TruTrak DFC Operation Manual

Operating Handbook

For

DFC SERIES AUTOPILOTS

TRUTRAK FLIGHT SYSTEMS

1500 S. Old Missouri Road

Springdale, AR 72764

Ph. 479-751-0250 Fax [phone]

www.trutrakflightsystems.com

1

Table of Contents

Operating Instructions

General Introduction....................................................2

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

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

Lateral Modes..............................................................4

Magnetic Back-Up Mode............................................6

Yaw Damper................................................................6

Vertical Modes............................................................6

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

Altimeter Sync.............................................................7

Altitude Select Mode...................................................7

VNAV Mode...............................................................8

Stopping the Transition to a Selected Altitude............8

Additional Operating Instructions

Initializing the Autopilot.............................................9

GPS Acquisition..........................................................9

Altitude Select with AP Off ........................................9

Gyro Set.......................................................................9

Engaging the Autopilot................................................10

Setting Pitch Trim .......................................................10

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

DFC-250 Setup Procedure

Lateral Setup................................................................11

Pitch Setup...................................................................14

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, pitch and yaw). 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 needed most.
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 as
well as 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 digital altimeter and
associated altitude selector capable of selection in increments as small as
fifty feet. Altitude transitions can be made by airspeed, vertical speed, or
horizontal distance (VNAV) selection. If and upward vertical speed is
selected which is beyond the capability of the aircraft, there will be no stall.
Instead, the autopilot will cause the aircraft to climb at a pre-set minimum
safe airspeed. This is the only known system to provide this safety 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.

2

POWER UP—AIRCRAFT STATIONARY

SEE INITIALIZING THE AUTOPILOT PAGE 9

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
electronic DG slaved to GPS
track. When the GPS track is
not available
replaced by
the autopilot now uses an
internal source of magnetic
information for direction. The
lower left display labeled
shows the selected direction of
flight. The upper right display
shows altitude or selected
altitude, and the lower right
display shows either selected
vertical speed or selected
airspeed.

the left and right hand display

DG SLAVED

→ ←

TO TRACK

SELECTED

→ ←

DIRECTION

TRK shows the

TRK will be

MAG, which means

SEL

The vertical space between

TRK*135 ALT 4500
SEL 135 ≡ SVS 500+

↑

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 between

TRK or MAG and the numerals

that follow. When there is no
GPS position input 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

GPSS option

has been added 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 (
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

VERTICAL SPEED

3

GPS NAV

INTERNAL

ALTIMETER

SELECTED

Controls

Switches labeled [MODE]
and [ALT] when depressed
sequentially step through the
respective lateral and vertical
mode setup screens. When the
desired setup screen is
displayed, the numerical data to
be entered will be underlined.
The data is then set by rotating
the encoder knob and entered
by depressing and then quickly
releasing the knob. This will be
referred to hereafter as enter.
Another means of entering
numerical data is the sequential
pressing of a [VS] switch.
Each time a [VS] switch is
pressed, the vertical speed will
be changed in increments of
100 feet per minute. Still
another means of altering the
display presentation is engaging
or disengaging the autopilot.
This is accomplished by using
the [ON OFF] switch on the
programmer or the switch
located on the control wheel or
stick. The control stick switch
serves a dual purpose.
Momentary closure will
disengage the autopilot. If the
switch is held closed more than
two seconds, the autopilot will
engage upon release. 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.

4

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. (See
figure on page 3.) Note: The
number following
direction) is underlined,
meaning that rotation of the
encoder will select heading.
Rotation of the knob when it is
not depressed will cause 5°
steps of
depressed the steps will be 1°.
When an external heading
source (DG or HSI) is present,
depressing [MODE] one time
will select the
screen. If this is the desired
mode, pressing the encoder
knob makes it the active lateral
mode. When in this mode the
heading “bug” within the
external DG or HSI will be used
to control direction.

TRK 135 ALT 4500
EXT DG SVS 500+

The next sequential entry
screen will be either

GPSS depending on which, if

either, steering signal is
available to the autopilot.
In
autopilot follows a flight plan
programmed into the GPS. The
autopilot will however overfly
each waypoint prior to turning
and intercepting the course line
to the next waypoint.

TRK+135 ALT 4500
GPS NAV SVS 500+

SEL and when it is

GPS NAV mode the

SEL (Selected

EXT DG entry

GPS NAV or

In the GPSS mode the
autopilot follows lateral
steering or bank commands
generated by a navigation
system (EFIS or GPS).

TRK+135 ALT 4500
GPSS SVS 500+

The next sequential entry
screen is

VOR NAV or LOC NAV,

depending on which is selected
by the navigation receiver. The
setup screen for this mode is
shown below.

LOC NAV CRS 183
INTRCPT ANGLE 30

The course numerals are
underlined. This means that the

VOR/LOC course is to be set by

rotating the encoder. As the
encoder is rotated, knob out
equals 5° steps while knob in
equals 1° steps. When course
has been set press enter. The
cursor (underline) has now
moved to intercept angle. The
default value will be 30°. The
intercept angle can be set from
15° to 45° by rotation of the
encoder knob. When the
desired intercept angle is set,
press enter.

LOC NAV CRS 183
INTRCPT ANGLE 30

The selected intercept
angle is now converted to an
intercept direction according to

5

which side of the course the
aircraft is on.

TRK 213 ALT 4500
INT 213 VS 500↑

Also, intercept direction is
underlined which means it can
be adjusted. With this feature
the system is in a selected
direction mode until the on
course turn (tracking phase) is
initiated. During the intercept
phase of the approach, the
lower left display will alternate
to show
of five. When the aircraft is
established on the inbound
portion of the approach, the
lower left display will indicate
the selected course.

glide slope is present (ILS),
flying below the glide slope in

ALT HOLD mode will arm the

glide slope coupler. When this
occurs, the display will be as
shown below

TRK 183 AH 4500
CRS 183 GS ARMED

When the Glide slope is
intercepted, the display will be
as shown below.

When glide slope coupling
is terminated, by entering either
the

CRS for one second out

TRK 213 ALT 4500
CRS 213 VS 500

If the above is LOC NAV and

TRK 183 ALT 2200
CRS 183 GS CPLD

ALT HOLD or VS mode, the