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Rotax Piston Meltdown

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Gents, the futility of diagnosis by long distance is generally due to lack of complete information.

In this case, at two weeks we continue to have incomplete information. Let's back it down until we see it, or the the thread dies.
 
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'm not talking theory here. I've seen the real world end results of both phenomenons for decades and I invite you to look at piston damage photos from other forums if you want another view from mine. 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. I was driving that engine when the wastegate failed and know the sequence of events that followed.

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. I've measured the static compression pressure below 40 psi on several engines after ring land failure. You cannot maintain high power with broken ring lands as you assert. Light detonation, even sustained, typically does little or no damage for quite sometime, depending on piston strength of course.

In the case at hand, the OP says one ground electrode was melted off. This never happens with detonation in my experience, almost always happens with pre-ignition.

Pre-ignition always shows localized damage as in the photos I published. It has to start somewhere which has an overheated component and since it is a normal combustion event started prematurely, I don't see why you'd expect to see otherwise? Your conclusion doesn't make sense.

Your statement about the duration of a detonation event being irrelevant to heat damage is also illogical. Things like pistons have thermal mass, it takes a finite amount of time to heat them up enough to melt them. A short event cannot do this no matter how intense. Detonation events are typically way less than 1 millisecond in duration. Typical detonation shockwaves travel at around 6800 fps while normal combustion is at around 40-75 fps.

Frame 3 shows a normal combustion pressure trace, frame 23 shows one with detonation. Notice the amplitude and duration differences.



Your conclusions are supported neither by experience in this field nor by the science and photographic evidence available.
 
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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.

Scott,
I?d like to go on record by saying that I personally appreciate and value your participation and contributions to this forum. I?m sure many others feel the same as I do. You insight to the products help us all to understand the complexities of creating some great airplanes.

It?s perfectly reasonable and I?d go as far as to say expected that you defend Vans products and the decisions made while developing those products. Anything less would be unacceptable in my option.

I don?t intend to go head to head with you in this forum as it serves to no ones benefit. I?m simply looking to those who are interested to help solve this failure and hopefully help others to avoid the same fate as my little engine and quite possibly save their investment or perhaps their life.

I expect bias on your part but as I pointed out in the original post I?d like to remain open and objective.

Thank you for the value you bring to all of us who have taken the Vans path with our time and money.
 
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.
 
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I totally agree Sam, I learned a lot from just reading the responses.
Valuable information I feel.

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.
 
Detonation and pre-ignition discussion. Bias?

I don't have an RV-12 and do not fly a Rotax, but am following this thread to learn something about engine detonation and pre-ignition. Responses by those with demonstrable extensive experience with "alternative" engines and a long history of contribution to this list are valuable and contribute to the knowledge base.
The public suggestion that rvbuilder 2002 has shown "bias" in his responses is unjustified by anything that was said and unfair. It is of great benefit to this list to have the attention of a Van's employee of long experience. The general high level of knowledge, assistance, and respectful discussion on VansAirforce is a refreshing change from some of what is out there. No need to undermine it.
Bill
 
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.
 
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.

I think you will find the time scale (x axis) is the same, the amplitude is what matters. The first big spike is the event followed by the pressure waves bouncing around the chamber.

I have a graph somewhere that shows the reflections, being measured by two very high speed probes at opposite sides of the head (two plugs) and you can see it clearly. This was data collected on the Carl Goulet memorial test facility at TAT and GAMI.

I think it is important to note that cylinders exposed to continual detonation testing (like done at GAMI) last a very long time. Hundreds of hours. To destroy a piston alone with detonation takes a very big pressure peak and high temps, and then do it long enough. I seriously doubt the average Rotax owner can do that, running on reasonable fuel and normal flying ops.

A damaged plug and the resulting preignition events can do it in minutes (and not many).
 
Pictures of the plugs, pistion, O-Rings and cylinder.

Pulled the engine out of the box today and took some pics.

Plugs look fine
Number 2 top is pretty fouled but the insulator looks intact.
Number 2 Bottom has ground pushed into the electrode otherwise intact. Most likely due to being struck FOD. Expect this is the cause of the failed ignition check post failure.
Plugs from number 4 look fine.

O-Rings on intake manifold at heads and carb are fine - always were. This is the conclusion Rotax came to once the found out the fuel met spec.

Piston, cylinder and head for your enjoyment.

Thanks to everyone that found this thread interesting and useful. Special thanks to Neil who put me in contact with Bill.
 
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.
 
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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.

Ross, thanks for looking at the photos and providing valuable input. I will post more detailed photos of the piston for you to examine. There were chunks of ring embedded in the piston - I have a picture of that from my initial borescope that I'll post now. There wasn't anything that I knew of that could have fallen into the intake but I'll recheck the butterfly screws. There's nothing else I could think of that could have made it's way into there. The #4 piston also has pitting on the head indicating that material had made it's way into that cylinder. My take on that was the FOD from #2 made it's way into #4 once the failed piston lost compression.
 
I just replaced a broken piston ring on my 360, removed the ring and reassembled in the bore and measured the ring end gap thinking a ring end butt condition may have happened but the specs came out within tolerances, my only guess would be that whoever did the last overhaul broke the top compression ring during assemble and did not know it. Could that have happened here, sure looks like a good portion to the 1st and 2nd compression rings got past the top land and got chewed up, question, how did they make it past the valves, can you pull the valves and look at the seats and valve face for marks, the seats I believe are harder than the rings so I wouldn't think there would be too much damage, maybe bend a valve a tad? I would argue that the erosion on the piston top is a sign of detonation, is there a hole going through the piston at the top ring land on the left in the photo? looks like a cutting touch path. in any case, this is an interesting failure. Root cause anyone?
 
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
 
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?
 
We all like a whodunit with the culprit revealed at the end. Unfortunately things aren't always that neat. I stand by my statement in post 75 that it looks most likely that the cause was simple overheating, due to the lengthy wait on the ground resulting in inadequate cooling margin when full power was applied - with possible contribution from factors like RPM and fuel.

Lets translate the engine data to Lycoming equivalents. Rotax temperature limit =120C, Lycoming 500F, so working with normal temperature ranges means 110C is approximately equivalent to 450F. 116C (maximum reached) would be eqivalent to 480F. 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.

Working off Lycoming and Rotax MP/RPM charts, Rotax 5100 looks approximately equivalent to Lycoming 2350.

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. 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?

Airflow turbulence that changes at certain velocities in the inlet and presents different local conditions at the point of measurement? Could this be a tripping boundary layer?
 
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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?

Impressive analysis of the data.
KCCR - Holding short on 32R for landing traffic on 19R (local carrier - Jet) thus the delay. So yea - we most likely went right through the wash. I never really though about it until you mentioned it.
 
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.

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.

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?

Good thought about what happens with a broken ring, but each engine, reacts differently to its balance of heat flows and cooling design basics. One recent broken ring event in a VAF members engine had extensive second land damage and down to the oil ring. There was no evidence of detonation or preignition on the piston crown, not even at the top land over the failed area. The rapid flow of combustion air that "blasts" the piston and wall, also has rapid heat transfer to cool the flow temps. It would seem that a Lyc with its air cooling would be less tolerant of broken rings and combustion blowby, but it certainly did not end in this type of failure. It was benign, oil consumption increase and some barrel damage. Each engine design is different.

This failure sure seems reluctant to be fitted cleanly in the detonation or preignition category, yet clearly has failed. If I was the warranty guy and could not see any clear reason for the failure thus could not say it was operator induced, warranty would be certainly awarded.

I have seen many boxers eat pieces and the combustion chamber damage is usually more evident, and extensive on the lower side of the chamber than on the upper. For this reason I had mentally put FOD as a low probability as root cause. Low piston-to-head clearance (squish) elevates the likelihood of to land damage.

I'm still puzzled after seeing those plugs. Is there any possibility for cross fire on this engine?
 
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.

For now I'll take instrumentation issues. Look at the oil and head coolant temperature plot. There's an anomaly at the same 640 time hack...a coolant temperature bump and a oil temperature drop at the same time.

Does anyone know the time hack units?

Waterboy, can you post the raw EMS file for download, or upload it to a tool like Savvy?
 
Possibly transmitted on Comm radio at 640?

Depending on radio frequency selection, I get a few data irregularities.
 
How well can we compare information from a air-cooled engine to one that has air-cooled cylinders and a water cooled head, especially considering what sensors we're using and where they are? We're not getting cylinder barrel temps on the Rotax - maybe when catastrophe strikes things go on in the Rotax cylinder that can't be inferred from the head temps. And one keeps in mind the Rotax cylinder is tight - often still getting nearly 80/80 at TBO. Might be a lot of fruit in the apples and oranges mix.
 
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.
 
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.
 
I think the RV-12 cools pretty good with Evans...

77F OAT, 214F Oil Temp, and 193/198 CHT's.

avk8yr.png
 
Someone once said they did that because the Evans does not absorb heat as well as ordinary antifreeze, even though it avoids hot spots better.
I use Evans in one of my RV12s, antifreeze in the other one.

QUOTE=Piper J3;1225986]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.[/QUOTE]
 
Evans works fine for installations where cooling isn't marginal (and this is the situations where there is not much point in using it because it is so much more expensive, and if away from home base there is no easy way to replenish if needed).

Evens has typically only been used in installations where coolant/CHT temps often run right near the limit. Since original version heads only had the CHT sensor inserted into a hollow bore (similar to a Lyc.) and not actually touching the coolant in the head, there was no way to know if the coolant temp. was actually exceeding the coolants boiling point inside of the cyl head (since the sensor wasn't in the coolant, there was no direct correlation between the two temps), so coolant of a higher boiling point (Evans) was used.
This was the primary reason for using Evans. The CHT reading could be in the normal range with the coolant temp already past boiling and not know it.
This is no longer the case with the new design cyl heads, but generally not an issue with the original heads as long as a typical installation isn't regularly running right at the temp limit.

As already mentioned, Evans doesn't have as good of heat transfer as standard coolant so actual temps would always be higher than they would using regular coolant. That means that you only gained a small margin increase because a lot of it got used up by the higher nominal operating temp.

The cyl heads on the engine that failed in this thread had the new style heads with the temp sensors actually protruding into the coolant within the head. On the 912ULS, coolant temp. sensors are only install on cyl 2 & 3 (fwd left and aft right). The failed cyl was # 2 / fwd left.
 
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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.

I flew with EGW and Evans for several years each and did extensive studies with multiple temp probes in various places on the engine. Coolant temps were about 13C higher on average under the same power setting, airspeed and OAT conditions with Evans which likely means metal temps were higher so while it won't boil, it's likely that critical parts such as chamber floors and exhaust seat areas also run hotter.

I removed the Evans about 8 years ago and never looked back. Coolant temps dropped back down to previous levels.

IF you want to use a non-aqueous coolant, just fill with 100% EG which has almost the same properties as Evans and is a lot cheaper and readily available. No engine is designed to run on Evans from the factory as far as I know. If it was really better all around, it would be common factory fill on most engines.

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.

Remember that the piston does not reside in the head, it resides in an aluminum barrel which transfers heat much faster than a steel Lycoming barrel though at the same time the specific hp output is also much higher so the heat flux is also higher.

FOD transfer between cylinders through the intake manifold is common.

The data log anomaly Dan brought out could be noise as Weasel suggested (that was my initial thought when I discussed this with Dan) Steve Smith's observation could also explain this spike. Excellent thoughts guys.

More photos and a deeper look into #2 head may open some new doors.

The factory pistons are cast so they will not transfer heat nearly as fast as a forged piston but they work well enough at these low outputs if everything is working as designed.

I've seen a number of broken rings in liquid cooled engines that had been that way for years, possibly right from the factory and they ran well with few outward signs except for slightly lower compression in that hole. One in particular was being totally flogged on a daily basis for something over 1000 hours. When taken apart for a rebuild, one top ring was found broken and well rounded, still in the somewhat worn groove. No other signs of distress.

We don't know how robust the Rotax piston is with a broken ring though and like I said before, I've never seen such huge pieces missing even on much more severely damaged pistons where a whole 1/4 of the piston is a melted blob in the bottom of the oil pan. Very high hot gas leakage could damage the aluminum piston but I've never seen it melt rings.

Maybe this isn't my place to say this but this is such a strange failure and doesn't help inspire confidence in the engine, if I were Rotax, I'd step up and cough up a new engine with my apologies and want the broken one back for detailed studies so I could learn something about the possible cause. This failure does not seem like it was caused by pilot abuse or oversight in any way from what we know so far. 47 hours is not acceptable life. The bigger problem is nobody in the Rotax world contacted seems to even care. That doesn't speak well for those contacted in my book. Yes, this an isolated failure but still a failure. Always good to learn why so maybe it can be prevented from happening again in the future IMO. That's how you can improve your products and reputation.
 
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Evans isn't authorised for the new Rotax heads as spelled out in the Installation manual in section 75-00-00 page 9. Evans carries a 20F- 30F heat penalty due to the fact it is waterless. Water has far better heat absorption and dissipation rate vs the waterless pure propylene glycol. This is one reason fire departments like water plus it's cheap and plentiful during a fire. Rotax still allows Evans in the older style head engines, but recommends watered coolant. Evans works much better in an open air engine because it can dissipate heat better and not so great in a tight cowled engine. Living in a cold environment helps the retained heat with Evans, but living in a warm climate works against you. 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.

75-00-00 page 9
"NOTICE WARNING
Are not authorized for ROTAX 912 Series with cylinder
head - new configuration
"

Using Evans in the new heads would most likely void your warranty or help after the warranty if Rotax finds out.
 
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'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.

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.
 
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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.

I'd be very interested to see photos of detonation damage to Rotax pistons. Email them to me if you can. They might help us understand more about the ways the piston fails.
 
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.

Great comments folks.

The intake O rings and water jacket O Rings were in place and there were no signs of being pinched or damaged. The carb manifold / drip pan assemble was as described by the Vans KAI. As Scott pointed out it would be nearly impossible to get the O Ring on the wrong side of the drip tray (someone did manage to as Scott pointed out). I checked the other day to see how hard it would be to get it wrong when I took the latest pictures. The rubber carb flange groves are much smaller than the O Ring in the manifold and the carb flange appears to have a molded O Ring in it. This part would be discarded at rubber change out I believe. I wanted t have a good look at this since in the illustrated parts book it actually shows the intake O Ring against the carb flange when using Rotax drip pans. It's the same part number in the drawing for either setup so I assume it's a mistake. The way Vans set this interface up is correct IMO and as Scott has said hundreds of these are flying this way.

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The compression on this engine was always 80/80 on all cylinders as was last checked at 25 hours TTSN.

I believe I mentioned this before but I'm using Prestone Dex Cool 50/50 which I picked somewhat randomly from the approved list. I believe it says it's good to 129C.

I had a great conversation with Bill Sherlock who I was introduced to by a fellow VAF member a couple days ago. He's a seasoned Rotax Mechanic who works locally in my area. One of the things he's mentioned is that the support for Rotax in the US is very different than overseas (he sounded British). My partner Andre, also a long time Rotax mechanic spent much of his time working on these engines in the United Emirates (very hot and no AvGas) and he's said all along that he is baffled by the lack of interest in this failure. He spoke highly of the Rotax factory folks and said they told him the customer always comes first. He's called the factory for me and they confirmed this would be a warranty issue but it would need to go through the right channels. I haven't exhausted all my options WRT getting around the US distributors yet.

I too would think they would be interested in the failure. I don't know if they know about it or how I would go about confirming that. Andre feels I should reach out to Eric Tucker - the guy in the Bahamas we register our engines with. That's my next step with the factory.
 
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How well can we compare information from a air-cooled engine to one that has air-cooled cylinders and a water cooled head

My point was that we would be concerned if a Lycoming hit 450F on the ground and 480F after takeoff, why are we not concerned about a Rotax similarly close to it's limits?

Is it just smaller numbers due to temps in C and liquid cooling just aren't as scary?
 
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.

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?

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.

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.

rv6ejguy; said:
the piston then loses gas seal, hot gas flow past the piston then quickly melts the aluminum.

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.
 
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 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.

This is why I mentioned another race failure where the driver noted the miss but continued to try to "drive through the miss" hoping it would clear out. What he did was completely destruct all 4 pistons with severe pre-ignition as well as melt the aluminum around the exhaust seats. This was the most destroyed engine I've ever seen that still had the rods attached to the crank.

Yes, you could be right, with a cast piston if you break the ring lands and leave it at high or full power for a few minutes, you might cause further piston damage. From photo 12, we can't see a broken ring land which is ALWAYS step 1 in a detonation failure on a cast piston. The land usually snaps right off from the piston body. If this had happened, there would be no more heat sink ability of that land to transfer heat to the piston and the lands would have quickly, completely melted away.

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 difference between real world experience in a field and reading some articles thinking you understand all facets of this topic should be obvious.

Part of my job for 25 years has been problem and failure investigation, often with multiple experts who can't agree on a cause or are all pointing the finger at each other. I have to research the problem and work with the experts to find a cause and solution.

In this thread we have:
  • 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.

So I am not an engine expert, but in other ways I am right at home. I know despite their expertise, experts are rarely right 100% of the time. A large part of the puzzle is researching opinions and evaluation how consistent they are with other information that is available.
 
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.

If you're at 200' after takeoff your reaction might be different.

We have the EFIS data. We can see that the manifold pressure is 30" from about point 800 through 910 (I think these are seconds).

RPM drops from a peak almost immediately, but severely drops at around point 850, varying around 4100-4500. At this point altitude was somewhere around 200-400 feet. Manifold pressure remained at 30" for perhaps another minute.

My opinion, if you lose 10% rpm at 300' you don't reduce power, you take whatever the engine is still giving you to get safely on the ground. If you reduce power, you might find you lose the rest.
 
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.

Andrew,

Detonation is not a definitive thing, I have participated in to a small extent the unleaded avgas certification of G100UL. I have plenty of material which I cannot release publicly but there are some things that George has publicly presented at OSH etc. 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.

Not every cycle will detonate, given there is 20 (or 40+) events per second, and then detonation intensity varies from each event. Now if you really go out of your way, use a very low octane for the CR of the engine, maybe advance the sparks a bit, heat up the oil to 240+, get the IAT up around 120, and cut off the cooling flow to the heads/cylinders and do that with an engine that has a propensity for it, then you might get destructive detonation. The thing is often the plug ceramic fails before anything else as it is fragile, and then mixed in with the badness already in place you add the occasional (not every cycle) a reignited one or two, and bingo, now we have broken ring lands or holes in pistons, whichever fails first.

Here is a cylinder, (I don't have the piston pic) that was sent to a big name shop in Tulsa, for comment. They thought it was quite new and in good shape. It had the following history;
1700 hours in a TNIO520 or 550(can't remember)
20 hours of light detonation testing
3 hours of medium detonation testing
30 minutes of heavy detonation testing.

All done with abusive parameters.

25395721_10213419033763904_3210686292787057040_n.jpg


Now to add another variable to this mix, think about the kind of detonation events, as they are all different. George describes it as like being in a hail storm. Lets assume you are going to get 'X' tons per acre of hail, and you have to leave your car outside in the storm. Do you want the hail to be pea sized or apple sized? It is the mixture of the events and the peak severity of them that matters. None are the same as the next, and of course not every cylinder comes to the same party. And some are born stronger than others.

Hope that helps.
 
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.

Absolutely. Which is why statements like detonation always breaks the second ring land, and does not cause heat damage seem a bit too absolute to me. Or that engines can run for hours with detonation without damage.

From the Allen W Cline article:
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

This makes me a little wary about extrapolating testing done on Lycoming to Rotax.

Another tidbit from someone I know who consults on engine management systems to the major auto makers: He said that this is all understood well enough that they don't use test cells so much anymore, a huge amount of it can be done with computer modelling. The manufacturers know what they are doing. I would treat information from them e.g. the Rotax service letter as reliable.
 
The manufacturers know what they are doing. I would treat information from them e.g. the Rotax service letter as reliable.

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.........
 
In my day job I have also seen instances where support staff in the field have given bad advice. When you ask the engineering staff they say "WTF, NO, they shouldn't be telling you that." Have Rotax North America seen the data the SL is based on?

Lets say Rotax had statistics that showed if you operate WOT below 5200 you have 1 failure in 100,000 hours (plucking a figure out of the air). That would be 1 in 50 engines before TBO, certainly high enough for Rotax to take notice and issue a bulletin.

But how many hours does the RV12 fleet do per year? How long on average before you see a 1 in 100,000 hour failure? If you did 1000 hours there would be a 1% chance you would see a failure. So talk of 1000 or 2000 hours without a failure is also meaningless - it's not enough hours to get a result.

No doubt there is margin in the 5200 figure and most of the time you can get away with lower RPM. But 5200 is the figure Rotax are happy with.

Wasn't it Vans who was talking about who the margin belongs to?

If/when I build a RV-9 I won't install a bigger engine than Vans specifies. I will also use Vans recommended gross weight, even though there is a long history of people ignoring both these recommendations without incident. Likewise, when Rotax recommends 5200 minimum for WOT operations, I take notice. They are both the same things - operating in the margins the engineers wanted to reserve for themselves.

I know that the engineers don't issue these sort of instructions for no reason. You can be sure that they have information that formed the basis for the recommendation.
 
Some engine owners may have a combo of these. A single one of these doesn't mean it is an absolute detonation issue.
Add a few together and you may be in trouble. In an aircraft engine you usually can't feel or hear detonation taking place and instrument indication may be a late indication that damage has already occurred. This is why we only see the aftermath.

Detonation causes:p
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.
As Scott mentioned 5100 rpm at take off is not a detonation problem.
 
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:p
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.

In this case:

High CHT
Yes. coolant temperature was 110-116C, CHT was not measured but whatever you get when you go to takeoff power when coolant temperature reached 110C at idle.

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)

Yes. OAT was 107F so the air was at least that hot. Under cowl air may have been hotter.

Wrong heat range spark plugs
Unlikely

Poor fuel quality. (either form long storage, exposure to costant heat or wrong octane rating)
Fuel was tested at 91, so it met the minimum but only the minimum. I have heard many fuels test higher than spec but that's only a rumor.

Lean air / fuel mixture (usually cause be an air leak at an "O" ring or carb flange)
Possibly. Fuel was 10% ethanol, which runs a few percent leaner than regular fuel in a carb engine.

High engine load (i.e. over pitching a prop)
Prop was over pitched according to the Rotax SL. MP was 1-1.5 inches over the chart limit for 5100 rpm.

I'm not saying any one of these factors was THE cause. But many of them came together on the day.

Add some of these together and you have the perfect storm.
 
Engine

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
 
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

LOL. This is a rhetorical question, I'm sure?
 
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.
 
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.

That statement is direct from the tech. guys at Kodiak. You know who they are. They handle tech support for all sales in North (USA and Canada) and I think South America
It was reiterated during communications I had with them on your behalf regarding the engine failure.
Specifically, that they were entirely confident that the prop pitch being used on the flight when the failure occurred had nothing to do with the failure.
Speaking publicly about any of the conversations beyond that would be inappropriate.

The Rotax 912 will never develop rated power (100 HP) with a fixed pitch prop unless you were to set the prop pitch to a value that would make the airplane only cruise about the same speed as it climbs, because to produce rated HP you need 5800 RPM and a low altitude MP. So it could be said that the engine is being lugged to some degree at anything less than 5800 RPM (unavoidable with a fixed pitch propeller).
 
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.
 
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.

The Rotax is rated at 100 HP at 5800 RPM, for take-off, for 5 minutes .
The continuous limit is 5500 RPM.
So Yes, I was meaning take-off since that is technically the only time use of full rated power is allowed (with a time limit).

The use of fixed pitch props on airplanes with a wide speed range between climb and cruise like RV's (even the RV-12), means we will never come anywhere close to max. rated power for take-off.
 
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