Vulnerability of liquid cooled engines

Denniss said:

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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I also read today that the MKII Lancaster had a lower service ceiling and a lower maximum bomb load (possibly because of the fuel you mention)

One issue that may be impacting the Lancaster is that it's much harder to design a cooling system for a radial engine than for a liquid cooled one. Many companies didn't get it right, with a resulting increase in drag.

swampyankee said:

One issue that may be impacting the Lancaster is that it's much harder to design a cooling system for a radial engine than for a liquid cooled one. Many companies didn't get it right, with a resulting increase in drag.

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The Lancaster became the Lancaster when the Manchester's Vulture engine was side lined. The USA produced radial engines eventually that did the job, the problem was getting the whole package together, power at all altitudes required combined with reliability and low drag.

Some of these statements about the Lancaster with merlin being better than Lancaster with Hercules don't make sense. The latter Hercules engines are considerably more power than the merlin about 1900 versus 1700. That's about 12 percent and should've allowed the Lancaster with Hercules engine to lift more fuel or more bombs easily compensating for the extra drag and more thirsty engine. Either we're not dealing with apples versus apples situation or we're dealing with an early weaker Hercules version or the Lancaster was limited by its fuel tankage, aiframe or undercarriage or type of airfields and was unable to exploit it's additional power in the type of ranges the Lancaster is flying.

Koopernic said:

Some of these statements about the Lancaster with merlin being better than Lancaster with Hercules don't make sense. The latter Hercules engines are considerably more power than the merlin about 1900 versus 1700. That's about 12 percent and should've allowed the Lancaster with Hercules engine to lift more fuel or more bombs easily compensating for the extra drag and more thirsty engine. Either we're not dealing with apples versus apples situation or we're dealing with an early weaker Hercules version or the Lancaster was limited by its fuel tankage, aiframe or undercarriage or type of airfields and was unable to exploit it's additional power in the type of ranges the Lancaster is flying.

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Avro Lancaster Mk II
The Mk II was the only version of the Lancaster not to be powered by Rolls Royce Merlin engines. Instead, it used Bristol Hercules radial air cooled engines. The aim was to provide an alternative source of Lancasters in case the supply of Merlin engines failed. British production was seen as vulnerable to German bombing, while there were worries that American production (by Packard) would be diverted or stopped if American entered the war.

Work on the prototype Mk II began soon after the Mk I was complete, and the first prototype flew on 26 November 1941. The new model was produced by Armstrong Whitworth, with work beginning in March 1942. Ironically, while Rolls Royce was free from serious attack, the Armstrong Whitworth factory was itself bombed in June 1942, delaying the appearance of the Mk II.

By the time the Mk II entered service in October 1942, the threat to the Merlin was already receding. Initial service tests with No. 61 Squadron early in 1943 reveals one serious limitation – it had an unexpectedly low service ceiling. On its first test, against Essen on 11/12 January, two Mk IIs joined a force of Mk Is. While the Mk I operated at 22,000 feet, the best the Mk II could achieve was an altitude of 18,400 feet, while the second aircraft only reached 14,000 feet!

After tests were complete, the Mk II was issued to No. 115 Squadron, in No. 5 Group. Despite the altitude problems, the Lancaster Mk II was a welcome improvement on their Wellingtons. In service the Mk II was slightly more robust than the Mk I, lacking the extensive liquid cooling systems needed by the Merlins, although at the lower altitude this would be put to the test. An additional aid to survival was the installation of a FN64 ventral turret below the aircraft, although this was sometimes removed to save weight.

A second problem with the Mk II was that it could only carry 14,000 lbs of bombs, compared to the 18,000 of the Mk I. Ironically, the Lancaster Mk II had a performance similar to the Merlin XX powered Halifax Mk II. By the end of 1943 the Lancaster Mk II was being phased out. Armstrong Whitworth had converted to production of the Mk I, Merlin engine production was keeping up with demand, and American production had increased after the U.S. entered the war. An example of how unpredictable aircraft design could be at this period was the case of the Halifax Mk III. This saw the Halifax switch from the Rolls Royce Merlin to the Hercules engine. The performance of the Halifax was improved by the swap to the Hercules in much the same way as the Lancaster had suffered from the same move!

From wiki
The first Hercules engines were available in 1939 as the 1,290 hp (960 kW) Hercules I, soon improved to 1,375 hp (1,025 kW) in the Hercules II. The major version was the Hercules VI which delivered 1,650 hp (1,230 kW), and the late-war Hercules XVII produced 1,735 hp (1,294 kW).

pbehn said:

The Lancaster became the Lancaster when the Manchester's Vulture engine was side lined. The USA produced radial engines eventually that did the job, the problem was getting the whole package together, power at all altitudes required combined with reliability and low drag.

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Arguably, bombers are more sensitive to drag than fighters, which can rely on brute force for high speed and for which cruise efficiency is a secondary consideration, whereas bombers need better cruise efficiency. Quite few US multi-engined aircraft used liquid-cooled engines after the development of cowlings, and many were more efficient than liquid-cooled contemporaries. Of course, serving bombers frequently had many drag-producing excrescences, making them flying airbrakes.

I think the US aerodynamicists and aeronautical engineers of the are frequently -- especially by Teutonophiles -- underrated, especially since they probably had the greatest collective expertise in the design of cooling systems, which is why the Mustang had the lowest zero-lift drag coefficient of any service aircraft with a single, piston engine, at about 0.017, vs 0.022 to 0.025 for the vast majority of fighters. Cooling drag can easily be 20% of an aircraft's zero-lift drag. That no US aircraft with fan-cooled radials entered service isn't because they didn't know and understand the concept; it was because they knew and understood the concept and didn't need the crutch.

swampyankee said:

Arguably, bombers are more sensitive to drag than fighters, which can rely on brute force for high speed and for which cruise efficiency is a secondary consideration, whereas bombers need better cruise efficiency. Quite few US multi-engined aircraft used liquid-cooled engines after the development of cowlings, and many were more efficient than liquid-cooled contemporaries. Of course, serving bombers frequently had many drag-producing excrescences, making them flying airbrakes.

I think the US aerodynamicists and aeronautical engineers of the are frequently -- especially by Teutonophiles -- underrated, especially since they probably had the greatest collective expertise in the design of cooling systems, which is why the Mustang had the lowest zero-lift drag coefficient of any service aircraft with a single, piston engine, at about 0.017, vs 0.022 to 0.025 for the vast majority of fighters. Cooling drag can easily be 20% of an aircraft's zero-lift drag. That no US aircraft with fan-cooled radials entered service isn't because they didn't know and understand the concept; it was because they knew and understood the concept and didn't need the crutch.

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I honestly don't think drag was a huge consideration for some bomber designers, possibly because they carried so much weight of bombs fuel crew and armament and had to have guns sticking out all over. Flying in a formation of 600+ aircraft means that cruise speed must be conservative anyway. Only with the B 29 was it seriously addressed.

Koopernic said:

Some of these statements about the Lancaster with merlin being better than Lancaster with Hercules don't make sense. The latter Hercules engines are considerably more power than the merlin about 1900 versus 1700. That's about 12 percent and should've allowed the Lancaster with Hercules engine to lift more fuel or more bombs easily compensating for the extra drag and more thirsty engine. Either we're not dealing with apples versus apples situation or we're dealing with an early weaker Hercules version .

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We are dealing with earlier versions of both engines. The Hercules used in the Lancaster MK II was good for 1615hp for take-off.
I would note that the 1900hp Hercules is pretty much a post war engine or perhaps 1945 engine.

For large bombers max power is pretty much useful for take-off. In flight max continuous or climb power is much more important. The time needed for a loaded bomber to climb even a few thousand feet or to accelerate from cruising speed to max speed pretty much uses up the noraml 5 minute time limit.

It took a while for the British to figure out radial engine cowlings.



leading edge of the cowl was the exhaust collector. Air intake isn't exactly low drag, little exhaust thrust from flame damping exhaust.

Some people think that the position of the propellers had something to do with it.

Center of the props more in line with the wing? Why the opposite seemed to work for the Halifax I have no idea.

swampyankee said:

I think the US aerodynamicists and aeronautical engineers of the are frequently -- especially by Teutonophiles -- underrated, especially since they probably had the greatest collective expertise in the design of cooling systems, which is why the Mustang had the lowest zero-lift drag coefficient of any service aircraft with a single, piston engine, at about 0.017, vs 0.022 to 0.025 for the vast majority of fighters. Cooling drag can easily be 20% of an aircraft's zero-lift drag. That no US aircraft with fan-cooled radials entered service isn't because they didn't know and understand the concept; it was because they knew and understood the concept and didn't need the crutch.

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never say never
There were a few (259 built) Martin PBM Mariners near the end of the war that used fan cooled 1900hp R-2600s. However the next model solved the cooling problem by switching to P & W R-2800s without fans.

Late model Water cooled inlines and Air cooled radials were cooled as much by the Oil as the Water/Air were Oil radiators just as vulnerable to damage as Water radiators.

Amazing what you find on the net, a google search brought me straight to this forum
Lancaster II vs Lancaster I and III

Shortround6 said:

never say never
There were a few (259 built) Martin PBM Mariners near the end of the war that used fan cooled 1900hp R-2600s. However the next model solved the cooling problem by switching to P & W R-2800s without fans.

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Thanks for that information. One problem with those fan-cooled engines is fans take power.

pbehn said:

I honestly don't think drag was a huge consideration for some bomber designers, possibly because they carried so much weight of bombs fuel crew and armament and had to have guns sticking out all over. Flying in a formation of 600+ aircraft means that cruise speed must be conservative anyway. Only with the B 29 was it seriously addressed.

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It wasn't the internally-carried bombs, internal fuel and crew that was the problem; it was the turrets and big-open holes for waist guns.

swampyankee said:

It wasn't the internally-carried bombs, internal fuel and crew that was the problem; it was the turrets and big-open holes for waist guns.

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Removing all the turrets and some of the crew on a Lancaster made little difference to a Lancaster. The wings were still thick, it was still big enough for a man to walk down and covered with panels and joints. For a bomber to be fast the designers have to have high speed cruising as a priority like a fighter, very few were. The Mosquito and Stirling could carry comparable payloads to Berlin in a raid because the Stirling transported a lot of men guns metal and empty space there and back along with the bomb load.

Both the Lancastrian and the Handley Page Halton can give a very good idea of what the turrets and other bumps/bulges cost.

310mph at 12,000ft full power and at 53,000lbs.
ib | lb | weak-mixture cruising | 1945 | 0222 | Flight Archive

fastmongrel said:

Late model Water cooled inlines and Air cooled radials were cooled as much by the Oil as the Water/Air were Oil radiators just as vulnerable to damage as Water radiators.

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Yes. Lundstrom relates in his First Team books that F4F Wildcats were vulnerable to oil cooler damage.

Pilots in China found the P-51 more vulnerable to cooling system damage than the P-40, as the cooling system of the P-40 was more compact.

My hypothesis is

Greg Boeser said:

Pilots in China found the P-51 more vulnerable to cooling system damage than the P-40, as the cooling system of the P-40 was more compact.

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Certainly, if the cooling system is bulkier it's more likely to get hit, but I think placement is also important, and the P-51's cooling system was in the rear of the aircraft, and fighters tended to be attacked from behind; a radiator in front, as on the P-40, Typhoon, and FW-190D's would be less likely to have their cooling systems damaged in fighter-fighter combat than P-51s.

Shortround6 said:

Both the Lancastrian and the Handley Page Halton can give a very good idea of what the turrets and other bumps/bulges cost.

310mph at 12,000ft full power and at 53,000lbs.
ib | lb | weak-mixture cruising | 1945 | 0222 | Flight Archive
]

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I wonder if a bomber designed from the start with no defensive armament would have suffered overall less losses, a cruising speed near 300MPH would have given night fighters and flak a bigger problem.

swampyankee said:

My hypothesis is


Certainly, if the cooling system is bulkier it's more likely to get hit, but I think placement is also important, and the P-51's cooling system was in the rear of the aircraft, and fighters tended to be attacked from behind; a radiator in front, as on the P-40, Typhoon, and FW-190D's would be less likely to have their cooling systems damaged in fighter-fighter combat than P-51s.

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The P 51 system stretched from the front to the rear of the aircraft, many more places to take a hit in a water pipe

By the time the P-51s entered service in China, the threat was more from ground fire than fighters.

pbehn said:

I wonder if a bomber designed from the start with no defensive armament would have suffered overall less losses, a cruising speed near 300MPH would have given night fighters and flak a bigger problem.

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I suspect -- I've not read the actual research -- that two major factors in the increase in casualties for bombers with heavy defensive armament was the increased crew size, which resulted in more casualties per aircraft shot down and in lower bombloads. Each one of those added weight -- I'd estimate at least 1,000 lb per turret and 250 lb per non-turreted flexible gun without gunners, plus 250 lb per position for gunners. Some turrets added a great deal of drag, but leaving that aside, an aircraft with the MTOW of a B-17 without the heavy and draggy turrets could carry 7,000 lb bombs to the same distance one with all the defensive weapons could carry 4,000, which would drop the aircraft required for a given mission by 75%, that is if one needed 1000 B-17s, each with ten crew members, to fulfill a mission, you'd need 250 defenseless bombers, each with no more than four. Even if both groups lost 20 bombers, the defenseless bombers would result in 80 casualties, while the armed bombers would lose 200. I don't think it would be that bad for the defenseless bombers.