Are Liquid Cooled Aircraft Engines Possible?

[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.

[Yukon]

Jenny was a military trainer. There were a number of water-cooled military aircraft, but none in commercial service.

I think it is very telling that after WW2, no commercial aircraft manufacturer elected to power their aircraft with liquid-cooled engines. If this technology was superior, you would think that Boeing and Douglas would rush to it's use.

[Mike S]

Originally Posted by Yukon

Jenny was a military trainer. There were a number of water-cooled military aircraft, but none in commercial service.

You dont think hundereds of barnstormers flying arround the country selling rides for $5 wasnt commercial???

Also, the Jenny was used for mail delivery.

Originally Posted by Yukon

I think it is very telling that after WW2, no commercial aircraft manufacturer elected to power their aircraft with liquid-cooled engines. If this technology was superior, you would think that Boeing and Douglas would rush to it's use.

Never said it was superior, just that there were L/C powered planes used.

As a matter of fact, I tend to agree, that with the current state of things, the air cooled engine is superior for most of the currently available airframes, and flight missions.

From a technology only standpoint, I believe that the L/C engine is vastly superior to the air cooled. More heat rejection allows more HP/CuIn, less wear, closer tolerances, and a host of other benefits.

That said, IMHO, what is standing in the way of a commercially viable L/C engine for certified aviation use, is development cost, and monatery return on investment.

Luckily, we have the homebuilt world to play in.

[SvingenB]

The Rotax 912 is produced in higher numbers than any other aircraft engine, and it IS watercooled. When looking at the facts, the numbers, watercooled engines clearly are the winners.

When looking at 4 stroke aircraft piston engines produced in the last 20 years, I would guess 80-90% are 912, and every single one of them are water cooled.

I think what is happening is that it takes so much recources to develop an aircraft engine, and the market (GA) is so limited, that the company that is lucky and comes out with something that works well enough to be accepted, will be able to (or be forced to) stick to that design for decades.

[Ted Johns]

I'll bet, right this very minute, that someone is flying behind a Thielert diesel. When the poor SOB lands, he's going to have to pay the FBO and / or the CFI. Seems like a commercial enterprise to me.

[David-aviator]

Originally Posted by Yukon

You say, what about the P-51! Since they got shot down or crashed on a very regular basis, I'll bet nobody has any real idea of long-term reliability issues with these engines. They were also flown by young, intensively trained men wearing parachutes. When they failed, you would step over the side, and a new one was waiting for you when you got back to base. Merlins and Allisons also had 12 cylinders, so power pulses came much more often,
making power-train vibrations less of an issue. To my knowledge, no liquid cooled aircraft engine has ever been in US commercial service.

My good friend Tom Watkins, who at age 21 flew 51's with the 52nd Fighter Group out of Italy, told me his airplane had 400 hours of combat time when maintenance insisted on a mandatory engine change. He protested, even had his CO fly the machine to confirm its smooth operation but to no avail of course - rules is rules.

The point being, your question has no merit. Like it or not, there have been successful liquid cooled aircraft engines. After all, it was an all liquid cooled operation that got Adm. Yamamoto, the Japanese officer responsible for the Pearle Harbor attack. Without those liquid cooled P-38's the war might have gone on for years.

[Yukon]

Originally Posted by David-aviator

My good friend Tom Watkins, who at age 21 flew 51's with the 52nd Fighter Group out of Italy, told me his airplane had 400 hours of combat time when maintenance insisted on a mandatory engine change. He protested, even had his CO fly the machine to confirm its smooth operation but to no avail of course - rules is rules.

The point being, your question has no merit. Like it or not, there have been successful liquid cooled aircraft engines. After all, it was an all liquid cooled operation that got Adm. Yamamoto, the Japanese officer responsible for the Pearle Harbor attack. Without those liquid cooled P-38's the war might have gone on for years.

There's a good data point, Dave. 400 hr mandatory removal time. Anyone else out there got any Merlin reliability info? They could easily have been suffering from the same torsional vibration issues we see today.

The P-38 was a heck of an airplane, and from what I read the Allisions were more reliable than the Merlins.

[John Clark]

Originally Posted by kcameron

Liquid cooled aircraft engines are impossible. None have ever been built; let alone flown.

OK, there has never been a truly liquid cooled aircraft engine. Stay with me here... Because the liquid is only a means to transfer the heat to the air. So, a "liquid cooled" aircraft engine is, in fact, air cooled. Same thing applies to the "oil cooled" argument. The only truly liquid cooled internal combustion engine that I can think of is in a boat. Take the water from the ocean or lake, transfer the heat, and return it to the source a little warmer. The plumbing would be a problem in an airplane.

John Clark
RV8 N18U "Sunshine"
KSBA

[Bevan]

If I recall, during the 1930's and 1940's when aircraft development was racing ahead and the various branches of the armed force was driving much of it, the Navy was favoring aircooled engines (or the companies that designed them), and the airforce favored aircooled. I always wondered why. It may have been that Navy and Air Force planes were designed by different companies and therefore used different technologies for competetive or business reasons. Or maybe it's just that the engineers there had different opinions as to which was best. If so, this thread proves that nothing has changed. I think that the environment in which they were to be used was a factor. Navy planes operate in relatively moderate climates and Airforce, operates in deserts to northern climates. In other words, more extreme and varied climates. Bottom line is, there were very successful aircraft represented by both the liquid and air cooled camps BUT as George said (and as I say has been the norm throughout aviation), the aircraft is designed around a particular engine, not the other way around. The demand has always been for bigger more powerful engines so that the airplane can do more, but the airframe must wait for the engine.

Bevan
RV7A wiring
air/oil/spit cooled IO-360

[rv6ejguy]

I researched and posted this a few months back on VAF:

This is a follow up to the discussion a couple weeks ago on the liquid cooled vs. air cooled - small vs. big after a bit of research.

I got in touch with several people who flew or worked on the R3350 in both military and civil service and was lucky enough to talk to a pilot/ engineer who still flies the Martin Mars water bombers up here.

OK TBO of 3500 hours in civil service. Well depends what you mean by TBO. The R3350 started out in 1944 with about a 30 hour lifespan in the severe duty on the B29 hauling heavy bomb loads to Japan. This was very hard on them at high power settings and in high blower for hours. Steady improvements were made post war to these engines. It appears as though Wright set the TBO at 2000 hours initially in the early '50s and increased this to 3500 hours in the early '60s when they started a SOAP program. My sources said few if any R3350s remained on wing for this period as the oil analysis showed problems well before this time and many jugs were replaced along the way. The jugs were often damaged by the sodium cooled exhaust valves disintegrating. All the people I contacted said that when operated in high blower, engine life plummeted by about 50%.

The US Forest Service sets the TBO on their R3350s in the Neptune at 1600 hours today and say they routinely make it there with no jugs replaced. Locked in low blower and limited to 51 inches dry.

The Martin Mars water bombers have their TBOs set at 800 hours. They are not turbo compound models. Steve Wall said only 2 engines ever made it that far with no jugs replaced. They have a problem with master rod thrust bushings disintegrating. The overhaul costs on these engines is over $200,000! Again this is a hard life with heavy loads but they limit manifold pressure and high blower is locked out.

In military service on the ASW mission and C-121 intelligence gathering at low altitude, the lifespan was pretty good due to low power settings and most of the time in low blower.

In civil use on the Super Connie, experiences seem at both ends of the spectrum and maybe time has made some forget the facts a bit. One quote stuck out: "... I don't remember ever having a flight of more than six hours that I landed with all four running. With the TC engines, the Connie became known as the Worlds Fastest Tri-motor".

The following link should provide a few chuckles. This is from a line mechanic with Quantas on the Connie: http://www.lockheed.adastron.com/constellation/da3.htm

Airline use was a hard life in high blower most of the time. The man hours per flight hour going into a four engined airplane were staggering and why the jet was such a leap forward despite the very high fuel consumption.

My piece of personal trivia on these engines involves living on an RCAF base in the '60s and having a four engined Argus take off over the house with full wet power-3700hp X 4. What a noise. The ground shook!

Now the 1650 cubic inch Merlin in airline service in the same era- Canadair Northstar (4 engines). Used by TCA, CPA and BOAC. Again life started out grim. TCA had 20 in flight shutdowns in one month! With takeoff power set at 1660hp at a staggering 71 inches. Cruise power was initially set at 40 inches and 1100hp. Engine life on wing was 200-450 hours in most cases. With a lowering of cruise power to 950hp, life picked up considerably. Over a one year period and 957 ocean crossings, 2 engines made it past 2000 hours, 7 made it to 1750 and the average life on wing was 654 hours (no jug changes on the Merlin). TBO was set at 1250 hours although this was just as meaningless as with the Wrights.

Initial problems were with the intercooler pump seals, compressor surging, coolant leaks and erroneous fire warning lights. Rolls Royce offered TCA a "won't be sorry" warranty on their Merlins- 6000 hours or 3 years. They would pick up the tab on any unreasonable wear or failures. RR probably lost money on this one! The Merlins on the North Stars were in a power egg which had rads and almost all parts attached in one piece for quick removal and replacement. Good idea. They needed it. It appears that very few Merlins had catastrophic failures- indeed, one was held at full takeoff power for 5 hours in a flight test until the oil supply ran low- pretty tough. Coolant leaks caused most of the shutdowns.

The RAF and SAAF also used the Rolls Royce Griffin in the Avro Shackleton ASW patrol aircraft. I was not able to contact anyone with experience on these 4 engined aircraft but they were in use many years over the oceans.

Research showed that the Pratt R-2800 was the engine to have in this era. Better reliability and fuel consumption than either the Merlin or the Wright. The Pratt 4360 was horrible by all accounts I found. In any case, the jet quickly replaced them all.

Well a lot has changed in 50 years. Subarus appear to hold their coolant more reliably than Merlins and don't require much maintenance. If they need work, they need to come out of the airframe like the Merlin. The Sube is about half the size of the Lycoming just like the Merlin was half the size of the radials.

The O-320/360 Lycoming could be compared to the R-2800 perhaps and generally reaches its TBO with few problems. Major work like jug replacements can be done while still mounted in the airframe. Where the radials used barrels of oil (literally) and the Merlin was topped up with 2 quart tins, the Lyco uses the occasional quart and the Sube nothing between changes.

Some similarities here. Hope you found this interesting. Remember that something over 350,000 liquid cooled engines (all with reduction gears) were produced by the combatants in WW2 alone. Must have worked ok or they would have switched.


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