Radial vs liquid cooled engines

[CobberKane]

Sumner Wiliiams Scout Force (Experimental) was hit by a B-17 and lost' three cylinders - left bank - over Paris and made it back to Steeple Morden. September Engineering Report 355th FG.

I thought about B-17s, but I imagine thatin most instances a pilot who knew an engine had sustained that kind of damage would have cut it and relied on the other three. Maybe in some cases the pilot might have been unaware how badly hit the engine was or had to keep it running due to other engines being knocked out, though.

 

[CobberKane]

"only two different engines though"

True, Shortround, and the R-2800 does seem to be a stand-out in this respect. I guess it would also help that the engine was so widely used and saw so mauch action, and that Japanese, Russian and German radials might be under-represented because most of the accounts we can sourse come from the english speaking allied nations. Still, if I was in a single engine aircraft listening to bullets hit the engine in front of me, I would hope the engine was a R-2800 above any other, I think...

 

[wuzak]

I thought about B-17s, but I imagine thatin most instances a pilot who knew an engine had sustained that kind of damage would have cut it and relied on the other three. Maybe in some cases the pilot might have been unaware how badly hit the engine was or had to keep it running due to other engines being knocked out, though.

Not a B-17, but hit by a B-17 and lost 3 cylinders one one bank - that was a V-12 and I presume a P-51.

 

[CobberKane]

Ah, I missread. A P51 you would assume - if it ahd been a P38 you would think it would have been mentioned. It would be interesting to know the nature of the dammage to the engine and how far he had to go to get back to base.

 

[wuzak]

He was over Paris and had to make it back to England, according to Drgondog. According to Google Maps it is about 300 miles.

 

[Timppa]

Chief mechanic Unteroffizier Rommer inspects his Fw 190 which returned from ops to Siverskaya in mid- 1943 with two complete cylinder heads shot away from its BMW engine by Soviet groundfire.
Despite chronic damage to the powerplant, the pilot returned safely and made a perfectly routine three point landing.

 

[drgondog]

I thought about B-17s, but I imagine thatin most instances a pilot who knew an engine had sustained that kind of damage would have cut it and relied on the other three. Maybe in some cases the pilot might have been unaware how badly hit the engine was or had to keep it running due to other engines being knocked out, though.

He didn't knw he had been hit. He stated that the engine (of his P-51D-5) was running rough but temps were only 'high normal'. He was prepared to bail out at first sign of dangerous engine temperatures.

 

[stona]

On 27/4/41 the minutes of a meeting with Milch,specifically in relation to the Bf 110 note.

"Combat experience has shown that 50% of aircraft put out of commission were done so by hits in the cooling system. New developments are therefore planned to include partial armour plating."

No comparison with radial engines and only relevant to one liquid cooled type,but it was obviously something of concern to the RLM.

Steve

 

[CobberKane]

On 27/4/41 the minutes of a meeting with Milch,specifically in relation to the Bf 110 note.

"Combat experience has shown that 50% of aircraft put out of commission were done so by hits in the cooling system. New developments are therefore planned to include partial armour plating."

No comparison with radial engines and only relevant to one liquid cooled type,but it was obviously something of concern to the RLM.

Steve

Fifty percent is a pretty powerful indication of the vulnerability of LC engines to battle damage, unless Damlier Benz was prticularly fragile, and I've never heard that before

 

[wuzak]

Fifty percent is a pretty powerful indication of the vulnerability of LC engines to battle damage, unless Damlier Benz was prticularly fragile, and I've never heard that before

Or just the vulnerability of the Bf 110.

 

[CobberKane]

Or just the vulnerability of the Bf 110.

You mean the cooling system of the 110 might have somehow been more vulnerable than that of another aircraft that used the same engine, like the 109? I would have thought that having an extra engine in reserve would have made the 110 less vulnerable - it would require hits to two seperate cooling systems to knock out both engines.

It would seem that:

1. Instances of radial engines continuing to run with one or more cylinders smashed certainly did exist and are not too difficult to find.
2. If instances of liquid cooled engines continuing to run with cylinders smashed exist, for some reason accounts are not easy to find.
3 In the case of the Bf110, which used the DB601 and DB605, two of the most widely produced liquid cooled engines of the war, a whopping fifty percent of combat losses were due to the cooling system being hit. And this in a twin engined aircraft with an extra donk to fall back on if only one was put out of action.

Come on over to the dark side, Wuzak. The water is fine.

 

[wuzak]

1. There are a few instances of radial engines aircraft having cylinders "smashed" and returning, but that doesn't tell us how many didn't return with cylinders being "smashed".
2. It is more difficult to "smash" cylinders in a liquid cooled V-12, because of the monoblock construction.
3. The installation of the cooling system can make a huge difference between its vulnerability. Just because 50% of combat losses are attributed to the cooling system in one aircraft it doesn't necessarily follow that the number would hold for another aircraft with the same engine. Also it may be that only one engine has to be compromised in the Bf 110 to cause its loss, which means that its two cooling systems make it twice as vulnerable as a single.

Looking back at Stona's post, the statement is that "50% of aircraft put out of commission". Does that mean that they are combat losses or merely unavailble due to requiring repair?

 

[CobberKane]

1. There are a few instances of radial engines aircraft having cylinders "smashed" and returning, but that doesn't tell us how many didn't return with cylinders being "smashed".
2. It is more difficult to "smash" cylinders in a liquid cooled V-12, because of the monoblock construction.
3. The installation of the cooling system can make a huge difference between its vulnerability. Just because 50% of combat losses are attributed to the cooling system in one aircraft it doesn't necessarily follow that the number would hold for another aircraft with the same engine. Also it may be that only one engine has to be compromised in the Bf 110 to cause its loss, which means that its two cooling systems make it twice as vulnerable as a single.

Looking back at Stona's post, the statement is that "50% of aircraft put out of commission". Does that mean that they are combat losses or merely unavailble due to requiring repair?

Wuzak my friend, you are an irredeemable contrarian. About the only point of consensus we share is that the Wallabies can't play rugby. Now if you will excuse me I hear some Jehovah's Witnesses coming up the driveway – perhaps they will prove less immune to the ravages of reasoned argument.

 

[wuzak]

Wuzak my friend, you are an irredeemable contrarian. About the only point of consensus we share is that the Wallabies can't play rugby. Now if you will excuse me I hear some Jehovah's Witnesses coming up the driveway – perhaps they will prove less immune to the ravages of reasoned argument.

You disagree that the same engine on two different aircraft can have two different levels of vulnerability depending on the details of the installation? That goes for air cooled engines too, btw.

 

[Shortround6]

There are a couple of things going on here;

1. is the likelihood of a particular airplane or engine installation to suffer a damaging hit ( or any hit).
2. is the likelihood of a particular airplane or engine installation to keep running, at least at low levels, once it has suffered the "hit".

Take for example an Allison powered P-40, an Allison powered P-51 and the P-38. With everything concentrated forward of the fire wall, logic would tell us that the P-40, presenting a smaller target area, would be less likely to suffer a hit to the propulsion system. Some people thought that, given most pilots/AA gunners failure to apply enough lead hits in the front half of the plane were less common that hits in the rear half. Take that as you will, since there was more vital STUFF in the front half of the plane you are not going to find many pictures of planes that made it back with multiple cannon hits to the nose. P-40 radiators/oil cooler were under the engine and the entire powerplant was a compact package. The P-51 was more spread out and the P-38 even more so. P-38 due to size was going to get hit more, effect of the hits is the other part of the question.
Given that all 3 had Allison engines I would guess that given equivalent hits in the radiator/oil cooler/piping that all three would pretty much react the same. Engine would keep running for about the same period of time at about the same power level. Subject to production variation of engines, actual amount of coolant in each system and actual amount of oil available.

Basically air-cooled engines had one less system to hit. This, from many target aspects, reduced the area of vulnerability. If the engine, fuel and oil systems were not hit few records were kept of hits that "might have" hit a radiator/s coolant had they been present.

Some radial engines did show an ability to run ( at least for a while) with complete cylinders missing, as in totally gone from the engine. Radial engines were a collection of individual cylinders. Pretty much separate or paired intakes, individual valve gear. While a good hit to the front crankcase could screw up the cam ring pushrod system to the entire engine a good hit anywhere along a V-12 head could screw up the valves of the entire bank or at least from the point of the hit to the end of the engine away from the cam/s drive. A V-12 can have some extremely battered cylinder blocks, to the point of seeing into a few cylinders, but the head/s have to stay where they are. Lifting the cylinder head ( assuming the engine has a separate cylinder head) means the cam drive is disconnected meaning 1/2 the engine is now longer producing any power. Maybe the V-12 can make it back on 6 cylinders ???? I don't know.

 

[CobberKane]

There are a couple of things going on here;

1. is the likelihood of a particular airplane or engine installation to suffer a damaging hit ( or any hit).
2. is the likelihood of a particular airplane or engine installation to keep running, at least at low levels, once it has suffered the "hit".

Take for example an Allison powered P-40, an Allison powered P-51 and the P-38. With everything concentrated forward of the fire wall, logic would tell us that the P-40, presenting a smaller target area, would be less likely to suffer a hit to the propulsion system. Some people thought that, given most pilots/AA gunners failure to apply enough lead hits in the front half of the plane were less common that hits in the rear half. Take that as you will, since there was more vital STUFF in the front half of the plane you are not going to find many pictures of planes that made it back with multiple cannon hits to the nose. P-40 radiators/oil cooler were under the engine and the entire powerplant was a compact package. The P-51 was more spread out and the P-38 even more so. P-38 due to size was going to get hit more, effect of the hits is the other part of the question.
Given that all 3 had Allison engines I would guess that given equivalent hits in the radiator/oil cooler/piping that all three would pretty much react the same. Engine would keep running for about the same period of time at about the same power level. Subject to production variation of engines, actual amount of coolant in each system and actual amount of oil available.

Basically air-cooled engines had one less system to hit. This, from many target aspects, reduced the area of vulnerability. If the engine, fuel and oil systems were not hit few records were kept of hits that "might have" hit a radiator/s coolant had they been present.

Some radial engines did show an ability to run ( at least for a while) with complete cylinders missing, as in totally gone from the engine. Radial engines were a collection of individual cylinders. Pretty much separate or paired intakes, individual valve gear. While a good hit to the front crankcase could screw up the cam ring pushrod system to the entire engine a good hit anywhere along a V-12 head could screw up the valves of the entire bank or at least from the point of the hit to the end of the engine away from the cam/s drive. A V-12 can have some extremely battered cylinder blocks, to the point of seeing into a few cylinders, but the head/s have to stay where they are. Lifting the cylinder head ( assuming the engine has a separate cylinder head) means the cam drive is disconnected meaning 1/2 the engine is now longer producing any power. Maybe the V-12 can make it back on 6 cylinders ???? I don't know.

Short of setting up a few hundred engines of different types and machine gunning them to see what happens we are never going to know exactly how damage resistant one is compared to another. However, anecdotal evidence is enough to draw some reasonable conclusions – for example the R2800 was a particularly tough engine. That doesn't mean the various fighters that used it were equally resistant to battle damage of course, although there does seem to have been a philosophy of over-engineering common to most American fighters. Even the relatively svelte P 51 was a fair bit heavier than contemporary spitfires.
The original question posed in this thread was; what were the relative advantages and disadvantages of air-cooled and liquid cooled engines and which was better than the other in WWII. As to the second part of the question, who can say? Many excellent fighters were powered by both types. I think you could say the air cooled motor was better in some roles, as in transport aircraft where drag was not such an issue because of low speed, or heavy daylight bombers where a radials resistance to battle damage could be incorporated into an overall design stressing toughness, like the B-17. But the LC engine also had its advantages and was undoubtedly a better choice in other cases.
The air-cooled radial design has inherent advantages over the liquid cooled V in terms of its capacity to withstand battle damage. This does not mean every radial was tougher than every inline V, or that every air-cooled fighter was more damage resistant than every liquid-cooled fighter, but its facile to say we should discount the weight of anecdotal evidence concerning these engines because the data cannot be correlated. Who cares if we cannot say whether a radial was on average " 1.8 times" more resistant to battle damage than an inline V? The practical experience was that radials frequently demonstrated an ability to withstand battle damage that would have incapacitated a contemporary inline V, and did so to a degree that made a useful contribution to the survivability of the aircraft.
Incidentally, one secondary benefit of the radial – it contributed greatly to the behaviour of the fighter in formation flying. The P 47 in particular had an excellent reputation as a formation aircraft because of the way it would 'stop' when throttled back. In contrast aircraft like the P51 were much more streamlined and even when the throttle was closed it took a while for the plane to slow. In effect, the P47 had better brakes, I guess.

 

[Rick65]

The Tempest is a plane of interest in this discussion because it was designed for both types of engine and was hence changed from in line to radial power with minimal change, certainly with less revisions than required to go the other way with the Fw 190.
As previously stated the performance of the Centaurus powered Tempest II was only marginally improved over the the Sabre IV powered Tempest V.
What is amazing is the difference in capacity of the engines, with the radial Centaurus being a 3270 cu inch engine that delivered 2520hp at 2700 rpm.
The Sabre IV produced 2240hp from 2240cu inch at a high 4000rpm. The two versions of the plane were similar in terms of performance, dry weight and I seem to remember (but can't find) a quote that the radial engined II was nicer to fly and had slightly better range despite the larger engine.
The Sabre was an idiosynchratic engine that was probably never fully developed (as was the also sleeve valve Centaurus) but the performance of the two engines in the Tempest supports the argument that the watercooled in line is more efficient in producing horsepower from a given capacity but was not necessarily lighter when cooling system etc is taken into account.

 

[CobberKane]

The Tempest is a plane of interest in this discussion because it was designed for both types of engine and was hence changed from in line to radial power with minimal change, certainly with less revisions than required to go the other way with the Fw 190.
As previously stated the performance of the Centaurus powered Tempest II was only marginally improved over the the Sabre IV powered Tempest V.
What is amazing is the difference in capacity of the engines, with the radial Centaurus being a 3270 cu inch engine that delivered 2520hp at 2700 rpm.
The Sabre IV produced 2240hp from 2240cu inch at a high 4000rpm. The two versions of the plane were similar in terms of performance, dry weight and I seem to remember (but can't find) a quote that the radial engined II was nicer to fly and had slightly better range despite the larger engine.
The Sabre was an idiosynchratic engine that was probably never fully developed (as was the also sleeve valve Centaurus) but the performance of the two engines in the Tempest supports the argument that the watercooled in line is more efficient in producing horsepower from a given capacity but was not necessarily lighter when cooling system etc is taken into account.

I agree - one of the big adavantages of liquid cooling is the ability to more effectively regulate engine temperature. This has benifits in that the engine can be more reliably maintained at optimum temperature, which will maximise engine efficincy and allow finer engineering tolerances than than an air-cooled engine. This will translate into more horsepower for a given capacity, or better fuel economy, or both.
Having said that, if a thirty litre aircooled engine running at a lower state of tune can return similar figures to a more highly tuned twently litre liquid cooled engine, what's the difference? Unlike car or motorcycle manufacturers of today, producers of WWII aero-engines has no incentive to restrict themselves to arbitrary capacity limits

 

[wuzak]

What's the difference? Frontal area, drag? For the same hp, that is.

 

[buffnut453]

Unlike car or motorcycle manufacturers of today, producers of WWII aero-engines has no incentive to restrict themselves to arbitrary capacity limits

But they still had to fit the engine into the form factor of an aircraft. Look at the late-war "next generation" radials that had 4 rows of cylinders - IIRC all of them had major cooling and reliability issues (although, granted, not many of them saw front-line service). You can't just keep adding capacity like it's a never ending supply of power - at some point, you'll reach some other logical design limit like cooling airflow to rear banks of cylinders or an engine that has too great a diameter to be a practical proposition.