(12) United States Patent
`Christensen et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,682,505 B2
`Mar. 25, 2014
`
`US008682505B2
`
`(54)
`
`(71)
`
`(72)
`
`(73)
`
`(*)
`
`(21)
`(22)
`(65)
`
`(63)
`
`(51)
`
`(52)
`
`(58)
`
`FLIGHT CONTROL LAWS FOR CONSTANT
`VECTOR FLATTURNS
`
`Applicant: Bell Helicopter Textron Inc., Fort
`Worth, TX (US)
`
`Inventors:
`
`Kevin Thomas Christensen, Plano, TX
`(US); Shyhpying Jack Shue, Grapevine,
`TX (US); Troy Sheldon Caudill,
`Burleson, TX (US)
`Textron Innovations Inc., Providence,
`RI (US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`Appl. No.: 13/711,234
`
`Assignee:
`
`Notice:
`
`Filed:
`
`Dec. 11, 2012
`
`Prior Publication Data
`US 2014/OO25237 A1
`Jan. 23, 2014
`
`Related U.S. Application Data
`Continuation of application No. 13/391.522, filed as
`application No. PCT/US2011/030498 on Mar. 30,
`2011, now Pat. No. 8,332,082.
`
`(2006.01)
`(2006.01)
`(2006.01)
`
`Int. C.
`G05D I/08
`B64C 9/00
`GO6F 7/OO
`U.S. C.
`USPC ........................ 701/3: 701/4; 701/7; 24.4/180
`Field of Classification Search
`USPC ................ 701/7, 3, 4, 14, 301: 244/180, 181;
`340/979
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,027,999 A * 6/1977 Durno ............................. 416/40
`2003. O191561 A1 10, 2003 VOS
`2008/0097.658 A1* 4/2008 Shue et al. ........................ TO1/8
`2008/0234881 A1* 9/2008 Cherepinsky et al. .
`7O 1/7
`2010/0324758 A1* 12/2010 Piasecki et al. ................... TO1/3
`
`FOREIGN PATENT DOCUMENTS
`
`WO
`
`2, 2007
`2007O18572 A2
`OTHER PUBLICATIONS
`
`International Search Report and the Written Opinion of the Interna
`tional Searching Authority mailed by ISA/USA, U.S. Patent and
`Trademark Office on Aug. 26, 2011 for corresponding International
`Patent Application No. PCT/US2011/030498, 7 pages.
`Notice of Allowance dated Aug. 8, 2012 from counterpart U.S. Appl.
`No. 13/391,522.
`
`* cited by examiner
`Primary Examiner — Tan Q Nguyen
`(74) Attorney, Agent, or Firm — James E. Walton; Richard
`G. Eldredge
`ABSTRACT
`(57)
`An aircraft and method to control flat yawing turns of the
`aircraft while maintaining a constant vector heading across a
`ground Surface. The aircraft includes a control system in data
`communication with a model, a lateral control architecture, a
`longitudinal control architecture, and an initialization com
`mand logic. The model decouples the directional movement
`of the aircraft into a lateral equation of motion and a longitu
`dinal equation of motion. The lateral control architecture
`utilizes the lateral equation of motion to control the aircraft in
`the lateral direction, while the longitudinal control architec
`ture utilizes the longitudinal equation of motion to control the
`aircraft in the longitudinal direction. The initialization com
`mand logic selectively activates the lateral control architec
`ture and the longitudinal control architecture.
`20 Claims, 9 Drawing Sheets
`
`901
`
`Dir Controller Out of Detent
`CWFTSet Logic
`
`OTLong SPD ON,
`ORNOT Lat SPDON
`CWFT ResetLogic
`
`Long Accel < Threshold
`Long SPDON
`Set Logic
`
`Long Controller Out of Detent
`Long SPD ON
`Reset Logic
`
`Lataccel < Threshold
`Long SPD ON
`SetLogic
`Lat Controllet Out of Detent
`ORBank TurnON,
`ORCrab ON,
`ORFwd. SPD. Threshold
`Lat SPD ON
`ResetLogic
`
`93
`
`
`
`911
`
`Long SPD ON
`
`Latch
`
`g05
`
`909
`
`Lat SPDON
`
`
`
`907
`
`DJI-1001
`IPR2023-01104
`
`

`

`U.S. Patent
`
`Mar. 25, 2014
`
`Sheet 1 of 9
`
`US 8,682,505 B2
`
`7
`
`8
`
`
`
`%
`
`
`
`s
`
`
`
`Z
`
`
`
`3.
`
`R
`
`
`
`2
`
`
`
`t
`
`: W.
`
`K Nx& -
`
`
`
`-
`
`5. NN
`it is
`SX21 X&
`
`3 :
`
`s
`
`S
`
`v
`
`S S
`
`or
`
`S S 3
`
`s
`
`:
`
`33
`
`

`

`U.S. Patent
`
`Mar. 25, 2014
`
`Sheet 2 of 9
`
`US 8,682,505 B2
`
`Step 1: FWD Flight
`2O1
`
`O
`
`10< V<35
`2O3
`
`Forward Flight <35 knots
`
`90
`
`D1
`
`
`
`Step 3: Pedal Turn
`
`R1
`
`90° turn to left sideward flight
`
`9 of
`
`Flight path vector constant
`D1
`
`l/ turn to rearward flight
`R1
`
`Flight path vector constant
`
`201
`
`
`
`Step 5: Pedal Turn
`
`R1
`
`90° turn to right sideward flight
`
`Flight path vector constant
`
`90° turn back to forward flight
`
`D1 Flight path vector constant
`
`F.G. 2
`
`

`

`U.S. Patent
`U.S. Patent
`
`Mar. 25, 2014
`Mar.25, 2014
`
`Sheet 3 of 9
`Sheet 3 of 9
`
`US 8,682,505 B2
`US 8,682,505 B2
`
`
`
`
`
`Lf 305
`
`
`
`Ljui.jw0i190|ii=jo||j
`aOLLtLlwowore°i)“aaii||
`Lgeld2---/f---19°°+[+++
`
`LdQ@__.2°9oF,ooP_m
`
`
`
`
`
`
`(Bap)Buipeay(Bep)49223puns()peedspunoidpuevepig
`
`fd—hot+o°°22oowoNoO—
`!||wf-two90|||
`eeePuieJoto.NoNNNoO®2|@
` _9__910+i+¥
`fo|_jo°__./._fle===
`lolo'oofa78Alar
`
`
`
`
`(p))peedspuncig(p)peedspunasrspuewe_
`
`
`
`
`
`
`
`
`
`FIG. 3
`FIG. 3
`
`
`

`

`U.S. Patent
`
`Mar. 25, 2014
`
`Sheet 4 of 9
`
`US 8,682,505 B2
`
`Step 1: Hover
`
`Step 2: Right lateral stick to
`generate left sideward flight
`
`Step 3: Right 90° pedal turn
`
`
`
`V, & O
`-
`Sideward flight changes to
`forward flight
`
`Sideward flight <35 knots
`
`Note:
`V - forward groundspeed
`W = sideward groundspeed
`
`FIG. 4
`
`Step 1: Hover
`
`
`
`Step 2: Forward longitudinal
`Stick to generate forward
`
`Note:
`V. F forward groundspeed
`V = sideward groundspeed
`
`Forward flight changes to
`sideward flight
`
`FIG. 5
`
`

`

`U.S. Patent
`
`Mar.25, 2014
`
`Sheet 5 of 9
`
`US 8,682,505 B2
`
`ALVYsu0T
`
`609
`
`209
`
`GLO
`
`a]|
`
`gBu07]
`
`S09
`
`
`
`uonezTena]
`
`o180'T
`
`LL9
`
`Jeulpnyisu0'7]
`
`Spueuruuo’)
`
`EL9
`
`€09
`
`\sec
`
`
`
`
`
`

`

`U.S. Patent
`
`Mar. 25, 2014
`
`Sheet 6 of 9
`
`US 8,682,505 B2
`
`
`
`
`
`
`
`94,9
`
`
`
`| GVHOTTET DE
`
`spuetuuuooZ0/
`
`| 1,9
`
`

`

`U.S. Patent
`U.S. Patent
`
`Mar.25, 2014
`
`Sheet 7 of 9
`
`US 8,682,505 B2
`US 8,682,505 B2
`
`
`
`
`
`£08208ee—
`
`BUOTIOOI
`
`ALVaHd
`
`spueuruio’)
`
`€L9
`
`
`beaniedHId|,"S08
`
` BOTPFuoreZterty]
`
`e09
`
`LL9
`
`YLee
`
`GLO
`
`8‘Old
`
`
`
`
`

`

`U.S. Patent
`
`Mar. 25, 2014
`
`Sheet 8 of 9
`
`US 8,682,505 B2
`
`901 l,
`
`Dir Controller Out of Detent L
`CVFT Set Logic
`
`NOT Long SPD ON
`OR NOT Lat SPD ON
`CVFT Reset Logic
`
`
`
`
`
`Long Accel < Threshold
`Long SPD ON
`Set Logic
`
`Tong Controller Out of Detent -
`Long SPD ON
`Reset Logic
`
`
`
`Lat Accel < Threshold
`Long SPD ON
`Set Logic
`Lat Controller Out of Detent,
`OR Bank Turn ON,
`OR Crab ON,
`OR Fwd SPD > Threshold
`Lat SPD ON
`Reset Logic
`
`
`
`
`
`
`
`CVFT ON
`
`911
`
`Long SPD ON
`
`903
`
`
`
`Latch
`
`905
`
`909
`
`Lat SPD ON
`
`907
`
`F.G. 9
`
`

`

`U.S. Patent
`
`Mar. 25, 2014
`
`Sheet 9 Of 9
`
`US 8,682,505 B2
`
`1001 ,
`
`Initial States
`
`Lateral = In Detent
`
`Longitudinal - In Detent
`
`Directional F Out of Detent
`
`
`
`Long SPD re-initialized
`Constant vector held
`
`Dir RATE
`Rate Command turn
`
`Lat SPD re-initialized
`Constant vector held
`
`707
`
`805
`
`Pedal in Detent
`Dir HDG re-initialized
`When pedal stops,
`If crab angle = 0°, then pure forward flight
`If crab angle = 90°, then pure right sideward flight
`If crab angle - 180°, then pure aft flight
`If crab angle - 270, then pure left sideward flight
`
`FIG. 10
`
`

`

`1.
`FLIGHT CONTROL LAWS FOR CONSTANT
`VECTOR FLATTURNS
`
`US 8,682,505 B2
`
`BACKGROUND
`
`10
`
`15
`
`25
`
`30
`
`35
`
`1. Field of the Invention
`The present invention relates generally to flight control
`systems, and more particularly, to a flight control system
`having flight control laws which enable precise aircraft
`maneuvering relative to the ground.
`2. Description of Related Art
`Aircraft which can hover and fly at low speeds include
`rotorcraft, Such as helicopters and tilt rotors, and jump jets,
`like the AV-8B Harrier and F-35B Lightning II. These aircraft
`can spend a large portion of their mission maneuvering rela
`tive to the ground. Sometimes, this maneuvering must be
`conducted in confined spaces around external hazards such as
`buildings, trees, towers, and power lines.
`For traditional flight control systems, ground-referenced
`maneuvering (GRM) requires the pilot to make constant con
`trol inputs in multiple axes in order to counter disturbances
`caused by wind, as well as to remove the natural coupled
`response of the aircraft. The pilot workload during such
`maneuvers can become quite high since the pilot must sense
`un-commanded aircraft motions and then put in the appropri
`ate control input to eliminate the disturbance. In a worst-case
`scenario, a pilot might be required to fly GRM in a degraded
`visual environment. With the lack of visual cues to detect
`off-axis motion, the pilot might accidentally fly into an exter
`nal hazard while maneuvering in a confined space.
`Traditional flight control law designs do not provide the
`pilot with an easy way to control aircraft crab angle during
`GRM. Crab angle is defined as the angle between the air
`craft's heading and its actual ground path. With these prior
`designs, adjusting crab angle while maintaining groundtrack
`took considerable pilot concentration, since the pilot had to
`coordinate inputs to both the lateral and directional control
`lers.
`Although pilots generally seek to minimize crab angle
`during GRM, some mission tasks may call for flat yawing
`turns while maintaining a constant vector across the ground.
`For example, on a steep approach, the pilot may need to fly
`with a crab angle so he or she can see the landing Zone.
`45
`Additionally, the pilot may want to quickly transition out of
`rearward or sideward flight while continuing along the same
`groundtrack. In a final example, the pilot may want to acquire
`and track a point on the ground without having to fly directly
`towards it. With prior flight control designs, such maneuvers
`required extraordinary pilot skill to coordinate the aircraft's
`motions in multiple control axes.
`Although the foregoing developments represent great
`strides in the area of flight control laws, many shortcomings
`remain.
`
`40
`
`50
`
`55
`
`DESCRIPTION OF THE DRAWINGS
`
`The novel features believed characteristic of the embodi
`ments of the present application are set forth in the appended
`claims. However, the embodiments themselves, as well as a
`preferred mode of use, and further objectives and advantages
`thereof, will best be understood by reference to the following
`detailed description when read in conjunction with the
`accompanying drawings, wherein:
`FIG. 1 is a flight envelope with control law modes designed
`to enable ground reference maneuvers;
`
`60
`
`65
`
`2
`FIG. 2 is a schematic of an aircraft utilizing a control
`system according to the preferred embodiment of the present
`invention;
`FIG. 3 is a set of plots comprising measured flight data of
`the aircraft of FIG. 2 while performing constant vector flat
`turns;
`FIG. 4 is a schematic view of the aircraft of FIG.2changing
`flight heading from sideward flight to forward flight;
`FIG.5 is a schematic view of the aircraft of FIG.2changing
`flight heading from forward flight to sideward flight;
`FIG. 6 is a schematic view of the control system architec
`ture for a set of longitudinal control laws;
`FIG. 7 is a schematic view of the control system architec
`ture for a set of lateral control laws;
`FIG. 8 is a schematic view of the control system architec
`ture for directional control laws;
`FIG. 9 is a schematic view of the control law logic for the
`control system; and
`FIG.10 is a schematic view a control law flow chart for the
`control system.
`While the control system of the present application is sus
`ceptible to various modifications and alternative forms, spe
`cific embodiments thereof have been shown by way of
`example in the drawings and are herein described in detail. It
`should be understood, however, that the description herein of
`specific embodiments is not intended to limit the invention to
`the particular embodiment disclosed, but on the contrary, the
`intention is to cover all modifications, equivalents, and alter
`natives falling within the spirit and scope of the process of the
`present application as defined by the appended claims.
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`Illustrative embodiments of the system and method are
`provided below. It will of course be appreciated that in the
`development of any actual embodiment, numerous imple
`mentation-specific decisions will be made to achieve the
`developer's specific goals, such as compliance with system
`related and business-related constraints, which will vary from
`one implementation to another. Moreover, it will be appreci
`ated that such a development effort might be complex and
`time-consuming, but would nevertheless be a routine under
`taking for those of ordinary skill in the art having the benefit
`of this disclosure.
`This invention will enable seamless and transient free
`GRM. More specifically this invention will enable a pilot to
`use the directional controller to command flatyawing turns at
`low groundspeeds, while maintaining a constant vector
`across the ground. The seamless integration of this design
`requires no manual cockpit Switches to select a Constant
`Vector Flat Turn (CVFT) mode. Instead, the control laws will
`automatically adjust pitch and roll attitude to keep the aircraft
`moving in the same directionata constant speed whenever the
`pilot inputs a directional command at low speed.
`The control system of the present application enables
`seamless and transient free GRM without the need for manual
`cockpit switches. The control system utilizes relative ground
`speed difference to automatically control pitch and roll atti
`tudes so that the aircraft will maintain a constant vector dur
`ing a low speed flat turn. The control system also allows the
`pilot to complete a CVFT with minimal workload since the
`ground vector will automatically be maintained by the control
`laws without the pilot having to use cockpit switches to
`change modes.
`Referring now to the drawings, FIG. 1 shows a represen
`tative flight envelope 101 with a plurality of control law
`
`

`

`US 8,682,505 B2
`
`5
`
`10
`
`15
`
`25
`
`3
`modes designed to enable GRM. Flight envelope 101 com
`prises a region 103 depicting the CVFT region, wherein the
`CVFT region is preferably from 10 to 35 knots groundspeed
`in any direction relative to the aircraft's body axis. The lower
`bound of region 103 is set by the Hover Hold and Transla
`tional Rate Command (TRC) region 105. The upper bound of
`region 103 is set by the aircraft's sideward and rearward flight
`airspeed limits.
`FIG. 2 is a schematic of an aircraft 201 utilizing a control
`system according to the preferred embodiment of the present
`invention. FIG. 2 shows aircraft 201 in forward flight within
`region 103. Directional inputs turn aircraft 201 in a complete
`360 degree yaw movement R1, stopping every 90 degrees,
`and without changing the speed and flight heading of aircraft
`201, as represented with arrow D1. In the preferred embodi
`ment, the control system is utilized with rotary aircraft, i.e., a
`helicopter; however, it should be appreciated that the control
`system is easily and readily adaptable with control systems of
`different types of aircraft, both manned and unmanned.
`FIG.2 depicts aircraft 201traveling between 10 to 35 knots
`in a forward direction. As is shown, aircraft 201 preferably
`turns in a yaw direction R1 at approximately 90 degrees
`relative to direction D1. Aircraft 201 continues to turn in
`direction R1 while maintaining a constant flight heading. It
`should be appreciated that the preferred control system is
`adapted to turn aircraft 201 at 90 degrees during each appli
`cation; however, it should be appreciated that alternative
`embodiments could easily include a control system adapted
`to turn the aircraft at differentangles, e.g., at 30 degrees in lieu
`of or in addition to 90 degrees. It should also be understood
`that although shown turning in a clockwise direction, the
`control system can also turn the aircraft in a counterclockwise
`moVement.
`FIG. 2 provides an exemplary depiction of aircraft 201
`turning 360 degrees while maintaining forward flight. Step 1
`shows aircraft 201 traveling in a constant forward flight, as
`depicted with arrow D1, between 10 and 35 knots. Step 2
`depicts application of the control system, namely, the pilot
`utilizes the control system to rotate aircraft 201 in the clock
`wise direction approximately 90 degrees, as indicated by
`arrow R1. Step 2 shows aircraft 201 traveling inforward flight
`while the fuselage faces 90 degrees relative to the directional
`movement. Steps 3-5 provide further illustration of the pro
`cess being repeated. In particular, each time the control sys
`tem is utilized, aircraft 201 rotates 90 degrees while main
`taining a constant forward heading.
`Referring now to FIG. 3 in the drawings, measured flight
`data 301 of aircraft 201 is shown during a 360 degree CVFT.
`A plot 303 provides measured data representing the turning
`movement R1 of aircraft 201 during the 360 degree turn. A
`50
`plot 305 provides measured data representing the ground
`speed of aircraft 201 during the 360 degree turn. Plot 305
`shows aircraft 201 initially starting at 20 knots forward
`groundspeed during the entire 360 degree CVFT. Plot 305
`shows that aircraft 201 holds a relatively steady groundspeed
`during the 360 degree CVFT. A plot 307 provides measured
`data representing the ground track of aircraft 201 during the
`360 degree CVFT. The forward groundspeed plotted on a plot
`309 essentially depicts a cosine curve during the turn, while
`the sideward groundspeed plotted on a plot 311 shows a sine
`CUV.
`Referring now to FIG. 4 in the drawings, a schematic view
`of aircraft 201 is shown changing flight heading from
`sideward flight to forward flight. In the exemplary embodi
`ment, the CVFT control system is utilized such that aircraft
`201 changes heading from a forward groundspeed VX of
`about 0 knots and a sideward groundspeed between 10-35
`
`30
`
`4
`knots to a forward groundspeed between 10-35 knots and a
`sideward groundspeed about 0knots. Step 1 of FIG. 4 shows
`aircraft 401 during hover, while a step 2 shows aircraft 401
`traveling in a sideward groundspeed between 10-35 knots, as
`depicted with arrow D2. In step 2, a right lateral control stick
`(not shown) is utilized to generate a left sideward heading.
`Thereafter, a right 90 degree petal turn is applied to rotate
`aircraft 201 in a forward heading with a petal 203. In the
`preferred embodiment, petal 203 is a petal manipulated with
`the pilots foot; however, it should be appreciated that other
`forms of devices, i.e., a hand Switch could be utilized in lieu of
`or in addition to petal 203. For purposes of this invention, a
`lateral controller, longitudinal controller, and directional con
`troller are characterized as petal 203 or similarly suited
`devices. Step 3 depicts application of the CVFT control sys
`tem, wherein aircraft 201 turns 90 degrees for changing the
`heading of aircraft 201.
`Referring now to FIG. 5 in the drawings, an alternative
`application of the CVFT control system is shown. In the
`exemplary embodiment, the CVFT control system is utilized
`to turn aircraft 201 from a forward groundspeed Vx between
`10-35 knots and a sideward groundspeed of about 0 knots to
`a sideward groundspeed between 10-35 knots and a forward
`groundspeed about 0knots. Step 1 shows aircraft 201 during
`hover, while a step 2 shows aircraft 201 traveling in a forward
`heading having a groundspeed between 10-35 knots, as
`depicted with arrow D3. In step 2, a forward longitudinal stick
`is utilized to generate forward flight. Thereafter, a left 90
`degree petal turn is applied to rotate aircraft 201 such that the
`forward flight of aircraft 201 changes to a sideward flight
`heading.
`Those skilled in the art will understand that the methods for
`aircraft guidance disclosed in this invention can be applied to
`any combination of the following: (1) full authority fly-by
`wire flight control systems, as well as partial authority
`mechanical systems; (2) traditional cockpit layouts with a
`center Stick for longitudinal and lateral control, pedals for
`directional control, and a collective stick for vertical control,
`as well as more advanced designs which combine multiple
`control axes into a center or side Stick controller, and, (3) any
`aircraft capable of GRM, including both rotorcraft and jump
`jets.
`The key to enabling seamless and transient free GRM lies
`in the advanced control law architecture of the CVFT control
`system as shown in FIGS. 6 to 8. FIG. 6 shows architecture
`601 of the CVFT control system operably associated with one
`or more longitudinal control laws, FIG. 7 shows architecture
`701 of the CVFT control system operably associated with one
`or more lateral control laws, and FIG. 8 shows architecture
`801 of the CVFT control system operably associated with one
`or more directional control laws according to the preferred
`embodiment of the invention.
`Referring now to FIG. 6 in the drawings, architecture 601
`includes one or more aircraft sensors 603 operably associated
`with the control laws to accomplish GRM. Aircraft sensors
`603 can include: an inertial Navigation System (attitudes,
`attitude rates, and translational accelerations); a Global Posi
`tioning System (ground-referenced speeds and positions); an
`Air Data Computer (airspeed and barometric altitude); and, a
`Radar or Laser Altimeter (above ground level (AGL) alti
`tude). An aircraft model can be obtained from aerodynamics
`data and a group of linear models can be developed based on
`its airspeed form aircraft sensors 603. These linear models
`include both lateral and longitudinal equations of motion.
`Since the aircraft model matrices are large and contain cou
`pling terms of lateral and longitudinal motions within the
`matrices, it is difficult to determine the best performance
`
`35
`
`40
`
`45
`
`55
`
`60
`
`65
`
`

`

`5
`control gains for all at the same time. In order to overcome
`these issues, the linear model of aircraft performance is
`decoupled first. After the aircraft model is decoupled to lateral
`and longitudinal equations of motion, the effect of coupling
`terms between lateral and longitudinal motions can be
`reduced to minimum, thus stabilizing the system.
`In the preferred embodiment, architecture 601 preferably
`comprises of a longitudinal control law for forward speed,
`represented as block 605“Long SPD'; alongitudinal control
`law for pitch angle, represented as block 607 “Long ATT':
`and, a longitudinal control law for pitch rate, represented as
`block 609 “Long RATE. Architecture 601 is further pro
`vided with initialization logic 611 adapted for determining
`which loop is active in each axis based on flight conditions
`and pilot control inputs. Logic 611 will also re-initializes
`inactive loops in order to eliminate control jumps when
`Switching between the loops to provide seamless and tran
`sient free mode changes.
`Architecture 601 further includes a longitudinal command
`613 generated in the control laws by referencing the pilots
`cockpit control input in each axis. The input to the control
`laws is the difference between the controller's present posi
`tion and the centered, no force position, which is also referred
`to as the “detent position. The control commands can also be
`25
`generated by a beep Switch located in the cockpit to command
`Small and precise changes in aircraft state. The control laws
`process these control inputs to generate the appropriate air
`craft response commands. These commands are then sent out
`to the control law guidance blocks to maneuver the aircraft.
`The control law outputs are routed to an actuator 615 for each
`dynamic axis. For a conventional helicopter, the control laws
`send control signals to the following actuators: longitudinal
`axis—main rotor longitudinal Swashplate angle; lateral
`axis—main rotor lateral Swashplate angle; vertical axis—
`main rotor collective pitch; and, directional axis—tail rotor
`collective pitch.
`Since pitch rate is the fastest longitudinal State, Long
`RATE 609 is the inner loop of the longitudinal control laws.
`Next, the Long ATT 607 loop feeds the Long RATE control
`law 609 loop to control pitch attitude. Finally, the Long SPD
`control law 605 loop feeds the Long ATT 607 loop to control
`forward speed.
`When flying with the longitudinal controller in detent out
`side of the Hover Hold/TRC region 105, depicted in FIG. 1,
`the Long SPD 605 loop will be active. At lower speeds, this
`loop will hold constant forward groundspeed, while at higher
`speeds, airspeed will be held. Once the pilot moves the lon
`gitudinal controller out of detent, the control laws can com
`50
`mand either pitch attitude (Long ATT 607) or pitch rate
`(Long RATE 609).
`Referring now to FIG. 7 in the drawings, architecture 701
`comprises one or more lateral control laws operably associ
`ated with sensors 603, logic 611, lateral commands 702, and
`actuators 615. The lateral control laws include: a lateral con
`trol of roll rate, represented as block 703 “Lat RATE"; a
`lateral control of the roll attitude, represented as block 705
`“Lat ATT'; a lateral control of sideward groundspeed, rep
`resented as block 707 “Lat SPD': a lateral control of the crab
`angle, represented as block 709 “Lat CRAB'; and, lateral
`control of heading, represented as block 711 "Lat HDG'.
`Similar to the longitudinal axis, Lat RATE 703 is the inner
`loop of the lateral control laws and the Lat ATT 705 loop
`feeds the Lat RATE 703 loop to control roll attitude. The
`Lat ATT 705 loop can be fed by one of three loops, Lat SPD
`707, Lat CRAB 709, or Lat HDG 711.
`
`6
`The crab angle used in the Lat CRAB 709 loop is com
`puted in the control laws using the following equation:
`
`V
`
`n=tan ()
`
`(1)
`
`where m is the crab angle, V is the sideward groundspeed
`with right positive, and V is the forward groundspeed. To
`avoid a singularity in Equation 1, V is limited to be above the
`Hover Hold/TRC region 103.
`When operating in the Ground-Coordinated Banked Turn
`(GCBT) envelope as shown by region 107 in FIG. 1, if both
`the lateral and directional controllers are in detent, lateral
`control law logic will hold crab angle through the Lat CRAB
`709 loop. If operating in the CVFT envelope, but not in the
`GCBT envelope, and the lateral and directional controllers
`are in detent, the control logic will hold sideward ground
`speed constant with the Lat SPD 707 loop. When operating
`at higher airspeeds with lateral and directional controllers in
`detent, the control logic will hold heading constant with the
`Lat HDG 711 loop. When the pilot moves the lateral control
`ler out of detent in any of these cases, the control laws can
`command either roll attitude (Lat. ATT 705) or roll rate (Lat.
`RATE 703).
`Referring now to FIG. 8 in the drawings, architecture 801
`comprises one or more directional control laws operably
`associated with sensors 603, logic 611, commands 613, and
`actuators 615. The directional control laws include: direc
`tional control of yaw rate, represented as block 803
`“Dir RATE'; directional control of heading, represented as
`block 805 “Dir HDG'; and, directional turn coordination,
`represented as block 807 “Dir TC”
`Since yaw rate is the fastest directional state, Dir RATE
`803 is the inner loop of the directional control laws. This loop
`is fed by the Dir HDG 805 loop to control aircraft heading at
`lower speeds. Unlike traditional control law designs, this
`invention includes an additional loop, parallel to the
`Dir HDG 805 loop, to feed the Dir RATE 803 inner loop.
`The Dir TC 807 loop is used to coordinate banked turns
`throughout the flight envelope.
`In the GCBT envelope 107 shown in FIG. 1, the Dir TC
`807 loop will control crab angle during banked turns. With no
`directional input, the Dir TC 807 loop will hold crab angle at
`Zero. Any directional control inputs during a GCBT will
`result in a change in crab angle in the appropriate direction.
`Additionally, if the aircraft is in the GCBT envelope, but
`above the CVFT envelope, directional controller inputs will
`command changes in crab angle through the Dir TC 807 loop
`even in non-turning flight. In this case, once the directional
`controller is returned to detent, heading hold will be re-en
`gaged (Dir HDG 805 loop) and the crab angle will be held
`though the Lat CRAB 709 loop.
`When in the BCBT envelope, the Dir TC 807 loop will
`automatically adjust yaw rate based on actual bank angle, true
`airspeed, and lateral acceleration in order to keep the slip ball
`centered. Any directional controller inputs in the BCBT enve
`lope will command a change in lateral acceleration, which
`will Subsequently result in sideslip away from the pedal input.
`Pedal inputs will also result in a slight roll in the direction of
`the input to provide lateral stability.
`In the absence of lateral or directional control inputs while
`operating in either the GCBT or CVFT envelopes, the direc
`tional axis will hold heading through the Dir HDG 805 loop.
`If the pilot moves the directional controller out of detent in the
`CVFT envelope with both the lateral and longitudinal con
`
`US 8,682,505 B2
`
`10
`
`15
`
`30
`
`35
`
`40
`
`45
`
`55
`
`60
`
`65
`
`

`

`US 8,682,505 B2
`
`7
`trollers in detent, the directional control laws will commanda
`yaw rate through the Dir RATE 803 loop. In this case, the
`control laws will maintain a constant ground vector by using
`the Long SPD 605 and Lat SPD 707 loops.
`During the CVFT, when the directional controller is first
`moved out of detent, the control laws will capture the air
`craft's current groundspeed in the earth axis coordinate sys
`tem. The control laws keep track of the difference between the
`aircraft's actual groundspeed and the captured groundspeed.
`This relative groundspeed difference is converted from the
`earth axis to the aircraft's body axis using the following
`equations:
`
`AVAV'cos +AV'sin
`
`(2)
`
`8
`The particular embodiments disclosed above are illustra
`tive only, as the invention may be modified and practiced in
`different but equivalent manners apparent to those skilled in
`the art having the benefit of the teachings herein. It is there
`fore evident that the particular embodiments disclosed above
`may be altered or modified, and all such variations are con
`sidered within the scope and spirit of the invention. Accord
`ingly, the protection sought herein is as set forth in the
`description. It is apparent that an invention with significant
`advantages has been described and illustrated. Although the
`present invention is shown in a limited number of forms, it is
`not limited to just these forms, but is amenable to various
`changes and modifications without departing from the spirit
`thereof.
`
`What is claimed is:
`1. A control system for an aircraft, comprising:
`a lateral control architecture configured to control lateral
`motion of the aircraft; and
`a longitudinal control architecture configured to control
`longitudinal motion of the aircraft;
`wherein the control system utilizes the lateral control
`architecture and the longitudinal control architecture to
`control yaw movement of the aircraft while the aircraft
`maintains a constant vector heading across a ground
`Surface; and
`wherein the aircraft continuously moves in a yaw direction
`while maintaining the constant vector heading.
`2. The control system of claim 1, wherein the control
`system is operably associated with a directional controller
`manually manipulated by a pilot.
`3. The control system of claim 2, further comprising:
`a directional control architecture, having:
`a directional heading control loop;
`a directional turn coordination control loop; and
`a directional yaw rate control loop.
`4. The control system of claim 3, further comprising:
`a directional control latch in data communication with the
`directional control architecture;
`wherein, as the directional controller is moved out of a
`detent position, the directional control latch activates a
`constant vector flat turn motion.
`5. The control system of claim 1, the lateral control archi
`tecture comprising:
`a lateral sideward groundspeed control loop;
`a lateral roll attitude control loop; and
`a lateral roll rate control loop.
`6. The control system of claim 5, further comprising:
`a lateral controller carried by the aircraft, the lateral con
`troller being manipulated by a pilot controlling the air
`craft, the lateral controller creating a lateral command in
`data communication with the lateral sideward ground
`speed control loop, the lateral roll attitude control loop,
`and the lateral roll rate control loop.
`7. The control system of claim 6, further comprising:
`a lateral control hatch in data communication with the
`control system;
`wherein, as the lateral controller is moved out of a detent
`position, the lateral control latch resets a lateral speed
`hold.
`8. The control system of claim 1, the longitudinal control
`architecture comprising:
`a long