Patent Description:
Gas turbine engines are typically inefficient to operate at low power settings. Operation of a gas turbine engine at idle is the typical lowest power setting available once the gas turbine engine has been started. In some instances, thrust produced at idle may be greater than the thrust needed for ground-based operations, such as taxiing and waiting in a parked position prior to takeoff or after landing. This can result in excess fuel consumption and may reduce engine component life with many repeated taxi, takeoff, and landing cycles.

In a hybrid gas turbine engine, an electric motor can be available to assist the gas turbine engine operation by adding rotational force to a spool of the gas turbine engine while fuel flow to the gas turbine engine is reduced below idle or shut off. Such a configuration can result in non-intuitive control from a pilot perspective, depending on how the two energy sources, fuel and electricity, are expected to be managed through the range of aircraft operation. In some control configurations, during operations such as engine start, thrust control may not be available to the pilot.

<CIT> discloses a method and an apparatus for a hybrid gas turbine engine starting control.

According to a first aspect of the invention a system is as claimed in claim <NUM>. According to another aspect of the invention a method is as claimed in claim <NUM>. Embodiments of these aspects of the invention are as claimed in the respective dependent claims thereof.

The above features and advantages, and other features and advantages, of the disclosure are readily apparent from the following detailed description when taken in connection with the accompanying drawings.

<FIG> schematically illustrates an aircraft <NUM> that includes a pair of hybrid electric propulsion systems 100A, 100B (also referred to as hybrid gas turbine engines 100A, 100B or hybrid propulsion systems 100A, 100B). Each of the hybrid electric propulsion systems 100A, 100B includes a gas turbine engine <NUM> with a low speed spool <NUM> configured to drive rotation of a fan <NUM>. Gas turbine engine <NUM> also includes a high speed spool <NUM> that operates at higher speeds and pressures than the low speed spool <NUM>. A low spool motor 12A is configured to augment rotational power of the low speed spool <NUM>. A high spool motor 12B can be configured to augment rotational power of the high speed spool <NUM>. At least one power source <NUM> of the aircraft <NUM> can provide electrical power to the low spool motor 12A and/or to the high spool motor 12B. The power source <NUM> can be a stored energy source or a generator driven by an engine. For example, the power source <NUM> can include one or more of a battery, a super capacitor, an ultra capacitor, a fuel cell, a flywheel, and the like. Where the aircraft <NUM> includes an additional thermal engine (not depicted), such as an auxiliary power unit (APU), the power source <NUM> can be a generator driven by the thermal engine. Further, a generator of one of the hybrid electric propulsion systems 100A, 100B can provide power to the other hybrid electric propulsion systems 100A, 100B. For example, if the hybrid electric propulsion system 100A is combusting fuel, the hybrid electric propulsion system 100B may operate without burning fuel and can drive the low speed spool <NUM> based on the low spool motor 12A receiving electric power from the hybrid electric propulsion system 100A and/or the power source <NUM>. Further, the high speed spool <NUM> can be driven based on the high spool motor 12B receiving electric power from the hybrid electric propulsion system 100A and/or the power source <NUM>.

While the example of <FIG> illustrates a simplified example of the gas turbine engine <NUM>, it will be understood that any number of spools, and inclusion or omission of other elements and subsystems are contemplated. Further, rotor systems described herein can be used in a variety of applications and need not be limited to gas turbine engines for aircraft applications. For example, rotor systems can be included in power generation systems, which may be ground-based as a fixed position or mobile system, and other such applications.

<FIG> illustrates a hybrid electric propulsion system <NUM> (also referred to as hybrid gas turbine engine <NUM> or hybrid propulsion system <NUM>) as a further example of the hybrid electric propulsion system 100A, 100B of <FIG>. In the example of <FIG>, the hybrid electric propulsion system <NUM> includes gas turbine engine <NUM> operably coupled to an electrical power system <NUM> as part of a hybrid electric aircraft, such as aircraft <NUM> of <FIG>. One or more mechanical power transmissions <NUM> (e.g., 150A, 150B) can be operably coupled between the gas turbine engine <NUM> and the electrical power system <NUM>. The gas turbine engine <NUM> includes one or more spools, such as low speed spool <NUM> and high speed spool <NUM>, each with at least one compressor section and at least one turbine section operably coupled to a shaft (e.g., low pressure compressor <NUM> and low pressure turbine <NUM> coupled to inner shaft <NUM> and high pressure compressor <NUM> and high pressure turbine <NUM> coupled to outer shaft <NUM>). The electrical power system <NUM> can include a low spool motor 12A configured to augment rotational power of the low speed spool <NUM> and a high spool motor 12B configured to augment rotational power of the high speed spool <NUM>. Although two motors 12A, 12B are depicted in <FIG>, it will be understood that there may be only a single motor (e.g., only low spool motor 12A) or additional motors (not depicted). Further, the motors 12A, 12B can be electric motors or alternate power sources may be used, such as hydraulic motors, pneumatic motors, and other such types of motors known in the art. The electrical power system <NUM> can also include a low spool generator 213A configured to convert rotational power of the low speed spool <NUM> to electric power and a high spool generator 213B configured to convert rotational power of the high speed spool <NUM> to electric power. Although two electric generators 213A, 213B (generally referred to as generators 213A, 213B) are depicted in <FIG>, it will be understood that there may be only a single electric generator (e.g., only electric generator 213B) or additional electric generators (not depicted). In some embodiments, one or more of the motors 12A, 12B can be configured as a motor or a generator depending upon an operational mode or system configuration, and thus one or more of the electric generators 213A, 213B may be omitted.

In the example of <FIG>, the mechanical power transmission 150A includes a gearbox operably coupled between the inner shaft <NUM> and a combination of the low spool motor 12A and low spool generator 213A. The mechanical power transmission 150B can include a gearbox operably coupled between the outer shaft <NUM> and a combination of the high spool motor 12B and high spool generator 213B. In embodiments where the motors 12A, 12B are configurable between a motor and generator mode of operation, the mechanical power transmission 150A, 150B can include a clutch or other interfacing element(s).

The electrical power system <NUM> can also include motor drive electronics 214A, 214B operable to condition current to the motors 12A, 12B (e.g., DC-to-AC converters). The electrical power system <NUM> can also include rectifier electronics 215A, 215B operable to condition current from the electric generators 213A, 213B (e.g., AC-to-DC converters). The motor drive electronics 214A, 214B and rectifier electronics 215A, 215B can interface with an energy storage management system <NUM> that further interfaces with an energy storage system <NUM>. The energy storage management system <NUM> can be a bi-directional DC-DC converter that regulates voltages between energy storage system <NUM> and electronics 214A, 214B, 215A, 215B. The energy storage system <NUM> can include one or more energy storage devices, such as a battery, a super capacitor, an ultra capacitor, and the like. The energy storage management system <NUM> can facilitate various power transfers within the hybrid electric propulsion system <NUM>. The energy storage management system <NUM> may also transfer power to one or more electric motors on the engine, or to external loads <NUM> and receive power from one or more external power sources <NUM> (e.g., power source <NUM> of <FIG>, aircraft power, auxiliary power unit power, cross-engine power, and the like).

A power conditioning unit <NUM> and/or other components can be powered by the energy storage system <NUM>. The power conditioning unit <NUM> can distribute electric power to support actuation and other functions of the gas turbine engine <NUM>. For example, the power conditioning unit <NUM> can power an integrated fuel control unit <NUM> to control fuel flow to the gas turbine engine <NUM>. The power conditioning unit <NUM> can also power a plurality of actuators (not depicted), such as bleed actuators, vane actuators, and the like.

One or more accessories <NUM> can also be driven by or otherwise interface with the gas turbine engine <NUM>. Examples of accessories <NUM> can include oil pumps, fuel pumps, and other such components. As one example, the accessories <NUM> include an oil pump driven through gearing, such as mechanical power transmission 150B, in response to rotation of the high speed spool <NUM> and/or the high spool motor 12B. Alternatively, accessories <NUM> can be electrically driven through power provided by the energy storage management system <NUM> or other such sources of electrical power.

Engagement and operation of the low spool motor 12A, low spool generator 213A, high spool motor 12B, and high spool generator 213B can change depending upon an operating state of the gas turbine engine <NUM> and any commands received. Collectively, any effectors that can change a state of the gas turbine engine <NUM> and/or the electrical power system <NUM> may be referred to as hybrid electric system control effectors <NUM>. Examples of the hybrid electric system control effectors <NUM> can include the motors 12A, 12B, electric generators 213A, 213B, integrated fuel control unit <NUM>, and/or other elements (not depicted).

<FIG> is a schematic diagram of control signal paths <NUM> of the hybrid electric propulsion system <NUM> of <FIG> and is described with continued reference to <FIG> and <FIG>. A controller <NUM> can interface with the motor drive electronics 214A, 214B, rectifier electronics 215A, 215B, energy storage management system <NUM>, integrated fuel control unit <NUM>, accessories <NUM>, and/or other components (not depicted) of the hybrid electric propulsion system <NUM>. In embodiments, the controller <NUM> can control and monitor for fault conditions of the gas turbine engine <NUM> and/or the electrical power system <NUM>. For example, the controller <NUM> can be integrally formed or otherwise in communication with a full authority digital engine control (FADEC) of the gas turbine engine <NUM>. Alternatively, the controller <NUM> can be an aircraft level control or be distributed between one or more systems of the aircraft <NUM> of <FIG>. In embodiments, the controller <NUM> can include a processing system <NUM>, a memory system <NUM>, and an input/output interface <NUM>. The controller <NUM> can also include various operational controls, such as a hybrid engine control <NUM> that controls the hybrid electric system control effectors <NUM> further described herein, for instance, based on a thrust command <NUM>. The thrust command <NUM> can be a throttle lever angle or a command derived based on a throttle lever angle control of the aircraft <NUM> of <FIG>.

The processing system <NUM> can include any type or combination of central processing unit (CPU), including one or more of: a microprocessor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. The memory system <NUM> can store data and instructions that are executed by the processing system <NUM>. In embodiments, the memory system <NUM> may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable medium onto which is stored data and algorithms in a non-transitory form. The input/output interface <NUM> is configured to collect sensor data from the one or more system sensors and interface with various components and subsystems, such as components of the motor drive electronics 214A, 214B, rectifier electronics 215A, 215B, energy storage management system <NUM>, integrated fuel control unit <NUM>, accessories <NUM>, and/or other components (not depicted) of the hybrid electric propulsion system <NUM>. The controller <NUM> provides a means for controlling the hybrid electric system control effectors <NUM> using a hybrid engine control <NUM> that can be dynamically updated during operation of the hybrid electric propulsion system <NUM>. The means for controlling the hybrid electric system control effectors <NUM> can be otherwise subdivided, distributed, or combined with other control elements.

The controller <NUM> with hybrid engine control <NUM> can apply control laws and access/update models to determine how to control and transfer power between the low speed spool <NUM> and high speed spool <NUM>. For example, sensed and/or derived parameters related to speed, flow rate, pressure ratios, temperature, thrust, and the like can be used to establish operational schedules and transition limits to maintain efficient operation of the gas turbine engine <NUM>. For instance, a mode of operation of the gas turbine engine <NUM>, such as idle, takeoff, climb, cruise, and descent can have different power settings, thrust requirements, flow requirements, and temperature effects. The hybrid engine control <NUM> can control electric current provided to the low spool motor 12A and high spool motor 12B and loading effects of the low spool generator 213A and high spool generator 213B. The hybrid engine control <NUM> can also determine a power split between delivering fuel to the combustor <NUM> and using the low spool motor 12A and/or high spool motor 12B to power rotation within the gas turbine engine <NUM>.

Referring now to <FIG>, plot <NUM> graphically illustrates a relationship between engine spool speeds and time when transitioning through multiple operating modes. Line <NUM> indicates a percent speed <NUM> of the low speed spool <NUM> as time <NUM> advances and the hybrid electric propulsion system <NUM> transitions between e-taxi <NUM>, engine start <NUM>, and conventional idle <NUM>. E-taxi <NUM> refers to a mode of operation where the low spool motor 12A drives rotation of the low speed spool <NUM> to produce thrust using the fan <NUM>, such that the aircraft <NUM> can be maneuvered on the ground without burning fuel in the combustor <NUM>. Line <NUM> indicates a percent speed <NUM> of the high speed spool <NUM> as time <NUM> advances and the hybrid electric propulsion system <NUM> transitions between e-taxi <NUM>, engine start <NUM>, and conventional idle <NUM>. As can be seen in <FIG>, the high speed spool <NUM> can remain undriven during e-taxi mode <NUM>, which conserves energy by avoiding fuel burn and power draw from the high spool motor 12B. In engine start <NUM>, the high spool motor 12B can be used to increase the speed of the high speed spool <NUM> for light off and fuel burn in the combustor <NUM>. In conventional idle <NUM>, the motors 12A, 12B may not be needed, and the gas turbine engine <NUM> may be power by fuel burn. Alternatively, the engine-on idle state may include a further hybrid element where the idle state of the engine includes both fuel input and electric input to the electric motors 12A, 12B, or draw through the electric generators 213A, 213B. This is referred to as sub-idle, being possibly below conventional fuel-only idle in terms of either fuel flow and/or thrust.

Referring now to <FIG>, plot <NUM> graphically illustrates a relationship between thrust <NUM> and throttle lever angle (TLA) <NUM>. Line <NUM> depicts an example thrust response starting at the e-taxi mode <NUM> of <FIG>, where thrust <NUM> can be commanded below idle by controlling the low spool motor 12A to drive rotation of the low speed spool <NUM> absent fuel burn in the combustor <NUM>. Generally, the operating mode of line <NUM> is for fuel off and electricity available as limited by a lower operating limit <NUM>. The lower operating limit <NUM> may be associated with a fuel-off detent of the TLA <NUM>. An idle level <NUM> may be associated with an idle detent of the TLA <NUM>. Line <NUM> depicts an example of a thrust response during engine start <NUM> of <FIG>, where thrust <NUM> can be provided below an idle level <NUM> using the low spool motor 12A to control thrust <NUM> while also using the high spool motor 12B to control the high speed spool <NUM> to provide sufficient compression in the gas turbine engine <NUM> for light off in the combustor <NUM>. Line <NUM> depicts an example of a thrust response after starting the gas turbine engine <NUM> at idle level <NUM>, such as idle <NUM> of <FIG>. Controlling the low spool motor 12A and high spool motor 12B can support a sub-idle operation state with thrust control at power settings lower than idle level <NUM>. Thrust <NUM> can be controlled at a demand and power output via the low spool motor 12A and/or high spool motor 12B for a thrust output less than a minimum thrust output at engine idle. The thrust response depicted at line <NUM> can start at idle level <NUM> and continue up in relation to TLA <NUM> along a response profile <NUM>. Although lines <NUM>, <NUM>, <NUM> and response profile <NUM> are depicted as substantially linear segments, it will be understood that lines <NUM>, <NUM>, <NUM> and response profile <NUM> can have other shapes and characteristics.

<FIG> further illustrates a first region <NUM> where the thrust response characteristic above the idle level <NUM> may be the same whether the fuel flow is on or off, and furthermore a second region <NUM> is defined below the idle level <NUM>. The similar thrust response characteristic can continue in the second region <NUM> to a lower thrust level before reaching the lower operating limit <NUM> at line <NUM>. A transition from the lower operating limit <NUM> to the idle level <NUM> can occur during engine start at line <NUM>. Line <NUM> is an example that can shift in position between lines <NUM> and <NUM> depending on the throttle lever angle <NUM> position for sub-idle operation. Power provided by the low spool motor 12A and/or the high spool motor 12B can support engine starting below idle level <NUM> within the second region <NUM>.

In embodiments, the controller <NUM> can blend the power distribution between the hybrid electric system control effectors <NUM> and fuel burn in the combustor <NUM>. From a pilot's perspective, the setting of throttle lever angle <NUM> produces thrust command <NUM> without the pilot having to distinguish between whether motor-based thrust or fuel burn based thrust is needed. While conventional systems may use detents to prevent a pilot from reducing thrust <NUM> below the idle level <NUM>, embodiments can support operation of thrust <NUM> down to line <NUM> to support e-taxi mode <NUM> and other intermediate modes of operation below conventional idle <NUM>. Thus, control of thrust <NUM> can be achieved before, during, and after engine start <NUM>. With respect to the aircraft <NUM>, the hybrid electric propulsion systems 100A, 100B can be independently controlled such that one of the hybrid electric propulsion systems 100A, 100B is operating in a fuel burning mode while the other of the hybrid electric propulsion systems 100A, 100B is operated using the low spool motor 12A and/or the high spool motor 12B or a blend of fuel burn and electric power. Such mixed modes of operation may be used, for instance, during descent of the aircraft <NUM>, where thrust <NUM> is desired from both gas turbine engines <NUM>, but only one of the gas turbine engines <NUM> actively burns fuel. Further, embodiments can support e-taxi mode <NUM> with warmup time to delay starting of the gas turbine engines <NUM> until reaching a location on the taxiway away from a boarding gate.

Referring now to <FIG> with continued reference to <FIG>, <FIG> is a flow chart illustrating a method <NUM> for providing hybrid gas turbine engine starting control, in accordance with an embodiment. The method <NUM> may be performed, for example, by the hybrid electric propulsion system <NUM> of <FIG>. For purposes of explanation, the method <NUM> is described primarily with respect to the hybrid electric propulsion system <NUM>; however, it will be understood that the method <NUM> can be performed on other configurations (not depicted).

Method <NUM> pertains to the controller <NUM> executing embedded code for the starting and thrust control using hybrid engine control <NUM> along with other control functions. At block <NUM>, the controller <NUM> can receive a thrust command <NUM> for a gas turbine engine <NUM>, where the gas turbine engine <NUM> includes a low speed spool <NUM>, a high speed spool <NUM>, and a combustor <NUM>. The controller <NUM> is configured to cause fuel flow to the combustor <NUM> under certain operating conditions.

At block <NUM>, the controller <NUM> can control a low spool motor 12A to drive rotation of the low speed spool <NUM> responsive to the thrust command <NUM> while the controller <NUM> does not command fuel flow to the combustor <NUM>, where the low spool motor 12A is configured to augment rotational power of the low speed spool <NUM>. Fuel flow can be reduced or completely shut off depending upon an operating state of the gas turbine engine <NUM>. For example, the controller <NUM> can output a command of no fuel, fuel flow off, and/or otherwise effectively disable or reduce fuel flow as targeted. The operating state can depend on a combination of commands, conditions, and modes, such as an e-taxi mode, a starting mode, a ground idle mode, a takeoff mode, a climb mode, a cruise mode, an in-flight idle mode, a descent mode, a landing mode, and other such modes. The controller <NUM> can determine an allocation of the thrust command <NUM> between commanding fuel flow to the combustor <NUM> and electric current to the low spool motor 12A based on the operating state of the gas turbine engine <NUM> and a throttle lever angle <NUM>, where the throttle lever angle <NUM> can be received from a pilot control, an auto-pilot control, or other such source on the aircraft <NUM>. The low spool motor 12A can be powered by one or more of a generator, an energy storage system, and a power source <NUM> external to the gas turbine engine <NUM>.

At block <NUM>, the controller <NUM> can control the low spool motor 12A responsive to the thrust command <NUM> during a starting operation of the gas turbine engine <NUM>. The starting operation can be a ground-based start or an in-flight restart.

At block <NUM>, the controller <NUM> can control the low spool motor 12A to drive rotation of the low speed spool <NUM> responsive to the thrust command at or above an idle condition of the gas turbine engine <NUM>.

In some embodiments, a high spool motor 12B can be used in conjunction with the low spool motor 12A. For example, the controller <NUM> can receive an engine start command <NUM>. At block <NUM>, the controller <NUM> can control a high spool motor 12B to accelerate the high speed spool <NUM> responsive to a start command while the low spool motor 12A controls thrust of the gas turbine engine <NUM> on the low speed spool <NUM>, where the high spool motor 12B is configured to augment rotational power of the high speed spool <NUM>. Control of the high spool motor 12B of block <NUM> can occur in parallel with control of the low spool motor 12A of block <NUM> or blocks <NUM> and <NUM> can be other sequenced, combined, or further subdivided. The controller <NUM> can be configured to control a thrust response of the gas turbine engine <NUM> to a response profile <NUM> based on the throttle lever angle <NUM> using any combination of the low spool motor 12A, high spool motor 12B, and fuel burn.

In some embodiments, a low spool generator 213A is configured to extract power from the low speed spool <NUM>, and a high spool generator 213B is configured to extract power from the high speed spool <NUM>. The controller <NUM> can be configured to selectively provide electrical power from the low spool generator 213A to the high spool motor 12B and selectively provide electrical power from the high spool generator 213B to the low spool motor 12A. The controller <NUM> can also be configured to selectively engage either or both of the low spool generator 213A and the high spool generator 213B to adjust a load and speed of either or both of the low speed spool <NUM> and the high speed spool <NUM>.

Also, it is clear to one of ordinary skill in the art that, the starting control described herein can be combined with and enhance other control features, such as valves, vanes, and fuel flow control.

Although some embodiments described herein relate to relighting an engine during or after an e-taxi event, it should be appreciated that the disclosed techniques for relighting an engine can also apply to other modes of operation and/or flight phases. For example, a mode of operation of the gas turbine engine <NUM> of <FIG> and <FIG>, such as idle, takeoff, climb, cruise, and descent can have different power settings, thrust requirements, flow requirements, and temperature effects.

An aircraft can selectively power a hybrid electric engine by providing electric power from various sources, such as a battery system, another engine, and/or an APU or secondary power unit (SPU). With respect to the aircraft <NUM> of <FIG>, the hybrid electric propulsion systems 100A, 100B can be independently controlled such that one of the hybrid electric propulsion systems 100A, 100B is operating in a fuel burning mode while the other of the hybrid electric propulsion systems 100A, 100B is operated using the low spool motor 12A and/or the high spool motor 12B or a blend of fuel burn and electric power. Such mixed modes of operation may be used, for instance, during descent of the aircraft <NUM>, where thrust is desired from both gas turbine engines <NUM>, but only one of the gas turbine engines <NUM> actively burns fuel. In such cases, it may be desirable, during descent, to restart (e.g., relight) the one of the gas turbine engines <NUM> that is not actively burning fuel.

During descent with one of the engines <NUM> operating on electric power and the other of the engines <NUM> operating with fuel burn, various aspects may be considered such that the engine system operates efficiently, and the one of the engines <NUM> operating on electric power can rapidly resume a fuel-burn mode of operation (e.g., restart or relight). However, in some cases, it may be desirable, during descent, to keep only one of the gas turbine engines <NUM> actively burning fuel while the other of the gas turbine engines <NUM> is operating on electric power. The choice of whether to use only one of the gas turbine engines <NUM> in fuel burning mode or to use both of the gas turbine engines <NUM> in fuel burning mode can depend, for example, on the descent angle (e.g., glide slope).

One or more embodiments described herein provides a process for determining when to enable a hybrid electric engine to operate in a fuel burning mode or to operate in an electrically powered mode during descent. For example, in some situations such as e-taxi or descent, an aircraft having two hybrid electric engines can operate with one of the engines in fuel-burning mode and the other engine operating in an electric power (non-fuel burning) mode. This can be referred to as single-engine descent when the aircraft is in a descent phase of flight.

During single engine descent, thrust matching is performed. For example, <NUM>,<NUM> pounds (<NUM>,<NUM> N) of thrust per each of the engines <NUM> can be achieved by driving a fan of one of the engines <NUM> electrically to provide <NUM>,<NUM> pounds (<NUM>,<NUM> N) of thrust, and the other of the engines <NUM>, operating in a fuel-burning mode, can generate power for the electrically-operated engine and produce <NUM>,<NUM> pounds (<NUM>,<NUM> N) of thrust.

In some cases, in some cases of descent, such as with a relatively shallower glide slope, it is more fuel efficient to operate both engines <NUM> in the fuel-burning mode. However, in cases with a relatively steeper glide slope, it is more fuel efficient to maintain a single engine descent (e.g., to operate only one of the engines <NUM> in the fuel-burning mode while the other engine <NUM> operates in the electrically powered mode).

A control strategy implemented by the hybrid electric engine system can consider a planned descent profile (e.g., a desired glide slope), a battery state of charge, and/or an estimate of transmission losses to decide whether to exercise this function of single engine descent. Other parameters may also be considered and can include, for example, the availability of power from an APU/SPU as a primary or backup power source for the electrically operated engine.

With a steep approach or continuous approach, it may make more sense to operate in single engine descent mode, which supports a steeper approach than a traditional duel fuel-driven engine approach. Glide range to alternate landing locations may also be considered as an input to activating single engine descent mode. For example, if the glide range to an alternate landing location is determined to exceed a distance threshold, the mode of the electrically powered engine can be changed to the fuel-burning mode. As an example, the distance threshold could be present, could be based on factors such as fuel burn rate, available fuel, environmental factors, pilot input, and the like, including combinations thereof.

According to one or more embodiments described herein, a tradeoff of expected fuel savings versus component wear effects can be determined prior to activating single engine descent mode. For example, where fuel savings is greater than any negative effects on component wear, it may be desirable to use single engine descent. However, where negative effects on component wear is greater, it may be desirable to use a traditional duel fuel-driven engine approach. Flight time with single engine descent mode active can be tracked for each engine as well as whether each engine operated as a fuel-driven engine or an electrically operated engine during single engine descent mode. This information can be used to determine lifetime estimates for engines/components.

<FIG> is a flow chart illustrating a method <NUM>, in accordance with an embodiment of the disclosure. The method <NUM> can be performed by any suitable system, device, controller, etc., such as the controller <NUM>. It should be appreciated that system, device, controller, etc., that performs the method can be located in a control unit of one of the engines <NUM>, both of the engines <NUM>, the aircraft <NUM>, combinations thereof, or at another location.

At block <NUM>, a controller (e.g., the controller <NUM>) determines a thrust requirement to satisfy a desired glide slope. The desired slope can be received, for example, from a system/controller of the aircraft, from the pilot, from a remote ground-based system, and/or the like. The desired glide slope indicates a desired path of descent of the aircraft preparing to land. Some landing locations (e.g., airports) require relatively higher glide slopes than other landing locations due to geographic conditions, environmental conditions, local regulations, etc. Further, some aircraft operate more efficiently at certain glide slopes than others.

At decision block <NUM>, the controller determines, based on the thrust requirement, whether thrust matching can be maintained while operating a first gas turbine engine (e.g., one of the engines <NUM>) in a fuel-burning mode and operating a second gas turbine engine (e.g., the other of the engines <NUM>) in an electrically powered mode. As described herein, during single engine descent, thrust matching is performed. For example, <NUM>,<NUM> pounds (<NUM>,<NUM> N) of thrust per each of the engines <NUM> can be achieved by driving a fan of one of the engines <NUM> electrically to provide <NUM>,<NUM> pounds (<NUM>,<NUM> N) of thrust, and the other of the engines <NUM>, operating in a fuel-burning mode, can generate power for the electrically-operated engine and produce <NUM>,<NUM> pounds (<NUM>,<NUM> N) of thrust. The controller determines whether the thrust matching can be maintained while the aircraft operates in single engine descent. Determining whether thrust matching can be maintained can include comparing a first thrust of the first engine with a second thrust of the second engine. It is determined that thrust matching can be maintained when the second thrust satisfies a threshold difference relative to the first thrust. However, it is determined that thrust matching cannot be maintained when the second thrust fails to satisfy a threshold difference relative to the first thrust. The threshold difference could be a percent difference between the first and second thrusts (e.g., <NUM>% difference), an absolute value difference between the first and second thrusts (e.g., <NUM> pounds (<NUM> N) of thrust difference), and/or the like.

If, at decision block <NUM>, it is determined that thrust matching cannot be maintained, the controller, at block <NUM>, commands fuel flow to a combustor of the second engine to cause the second gas turbine engine to operate in the fuel-burning mode. That is, the second engine ceases to operate in the electrically powered mode and switches to fuel-burning mode, thus providing the aircraft with dual engine descent. This ensures that the thrust matching can be maintained while maintaining the desired glide slope.

If, at decision block <NUM>, it is determined that thrust matching can be maintained, at block <NUM>, the first gas turbine engine continues to operate in the fuel-burning mode and the second gas turbine engine continues to operate in the electrically powered mode.

Additional processes also may be included. For example, the method <NUM> can include determining a glide range to an alternate landing location and then, responsive to determining that the glide range exceeds a distance threshold, commanding fuel flow to a combustor of the second engine to cause the second gas turbine engine to operate in the fuel-burning mode.

According to one or more embodiments described herein, the method <NUM> includes tracking a first amount of time the second engine spends in the fuel-burning mode and a second amount of time the second engine spends in the electrically powered mode. The commanding can then be based on the first and/or second amount of time. For example, commanding the fuel flow to the combustor of the second engine to cause the second gas turbine engine to operate in the fuel-burning mode is based at least in part on at least one of the first amount of time or the second amount of time.

It should be understood that the process depicted in <FIG> represents an illustration, and that other processes may be added or existing processes may be removed, modified, or rearranged without departing from the scope of the present disclosure.

Claim 1:
A system comprising:
a first gas turbine engine (<NUM>) for an aircraft (<NUM>), the first gas turbine engine (<NUM>) comprising a first low speed spool (<NUM>), a first high speed spool (<NUM>), and a first combustor (<NUM>);
a first high spool motor (12B) configured to augment rotational power of the first high speed spool (<NUM>);
a second gas turbine engine (<NUM>) for the aircraft (<NUM>), the second gas turbine engine (<NUM>) comprising a second low speed spool (<NUM>), a second high speed spool (<NUM>), and a second combustor (<NUM>);
a second high spool motor (12B) configured to augment rotational power of the second high speed spool (<NUM>); and
a controller (<NUM>) to:
determine a thrust requirement to satisfy a desired glide slope;
determine whether thrust matching between the first gas turbine engine and the second gas turbine engine can be maintained while operating the first gas turbine engine (<NUM>) in a fuel-burning mode and operating the second gas turbine engine (<NUM>) in an electrically powered mode; and
responsive to determining that thrust matching cannot be maintained, command fuel flow to the second combustor (<NUM>) of the second gas turbine engine (<NUM>) to cause the second gas turbine engine (<NUM>) to operate in the fuel-burning mode.