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?
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 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.
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.
I don't have a dog in this hunt....but I've detected "bias" on more than one side of this discussion (and a previous fuel thread).
I'm enjoying the exchange of info, my personal understanding (bias...?) has been expanded as a result of it. Looking forward to a resolution of the engine failure.
On post 102 can you explain the photos, trying to learn something here, if photo 3 is normal combustion at 40 FPS and photo 23 is detonation at 6,800 FPS, are we to compare the ripple length or amplitude, if length, are they on the same time scale, because the first ripple is not 1,700 times as long, more like 5? Not at all questioning your experience, just trying to comprehend the above photos. Thanks.
Thanks for posting the detailed photos of the plugs and piston. Plugs look totally fine and heat range is 8 which is stock for this engine. Insulator color looks good too so I don't see evidence of an overly lean condition.
I would say from these better photos and the fact that the ground electrodes are intact and the insulators don't show any cracking, heat distress or aluminum micro spheres on them, this was probably not a pre-ignition event and certainly not a detonation event.
Photo 12 of the piston shows an overheated crown failure very much like the 3rd photo I put up in Post #58 which is of a Subaru EZ36 piston and a typical failure mode on these engines. On the 912, this is hard to explain since they are very well proven at high continuous power levels. I have a customer who's been doing flight training on these engines for over 15 years and has over 4000 hours on them with no issues. His last engine had EFI on it and went right to TBO with no work inside.
One unusual thing I see is that a large portion of the #1 and a smaller portion of the #2 rings seems to be missing. As you can see in photos 3 and 4 in post #58, the rings are intact, even though in photo 4, they are completely unsupported. I've never seen rings melt or break in this sort of failure or even from pre-ignition as the melting points of the rings are around double that of the aluminum. Did you find any large ring bits in the debris? It looks from some of the impressions in the piston crowns that hard, sharp edged objects made some of these marks.
Does anyone know the ring material used on these engines? Are the pistons cast or forged?
Is it possible to get a clear photo of the edge section of what is remaining on the 2 top rings?
Any screws or other bits missing from the carbs?
This is a very unusual failure mode but there has to be a reason for it.
No noticeable plug damage, or heat damage to the squish area at 12 o'clock in the area mirroring the piston damage. Hot plug induced preignition unlikely. Detonation still possible, but I remain mystified by the lack of blasting and splatter evidence.
There is an anomaly in the EMS dowloads. Put MP and RPM up on the same screen and align 'em. Compare the plots. They match very well (as they should; fixed pitch)...except at 640 on the time hack, where MP drops about 5" with an RPM rise. I'll need to think about it.
http://912ulsenginefailure.blogspot.com/2017/12/efis-charts.html
Other than instrumentation issues, the only way to explain that is that something changed in the environment of the propeller to change its ability to absorb power. The airplane is on the ground at this point, right? A very strong headwind gust or turning from downwind to upwind?
A sudden drop in air density would cause the MP to drop too, as well as cause the RPM to increase. But how do you get a region of much lower air density? taxi through a hot jet wake?
Other than instrumentation issues, the only way to explain that is that something changed in the environment of the propeller to change its ability to absorb power. The airplane is on the ground at this point, right? A very strong headwind gust or turning from downwind to upwind?
A sudden drop in air density would cause the MP to drop too, as well as cause the RPM to increase. But how do you get a region of much lower air density? taxi through a hot jet wake?
However the Rotax limit is a harder limit - if you exceed the coolant boiling point it's all over, whereas probably nothing immediately happens if you exceed 500F on a Lycoming.
Lets imagine a Lycoming broke it's rings and burned out the side of a piston. The data shows OAT was 107F, a long wait on the ground meant CHT reached 450F prior to takeoff, climb was at 30" manifold pressure and 2350RPM with CHT reaching 480F - what cause of failure would you suspect?
Other than instrumentation issues, the only way to explain that is that something changed in the environment of the propeller to change its ability to absorb power.
Where temperatures are measured and where they occur in a liquid cooled engine are very important to what happens. If this temperatures occur at the high heat transfer surfaces, incipient boiling, then nothing much typically happens. The vapor is swept away with coolant flow and re condenses in the cooler bulk flow. It happens all the time and many engines with no detrimental effects. It is better from a design standpoint that the heat transfer and coolant flow keep it from happening, but there is no catastrophic issue. It may result in fatigue and cracks in the long run. Heat transfer increases dramatically with incipient boiling that keeps the temperature of the parent material (head, port) from further rapid rise. Many SAE papers have been written on this effect. Too long ago to provide quotes.
For the cooling system to suddenly cease to function entirely, the coolant pump would have to cavitate and reduce head dramatically. The temp at suction is typically the lowest in the system for this reason. Cavitation can be related to some more easily measured temperature like top tank temps or the radiator/heat-x exit temps. The pump also needs some mechanical head which is hard to do in an aircraft installation. So, if (IF) cavitation had happened then there would have been a rapid rise of temps within the engine that would have caused substantial boiling, temp rise, pressure rise, and exceeded the pressure cap limits very quickly. A cooling system does not recover from this easily. Actual systems testing is needed to quantify cavitation in a system due to several effects that are difficult to quantify in modeling. Then a limit temperature can be provided for a specific coolant, be it water, or EGW mix.
Been lurking here but this prompts the question... why did Rotax change from Evans Waterless Coolant if localized boiling can be problematic? Seems it would be better to error on safe side and have coolant that can tolerate more heat. I'm still using original Evans coolant in my RV-12 since 2013 with good success.
Can't speak to the RV-12, but I have some experience with the Evans NPG+ in our tightly cowled Rotax 912F (81 hp) DA20 Katana. When the AD was issued (2005 I recall) we had to switch from 50/50 glycol/water mix to Evans or lower the CHT limits. Running near redline on CHT and oil temps during the summer was pretty routine for us. The Evans made the situation worse.
Water has a specific heat of 1.00, 50/50 ethylene glycol/water is around 0.82 and the Evans NPG+ is approximately 0.65. So while the Evans has a much higher boiling point and will reduce the localized boiling around the combustion chamber of the liquid cooled head, it was a poor heat transfer fluid and we were very limited on operations in the Georgia summer using the Evans.
I offered our aircraft to Diamond for testing and as a result, they were able to develop an AMOC which really consisted of an idiot light tied to a thermostatic switch in the coolant lines. We were able to return to the original temperature limits using 50/50. We did some other modifications as well to assist in cooling, but I was very glad to be rid of the Evans.
The Evans might work well in cooling systems designed around it, but I found it to be a poor choice for the already optimized (read: barely adequate) cooling system on our DA20.
Again, not sure if the RV-12 system would be similar.
The 912 has a well proven liquid cooling design so I don't suspect any issues with that in this case unless there was an unusual problem with water flow from a pump or blockage issue. Maybe worth inspecting #2 head internally for casting flash or FOD in the water jacket area.
I'm not meaning to imply that it was an influence in this case, but I have worked on one 912ULS that had a blockage because of assembly error (it would be easy to confirm or rule out by physical inspection for this engine failure).
When the cooling shroud was being used on the RV-12, it required the builder to remove the expansion tank and cooling hose network from the top of the engine to get the shroud in place. The shroud was held/sealed in place with the use of high temp RTV.
In this particular case, the coolant hose network was reinstalled immediately while the RTV was still wet. Apparently the tip of one of the hose nipples was inadvertently pushed into the wet RTV while setting the assembly in place and it wasn't noticed.
At a later date when the hose manifold was removed from the top of the engine for other maint. (I don't remember the specifics of why but the engine had run for many hours without having any type of failure), the hose fitting was found to be 50% blocked with RTV. There was nothing notable with the instrumentation readings because it was on cyl #1 which has no temp sensor installed.
I have gathered at least a dozen pictures from detonated Rotax engines from classes I have taken. I would post them, but not sure how to post a picture here. The three top common causes are air leak, someone leaning or playing with carb jetting and bad or low octane fuel. Having a seriously over pitched prop could add to your trouble if the right conditions existed. Detonation can happen fast enough that you won't know it until it's too late which is why you see the aftermath with the detonated damage.
Yes, all good points and I think that should be investigated in this case because it's so odd. I've found things like this before too- like paper towel, rags stuck inside water/ oil passages somewhere, core or oil plugs missing etc.
How well can we compare information from a air-cooled engine to one that has air-cooled cylinders and a water cooled head
I think you'll find the detonation failures will all look pretty much like the photos I've already posted with simple fracture of the 2nd and 3rd ring lands. You won't find heat damage to the crown unless pre-ignition follows the detonation like in the second photo I published.
Heavy detonation usually ends with the failure of the ring lands because of the massive compression loss which lowers the cylinder pressure below the point where detonation can occur.
rv6ejguy; said:the piston then loses gas seal, hot gas flow past the piston then quickly melts the aluminum.
This looks like textbook detonation damage. I haven't found any other references saying you won't find heat damage from a detonation event - everything seems to say the opposite.
You said your photos were of events that lasted only seconds. What would they look like if the engine continued to run WOT for another minute or 2?
Sure, the detonation ends but what does the loss of compression mean? It means that gas is escaping past the rings. At WOT, a lot of gas.
After the ring land breaks, you have a loss of compression and lot of blowby. That chunk of ring land suddenly has a lot more surface area, hot gases blowing past, some nice sharp corners to absorb heat and no path to sink heat back into the rest of the piston. So it will melt. The rings are unsupported at that point so being brittle, they are likely to break. The next part of the piston to melt due to the blowby is probably the crown/top ring land because it also has a lot of surface area, only a small cross section to sink heat into the rest of the piston, and it's in the hottest area anyway.
My opinion: that's what your detonation photos would show if you maintained full power for long enough after the ring land broke. The end result would look a lot like this failure.
The difference between real world experience in a field and reading some articles thinking you understand all facets of this topic should be obvious.
The thing you're missing is that when the ring lands break the engine will effectively go down to about half power on that cylinder and it's immediately obvious due to engine roughness. Break lands on 2 or more cylinders and it turns into a severely vibrating beast. The instinctive reaction in a plane or car is to reduce power immediately, not to leave it WOT.
Rotax via a SL saying that operation in this regime can cause detonation and engine damage
Vans saying they have demonstrated that it does not cause engine damage
APS saying this is obviously not detonation because engines can operate for hour with detonation without damage
Yourself saying it is not detonation because detonation can break the ring lands within seconds, but does not cause heat damage.
Detonation is not a definitive thing... The take away from this is detonation is a bit like saying weather. The weather could be cool, mild warm, warmer, hot, quite hot, really hot unbearably hot......you get the idea.
The manufacturers know what they are doing. I would treat information from them e.g. the Rotax service letter as reliable.
A single one of these doesn't mean it is an absolute detonation issue.
Add a few together and you may be in trouble.
Detonation causes
High CHT
High air intake temps ( like aircraft with filters on the intakes under the cowl. It's always better for the engine and combustion to have cool outside air)
Wrong heat range spark plugs
Poor fuel quality. (either form long storage, exposure to costant heat or wrong octane rating)
Lean air / fuel mixture (usually cause be an air leak at an "O" ring or carb flange)
High engine load (i.e. over pitching a prop)
Add some of these together and you have the perfect storm.
Add some of these together and you have the perfect storm.
The real question is were is the factory support this man has bought 2 engines a no one has lent a hand to help him from the factory or who ever he bought the engines from.The company he purchased the engines from should stand behind him and demand the factory help him.Im reading this thread and I'm in disbelief a major engine manufacturer has not stepped up to the plate. It very well could be the piston was defective and waiting to fail.I bought a new Ford van and was going 35mph down the road and a rod broke into it looked like it had been machined into and polished and Ford repaired it were is Rotax and its reps?
Bob
Like you already said, there are no absolutes, and all of the experts aren't always right 100% of the time.
In recent communications with a spokes person for Rotax North America......
"I am not concerned about 5100 RPM at take-off power, and it is quite common with many of the LSA manufacturers."
Does that entirely match up with the SB? No. But it is from someone that has worked as a representative of Rotax for many years.........
I've spoken to quite a few Rotax folks since this failure. I've never heard anyone make that statement about 5100 WOT. In fact, it's quite the opposite.
There's no arguing that at 5100 RPM the engine is being lugged and is not developing it's rated power.
Scott,
I assume that last statement was referring to 'in a climb', or 'on takeoff', or something like that? The only properly pitched prop/engine I know know about that won't reach rated rpm is the metal Sensenich for a Lyc 320, and that's a placard limit.