TruTrak Yaw Damper - Manual (Page 4)

TruTrak Flight Systems Yaw Damper Installation Manual
December 2009 2 8300-063 Rev C
Servo Installation
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. 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
NICO press or swedge a fitting on to the cable so as to provide added assurance that the cable will