GRT Electronic Flight Instrument System (EFIS)
The EFIS I am using is the Grand Rapids dual high resolution HX displays. This EFIS has synthetic vision meaning that it draws a picture
of the terrain as seen from the cocpit on the main display. The second display will be used for engine instruments and moving map. I opted
for the dual air data computer and dual magnetometers. It sounds like a good idea for redundancy but I have to warn you that it is also twice
the wire harnesses, weight and volume.
The GRT system came without mounting hardware, missing ARINC connectors, no connector pins, missing Ethernet cable, no
harness lacing and incorrect documentation. If it wasn't for these discrepancies I would only be severely disappointed in their quality
control. It is up to the end user to identify all the missing items, research the documentation you need for HX displays from their website,
then cut the harness and reinstall pins so it is the length and configuration you need it to be.
I fabricated a AHRS mounting shelf which flange mounts to the sub-panel. I strongly advise you to not
mount anything behind the subpanel unless it is accessible from the front. You will notice that the rear of my AHRS does not require any
access to screws. It is strictly a friction fit lip that holds the back down. All retaining screws are in the front.
GRT wants the AHRS aligned with the pitch and roll axis of the airplane but don't give any specification as to the accuracy.
I raised the airplane tailstand and set the longitudinal axis to within 0.2 degrees of level. Then using a digital level, I zero'd on the
main longeron and transferred the level to the AHRS shelf. After riveting the shelf in place, I realized that just by shifting my body from
the longeron measurement(behind me) to leaning forward to make the shelf measurement would compress the nose wheel enough to introduce a 0.5
degree error. Without any manufacturer specification to mounting accuracy, I went ahead and tried to level further with washers under the
forward AHRS mounting screws.
The magnetometer interfaces consist of 6 wires each to a DB-9 connector which faces aft. The units
are supposed to be mounted 18" away from steel, strobe power supplies and batteries. The location I chose is the first bulkhead behind the
baggage compartment. I made a shelf from 0.060 sheet that hangs from the bulkhead using angle. Unfortunately, the bulkhead flexes
considerably and I had to add braces from the shelf to the lateral skin stiffeners. It was tough working in the tailcone, especially
tightening the aft facing connector screws. I would not want to mount any further aft than I did.
The flight system installation is complete. I haven't decided yet if I am going to install the display computers and test
now or wait. I may go ahead and install the radio harness and then install the computers and start system test.
I will be posting pictures of the operational system a few sections down when I get to system test.
Harness Integration Facility
EFIS Harness Installed
AHRS Test Fit
Change the way you look at things and
the things you look at will change.
GRT RAIM GPS
I chose a RAIM GPS as a back-up to the GNS-430. It is a small module that I mounted to the subpanel and has an antenna that I mounted to the forward
area under the windshield. It then connects via a RS-232 serial interface to the EFIS.