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Rotax Piston Meltdown

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detonation typically takes a while to progress to serious damage

That might be true for a Lycoming, is it also true of a Rotax?

One of the documents I have read on detonation says
"An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes."

A Lycoming is about 0.5 HP/in3, a Rotax is 1.2 I think.
 
Looks like pre-ignition damage, not detonation. I'd also be interested in seeing the other spark plug electrode.

rv6ejguy = ON THE MONEY

That might be true for a Lycoming, is it also true of a Rotax?

Applies to all spark ignition gasoline engines. ALL of them.

APS/ GAMI many years ago contracted Air Data research to compile all the engine SDR's and crash reports into a massive pile.....yes massive, measured in feet. George Braly painstakingly went trough them all weeding out what was allegedly reported was detonation and what was not, what actually was preignition. The conclusion to this research was best summed as as;

All conforming engines on conforming fuel, only a mismanaged Turbocharged engine could detonate, a NA engine would not.

Preignition however will destroy a Rotax a Lycoming or a Stihl chainsaw. The most common cause is from a cracked ceramic, probably around 90+% with a few %, say 5% from cross firing mags/harness. maybe 1% from helical tangs.

DanH is onto it with a plug failure, being the ceramic as the most likely almost for certain cause., perhaps a poor fit and this not heatsinking.

The fuel was stated as being 91ULP, is that MON, RON, (R+M)/2 ? I am assuming this is the (R+M)/2 or AKI number, which is around 95 RON or 85MON (avgas language)

The likelihood of detonation causing a ceramic failure is low, but a dropped spark plug is very high indeed.
 
You said you thought it was piston meltdown, but could it be debris inside the cylinder? Just thinking out of the box.

Don't think so John. The debris was an intermediate result of the root cause. The top edge of the piston is clearly melted on the surface. DanH has been asking for a week about the top plug for a reason. Ross has lots of experience with small bore, high power engines. While still no clear root cause it is in the preignition/detonation mix. Could be as simple as a broken electrode insulator.

The static RPM, and cooling shroud are red herring items as Scott has pointed out.

Just my opinion.
 
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The barrel temperature is not normally measured on Rotax or Lycoming.

Can't speak for Rotax. True at Lycoming; I asked some years ago.

So I don't think the cooling duct is likely to have contributed. (My opinion only, I am certainly not an expert!)

Nor do I. Nor am I. But don't cut yourself short. You post good stuff.

Re .."takes a while to progress..";
One of the documents I have read on detonation says
"An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes." A Lycoming is about 0.5 HP/in3, a Rotax is 1.2 I think.

Note "within minutes". I too hesitate to assign a hard time period, just like the above author, as it depends on severity. In this case, let's see about the time hack units. The RPM plot seems to suggest a very short period at WOT.

All conforming engines on conforming fuel, only a mismanaged Turbocharged engine could detonate, a NA engine would not.

I have repeatedly posted detonation plots from Lycoming (IO-360) and the FAA (IO-540K). A normally aspirated Lycoming will detonate given the necessary conditions. Let's not go there....subject is a Rotax failure.
 
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In this case, let's see about the time hack units. The RPM plot seems to suggest a very short period at WOT.

I agree. The time period at max. RPM and at 4000 for the run up / ign. check are about the same. It would be unusual for an ign chech to take more than 30 seconds.... and 15 seconds would probably be more typical.
 
As someone who's built over 150 turbocharged engines, driven, raced and flown them for the last 40 years and done thousands of dyno pulls, here is what I have observed:

Detonation almost always breaks the 2nd ring land first, 3rd ring land next, almost always with no major crown damage and usually leaving the plug ground electrode intact. The ceramic on the plug may be cracked in some cases. Depending on severity and piston design and material, this damage can take place in 1 second to many hours.

Pre-ignition will melt the piston crown in as little as 5 to 15 seconds and no piston can withstand continuous pre-ignition for even 1 minute, no matter how strong, what coatings are applied etc. Pre-ignition, again depending on severity and duration, most often removes the ground electrode closest to where the event is occurring also.

The higher the specific output, the higher the heat flux on the piston crown. As pointed out, the Rotax has much higher specific output than a Lycoming. This in itself is not a problem on a well designed engine but can be expected to shorten the time it takes for pre-ignition to take out a piston.

Pre-ignition is most likely to occur with high IATs and head/ chamber temps and as Dan pointed out, plug heat range and/or heat transfer through the plug can also initiate it.
 
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Three different piston failure modes.

Here is what a typical detonation failure looks like on a cast piston.



Note broken ring lands but totally intact crown.

Below. Detonation induced pre-ignition failure on a forged piston with central plug location. Ring lands on the forged piston were able to take the detonation without breaking but it was no match for the pre-ignition that followed. Spark plug ground electrode melted off.



Below, 2 bottom photos. Crown and land distortion below caused by excessive heat flux for the piston design. Aluminum gets to plastic state and combustion pressure reshapes the piston which then loses gas seal, hot gas flow past the piston then quickly melts the aluminum.





These would all give you a bad day but detonation failures typically are more benign and besides a big loss of compression and tons of blowby, the engine continues to run in some fashion. Not so much on the others.
 
Thanks everyone for your input and wanting to help solve this issue. I will get the head and plug pics posted.

The x axis on my charts is data points I believe. I can change it to time.


While I agree that the 575 RV12’s flying speaks to the success of this plane I think the number is being thrown around and cannot ever tell the whole story. Vans nor anyone else has actual data on how people pitch the prop, what fuel they use, what MAP they see on WOT. Rotax published the SL because failures were reported.

Again thanks. Let’s keep looking. I’ll post pics this week.
 
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There seemed to be some intimation earlier in the thread that the RV-12 uses a non-standard air filter set up (dual K&N filters taking air from inside the cowling).

In my experience, this is standard on non-certified 912 installations, with certified installations (Tecnam P2002JF and P2006T) using a single airbox with muffler fed hot air for carb heat.

Seeing as Rotax supply the filters, surely they don't consider it a problem?
 
There seemed to be some intimation earlier in the thread that the RV-12 uses a non-standard air filter set up (dual K&N filters taking air from inside the cowling).

In my experience, this is standard on non-certified 912 installations, with certified installations (Tecnam P2002JF and P2006T) using a single airbox with muffler fed hot air for carb heat.

Seeing as Rotax supply the filters, surely they don't consider it a problem?

It's mentioned in the service letter. Rotax-Owners also mentioned it. I couldn't tell you if the carbs were set up to run in hot or cold air but I would assume when tested at the factory they're sucking up cool air.

Carb heat robs the engine of power. Getting cool ram air might make a noticeable difference. Not sure if the Rotax air box would even fit under the cowl.

- SL-912-016R1
Excessively high intake air temperature.
Fresh air intake receiving hot air (e.g. carburetor heat on,
engine installation). Incorrect use of carburetor heat.
 
As mentioned by Jerry, the use of individual filters on the carbs is very common with many different aircraft manufacturers/designs.

The filters are supplied by Rotax with the engine and in fact are custom designed for them by K&N.
Rotax owns the distribution rights. You can not buy that particular filter anywhere other than a Rotax parts dealer.

It would be incorrect to assume that induction air being drawn from inside a cowling would be of equivalent temp to what would be provided by a carb heat system. Would it be warmer than ambient outside air. Sure, but no where near as high as from carb heat supplied via the Rotax airbox.
 
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As mentioned by Jerry, the use of individual filters on the carbs is very common with many different aircraft manufacturers/designs.

The filters are supplied by Rotax with the engine and in fact are custom designed for them by K&N.
Rotax owns the distribution rights. You can not buy that particular filter anywhere other than a Rotax parts dealer.

It would be incorrect to assume that induction air being drawn from inside a cowling would be of equivalent temp to what would be provided by a carb heat system. Would it be warmer than ambient outside air. Sure, but no where near as high as from carb heat supplied via the Rotax airbox.


Perhaps, in this case the plane wasn't flying - just building heat. The fact that there is no carb heat on the 12 would indicate the temp of the air in the cowl is enough to avoid any carb ice. Was this tested? Do you have any data?
 
Seeing as Rotax supply the filters, surely they don't consider it a problem?

Rotax supply the filters, but will tell you it's the airframe designer's problem to feed them cool air. But it is certainly very common to have the carbs taking hot air from inside the cowl.

My own aircraft is possibly the worst, as the carbs are sucking hot air from the radiator. I don't like it, but haven't figured out how to change it yet.

As with all these things none are the cause on their own, but they all reduce the available margin.
 
I had a look at your blog and the heads look like the post 2013 heads, so the measured temperature is coolant temperature and the limit is 120C. The actual CHT isn't measured.

Looking at the charts, it looks like the engine was pretty hot before takeoff - I'm not sure whether something unusual may have happened there? Maybe a long downwind taxi limiting airflow over the radiator? Whatever it was, it looks like the engine barely had enough cooling capacity during that low power period prior to takeoff. It looks like the coolant reached 105-110C on the ground.

I'm not sure of the dynamics of the cooling system when you then go to full power - my SWAG is that you have maybe 5 seconds where the cooling in the heads is very limited, before cooler water from prop blast through the radiator arrives.

One problem with liquid cooled engines is that when the metal is above the coolant boiling point, a layer of vapor can form and insulate the metal from the coolant. Without cooling, that spot then gets even hotter. That's why overheating can be so catastrophic for liquid cooled engines. The difference between adequate cooling and failure might be only a few degrees.

Prior to takeoff the coolant temperature was around 104C. I don't know the likely difference between head and coolant temperature, but head temperature is presumably somewhat higher. The coolant boiling temperature is probably around 130.

A possible theory:
On applying full power, before the cooler water arrived from the radiator, that cylinder just tipped over the point where the hottest areas boiled. This can be quite localized, with the vapor condensing back into the coolant but it still prevents that spot from cooling.
The hot spot in the head triggered some detonation, which further heated the head in a feedback loop until the damage was done.

The piston damage looks like detonation damage on the top (coolant outlet, presumably hotter) side, and debris damage on the bottom.

It makes me wonder whether the 120C temperature limit is OK for steady state i.e. in flight, but a lower limit might be needed before going to takeoff power...
 
The piston damage looks like detonation damage on the top (coolant outlet, presumably hotter) side, and debris damage on the bottom.

IMO this failure is not due to detonation as I outlined in a previous post. There is a big difference in failure modes and length of time to failure between detonation and pre-ignition. They are not the same at all.
 
I recently had a chance to discuss the Rotax SL-912-016 with a UK-based Rotax engineer who does Rotax maintenance lectures and used to work at Rotax.

Apparently he was involved with the issue of SL-912-016 and said the majority of problems were on Katanas with CS props that were doing a lot of circuit flying and operated a lot with the prop pulled back.

It was his opinion that short term WOT wasn't an issue above 5000/5100 rpm. No doubt Rotax build in a safety factor into the SL.

Regarding the Rotax airbox used on the certified installations, to clarify: the airbox is fed with cold air (from a single filter) for normal use, with hot air on demand from inside the muffler shroud for carb heat.

Slightly off topic but may be of interest, we use this system:

http://www.skydrive.co.uk/proddetail.asp?prod=CH-912-3

which has the advantage of warming the carbs to prevent ice forming. As the induction air remains cold there is no loss of power.
 
updated charts

I've changed the X Axis on the charts to session time.

There was a fair bit of time holding short waiting for a regional to land on the crossing runway. The temps were still in spec per Rotax and the Vans 12 EFIS config but clearly not enough margin for safety.

I'll pull the heads this week and also get some clearer pics of the piston. It melted down near the coolant outlet / exhaust valve.

Also - there are a couple posts on age of engine and spark plugs etc.
The engine was delivered May 2016. It had 47 hours on it at time of failure and was using the original plugs (the automotive style NKG's).
 
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Rotax supply the filters, but will tell you it's the airframe designer's problem to feed them cool air.

Actually they do tell you it is the designers responsibility to assure all of the install requirements are met. It is clearly spelled out in the install manual. But they don't tell you that you must supply the engine with ambient outside temp air.

Testing was done on the original proof of concept prototype.
Vans-AIrcraft-RV-12-N912VA-Proof-Of-Concept-Prototype-LSA-Aircraft.jpg


Part of that testing included evaluating a cold air induction system (using a custom built airbox vs the expensive Rotax one). The test results indicated that the HP difference was small and that Rotax's installation requirements were met using just the two filters so that method was rolled into the final design.
 
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For 1352CC engine the RV-12 literally leaps off the ground. I fly off grass usually with two people @ 200# each and often with full fuel.

The beauty of the 912 engine installation in the 12 is no carb heat and no mixture control. Single control is for engine speed. If you didn't know better it operates and appears like FADEC.
 
IMO this failure is not due to detonation as I outlined in a previous post. There is a big difference in failure modes and length of time to failure between detonation and pre-ignition. They are not the same at all.

I'm not convinced anything would get hot enough at idle to induce pre-ignition when takeoff power was applied. Whereas engines definitely can get hot enough at idle power to detonate at higher power.

I am basing a lot of my posts on information found here:
http://www.contactmagazine.com/Issue54/EngineBasics.html
(by a GM engine designer/developer)

From that article, signs of detonation:
  • damage at area furthest away from the spark plugs or near heat sources like the exhaust valve
  • sandblasted appearance on the piston
  • scuffed piston
  • broken ring lands

Preignition:
  • more general heat damage, particularly in the areas that can't shed heat fast i.e. spark plug tips and the center of the piston
 
Ummm, Andrew....you really want to argue that point with Ross, based on a Contact article? ;)
 

Note that some of that is old information, e.g. the post 2013 heads measure coolant temperature not head temperature, and waterless coolant is not permitted.

The temps were still in spec per Rotax and the Vans 12 EFIS config but clearly not enough margin for safety.

Has the EFIS config been updated for the new heads? I agree the temps were within spec, but a lot closer to the limit if the limit is 120C not 130C.

I think the margin for safety is the key factor. Factors that affect detonation margin are:
  • head temperature
  • intake air temperature
  • RPM
  • manifold pressure
  • mixture
  • fuel octane

Coolant temperature was close to the limit. Head temperature might have gone over the old limit of 130C metal temperature. Rotax don't provide a facility to measure it anymore. The 130C limit was stated as being for detonation resistance with the 912S compression.

RPM was below the recommended range for that manifold pressure.

Mixture - an interesting one. Fuel was 10% ethanol, which as I understand it results in a slightly leaner mixture so maybe more prone to detonation.

Octane - measured as 91 which is in spec. However, do fuel companies typically deliver minimum octane possible or do they have a margin? e.g. nominal 91 octane might measure 91-93? If that was the case the fuel might have been lower octane than on other flights, despite being in specification.

My best guess, if you don't find an obvious cause, is it was overheating based on the time waiting on the ground which lead to detonation.

Takeoff RPM may have been a contributing factor by reducing the detonation margin.

The published limit on coolant temperature might also have contributed, if it is based on in flight power and cooling and doesn't provide margin for applying takeoff power in an already hot engine.
 
Ummm, Andrew....you really want to argue that point with Ross, based on a Contact article? ;)

I did research the qualifications of the author as best I can. He is described in many places as the "designer of the Northstar V8". Assuming that's correct, and based on the article, I would guess he has failed a large number of engines under well instrumented conditions.

Short of ringing up to check references, that's the best I can do.

If you can find anything better on the topic, I am very interested to read it.
 
Actually they do tell you it is the designers responsibility to assure all of the install requirements are met. It is clearly spelled out in the install manual. But they don't tell you that you must supply the engine with ambient outside temp air.

Testing was done on the original proof of concept prototype.
Vans-AIrcraft-RV-12-N912VA-Proof-Of-Concept-Prototype-LSA-Aircraft.jpg


Part of that testing included evaluating a cold air induction system (using a custom built airbox vs the expensive Rotax one). The test results indicated that the HP difference was small and that Rotax's installation requirements were met using just the two filters so that method was rolled into the final design.



I did some testing early on with the Kitfox in the 90's, trying to figure out if we needed a cold air box and carb heat. It appeared that the ducting required for the cold air source was less efficient than just using the air filter on each carb. It could also mean I didn't construct an efficient source of cold air, but I decided why mess with something that seemed to work. :)

Vic
 
My experience is working with turbo engines on a almost daily basis for about 40 years now where detonation in some form is a common occurrence. Broken many ring lands in my time on cast pistons from detonation. The failures never looked like the Rotax piston here.

Pre-ignition experience was confined to race engines where there were wastegate failures, high IATs, high coolant temps, too hot heat range plugs or dumb guys trying drive engines through a lean miss condition.

Seen a number of pre-ignition failures where the side of the piston was blowtorched straight through with big spherical blobs of aluminum in the oil pan- certainly not from detonation.
 
Pre-ignition experience was confined to race engines where there were wastegate failures, high IATs, high coolant temps, too hot heat range plugs or dumb guys trying drive engines through a lean miss condition.

I would have thought wastegate failures, high IATs, high coolant temps or dumb guys trying drive engines through a lean miss condition were detonation triggers not pre-ignition. (Or detonation induced pre-ignition.) Too hot heat range plugs would be a more classic pre-ignition trigger?

I acknowledge you have infinitely more experience with this stuff than I do. However, my job and my nature is to question (and in the process learn from!) experts.

I am interested in any comments you have on the article I linked to.
 
Andrew, IMO, that article is actually quite good. It is very broad and while factual, would not be a good guide due to he number of other indicators leading to a root cause diagnosis of a particular failure mode.

The pre-ignition section actually gives a good description. Note it always mentions melting of the piston, and the picture of this Rotax clearly shows the melted top land.

Hot aluminum is weak, pressures are high with PI and could either allow the top land to collapse or to stick to the wall and get pulled off. That leaves the rings unsupported and the failure progresses. FOD everywhere.
 
Note it always mentions melting of the piston, and the picture of this Rotax clearly shows the melted top land.

The reason I was looking at this as a sign of detonation was this section:

Some engines ... have a very common detonation failure mode. What typically happens is that when detonation occurs the piston expands excessively, scuffs in the bore ... and wipes material into the ring grooves. The rings seize so that they can't conform to the cylinder walls. Engine compression is lost and the engine either stops running, or you start getting blow-by past the rings. That torches out an area. Then the engine quits.

In the shop someone looks at the melted result and says, "pre-ignition damage". No, it's detonation damage. Detonation caused the piston to scuff and this snowballed into loss of compression and hot gas escaping by the rings that caused the melting. Once again, detonation is a source of confusion and it is very difficult, sometimes, to pin down what happened, but in terms of damage caused by detonation, this is another typical sign.


The description of pre-ignition suggests the heat is felt through the whole combustion chamber, and the areas that melt are the areas least able to absorb the heat e.g. the centre of the piston. I don't see how pre-ignition melting would be confined to such a localized spot.

On the other hand, if the melting is due to hot gases blowing past a section where the rings lost their seal, that is more like what I would expect.

But pre-ignition or detonation is a bit of an academic distinction at this point (albeit interesting!).
 
The 1st ring land is sometimes described as part of the crown. This is the portion above the top ring. I've never seen this break from detonation. The 2nd and 3rd commonly break from detonation as below:





There is usually no further damage to the crown from this failure because parts can't migrate upwards into the chamber.
 
The reason I was looking at this as a sign of detonation was this section:

Some engines ... have a very common detonation failure mode. What typically happens is that when detonation occurs the piston expands excessively, scuffs in the bore ... and wipes material into the ring grooves. The rings seize so that they can't conform to the cylinder walls. Engine compression is lost and the engine either stops running, or you start getting blow-by past the rings. That torches out an area. Then the engine quits.

In the shop someone looks at the melted result and says, "pre-ignition damage". No, it's detonation damage. Detonation caused the piston to scuff and this snowballed into loss of compression and hot gas escaping by the rings that caused the melting. Once again, detonation is a source of confusion and it is very difficult, sometimes, to pin down what happened, but in terms of damage caused by detonation, this is another typical sign.


The description of pre-ignition suggests the heat is felt through the whole combustion chamber, and the areas that melt are the areas least able to absorb the heat e.g. the centre of the piston. I don't see how pre-ignition melting would be confined to such a localized spot.

On the other hand, if the melting is due to hot gases blowing past a section where the rings lost their seal, that is more like what I would expect.

But pre-ignition or detonation is a bit of an academic distinction at this point (albeit interesting!).

From my experience, this is totally incorrect. You can see that detonation from the 2 latest photos I posted, simply snapped the ring lands with no other skirt or heat damage anywhere.

I've driven engines for hours after the rings lands broke from detonation. You just have to add lots of oil as it's woofing out the breathers. Never had one stop running yet and I've broken my fair share.
 
You can see that detonation from the 2 latest photos I posted, simply snapped the ring lands with no other skirt or heat damage anywhere.

How long was that engine detonating at WOT? This engine might have been 1-2 minutes in detonation at WOT.
 
How long was that engine detonating at WOT? This engine might have been 1-2 minutes in detonation at WOT.

The first set of 4 photos I posted, photo 1, the engine detonated moderately to heavily for about 1 second, 5 or 6 times over a couple days. I got out of the throttle/ boost immediately each time. Then this happened the 7th or so time. Immediately down on 3.5 of 4 cylinders. Looked at the breathers and knew the rings lands were broken.

Several nearly identical incidents driving turbo street cars.

I lightly detonated this same engine dozens of times over the next 15+ years and never broke any pistons.

On another turbo engine, the water injection tank ran dry at full boost. Instant, severe detonation broke ring lands on all 4 pistons and the head gasket in less than 1 second.
 
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Cruise MP vs RPM

Rotax 912 % Power Graph...
-
2dbo5yb.jpg

When I look at this chart I see a cruise chart with limited excursions into the grey area. What I take away from it is this. Take off with WOT and convert to cruise climb when able. Set your cruise power to the values in the white area.
Best regards,
Art
 
When I look at this chart I see a cruise chart with limited excursions into the grey area. What I take away from it is this. Take off with WOT and convert to cruise climb when able. Set your cruise power to the values in the white area.
Best regards,
Art

The note that just precedes this chart is "NOTE: Only applicable on pressure altitude below 3500 ft." (sl-912-016-r1). Not what the situation is above that ...
 
Did I read that there was an ignition failure on one plug? if not, skip the rest of this but here is a theory from a HS grad with no formal training, so here is my uneducated guess, So everything is hot and ready for a detonation event, if one plug fires and as the flame front travels across the CC from the one good plug but with the flame front propagation not completely consuming all the gasses and then you have the (end) gasses spontaneously ignite and detonate with abnormal combustion that blows away the piston boundary layer you have heat transfer to the piston top that is no longer protected by the boundary layer and now exposed to that 1800 degree flame, then the explosive force and pressure of detonation to break stuff and blow holes through weakened soft hot aluminum? all happening within seconds depending on piston thermal inertia rejection capabilities. And this also might snowball by the head boundary layer absent and superheating the coolant in the head and vaporizing it making the coolant ineffective. May be jiberish, just kick me out of the sand box if I'm off base here :D
 
Did I read that there was an ignition failure on one plug? if not, skip the rest of this but here is a theory from a HS grad with no formal training, so here is my uneducated guess, So everything is hot and ready for a detonation event, if one plug fires and as the flame front travels across the CC from the one good plug but with the flame front propagation not completely consuming all the gasses and then you have the (end) gasses spontaneously ignite and detonate with abnormal combustion that blows away the piston boundary layer you have heat transfer to the piston top that is no longer protected by the boundary layer and now exposed to that 1800 degree flame, then the explosive force and pressure of detonation to break stuff and blow holes through weakened soft hot aluminum? all happening within seconds depending on piston thermal inertia rejection capabilities. And this also might snowball by the head boundary layer absent and superheating the coolant in the head and vaporizing it making the coolant ineffective. May be jiberish, just kick me out of the sand box if I'm off base here :D


The ignition check failed after the engine melted down. Perhaps one of the #4 plugs was taken out - I'll check. Once I found the #2 melted I stopped looking at the ignition. I can't reason a dead cylinder causing a difference in RPM during an ignition check (500 RPM).
 
A melted ground electrode is usually a sure sign of pre-ignition which follows with the type of piston damage in the photos too. In all my years detonating turbo engines, never saw it melt off a ground electrode.

Detonation results in pressure spikes many times what you would get during normal combustion but it is of extremely short duration so it does not transfer much heat to anything which is why you see pressure damage but no heat damage.

Detonation also always occurs ATDC where cylinder volume is increasing and crank angle is more optimal where pre-ignition is of long duration (normal combustion started before spark initiation) and always occurs BTDC so pre-ignition adds a ton of heat while effective cylinder volume is decreasing, adding even more heat.
 
MP vs RPM

The note that just precedes this chart is "NOTE: Only applicable on pressure altitude below 3500 ft." (sl-912-016-r1). Not what the situation is above that ...

That makes sense. In a normally aspirated engine you loose 1in per 1000 ft of altitude gain. Taking off above 3500 ft you probably could not generate enough Manifold pressure to get into the shaded area of the chart.

My home airfield is at sea level. I would probably fly a different take off profile if I were operating above 3500 ft.

Best regards,
Art
 
Question

Loads of discussion here on this failure. However, does anyone know how many other similar failures on the flying RV12?s have occurred (if any).
 
Justy asking - -

Did you take a sample of the fuel to an independent analyzer to verify it was at least 91 ?
 
Loads of discussion here on this failure. However, does anyone know how many other similar failures on the flying RV12?s have occurred (if any).

Or to add to this question... Scott mentioned that the 12 demonstrator has more than 2000TT. I'm wondering if its still on it's first engine? Has any top-end work been done to it? Compressions still good?

Perhaps someone else with high-time RV-12 can chime in...
 
Loads of discussion here on this failure. However, does anyone know how many other similar failures on the flying RV12?s have occurred (if any).

The only other engine failure in an RV-12 was builder induced.
I mentioned it earlier in this thread. You can read about it on page 13
in this old RVator

Or to add to this question... Scott mentioned that the 12 demonstrator has more than 2000TT. I'm wondering if its still on it's first engine? Has any top-end work been done to it? Compressions still good?

The engine was replaced (but don't remember the exact total time... maybe 1700 hrs). The core engine was fine and had never had anything done to it other than the Rotax prescribed inspections and maint. I am confident it would still be running great right now if not removed but the sprag clutch was acting up. Doing demo flights and other flight test operations the prototype probably has at least double the engine starts per flight hour (and probably way more than that) that a typical RV-12 does. Replacing the sprag clutch requires opening up the engine. Down time during peak season has to be kept to a minimum so swapping in a spar that we had made the most sense.
 
Not an RV but just a reference point. I built a Zenair CH601HDS in 1995 with a Rotax 912UL (80hp). That engine now has almost 2000 hrs with nothing but routine maintenance and still runs like new.
 
While discussing this with some mechanic buddies they mentioned a 12 here in CA for sale because the engine gave out. Don't have the specifics.

I don't think it's reasonable to imply there is only "one" other failure in the fleet given my experience. Vans never asked me anything about the engine - they simply told me to call Lockwood. I doubt there's any record of my failure with the mothership prior to this thread and I started this thread six months after the failure.

If there's a desire to make statements as to the number of engine failures perhaps a protocol could be established when builders call in. I've spoke to five people at Vans, seven if you include Scott and Vic.

If we really want to know the details gather up the builder info and send out a short survey. That would be useful data in my book.

The fuel was tested by the company Phillips 66 uses for all the SF Bay Area fuel they supply. The report is on the blog.
 
While discussing this with some mechanic buddies they mentioned a 12 here in CA for sale because the engine gave out. Don't have the specifics.

I don't think it's reasonable to imply there is only "one" other failure in the fleet given my experience. Vans never asked me anything about the engine - they simply told me to call Lockwood. I doubt there's any record of my failure with the mothership prior to this thread and I started this thread six months after the failure.

If there's a desire to make statements as to the number of engine failures perhaps a protocol could be established when builders call in. I've spoke to five people at Vans, seven if you include Scott and Vic.

I am not at all clear how if no one at Van's asked you about your engine and that you have spoken (or communicated via text message) with seven people there, that it implies there could be other failures that are not known about.
You mentioned you were calling because of an engine failure, correct?

I also don't understand what is unreasonable about saying there has only been one other failure if that is all of the information that is publicly available.

Nothing in the world is a certainty.
I admit it is possible the other one I mentioned isn't the only one, assuming someone had a failure and told no one at Van's, told no one else that took the time to mention it on line (until now like you have, which would be extremely rare) and didn't make any attempt to file a warranty claim with one of the Rotax Dealers.
I think most people would agree that was rather unlikely, but yes, not impossible.

If the one you mention is real, can you provide some details? A link to a for sale ad of an airplane with a broken engine perhaps?


Your post seems to have a desire of inducing doubt that there are only two (for what reason I am not entirely sure).
Maybe there is one there in CA for sale with a failed engine, but without knowing what the cause was it is not relevant to implying a problem with RV-12's......... an engine failure could be caused by something as simple as an improperly tightened oil hose coming loose in flight causing a loss of oil and failure of the engine. Surely you can agree that though unfortunate, that would be entirely the fault of the builder/maintainer

I think it would be of more value if there was emphasis on discovering what the cause of your engine failure was.
I think there has been requests for more info/photos that might provide some answers, but I haven't seen that info presented yet.
 
From my experience, this is totally incorrect. You can see that detonation from the 2 latest photos I posted, simply snapped the ring lands with no other skirt or heat damage anywhere.

The first set of 4 photos I posted, photo 1, the engine detonated moderately to heavily for about 1 second, 5 or 6 times over a couple days. I got out of the throttle/ boost immediately each time. Then this happened the 7th or so time.

That is very different to detonation sustained for a minute or 2 at maximum power. There is detonation that breaks things within seconds. There is detonation that can continue for a long time without damage. Presumably, somewhere in the middle is detonation that does damage over 1-2 minutes. What does that damage look like?

Detonation results in pressure spikes many times what you would get during normal combustion but it is of extremely short duration so it does not transfer much heat to anything which is why you see pressure damage but no heat damage.

Everything I have seen on detonation says it can shock the boundary layer that protects the piston and head from the heat of combustion, with the result that they overheat. That is not consistent with "no heat damage".

Another thing that destroys the protective boundary layer is hot gas escaping through a small gap. So if you damage the ring seal and the blow by is severe enough i.e. you maintain high power, the combustion gases act like a blow torch on that area of metal.

Detonation also always occurs ATDC where cylinder volume is increasing and crank angle is more optimal where pre-ignition is of long duration (normal combustion started before spark initiation) and always occurs BTDC so pre-ignition adds a ton of heat while effective cylinder volume is decreasing, adding even more heat.

Detonation is short enough that cylinder volume change and crank angle are irrelevant.

Your point about pre-ignition is important though, it occurs before normal ignition so you have a cylinder full of unburnt mixture. The heat and pressure are applied to the whole combustion chamber so you would expect to see generalized heat damage - not just one area. With pre-ignition I would expect to see some evidence of melting on e.g. other areas of the piston. I do not understand how pre-ignition damage would be so localized.

Detonation on the other hand is likely to happen in the areas furthest from the plug and last to burn. The damage could quite reasonably be localized to those areas, and that is what I see here.
 
Your last part is where I agree with you, in post 88 I was thinking the same thing, one plug not firing, end gasses detonating opposite the firing plug. detonation can happen after one plug firing. Think of speed of flame front verses detonation, turtle is the flame front starting the burn at one end and then the rabbit blows the rest up at the other end.
 
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