Optimizing usage of supplemental engine power

In an embodiment, an aircraft includes a drive system, a main engine coupled to the drive system to provide first power, and a supplemental engine coupled to the drive system to provide second power additive to the first power. The aircraft also includes a control system to control the main engine and the supplemental engine to optimize usage of the supplemental engine. The control system is operable to maintain the supplemental engine in a reduced power state at least until a determination is made that supplemental power is needed to satisfy a total power demand of the drive system. The control system is also operable to determine that supplemental power is needed to satisfy the total power demand of the drive system. The control system is further operable to increase a power level of the supplemental engine in response to the determination that supplemental power is needed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application incorporates by reference the entire disclosure of U.S. patent application Ser. No. 17/342,963, filed on Jun. 9, 2021.

TECHNICAL FIELD

This disclosure relates in general to the field of aircraft, and more particularly, but not by way of limitation, to optimizing the distribution of power between main and supplemental engines.

BACKGROUND

Conventionally, certain rotorcraft have employed some level of rotor speed control in a fly-by-wire flight control system. For example, rotor speed can be controlled by an engine control unit. However, controlling rotor speed with the engine control unit of a supplemental engine may have shortcomings.

SUMMARY

In one general aspect, in an embodiment, an aircraft includes a drive system, a main engine coupled to the drive system to provide first power, and a supplemental engine coupled to the drive system to provide second power additive to the first power. The aircraft also includes a control system to control the main engine and the supplemental engine to optimize usage of the supplemental engine. The control system is operable to maintain the supplemental engine in a reduced power state at least until a determination is made that supplemental power is needed to satisfy a total power demand of the drive system. The control system is also operable to determine that supplemental power is needed to satisfy the total power demand of the drive system. The control system is further operable to increase a power level of the supplemental engine in response to the determination that supplemental power is needed. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

In another general aspect, in an embodiment a computer system includes a processor and memory. The processor and the memory in combination are operable to implement a method. The method includes operating an aircraft that includes a multi-engine drive system such that a main engine applies a first power to the multi-engine drive system and such that a supplemental engine applies a second power to the multi-engine drive system. The method also includes maintaining the supplemental engine in a reduced power state at least until a determination is made that supplemental power is needed to satisfy a total power demand of the multi-engine drive system. The method also includes determining that supplemental power is needed to satisfy the total power demand of the multi-engine drive system. The method also includes increasing a power level of the supplemental engine in response to the determining. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

In an embodiment, another general aspect includes a method. The method includes operating an aircraft that includes a multi-engine drive system such that a main engine applies a first power to the multi-engine drive system and such that a supplemental engine applies a second power to the multi-engine drive system. The method also includes maintaining the supplemental engine in a reduced power state at least until a determination is made that supplemental power is needed to satisfy a total power demand of the multi-engine drive system. The method also includes determining that supplemental power is needed to satisfy the total power demand of the multi-engine drive system. The method also includes increasing a power level of the supplemental engine in response to the determining. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various illustrative embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. For example, a figure may illustrate an illustrative embodiment with multiple features or combinations of features that are not required in one or more other embodiments and thus a figure may disclose one or more embodiments that have fewer features or a different combination of features than the illustrated embodiment. Embodiments may include some but not all the features illustrated in a figure and some embodiments may combine features illustrated in one figure with features illustrated in another figure. Therefore, combinations of features disclosed in the following detailed description may not be necessary to practice the teachings in the broadest sense and are instead merely to describe particularly representative examples. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not itself dictate a relationship between the various embodiments and/or configurations discussed.

In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present application, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “inboard,” “outboard,” “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction. As used herein, the terms “connect,” “connection,” “connected,” “in connection with,” and “connecting” may be used to mean in direct connection with or in connection with via one or more elements. Similarly, the terms “couple,” “coupling,” and “coupled” may be used to mean directly coupled or coupled via one or more elements. Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include such elements or features.

Referring toFIG.1, a rotorcraft in the form of a helicopter is schematically illustrated and generally designated10. The primary propulsion assembly of the helicopter10is a main rotor assembly12. The main rotor assembly12includes a plurality of rotor blades14extending radially outward from a main rotor hub16. The main rotor assembly12is coupled to a fuselage18and is rotatable relative thereto. The pitch of the rotor blades14can be collectively and/or cyclically manipulated to selectively control direction, thrust, and lift of the helicopter10. A tailboom20is coupled to the fuselage18and extends from the fuselage18in the aft direction. An anti-torque system22includes a tail rotor assembly24coupled to an aft end of the tailboom20. The anti-torque system22controls yaw of the helicopter10by counteracting torque exerted on the fuselage18by the main rotor assembly12. In the embodiment inFIG.1, the helicopter includes a vertical tail fin26that provides stabilization to the helicopter10during high-speed forward flight. In addition, the helicopter10includes wing members28that extend laterally from the fuselage18and wing members30that extend laterally from the tailboom20. The wing members28,30provide lift to the helicopter10responsive to the forward airspeed of the helicopter10, thereby reducing lift requirements imposed on the main rotor assembly12and increasing top speed of the helicopter10.

The main rotor assembly12and the tail rotor assembly24receive torque and rotational energy from a main engine32. The main engine32is coupled to a main rotor gearbox34by suitable clutching and shafting. The main rotor gearbox34is coupled to the main rotor assembly12by a mast36and is coupled to the tail rotor assembly24by a tail rotor drive shaft38. In the embodiment illustrated inFIG.1, a supplemental engine40(i.e., supplemental power unit) is coupled to the tail rotor drive shaft38by a supplemental engine gearbox42that provides suitable clutching therebetween. In other embodiments, the supplemental engine40is coupled directly to the main rotor gearbox34. Together, the main engine32, the main rotor gearbox34, the tail rotor drive shaft38, the supplemental engine40, and the supplemental engine gearbox42, as well as the various other shafts and gearboxes coupled therein, may be considered as a torque-summing powertrain of the helicopter10. In various embodiments, the supplemental engine40is operable as a supplemental power unit (“SPU”) to provide supplemental power that is additive to the power provided by the main engine32.

The helicopter10is merely illustrative of a variety of aircraft that can implement the principles disclosed herein. Indeed, the torque-summing powertrain of the present disclosure may be implemented on any rotorcraft. Other aircraft implementations can include hybrid aircraft, tiltwing aircraft, tiltrotor aircraft, quad tiltrotor aircraft, fixed-wing aircraft, unmanned aircraft, gyrocopters, propeller-driven airplanes, compound helicopters, drones, and the like. As such, those skilled in the art will recognize that the torque-summing powertrain of the present disclosure can be integrated into a variety of aircraft configurations. It should be appreciated that, even though aircraft are particularly well-suited to implement principles of the present disclosure, non-aircraft vehicles and devices can also implement the principles disclosed herein.

Referring also toFIG.2, an illustrative torque-summing powertrain100for a rotorcraft is illustrated in a block diagram format. The torque-summing powertrain100includes a main engine102, such as, for example, a turboshaft engine capable of producing 2,000 to 4,000 horsepower, or more or less, depending upon the particular implementation. The main engine102is coupled to a freewheeling unit depicted as sprag clutch104that acts as a one-way clutch enabling a driving mode, wherein torque from the main engine102is coupled to the main rotor gearbox106when the input side rotating speed to the sprag clutch104is matched with the output side rotating speed from the sprag clutch104. For convenience of illustration, the input side of the sprag clutch104is depicted as the apex of the greater than symbol and the output side of the sprag clutch104is depicted as the open end of the greater than symbol. The sprag clutch104has an overrunning mode in which the main engine102is decoupled from the main rotor gearbox106when the input side rotating speed of the sprag clutch104is less than the output side rotating speed of the sprag clutch104. Operating the sprag clutch104in the overrunning mode allows, for example, the main rotor108of the helicopter10to engage in autorotation in the event of a failure of the main engine102.

In the illustrated embodiment, the main rotor gearbox106is coupled to the sprag clutch104via a suitable drive shaft. In addition, the main rotor gearbox106is coupled to the main rotor108by a suitable mast. The main rotor gearbox106includes a gearbox housing and a plurality of gears, such as planetary gears, used to adjust the engine output to a suitable rotational speed so that the main engine102and the main rotor108may each rotate at optimum speed during flight operations of the helicopter10. The main rotor gearbox106may be coupled to a tail rotor gearbox110via a suitable tail rotor drive shaft. The tail rotor gearbox110includes a gearbox housing and a plurality of gears that may adjust the main rotor gearbox output to a suitable rotational speed for operation of the tail rotor112. The main engine102, the sprag clutch104, the main rotor gearbox106, and the tail rotor gearbox110, as well as the various shafts and gearing systems coupled therewith are shown as a main drive system109of the torque-summing powertrain100.

The torque-summing powertrain100includes a supplemental engine114, such as, for example, a turboshaft engine capable of producing 200 to 600 horsepower, or more or less, depending upon the particular implementation. In the illustrated embodiment, the supplemental engine114may generate between about 5% and about 20% of the horsepower of the main engine102, or more or less, depending upon the particular implementation. In other embodiments, the supplemental engine114may generate between about 10% and about 15% of the horsepower of the main engine102. The supplemental engine114is coupled to a freewheeling unit depicted as a sprag clutch116that acts as a one-way clutch enabling a driving mode, wherein torque from the supplemental engine114is coupled through the sprag clutch116from the input side to the output side. The sprag clutch116has an overrunning mode in which the supplemental engine114is decoupled from torque transfer with the sprag clutch116when the input side rotating speed of the sprag clutch116is less than the output side rotating speed of the sprag clutch116. Operating the sprag clutch116in the overrunning mode allows, for example, the main engine102to drive the rotorcraft accessories such as one or more generators118, one or more hydraulic pumps120, or other accessories122when the supplemental engine114is not operating. The supplemental engine114and the sprag clutch116as well as the various shafts and gearing systems coupled therewith may be considered a secondary drive system of the torque-summing powertrain100.

Disposed between the main drive system109and the secondary drive system of the torque-summing powertrain100is a selectable clutch assembly124that has a unidirectional torque transfer mode and a bidirectional torque transfer mode. In the unidirectional torque transfer mode of the selectable clutch assembly124, torque can be driven from the main drive system109to the secondary drive system of the torque-summing powertrain100but torque cannot be driven from the secondary drive system to the main drive system109of the torque-summing powertrain100. In the bidirectional torque transfer mode of the selectable clutch assembly124, torque can be driven from the main drive system109to the secondary drive system of the torque-summing powertrain100and torque can be driven from the secondary drive system to the main drive system109of the torque-summing powertrain100. In the illustrated embodiment, the selectable clutch assembly124includes a freewheeling unit depicted as a sprag clutch126and a bypass assembly128. The sprag clutch126acts as a one-way clutch enabling a driving mode, wherein torque from the main drive system109is coupled through the sprag clutch126from the input side to the output side. The sprag clutch126also has an overrunning mode wherein the main drive system109is decoupled from torque transfer with the sprag clutch126when the input side rotating speed of the sprag clutch126is less than the output side rotating speed of the sprag clutch126. When the overrunning mode of the sprag clutch126is enabled, the selectable clutch assembly124is in the unidirectional torque transfer mode. The overrunning mode of the selectable clutch assembly124can be disabled by engaging the bypass assembly128with the sprag clutch126. When the bypass assembly128prevents the sprag clutch126from operating in the overrunning mode, the selectable clutch assembly124is in the bidirectional torque transfer mode.

When the main engine102is operating, torque is delivered through the main drive system109as indicated by the solid lines and arrowheads between the components within the main drive system109. In addition, as the main drive system109is turning, torque may be applied to the selectable clutch assembly124. As discussed herein, in order to shift the selectable clutch assembly124from the unidirectional torque transfer mode to the bidirectional torque transfer mode, power should be applied to the input side of the sprag clutch126from the main drive system109such that the input side and the output side of the sprag clutch126are turning together. The bypass assembly128can now be actuated from the disengaged position to the engaged position, placing the selectable clutch assembly124in the bidirectional torque transfer mode. The operations of engaging and disengaging the bypass assembly128may be pilot controlled and/or may be automated by the flight control computer of the helicopter10and may be determined according to the operating conditions of the helicopter10. In this configuration, power from the supplemental engine114augments the power of the main engine102within the main drive system109, as indicated by the solid lines and arrowhead from the selectable clutch assembly124to the main drive system109. This configuration may be referred to as the enhanced power configuration of the torque-summing powertrain100wherein the main engine102and the supplemental engine114are operating together and the selectable clutch assembly124is in the bidirectional torque transfer mode. The selectable clutch assembly124may be engaged and additive supplemental power applied to the main rotor during normal operations in which the load that on the main engine is sufficient to govern the rotor speed. For example, the selectable clutch assembly124may not be engaged if the supplemental power would reduce the load on the main engine below that under which the main engine can govern rotor speed. Aspects of the torque-summing powertrain100are disclosed in US Patent App. Publication No. 2020/0248760, which is incorporated herein by reference.

Referring now also toFIGS.3and4, a system300is illustrated in conjunction with the helicopter10and the torque-summing powertrain100. It should be appreciated that though system300is illustrated with regard to the helicopter10, the system300may also be implemented on other aircraft. Further, it should be appreciated that the system300can be implemented in a wide variety of configurations, depending in part on the flight control configuration of the aircraft.

The system300is particularly well-suited for implementation in aircraft having a fly-by-wire flight control computer, such as a flight control computer325; however, non-fly-by-wire aircraft can also utilize the system300. For example, the system300can be utilized in a flight control system having collective actuators that can receive commands from a trim motor, autopilot system, or any other system that allows collective commands to be realized by collective actuators. Further, the system300is particularly well suited for implementation with aircraft having engines controlled by an engine control unit327, such as a FADEC (full authority digital engine control) system. However, the system300can also be implemented on an aircraft having an engine that is not controlled by an engine control unit such as the engine control unit327; in such an embodiment, the system300can make fuel control commands directly to a fuel control unit329, for example. The system300is preferably integrated with a flight control computer325; however, in another embodiment, the system300can be a standalone computer system within the aircraft.

The system300can include a processor303configured for processing receivable data in one or more algorithms350for calculating total power demand, supplemental power demands, and subsequently making commands, e.g., a main engine speed command, and supplemental engine power command, to adaptively affect rotor speed. The processor303can receive real time operational data from sensors, instrumentation, and the like. For each of the main engine and the supplemental engine, the processor303can separately receive real time data pertaining to a measured gas temperature (MGT)305, engine torque (Qe)307, gas generator speed (Ng)309approximating power, and rotor speed (Nr)311, which corresponds to a power-turbine speed (Np). In similar fashion, the main engine and the supplemental engine can each have separate allowable engine limits, such as a MGT limit313, a gas generator speed limit317, and a torque (Qe) limit315. For each of the main engine and the supplemental engine, the MGT limit313, the gas generator speed limit317, and the torque (Qe) limit315are in data communication with processor303and can be stored in a database within the processor303, or can be stored remotely, as long as such limits are available for analysis. The processor303is configured to perform analysis using one or more algorithms and subsequently issue supplemental engine power commands319and a main engine speed command321.

The main engine102and the supplemental engine114are different sizes, i.e., different horsepower ratings, and may be from different manufacturers. The system300is configured to separately control the main engine102and the supplemental engine114to supply total power required to maintain the main rotor speed within an acceptable range. The system300controls the main engine102to govern the main rotor speed (Nr), for example in similar manner as with a conventional single engine or twin-engine powertrain. The system300implements the supplemental engine114power control via an Ngs (supplemental-engine gas generator speed) command to provide a proportion of the total power demand, which is subtracted from the main engine102power compensation command. The supplemental engine114only receives a supplemental power demand and does not respond to changes in rotor speed. The system300facilitates operating the supplemental engine114in the enhanced power configuration when the proportion of the total power demand of the main engine102is sufficient for the main rotor speed to be governed by the main engine102.

A system computed main engine power compensation command is used to adjust the power output of the main engine to reduce rotor speed variation in response to load variations. The main engine power compensation command may be calculated by the system anticipating the power demand on the engine and transmitting the main engine power compensation command to the governor on the main engine to adjust the power output of the main engine. Non-limiting illustrative methods and systems for governing rotor speed are disclosed in US Patent Application Publication Nos. 2014/0252158, 2014/0363288, and 2018/0222597, each of which is incorporated herein by reference.

The system controls the supplemental engine to provide a proportion of the total power demand. The supplemental engine provides power in response to a system computed supplemental engine power demand signal, effectively decoupling the dynamics of the main engine and the supplemental engine. The main engine power compensation command is adjusted to account for the supplemental engine power demand. The supplemental engine power demand can be computed as a function of control inputs and flight conditions or in proportion to the total power demand. The supplemental engine power demand may be computed per schedule and limits.

Referring also toFIG.5, a rotorcraft500includes a main rotor drive system502(e.g., main rotor and main rotor gearbox) and a main engine504and a supplemental engine506coupled to the drive system. The supplemental engine506is smaller than the main engine504; for example, the supplemental engine506may be approximately 20% of the size of the main engine504. A computer508(e.g., flight computer) is configured to divide the control domain between the main engine504and the supplemental engine506. The main engine504controls main rotor speed (Nr), which is proportional to main-engine power turbine speed (Np), for example in a similar fashion to a traditional system with a single turboshaft engine or twin identical engines. The main engine504provides power to maintain the main rotor speed with a level of compensation for load variation. The main engine504has an engine controller that measures the main rotor speed (Nr) and adjusts main engine power504ato reduce RPM variation in response to load variations. The computer508can communicate a main engine power compensation command510to the main engine504(e.g., the power turbine) in anticipation of the load variations for example due to flight conditions, ambient conditions, and pilot inputs.

The supplemental engine506works to satisfy a power demand as opposed to the main engine504which works to satisfy an RPM demand. Total power demand512is calculated for what the rotorcraft500is currently doing and is routed toward the main engine504as the power compensation command. A portion of total power demand512is allocated to the supplemental engine506, as a supplemental engine power demand514, based on logic516(e.g., schedules and limits). Different techniques can be used to control the supplemental engine506. For example, the supplemental engine power demand514may be supplemental-engine gas generator speed (Ngs) based (demanding Ngs is proportional to power), measured gas temperature (MGT) based (demanding a temperature), fuel flow (WF) based (demanding a rate of fuel flow), or engine torque (Qe) based (demanding a torque). Ambient correction and low frequency closed-loop correction may be applied to reduce errors, if necessary.

To mitigate supplemental engine power506afrom being perceived by the main engine504as a disturbance, supplemental engine power demand514is subtracted at block518from total power demand512, resulting in main engine power compensation command510.

The schedules are built to achieve certain attributes. For example, and without limitation, the supplemental engine should be at maximum power when regard for efficiency in some flight envelopes and for safety. The supplemental power demand is forced to maximum power for autorotation if the main engine fails or due to rotor speed droop, which is indicative of a main engine failure. In low-power conditions, the supplemental engine power demand is reduced to ensure adequate load remains on the main engine so that it can continue to govern rotor speed. A low limit may be placed on the supplemental engine power demand to ensure that the supplemental engine sprag clutch, e.g., the clutch126of the selectable clutch124, remains engaged. The high limit takes priority over the low limit during normal operation when the main engine is controlling rotor speed. Limits, gains, and other parameters can be varied with flight condition to optimize performance. Supplemental engine limiting loops, such as MGT, Ngs, and Qe, may be utilized, and the system control algorithm adjusts when the limiting loops are active. The supplemental engine power demand control may have a supplemental-engine power-turbine speed (Nps) loop in case of overspeed, for example approximately 3%, to switch the supplemental engine to rotor speed (RPM) command to avoid increasing the rotor overspeed.

FIG.6illustrates an illustrative method600for power control of a supplemental engine, which is described with additional reference toFIGS.1-5. At block602, a rotorcraft is operated. The rotorcraft includes a drive system having a main rotor coupled to a main rotor gearbox. A main engine applies a main engine power to the drive system and a supplemental engine applies a supplemental engine power to the drive system when a first clutch, e.g., clutch126(FIG.2), is engaged. At block604, a total power demand, to drive the main rotor at a rotor speed, is determined. The total power demand accounts the main engine power and the supplemental engine power. At block606, the main engine governs the rotor speed. The governing comprises, for example, using a power compensation command generated in response to anticipated load variations to reduce rotor speed variation. At block608, the main engine power is provided to the drive system in response to receiving the power compensation command. At block610, the supplemental engine is controlled with a supplemental power demand. At block612, the supplemental engine power is provided to the drive system in response to the supplemental power demand.

In various embodiments, a distribution of power between the main engine (e.g., main engine32) and the supplemental engine (e.g., the supplemental engine114) can be optimized to improve fuel efficiency and/or other flight factors. For example, the supplemental engine can be maintained in a reduced power state until a determination is made that supplemental power is needed to satisfy a total power demand of the drive system. In general, the reduced power state represents a reduction relative to another power setting, such as maximum continuous power (MCP), in which the supplemental engine might otherwise operate by default. In various embodiments, the reduced power state can be the lowest power setting of the supplemental engine such as, for example, an IDLE state (e.g., approximately 65% RPM). As further examples, the reduced power state can be an OFF state of the supplemental engine.

FIG.7illustrates an example of optimizing usage of the supplemental engine based on flight segment. In the example ofFIG.7, seven flight segments for an example mission are shown, namely: (1) warmup; (2) hovering out of ground effect (HOGE); (3) cruise; (4) HOGE capable; (5) loiter; (6) cruise; and (7) reserve. In various embodiments, the supplemental engine can be maintained in the reduced power state when the rotorcraft is in cruise (e.g., segments (3) and (6) in the example ofFIG.7). The supplemental engine can otherwise maintain an increased power level consistent with applicable logic such as schedules and limits. For example, the power level of the supplemental engine can be increased when the rotorcraft is no longer in cruise. In some cases, the supplemental engine can be operated at MCP for non-cruise segments.

In various embodiments, a particular flight segment associated with low power demand, such as cruise, can be detected automatically based on flight conditions such as, for example, airspeed (e.g., cruise can be detected if airspeed is between 150-170 knots true airspeed (KTAS)). In other embodiments, an indication of cruise and/or a determination to enter the reduced power state can be supplied manually via pilot command. Maintaining the supplemental engine in the reduced power state can produce various advantages such as extending loiter time, increasing range, and improving fuel efficiency.

FIG.8illustrates an example of logic800for optimizing usage of supplemental engine power based on flight conditions, ambient conditions and/or demand. In various embodiments, the logic800can be performed by a computer such as the computer508ofFIG.5. As shown, inputs802are provided to a total horsepower schedule806to produce a total power demand for the drive system, for example, in shaft horsepower (SHP). The inputs802can include, for example, flight control inputs, flight conditions, ambient conditions and/or the like. In the example ofFIG.8, the inputs802include collective position, airspeed, and density altitude (Hd). An airspeed input804is provided to a flag808, while the total power demand is provided to the flag810, the flag812, and difference calculation824(described further below). In the example ofFIG.8, the flags808,810, and812are initially set to OFF.

The flag808is set to ON if the airspeed input804is at least a first airspeed threshold (e.g., 170 KTAS). Once the flag808is set to ON, it remains ON until the airspeed input804is no more than a second airspeed threshold (e.g., 155 KTAS), which value may be the same as or different from the first airspeed threshold. The flag810is set to ON if the total power demand is at least a first specified proportion of a rated power of the main engine (e.g., 0.9 MCP). Once the flag810is set to ON, it remains ON until the total power demand is no more than a second specified proportion of the rated power of the main engine (e.g., 0.85 MCP), which proportion may be the same as or different from the first specified proportion. The flag812is set to ON if the total power demand is at least a first specified proportion of a rated power of the main engine (e.g., 1.0 MCP). Once the flag812is set to ON, it remains ON until the total power demand is no more than a second specified proportion of the rated power of the main engine (e.g., 0.95 MCP), which proportion may be the as or different from the first specified proportion.

Outputs of the flags808and810are provided to an OR gate814. If the flags808and810are both set to OFF, the OR gate814outputs a zero to block816; otherwise, if one or both of the flags808and810are set to ON, the OR gate814outputs a one to block816. At block816, a power level of the supplemental engine is determined based on the output of the OR gate814, and a corresponding supplemental power demand is output to summation818. For example, if the output of the OR gate814is a zero, the supplemental power demand can correspond to an IDLE state of the supplemental engine (or a different reduced power state); otherwise, if the output of the OR gate is one, the supplemental power demand can be a calculated or determined value corresponding to a rated power of the supplemental engine (e.g., MCP).

Output of the flag812is provided to block817, where additional supplemental power demand, if applicable, is determined based thereon. If the flag812is set to OFF, the additional supplemental power demand is determined to be zero; otherwise, if the flag812is set to ON, an additional supplemental power demand can be determined as a function, for example, of a rated power of the supplemental engine. For example, in the embodiments described above in which the block816utilizes MCP, the additional supplemental power demand can utilize intermediate rated power (IRP), where the additional supplemental power demand is an amount by which the IRP of the supplemental engine exceeds its MCP. As shown, the additional supplemental power demand is output to the summation818.

At the summation818, the supplemental power demand and the additional power supplemental demand, if any, are summed to produce a total supplemental power demand, which is output to both schedule820and block822. The schedule820outputs a supplemental-engine gas generator speed (NgsRef) for implementation by the supplemental engine. As described further below, block822, difference calculation824, and conversion block826, in combination, can be used to provide a compensation command similar to the main engine power compensation command510ofFIG.5.

As described previously, the block822receives total supplemental power demand from the summation818. The block822also receives an on-limit indicator823that indicates whether the supplemental engine is already producing at its limit. Based on this information, the block822produces an adjusted supplemental-power value (e.g., Y[n]) that approximates supplemental power that will be produced by the supplemental engine in response to the supplemental-engine gas generator speed. In various embodiments, the block822can function as a transient free switch that, through each iteration, programmatically and configurably adjusts (e.g., increases) the adjusted supplemental-power value until it reaches the total supplemental power demand (e.g., X[n]). In this way, the block822can cause the adjusted supplemental-power value to adjust gradually, rather than suddenly, to the total supplemental power demand. However, in various embodiments, if the on-limit indicator823indicates that the supplemental engine is already producing at its limit (e.g., a value of TRUE), the block822can output the same value that was output in the most recent iteration (e.g., Y[n−1]). In some embodiments, the block822can be omitted such that the total supplemental power demand is passed directly from the summation818to the difference calculation824.

The difference calculation824computes a difference between the total power demand from the total horsepower schedule806and the adjusted supplemental-power value from the block822. This difference is output to the conversion block826, where the difference is converted from SHP to engine torque (e.g., QE_COM). The engine torque can be supplied to the main engine as a compensation command similar to the main engine power compensation command510ofFIG.5.

FIG.9illustrates a method900for optimizing usage of supplemental engine power, which is described with additional reference toFIGS.1-8. The method900can begin, for example, at the start of a mission. In various embodiments, the method900can be performed, at least in part, by a computer such as the computer508ofFIG.5. At block902, a rotorcraft is operated. The rotorcraft includes a multi-engine drive system having a main rotor coupled to a main rotor gearbox. A main engine applies a main engine power to the multi-engine drive system and a supplemental engine applies a supplemental engine power to the multi-engine drive system when a first clutch, e.g., clutch126(FIG.2), is engaged. In general, the block902can include driving the main rotor by the main engine.

At block904, data inputs are monitored. The data inputs can include, for example, control inputs, data indicative of flight conditions, data indicative of ambient conditions, etc. At block906, a total power demand of the multi-engine drive system is determined. At decision block908, it is determined whether supplemental power is needed to satisfy the total power demand of the multi-engine drive system. In some embodiments, as described relative toFIG.7, the need for supplemental power can be determined based on flight segment. For example, in certain embodiments, if it is indicated, automatically or manually, that the rotorcraft is in cruise, it may be determined that supplemental power is not needed. Conversely, continuing this example, if it is indicated, automatically or manually, that the rotorcraft is not in cruise (or is no longer in cruise), it may be determined that supplemental power is needed. In addition, or alternatively, in some embodiments, as described relative toFIG.8, the need for supplemental power can be determined based on flight conditions, ambient conditions, and/or demand.

If it is determined at the decision block908that supplemental engine power is not needed to satisfy the total power demand of the multi-engine drive system, the method900proceeds to block910. At block910, the supplemental engine is maintained in a reduced power state at least until a determination is made that supplemental power is needed to satisfy the total power demand of the multi-engine drive system. As described previously, in some embodiments, the reduced power state can correspond to the lowest power setting of the supplemental engine. The reduced power state can be, for example, an IDLE state, an OFF state, and/or the like. In general, the block910can involve keeping the supplemental engine in the reduced power state until configurable logic indicates, for example, that the rotorcraft is in no longer in cruise as described with respect toFIG.7, or that supplemental power is otherwise needed as described with respect toFIG.8.

If it is determined at the decision block908that supplemental engine power is needed to satisfy the total power demand, at block912, logic is executed for supplemental power. In some embodiments, the logic that is applied can involve increasing a power level of the supplemental engine. In some embodiments, the power level of the supplemental engine can be increased to the MCP of the supplemental engine or to another rated power of the supplemental engine. From either block910or912, the method900returns to the block904and executes as described previously. In various embodiments, the method900can continue until conclusion of a mission, until stopped by a pilot, or until other suitable stop criteria is satisfied.

FIG.10illustrates example fuel-efficiency advantages of optimizing usage of supplemental engine power. In the example ofFIG.10, fuel savings (in percent) are shown relative to the supplemental engine's power level (shown as a percentage of MCP). In certain embodiments, approximately 30 percent of MCP approximates the IDLE state of the supplemental engine, although it should be appreciated that the IDLE state can vary by engine, engine configuration, and/or other factors.

FIG.11illustrates an example of graph1100that shows total power demand in SHP versus collective position. In certain embodiments, the graph1100can be displayed, for example, on a screen of a user device such as, for example, a computer system. The graph1100is overlayed with ratings from the main engine and the supplemental engine. More particularly, the graph1100includes time-limited zones1102,1104,1106, and1108. The graph1100also shows supplemental engine power1110, main engine power1112, and total power1114.

The time-limited zones1102,1104, and1106correspond to the main engine operating at power levels corresponding to intermediate rated power (IRP), maximum rated power (MRP), and contingency rated power (CRP), respectively. The time-limited zone1108corresponds to the supplemental engine operating at a power level corresponding to take-off power (TOP). In some embodiments, the graph1100, or a similar display, can be shown in real-time to a pilot or other personnel.

In the graph1100, the main engine is shown to enter and exit the time-limited zone1102at the collective positions indicated. In the illustrated embodiment, the supplemental engine does not have a time-limited zone corresponding to the collective positions of the time-limited zone1102. Somewhat differently, the time-limited zone1108of the supplemental engine spans the entire range of collective positions defined by the time-limited zones1104and1106of the main engine. More particularly, the lower boundary of the time-limited zone1104of the main engine is the same, or approximately the same, as the lower boundary of the time-limited zone1108. In like manner, the upper boundary of the time-limited zone1106of the main engine is the same, or approximately the same, as the upper boundary of the time-limited zone1108. Thus, the main engine enters and exits the time-limited zone1104at the same lower-boundary collective position at which the supplemental engine enters and exits the time-limited zone1108(or at approximately the same lower-boundary collective position). Since the time-limited zone1108spans a larger range of collective positions, the supplemental engine remains in the time-limited zone1108at the lower-boundary collective position at which the main engine enters and exits the time-limited zone1106.

Although various commands have been described herein as being pilot-initiated, those having skill in the art that any of the commands can be initiated by the pilot or by an FCC or other avionics, either onboard or remote from the aircraft, without departing from principles disclosed herein. The terms “substantially,” “approximately,” “approximately,” and “about” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., “substantially 90 degrees” includes 90 degrees and “substantially parallel” includes parallel), as understood by a person of ordinary skill in the art. The extent to which the description may vary will depend on how great a change can be instituted and still have a person of ordinary skill in the art recognized the modified feature as still having the required characteristics and capabilities of the unmodified feature. In general, but subject to the preceding, a numerical value herein that is modified by a word of approximation such as “substantially,” “approximately,” and “about” may vary from the stated value, for example, by 0.1, 0.5, 1, 2, 3, 4, 5, 10, or 15 percent.