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Rotax Piston Meltdown

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waterboy2110

Well Known Member
As Promised - here's the thread.
Hope to keep it as objective as possible.
At 47 hours on a 103F day the #2 piston melted down. Temps from the EFIS showed engine running warm at 116 Celsius. Rotax documentation states 130C is red line and 120C caution should be used. This engine has only seen 91 UL 10% ethanol fuel and I flew it often during phase one in triple digit F temps - up to 107F I recall.

Contacted Vans and all they could tell me was to contact Lockwood. They didn't know of any other Rotax dealers.

Contacted Lockwood and guy on phone suggested filling out a word doc in instead of the Rotax web form - big mistake - don't make it if you have warenty issues. Never heard from Lockwood again. Repeated emails and calls went unanswered.

Contacted CPS while out on the road as the filing of the Rotax form is time sensitive. I did my training with Bryan and Ronnie Smith. Bryan was sympathetic and I forwarded him the form. He was getting ready for OSH but said he would take care of it. To this date (6 months later) I have no idea if Rotax actually knows of this form or my experience.

Met with Ronnie and Bryan at OSH and was literally laughed out of the Rotax tent for using bad fuel - Sad. Vans could only offer that perhaps I write to the forums - even sadder.

Vans doesn't make the engine - Rotax does. Rotax doesn't sell you the engine - Vans does. Imagine buying a Samsung television from Best Buy and having it fail under warranty only to be told to contact Samsung and then being told you plugged it in to the wrong voltage without ever having seen the failed product... I digress..

Reached out to Phillips 66 (parent of Union 76) and they were very concerned that their fuel may have damaged my engine. They responded within two days and once they found out it was an aircraft engine they escalated their investigation. The next day I was on the phone with the head of Quality for the west coast aviation fuel supply. Once he found out I was using MoGas he became very concerned. They sent out a test crew and pulled a sample from the tank. The sample came back as advertised - 91 UL.
I expect Phillips spent a few thousand on helping me. They ran the incident through legal and I was told they are 100% defensible. They absolutely DO NOT advocate the use of their MoGas for aviation - under any circumstances. They felt that if someone would have been hurt Rotax would be accountable.

So back to Rotax - good fuel - now what.
Scratch their shade tree mechanic ars and settle on the cooling shroud Vans has you put on.
It's plausible - the design is such that #2 is starved until the plenum is fully charged. Interesting that Vans eliminated this from the kit. My personal opinion is that they were pressured by Rotax because they were asking non certified builders to dissembled a new engine. This in itself would violate the warenty.

So here we stand, 6 months later.... crickets.

I've replace the engine and now that the rose colored glasses have come off this will be my last Rotax. There's no doubt it's experimental. Nylocs firewall forward, no safety nubs for safety wire. Oil filter safety non-existant. Throttle linkage - I could go on and on.

A close friend was a Rotax distributor for many years overseas and phoned the factory. They asked him a series of questions and at the end of the call they said they would replace the engine. No one in the US ever asked me those questions (did I do the 100 hour at 25 hours - can we see the EFIS data?) That call was of no use since you have to work through you local distribution and they've settled on "it's my fault".

My conclusion is that the engine is "marketed" to operate on 91UL to 130C but I have a box of parts and EFIS data that says it won't. The cooling shroud most certainly contributed to the problem and I suspect there's something to Rotax pressuring Vans to remove that from the kit. I sincerely doubt that Vans simply forgot to put the shroud back on while checking the engine mount and just flew it for a year. There's also the fact that the engine post failure would not pass ignition check. I cannot reason that a dead cylinder would cause a drop on one ignition. Rotax completely blew this off. I may never know unless I get around to swapping out ignitions.

I do love this little plane but you should understand I'm $47000.00 into my firewall forward at less than 60 hours and not happy about that. I'm still struggling to get all the vibration out of the new engine and have no faith in Rotax or their support. I've heard everything from this has never happened to you should get a new engine.

The Cessna is nearly sold and I may begin on a 7 and get back to Lycons and Mags that I can trust.

Lots of pictures - Attaching them here screws up the page format. The story will evolve perhaps with your input.
 
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I appreciate the information. It?s no fun getting the run-around indeed. I?m admittedly not that familiar with Rotax, but why do you need to get a whole new engine if it?s one cyclinder that failed? If I had a failed cylinder on my Baron?s IO-520, and I have - I just replaced that cylinder and then kept on flying.

The same would be true for the UL engine, where each cylinder is essentially a separate accessory on the engine - just replace it. Is this not possible on Rotax?
 
Based on the attached documents it appears this was a 912ULS, do I have it right? Good luck on keeping this thread objective. I hope you can so we can all benefit from your findings.
 
Hi Ron,

The crank in these engines are pressed assembled around each big end rod that isn't split. There's no way to confirm that the crank is airworthy. CPS said they split the case and the cam was pitted. I have no evidence of that but I have the engine.

This is why I was looking into the UL. If I was going new engine why not now. But after speaking to Ray it was clear it would be $27k. If I had more patients perhaps, but I just spent nearly 5 years building it and honestly it's a bit embarrassing.

Yea - any other engine - just clean it out and replace the parts. These engines aren't really serviceable beyond TBO IMO.
 
That’s really disappointing to hear Jim.

And I completely understand the cost to change to a different engine; it would definitely not be a simple swap out, but would be cost effective if you were doing it from the start.

I had thought Rotax’s were fairly simple to dissemble and repair; it sounds like that’s a misperception on my part. One of my attractions to the UL was the simplicity, documentation and availability of a complete OH kit at a low cost.
 
Well, this all really sucks. Sorry for your experience.

I wonder how widely known it is that the engine is not really serviceable. I know there are motorcycles where the crank and rods are assembled this way, but I think you can push out roll pins and disassemble the crank.
 
Well, this all really sucks. Sorry for your experience.

I wonder how widely known it is that the engine is not really serviceable. I know there are motorcycles where the crank and rods are assembled this way, but I think you can push out roll pins and disassemble the crank.

Yea - Harley's have solid big ends - but they're serviceable.

I'm sure I could have rebuilt the engine for maybe $5k less than new but I would not have been comfortable with it. Besides, if Rotax were to ever come through with a warranty this engine belongs to them.

I needed to get the plane back in the air and move on. I didn't spend north of $70K for and 4 years for lawn art.
 
That’s really disappointing to hear Jim.

And I completely understand the cost to change to a different engine; it would definitely not be a simple swap out, but would be cost effective if you were doing it from the start.

I had thought Rotax’s were fairly simple to dissemble and repair; it sounds like that’s a misperception on my part. One of my attractions to the UL was the simplicity, documentation and availability of a complete OH kit at a low cost.

I wouldn't say Rotax isn't serviceable, the are pretty simple engines sans the gear box. This engine made major metal and the only way to return it to service is to completely go through it. It took out #2 and #4 perhaps from FOD bounce.

I dug up a Rotax vs UL thread yesterday and it seemed the pushback was the ECM being powered by the ship in case of Alt failure ( I admit skimming the tread). Given that they're moving onto the 914 and it has the same brain to keep alive perhaps Vans will consider the UL.

I do want to see your install. Ray made a good pitch. Going EAB is no big deal. I hope you have success and publish the results for all to see.
 
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Where did the manifold pressure and RPM fit in with the chart in Rotax SL-912-016? I know there has been debate in the past because the RV-12 has trouble meeting the minimum 5200rpm specified at WOT. Maybe we are learning the conditions where that is important.

What was the 116C measuring? Temperature measurement in the Rotax is confusing due to a number of changes along the way. From my memory of trying to keep track of the changes (check your manual, don't rely on these numbers!):

Originally the measurement was head temperature and 130C was the limit. This is due to detonation margin - the lower compression 912UL has 150C limit.

Then they introduced an additional 120C limit on coolant output temperature due to the potential of coolant boiling at higher temperatures.

The most recent heads measure only coolant temperature, and 120C is the limit.

In between times there were options for waterless coolant, which dispensed with the 120C coolant limit but made the whole engine run hotter. That doesn't seem to be permitted with the latest heads.

Even if it is head temperature, 116 seems very hot.

Rotax also list taking hot air from under the cowl as another potential contributor to detonation. I know many Rotax powered aircraft do the same, but it's possible that with hot under-cowl air, high CHT and high engine load due to low RPM at WOT that you found the combination that Rotax are warning about.
 
Could we see the upper half of the affected cylinder head's combustion chamber, and the upper spark plug?
 
Cooling Shroud Removal

Not to hijack the thread, but I will be doing my 1st condition inspection next month and was wondering if anyone else has removed the cooling schroud installed on earlier 12s.

Would it be OK to just remove it or is there other parts or procedures required? I have not seen the newer plans.

Sorry to hear of your issue. Definitely heartbreaking after spending so much time and money to build your dream.
Thanks,
Dan
 
Could we see the upper half of the affected cylinder head's combustion chamber, and the upper spark plug?

What are you looking for , Dan? It was clearly detonation/preignition that damaged the piston. But . . it was still cool enough not to scuff the skirt. Still, it does look a little funny. curious.

I wonder why no other piston had any sign at all.
 
I dug up a Rotax vs UL thread yesterday and it seemed the pushback was the ECM being powered by the ship in case of Alt failure ( I admit skimming the tread). Given that they're moving onto the 914 and it has the same brain to keep alive perhaps Vans will consider the UL.

I do want to see your install. Ray made a good pitch. Going EAB is no big deal. I hope you have success and publish the results for all to see.

I?m hoping to move it out at the airport (Byron) in January; you?re very welcome to come on by. I have quite a few thoughts/comments on ECU?s and reliability/backup, but we can discuss separate to this thread if you want.
 
This stinks, sorry to hear about your troubles.

Nowhere in your message does it say you actually contacted Rotax directly, only a dealer. What did Rotax say?

At very least they should be willing to sell you a replacement at cost.

I don't know anything about Rotax engines but amazed that it can't be repaired.

I'm also curious when the 'melting down' actually took place what happened? How did you handle the situation? Did the engine seize or did you run it home that way?
 
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Not to hijack the thread, but I will be doing my 1st condition inspection next month and was wondering if anyone else has removed the cooling schroud installed on earlier 12s.

Would it be OK to just remove it or is there other parts or procedures required? I have not seen the newer plans.

Sorry to hear of your issue. Definitely heartbreaking after spending so much time and money to build your dream.
Thanks,
Dan

I would absolutely remove that shroud. Vans states after a year of testing they've determined it didn't make a difference. If it didn't make a difference it wasn't needed in the first place. The folk at Rotax I've talked to don't like it either.
 
This stinks, sorry to hear about your troubles.

Nowhere in your message does it say you actually contacted Rotax directly, only a dealer. What did Rotax say?

At very least they should be willing to sell you a replacement at cost.

I don't know anything about Rotax engines but amazed that it can't be repaired.

I'm also curious when the 'melting down' actually took place what happened? How did you handle the situation? Did the engine seize or did you run it home that way?

The engine can be repaired. If Rotax steps up with warranty they get all parts they are willing to replace up to and including the entire engine. I was led to believe they would replace the engine. When that didn't happen I cut a check and got the plane flying.

The plane flew for approximately 0.1 hours - just ran rough and made it back to the airport at which point an FAA report was filed by the airport crew. Could have been much worse.

I've had several engine mishaps but this was the closest to having an engine try to kill me.
 
I?m hoping to move it out at the airport (Byron) in January; you?re very welcome to come on by. I have quite a few thoughts/comments on ECU?s and reliability/backup, but we can discuss separate to this thread if you want.

Cool, I'm out at Byron every week for fuel. Let's hook up.
 
Jim - This situation sucks for you, lots of unknowns.

You took the engine to CPS and they broke it down, they are a lic. service centers in the US, if you acquired the engine in the US which you did through Vans then they are a good contact for Rotax for you.

In that breakdown they should have done a parts count and verified what was part of the engine and what was foreign - did that happen ?

What did Bryan say next steps were now ? We can all speculate as to cause on this forum but they are the certified experts and have access to the engine. At an absolute minimum you should get a formal response from CPS.
 
Looks like pre-ignition damage, not detonation. I'd also be interested in seeing the other spark plug electrode.
 
Jim - This situation sucks for you, lots of unknowns.

You took the engine to CPS and they broke it down, they are a lic. service centers in the US, if you acquired the engine in the US which you did through Vans then they are a good contact for Rotax for you.

In that breakdown they should have done a parts count and verified what was part of the engine and what was foreign - did that happen ?

What did Bryan say next steps were now ? We can all speculate as to cause on this forum but they are the certified experts and have access to the engine. At an absolute minimum you should get a formal response from CPS.

When I went to pick up the engine Bryan and Ronnie were getting ready to teach a class. Ronnie made the statement that since the quality of the fuel was no longer in question then the shroud or the installation of the shroud was the new point of focus. He mentioned the O rings being pinched. They are not and fully in tack. He mentioned the manifold coming loose - it was torqued to spec and torque sealed with no signs of movement. From what I can tell the "official" expert analysis from Rotax is what ever Ronnie says it is. I've seen no evidence of the engine being opened. I was never shown pictures of the cases split. We took plenty of pictures of the cylinders coming off. I have no reason to doubt Bryan did what he said he did but I have only his word.
 
Do you have a photo of piston #4? I see you have #1 and #3, but not of #4?

You've grounded the aircraft until you have found your vibration issue, correct? The #1 cause is incorrect carb sync, which could be related to your first engine failure.
 
A few comments based on previous posts......

When I went to pick up the engine Bryan and Ronnie were getting ready to teach a class. Ronnie made the statement that since the quality of the fuel was no longer in question then the shroud or the installation of the shroud was the new point of focus. He mentioned the O rings being pinched. They are not and fully in tack. He mentioned the manifold coming loose - it was torqued to spec and torque sealed with no signs of movement. From what I can tell the "official" expert analysis from Rotax is what ever Ronnie says it is. I've seen no evidence of the engine being opened. I was never shown pictures of the cases split. We took plenty of pictures of the cylinders coming off. I have no reason to doubt Bryan did what he said he did but I have only his word.


Van's is switching to using the Rotax 912iS on the RV-12, (not the 914).
There are no airframe electrical dependency issues with the 912iS like there is with the UL engine. Once it has been started, the iS engine generates its own electrical power... fully independent of the aircraft's electrical system. There are back-up modes of operation designed in so that power could be supplied by the airframe electrical system if the Two (fully redundant) methods on the engine both failed at the same time (unlikely).

The decision to delete the cooling shroud from the kit was the result of flight testing done during the development of the iS FWF installation. The iS has cyl temp measurement on all 4 cyl (unlike the ULS which only checks Cyl 2 & 3..... which notedly one of those happens to be the cyl that failed in this case) which allowed a more detailed understanding of what temperatures the entire engine was running at.

The shroud was deleted for the purpose of simplifying the build and to reduce the kit cost. Deleting the shroud removed the need for disassembly of the top of the engine, and thus the potential for a builder to make a mistake.
It was not done under pressure from anyone associated with Rotax. In fact there has never been any mention of a concern with the design of the shroud to Van's by anyone at Rotax.

The blog photos show the removed cooling shroud and speculation that cyl # 2 wasn't getting enough cooling air because of the visible evidence on the shroud showing that cyl #2 had gotten much hotter than the other 3. There is no evidence at this point to indicate that the shroud precipitated the failure (see comments that follow). It is entirely possible that some anomaly caused the pre-ignition / detonation type event and that the very high cyl head temps that would result from that, caused the darkening of the cooling shroud in that area.

- There is now 575+ RV-12's flying.
- The majority of those have the cooling shroud installed.
- There is a lot of RV-12's that regularly fly in very hot temps. There is nothing special about the conditions in southern CA that are more severe than Southern AZ, NM, TX, FL, GA, LA, AL, etc., along with the hot temps that can happen during the summer in the northern states (and other parts of the world for that matter).
- With 575+ RV-12's and almost 10 years now since the first customer built example flew, there is only one other instance of similar engine damage and the cause of it is well understood. In a nut shell, the plans were not followed and the builder made a mistake, and two cyl on one side of the engine were damaged as the result of an excessively lean condition. You can see photos and read about it in the side bar on page 13 of this old RVator Issue. In this particular case the engine was repaired (by CPS), though not under warranty, and as far as I am aware is still happily flying today.

Rotax has clearly specified the procedures for filing a warranty claim. The documentation is supplied with every new engine and is also available in digital form on line to all engine owners. In this case the second engine was I presume purchased directly from a dealer, and not Van's (CPS?). If something failed on that engine, the dealer would not personally warranty it. They would process it the exact same way that this incident needed to be.

So as this discussion continues my hope is that everyone involved will keep in mind all of the facts that we actually know for certain...........

That 575+ RV-12's (most with the cooling shroud installed) have been flying for many thousands of hours, spread over an almost 10 year period of time. Many of those hours were in extreme temperatures (some even hotter than when this incident occurred), while using 91UL fuel.
And with other than this one instance, zero reports of engine damage.

I feel bad that this has happened. The whole purpose of Van's being in this business is to provide kits for airplane that people can build themselves, that have an unprecedented cost vs performance ratio. This occurrence bothers us just like it would anyone else in the RV community.

Having said that, I still think there are details regarding this that haven't been discovered yet.
I have only a limited knowledge in analyzing engine damage such as this so I will leave those comments to those that do, but there are some things in the photos that I think raise some (so far) unanswered questions.

At least one of them would be to see the Cyl head temps and other engine temp readings for the flight posted on the blog. As mentioned earlier, the failed cyl is one of the two that has a cyl temp sensor installed.
<EDIT> After a closer look I see that the CHT data is available and that it shows there was only a 5 deg difference between the left and right side of the engine (CYL 2 & 3).

It looks like damage was beginning to occur on cyl #4 (small holes in the combustion chamber portion of the cyl head). This would jive with something abnormal going on on the left half of the engine. Could be anywhere from an induction leak on that side like the other engine failure i linked too, or improper carb synch, or a carb problem, etc. (but all purely speculation).
There is also an asymmetrical appearance to the carbon pattern on the #4 piston and the combustion chamber portion of the cyl head.
 
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Van's is switching to using the Rotax 912iS on the RV-12, (not the 914).
There are no airframe electrical dependency issues with the 912iS like there is with the UL engine. Once it has been started, the iS engine generates its own electrical power... fully independent of the aircraft's electrical system. There are back-up modes of operation designed in so that power could be supplied by the airframe electrical system if the Two (fully redundant) methods on the engine both failed at the same time (unlikely).

This is misleading in the that UL engine is powered by a permanent magnet alternator that requires no external input. If the airframe electrical system fails, the engine keeps running. The battery is simply a backup power supply. Additionally, the UL engine has redundant ignitions with an option for even more redundancy of another backup alternator.
 
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This is misleading in the that UL engine is powered by a permanent magnet alternator that requires no external input. If the airframe electrical system fails, the engine keeps running. The battery is simply a backup power supply. Additionally, the UL engine has redundant ignitions with an option for even more redundancy of another backup alternator.

You must have misunderstood......

My comment was in regards to the 912iS engine.
In a previous post it was questioned whether the iS engine was reliant on airframe power to run like the UL Power engine (Not UL Rotax).
 
There are no airframe electrical dependency issues with the 912iS like there is with the UL engine.

I don?t believe I misunderstood. Your statement appears to be in reference to the UL Power engine, stating that it is dependent on the airframe electrical system. Whether intended purposefully or otherwise, it is incorrect and misleading.
 
I dug up a Rotax vs UL thread yesterday and it seemed the pushback was the ECM being powered by the ship in case of Alt failure ( I admit skimming the tread). Given that they're moving onto the 914 and it has the same brain to keep alive perhaps Vans will consider the UL.

I don?t believe I misunderstood. Your statement appears to be in reference to the UL Power engine, stating that it is dependent on the airframe electrical system. Whether intended purposefully or otherwise, it is incorrect and misleading.

My original comment was based on the other one above.
I stand correct. Though there is still a large difference between the generation of electrical power for the 912iS and the UL power.

When the engine was being considered for the RV-12, the electrical scheme used on the UL Power at that time was one of the disqualifying factors. It may be different now (11 years later).
 
I see the EFIS data, but it doesn't seem to include RPM. If your setup is the same as others have described here, with takeoff and climb RPM below 5200 at WOT, you were right in the zone Rotax says in SL-912-016 to avoid due to the risk of detonation and/or preignition.
- high engine load (<5200 RPM at WOT)
- high CHT
- probably high intake air temperature

"one or more parameter is exceeded and/or a combination at or near the
limit can result in a higher risk of engine damage"

https://legacy.rotaxowner.com/si_tb_info/serviceletter/sl-912-016-r1.pdf

if I owned a RV-12 (I own a different Rotax powered aircraft) I would be taking notice of this service letter and making sure I had 5200 rpm minimum on takeoff/climb out.
 
Do you have a photo of piston #4? I see you have #1 and #3, but not of #4?

You've grounded the aircraft until you have found your vibration issue, correct? The #1 cause is incorrect carb sync, which could be related to your first engine failure.

The first engine was a bit smoother throughout the range (as I recall -it's been 6 months). Myself and my partner (Rotax representative for United Emirates for many years) are very familiar with carb balancing (both A&P's). The new engine has to come apart for the pushrod / rocker replacement. Not too happy about that either - they cover parts but not labor.
 
My original comment was based on the other one above.
I stand correct. Though there is still a large difference between the generation of electrical power for the 912iS and the UL power.

When the engine was being considered for the RV-12, the electrical scheme used on the UL Power at that time was one of the disqualifying factors. It may be different now (11 years later).

ok, I’ll bite, it’s divergent from the thread, but you keep making statements that don’t appear to be factual. Both the 912iS and the UL Power engine use a permanent magnet alternator, both use a solid state VR, both are 12VDC. The Rotax is a 30A, the UL has a 30A and 50A option. The rotax has the alternator pulley driven, the UL is mounted on the end of the crankshaft. What’s the large difference?

And for the record, the UL260 and UL350 were both designed with a permanent magnet alternator in their initial version. Van’s may have dismissed the UL Power engine for a number of reasons, but if it was based on a perceived unreliable electrical or ignition scheme, then that decision was poorly made.
 
Rotax has clearly specified the procedures for filing a warranty claim. The documentation is supplied with every new engine and is also available in digital form on line to all engine owners. In this case the second engine was I presume purchased directly from a dealer, and not Van's (CPS?). If something failed on that engine, the dealer would not personally warranty it. They would process it the exact same way that this incident needed to be.

Scott - Thanks for the reply. I certainly appreciate your input and insight even with the standard "my opinion" disclaimer.

To be clear -
I called Vans, they said call Lockwood, Lockwood said fill out the word doc and send it to them and after several failed attempts to verify they received the doc I turned to Bryan who said he could handle it. IMO - I've done what needed to be done. I have been told by Bryan that he discussed this with the factory on a recent trip there. I'm confident I've followed the warranty correctly.

I did buy the failed engine from Vans. I spoke to them on three occasions and they really seemed to have no idea on what to tell the customer.
 
I see the EFIS data, but it doesn't seem to include RPM. If your setup is the same as others have described here, with takeoff and climb RPM below 5200 at WOT, you were right in the zone Rotax says in SL-912-016 to avoid due to the risk of detonation and/or preignition.
- high engine load (<5200 RPM at WOT)
- high CHT
- probably high intake air temperature

"one or more parameter is exceeded and/or a combination at or near the
limit can result in a higher risk of engine damage"

https://legacy.rotaxowner.com/si_tb_info/serviceletter/sl-912-016-r1.pdf

if I owned a RV-12 (I own a different Rotax powered aircraft) I would be taking notice of this service letter and making sure I had 5200 rpm minimum on takeoff/climb out.

Hi Andrew - max RPM was 5098. I've posted the graph on the blog. I have read that document. Thanks for asking for this data!
 
And for the record, the UL260 and UL350 were both designed with a permanent magnet alternator in their initial version. Van’s may have dismissed the UL Power engine for a number of reasons, but if it was based on a perceived unreliable electrical or ignition scheme, then that decision was poorly made.

That wasn't what I was remembering when it was originally looked at so that was what caused my confusing post , but that was more than 10 years ago (sorry, my memory is not what it used to be).
Not really relevant to this thread though, anyway.

And as I mentioned already, that was a minor reason.
The major reason being a desire to have an engine with a long term proven track record and available in a certified version for use on S-LSA's
 
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I did buy the failed engine from Vans. I spoke to them on three occasions and they really seemed to have no idea on what to tell the customer.

I understand that.
Like I already said, it is not Van's warranty (just like the business you bought your replacement engine from, it is not their warranty for your replacement either).

There is a process that Rotax requires be followed.
You may have gotten someone on the phone at Van's that doesn't know much about it, but in the end that doesn't really matter. The warranty process has to be handled through one of the designated U.S. dealers... Lockwood Aviation is one of those, and from what you have said, it was suggested that you contact them so you were not given bad information, you are just not happy with the way they handled it.
If they did not properly follow procedures after you contacted them that is frustrating for sure, but from what you have written it sounds like in the end your claim either is under review or has been.
Hopefully you don't hold Van's accountable for what happens at another business 2500 miles to the east. Van's has done a lot of business with Lockwood over the years and has a good working relationship with them and has always gotten great service there. That is one reason they are often recommended.
 
I see the EFIS data, but it doesn't seem to include RPM. If your setup is the same as others have described here, with takeoff and climb RPM below 5200 at WOT, you were right in the zone Rotax says in SL-912-016 to avoid due to the risk of detonation and/or preignition.
- high engine load (<5200 RPM at WOT)
- high CHT
- probably high intake air temperature

"one or more parameter is exceeded and/or a combination at or near the
limit can result in a higher risk of engine damage"

https://legacy.rotaxowner.com/si_tb_info/serviceletter/sl-912-016-r1.pdf

if I owned a RV-12 (I own a different Rotax powered aircraft) I would be taking notice of this service letter and making sure I had 5200 rpm minimum on takeoff/climb out.


Hi Andrew - I've read that document before and re-read it again after discussing it with my Rotax partner this morning. I re-read your post and now it makes more sense. In essence, Vans is having you set the pitch so that the engine is running in a dangerous area of operation. Coupled with what I consider a poor design for that cooling shroud most likely pushed it over the edge.

My Rotax buddy has been harping on me from the beginning to pitch the prop for a higher RPM - I liked the 71.4 degrees that Vans has you set it to because it gets me good cruise performance. When we set it for 5300 static the plane would barley cruise in the mid 90's. My box truck Cessna will do that. Also, only when you are unwinding this engine at max RPM (any engine for that matter) do you see rated horsepower. I'll have to double check but at 5200 RPM I think the engine is only putting out 80HP.

I have a Keiv 3 blade prop that we're going to try out to see if we can get the static RPM up and get decent cruise performance. My buddy says it's all they used in the UA on Rotax engines.
 
Rotax 912 % Power Graph...
-
2dbo5yb.jpg
 
Hi Andrew - max RPM was 5098. I've posted the graph on the blog. I have read that document. Thanks for asking for this data!

Here I assume: http://912ulsenginefailure.blogspot.com/

Jim, what does the X-axis represent, and in what units?

In your first post you stated:

There's also the fact that the engine post failure would not pass ignition check.

Could you tell us a bit more about that check? And where is the top spark plug from the failed cylinder?

Do you have a record of individual CHT?
 
In essence, Vans is having you set the pitch so that the engine is running in a dangerous area of operation. Coupled with what I consider a poor design for that cooling shroud most likely pushed it over the edge.

Yes. You might find a smoking gun cause, but Rotax documentation suggests the situation described is enough on its own to cause detonation, if you are unlucky.

I have my doubts that the cooling shroud was a contributor. I think the head is probably the critical temperature. The head is limited to 130C. I think the limit on the barrel temperature is 200C but I have not heard of anyone measuring it.
 
The head is limited to 130C. I think the limit on the barrel temperature is 200C but I have not heard of anyone measuring it.

Can you cite the reference for that, please? I see CHT 150?C and coolant exit temp 120?C in the Apr 16 operators manual. Am I looking in the wrong place?
 
Yes. You might find a smoking gun cause, but Rotax documentation suggests the situation described is enough on its own to cause detonation, if you are unlucky.

I have my doubts that the cooling shroud was a contributor. I think the head is probably the critical temperature. The head is limited to 130C. I think the limit on the barrel temperature is 200C but I have not heard of anyone measuring it.

Agreed - Using the graph and the EFIS data I would say the engine failed because it was run at less than 5200 RPM and at 30 inches of manifold. Also, the document mentions pulling in hot air - which this installation design does - basically it's in "carb heat" all the time.

I'm going to pitch the prop on the new engine and get it out of this danger zone. After that we're going to give the Keiv prop a try and see what we see.

At some point I may look into a solution to get cool air to the carbs. The engine would not have been set up by the factory to run in hot air so I expect it's running rich by this design and losing horse power.

Roger Lee from Rotax-Owner has this to say:
"They are better tuned for the engine and setup for proper cool air flow to the carbs. Using air filters on each carb under the cowl isn't a good way to go. The guys that have air filters under the cowl attached right to the carbs are flying in carb heat all the time. It makes for a rich fuel mixture. Cool or cold (depending on your definition) dry air for combustion would be better."

DanH - the X axis is RPM, Y is manifold pressure. The prop should be pitched so that it avoids the gray area on takeoff. Much the way a constant speed would be set when every this is forward. Managing these parameters on takeoff roll would seem to me to be problematic.

As mentioned earlier - my partner - a solid Rotax guy, had been dogging me to pitch the prop for higher RPM. We did at one point but the cruise suffered. If this graph was in front of me then that would have been all I needed to see.
I fell back on Vans documentation for prop pitch because that was data I could put my hands on. I regret that decision now.
 
No smoke visible yet.......

Investigating and evaluating failure modes can be very challenging, but finding the real answer can be made much more difficult if some info is accepted as fact and other info is ignored.

What should not be ignored is the fact that RV-12's have been flying with the same engine and propeller configuration since 2007. The first customer built RV-12's began flying in 2009.

Nor can we ignore that there are now more than 575 RV-12's flying with the prop. pitch set at a value to achieve best overall performance. The actual setting varies from one RV-12 to another because of personal preference with how the airplane is flown and what the typical operating conditions are (home airport elevation near sea level vs 5000 ft or more). That is one of the benefits of a ground adjustable propeller. The setting chosen by a particular operator may not assure operation outside of the "recommended to avoid" range of the linked chart for all portions of a particular flight, but that is the case for all of the LSA aircraft on the market that come anywhere close to achieving the maximum speed performance allowed by LSA rules. It is not possible to have a pitch set for a reasonable cruise power setting on low drag LSA airframe and fully meet Rotax's recommendation.

Is that bad? That is a question worth an answer....

In the context of the RV-12 I think the answer can be determined by looking at the fact that 575+ RV-12's have been flying (many in OAT's higher than the conditions when this engine failure occurred), using 91UL fuel, with a propeller pitch setting that only allows for ~5100 RPM during initial climb, for 11 years and 10's of thousands of hours without having a failure. Many of these RV-12's operate where it is hot a good majority of the time (South America, etc.).

I think your best chance of finding smoke is to stop looking at things that a few of the experts zero you in on, and start looking for what was different on this particular failure flight, when compared to the other 574+ RV-12's that are flying every day with the same settings and conditions.
 
DanH - the X axis is RPM, Y is manifold pressure. The prop should be pitched so that it avoids the gray area on takeoff.

Not the Rotax graph. I was asking about the RPM graph you posted to your blog. Y is RPM, X appears to be time, and I was curious about the units. You see, detonation typically takes a while to progress to serious damage.

The physical damage to the top of the piston is largely mechanical, from chunks of broken ring and piston. There's a little splatter, but not a lot. Splatter and a sand-blasted surface is a tell-tale. It's due to the shock wave. Not much splatter, not much shock.

What I think happened here is light detonation, the kind most engines will shrug off if it isn't prolonged. The stated RPM, MP, coolant temperature, and intake air temperature are all pro-detonation, plus the front cylinders appear to have been running a little leaner than the rear pair (note the carbon difference).

However, if it overheats a plug, the failure progresses to preignition, which runs peak cylinder pressure way up. So a ring land, already at an elevated temperature and weakened a bit, breaks away. The ring, now without support, breaks next.

So why would a plug overheat a bit too easily? One reason could be the wrong heat range. It wouldn't be the first time plugs got mixed in the same engine. Another is lack of heat sink paste, which seems to be a required item in order to run the recommended heat range. The third would be a loose plug. If it's not tight, it can't transfer sufficient heat energy to the cylinder head and coolant.

It would be interesting to take a look at the missing spark plug, and the combustion chamber surface at 12 o-clock, which is why I've been asking. My supposition could be wrong, but I'll present it here prematurely in hope of seeing all the evidence.
 
In the context of the RV-12 I think the answer can be determined by looking at the fact that 575+ RV-12's have been flying (many in OAT's higher than the conditions when this engine failure occurred), using 91UL fuel, with a propeller pitch setting that only allows for ~5100 RPM during initial climb, for 11 years and 10's of thousands of hours without having a failure. Many of these RV-12's operate where it is hot a good majority of the time (South America, etc.).

Wait, wait.... Vans is actually instructing folks to bog down their engine down to 5,100 RPM during take off. This isn't a typo? Everyone here who followed that needs to re-pitch their prop before next flight. Wow!!
Marketing specs > Engine safety.
 
Wait, wait.... Vans is actually instructing folks to bog down their engine down to 5,100 RPM during take off. This isn't a typo? Everyone here who followed that needs to re-pitch their prop before next flight. Wow!!
Marketing specs > Engine safety.

Read my post again......

I said the pitch value people are flying with.
I didn't say the value that Van's makes them use.

And then go read the entire document.
No where does it say that if you do not 100 % meet this specification your engine will blow up.


Next I guess you need to go on all of the web sites for all the other fast LSA's and give them the same advice.
 
Without throwing gas on this fire, and separately from my affiliation with Van's, I vehemently agree with Scott. I have over 1300 hours behind 912's, in a number of different types of airplanes, using different propellers (including in-flight adjustable), running both mo-gas and 100LL, since the early 90's. I have found it to be pretty much a bullet-proof engine. Early on we didn't have quite the choice of propellers we had today, and I assure you we ran some of these engines down around 5000 or lower for takeoff. They didn't blow up.

The one failure noted here in this thread is 1 in over 575 flying engines on RV-12's, or 2/10's of 1 percent. I really don't think we need to jump to conclusions that the whole fleet is at risk. There's lots of reasons why an engine can fail, and some of them are due to metallurgy or manufacturing problems, operator issues, environment, or fuel problems, and ignition problems. But I think it is pretty safe to think that the particular configuration with the heat shroud has enough time on it that if it were the problem we should have seen some other failures by now. Even if they weren't as serious as this one.

They aren't out there. The 912 in the RV-12 seems to be quite reliable. Having a lot of time behind 912's I was anxious to get the factory RV-12 so I could spend more time with it. I had flown some first flights on RV-12's and I was amazed at the cooling, compared to what I had seen over the years on other non-RV aircraft. Now, having spent time with the factory RV-12, in both hot weather and high altitudes at gross weights, I am pleasantly surprised at the performance with regards to cooling.

To me, it's not unlike the rest of the RV fleet. The majority of the fleet does not have any overheating problems. But every once in a while you will see on this web site that someone does have a problem. Usually, it gets solved. Remember, as much as these are called kits, every single one is really different. I have yet to see 2 alike in the hundreds I've inspected, except for the SLSA's of course.

I think we should see all of the evidence before jumping to conclusions. As Dan mentioned, let's take a look at the plugs, and understand any ignition anomalies before jumping to grander conclusions.

Vic
 
Piston elt?

You said you thought it was piston meltdown, but could it be debris inside the cylinder? Just thinking out of the box.
 
Originally Posted by AndrewR
The head is limited to 130C. I think the limit on the barrel temperature is 200C but I have not heard of anyone measuring it.
Can you cite the reference for that, please?

The barrel temperature is in the Installation Manual, but it's directed at people designing the cooling system rather than the general user. It also says:
NOTE: As long as the oil and coolant temperatures are within the operating limits, no cooling air ducts are necessary

The barrel temperature is not normally measured on Rotax or Lycoming. If you compare the fins on a Lycoming head vs. barrel the head seems to be the critical area. So I don't think the cooling duct is likely to have contributed. (My opinion only, I am certainly not an expert!)

I see CHT 150?C and coolant exit temp 120?C in the Apr 16 operators manual. Am I looking in the wrong place?

CHT limit of 150C is for the 80hp 912. The 100hp 912S is 135C (maybe 130 in earlier manuals). I understand the difference is for detonation margin with the higher compression.
 
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