method of the invention, an eighth series of checks is carried out by the avionics A to verify the correct operation of the supply device DaUm to restart the gas generator G of the second turbine engine M2.

[0060] The eighth series of checks includes at least one of the following two checks at the second turbine engine M2: • while the solenoid valve Ev is open, the reactivation of the metering valve Do to supply fuel to the combustion chamber Cc and the starting of the engine / generator SG to rotate the drive shaft XE2 cause an increase in the internal temperature T4 of said combustion chamber Cc; and • while the metering device Do is active, the reopening of the solenoid valve Ev to supply fuel to the combustion chamber Cc and the starting of the motor / generator SG to rotate the drive shaft XE2 cause an increase in the internal temperature T4 of said combustion chamber Cc.

[0061] If the conditions listed in the eighth series of checks are not verified, the avionics A is configured to inform the pilot via the human-machine interface of the unavailability of the eco mode and carries out a realignment of the first turbine engine Mi and the second turbine engine M2.

[0062] Otherwise, the avionics A again cuts off the fuel supply to the combustion chamber Cc of the second turbine engine M2 via the solenoid valve Ev and / or the metering valve Do of the supply device DaUm so as to put said second turbine engine M2 on standby (step 120).

[0063] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0064] The propulsion system may comprise more than two turboshaft engines.

[0065] It is not always the same turboshaft engine that is put on standby.

[0066] Although the pilot is here informed of the availability of eco mode before entering it, request activation, he can also be informed about it after requesting activation.

[0067] The method according to the invention comprises at least the steps of: - while the propulsion system is in nominal mode, check the compatibility of the aircraft operating parameters with eco mode; - if so and if an order to switch to eco mode is received, stop the air / electricity samples taken from the second turbo-engine and check the compatibility of the operating parameters of the first turbo-engine with eco mode; - if so, idle the second turbine engine so that its output shaft has a lower speed than that of the rotor; - check the correct operation of the starter of the second turboshaft engine; - if so, put the second turboshaft engine on standby by interrupting the fuel supply to the second turboshaft engine to switch to eco mode.

[0068] These steps may be carried out in a manner other than that described and the method may comprise additional steps.

[0069] The invention is applicable to any aircraft comprising a propulsion system which comprises at least two turbomachines and which is capable of switching from a nominal operating mode to an economical operating mode.

Claims

Claims

1. Method for controlling an aircraft propulsion system (S), comprising a rotor (R), at least one first turboshaft engine (MJ) and a second turboshaft engine (M2) which have output shafts (XSi, XS2) connected to said rotor via a main gearbox (BTP) and which are respectively controlled by a first regulation computer (Ci) and a second regulation computer (C2) connected to each other by a digital link (L) and both connected to avionics (A), and at least one electric starter coupled to each turboshaft engine;the propulsion system being arranged to have a nominal mode in which the two turbine engines drive the rotor and air / electricity sampling is carried out on the two turbine engines, and an eco mode in which only the first turbine engine drives the rotor, the second turbine engine being on standby, and the air / electricity sampling is carried out only on the first turbine engine, the rotor having a set speed in both modes; characterized in that the method comprises: - while the propulsion system is in the nominal mode, checking the compatibility of operating parameters of the aircraft with the eco mode; - if so and in the event of receiving a command to switch to eco mode, stopping the air / electricity sampling carried out on the second turbine engine and checking the compatibility of operating parameters of the first turbine engine with the eco mode;- if so, idling the second turbine engine so that its output shaft has a lower speed than that of the rotor; - checking that the starter of the second turbine engine is working correctly; - if so, putting the second turbine engine on standby by interrupting the fuel supply to the second turbine engine to switch to eco mode;

2. The method of claim 1, wherein checking the compatibility of flight conditions with eco mode comprises a first verification by each computer that the associated turbine engine has an internal operation compatible with eco mode and a second verification by the avionics that the aircraft has operating parameters compatible with eco mode.

3. Method according to claim 1 or 2, in which the idling of the second turboshaft engine comprises a misalignment of the two turboshaft engines to bring the first turboshaft engine to a power level close to that required in eco mode and a verification that the rotor maintains the set speed.

4. The method of claim 3, wherein idling the second turbine engine comprises controlling the second turbine engine to bring it into a zero-power thermal stabilization regime.

5. A method according to claim 4, wherein idling the second turbine engine comprises checking the operating margins of the first turbine engine.

6. Method according to any one of the preceding claims, in which, the starter being coupled to the second turbine engine via a freewheel, the verification of the correct operation of the starter of the second turbine engine comprises an activation of the starter up to a predetermined speed then a regulation of the starter speed up to a standby mode speed.

7. The method of claim 6, wherein the standby mode speed is equal to approximately 10% of the nominal speed of the second turbine engine.

8. Method according to any one of claims 1 to 5, in which, the starter being coupled to the second turbine engine in direct drive, the verification of the correct operation of the starter of the second turbine engine comprises an activation of the starter of the second turbine engine to drive the second turbine engine in rotation and a verification that the second turbine engine has operating parameters showing a representative evolution of a generation of power by said starter.

9. A method according to any preceding claim, wherein putting the second turbine engine on standby comprises restoring the fuel supply to the second turbine engine and activating the starter, checking for a rise in temperature of the second turbine engine and, if so, interrupting the fuel supply to the second turboshaft engine to switch to eco mode.

10. Aircraft comprising a propulsion system (S) comprising a rotor (R), at least a first turboshaft engine (MJ and a second turboshaft engine (M2) which have output shafts (XSb XS2) connected to said rotor via a main gearbox (BTP) and which are respectively controlled by a first regulation computer (Ci) and a second regulation computer (C2) connected to each other by a digital link and both connected to an avionics system A, and at least one electric starter coupled to each turboshaft engine;the avionics being arranged to implement the control method according to any one of the preceding claims to switch the propulsion system from a nominal mode in which the two turbine engines drive the rotor and air / electricity sampling is carried out on the two turbine engines, to an eco mode in which only the first turbine engine drives the rotor, the second turbine engine being on standby, and the air / electricity sampling is carried out only on the first turbine engine, the rotor having a set speed in both modes.;

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