TruTrak ADI Pilot II - Manual (Page 4)

ADI Pilot II Pitch Axis Operation
Once the aircraft is off the ground and at a safe altitude, the autopilot can be engaged. Pressing and releasing the lower left
knob will engage the pitch axis of the autopilot and the “ALT” light will light up. The autopilot will now hold the current
altitude. The pitch axis can be used independently of the roll axis. If there is a trim sensing servo installed and the aircraft
becomes out of trim then you will see a moving bar on the left side of the display telling the pilot which way to trim the
aircraft. The altitude hold must be engage to show out of trim. When the difference between the current altitude and the initial
selected altitude is more than approximately 50 feet you will see a moving bar on the left side of the display, showing which
way to go to correct the difference in altitude. Many times on a long flight the barometric setting on the altimeter will need to
be adjusted, the pitch axis does NOT have to be disengaged to move the aircraft to the correct altitude. Once the aircraft
altimeter is correctly set, push and hold the left knob of the autopilot. While continuing to hold the knob in, the current altitude
can be adjusted up to 90 feet in either direction.
Disengaging the pitch axis of the autopilot can be done in three different ways. Pressing and releasing the lower left knob will
disengage the pitch axis of the autopilot. If the roll axis is engaged, push and holding the lower right knob for approximately
1-1/2 seconds will disengage both the roll and pitch axis of the autopilot. Another way to disengage the autopilot is with the
Control-Wheel Switch. Momentarily pushing and releasing the Control-Wheel Switch will disengage both the roll and pitch
axis of the autopilot.
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. Some aircrafts mechanical primary control installations will not allow this to
occur and do not need the servo stops.
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 exceeds 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.
TruTrak Flight Systems ADI Pilot I & II Autopilot Installation Manual
December 2009 2 8300-012 Rev B