Of all the tasks and skills required in building an airplane, wiring is one of the things I like to do most — I've been looking forward to it the entire project. 

I've also been researching materials and techniques for some time now. In preparation I read Bob Nuckoll's book, the AeroElectric Connection, and attended his weekend seminar in Eugene, Oregon. I highly recommend this looseleaf book. Bob has a way of taking the fundamentals and relaying them in ways that are easily understandable. You can find out more about Bob as well as learn much about aircraft electrical systems from his web site at www.aeroelectric.com.  Along with the pictures below I'll try to incorporate comments on some of the methods and techniques I've used.

After I took my fuselage out of the jig and flipped it over I began to think about my battery installation since it was only a few steps down the road. I began hearing from builders who were flying their RV-8s with the same engine/prop combos I will be installing (O-360 A1A, Hartzell constant speed). All of them had gone with the standard firewall battery location. They were reporting that they were operating at the front edge of the CG envelope once they weighed everything. This was resulting in almost running out of elevator in the landing flare. Hmm.

Now a forward CG loading is not altogether bad. It allows you to put a significant "bubba" in the back seat, and/or to load up the rear baggage compartment and still stay with the CG envelope. However when doing solo aerobatics you would be doing so at the fwd edge of the CG envelope and would experience higher stick pressures. 

Van's specifies two possible battery locations: the firewall, and behind the rear baggage bulkhead. They specifically recommend the rear location when installing the heavier IO-360, but provide no recommendations otherwise. So which battery location should I go with?

Many months earlier I had decided that I didn't like that vertical portion at the right end of the forward baggage compartment. I was going to install a flat floor all the way across as I had seen a couple of other builder's do on the web sites. Then an idea struck... why not put the battery in the bottom of that compartment? The benefits:

• Keeps battery out of hot firewall-forward environment — improves battery life.
• Reduces clutter on firewall — allows better organization of components.
• Requires no additional firewall wire penetrations — less chance of leaks, shorts, or weakness.
• Moves it rearward for a small aft shift in CG — helps with the normally fwd CG bias.

I have not calculated the actual CG shift this will cause, but I know it will be in the right direction thus mitigating some of the characteristics mentioned above. I have been told that it will be a SMALL change, but I get all of the other benefits listed above so I have opted for this installation method. Then I began thinking about a way to mount the battery and make the change possible. See below for the results.

(click on a pic to see a larger version)

First off, my overall wiring schematic is a combination of the concepts explained in Bob Nuckoll's book and traditional 40 year old aircraft wiring concepts as manifest in the Van's supplied diagram. Literally, my system is a hybrid of the two taking what I think is the best of both. Specifically, The way Bob recommends routing the alternator output, and using single point ground the system make complete sense. I've had a bit of experience with car stereo years ago and learned the hard way that ground loops are something to be avoided, and single point ground is the way to do it.

If time allows, and I can get familiar with an appropriate CAD package, I'd like to diagram out my system. Until then it exists in my mind quite clearly. In the mean time, I have listed below some of my personal notes from the Nuckoll's seminar that I've incorporated into my system:

• Use single point ground throughout, use Nuckolls tab system on firewall
• Solder all battery & bus wire terminals, all others crimped only
• Shielded wire: p-leads and headset/mic cables only
• Use RG400 instead of RG58 for all antennas
• Alternator output (B lead) to starter contactor rather than bus
• Use 6 awg for alternator output to starter contactor
• Use 8 awg battery contactor to volt/amp meter
• Use 10 awg from volt/amp meter to main bus input & lighting buses (both from output post of meter)
• Use 14 awg for aux outlets
• Use 14 awg for landing lights
• Wire Hobbs from hot side of Master switch with inline fuse

Oh, regarding what coax cable to use, here's a quote from Bob Nuckolls: "I would recommend RG-400 as the modern coaxial cable of choice. It uses silver-plated double shielding and modern insulations like tefzel. RG-58 is an obsolete specification and no longer controlled for quality. It uses polyethylene and PVC for insulation . . . no longer allowed in certificated aircraft". 

(click on a pic to see a larger version)

The finished lighting switch panel