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Re: Engine Vibration

PostPosted: Sun Aug 30, 2015 9:27 am
by gkremers
Really glad you isolated the issue and got it fixed.

I'm sure we would all like some choices when it comes time to picking an engine manufacturer. My experiences with the Rotax have been overall positive. I've built 2 planes that used the 912. The only issue I had was a bad regulator on my Pulsar that had 550 hours on it. So far the 912ULS in the Highlander is running well. The carb float issue was a real fiasco but luckily it didn't create much down time for me. I've owned many planes over 30 years of flying and the "certified" stuff have also had issues. The difference is the certified stuff is really expensive to fix. My RV7A was caught up in a Superior cylinder issue, again I was very lucky mine just needed additional compression tests. A large number needed to have them replaced, some got help from the company and some did not.

Lets hope the Gemini gives everyone another option but I'm sure it will not be perfect either, nothing is in aviation.

Gary
N325AB
Just under 100 hours

Re: Engine Vibration

PostPosted: Sun Aug 30, 2015 11:32 am
by kenryan
I take these reports of new engines with a huge grain of salt. Over the years many have announced that their (breakthrough) engine will be "available soon." Very few ever make it to the market, and even fewer succeed. If Gemini were to come through with their promises it would be terrific but for me at this point it's nothing more than wishful thinking. And even if they did get something on the market, I don't think I would want to be a beta tester for it. It will be a 914 for me. It will hurt bad to put out that kind of cash, but hopefully it will be a good, strong reliable engine. The odds say that it will be.

Re: Engine Vibration

PostPosted: Sun Aug 30, 2015 3:16 pm
by R Rinker
I totally hear what your saying Ken..I guess as humans 'hope springs eternal'. We can't live in a negative mindset because we know, eventually, something better is usually the progression of engineering. I think we have to apply reason here, and from the information I've seen, there is a lot of good sound reason to hope in the Gemini. The purpose of talking about it is to find those tell tale indicators that helps us make intelligent attitudes. There has to be people out there with some good information. I gave up on the UL after finding exactly that. By now we kind of know what to look for as to whether a company is doing it right or heading for oblivion. I've got 34 years of trusting my neck to a Cont. or Lyc. in the Arctic and even Siberia, so I'm going into this basically 'ultralight' world very timidly. It raises my eyes quite wide to see people willing to put their necks out to an engine that has issues such as is common with Rotax.

Re: Engine Vibration

PostPosted: Sun Aug 30, 2015 4:23 pm
by SheepdogRD
Steve Wittman's take on the issue was that you pick your engine, and then you design the airplane to fit it. Troy said much the same thing -- the Just airplanes are designed around the Rotax.

I find the Gemini concept fascinating, and I hope it becomes a successful production engine. I'd love to fuel up with Jet-A instead of gas, and I'd appreciate the simpler maintenance. The Gemini's torque output may make it a fantastic STOL engine.

But there are lots of issues to work out and test. I agree with Ken:
kenryan wrote:... I don't think I would want to be a beta tester for it.

I've been on that road. I started down the path of Corvair power, invested good money and lots of time, only to find that a reliable 100hp Corvair engine is a good bit heavier, isn't significantly cheaper to build, is a lot harder to keep cool, and simply can't perform like the geared, torque-multiplying Rotax. So I'm gun-shy about going away from the comfortable, known-quantity aspects of the 912S. It has thousands and thousands of predecessors whose pilots have helped make it reliable.

I'll test for the first 40 hours. After that, I just wanna go fly.

Re: Engine Vibration

PostPosted: Sun Aug 30, 2015 9:55 pm
by User GDS
So often its-- get it going & mess around with it, fly a little bit, mess around some more, and on and on.
In my experience, this is very unusual. I've had a lot more trouble with my brakes then I have with my Rotax.

Every machine ever made will fail and power plants are especially complicated machines. I put a factory reman IO520 in my C206 and had a mandatory service bulletin come out on it before I even started it for the first time. We have four Subarus in the family, ultra reliable motor vehicles, but one of them broke the valve timing belt at 90K miles and bent the valves. I had a catastrophic engine failure in my BMW motorcycle. Doesn't matter if it's a Rotax, a Gemini or Apollo 13, they will all fail, it’s just a matter of when and whether or not they give you some warning first.

Despite my gearbox problems, I am satisfied with Rotax power. Their reliability is suitable, even for the extreme duty that I use them for. I’ve had two now and this is my first real problem. If I were building another Highlander I would not hesitate to use a Rotax, probably the fuel injected version. I lost confidence in mine when I couldn't figure out what the problem was, but now that it's fixed, I went out and put on ten hours over unforgiving mountains and rocky deserts. I like using an engine that is flying in thousands of other airplanes.

This week I'll try to get you guys some pictures of the gears and the tool I made to service the gearbox.

Re: Engine Vibration

PostPosted: Mon Aug 31, 2015 11:25 am
by Swoopjack
Roger, please share what you have learned about UL that turned you against them.

Re: Engine Vibration

PostPosted: Mon Aug 31, 2015 2:15 pm
by User GDS
ImageGear press to disassemble gearbox. It's made of two pieces of C-channel steel, all thread rods and a couple of blocks of aluminum. It takes a lot of pressure to compress the springs. The Rotax heavy maintenance manual describes the process.

Image This is the gear that came out. The gear faces look like brand new, the only wear is on the "dogs"

Image This is the back of the clutch, there is some wear on these dogs.

Image this is a brand new gear.

Re: Engine Vibration

PostPosted: Mon Aug 31, 2015 3:05 pm
by R Rinker
Reply to Swoopjack: I'm not trashing UL. I know little about their engines. You & I as homebuilders are really in the dark and have to rely on red flags or certain indicators that we depend on to pass judgement where to put our money and eventually our necks. We simply do not have the information we need..people just won't share it. My 'personal' judgement is that UL is basically a good engine, but has some things to be worked out that scare me off because of where we live and fly, and the budget we do it on, could not bear up to what would be required to get it operational. The engine is made in Europe and one builder couldn't get his working and sent it back to Europe...they sent it back to the States and assured him it was fine! He had it on and off about 3 times before he ever got it working..well, kinda working..That is actually the only detailed account I know of..Another deal breaker for me is that at max output the prop turns (I believe) at over 3,000 rpm. That's out of my acceptance range if I have any choices. I stand on the curb and cheer, but until I see people bolting one on and going flying with minimal headaches I won't join the parade..

Re: Engine Vibration

PostPosted: Tue Sep 01, 2015 5:21 am
by Jack L
GDS,

Thanks for sharing all that you have on this topic, this is great information. Could you describe the symptoms that you experienced a little more? Where did you feel the vibration? Stick, pedals throttle? Could you hear anything? Would you describe it as a buzz, a shake or an imbalance?

Rotax released its 50,000th Rotax 912 in 2014, the first 912 was released in 1989 so they have been producing approximately 2000 engines a year for 25 years now. The guys at Just Aircraft have seen or tried just about every engine in the Rotax 912 class available and today they all fly the Rotax, that has to mean something. Since the early 90's there have been so many engine prospects but none of them developed in the way that Rotax did.

I like that Rotax advises its users of issues through Service Bulletins, Service Letters etc. Technical support and parts availability are outstanding when compared to other choices and the TBO is what should be expected of any aircraft engine. Yes there are issues but I cannot see a better choice if you are looking for a proven engine.

Jack

Re: Engine Vibration

PostPosted: Tue Sep 01, 2015 2:00 pm
by Swoopjack
Thanks Roger, All very good points. I'm trying to learn all I can B4 throwing down the money

Jack

Re: Engine Vibration

PostPosted: Tue Sep 01, 2015 8:49 pm
by User GDS
It was a vibration that I could feel mostly through my feet, they're in close contact with the airframe. It started out very light and barely noticeable. I flew with Trilander Ted in the spring and he felt it, too, so I knew it wasn't just my imagination. Over about 60 hours it increased steadily, to the point that it felt like I had orbital sanders under the rudder pedals. I couldn't feel it on the ground, only in the air. At that point I wasn't flying except to troubleshoot.

Rotax released its 50,000th Rotax 912 in 2014, the first 912 was released in 1989 so they have been producing approximately 2000 engines a year for 25 years now. The guys at Just Aircraft have seen or tried just about every engine in the Rotax 912 class available and today they all fly the Rotax, that has to mean something. Since the early 90's there have been so many engine prospects but none of them developed in the way that Rotax did.

I like that Rotax advises its users of issues through Service Bulletins, Service Letters etc. Technical support and parts availability are outstanding when compared to other choices and the TBO is what should be expected of any aircraft engine. Yes there are issues but I cannot see a better choice if you are looking for a proven engine.
Yep ++

Re: Engine Vibration

PostPosted: Fri Sep 04, 2015 1:09 pm
by Johnny C!
Did anyone with Rotax offer an idea of
why this failure occurred?

And how many hours on the power plant?

Thanks!

John

Re: Engine Vibration

PostPosted: Fri Sep 04, 2015 2:34 pm
by sonex293
In July, he reported 320 hours while still working on the problem...

==
Michael

Re: Engine Vibration

PostPosted: Fri Sep 04, 2015 10:33 pm
by Av8r3400
I did the same repair on my 912 UL (80 hp, no clutch) at approximately 400 hours. Galling on the drive and driven dogs, just as shown here. I was also showing some wear on the gear teeth. Engine vibrations at 2500-4000 rpm. After re-shimming the gearbox some improvement was noticed. After replacement of the parts and another re-shimming the vibration was all but gone.

All of the engine time was with a 3-blade Warp Drive, 72" diameter, taper tip, nickel leading edge prop. IMO, prop weight (mass) has something to do with this accelerated gearbox wear. Warp drive props are great, stout and very durable, but extremely heavy.

Re: Engine Vibration

PostPosted: Sat Sep 05, 2015 12:41 am
by Johnny C!
So rotax's with lighter props and or clutces
are to be less likely to have failure?

John