GRT Avionics, Inc.
May 2019
Sport SX Install. Manual
8
Rev. A
The inter-display unit link can also share specified data that only a single display unit may
be receiving, including any analog inputs.
2-2-2: Autopilots
An autopilot provides the greatest benefit for the cost of almost any addition to the
airplane. It is an essential tool for single pilot IFR and highly beneficial for any VFR pilot
that undertakes cross-country flights. The autopilot frees up the pilot to perform other vital
tasks, such as looking for traffic, radio tuning, evaluating imminent weather, etc
… We
highly recommend it for all airplanes, with the exception of those that are not flown cross-
country. If you have chosen not to install an autopilot, but may do so in the future, we
recommend installing the servo wiring at the very least, and possibly installing the servo
mounting kits as well. This will make the addition of the servo easier in the future. This
also increases the value of the airplane for any future owner if it is sold without an autopilot
installed.
2-2-3: Autopilot Using GRT Avionics Servos
An autopilot using GRT Servos provides excellent performance and is the easiest
configuration to implement. The installation will require wiring for the servos, mounting
kits to attach the servos to your airplane, a power-switch for the servos and an
engage/disengage button. A single serial port is used to control both the roll and pitch
servos.
When using multiple GRT EFIS display units, any display unit can function as the autopilot
mode controller. Adding an autopilot switch to a second display unit ensures functionality
in the event that the primary autopilot-controlling display unit fails.
2-2-4: Trio Avionics and TruTrack Flight Systems External Autopilots
Most of our customers use GRT Servos for their autopilot needs. However, airplanes with
existing autopilots can still interface with any GRT EFIS. This is accomplished via a serial
output from the EFIS for lateral-only steering. Autopilots that provide vertical steering
require an ARINC 429 adapter to receive GPSS and GPSV commands, which requires
the use of both a serial input and an output from the EFIS.
External autopilots that include their own source of gyro data provide some degree of
redundancy with the AHRS data from the EFIS when the autopilot is coupled. This benefit
is offset by slight transients in pitch when the autopilot is initially coupled to the EFIS. It
also requires more button presses than when GRT servos are used. Since GRT servos
can be mounted in place of TruTrak or Dynon servos, many of our customers choose to
sell their autopilot and install GRT servos; in this instance, the existing mounting kits and
wiring can be used. The required changes to the electrical connections for this switchover
are not difficult to make.
