Patent Publication Number: US-11377222-B2

Title: Power management between a propulsor and a coaxial rotor of a helicopter

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application and claims priority to pending U.S. National Stage application Ser. No. 15/504,248, filed Feb. 15, 2017, which claims priority to PCT Application No. PCT/US 2015/053116, filed Sep. 30, 2015, which in turn claims priority to U.S. Provisional Application Ser. No. 62/058,133, filed Oct. 1, 2014, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Embodiments of the invention generally relate to a control system of a rotary wing aircraft, and more particularly, to power management between a propulsor and a coaxial rotor of a helicopter. 
     A rotary wing aircraft with a coaxial contra-rotating rotor system is capable of higher speeds as compared to conventional single rotor helicopters due in part to the balance of lift between advancing sides of the main rotor blades on the upper and lower rotor systems. To still further increase airspeed, supplemental translational thrust is provided by a translational thrust system including an integrated propulsor unit with a propulsor (e.g., a propeller) oriented substantially horizontal and parallel to the aircraft longitudinal axis to provide thrust for high speed flight. 
     In a rotary-wing aircraft application, engine anticipation may be part of the engine control system to maintain rotor speed within a relatively narrow range in response to demanded torque from the rotary-wing aircraft rotor system. The capability of the engine control system to correctly anticipate changes in power required directly impacts rotor speed governor performance. Engine anticipation conventionally focuses on collective changes affecting main rotor power demand. On a helicopter with an integrated propulsor unit, the propulsor contributes a significant fraction of the total power required in many flight regimes, and collective-based anticipation is insufficient to adequately control rotor speed. 
     Therefore, a need exists for an improved control for engine anticipation for propulsor loads on a helicopter. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one embodiment, a flight control system for a rotary wing aircraft that includes a main rotor system, a translational thrust system, and an engine control system is provided. The flight control system includes a flight control computer configured to interface with the main rotor system, the translational thrust system, and the engine control system. The flight control computer includes processing circuitry configured to execute control logic. The control logic includes a primary flight control configured to produce flight control commands for the main rotor system and the translational thrust system. The control logic also includes main engine anticipation logic and propulsor loads engine anticipation logic. The main engine anticipation logic is configured to produce a rotor power demand associated with the main rotor system. The propulsor loads engine anticipation logic is configured to produce an auxiliary propulsor power demand associated with the translational thrust system. The flight control computer providing the engine control system with a total power demand anticipation signal based on a combination of the rotor power demand and the auxiliary propulsor power demand. 
     In addition to one or more of the features described above or below, or as an alternative, further embodiments include where the propulsor loads engine anticipation logic further includes a shaped propeller power demand model configured to produce a propulsor power demand value based on aircraft state data, and the auxiliary propulsor power demand is based on the propulsor power demand value. 
     In addition to one or more of the features described above or below, or as an alternative, further embodiments include where the translational thrust system has an auxiliary propulsor including a plurality of propeller blades. 
     In addition to one or more of the features described above or below, or as an alternative, further embodiments include where the aircraft state data includes a propeller pitch command for the propeller blades and a reference rotational rate of the auxiliary propulsor. 
     In addition to one or more of the features described above or below, or as an alternative, further embodiments include where the propeller pitch command and the rotational rate of the auxiliary propulsor are modeled parameters, and the aircraft state data further comprises: an airspeed of the rotary wing aircraft and a density of air as sensor-based data. 
     In addition to one or more of the features described above or below, or as an alternative, further embodiments include where the aircraft state data includes a propeller clutch engagement state of a propeller clutch and a propeller speed. 
     In addition to one or more of the features described above or below, or as an alternative, further embodiments include where the propulsor loads engine anticipation logic includes a filter configured to filter the propulsor power demand value to produce a filtered power demand value, and a drivetrain loss adjustment gain applied to the filtered power demand value to produce the auxiliary propulsor power demand. 
     These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a general side view of an exemplary rotary wing aircraft for use in accordance with embodiments; 
         FIG. 2  is a perspective view of the exemplary rotary wing aircraft of  FIG. 1 ; 
         FIG. 3  is a schematic diagram of a flight control system of a rotary wing aircraft according to an embodiment; 
         FIG. 4  is a schematic diagram of control logic in a flight control computer of a rotary wing aircraft according to an embodiment; and 
         FIG. 5  is a schematic diagram of propulsor loads engine anticipation logic in a flight control computer of a rotary wing aircraft according to an embodiment. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Exemplary embodiments provide enhanced anticipation of aircraft power demand changes for a rotary wing aircraft employing auxiliary propulsion via a translational thrust system coupled to a primary drivetrain. Engine anticipation can be used to maintain rotor speed within a relatively narrow range in response to demanded torque. The ability to correctly anticipate changes in power required directly impact propulsion system performance. Embodiments allow an engine control system to more accurately and rapidly respond to changes in power demand due to an auxiliary propulsor that would otherwise generate fluctuations in drivetrain rotational speed. An embodiment is implemented via a shaped propeller power demand model that is a function of aircraft state data, such as airspeed, air density, propeller pitch of the auxiliary propulsor, and propeller rotational speed of the auxiliary propulsor. The shaped propeller power demand model can be embedded in a fly-by-wire control system of the aircraft and utilizes available aircraft state data. An estimated power demand for the auxiliary propulsor is combined with other power demand sources and provided to the engine control system as a feed forward anticipation signal. 
       FIGS. 1 and 2  illustrate an exemplary vertical takeoff and landing (VTOL) high speed compound or coaxial contra-rotating rigid rotor aircraft  10  having a dual, contra-rotating main rotor system  12 , which rotates about a rotor axis of rotation R. The aircraft  10  includes an airframe  14  which supports the dual, contra-rotating, coaxial main rotor system  12  as well as a translational thrust system  30  which provides translational thrust generally parallel to an aircraft longitudinal axis L. Embodiments also apply to compound helicopter designs that may include, for example, wings that provide a significant contribution to high speed lift, offloading the rotor system. 
     With reference to  FIGS. 1 and 2 , the main rotor system  12  includes an upper rotor system  16  and a lower rotor system  18  as dual contra-rotating main rotors in a coaxial configuration. A plurality of rotor blade assemblies  20  are mounted to a rotor hub  22 ,  24  of each rotor system  16 ,  18 , respectively. The main rotor system  12  is driven by a transmission  25 . The translational thrust system  30  may be any propeller system including, but not limited to a pusher propeller, a tractor propeller, a nacelle mounted propeller, etc. In the example of  FIGS. 1-2 , the translational thrust system  30  includes an auxiliary propulsor  32 . In an embodiment, the auxiliary propulsor  32  is a pusher propeller system with a propeller rotational axis P oriented substantially horizontal and parallel to the aircraft longitudinal axis L to provide thrust for high speed flight. The auxiliary propulsor  32  can be a puller propeller, for instance, a propeller mounted in front of the cockpit. The translational thrust system  30  may be driven through a main gearbox  26 , which also drives the main rotor system  12 . The auxiliary propulsor  32  may also provide reverse thrust, either for braking from high speed flight or for initiating rearward flight, or to achieve unusual hover attitudes. 
     The transmission  25  includes the main gearbox  26  driven by one or more engines, illustrated schematically at E. The main gearbox  26  and engines E are considered as part of the non-rotating frame of the aircraft  10 . In the case of a rotary wing aircraft, the main gearbox  26  may be interposed between one or more gas turbine engines E, the main rotor system  12  and the translational thrust system  30 . In one embodiment, the main gearbox  26  is a split torque gearbox which carries torque from the engines E through a multitude of drivetrain paths. Although a particular rotary wing aircraft configuration is illustrated and described in the disclosed non-limiting embodiment, other configurations and/or machines with rotor systems are within the scope of the present invention. 
     The transmission  25  may also include a combiner gearbox  36  in meshing engagement with the main gearbox  26  and driven by one or more engines E. The engines E may drive the combiner gearbox  36  and the main gearbox  26  through a disconnecting mechanism, such as an overrunning clutch  38 . The translational thrust system  30  can include a drive shaft  40  which is driven by the combiner gearbox  36  to drive the auxiliary propulsor  32  through an auxiliary propulsor gearbox  42 . It should be understood that although the combiner gearbox  36  is schematically illustrated as a separate component, the combiner gearbox  36  may alternatively be incorporated directly into the main gearbox  26 . A propeller clutch  43 , similar to a manual clutch in an automobile, may be located at various positions in the transmission  25  or the translational thrust system  30  to clutch allows the pilot to operate with the propeller system disengaged, and the propeller spinning either at very low speed or not at all. For example, the propeller clutch  43  can be located up near the main gearbox  26 , or near the auxiliary propulsor  32  itself, or anywhere in between. 
     In the example of  FIGS. 1 and 2 , the auxiliary propulsor  32  includes a plurality of propeller blades  33  and is positioned at a tail section  41  of the aircraft  10 . During flight regimes, power demand can shift between the main rotor system  12  and the translational thrust system  30  due to a number of factors, which impacts overall power demand of the engines E. Exemplary embodiments provide a feed forward power demand to anticipate loads and conditions before they may be detectable by sensor based feedback. 
     Portions of the aircraft  10 , such as the main rotor system  12  and the translational thrust system  30  for example, are driven by a flight control system  70  illustrated in  FIG. 3 . In one embodiment, the flight control system  70  is a fly-by-wire (FBW) control system. In an FBW control system, there is no direct mechanical coupling between a pilot&#39;s controls and movable components such as rotor blade assemblies  20  or propeller blades  33  of the aircraft  10  of  FIGS. 1 and 2 . Instead of using mechanical linkages, an FBW control system includes a plurality of sensors  72  which can sense the position of controlled elements and generate electrical signals proportional to the sensed position. The sensors  72  may also be used directly and indirectly to provide a variety of aircraft state data to a flight control computer (FCC)  75 . The FCC  75  may also receive pilot inputs  74  as control commands. In response to inputs from the sensors  72  and pilot inputs  74 , the FCC  75  transmits signals to various subsystems of the aircraft  10 , such as the main rotor system  12  and the translational thrust system  30 . 
     The main rotor system  12  can include a main rotor controller  50  configured to receive commands from the FCC  75  to control one or more actuators  55 , such as a mechanical-hydraulic, electric, or electrohydraulic actuator, for the rotor blade assemblies  20  of  FIGS. 1 and 2 . In an embodiment, pilot inputs  74  including cyclic, collective, and throttle commands may result in the main rotor controller  50  driving the one or more actuators  55  to adjust a swashplate assembly (not depicted) for pitch control of the rotor blade assemblies  20  of  FIGS. 1 and 2 . Alternatively, pitch control can be performed without a swashplate assembly. 
     The translational thrust system  30  can include a propeller pitch controller  60  configured to receive commands from the FCC  75  to control one or more actuators  65 , such as a mechanical-hydraulic, electric, or electrohydraulic actuator, for the propeller blades  33  of  FIGS. 1 and 2 . In an embodiment, pilot inputs  74  include a propeller pitch command for the propeller pitch controller  60  to drive the one or more actuator  65  for pitch control of the propeller blades  33  of  FIGS. 1 and 2 . 
     The FCC  75  can also interface with an engine control system  85  including one or more electronic engine control units (EECUs)  80  to control the engines E. Each EECU  80  may be a digital electronic control unit such as Full Authority Digital Engine Control (FADEC) electronically interconnected to a corresponding engine E. Each engine E may include one or more instances of the EECU  80  to control engine output and performance. Engines E may be commanded in response to the pilot inputs  74 , such as a throttle command. Although controllers  50 ,  60 ,  75 , and  80  are separately depicted, it will be understood that one or more of the controllers  50 ,  60 ,  75 , and  80  can be combined, e.g., main rotor controller  50  can be implemented within FCC  75 . 
     Rather than simply passing pilot inputs  74  through to various controllers  50 ,  60 , and  80 , the FCC  75  includes a processing system  90  that applies models and control laws to augment commands based on aircraft state data. The processing system  90  includes processing circuitry  92 , memory  94 , and an input/output (I/O) interface  96 . The processing circuitry  92  can be any type or combination of computer processors, such as a microprocessor, microcontroller, digital signal processor, application specific integrated circuit, programmable logic device, and/or field programmable gate array, and is generally referred to as central processing unit (CPU)  92 . The memory  94  can include volatile and non-volatile memory, such as random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable storage medium onto which data and control logic as described herein are stored. Therefore, the memory  94  is a tangible storage medium where instructions executable by the processing circuitry  92  are embodied in a non-transitory form. The I/O interface  96  can include a variety of input interfaces, output interfaces, communication interfaces and support circuitry to acquire data from the sensors  72 , pilot inputs  74 , and other sources (not depicted) and communicate with the main rotor controller  50 , the propeller pitch controller  60 , the EECUs  80 , and other subsystems (not depicted). 
       FIG. 4  depicts a portion of control logic  100  in the FCC  75 . The control logic  100  may be embodied as executable instructions in the memory  94  of  FIG. 3 , where the processing circuitry  92  of  FIG. 3  is configured to read and execute the control logic  100 . The control logic  100  can include a primary flight control (PFC)  102  and a flight augmentation and cueing system (FACS)  104 . The PFC  102  and FACS  104  may execute model following control laws to provide both control and stability augmentation such that pilot inputs  74  are shaped into desired aircraft responses. Desired aircraft responses may be passed through an inverse aircraft model to obtain (e.g., after mixing and kinematics) flight control commands  106  to make the aircraft  10  of  FIGS. 1 and 2  produce an aircraft response. The difference between the desired response and the aircraft response can be fed back to drive errors towards zero. Separate control laws can be implemented for controlling yaw, pitch, roll and collective of the aircraft  10  of  FIGS. 1 and 2 . The PFC  102  may provide control command signals, while the FACS  104  can provide conditioning and/or trimming for the PFC  102  to produce the flight control commands  106 . The flight control commands  106  are routed to various subsystems to control the aircraft  10 , such as to the main rotor system  12  and the translational thrust system  30  of  FIGS. 1-3 , in addition to other controllers (not depicted). 
     The PFC  102  and FACS  104  can receive and/or produce aircraft state data  108  based on the sensors  72 , pilot inputs  74 , and other derived or received parameters. The FACS  104  may include main rotor engine anticipation logic  110  and propulsor loads engine anticipation logic  112 . Alternatively, the main rotor engine anticipation logic  110  and propulsor loads engine anticipation logic  112  are located elsewhere within the FCC  75  as part of the control logic  100 . The main rotor engine anticipation logic  110  determines an estimate of power required to maintain a reference rotor speed (such as, for example, 100% rotor speed) as rotor power demand  114  (anticipated rotor power demand), when the flight control commands  106  are applied to the main rotor system  12 . The main rotor engine anticipation logic  110  may provide specific rotor control shaping based on the aircraft state data  108  and model-following control logic for each controlled axis of the PFC  102  and FACS  104 . 
     The propulsor loads engine anticipation logic  112  determines an estimate of power required for the auxiliary propulsor  32  of the translational thrust system  30  according to the aircraft state data  108 . The propulsor loads engine anticipation logic  112  outputs an auxiliary propulsor power demand  116  (anticipated auxiliary propulsor power demand) that is combined (e.g., summed) with the rotor power demand  114  to produce total power demand anticipation signal  118  (also referred to as power demand  118 ) for one or more instances of the EECU  80  in the engine control system  85  of  FIG. 3 . The total power demand anticipation signal  118  is a feed forward anticipation signal to request a corresponding amount of power from the engines E via engine control commands  120 . Based on timing differences between the engines E and flight surfaces, the engine control commands  120  may take effect ahead of the flight control commands  106 . 
       FIG. 5  depicts an example of the propulsor loads engine anticipation logic  112  in greater detail. In an embodiment, the propulsor loads engine anticipation logic  112  includes a shaped propeller power demand model  202 , a filter  204 , and a drivetrain loss adjustment gain  206 . The shaped propeller power demand model  202  may receive a variety of aircraft state data  108  to perform a table lookup operation to produce a propulsor power demand value  208 . For example, the aircraft state data  108  can include a propeller pitch command (B prop )  210  for the propeller blades  33  of the auxiliary propulsor  32  of  FIGS. 1-2  as a modeled parameter. The aircraft state data  108  may also include a reference rotational rate (Nr)  212  of the auxiliary propulsor  32  about axis P of  FIG. 1  as a modeled parameter, where Nr is a reference drivetrain/rotor rotational speed rather than a sensed speed. The aircraft state data  108  can also include sensor-based data, such as an airspeed or true airspeed (TAS)  214  of the aircraft  10  and a density of air (DA)  216 . Together, B prop    210 , Nr  212 , TAS  214 , and DA  216  collectively define flight regimes where power demand for the auxiliary propulsor  32  represents a significant fraction of total power from the engines E. For example, the propulsor power demand value  208  may be greater for higher Nr  212 , higher TAS  214 , and lower DA  216 . Thrust provided by the auxiliary propulsor  32  may vary as a function of the B prop    210  and Nr  212 , where a greater propulsor power demand value  208  may be needed for higher thrust regimes. Extrapolating equations may be employed by the shaped propeller power demand model  202  when one or more of the B prop    210 , Nr  212 , TAS  214 , and DA  216  are received as values defined outside of table index limits. One or more range limits can be applied rather than an extrapolation. As an alternative to table-based operations, the shaped propeller power demand model  202  can be implemented using physics-based equations based on the aircraft state data  108  such as B prop    210 , Nr  212 , TAS  214 , and DA  216  to produce the propulsor power demand value  208 . 
     In embodiments that include the propeller clutch  43  of  FIG. 1 , the shaped propeller power demand model  202  may produce the propulsor power demand value  208  based on a propeller clutch engagement state  218  and a propeller speed  220  (N prop ). Engaging and disengaging the propeller clutch  43  can produce a transient power demand change. Propeller clutch  43  engagement, as indicated by the propeller clutch engagement state  218 , produces an increase in aerodynamic load as propeller speed  220  increases, and also requires additional power to accelerate propeller inertia up to a target speed. Propeller clutch  43  disengagement, as indicated by the propeller clutch engagement state  218 , removes a potentially significant load from the drive train. Additional engine anticipation algorithms to predict and provide anticipation for the aerodynamic and inertial load demands associated with engagement/disengagement of the propeller clutch  43  further enhance engine control. Pre-knowledge of a requested change in the propeller clutch engagement state  218  assists in anticipation computations. To predict the load demand change associated with accelerating the propeller to speed may also be based on the inertia of the propeller, the desired change in propeller speed  220 , and the duration/shape of the desired rotor speed response during clutch engagement. 
     The propeller speed  220  represents a rotational speed of the propeller (i.e., the auxiliary propulsor  32  of  FIGS. 1 and 2 ), while Nr  212  is a reference rotor/drive train rotational speed, e.g., a reference rotational speed of drive shaft  40  of  FIG. 1 . The FACS  104  of  FIG. 4  provides the estimated power demand of the main rotor and propeller systems at a specified reference rotational speed, and the EECU  80  uses the total power demand anticipation signal  118  to help minimize error between actual (sensed) Nr and reference Nr  212 . When the propeller clutch  43  of  FIG. 1  is engaged, the actual propeller rotation rate (propeller speed  220 ) can be compared to a reference rotational rate (Nr  212 ), and a change in propeller rotational speed that needs to be achieved during engagement of the propeller clutch  43  is computed. The power required to effect this change in propeller speed  220  over the desired time frame is also computed, and included as part of the propulsor power demand value  208 . 
     The filter  204  can be applied to the propulsor power demand value  208  to produce a filtered power demand value  222 . In an embodiment, the filter  204  is a lag filter configured to smooth transitions between discrete values of the propulsor power demand value  208  over a period of time. The filter  204  can also provide a time delay to the propulsor power demand value  208  to approximate dynamics of the auxiliary propulsor  32 . For example, changes to the translational thrust system  30  may occur more rapidly than changes to the main rotor system  12 . 
     The drivetrain loss adjustment gain  206  can be applied to the filtered power demand value  222  to produce the auxiliary propulsor power demand  116 . The drivetrain loss adjustment gain  206  may be used to account for drivetrain losses in the transmission  25 , including losses through the drive shaft  40  and the auxiliary propulsor gearbox  42  of  FIG. 1 . Although depicted separately, it will be understood that the drivetrain loss adjustment gain  206  can be incorporated into one or more coefficients of the filter  204  or incorporated into the shaped propeller power demand model  202 . Accordingly, the auxiliary propulsor power demand  116  is based on the propulsor power demand value  208 , as well as effects of the filter  204  and the drivetrain loss adjustment gain  206 . When the propeller clutch  43  of  FIG. 1  is included, the auxiliary propulsor power demand  116  is also based on characteristics associated with engagement/disengagement of the propeller clutch  43 , e.g., propeller clutch engagement state  218  and propeller speed  220 . 
     Exemplary embodiments include a method of providing engine anticipation for propulsor loads on a rotary wing aircraft, such as the aircraft  10  including a main rotor system  12 , a translational thrust system  30 , and an engine control system  85  as described in reference to  FIGS. 1-5 . The FCC  75  produces flight control commands  106  for the main rotor system  12  and the translational thrust system  30 . The FCC  75  also produces a rotor power demand  114  associated with applying the flight control commands  106  to the main rotor system  12 . The FCC  75  additionally produces an auxiliary propulsor power demand  116  associated with applying the flight control commands  106  to the translational thrust system  30 . The FCC  75  provides the engine control system  85  with a total power demand anticipation signal  118  (i.e., a power demand feed forward anticipation signal) as a combination (e.g., a summation) of the rotor power demand  114  and the auxiliary propulsor power demand  116 . The propulsor loads engine anticipation logic  112  can perform a table lookup operation and/or perform calculations using a shaped propeller power demand model  202  based on aircraft state data  108  to produce a propulsor power demand value  208 , where the auxiliary propulsor power demand  116  is based on the propulsor power demand value  208 . Filtering of the propulsor power demand value  208  by the filter  204  produces a filtered power demand value  222 , and applying a drivetrain loss adjustment gain  206  to the filtered power demand value  222  produces the auxiliary propulsor power demand  116 . 
     Technical effects include an enhanced ability of an engine control system to maintain constant rotational speed of a drive system during aircraft maneuvers that either involve commands to an auxiliary propulsor, i.e., changes to propeller blade pitch, or that change an aircraft flight condition in a way that otherwise affects the power demand of the propulsor, i.e., changes to airspeed or drivetrain reference speed. In a coaxial helicopter with a propulsor, collective-based anticipation alone may be insufficient to adequately control rotor speed where the propulsor contributes a significant fraction of total power in a number of flight regimes. Including propulsor loads engine anticipation logic as a feed-forward signal to an engine control system can enable predictive adjustments to power requirements as the helicopter initiates a maneuver that changes an amount or fraction of power demanded by the propulsor. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.