Down to Earth

Finally, an electrical fix.


Electrical problems on an airplane as low-draw as our Kitfox IV are insidious: you hardly know you have them at first. Our panel setup is so minimal, with just a Grand Rapids Technology EIS, one radio, one transponder, barely an intercom, and some Whalen strobes/nav lights pulling power (and rarely all at once), you need to watch the voltmeter in cruise to even notice that the battery is draining. Waiting until the battery won’t start the darned thing at an outstation brings on the wrath of my mechanic-builder-husband. I learned to pay regular attention to electrical output on this airplane.

The original 9-pole stator was mounted to this X plate at the back of the engine. It was removed and a new bracket was fabricated for the Nippon Denso alternator.

But honestly, the problem was getting old. That’s why we finally bit the bullet and did it: retrofitted the electrical power supply on our 22-year-old Jabiru-powered Kitfox IV. It only took two burnt out stators and the company abandoning the original technology to convince us (if you read this column regularly you know we are rarely on the burning tip of the aviation tech revolution).

A Problem From the Beginning

Here’s some history to catch you up. The airplane started life with a Rotax 582 two-stroke engine, which was adequate for lifting our rears off terra firma, but let’s just say its electrical output, for radios, lights and such, was a little on the tepid side. Unless you were at high cruise you’d be draining the battery with the strobes, transponder and radio on. We managed by pretty much never flying it before dawn or through twilight, even though we had equipped it with the proper lighting to do so.

At TBO we swapped the Rotax for a four-stroke Jabiru 2200, a solid little four-cylinder, air-cooled, direct drive engine—but it, too, had weaknesses when it came to electricity generation. It came with a 9-pole stator; something roughly akin to what you’d find on a lawnmower.

The stator was mounted on an X plate right to the back of the engine, with a magnet ring fixed to the flywheel that rotated around it. As the magnetic field cut across the winding, an AC current was produced and was connected to a Key West voltage regulator and converted to DC for aircraft use.

Though the clearance behind the engine was better than it had been on the Rotax 582 installation, it still got hot there. Anytime you put something that is supposed to generate electricity in an engine hotspot with inadequate cooling, you’ll have troubles sooner or later.

The best the original installation was rated for output was 44 volts (AC) with a maximum current of 10 amps at 3100 rpm. Since economy cruise is at about 2900 rpm, we weren’t getting full electrical output unless we were near full power, which is 3300 rpm. But we’d had the same issue with the Rotax 582, so we hardly noticed. We just kept avoiding low-light flying. Seemed simple enough, even if it was limiting.

That said, it wasn’t a surprise when the first installation failed.

The 3/8-inch thick aluminum bracket resembled something you might see in a classic ukiyo-e woodblock print by Japanese artist Hokusai. It was trimmed to shape with a bandsaw and looks nothing like the X bracket that had been the original mount.

Failure is the Mother

A one-time failure of an aircraft or engine part is generally acceptable in my book. I mean, even with good quality control from the manufacturer the occasional problem part slips through, right? Besides, at the moment the original equipment failed, we were struggling in our relationship with the Jabiru anyhow, working to get the cooling right. New heads with more fins and a precisely tuned plenum took care of the issues we’d had with the cylinder head cooling, and we figured that would help with the electrical cooling issue, too.

It didn’t. The new stator lasted about the same as the one before. Then the voltmeter began its telltale wobble, refusing to show 14 volts even at full power. We kept the battery on a trickle charger, and my mechanic began looking at alternator options. It was 2014, and surely the OEM had a better solution to this problem.

Turns out, the OEM did. It had discontinued the use of the 9-pole stator and moved to a 12-pole stator. And yes, you could get a retrofit, if you were willing to part with the appropriate number of AMUs (aviation monetary units). Really, quite a lot of them for such a small airplane. We kept looking.

There were options. One of them was going with a classic ram-air driven alternator. It is a relatively elegant solution employed as a backup electrical generator on large aircraft. The ram-air alternator pops out the bottom of, say, an Airbus, in the unlikely case of a total electrical failure, and, given the proper airspeed, spins up to power the emergency bus. Several companies adapted this technology for light aircraft, and at least one created a product that could be mounted on the belly of super-lights, such as the Kitfox, to provide exclusive electrical current during flight. Of course, that meant our battery would have to start and run all electrical components on the ground every time. Using this technology also meant wading deep into the mucky pool of Experimental aviation, since we had not seen it on any other Kitfox, nor on any other Jabiru engine installation. Mmm, cutting edge. Trial and error and trial and…probably more AMUs than originally estimated. (What am I saying? Always more AMUs than originally estimated.) Just thinking about it made me squirm.

A couple weeks before Sun ‘n Fun 2014, my mechanic came to me with another idea. Rotec, an Australian company, had a retrofit alternator kit for Jabiru 3300 engines that employed a real Nippon Denso 100211-4540 IR/IF 45 amp alternator. Yes, there were AMUs involved, but no more than the OEM kit, and the result, if it worked, would be stable and provide ample electrical power to the aircraft. The upgrade is relatively simple, with the original stator and magnet being replaced with a new alternator bracket and pulley. The alternator is then mounted, plugged in, and the installation is complete.

There was one problem, though. Our engine was a Jabiru 2200. But surely the company had or was working on a kit for our engine, too? A phone call enlightened us. Turns out, there wasn’t exactly a screaming mob of Jabiru 2200 operators lighting up the communications lines to Rotec demanding a retrofit kit. That said, the company was open to working with us, if we were willing to do a bit of the work.

After a face-to-face meeting at Sun ‘n Fun, the deal was settled. If my mechanic could create the proper mounting plate to marry the Rotec alternator system to the Jabiru 2200 engine, Rotec would sell us the system. And if we gave the design back to Rotec, there’d be a discount in it; enough of a discount to make it worthwhile.

Yes, there I was, squirming at the cutting edge again, but this time the carrot on the stick—stable and ample electricity—was a big enough reward. My mechanic put his designer hat on and went to work.

The Nippon Denso alternator installed on the Jabiru 2200. The mounting bracket’s unusual shape provides clearance around the engine mount.

Off With the Old

First things first: he had to remove the air filter box to make room for the alternator to fit behind the engine. Then he removed the X bracket, which the stator is bolted to, and removed the ailing stator. He removed the magnet ring, which was bolted to the flywheel with button head cap screws. Those didn’t want to come loose, but he got them off, stripping two of them in the process (insert expletive here).

“I had to remove the flywheel and drill out the stripped screws and then apply some heat to the studs to get them loose,” he said, describing the workday grumpily. “Be careful about heat around the magnets on the flywheel,” he warned. “Heat can weaken the magnetism. Also, remember to mark the flywheel position and do not move the crankshaft, so that the flywheel will be in the same position for the new installation.”

Unconventional, Maybe Inspired

The bracket took some doing. In the end it looked nothing like the X bracket that had been the original mount. Instead it resembled something you might see in a classic ukiyo-e woodblock print by Japanese artist Hokusai, a cresting wave. First there were paper templates, then cardboard templates, and finally plywood of the proper thickness. He consulted with several CNC saw operators, who told him that the labor involved in digitizing the design for the plate on a one-off wasn’t worth it. The 3/8-inch thick 6061-T651 aluminum blank he’d ordered for the bracket plate could just as easily be trimmed to shape with the ordinary Delta band saw he kept in the back of the hangar.

They were right. With the right blade and cutting oil, the saw cut the plate slow but steady. He used Scotch-Brite wheels, along with a sander, to smooth out the tooling marks on the cuts and plate, then primed and painted it, leaving a clean area for the ground connection. Perfectly honed and professionally smooth it was not, but it was structurally solid and promised to hold an alternator in place, up high enough on the back of the engine to facilitate good cooling (and not so high as to require a modification to the Kitfox’s unique, bulbous cowling).

He used four 10-24×3/4-inch socket head cap screws to bolt the pulley to flywheel, then mounted the alternator bracket in place. Next came attaching the alternator to the bracket and connecting it to the pulley via a Napa 4L220 drive belt and wiring it up as per Rotec instructions. It looked good, so he fired it up—and it ran bad, with no alternator output at all. Argh. Time to walk away and think, because, after all, this is Experimental aviation.

After a good meal and a night’s sleep, he returned to the project and decided to use the other spade terminal on the alternator, then re-time the flywheel. The engine started up smooth, and the alternator put out a delightful 14.2 volts. At that point he fitted a new K&N RU-0500 air filter and blast tube to the engine and then took it up for a test flight. Success!

I’d like to say it’s great to have an airplane I can comfortably fly in the dark, but really, who wants to fly a Kitfox in the dark (I mean, taildragger landings are just freaky at night)? What I do love is seeing the voltmeter needle pop to life with each engine start, and consistently show me a steady 14 plus volts on every flight. It doesn’t seem to care anymore if I want to be an energy hog and use my strobes and transponder at the same time (really nice when going into a controlled airfield). I can use the intercom to keep up a steady stream of conversation with my passenger, appreciated or not. And I don’t need to worry if a headwind has me out past sundown on the run home.

Maybe the bleeding edge of Experimental aviation isn’t so bad, after all.

Amy Laboda has taught students how to fly in California, Texas, New York and Florida. She’s towed gliders, flown ultralights, wrestled with aerobatics and even dabbled in skydiving. She holds an Airline Transport Pilot rating, multi-engine and single-engine flight instructor ratings, as well as glider and rotorcraft (gyroplane) ratings. She’s helped with the build up of her Kitfox IV and RV-10.


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