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Chapter 4

Method

4.1 Overview

An autopilot system is to be implemented in a Flight Simulator environmentby software. The project methodology is divided into three major stages:

1. First all specifications are collected. The system should behave as anAPS implemented in a real aircraft.

2. Secondly a general design is to be made. It should be independent fromsource code and must cover all specifications first collected.

3. Finally, the application is to be created following the design previouslymade.

4.2 Specifications

This APS is built following the Operator’s Guide [2] and the Technical De-scription paper [3] provided by the manufacturer. A diagram of the systemis shown in figure 4.1.

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Figure 4.1: Flight Guidance System Diagram

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4.2.1 Autopilot System Overview

The Autopilot System is an integrated flight director, autopilot, and yawdamper.The installation includes dual flight directors, a 2-axis autopilot, yawdamper, and automatic pitch trim control. All computations are performedby a pair of flight guidance computers.

The flight guidance computers (FGCs) compute pitch and roll commandsthat can be coupled to the autopilot and flight director steering commandsthat show on the PFDs. The pitch and roll commands are based on thecurrently active modes. Steering commands show on a portion of the PFDreferred to as the flight director. Mode messages show on the PFD if theautopilot is engaged or if the onside flight director is on. Two channels offlight guidance are provided.

The primary controls for the flight guidance system are on the MSP-85Mode Select Panel(s) and APP-85 Autopilot Panel. Other panels locatedelse where on the flight deck accommodate the Course, Heading, and AltitudePreselect functions.

The MSP contains the lateral and vertical mode select buttons.Roundindicator lights are located in the center of each button.

The APP contains the roll knob and the VS/Airspeed/pitch wheel, au-topilot TURB mode and transfer (APXFR) buttons, and autopilot and yawdamper engage switches. All panel legends and arrows are illuminated.Round indicator lights are located in the center of each button.

Additional controls consist of yoke-mounted buttons for AP synchroniza-tion ("‘AP-SYNC"’) and autopilot disengage, and one throttle-mounted GoAround ("‘GA"’) button.

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Figure 4.2: Course Heading Panel

Figure 4.3: Copilotťs course knob

Figure 4.4: Mode Select Panel

Figure 4.5: Autopilot Panel

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Figure 4.6: Flight Directorťs steering commands

4.2.2 Flight Director

( ) The flight directors are the visual lateral and vertical steering commandspresented for the pilot on the PFD and the text messages representing theselected modes. The mode messages show in lateral and vertical fields abovethe attitude display. If the flight directors are turned on using the onside FDbutton, the active modes are basic Roll and Pitch. If the offside is turnedoff then back on using the offside FD button, the currently active modes areretained.

The flight director turns on at the occurrence of:

- Selection of a lateral or vertical mode and the autopilot is not engaged.

- Engaging the autopilot.

- Activation of Go Around or Overspeed modes.

- The pushing of the FD button.

If only the offside flight director is off, the offside flight director turns onat the occurrence of:

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- Pushing the offside FD button.

- Selecting the offside as onside by pushing the AP XFR button.

The flight director is turned off when the FD button on the MSP is pushed(except whenever Overspeed mode is active). If the FD button is pushedwhile the autopilot is engaged, only the steering commands are turned off,and the active/armed mode messages are not removed.

When both flight directors are on and the autopilot is not engaged, pushingthe onside FD button turns off steering commands but the mode messageremains. When one flight director is on and the autopilot is not engaged,pushing the onside FD button turns off the flight director, turns off thesteering commands and removes both onside and offside mode messages.

4.2.3 Flight Guidance Transfer

The Autopilot Panel XFR button controls which flight guidance channel,left or right, supplies commands to the autopilot. Except for Go Around andApproach modes, where guidance is independent, the AP XFR button alsocontrols which channel supplies steering commands to the PFDs. When theright (copilotŠs side) guidance is selected, the FGS is considered transferred.

Transfer is selected by pushing the XFR button on the APP. Selectionof transfer selects Pitch and Roll modes. Transfer is deselected by pushingthe XFR button on the APP. Deselection of transfer selects Pitch and Rollmodes.

If transfer is selected, the copilotŠs side flight guidance supplies commandsto the autopilot. If Transfer is not selected, the pilotŠs side flight guidancesupplies commands to the autopilot.

If the flight directors are dependent and transfer is selected, the copilotŠsside flight guidance supplies steering commands to both PFDs. If the flightdirectors are dependent and transfer is not selected, the pilotŠs side flightguidance supplies steering commands to both PFDs.

4.2.4 Autopilot

The autopilot is engaged by lifting the AP ENG lever on the APP. Uponengagement the autopilot couples the selected guidance commands (pilotŠs

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side or copilotŠs side) to the elevator and aileron servos and engages theservo clutches. Engagement turns on the flight directors if they are off.Flight guidance remains in the currently active modes, unless the modes arelateral and vertical Go Around which are cleared by engagement. Activemode references are synchronized by engagement.

The message "‘AP"’ shows in green on the PFD when the autopilot isengaged. "‘AP"’ shows in flashing red to indicate an autopilot disengage.

The autopilot is manually disengaged by any of the following actions:

- Pushing either of the AP disconnect buttons.

- Lowering the AP ENG lever.

- Pushing the Go Around button.

- Pushing either manual pitch trim switch.

The autopilot is automatically disengaged by any of the following condi-tions:

1. Disengagement of the yaw damper.

2. An internal autopilot failure is detected.

3. The stick shaker activates.

4. An excessive attitude exists. Excessive attitude is defined as a pitchangle greater than 25ř nose up or 15ř nose down, or roll angle beyond45ř, or a combination of excessive pitch and roll.

4.2.5 Turbulence Mode

Turbulence mode provides lateral and vertical motion damping to the au-topilot to maintain steady flight in turbulence conditions. Turbulence modeis selected by pushing the turbulence (TURB) button on the APP.

Turbulence mode cannot be selected if the onside localizer is captured orthe autopilot is disengaged. Turbulence mode is manually cleared by eitherpushing the TURB button on the APP, an onside localizer capture, or byautopilot disengagement. The light in the center of the TURB button on theAPP comes on to indicate turbulence mode is active.

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4.2.6 Yaw Damper

The yaw damper provides damping of the aircraftŠs inherent Dutch rollcharacteristic. It also provides turn coordination. The yaw damper is en-gaged by lifting the "‘YD ENG"’ lever on the APP.

The yaw damper is engaged by lifting the "‘YD ENG"’ or "‘AP ENG"’ leveron the APP if no yaw damper failures are detected and the aircraft yaw ratedoes not exceed limits.

The yaw damper is manually disengaged by lowering the "‘YD ENG"’ leveron the APP or pushing either of the AP disconnect buttons. The yaw damperis automatically disengaged when a YD failure is detected.

The message "‘YD"’ shows on the PFD in green when the yaw damper isengaged and the autopilot is not engaged. "‘YD"’ flashes in yellow on thePFD for 2 seconds when the yaw damper is manually disengaged. "‘YD"’flashes continuously until cancelled for automatic disengagement. "‘YD"’shows continuous after being cancelled for automatic disengagement.

4.2.7 Roll Mode

The basic lateral mode of the system is Roll mode. Roll mode is activewhen no other lateral modes are active, even though the guidance may notbe coupled to the autopilot or shown by the flight director. Roll mode iscomprised of a Heading Hold and a Bank Hold state. The reference valuefor either state can be synchronized by the pilot with the SYNC button(s)or synchronized by flight guidance.

Roll Heading Hold

The Heading Hold state maintains the current heading of the airplane.

SelectionRoll Heading Hold is set by the flight guidance computer (no button is

provided) if the roll angle is less than or equal to 5ř and upon the occurrenceof any of the following:

- Power up sequence is complete and prior to autopilot engagement orFD On.

- Any other active lateral mode has been deselected.

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- Both flight directors are turned off while the autopilot is disengaged.

- The autopilot is disengaged while both flight directors are off.

- The SYNC button is pushed in Go Around or Takeoff mode.

Deselection Roll Heading Hold is deselected when another lateral modeis selected.

Operation The Heading reference is synchronized to the current headingupon the occurrence of any of the following:

- Selection of the mode

- The SYNC button is pushed

- The autopilot is engaged

- Continuously when on the ground (weight-on-wheels switch activated).

Display "‘ROLL"’ shows in green on the PFD.

Roll Hold

Bank Hold maintains the current bank angle of the airplane. The BankHold reference can be adjusted by the pilot with the Roll knob on the APP.

Selection Roll Hold is selected if the Roll Knob on the APP is displacedfrom detent. Roll Hold is set by the flight guidance computer if the roll angleis greater than 5ř and upon the occurrence of any of the following:

- Power up sequence is complete and prior to autopilot engagement orFD On.

- Any other active lateral mode has been deselected.




Deselection Roll Hold mode is deselected when another lateral mode isselected.

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Operation Roll Hold holds the reference roll angle. The Roll Hold Rollreference can be set using the Roll Knob on the APP or synchronized to theroll angle existing upon the occurrence of any of the following:

- Selection of the state


- The autopilot is engaged.

The Roll Hold roll reference can not be set or synchronized to a valuegreater than the bank limit, 32ř.

Display "‘ROLL"’ shows in green on the PFD.

Heading Select Mode

Heading Select mode generates commands to capture the Selected Headingreference shown on the PFD. The reference can be adjusted by the crew withthe HDG knob on the CHP or synchronized by pushing the inset of the HDGknob on the CHP.

Selection Selection of Heading Select mode occurs when HDG button onthe MSP is pushed.

Deselection Pushing the HDG button on the MSP or selection and cap-ture of any other lateral mode deselects Heading Select mode.

Operation Heading Select mode generates commands to capture andmaintain the Selected Heading reference. When first selected, commandsare generated to turn in the direction closest to the Selected Heading ref-erence. If the Selected Heading reference is adjusted by more than 180ř,commands are generated to turn in the same direction the knob was rotated.The Heading reference is controlled by the HDG knob on the CHP. Pushingthe HDG knob inset button synchronizes the selected heading reference tothe current aircraft heading.

Display "‘HDG"’ shows in green on the PFD. The selected heading refer-ence value shows on the PFD. A heading bug shows on the compass rose.

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Selection of Heading Select mode lights the indicator in the center of theHDG button on the MSP.

4.2.8 Navigation Mode

Navigation mode generates commands to capture and track lateral guid-ance for en route navigation and non-precision approaches. En route guid-ance can be from a VOR or FMS. Approach guidance can be from a VOR orLocalizer. course). Lateral Navigation is comprised of Arm and Track states.

Navigation Arm Mode

The Navigation Arm state can be selected while other lateral modes areactive. At capture, the Track state is selected and the mode becomes active.

Selection The Navigation Arm state is selected by pushing the NAV but-ton on the MSP when a valid navigation source is selected.

- The VOR Navigation Arm state is selected when the NAV button onthe MSP is pushed and a valid VOR is the selected navigation source.

- The Localizer (LOC) Navigation Arm state is selected when the NAVbutton on the MSP has been pushed and a valid localizer is the selectednavigation source.

- The FMS Navigation Arm (LNV) state is selected when the NAV but-ton on the MSP has been pushed and FMS is the selected navigationsource.

Deselection The VOR, FMS and LOC Navigation Arm states are dese-lected when:

- Automatic capture of the Track state occurs.

- Another lateral mode is selected.

- The NAV source or frequency is changed.

- The NAV button on the MSP is pushed.

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Operation Prior to capture, flight guidance retains the active lateral modeexisting at NAV selection. If no lateral mode was active, Roll mode is se-lected. The VOR, FMS, and LOC Navigation Arm states monitor aircraftclosure rate (lateral deviation) towards the target flight path, and calculatethe capture point. If VOR is the selected source and Half Bank is active, thecapture point is optimized accordingly. Armed modes show in white. Theleft CRS knob is used to select the pilotŠs VOR course which shows on theleft PFD. The right CRS knob is used to select the copilotŠs VOR coursewhich shows on the right PFD.

Display The following displays show to indicate the Navigation Arm state:

- VOR, LNV, or LOC shows in white (armed), yellow (armed but thesignal is not valid) or green (capture / tracking) on the PFD.

- ROLL or HDG shows in green on the PFD.

- The light in the center of the NAV button on the MSP comes on toindicate the Navigation mode (Arm or Track) is active.

Navigation Track Mode

The Navigation Track state generates commands to maintain the flightpath.

Selection The VOR, FMS, and LOC Navigation Track state is selectedwhen automatic capture of the Track state occurs.

Deselection The Navigation Track state is deselected when:


- The NAV source or frequency (VOR or LOC) is changed.

- The NAV button on the MSP is pushed.

Operation If VOR is selected as the navigation source, flight guidance:

- Generates commands to capture and track the selected VOR radial.

- If Half Bank is selected, flight guidance adjusts the capture to compen-sate

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- Provides Dead Reckoning operation (DR, based on memorized heading)during VOR station passage

- Automatically adapt outputs to en route or approach type conditions.

If LOC is selected as the navigation source, flight guidance generatescommands to capture and track the localizer.

If FMS is selected as the navigation source, flight guidance generatescommands to capture and track the course for the FMS active leg.

Display The following displays show to indicate the Navigation Trackstate:

- DR shows in white on the PFD when flight guidance is providing DeadReckoning operation.

- VOR, LNV, or LOC shows in green on the PFD.

- VOR, or LOC shows in green with yellow strikethrough (lost signal) onthe PFD.

- The light in the center of the NAV button on the MSP comes on toindicate the Navigation mode (Arm or Track) is active.

4.2.9 Approach Mode (Lateral)

Approach mode, selected by pushing the APPR button on the MSP, isunique in that it enables both lateral and vertical guidance. See the AP-PROACH MODE (VERTICAL) section for a description of the verticalguidance. Approach mode generates commands to capture and track lat-eral guidance for ILS precision localizer approaches and VOR non-precisionapproaches.

Lateral Approaches are comprised of Arm and Track states. The Armstate can be selected while other lateral modes are active. For precisionapproaches, aircraft closure rate towards the target flight path is monitored(lateral deviation) and the capture point is determined. At capture the Trackstate is selected and the mode becomes active. The Track state generatescommands to maintain the flight path.

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Approach (Lateral) Arm Mode

The Approach Arm state can be selected while other lateral modes are active.For precision approaches, aircraft closure rate towards the target flight pathis monitored (lateral deviation) and the capture point is determined.

Selection The Approach Arm state is selected by pushing the APPRbutton on the MSP when a valid navigation source is selected.

- The VOR (VOR) Approach Arm state is selected when the APPRbutton on the MSP is pushed and a VOR is the selected navigationsource.

- The Localizer (LOC) Approach Arm state is selected when the APPRbutton on the MSP is pushed and a localizer is the selected navigationsource.

- The FMS (LNV) Approach Arm state is selected when the APPR but-ton on the MSP is pushed and a FMS is the selected NAV source.

Deselection The Localizer, FMS (LNV), or VOR Approach Arm state isdeselected when:




- The APPR button on the MSP is pushed.

Operation The Localizer, and VOR Approach Arm states monitors air-craft closure rate (lateral deviation) towards the target flight path and calcu-late the capture point. Consistent with Navigation mode operation, the leftCRS knob is used to select the pilot’s course, shown on the left PFD. Theright CRS knob is used to select the copilotŠs course, shown on the rightPFD.

Display The following displays show to indicate the Approach Arm state:

- ŞLOCŤ, ŞLNVŤ, or ŞVORŤ show in white (armed) or green (capture/ tracking) on the PFD.

- ŞROLLŤ or ŞHDGŤ show on green on the PFD.

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- The light in the center of the APPR button on the MSP comes on toindicate the Approach mode (Arm or Track) is active.

Approach (Lateral) Track Mode

For precision approaches, aircraft closure rate towards the target flightpath is monitored (lateral deviation) and the capture point is determined.At capture the Track state is selected and the mode becomes active. TheTrack state generates commands to maintain the flight path.

Selection The Localizer or VOR Approach Track state is selected whenautomatic capture of the Track state occurs.

Deselection The Approach Track state is deselected when:


- The NAV source or frequency (VOR or LOC) is changed.


Operation The Localizer, FMS (LNV), or VOR Approach state gener-ates commands to capture and track the final approach course. Selection ofthe Approach Track state switches the flight director commands to a dual-independent configuration.

Display The following displays show to indicate the Approach Track state:

- ŞLOCŤ, ŞLNVŤ, or ŞVORŤ shows in green (tracking) or in green witha yellow strikethrough (lost signal) on the PFD.

- The light in the center of the APPR button on the MSP comes on toindicate the Approach mode (Arm or Track) is active.

4.2.10 Back Course Mode

Back Course (B/C) mode is selected by pushing the B/C button on theMSP. The B/C mode generates commands to capture and track lateral guid-ance for localizer back course approaches.

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Back Course approaches are comprised of Arm and Track states. The Armstate can be selected while other lateral modes are active. Aircraft closurerate towards the target flight path is monitored (lateral deviation) and thecapture point is determined. At capture, the Track state is selected and themode becomes active. The Track state generates commands to maintain theflight path.

Back Course Arm Mode

The B/C Arm state can be selected while other lateral modes are active.Aircraft closure rate towards the target flight path is monitored (lateral de-viation) and the capture point is determined.

Selection The B/C Arm state is selected by pushing the B/C button onthe MSP when a valid navigation source is selected. The B/C Arm stateis selected when the B/C button on the MSP is pushed, a localizer is theselected navigation source and the front course error is greater than 105ř.

Deselection The B/C Arm state is deselected when:




- The B/C button on the MSP is pushed.

Operation The B/C Arm state monitors aircraft closure rate (lateraldeviation) towards the target flight path and calculates the capture point.

Display The following displays indicate the B/C Arm state is active:

- B/C shows in white (armed) or green (capture / tracking) on the PFD.

- ROLL or HDG show on green on the PFD.

- The light in the center of the B/C button on the MSP comes on toindicate the B/C mode (Arm or Track) is active.

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Back Course Track Mode

Aircraft closure rate towards the target flight path is monitored (lateraldeviation) and the capture point is determined. At capture, the Track state isselected and the mode becomes active. The Track state generates commandsto maintain the flight path.

Selection The B/C Track state is selected when automatic capture of theTrack state occurs.

Deselection The B/C Track state is deselected when:



- The B/C button on the MSP is pushed.

Operation The B/C Track state generates commands to capture andtrack the final approach course.

Display The following displays indicate the B/C Track state is active:

- B/C shows in green (tracking) or in green with a yellow strikethrough(lost signal) on the PFD.

- The light in the center of the B/C button on the MSP comes on toindicate the B/C mode (Arm or Track) is active.

4.2.11 Go Around (Lateral) Mode

Go Around mode generates commands to track a Heading Hold reference.The reference is set when the mode is selected and is not adjustable. Theflight director can show the commands, but the autopilot can not be coupledto the Guidance.

Selection Go Around mode is selected by pushing the GA button whenthe aircraft is in the air.

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Deselection Go Around mode deselection occurs due to:

- Autopilot Engagement.

- Selection of another lateral or vertical mode.

- Pushing the SYNC button.

Operation Lateral Go Around mode generates commands in the lateralaxis to hold the heading existing when the GA button is pushed. The rollcommands are limited to 5ř in Go Around. Selection of Go Around disengagesthe autopilot (but not the yaw damper). Selection of GA clears all otherlateral modes.

Display GA shows in green on the PFD.

4.2.12 Take Off (Lateral) Mode

Takeoff mode generates commands to track a Heading Hold reference.The reference is set when the aircraft becomes airborne and is not adjustable.The flight director can show the commands, but the autopilot can not becoupled to the Guidance.

Selection Takeoff mode is selected by pushing the GA button when theaircraft is on the ground.

Deselection Takeoff mode deselection occurs due to:

- Autopilot Engagement

- Selection of another lateral or vertical mode

- Pushing the SYNC button.

Operation Lateral Takeoff mode generates a wings-level command whileon the ground. Lateral Takeoff mode generates commands in the lateral axisto hold the heading existing when the aircraft becomes airborne. The rollcommands are limited to 5ř in Takeoff. Selection of Takeoff disengages theautopilot (but not the yaw damper). Selection of TKO clears all other lateralmodes.

Display TKO shows in green on the PFD.

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4.2.13 Half Bank Mode

Half Bank mode is unlike the other lateral modes in that it does not calcu-late lateral guidance, but instead limits the magnitude of the lateral guidanceto a lower bank angle (15ř). Lower bank angles are used for passenger com-fort. Half Bank can be active concurrent with many of the other lateralmodes. Some lateral modes preclude Half Bank and automatically deselectit. Half Bank is particularly useful at cruise altitudes, and as such is selectedby the flight guidance computer (automatically) when climbing through thehalf bank transition altitude. The half bank transition altitude for the CJ1+and CJ2+ is 30,610 feet. The half bank transition altitude for CJ3 is 31,155feet.

Selection The 1/2 BANK button on the MSP is used to select Half Bankexcept when any of the following modes are active: Approach, Go Around,or NAV with a Localizer source.

Automatic selection of Half Bank occurs when climbing through 18,500feet pressure altitude, or if above this altitude when the flight director isturned on except when any of the following modes are active: Approach, GoAround, or NAV with a Localizer source.

Deselection Half Bank is deselected upon:

- Selection of Go Around or Takeoff mode.

- Localizer capture (back or front course)

- Lateral Approach capture.

- Descent through the half bank transition altitude.

- Pushing the 1/2 BANK button on the MSP.

- Navigation, FMS LNV capture, if the FMS source is type GAMA.

Display The following displays show to indicate the Half Bank mode isactive.

- A white arc shows above the Roll Pointer on the PFD.

- The light in the center of the 1/2 BANK button on the MSP comes onto indicate the Half Bank mode is active.

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4.2.14 Pitch Mode

The basic vertical mode is Pitch mode. Pitch mode is active when noother vertical modes are active, even though the guidance may not be cou-pled to the autopilot or shown by the flight director. Pitch mode generatescommands to maintain a reference pitch angle. The reference value can beadjusted by the crew with the Pitch Wheel on the APP, synchronized by thecrew with the SYNC button, or synchronized by flight guidance when themode is selected.

Selection Pitch mode is selected by flight guidance (no button is provided)upon the occurrence of any of the following:

- Power up sequencing is complete and prior to autopilot engagement orFD On.

- Any other active vertical mode has been deselected.




- The selected altitude is changed during an Altitude Select Capture.(Altitude Select rearms, and typically transitions immediately back tothe Capture state for small changes of the preselector.)

- The APP pitch wheel is moved while in Altitude Select Track, AltitudeHold, Vertical Go Around, or Vertical takeoff modes.

Deselection Pitch mode is deselected due to selection or automatic cap-ture of another vertical mode.

Operation Pitch mode generates commands to hold the reference pitchangle. The Pitch reference is synchronized to the pitch angle existing uponthe occurrence of any of the following:

- Selection of the mode


- The autopilot is engaged

- Pitch wheel operation.

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Display PTCH shows in green on the PFD.

4.2.15 Altitutde Select Mode

Altitude Select Mode is comprised of Arm, Capture, and Track states. TheArm state can be selected while other vertical modes are active. It monitorsaircraft closure rate towards the target altitude and determines the capturepoint. Capture generates commands for a smooth, low g acquisition of thetarget altitude. Track generates commands to maintain the target altitude.

There are two potential target altitudes associated with Altitude Selectmode. The Altitude Select knob on the CHP is used to change the SelectedAltitude. Selected Altitude is selectable in one hundred foot increments. Thesecond is the VNAV FPTA (Flight Plan Target Altitude) provided by theFMS, this may only be active when VNAV mode is selected. Altitude Selectmode Captures and Tracks the altitude that is closest in the direction theaircraft is descending or climbing.

Altitude Select Arm Mode

The Altitude Select Arm state can be selected while other vertical modesare active. It monitors aircraft closure rate towards the target altitude anddetermines the capture point.

Selection Altitude Select Arm is selected by flight guidance (no button isprovided) upon the occurrence of any of the following:

- Turning on a flight director or engaging the autopilot.

- Selection of any vertical mode other than glideslope track, vertical goaround, or altitude hold.

- Rotation of the Altitude Preselect Knob, when not in Altitude Holdmode.

- Selection of Vertical Go Around or Vertical Takeoff mode when theaircraft is not within 75 feet of the target altitude.

Deselection Altitude Select Arm is deselected upon the occurrence of anyof the following:

- Automatic transition to the Capture state.

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- Activation of Glideslope Capture.

- Selection of Vertical Go Around or Altitude Hold.

- Selection of Vertical Go Around or Vertical Takeoff mode when theaircraft is within 75 feet of the target altitude.

Operation The Arm state monitors aircraft closure rate towards the tar-get altitude and calculates the capture point.

The Altitude Select arm state monitors aircraft closure rate towardsthe target altitude and calculates the optimum capture point. If the SelectedAltitude and VNAV target altitude are both valid and the same value, theFGC uses the Selected Altitude value. If VNAV mode is not selected, thetarget altitude is always the Selected Altitude. If VNAV mode is selected,but the FMS is not providing a valid VNAV altitude, the target altitude isthe Selected Altitude. If VNAV mode is selected, and the FMS is providinga valid VNAV altitude, the target altitude is selected as follows:

- The target altitude is the closest altitude in the direction of verticalmotion of the aircraft.

- A minimum vertical rate of 300 ft/min for 2 seconds or more is usedto determine the direction of vertical motion.

- If there is no apparent vertical motion of the aircraft, then the closestaltitude is used as the target altitude.

- If the closest altitude changes due to aircraft motion, the target altitudechanges respectively.

Display ALTS shows in white (armed) on the PFD.

Altitude Select Capture Mode

Altitude Select Capture generates commands for a smooth low g acquisi-tion of the target altitude.

Selection Altitude Select Capture is selected by flight guidance (automat-ically) when the capture conditions are met. Capture does not occur if thetarget altitude is slewed through the current altitude.

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Deselection Altitude Select Capture is deselected upon the occurrence ofany of the following:

- Automatic transition to the Track state.

- Activation of Glideslope Capture mode.

- Selection of any other vertical mode.

Deselection of Altitude Capture due to activation of the APP PitchWheel or the preselector knob causes the FGS to send a command to thePFD to alert the crew.

If altitude capture is aborted, a flag (Altitude Abort) is set for 10-seconds, then removed. If the Capture state is re-selected while the alertis still active, or if Altitude Select Arm is selected, the Altitude Abort iscanceled.

Operation The Capture state generates commands for a smooth low gacquisition of the target altitude. Pushing SYNC during ALTS CAP changesthe level off altitude to the new SYNC altitude, and selects Altitude Holdmode.

Display The following displays show to indicate the Altitude Select Cap-ture state is active:

- ALTS CAP shows in green on the PFD.

- ALTS shows in flashing yellow on the PFD if an Altitude Capture abortoccurs.

4.2.16 Altitude Hold Mode

Altitude Hold mode generates commands to capture and track the Al-titude Hold reference. Altitude Hold uses pressure altitude.

Selection Selection of Altitude Hold mode occurs due to the following:

- Pushing the ALT button on the MSP.

- Automatic if the SYNC is pushed while in Altitude Select Track.

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Selection is inhibited if in Glideslope Track Mode.

Deselection Pushing the ALT button on the MSP or selection and captureof another vertical mode deselects Altitude Hold mode.

Operation At selection, flight guidance synchronizes its Altitude Holdreference to the current pressure altitude. If after selection the autopilot isengaged, flight guidance re-synchronizes its Altitude Hold reference to thecurrent pressure Altitude.

If automatically selected by pushing SYNC while in Altitude SelectTrack, the Altitude Hold reference is set to the pressure altitude equivalentof the previous Selected Altitude (barometric). Altitude Hold mode generatescommands to capture and maintain the altitude reference. The Altitude Holdreference is reset to the current pressure altitude when the SYNC button ispushed.

Display The following displays show to indicate the Altitude Hold modeis active:

- ALTS shows in green on the PFD.

- The light in the center of the ALT button on the MSP comes on toindicate the Altitude Hold mode is active.

4.2.17 Vertical Speed Mode

Vertical Speed mode generates commands to capture and track the VerticalSpeed reference shown on the PFD. The Reference are adjusted by the crewwith the Pitch Wheel on the APP, or synchronized by flight guidance.

Selection Selection of Vertical Speed mode occurs when the VS button ispushed on the MSP. If the VS button is pushed while in Altitude Select Cap-ture or Track without first moving the altitude preselector, flight guidancearms and recapture the Preselector altitude. The VS mode message mayflash momentarily in response to pushing the button, but ŞALTS CAPŤreplaces it as the altitude capture cycle occurs. Selection is inhibited if inGlideslope Track, or Overspeed Modes.

Deselection Pushing the VS button on the MSP or selection and captureof another vertical mode deselects VS mode.

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Operation At selection, flight guidance synchronizes the Vertical Speedreference to the present Vertical Speed. After selection, if the autopilot isengaged, flight guidance re-synchronizes the Vertical Speed reference to thepresent Vertical Speed.

Vertical Speed (VS) mode generates commands to capture and trackthe vertical speed reference. The Vertical Speed reference on the PFD canbe adjusted by rotating the pitch wheel on the APP. The pitch wheel has aspring return to center. For small displacements of the wheel, flight guidancechanges the vertical speed reference by 100 fpm, and in the direction ofrotation. For larger displacements flight guidance changes the Vertical Speedreference by progressively larger amounts. The VS reference is reset to thecurrent vertical speed whenever the SYNC button is pushed.

Display The following displays show to indicate the Vertical Speed modeis active:

- VS. NNNN or VS. NNNN shows in green on the PFD. The arrow givesthe direction, up or down, and NNNN is the value of the vertical speedreference in feet per minute (fpm).

- A vertical speed bug shows on the vertical speed scale when VS modeis selected indicating the reference value.

- The light in the center of the VS button on the MSP comes on toindicate Vertical Speed mode is active.

4.2.18 Flight Level Change Mode

Flight Level Change (FLC) mode generates commands to capture andtrack a reference airspeed taking into account the crewŠs intent to climb ordescend, as indicated by the relative value of the Altitude Preselector, andthe ability of the aircraft (i.e., thrust level) to accomplish that intent.

The Reference can be adjusted by the crew with the Pitch Wheel on theAPP or synchronized by flight guidance.

Flight Level Change mode is comprised of a Track and an Overspeed state.Track is the normal state, generating commands to maintain the reference.Overspeed generates the same commands except the reference is forced belowVMO/MMO.

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Flight Level Change Track Mode

The Flight Level Change Track state generates commands to maintain thecurrent vertical speed reference.

Selection Flight Level Change (FLC) mode is selected by pushing theFLC button on the MSP. If the FLC button is pushed while in AltitudeSelect Capture or Track, without first moving the altitude preselector, flightguidance arms and recaptures the Preselector altitude. The FLC mode mes-sage may flash momentarily in response to pushing the button, but "‘ALTSCAP"’ replaces it as the altitude capture cycle occurs.

Selection is inhibited if in Glideslope Track, or FLC Overspeed Modes.

FLC Track mode automatically transitions from FLC Overspeed modewhen "‘IAS / Mach"’ has dropped below "‘Vmo/Mmo"’.

Deselection Pushing the FLC button on the MSP twice or selection orcapture of another vertical mode deselects FLC mode.

Operation At selection, flight guidance synchronizes the Airspeed refer-ence to the present Airspeed.

After selection, if the autopilot is engaged, flight guidance synchronizesthe airspeed reference to the current airspeed.

The airspeed reference can be set by rotating the Pitch Wheel. Theairspeed reference is limited to settings between 70 kts. and VMO/MMO.

Pushing the FLC button on the MSP a second time toggles the airspeedreference from Mach to IAS, or IAS to Mach. A third push deselects the FLCmode.

When the speed reference is IAS, climbing through the IAS/Mach tran-sition altitude toggles the speed reference to Mach. When the speed referenceis Mach, descending through the IAS/Mach transition altitude toggles thespeed reference to IAS.

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If the Preselected altitude is above the current altitude (i.e., a climb isintended), FLC mode generates commands to maintain the airspeed referenceif there is sufficient thrust to accomplish a climb (i.e., vertical speed greaterthan zero). Otherwise, FLC mode generates commands to fly level (i.e., zerovertical speed).

If the Preselected altitude is below the current altitude (i.e., a descent isintended), FLC mode generates commands to maintain the airspeed referenceif the thrust setting is appropriate to accomplish a descent (i.e., vertical speedless than zero). Otherwise, FLC mode generates commands to fly level (i.e.,zero vertical speed).

If FLC mode is in a climb configuration and the Preselected altitudeis changed from above the current altitude to below the current altitude,the FLC mode smoothly changes from a climb configuration to a descendconfiguration. If FLC mode is in a descend configuration and the Preselectedaltitude is changed from below the current altitude to above the currentaltitude, FLC mode smoothly changes from a descend configuration to aclimb configuration.

Display The following displays show to indicate the Flight Level ChangeTrack mode is active:

- FLC NNN shows in green on the PFD. ŞNNNŤ is the value of theAirspeed Reference in Knots; Ş.NNŤ is the Mach reference value.

- A speed bug shows next to the airspeed tape on the PFD when thespeed reference is IAS. When the speed reference is Mach, a Mach bugshows next to the IAS tape as an ŞIAS equivalentŤ Mach reference.

- The light in the center of the FLC button on the MSP comes on toindicate Fight Level Change mode (Track or Overspeed) is active.

Flight Level Change Overspeed Mode

Flight Level Change Track is the normal state, generating commands tomaintain the reference. Overspeed generates the same commands except thereference is forced below VMO/MMO.

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Selection FLC Overspeed is selected by flight guidance (automatically)when a significant overspeed occurs (.015 Mach above MMO or 5 knots aboveVMO) from all vertical modes except Altitude Select Capture or Track, andAltitude Hold.

Deselection FLC mode is deselected when either of the following is true:

- FLC Overspeed mode automatically transitions to FLC Track modewhen "‘IAS/Mach"’ has dropped below "‘Vmo/Mmo"’.

- FLC Overspeed is automatically deselected at the occurrence of anAltitude Select capture.

FLC Overspeed inhibits turning off the flight directors.

Operation At selection, if above the transition altitude, flight guidancesets the Mach reference to 0.02 Mach below MMO. At selection, if below thetransition altitude, flight guidance sets the IAS reference to 5 knots belowVMO.

While in FLC Overspeed, the IAS or Mach reference never increases,but may decrease, to stay below VMO/MMOo (as VMO/MMO changes withaltitude).

The IAS or Mach reference is not adjustable by the Pitch Wheel whilein FLC Overspeed. While in FLC Overspeed, commands are generated tocapture the reference airspeed.

Display The following displays show to indicate FLC Overspeed mode isactive:

- FLC NNN shows in flashing yellow on the PFD. NNN is the value ofthe Airspeed Reference in Knots, or .NN would be the Mach referencevalue.

- A speed bug shows next to the airspeed tape on the PFD when thespeed reference is IAS. When the speed reference is Mach, a Mach bugshows next to the IAS tape as an ŞIAS equivalentŤ Mach reference.

- The light in the center of the FLC button on the MSP comes on toindicate FLC mode (Track or Overspeed) is active.

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4.2.19 Approach (Vertical) Mode

Approach mode, selected by pushing the APPR button on the MSP, isunique in that it enables both lateral and vertical guidance. See APPROACHMODE (LATERAL) for a description of the lateral guidance. Approachmode generates commands to capture and track vertical guidance for ILSprecision Glideslope approaches, and FMS non-precision approaches

Vertical Approaches are comprised of Arm and Track states. The Armstate can be selected while other vertical modes are active. For precisionapproaches, aircraft closure rate towards the target flight path is monitored(vertical deviation) and the capture point is determined.

For FMS approaches, capture and track are calculated by the FMS whichprovides steering commands to the FGC. At capture the Track state is se-lected and the mode becomes active. Automatic capture occurs from anyvertical mode. The Track state generates commands to maintain the flightpath.

Approach (Vertical) Arm Mode

The Arm state can be selected while other vertical modes are active. Forprecision approaches, aircraft closure rate towards the target flight path ismonitored (vertical deviation) and the capture point is determined.

Selection The Glideslope Approach Arm state is selected when the APPRbutton on the MSP has been pushed, a valid Glideslope signal is being re-ceived, and the Localizer Capture state has been selected by the flight guid-ance computer (automatically).

The FMS Glideslope Approach Arm stare is selected when the APPRbutton on the MSP has been pushed, a valid FMS is the selected navigationsource, VNAV mode is selected, and the FMS requests glidepath arm.

Deselection The Approach Arm state is deselected when:


- A lateral mode other than Lateral Approach is selected.

- The NAV source or frequency is changed or becomes invalid.

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- VNAV is deselected (FMS Glidepath only).

Operation Approach Arm monitors aircraft closure rate towards the ap-proach path and calculates the capture point.

Display The following displays show to indicate the Glideslope ApproachArm state is active:

- GS, or GP shows in white (armed) on the PFD.

- The light in the center of the APPR button on the MSP comes on toindicate the APPR mode (Glideslope/Glidepath Arm) is active.

Approach (Vertical) Track Mode

At capture the Track state is selected and the mode becomes active. Au-tomatic capture occurs from any vertical mode. The Track state generatescommands to maintain the flight path.

Selection Glideslope Approach Track is selected when automatic captureof the Track state occurs.

Deselection Glideslope Approach Track state is deselected when:

- Go Around mode is selected.

- A lateral mode other than Lateral Approach is selected.


- The APPR button is pushed on the MSP.

The Approach Track state inhibits the activation of any other verticalmode except Go Around, Takeoff or the Overspeed state of FLC.

Operation Approach Track generates commands to track vertical guid-ance from precision approach sources (ILS). Glideslope Approach Track gen-erates commands to acquire the vertical approach path from either above orbelow the target path. Glideslope Approach Track uses commands computedby the FMS to track vertical guidance.

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Display The following displays show to indicate the Glideslope ApproachTrack state is active:

- GS, or VGP shows in green (tracking) on the PFD.

- The light in the center of the APPR button on the MSP comes on toindicate the APPR mode (Glideslope/Glidepath Track) is active.

4.2.20 Go Around (Vertical) Mode

Go Around mode generates commands to track a fixed pitch reference. Thereference is not adjustable. The flight director may display the commands,but the autopilot can not be coupled to the guidance.

Selection Go Around mode is selected by pushing the GA button whenthe aircraft is in the air.

Deselection Go Around mode deselection occurs due to:

- Turning off the flight directors.

- Autopilot engagement.

- Selection of another lateral or vertical mode.

- Pushing the SYNC button. When the SYNC button is pushed in GoAround, Pitch Hold mode is selected and shown; the pitch reference isreset to the current pitch attitude.

- Rotation of the pitch wheel.

Operation

Vertical Go Around mode generates a 7 degree fixed pitch up command.

Go Around disengages the autopilot (but not the yaw damper).

Selection of Go Around clears all other vertical modes.

Upon selection of Go Around mode the altitude preselector is armedif the current aircraft altitude is more than ś75 feet from the value of thepreselected altitude. The altitude preselector is not armed if the aircraft iswithin 75 feet of the preselect altitude value when Go Around is selected.

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Display GA shows in green on the PFD.

4.2.21 Vertical Navigation Mode

When selected on the MSP, VNAV works in all vertical modes and is annun-ciated to the pilot by adding a V to the mode on the display (e.g., VPTCH,VVS, VFLC). The pilot has full command of pitch, vertical speed, flight levelchange, altitude hold mode, and altitude preselect autopilot modes whileVNAV is active. When VPTCH and VVS are the active modes and the air-craft is climbing, these modes operate as normal. The aircraft levels at thepreselector altitude and the VNAV altitudes from the FMS. When VPTCHand VVS are the active modes and the aircraft is descending, these modesoperate as normal, except not only will the aircraft level at the preselectoraltitude but will also level at the VNAV altitudes from the FMS. It willalso automatically switch to VPATH (vertical path) if it comes upon a pathselected from the FMS. When VFLC is the active mode, it will operatenormally with the same constraints as VPTCH and VVS, but will also becapable of flying program speeds from the FMS. VPATH is the vertical pathcontrolled by the FMS to maintain the desired GP. When NAV is the se-lected navigation source, the aircraft will level at the preselector altitude orthe FMS VNAV altitude. VGP is a mode that was designed to let an FMSapproach operate like a normal ILS approach. When APPR is the selectedlateral mode, and the leg into the final approach fix (FAF) or the missedapproach point (MAP) is the active leg, VGP shows as the active verticalmode, and the aircraft will not level at the preselector altitude. This allowsthe pilot to set the preselector to the missed approach altitude like an ILSapproach when glideslope is the active vertical mode.

Selection Push the VNAV button on the MSP to select VNAV mode(push-on/push-off). Selection of VNAV is inhibited when:

- Glideslope approach mode is active

- There is no active flight plan in the FMS

- FMS is not the active NAV source on the transfer side.

Deselection VNAV mode is automatically deselected by:

- Selection of go around mode

- Glideslope capture

- Changing the NAV source on the coupled side.

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Operation VNAV automatically commands the autopilot to sequencemodes and set target speeds and target altitudes to ensure the requirementsare honored with the constraints of the preselector altitude setting. For de-scent VNAV defines a geographic path into each descent altitude constraintand provides vertical guidance relative to that path, ensuring the descentaltitude constraints are honored. Vertical guidance is provided with VPATHor VGP modes, which are only available through VNAV operation. The pilothas full command of pitch, vertical speed, flight level change, altitude holdmode, and altitude preselect autopilot modes while VNAV is active.

Display The letter V is prefixed to all vertical mode messages that aresupported by VNAV. If VNAV is selected on the MSP when VNAV is notvalid (such as no active flight plan, or the NAV source on the transfer sideis not FMS), a yellow lined VNAV shows in the arm field of the PFD.

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4.3 Design

Based on the specifications, the next entities are defined:

- Autopilot System module

- Flight Guidance Computer module

- Generic Mode

4.3.1 Entities

Flight Simulator Network

The application is connected to the Flight Simulator Network which pro-vides access to the avionics data. Data can be any of the following: Switchesor Button states from the cockpit panels or controls, attitude or other datarelative to the flight motion (such as airspeed, vertical speed, etc.), visual oraural indications and other data gather from other systems in the aircraftsuch as the FMS, Flight Guidance Indication Data or GPS.

APS Module

The Autopilot System Module retrieves raw data from the network, con-nected to the Flight Simulator and sends computed data from the FGCModule. All data is converted to the apropiate units and itťs offered to theFGC Module in suitable way. Itťs also, the entry point to the application.

FGC Module

The Flight Guidance Computer Module manages all incoming/outcomingcomputed data. It also contains all the logic to interact with the Modes.

Modes

A Mode is defined as one entity with two possible states (selected / deselec-ted) and capable of generating output data from a subset of data performinga control algorithm or some logic. In this way, autopilot, flight director andyaw damper functionalities are treated as Modes, as well as all the AutopilotModes defined in the specifications.

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Figure 4.7: Design Diagram

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4.3.2 Global Performance

Performance of the system depends primarly on robustness and efficiencyof the controllers. A low and constant cycle time is needed to provide a goodimplementation base for the control algorithms. Besides, a well implementedand tuned control algorithm is also important.

Time Performance

The system will be running in a Flight Simulator environment with its owncycling demands. It will also be probably installed in a computer sharingresources with other applications that cannot be blocked. Furthermore, thecomputer will have installed some Windows or Linux operating system whichwill make time accuracy quite poor. And additionally, the Java languagemakes real time programming if not impossible, unfeasible. However, thecontrols algorithm require high precission and low cycle times. In orderto accomplish the cycle requirements, these previous concernings must beconsidered. The following statements are commanded:

- The system must have as few threads as possible. In fact, only onethread is really needed for the FGC. Within this thread data can becollected, the Modes can be called to perform their operation and theoutput data can be sent to the network. One additional very low com-putation thread, can trigger the selection Modeťs states if neccesary.

- The whole system must be optimized for high performance, speciallythe control algorithms. PID algorithms offer really low computationrequirements, while reliability. In addition, theyťre easy to implement,so PIDťs will be used throughout this project.

- Another procedure to increase performance, is reducing eventťs pro-gramming. When triggering an event, a lot of computation has to bemade to change the context of the threads. Data can be collected andsent using the same thread that calls the Modesť computations so thememory usage will increase, but lowering the time consumption. Thememory usage is not a real problem in modern computers while notaccessing images or databases with very large amounts of data.

Control Performance

An aircraft is a multivariable non-linear system that for most cases cannotbe decoupled. It becomes really complicated when approaching its behaviourfrom a strict way, in which all attitudes and flight motions are contemplated.

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Fortunately, in stable flight very few attitudes and flight motions are permit-ted and autopilots consider even fewer. Stability is the highest priority andrapidness has relative low importance which lowers control requirements.

PID’s algorithms can be easily designed for high stability and robustnesswhile maintaining low computation needs. However, their performance is notsuitable for non-linear systems and they are not capable of handling multi-variable systems. The linear approximation of the system at each relevantpoint, can be used for designing the controllers at these points; defining apoint as a specific set of values that can take the parameters. This controllerswill be only valid in a resctrictive range of operation. So to control widerranges more controllers will be have to be designed, each one at a particularoperation point.

Designing the controllers presents the next steps:

- First, the input and output variables are selected. Because PID’s areSingle Input, Single Output controllers (SISO), one input and one out-put variable are defined. They can be either one of the selected vari-ables or derived from them, so higher decoupling of the system can beachieved.

- Secondly, a defined range of operation is defined so the controllerachieves the specifications within it. The controller may not be re-liable outside of it, so its use is restricted to the define range.

- Finally, the controller is tuned choosing appropiate parameters. Thesystem response is measured from different inputs at the operationpoints selected. Then the parameters are calculated using a tuningalgorithm. Finally fine-tuning is used if necessary.

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4.4 Implementation

4.4.1 Location

This system is implemented as a stand alone software application workingtogether with the TU-Graz Flight Simulator. All Flight Simulator data isaccessed through a network, which is defined in a Java library included inthis application. This network makes the application portable to any com-puter connected. Besides, Java is platform independent, so theoretically theprogramm can run in any computer with any operating system.

4.4.2 Software

The following software is required for this project:

- Java JDK 6 platform to compile the application source code.

- Java libraries provided by the TU-Graz Flight Simulator to access itsdata.

- JCreator programming tool software to generate the source code.

4.4.3 UML Diagram

The programm is coded following the design previously introduced. Thenext classes are defined:

- APS.java: Main entry point of the application. Contains all methodsto access data from the Flight Simulator network.

- FGS.java: Thread of the application. Manages the workflow of theprogramm.

- SafeThread.java: An abstract class for creating precission time threadswith safe added functionalities.

- ToggleButton.java: A flip-flop object with filtering capabilities to readbutton states.

- Mode.java: An abstract class which models the operation and state ofan autopilot mode.

- AutopilotMode.java: A Mode subclass which generates surface controlcommands from an attitude requested.

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Figure 4.8: UML Diagram

- FlighDirectorMode.java: A Mode subclass which generates visual aidcommands and autopilot attitude references from other Mode sub-classes output.

- YawDamper.java: A Mode subclass which generates rudder controlcommands in order to decrease Dutch Effect.

- LateralModes: Subdivision of the Mode subclasses which generate rollcommands.

- VerticalModes: Subdivision of the Mode subclasses which generatepitch commands.

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4.4.4 Operation

The application is started by entry point of the APS class. All necessarydata objects to communicate with the network are created by this class.Then, a FGC instance is created with a reference to the APS instance. ThisFGC instance creates all Mode’s objects and other useful objects for storingdata. Finally the Thread is started and the application workflow begins.

Workflow

The workflow of the programm is resumed in the next steps:

1. Data is retrieved from the Simulator network and converted to appropi-ate units if necessary.

2. If the data retrieved was found to be invalid then skip to the nextcycle. Otherwise the operation methods of the active Mode’s objectsare called.

3. Data computed by the control algorithm of the active Mode’s is for-matted to appropiate units and sent back to the Simulator network.

4. Finally, for each Mode a selection checking logic algorithm is appliedso each mode state is updated.

Mode Operation

For each Mode an operation algorithm is executed if selected. This methodis called each cycle if there were no errors retrieving data from the Simulator’snetwork. Otherwise, if the error was not severe, the method is called the nextcycle or the Mode is deselected. This method performs the same calculationsas described in the specifications. It is comprised of the next steps:

1. Necessary data is get from the FGC object. If a Button or Lever isassociated to this Mode, the respective ToggleButton is updated, so itsynchronizes with the Flight Simulator. This step is performed even ifthe Mode is deselected.

2. The reference values are calculated and then the control algorithm isexecuted. In some cases more than one control algorithm can be exe-cuted depending on auxiliary data.

3. Output data is shorten to boundaries if necessary and sent to the FGCobject.

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4. if any visual or aural signal is associated to the Mode, it’s updated andsent to the FGC object which will manage it.

Mode Selection

Mode’s can be selected or deselected. If deselected they don’t perform anyoperation algorithm, but they still updating it’s reference data and otheruseful information. Each cycle the selection status of each Mode is updated.It is comprised of the next steps:

1. Selection is inhibited if data errors or the system is deactivated (Au-topilot and Flight Director Mode’s deselected).

2. Selection conditions are checked.

3. Deselection conditions are checked.

4. If the Mode is deselected, selection conditions are satisfied and deselec-tion conditions are not satisfied, the Mode is selected and the methodOnSelection is called.

5. If the Mode is deselected, selection conditions are satisfied and dese-lection conditions are also satisfied, the Mode is not selected and themethod OnFailedSelection is called.

6. If the Mode is selected and the deselection conditions are satisfied, theMode is deselected and the method OnDeselection is called.

Control Algorithm

PID algorithms type are used primarly. If no integrative contribution isneeded, then a simple proportional controller is implemented, otherwise thepid incremental form is implemented.

In this project, a modified "‘Allen Bradley PID"’ algorithm [1] is used.This algorithm contains only independent parameters, so a change in theproportional gain doesn’t affect the integrative and derivative terms. Also,the setpoint is removed from the derivative term (PID Type B), so it pre-vents from unwanted changes in the setpoint. Finally, the control algorithmparameters have been grouped into three new parameters (Kp, Ki,Kd) foreasier programming. This only applies to the full PID algorithm.

Algorithm 4.1 (Proportional Controller).

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uk = Kp · ek

Algorithm 4.2 (PID incremental form Controller).

uk = Kp(ek − ek−1) + Ki · ek + Kd(yk − 2yk−1 + yk−2) + Bias

Figure 4.9: PID Block Diagram

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Linearization If the system has a strong dependency to other variablethan the error signal, the system must be linearized first. Controlling thesystem manually, while maintaining the reference constant, it’s possible tomake the error signal acceptable for different values of the external variable.The output commands at these values are logged and can be used to estimatea correction term. This term is added to the PID computed output.

PID tuning In general there are two approaches of PID tuning, fromthe system transfer function and through some looping tuning algorithm.The transfer function calculations that would permit to calculate the properparameters, exceeds the scope of this thesis. An aircraft is a multivariablesystem strongly dependent that it’s not suitable for most high sophisticatedlooping tuning algorithms. Therefore a very simple tuning algorithm is in-troduced, leaving other approaches for further development:

1. Turn off the integral and derivative gain.

2. Increase the proportional gain of the loop in small increments until theloop just begins to cycle. This is the gain at which the system beginsto become unstable.

3. Reduce by a 20% approximately the proportional gain. If the systemaccomplishes the specifications no further tuning is required.

4. If the system doesn’t reach the reference or takes too long, set theintegrative gain to 1% of the proportional gain.

5. While the system doesn’t start to oscilate keep increasing the integra-tive gain until 10% of the proportional gain.

6. If the system doesn’t accomplish the specifications, turn off the integraland derivative gain, increase the proportional gain below the cyclinggain and set again the integrative gain.

7. Derivative gain can be added to make the system faster and preventsome oscillation, but can also make the system unstable. Typical valuesare of the same order as the integrative gain and smaller.

8. Monitor the performance of the loop and make minor adjustments asrequired to optimize the performance of the system.

9. Subject the loop to upsets by making acceptable set point changesand/or shutting down and restarting the system.

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This algorithm is not optimum in the way it doesn’t provide best perfor-mance parameters. However it provides safe parameters with a reasonablegood performance in a wide range. Aditionally, in the current state of theproject it is necessary to have some modes working. So the overall applicationcan be tested properly in the sense of integrity, workload and programmingbugs. Furthermore, this is the first step to tune the system using a moresophisticated technic, or other control algorithm. Nevertheless, it results un-acceptable for any release of the application other than a beta for testingpurposes.

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