TruTrak DFC Install Manual

Installation Manual

For

DFC Series Autopilots

TRUTRAK FLIGHT SYSTEMS

1500 S. Old Missouri Road

Springdale, AR 72764

Ph. 479-751-0250 Fax [phone]

www.trutrakflightsystems.com

INSTALLATION MANUAL

TABLE OF CONTENTS

Mechanical Considerations.................................................................................................1

Pitot and Static Connections...............................................................................................2

Magnetic Considerations....................................................................................................2

RFI/EMI .............................................................................................................................2

FOR

DFC-Series Autopilots

Electrical Wiring.................................................................................................................3

Connecting GPS Units

Garmin 430/530..............................................................................................................4

UPS GX-50/60/65...........................................................................................................5

UPS GX-50/60/65 w/SL-30............................................................................................6

Initial Checkout..................................................................................................................7

Yaw Damper Initial Checkout............................................................................................8

First Flight..........................................................................................................................9

Magnetic Calibration........................................................................................................10

Yaw Damper In-Flight Adjustment..................................................................................11

DFC-200/250Wiring Diagram..........................................................................................12

DFC-200/250Wiring Diagram..........................................................................................13

Mechanical Considerations

The installation information in this section is extremely important and must be clearly
understood by the installer. Improper servo installation or failure to observe and diagnose
installation problems prior to flight can result in extremely serious consequences, including
loss of ability to control the aircraft. If there are any questions on the part of the installer it
is mandatory to resolve these questions prior to flight of the aircraft.

Most modern experimental aircraft use push-pull tubes to drive the primary controls. These tubes generally have a total travel
of 3” or less; therefore, it is best to connect the autopilot servo to the primary control by the same method. This connection
consists of an arm on the servo connected by a push-pull rod to the primary control. Rod-end bearings are required on each
end of the push-pull rod.

The servo arm must not rotate even near to the point called OVER CENTER, the point at which the primary
aircraft control would lock up.

This is a condition that would result from the servo being back driven when the pilot operates the controls, or
from the servo itself driving the controls to a stop. To protect against this mechanical stops are supplied with the
servos. These stops are drilled so that they can be mounted at different angles as required (18° intervals)

In addition to the proper use of the stop it is important to know the amount of travel on the primary control that
the servo can handle. With the push rod connected to the outermost hole (1 ½”) the travel on the primary cannot
exceed 2 ½”, the intermediate hole 2 1/16”, and the inner hole 1 5/8”.

It is important to note that at the neutral point of the control the SERVO ARM must be PERPENDICULAR to the
push rod, and that the stop must be mounted so as to limit travel as near as possible to equal amounts in both
directions. In certain factory-designed installations there may be well-proven exceptions.

There will be installations in which space does not permit the use of the stop. When this is done the aircraft’s primary control
stops must be positive and care must be taken to be sure that at the neutral point the servo arm is perpendicular to the push rod,
and that the travel limits of the servo arm are not exceeded.

There are installations in which the travel of the push-pull tube exceed s the allowable 2 ½”. For such installations, the drive
can be applied to a bell crank at a radius point that moves the desired 2 ½” of maximum allowed travel in the outermost hole of
the arm.

When there is no way to have a drive point of less than 2 ½” or when the primary control is cable-driven it is necessary to use
the capstan-cable servo drive. When this is done the servo should be mounted so that the 1/16” diameter cable which wraps
around the capstan when extended parallel to the primary cable is approximately 3/16” from the primary cable. If the primary
control travel does not exceed 5” the cable locking pin will be 180° away from the point at which the cable leaves the capstan.
When the primary control is at the neutral point this means the total cable wrap around the capstan is 360°. If the primary
control travel is greater than 5” the cable wrap is 720°and the pin is adjacent to the output point when the primary control is at
the neutral point.

The cable clamps when properly installed will not slip and thus get loose, but it is desirable to nicopress or swedge a fitting on
to the cable so as to provide added assurance that the cable will not become slack. If the bridle cable is not sufficiently tight
there will be lost motion in the autopilot drive. This will result in hunting (oscillation).

TruTrak Flight Systems DFC Autopilot Installation Manual
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Pitot and Static Connections

All multi-servo TruTrak autopilots require connections to the pitot and static lines. The preferred method of this connection
would be tee fittings near the aircraft’s altimeter. The static line for the autopilot requires due care in its construction, as
excessive lag or insufficient static orifices can cause the autopilot to oscillate (hunt) in pitch. Although there is compensation
within the autopilot sufficient to handle moderate amounts of lag, the importance of a good static port and line cannot be
overstated. In some cases problems can be caused by having a large number of devices (including the autopilot) connected to a
single, insufficient, static port. In other cases, the static line itself is adequate but there are one or more devices connected to the
same line, one of which has a large static reservoir. A simple remedy for this problem if it occurs is a tee-fitting near the static
port, and a dedicated line to the autopilot only. Obviously, an insufficiently-large orifice coupled with large static reservoirs
can aggravate the problems associated with lag.

Magnetic Considerations

Because the autopilot contains a built-in magnetometer for a backup source of heading in the event of GPS loss, it is important
to try to locate the programmer away from known sources of magnetic disturbance. Th e calibration procedure can account for a
moderate amount of fixed disturbance (for example, nearby iron objects) but it cannot adjust for changing magnetic fields such
as might be generated by certain electrical devices. One known source of such problems is the “Flag” mechanism in some older
DG or HSI devices. These units use a solenoid to hold the flag out of sight, and the magnetic field will then change when the
flags come and go. If at all possible, place the autopilot so as to be as far as possible from such devices. A hand-held compass
can be used to assist in finding such problems prior to installation of the autopilot. Even a few inches can make an appreciable
difference in the magnetic disturbance level. It should be noted also that strobe light controls generate very strong currents in
their wiring, thus they will create a periodically pulsating magnetic field disturbance. Shielding has no effect on this problem;
the only solution is to keep strobe light, landing light, navigation light, and Pitot heater wiring as far away as possible from any
electronics which can be affected by pulsating magnetic fields.

RFI/EMI considerations

The autopilot programmer is shielded and does not generate any appreciable level of electromagnetic interference. Moreover,
the servo lines (except for power and ground) are low-current and cannot contribute to RF interference. The servo power and
ground lines do have switching currents through them, but so long as there are no parallel runs of servo power and ground lines
with such things as poorly-shielded antenna lines or strobe light power lines, there is no need to shield the servo harnesses.

The autopilot itself has been internally protected from RF interference and has been tested under fairly extreme conditions,
such as close proximity to transmitting antennas. However, it is always good practice to insure that such antennas are properly
shielded and not routed directly over or under sensitive panel-mounted electronic equipment. Most problems in this area are the
result of improper RF shielding on transmitting antennas, microphone cables, and the like. The most sensitive inputs to the
autopilot are the CDI, Glideslope, and Control Wheel Switch inputs. These lines should not be routed in parallel with
transmitting antennas or other sources of known RF interference. If necessary, they can be shielded with the shield connection
to pin 19 of the autopilot connector.

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Electrical Wiring

All TruTrak DFC series (DFC-200, DFC-200AS, DFC-250, DFC-250AS, DFC-300, DFC-300AS) autopilots have consistent
wiring requirements. Therefore, this manual covers all such units, with special notations covering any differences between the
units. The DFC-200 programmer is mechanically identical to the DFC-250 and differs only in its internal circuitry and
software. The DFC-300 autopilot system consists of a DFC-250 programmer and a YD-300 yaw damper module, together with
the three servos that constitute the system.

The table below provides a brief explanation of each pin function on the main 37-pin connector P101.

P101 Autopilot Rear Connector (Viewed from rear of autopilot)

P101

Pin

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Function Notes

1 Dedicated ground connection for Pitch Reverse Jumper.

Pitch Reverse Jumper,

2

present or absent, as follows:

Pin 2 open (no connect): Servo CCW (counter-clockwise) Î UP
Pin 2 Jumpered to pin 1: Servo CW (clockwise) Î UP

3 Auxiliary RS-232 Output. Presently unused, intended for future expansion.
4 LAMP1 (see also pin 18) A source of variable DC from external dimming source. Drives the

LCD backlighting circuit and six 60 mA lamps. If left disconnected, backlight will be full-on
and buttons will be unlighted. Draws approximately 500 mA at 12v, 250 mA at 28v.

5 Yaw Damper Gyro Gain. A signal from the autopilot which sets the amount of response the

yaw damper exhibits to azimuth disturbances.

6 Yaw Damper Tilt Gain. A signal from the autopilot which sets the amount of response the

yaw damper exibits to a given amount of deflection of the “ball”.

7 No Connection. Reserved for future expansion.
8 Yaw Damper Activate. A signal from the autopilot which turns on the yaw damper function. DFC-300 only
9 Analog DG/HSI Input. A zero to 5V DC signal centered at 2.5 volts from an external steering

device. An adapter specific to a given DG or HSI is required. Consult factory for details on this
adapter.

10 Pitch Servo Torque Control. A signal from the autopilot to the pitch servo which sets the

amount of torque to be delivered by the servo.

11 Pitch Servo Trim Sensor. A signal from the pitch servo to the autopilot which indicates an

out-of-trim condition and its direction.

12 Autopilot Master (+12 to +28 V DC). The autopilot itself draws less than ½ ampere. Most of

the current required by the autopilot system is used by the servos (up to 1A per servo).

13 Audio alerter signal. This pin may be wired to an unswitched input of an audio panel. The

autopilot uses various tones to denote specific events (loss of GPSS, capture Glideslope, etc).
Volume is adjustable within a setup screen of the autopilot.

14

Pitch Servo control lines. These lines cause the stepping motor in the pitch servo to run in the
appropriate direction at the desired velocity. They are small-signal lines and do not have any

15

substantial current-carrying capability or require any special shielding. Connect to pitch servo

16

as shown on wiring diagram.

17
18 LAMP2 (see explanation for pin 4, above).
19 Ground Connection. Provide #20 AWG to common grounding point.
20 Control Wheel Switch. Connect as shown in wiring diagram to a SPST momentary switch

located remotely to the autopilot for convenient engage/disengage func tion.

21

CDI LEFT

22

CDI RIGHT

Analog +/- 150 mV differential signals from Nav receiver. Pin 22 more
positive than pin 21 indicates CDI needle right-of-center.

Direction of servo arm / capstan rotation

(as viewed from face of the servo body)

for UP elevator

See note 4 on wiring
diagram

Dimmer is wired
based on supply
voltage. See note 2
on wiring diagram
DFC-300 only

DFC-300 only

not attempt to

Do
reverse servo
direction by
swapping wires