TruTrak Digiflight II Operation Manual

Operating Handbook

For

Digiflight II SERIES AUTOPILOTS

TRUTRAK FLIGHT SYSTEMS

1500 S. Old Missouri Road

Springdale, AR 72764

Ph. 479-751-0250 Fax [phone]

Toll Free: 866-TRUTRAK

66-(878-8725)

8

www.TruTrakap.com

1

General Information

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

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

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

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

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

Digiflight II

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

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

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

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

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

Digiflight IIVS

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

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

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

Minimum and Maximum Airspeed...........................9

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

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

Setup Procedure

Digiflight Setup.......................................................10

Table of Contents

2

General Introduction

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

his means that gyroscopic rate sensors are installed so as to sens e motion

T
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. 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, yaw disturbances in turbulence 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 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 all the electronic
and sensing elements needed for the roll and pitch functions and interfaces to
a rate-gyro-controlled yaw damper within a single panel-mounted
programmer/computer package.
Basic directional control is provided by digital selection of a GPS track
to be flown. This replaces heading selection on the DG and e liminates drift
as well as crosswind correction. In the GPS steering mode of operation, th e
system responds to digital guidance information 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.
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 syste m,
the following describes the presentation of data, the operating controls, and
the procedures for selecting modes of operation.

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

3

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 BANK, which
means the autopilot now uses
an internal source of gyro
information for bank angle.
The lower left display shows
the selected bank angle 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 four
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 NO

. When there is GPS serial

FIX

data present but no position fix,
this will be a flashing period.
Once GPS position data
becomes valid this will be a
flashing asterisk and GPS OK.
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 can be set by rotation of
the encoder knob.

DG SLAVED

→

TO TRACK
SELECTED

→ ←

DIRECTION

TRIM INDICATOR

↑

SELECTED

VERTICAL SPEED

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
mode (or GPS

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
mode, the ALT button will
engage the
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 either by
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

NAV mode if

GPSV mode, if it is

GPSS

GPSS

4

as Control Wheel Steering in
that the autopilot synchronizes
to both direction and vertical
speed upon being engaged.

Initializing the
Autopilot

The autop ilot 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. The model and
software version will be
displayed for approximately ten
seconds in the lower left. Then

PWR UP in the lower right

takes approximately another ten
seconds.

When initializing is complete

PWR UP will change to AP
OFF