Hybrid propulsion engines for aircraft

FIELD OF THE DISCLOSURE

0001This disclosure relates generally to aircraft and, more particularly, to hybrid propulsion engines for aircraft.

BACKGROUND

0002Aircraft typically include one or more engines to produce thrust. There are many different types or arrangements of engines, such as turbofan engines, turboprop engines, etc. These engines include a propulsor, such as a fan or propeller, for producing thrust and an engine core, such as a gas turbine engine, that drives the propulsor. While effective for certain flight conditions, these engines are typically limited in the altitude at which they can operate. Also, for longer distance flights, larger engines are needed, which are typically heavy and, thus, decrease the efficiency of the aircraft. Further, longer flights require more fuel, which further adds weight to the aircraft.

0003<patcit id="pcit0001" dnum="EP3335995A1"><text>EP 3335995 A1</text></patcit> discloses, according to its abstract, "A propulsion system 10 includes a propulsor 12 having a driveshaft 72, an electric machine 14 coupled to the driveshaft 72 of the propulsor 12, and a combustion engine having an output shaft. The propulsion system 10 additionally includes a one-way clutch 16 operable with at least one of the driveshaft 72 of the propulsor 12 and the output shaft of the combustion engine. The one-way clutch 16 allows for a differential angular velocity of the driveshaft 72 relative to the output shaft in a first circumferential direction and prevents a differential angular velocity of the driveshaft 72 relative to the output shaft in a second circumferential direction".

0004<patcit id="pcit0002" dnum="DE102013209538A1"><text>DE 102013209538 A1</text></patcit> appears to disclose, according to its abstract, a hybrid drive for a power-driven aircraft, which has a primary shaft (11) coupled to a gas turbine (10) and a secondary shaft (21) coupled to an electrical machine (20), and with the secondary shaft (21) a turbine wheel (23) is rotatably coupled, by means of which an exhaust gas flow generated during operation of the gas turbine (10) can be used to drive the secondary shaft (21). The hybrid drive has a propeller (40) to which a torque of the primary shaft (11) and/or a torque of the secondary shaft (21) can be transmitted.

0005<patcit id="pcit0003" dnum="DE102014224637A1"><text>DE 102014224637 A1</text></patcit> appears to disclose, according to its abstract, a hybrid electric drive system for an aircraft. The system comprises a single main internal combustion engine (10), a first thrust unit (50) and a second thrust unit (55). The single main internal combustion engine (10) is designed to drive the first thrust unit (50) by means of a mechanical connection (60). The system further comprises an electric motor (25) which is designed to drive the second thrust unit (55). A generator (20) is further provided which is designed to convert mechanical energy generated by the internal combustion engine (10) into electrical energy, the generator being designed to supply the electric motor (25) with electrical energy. According to the invention, both thrust units can be driven by the single main internal combustion engine (10), which enables the use of a larger, more efficient main internal combustion engine (10) during normal flight operations.

0006<patcit id="pcit0004" dnum="EP2924247A1"><text>EP 2924247 A1</text></patcit> discloses, according to its abstract, that "A gas turbine engine (20) has a fan drive turbine (28) for selectively driving a fan rotor (45). A drive shaft (30) between the fan drive turbine (28) and the fan rotor (45) includes a clutch (36), and an electric motor (38). The electric motor (38) is positioned such that it is not downstream of a flow path relative to the fan drive turbine (28)".

0007<patcit id="pcit0005" dnum="EP3421366A1"><text>EP 3421366 A1</text></patcit> discloses, according to its abstract, that "A propulsion system 100 for an aircraft 10 includes a propulsor 204; a turbomachine 202 mechanically coupled to the propulsor 204 for driving the propulsor 204 during a combustion operating mode of the propulsion system 100 and mechanically decoupled from the propulsor 204 during an electric operating mode of the propulsion system 100; and an electrical power source 246. The propulsion system 100 further includes an electric machine, the electric machine being electrically coupled to the electrical power source 246 and mechanically coupled to the propulsor 204 during the electric operating mode of the propulsion system 100 such that the electric machine drives the propulsor 204 during the electric operating mode of the propulsion system 100".

SUMMARY

0008In a first aspect there is provided a method of operating a hybrid propulsion engine, the method as defined in claim 1 of the appended claims. In a second aspect there is provided a hybrid propulsion engine as defined in appended claim 6. In a third aspect there is provided an aircraft as defined in appended claim 15. Disclosed herein is a hybrid propulsion engine for an aircraft. The hybrid propulsion engine includes a propulsor and a gas turbine engine having a first drive shaft. The hybrid propulsion engine also includes an electric motor having a second drive shaft, and the propulsor is coupled to the second drive shaft. The hybrid propulsion engine further includes a clutch coupled between the first drive shaft and the second drive shaft to enable the gas turbine engine to drive the propulsor, via the clutch, during a first mode of operation and to enable the electric motor to drive the propulsor during a second mode of operation and a controller arranged to carry out the method of any one of claims 1 to 5.

0009A method of operating a hybrid propulsion engine disclosed herein includes operating a hybrid propulsion engine during a first segment of flight of an aircraft in a first mode of operation. The hybrid propulsion engine includes a propulsor, a gas turbine engine, and an electric motor. In the first mode of operation, the gas turbine engine is driving the propulsor. The example method also includes operating the hybrid propulsion engine during a second segment of flight of an aircraft in a second mode of operation where the electric motor is driving the propulsor. The method further includes: prior to operating the hybrid propulsion engine in the second mode of operation: receiving, at a controller, an input signal requesting to switch modes from the first mode of operation to the second mode of operation; determining, via the controller, whether one or more mode-change parameters are satisfied; based on a determination that the one or more mode-change parameters are satisfied, sending a first command signal, via the controller, to start the electric motor; sending a second command signal, via the controller, to shut down the gas turbine engine; and prior to sending the second command signal to shut down the gas turbine engine, verifying, via the controller, that the electric motor has started and is driving the propulsor.

0010An aircraft disclosed herein is according to claim 15 and includes a hybrid propulsion engine including a propulsor, a gas turbine engine, an electric motor, and a clutch operatively coupled between the gas turbine engine and the electric motor to enable the electric motor to drive the propulsor independently of the gas turbine engine.

BRIEF DESCRIPTION OF THE DRAWINGS

0011<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> illustrates an aircraft in which the examples disclosed herein can be implemented.</li><li><figref idref="f0002">FIG. 2</figref> is a schematic diagram of an example hybrid propulsion engine constructed in accordance with the teachings of this disclosure.</li><li><figref idref="f0003">FIG. 3</figref> is a schematic diagram of two example hybrid propulsion engines.</li><li><figref idref="f0004">FIG. 4</figref> is a partial cutaway view of an example hybrid propulsion engine implemented in connection with a turbofan engine including a gas turbine engine and electric motor.</li><li><figref idref="f0005">FIG. 5</figref> is a partial cutaway view of an example hybrid propulsion engine implemented in connection with a turboprop engine including a gas turbine engine and electric motor.</li><li><figref idref="f0006">FIG. 6</figref> is an enlarged view of the electric motor of the hybrid propulsion engine of <figref idref="f0004">FIG. 4</figref>.</li><li><figref idref="f0006">FIGS. 7A and 7B</figref> are cross-sectional views of an overrunning clutch from <figref idref="f0006">FIG. 6</figref>.</li><li><figref idref="f0007">FIG. 8A</figref> is a flowchart representative of an example method of changing a hybrid propulsion engine from a first mode of operation to a second mode of operation.</li><li><figref idref="f0008">FIG. 8B</figref> is a flowchart representative of an example method of changing a hybrid propulsion engine from the second mode of operation to the first mode of operation.</li></ul>

0012The figures are not to scale. In general, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this patent, stating that any part (e.g., a layer, film, area, region, or plate) is in any way on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, indicates that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. Stating that any part is in contact with another part means that there is no intermediate part between the two parts.

DETAILED DESCRIPTION

0013Disclosed herein are example hybrid propulsion engines for aircraft. The hybrid propulsion engines include an internal combustion engine, such as a gas turbine engine, and an electric motor that are coupled to a propulsor such as a fan or a propeller and operate in parallel manner to drive the propulsor. The hybrid propulsion engines described herein can operate between different modes of operation in which the gas turbine engine and/or the electric motor are used to drive the propulsor to produce forward thrust. For example, in a first mode of operation, the gas turbine engine drives the propulsor to produce forward thrust when an increased level of thrust is desired. In the first mode of operation, the electric motor can be off and/or otherwise not powering the propulsor. In a second mode of operation, the electric motor drives the propulsor to produce forward thrust (while the gas turbine engine is off and/or otherwise not powering the propulsor), as electric motors are more efficient at driving the propulsor during certain flight conditions. For example, the gas turbine engine can be used during take-off and landing when an increased level of thrust is required. Whereas the electric motor can be used during cruise, where the aircraft is at higher altitudes and subject to less drag. As such, the gas turbine engines are used for less time during the flight. As a result, less fuel is needed onboard the aircraft, thereby further decreasing the overall weight of the aircraft. Further, in some instances the electric motor may be used to supplement the gas turbine engine during take-off and/or climb and, thus, a smaller, lighter gas turbine engine can be utilized.

0014The example hybrid propulsion engines described herein include a clutch disposed between the gas turbine engine and the electric motor that enables the electric motor to operate independently of the gas turbine engine and without driving or rotating the output shaft of the gas turbine engine. For example, the gas turbine engine includes a first drive shaft (e.g., an output shaft), and the electric motor includes a second drive shaft. The propulsor is coupled to the second drive shaft, and the first drive shaft is coupled to the second drive shaft via a clutch, such as an overrunning clutch. As such, when the gas turbine engine is running during the first mode of operation, the first drive shaft rotates the second drive shaft and, thus, transfers power to the propulsor. During the first mode of operation, the electric motor is off and not affected by the rotating second drive shaft. In the second mode of operation, the electric motor is turned on and used to rotate the second drive shaft, which drives the propulsor and produces forward thrust. During the second mode of operation, the gas turbine engine can be turned off. The overrunning clutch enables the second drive shaft to rotate independent of the first drive shaft and, thus, does not drive or rotate the first drive shaft. In other words, the overrunning clutch enables the gas turbine engine and the electric motor to operate in a parallel manner, rather than in series, such that operation of one does not require operation of the other. In other examples, other types of clutches can be implemented to connect or disconnect the first and second drive shafts.

0015In some examples, while the gas turbine engine is driving the propulsor in the first mode of operation, the electric motor can be energized and used to overspeed or overdrive the gas turbine engine. This operation can be used to provide temporary bursts of power to the propulsor (e.g., in the event of an engine-out scenario), for example. In other examples, the electric motor can be operated at approximately the same rotational speed as the gas turbine engine to provide torque to the propulsor without overrunning the gas turbine engine. This operation can reduce the load on the gas turbine engine, for example.

0016<figref idref="f0001">FIG. 1</figref> illustrates an aircraft 100 in which the examples disclosed herein can be implemented. The aircraft 100 includes a fuselage 102, a first wing 104 (a left wing) coupled to the fuselage 102, and a second wing 106 (a right wing) coupled to the fuselage 102. In the illustrated example, the aircraft 100 includes a first propulsion generator 108 and a second propulsion generator 110 carried by the first and second wings 104, 106, respectively. In other examples, the aircraft 100 may include only one propulsion generator or may include more than two propulsion generators. The propulsion generator(s) can be coupled to the first and second wings 104, 106 and/or another structure on the aircraft 100 (e.g., on the tail section of the fuselage 102). The aircraft 100 may be a manned or unmanned aircraft.

0017<figref idref="f0002">FIG. 2</figref> is a schematic diagram of an example hybrid propulsion engine 200 constructed in accordance with the teachings of this disclosure. The hybrid propulsion engine 200 can be implemented as one or both of the propulsion generators 108, 110 of the aircraft 100 (<figref idref="f0001">FIG. 1</figref>). As shown in <figref idref="f0002">FIG. 2</figref>, the hybrid propulsion engine 200 includes an internal combustion engine 202 and a propulsor 204 that can be driven by the internal combustion engine 202 to produce forward thrust. In this example, the internal combustion engine 202 is implemented as a gas turbine engine 202. The propulsor 204 can be a fan of a turbofan engine, for example, such as in the turbofan engine shown in <figref idref="f0004">FIG. 4</figref> and described in further detail herein. In other examples, the propulsor 204 can be a propeller of a turboprop engine, such as in the turboprop engine shown in <figref idref="f0005">FIG. 5</figref>. The propulsor 204 can be on the front of the hybrid propulsion engine 200 (known as a tractor configuration) or on the rear of the hybrid propulsion engine 200 (known as a pusher configuration). Also, the propulsor 204 can include two or more propulsors, such as two counter-rotating propellers. The gas turbine engine 202 is powered by fuel from a fuel tank 206. A controller 208 (e.g., an electronic engine controller (EEC), a processor, etc.) controls the on/off operations of the gas turbine engine 202. The controller 208 operates a valve 210 that controls the flow of fuel from the fuel tank 206 to the gas turbine engine 202 and may also control the ignition component(s) and/or a starter of the gas turbine engine 202.

0018The hybrid propulsion engine 200 of <figref idref="f0002">FIG. 2</figref> also includes an electric motor 212 that can be used to drive the propulsor 204 in addition to or as an alternative to the gas turbine engine 202. The electric motor 212 is separate from any starter or auxiliary power unit (APU) (e.g., an electric motor, a pneumatic motor, a small gas turbine, etc.) associated with the hybrid propulsion engine 200 for starting purposes. The electric motor 212 is powered by an electrical power source 214 and controlled via the controller 208. In the illustrated embodiment, the power source 214 is a battery 214. The gas turbine engine 202 and the electric motor 212 are coupled to the propulsor 204 in a manner that enables each to drive the propulsor 204 independently of the other. In particular, the hybrid propulsion engine 200 is operable in different modes of operation where the gas turbine engine 202 and/or the electric motor 212 is used to drive the propulsor 204 to produce thrust. For example, the hybrid propulsion engine 200 is operable in a first mode of operation where the gas turbine engine 202 is running and the electric motor 212 is off. In this first mode of operation only the gas turbine engine 202 drives the propulsor 204. In a second mode of operation the electric motor 212 is running and the gas turbine engine 202 is off, such that only the electric motor 212 drives the propulsor 204. Using this arrangement and combination of the gas turbine engine 202 and the electric motor 212 enables the gas turbine engine 202 to be smaller and lighter and, thus, reduces the overall size and weight of the hybrid propulsion engine 200. For example, the gas turbine engine 202 can be used to drive the propulsor 204 during take-off and/or landing where more power and/or control is needed, and the electric motor 212 can be used to drive the propulsor 204 during cruise (which accounts for a majority of the flight time). During cruise, the aircraft 100 is generally at a higher altitude where the atmosphere is thinner and, thus, produces less drag on the aircraft 100. As such, less power is usually needed to drive the propulsor 204 to produce sufficient thrust. The electric motor 212 can be used to drive the propulsor 204 at cruise more efficiently than the gas turbine engine 202. Therefore, the gas turbine engine 202 may be used less during normal flights than conventional gas turbine engines that are used throughout the whole flight. As a result, less fuel is needed onboard the aircraft 100, which reduces the overall weight of the aircraft 100.

0019To enable the electric motor 212 to drive the propulsor 204 independently of the gas turbine engine 202 (and vice versa), the example hybrid propulsion engine 200 includes a clutch 216. In this example, the clutch 216 is implemented as an overrunning clutch (sometimes referred to as a freewheel, a no-back clutch, or a one-way roller clutch). The overrunning clutch 216 is disposed between the gas turbine engine 202 and the electric motor 212. In the illustrated example, the gas turbine engine 202 includes a first drive shaft 218 (an output shaft) that is driven when the gas turbine engine 202 is running. In some examples, the gas turbine engine 202 is a multi-spool engine and the first drive shaft 218 corresponds to a low pressure compressor (LPC) shaft of the gas turbine engine 202.

0020The propulsor 204 is coupled, directly or indirectly, to a second drive shaft 220. In some examples, the second drive shaft 220 is formed integrally with the electric motor 212. Specifically, the second drive shaft 220 can also function as the rotor shaft of the electric motor 212. Optionally, the second drive shaft 220 can be coupled directly to an output of the electric motor 212, e.g. the second drive shaft 220 is coupled to an end of the electric motor 212 rotor. The hybrid propulsion engine 200 can include a transmission 222 (sometimes referred to as a gear box) coupled between the second drive shaft 220 and the propulsor 204. The transmission 222 changes the rotational speed between the second drive shaft 220 and the propulsor 204. Thus, the propulsor 204 is driven by rotating the second drive shaft 220.

0021During a first mode of operation, the gas turbine engine 202 is running and the electric motor 212 is off. The first drive shaft 218 of the gas turbine engine 202 rotates the second drive shaft 220 via the overrunning clutch 216 and, thus, rotates the propulsor 204. Therefore, in the first mode of operation, the gas turbine engine 202 drives the propulsor 204 via the overrunning clutch 216 to produce forward thrust. While the second drive shaft 220 is rotating, the electric motor 212 is off (e.g., no current is being applied to the coils of the electric motor 212). Conversely, during a second mode of operation, the electric motor 212 is running and the gas turbine engine 202 is either off or transitioning to an off-state. The electric motor 212 rotates the second drive shaft 220 and, thus, drives the propulsor 204. Thus, in the second mode of operation, the electric motor 212 is used to drive the propulsor 204 to produce forward thrust.

0022In the second mode of operation, the overrunning clutch 216 enables the second drive shaft 220 to rotate without rotating the first drive shaft 218. In other words, when the electric motor 212 is driving the second drive shaft 220, the gas turbine engine 202 is off and the first drive shaft 218 is approximately stationary (not rotated).

0023In one example, during take-off for example, the aircraft 100 can be configured to operate in the first mode of operation, i.e. the gas turbine engine 202 is driving the propulsor 204 and the electric motor 212 is off. After take-off, it may be desirable to transition from the first mode of operation to the second mode of operation wherein the electric motor 212 is driving the propulsor 204. To transition from the first mode to the second mode, the controller 208 transmits a start command to the electric motor 212 and also transmits a separate command to the gas turbine engine 202. The command to the gas turbine engine may be a stop command or a command to reduce an operational speed of the gas turbine engine 202, e.g. a command to operate the gas turbine engine 202 at idle speed.

0024When transitioning from the first mode of operation to the second mode of operation, the rotational speed of the gas turbine engine 202 decreases and the rotational speed of the electric motor 212 increases. When the rotational speed of the electric motor 212 is greater than the rotational speed of the gas turbine engine 202, i.e. the rotational speed of the second drive shaft 220 is greater than the rotational speed of the first drive shaft 218, the overrunning clutch 216 disengages such that the electric motor 212 is driving the propulsor 204.

0025Conversely, when transitioning from the second mode of operation to the first mode of operation, the rotational speed of the gas turbine engine 202 increases and the rotational speed of the electric motor 212 decreases. When the rotational speed of the gas turbine engine 202 is greater than the rotational speed of the electric motor 212, i.e. the rotational speed of the second drive shaft 220 is less than the rotational speed of the first drive shaft 218, the overrunning clutch 216 engages such that the gas turbine engine 202 is driving the propulsor 204 via the first and second drive shafts 218, 220.

0026As such, the overrunning clutch 216 enables the gas turbine engine 202 and the electric motor 212 to operate in a parallel manner, such that the gas turbine engine 202 and the electric motor 212 can operate to drive the propulsor 204 independent of the other. Thus, while the gas turbine engine 202 and the electric motor 212 are shown as mechanically coupled in series to the propulsor 204, the overrunning clutch 216 enables the gas turbine engine 202 and the electric motor 212 to operate in a parallel manner. The controller 208 controls the on/off operations of the gas turbine engine 202 and the electric motor 212 to switch between the first mode of operation and the second mode of operation based on pilot input (e.g., via activation of a button or switch) and/or an auto-pilot program. In other examples, other types of clutches can be used as an alternative to the overrunning clutch 216. Further, while in this example the hybrid propulsion engine 200 utilizes the gas turbine engine 202, in other examples the hybrid propulsion engine 200 can be implemented in connection with other types of internal combustion engines, such as a reciprocating piston engine or a rotary engine (e.g., a Wankel engine).

0027In <figref idref="f0002">FIG. 2</figref>, the propulsor 204, the electric motor 212, and the gas turbine engine 202 are all axially aligned. In particular, the rotational axis of the propulsor 204 is coaxial with the first drive shaft 218 and the second drive shaft 220. In other examples, the rotational axis of the first drive shaft 218 and the second drive shaft 220 remain aligned. However, the propulsor 204 can be offset from the rotational axis of the first drive shaft 218 and the second drive shaft 220. For example, the transmission 222 can include a gear and pinion arrangement that separates the rotational axis of the propulsor 204 from the rotational axes of the first and second drive shafts 218, 220.

0028In some examples, the hybrid propulsion engine 200 can operate in a third mode of operation where the electric motor 212 is used to supplement the gas turbine engine 202 in driving the propulsor 204 for a period of time without powering down the gas turbine engine 202. For instance, the gas turbine engine 202 may be running and driving the propulsor 204 via the first and second drive shafts 218, 220 (e.g., in the first mode of operation). The overrunning clutch 216 is engaged, such that the gas turbine engine 202 is powering the propulsor 204. Then, the electric motor 212 can be energized. The electric motor 212 can be used to drive the second drive shaft 220 faster than the first drive shaft 218 for a period of time to produce additional thrust. For example, during taxi, the electric motor 212 can be used to add bursts of power to the propulsor 204. The overrunning clutch 216 enables the second drive shaft 220 to rotate faster than the first drive shaft 218. Then, when the electric motor 212 is turned off, the second drive shaft 220 slows down until its speed matches the speed of the first drive shaft 218, at which point the overrunning clutch 216 reengages and the gas turbine engine 202 continues to power the propulsor 204. In other examples, the electric motor 212 can be operated to rotate the second drive shaft 220 at substantially the same speed as the gas turbine engine 202, thereby adding torque to the system and reducing some of the load on the gas turbine engine 202. In other words, the gas turbine engine 202 and the electric motor 212 can both drive the propulsor 204.

0029In an example operation, assume the hybrid propulsion engine 200 is operating in the first mode of operation, where the gas turbine engine 202 is driving the propulsor 204 and the electric motor 212 is de-energized. The gas turbine engine 202 can be used during take-off and climb, for example, where more thrust is desired. Then, the controller 208 receives an input signal 224 requesting to switch modes from the first mode of operation to the second mode of operation. The input signal 224 can be generated by a pilot in a cockpit 225, for example. Additionally or alternatively, the input signal 224 can be generated by an auto-pilot program (e.g., based on a segment of flight). For example, once a certain altitude is reached, the auto-pilot program can request a mode change to switch to using the electric motor 212 instead of the gas turbine engine 202.

0030In response to the input signal 224, the controller 208 checks one or more mode-change parameters or conditions to verify whether the mode-change can occur. For example, the controller 208 receives status signals 226, 228 from the gas turbine engine 202 and the electric motor 212, respectively, regarding the operating states of the gas turbine engine 202 and the electric motor 212. The status signals 226, 228 can be generated from one or more sensors associated with the gas turbine engine 202 and/or the electric motor 212. The controller 208 can also receive information from various other flight systems. The mode-change parameter(s) can include the operational conditions of the electric motor 212 and the gas turbine engine 202, the temperature of the gas turbine engine 202, the altitude of the aircraft 100, the speed of the aircraft 100, the segment of flight of the aircraft 100 (e.g., whether the aircraft 100 is in take-off, climb, cruise, etc.), the ambient temperature, any/or any other conditions that may be of interest prior to changing the mode of operation.

0031The controller 208 may compare the mode-change parameter(s) to one or more threshold(s). If the mode-change parameter(s) is/are not satisfied (e.g., the parameter(s) do not meet the threshold(s)), the controller 208 generates an alert signal 230. In some examples, the controller 208 sends the alert signal 230 to the cockpit 225 to be displayed to a pilot or other aircraft personnel. In such an example, the mode-change does not occur, and the hybrid propulsion engine 200 continues to operate in the first mode of operation where the gas turbine engine 202 is driving the propulsor 204.

0032If the mode-change parameter(s) is/are satisfied (e.g., the parameter(s) do meet the threshold(s)), the controller 208 sends a command signal 232 (e.g., a start command) to start the electric motor 212. The controller 208 can control the flow of electrical power from the battery 214 to the electric motor 212. Once the controller 208 determines the electric motor 212 is operational and driving the propulsor 204 (e.g., based on the status signals 228 from the electric motor 212), the controller 208 sends a command signal 234 (e.g., a shut-down command) to the gas turbine engine 202 to power down. When switching from the second mode of operation to the first mode of operation, the reverse process occurs. Examples of these processes are disclosed in further detail in connection with the flowcharts in <figref idref="f0007">FIGS. 8A</figref> and <figref idref="f0008">8B</figref>.

0033In some examples, while the gas turbine engine 202 is running and driving the propulsor 204, the electric motor 212 is used as a generator to charge the battery 214. In other words, while the second drive shaft 220 is rotating, the electric motor 212 generates electrical power that can be used to charge the battery 214. The battery 214 can also be recharged when the aircraft 100 is on the ground (e.g., while waiting at an airport terminal). The controller 208 manages the flow of electrical power between the electric motor 212 and the battery 214. The electrical power stored in the battery 214 is used to power the electric motor 212 at a later time and/or used to power one or more other electrical system(s) of the aircraft 100. Additionally or alternatively, the electrical power generated by the electric motor 212 can be provided directly to one or more electrical system(s) of the aircraft 100 (without going through the battery 214). In other examples, instead of using the electric motor 212 as a generator, the controller 208 can disconnect the electric motor 212 from the battery 214, such that no power is generated by the electric motor 212, which reduces torque on the second drive shaft 220 that may otherwise be caused by the electric motor 212 when operating as a generator. While in the illustrated example the battery 214 is used to store electrical power, in other examples, the battery 214 can be implemented as a fuel cell, a capacitor, and/or any other device capable of storing electrical power. Thus, the electric motor 212 can be used to drive the propulsor 204 to produce thrust during flight (e.g., during cruise), can be used when there is a failure in the gas turbine engine 202, can be used supplement the gas turbine engine 202 (e.g., to provide extra power for short periods), and/or can be used to produce electrical power for the aircraft 100.

0034<figref idref="f0003">FIG. 3</figref> is a schematic showing two hybrid propulsions engines, including the first hybrid propulsion engine 200 from <figref idref="f0002">FIG. 2</figref> and a second hybrid propulsion engine 300. In the illustrated example, the second hybrid propulsion engine 300 is substantially the same as the first hybrid propulsion engine 200. In particular, the second hybrid propulsion engine 300 includes a second propulsor 302, a second gas turbine engine 304, a second electric motor 306, and a second overrunning clutch 308 operatively coupled between the second gas turbine engine 304 and the second electric motor 306 to enable the second electric motor 306 to drive the second propulsor 302 independent of the second gas turbine engine 304. The second hybrid propulsion engine 300 also includes a second controller 310 that controls the on/off operations of the second gas turbine engine 304 (e.g., by controlling a second valve 312) and/or the second electric motor 306. In some examples, the controllers 208, 310 are implemented by the same controller. In some examples, the second hybrid propulsion engine 300 includes a second transmission 314. The second hybrid propulsion engine 300 can operate in substantially the same modes of operation as the hybrid propulsion engine 200. Thus, to avoid redundancy, a description of the operations of the second hybrid propulsion engine 300 is not provided again in connection with <figref idref="f0003">FIG. 3</figref>. The first and second hybrid propulsion engines 200, 300 may correspond to the first and second propulsion generators 108, 110 (<figref idref="f0001">FIG. 1</figref>), respectively, of the aircraft 100.

0035In <figref idref="f0003">FIG. 3</figref>, the first and second hybrid propulsion engines 200, 300 share the battery 214 and the fuel tank 206. Thus, in some examples, two or more hybrid propulsion engines can utilize the same resources. As mentioned above, the aircraft 100 may include more than two hybrid propulsion engines, all of which can share the same resources. In other examples, the hybrid propulsion engine(s) can utilize their own dedicated resource(s) and/or may be grouped together in other arrangements (e.g., right wing engines share the same resources and left wing engines share the same resources). In still other examples, one of the hybrid propulsion engines 200, 300 can be used to power multiple propulsors on an aircraft. For example, an aircraft can include a plurality of propulsors spaced apart on a wing of the aircraft. The hybrid propulsion engine 200 can be coupled to the propulsors via a transmission, such that the hybrid propulsion engine 200 can be used to power all of the propulsors using the gas turbine engine 202 and/or the electric motor 212.

0036<figref idref="f0004">FIG. 4</figref> is a partial cutaway view of an example hybrid propulsion engine 400 that can be implemented as the hybrid propulsion engine 200 of <figref idref="f0002">FIGS. 2</figref> and <figref idref="f0003">3</figref> and used as one of the propulsion generators 108, 110 on the aircraft 100. In the illustrated example, the hybrid propulsion engine 400 is implemented as a turbofan engine. The hybrid propulsion engine 400 includes a gas turbine engine 402, a fan 404, and an electric motor 406, which correspond to the gas turbine engine 202, the propulsor 204, and the electric motor 212, respectively, of the hybrid propulsion engine 200 of <figref idref="f0002">FIG. 2</figref>. The gas turbine engine 402 and the electric motor 406 operate in different modes to drive the fan 404 to produce thrust.

0037In the illustrated example, the hybrid propulsion engine 400 includes a nacelle 408. The gas turbine engine 402 and the electric motor 406 are disposed within (e.g., surrounded by) the nacelle 408. The fan 404 rotates within a fan cowl 410 (e.g., a fan frame) of the nacelle 408. A fan duct 412 (e.g., a bypass, a passageway, a channel, a nozzle duct, etc.) is defined between an outer wall 414 (sometimes referred to as a core cowl) of the gas turbine engine 402 and an inner wall 416 of the nacelle 408. As the fan 404 rotates, the fan 404 produces airflow (as shown by the arrows), at least a portion of which flows through the fan duct 412 (e.g., aft of the fan cowl 410) and produces forward thrust.

0038As shown in <figref idref="f0004">FIG. 4</figref>, the gas turbine engine 402 includes a first drive shaft 418. The fan 404 is coupled (directly or indirectly) to and driven by a second drive shaft 420. The second drive shaft 420 is the output shaft (e.g., the rotor) of the electric motor 406. The first and second drive shafts 418, 420 are coupled via an overrunning clutch 422. The first drive shaft 418, the second drive shaft 420, and the overrunning clutch 422 may correspond to the first drive shaft 218, the second drive shaft 220, and the overrunning clutch 216, respectively, of the example hybrid propulsion engine 200 of <figref idref="f0002">FIG. 2</figref> and operate in substantially the same manner.

0039The gas turbine engine 402 operates by drawing air through a core air intake 424 (at a fore end of the gas turbine engine 402) and into a compressor 426. In particular, when the gas turbine engine 402 is running, a portion of the airflow from the fan duct 412 is diverted through the core air intake 424 and into the compressor 426 of the gas turbine engine 402. The compressor 426 can include multiple compressor sections. For example, the compressor 426 of <figref idref="f0004">FIG. 4</figref> is a dual-axial compressor that includes two compressors, a first compressor 428 and a second compressor 430. Each of the first and second compressors 428, 430 includes various compressor stages that progressively increase the pressure of the air as the air flows from the core air intake 424 to a combustion chamber 432. The first compressor 428 is a low-pressure compressor (LPC) that provides relatively low pressure air and the second compressor 430 is a high-pressure compressor (HPC) that provides relatively high pressure air. The first compressor 428 is coupled to the first drive shaft 418, and the second compressor 430 is coupled to a third drive shaft 434 (e.g., a second drive shaft of the gas turbine engine 402). The first drive shaft 418 (e.g., the LPC shaft) is coupled to and driven by a first turbine 436 (e.g., a low-pressure turbine) and the third drive shaft 434 (e.g., a HPC shaft) is coupled to and driven a second turbine 438 (e.g., a high-pressure turbine). In this example, the compressor 426 is a dual-axial compressor that includes the two compressors 428, 430. However, in other examples, the compressor 426 can include more or fewer compressor sections, each coupled to a turbine via a respective shaft.

0040After exiting the second compressor 430 (the HPC), the highly pressurized air is provided to the combustion chamber 432, where fuel (e.g., from the fuel tank 206 of <figref idref="f0002">FIG. 2</figref>) is injected and mixed with the highly pressurized air and ignited. The high energy airflow exiting the combustion chamber 432 turns the blades of the first and second turbines 436, 438, which are coupled to respective ones of the first and third drive shafts 418, 434. The first drive shaft 418 extends through and rotates independently of the third drive shaft 434. As such, rotation of the first and third drive shafts 418, 434 turns the blades of the first and second compressors 428, 430, respectively. The heated air is exhausted via a nozzle 440, aftward, where it mixes with the accelerated airflow provided by the fan 404 in the fan duct 412 to produce forward thrust that propels the aircraft 100 in a forward direction.

0041In this example, the rotational axis of the fan 404 is coaxial with the first drive shaft 418 and the second drive shaft 420. In other words, the fan 404, the first drive shaft 418, and the second drive shaft 420 are axially aligned. In other examples, the rotational axis of the fan 404 is parallel to and offset from the first and second drive shafts 418, 420.

0042In a first mode of operation, the gas turbine engine 402 is running and the electric motor 406 is off. The gas turbine engine 402 produces rotation in the first drive shaft 418, which rotates the second drive shaft 420 via the overrunning clutch 422 and, thus, rotates the fan 404. In a second mode of operation, the electric motor 406 is running and the gas turbine engine 402 is off. The electric motor 406 operates to rotate the second drive shaft 420, thereby rotating the fan 404. The overrunning clutch 422 enables the second drive shaft 420 to rotate independently of the first drive shaft 418. In some examples, a transmission is disposed between the second drive shaft 420 and the fan 404 to change the rotational speed between the second drive shaft 420 and the fan 404.

0043Turning briefly to <figref idref="f0006">FIGS. 6, 7A, and 7B, FIG. 6</figref> shows an enlarged view of the electric motor 406, the first drive shaft 418, the second drive shaft 420, and the overrunning clutch 422. In the illustrated example, the electric motor 406 includes an armature 600 coupled to the second drive shaft 420 and a stator 602 surrounding the armature 600. The armature 600 may be formed unitarily with the second drive shaft 420. The armature 600 may include coils and the stator 602 may include magnets (or electromagnets), or vice versa. When the electric motor 406 is energized (e.g., via the controller 208 of <figref idref="f0002">FIG. 2</figref>), the armature 600 rotates, thereby rotating the second drive shaft 420. When the electric motor 406 is de-energized the armature 600 no longer functions as the primary driver of the fan 404. However, the armature 600 and therefore, the second drive shaft 420 are still free to rotate within the stator 602. In some examples, the electric motor 406 operates as a generator to charge a battery (e.g., the battery 214 of <figref idref="f0002">FIG. 2</figref>) and/or provide electrical power directly to one or more electrical system(s) of the aircraft 100. The electric motor 406 can be implemented as any type of electric motor (e.g., an induction motor, a DC/AC permanent magnet motor, etc.) and is not limited to the example electric motor 406 shown in <figref idref="f0006">FIG. 6</figref>. Instead, it is understood that other types of electric motors can be similarly used, and the armature, stator, commutator, etc. may be arranged differently depending on the type of motor.

0044In the illustrated example, the overrunning clutch 422 is implemented as a sprag clutch 604. The sprag clutch 604 includes an outer race 606, an inner race 608, and a plurality of movable sprags 610 disposed between the outer race 606 and the inner race 608. In this example, the first drive shaft 418 (which is powered by the gas turbine engine 402 (<figref idref="f0004">FIG. 4</figref>)) is coupled to the outer race 606 and the second drive shaft 420 (which is coupled to the fan 404 (<figref idref="f0004">FIG. 4</figref>)) is coupled to the inner race 608. <figref idref="f0006">FIGS. 7A and 7B</figref> are cross-sectional views of the example overrunning clutch 422. The sprags 610 (one of which is referenced in each figure) are pivotable about their centers (extending into the page). In <figref idref="f0006">FIG. 7A</figref>, the outer race 606 is rotating in the clockwise direction. This occurs, for example, during the first mode of operation when the gas turbine engine 402 is on and the electric motor 406 is off. The interaction between the outer race 606 and the sprags 610 causes the sprags 610 to pivot into and engage the inner race 608. As a result, the outer race 606, the sprags 610, and the inner race 608 all rotate together, in the clockwise direction. Therefore, when the first drive shaft 418 rotates the outer race 606, the outer race 606 rotates the inner race 608 and, thus, rotates the second drive shaft 420 in the same direction. In <figref idref="f0006">FIG. 7B</figref>, the inner race 608 is rotating in the clockwise direction independent of the outer race 606. This occurs, for example, during the second mode of operation when the gas turbine engine 402 is off and the electric motor 406 is instead driving the second drive shaft 420. As shown in <figref idref="f0006">FIG. 7B</figref>, the inner race 608 slides along the inner surfaces of the sprags 610. However, this interaction does not cause the sprags 610 to frictionally engage the outer race 606. As such, the inner race 608 rotates in the clockwise direction without causing rotation of the outer race 606. If the outer race 606 is rotated up to match the rotational speed of the inner race 608, the sprags 610 are rotated into the inner race 608 and the outer race 606 eventually overdrives the inner race 608. As such, the inner race 608 rotates at least as fast as the outer race 606. Conversely, while the outer race 606 is rotating, the inner race 608 can be rotated independently at a faster rotational speed, which does not affect the outer race 606. The overrunning clutch 422 advantageously enables the gas turbine engine 402 and the electric motor 406 to independently drive the propulsor 204 without additional actuating components that are found in other types of clutches. Thus, no power is needed to operate the clutch.

0045While in this example the first drive shaft 418 is coupled to the outer race 606 and the second drive shaft 420 is coupled to the inner race 608, in other examples, the first and second drive shafts 418, 420 may be coupled to other of the outer and inner races 606, 608 and the direction of rotation may be switched, which results in the same effect. Also, while in this example the overrunning clutch 422 is implemented as the sprag clutch 604, in other examples, the overrunning clutch 422 cab be implemented by another type of overrunning clutch, such as a roller ramp clutch, a wrap spring clutch, or a wedge style clutch.

0046Now referring to <figref idref="f0005">FIG. 5, FIG. 5</figref> shows a partial cutaway view of another hybrid propulsion engine 500 that can be implemented as the hybrid propulsion engine 200 of <figref idref="f0002">FIGS. 2</figref> and <figref idref="f0003">3</figref> and used as one of the propulsion generators 108, 110 on the aircraft 100. In this example, the hybrid propulsion engine 500 is implemented as a turboprop engine. The hybrid propulsion engine 500 includes a gas turbine engine 502, a propeller 504, and an electric motor 506, which correspond, respectively, to the gas turbine engine 202, the propulsor 204, and the electric motor 212 of the hybrid propulsion engine 200 of <figref idref="f0002">FIG. 2</figref>. Similar to the hybrid propulsion engine 400 of <figref idref="f0004">FIG. 4</figref>, the gas turbine engine 502 includes a first drive shaft 508, the propeller 504 is coupled (directly or indirectly) to and driven by a second drive shaft 510, the electric motor 506 includes the second drive shaft 510, and the first and second drive shafts 508, 510 are coupled via an overrunning clutch 512. Similar to the examples disclosed above, the gas turbine engine 502 and the electric motor 506 operate in different modes to drive the propeller 504 to produce thrust. Thus, to avoid redundancy, a description of the mode operations is not provided again in connection with <figref idref="f0005">FIG. 5</figref>. Instead, the interested reader is referred back to description above in connection with <figref idref="f0002 f0003 f0004">FIGS. 2-4</figref> for a full written description of the operations.

0047Unlike the turbofan engine of <figref idref="f0004">FIG. 4</figref>, the turboprop engine of <figref idref="f0005">FIG. 5</figref> does not include a nacelle or cowl around the propeller 504. Instead, the propeller 504 is an open-air propulsor. Turboprop engines are typically used for lower altitudes and shorter flights compared to turbofan engines. The gas turbine engine 502 of <figref idref="f0005">FIG. 5</figref> is substantially similar to the gas turbine engine 402 of <figref idref="f0004">FIG. 4</figref> and includes a core air intake 514, a first compressor 516 (a LPC) coupled to a first turbine 518 (a LPT) via the first drive shaft 508, a second compressor 520 (an HPC) coupled to a second turbine 522 (an HPT) via a third drive shaft 524, a combustion chamber 526, and a nozzle 528. In other examples, the gas turbine engine 502 can be arranged differently and/or have more or fewer compressor/turbine sections. Further, the hybrid propulsion engine 500 of <figref idref="f0005">FIG. 5</figref> is arranged as a tractor configuration with the propeller 504 on the front of the hybrid propulsion engine 500. However, in other examples, the hybrid propulsion engine 500 can be arranged as a pusher configuration with the propeller 504 in the rear.

0048As shown in <figref idref="f0005">FIG. 5</figref>, the hybrid propulsion engine 500 includes a transmission 530 (e.g., a planetary gear system) that couples the second drive shaft 510 to the propeller 504. The transmission 530 is arranged such that the rotational axis of the propeller 504 is coaxial with the first drive shaft 508 and the second drive shaft 510. In other words, the propeller 504, the first drive shaft 508, and the second drive shaft 510 are axially aligned. In other examples, the rotational axis of the propeller 504 is parallel to and offset from the first and second drive shafts 508, 510. For instance, some turboprop engines utilize a transmission that offsets the propeller from the longitudinal axis of the associated turbine gas engine. In other examples, no transmission is included and the second drive shaft 510 is coupled directly to the propeller 504.

0049<figref idref="f0007">FIG. 8A</figref> is a flowchart of an example method 800 of changing an operating-mode of a hybrid propulsion engine from a first mode of operation to a second mode of operation. The method 800 is described in connection with the hybrid propulsion engine 200 of <figref idref="f0002">FIG. 2</figref>, which can be implemented as a turbofan type of hybrid propulsion engine, such as the hybrid propulsion engine 400 of <figref idref="f0004">FIG. 4</figref>, or a turboprop type of hybrid propulsion engine, such as the hybrid propulsion engine 500 of <figref idref="f0005">FIG. 5</figref>. The method 800 is performed at least in part by the controller 208 of <figref idref="f0002">FIG. 2</figref>, which controls the on/off operations and/or speed control of the gas turbine engine 202 and the electric motor 212.

0050At block 802, the hybrid propulsion engine 200 is operating in a first mode of operation where the gas turbine engine 202 is driving the propulsor 204. In the first mode of operation, the electric motor 212 is de-energized and/or otherwise not providing power to the propulsor 204. The gas turbine engine 202 drives the first drive shaft 218, which rotates the second drive shaft 220 via the overrunning clutch 216 and, thus, drives the propulsor 204 to produce forward thrust. In some examples, during the first mode of operation, the electric motor 212 operates as a generator to charge the battery 214 and/or provide electrical power directly to one or more system(s) of the aircraft 100.

0051At block 804, the controller 208 receives the input signal 224 requesting to switch from the first mode of operation to the second mode of operation. The input signal 224 can be generated by a pilot in the cockpit 225, for example. In other examples, the input signal 224 can be generated by an auto-pilot program based on a flight condition. For example, once a certain altitude is reached, the auto-pilot program may request the hybrid propulsion engine 200 to switch modes so the electric motor 212 can be used to more efficiently power the aircraft 100.

0052At block 806, the controller 208 determines whether one or more mode-change parameter(s) is/are satisfied. The mode-change parameter(s) can include one or more of the operational conditions of the electric motor 212 and the gas turbine engine 202, the temperature of the gas turbine engine 202, the altitude of the aircraft 100, the speed of the aircraft 100, the segment of flight of the aircraft 100 (e.g., whether the aircraft 100 is in cruise or climb), the ambient temperature, etc. The mode-change parameter(s) can be based on information received via the status signals 226, 228 from the gas turbine engine 202 and the electric motor 212.

0053If the mode-change parameter(s) is/are not satisfied (determined at block 806), the controller 208 generates the alert signal 230 at block 808, and the example method 800 ends. The alert signal 230 can be sent back to the cockpit 225, for example, and displayed to the pilot or another aircraft personnel. In this event, the hybrid propulsion engine 200 does not change modes of operation. For example, if the controller 208 determines the mode-change should not occur because the aircraft 100 is still climbing, the controller generates an alert (block 808) and continues to operate the hybrid propulsion engine 200 in the first mode of operation.

0054If the mode-change parameter(s) is/are satisfied (determined at block 806), the controller 208 sends the command signal 232 (e.g., a first command signal) to start and/or otherwise energize the electric motor 212 at block 810. For example, if a certain altitude is reached, the controller 208 may determine the mode-change parameter(s) is/are satisfied. The controller 208 can supply power to the electric motor 212 from the battery 214. The electric motor 212 begins driving the second drive shaft 220.

0055At block 812, the controller 208 verifies that the electric motor 212 has started and is driving the propulsor 204, which may be based on the status signals 228 from the electric motor 212. If the electric motor 212 has not started or is otherwise not operating correctly, the controller 208 generates the alert signal 230, which may be displayed to the pilot, and the example method 800 ends.

0056If the controller 208 determines the electric motor 212 has started and is powering the propulsor 204, the controller 208, at block 814, sends the command signal 234 (e.g., a second command signal) to the gas turbine engine 202 to shut down and/or otherwise reduce power. The command signal 234 may shut off ignition and/or stop fuel supply (e.g., via the valve 210 of <figref idref="f0002">FIG. 2</figref>) to the gas turbine engine 402. Thus, the controller 208 ensures the electric motor 212 is powered up prior to shutting down the gas turbine engine 202 to ensure no lapse in power occurs. This transition period can occur over a period of time, such as 30 seconds. Once the electric motor 212 is driving the propulsor 204 and the gas turbine engine 202 is shut down and/or otherwise not providing power to the propulsor 204, the hybrid propulsion engine 200 is operating in the second mode of operation and the mode change is complete (block 816). The example method 800 may then end or proceed to <figref idref="f0008">FIG. 8B</figref>, which is an example method of switching back to the first mode of operation.

0057<figref idref="f0008">FIG. 8B</figref> is a flowchart of an example method 818 of changing an operating-mode of a hybrid propulsion engine from a second mode of operation to a first mode of operation. The method 818 is described in connection with the hybrid propulsion engine 200 of <figref idref="f0002">FIG. 2</figref>, which can be implemented as a turbofan type of hybrid propulsion engine, such as the hybrid propulsion engine 400 of <figref idref="f0004">FIG. 4</figref>, or a turbo-prop type of hybrid propulsion engine, such as the hybrid propulsion engine 500 of <figref idref="f0005">FIG. 5</figref>, for example. The method 818 is performed at least in part by the controller 208 of <figref idref="f0002">FIG. 2</figref>, which controls the on/off operations and/or speed control of the related gas turbine engine and electric motor.

0058At block 820, the hybrid propulsion engine 200 is operating in the second mode of operation where the electric motor 212 is driving the propulsor 204. In the second mode of operation, the gas turbine engine 202 is off and/or otherwise not providing power to the propulsor 204 (e.g., operating at idle). The electric motor 212 drives the propulsor 204 via the second drive shaft 220. The overrunning clutch 216 enables the electric motor 212 to drive the second drive shaft 220 (and, thus, the propulsor 204) independent of the gas turbine engine 202.

0059At block 822, the controller 208 receives the input signal 224 requesting to switch from the second mode of operation to the first mode of operation. Similar to block 804 above, the input signal 224 can be generated by a pilot in the cockpit 225 and/or an auto-pilot program.

0060At block 824, the controller 208 determines whether one or more mode-change parameter(s) are satisfied. The mode-change parameter(s) can include one or more of the operational conditions of the electric motor 212 and the gas turbine engine 202, the temperature of the gas turbine engine 202, the altitude of the aircraft 100, the speed of the aircraft 100, the segment of flight of the aircraft 100 (e.g., whether the aircraft 100 is in cruise or climb), the ambient temperature, etc.

0061If the mode-change parameter(s) is/are not satisfied (determined at block 824), the controller 208 generates the alert signal 230 at block 826, and the example method 818 ends. The alert signal 230 can be sent back to the cockpit 225, for example, and displayed to the pilot or another aircraft personnel. In this event, the hybrid propulsion engine 200 does not change modes of operation.

0062If the mode-change parameter(s) is/are satisfied (determined at block 824), the controller 208 sends the command signal 234 (e.g., a third command signal) to start and/or otherwise power-up the gas turbine engine 202 at block 828. Once the first drive shaft 218 is rotating faster than the second drive shaft 220, the overrunning clutch 216 engages such that the first drive shaft 218 is powering the second drive shaft 220 and, thus, powering the propulsor 204.

0063At block 830, the controller 208 verifies that the gas turbine engine 212 has started and is driving the propulsor 204, which may be based on the status signals 226 from the gas turbine engine 202. If the gas turbine engine 202 has not started or is otherwise not operating correctly, the controller 208 generates the alert signal 230, which may be displayed to the pilot, and the example method 818 ends.

0064If the controller 208 determines the gas turbine engine 202 has started and is powering the propulsor 204, the controller 208, at block 832, sends the command signal 232 (e.g., a fourth command signal) to the electric motor 212 to shut down and/or otherwise reduce power. The controller 208 may cut-off electric power from the battery 214, for example. Once the gas turbine engine 202 is driving the propulsor 204 and the electric motor 212 is de-energized and/or otherwise not providing power to the propulsor 204, the hybrid propulsion engine 200 is operating in the first mode of operation and the mode change is complete (block 834). The example method 818 may then end or proceed to <figref idref="f0007">FIG. 8A</figref>, which is an example method of switching back to the second mode of operation.

0065The example methods 800, 818 can be repeated any number of times to switch between using the gas turbine engine 202 and the electric motor 212. The hybrid propulsion engine 200 can operate between the first mode of operation and the second mode of operation during different flight segments or conditions. For example, the gas turbine engine 202 can be used to drive the propulsor 204 in the first mode of operation during a first segment of flight, such as take-off and/or landing, and the electric motor 212 can be used to drive the propulsor 204 in the second mode of operation during a second segment of flight, such as cruise. As such, the gas turbine engine 202 is used when more power is typically needed, and then the electric motor 212 is used where less power is needed to improve efficiency. The gas turbine engine 202 and the electric motor 212 can be used in other segments of flight as desired.

0066From the foregoing, it will be appreciated that example hybrid propulsion engines have been disclosed that enable the use of one or both of a gas turbine engine and an electric motor to produce more efficient flight. In particular, using an electric motor during certain flight segments can significantly increase the overall efficiency of a flight. Further, by using an electric motor during certain flight segments, such as cruise, smaller, lighter gas turbine engines can be implemented, which reduces the weight to the aircraft and, thus, increases the overall efficiency of the aircraft.

0067Although certain example methods, apparatus, systems, and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus, systems, and articles of manufacture falling within the scope of the claims.