912 ULS gearbox problems.

by James Christison in General Tech Discussion 8 years ago

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Re: 912 ULS gearbox problems.

by Rob Seaton » 6 years ago

Rob Seaton

3 1.32k 240

What failed? I don't see any broken parts? or is this an english translation issue, and you mean "worn"?? The dogs are sacrificial parts and will always show some wear.
I don't know about the lubricants but I think there is a big difference between a turbine transmission and a piston engine gearbox? Does a turbine transmission have any torsional vibration?

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Re: 912 ULS gearbox problems.

by Roger Lee » 6 years ago

Roger Lee

126 5.13k 4.58k

Hi Rodrigo,
I don't think this has anything to do with prop weight. Too many of these props being used around the world without any issues on the 912 engines.

I flew helicopters for 6 years. Your helicopter gearbox oil isn't used for the engine like a Rotax. Don't compare. There is no similarity between a helicopter and Rotax gearbox. The forces involved are different. The Rotax is closer to a motorcycle than a helicopter. You must use an oil that is compatible with the engine and the gearbox. The dog gear wear can come from several things, but you haven't addressed those. Things like did you keep the carbs synced, was the prop blades in track, were the prop blades dynamically balanced, the way you start and stop the engine, the oil you use, ect.. These are only a couple of things that can cause excessive gearbox wear and there are others. A 912ULS engine doesn't wear out a gearbox in 160 hrs. unless something either wasn't done to the engine that should have or something was done that shouldn't have been done. I have never seen a 912ULS gearbox wear out in 160 hrs.
A couple of your parts almost look like they have been exposed to water? If so then running an engine too cold would allow this because it wouldn't burn off contaminates.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: 912 ULS gearbox problems.

by Rodrigo Echenique » 6 years ago

Rodrigo Echenique

5 19 0

What failed? I don't see any broken parts? or is this an english translation issue, and you mean "worn"?? The dogs are sacrificial parts and will always show some wear.
I don't know about the lubricants but I think there is a big difference between a turbine transmission and a piston engine gearbox? Does a turbine transmission have any torsional vibration?

I said my gearbox failed not broked, any part can fail and it don´t need to be broken, it failed to work propperly and this is a fail.

Yes, the dogs are sacrificial parts as well as de pistons, rings, crankshaft, cam, valves, etc. etc. they are not suposed to last forever but in a aicraft engine that have a TBO of 1500 or 2000 hrs the gearbox is not sipòsed to fail at 160 hrs.

And your last question if the helicopter gearboxes have any torsional vibration? they not only have torsional vbibration, also resonance from the frecuancy of the blades, stress of lift, stress of the torque of very large blades and they last in some helicopters more tan 2000 hrs and this are also sacrificial parts

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Re: 912 ULS gearbox problems.

by Rodrigo Echenique » 6 years ago

Rodrigo Echenique

5 19 0

Hi Roger,
This is exactly the problema, this plane has been maintaned by me and I can tell you that I did everything!
The propeller is a three blade Woodcomp in flight adjustable and now I changed it to a Bolly Prop of carbón fiber and very light because my engine is not the only Rotax 912 with this problem, all the Pipistrel Virus planes that uses the same prop have the same problem.

I check my carburators every oil change and at least I verify the sincronization, my propellers are balanced in a profesional propeller balancer to cero tenths of a gram at the tips, I uses for some time Mobil 1 sinthetic sugested by Rotax and I only use high octane auto gas, at 100 hrs I changed the oil to Aero Shell Sport Plus 4, and I change my oil every 50 hrs, I use a full changed battery with lot of power to start the engine and to turn off the engine I always set to iddle, then turn off one ignition circuit and in one or two seconds the second magneto, I think I have done it correctly.

The engine have never been exposed to wáter or coast and never in cold weather and as you can see I found some corrosión inside the gearbox and this was caused by the Isoflex that is very acid, the fuel pump lobe had corrosión, I resurfaced it and polished to like new condition and now my gearbox is working like new and I think I didn´t do any abuse to the engine in fact I maintain this engine with change of oil and spark plugs at shorter intervals because the oil is the life of any engine.

Here in the air club are one guy that have a Pipistrel with a Rotax 912 of 80hp, he flies every day all day and his engine is perfect!

Why is no notorius that the 80hp engine have a much better and reliable gearbox?
If the gearbox is the headache of Rotax why they don´t make a forged and stronger gears with dogs and if the clutch is giving trouble why not use the non clutch gearbox in all the engines?

In this same post above you can read that in New Zeland many gearboxes are failing at very low hours, I think mine is not the only one.

Regards

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Re: 912 ULS gearbox problems.

by Roger Lee » 6 years ago

Roger Lee

126 5.13k 4.58k

Hi Rodrigo,
Looks like you have done well in maintaining the engine. The gearbox on a ULS is no more unreliable than a UL. If the dog gears wear out prematurely on a ULS vs a UL then it would be because of the higher compression in the ULS and then the operator idling under 2K (i.e. 1550-1800) rpm for extended hours over the total run time of the engine. This would also take into account the other factors I listed in my last post have all been ruled out. If a gearbox on a UL or ULS wears out at 160 hrs. then there is a serious problem that needs to be identified. I don't have any UL's that come to my shop. All are ULS and they all have 500 -3000 hours on them and not a single one has ever had a problem like yours. Most times when the service centers do at the 600 or 1000 hr. gearbox inspection it replaces a few minor worn parts. Yes there have been some with some dog gear wear more than others, but that's certainly a minority.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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912 ULS gearbox problems.

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