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

866-(878-8725)

www.TruTrakap.com

1
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
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

2

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, 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 eliminates drift as well as crosswind correction. In the GPS steering mode of operation, the 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 system, the following describes the presentation of data, the operating controls, and the procedures for selecting modes of operation.

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

DG SLAVED	→
TO TRACK	→
SELECTED
DIRECTION

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 FIX. 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 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.

← SELECTED VERTICAL SPEED

↑TRIM INDICATOR

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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 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

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. 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