Builders,
In 2016, we had two different Zenith builders fly in to the same event. They had never met each other. I studied both of their engine installations, which has cumulatively about 500 hours of flight time. They were different, but both airworthy. They had an odd thing in common; They both ad an engine ground cable that was 3 feet too long, and it terminated at the same points, the center of the firewall and the starter mounting brackets on each plane. Most people would not have noticed this commonality, but it told me something important: Both of these guys who had never met each other were listening to the same idiot on the internet, rather than following examples we show or even common sense. Somewhere out there in cyberville was a moron gleefully dispensing poor advice on ground cables. While this particular error just added weight and looked dumb, I am sure the same expert had doled out plenty of other electrical advice that was far more dangerous.
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Above, the ground strap location for a Corvair engine. This is the aft end of the co-pilots side head. The head has a 3/8″-16 tapped hole, perfect for grounding, the cable is 9 inches long, it is #2 wire. You can even use wire without insulation, ( it is a ground) or go to your auto parts store and buy a premade cable, and it can even be one of the ones that look like bare woven metal, a ‘bonding jumper’. Yes, the powder coating has to be scraped off where the 5/16″ bolt goes through, and it does have to have a metal lock nut. Every motor mount I have ever made has a tab or a corner brace at this intersection for a ground cable. If anyone suggests that a 4130 motor mount or an aluminum fuselage don’t conduct electricity, they are not just wrong, they are probably mentally ill, just nod politely, smile and back away slowly.
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Your Vote Counts: In the comments section, please vote for one of three following examples from my experience:
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A) “Led Zenith” 10 years ago I went to inspect a Zenith. The builder had placed a group 24 lead acid truck battery in the tail cone, (because he had made an error doing his weight and balance on a set of $10 bathroom scales.) but he also insisted that he needed to run a 00 copper battery ground cable all the way from the battery, 12 feet to the motor, and insisted that it also had to have insulation on it. A very nice gentleman, had been a pilot for 35 years, built a number of planes, and had a long and lucrative career as a mechanical engineer.
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B) “Ungrounded Claims” A second owner of a Corvair powered plane called both Dan and Myself, because his “Starter was burned out”. He was on a cross country, far from home, the starter had previously worked without a hint of a problem for years. Dan tells him to directly put the jumper cables on the starter, to isolate the starter to test it. Guy claims he did this, no dice. His solution was to rent a motel and a car, drive 200 miles to a city where he paid a guy several hundred bucks to hand rebuild the starter on a Sunday, in spite of the fact the guy said there was nothing wrong with it. About $1,000 later, the starter is back on the plane, and it still doesn’t work. Local EAA chapter experts say the issue is because it is a Corvair. After another day, he discovers that the ground cable to the motor has become disconnected, something he would have known had he actually put the jumper cables on the motor as instructed.
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C) “The sticky throttle cable and $7,000 worth of starters” Back in the 1990s, when I had a lapse of moral judgement and built Lancair IVPs for rich guys, we has a guy with a flying plane call the shop asking if we could install a new starter on his TSIO-550B Continental, which, on, by the way also needed a new throttle cable every 25 hours. He had spend thousands of dollars with other shops, but he was now willing to pay our “Overpriced labor for A&Ps” ($50/hr in 1996). He initially didn’t want to use A&Ps because technically experimental didn’t require it. We solved his problem in 10 minutes: he never had an engine ground strap, and the throttle cable by default was functioning as a high resistance one. He has instead purchased one rebuilt starter for $2,500 and had later purchased a factory new starter from TCM, and it was about $4,500. The logs showed the throttle cable had been replaced 4 times. Good thing he didn’t get ripped off by trained mechanics.
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-ww.
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