190-01115-01 G3X™/G3X Touch™ Avionics Installation Manual
Rev. AV Page 17-5
17.4 Unit Installation
Fabrication of a wiring harness is required. Sound mechanical and electrical methods and practices should
be used for installation of the GSU 25. Refer to Section 2.3
for wiring considerations, and to Section 23.14
for pinouts.
The GSU 25 connects to other LRUs in the G3X system using the CAN bus. To provide an optional
redundant path for attitude and air data, a secondary RS-232 connection to a single GDU™ display
(typically PFD1) is also supported. See Figure 24-1.11
for wiring and configuration information.
Connector kits include backshell assemblies. Garmin’s backshell connectors give the installer the ability to
quickly and easily terminate shield grounds at the backshell housing. The instructions needed to install the
jackscrew backshell are located in Section 22
.
NOTE
Connection to a GMU magnetometer and GTP 59 is required for ADAHRS 1 but optional
for ADAHRS 2 & 3.
NOTE
Make sure that backshell connectors are fully tightened. Loose connectors may cause
vibration-related performance issues that are difficult to troubleshoot.
17.4.1 Mounting/Calibration Overview
It is critical the GSU 25 is mounted in alignment with the centerline of the aircraft. The GSU 25 must be
mounted with the connectors aligned within 1.0 degree
of either the longitudinal or lateral axis of the
aircraft. (see Section 17.4.1 for complete requirements)
The specification for mounting the GSU 25 such it is level with respect to pitch/roll of the aircraft is not
nearly as restrictive, and must only be within 30.0 degrees
in each axis. In most installations, the
GSU 25 is mounted relatively level with respect to the zero waterlines of the aircraft (e.g. longerons), even
though it is not required (again, must only be within 30.0 degrees)
. (see Section 17.4.2 for complete
requirements
Calibrating the pitch/roll offsets is also a crucial part of the installation (see Section 30.4.7
). During
calibration, while on the ground
, the aircraft must be level in both pitch/roll so it accurately represents the
in-cruise attitude of the aircraft. This part of the calibration determines the displayed measured attitude of
the GSU 25 is zero degrees in pitch/roll when the aircraft is in level, coordinated cruise flight. (Note the
PFD allows +/- 5 degrees of pitch offset adjustment in flight
. This allows the pilot to adjust the pitch offset
while in flight to show a correct attitude indication on the PFD, even if the pitch attitude was slightly off
when the on the ground
pitch/roll offset calibration was performed.)
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