Recent Projects

G3X Retrofit in an RV-8

The Garmin G3X is a state of the art Electronic Flight Instrument System (EFIS) designed for experimental aircraft.  This system is capable of displaying primary flight instruments with “Synthetic Vision” 3D terrain, HSI, moving map with terrain and traffic, XM weather and entertainment programming, and full digital engine monitoring.

This system has been popular not only for new installations but also as a retrofit into flying airplanes who’s avionics and instruments are from the “pre-glass” generation.  Even older EFIS systems have been superseded by the advanced features of the G3X system.

Recently we undertook a project that involved turning an existing RV-8 instrument panel into a G3X instrument panel.  This particular panel was built five years ago in 2006, and while it is IFR capable, the airline captain owner / builder had to have the G3X when he saw it at our booth at Oshkosh. 

Because we did build this instrument panel in 2006, we already had all the documentation regarding connector pin assignments.  However, the panel had undergone several smaller retrofits by the owner in the past few years so we were not exactly sure of what condition all of the wiring would be in once we got the old panel back for the retrofit. 

Follow along as we make a slightly dated panel into a modern and capable one that would be the desire of any pilot.

Click the image to see the wiring diagram we made to document the installation.


(Click images to view full size)

This is the original panel as it was built in 2006. The GNS-430 and GTX-330 are still very modern avionics, and the Dynon display was an economical electronic display at the time. The Trutrak autopilot is capable of following a GPS course and altitude hold. Overall this is a basic but capable IFR panel.

Here is the panel as we received it back from the customer. He had already removed the avionics and instruments, leaving just the electrical components and wiring, some of which will be used in the new installation.

This rear view shows that we have a lot of old wiring to remove and neatening up of the rest to do.

From the start we decided to mount the AHRS gyro to the back of the instrument panel. The AHRS gyro contains the gyros for attitude and heading and rate, plus the airdata computer for altitude, airspeed, and vertical rate, and the engine monitoring processor. All of the engine probes plug into the AHRS gyro so having it behind the panel would be a convenient location for wire routing, and future servicing. We started by making a set of brackets on the laser cutter that will be riveted together into a bracket that will mount to the panel. If this idea works out, we will make future brackets by laser cutting the whole bracket as a flat piece then bending it on a brake into the final shape that will eliminate the rivets.

Here is a look at the bracket after riveting.

And with the gyro placed onto it. 

This is the new instrument panel that was laser cut with the AHRS bracket fit for the first time.  So far it looks as if this idea will work out well.

Here, one of the G3X displays has been placed into the panel.  You can see that the AHRS gyro has to be located on the bracket to make room for the connector that will plug into the G3X display.  We took that into consideration when designing the bracket and it looks like the AHRS will easily clear the G3X display connector. 

The next step is to mount the radio trays. The new panel is re-using the GNS-430 and GTX-330, and is also adding a Garmin SL-40 for a second com. First we put the three radios into their trays, and stack them with the front of the faceplates flush with each other.

Next we use a marker to draw a straight line along the side of the radio stack to make an alignment mark we will use to keep the trays aligned while making the tray mounting brackets.  

With the radios removed and the trays aligned with the mark we made, a piece of ½” x ¾” aluminum angle is held up to the side of the trays, and a marker used to mark the mounting holes for drilling. 

The brackets are then drilled for # 6 hardware. 

Before attaching the brackets to the trays, we put nylon washers on the screws for the SL-40 tray.  The reason is that all the trays from Garmin AT (the old Apollo) are a little narrower than the trays from Garmin and the washers are needed to take up the space.. 

The top and bottom radios are place into the trays in order to make sure the trays are aligned with the opening in the panel, then the brackets are match-drilled through the holes that were laser cut into the panel.  The holes are countersunk and the brackets are riveted in place.

Here is the panel with the radio tray brackets riveted and the trays installed.  Now it is time to get busy wiring. 

We started with the GNS-430 and GTX-330 connectors.  Because the G3X wiring is very different from the existing connections, we decided to just remove all of the existing wiring and start from scratch. 

This is the green/white extractor used on the high-density D-sub connectors.  Garmin avionics use the high-density connectors extensively, as well as standard density.  Note that these extractors don’t last forever, as they are very fragile.  We usually keep at least a dozen in stock of the high-density green/white and standard density red/white extractors so they are always on hand.  There are several makers of these extractors but we only use the ones from Aiconics, they work by far the best of all the ones we’ve tried. 

Here is another tool that is mandatory for doing this type of work.  It’s a Daniels / Astro D sub crimper with a variety of interchangeable turrets and adjustable crimping range.  These mil-spec tools are not cheap but will last forever, and there is no substitute. 

Almost all of the wiring in a G3X system is shielded.  To prepare the end of a piece of shielded wire, about two inches of outer jacket are removed by scoring the jacket with a razor and pulling it off. 

The outer braid is pushed back and cut off so that ½” of braid remains. 

Now a solder terminal sleeve is slid onto the braid until the solder band is about halfway down the exposed braid. 

Then the sleeve is shrunk over the nozzle of a heat gun, melting the solder back to the exposed braid. 

Another tip is that some harnesses, especially the engine sensor harness, require one or two wires to split off into several different connector pin locations.  TO accomplish this, multiple leads can be soldered onto the wires.  We cover the solder connections with heat shrink tubing. 

The first harness we built was the engine sensor harness that will connect the engine sensors to the AHRS gyro.  Here it is with most of the wires inserted.  The brown jacketed wire is thermocouple extension wire that is required to connect the EGT and CHT probes to the connector, regular wire cannot be used.  You can see here that the white / black wires from the solder terminal sleeves have been bent back as they do not plug into the connector. 

The connector is then laid into the connector hood.  We cover the strain relief bar with a piece of heat shrink tubing to act as cushion as it presses down on the wire, and add a piece of heat shrink tubing under the wires. 

Here is the assembled connector with the strain relief in place.  The wires that were split off to multiple pins can be seen with white heat shrink tubing over the connections. 

This is the backside of the connector hood, and the terminal sleeve ground wires are seen here crimped into ring terminals and attached to the hood. 

The other end of each wire is labeled with a piece of heat shrink tubing that was marked with a Sharpie. 

Now we are ready to begin wiring the radio stack.  A couple of tools that are helpful are a Pana-Vise to hold the connector while inserting pins, and if you are over 35 years old, a big magnifying glass so you can actually see the pin assignments embossed on the connector. 

The first connector was the GNS-430 main connector.  From this point, the wiring consists of following the wiring diagrams for each radio and working our way down the radio stack. 

The GNS-430 solder terminal grounds terminate into a ground block that is supplied with the GNS-430 installation kit, and plugs into a ground tab on the back of the GNS-430 tray.  Each wire gets a pin crimped onto it using an AMP terminal crimper. 

After the three GNS-430 connectors are wired, they are attached to the back of the GNS-430.  The harness is then tied and routed to the side of the radio stack where it will join the other radio wiring. 

The SL-40 com connector was then wired and attached to the mounting tray, and the harness routed similar to the GNS-430. 

The last connector in the radio stack is the GTX-330, and the connector was wired and attached, and the harness routed to meet the other harnesses. 

The next connector wired was for the G3X primary flight display, since a lot of it’s wiring splits off from the radio stack wiring. 

A harness for the Trutrak GX Pilot autopilot was made, and added to the radio stack harness. 

Here is a view of the radio stack with all the stack wiring complete and tied. 

Because this panel is going from one to two coms, some changes to need to be made to the audio system.  First, because we will be feeding several audio sources into an intercom that only has one audio input, we installed this unit from Flight Datasystems.  It will combine all of the audio from the coms, EFIS, and transponder into one output that will feed into the transponder. 

The audio output of com 1, com 2, the transponder, and the G3X system are wired into the inputs of this unit.  Then the single output connects to the headphone input of the intercom.  The DC power connection will go to the intercom circuit breaker. 

To control the audio from com 1 and com 1, we added two switches that will allow the pilot to turn the com audio on or off in the same manner as an audio panel.  These switches simply interrupt the com audio line running from the com radio to the Flight Datasystems audio amp.  Also installed was a com 1 / com 2 transmit select switch that switches both the com push to talk wire and com audio wire that runs from each com radio to the intercom.  This way, only one com may be selected at a time to transmit. 

We installed the switches and circuit breakers form the old panel with the old harness.  We will try to use as much of the old harness here as possible since the new wiring for these is fairly similar to the old wiring. 

Since the wiring for the switches will not change, we just re-tied the harness to the switches, and routed the wiring off toward the circuit breakers. 

With the old wiring labeled with tape, and the new power wires from the avionics routed to the circuit breakers, it is time to complete the wiring to the breakers 

The wires to the top row of breakers was cut to length, terminals crimped on, and attached. 

The top row harness was tied and the bottom row wires routed. 

To access the bottom row, the top row of breakers was temporarily removed.  Then the bottom row harness was cut to length and terminals crimped on. 

This is an overall view of the almost completed wiring.  We installed the standby flight instruments to check fit.  The next step is to install pitot and static plumbing. 

The pitot and static tubing was routed to each instrument: airspeed indicator, Trutrak ADI, altimeter, Trutrak autopilot, and AHRS gyro.  We use white tubing for static and blue for pitot.  The fittings at the AHRS gyro are “tee” fittings so the aircraft main pitot and static sources will connect there. 

We use DuPont products to paint our panels applied with an HVLP gun.  This paint is easy to apply and durable.  We make our own decals with a Micro Dry printer.  The decals are sealed onto the panel when the matted clear is applied. 

First panel power up and test.  The radios, G3X displays, autopilot, and instruments were all connected and powered up.  The initial system configurations were made by following the steps in the installation manuals.  We also connect a static test box to make sure the pitot and static plumbing system is leak-free, and the instruments read correctly. 

After the final checks and tests on the coms, nav, GPS, transponder, and autopilot, this panel is complete and ready to mount back into the airplane. 

Stay tuned for an update on this project and first flight report!