Matt's RV-7 Project

Today I did some more firewall-forward wiring. For all the "big" wires, I'm using double-wall heatshrink tubing over the crimp terminals. This stuff is like normal heatshrink, plus an extra layer of hot-melt glue inside. It provides a lot of extra mechanical stability, which I like.

I ran a 10 gauge wire from the always-hot side of the master contactor to the battery bus fuse block:

A short jumper wire connects the battery to the hot side of the E-bus relay. Note the use of all-metal hardware… no nylon nuts forward of the firewall.

Some more short little jumpers connect the switched side of the E-bus relay to the two midi fuseholders, shown here with fuses installed.

At the bottom of the firewall, I installed the ANL fuses and finished connecting everything together with copper bus bars. I ended up removing the rubber terminal boots I had on here before, as they were pretty unwieldy (as in hard to scrunch out of the way while tightening the mounting hardware).

I decided to wait on mounting the big fuseblocks inside the cockpit until I get my radio stack installed, so I can figure out where to run the big wires without having them interfere with the radio trays.

This weekend's big accomplishment was getting the remainder of the major electrical components mounted on the firewall:

Down by the starter contactor, I installed bases for ANL current limiters. One is where the main alternator B-lead will attach, and the other will feed the main electrical bus through the firewall. They both take power from the upstream side of the starter contactor via copper bus bars. I'll insulate this area with rubber terminal boots when I bolt down the fuses.

This 6-position fuseblock comprises my always-hot battery bus. It will be fed by a short 10 AWG wire directly from the hot side of the master contactor, and will power things like the hourmeter, the electronic ignition, and so forth. Just above the fuseblock is the relay that energizes the E-bus. By the way, these are all automotive-grade components, so I don't have any qualms about mounting them on the hot side of the firewall.

Above the E-bus relay are two holders for Littelfuse Midi fuses, with I think are the same as a Bussman AMI fuse. These do the same job as their cousins down below, they're just smaller… one will connect to the standby alternator B-lead, and the other will feed the E-bus through the firewall. Since they are OEM automotive components these fuse blocks have 5mm studs, which may end up being the only metric hardware on the whole airplane.

All this stuff is attached to the firewall with nutplates – lots of nutplates. I fabricated a whole series of doublers to mount everything, which is what consumed the majority of my building effort this weekend. Then Mary, who is awesome, took time off from studying to help me rivet them to the firewall, even though she has exams this week, because that's how awesome she is.

Seriously, did I mention she is awesome?

I was occupied doing various other things for most of the weekend, so I didn't get much done on the airplane. I did manage to make another little doubler for the firewall, to secure a cable clamp next to the master contactor. One of the rivets ties into the diagonal firewall stiffener:

Mary was nice enough to come help me rivet on the two doublers that needed to be installed. We back riveted them, with her doing the bucking on the outside and me taking many trips down between the rudder pedals to drive the shop heads:

Here's the same doubler riveted in place. It supports a nutplate that anchors the lower end of the positive battery cable near where it connects to the master contactor.

Up above, I riveted another nutplate to the firewall stiffener to capture the other end of the cable. Now the cable is mechanically secured by the clamps, and there isn't any stress on the terminals. The battery cable is from B&C, by the way.

We also riveted on the doubler for the fuel fitting:

Even though I moved it a bit, the fuel hose is still going to be quite close to the starter contactor, though apparently that's normal. This photo exaggerates the effect – there's really a half-inch of clearance between the two components. I'll just insulate and clamp everything really well so there won't be any interference issues.

You can also see in the photo above how I insulated the copper bar between the master and starter contactors with some rubber terminal boots.

I just had time to start sketching where I want to put the remaining firewall-mounted electrical components before I had to call it quits.