Engine shaft integrated motor

A method of integrating an electric motor or generator as part of an aircraft engine shaft. The motor is used to rotate the rotor so as to cool the rotor in a temperature gradient. The generator is used to provide power to the aircraft. In one or more examples, a power generation device includes a gas turbine engine including a rotor shaft and a first casing around the rotor shaft; a transmission connecting the rotor shaft to a gearbox, the transmission comprising a drive shaft and a second casing around the drive shaft; and a brushless DC motor integrated with the engine and including one or more permanent magnets and one or more coils.

BACKGROUND

The present disclosure relates to a system for connecting a motor and/or generator to an aircraft gas turbine engine.

2. Description of the Related Art

FIG. 1illustrates an aircraft engine comprising a fan100, a low pressure (LP) compressor102, a fan case104, an engine casing106, a High Pressure (HP) compressor108, a HP turbine110, a LP turbine112, and a LP shaft114connecting the LP compressor102and the LP turbine112. After engine shutdown on the ground, residual hot air116in the engine core rises118and is trapped by the engine casing106. As the hot air rises118, the upper portion120of the HP compressor's (engine's rotor)108rotor shaft122becomes hotter than the lower portion124of the rotor shaft122and causes uneven cooling and thermal deformation of the engine rotor shaft122(i.e., rotor bowing, where the upper portion120of the rotor shaft122becomes longer than the lower portion124). Upon engine restart (e.g., prior to fuel ignition in the combustor126), even tiny fractions of rotor shaft bowing can cause the HP compressor (engine's rotor)108to rub against the engine's casing106. The rub causes vibrations (manifested as disconcerting noise in the aircraft cabin) or even damage to the aircraft (e.g., engine damage, damage to the engine case lining, damage to the air pre-cooler used by the environmental control system, or damage to other accessories).

One method to mitigate these problems is to build the engine with wider cold build clearances (“opened up” clearances), so that the compressor rotor shaft122can bow without causing blades to rub on the engine casing106. However, more advanced engine designs prefer less “gap” between the engine casing and the compressor rotors (tighter “cold build clearances”) to reduce air leakage and improve thrust specific fuel consumption (TSFC). Thus, the overriding need to reduce fuel consumption renders wider cold build clearances less desirable. Indeed, as ever tighter cold build clearances are implemented, the problems caused by engine rub will become more severe.

Conceivably, an engine architecture could add rotor stiffening or bearing arrangements to reduce the amount of rotor shaft bow that is physically possible. However, these architecture changes would add weight and manufacturing cost to the engine.

Other methods of mitigating rotor shaft bow comprise rotating the shaft (1) so that the shaft cools uniformly, returns to thermal equilibrium, and straightens, and/or (2) so that centrifugal forces straighten the bow. The shaft rotation is achieved (1) by motoring the engine at relatively low revolutions per minute (RPM) after starting the engine (but before running the engine at high RPM) and/or (2) using an Engine Turning Motor (ETM) to turn the rotor shaft when the engine is off.

However, conventional methods for providing power to the ETM or the engine so as to straighten the bow can be problematic. Some smaller aircraft, such as the Boeing 737 airplane, fly into remote airports where facility power is not available to power the ETM or engine. Furthermore, auxiliary power unit (APU) power on the aircraft is not always available to power the engine or ETM because some airports limit APU use at gates due to emissions and noise concerns and aircraft are not powered when they are towed between gates. In addition, airplanes may operate with a nonfunctional APU or the powering of the ETM or engine may cause undesirable APU wear (extended motoring prolongs the APU's exposure to main engine start (MES) mode, reducing APU life). Finally, the use of lithium-ion and nickel-cadmium batteries for powering the ETM is problematic due to high failure rates and flammability concerns associated with the engine environment (extreme heat, extreme cold, and high vibration).

Moreover, rotating the shaft shortly before departure causes departure delays, especially if reduced engine clearances require turning the rotor at low speeds. These delays not only inconvenience the passengers but also increase costs associated with increased waiting times and parking fees.

What is needed then, is a more efficient method for mitigating rotor shaft bowing that simplifies ground logistics. The present disclosure satisfies this need.

SUMMARY

The present disclosure describes a motor (e.g., a direct current motor), including a gas turbine engine including a rotor shaft and a first casing around the rotor shaft; a transmission connecting the rotor shaft to a gearbox, the transmission comprising a drive shaft and a second casing around the drive shaft; one or more permanent magnets attached to the rotor shaft and/or the drive shaft; one or more electromagnets attached to the first casing and/or the second casing; and a power supply connected to the electromagnets. The rotor shaft turns when (1) the electromagnets generate first magnetic fields in response to current supplied from the power supply and (2) the first magnetic fields interact with second magnetic fields generated by the permanent magnets.

In one embodiment, a nacelle houses the gas turbine engine. When the nacelle traps hot air, a temperature gradient is created perpendicular to the longitudinal axis of the rotor shaft. However, when the motor is operated, interaction of the first and second magnetic fields turns the rotor shaft so as to reduce or prevent thermal bowing of the rotor shaft in the temperature gradient when the gas turbine engine is cooling down after shutdown of the gas turbine engine.

The present disclosure further describes a power generation device, including a gas turbine engine including a rotor shaft and a first casing around the rotor shaft; a transmission connecting the rotor shaft to a gearbox, the transmission comprising a drive shaft and a second casing around the drive shaft; one or more permanent magnets attached to the rotor shaft and/or the drive shaft; one or more coils attached to the first casing and/or the second casing; and an energy storage device (e.g., a battery) connected to the coils. The energy storage device stores electrical energy generated by the coils when (1) the engine is running so as to rotate the permanent magnets on the shaft and (2) magnetic fields generated by the permanent magnets interact with the coils. The electrical energy is used to reduce transient and peak electrical power demands on the engine.

The present disclosure further describes a power generation device, comprising a gas turbine engine including a rotor shaft and a first casing around the rotor shaft; a transmission connecting the rotor shaft to a gearbox, the transmission comprising a drive shaft and a second casing around the drive shaft; one or more permanent magnets attached to the rotor shaft and/or the drive shaft; one or more coils attached to the first casing and/or the second casing; and an aircraft electrical system connected to the coils. The aircraft electrical system receives electrical power generated by the coils when (1) the engine is running so as to rotate the permanent magnets on the shaft and (2) magnetic fields generated by the permanent magnets interact with the coils. The electrical power is used to either power an airplane system or an engine system.

In one embodiment, an aircraft comprises a computer connected to the engine. The current generated in the coils powers the electrical system during times of peak electrical loading of the electrical system. In this case, fuel consumption in the gas turbine engine can be reduced (as compared to when the gas turbine engine is used to power the electrical system without the current from the power generation device).

DESCRIPTION

In the following description, reference is made to the accompanying drawings which form a part hereof, and which is shown, by way of illustration, several embodiments. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present disclosure.

Technical Description

Motors and generators, such as brushless direct current (DC) motors and generators, are fabricated by attaching permanent magnets on a rotor and using a series of electromagnets or coils on a fixed structure (stator) surrounding the rotor.

The present disclosure describes integrating the motor and/or generator in an airplane engine, wherein the airplane engine's shaft comprises the rotor and an engine casing or fixed mounting in the engine comprises the stator.

FIG. 2AandFIG. 2Billustrate a gas turbine engine200including permanent magnets202attached to the rotor shaft204; and a series of coils206(or electromagnets comprising coils206) attached on a casing208surrounding or around the shaft204.FIG. 2Afurther illustrates a gearbox210attached to the casing104.

FIG. 2Cillustrates a gas turbine engine200including a rotor shaft204and a first casing208around the rotor shaft204; a transmission212connecting the rotor shaft204to a gearbox210, the transmission212comprising a bevel gears214and a drive shaft216; a second casing218around the drive shaft216; one or more permanent magnets202attached to the drive shaft216; and one or more coils206(or electromagnets comprising coils206) attached to the second casing218.

In a motor embodiment, the permanent magnets202are repelled and/or attracted by the series of electromagnets, thereby causing the shaft204,216to rotate220. In one embodiment, the gearbox210does not include an engine turning motor because the motor300comprising permanent magnets202and electromagnets302is used to turn the rotor shaft204.

In a generator embodiment, the rotor shaft204and the permanent magnets202rotate220(e.g., when the engine is operated in combustion mode with an air128intake) and the permanent magnets202induce current in the coils206when magnetic fields generated by the magnets202move through or interact with the coils206.

First Example: Integrated Motor Operation

FIG. 3Aillustrates an integrated motor300comprising a plurality of electromagnets302comprising coils206(numbered 1-6) attached to the inner surface304of the casing208. The electromagnets302and the permanent magnets202are positioned so that the shaft204rotates306about axis AA′ when first magnetic fields M1generated by the electromagnets302interact with (or have a force interaction with) second magnetic fields M2generated by the permanent magnets202.

In one or more embodiments, the permanent magnets202and the coils206are disposed symmetrically about a center point P on the longitudinal axis AA′.

Electrical wires308connect a driving circuit310(comprising or connected to a power supply310a) to the electromagnets302. The power supply310aand circuit310supply current to the electromagnets302so as to generate the first magnetic fields M1. The current comprises a pulse sequence or waveform so that the first magnetic fields M1are switched on and off to repel and/or attract A the permanent magnets202with synchronized timing that causes the rotor shaft204to turn306.

FIG. 3Billustrates a timing sequence for energizing the coils206, wherein coil1is first energized using a voltage so that coil1has a magnetic field M1with South (S) polarity that attracts the magnet202having North (N) polarity. At later times, coils2and3are energized so as to attract the magnet having N polarity as the magnet nears coils2and3, respectively. In this example, diametrically opposite coils are electrically connected (coil1is connected to coil4, coil2is connected to coil5, and coil3is connected to coil6) so that the magnetic fields in the opposite coils have opposite polarity (i.e., coil1has N polarity when coil4has S polarity).

FIG. 3Cillustrates another timing sequence for energizing the coils206, wherein coils1and5are connected and first simultaneously energized using voltages so that coil1has a magnetic field with S polarity that attracts the magnet202having N polarity and coil5has a magnetic field with polarity N to repel the magnet202having N polarity. Coils2and6are also simultaneously energized but out of phase with coils1and5, so as to attract and repel the magnet having N polarity, respectively. Coils3and1are then subsequently energized at the same time so as to attract and repel the magnet having N polarity.

Second Example: Integrated Generator Operation

FIG. 4Aillustrates an integrated generator400comprising the coils206and the permanent magnets202positioned so that a current is generated in the coils206when the shaft204is rotating402(as a result of the engine200running in combustion mode and burning fuel when air128is inputted into the engine). The moving magnetic fields M2generated by the permanent magnets202interact with, or pass through, the coils206and generate current according to Faraday's law.

Electrical wires308connect the coils206to a circuit404that comprises, or is connected to, an energy storage device406(e.g., battery) and/or an electrical system408on the aircraft, so that the current generated in the coils206charges the energy storage device406and/or supplies power to the electrical system408.

The aircraft's electrical system408(e.g., powering air conditioning, cabin pressurization, and plumbing) adds various electrical loads during operation of the aircraft. Typically, some of the engine's rotational energy is converted into electrical energy in order to handle these additional loads. In this case, the engine then has to burn more fuel to maintain its original rotation speed. Consequently, the engine must be operated in such a way (i.e., with high enough speed) that it can withstand a sudden electrical load and maintain stability.

In one embodiment, the airplane extracts electrical power from the coils206in the integrated generator400to help power the electrical systems on the aircraft at various times, e.g., during peak electrical demands. This alleviates the burden on the engine, enabling less fuel burn and lower engine speeds for most of the flight while still accommodating sudden electrical loads applied to the electrical system.

FIG. 4Billustrates an airplane410comprising a computer412,602comprising an engine control system connected to the engine200housed in a nacelle414; and the electrical system408and energy storage device406connected to the coils206via wiring416. The current from the coils206is used to power the electrical system, e.g., during times of peak electrical loading of the electrical system. The computer412or418reduces fuel consumption in the gas turbine engine200as compared to when the gas turbine engine is used to power the electrical system without the integrated generator400. In another example, the integrated generator400is used as a load source or sink by the engine's control system so as to aid engine operability and engine acceleration rates, e.g., during abnormal flight conditions.

Peak electrical demands also impact engine sizing conditions. Conventionally, larger engines are used to mitigate for worst case energy scenarios. Use of the integrated generator system400to power the electrical system408enables implementation of smaller, lighter engines that burn less fuel.

Third Example: Rotor Shaft Bow Mitigation

Air128inputted into the nacelle414or fan casing104is trapped in the nacelle414and is heated by the engine200so as to form trapped hot air116. The trapped hot air116creates a temperature gradient T perpendicular to a longitudinal axis AA′ of the rotor shaft204. In one embodiment, current I is provided to the electromagnets302so as to drive the shaft204when the gas turbine engine200is cooling down (e.g., after engine shut down) in the temperature gradient T, thereby reducing or preventing thermal bowing of the rotor shaft204in the temperature gradient T.

In one or more embodiments, the integrated motor300rotates306the rotor shaft204at one or more speeds, using one or more torques, and/or for one or more durations, so as to reduce or prevent the thermal bowing of the rotor shaft204in the temperature differential. Examples of rotation speeds include, but are not limited to, low speeds such as between 0.5-2.0 rpm (revolutions per minute).

Rotation306of the rotor shaft204includes, but is not limited to, pulsed rotation, continuous rotation, a combination of both pulsed rotation and continuous rotation, clocked rotation, and/or sporadic rotation.

In one embodiment, the integrated motor300turns the rotor shaft204slowly so that the rotor shaft204is slowly cooled and returned to thermal equilibrium. In another embodiment, the power to the motor300from the circuit310is pulsed or supplied periodically (i.e. once every 10 minutes, 30 minutes, hour, etc.) over a period of time (e.g., 8 hours) so that the rotor shaft204is rotated 220 periodically to promote an even temperature profile in the rotor shaft204.

In another periodic pulsing scheme, power supplied to the motor300from the circuit310is applied every plurality of minutes (e.g. every 5-15 minutes) so that the rotor moves a partial turn or in increments. In one embodiment, partial turns are ‘clocked,’ e.g., for a one-half turn. In another example, a current pulse from the circuit310provides random rotor shaft204movement. In one embodiment, pulse modulation is achieved by programming the motor300to transfer increments of torque. In one embodiment, the motor300rotates220the shaft204by turning the shaft204in one or more increments comprising a partial revolution of the shaft.

In one example, the rotation speed and duration are such that the probability of a compressor rub is less than e-8 per flight-hour.

Example System Features

One or more embodiments of the integrated motor/generator300,400are installed in an aircraft using components such that:the aircraft is capable of being dispatched for at least 10 days after a failure of the integrated motor/generator;failure of the integrated motor/generator does not require line maintenance to dispatch the aircraft;failure of the integrated motor/generator does not interfere with engine operation, and in particular, does not interfere with engine start;failure rate of the integrated motor/generator system is e-5 per flight hour or better;the integrated motor/generator is sufficiently reliable that a backup scheme is not required (e.g., the integrated motor/generator has a reliability of at least e-6 per flight hour or at least e-7 per flight hour);the integrated motor/generator has a lock out feature, in case unforeseen issues arise and the system must be easily disabled;energy demands for rotating the rotor and reducing the thermal bowing are reduced as compared to systems using an electric motor to rotate the rotor; and/orthe installation and certification is easier as compared to systems using an electric motor to rotate the rotor (e.g., the integrated motor/generator does not include a new ignition source or fuel source adding to engine fire protection designs).

Process Steps

FIG. 5illustrates a method of fabricating a motor or generator, according to one or more embodiments. The method comprises one or more of the following steps.

Block500represents attaching one or more magnets to an outer surface204aof a shaft204,216, e.g., as illustrated inFIG. 2B,FIG. 2C,FIG. 3A, andFIG. 4.

Examples of methods for attaching the magnets202include, but not limited to, printing the magnets on the shaft204,216(using, for example, ink jet printing, functional ink, or magnetic ink), painting the magnets202on the shaft204,216, mechanically attaching the magnets202to the shaft204,216(using, for example, adhesive or fasteners), or welding the magnets202onto the shaft (reference used as bevel gear),216(using, for example, dry welding). Examples of magnets202include, but are not limited to, permanent magnets such as rare-earth magnets (e.g., Neodymium magnets).

In one or more embodiments, the magnets202are disposed concentrically about a point P on the longitudinal axis In one example, the magnets202are disposed in pairs on the shaft204,216, wherein the magnets202in each pair are placed on opposite sides of the shaft204,216or diametrically opposite one another. In one embodiment, the magnets202are placed symmetrically about the shaft204,216. In yet another embodiment, the magnets202are disposed in a ring around a center point P of the shaft204,216. In one or more embodiments, the magnets202comprise materials selected after a materials analysis determining the materials' ability to withstand the high temperature environment in the engine200.

Block502represents attaching coils206, or electromagnets302each comprising at least one coil206, to an inner surface304of a casing208or sheath.

In one or more embodiments, the coils206comprise metal wires coated with an insulator. Examples of metal used for the wires include, but are not limited to, aluminum or copper. Examples of the insulator include, but are not limited to, high temperature polymers or ceramics. In one or more embodiments, the coil206comprises twisted shielded pairs of wires.

In one or more embodiments, the coils206are disposed in pairs on the casing208,218, wherein the coils206in each pair are placed on opposite sides of the casing208,218or diametrically opposite one another. In another embodiment, the coils206are placed symmetrically about the shaft204,216. In yet another embodiment, the coils206are disposed in a ring around a center point P of the shaft204,216or are wrapped around the rotor shaft204,216. In one or more embodiments, the coils206are fabricated from materials selected after a materials and/or metallurgy analysis determining the materials' ability to withstand the high temperature environment in the engine200.

The coils206are attached using a variety of methods including, but not limited to, using adhesive.

In one or more embodiments, the magnets202are attached to the shaft204,216in a relatively cold area of the shaft204,216, so as to reduce risk of damage to the coils and the magnets.

Block504represents optionally positioning sensors, e.g., on the casing208,218so as to measure a location of the magnets202and/or coils206as they rotate306. The location information is used to optimize timing of the current/voltage waveforms applied to the coils206by the circuit310so as to optimize rotation of the shaft.

Block506represents positioning the casing208,218so that the inner surface304faces the outer surface222of the shaft204,216. In one or more embodiments, the casing208,218is disposed concentrically about the shaft204,216.

Block508represents assembling the remainder of the gas turbine engine200, including positioning the nacelle414.

Block510represents connecting a circuit310,404. The electromagnets generate first magnetic fields M1when current is supplied to the electromagnets302from the circuit310(when the apparatus is operating as a motor300) or the circuit404receives current I induced in the coils206when the apparatus is operating as a generator400.

Block512, represents the end result, an apparatus comprising a motor300and/or generator/power generation device400.

The motor300comprises a gas turbine engine200including a rotor shaft204,216and a first casing208around the rotor shaft204,216; a transmission212connecting the rotor shaft204to a gearbox210, the transmission212comprising a drive shaft216and a second casing218around the drive shaft216; one or more permanent magnets202attached to the rotor shaft204and/or the drive shaft216; one or more electromagnets302attached to the first casing208and/or the second casing218; and a power supply310aconnected to the electromagnets302. The rotor shaft204turns220when the electromagnets302generate first magnetic fields M1in response to current I supplied from the power supply310aand the magnets202and electromagnets302are positioned such that the first magnetic fields M1interact with second magnetic fields M2generated by the permanent magnets202.

In one or more embodiments, the apparatus comprises a brushless DC motor300integrated with, or in situ on, the engine200, wherein the brushless DC motor300comprises the permanent magnets202and the electromagnets302.

In one embodiment, the rotating306comprises turning the shaft204by one or more partial turns (each partial turn less than one revolution) about axis AA′. In another embodiment, the rotating220comprises turning the shaft by more than one revolution about axis AA′.

The power generation device400includes a gas turbine engine200including a rotor shaft204and a first casing208around the rotor shaft204; a transmission212connecting the rotor shaft204to a gearbox210, the transmission212comprising a drive shaft216and a second casing218around the drive shaft204; one or more permanent magnets202attached to the rotor shaft204and/or the drive shaft216; and one or more coils206attached to the first casing208and/or the second casing218.

In one embodiment, an energy storage device406(e.g., a battery) is connected to the coils206. The energy storage device406stores electrical energy E generated by the coils206when the engine200is running so as to rotate220the permanent magnets202on the shaft204,216and magnetic fields M2generated by the permanent magnets202interact with the coils206.

In another embodiment, an aircraft electrical system408is connected to the coils206. The aircraft electrical system408receives electrical power P generated by the coils206when the engine200is running so as to rotate220the permanent magnets202on the shaft204,216, and the coils206and the permanent magnets202are positioned such that current I is generated in the coils206when the shaft216,204is rotating220and magnetic fields M2generated by the permanent magnets202interact with the coils206.

In one or more embodiments, the apparatus comprises a brushless DC generator400integrated with, or in situ on, the engine200, wherein the brushless DC generator400comprises the permanent magnets202and the coils206.

In one or more embodiments, the apparatus has dual use and the magnets202, the coils206, and the circuit310,404are configured so that the apparatus can be operated either as the generator400or the motor300. In one embodiment, a circuit is provided that includes circuits310and404, wherein the circuit comprise a switch switching between generator and motor operation.

Examples of the rotor shaft204include a low-pressure or a high-pressure shaft in a 2-spool engine200, or a low-pressure or intermediate-pressure shaft in a 3 spool engine.

Block514represents connecting the generator or motor to an aircraft system.

In one embodiment, the generator400is connected to an electrical system408and/or energy storage device406, so that the current I generated by the generator charges the energy storage device406or provides current I to the electrical system408. The electrical power P is used to either power the airplane system408or an engine200system, e.g., to reduce transient and peak electrical power demands on the engine200. Typically, the engine is responsible for generating electrical power for its own engine systems using two different and conventional electrical generators on the engine. However, in one embodiment, the power generation device400could replace either of the conventional electrical generators on the engine200.

In another embodiment, the motor300is connected to a controller wherein the controller controls the rotation of the rotor108using the motor. The nacelle414comprises trapped air116creating a temperature gradient perpendicular to a longitudinal axis AA′ of the rotor shaft204. Interaction of the first magnetic field M1and second magnetic field M2turns306the rotor shaft204so as to cool the rotor shaft204and/or reduce or prevent thermal bowing of the rotor shaft204in the temperature gradient T when the gas turbine engine200is cooling down after shutdown of the gas turbine engine200. In one example, the motor300is activated to rotate306,220the rotor shaft204prior to engine start (i.e., prior to motoring the engine200, and wherein motoring refers to rotating the shaft after engine start but prior to fuel on).

Processing Environment

FIG. 6illustrates an exemplary system600that could be used to implement processing elements needed to control the integrated motor or generator300,400described herein. The computer system is typically located on the aircraft e.g., but not limited to, in a box mounted on the engine fan case or inside the aircraft.

The computer602comprises a processor (general purpose processor604A and special purpose processor604B) and a memory, such as random access memory (RAM)606. Generally, the computer602operates under control of an operating system608stored in the memory606, and interfaces with the user/other computers to accept inputs and commands (e.g., analog or digital signals) and to present results through an input/output (I/O) module610. The computer program application612accesses and manipulates data stored in the memory606of the computer602. The operating system608and the computer program612are comprised of instructions which, when read and executed by the computer602, cause the computer602to perform the operations herein described. In one embodiment, instructions implementing the operating system608and the computer program610are tangibly embodied in the memory606, thereby making a computer program product or article of manufacture. As such, the terms “article of manufacture,” “program storage device” and “computer program product” as used herein are intended to encompass a computer program accessible from any computer readable device or media.

In one embodiment, computer602comprises one or more field programmable gate arrays (FPGAs).

The computer system600is connected a circuit energizing the electromagnets or receiving current generated in the coils.

In one embodiment, an Electronic Engine Control (EEC) sending a digital request to the computer602through I/O610to reduce, increase, select timing of, and/or modify electrical current and/or voltages supplied to the integrated motor300in order to rotate the rotor204, thus controlling HP compressor108speeds.

In another embodiment, the EEC unit sends a digital request to the controller602through I/O610to control current and/or voltage outputted from the integrated generator400, so as to control flow the current or application of the voltage to the electrical system408or energy storage device406. In yet another embodiment, the computer provides status to the EEC so that the controller and/or the EEC monitor system monitor performance and/or control the rotation of the rotor or supply of power to the electrical system.

In one embodiment, the computer602is connected to a flight management system via I/O610. The flight management system comprises a computer418controlling fuel consumption of the engine200during flight, in response to power P provided to the electrical system408or the engine200by the integrated generator400.

In one embodiment, the I/O610receives signal from an engine shut off switch after engine200shut down, thereby activating the integrated motor300so as to transfer energy/torque to the rotor shaft204. In one example, the integrated motor300rotates the rotor soon/immediately after engine shut down so as to minimize aircraft departure delays caused by mitigating rotor shaft bow. In another embodiment, the computer602activates the means transferring energy from the flywheel to the rotor, so as to rotate the rotor prior to engine start (i.e., prior to motoring the engine).

In another embodiment, the duration of rotation306is optimized by having the computer602estimate the amount of bow (based on time since last engine shutdown) and calculate the required rotation duration to be implemented. Various instrumentation to monitor the bowing can include accelerometers already used for vibration monitoring or microwave-based gap measuring sensors.

FIG. 6further illustrates a power source616for providing power to the system600.

Those skilled in the art will recognize many modifications may be made to this configuration without departing from the scope of the present disclosure. For example, those skilled in the art will recognize that any combination of the above components, or any number of different components, peripherals, and other devices, may be used.

CONCLUSION

This concludes the description of the preferred embodiments of the present disclosure. The foregoing description of the preferred embodiment has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of rights be limited not by this detailed description, but rather by the claims appended hereto.