Method and system for assisting with the piloting of a rotary wing aircraft in a fuel economy mode

Abstract

The invention relates to a system for assisting with the piloting of a rotary wing aircraft (10), including two engines, a first engine of which is put on standby to ensure an operation in a fuel economy mode referred to as ECO, the second engine remaining active in the ECO mode, in which system, in order to enable the activation of the ECO mode by a pilot, a flight computer (20) is configured to check in real time the fulfilment of the following conditions to authorise the entry into ECO mode: the sum of the powers supplied by the engines is less than a continuous maximum power, the speed of rotation N2 of a free turbine of the second engine is greater than a predetermined speed threshold that is comprised between 80% and 90% of the maximum speed of the engine, the altitude of the aircraft is greater than a minimum value allowing a transient autorotation phase during the reactivation of the engine in standby in the event of failure of the active engine, and there is no critical failure.

Description

[0001] Description

[0002] Title of the invention: Method and system for pilot assistance in a fuel-saving mode of a rotary-wing aircraft

[0003] Technical Field

[0004] The present invention relates to the field of assistance in piloting rotary-wing aircraft, in particular helicopters or drones, and it refers more particularly to a fuel-saving mode or "ECO mode" consisting of putting one of the two engines of a twin-engine aircraft, for example in standby mode (or "stand-by state") during the cruise or waiting and search flight phases (or "loitering"), in order to achieve fuel savings.

[0005] Prior art

[0006] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various carbon emission restrictions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new aircraft types and those currently in operation, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been mobilizing for several years now to contribute to the fight against climate change.

[0007] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into consideration the impacting factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental impacts with the aim of improving the energy efficiency of aircraft. Consequently, the Applicant is constantly working to reduce its climate impact by using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible to reduce the environmental footprint of its activity.

[0008] This ongoing research and development work focuses on new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and finally aeronautical biofuels.

[0009] In this context, it is known for twin-engine aircraft to resort to using the engines in fuel-saving mode known as ECO mode, whether this is carried out with the engine combustion chamber on or off, during cruise or loitering phases. In such a mode, for example usable in twin-engine rotary-wing aircraft, one of the two engines of the aircraft is placed in standby mode.

[0010] However, if used incorrectly, this operating mode can lead to premature wear of the motor providing power during use in ECO mode, i.e. the one of the two motors which remains active.

[0011] For safety reasons, authorization and then maintenance of ECO mode are necessary and involve carrying out a safety test (or “Safety Check”) to determine the value of the engine parameters and then verify whether these engine parameters are within adequate operating ranges to engage and then maintain ECO mode.

[0012] However, carrying out such a safety test takes a certain amount of time and is therefore particularly restrictive for the pilot who must then manoeuvre the aircraft to stabilise the engine speeds and thermals.

[0013] Statement of the invention

[0014] The present invention therefore relates to a driving assistance method which overcomes the aforementioned drawbacks and allows optimal use of ECO mode so as to achieve fuel savings. The invention also aims to ensure that ECO mode can be used in complete safety.These aims are achieved by a method for assisting in piloting a rotary wing aircraft, comprising two engines, a first engine of which is put on standby to ensure operation of the aircraft in fuel economy mode known as ECO mode, the second engine remaining active in said ECO mode, the method being characterized in that to allow activation by a pilot of the ECO mode, a flight computer of the aircraft verifies in real time the fulfillment of the following conditions for authorization to enter ECO mode: the sum of the powers supplied by the engines is less than a maximum continuous power, the rotation speed N2 of a free turbine of the second engine is greater than a determined speed threshold, the altitude of the aircraft is greater than a minimum value allowing a transient autorotation phase during the reactivation of the standby engine in the event of failure of the active engine, and there is no critical failure detected.

[0015] Similarly, to allow the reactivation of the first engine and therefore exit ECO mode at least one of the previous conditions for entering ECO mode or one of the following additional conditions must be false: no acceleration limit is reached, the oil temperature Th is above a determined temperature threshold allowing rapid reactivation of the engine in standby, the fuel temperature Tcarb is above a determined temperature threshold allowing rapid reactivation of the engine in standby, and there is no loss of power of the active engine.

[0016] Thus, the value of the speeds and the margins of the engine parameters in the event of activation of the ECO mode are estimated directly from the engine model implemented in the flight computer, and their updating, like their display, can therefore be done more regularly and transparently for the pilot.

[0017] Preferably, critical failures include data failures that impede the proper operation of the engine and / or its equipment, serial link failures, electrical system failures, failures resulting in loss of engine regulation, regulation system failures, hydraulic system failures. Advantageously, the fulfillment or non-fulfilment of the authorization conditions is displayed on an indicator dial comprising three power ranges corresponding respectively to the fulfillment of the authorization conditions, to the possible fulfillment of the authorization conditions and to the non-fulfilment of the authorization conditions.

[0018] Preferably, the rotation speed N2 of the free turbine is greater than a threshold between 80% and 90% of the maximum engine speed, the oil or fuel temperature threshold is 5°C and the minimum value of the minimum altitude is equal to 300m.

[0019] The invention also relates to the piloting assistance system implementing the aforementioned method, as well as an aircraft, preferably a twin-engine helicopter, implementing such a piloting assistance system.

[0020] Brief description of the drawings

[0021] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the single figure which illustrates an exemplary embodiment thereof without any limiting character, and in which:

[0022] [Fig. 1] Figure 1 schematically illustrates an aircraft comprising a pilot assistance system in ECO mode according to an example of the invention.

[0023] Description of the embodiments

[0024] The principle of the invention is based on a real-time determination by the aircraft's flight computer of various parameters which are then synthesized to provide the pilot on a screen in the aircraft's cockpit (for example the first limit indicator, or FLI for "First Limit Indicator") with a piloting indication indicating whether entry into fuel economy mode (ECO mode) is authorized or not. Preferably, the pilot may also have indicators to know whether maintaining this ECO mode is authorized or not, once said mode is activated. For example, if the duration of the cruise phase is sufficient, typically at least greater than 10 minutes, and the power requested during this phase is not too high (corresponding to an engine control temperature typically greater than 1400K) then the pilot may engage ECO mode provided that the authorization conditions defined by the flight computer are met.

[0025] To do this, all engines being operational and conventionally regulated to their nominal speed and / or torque setpoint, the flight parameters must meet the following authorization conditions to allow activation of ECO mode:

[0026] - the sum P of the powers supplied by the motors is less than the maximum continuous power (PMC),

[0027] - the rotation speed N2 of the free turbine of the active engine is greater than a determined speed threshold (preferably corresponding to a threshold between 80% and 90% of the maximum speed of the engine),

[0028] - the altitude of the aircraft H is greater than a minimum value allowing a transient autorotation phase during the reactivation of the standby engine in the event of failure of the active engine (safety criterion), typically Alt>300m, and

[0029] - there is no critical failure detected (nonPa). Critical failures are understood to mean failures of certain data (NR i.e. rotor rotation speed, selector, fuel pressure) which hinder the proper functioning of the engine and / or its equipment, failures of serial links (intercomputers and computer - aircraft), failures of the electrical system, failures of the IGVs, failures which may have effects on the regulation system (limited acceleration / deceleration speed), failures of the hydraulic system and any other failure leading to the loss of engine regulation.

[0030] Having an N2 rotation speed above a threshold that is between 80% and 90% of the maximum engine speed makes it possible to include the cruising or holding flight phases and the aircraft's taxiing and ground idling phases.

[0031] In other words, an N2 rotation speed greater than 80% of the maximum engine speed allows the aircraft to operate in a fuel-saving mode, known as ECO mode, during a taxiing and ground idling phase.

[0032] Similarly, an N2 rotation speed greater than 90% of the maximum engine speed allows the aircraft to operate in a fuel-saving mode, known as ECO mode, during a cruise phase. These conditions for authorizing entry into ECO mode must be met cumulatively for activation of ECO mode to be permitted. For entry into ECO mode, the computer of the engine to be put into standby preferably performs several checks. The first consists of verifying that an authorization from the avionics has been received.

[0033] The computer also performs consistency tests to verify that the request to enter ECO mode has been correctly formulated and to avoid the activation of ECO mode inadvertently. The computer also checks for the absence of one or more critical faults. These faults include, for example: faults that may affect the operation of ECO mode, the operation of the engines, or the operation of the engine reactivation system, which will be put on standby.

[0034] Once all these checks have been carried out and only if the conditions are met, the first engine preferably switches to ECO mode gradually. When entering ECO mode, the power of the first engine is preferably gradually reduced until it reaches a minimum power. The operation of the first engine at minimum power is maintained for a time interval of, for example, between 1 and 2 minutes. Then, the starter is activated to check the operation of the ECO mode. If it operates correctly, the first engine is then put into standby.

[0035] As illustrated in Figure 1, in an aircraft 10, when all the engines are operational and regulated to their nominal setpoint, the flight computer 20 can calculate the power that should be provided by the engine that would remain active in ECO mode (ECO estimated power). Furthermore, by adding the power provided by each engine and using an engine model implemented in the flight computer, it is possible to determine what the engine parameters (NI, TC and torque) would be corresponding to this power and the level of damage to the engine remaining active.

[0036] In particular, the engine model implemented in the computer is used to evaluate in real time the health status of the second engine remaining active and to determine in real time whether the second engine remaining active in ECO mode is capable of providing the power necessary to continue the flight.

[0037] All these data can be used to determine whether entry into ECO mode is authorized or not and whether this ECO mode is recommended. They can also be displayed (permanently or on request, in the first limit indicator dial 22 for example) in order to help the driver position himself in the power range 100 most suited to ECO mode for example (the following ranges illustrating respectively a power range 102 that may be possible and a prohibited power range 104). The driver thus has a forecast display of the engine parameters if ECO mode were activated. He can thus anticipate the margin in power available compared to the maximum power available in ECO mode and the gain in fuel consumption compared to operation with all engines. This indicator can be associated with several parameters (NI, TC, torque, power, etc.).

[0038] Similarly, when ECO mode is active, the engines and the entire electrical system dedicated to reactivating the standby engine are monitored so as to initiate reactivation of the standby engine if necessary. The flight computer can thus continuously monitor the complete state of the engines and the electrical system, and can in particular determine in real time whether conditions for maintaining ECO mode are met. If a failure or loss of power of the active engine is detected, the standby engine is then reactivated.

[0039] It should be noted that the previous authorization to enter ECO mode is not necessarily subject to the same conditions, and is therefore not necessarily calculated in the same way, as the authorization to remain in ECO mode (or any request to exit ECO mode). For example, the engine in standby mode will be reactivated (therefore resulting in an exit from ECO mode) if at least one of the following conditions for maintaining ECO mode becomes false, namely:

[0040] - the power supplied by the active engine is less than a determined maximum power, typically the PMC,

[0041] - the rotation speed N2 of the free turbine of the active engine is greater than a determined speed threshold,

[0042] - the altitude H is higher than a minimum value allowing a transient autorotation phase during the reactivation of the standby engine in the event of failure of the active engine (safety criterion), typically Alt>300m,

[0043] - there is no critical failure detected (nonPa),

[0044] - no acceleration limit is reached, these acceleration limits being essentially a surge protection limit, a gas generator acceleration limit, or a fuel flow rate greater than or equal to a maximum flow rate, typically 500 kg / h.

[0045] - the oil temperature Th is higher than a determined temperature threshold allowing rapid reactivation of the engine from standby, typically Th > 5°C,

[0046] - the fuel temperature Tcarb is higher than a determined temperature threshold allowing rapid reactivation of the engine on standby, typically Tcarb > 5°C, and

[0047] - there is no loss of power from the active engine.

[0048] When the aircraft is in ECO mode and a failure is detected, if the detected failure prevents or threatens to prevent the proper operation of ECO mode, the engine placed in ECO mode will exit ECO mode. This type of failure is considered critical for the operation of ECO mode. Thus, the criticality of the failure(s) has an influence on the exit from ECO mode. The presence of a single failure preventing the proper operation of ECO mode causes the exit from ECO mode. However, if the detected failure does not affect or threatens to affect the operation of ECO mode, nor the power availability of the engine remaining active, ECO mode is preferably maintained. For example, when there is a failure in the in-flight recording system, this will not constitute an obstacle for continuation in ECO mode.On the other hand, when there is a fault in the system for measuring the rotation speed of a free turbine of the active engine, the ECO mode will preferably not be maintained and we will not wait for the presence of a new fault to exit the ECO mode. Indeed, such a fault can cause damage to the engine remaining active.

[0049] It should also be noted that several indications relating to ECO mode may be issued in order to inform the pilot about the use of ECO mode (ECO mode active, ECO mode authorized, ECO mode interrupted), such as indications relating to a transition to the standby phase; and / or to an engine on standby; and / or to a reactivation in progress (and the type of reactivation); and / or to an interruption of the reactivation.

[0050] It should be noted that although reference has been made essentially to classic twin-engine applications, the invention naturally finds application to multiple engines such as in drones where a recommendation for the use of the engines could also be made to the pilot or the piloting system.

Claims

Claims

1. Method for assisting in piloting a rotary wing aircraft (10), comprising two engines, a first engine of which is put on standby to ensure operation of the aircraft in a fuel economy mode, called ECO mode, the second engine remaining active in said ECO mode, the method being characterized in that to allow activation by a pilot of the ECO mode, a flight computer (20) of the aircraft verifies in real time the fulfillment of the following conditions for authorizing entry into ECO mode: - the sum of the powers supplied by the motors is less than a maximum continuous power, - the rotation speed N2 of a free turbine of the second engine is greater than a determined speed threshold which is between 80% and 90% of the maximum speed of the engine, - the aircraft altitude is above a minimum value allowing a transient autorotation phase during reactivation of the standby engine in the event of failure of the active engine, - and there are no critical failures detected.

2. Method according to claim 1, in which, to allow the reactivation of the first engine and thus exit from ECO mode, at least one of the preceding conditions for entering ECO mode or one of the following additional conditions must be false: - no acceleration limit is reached, - the oil temperature Th is higher than a determined temperature threshold allowing rapid reactivation of the engine on standby, - the fuel temperature Tcarb is higher than a determined temperature threshold to ensure rapid reactivation of the engine on standby, - and there is no loss of power from the active engine.

3. The method of claim 2, wherein the oil or fuel temperature threshold is 5°C.

4. A method according to any one of claims 1 to 3, wherein the critical failures include data failures that impede the proper operation of the engine and / or its equipment, serial link failures, electrical system failures, failures resulting in loss of engine regulation, regulation system failures, hydraulic system failures.

5. Method according to any one of claims 1 to 4, in which the fulfillment or non-fulfilment of the authorization conditions is displayed on an indicator dial (22) comprising three power ranges (100, 102, 104) corresponding respectively to the fulfillment of the authorization conditions, to the possible fulfillment of the authorization conditions and to the non-fulfilment of the authorization conditions.

6. A method according to any one of claims 1 to 5, wherein the minimum value of the altitude is equal to 300m.

7. Pilot assistance system for a rotary wing aircraft (10), comprising two engines, a first engine of which is put on standby to ensure operation in fuel economy mode called ECO mode, the second engine remaining active in said ECO mode, characterized in that to allow activation by a pilot of the ECO mode, it comprises a flight computer (20) configured to verify in real time the fulfillment of the following conditions for authorization to enter ECO mode: the sum of the powers supplied by the engines is less than a maximum continuous power, the rotation speed N2 of a free turbine of the second engine is greater than a determined speed threshold which is between 80% and 90% of the maximum speed of the engine, the altitude of the aircraft is greater than a minimum value allowing a transient autorotation phase during the reactivation of the engine on standby in the event of failure of the active engine,and there are no critical failures detected.,

8. The system of claim 7, further comprising an indicator dial (22) connected to the flight computer and configured to display according to three power ranges (100, 102, 104) respectively the fulfillment of the authorization conditions, the possible fulfillment of the authorization conditions and the non-fulfillment of the authorization conditions.

9. An aircraft (10), preferably a twin-engine helicopter, comprising a pilot assistance system according to any one of claims 7 or 8.

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