Vulnerability of liquid cooled engines

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Jenisch said:
Dont know if started in specific model, but the 109 could fly with a radiator out.
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Certainly the F,initially as a modification, and it seems now the Gs onwards,despite what Prien stated in his F,G,K book.

You still lose 50% of the cooling capacity which means you are not going to have the engine running indefinitely. Cooling on the DB engines in the Bf 109 (and almost every other aircraft/engine combination) was marginal even at 100% capacity.
The assumption in order to maintain even this level of cooling is that the damage is specific to one radiator and that the pilot has correctly identified it.

The Bf 109 E did not have this feature. Luftwaffe pilots during the BoB were supposed to head for the French coast with damaged aircraft but I have read at least half a dozen accounts where this was simply not considered an option. A forced landing in an English field and inevitable captivity was a safer bet than a mid Channel ditching for most. This despite the Germans' relatively efficient air sea rescue system.

Cheers

Steve
 
davebender said:
Experts such as Hartmann can aim for the relatively small oil cooler. Normal pilots aim for center of mass and are lucky to land a burst on target.
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Short burst from below was effective -bouncing 7.7 bullet is enough for sufficient cooler damage.
Same burst from above is probably enough to silence poor rear gunner(but rear gunner of attacked craft, not surrounding ones!), but not to bring craft down. Anything greater(time wise) is way too dangerous for bf-109 anyway.
 
Il2 gunners apparently had quite a bit of success against German fighters after the two,seat version was introduced (1942?) as LW pilots initially continued to attack as against an undefended target. But being an IL2 gunner was a dangerous job - seven times as many gunners were killed as pilots.
 
As for the LW pilots hit the radiator, if the IL2s were flying very low, it would be difficult to hit it.
 
I hope it's ok to bring this old thread back from the dead. This is a topic that is of interest to me, and I see a lot of new and very knowledgeable posters here. A lot of the articles I read mention the vulnerability of liquid cooled engines, and how "one bullet in the cooling system" will bring a plane down. Others comment about how the '51 was especially vulnerable due to the location of the radiator.

It certainly seems to make sense. It would also seem like this wouldn't be that big an issue in a "point defense" fighter (interceptor), where cooling system damage might still provide time to land safely, or worst case either dead stick or bail out over friendly territory and catch a ride to base. OTOH-a long distance flight over the Pacific or 400 miles into enemy territory would be a different story. As I said-seems to make sense...but lots of other things that seem like common sense turn out to be fiction. Is there any evidence that losses due to cooling system damage really was a significant factor in overall losses? Was this part of the reason that '38s (with at least a redundant liquid cooled engine) and the '47 were used so heavily for ground attack/bombing vs the '51 (and was that actually the case-or another bit of urban legend? The more I learn from this site the more I question everything I thought I understood about WWII aviation).
 
How could the Bf109 fly with a radiator out? Was the engine designed with multiple internal cooling passages or was there an isolation valve the pilot had to close to keep all the coolant from leaking out?

My suspicion in the liquid- vs air-cooled engine vulnerability debate is that the average vulnerability of the liquid-cooled engines is exaggerated, as air-cooled engines still had oil coolers, and putting holes in those would tend to reduce engine life to zero. On the other hand, a radiator on an liquid-cooled engine has to have about the same, or more, net surface area as the fins on on radial engine, as that area is determined by the heat transfer properties of air (and the radiator has a hard limit on the temperature of the liquid used as an intermediate heat transfer agent; the fins on a radial don't; in other words if a 2,000 hp radial needs 20 square feet of fins, so does the radiator for a liquid-cooled engine), and that radiator can be placed anywhere, including places far from the nose of the aircraft; since aircraft were usually shot from behind on would expect the radiator of an aircraft like the Bf109 or P-51 to be hit more often than the radiator of a V-12 FW190 or a P-40.
 
swampyankee said:
How could the Bf109 fly with a radiator out? Was the engine designed with multiple internal cooling passages or was there an isolation valve the pilot had to close to keep all the coolant from leaking out?
Click to expand...

There were cut-off valves installed for each of two coolant radiators, so with one radiator punctured there was still a good deal of cooling capacity left. IIRC the valves were standard from Bf 109F onwards.
 

Trouble is that a "Shot to the cooling fins" of an air-cooled engine often won't bring the plane down.

lots of space for merely broken/dented fins. Even blowing off a rocker arm/valve won't totally stop the engine. Although you now have a pretty good oil leak.
Hawker Hurricane radiator

hole through the middle is for the oil cooler. one or two rifle bullets through the matrix is going to cause a pretty good leak.

In actual practice they found the radiators near the front suffered less damage than radiators further back. Most people assume that this is because most ground gunners (and most pilots) didn't use enough lead on the plane when firing and were more likely to hit the rear of the plane than the front. A lot more misses behind than misses in front of the target plane.
 

Thanks for the picture of that Hurricane radiator. In a past life I used to work at GMs radiator plant, so the heat exchanger design/production processes is interesting to me. I hadn't realized how sophisticated HE design had gotten as early as the 30s-40s. The hexagonal core design had been around for a while (IIRC the CO I worked at actually had the patent on it) but I had only seen them on soldered copper/brass cores. I hadn't realized that what appears to be a dip brazed aluminum cores were around that early. Up until the mid 80s that company had a small AC HE department, and they were dip brazed, but a "bar and plate" construction. I'd love to see some videos or pics of the production plant where that Hurricane radiator was built.

One thing that has amazed me about WWII aircraft (as well as other products) was how sophisticated things had gotten with the tools available at the time. No CAD designs, everything on the drafting board. No CNC machining. No computers for design calculations, let alone computational fluid dynamics programs for airflow studies. To go from the Wright Flyer to the ME-262 in just 40 years is amazing progress. Strange how it now takes us upwards of 20 years to get a new fighter into production and service.
 
The 109s use of separation valves, while interesting, is somewhat overrated. Not all Fs had them and certainly not all Gs. There doesn't seem to be a "before and after date" and such valves were in short supply and salvaged from wrecks whenever possible so it seems they weren't really avaialbe in the supply chain for replacement or retrofit.
 
The cooling system ran at high pressure and hotter than boiling point at normal pressure. Any hit anywhere in the system had a cloud of coolant spray coming from the plane. After being hit the pilot had a few minutes at most to get out or land.
 
Bomber Command found that statistically, liquid-cooled engines were more than twice as vulnerable to enemy action as air-cooled engines. The large number of failures were mainly due to damage to the coolant system and in particular to the radiators. Over half of the cases of engines failing due to coolant system damage were hit in the radiator.

They had very similar aircraft flying the exact same operations - just with different engines. Seems like a reasonable comparison.

Wellingtons, Halifaxes, Lancasters all had Hercules and Merlin powered versions.
 
Interestingly enough, the late 1940s british 4-engined bombers used liquid cooled engines.
 
Hercules was heavier, bulkier and consumed more fuel, the Merlin versions of the Lancaster were better climbers, slightly faster and had more range.
The Lancaster datacards show for the Hercules VI equipped version 2150 gals fuel load, 395 gals allowance and 2070 miles range with 6k lbs of bombs (Lancaster II with 65k lbs max weight)
Lancaster I/III with 68k max weight, the same fuel load has 270 gals allowance and 2250 miles range with 10k lbs bombload
difference in climb to reach 20k ft is 4 mins in favor of the Merlin versions, 41.5 vs 45.5 mins
 
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