(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2010/0324758 A1
`Dec. 23, 2010
`(43) Pub. Date:
`Piasecki et al.
`
`US 20100324758A1
`
`(54)
`
`COMPOUND AIRCRAFT CONTROL SYSTEM
`AND METHOD
`
`(76)
`
`Inventors:
`
`Frank N. Piasecki, Haverford, PA
`(US); Andrew S. Greenjack,
`Thornton, PA (US); Joseph F.
`Horn, State College, PA (US)
`
`Correspondence Address:
`ROBERT.J.YARBROUGH, ATTORNEY AT LAW
`2O1 NORTHUACKSON STREET
`MEDIA, PA 19063 (US)
`
`(21)
`
`Appl. No.:
`
`12/825,963
`
`(22)
`
`Filed:
`
`Jun. 29, 2010
`
`(60)
`
`Related U.S. Application Data
`Continuation of application No. 12/168,051, filed on
`Jul. 3, 2008, which is a division of application No.
`11/505,235, filed on Aug. 16, 2006, now Pat. No.
`7,438,259.
`Publication Classification
`
`(51)
`
`Int. C.
`(2006.01)
`GOSD L/00
`(52)
`U.S. Cl. ............................................................ 70 1/3
`(57)
`ABSTRACT
`The Invention is a control system for a compound aircraft. A
`compound aircraft has features of both a helicopter and a
`fixed wing aircraft and provides redundant control options.
`The control system allows an authorized person to select any
`of plurality of operational objectives each of which is
`designed to achieve any particular command.
`
`Primary Flight
`Controls 36
`
`Microprocessor
`38
`
`Computer memory 60
`
`Cyclic actuator 42
`
`Collective actuator44
`
`Throttle actuator
`
`6
`
`ra
`
`First flaperon actuator 48
`
`Second flaperon actuatos
`
`Elevator actuator 52
`
`Rudder actuator 54
`
`Sector actuator 56
`
`ropeller pitch actuates
`
`DJI-1013
`IPR2023-01104
`
`

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`Patent Application Publication
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`Fig. 1
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`Fig. 2
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`Primary Flight
`Controls 36
`
`Sensors 40
`
`Microprocess
`
`Computer memory 60
`
`Cyclic actuator 42
`
`Collective actuator44
`
`Throttle actuator
`
`First flaperon actuator 48
`
`Second flaperon actuato
`
`Elevator actuator 52
`
`Rudder actuator 54
`
`Propeller pitch actuator
`58
`
`Fig. 4
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`Patent Application Publication
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`US 2010/0324758 A1
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`64
`Pilot
`command
`
`
`
`Aircraft 66
`Condition
`information
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Optimum trim 68
`
`Speed Command/
`Speed hold
`70
`
`Longitudinal/
`Vertical control 72
`
`Lateral/Directional
`Control
`74
`
`
`
`Turn Coordination
`
`Tuncoordination 6
`
`Control system 62
`
`
`
`
`
`
`
`Fig. 5
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`Aircraft Control
`Settings
`78
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`Patent Application Publication
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`Dec. 23, 2010 Sheet 6 of 11
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`US 2010/0324758A1
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`W
`Pamb
`Tomb
`GW
`WC
`
`
`
`
`
`
`
`
`
`
`
`
`
`(2 hr.
`trim
`
`
`
`Optimal
`Trim
`Schedule
`68
`
`FADEC
`80
`
`To Engine
`
`6trim
`d
`long) trim
`(cell) trim
`6
`e) trim
`(FO) trim
`Ap
`
`(Ap) tri
`pl trim
`Speed
`Commond/
`Speed Hold with
`
`Torque Limiting life
`
`46cmd
`
`Longitudinal
`/ Vertical
`AFCS
`
`E. To Swashplate:
`Collective
`84
`Cyclic Pitch
`
`don
`
`To Wing:
`Floperons
`
`To VTDP
`
`Elevotor
`
`Sector
`Propeller Pitch
`
`Directional
`AFCS
`
`(aw
`
`Q
`88
`
`D
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`

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`s
`Q)
`S
`N
`NN
`Q
`
`05
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`douddH
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`
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`udlø7
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`
`
`YaW.d
`-1 to
`
`50 kts
`
`60 kts
`V
`
`
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`(cmd)low speed
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`US 2010/0324758 A1
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`Dec. 23, 2010
`
`COMPOUND AIRCRAFT CONTROL SYSTEM
`AND METHOD
`
`RELATED APPLICATIONS
`0001. This application is a continuation of U.S. patent
`application Ser. No. 12/168,051, filed Jul. 3, 2008, which is
`itself a divisional application from U.S. patent application
`Ser. No. 1 1/505.235 by Frank N. Piasecki, etal, filed Aug. 16,
`2006, issued as U.S. Pat. No. 7,438,259 on Oct. 21, 2008.
`
`BACKGROUND OF THE INVENTION
`0002 1. Field of the Invention
`0003. The Invention is a control system for a compound
`aircraft. For trimmed flight, the control system selects a com
`bination of trim control settings for the redundant controls of
`the compound aircraft to achieve a pilot's command consis
`tent with a user-selectable objective, such as speed maximi
`Zation, fuel consumption minimization, vibration reduction
`or lifecycle cost reduction. For maneuvering flight, the con
`trol system distributes control among the redundant control
`options of the compound aircraft and may perform that dis
`tribution consistent with the user-selectable objective. The
`Invention is also a method for controlling a compound air
`craft.
`0004 2. Description of the Related Art
`0005. A compound aircraft is an aircraft that includes
`features of both fixed wing aircraft and rotary wing aircraft.
`The compound aircraft includes the elements of a helicopter,
`including at least one main rotor and a mechanism to over
`come the torque response of the rotating main rotor. The
`compound aircraft also includes elements of a fixed-wing
`aircraft, Such as a wing. The wing may be equipped with
`ailerons, flaps or a combination of flaps and ailerons known as
`flaperons. The compound aircraft may be equipped with a
`separate thrust mechanism to drive the aircraft forward, such
`as a propeller in a ducted fan. Through the use of appropriate
`Vanes or sectors that change the configuration of the duct, the
`ducted fan may serve as the mechanism to overcome the
`torque response of the rotating rotor blades and to provide
`yaw control.
`0006. A compound aircraft offers several advantages over
`a conventional helicopter. Those advantages include achiev
`ing higher flight speeds and delayed onset of retreating blade
`stall and leading blade compression effects. Although the
`advantages of a compound helicopter are well known, no
`compound helicopters have been placed in regular operation
`in commercial or military fleets. One reason is the control
`complexity of the compound aircraft.
`0007. The pilot of a conventional helicopter has only lim
`ited controls. The controls available for a conventional heli
`copter having a single main rotor and a tail rotor are:
`0008 Throttle The pilot can control the amount of
`power supplied to the rotor blades and to the tail rotor.
`0009 Collective pitch. The pilot contemporaneously can
`change the pitch of all main rotor blades by an equal amount
`using the collective pitch control, also known as the collec
`tive. Contemporaneously changing the pitch angle of all
`main rotor blades increases or decreases the lift Supporting
`the helicopter. Increasing the collective and the power will
`cause the helicopter to rise. Decreasing the collective and the
`power will call the helicopter to sink.
`0010 Cyclic pitch. The pilot may use the cyclic pitch
`control, also known as the cyclic, to cause the pitch angle of
`
`the main rotor blades to change differentially as the main
`rotor rotates through 360 degrees. The cyclic pitch control is
`used to control the pitch and roll of the helicopter. For
`example, increasing the pitch angle of a rotor blade when the
`rotor blade is retreating toward the rear of the helicopter and
`decreasing the pitch angle when the rotor blade is advancing
`toward the front of the helicopter will cause the main rotor
`plane of rotation to tilt forward and hence will cause the
`helicopter to move forward.
`0011 Tail rotor pitch control For a conventional heli
`copter having a tail rotor mounted on a boom, a pedal-oper
`ated yaw control changes the pitch of the tail rotor blades so
`that the tail rotor presents more or less force countering the
`torque response of the rotating main rotor. The pitch of the tail
`rotor blades therefore controls the yaw of the conventional
`helicopter.
`0012 For a conventional helicopter and for a particular
`throttle setting, there is only one combination of trim control
`settings for the collective, cyclic and tail rotor pitch controls
`to achieve any particular desired trimmed condition of the
`helicopter. The pilot of the conventional helicopter therefore
`has few control options.
`0013. A compound aircraft will have the aforementioned
`controls and in addition will have other controls. For example,
`the compound aircraft may feature the following controls:
`0014 Flaperon controls The flaperons (a combination
`of flaps and ailerons) are located on the wings. When
`deflected differentially like ailerons, the flaperons may cause
`the aircraft to roll. When deflected in unison like flaps, the
`flaperons may increase or decrease lift generated by the wing.
`In hovering flight, the flaperons may be deployed to reduce
`the effective wing area and hence reduce the downward force
`on the wings from the downwash of the main rotor.
`0015 Forward thrust control The compound aircraft
`may be equipped with a ducted fan or other mechanism to
`provide forward thrust. Thrust provided by the ducted fan or
`by another mechanism that is not the main rotor is referred to
`in this application as “non-rotor forward thrust.”
`0016 Rudder/stabililator The compound aircraft may
`be equipped with a rudder and with an elevator or stabilator.
`The rudder controls the yaw of the aircraft, in cooperation
`with the tail rotor, ducted fan, or other mechanism countering
`the torque reaction of the rotating main rotor. An elevator or
`stabilator controls the pitch of the compound aircraft, in coop
`eration with or instead of the cyclic pitch control.
`0017. The pilot of the compound aircraft is presented with
`a variety of control combinations to achieve a desired flight
`condition. For example, if the pilot desires to increase the
`forward speed of the compound aircraft, the pilot can increase
`the non-rotor forward thrust using the forward thrust control,
`can use the cyclic pitch, stabilator and throttle controls to
`pitch the aircraft forward, or can use any combination of
`forward thrust control, stabilator, cyclic pitch control and
`throttle. Each of the possible combinations of trim control
`settings offers advantages and disadvantages. A combination
`of trim control settings that is optimal for one objective (for
`example, minimizing fuel consumption) may not be optimal
`for another objective (for example, minimizing vibration).
`0018. Only one combination of trim control settings for
`the compound aircraft will be optimal for achieving a particu
`lar trimmed condition or for implementing maneuvering
`flight commands consonant with also achieving a particular
`operational objective. The prior art does not disclose a control
`system for a compound aircraft that allows selection among a
`
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`

`US 2010/0324758 A1
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`Dec. 23, 2010
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`plurality of objectives and that then automatically optimizes
`control settings to achieve pilot control commands consistent
`with the selected objective.
`
`BRIEF DESCRIPTION OF THE INVENTION
`0019. The Invention is a control system for a compound
`aircraft. A user selects an overall objective for the control
`system, Such as reducing vibration, increasing performance
`and speed, reducing lifecycle costs, reducing loading of one
`or more components, reducing fuel consumption, or any com
`bination of these objectives or of any other desired objectives.
`The overall objective is pre-selected from among a plurality
`of overall objectives by the pilot or by another authorized
`person; for example, by the owner of the compound aircraft.
`The control system receives a command from a pilot for
`trimmed flight. The control system also receives information
`from sensors relating to current aircraft condition (Such as
`attitude, altitude, Vertical speed, airspeed, main rotor speed,
`control Surface positions, acceleration and angular rates).
`0020. The control system compares the pilot command to
`the current aircraft condition as detected by the sensors and
`consults a look-up database of combinations of trim control
`settings. The control system applies the user-selectable over
`all objective in consulting the look-up database. The control
`system selects one of the combinations of trim control set
`tings for trimmed flight from the look-up database. The
`selected combination of trim control settings provides a con
`trol setting for each of the various control effectors of the
`compound aircraft to achieve the pilot's intended trimmed
`flight condition consistent with the pre-selected overall
`objective. As used in herein, the term control effector means
`collectively all of the various flight control surfaces and
`engines of the compound aircraft. The control system applies
`the selected combination of trim control settings to the con
`trol effectors of the compound aircraft, including the redun
`dant control effectors.
`0021. The sensors monitor the current condition of the
`aircraft and provide constant feedback to the control system.
`The control system continuously selects and applies different
`combinations of trim control settings from the look-up data
`base as needed to achieve the selected overall objective for
`trimmed flight. If the pilot control inceptors are in detent,
`which is a neutral position that does not indicate a com
`manded change in aircraft condition, a feedback controller
`regulates the aircraft control effectors so that the aircraft stays
`in trim and the selected overall objective is achieved.
`0022. In the event the pilot maneuvers the aircraft, the
`control system will receive a pilot command from a control
`inceptor operated by the pilot and will filter the pilot com
`mand using a command filter to determine the commanded
`change in aircraft condition. The command filter determines
`the dynamic response and thus the handling qualities of the
`compound aircraft. The control system compares the filtered
`pilot command to the condition of the aircraft as detected by
`the sensors and selects a combination of control effector
`settings to achieve the maneuver.
`0023 The control system applies weighting factors to
`control the distribution of control among the redundant con
`trol effectors in maneuvering flight. The control designer can
`select a combination of weighting factors to achieve an over
`all objective for maneuvering flight, such as minimization of
`certain structural loads. An authorized person, such as the
`pilot or owner of the aircraft, may select an overall objective
`for maneuvering flight from among a plurality of objectives.
`
`The selected overall objective for maneuvering flight may be
`the same as or different from the selected overall objective for
`trimmed flight. The control system may consult a look-up
`database and select a combination of weighting factors asso
`ciated with the selected overall objective for maneuvering
`flight. The control system applies the selected combination of
`weighting factors in allocating control among the redundant
`control surfaces. The control system will supply the selected
`control settings to the appropriate actuators to achieve the
`maneuver. When the control inceptors are returned to detent,
`the aircraft will once again reach trim, with the appropriate
`control settings to achieve the selected overall objective for
`trimmed flight.
`0024. The pilot may change the overall objective for
`trimmed or maneuvering flight and hence the applied control
`trim settings or weighting factors during flight. For example,
`the pilot may change the overall objective for trimmed flight
`from reduce vibration to maximize speed. The control
`system then will selecta different combination of trim control
`settings to accomplish the new overall objective for trimmed
`flight. Alternatively, the pilot may not beauthorized to change
`the overall objective for trimmed or maneuvering flight and
`the function of selecting the overall objective may be reserved
`to another person, such as the owner of the aircraft.
`0025. In an important application of the Invention, a pilot
`will fly a compound aircraft using only the familiarhelicopter
`flight controls of collective pitch, cyclic pitch and tail rotor
`pitch (pedal yaw control), just as if the pilot were flying a
`conventional helicopter. The control system receives the col
`lective, cyclic and tail rotor inputs from the pilot and infers the
`intent of the pilot. The control system then selects an appro
`priate combination of trim control settings for the collective,
`cyclic, flaperon, forward thrust, elevator, sector, rudder and
`any other available control effector to best achieve the pilot's
`intent, consistent with the pre-selected overall objective for
`trimmed or maneuvering flight. A pilot skilled in flying a
`conventional helicopter may therefore pilot a compound air
`craft using the control system of the Invention and achieve the
`selected overall objective without simultaneously applying
`the skills of a fixed-wing pilot.
`0026. The control system of the Invention may be a com
`ponent of a fully authorized “fly-by-wire” system in which
`the control system operates all aircraft flight controls. Alter
`natively, the control system of the Invention may be config
`ured to operate only a portion of the controls of the aircraft.
`For example, the pilot may directly control the collective,
`cyclic pitch and throttle controls, while the control system of
`the Invention automatically controls the flaperons and for
`ward thruster.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0027 FIG. 1 is a perspective view of a compound aircraft.
`0028 FIG. 2 is a side view of a compound aircraft.
`0029 FIG. 3 is a rear view of a compound aircraft.
`0030 FIG. 4 is a schematic representation of the control
`system of the invention.
`0031
`FIG. 5 is a schematic representation of information
`flow through the control system of the Invention.
`0032 FIG. 6 illustrates the overall control system archi
`tecture.
`0033 FIG. 7 illustrates the longitudinal/vertical control
`Subsystem.
`0034 FIG. 8 illustrates the speed command/speed hold
`Subsystem.
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`Dec. 23, 2010
`
`0035 FIG. 9 illustrates the engine torque limiting module
`0036 FIG. 10 illustrates the lateral/directional control
`Subsystem.
`0037 FIG. 11 illustrates the turn coordination/yaw rate
`command module.
`
`DESCRIPTION OF AN EMBODIMENT
`A. Compound Aircraft Features
`0038. The apparatus of the Invention is a control system
`for a compound aircraft 2. As shown by FIGS. 1 and 2, the
`compound aircraft 2 includes features of both a helicopter and
`a fixed wing aircraft. Those features include a fuselage 4, a
`main rotor (or rotating wing) 6, a hub 8 about which the main
`rotor 6 rotates and wings 10. Rotation of main rotor 6 about
`hub 8 induces main rotor lift 12. Movement of air across
`wings 10 in response to the forward motion 14 of the com
`pound aircraft 2 generates wing lift 16. Rotor lift 12 and wing
`lift 16 provide lift to the compound aircraft 2.
`0039 Wings 10 feature a wing control surface known as a
`flaperon 18. Flaperon 18 may be moved differentially, in
`which event flaperons 18 act as ailerons. When used as aile
`rons, the flaperons 18 in conjunction with wings 10 impart a
`rolling 8 to fuselage 4. The flaperons 18 also may be moved in
`unison, in which event the flaperons 18 act as flaps. When
`used as flaps, flaperons 18 change the aerodynamic charac
`teristics of the wing 10 and change wing lift 16.
`0040 FIG. 3 is a rear view of the compound aircraft2. As
`shown by FIGS. 1, 2 and 3, the tail of the compound aircraft
`2 features a forward thruster 20. Forward thruster 20 is pref
`erably a ducted fan 22. Ducted fan 22 features a shroud 24.
`Shroud 24 improves safety and reduces the likelihood of
`damage to the propeller 26 resulting from contact between the
`propeller 26 and the ground.
`0041) Propeller 26 rotates about a ducted fan axis of rota
`tion 28, which is generally parallel to the forward direction 14
`of compound aircraft 2. Propeller 26 is directly connected to
`the drive system for main rotor 6, and so the speed of rotation
`of propeller 26 is directly proportional to the speed of rotation
`of main rotor 6 and is not independently controllable. The
`pitch of propeller 26 is variable, allowing adjustment of the
`amount of thrust provided by ducted fan 22.
`0042 Sectors 30, shown by FIG. 3, form an adjustable
`segmented duct to selectably change the direction of thrust of
`ducted fan 22. Sectors 30, in conjunction with rudder 32.
`serve to selectably direct the thrust of ducted fan 22 to apply
`a torque to fuselage 4 contrary to the torque applied by main
`rotor 6. FIG.3 shows the sectors 30 in a deployed position and
`ready to direct ducted fan 22 thrust to counter the torque of the
`main rotor 6.
`0043. Rudder 32 is adapted to cooperate with sectors 30 to
`control the direction of thrust of ducted fan 22. Rudder 32 is
`in the air stream of fan rotor 26 and therefore is capable of
`affecting yaw of the compound aircraft 2 at any speed.
`0044 Elevator 34 corresponds to the elevator of a fixed
`wing aircraft. Elevator 34 is in the air stream of fan rotor 26
`and is capable of affecting the pitch of the compound aircraft
`2 at any speed.
`
`B. Control System Overview
`FIG. 4 describes the operational relationship
`004.5
`between the physical components of the control system of the
`Invention. A pilot operates control inceptors 36. The control
`inceptors 36 correspond to the flight controls of a conven
`
`tional helicopter, with a collective pitch control, a cyclic pitch
`control, pedal yaw control and throttle. A person skilled at
`flying a helicopter therefore may operate the compound air
`craft 2 without simultaneously applying the skills of a fixed
`wing pilot. The control inceptors 36 are connected to a micro
`processor 38.
`0046 Sensors 40 monitor the condition of the compound
`aircraft 2 and are connected to the microprocessor 38. The
`sensors 40 may monitor compound aircraft 2 variables Such
`as airspeed, weight and balance parameters, ambient atmo
`spheric conditions, engine torque, propeller 26 torque, Verti
`cal speed, pitch rate and attitude, roll rate and attitude, and
`yaw rate.
`0047 Microprocessor 38 is operably connected to actua
`tors for each of the control effectors of the compound aircraft
`2. Those control actuators include the cyclic pitch actuator 42.
`the collective pitch actuator 44, the throttle actuator 46, the
`first and second flaperon actuators 48, 50, the elevator actua
`tor 52, the rudder actuator 54, the sector actuator 56 and the
`propeller pitch actuator 58. Each of the actuators is adapted
`by conventional means to operate its associated control effec
`tor under the command of the microprocessor 38.
`0048 Computer memory 60 is connected to microproces
`sor 38. Computer memory 60 includes a plurality of select
`able overall operational objectives for the compound aircraft
`2. Memory 60 also contains a trim schedule comprising a
`look-up database of combinations of trim control settings
`selected to achieve each of the selectable overall operational
`objectives for any given condition of the aircraft and any
`given pilot command. The microprocessor 38 consults the
`database and selects the combination of trim control settings
`applicable to the condition of the aircraft, the pilot command.
`and the selected overall operational objective. The micropro
`cessor constantly updates the selection of the combination of
`trim control settings based on feedback from the sensors
`detecting the changing aircraft conditions.
`0049. The microprocessor applies the selected combina
`tion of trim control settings for trimmed flight. “Trimmed
`flight” includes coordinated, level flight and also may include
`a steady climb or descent or a coordinated turn.
`0050. The control system 62 of the Invention uses a
`“unique trim’ concept; that is, when the pilot places the
`control inceptors in a neutral, or detent, position, the control
`system 62 of the compound aircraft 2 automatically goes to a
`trimmed flight condition. The way in which the compound
`aircraft 2 is trimmed is selected by the control system 62 of
`the Invention based upon the selected overall operational
`objective and based upon the condition of the aircraft 2 as
`detected by the sensors.
`0051. The selected combination of trim control settings
`defines the control effector positions and trimmed attitude of
`the compound aircraft 2 required to achieve the optimal trim
`to accomplish an overall operational objective. Sensors 40
`determine the deviation by the compound aircraft 2 from the
`selected combination of trim control settings. Feedback paths
`in the control system 62 can add or subtract to the effector
`positions or attitude commands. Since the compound aircraft
`2 is closed-loop stable, over time if the pilot keeps the control
`inceptors in detent, the aircraft 2 will eventually settle into a
`trimmed condition very close to the optimal trim.
`C. Control System Information Flow
`0.052 FIG. 5 provides an overview of the flow of informa
`tion through the control system 62 and the principal functions
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`US 2010/0324758 A1
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`Dec. 23, 2010
`
`of the control system 62. The control system 62 receives a
`pilot command 64. The pilot command 64 is generated by the
`control inceptors 36 of FIG. 4 and represents an instruction by
`the pilot of the compound aircraft 2. The control system 62
`also receives a variety of aircraft condition information 66.
`The aircraft condition information 66 is generated by sensors
`40 as shown by FIG. 4 and provides the microprocessor 38
`with the status of the compound aircraft 2.
`0053. The control system 62 examines the sensor infor
`mation 66 to determine the condition of the compound air
`craft 2 and to evaluate the pilot command 64 to determine how
`the condition of the aircraft will be affected by the pilot
`command 64. The control system 62 is fully authorized to
`operate all of the control effectors of the compound aircraft 2.
`The control system 62 includes Subsystems for selecting opti
`mal trim 68, speed command/speed holding 70, longitudinal/
`vertical control 72, lateral/directional control 74 and turn
`coordination 76. The control system 62 determines the appro
`priate Subsystem to apply based on the pilot command 64 and
`aircraft condition information 66 received. The control sys
`tem 62 then applies the protocols of the appropriate sub
`system to determine the appropriate aircraft control settings
`78 to accomplish the pilot command 64 and transmits those
`control settings 78 to the appropriate actuators illustrated by
`FIG. 4.
`0054 The control system 62 relies on feedback to imple
`ment the commands of the pilot and preferably will incorpo
`rate explicit model-following control architecture, as is
`known in the art. In such a system, a pilot commands that the
`compound aircraft 2 assume a selected flight condition. The
`control system 62 determines the condition of the aircraft 2
`utilizing sensors 40. The control system 62 determines the
`changes to the condition of the aircraft required to reach the
`commanded condition. The control system 62 applies an
`inverse model to determine the specific control settings 78
`required to achieve the commanded condition and applies
`those control settings 78 to the control effectors of the aircraft
`2. To compensate for disturbances and modeling or inversion
`error, the control system 62 measures the changing state of the
`aircraft 2 using the sensors 40 and feeds back the information
`to update the control settings 78 and achieve the commanded
`condition of the aircraft 2.
`0055 For a conventional helicopter without the redundant
`controls of a compound aircraft, the prior art model follow
`ing/model inversion process is straightforward. The model
`inversion determines the single combination of trim control
`settings 78 that will achieve the desired change in the state of
`the aircraft and dynamically updates that combination of trim
`control settings 78 to accommodate changing conditions and
`modeling errors.
`0056. For a compound aircraft 2 with redundant controls,
`the model inversion process is more complex. Because of the
`redundancy, many different combinations of trim control set
`tings 78 can achieve a particular change in aircraft state. For
`any particular change in aircraft state, the forces to achieve
`that change in state can be allocated among the applicable
`control effectors and the control settings adjusted accord
`ingly.
`0057 The control subsystems 68-76 illustrated by FIG. 5
`require different aircraft condition information 66 and require
`adjustment of different combinations of control actuators
`42-58, from FIG. 4.
`D. Control System Architecture
`0058. Each of the control subsystems 68-76 is discussed
`below and is illustrated in more detail by FIGS. 6-11. The
`following terms have the following meanings in FIGS. 6-11
`and in the discussion below.
`
`f, is the propeller pitch in degrees.
`6, is the collective control to the mixer in inches.
`8 is the elevator deflection in degrees.
`Ö,
`is the symmetric flaperon deflection in degrees.
`6, is the differential elevator deflection in degrees.
`Ö is the lateral control to the mixer.
`8,
`is the longitudinal control to the mixer.
`8,
`is the yaw control to the VTDP mixer.
`cp is the roll attitude in radians.
`0 is the pitch attitude in radians.
`S2 is the rotor speed in radians/second.
`T, is the yaw response time constant.
`a, is lateral acceleration in ft/ sect.
`'c' subscript means post-command filter.
`cmd. Subscript means command.
`FADEC means “Fully Automatic Digital Electronic Control.
`The FADEC controls fuel to the engine to regulate rotor
`speed.
`GW means gross weight.
`HP is the engine power in standard horsepower.
`0059. HP the power utilized by the VTDP in standard
`horsepower.
`K is the ratio of forward thrust from the rotor to one plus
`forward thrust from the propellers.
`K, is the derivative gain.
`K is the integral gain.
`K is the proportional gain.
`P, is the ambient pressure in pounds per square inch.
`P is the roll rate in radians/second.
`q is the pitch rate in radians/second.
`r is the yaw rate in radians/second.
`S is the Laplace operator.
`T, is the ambient temperature.
`T, is the vertical response time constant.
`trim subscript means optimal trim value.
`U is a pilot command that is filtered to avoid exceedence of
`operating parameters.
`V is the forward speed in knots or feet/second.
`VTDP means vectored thrust ducted propeller and is the
`ducted fan.
`V is the vertical speed feet/second. Downward is positive.
`(), is the pitch response natural frequency.
`W is the vertical body velocity in feet/second.
`X is the relationship between propeller pitch and the amount
`of thrust generated by the propellers, and varies with airspeed.
`X is the longitudinal center of gravity (CG) position.
`0060 FIG. 6 is a more detailed diagram of the overall
`control system 62 architecture. Optimum trim schedule 68 is
`a lookup database of combinations of trim control settings 78
`and provides control settings and aircraft attitude for trimmed
`flight. Optimum trim schedule 68 schedules the combinations
`of trim control settings 78 based on control inceptor input,
`aircraft condition information 66 and the selected overall
`operational objective. The aircraft condition information 66
`for the optimum trim schedule 68 may include airspeed,
`weight and balance parameters and ambient conditions. The
`output of the optimum trim Schedule 68 comprises optimum
`trim control settings 78 for all control subsystems 70-76. As
`noted, the overall operational objective is selectable and may
`include minimizing fuel consumption, minimizing fatigue
`damage or any other objective or combination of objectives.
`As shown by FIG. 6, the optimal rotor speed (S2) Selected
`by the optimal trim schedule subsystem 68 is supplied
`directly to the FADEC and determines engine power output.
`
`

`

`US 2010/0324758 A1
`
`Dec. 23, 2010
`
`0061. As shown by FIG. 6, the pilot manipulates the con
`trol inceptors 36 of cyclic pitch, collective pitch, pedal yaw
`control and throttle. The pilot command is processed and the
`relevant components, as indicate by FIG. 6, are directed to the
`subsystems of speed command/speed hold control 70, longi
`tudinal/vertical control 72, lateral/directional control 74 and
`turn coordination/yaw rate command 76. Each of the sub
`systems 70-76 also receives the trim control settings selected
`by the optimal trim schedule subsystem 68 and relevant air
`craft condition info