TruTrak Digiflight II Series Manuel utilisateur

Operating Handbook

For

Digiflight II SERIES AUTOPILOTS

TRUTRAK FLIGHT SYSTEMS

1500 S. Old Missouri Road

Springdale, AR 72764

Ph. 479-751-0250 Fax 479-751-3397

www.TruTrakap.com

Table of Contents

General Information

Introduction...............................................................2

Mode and Data Display.............................................3

Controls.....................................................................4

Initializing the Autopilot...........................................4

GPS Acquisition .......................................................5

Digiflight II

Lateral Modes............................................................5

Magnetic Back-Up Mode..........................................5

Altitude Hold Mode...................................................6

Minimum and Maximum Airspeed ...........................6

Gyro Set.....................................................................6

Power Loss................................................................7

Digiflight IIVS

Lateral Modes............................................................7

Magnetic Back-Up Mode..........................................8

Vertical Modes..........................................................8

Setting Pitch Trim .....................................................9

Minimum and Maximum Airspeed .........................10

Gyro Set...................................................................10

Power Loss..............................................................10

Setup Procedure

Digiflight Setup.......................................................11

General Introduction

The TruTrak autopilot can be defined as being an orthogonal rate system.

This means that gyroscopic rate sensors are installed so as to sense motion

about each of the major axes (roll, yaw, and pitch). These sensors generate

the fast signal responses necessary to create an autopilot with the best

possible dynamic performance.

To fly an aircraft well about the axis controlled by the ailerons, velocity

of aileron movement must be directly proportional to the rate of roll for small

movement. This means that aileron position corrections do not lag behind

motion of the craft about the roll axis. Aileron control systems that use a

turn coordinator, which senses twice as much azimuth as roll rate, cannot do

this. Instead, in turbulence, yaw disturbances cause undesired aileron

movement. In some aircraft this effect is so severe that the controls may

even move momentarily in the wrong direction.

The challenge at TruTrak is to create, beyond question, systems with the

very best dynamic performance available—systems that need not be

disengaged in turbulence, but instead provide function when most needed.

The complete TruTrak flight control system combines within a single

panel-mounted programmer/computer package which includes all the

electronic and sensing elements needed for the roll and pitch functions and

interfaces to a rate-gyro-controlled yaw damper.

Basic directional control is provided by digital selection of a GPS track

to be flown. This replaces heading selection on the DG, and eliminates drift

as well as crosswind correction. In the GPS steering mode of operation, the

system responds to digital guidance information so as to fly a complex

navigation program.

The vertical portion of the system contains a pressure signal source for

altitude and vertical speed information, an airspeed signal source, and a high

performance pitch rate gyro. These signals are combined to provide

performance equal to that of the most expensive autopilots. Also by having

airspeed information the system is stall proof. It is expected that other

systems will soon be coming out with this same feature.

For any set of features all TruTrak computers are identical. Servos

likewise are identical in velocity response. Servos do differ according to

total torque required. By providing setup functions in the programmer for

system activity and torque, one TruTrak programmer-servo combination can

fly any aircraft.

As a starting point in understanding how to operate the TruTrak system,

the following describes the presentation of data, the operating controls, and

the procedures for selecting modes of operation.

POWER UP—AIRCRAFT STATIONARY

SEE INITIALIZING THE AUTOPILOT PAGE 4

Mode and Data

Display

This display normally

shows operating modes and

associated numerical data. It is

also used to display setup mode

screens and the setting of

associated numerical data.

When displaying operating

modes, the left side shows

lateral data and the right side

shows vertical data. (See figure

below.) The upper left display

labeled TRK shows the

electronic DG slaved to GPS

track. When the GPS track is

not available TRK will be

replaced by HDG, which means

the autopilot now uses an

internal source of magnetic

information for direction. The

lower left display labeled SEL

shows the selected direction of

flight. In the Digiflight II and

IIVS, the upper right shows

whether or not the unit is in the

altitude hold mode. The lower

right display shows selected

vertical speed or whether the

autopilot is on or off.

With the Digiflight IIVS,

the vertical space between the

left and right hand display

area is used to show pitch trim.

This display consists of three

horizontal bars spaced

vertically as the rungs on a

ladder, and are made to move

up or down when the aircraft is

in need of being trimmed.

In the upper left where

direction is shown, a flashing

indicator is present beneath TRK

or HDG.When there is GPS

serial data present but no

position fix, this will be a

flashing period. Once GPS

position data becomes valid this

will be a flashing asterisk. If

GPS flight plan information is

being received over the serial

channel or if the programmer is

a Digiflight IIVSG and GPS

steering information is being

received, a flashing plus sign

will indicate the presence of a

useable steering (GPSS mode)

or waypoint to waypoint (GPS

NAV mode) signal.

A cursor in the form of an

underline is shown beneath the

SEL numerals. This is used to

indicate that an underlined

number will be set by rotation

of the encoder knob.

→

→←

↑TRIM INDICATOR

DG SLAVED

TO TRACK =

=ALTHO

TRK 005 LD

SELECTED

DIRECTION

SELECTED

VERTICAL SPEED

SVS

005

SEL

Controls

The Digiflight II series

autopilot uses the simplest

controls available. All

programming is done via a

rotary encoder knob and two

buttons labeled MODE and

ALT. The MODE button

toggles between the default

(TRK) mode and the GPSS

mode (or GPS NAV mode if

GPS steering is not available),

as well as moves the cursor

back to the SEL numerals. The

ALT button engages altitude

hold or moves the cursor to the

SVS numerals. If in the GPSS

mode, the ALT button will

engage the GPSV mode, if it is

available. Both buttons are also

used to enter the setup modes as

well as maneuver through the

setup screens. Engaging the

autopilot can be done by either

momentarily pushing and

releasing the encoder knob on

the programmer or by pushing

and holding the switch located

on the control wheel or stick for

more than two seconds and then

releasing. Disengaging can be

done either of two ways: by

pushing and holding the

encoder knob on the

programmer for approximately

three seconds and then releasing

the knob, OR by momentarily

pushing and releasing the

switch located on the control

wheel or stick. This means that

in addition to disengaging the

autopilot, this switch also

provides the function referred to

as Control Wheel Steering in

that the autopilot synchronizes

to both direction and vertical

speed upon being engaged.

Initializing the

Autopilot

The autopilot master switch

should be in the off position

when the engine is started.

Aircraft electrical systems can

generate voltage transients

during an engine start, and like

other avionics systems, the

autopilot should not be

subjected unnecessarily to these

conditions. After start up, turn

on the autopilot master switch

and hold the aircraft stationary

as the internal gyros are

initialized. This takes

approximately ten seconds

during which time the display

will show the words PWR UP

in the lower right. The software

version will be momentarily

displayed in the lower left.

HDG

V X.X

005

PWR UP

When initializing is

complete PWR UP will change

to AP OFF

AP OFF

005

HDG

GPS Acquisition

Beneath the word HDG a

flashing period •will appear

each time the GPS sends a

message to the autopilot (once

per second). This indicates the

GPS is working but has not yet

obtained a position fix. As long

as the period is shown, the

heading display cannot

transition to the TRK mode.

When the GPS does obtain

a fix, the period will be

replaced by an asterisk *. This

means that when a certain

velocity is attained HDG will be

replaced by TRK. This happens

at approximately 10 Knots

ground speed as detected by

GPS and will even occur at

rapid taxi speeds.

Digiflight II

Lateral Modes

Upon being engaged, the

autopilot will be in the basic

lateral mode, and it will be

synchronized to the direction

being flown at the time. The

number following SEL

(Selected direction) is

underlined, meaning that

rotation of the encoder will

select heading. Rotation of the

knob when it is not depressed

will cause 1°steps of SEL and

when it is depressed the steps

will be 5°.

If a GPS flight plan has

been entered into the GPS,

pushing the MODE will engage

the GPS NAV mode and a

flashing plus sign will show. In

the GPS NAV mode, the

autopilot will follow a flight

plan programmed into the GPS.

The autopilot must, however,

over-fly each way point prior to

turning and intercepting the

next course line.

AP ON

NAV

005

TRK

GPS

If the

GPSS option has

been added, pushing the MODE

button will engage the GPS

steering. In the GPSS mode the

autopilot follows lateral

steering or bank commands

generated by a navigation

system (EFIS or GPS).

AP ON

SEL 005

005

TRK

GPSS

TRK 005

AP ON

Magnetic Back-

Up Mode

The lateral modes

previously described are based

on GPS track being present.

When GPS is lost, the DG

display is slaved to a magnetic

heading source contained

within the programmer and TRK

is replaced with HDG. This

magnetic mode is only a backup

and would seldom be needed;

however, it does provide a

means of selecting and

maintaining a drift-free

direction of flight. If the GPSS

signal source is functional, the

GPSS mode will remain

functional.

Altitude Hold Mode

When the autopilot is

engaged it will be in the basic

lateral mode, and will

synchronize to the direction

being flown at the time. The

pitch servo will not be engaged

at this time. To engage the

altitude hold the aircraft must

be at the desired altitude and be

trimmed for level flight. After

trimming the aircraft, to enter

the altitude hold mode, simply

press and release the ALT

button. The display will show:

If an altitude change is

desired, it is necessary to turn

off the altitude hold. To do

this, press and release the ALT

button. The display will show:

Minimum and

Maximum Airspeed

The Digiflight II series

autopilots have a minimum and

maximum airspeed feature.

These are added only for safety.

If the autopilot is in altitude

hold and the pilot reduces

power to a point at which the

airspeed falls below the

minimum airspeed set in the

autopilot, the autopilot will

allow the aircraft to begin a

descent and flash MIN AS on

the display.

AP ON

SEL 005

005

TRK

*MIN AS

Likewise if the autopilot is in

altitude hold and the pilot adds

power to a point at which the

airspeed reaches the maximum

airspeed, the autopilot will

allow the aircraft to climb and

will flash MAX AS on the

display.

AP ON

TRK 005

005

SEL

MAX AS

AP ON

SEL 005

005

TRK

*HOLD

ALT

Gyro Set

When the initializing has

been done correctly, the gyros

should already be centered at

the time of take off. If

confirmation of this is desired,

with the aircraft stationary on

the runway and the autopilot

disengaged, pressing and

AP ON

SEL 005

005

TRK

holding the encoder knob will

put the gyros in the fast

centering mode. The knob

should be depressed for

approximately 3 seconds during

which time the words GYRO

SET will be displayed.

Power Loss

If there is a momentary

loss of electrical power, the

autopilot will disengage. The

autopilot gyros must now be

manually re-initialized using

the GYRO SET operation.

Manually fly the aircraft in a

straight line as steadily as

possible, while holding in the

knob for at least ten seconds

after the words GYRO SET

appear in the display. After

approximately ten seconds have

elapsed, release the knob. The

autopilot may now be re-

engaged, and any residual gyro

offset will be slaved away

automatically.

SET

GYRO

005

HDG

Digiflight IIVS

Lateral Modes

Upon being engaged, the

autopilot will be in the basic

lateral mode, and it will

synchronize to both the

direction and vertical speed

being flown at the time. The

number following SEL

(Selected direction) is

underlined, meaning that

rotation of the encoder will

select heading. Rotation of the

knob when it is not depressed

will cause 1°steps of SEL and

when it is depressed the steps

will be 5°.

If a GPS flight plan has

been entered into the GPS,

pushing the MODE button will

engage the GPS NAV mode and

a flashing plus sign will show.

In the GPS NAV mode the

autopilot will follow a flight

plan programmed into the GPs.

The autopilot must, however,

over-fly each way point prior to

turning and intercepting the

next course line.

GPSNAV 0

SVS

HOLD

ALT

005

TRK

ALTHOLD

SVS 0

TRK 005

005

SEL If the

GPSS option has

been added, pushing the MODE

button will engage the GPS

steering. In the GPSS mode the

autopilot follows lateral

steering or bank commands

generated by a navigation

system (EFIS or GPS). Once in

the GPSS mode, pushing the

ALT button will enter the

GPSV mode as well. This

feature will only be available

when coupled to certain EFIS

systems or a GPS with vertical

GPS steering outputs.

TRK 005 ALTHOLD

GPSS SVS

Magnetic Back-Up

Mode

The lateral modes

previously described are based

on GPS track being present.

When GPS is lost, the DG

display is slaved to a magnetic

heading source contained

within the programmer, and

TRK is replaced with HDG. This

magnetic mode is only a backup

and would seldom be needed;

however, it does provide a

means of selecting and

maintaining a drift-free

direction of flight. If the GPSS

signal source is functional, the

GPSS mode will remain

functional.

Vertical Modes

When the autopilot is

engaged it will synchronize to

the direction and vertical speed

being flown at the time, the

lower right section of the

display shows SVS (selected

vertical speed). To enter

altitude hold at any time, push

and release the ALT button two

times.

ALTHOLD

SVS 0

TRK 005

005

SEL

If an altitude change is

desired, momentarily push and

release the ALT button and the

cursor will move over to the

selected vertical speed.

400

SEL 005

005

TRK

*SVS

Rotation of the encoder

knob will now change the

selected vertical speed. If the

cursor is under the SVS number

a single click of the ALT button

will select zero vertical speed.

If the selected vertical speed is

set to zero, the display will

show:

ALTHOLD

SVS 0

TRK 005

005

SEL

Once the desired vertical

speed has been selected,

momentarily pushing and

releasing the MODE button will

move the cursor back to SEL, or

after approximately seven

seconds without moving the

encoder, the cursor will move

back to SEL.

If the autopilot is coupled to a

GPS or EFIS system which can

provide vertical GPS steering,

once in the GPSS mode,

pushing the ALT button will

enter the GPSV mode as well.

To use the GPSV mode with the

GNS 480, the aircraft must be

below the virtual glide slope

and the autopilot must be in

altitude hold. When approach

is initiated and the CDI

becomes active, the GPSV

button can then be pushed and

the unit will enter the GPSV

mode. The first screen will

show as below:

FLG

GPSS

005

TRK

+GPSV HOLD

ALT

When the VDI is no longer

flagged, the unit will enter

GPSV hold, and the display will

show as below:

HLD

GPSS

005

TRK

+GPSV HOLD

ALT

Once the VDI has been above

the center by one dot for at least

7 seconds the GPSV mode will

ARM, and the display will

show:

ARM

GPSS

005

TRK

+GPSV HOLD

ALT

As the VDI passes through

center, the autopilot will couple

to the virtual glide slope, and

the display will show that the

autopilot is now coupled to the

virtual glide slope as below:

GPSS

005

TRK

+GPSV↓

Setting Pitch Trim

The pitch servo contains a

torque sensor that sends a signal

to the computer when the up or

down force greater than a

threshold value is required to

fly a selected flight condition.

When this signal indicates an

out of trim condition that

persists in one direction for

more than a pre-set length of

time, the three moving

horizontal bars will come into

view and move according to the

direction in which trim is

required. The pilot is then

required to operate the trim

control (electric or manual) so

as to bring the system to neutral

trim. With mechanical trim this

is easily done, but with electric

systems it may be necessary to

develop a technique. If the trim

is slow enough, the pilot has

plenty of time to react when the

bars disappear before the trim

condition is reversed. With a

fast trim it will be necessary to

tap or pulse the trim button so

that it will be slow enough to

turn it off before going too far.

When a reversal takes place, a

slight tap in the opposite

direction may be required to get

the bars to stay off. Finally

when the bars have been made

to disappear and there has been

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