Fuselage Wiring Harness, Part 1

After the fuel system plumbing was finalized, it was time to install the instrument panel base to the longerons and upper firewall.  Below are a couple of pictures showing the interior and exterior views of the firewall with the panel base installed.  Of note are the mocked-up engine mounts which had previously been installed to take some measurements (of the fuel rail's proximity to the firewall) with the engine hoisted in place.  Also, the brake fluid reservoir is temporarily installed, also to check for fit of the final length of fuel line from the high pressure fuel filter to the engine's fuel injection rail.

 

And a quick few shots of the Viking hoisted into relative position with respect to the firewall.

Now, on with the wiring harness!  

The first order of business was to string the radio, transponder, ELT and ADS-B antennae from the top of the panel base down and around the rudder pedal torque tubes and into the bowels of the forward tunnel.

Below is a shot of the termination of the four antennae leads at the top of the panel base.  Note that the fuselage is laying on its side, which explains the odd orientation of the photo.  Of further note is the inclusion of the avionics cooling fans which have also been installed at this point.

As the antennae drop beneath the panel base, they curl around and behind the rudder torque tubes, shown at the extreme right of the photo below.

The transponder antenna terminates at the floor of the forward tunnel, just above and to the left of the pilot side fuel pump.  You will notice a small hole where it will be secured to the external antenna.

 The ELT, radio and ADS-B antennae continue their course toward the aft end of the aircraft, shown below as they enter the seat bottom ribs, flanked by the stabilator/flaperon torque tube and flaperon mixer.

The ELT antenna exits the center section and emerges above into the outer channel, where it will be housed in the yet-to-be-installed wire run conduit.  The radio antenna also terminates inside the bowels of the center section where it mounts to the external antenna on the belly of the fuselage.

Finally, the ADS-B antenna runs the entire length of the forward fuselage and will probably terminate on the main bulkhead of the tailcone, which of course, is not yet installed onto the forward fuselage section.  Below is the coiled extra length of the ADS-B antenna awaiting its termination on the tailcone bulkhead.
 

Next, the main harness, WH-00046 will be laid from the top of the panel base where it will snake its way downward and then throughout the center tunnel section of the fuselage.  The final connections of the main harness will feature a couple of spade terminated wires that connect to the avionics cooling fans.

No landing gear nor tailcone attached to the forward fuselage make for a much simpler effort at laying in wiring harnesses....as the fuselage is easily laid on its side and then belly and then other side...rinse and repeat.  I can't count the number of times I've done it, but I'm grateful for the mobility!

A s hot of the WH-00046 wiring harness as it descends down below the instrument panel base and around the rudder torque tubes.  The blue painters tape helps manage the individual wires of the bundle as it snakes around to various locations.

More wire pulling to proceed aft with the harness.  The red and black wires dangling from above are actually the external wires that attach to the Viking engine fuel pump module.

Van's calls for the ends of a few wires to be heat-shrunk together and laid aside awaiting further instruction.  The photo below show that process beginning.

Next picture is a brief, true confession of an error.  Thankfully a couple of fellow RV-12 builders helped me to realize that I had used AWG 18 wire for the fuel pump module.  The Viking wiring schematic clearly shows AWG 16 wire as these pumps pull considerably more current than the single Facet fuel pump used by the Rotax 912S.  So, I had to completely extricate the fuel pump module, remove the smaller wiring and replace it with the correct next larger size.  This was a process I was dreading.  As it turned out, the entire assembly was removed in about 10 minutes thanks to the AN fittings and 8 bolts that hold the assembly in place with nutplates.  Below are a few shots of the newly installed 16 gauge wire with the pump module prior to re-installation.

A second wiring harness, WH-00045 is installed for most of the options available for the RV-12, such as lights, autopilots and the like.  It is also threaded down from the panel base through a second (aft) hole and is routed similarly like the -00046 harness, namely around the rudder pedal torque tubes and down through the centerline of the fuselage.

The picture below is of the auxillary music jack and the larger 12-volt power outlet, immediately below it.  Both are shown just above and forward of the white, control stick torque tube.

Next is a picture looking aft of the front of the power outlet with its cover closed and the music jack.

One of the larger concentration of wires in the WH-0045 harness terminates in this Molex connector which is dedicated to the roll axis autopilot.  This location is the terminus of the forward fuselage, where the tailcone will be attached.

Fuel Tank, Part 3 - Leak Testing

Upon completion of the fuel tank the task of leak testing was scoped.  After researching Van's prescribed "balloon" method of leak testing, it was determined that a water manometer approach would provide a more accurate means of providing an internal pressure.  27 inches of water column is equal to 1 pound of air pressure per square inch.  Reports from other RV-12 builders indicated that the balloon-based approach to leak testing was only providing approximately 1/4 to 1/2 psi of internal tank pressure.

I built the following water manometer for my tank testing.  Note that I suspended the tank by 3 nylon cords in order to have complete visibility of the tank, once it was under pressure.

The zero-pressure water column rested at about 13 inches on the metal yard stick.  After several strokes of the bike pump, the column approached 40 inches, resulting in 1 psi of tank pressure.  I then proceeded to spray and brush on a water solution of glycerin and dish soap to detect any air leaks identified by bubbles.  Unfortunately, I found 3 small leaks in the aft upper corners of the tank and had to end the testing.  Thankfully, they were easy to spot.  The locations of the leaks were marked with a Sharpie, the tank depressurized and cleaned up and the repair process began with another new batch of ProSeal.  After 3 days in a very hot (95-100 degrees) garage with the ProSeal fully cured, the second pressure testing began.  Following is a quick shot of the tank being raised to 1 psi.

The previous leaks held beautifully, but I found 3 more even smaller leaks in the opposite corners of the aft panel and around 1 rivet on the tank bottom and from a couple of rivets which attach the left lower mounting bracket.

Again, the tank was depressurized, cleaned up and another round of ProSealing ensued.  Same 3 days in an even warmer garage and the tank was ready for the third test.  This time as I pressured up the tank, I noticed the water column slowing dropping again, but could not find any leaks from the tank so I began double-checking all of my hose connections.  Sure enough, the bike pump attach point was leaking as was the tank outlet, connected to the manometer.  After removing the bike pump and then tightening the hose clamp on the outlet, the water column remained completely stable!

Needless to say, I was quite happy.  I left the garage and came back an hour later to find that the water column had actually risen 1.5 inches as the garage temperature began to drop as the sun was setting.  At this point, I declared the tank to be stable and free from leaks.

Fuel System, Part 2

After a considerable wait, the Viking Aircraft Engines fuel module finally arrived.  The following picture only shows the manifold with the 1/4 to 1/8 NPT connector and the fuel flow transducer (Red Cube).  They have now been joined with Loctite 567 thread sealer.

Down stream of the manifold will be the fuel pumps.  I am currently awaiting the arrival of some AN3 to 5/16 hose barb fittings from the UK.  I initially ordered the 7-8 mm for the 5/16 barb and needed the 8-9 mm, so they are enroute and once here, will enable me to continue the installation of the complete fuel module.  Stay tuned.

Now, a week later....

Once the hose barb fittings arrived, it was a quick matter to bend up some of the 3/8 aluminum fuel line and then drill one additional hole in the seat bottom bulkhead and begin routing the lines.  The terminus of each line was snaked through the snap bushings, flared and the fittings installed as shown below.

Next, the fuel manifold and fuel flow transducer were temporarily mated to the fuel pumps, as shown below.

 
Now it was time to start spec'ing the installation location in the forward compartment.  The pumps were uninstalled and the forward portion of the fuel module was installed.

 After I was happy with the location, I re-installed the pumps and identified where they would need to be installed.  Finally the last 2 lines, one from the fuel flow transducer to the firewall shelf and the fuel return line, were plumbed into the fuel module and installed into the compartment, as shown below.

Fuel module sans the pumps.

Fuel Tank, Part 2

Part of the process involved in building the tank was to consider some alternatives that other builders have previously encountered.

First item of consideration was the sight gauge.  After reading numerous stories of leaks around the sight gauge as well as it practical uselessness for the intended purpose, I somewhat reluctantly decided to forgo the installation.  The next issue was to decide whether or not to install the Moeller mechanical fuel gauge as an adjunct to the sight gauge.  Again, after reading what turned out to be all of the glowing remarks about its usefulness, it became a no-brainer to jump on the bandwagon.

Below is a shot showing the Moeller unit with its nutplated mounting hole at the prescribed dimension of the fuel tank lid by a successful user.  The unit appears to function quite nicely and should be readable both from the pilot's seat as well as when refueling from outside the aircraft.

 A third and final consideration to be made involved the purported problem with the fuel tank reuturn line fitting coming loose and causing a leak.  Several builders have constructed hold down clamps (for lack of a better term) that get riveted to the bottom of the tank and attempt to keep the fitting from rotating when torqued upon with a wrench for final fuel line attachment.  I could never fabricate one to the tolerances required to keep the fitting absolutely fixed and free from rotation under a torque load.  After some thought, another builder, Donald suggested the use of a weldable, threaded bung...in fact two of them, back to back, each one holding the AN fuel fitting.  That's what I decided to do.  It was a bit of work, but the fittings will be riveted onto the bottom of the tank, in a similar fashion to the fuel pick up line.  There will be one on the outside and another on the inside of the tank as shown below.

 The final steps prior to assembling were all about surface preparation which mainly consisted of aggressive scruffing up of the mating or faying surfaces of the tank components.  Note the scuff marks on the interior of the bottom skin as shown above.

Without much further to do, it was...Proseal time!

Unfortunately, the process as yet undetermined by a leak  test, was not as I had envisioned.  It was fraught with breakages of my 3 riveters and the need to constantly clean up the internals of each tool after only a few driven rivets.  I ended up breaking my awesome Avery Tools Tight Space Pop Riveter (but there's a happy ending to that story featuring Bob Avery who will be mailing me a replacment part at no charge) tool in the heat of the battle.  I am still dumbstruck to think that I could have been using too much Proseal that it caused these numerous problems.

Undoubtedly, there were other issues such as the MS-42 rivet stems being too large to fit in any of the standard nose pieces as well as the necessity to drill out my other awesome Avery Tools angled rivet holder thingy so they would fit in it as well.  To top things off, I must have had a bad batch of the AD-41H tank rivets as I had several pull the stem out without breaking!!!!!

Here is the documented mess, in no particular order.

Noteworthy is the fact that I am without my fourth pair of gloves as I finally gave up in frustration with the lack of dexterity since I was disassembling/reassembling/repairing riveters throughout the process.  In the shot below, I am attempting to do some cleaning up of excess Proseal.

This was some of the final riveting of the front panel...followed by an attempt to clean up.

Same as above.

A decent view of the two fuel fittings - the inlet and return.

More cleaning.

A view of the forward underbelly of the beast.

Picture showing the blobs in the inboard forward corner of the tank.  I was very careful to keep the 4 baffle passageways (not really visible here) clear to maintain the prescribed fuel flow at low tank levels.

Close up of the fittings and more of the "blobs".

Shot of the external fittings.

The fuel sender mounting plate gets 5 nutplates.

The finished product now awaits its turn for final mounting during the second major ProSeal effort to come later.

In the mean time, the fuel tank's filler neck must be fitted to the fuselage skin adjacent to the bulkhead wall.  Once it is cleco'd into place the neck is match drilled to the pre-drilled holes in the fuselage skin.

The neck is removed and minor bends added to the mounting flange such that it makes a nice uniform junction with the skin.  After several iterations, the junction between the filler neck flange and the fuselage skin is perfect.

 Following are some pictures of the tank temporarily mounted into the fuselage to accomplish the fuel filler neck fitting.

Prior to the final ProSealing was the installation of the fuel return line.  Shown below is the AN fitting with the 1/4 inch line after it was torqued down to the welded fuel bung for the return.

A more complete picture of the return line shows the terminus taking a final upward bend into the future location of the filler neck, as specified in the plans.

The next picture is of the top skin of the tank with the mounting ring ProSealed and riveted into place.  Note also that one of the return line clips is in place as evidenced by the cleco.