13.2.0 Instrument Panel

I’ve also been working on the mechanical design for both the overhead and instrument panels. Here’s a CAD drawing of the overhead panel switches.

Here's the layout that everyone is interested in - the main instrument panel. This is going to be a Garmin G3X system panel that includes both the 10.5” and 7” screens. The equipment in the middle includes the intercom panel, COM 2 radio (COM 1 is a blind radio controlled by the G3X panel), IFR navigator and autopilot controller. The main system switches and annunciators are located between the center radio stack and the 7” panel.

There is a lot of wiring that needs to be completed for a project like this, being an all-electric system! The heart of the audio portion of the avionics is the intercom / audio panel. In my case, I’m using Garmin’s GMA 245 Audio Panel. Because there are so many connections, I decided to break it down into two separate prints (VELO-AVNCS-01 and VELO-AVNCS-02) based on the two HUGE connectors on the 245. The first interfaces the two COM radios, the GTR 20 which is a blind radio controlled via the main panel, and the GTR 200B which is basically the same radio that is panel mounted and has a full control panel on it. I decided to install at least one of the radios this way in case my main panel fails. Manual control is always a good thing in an emergency! Of course, the G3X display panels can also control this radio if I so desire.

The second drawing completes the wiring for the GMA 245 which includes power for the device as well as the rest of the headset connections. I’m also showing a speaker although I haven’t yet figured out where to mount it!!!

The drawing below (VELO-AVNCS-03) shows the CAN Bus (Controller Area Network) which Garmin uses heavily for communication between devices. The CAN Bus is also used in automobiles and other transportation devices. It was originally invented by Bosch. While wiring the CAN Bus is a bit tricky due to length limitations, etc., it really does simplify wiring between devices! The print below also includes power to some of the other LRU’s (Line Replaceable Units - as Garmin calls them).

This print also shows two GSU-25’s. These are the Air Data Sensor Units (AHRS). Only one is required; however, many people include a second as a backup. I may only install one to begin with but the print shows two of them (as well as two magentometers, the GSU-11’s). I’ll include wiring for both.

VELO-AVNCS-04 shows two systems. The first system (on the right side of the print) includes all of the engine monitoring probes for EGT and CHT. That’s pretty straight forward. The LRUs on the left side of the print are the two autopilot control servos - one for pitch and one for roll. Since this airplane does not have a standard rudder there is no need for a yaw servo.

There’s more to engine monitoring that just EGT (Exhaust Gas Temperature) and CHT (Cylinder Head Temperature) though, so once again I broke the Garmin GEA-24 EIS Interface LRU into two separate prints. This 2nd print (VELO-AVNCS-05) shows everything else. It includes probes for fuel pressure and flow, engine RPM, manifold pressure, oil pressure and temperature, and finally, fuel tank levels. For whatever reason, this unit also includes outputs for the “Master Warning” and “Master Caution” annunciators.

The last avionics print (VELO-AVNCS-06) is for the GNS 375. This unit is actually a certified unit but is required for IFR flight since it includes a WAAS-enabled GPS navigation system. It also includes a transponder with ADS-B In/Out. The GNS 375 can do a LOT of stuff. I’ll be using many of its functions, but some functions are included for interfacing to older and non-Garmin equipment. It’s a beast with two huge (62 pin and 44 pin) connectors! In order to interface it to the G3X system, another LRU called the GAD 29 is required. The two devices talk via a standard aviation ARINC bus. The GNX 375 interfaces to a lot of other equipment over standard RS-232 serial connections, including both display screens (the PFD and MFD) as well as the GSU 25 AHRS and the audio panel.

I still have some mechanical panel layouts to finish, including the instrument panel switches and annunciators as well as the circuit breaker panel. Once all of the prints are finished it's time to start wiring.

ui© John Trautschold 2018