Method for controlling an aircraft capable of hovering and related aircraft

Abstract

A method of controlling an aircraft (1) capable of hovering is described, comprising a first engine (10a); a second engine (10b); at least one rotor (3); and a transmission (8) between the first and second engines (10a, 10b) and the rotor (3), the transmission (8) comprising first and second input members (12a, 12b) connected to a first output member (11a) of the first engine (10a) and a second output member (11b) of the second engine (10b), respectively; the method comprising setting the aircraft (1) so that the first and second engines (10a, 10b) 0b) provides a first configuration of first and second power values ​​(P1, P2) or a second configuration in which the first engine (10a) provides a third power value (P3) greater than the first power value (P1) to the first input member (12a) and the second engine (10b) delivers a zero power value (P4) to the second input member (12b); the method also includes a step ii) of detecting a series of parameters related to the operating state of the aircraft (1) and a step iii) of enabling the aircraft (1) to change from the first configuration to the second configuration when the parameters exhibit corresponding first values.

Description

[0001] Cross-reference to related applications

[0002] This patent application claims the priority of European Patent Application No. 20189398.9, filed on August 4, 2020, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to a method for controlling an aircraft capable of hovering and to the aircraft itself.

[0004] More specifically, the aircraft is a helicopter or a thrust-reversing aircraft. Background art

[0005] Helicopters are known to generally include a fuselage, a main rotor rotatable about a first axis and disposed on top of the fuselage, and an anti-torque rotor disposed at the tail end of the helicopter and rotatable about a second axis transverse to the first axis.

[0006] Known types of helicopters also include an engine system and a transmission unit for transmitting motion from the output shaft of the engine system to the main rotor.

[0007] In a multi-engine configuration, the engine system includes at least a pair of engines, more precisely turboshaft engines, which are provided with respective output shafts connected to the transmission.

[0008] At least in twin-engine helicopters, each "turboshaft" engine is oversized to ensure the required power in the event of a failure of the other turboshaft engine.

[0009] Thus, each turboshaft engine is capable of delivering a maximum power greater than the power required by the helicopter when both turboshaft engines are operating.

[0010] Such oversizing is sub-optimal in terms of the weight and fuel consumption rate of the turboshaft engine.

[0011] In fact, at the cruise speed of forward flight, the turboshaft engine delivers a corresponding power level approximately between 55% and 80% of the maximum power value.

[0012] At these power levels, the engine efficiency is much lower than at power levels close to 100%, with a higher specific fuel consumption rate.

[0013] In other words, generally, a turboshaft engine operating at a level equal to 60% of the maximum deliverable power has a higher specific fuel consumption rate than when it delivers the maximum power.

[0014] This means that generally a turboshaft engine on a helicopter has a sub-optimal specific fuel consumption rate at cruise speed.

[0015] To reduce the specific fuel consumption rate in the cruise state, it is proposed to shut down one of the turboshaft engines and fly using the remaining engine. In this way, the one or only operating turboshaft engine delivers more power than it would deliver if all turboshaft engines were operating, and thus can be operated at a relatively low specific fuel consumption rate.

[0016] However, this flight mode with a turboshaft engine shut down can only be achieved in certain operating states of the helicopter.

[0017] There is also a felt need in the art to quickly determine whether a helicopter meets the said operating state.

[0018] In addition, there is a felt need in the art to prevent this flight mode and assist in exiting this flight mode with a shut-down turboshaft engine when the helicopter departs from these operating states.

[0019] There is also a felt need in the art to quickly indicate to the pilot the correct operations for bringing the helicopter back to these operating states when the helicopter does not meet these operating states and the said flight mode is required.

[0020] There is also a felt need in the art to continuously verify whether the helicopter is at risk of departing from these operating states when the said flight mode is requested and quickly warn the pilot of this risk.

[0021] Finally, there is a felt need to maintain as much as possible the coupling that normally exists between the turboshaft engine and the transmission while implementing the said flight mode with a shut-down turboshaft engine. This is to be able to apply this flight mode to existing helicopters without re-designing the said coupling.

[0022] For example, document US-A-2016 / 0237917 describes a method for optimizing the specific fuel consumption rate of a twin-engine helicopter. The method involves driving one turboshaft engine at a speed represented as "stable flight speed" and driving the other engine at a speed represented as "zero power over-idle". In particular, in the "zero power over-idle" state, the turboshaft engine opens the combustion chamber of the gas generator and at the same time tries to keep the speed to a minimum to reduce the operating temperature and the fuel consumption rate of the gas generator.

[0023] US-A-2013 / 0219905 describes a method for reducing the specific fuel consumption rate of a helicopter, in which one turboprop engine operates at a speed denoted as "steady flight speed" and the other engine operates at a speed denoted as "super-idle zero-power speed".

[0024] US-B-10,487,733 describes a method for controlling a twin-engine helicopter, in which in the cruise state one turboprop engine provides the required power and the other engine is kept in a so-called "idle" state by using the electric power generated by using the mechanical energy provided by the "power rotor" of the first turboprop.

[0025] US-A-2020 / 049025 discloses a method for controlling an aircraft according to the preamble of claim 1 and a method for controlling an aircraft according to the preamble of claim 12.

[0026] EP-A-2886456 discloses a method for managing the power plant of a rotary-wing aircraft, which aircraft includes two main engines, a secondary engine and a main gearbox. The main engines and the secondary engine mechanically drive the main gearbox to rotate the main rotor of the aircraft. The secondary engine delivers two different levels of mechanical power such that the main engines and the secondary engine together deliver sufficient mechanical power for the aircraft to fly, first a first secondary mechanical power MPS1 and secondly a second secondary mechanical power MPS2, which are adapted to compensate for the main mechanical power losses of at least one main engine. Summary of the Invention

[0027] The object of the present invention is to implement an aircraft capable of hovering, which allows to meet the above requirements in a simple and economical way.

[0028] According to the present invention, the above object is achieved by a method for controlling an aircraft according to the present invention.

[0029] The present invention also relates to an aircraft capable of hovering according to the present invention. Brief Description of the Drawings

[0030] The following embodiments are provided by way of non-limiting example with reference to the drawings for a better understanding of the present invention, in which:

[0031] Figure 1 A perspective view of a twin-engine helicopter implemented according to the provisions of the present invention is shown;

[0032] Figure 2 Is a flow chart schematically showing a method for controlling an aircraft implemented according to the provisions of the present invention;

[0033] Figure 3 Is shownFigure 2 Diagram of some important parameters of the method;

[0034] Figure 4 Showing the trend of the power and rotational speed delivered by the output shaft of the turboshaft engine of a helicopter changing with time starting from the first flight state where power is delivered from both engines and instantaneously entering the second flight state where one engine does not deliver engine power; Figure 1 ;

[0035] Figure 5 Showing the trend of the power and rotational speed delivered by the output shaft of the turboshaft engine of a helicopter changing with time starting from the second flight state and instantaneously leaving the second operating mode and returning to the first flight state; Figure 1 ;

[0036] Figure 6 Showing the time trend of some flight commands during the recovery operation performed in the above-mentioned second flight state of the helicopter;

[0037] Figure 7 Is Figure 1 Functional diagram of some components of the engine system of a helicopter;

[0038] Figure 8 Schematically showing Figure 7 Cross-sectional view of some details of the engine system; and

[0039] Figure 9 Is Figure 1-8 Functional diagram of some components of a helicopter. Detailed description of the specific implementation

[0040] Referring to Figure 1 , 1 represents a helicopter, which basically includes a fuselage 2 provided with a front head 5, a main rotor 3 located at the top of the fuselage 2 and rotatable about an axis A, and a tail rotor 4 carried by an offset portion protruding from the fuselage 2 on the opposite side of the head 5 and rotating about an axis B transverse to the axis A.

[0041] More specifically, the rotor 3 includes a hub 9a of the axis A and a plurality of blades 9b extending radially of the axis A and constrained thereto in a cantilever manner.

[0042] The blades 9b are hinged to the hub 9a so as to be able to change their orientation relative to the relevant extension axis to adjust the corresponding pitch angle relative to the air flow.

[0043] It should be noted that in the remaining part of this specification, expressions such as "above", "below", "front", "rear", etc. are used with reference to Figure 1 the forward flight or "hovering" state of the helicopter 1 shown, and where the main rotor 3 is arranged above the fuselage 2 and the head 5 is located in front of the tail rotor 4.

[0044] The helicopter 1 further includes:

[0045] A flight controller 14a (only schematically shown in Figure 9 ), which can be actuated by the pilot and is called "collective pitch", and can be actuated to jointly change the pitch angle of the blade 9b, so as to increase or decrease the lift generated by the helicopter 1; and

[0046] A flight controller 14b (also only schematically shown in Figure 9 ), which can be actuated by the pilot and is called "cyclic pitch", and can be actuated to periodically change their pitch angles according to the relative positions of the blades 9b with respect to the axis A.

[0047] The helicopter 1 further includes ( Figure 7 ):

[0048] An engine system 7 adapted to drive the main rotor 3 and the tail rotor 4; and

[0049] A transmission 8, which receives motion from the engine system 7 and is configured to provide mechanical power with an appropriate rotational speed to the drive shafts of the main rotor 3 and the tail rotor 4.

[0050] The engine system 7 further includes a pair of engines 10a, 10b.

[0051] In the example shown, the engines 10a, 10b are of the turboshaft type, which are of a known type, and thus will only be described below within the scope required by the present invention.

[0052] More specifically, the engines 10a, 10b each represent a gas turbine system that performs an open Joule - Brayton thermodynamic cycle.

[0053] The engines 10a, 10b each include associated output shafts 11a, 11b that can rotate about the associated axis C.

[0054] The engines 10a, 10b each basically include:

[0055] An air intake (not shown) formed on one side of the fuselage 2;

[0056] A compressor (not shown) that supplies a fresh air flow through the air intake and is adapted to compress the air flow;

[0057] A combustion chamber (not shown), in which the air flow compressed by the compressor reacts with a fuel flow to generate a high - temperature exhaust gas flow; and

[0058] A pair of turbines (only schematically shown), in which the flow of the hot exhaust gas leaving the combustion chamber expands, drives the compressor and the associated output shafts 11a, 11b to rotate about the associated axis C.

[0059] Each state of the engines 10a, 10b corresponds to a corresponding value of a specific fuel consumption rate, the rotational speed of the associated output shafts 11a, 11b about the axis C, and the power that the associated output shafts 11a, 11b can provide.

[0060] Reference Figure 7 , the output shafts 11a, 11b of the engines 10a, 10b are connected to the corresponding input shafts 12a, 12b of the transmission 8 via the associated flywheels 13.

[0061] The flywheels 13 of the engines 10a, 10b are each arranged to allow the associated input shafts 12a, 12b of the transmission 8 to rotate when the associated output shafts 11a, 11b stop.

[0062] In other words, the flywheels 13 allow the operation of the transmission 8, and thus the main rotor 3 and the tail rotor 4, to be maintained by means of the power delivered by the other of the engines 10a, 10b in the event of a failure in one of the engines 10a, 10b or by means of autorotation in the event of a failure in both of the engines 10a, 10b.

[0063] Reference Figure 8 , each flywheel 13 basically comprises:

[0064] A wheel 15, which is radially located outside the axis C and is operatively connected to the corresponding output shafts 11a, 11b;

[0065] A wheel 16, which is radially located inside the axis C and is connected to the associated input shafts 12a, 12b; and

[0066] A wheel 17, which is radially located between the wheels 15, 16.

[0067] The wheel 17 of each flywheel 13 further includes a plurality of associated angularly spaced stop teeth 18 (only one of which is shown in Figure 8 ) and an associated spring 19 that elastically locks the associated teeth 18.

[0068] When power is applied to the output shafts 11a, 11b of the engines 10a, 10b respectively, the wheel 15 of the associated flywheel 13 drives the associated wheel 16 and the associated input shafts 12a, 12b to rotate.

[0069] In the case where the assembly formed by the wheels 16 and the associated input shafts 12a, 12b of the transmission 8 rotates at a speed greater than the speed of the associated output shafts 11a, 11b (for example, in the case of an engine sudden stop), the associated flywheels 13 allow the associated input shafts 12a, 12b to be separated from the corresponding output shafts 11a, 11b.

[0070] The helicopter 1 further includes ( Figure 9 ):

[0071] A plurality of sensors 21, which are adapted to provide corresponding measured values of corresponding flight parameters and indications related to the correct operation / fault status of devices and systems that do not form part of the engine system 7 of the helicopter 1;

[0072] A digital control system of the engine system 7, hereinafter referred to as FADEC 22;

[0073] A plurality of sensors 23, which are arranged within the engine system 7 and are adapted to provide measured values of the angular velocity of the engine system 7 itself; and

[0074] An avionics system 30.

[0075] The sensors 21 are configured to measure at least the following parameters: outside air temperature OAT; barometric altitude; altitude above ground; altitude above sea level; indicated airspeed IAS; density altitude; altitude above minimum flight altitude and variometric speed; the attitude of the helicopter 1 and the position of the helicopter 1.

[0076] The avionics system 30 is programmed to:

[0077] Provide at least some of the parameters of the sensors 21 to the FADEC 22; and

[0078] Obtain important parameters of the performance of the engines 10a, 10b and the commands applied by the pilot on the main rotor 3 and the tail rotor 4.

[0079] The FADEC 22 is programmed to generate a control law for the fuel flow provided to the corresponding combustion chambers of the engines 10a, 10b based on the above parameters.

[0080] More precisely, the FADEC 22 generates the control laws of the engines 10a, 10b independently of the avionics system 30.

[0081] The helicopter 1 has a first operating configuration, hereinafter referred to as the normal operating configuration, in which ( Figure 4 ) the engines 10a, 10b provide corresponding power values P1, P2 that are substantially equal to each other to the corresponding output shafts 11a, 11b.

[0082] The sum of the powers P1 and P2 is equal to the power P required for the correct operation of the main rotor 3 and the tail rotor 4.

[0083] The helicopter 1 has a second operating configuration, hereinafter referred to as the ACR operating configuration, i.e., the asymmetric cruise state, in which ( Figure 5 and 6 ) the engines 10a, 10b supply respective power values P3, P4 that are different from each other to the respective output shafts 11a, 11b.

[0084] In particular, the power P4 is zero, while the power P3 is greater than the power P1 and equal to the power P.

[0085] Preferably, in the ACR mode, the consumption of the engine 10b is minimized.

[0086] In other words, the engine 10b is not shut down in the ACR mode, but drives the output shaft 11b to rotate without delivering the engine power to the output shaft 11b itself.

[0087] The avionics system 30 is operatively connected to the sensors 21, 23 and the flight controllers 14a, 14b and interfaces with the FADEC 22.

[0088] The avionics system 30 is also configured to continuously monitor the operating state of the helicopter 1 and command the FADEC 22 to place the helicopter 1 in the operating configuration or the ACR configuration automatically or following the instructions of the crew.

[0089] For this purpose, the avionics system 30 basically includes:

[0090] The instrument 31, which is configured to provide the pilot with indications related to the operating parameters of the helicopter 1 itself;

[0091] The display device 32 (e.g., called CDS) for a series of messages for the crew;

[0092] The control unit 33, also called the "aircraft management system, AMS"; and

[0093] The interface 34, which can be actuated by the crew to command the helicopter 1 to change from the conventional configuration to the ACR configuration or vice versa.

[0094] The avionics system 30 also includes the storage station 37.

[0095] More specifically, the interface 34 includes ( Figure 2 ):

[0096] An ACR Request instruction, which can be initiated by the aircrew and can be moved between an enabling position for requesting a transition from a normal operating mode to an ACR operating mode and a disabling position for requesting a transition from the ACR operating mode to the normal operating mode; and

[0097] An ACR Arm instruction that can be initiated by the aircrew.

[0098] More specifically, the ACR Arm instruction is a monostable instruction in the form of an "instantaneous button" in the example shown.

[0099] If the helicopter 1 is in the ACR configuration, activation of the ACR Arm instruction will result in an operation for the helicopter 1 to emergently disengage from the ACR configuration, which will become clearer in the remaining part of this specification.

[0100] If the helicopter 1 is in the normal configuration, subsequent activation of the ACR Arm and ACR Request instructions will result in a request for the helicopter 1 to enter the ACR configuration.

[0101] More specifically, the ACR Arm instruction is used to prevent the ACR Request instruction from accidentally causing a transition to the ACR configuration.

[0102] In the example shown, the ACR Arm instruction is set on the flight controller 14a of the collective pitch.

[0103] The avionics system 30 is programmed to cause a change in the state of the FADEC 22 after activation of the ACR Arm and ACR Request instructions.

[0104] The FADEC 22 also acknowledges the receipt of the instruction and the subsequent state change.

[0105] The helicopter 1 also includes a power generation and distribution system 100 ( Figure 7 ), also known as the EPGDS (Power Generation and Distribution System).

[0106] The system 100 basically includes, for each of the engines 10a, 10b, a starter 101a, 101b adapted to generate the self-start of the engines 10a, 10b themselves and generators 102a, 102b driven by the engines 10a, 10b themselves.

[0107] In the example shown, the generators 102a, 102b are connected to the respective accessory drives 110a, 110b of the respective engines 10a, 10b. The accessory drives 110a, 110b are connected to the respective engines 10a, 10b in parallel with the respective shafts 12a, 12b of the transmission 8.

[0108] The system 100 also includes, for each of the engines 10a, 10b:

[0109] Units 103a, 103b, referred to as REPU (Remote Electric Power Unit), which are used to distribute power to the main loads necessary for the operation of helicopter 1; and

[0110] Units 104a, 104b, which are used to distribute power to the secondary loads unnecessary for the operation of helicopter 1.

[0111] When helicopter 1 is in the normal operation configuration, both generators 102a, 102b are activated and supply power to units 103a, 104a; 103b, 104b respectively.

[0112] When helicopter 1 is in the ACR operation configuration, the electrical system 100 is reset to deactivate the generator 102b connected to engine 10b and supply power only to the electrical loads necessary for the operation of helicopter 1 through the generator 102a driven by engine 10a.

[0113] Preferably, the unnecessary secondary load of unit 104b is partially powered by generator 102a.

[0114] In addition, unit 104b is deactivated.

[0115] The display device 32 is programmed to display:

[0116] The ACR READY signal indicating that helicopter 1 is in the state of operating in the ACR operation configuration;

[0117] The ACR ARMED signal indicating that the ACR equipment instruction is in the enabled position;

[0118] The 1(2) ACR TRANSITION signal indicating that the ACR request instruction has moved to the enabled position and the avionics system 30 continues to perform the reset of the electrical system 100; and

[0119] The ACR signal indicating that the ACR request instruction has moved to the enabled position, the electrical system 100 has been reset, and the FADEC 22 continues to perform the reset of engines 10a, 10b.

[0120] Alternatively, the transition of helicopter 1 from the normal configuration to the ACR configuration can be initiated on one of engines 10a, 10b.

[0121] The control unit 33 of the avionics system 30 is programmed to detect a series of parameters related to the operation state of helicopter 1 and enable helicopter 1 to transition from the normal configuration to the ACR configuration when the parameters exhibit corresponding first values.

[0122] The term "operating state" in the remainder of this specification refers to a second parameter representing the operating state of the systems and devices of the helicopter 1 necessary for the correct operation of the helicopter 1 itself and a first operating flight parameter of the helicopter 1.

[0123] More specifically ( Figure 2 and 9 ), the avionics system 30 is programmed to assign a true or false value to the "ACR helicopter availability" parameter based on the first parameter detected by the sensor 21 and the content of the storage station 37.

[0124] In particular, the avionics system 30 is programmed to assign a true value to the "ACR helicopter availability" parameter when the helicopter 1 is in a state to be operated in the ACR configuration without considering the engine system 7. In addition, the avionics system 30 is programmed to assign a false value to the "ACR helicopter availability" parameter.

[0125] The FADEC 22 is also programmed to evaluate whether the engine system 7 is in a state to be operated in the ACR configuration.

[0126] More specifically, the FADEC 22 is configured to assign a true value to the "engine availability" parameter when the engine system 7 is in a state to be operated in the ACR configuration. In addition, the FADEC 22 is programmed to assign a false value to the said "engine availability" parameter.

[0127] The FADEC 22 is also configured to assign a true value to the "ACR ready" parameter for the avionics system 30 when both the "engine availability" and "ACR helicopter availability" signals present true values.

[0128] Alternatively, the avionics system 30 is configured to assign a true value to the said "ACR ready" parameter when both the "engine availability" and "ACR helicopter availability" signals present true values.

[0129] In addition, the FADEC 22 or the avionics system 30 is configured to assign a false value to the said "ACR ready" parameter when at least one of the "engine availability" and "ACR helicopter availability" signals presents a false value.

[0130] The avionics system 30 is programmed to display an "ACR ready" signal on the display device 32 when the FADEC 22 or the avionics system 30 assigns a true value to the "ACR ready" parameter.

[0131] The avionics system 30 is also programmed to allow the pilot to initiate an ACR equipment instruction through the interface 34 and place the ACR request instruction in an enabled position when the FADEC 22 assigns a true value to the "ACR ready" parameter.

[0132] The avionics system 30 or the FADEC 22 is also programmed not to initiate the ACR equipment command when the FADEC 22 does not provide an "ACR ready" signal.

[0133] The FADEC 22 is programmed to request the system 100 to reset itself by deactivating the generator 103 and to control the engines 10a, 10b to transition from the normal configuration to the ACR configuration after the ACR equipment and ACR request commands are input.

[0134] Preferably, the FADEC 22 is programmed to verify the successful reset of the system 100 before transitioning the engines 10a, 10b from the normal configuration to the ACR configuration. In particular, the above verification is performed by monitoring the current and voltage values of the generator 103b provided by the avionics system 30 to the FADEC 22.

[0135] More precisely, the above first parameter represents the following states:

[0136] i) The helicopter 1 is within a defined flight envelope required for the helicopter 1 to operate in the ACR configuration;

[0137] ii) The helicopter 1 is in an area without obstacles or flight restrictions;

[0138] iii) The angular velocity of the rotor 3 is within a defined value range required for the helicopter 1 to operate in the ACR configuration;

[0139] iv) The indicated airspeed TAS is within a defined interval required for the helicopter 1 to operate in the ACR configuration; and

[0140] v) The climb speed and the torque delivered by the engine 10b are within the corresponding intervals ensuring a reduced fuel consumption rate.

[0141] The avionics system 30 is programmed to compare the data detected by the sensors 21, 23 with the above intervals stored in the storage station 37.

[0142] More precisely, the control unit 33 is programmed to assign a true value to the "ACR helicopter availability" signal when the above states represented as i), ii), iii), iv) and v) occur.

[0143] In particular, state i) occurs when:

[0144] The outside air temperature OAT is included between a first design value and a second design value;

[0145] The barometric altitude is included between a third design value and a fourth design value;

[0146] The density altitude is between a fifth value and a sixth value.

[0147] State ii) occurs at the following times:

[0148] The height above the ground is preferably between 50 feet and 1000 feet; and

[0149] The height above the sea level is preferably between 50 feet and 1000 feet.

[0150] Preferably, state ii) is also verified when the height above the minimum flight altitude is preferably between 50 feet and 1000 feet.

[0151] State iii) occurs when the angular velocity Nr of the main rotor 3 is between a minimum seventh value and a maximum eighth value, where the seventh value is preferably between 0.85 times and 1 times the nominal angular velocity of the rotor 3, and the eighth value is between 1 times and 1.15 times the nominal angular velocity of the rotor 3.

[0152] The term "nominal angular velocity" of the rotor 3 in this specification refers to the angular velocity at which the rotor 3 is normally started during the operation of the helicopter 1.

[0153] State iv) occurs when the indicated airspeed IAS is between a ninth value and a tenth value, where the ninth value is preferably between 0.5 times and 1.5 times the level flight speed required for the minimum power at the temperature and operating level, and the tenth value is preferably between 1 times and 2.5 times the aforementioned level flight speed required for the minimum power.

[0154] State v) occurs at the following times:

[0155] The torque delivered by the engines 10a, 10b is between an eleventh value and a twelfth value, where the eleventh value is preferably between 0.5 times and 1 times the torque required for straight and level flight at the aforementioned speed required for the minimum power, and the twelfth value is preferably between 1 times and 3 times the aforementioned torque required for straight and level flight at the aforementioned speed required for the minimum power.

[0156] Preferably, state v) is also verified when the vertical speed VS is between a thirteenth value and a fourteenth value, where the thirteenth value is preferably between 0.1 times and 1 times the autorotation vertical speed, and the fourteenth value is preferably between 0.1 times and 1 times the maximum vertical speed at the aforementioned speed required for the minimum power.

[0157] The second parameter also represents the fact that sensors 21, 23 do not detect a fault that does not match the ACR configuration and that the operating states of the subsystems and devices do not mismatch the ACR configuration. Examples of such faults that do not match the ACR configuration are faults in the on-board systems required to deliver power to aircraft 1 or faults in the functions of the automatic flight control system, hereinafter referred to as AFCS, required to assist the pilot.

[0158] Non-limiting examples of faults that can be confirmed by avionics system 30 are as follows:

[0159] Missing parameters indicating whether helicopter 1 is within the above-mentioned flight envelope;

[0160] Missing parameters for confirming the operation of electrical system 100 and engines 10a, 10b;

[0161] Missing parameters related to any faults in engines 10a, 10b;

[0162] Errors related to engines 10a, 10b and electrical system 100 that can be confirmed by the pilot in the parameters, including erroneously issuing warning signals related to faults;

[0163] Missing or erroneously providing parameters necessary for the flight of helicopter 1 that can be confirmed by the pilot, such as those related to the hydraulic system or transmission 8;

[0164] Generating warning messages that require immediate pilot intervention; and

[0165] Faults in generator 102a that will result in shutdown or loss of operability.

[0166] It should be emphasized that the expression "missing parameter" used previously is used to indicate that these parameters are not available in display device 32 or FADEC 22 and that these parameters cannot be detected by sensors 21, 23 and fail in the unit between sensors 21, 23 and display device 32 or in FADEC 22.

[0167] Avionics system 30 is also programmed to control FADEC 22 to transition helicopter 1 between a conventional operation configuration and an ACR operation configuration.

[0168] More specifically, avionics system 30 is configured to control helicopter 1 to transition from a conventional operation configuration to an ACR operation configuration when both the "ACR helicopter availability" and "ACR ready" parameters are true and when the ACR request instruction is in the enabled position and the ACR equipment instruction has been previously initiated.

[0169] More precisely, during the transition of the helicopter 1 from the conventional operating configuration to the ACR operating configuration, the avionics system 30 preferably generates a time pause of ten seconds in the example shown before placing the engine 10b in the state of its delivery power P4.

[0170] The avionics system 30 is programmed to:

[0171] Control the reset steps of the electrical system 100; and

[0172] Control the FADEC 22 to perform the reset steps of the engines 10a, 10b.

[0173] In particular, this reset of the engines 10a, 10b includes:

[0174] Closing the valve plugged into the bleed line of the compressor of the engine 10b;

[0175] Deactivating the generator 102b driven by the engine 10b; and

[0176] Resetting the system 100 so that some of the electrical loads of the units 103b, 104b are powered by the generator 102a connected to the engine 10a.

[0177] More specifically, the electrical loads necessary for the operation of the helicopter 1 of the unit 103b are electrically connected to the generator 102a driven solely by the engine 10a, and the non-essential secondary electrical loads are deactivated in this reset step or are also at least partially separately electrically connected to the generator 102a.

[0178] Preferably, the above reset is performed automatically.

[0179] The display device 32 is also controlled by the avionics system 30 to display the ACR signal and remove the 1(2)ACR transition signal at the end of the above reset steps.

[0180] More specifically, referring to Figure 4 , from the moment t0 when the reset of the system 100 has been completed to the moment t1 when the transition from the conventional configuration to the ACR configuration has been completed, the avionics system 30 is configured to request the FADEC 22:

[0181] Increase the power of the engine 10a from the value P1 to the value P3 reached at the moment t1;

[0182] Decrease the power of the engine 10b from the value P2 to the value P4 reached at the moment t1; and

[0183] Maintain the powers of the engines 10a, 10b at the corresponding values P3, P4 after the moment t1 while the helicopter 1 is operating in the ACR configuration.

[0184] It should be emphasized that the value P4 is greater than zero. Thus, the engine 10b is on when the helicopter 1 is operating in the ACR configuration.

[0185] Reference Figure 4 , starting from the moment t0 when the angular velocities of the output shafts 11a, 11b are equal to each other and equal to the value n1, the avionics system 30 is also configured to request the FADEC 22:

[0186] During the time interval included between the moments t0, t1, reduce the angular velocity of the output shaft 11b from the value n1 to a value n2 smaller than the value n1;

[0187] During the time interval included between the moments t0, t1, keep the angular velocity of the output shaft 11a at the value n1; and

[0188] After the moment t1, keep the angular velocities of the output shafts 11a, 11b at the corresponding values n1, n2.

[0189] In particular, after the moment t1, the flywheel 13 allows the separation between the output shaft 11b rotating at the angular velocity n2 and the corresponding input shaft 12b to the transmission 8. In particular, the angular velocity of the input shaft 12b is kept constant by increasing the driving torque provided by the input shaft 12a connected to the engine 10a.

[0190] Preferably, in the case where the ACR request instruction is placed in the enabled position when the helicopter 1 is outside a determined flight envelope, the avionics system 30 is configured to assist the crew in the operation of bringing the helicopter 1 into the flight envelope.

[0191] More specifically, the avionics system 30 is configured to:

[0192] Compare the data detected by the sensors 21, 23 with the data stored in the storage station 37 of the avionics system 30 itself;

[0193] Confirm that the detected data is outside the said envelope; and

[0194] Display the detected data to the crew through the display device 32.

[0195] Preferably, the control unit 33 of the avionics system 30 is programmed to:

[0196] Continuously obtain at least some parameters of the actual flight envelope of the helicopter 1 from the sensors 21, 23 when the helicopter 1 is in the ACR configuration and monitor that at least these parameters of the actual flight envelope are within the determined envelope of a determined flight;

[0197] Obtain the trend of the said parameters; and

[0198] Display a warning message indicating the trend of the parameter on the display device 32 to cause the helicopter 1 to leave the determined flight envelope.

[0199] In particular, the trend is continuously obtained for any operating configuration of the helicopter 1 itself.

[0200] More specifically, the parameters of the actual flight envelope obtained by the avionics system 30 at least include the indicated airspeed IAS, vertical speed VS, and altitude ALT.

[0201] More precisely, the avionics system 30 is programmed to detect the trend of the vertical speed and compare it with the climb rate of the determined flight envelope.

[0202] The avionics system 30 is also programmed to detect the altitude trend, compare it with the trend obtainable from the database stored in the station 37, and the altitude of the determined flight envelope.

[0203] In particular, the database includes altitude values above sea level for each latitude and longitude value.

[0204] The avionics system 30 is also configured to perform a transition of the helicopter 1 from the ACR operating configuration to the normal operating configuration in the following cases:

[0205] To perform a controlled normal emergency disengagement from the ACR operating configuration;

[0206] To perform a controlled emergency disengagement from the ACR operating configuration;

[0207] To perform an automatic emergency disengagement from the ACR configuration when the "ACR helicopter availability" parameter presents a false value; and

[0208] To perform an automatic normal disengagement in the case of minor anomalies of the helicopter 1 that do not require an automatic emergency disengagement.

[0209] Preferably, the time for performing the controlled normal disengagement operation and the automatic normal disengagement operation is longer than that of the controlled emergency disengagement operation and the automatic emergency disengagement.

[0210] More specifically, in the ACR configuration of the helicopter, when the crew moves the ACR request instruction to the deactivation position, the control unit 33 of the avionics system 30 is programmed to request the FADEC 22 to perform a controlled normal disengagement from the ACR configuration.

[0211] Following the movement of the ACR request instruction to the deactivation position, the display device 32 is programmed to:

[0212] Display the 1(2) ACR transition indication after approval by the FADEC 22;

[0213] Remove the ACR indication after engines 10a and 10b both deliver the same power P1, P2; and

[0214] Remove the 1(2) ACR transition indication and display the ACR equipped indication after helicopter 1 is outside the ACR configuration.

[0215] Alternatively, following movement of the ACR request command to the deactivated position, display device 32 is programmed to remove the indication after engines 10a and 10b have the same outlet temperature as the hot gas from the associated turbines.

[0216] The control unit 33 of the avionics system 30 is also programmed to perform a controlled emergency disengagement operation when the ACR equipment command is initiated with helicopter 1 in the ACR operating configuration.

[0217] In these cases, display device 32 is programmed to:

[0218] Display the 1(2) ACR transition indication after confirmation by FADEC 22 and during reset of engines 10a and 10b;

[0219] Remove the ACR indication after engines 10a and 10b both deliver the same power P1, P2; and

[0220] Remove the 1(2) ACR transition indication and display the ACR ready indication after helicopter 1 is outside the ACR configuration.

[0221] Display device 32 is also programmed to during a controlled emergency disengagement from the ACR configuration:

[0222] Display the 1(2) ACR transition indication;

[0223] Remove the ACR indication after engine 10b delivers the same power as engine 10a; and

[0224] Remove the 1(2) ACR transition indication after reset of helicopter 1 has been completed.

[0225] The control unit 33 of the avionics system 30 is also programmed to perform an automatic normal disengagement operation in the case of a minor anomaly in helicopter 1 that does not require an automatic emergency disengagement.

[0226] During this automatic normal disengagement operation, display device 32 is programmed to:

[0227] Display the 1(2) ACR transition indication after approval by FADEC 22;

[0228] Remove the ACR indication after engines 10a and 10b both deliver the same power P1, P2;

[0229] After the helicopter 1 is outside the ACR configuration, remove the 1(2) ACR transition indication and display the ACR equipped indication.

[0230] The avionics system 30 is also programmed to inhibit the equipment request function and assign false values to the ACR equipment parameters when the automatic emergency disengagement operation is completed.

[0231] In the case of automatic emergency disengagement, the avionics system 30 switches the ACR request command to the corresponding deactivated position and inhibits its use.

[0232] In the case of automatic emergency disengagement, the avionics system 30 monitors the systems of the helicopter 1 and determines any faults.

[0233] Reference Figure 5 , starting from the moment t3 when the transition from the ACR configuration to the conventional configuration is commanded, the FADEC 22 is programmed to:

[0234] Increase the angular velocity of the output shaft 11b from the value n2 to the value n1 during the time interval included between the moment t3 and the moment t4;

[0235] Maintain the angular velocity of the output shaft 11a at the value n1 during the time interval included between the moments t3 and t4; and

[0236] Maintain the angular velocities of the output shafts 11a and 11b at the corresponding equal values n1 to each other after the moment t4.

[0237] In particular, during the time interval included between the moments t3 and t4, the engine 10b accelerates and gives the output shaft 11b the same angular velocity as the associated input shaft 12b of the transmission 8.

[0238] The FADEC 22 is also programmed to:

[0239] Reduce the power of the engine 10a from the value P3 to the value P1 during the time interval included between the moment t4 and the moment t5 when the above transition is completed;

[0240] Increase the power of the engine 10b from the value P4 to the value P2 reached during the time interval included between the moments t4 and t5; and

[0241] Maintain the powers of the engines 10a and 10b at the corresponding equal values P1 and P2 to each other after the moment t5 while the helicopter 1 is operating in the conventional configuration.

[0242] Preferably, the FADEC 22 is programmed during the transition of the helicopter 1 from the ACR operating configuration to the conventional operating configuration in the cases of controlled conventional disengagement, automatic conventional disengagement, automatic emergency disengagement, and controlled emergency disengagement:

[0243] Generate respective time transient values for resetting the engines 10a, 10b that are different from each other;

[0244] Generate different time trends of the slip speed between the wheels 16, 15 of the flywheel 13; and

[0245] Generate different power values provided by the engines 10a, 10b after the respective flywheels 13 allow angular rotation of the respective output shafts 11a, 11b and input shafts 12a, 12b.

[0246] The helicopter 1 further includes an automatic flight control system AFCS, which is programmed to:

[0247] Receive information related to the fact that the helicopter 1 transitions between a conventional configuration and an ACR configuration from the FADEC 22;

[0248] Evaluate any corrections to the flight controllers 14a, 14b;

[0249] Display the above-mentioned corrections to the crew via the display device 32 or directly implement these corrections on the flight controllers 14a, 14b to minimize disturbances in the trajectory and / or attitude of the helicopter 1 and the angular velocity of the rotor 3.

[0250] Preferably, in the case where the engine 10a loses power when the helicopter 1 is in the ACR configuration, the pilot or the AFCS flight control system acts on the flight controllers 14a, 14b to perform a recovery operation.

[0251] Such a recovery operation is adapted to compensate for the loss of instantaneous power during the time interval between the moment when the engine 10a starts to fail and the moment when the engine 10b can deliver the power required to maintain the helicopter 1.

[0252] Therefore, the helicopter 1 can be maintained within the relevant operating and design limits during the above-mentioned time interval.

[0253] Preferably, the recovery operation reduces the altitude and speed of the helicopter 1 ( Figure 6 ). In particular, the recovery operation sets the helicopter 1 in a diving attitude and obtains a vertical descent speed by reducing the pitch angle of the blade 9b by means of the flight controller 14a. For example, the recovery operation is a autorotation operation in an emergency situation.

[0254] When the helicopter 1 is in the ACR configuration, the flywheel 13 between the output shaft 12b and the input shaft 11b bears a mechanical load due to the relative slip between the corresponding wheels 15, 16. More specifically, the rotational speed difference between the wheels 16, 15 is selected to reduce the local pressure load on the components of the flywheel 13. In addition, the flywheel 13 is generally sized to allow these speed differences while reducing the impact on fatigue life.

[0255] The operation of the helicopter 1 is described starting from the state where the helicopter 1 is in the conventional configuration and the ACR request command is in the deactivated position ( Figure 2 ).

[0256] In these states, the engines 10a, 10b deliver the respective powers P1, P2 and the output shafts 11a, 11b rotate integrally with the respective input shafts 12a, 12b of the transmission 8 at the respective equal angular velocities n1.

[0257] The generators 102a, 102b are driven by the respective engines 10a, 10b and supply power to the respective units 103a, 103b; 104a, 104b.

[0258] The control unit 33 of the avionics system 30 obtains from the sensors 21 a first parameter related to the operating state of the helicopter 1 and a second parameter related to any faults in the systems and devices of the helicopter 1.

[0259] The control unit 33 compares these first parameters with the values stored in the station 37.

[0260] More specifically ( Figure 9 ), the control unit 33 of the avionics system 30 assigns a true or false value to the "ACR helicopter availability" parameter based on the first parameters detected by the sensors 21, the content of the storage station 37, and any faults found by the avionics system 30.

[0261] In particular, the control unit 33 of the avionics system 30 assigns a true value to the "ACR helicopter availability" parameter when the helicopter 1 is in a state to operate in the ACR configuration without considering the engine system 7.

[0262] More precisely, the control unit 33 of the avionics system 30 assigns a true value to the "ACR helicopter availability" parameter when all the conditions i), ii), iii), iv) and v) occur and there are no significant faults in the helicopter system 1.

[0263] Conversely, the control unit 33 assigns a false value to the "ACR helicopter availability" parameter when the helicopter 1 cannot operate in the ACR configuration.

[0264] FADEC22 gives a true value to the "engine availability" parameter when the engine system 7 is in a state to operate in the ACR configuration.

[0265] FADEC22 or the avionics system 30 gives a true value to the "ACR ready" parameter of the avionics system 30 when both the "engine availability" and "ACR helicopter availability" signals present true values.

[0266] Therefore, the display device 32 displays the "ACR ready" parameter.

[0267] In these cases, the crew can request a transition to the ACR configuration by first activating the ACR equipment command and then placing the ACR request command in the enabled position. After the ACR equipment and ACR request commands are input, the avionics system 30 resets the system 100 and requests FADEC22 to change the engines 10a, 10b from the conventional configuration to the ACR configuration.

[0268] In particular, the system 100 preferably automatically resets to deactivate the generator 102b connected to the engine 10b and keep the generator 102a connected to the engine 10a enabled, so as to supply power to the units 103a, 104a.

[0269] The necessary electrical loads of the unit 103b are separately electrically connected to the generator 102a driven solely by the engine 10a, and the non-necessary electrical loads are deactivated during the reset step.

[0270] Preferably, FADEC22 verifies that the system 100 has been reset before changing the engines 10a, 10b from the conventional configuration to the ACR configuration.

[0271] In particular, during the reset step of the system 100, the display device 32 displays the 1(2) ACR transition indication.

[0272] During the reset step of the engines 10a, 10b, the display device 32 displays the ACR indication.

[0273] Preferably, the reset of the helicopter 1 starts after a certain time interval has elapsed after the ACR request command is placed in the enabled position.

[0274] At the end of this time interval, FADEC22 reduces the fuel supplied to the combustion chamber of the engine 10b and starts the reset of the engines 10a, 10b.

[0275] More specifically, FADEC22 starts from the moment t0 ( Figure 4 ) when the system 100 has been reset until the moment t1 when the transition from the conventional configuration to the ACR configuration has been completed:

[0276] Increase the power of engine 10a from value P1 to value P3 reached at time t1;

[0277] Decrease the power of engine 10a from value P2 to value P4 reached at time t1; and

[0278] While helicopter 1 is operating in ACR configuration, maintain the power of engines 10a, 10b at respective values P3, P4 after time t1.

[0279] FADEC 22 starts from time t0 when the angular velocities of output shafts 11a, 11b are equal to each other and equal to value n1:

[0280] During the time interval included between times t0, t1, decrease the angular velocity of output shaft 11b from value n1 to a value n2 smaller than value n1;

[0281] During the time interval included between times t0, t1, maintain the angular velocity of output shaft 11a at value n1; and

[0282] After time t1, maintain the angular velocities of output shafts 11a, 11b at respective values n1, n2.

[0283] In particular, the input shaft 12a of transmission 8 is driven to rotate by the output shaft 11a of engine 10a that delivers power P1. The angular velocity of input shaft 12b is kept constant by increasing the drive torque provided to input shaft 12a connected to engine 10a.

[0284] After time t1, flywheel 13 allows relative rotation through the slip between input shaft 12b of transmission 8 and output shaft 11b of engine 10b that rotates at angular velocity n1.

[0285] The avionics system 30 continuously obtains the signals of sensors 21, 23 and makes comparisons so that the operating parameters continue to be maintained within the intervals stored in station 37.

[0286] If some operating parameters are outside the intervals stored in station 37 and / or a fault that does not match the ACR configuration is detected, system 100 and engines 10a, 10b return to the normal configuration.

[0287] When helicopter 1 is operating in ACR configuration, control unit 33 monitors that some parameters of the actual flight envelope of helicopter 1 are maintained within the defined flight envelope of a certain flight and obtains the trends of the above-mentioned parameters.

[0288] Display device 32 provides the pilot with warning information related to the trends of the parameters that cause helicopter 1 to deviate from the aforementioned defined flight envelope.

[0289] In the event of a loss of power of engine 10a when helicopter 1 is in ACR configuration, the pilot or the AFCS flight control system acts on flight controllers 14a, 14b to perform a recovery operation to compensate for the instantaneous power loss during the time interval between the moment when engine 10a starts to fail and the moment when engine 10b can deliver the power required to maintain helicopter 1.

[0290] Preferably, the recovery operation reduces the altitude and speed of helicopter 1 ( Figure 6 ). In particular, the recovery operation sets helicopter 1 in a diving attitude and obtains a vertical descent speed by reducing the pitch angle of blade 9b by means of flight controller 14a.

[0291] The transition of helicopter 1 from ACR configuration to conventional configuration is performed by a controlled normal disengagement or a controlled emergency disengagement or an automatic emergency disengagement or an automatic normal disengagement.

[0292] In particular, the crew performs a controlled normal disengagement by placing the ACR request command in the deactivated position.

[0293] In response to this deactivation of the ACR request command, display device 32 displays a 1(2) ACR transition indication after being approved by FADEC 22; removes the ACR signal after engines 10a, 10b both deliver the same power P1, P2; removes the 1(2) ACR transition indication; and displays an ACR equipped indication after helicopter 1 is in conventional configuration.

[0294] The crew performs a controlled emergency disengagement by activating the ACR equipment command.

[0295] In response to the activation, display device 32 displays a 1(2) ACR transition indication after being confirmed by FADEC 22, removes the ACR indication after engines 10a, 10b both deliver the same power P1, P2; removes the 1(2) ACR transition indication after helicopter 1 is outside ACR configuration; and displays an ACR ready indication.

[0296] The avionics system 30 places the ACR request command in the deactivated position, thus preventing the possibility of returning to ACR configuration.

[0297] The control unit 33 or the alternative FADEC 22 itself commands FADEC 22 to perform an automatic emergency disengagement from ACR configuration when one of the "ACR helicopter availability" and "engine availability" parameters presents a false value, i.e., when at least one of the verification conditions i), ii), iii), iv) and v) is not verified.

[0298] In these cases, the display device 32 displays the 1(2) ACR transition indication, removes the ACR indication after the engine 10b delivers the same power as the engine 10a, and removes the 1(2) ACR transition indication after the reset of the helicopter 1 has been completed.

[0299] The control unit 33 resets the ACR equipped state at the end of the automatic emergency disengagement operation, does not display the ACR equipped indication, and places the equipment request command in the disabled position.

[0300] The display device 32 displays the 1(2) ACR transition indication during the transition from the ACR configuration of the helicopter 1 to the conventional configuration and removes the ACR indication at the end of the above transition.

[0301] In the automatic emergency disengagement state, the sensor 21 senses the presence of one or more faults that do not match the ACR configuration, monitors the systems of the helicopter 1 regardless of the engines 10a, 10b, and sends this fault to the avionics system 30.

[0302] The FADEC 22 is controlled to execute the control law of the output shaft 11b of the engine 10b to ensure the correct power value for the input shaft 12b of the transmission 8.

[0303] The avionics system 30 is also programmed to quickly initiate assistance to the pilot to reset the system 100.

[0304] The control unit 33 requests the FADEC 22 to perform an automatic conventional disengagement operation in the case of a minor anomaly of the helicopter 1 that does not require automatic emergency disengagement.

[0305] More specifically, starting from the moment t3 when the transition from the ACR configuration to the conventional configuration is commanded, the control unit 33 also requests the FADEC 22:

[0306] to increase the angular velocity of the output shaft 11b from the value n2 to the value n1 during the time interval included between the moment t3 and the moment t4;

[0307] to keep the angular velocity of the output shaft 11a at the value n1 during the time interval included between the moments t3, t4; and

[0308] to keep the angular velocities of the output shafts 11a, 11b at the corresponding equal values n1 to each other after the moment t4.

[0309] In particular, during the time interval included between the moments t3, t4, the engine 10b accelerates and gives the output shaft 11b the same angular velocity as the relevant input shaft 12b of the transmission 8.

[0310] The control unit 33 also commands the FADEC 22:

[0311] During the time interval included between time t4 and time t5 when the above-mentioned transition has been completed, reduce the power of engine 10a from value P3 to value P1;

[0312] Increase the power of engine 10a from value P4 to value P2 reached during the time interval included between times t4 and t5; and

[0313] While helicopter 1 is operating in the conventional configuration, maintain the powers of engines 10a and 10b at respective equal values P1 and P2 after time t5.

[0314] Based on the type of operation for disengaging from the ACR configuration, the control unit commands the FADEC 22 to generate different time trends of the slip speed between wheels 16 and 15 of the flywheel 13, different time trends of the slip speed between wheels 16 and 15 of the flywheel 13, and generate different power values provided by engines 10a and 10b after the respective flywheel 13 allows angular rotation of the respective output shafts 11a, 11b and input shafts 12a, 12b.

[0315] For each of the above-mentioned disengagement operations, at the end of the transition of helicopter 1 from the ACR configuration to the conventional configuration, the generator 102b connected to engine 10b starts again and units 103b, 104b are electrically connected to the generator 102b itself.

[0316] By examining the characteristics of helicopter 1 according to the present invention, the advantages that can be obtained are obvious.

[0317] In particular, the control unit 33 of the avionics system 30 is programmed to:

[0318] Obtain a series of parameters related to the operating state of helicopter 1; and

[0319] Implement the transition from the conventional configuration to the ACR configuration when the said parameters exhibit respective first values.

[0320] In this way, it is possible to ensure that helicopter 1 operating in the ACR configuration has a lower specific fuel consumption rate only when it is within a determined flight envelope and in the absence of faults in the necessary components of helicopter 1 itself that affect its operability in the ACR configuration.

[0321] This ensures that the engine system 7 can deliver the maximum power when required by the operating state of helicopter 1 and can minimize its consumption when permitted by the operating state of helicopter 1.

[0322] Since the control unit 33 continuously acquires parameters related to the operating state of the helicopter 1, it is possible to perform an automatic emergency disengagement from the ACR configuration to the operating configuration when the helicopter 1 is outside the defined flight envelope of a defined flight or when there is a fault in the helicopter 1.

[0323] When the helicopter 1 is operating in the ACR configuration, the control unit 33 monitors some parameters of the actual flight envelope of the helicopter 1 to be within the defined flight envelope of a defined flight and derives the trends of these parameters.

[0324] The display device 32 provides the pilot with warning information related to the fact of the trend of the parameters that cause the helicopter 1 to leave the defined flight envelope.

[0325] Therefore, it is possible to notify the crew in a timely manner that the helicopter 1 is approaching a flight envelope that does not allow the ACR configuration.

[0326] In the case where the engine 10a loses power when the helicopter 1 is in the ACR configuration, the pilot or the AFCS flight control system acts on the flight controllers 14a, 14b to perform a recovery operation suitable for compensating for the instantaneous power loss during the time interval between the moment when the engine 10a starts to fail and the moment when the engine 10b can deliver the power required to maintain the helicopter 1.

[0327] Therefore, it is possible to keep the helicopter 1 within the relevant operating and design limits during the above time interval.

[0328] The control unit 33 of the avionics system 30 also allows:

[0329] To perform a controlled normal disengagement from the ACR operating configuration when the crew deems it necessary; and / or

[0330] To perform an automatic non-emergency disengagement from the ACR operating configuration in the case of minor anomalies of the helicopter 1 that do not require an automatic emergency disengagement.

[0331] More specifically, even when the parameters present a first value, a controlled normal disengagement operation can be requested by the crew.

[0332] In this way, it is possible to disengage from the ACR configuration according to the needs encountered by the crew, for example, because the performance in this mode is considered unsuitable for a specific flight state and mission or because of an anomaly that is not included in the anomalies for which the avionics system 30 automatically detects the need to re-store the manual configuration.

[0333] Therefore, it is possible to ensure the maximum operational flexibility of the helicopter 1 and reduce the possibility of consumption in the ACR configuration.

[0334] It should be emphasized that in the ACR configuration, engine 10b is not shut down, but delivers a power P2 that is substantially zero.

[0335] Therefore, since engine 10b also remains active in the ACR configuration, the time required to place helicopter 1 in a conventional configuration in which engine 10b delivers power P2 is particularly reduced compared to known solutions where one engine is completely shut down.

[0336] In the ACR configuration of helicopter 1, due to the presence of flywheel 13, the output shaft 11b of engine 10b rotates at an angular velocity n1 that is smaller than the angular velocity n2 of the input shaft 12b of the transmission.

[0337] In other words, flywheel 13 allows the mechanical load that persists for the entire time helicopter 1 is in the ACR configuration due to the relative slip between wheels 16 and 15 to be supported.

[0338] In this way, the same flywheel 13 is generally used to allow the operation of rotor 3 to be maintained for a short time in the event of an abnormal failure of engine 10b, and is also advantageously used to allow the operation of rotor 3 for an extended period in the ACR configuration.

[0339] This is achieved by selecting the speed difference between wheels 16, 15 to reduce the local pressure load on the components of flywheel 13 and since the size of flywheel 13 is generally set to allow these speed differences while reducing the impact on fatigue life.

[0340] Finally, it is clear that modifications and variations can be made to the previously described aircraft 1 without thereby departing from the scope of protection of the present invention.

[0341] In particular, the aircraft capable of hovering can be a thrust-reversing aircraft instead of helicopter 1.

[0342] More specifically, the aircraft capable of hovering can be a multi-rotor aircraft, such as having two coaxial rotors or being of the intermeshing type.

[0343] Condition ii) can be verified not by the avionics system 30 but by the pilot in the manual flight state.

[0344] Engines 10a, 10b can be heat engines different from turbine shaft engines or electric engines driven by batteries or hybrid engines.

Claims

1. A method for controlling an aircraft (1) capable of hovering, the aircraft (1) comprising: A first engine (10a); A second engine (10b); at least one rotor (3) operatively connected to the first engine (10a) and the second engine (10b); and a transmission device (8) between the first engine (10a) and the second engine (10b) and the rotor (3), The transmission device (8) comprises a first input member (12a) and a second input member (12b) connected to a first output member (11a) of the first engine (10a) and a second output member (11b) of the second engine (10b), respectively. The method comprises the step i) of arranging the aircraft (1) into the following configuration: a first configuration, wherein the first engine (10a) and the second engine (10b) provide substantially equal first power values ​​(P1) and second power values ​​(P2) to the first input (12a) and the second input (12b) of the transmission (8), respectively, the sum of the first power value (P1) and the second power value (P2) being equal to the power (P) required for proper operation of at least one of the rotors (3); or a second configuration, wherein the first engine (10a) provides a third power value (P3) greater than the first power value (P1) to the first input (12a), and the second engine (10b) delivers a zero power value (P4) to the second input (12b), the third power value (P3) and the zero power value (P4) being different from each other, the third power value (P3) being greater than the first power value (P1) and equal to the power (P), The method further comprises the following steps: ii) detecting a series of parameters related to the operational state of the aircraft (1); and iii) enabling the aircraft (1) to transition from the first configuration to the second configuration when the parameter assumes a corresponding first value, Characterized in that the step iii) includes a step xiii) of checking the following conditions: an outside temperature (OAT) comprised between a first operating value and a second operating value; The pressure altitude is comprised between the third operating value and the fourth operating value; The density altitude is contained between the fifth operating value and the sixth operating value; The height above ground level is between 50 feet and 1000 feet inclusive; The height above sea level is between 50 feet and 1000 feet inclusive; The angular velocity of the rotor (3) is comprised between a seventh minimum operating value and an eighth maximum operating value, wherein the seventh operating value is comprised between 0.85 and 1 times the nominal angular velocity and the eighth operating value is comprised between 1 and 1.15 times the aforementioned nominal angular velocity; the indicated speed (IAS) is comprised between a ninth value and a tenth value, wherein the ninth value is comprised between 0.5 and 1.5 times the level flight speed at which the minimum power and operating temperature are required, and the tenth value is comprised between 1 and 2.5 times the aforementioned level flight speed at which the minimum power is required; and the torque delivered by said first engine (10a) and said second engine (10b) being comprised between an eleventh operating value and a twelfth operating value, wherein the eleventh value is comprised between 0.5 and 1 times the torque required for straight level flight at said level flight speed requiring minimum power, and the twelfth value is comprised between 1 and 3 times the said required torque, The step iii) further comprises the step xiv) of verifying the following: The altitude above the minimum flight altitude is between 50 feet and 1000 feet inclusive; and the vertical velocity (Vz) is comprised between a thirteenth operating value and a fourteenth operating value, wherein the thirteenth operating value is comprised between 0.1 and 1 times the autorotation vertical velocity, and the fourteenth value is comprised between 0.1 and 1 times the maximum vertical velocity at the aforementioned velocity requiring minimum power, The method comprises the following additional steps: performing a controlled conventional disengagement of the aircraft (1) from the second configuration to the first configuration; performing a controlled emergency disengagement of the aircraft from the second configuration to the first configuration; performing an automatic emergency transition of the aircraft (1) from the second configuration to the first configuration when at least one of the parameters assumes a respective second value different from the first value; performing an automatic non-emergency transition of the aircraft (1) from the second configuration to the first configuration in the event of a minor anomaly of the aircraft (1) that does not require an automatic emergency disengagement, The controlled non-emergency transition and the automatic non-emergency transition take longer than the automatic emergency transition.

2. The method according to claim 1, characterized in that At least some of said parameters define a flight envelope of said aircraft (1); and / or at least another of said parameters is indicative of a malfunction of said aircraft (1).

3. The method according to claim 1, characterized in that It comprises a step iv) of preventing said aircraft (1) from transitioning from said first configuration to said second configuration when at least one of said parameters exhibits a respective second value different from said first value; and / or Characterized in that it comprises a step vi) of causing said aircraft (1) to perform a controlled emergency transition from said second configuration to said first configuration when said parameter assumes a first value and following a first instruction.

4. The method according to claim 1, characterized in that: It includes the following steps: vii) generating trends of at least some of said parameters when said aircraft (1) is in said second configuration; as well as viii) generating a warning signal in case said trend causes at least some of said parameters to assume second values ​​different from said first values.

5. The method according to claim 1, characterized in that It includes the following steps: ix) detecting that the first engine (10a) begins to fail; x) reducing the altitude and vertical speed of the aircraft (1); and xi) Increasing the power delivered by said second engine (10b).

6. The method according to claim 1, characterized in that It comprises the step xv) of controlling said second engine (10b) so that the associated second output member (11b) rotates at an angular velocity greater than zero in said second configuration.

7. The method according to claim 1, characterized in that It comprises a step xvi) of generating a relative angular slip between the second output member (11b) and the second input member (12b) by means of a one-way clutch (13) when the aircraft (1) is in the second configuration and in the event of a failure of the second engine (10b), The one-way clutch (13) comprises a first element (16) rotationally integrated with the associated second input member (12b) and a second element (15) rotationally integrated with the second output member (11b), the clutch (13) rotationally decouples the second input member (12b) from the second output member (11b) when the first element (16) rotates at a speed lower than that of the second element (15), and rotationally couples the second input member (12b) to the second output member (11b) when the first element (16) and the second element (15) rotate at the same angular velocity.

8. The method according to claim 7, characterized in that It includes the following steps: xvii) generating different time trends of the sliding speed between the first element (16) and the second element (15) depending on the type of transition from the second configuration to the first configuration; and / or xviii) generating different power values ​​respectively available from the first engine (10a) and the second engine (10b) after the one-way clutch (13) couples the second input member (12b) with the second output member (11b) depending on the type of transition from the second configuration to the first configuration.

9. The method according to claim 1, characterized in that: It includes the following steps: xix) mechanically connecting a first generator (102a) to the first output member (11a) of the first engine (10a); xx) supplying power to a first electrical load (103a, 104a) via the first generator (102a) when the aircraft (1) is in the first configuration; xxi) mechanically connecting a second generator (102b) to the second output member (11b) of the second engine (10b); xxii) supplying power to a second electrical load (103b, 104b) via the second generator (102b) when the aircraft (1) is in the first configuration; xxiii) shutting down the second generator (102b) and non-essential parts of the second electrical loads (103b, 104b) when the aircraft (1) is in the second configuration and supplying power to at least a significant part of the second electrical loads via the first generator (102a).

10. An aircraft (1) capable of hovering, comprising: A first engine (10a); A second engine (10b); at least one rotor (3) operatively connected to the first engine (10a) and the second engine (10b); a transmission device (8) interposed between the first engine (10a) and the second engine (10b) and the rotor (3) and comprising a first input member (12a) and a second input member (12b) connected to the first engine (10a) and the second engine (10b) respectively; and A control unit programmed to set the first engine (10a) and the second engine (10b) to the following configuration: a first configuration, in which they provide to the respective first input (12a) and second input (12b) first power values ​​(P1) and second power values ​​(P2) which are equal to each other, the sum of the first power value (P1) and the second power value (P2) being equal to the power (P) required for the correct operation of at least one of the rotors (3); or a second configuration, wherein the first engine (10a) delivers a third power value (P3) greater than the first power value (P1) to the first input (12a), and the second engine (10b) delivers a zero power value (P4) to the second input (12b), the third power value (P3) and the zero power value (P4) being different from each other, the third power value (P3) being greater than the first power value (P1) and equal to the power (P), The control unit is programmed to: effecting a transition from the first configuration to the second configuration when a series of parameters related to the operational state of the aircraft (1) assumes a first value; inhibiting said transition when at least one of said parameters relating to the operational state of said aircraft (1) exhibits a second value different from said first value, Characterized in that the control unit is programmed to check the following conditions: an outside temperature (OAT) comprised between a first operating value and a second operating value; The pressure altitude is comprised between the third operating value and the fourth operating value; The density altitude is contained between the fifth operating value and the sixth operating value; The height above ground level is between 50 feet and 1000 feet inclusive; The height above sea level is between 50 feet and 1000 feet inclusive; The angular velocity of the rotor (3) is comprised between a minimum seventh operating value and a maximum eighth operating value, wherein the seventh value is comprised between 0.85 and 1 times the nominal angular velocity, and the eighth value is comprised between 1 and 1.15 times the nominal angular velocity; the indicated speed (IAS) is comprised between a ninth value and a tenth value, wherein the ninth value is comprised between 0.5 and 1.5 times the level flight speed at which the minimum power and operating temperature are required, and the tenth value is comprised between 1 and 2.5 times the aforementioned level flight speed at which the minimum power is required; and The torque delivered by the first engine (10a) and the second engine (10b) is comprised between an eleventh operating value and a twelfth operating value, wherein the eleventh value is comprised between 0.5 and 1 times the torque required for straight level flight at the aforementioned level flight speed requiring minimum power, and the twelfth value is comprised between 1 and 3 times the aforementioned required torque; The control unit is programmed to check the following conditions: The altitude above the minimum flight altitude is between 50 feet and 1000 feet inclusive; and the vertical velocity (Vz) is comprised between a thirteenth operating value and a fourteenth operating value, wherein the thirteenth operating value is comprised between 0.1 and 1 times the autorotation vertical velocity, and the fourteenth value is comprised between 0.1 and 1 times the maximum vertical velocity at the aforementioned velocity requiring minimum power, The control unit is further programmed to: performing a controlled conventional disengagement of the aircraft (1) from the second configuration to the first configuration; performing a controlled emergency disengagement of the aircraft from the second configuration to the first configuration; performing an automatic emergency transition of the aircraft from the second configuration to the first configuration when at least one of the parameters assumes a respective second value different from the first value; performing an automatic non-emergency transition of the aircraft (1) from the second configuration to the first configuration in the event of a minor anomaly in use of the aircraft (1) that does not require an automatic emergency disengagement, Wherein the controlled non-emergency transition and the automatic non-emergency transition are performed for a longer period of time than the automatic emergency transition.

11. The aircraft according to claim 10, characterized in that It includes: a plurality of sensors (21, 23) adapted to detect a first said parameter defining the flight envelope of said aircraft (1) and a second said parameter indicative of a malfunction of said aircraft (1) and functionally connected to said control unit; and A FADEC (22) configured to control the first engine (10a) and the second engine (10b) and controlled by the control unit.

12. The aircraft according to claim 10, characterized in that The control unit (30, 33) comprises a storage station (37) for the first value; and / or Characterized in that it comprises a display device (32) controlled by the control unit and configured to display the following to the crew: a first signal (ACR READY) indicative of the fact that the aircraft (1) comprising the first engine (10a) and the second engine (10b) is in a state to be operated in an ACR configuration; and / or a second signal (ACRARMED) indicating the fact that a transition from said first configuration to said second configuration can be made; and / or A third signal (ACR) indicative of the fact that the aircraft (1) is operating in use in the second configuration.

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