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Avionics

This page documents the cockpit control panel fabrication, installation of the flight instruments and installation of the avionics.

 

Date

Hours

Notes and Photos

8/13 to 10/31/10

15 hrs

Panel Fabrication
I cut the panel into three pieces; left, radio stack outline, and right. The left panel is where most of the action is and the right panel is mostly blank except for a couple of 12VDC outlets.

I learned that when the manufacturers provide a drawing with dimensions for creating a mounting hole, it is the dimension of the device and not the hole. You have to add 20 to 30 thousandths to each dimension to allow the device to pass through. My milling machine table did not have enough travel to cut a complete square for the EFIS so I had to cut part of it and then reposition on the table. This introduces some set up error into the cuts. My EFISs slope about 0.020" down to the right because of this -totally unnoticeable- but I know it is there. :). The cut for the TruTrak autopilot was challenging because of the angled corners. The hole for the ignition switch has a key to it and that took a combination of milling and filing by hand.

The four indicator lights across the top are Alternator, Bus CrossFeed, Left Door and Right Door. They are military style indicators with push-to-test capability. They are connected by a Molex so the panel can be removed with them still in place. The pitch and roll indicators are connected with a Molex micro-connector.

Machining

More Milling

Painted

Right Panel

9/18 to 11/1/10

32 hrs

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.

AHRS
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.

Magnetometers
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 Shelf

AHRS Test Fit

Magnetometers

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.

GPS

GPS Antenna

8/27 to 10/17/10

7 hrs

Pitot-Static and Autopilot
Pitot-Static
The pitot static air system was bought from Safair. They provide air brake nylon hose and quick release tee and 90 degree connectors. Additional connectors are available from McMaster Carr. I found that tighter turns can be made with the hose if you heat it with a heat gun and then form the turn before it cools. My alternate static air valve is located on the co-pilot side beneath the control panel. It is visible from the pilot seat looking across.

Static Bypass

AHRS and AP

Autopilot
The autopilot is the TruTrak DigiFlight II VSG. It is capable of both heading and altitude navigation when coupled to either the EFIS or GPS. The controller requires its own pitot and static air connections, a ARINC 429 connection to the EFIS and GPS and a serial connection to the EFIS. The autopilot servos were bought some time ago and installed during the wing and tailcone build. See those sections for servo install photos if needed. I recently bought the controller and wired the DB25 connector. It mainly gets the wire harnesses from the servos with the addition of power and ground and the signals mentioned above. It did not take very long to hook up.

10/29 to 11/22/10

26 hrs

Radio Stack
All my radios were purchased from Stark Avionics. Stark Avionics. He has an easy to use web page with an email reply system to get you real time pricing. The best part is that his advertised price actually matches what he charges you, meaning no bait and switch. The harness from Stark Avionics was in my engineering opinion a professionally made aviation grade product. They even included extra connector pins and installation tool.

The Garmin GMA-240 wiring harness was quite complicated and I'm glad I subcontracted it out. Stark Avionics brought out all the audio signals even though I didn't need them for my installation. I didn't want to just cut them off since they went through all that work, so I took all the unused audio signals and put them onto a DB-15 connector about 2' long pigtail. That way if I ever want to add unswitched audio or auxiliary input, I just have to make a mating connector. I'm pretty convinced I never want to go too far behind my panel ever again once it is completed.

Every Garmin radio installation tray is a different width. They are supposed to be standardized to 6.300 inches but the SL-40 was narrowest at 6.255" and the GNS-430 was widest at 6.314". This variation was enough to require removal of one of my vertical mounting angles and milling 0.030" off to widen my opening. The narrow SL-40 required washers in between the tray and supports and they were a real PITA to install.

Radio Harness Work

Stacking Trays

Trays Installed

Improvise, Adapt and Overcome

11/23 to 12/9/10

5 hrs

System Test
For the first time, I turned on the Master and Auxillary switches.

  • Number of fires: 0
  • Smell of Smoke: None
  • Number of explosions: 0

The data units booted up, determined where they were from the GPS and promptly drew Superstition Mtn on the primary flight display. They also gave the altitude of my garage and the heading of the airplane in it. That was the end of the easy part as the two displays are not talking to each other or the other radios yet.

The task at hand is to get the EFIS computers to talk to each other and to the other radios, GPSs and transponders by the mix of RS-232 and ARINC-429 ports connecting them. Each has its own data format and baud rate to set.

I solved the display problem by using a cross over ethernet cable. That was something that should have been in the EFIS documentation. Then I established a serial interface to the transponder. Then I set the primary display as the one that sends SL-30 commands and told the second display to relay its commands through the first. So now I can pull up an airport on either display and tell it to send the comm frequency to the radio. Lastly, I brought the GNS-430W on line and configured the ARINC and RS-232 interfaces to the displays. Everything seems happy talking to everything now. That is about as far as I can take it without flight testing.

Powered Up!

Final Panel

11/23 to 12/7/10

12 hrs

Antennas
After spending the past couple of years doing everything you can to protect the aircraft skin, you now get to drill big holes through it for antennas. I put the transponder antenna on the belly under the copilot seat. The comm 2 antenna from the SL-40 is also on the belly, aft of the baggage bulkhead. It is a bent whip VHF antenna. The comm 1 antenna from the GNS-430 is on the top aft fuselage and the GPS antenna is further back. The GNS-430 VHF comm has an internal filter to prevent GPS interference so I chose it for the top and put the SL-40 on the bottom. The VHF VOR/ILS and UHF Glide Slope antenna are one in the same and is a cat whisker located on top of the vertical stabilizer. The glide slope is on the third harmonic of the VOR/ILS. The two signals are separated by a diplexer before being connected to the GNS-430 navigation receiver.

I made all my own cables using RG-400 coax. I soldered the center pins even if they were crimp type. Then the outside ring was crimped with a borrowed crimper designed for that purpose. All antenna connections are BNC except for the GPS which is TNC.

Transponder

Comm1 and GPS1

Comm 2

GS and VOR

12/4 to 12/13/10

7 hrs

ELT
I installed a 121.5 MHz ELT based on price. The whole ELT concept seems outdated to me with the advent of ADS-B. The 406 MHz ELTs are still 10x the price of the 121.5 MHz. I mounted the ELT to my extended battery shelf in the tailcone. The antenna will be mounted horizontally under the empannage fairing. I hate to add another antenna to the airplane for the ELT but have no choice. The control head was installed on the rightmost panel in front of the copilot. The control wire is a standard type telephone wire with connectors already installed. The connectors need 0.5" holes for pass through. I wish I bought the cable earlier becasue even though I had room in some snap bushings for the wire, I could not pass it through because I did not have enough room for the connector. So in some bulkheads I had to add new snap bushings. It is amazing to me that I now have four 1" conduits to the aft almost completely full with wires.

ELT

-

-

Final Thoughts on Avionics
I am glad I had Stark Avionics build my harness. I'm amazed that with the amount of wires that I installed in the panel that I didn't have to rewire anything. I've learned that any time you add a snap bushing, cushion clamp or conduit for wiring, ALWAYS double the size you think you will need. It is amazing how many wires you will run in the airplane. If I did it again, I would not go dual redundant on the AHRS and magnetometer. I think it add a lot of complexity and wiring for little gained.

Mike Andresen
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