By Vic Syracuse, EAA Lifetime 180848
This piece originally ran in Vic’s Checkpoints column in the April 2021 issue of EAA Sport Aviation magazine.
There’s no doubt that our homebuilt aircraft today are different than the homebuilt aircraft of yesteryear, from ease of construction to performance and capabilities. We now achieve faster and higher completion rates and travel farther, faster, and in more comfort than was ever dreamed. The airplanes that inspired me as a kid were single-seat, open-cockpit airplanes, like the Teenie I flew when I was 12 years old. Now we can build four-seat, pressurized, turbine-powered aircraft, or even more common ones like RV-10s, and enjoy flying on vacations with the family rather than short, solo Saturday outings with our flying friends.
For the most part, many of the kitbuilt aircraft have eliminated the need to learn some of the more craftsman-like skills, such as welding, fabrication, and sheet metal work. Some kit manufacturers provide firewall-forward kits that are so complete that the builder just has to follow the instructions and hook up everything as per the pictures without any real understanding of how various systems work. Instrument panels can be provided that are just as complete, requiring the builder to just interface some wires with the rest of the aircraft. It’s almost like hooking your house up to the utility company, with the same consequences. It can all go dark if not done correctly, usually at the most inopportune time.
Many of the homebuilt aircraft of yesteryear did not even have an electrical system. Even some military aircraft of not too long ago didn’t have electrical systems, such as the Stearman. Engines were hand-cranked or hand-propped, so a starter wasn’t needed. Oil pressure and temperature gauges were direct-reading, and the airspeed indicator didn’t need any power. Daytime flying didn’t require lights. And who needs a radio? There weren’t as many towered fields or the density of traffic there is today.
Our cockpits are a much different story today. Most of the ones I see today have no instruments installed that work without some kind of electrical power. Even the installed or required backup instruments have a battery in them. Dual electronic ignition systems are becoming more prevalent as well, and some of them require a reliable source of electrical energy. So, I would say keeping the lights on is pretty important. Unfortunately, the understanding of best practices when it comes to aircraft wiring is an area where most aircraft builders fall short. Much like the maintenance side, there is not much guidance provided on the proper ways to wire the aircraft.
Many books have been written about this subject, from Tony Bingelis’s books to Marc Ausman’s Aircraft Wiring Guide, and there is no way I can cover all of it in a monthly column. However, I do want to cover some of the basic do’s and don’ts, as the NTSB has investigated some accidents lately that were the result of failed connectors, causing nonfatal crashes. Much of this will come from what I have seen on aircraft that come through our shop and from my own experience building and wiring a number of aircraft.
First, plan on using high-quality wire, connectors, and tools. Sure, on the Teenie it may have been practical to run down to the local automotive parts store to procure these things, but that was yesteryear, and reliability and availability didn’t necessarily run together. The quality of the spade connectors, butt splices, and terminal connectors sourced at your typical automotive store might be okay to add some external lights or a nitrous injection system in your car or beach buggy, but I assure you they are not okay for your airplane. The crimpers are a single-crimp-type tool. The reliability of the crimp is dependent upon the strength in your hand, which will vary from crimp to crimp. The wire is usually copper, and the individual strands are fewer and of a much heavier gauge, and therefore they are prone to breaking in the high-vibration environment of our airplanes. The insulation on the wire and connectors is usually vinyl or plastic and will give off noxious fumes when overheated or burned. Not ideal for the cockpit! The quality of the spade connectors is usually poorer, and they do not tend to hold the grip over time, resulting in a loose, intermittent, and oxidized connection that only worsens.
Start by sourcing only quality components from the aircraft supply shops, such as high-quality Tefzel wire and AMP connectors. Some of the proper tools will be worth purchasing for yourself, such as double-crimp crimpers, and you will continue to use them throughout the life of the aircraft. You may be able to borrow high-end tools, such as pin crimpers, from your local EAA chapter or a local mechanic. But don’t substitute. No sense crimping a high-quality crimp with an improper crimper. It will defeat the purpose.
For the radios and GPS antennas, use RG-400 instead of the older RG-58 coaxial cable. The RG-400 is double-shielded, has a better inner conductor, and will last the life of the aircraft if installed properly. Be sure to use the proper crimper designed for the cable.
Some practices in the automotive industry are applicable, but some aren’t. As an example, I like to use circuit breakers and switches with screw terminals, as opposed to spade connectors. The screw terminals tend to be more reliable in an aircraft environment and less prone to intermittent behavior over time. In some cases, like attachment to backup batteries or voltage regulators, the only choice is to use a high-quality spade terminal. Be sure to properly support the wires close to the attach point so there is no chance of the spade connector being disconnected from the terminal. If it’s a really critical connection, meaning if it comes loose bad things could happen, then you might consider securing it through some physical means. Think of using heat shrink as an example. Another approach would be to drill a tiny hole right through the spade connector and terminal, through which a cotter key can be inserted. Then apply heat shrink over that. Be careful to ensure the cotter key is cut short on the back side, so as to not touch any other part of the aircraft. No sense shorting out a connection you were trying to make reliable!
Many of the current, high-quality, environment-proof connectors used in the automotive industry can be used in our aircraft. Many of them take specialty tools to properly crimp and insert the pins. I do not like the Molex connectors typically found in the auto stores or Radio Shack. They seem to be the most often-found source of intermittent electrical problems we find, especially when used in the wing root connections. As a side note, I would encourage all of you to rethink the need for wing root connections. The chances for needing to disconnect the wings during the life of the aircraft are rather few. If you do install them, at least use high-quality weatherproof connectors.
The last part of ensuring reliable electrical connections has to do with maintenance, especially on those critical connections, like backup batteries or coils on electronic ignition systems. Be sure to check them regularly, at least during the condition inspection. Those that are exposed to the elements, such as in the engine compartment, should constantly be checked for security and corrosion. I find that putting some Dow 4 grease on the connection helps with preventing corrosion. The connections to the coils, especially the ones that sit on top of the engine and are exposed to heat and rain, may need to be tightened once in a while. This can easily be done with a pair of needle-nose pliers. If the connector feels loose, pull it off and tighten the connector with a little pressure from a pair of pliers or, even better, replace the connector. You did leave some extra length at installation time, right?
For those who are just starting to wire, please take the time to get educated. For those who have already wired their aircraft, hopefully I’ve given you some food for thought on the areas you may want to go check. I assure you that keeping the lights on will keep the fun factor alive.
Vic Syracuse, EAA Lifetime 180848 and chair of EAA’s Homebuilt Aircraft Council, is a commercial pilot, A&P/IA, DAR, and EAA flight advisor and technical counselor. He has built 11 aircraft and has logged more 9,500 hours in 72 different types. Vic also founded Base Leg Aviation and volunteers as a Young Eagles pilot and an Angel Flight pilot.