Aircraft wiring 101

Builders:

I bring this up because it is the most common mistake I see in homebuilding, and oddly enough, it is about the easiest skill to posses, the tools are cheap, and there is no valid reason for doing this wrong……but 75% of the planes I look at have terrible wiring, particularly the terminal crimps.

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Below is a photo that has been on our main page for nine years. It is also in our Zenith installation manual, and I have reprinted it before. Search “wiring crimp” on the main page search block and it pops right up. Think most people read it? The wiring I see suggests otherwise.

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This isn’t an academic nor style point, this is airworthiness 101. Two years ago we had a builder spend several months of very frustrating searching, looking for a defect that made his plane have a bad miss at times. He sent the distributor back to me more than once with the clear implication that it was defective even though it tested fine. Next suspect was the certified yellow tagged carb. All the while, the people at his airport are being treated to a demonstration they perceive as “Auto engines are unreliable” and “Not even the guru knows how to fix it.” When it was all said an done, the 100% culprit was a shitty crimp done by the builder on the 12V line going to the coil. I do not like my designs and work being considered as the prime suspects when the issue is people who are doing wiring at a quality we could expect from a weed smoking high school boy in 1978, trying to install his 8-track player in a ’69 Valiant, so he could listen to his new Ted Nugent Cat Scratch fever tape.

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Your Corvair needs good wiring on the ignition system to run properly. You need to make as few connections as possible, and have a simple design for the critical wiring. Leave out all the junction strips and additional connections. To make the distributor easily removable, consider using the Weatherpack connector we have on EP-X distributors. If you are headed to a college and already have a distributor, bring it, I will upgrade it on the spot.

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Now, as we read this, some dope is going to post a link on a discussion group saying that “Corvairs have critical wiring and that is why I am glad I picked an A-65 Continental with mags.” OK, get this: Hand prop planes with mags have an even more critical connection than a Corvair. The P-lead grounds to the mag have to be done perfectly, because you count on them to protect your life every time you touch the prop.  If one of the P-leads has a shitty crimp, the key can be in the off position and the engine will easily start or kick over with lethal force.  Think I am exaggerating? At the very bottom of this story are a few photos of a great guy Gary Collins, who attended many Corvair Colleges and built a very nice Corvair Powered Carlson Sparrow II. In June of 2013 he was struck by the prop on his Lycoming O-320 powered Tailwind while simply working in his hangar. He died several days later.

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I want to clearly state that I am in no way implying that Gary’s plane had anything wrong with the wiring or he that was an unsafe guy.  He was an outstanding human being, and I include his accident here because I want to make builders understand that accidents involving props are not a myth, and they do happen. (Gary did not build nor wire the plane that killed him) By putting a person’s name on one I want people to think about this as possible. I have seen a number of homebuilts with poor wiring and magneto ignition. You can assume the builder also did poor work on making the P-leads. Moving such a plane by touching the prop, or rotating the prop to prime it is the absolute equivalent of pointing a loaded gun with a known defect in the safety at your head.  All planes have critical points where the wiring quality must be 100%. Anyone who implies it is OK to have “It will be alright” level of quality on the P-leads of planes with mags is a dangerous fool.

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Go on any internet forum on homebuilding you like and bring up the topic of wiring. You will get hours of reading and opinion on electrical theory, written by people who think they have something to teach Nikola Tesla. It is all a giant waste without simple crimping tools and skills, but the armchair electrical engineers never bring that up. Good homebuilding is about mastery of basic skills like crimping. It is that simple.

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Here are the basic elements of good wiring for experimental airplanes. Tefzel clad wiring is available from all the  aircraft supply houses. This jacketing is many times tougher than typical insulation, especially at elevated temperatures.  Real aircraft grade terminals have soft insulation, which does not crack when it’s crimped. The crimpers in the photo  above are available from mcmaster.com. They’re just under $50, and worth every penny. There are many good books on  aircraft wiring, and some discussion groups about it. Unfortunately, most Internet discussions devolve into giant debates about  massive redundancy, counter EMF, diodes and bridges, and how the letter i represents the square root of -1, which can  be used to describe the behavior of alternating current. Perhaps you, like me, get sleepy reading this stuff and wonder  what it has to do with your airplane. Answer is: not much. But do not wholesale cash in all of aircraft wiring. The  basic materials and tools are important to incorporate into your own project. Don’t let the complex discussions  completely turn you off.

Above are things that should not be in your aircraft workshop. Typical automotive store wiring has very soft, poor  insulation. The crimpers do a terrible job, and the terminals have hard insulation that cracks when crimped, and is  then prone to falling off. Wiring like this is one of the first things that catches my eye when inspecting a project or  scanning a photo. Your DAR, when inspecting the airplane, will notice this also. Many DARs I know are very reluctant  to sign off airplanes with this type of wire. Five minutes of exposure to the right stuff and you’d never consider  using the wrong stuff again.

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The following excerpt is form a story I wrote called Spark Plug Issue resolved….. you can click on the title to read the whole story after reading and thinking about the words below. It is fine to have dreams and complex interests in aviation, but you must also strive to cover the fundamentals. like being able to do a 100% airworthy crimp. Being able to fly a jet is an admirable skill that takes real effort to learn, but in successful homebuilding the basic stick and rudder guy who spent 30 minutes learning how to do good crimps is going to have a lot more success than a 10,000 hour jet pilot

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“In an average year, I will get 200 emails asking about things like constant speed props and elaborate injection systems. If you read all of them, it is easy to tell that 95% of these come from people with little experience. If I lined up these 95% and asked them to install a distributor and time it, or to explain to me how you could tell if the engine was on the top of the exhaust stroke of compression by looking at the motion of the rockers,(both things we teach at Colleges,) I am sure these people would be at a loss. Is there anything wrong with their dreaming of injected constant speed planes? Of course not…if the extent of what they came to aviation to do is dream about things. Conversely, if actually achieving things is the goal, dreaming can not take the place of a rock solid foundation of the basics.

None of us were born knowing this stuff. I am glad to teach it to anyone who wishes to learn instead of day dreaming. I can make a very good argument that the builder who creates and masters the operation of a basic aircraft, is a lot safer, and will experience far greater rewards that any builder operating a plane he really doesn’t understand, or is sketchy on the details of a complex aircraft’s function. The guy with the most basic plane has won the game. The guy who consigns himself to daydreaming has not lost the game…..he wasn’t ever playing.  Once the basics are mastered, then moving forward can be done with the understanding that you are not posing or posturing as your own mechanic, you actually have earned the confidence in yourself, the real reward for knowing the subject. -ww

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I took the comments below from Gary Collins’s Facebook page. They were written by his son in law as Gary lay dying in the hospital. Learn from this tragedy. Gary was a life long aviator with a very safety minded attitude. I worked with him at many Colleges, and I would never have suspectled he would have this type of accident. Learn to treat props with the same care you handle firearms.

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 “I will miss you Gary.  You have always been very generous with me and Jennifer and the girls.  I enjoyed the time we spent together.  I pray that you can still hear the words of love that your family and friends give as they visit you in the hospital.  I pray that you have no pain or discomfort in your last days.  And I pray that you find peace with the Lord so we can see each other again someday in heaven.  God bless you.”

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About William Wynne
I have been continuously building, testing and flying Corvair engines since 1989. Information, parts and components that we developed and tested are now flying on several hundred Corvair powered aircraft. I earned a Bachelor of Science in Professional Aeronautics and an A&P license from Embry-Riddle Aeronautical University, and have a proven 20 year track record of effectively teaching homebuilders how to create and fly their own Corvair powered planes. Much of this is chronicled at www.FlyCorvair.com and in more than 50 magazine articles.

3 Responses to Aircraft wiring 101

  1. jaksno says:

    As usual, an excellent educational, life saving article. I did not know anything about aircraft wiring/crimping; now I at least have seen the words. I certainly have experienced re-crimping in auto applications due to cracked crimps – I re do them, and often use heat shrink tubing as well (is that a good idea for aircraft or not?). Thanks for the tool tip, too. I know this article is life/death serious, but paragraph 3 did cause me to drool on myself while laughing. Sorry to hear about your friend. I had no idea poor P (primary, right) connections in magged engines could create ‘contact’ conditions when the switch was off. Thanks!

  2. Tom Graziano says:

    Spot on, William!

    It’s incredible the messed up wiring I’ve seen in homebuilt airplanes….but certified planes aren’t exempt…mostly due to non-A&P owners trying to (illegally) do it themselves.

    Builders would save themselves a lot of headache if they would take the time to research and study things a bit. The information needed is readily available in AC43.13-1B and AC43.13-2B as well as Tony Bingelis’ four books: Sportplane Constructions Techniques; Sportplane Builder Aircraft Construction; Firewall Forward; and Tony Bingelis on Engines. These six books should be considered mandatory for anyone building an airplane, but it’s amazing how many builders don’t have them…!

  3. Gaston Brawley says:

    Ordered McMaster Carr crimpers today.

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