TruTrak DFC Operating Manual - Manual (Page 11)

10
which time the words
GYRO SET
will be displayed.
Engaging the
Autopilot
Since the autopilot
synchronizes to VS, the VS at
the time of engaging should be
a value that can be sustained.
Otherwise airspeed will
diminish as the aircraft attempts
to sustain VS. As
airspeed then
diminishes to the pre-set
minimum it will hold this value
and thus prevent a stall.
When aircraft vertical speed
is less than approximately 350
feet per minute, the autopilot will
initially select zero vertical speed.
The [VS UP] and [VS DN] keys
can be used to change the initial
value if desired.
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 few
seconds, 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 reverse direction may be
required to get the bars to stay
off. Finally, when the bars have
been made to disappear and there
has been no speed change, the
bars can be ignored if they
reappear if it is known the aircraft
is close to being in trim.
MAG*180 ALT 1350
GYRO SET
Power Loss
If there is a momentary loss
of electrical power, the autopilot
will disengage. When this
happens it is necessary to do a
GYRO SET before re-engaging
the autopilot. To accomplish this,
the aircraft must be held very
straight during which time the
encoder knob is pressed to do
GYRO SET. After this, engage
the autopilot and note the extent
to which
TRK differs from SEL.
If this is more than 15
° repeat the
gyro set procedure. The
difference between
TRK and SEL
will be reduced at the rate of 8
°
per minute by the automatic gyro
centering system within.