19 April 2017

Avionics: The big master wiring post.

It turns out that it's difficult to find pictures of how folks wired their airplanes.  Based on my experience wiring an airplane for the first time, I think I understand why folks tend not to share their work.  One of the goals for my blog was to share all of my work, no matter the quality.  So, though I'm not proud of my wiring work, this post discloses it fully.

I opted to do the wiring myself after learning that the cost to have it done professionally would be between $3k and $5k.  My time tracking spreadsheet shows I spent 220.14 hours on avionics (wiring and mounting).  That's under-reported.  It's probably in the 300 hour range.

Wiring planning began in December of 2015.  Physical wiring began in February of 2016 and continued in fits and spurts until April of 2017.

Here are the posts outlining my harness construction and wiring routings.
Here is a high level electrical diagram for the airframe.  You can read about my topology here.

Bringing the harnesses into the airframe is a gentle affair.  The wire ends are then temporarily labeled so that pins can be later added.

It gets really messy inside, especially at the outset.

Routing wires down the tunnel.

I used wire tie mounts to fasten down the wires adjacent to the fuel pump.  These are from Panduit and are shown on the left.  Some folks use Adel clamps.  Those "nut launchers" are evil, so I wanted to avoid using them, especially in a confined space.  The right image shows how the wire tie mounts were attached to the F-14103 Fuel Pump Brackets with nutplates and #8 screws.  I used four wire tie mounts (not shown), two on each side.

Wires going outboard from center under the seat pans (left is left, right is right).

The harnesses to the wings are set outside the airframe.  Visible on the right image is a temporary min-harness I made to test my landing and nav/strobe lights.

When connecting pins, I used the rungs on my ladder as shelves to hold my various tools.  Nearly every wire was labeled on both ends.  Go to the end of this post to see how I labeled my wires.

Final layout of airframe and tail harnesses going down the baggage area.

The top images show the left side LEMO connector wiring whilst the bottom shows the right side.  I wanted a large service loop on each.  You can also see that I put on little Molex connectors to accommodate later replacement of the LEMO socket.  This whole approach is detailed in this post.

Canopy harness, detailed in this post.

The left side behind the panel, detailing the GRT AHRS and EIS.  Go here for details on the AHRS mounting and here for details on the EIS mounting.

The right side behind the panel detailing the SkyRadar DX, whose installation is detailed here.  You can see the main ground lug at the bottom of the picture.  It just goes into a nutplate on the firewall with an AN3 bolt.

The center behind the panel.  It looks hideous and it is.  However, those wire bundles are so incredibly stout that I'm entirely confident they will not move appreciably during flight.  Also, you can see the MAP sensor on the right side of the plane (left side of image).  It's the black box fastened to the F-01456-R Fwd Fuse Rib.   Details of the MAP install are found here.

A larger-picture view of the entire area behind the panel.

Left side of subpanel.  I plan to spiral wrap the wires along the TruTrak ADI2.

Right side of subpanel.  As an aside, the instrument on the bottom left of the image is my lift reserve indicator (LRI).  Go here to read about an LRI.  A forthcoming post will provide additional details on what I ultimately did to construct my LRI.  Until that time, I'll record here that I used a Manostar FR51AHV-500D differential pressure gauge.

A closer shot of the right side subpanel showing the main ground distribution bus, AE Fuel Guardian and SSR for Avionics Bus 2.

Center of subpanel.

Wider shot of subpanel.

Canopy underside showing the LED strip and defrost fans.  Canopy wiring is detailed here.

CHT and EGT wire routing along engine mount.  This process was detailed here.

The GRT pitch servo.  This was taken prior to replacement of the DB9 hood (explained below).

I replaced all hoods with ones that can be finger tightened (DB9 and DB25).  These were to the AHRS, MAP sensor, GRT HXr EFISs, TruTrak ADI2 and pitch/roll servos.  This allows easier work to be done because I didn't have to use a screw driver.

ELT.  Details of its installation are here.  Just need to route the wires.  I'm waiting for the tail to be mounted to be sure they are routed correctly.

ELT antenna coax running on left side of baggage area.  I used silicone and edge grommets to lock it into place to avoid chaffing.

Wire routing on left side of tailcone.

Here is the magnetometer.  Details of its mounting are here.

Some additional thoughts:
  • I did not plan my wiring well at all.  I just routed wires as I went along, so I didn't plan things ahead of time.  
  • If I were to do this again (ha!), I would plan accordingly so as to have a much nicer wiring layout.  
  • I would add service loops and consider better positioning of the various constituents.  
  • I would use the "forest of tabs" approach for the ground bus and leave extra tabs for later additions.
  • I would leave accommodations to power additional, future components.
However ugly as it is, I'm confident that my wiring is stout, resilient and ready for flight.  It just could have been a lot nicer.

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