ROTAX 912 Voltage Regulator Failure Mode?

[FastEddieB]

My Sky Arrow has a ROTAX 912ULS2, and uses a Ducati voltage regulator with a multi-pin connector.

I flew it Thursday for the first time since May (I'll report on the reasons for that elsewhere). On that flight, everything was fine - the "GEN" light would go off above about 1,400 rpm and the voltmeter would settle down at about 15v indicated (about 13.7 or 13.8 as indicated by my Garmin, so I think the panel gauge just reads about 1v high).

Yesterday I did a flight with my wife to Anniston, AL, about 1:15 flight time. Taxiing out, I noticed the "GEN" light would flicker on at about 2,000 rpm or so - its never done that before. On the actual flight the "GEN" light was out and voltages were normal.

I went for a local flight at Anniston. I aborted it because I noticed the voltage was indicating about 12v (on a gauge that reads about 1v high) on full-power climbout. I wanted to be sure I had enough battery power to start up and, hopefully, make it back to the GA mountains.

On the flight home, the voltage showed about 13v on climbout, but over the first 10 minutes or so gradually went up to indicating 15v, which the Garmin confirmed was about 13.7 v. On landing at my home base, it seemed the "GEN" light was flickering on at about 2,200 rpm.

As a side note, I ferried a Sky Arrow with a new owner (just one serial # off from mine) and on a touch and go training flight it exhibited the same "GEN" light issue at about 2,000 rpm and 12v indication. On the flight from Dallas to Tampa, it seemed to sort itself out with normal voltage indications once the flight began.

This is my original voltage regulator, at about 3 years and 200 hours. I know others have had problems with them, possibly due to high temps in the Sky Arrow installation. I had a solid "GEN" once on startup, and ordered two voltage regulators - to install one and keep the second as a spare. Turned out to be just a corroded plug into the voltage regulator - upon cleaning it up it was back to normal. So, the good news is I have a two spare voltage regulators to try out. Bad news is the location of the voltage regulator in the Sky Arrow is VERY difficult to access.

The battery is a one-year-old Odyssey that seems to hold a charge well and cranks the engine strongly.

Anyway, a voltage regulator swap would seem to be my first step (after checking the connection again, and this time applying some Stabilant™). Has anyone seen this type of behavior before, and is it a common failure mode for the ROTAX 912?

To reach a different audience, I'm cross-posting this to the "CTFlier" forum as well.

Thanks!

[roger lee]

Hi Eddie,

I'll see this on many planes when people have a low rpm (below 1800) and a high voltage drain with lights and avionics, especially with a landing light on. Bad connections will cause this which includes corroded ones. Bad or corroded main ground wires especially on the engine side. My bet is not the regulator, but one of these wiring issues.
let us know what you find out.

[FastEddieB]

Roger,

Thanks for the quick reply.

I'm going to try to get over to the airport today to start troubleshooting.

I'll start with the cleaning and re-seating the multi-pin connector and checking all the grounds.

If that doesn't work I may try the voltage regulator swap and see what that does.

I'll let you know how it works out.

[DKarnage]

I had the same problem. Turned out to be a loose wire on the rectifier / regulator. Caused me to scrub the first attempt at the flying portion of my checkride.

[FastEddieB]

Pretty darn sure its the voltage regulator.

I removed the multi-connector plug and cleaned the contacts and applied some Stabilant. Also checked any grounds I could find and the battery posts. All seemed OK and on restart the problem was still there.

Hooked up one of my spare voltage regulators and grounded it with alligator clips to a good ground. On engine start the "GEN" light went out immediately, like it did before.

The only problem is the darn voltage regulator is about impossible to reach. I'm going to call Chesapeake and see if they have any hints. I'm flying over to Dahlonega tomorrow to have Tim Dawson help with the voltage regulator replacement - since I'm Experimental now we can possibly fabricate a bracket that will make future replacements easier.

Tim also said that Remos was having so many problems with the Ducati part that they sourced their own - so I may consider using one of theirs in the future if its compatible.

You can see how hard it is to reach the voltage regulator here:



It's directly below the plug, in an area that seems almost impossible to reach.

[FastEddieB]

Tim Dawson and I had some fun at Wimpy's airport in Dahlonega, GA today.

First, we looked at the location of the existing voltage regulator. "Difficult to reach" is an understatement! I had tried to see the lay of the land with flashlights and mirrors. Tim got a better look with a fiber-optic camera! It really seems that 3i gave NO consideration to the possible replacement of the voltage regulator - its almost like the plane is built around it. Not to mention that these things seem to fail with some regularity.

Yesterday, I had called Chesapeake Sport Pilot and spoke to Jamie about any hints, since they own a couple Sky Arrows. When I mentioned that my Sky Arrow was Experimental, and I was considering removing the old one and fabricating an easier-to-reach bracket, he suggested just leaving the old regulator in place and just mounting the new one wherever there was space. Next time the engine was out just go ahead and pull the old one then when there's halfway decent access.

Voila (again)!



We secured the new voltage regulator to an existing strut via Adel clamps, and ran a ground wire to a convenient engine boss. Worked fine on startup and on the flight home. I still have a spare voltage regulator which I will carry with me, and if I need to install it its now an easy field repair (just two easily accessible nuts and one plug).

We both had concerns about the proximity of the exhaust pipe. In flight, the air will enter from the right of the photo, and I'd think if anything cooling will be more efficient than before. I'll probably go ahead and wrap that exhaust pipe with insulating wrap next time I have the cowling off*.

Ah, the joys of being Experimental!


*Tim says Paradise Aircraft use insulating wrap on certain portions of the exhaust stacks of their aircraft to avoid or minimize heat issues.

[FastEddieB]

One more thing...

...does anyone know of a source for the rubber boot that is supposed to protect the multi-pin plug? Mine disintegrated.