Getting Back to Eggenfellner history? (is like Lyc history?)
Air cooled engines operate at higher thermal stress levels and heads operate in a permanently annealed condition- hence their issues with cracking heads to this day. Mechanical stresses are similar on both types as has been shown before.
Ross I have to call you on that my friend. With all due respect CHT of 400F or even 500F is no where near annealing aluminum. I agree, with a CHT of 500F, red line, aluminum starts to lose strength. However most RV's keep their CHT below 400F unless under hot heavy duty. Even HOT RV's stay below 425F. I agree if you're running CHT's of 490F, you will not make TBO, no doubt about it. The oil cooks in the valve guides, leaves deposits and you get valve issues. To
get back to Eggenfellner or Subaru's, water cooling is good for the engine, but adds weight, complexity and sadly with a RV tractor configuration, probably a little more cooling drag (but improvements are being made all the time in this area).
PS: The Lyc is not only air cooled it's liquid cooled, i.e., oil cooled. Oil runs around the heads and valve guides, especially the exhaust valve guides, carrying heat away, as it drains back into the crankcase. Your indicated oil temp is actually about 20F to 25F higher in the head, where oil temp is highest.
You might say, "But George the combustion gases are at 4000F?" That is true, but because of the carbon coating on the metal, built up from combustion and intentional air swirling, the metal does not really see the full temp of the gas, which is held away from the metal. The combustion process is also not continuous. It's like running your hand through a candle flame fast, no damage. Even the "burner cans" in a jet engine don't see the full temp of combustion; "air jets" are used to corral or channel the REAL hot gas in the middle of the burner away from the side walls. That is partly why jets get "spooled" up to a min RPM before the fuel is added. If you bring in fuel too soon before you have enough air, the fuel can cause a "HOT START" and actually melt the engine. Of course jets operate at much higher temps and continuously! They use exotic metals to handle this as well.
I do agree that the clones are overall better engines today than Lycoming's original design.
This is myth based on clever marketing propaganda. When Superior and ECI came out with their cylinder assemblies each was WAY better than Lyc, better still than the other. Lycoming is the
onlymanufacture of the roller cam, which is the state-O-art, by the way.
Clone's are made to the exact specs as the Lyc parts! So what is better? Some clones argue they have better manufacturing or finishes. OK I'll bite there are differences there, but better? Different, yes.
Superior claims or implies they have a better steel forging process for their
crankshaft. Well that is not really true, different yes but not better. They use an electric remelt process for environmental manufacturing issues, i.e., less pollution. The way Lyc forges its steel is still as good (really better), but it does pollute a little more, giving off more gases. We know there was a few years where the Lyc process fell apart and bad cranks got out. It was a few years in a +50 year production run. Stuff happens. Not good but what can you say, problem solved.
Reading sales propaganda during the early "
Jug wars", they all said their jugs where better. The last joke, smooth cast v. the rougher sand cast heads. Yes some casting methods are prettier to look at but not better. In fact the pretty heads years later ended up having some services issues. The rough ones, like the OEM Lycoming jugs, where fine as always. Lyc even came up with their own "sales pitch", the rough surface was better for heat transfer and air flow. They my be right? My opinion, it does not matter, go with price AND service. They are all pretty close in price. The legacy Lyc parts are a little more, but thanks to the clones they have to be price competitive. I'm critical of one thing, casting flash left over after manufacturing, blocking critical areas of the head, causing high CHT's. Who made them and sold them this way? I don't recall, but it's unacceptable and can easly be noticed and corrected before the customer gets it.
They all (Lyc, ECI, Superior) make good products. The real issue is price (the clones have a small advantage) and
customer support. Since Superior had their AD issue and they were bought by a German company, I have some small (very small) loss of confidence. To be honest never dealt with Superior. I have worked with both Lyc and ECI folks. They know what they are doing and you can get them on the phone for help and support, especially Lycoming, world wide 24/7.
Other "better stuff" like
composite sumps? Nice but that was a problem; to the companies credit, they handled it as well as you can expect. Another clone says they do some "special porting" or add ridges to their sump that makes it better? OK, prove it.
Getting back to Subaru engines, they have excellent, pretty manufacturing. They can cast a 1000 blocks a day, and they all are in spec and pretty. That does not mean the Lyc is crude or out of tolerance, just low production. In fact some "Lyc" tolerances, fit and flatness requirements are as tight as you can get. Of course piston to cylinder wall, valve to guide clearances are intentionally looser, to account for higher expansions with air-cooling.
Water cooling is technically better (yes Ross I wrote that). In fact most motorcycles, including racing dirt bikes have gone to water cooling, but in airplanes minimizing weight and aerodynamic drag are at a premium. It's that water cooling and the less mechanical "clacking" sound, pistons, valves and gears make in a water cooled engine is what makes people think its of higher quality or smoothness.
Encasing the whole engine in a water jacket no doubts dampens noise and vibrations.
Fewer motor vehicles (bikes, cars, jet ski, snowmobile), are air-cooled today. This is mostly due to pollution standards and noise standards. Water cooling allows a tighter top end, with less blow-by. The water jacket also makes the engine quieter. That is why your cars oil does not get dirty as fast as your Lycoming. Porsche finally went to water cooling for their venerable 911 in the late 90's. BMW and Harley Davidson motorcycles both made famous with their air cooled twins, both have a water cooled line of bikes as well.
Water cooling is COOL!
One problem is working water radiators/heat exchangers into the plane, while not causing extra drag and weight. Air frames have been optimized for air cooled engines. Also planes have plenty of air to cool usually, so any lack of efficiency is not super critical. However applications like jump plane or tow plane, water cooling I think wins in that application. Reliability of water cooling should be excellent with high quality parts and preventive maintence. Air cooling does have the advantage of not needing pumps, radiators and hoses. If they are not there, they can't fail, ever.
"If it ain't broke, don't fix it"
Again, there have been hundreds of thousands of electric props built and they work just fine unless you are doing aerobatics.
Yea I like doing aerobatics.
Like I said a Subaru 3.6 liter is like a Lycoming 6 liter except for cooling, one water the other air. They both are piston engines in the "boxer" configuration. If you strip away the electronic fuel injection and the water jacket, the Subaru is a baby Lyc in many ways. If you took all the water jackets off a Subaru and added big air cooling fins it would sound like a Lycoming.