Multi-engine aircraft with economic operation mode and method of application

Abstract

The invention relates to a multi-engine aircraft having an economic operation mode and a method of application, the aircraft (1) having a rotary wing (5) having a power plant (10) comprising a plurality of engines (11, 12), said aircraft (1) comprising a human-machine interface (20) controlling a control member (7) capable of acting on the longitudinal acceleration of the aircraft (1). During the economic operation mode in which one of the engines does not provide power, the method comprises: (i) measuring the forward speed of the aircraft (1), (ii) using a flight control computer (80) to adjust the authority of said human-machine interface (20) on said longitudinal acceleration as a function of the forward speed (V).

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of FR2102873, filed on March 23, 2021, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to a multi-engine aircraft with an economical operating mode, and methods for using it.

[0004] For example, an aircraft may include various rotating components that move via a power unit. Therefore, an aircraft may have a rotating wing and possibly a yaw control rotor.

[0005] In a twin-engine helicopter, the necessary power supplied by the power plant varies with the forward speed. The required power gradually decreases from zero forward speed to an intermediate speed, and then gradually increases as the forward speed increases. Within the speed range from a first lower speed limit to a second upper speed limit, all the necessary power to drive the rotating components can be provided by a single engine.

[0006] Therefore, during the economic operating mode, while the aircraft is operating within this speed range, one engine can be in standby mode—that is, shut down or idled—to optimize fuel consumption. However, as the aircraft decelerates and approaches the first speed, the standby engine must be reactivated before reaching that first speed. Due to the aircraft's ability to decelerate rapidly and the time required to reactivate the engine, the standby engine may need to be reactivated at speeds significantly higher than the first speed to provide mechanical power. This limits the advantages of the economic operating mode. Background Technology

[0007] Patent EP3209563B1 discloses an economical operating mode in which the engines of a multi-engine power unit produce far less power than nominal power, or are even shut down during flight. The engines are then quickly reactivated using an electrical system powered by an onboard network or a specific power supply network.

[0008] Such a system is advantageous, but it requires a dedicated electrical system, which may have a significant impact on weight.

[0009] Patent FR2967132B1 describes a method for optimizing the specific fuel consumption of a helicopter having two turboshaft engines. According to this method, the two turboshaft engines provide significantly different amounts of power. One of the turboshaft engines is able to operate in a continuous operation mode, while the other turboshaft engine is in standby at zero power and the combustion chamber is extinguished, while the rotation is maintained by a main drive mechanism, to enable a reliable restart. If the conventional restart fails, the restart can be performed by emergency assistance of an additional ignition of the combustion chamber. This additional ignition can be achieved by a hot wire igniter, laser radiation or a pyrotechnic device.

[0010] Patent FR2967133B1 describes a method for optimizing the specific fuel consumption of a helicopter having two turboshaft engines. According to this method, one of the turboshaft engines is able to operate in a continuous operation mode, while the other turboshaft engine is operated in an ultra-slow mode at zero power. If the conventional restart fails, the turboshaft engine operated in ultra-slow mode can be restarted by emergency assistance produced by an independent energy source dedicated to this restart.

[0011] Documents EP3170744A1, EP3069990 and EP3095695 are also known. SUMMARY

[0012] It is therefore an object of the present application to propose an alternative multi-engine aircraft aimed at optimizing fuel consumption during flight.

[0013] The present application therefore relates to a method for controlling a rotary-wing aircraft having a power plant comprising a plurality of engines that move said rotary wing, said aircraft comprising a human-machine interface that controls a control channel to a control member capable of acting on the longitudinal acceleration of the aircraft, said aircraft comprising a flight control computer, said aircraft being able to operate in an economic operation mode in which at least one of said plurality of engines does not provide mechanical power to said rotary wing and at least one of said plurality of engines provides mechanical power to said rotary wing.

[0014] During the economic operation mode, the method comprises the following steps:

[0015] • measuring the forward speed of the aircraft; and

[0016] • using the flight control computer to adjust the authority of said human-machine interface on said longitudinal acceleration as a function of the forward speed.

[0017] The economic operation mode can be triggered by the pilot or co-pilot operating a dedicated interface, or indeed automatically.

[0018] Accordingly, each engine includes a combustion chamber and a working shaft capable of transmitting power to the rotary wing. During the economic operation mode, at least one engine is in a stand-by state, i.e., it does not produce mechanical power that moves the rotary wing. An engine in a stand-by state can be shut down or idling. The term "idling" refers to a state in which movable components of the engine, separate from the working shaft, are moving whether or not the combustion chamber is ignited.

[0019] Accordingly, an engine in a stand-by state can have a combustion chamber that remains ignited to move movable components of the engine without providing power. For example, the shaft of a gas generator of a free turbine turbo-shaft engine rotates at about 20% to 80% of its nominal speed, the free turbine not being moved by the turbo-shaft engine.

[0020] According to another example, the combustion chamber of an engine in a stand-by state can be extinguished, the movable components of the engine being stationary, or the movable components being moved by another drive member, such as an electric machine. On a turbo-shaft engine, the shaft of a gas generator can be moved by an electric machine at a speed of about 5% to 20% of its nominal speed to help facilitate a restart.

[0021] Accordingly, if the engine is a turbo-shaft engine of a free turbine, the free turbine is not moved by the turbo-shaft engine during the stand-by mode. The gas generator can also be stationary or moved by a small amount of fuel combustion and / or by the action of an auxiliary engine.

[0022] During the economic operation mode, the flight control computer adjusts the authority of the human-machine interface as a function of the forward speed. The authority represents the extreme order that can be imparted by the human-machine interface. For example, for a human-machine interface that includes movable components, the same movement of the movable components results in different longitudinal accelerations in the presence of two forward speeds of 100 knots and 150 knots. It is noted that one knot equals 1.852 kilometers per hour or 1.1508 miles per hour. By convention, negative longitudinal acceleration can be a longitudinal deceleration.

[0023] For the record, the economic operation mode can be implemented over a range of forward speeds ranging from a minimum speed threshold to a maximum speed threshold.

[0024] The authority of the human-machine interface can be maximized when the forward speed is well above the lower limit of the range of speeds. For example, when the human-machine interface includes a joystick, the maximum possible movement of the joystick produces the maximum longitudinal deceleration, which tends to rapidly reduce the forward speed of the aircraft. In practice, in this case, the engine in stand-by can be reactivated before the lower limit is reached, if necessary. By way of example, 30 seconds can be required to reactivate the engine.

[0025] Such reactivation can be achieved by increasing the flow rate of fuel supplied to the engine in question, so as to use the engine to generate stored non-zero mechanical power. Reactivation can be achieved by applying a method for starting the engine. Reactivation includes a conventional starting procedure, in which at least one movable component of the reactivated engine is not necessarily stationary when the method for starting the engine is initiated.

[0026] However, when the forward speed approaches the lower limit, the flight control computer will reduce the human-machine interface's permissions regardless of the user's actions, in order to ensure that the standby engine can be reactivated before reaching the lower limit.

[0027] For example, an aircraft's optimal deceleration capability allows it to reach its lower limit within 15 seconds at such a forward speed, while the time required to restart the engines is 30 seconds. Therefore, the flight control computer reduces the permissions of the human-machine interface to constrain the aircraft and reduce its deceleration capability. Due to the reduced permissions of the human-machine interface, the aircraft can reach its lower limit after 30 seconds or more.

[0028] Based on the examples above, the maximum possible movement of the joystick produces a smaller deceleration than before. The slower rate of decrease in forward speed helps ensure that the engine in standby mode can be reactivated before reaching the lower limit and before applying emergency operating status if needed.

[0029] Therefore, this method may tend to increase the time the engine is in standby mode in order to optimize fuel consumption. Thus, this method can prevent the need for unnecessary emergency restarts.

[0030] It can also optimize the flight envelope that allows the use of the economy mode.

[0031] The method may also include one or more of the following features, used individually or in combination.

[0032] According to one possibility, the flight control computer can issue control signals that are transmitted to at least one variable geometry component of the control channel.

[0033] Such variable geometry components can be linear or rotary actuators, cranks of variable length, etc.

[0034] This method can include the following steps during economic operation:

[0035] • When the forward speed is between the minimum speed threshold and the maximum speed threshold, adjusting the human-machine interface's authority over the longitudinal acceleration includes using the flight control computer to generate the control signal at least based on the forward speed or a command signal actually issued by the human-machine interface.

[0036] The flight control computer is configured to also consider forward speed when necessary to reduce the permissions of the human-machine interface.

[0037] At least one of the maximum speed threshold and the minimum speed threshold is fixed or can vary according to at least one positioning parameter.

[0038] For example, the maximum speed threshold and / or minimum speed threshold can be fixed after testing or calculation.

[0039] Alternatively, the maximum speed threshold and / or minimum speed threshold can be variable to take into account various parameters that may affect engine operation and the power required to follow the aircraft's flight scenario.

[0040] Optionally, since the economic operating mode can be implemented within a forward speed range from a minimum speed threshold to a maximum speed threshold, the method includes the following steps during the economic operating mode:

[0041] When the forward velocity is between an intermediate velocity threshold and a maximum velocity threshold, and the maximum velocity threshold is greater than the intermediate velocity threshold, adjusting the human-machine interface's authority over the longitudinal acceleration includes using the flight control computer to generate the control signal according to the first law; and

[0042] • When the forward speed is between a minimum speed threshold and an intermediate speed threshold, and the minimum speed threshold is less than the intermediate speed threshold, adjusting the human-machine interface's authority over the longitudinal acceleration includes using a flight control computer to generate the control signal according to a second law, wherein the first law grants the human-machine interface greater authority than the second law.

[0043] Each law can be in the form of at least one equation, numerical table, etc.

[0044] When the forward speed is greater than the minimum speed threshold or greater than an intermediate speed threshold greater than the minimum speed threshold, the flight control computer applies the stored first law. However, when the forward speed approaches the minimum speed threshold, the flight control computer applies the second law, which restricts the permissions of the human-machine interface.

[0045] The method may optionally include a transition phase between the application phase of the first law and the application phase of the second law.

[0046] This possibility could help prevent drivers from experiencing changes in the laws.

[0047] According to one possibility compatible with the foregoing possibilities, the intermediate speed threshold can be fixed or can vary according to at least one positioning parameter.

[0048] In addition, a positioning parameter that may affect one of the above thresholds is the aircraft's current density altitude.

[0049] According to one possibility compatible with the foregoing possibilities, during economic operating mode, when the forward speed drops below the reactivation speed threshold, the method may include reactivating the engine that does not provide mechanical power to the rotary wing to use the engine to transmit mechanical power.

[0050] The re-enable speed threshold is greater than the minimum speed threshold. The re-enable speed threshold is lower than the maximum speed threshold and the intermediate speed threshold. The re-enable speed threshold can be fixed or can vary based on at least one operating parameter.

[0051] According to one possibility compatible with the foregoing, the method may include limiting the maximum forward speed to a maximum speed threshold via a flight control computer.

[0052] During economic operating mode, the flight control computer can act on the aircraft to prevent it from exceeding its maximum speed, which causes the engines that were initially in standby mode to be reactivated.

[0053] The economic operating mode can then be deactivated to reactivate the engine and achieve greater forward speeds for the aircraft.

[0054] According to one possibility compatible with the foregoing, the method may include automatically disabling the economic operating mode based on a command from the flight control computer when the forward speed is less than a minimum speed threshold.

[0055] In addition to the method, the present invention also relates to an aircraft in which the method is applied.

[0056] This aircraft has a rotary wing and a power plant including multiple engines that move the rotary wing. The aircraft includes a human-machine interface that controls a control channel leading to a control component capable of applying longitudinal acceleration to the aircraft. The aircraft includes a flight control computer and is capable of operating in an economic mode in which at least one of the multiple engines does not provide mechanical power to the rotary wing and at least one of the multiple engines does provide mechanical power to the rotary wing.

[0057] The aircraft also includes a forward speed sensor, and the flight control computer is configured to apply the method according to the invention.

[0058] The aircraft may include a variable geometry component that acts on the position of the control components, and the flight control computer communicates with the variable geometry component. Attached Figure Description

[0059] The invention and its advantages will appear in more detail in the context of the following description of embodiments given by way of example and with reference to the accompanying drawings, in which:

[0060] · Figure 1 This is one embodiment of the aircraft according to the present invention;

[0061] · Figure 2 This is one embodiment of the aircraft according to the present invention; and

[0062] · Figure 3 This is a diagram illustrating the method of the present invention. Detailed Implementation

[0063] Elements present in more than one figure are given the same reference numerals in each of them.

[0064] Figure 1 and Figure 2 An embodiment of an aircraft suitable for implementing the method of the present invention is shown.

[0065] In any implementation, and referring to Figure 1 For example, the aircraft 1 according to the invention may include a body schematically shown in dashed lines. The body extends along a longitudinal axis and from rear to front, from tail 2 to nose 3. The term "longitudinal" refers to the direction from tail 2 to nose 3, which is substantially parallel to the roll axis. The expression "longitudinal acceleration" is commonly used by those skilled in the art.

[0066] The aircraft 1 includes a rotary wing 5 with blades 6. Optionally, the aircraft 1 may include at least one other rotor (not shown here), such as a side rotor, a rear rotor, another rotary wing, etc.

[0067] To specifically move the rotor 5, or in fact one or more rotors, the aircraft 1 includes a power unit 10. This power unit includes several engines 11, 12, each capable of moving the rotor 5. The engines 11, 12 can be controlled by at least one engine computer (not shown here). For example, the engines 11, 12 are mechanically connected to the rotor 5 via a power transmission system 15. This power transmission system 15 may include a rotor shaft 17 fixed to the rotor 5, a gearbox 16 housing the rotor shaft 17, at least one shaft, and / or at least one coupling device, etc. According to the example shown, each engine 11, 12 includes a power shaft that drives the gearbox 16 via a connector 18, the gearbox including the rotor shaft 17. On an aircraft equipped with at least one other rotor, the gearbox 16 or another gearbox may be connected to each rotor via a dedicated transmission device.

[0068] To control the movement of the aircraft 1, the aircraft 1 includes a human-machine interface 20. Such a human-machine interface may include a joystick, handle 21, mini-grip, knob, touchpad, etc. Optionally, the human-machine interface 20 includes a sensor 22, which transmits at least one command signal 102 based on the actuation of the human-machine interface 20.

[0069] For example, the human-machine interface 20 includes a handle 21 that can rotate about two axes. The sensor may include a position sensing device, such as a potentiometer, for each axis.

[0070] The term "signal" refers to analog signals, digital signals, electrical signals, or optical signals.

[0071] The human-machine interface 20 engages with a control channel 30 leading to a control component 7, which is capable of applying longitudinal acceleration to the aircraft 1. This control component 7 may be, for example, in the form of a blade 6 of a rotating wing 5 and / or a blade of another rotor, and may be, for example, a propeller or actually a flap (if present).

[0072] Figure 1 An example of conventional auxiliary mechanical flight control is shown. Figure 2 An example of electronic flight control is shown.

[0073] according to Figure 1 The human-machine interface 20 is mechanically connected to a mechanical control channel 30. The mechanical control channel 30 may include mechanical connectors 36 leading to one or more servo controllers 43. The mechanical connectors 36 may have at least one shaft 31, and / or at least one crank 32, and / or at least one series actuator 34, and / or at least one parallel actuator 35; these actuators are generally referred to as “fine-tuning actuators.” Each servo controller 43 is connected to a fixed swashplate 42 of a swashplate assembly 40. The swashplate assembly 40 also includes a rotating swashplate 41 connected via a rod 45 to a corresponding blade 6 of the rotor blade 5.

[0074] By controlling the cyclic pitch of the blades 6 of the rotating wing 5, the human-machine interface 20 can control the longitudinal acceleration of the aircraft 1 in a conventional manner.

[0075] According to a possibility not shown here, the human-machine interface can jointly control the pitch of the rotor blades and / or at least one other rotor blade for this purpose.

[0076] according to Figure 2One or more servo controllers are controlled by at least one control actuator 38, which is controlled by a flight control computer 80. The flight control computer 80 stores at least one law that provides setpoints to be transmitted to the control actuator 38 based on command signals 102 issued by the human-machine interface 20.

[0077] Figure 1 and Figure 2 An example of an architecture is shown that indicates how the human-machine interface 20 can control the longitudinal acceleration of the aircraft 1 by controlling the control components. Other architectures can be considered without departing from the context of the claimed invention.

[0078] In any architecture, and refer to Figure 2 For example, aircraft 1 includes a flight control computer 80.

[0079] The term "computer" can include, for example, one or more units, each having at least one processor and at least one memory, at least one integrated circuit, at least one programmable system, and at least one logic circuit; these examples do not limit the scope of the term "computer." The term "processor" can be equivalently used to refer to a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), a microcontroller, etc. Several computers described can be combined to form a single computer.

[0080] The flight control computer 80 can be a computer of a system represented by the acronym AFCS, which stands for Automatic Flight Control System.

[0081] If appropriate, the flight control computer 80 can be connected to the human-machine interface 20 via a wired or wireless link to receive command signals 102.

[0082] The flight control computer 80 can be connected via a wired or wireless link to a forward speed sensor 27 that measures the forward speed V of the aircraft 1. For example, the forward speed can be actual airspeed, airspeed, etc. This forward speed sensor 27 may include a pitot tube system, a satellite positioning system, etc. The forward speed sensor 27 transmits a speed signal 103 carrying the forward speed V to the flight control computer 80.

[0083] The flight control computer 80 can be connected to at least one positioning sensor 25 via a wired or wireless link. Each positioning sensor 25 emits a positioning signal, which is transmitted to the flight control computer 80. For example, the positioning sensor 25 measures density altitude and includes, for example, a temperature sensor and a pressure sensor. The positioning sensor 25 transmits a positioning signal 104 carrying the values ​​of positioning parameters to the flight control computer 80.

[0084] Aircraft 1 can operate in an economic operating mode. During this economic operating mode, and at least within its speed range, at least one engine 11 or 12 is operational, generating mechanical power to move the rotor wing 5. Additionally, at least one engine 11 or 12 is in a standby state. Engines in standby state do not provide any mechanical power to move the rotor wing 5. Engines in standby state are stopped or idling. For example, engines 11 and 12 are free-turbine turboshaft engines.

[0085] In a standby turboshaft engine, the free turbine is stationary, or moves only due to the airflow passing through the engine as the aircraft moves forward. In this case, it is not the engine that moves the free turbine. The statement "an economical operating mode in which at least one of the plurality of engines does not provide mechanical power to the rotor" means that the engine itself does not rotate its output shaft connected to the rotor, which can be moved by the wind.

[0086] The shaft of the gas generator in a turboshaft engine in standby mode is also stationary or rotates at a reduced speed driven by auxiliary drive components, low fuel combustion, or even wind. For example, the speed range could be from a reactivation threshold to a maximum speed threshold, which will be mentioned below.

[0087] For example, aircraft 1 may include a controller 26, which can be operated by the pilot to request the implementation of an economical operating mode. The controller 26 issues an operation signal, which is transmitted to a computer to put at least one engine 11 or 12 into standby mode. For example, the operation signal is transmitted to an engine computer. Flight control computer 80 may also receive the operation signal.

[0088] Therefore, during economic operation mode, the flight control computer is configured to apply the method of the present invention. Specifically, the flight control computer is configured to control the position of a variable geometry member 60 acting on the control member 7 according to the forward velocity V. Thus, the flight control computer 80 is configured to transmit control signals to at least one variable geometry member 60. This variable geometry member 60 may be a variable geometry crank 32, a series actuator 34, a parallel actuator 35, or a control actuator 38. The term "variable geometry member" refers to any member that can be geometrically modified to restrict the permissions of the human-machine interface 20.

[0089] Figure 3 This is a diagram illustrating the method of the present invention. The diagram shows the forward velocity V on the X-axis and the power on the Y-axis.

[0090] Curve C illustrates the necessary power PNEC required to sustain the movement of the various components at each instant. Starting from zero forward speed, the required power PNEC decreases as the forward speed V increases until it reaches a minimum, and then increases. The power units, particularly the engines 11 and 12, are sized to provide the necessary power PNEC required at each instant.

[0091] Horizontal line C1 indicates the power that can be provided by a single engine. This power is, for example, less than or equal to the maximum continuous power the engine can provide, such as approximately a predetermined percentage of the maximum continuous power. This maximum continuous power is represented by the acronym MCP. The power level shown by horizontal line C1 represents a trade-off between the impact of the engine's power on its damage and the resulting consumption gains.

[0092] Therefore, when the necessary power is located on or below line C1, at least one engine can be kept in standby mode.

[0093] During economic operation mode, the method includes measuring the forward velocity V of the aircraft 1. The forward velocity sensor 27 transmits the velocity signal 103 to the flight control computer 80.

[0094] Therefore, the flight control computer 80 is configured to adjust the human-machine interface 20's authority over longitudinal acceleration based on the forward speed V.

[0095] For example, the flight control computer 80 can issue a control signal 101 that reduces the privilege, which is transmitted to at least one variable geometry member 60.

[0096] Alternatively, at least in the context of an architecture with electronic flight control, the control signal 101 may also depend on the command signal 102 issued by the human-machine interface 20.

[0097] Specifically, when the forward speed V is between the minimum speed threshold V3 and the maximum speed threshold Vmax, the permissions of the human-machine interface 20 are adjusted by generating a control signal 101 based on the forward speed V. The flight control computer is then configured to compare the forward speed V with the various thresholds mentioned above.

[0098] For example, the minimum speed threshold V3 is in the range of 80 knots, and the maximum speed threshold Vmax is in the range of 160 knots. The minimum speed threshold V3 and the maximum speed threshold Vmax are located at the intersection of curve C and line C1, which represent the necessary power PNEC.

[0099] Within the forward speed range from the minimum speed threshold V3 to the maximum speed threshold Vmax, the engine can be in standby mode or in the reactivation phase.

[0100] At least one of the maximum speed threshold Vmax and the minimum speed threshold V3 can be fixed.

[0101] At least one of the maximum speed threshold Vmax and the minimum speed threshold V3 can be variable based on at least one positioning parameter. The flight control computer 80 is configured to determine the threshold in question based on the value of the positioning parameter. For example, the flight control computer stores a table or an equation that calculates the value of the threshold based on one or more positioning parameter values. The intermediate speed threshold and the reactivation threshold mentioned below can also be fixed or variable based on at least one positioning parameter.

[0102] More precisely, when the current forward speed V is between the intermediate speed threshold V1 (e.g., within the range of 110 knots) and the maximum speed threshold Vmax, the flight control computer 80 can generate control signal 101 according to the first law.

[0103] When the current forward speed V is between the minimum speed threshold V3 and the intermediate speed threshold V1, the flight control computer 80 can generate a control signal 101 according to the second law.

[0104] The first law grants greater permissions to the human-machine interface 20 than the second law grants.

[0105] Each law can generate control signals based on various parameters (e.g., based on command signals or other parameters that actually depend on the control mode). Figure 1 Typically, tandem actuators are controlled to stabilize the aircraft, and tandem actuators can be controlled in this way. The laws used according to the invention also tend to limit the authority of the human-machine interface 20. Orders given by the human-machine interface 20 can be forwarded according to the first law and reduced by the second law. For example, the first and second laws have a gain. The first and second laws are the same, except for the gain.

[0106] As a basic example, if operating the human-machine interface 20 causes the axis to translate by 1 centimeter, then the second law can be applied to the actuator so that the axis moves less than that distance of centimeter.

[0107] According to another example, the first law can be applied to instructions carried by command signals. However, the second law can reduce that instruction, for example, by dividing it by a predetermined coefficient.

[0108] For example, the first and second laws can be expressed in the following form: S = G * D, where "S" represents the command signal, "G" represents the gain, and "D" represents the movement of the human-machine interface. G can be equal to 1 under the first law and equal to 0.5 under the second law.

[0109] The flight control computer 80 can also be configured to apply a transition phase between the application phase of the first law and the application phase of the second law. For example, when switching from the first law to the second law, an intermediate law can be applied for a predetermined period of time, and vice versa.

[0110] Optionally, when the forward speed V drops below the reactivation speed threshold V2, for example within the range of 100 knots, the method may include reactivating a standby engine to generate mechanical power. Reactivation can be achieved according to a conventional startup procedure. In other words, the flight control computer, for example, transmits a signal to the engine computer, which restarts the engine according to a stored method, such as by modifying the fuel flow rate.

[0111] When the forward speed V drops below the minimum speed threshold V3, the method includes automatically disabling the economic operating mode according to a command from the flight control computer 80. The flight control computer 80 may transmit a signal to the engine computer or even an alarm to stop the mode. The alarm generates an alert to notify the crew. The alarm may include a screen, an acoustic system, a touch-sensitive system, etc.

[0112] Conversely, the method may include limiting the forward speed V to a maximum speed threshold via flight control computer 80.

[0113] The flight control computer is configured to control at least one variable geometry element to maintain the forward speed within a range that allows the engines to remain in reserve. This speed limit can be achieved through conventional means.

[0114] Naturally, there are many variations in the implementation of this invention. Although several embodiments have been described above, it should be readily understood that it is impossible to identify all possible embodiments exhaustively. Any device described can naturally be replaced by an equivalent device without departing from the context of this invention.

Claims

1. A method for controlling an aircraft (1) having a rotary wing (5), the rotary wing (5) having a power unit (10) comprising a plurality of engines (11, 12) for moving the rotary wing (5), the aircraft (1) including a human-machine interface (20) controlling a control channel (30) leading to a control member (7) capable of acting on the longitudinal acceleration of the aircraft (1), the aircraft (1) including a flight control computer (80), the aircraft (1) being capable of operating in an economic operating mode in which at least one of the plurality of engines (11, 12) does not provide mechanical power to the rotary wing, and at least one of the plurality of engines (11, 12) provides mechanical power to the rotary wing. in, During the economic operating mode, the method includes the following steps: • Measure the forward speed (V) of the aircraft (1); and • The flight control computer (80) generates control signals to adjust the gain of command signals applied from the human-machine interface (20), thereby reducing the authority of the longitudinal acceleration as the forward speed (V) decreases within a defined range.

2. The method according to claim 1, in, The flight control computer (80) issues a control signal (101), which is transmitted to at least one variable geometry element (60) of the control channel (30), and the method includes the following steps during the economic operating mode: • When the forward speed (V) is between the minimum speed threshold (V3) and the maximum speed threshold (Vmax), the flight control computer (80) generates the control signal (101) based on the forward speed (V).

3. The method according to claim 2, in, At least one of the maximum speed threshold (Vmax) and the minimum speed threshold (V3) is fixed or can vary according to at least one positioning parameter.

4. The method according to claim 2, in, The economic operating mode is implemented within a forward speed range from a minimum speed threshold to a maximum speed threshold, and the method includes the following steps during the economic operating mode: • When the forward velocity (V) is between the intermediate velocity threshold (V1) and the maximum velocity threshold (Vmax), and the maximum velocity threshold (Vmax) is greater than the intermediate velocity threshold (V1), the flight control computer (80) generates the control signal (101) according to the first law; and • When the forward speed (V) is between the minimum speed threshold (V3) and the intermediate speed threshold (V1), and the minimum speed threshold (V3) is less than the intermediate speed threshold (V1), the flight control computer (80) generates the control signal (101) according to the second law, which gives the human-machine interface (20) greater authority than the second law.

5. The method according to claim 4, in, The method includes a transition phase between the application phase of the first law and the application phase of the second law.

6. The method according to claim 4, in, The intermediate speed threshold (V1) is either fixed or can vary according to at least one positioning parameter.

7. The method according to claim 3, in, The positioning parameter is the current density altitude of the aircraft (1).

8. The method according to claim 1, in, During the economic operating mode, when the forward speed (V) drops below the reactivation speed threshold (V2), the method includes reactivating the engine (11) that does not provide mechanical power to the rotary wing to transmit mechanical power using the engine (11).

9. The method according to claim 1, in, The method includes limiting the forward speed (V) to a maximum speed threshold via the flight control computer (80).

10. The method according to claim 1, in, The method includes automatically disabling the economic operating mode according to a command from the flight control computer (80) when the forward speed (V) is less than a minimum speed threshold (V3).

11. An aircraft (1) having a rotary wing (5) and a power plant (10), the power plant (10) comprising a plurality of engines (11, 12) for moving the rotary wing (5), the aircraft (1) including a human-machine interface (20) controlling a control channel (30) leading to a control member (7) capable of acting on the longitudinal acceleration of the aircraft (1), the aircraft (1) including a flight control computer (80), the aircraft (1) being capable of operating in an economic operating mode in which at least one of the plurality of engines (11, 12) does not provide mechanical power to the rotary wing and at least one of the plurality of engines (11, 12) provides mechanical power to the rotary wing. in, The aircraft (1) includes a forward speed sensor (27), and the flight control computer (80) is configured to apply the method according to claim 1.

12. The aircraft according to claim 11, in, The aircraft (1) includes a variable geometry member (60) that acts on the position of the control member (7), and the flight control computer (80) is configured to modify the geometry of the variable geometry member (60).

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