Are Liquid Cooled Aircraft Engines Possible?

[Yukon]

Great post, Ross. You are now in George's league for detailed posts.

Did you by chance gather any info on gearbox reliability? The radials all have planetary gearboxes, and I know they are very sensitive to being backdriven by the prop. The R-2800 was definitely the "sweet spot" in radial developement.

It's the Merlin and Allison spur gear reliability that interests me. Any info?

[rv6ejguy]

The Merlin appeared to have very good reliability from its reduction gear. The early Allison used epicyclic gearing which proved unreliable as power crept up over 1200hp. A later gear design solved this and I could find few reports of gearbox failures.

In operational use, the Allison suffered from inadequate intercooling initially using surface conduction types in the P38. This contributed to detonation at high altitude and piston failures. Also contributing was the lower octane fuel available initially in the ETO. Many changes in the intercooler and radiator setups were made to the P38 airframe during the war years. They finally got it right with the J model in 1944 and reliability on all fronts as well as sustained power above 25,000 feet was excellent.

I've read a lot of books on WW2 and engines in particular and other than the early weakness in the Allison gearbox there are almost no references to gearbox troubles. Almost all liquid cooled engines used straight cut spur gearing. This includes the DB601-603 engines and the RR Merlin- about 160,000 of each of these were produced. V12s are more friendly when it comes to torsional vibration due to the close power pulses.

Most aero engines went through considerable development during the war. The liquid cooled ones about doubled in hp in 5 years while sustaining initial levels of reliability. Much of this was due to supercharger development, higher octane fuels, intercooling improvements, and technologies such as water/methanol and nitrous oxide injection. Cubic displacement remained unchanged during this period on the 3 most popular V12s.

Here is a concise link on the DB600 engines used by many German aircraft during WW2. It had direct injection (now back in use today) and a clever, variable drive single stage supercharger. http://www.aviation-history.com/engines/db605.htm

[szicree]

Something I've been wondering about lately is whether it might be possible with the right materials (perhaps not yet invented) to make a piston engine that requires no cooling. I have no engineering knowledge whatsoever (obviously) but figure that perhaps the internals could be made of something that doesn't so readily soak up heat. Maybe?

[n5lp]

Originally Posted by szicree

Something I've been wondering about lately is whether it might be possible with the right materials (perhaps not yet invented) to make a piston engine that requires no cooling...

Others have wondered about that. One of the better known names is the late Smokey Yunick http://en.wikipedia.org/wiki/Smokey_Yunick
who was reputed to be working on engines with ceramic parts that would not need additional cooling.

[rv6ejguy]

Originally Posted by john kelley

After an RV, that I may actually be able to afford. I always liked the thunder mustang for that ultimate toy fighter, since I know I can't afford the real deal. I think scaling the wing sub 3/4 scale for max speed was a mistake and even should have been 80% scale. I see there are several kits for sale firewall back. Is there a problem with the Falconer liquid cooled V12? Several builders have been switching to a walter turbine instead of the Falconer. I know several of the racers were working on supercharging the engine with limited success. A few years back there was a company trying to sell a liquid cooled V8 conversion as a cheaper replacement for turbine engines. I think it was called Ondaira. Then there is the current crop of diesel engines that are mostly water cooled.

The Thunder Mustang is a very cool plane. It is blasphemy to put a turbine is this airframe. Surely the sound of the V12 is as important as the airplane! The supercharged Falconer V12 has been shown to be very powerful and the basic engine reliable. A small problem with the belt slipping cost it the win in Sport Class at Reno in 2006 after setting the qualifying record and fastest lap that year.

Orenda developed the very expensive V8 and that project was sold to a company in Texas who says it will rise from the ashes again. http://www.traceengines.com/

BTW Titan aircraft announced that they are planning to offer a full size P51 replica kit to be powered by a Chevrolet LS7 conversion.

Just hope they get someone like EPI or the fellow who designed the drive for the Falconer V12 ( he worked on the RR Merlin gearbox!) to do their drive.

[David-aviator]

Originally Posted by szicree

Something I've been wondering about lately is whether it might be possible with the right materials (perhaps not yet invented) to make a piston engine that requires no cooling. I have no engineering knowledge whatsoever (obviously) but figure that perhaps the internals could be made of something that doesn't so readily soak up heat. Maybe?

Or can absorb heat without melting down. This is what makes modern turbine engines so reliable and efficient.

Such metal technology may have been looked at with internal combustion engines and probably does make sense in terms of efficiency. At the cost it would make more sense to go straight turbine, why have all those moving parts?

[airguy]

Originally Posted by rv6ejguy

Orenda developed the very expensive V8 and that project was sold to a company in Texas who says it will rise from the ashes again. http://www.traceengines.com/

And they appear to be headed in the right direction. They are located just a couple miles from my house, and I've seen several advertisements for open positions in the local paper, and there are many vehicles parked at their building everyday. It certainly does not appear as if they are steady-state or even declining.

[cjensen]

I don't have anything to add to this discussion at this point, but I do want to commend everyone for the civility of this thread thru three pages. Great job, and a very interesting topic! Keep it up, and these threads can be very informative, and FUN to follow!

[rv6ejguy]

That's good news on the Orenda V8 Greg. The price is the killer I think though and the PT6 replacement idea might make sense- or not. I'd love to hear this engine flying in something. I recommend they install in a Sport Class entry at Reno and show it's stuff. That might attract some interest.

Chad, quit fooling around. Are you installing an air or liquid cooled engine in your RV? Nice flap system there BTW.

[SvingenB]

Originally Posted by szicree

Something I've been wondering about lately is whether it might be possible with the right materials (perhaps not yet invented) to make a piston engine that requires no cooling. I have no engineering knowledge whatsoever (obviously) but figure that perhaps the internals could be made of something that doesn't so readily soak up heat. Maybe?

In a diesel that could be almost possible by increasing the compression to insane numbers. In fact, high efficiency in modern diesel engines in cars cause some peculiar problems already today. The heat in the cabin is made by the a radiator using warm cooling water from the engine. A modern diesel has so high efficiency that there is not enough waste heat from the engine to even warm up the cabin in the winter. VW have for several years now used additional electric heating for their larger saloons and vans/buses, and I guess others are doing this also now. This means larger battery, larger alternator, added complexity of electric heating elements, so high efficiency is not always only a good thing. The cooling needed for a modern diesel is very little on other words. A lot of heat goes out with the exhaust also.

In an otto engine with a restricted compression ratio the thermodynamic efficiency will never be better than 40-50% or something (don't remember the exact numbers), so about 50% will be lost in heat energy no matter what you do.


Have to correct some numbers I presented. Did a search on the internet, and there are "only" produced 15,000 units of Rotax 912, but most of them during the last 10 years. Of other noteworthy liquid cooled engines:
DB 601: 20,000 units
DB 605: 42,000 units
Junker-Jumo 211: 70,000 units
Allison V-1710: more than 70,000 units
RR Merlin: 100-200k ? Packard alone built more than 60,000 units.