Inline engines: Modern air cooled vs WWII water cooled

[gjs238]

Can modern air cooled inline engines compete with the water cooled engines of WWII?

Perhaps there are no modern engines of those ratings being produced, if that is the case, then could modern air cooled technology produce engines competitive with water cooled engines of WWII?

 

[Shortround6]

A lot depends on what kind of service life you are expecting, what advantages in metallurgy 60 years may give you and what advantages in foundry work or fin making.

Some disadvantages of the time that may be hard to get around is that a V-12 air-cooled engine required more space between the cylinders for the fins and airflow than a liquid cooled engine needed. This means a longer, heavier crankcase and crankshaft for starters, it means more problems from torsional vibration. Then you have the cooling problem of the cylinder heads. American radials of the time used a two valve head with widely splayed valves in a hemi style head
with the valves operated by push rods. The liquored cooled engines used four valve heads and overhead cam/s. The more complicated valve gear sucks up space (volume) that the simpler radials used for head fining.

AS you move from motorcycle/small racecar air cooled cylinders (Early Porsche 917 had cylinders of 375cc while a Merlin had 2250cc cylinders) the ratio of cylinder wall to cylinder volume changes (goes down) meaning each sq in or sq cm of cylinder wall and fins has to get rid of more heat. I would also note that the early Porsche 912 engine (used in the 917 car,confusing?) weighed 540lbs for 580hp at 8,400rpm.

I am sure they can do better now but lets remember that the aircraft designer doesn't really care how the engine is cooled and sure doesn't care about the displacement of the engine. He cares about "installed" weight for power and about the total volume of the engine (and airflows) for structure and drag.

 

[GrauGeist]

With modern technology, an engine manufacturer can deliver more bang for the buck today, than was possible back in the late 1930's and early 1940's.

In the automotive world, for comparison, a Ford 49A flathead V-8 of the late 1940's was a real solid performer in it's day, but you compare that to a Chevy 409 of the early 60's, and there's no contest: the 409 was producing over 375 horsepower BUT, it weighed 1,100 pounds. Compare that 409 to a modern V-8 and the 409 comes up woefully short in contrast.

So with the advances in engine performance and technology, the engines of WWII would not be able to compare.

 

[Shortround6]

all that is true but the Ford 49A flathead V-8 was an up-dated 1931-32 design. The 409 was a hot rodded truck engine.

High powered aircraft engines were the hi-performance engines of their day. They often had better power to weight ratios than Formula I (or other ) racing car engines of their day (pre war) and for a few years after the war and into the the 1950s.

Better material have allowed even low-powered air cooled engines to more than double their overhaul life at similar power levels from the 1940s to the 1980/90s so you could probably trade some engine life for higher performance but that only goes so far as the critical limits on air cooling are the head and barrel temperatures. If you 'cook' the oil the engine is going to stop pretty quick no matter what you make it out of.

In a V-12 you can get 'beam' strength from the crankcase, cylinder blocks and heads. Air cooled engines are going to have separate cylinder barrels even if you can use a common cylinder head (some WW II air cooled engines used seperate barrels and heads and a common cam housing/s which might have added structural strength). Maybe modern material can help with the strength/weight of the construction?

 

[tyrodtom]

A Chevy 409 was a heavy engine, but it didn't remotely weigh 1100 lbs, try about 700 lbs.

Even the old original Chrysle 392 hemis didn't weigh much more than high 700 lbs. range.

A lot of the performance increases in modern engines come from the electronic controls on fuel injection, spark, and even cam timing.

There's some flathead Ford nut's out there putting electronic fuel injection, etc. on those old flatheads, even they respond with a HP increase. Where the original 239 was 110 hp, there's some modern examples over 250 hp.

 

[pbehn]

At the end of the "Turbo Era" in F1 a 1.5 litre engine was putting out 900 -1000HP in race trim and up to 1300HP in qualifying. Those engines frequently didnt finish a 2 hr race and used some very exotic metals that you may not want in a fighter and the fuels cost a fortune. You cannot up scale BHP by litre, or everyone would be using two stokes but it gives an idea of what is possible. I would say using modern technology a reliable 2000BHP is possible from 10 litres but liquid cooling is a must. Motorcycles produce hi BHP in aircooled engines nowadays (or could do but wouldnt meet noise tests I dont know if the technology would brige the problems of cooling though.

 

[Shortround6]

There are a couple of problems with comparing race car/motorcycle engines with WW II aircraft engines.

1. Take modern race car/motorcycle engine to the top of Pikes peak and see how much power it makes.
2. Take modern race car/motorcycle engine and bolt it to a dyno and run it at full power for 5 minutes, then drop back to a 20-50% power setting for 5 min and then back to 100% power for 5 minutes and keep repeating until you get 7 1/2 hours at 100% power. That was the US standard for WEP ratings.

I am sure that modern materials and modern heat/surface treatments can improve things quite a bit from the durability stand point but modern race car/motorcycle engines don't run at 100% power for 7 1/2 hours total without a tear down.
Even at Le mans it might be hard for an engine to accumulate more than a few hours at 100% power. 100% power being engine running at it's power peak rpm with throttles wide open. Accelerating up to speed (even 500-600rpm below peak power) with throttle wide open is not 100% power let alone decelerating for corners.

The original question was also air cooled vs water(liquied) cooled and you still have the heat rejection/dissipation problem. You can make the power, you can get the engine parts not break under the load, can you keep the engine temperature within limits while making that power and can you do it in an installation as small (low drag) and light as a WW II liquid cooled engine. Original question just specified inline engine so X or H 24s ( or more cylinders) could be used instead of limiting to V-12s.

 

[pbehn]

I agree shortround , I was just pointing out how much the peak technology had moved on. Todays technology can produce more power from smaller cylinders and total swept volume. An aircooled design could therefore have fewer and smaller cylinders allowing more space for cooling finning and airflow. I know racing engines are not really comparable to aero engines apart from to show how much things have moved on. Car engines are at peak power much longer than mcycle engines, in a car the power is transferred into down force for much of each lap , for mcycles on some circuits the bike maybe only at peak power in top gear for a few seconds per lap.

Before bikes turned to water cooling the kawasaki 4 cylinder 1000s could produce 100BHP in standard trim and was unburstable. a 24 cyclinder x or H motor based on that is circa 600BHP before any mods/turbo or supercharger is fitted, for a 6 litre.

I agree with all you say about testing but in F1 for example they were limited to 4 bar on turbo boost, it was rarely the engines that gave way but more likely the turbos constantly changing speed with gear changes and being on the end of some short almost white hot exhausts. Up and down shifting may not be at peak power but puts loads on an engine/gearbox that flying doesnt.

 

[Balljoint]

With materials and electronics either engine could be substantially improved. Keep in mind that "air-cooled" engines reject much, probable most, heat through the oil.

If someone wanted to invest cubic dollars and sacrifice a few engines the Merlin could gain from improved combustion rate (squish and tumble), heat rejection and improved engine controls. The guys who build for Reno are wonderfully crazy but not that crazy. Taken to the ultimate I would think liquid cooled would prevail through better combustion chamber temperature control as in land vehicles.

 

[FLYBOYJ]

Gentlemen, for the record, the only liquid cooled reciprocating AVIATION engines being produced today are being manufactured by Rotax and Metalwork, AFAIK. I'm not sure if the latter has a type certificate from any civil aviation authority.

 

[gjs238]

Gentlemen, for the record, the only liquid cooled reciprocating AVIATION engines being produced today are being manufactured by Rotax and Metalwork, AFAIK. I'm not sure if the latter has a type certificate from any civil aviation authority.

How many air cooled manufacturers are still in business (aviation)?

 

[Balljoint]

How many air cooled manufacturers are still in business (aviation)?

And when were they designed?

 

[Shortround6]

Not modern technology by any means but what was going on in the 1930s see: http://www.ww2aircraft.net/forum/aviation/liquid-cooled-napier-dagger-37091-2.html

The Napier Dagger was an air cooled 24 cylinder engine;

Type: Twenty-four-cylinder supercharged air-cooled H engine
Bore: 3.813 in (96.8 mm)
Stroke: 3.75 in (95.25 mm)
Displacement: 1,027 in³ (16.8 L)
Length: 80 in (2,032 mm)
Width: 22.5 in (584 mm)
Height: 45.125 in (1,146 mm)
Dry weight: 1,358 lb (616 kg)

That gave about 1000hp at 4200rpm at 8750ft using 6lbs of boosst (?), it had cooling problems (supposedly solvable with different ducts/outlets).

Now with modern practice we might get the rpm up to 4800rpm or even higher (and even a 20% increase gives you 5040rpm) and still keep reasonable piston speeds. Again aircraft engines have to run at their upper rpm limit for several minutes at a time, not seconds. Modern valves and valve springs should have no problem at this rpm. Going to 4 valve heads should improve power but how much considering the engine is already supercharged?

engine at 16.8 liters is already as long, higher but narrower and just as heavy (but needing no radiators/coolant) as a 27 liter Merlin or 28 liter Allison. It is going to need to turn at 4800 rpm or better to move as much air.
Better casting/forging/machining of fins (or bonded sheet metal fins ?) can help cylinder cooling, longer valve stems might allow cam boxes to be spaced further from heads for more fins area/airflow for heads (at the cost of more bulk and weight), more oil spray on piston bottoms may help ( bigger oil cooler).

Now to compete with late war V-12 liquid cooled engines the air-cooled engine has to make 1500-1750hp. It also has to run at 75-80% power for hours (tens of hours) on end (not 5 minutes spurts).

Can you improve the cooling enough to handle the extra heat transfer without a major increase in weight and bulk, we can assume the the actual engine strength and ability to make the power are a given considering better materials/alloys and better understanding of gas flows through manifolds, heads and valves and fuels, etc.
Note that using the same fuel the Merlin gave almost the same net power about 8000 ft higher in thinner air and using more of it's 'gross' power to drive the supercharger at a cost of around 300lbs more in radiator and coolant.

and again with aircraft, at 20,000ft to get the cooling you want you need xxx pounds or kilograms of air through the fins per minute and at 20,000 ft that means a lot more cubic ft (or cubic meters) to get the same mass of air. Granted it is colder but you only have micro seconds to make the heat transfer.

 

[FLYBOYJ]

How many air cooled manufacturers are still in business (aviation)?

Quite a few - off the top of my head, Lycoming, Continental, Rotax, Harbin, PZL, Verner, I know there are more.

And when were they designed?

Some recent, some 70 years ago...

 

[GrauGeist]

An example of an air-cooled V-12 from WWII would be the Argus As410 and As411, both used in a variety of Luftwaffe aircraft.

The Argus As411 was manufactured after WWII under Renault/SNECMA as the 12T.

Other aircooled V-12s of the WWII era were the Ranger V-770, Isotta-Fraschini Delta series, de Havilland Gipsy "Twelve".

 

[gjs238]

If power levels were high enough, and evidently they were not, air cooled would seem to be a great benefit for extremely cold conditions.
How many Allied Axis engines froze?

 

[GregP]

We're overhauling an Argus AS-10 inverted V-8 right now for our Fieseler Storch at the Planes of Fame. It is progressing nicely.

Modern piston engines are not MADE for aviation in anywhere NEAR the power levels that were being flown every day in WWII.

If the modern guys scaled up, they might do better and might not ... they have forgotten a LOT of tribal knowledge about large piston engines because they aren't made and have't been made for 50+ years. Go look at an Allison V-1710 or a Merlin 1650 V-12. 4 valves per cylinder and made very close to 1 HP per cubic inch or 61.02 Hp per liter and better.

Yes there are modern engines out there that make that power level, but do they do it like an aviation engine? Like maybe 100% power for takeoff and climb (say 15 - 20 minutes) and then 60 - 75% power for another 5 - 8 hours, and do it every other day or so for 400+ hours, and do it efficiently at 25,000 feet? Maybe four at a time as in a 4-engine bomber? And continue to run with bullet holes in the crankcase? With maintenance out in the open on an airfield that was recently a farmer's field, complete with rain, dust, bugs, birds, and everything else?

I could throw a handful of sand into the intake of ANY Formula 1 car and it would expire in less than 10 minutes. The big engines of WWII ate dust for months between overhauls. Ask ANYONE who flew from, say, Malta or in North Africa. I have and they ran just fine for longer than anticipated.

I can't think of even ONE modern engine that could do it except maybe a diesel ... and they were NOT the engines of choice in WWII. The ONLY reason we are flirting with diesels in aviation today is the cost of fuel. If it weren't that, nobody would bother with them at all except in trucks hauling freight and large boats and ships. They are good for good torque at low RPM at one speed for a long time ... hardly an aviation need.

 

[GrauGeist]

If power levels were high enough, and evidently they were not, air cooled would seem to be a great benefit for extremely cold conditions.
How many Allied Axis engines froze?

None of the aircraft engines, air-cooled or water-cooled, liked sub-zero temps. Without pre-heating, they wouldn't operate.

Fw190 on the Eastern Front

A-20 in Alaska

P-40 in Alaska

 

[GregP]

Great pics, Graugeist!

Thanks!

I was gonna' like this post but can't seem to find the means to do it ... the like/nacon stuff disappeared on my PC ... WTF?

 

[pbehn]

If the modern guys scaled up, they might do better and might not ... they have forgotten a LOT of tribal knowledge about large piston engines because they aren't made and have't been made for 50+ years. Go look at an Allison V-1710 or a Merlin 1650 V-12. 4 valves per cylinder and made very close to 1 HP per cubic inch or 61.02 Hp per liter and better.

I can't think of even ONE modern engine that could do it except maybe a diesel ... and they were NOT the engines of choice in WWII. The ONLY reason we are flirting with diesels in aviation today is the cost of fuel. If it weren't that, nobody would bother with them at all except in trucks hauling freight and large boats and ships. They are good for good torque at low RPM at one speed for a long time ... hardly an aviation need.

Greg I think they easily could if they wanted to, but who would want to, getting an engine approved is an arduous process I believe, if you want to do 500MPH in a plane just buy a jet. Diesels only good for freight boats and ships? WAAAAAAH my Audi is a diesel actually its just as fast as the petrol version (governed to 155MPH) 0.1 sec slower to 60MPH but way better on economy....especially at 90/100MPH the normal cruising speed here.