# Vulnerability of liquid cooled engines



## Jenisch (Apr 2, 2013)

Hello,

Liquid cooled engines have a popular fame of being vulnerable. In the case of the P-51, this is well know. However it's practically not mentioned in the case of other acft like the Spit, 109 and Yak. And perhaps what is most curious: the IL-2 used a liquid cooled engine.

I'm wondering at which point such "vulnerability" is a myth or not...


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## tyrodtom (Apr 2, 2013)

Look at a cutaway of a IL-2, and you'll see lots of armor of various thickness covering all the important points. 
A good example is the coolant radiator, it has a air intake in front of the cockpit, that then goes down to below the floor to the radiator itself buried in the middle of the fuselage, protected on all sides by armor.


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## CobberKane (Apr 3, 2013)

there was a pretty comprehensive thread on this forum a while back concerning the relative durability of radial v inline engines. One body of thought held that the difference between was overstated, the other was that the weight of anecdotal evidence and pilot opinion was right and the radial engines were much more battle resistant. Personally I'm in the latter camp. There are just too many accounts of radial engine fighters returning with massive engine damage, and as many of inline engines stopped by minor hits to the cooling system


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## Shortround6 (Apr 3, 2013)

Comparing a protected engine/radiator like an IL-2 to a naked engine installation isn't quite fair unless you count the the weight of the protection (armor) as part of the powerplant. 

Some radials had partially armored cowling and or armored oil coolers. We start arguing about the amount of protection each engine had instead of the engines themselves.


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## Balljoint (Apr 3, 2013)

While not statistically sound, the film of the navy fighter –probably a Hellcat- still on the arresting cable with white hot metal gushing from the engine cowling makes a strong case.


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## Ainene (Apr 3, 2013)

Jenisch said:


> Hello,
> 
> Liquid cooled engines have a popular fame of being vulnerable. In the case of the P-51, this is well know. However it's practically not mentioned in the case of other acft like the Spit, 109 and Yak. And perhaps what is most curious: the IL-2 used a liquid cooled engine.
> 
> I'm wondering at which point such "vulnerability" is a myth or not...


P-51 is obviously getting compared with other American fighters.
But comparing with lighter European fighters... 3 fighters you mentioned(spit, bf-109, yak) - all were among easier ones to shoot down(damage-absorbing ability wise).
And Il-2 is very good example: how heavily armoured craft's survivability may be lowered thanks to water-cooled engine, with radiator(underbelly) damage among the most stable loss reasons.
example:
from soviet Il-2 pilot interview:


> Один раз уже на пути домой: смотрю, температура воды больше 100 градусов. Видимо, в маслорадиатор попал осколок или пуля. Ведь в атаке бронезаслонку мы не закрывали — жарко, а двигатель работал на полной мощности. Это можно делать, только если погода прохладная, иначе мотор перегревался. Пришлось садиться в поле. Сел, покатился, остановился. Вылез из кабины и пошел по колее посмотреть. Оказалось, что в самом начале пробега самолет перепрыгнул траншею. Хорошо, что траншея была с бруствером и был запас скорости, а то бы скапотировал или сломал бы «ноги» шасси. Пришел домой: «Сержант Пургин, сел на вынужденную». В тот же день самолет привезли на машине.
> В другой раз атаковали, вывел самолет из пикирования — та же история: давление масла падает, температура растет. Надо садиться на вынужденную, а РС еще не сбросил. Отстрелил РС. Скорость большая, высота — метров пятьдесят, а впереди, в трех километрах, — лес. Вот и решай, то ли машину разбить и самому погибнуть, пытаясь посадить ее на большой скорости, то ли скорость гасить, но тогда точно в лесу разобьешься. Кое-как, юзом, сбросил скорость, плюхнулся в поле. Когда меня потащило, то я по инерции дернулся вперед, и предохранительная скоба гашетки, которую я забыл закрыть, ударила меня в правый глаз. Выскочил из кабины, — я же не знаю, куда сел, то ли у наших, то ли у немцев — побежал в кусты, что росли у речки. Залез. Видеть уже могу только одним глазом. Смотрю, бегут из леса к самолету люди, добежали до самолета и бегут ко мне. Я пистолет достал, приготовился отстреливаться. Смотрю, звезды на фуражках, оказалась наши энкавэдэшники. Меня взяли, отвезли к врачу. Врач посмотрел: «Ничего, глаз не поврежден. До свадьбы заживет». Дал полстакана спирта, я выпил и пошел спать в сарай. Утром опухоль спала, глаз стал открываться. Собрался, позавтракал у них и пошел на аэродром.
> Третий раз меня сбили, когда мы ходили на штурмовку станции Мерефа, южнее Харькова, который был у немцев. Наши войска еще только готовились к его штурму. Вел нас комэск Нютин. Атаковали станцию, а на выходе нас атаковал один «мессершмит». Надо же ему было попасть мне опять в маслорадиатор! Та же история — давление упало. Группа развернулась влево, а я, решив, что линия фронта ближе справа, развернулся туда. С трудом перетянул машину через город, тракторный завод, который был у немцев, прошел ниже труб и сразу за ним упал в поле с копнами сена.


Google translation(fixed it a bit)


> One time on the way home: look, the water temperature is greater than 100 degrees. Apparently, the oil cooler had a splinter or a bullet. After the attack, we did not close bronezaslonku(=armoured door) - hot and the engine is running at full capacity. This can be done only if the weather is cool, or the motor overheating. I had to get into the field. He sat down, rolled and stopped. Got out of the plane and went on the track to watch. It turned out that at the beginning of run aircraft jumped the trench. Well, that was a trench parapet and had a stock speed, but it would skapotiroval(=nosed over) or would break the "legs" chassis. I came home, "Sergeant Purgin, sat on an emergency." On the same day the aircraft was brought to the car.
> At other times attacked, brought the plane out of a dive - the same story: the oil pressure drops, the temperature rises. It should be forced to sit on, and the PC is not folded. Shot off the PC(RS-82). Great speed, height - fifty meters, and in front, three kilometers - wood. So decide, whether a plane smash and kill yourself trying to put her at high speed, or the speed to put out, but then just break it in the woods. Somehow, skid, slowed, plopped down in a field. When I was dragged, I jerked forward by inertia and trigger guard trigger, I forgot to close, hit me in my right eye. Jumped out of the car - I do not know where I landed, or our, or the Germans - ran into the bushes that grew by the river. Climbed. I can already see with only one eye. Look, running out of the forest to the airplane people ran to the plane and run to me. I've got a gun, ready to shoot. Watching the stars on their caps, was our enkavedeshniki(NKVD). I was taken, was taken to the doctor. The doctor looked, "Nothing, eye is not damaged. Before the wedding will live. " Given half a glass of alcohol, I drank and went to sleep in the barn. Morning swelling subsided, his eyes open. Going, they had breakfast and went to the airport.
> The third time I was shot down when we went to attack the station Merefa, south of Kharkov, which was in German hands. Our troops were still preparing it's assault. Nyutin squadron commander led us. Attacked the station, and at the output we were attacked by one "Messerschmitt". Wow he had to get me back into the oil cooler! The same story - the pressure dropped. The group turned to the left, and I decided that the front line was closer to the right, turned back. Hardly a car pulled through the town tractor factory, which was the Germans, was below the pipe and immediately after it crashed into a field with haystacks.


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## dobbie (Apr 3, 2013)

Unless there is armor applied, the liquid cooled engine is going to be more vulnerable than an air cooled engine simply because of the fact that the radiator and the piping present more area. And with an air cooled engine, less armor would be needed to protect it because you have less mass to cover.

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## tomo pauk (Apr 3, 2013)

Ainene said:


> ...
> And Il-2 is very good example: how heavily armoured craft's survivability may be lowered thanks to water-cooled engine, with radiator(underbelly) damage among the most stable loss reasons.
> example:
> ...



Thanks for posting the excerpt.
The radiator at underbelly was oil cooler, the water-glycol cooler being well protected in the tunnel shaped like shallow S letter. The experienced LW fighter pilot would try to sneak under and give it a burst or more; the experienced Stormovik pilot will of course try to deny that opportunity. Those less experienced being majority, however.


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## davebender (Apr 3, 2013)

Liquid cooled engine block is probably tougher then an air cooled engine. 

Wing mounted radiators and associated piping are the real problem. An easy way to place the heavy cooling system over aircraft center of gravity but fatal if aircraft gets shot in the wing.


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## davebender (Apr 3, 2013)

Why go to that trouble if you have 20mm cannon with decent HE shells? Just rip big holes in the unarmored wings.


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## drgondog (Apr 3, 2013)

A challenge for the statistics hounds is to narrow the data to relevant 'packages'

What was the threat envirionment?

What was the probabilty of a fatal hit at the altitude, speed and time acquired as a target?

How many times was the subject aircraft/powerplant exposed to a high threat environment?

What is the % of defined and verifiable losses?

Any set of data that anybody is aware of that address these discrimants?


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## Ainene (Apr 3, 2013)

davebender said:


> Why go to that trouble if you have 20mm cannon with decent HE shells? Just rip big holes in the unarmored wings.


Another hint: 
(soviet statistics)
More then 20% damaged craft had damage to wings, but only 3% to oil cooler. Of aircraft that *made it back*(i.e. landed safely/crash-landed on field),not shoot down.
Il-2 was quite resistant to simple holes, and control wires in the wings were reserved. It is possible, but for this kind of kill better shoot tail(here control can be denied by single lucky shell,and tail control surfaces much simpler to rip off anyway).


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## davebender (Apr 3, 2013)

MG151/20 fired 750rpm and 20mm mine shells contained 18 grams of HE. Why wouldn't you hit IL2 wing with several shells, each of which punches a 1 foot or larger hole? Single hit might not be fatal but 5 probably will be.


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## GregP (Apr 3, 2013)

Regarding post # 11 Drgondog, as an engineer, it has always been my contention that if you don’t save the data, there is virtually no chance of using it to discover how to best improve the process. I have always wanted to save the data once avionics became good, and use it to analyze missions for potential improvement. For instance, with today’s avionics, it should be possible to know how many bullets/missiles. Etc. were shot, at what speed, at what power level, at what attitude and rate of climb or descent, at what angle, the g-load, and the relative coordination of the turn and bank indicator.

Even in WWII, it should have been possible to install bullet counters and have gun cameras on most WWII fighters. The fact that we didn’t pay attention to these data mean the sum total of the biggest aerial war in history is difficult or impossible to analyze correctly since the available data are so inconsistent in their availability and are largely totally missing. 

There is almost no excuse in modern warfare. The measn to record such things are light, relatively inexpensive relative to the rest of the aircraft, and would simplify analysis in all encounters.


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## tyrodtom (Apr 3, 2013)

I remember in Hartmanns book he mentioned aiming for the oil cooler, as being his favorite way of bring down the IL-2.
The wings from behind are not a very big target, and if the other aircraft is manuvering, they're always changing position relative to you, while the fuselage will be in a more constant position as you mannuver with the other aircraft.


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## Ascent (Apr 4, 2013)

The Mosquito and Beaufighter were both used in the anti shipping role, often on the same missions. Both are twin engined ,one is liquid cooled, the other air.

Do we have any direct comparison about engine survivability between the two?


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## davebender (Apr 4, 2013)

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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## R Pope (Apr 4, 2013)

A bullet in the rad would be much more serious in a Mustang over Berlin than say a Spitfire over 
London.......

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## Jenisch (Apr 4, 2013)

Dont know if started in specific model, but the 109 could fly with a radiator out.


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## Shortround6 (Apr 4, 2013)

Only specifically equipped aircraft of certain models.


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## Jenisch (Apr 4, 2013)

It was heavy and/or expensive?


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## stona (Apr 5, 2013)

Jenisch said:


> Dont know if started in specific model, but the 109 could fly with a radiator out.



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


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## Ainene (Apr 5, 2013)

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.


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.


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## Jenisch (Apr 5, 2013)

How effective the IL-2 gunners were in bring down fighters?


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## CobberKane (Apr 5, 2013)

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.


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## Shortround6 (Apr 5, 2013)

There were also different gun mounts as some of the first ones proved almost impossible for an average gunner to aim much more than 40 degrees from the aircraft centerline due to the slipstream.


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## Jenisch (Apr 5, 2013)

As for the LW pilots hit the radiator, if the IL2s were flying very low, it would be difficult to hit it.


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## Jenisch (Apr 5, 2013)

_View: https://www.youtube.com/watch?v=Yr7C3YawF5k_


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## IdahoRenegade (Dec 13, 2017)

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).


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## swampyankee (Dec 13, 2017)

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.

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## tomo pauk (Dec 13, 2017)

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?



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.

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## Shortround6 (Dec 13, 2017)

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?
> 
> 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.



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.


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## IdahoRenegade (Dec 13, 2017)

Shortround6 said:


> Trouble is that a "Shot to the cooling fins" of an air-cooled engine often won't bring the plane down.
> View attachment 475832
> 
> 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.
> ...



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.

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## BiffF15 (Dec 13, 2017)

Jenisch said:


> Dont know if started in specific model, but the 109 could fly with a radiator out.



Jenisch,

It also helps when you are fighting over your home and can land in a farmers field if push comes to shove. Plane is saved, or mostly so. Pilot is saved (hardest weapon to produce), and able to return to battle shortly. 

Cheers,
Biff

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## Shortround6 (Dec 13, 2017)

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.


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## pbehn (Dec 13, 2017)

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.


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## Greyman (Dec 13, 2017)

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.


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## tomo pauk (Dec 13, 2017)

Interestingly enough, the late 1940s british 4-engined bombers used liquid cooled engines.


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## Shortround6 (Dec 13, 2017)

Might be cost. Nobody has ever announced in public what the Price of the Hercules or Centaurus Radials were. 

Estimates are as high as 4 times that of a Merlin on a per horsepower basis, but even if only double that is a lot of money if you are buying hundreds/thousands of engines.

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## Denniss (Dec 14, 2017)

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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## pbehn (Dec 14, 2017)

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


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)

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## swampyankee (Dec 14, 2017)

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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## pbehn (Dec 14, 2017)

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.


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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## Koopernic (Dec 15, 2017)

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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## pbehn (Dec 15, 2017)

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.


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).

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## swampyankee (Dec 15, 2017)

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.



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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## pbehn (Dec 15, 2017)

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.


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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## Shortround6 (Dec 15, 2017)

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 .



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.

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## Shortround6 (Dec 15, 2017)

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.



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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## fastmongrel (Dec 15, 2017)

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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## pbehn (Dec 15, 2017)

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


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## swampyankee (Dec 15, 2017)

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.



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.




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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## pbehn (Dec 15, 2017)

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.


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.


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## Shortround6 (Dec 15, 2017)

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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## Greg Boeser (Dec 15, 2017)

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.


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.


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## swampyankee (Dec 16, 2017)

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.



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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## pbehn (Dec 16, 2017)

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
> ]



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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## pbehn (Dec 16, 2017)

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.


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


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## Greg Boeser (Dec 16, 2017)

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


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## swampyankee (Dec 16, 2017)

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.




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.


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## Greg Boeser (Dec 16, 2017)

Except, of course, The defenseless bombers would suffer higher casualties as the defending fighters would have no return fire to contend with, which means that they can press their attacks closer and longer. Plenty of reports of bomber formations being stalked by fighters that remained just outside effective gun range, that might make one or two half-hearted passes without risking return fire. Can this be said for unarmed bombers? I think not. The only thing to end a fighter attack on an unarmed bomber is the limit of the fighter's range/endurance and ammo.

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## Milosh (Dec 16, 2017)

or escort fighters.

How many Mosquito bombers were shot down by fighters?


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## Shortround6 (Dec 17, 2017)

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.



It might have but trying to cruise at 300mph is not easy for a large plane, especially one designed in the late 30s. Granted a 4 engine "fast" bomber would not have to keep the legacy fuselage of the Lancaster and Halifax if reduced to a 3-5 man crew. 

However whatever plane is being designed in the late 30s has to operate out of the existing airfields or the size of the airfields in the foreseeable future,
NOT the airfields that would exist in 1944-45. This means the thick, high drag wings (Fowler flaps and other aerodynamic trickery helps a lot more on landing than taking off) cannot be totally abandoned. 

For Example a B-24 ( Liberator VI) needed 2100 yds to take-off and clear 50ft at 62,000lbs. A Fortress III needed 1560yds at 64,000lbs
A Halifax I (with Merlin X engines) need 1400yds at 59,000lbs, A Halifax II (with Merlin XX) needed 1200yds at 60,000lbs and a Lancaster I needed 1500 yds at 68,000lbs and 1200yds at 45,000lbs. 
Everybody agrees the B-24 had the lowest drag wing, Now can you actually fly the B-24 from British 1938-39-40 airfields? even if you chop 10,000lbs out of it? 

A Mosquito IV needed 840 yds at 21,462lbs using 12lbs of boost. but was only carrying four 500lb bombs. 

Hooker only gets to RR and modifies the supercharger in late 1939, so any planning done in 1938-39 has to be done with the Merlin X in mind.

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## swampyankee (Dec 17, 2017)

Greg Boeser said:


> Except, of course, The defenseless bombers would suffer higher casualties as the defending fighters would have no return fire to contend with, which means that they can press their attacks closer and longer. Plenty of reports of bomber formations being stalked by fighters that remained just outside effective gun range, that might make one or two half-hearted passes without risking return fire. Can this be said for unarmed bombers? I think not. The only thing to end a fighter attack on an unarmed bomber is the limit of the fighter's range/endurance and ammo.




And the bombers' escorting fighters. I think the USAAF found, much to the dismay and surprise of its planners, that unescorted bombers, regardless of how heavily armed, were highly vulnerable to fighter attack.


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## swampyankee (Dec 17, 2017)

Shortround6 said:


> It might have but trying to cruise at 300mph is not easy for a large plane, especially one designed in the late 30s. Granted a 4 engine "fast" bomber would not have to keep the legacy fuselage of the Lancaster and Halifax if reduced to a 3-5 man crew.



The cruise speed of the first model of the Lockheed Constellation _cruised _at 340 mph (295 knots) and entered service in mid-1943. It could have been done, but USAAF planners had decided that bombers needed to have heavy defensive armament. 

Advocates of strategic bombing, in general, both radically overestimated the effectiveness of bombing and the effectiveness of bombers' defensive armament.

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## tomo pauk (Dec 17, 2017)

Shortround6 said:


> ...
> However whatever plane is being designed in the late 30s has to operate out of the existing airfields or the size of the airfields in the foreseeable future,
> NOT the airfields that would exist in 1944-45. This means the thick, high drag wings (*Fowler flaps and other aerodynamic trickery helps a lot more on landing than taking off*) cannot be totally abandoned.
> ...



(my bold)
Fine post, however I disagree with bolded part. The Fowler flaps not just increased curvature (camber?) of the wing section the spanning, they also increased wing chord and thus wing area. Fowler flaps (and derivatives) directly contibute to improvement of lift coeficient and wing loading - meaning that either an aircraft can take off from same strip with bigger payload, or that it will use shorter strip for same payload, or a combination.


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## Shortround6 (Dec 17, 2017)

swampyankee said:


> The cruise speed of the first model of the Lockheed Constellation _cruised _at 340 mph (295 knots) and entered service in mid-1943. It could have been done, but USAAF planners had decided that bombers needed to have heavy defensive armament.


Do you have a source for that _cruise_ speed?
Most of what I can find is cruise speeds somewhat lower, like 275mph on 52% power at 10,000ft or 309MPH at 19,000ft on 60% power (with a post war engine) or 327 mph at 23,000ft at 65% power (also post war engine).
Please note the Constellation first grossed 86,500lbs but post war versions soon went to 102,000lbs which makes a tremendous difference to payload and range. For example the early ones did have fuel tanks holding 4690 gallons but if full that left only 3015lbs of useful load. after filling the oil tanks you barely have enough weight for crew. Payload with 2350 gals of fuel, 200 gals of oil and and crew of 4 was 15,245lbs. But at 368 gallons an hour at 275mph (52%power) that gave a range (not radius) of 1756 miles.
I believe early Constellations had a bit of trouble with their R-3350 engines overheating?

A Constellation was not going to be able to substitute for the B-29.


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## pbehn (Dec 17, 2017)

swampyankee said:


> 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.





Shortround6 said:


> It might have but trying to cruise at 300mph is not easy for a large plane, especially one designed in the late 30s. Granted a 4 engine "fast" bomber would not have to keep the legacy fuselage of the Lancaster and Halifax if reduced to a 3-5 man crew.
> 
> However whatever plane is being designed in the late 30s has to operate out of the existing airfields or the size of the airfields in the foreseeable future,
> NOT the airfields that would exist in 1944-45. This means the thick, high drag wings (Fowler flaps and other aerodynamic trickery helps a lot more on landing than taking off) cannot be totally abandoned.
> ...



It was a purely theoretical idea which would need such a change in everyones strategy philosophy and experience that it is akin to science fiction. I was thinking mainly in terms of Bomber Command. In fact the front turret was dropped on the Halifax, and the mid upper was dropped on some Lancasters. Not only did the turrets, guns, ammunition with boxes and channels, and crew weigh a lot, the structure of the airplane needed to be strong enough to bear the weight throughout the mission. The three Turrets and crew added about 1.5 tons to the weight as far as I can read so a turret less aircraft could be 2 tons lighter. The inclusion of turrets must have been a major task in design calculations, they could have used that design time to reduce drag as per a fighters design, better surface finish, retractable rear wheel etc. 

The use of turrets must have been an industry in itself, not only to make the tens of thousands that were made but to service, repair and crew them. Use that investment cost and manpower to produce bombers to fighter quality finish. 

On night time operations the speed and concentration of the bomber stream passing over the flak defences reduced losses, while with LW night fighters higher speed was a problem to cope with.



For daylight operations it is true that the defensive fire was significant, the raids that were considered a disaster like Schweinfurt also imposed heavy losses on the LW. However, on the deepest raids many waves of fighters were used. If the Bombers had a cruising speed similar to the escorts then the USA forces could use many more fighters on each mission. Also, on a USA bomber the total weight of all that was required for defensive fire, in weight of guns turrets armour oxygen crew and strength in the airframe amounted to the bomb load and more in many cases so fewer bombers would be needed for the same tonnage of bombs.

All theory and conjecture and pie in the sky of course but things could have been done differently.


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## Shortround6 (Dec 17, 2017)

Perhaps but then, due to the size/complexity of the big bombers they were always going to be a bit behind single engine fighters in aerodynamics/structure. 
Trying to design a 50,000lb airplane (and the tooling to build it) is always going to take longer than a 10,000lb airplane. 

The Connie was an Amazing airplane but flying the Prototype in Jan 1943 (or even several months earlier) means it is two-three years *after *the decision to build three factories for the B-17 and use five factories to build B-24s. Brand new factories were built to build the engines for both programs. Trying to shift such programs to new types was going to be extremely difficult. 

This brings us back to *what* was possible *when*. Could you build an unarmed heavy bomber, using the knowledge of the time, that had high enough performance to keep losses to a minimum in the late 30s or 1940-42? And using airfields of the time? 
Progress was moving quick. The US did have the A-26 flying in mid 1942 with one of the most advanced wings used in WW II. However even with a pair of R-2800 engines and top speed of 355mph or over it still _cruised _at around 280-290mph. 
The NA XB-28 is also instructive. 





granted it has three turrets but it used the same engines as an early P-47 and the same turbos. It was roughly 50mph slower than P-47. Top speed was 370mph and the cruise was under 300mph. Do we think that deleting the three remote gun mounts and two gunners is going to gain 30-40mph? 

And that is a major problem for the "high speed" bomber. It has to _cruise _fast. The B-28 or A-26 went over 22,000lbs empty and well over 30,000lbs loaded (over 35,000lbs full load) so trying to accelerate from "lean" cruise to top speed (or even a high cruise) was going to take a while, time the plane is not going to have if bounced. These radial engine bombers could use 300-400 gallons an hour if cruised at rich settings and well over 500 gallons an hour(8 gallons a minute) at full power. 

Liquid cooled engines may do better. 


The B-29 Program had full scale mock ups being inspected in Nov of 1940, just a few months after the BoB. First prototype flew in Sept 1942, just 35 days after the B-17E makes it's first combat mission in Europe. 

At what point do you make the gamble for an unarmed (or lightly armed) high speed bomber? 

Depending on your enemy to make mistakes or fumble his engine programs/aircraft development is also not very good planning. Depending in 1941-42 that the Germans would NOT develop (and have in mass production) a 425-440mph single engine day fighter with four 20mm cannon by 1944 is not good planning. Depending on the Germans to be using converted bombers as night fighters or still be using Bf 110s in late 1943 and 1944 is also not good planning. 
What would have happened if the Germans had lowered the compression in their engines and used higher boost? 
What would have happened if the Germans had gotten two stage superchargers into use sooner? 

How well would an unarmed, high speed bomber have fared against allied planes? 

What kind of bomber do you need to penetrate airspace defended by P-47s or Spitfire MK XIVs?

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## swampyankee (Dec 18, 2017)

Shortround6 said:


> Perhaps but then, due to the size/complexity of the big bombers they were always going to be a bit behind single engine fighters in aerodynamics/structure.
> Trying to design a 50,000lb airplane (and the tooling to build it) is always going to take longer than a 10,000lb airplane.
> 
> The Connie was an Amazing airplane but flying the Prototype in Jan 1943 (or even several months earlier) means it is two-three years *after *the decision to build three factories for the B-17 and use five factories to build B-24s. Brand new factories were built to build the engines for both programs. Trying to shift such programs to new types was going to be extremely difficult.
> ...



Yes. See, for example, the Mosquito. Before that, the US B-9 was faster than its contemporary fighter aircraft.



Shortround6 said:


> Progress was moving quick. The US did have the A-26 flying in mid 1942 with one of the most advanced wings used in WW II. However even with a pair of R-2800 engines and top speed of 355mph or over it still _cruised _at around 280-290mph.
> The NA XB-28 is also instructive.
> View attachment 476194
> 
> ...



You're correct that progress was moving quickly in the mid to late 1930s, but that progress was equally beneficial for large aircraft as for fighters. In any case, I think the main barrier to the pre-war development of an unarmed or minimally armed, fast heavy bomber was not technological but internal air force ideology, that being that the bomber will always get through _without fighter escort_; this assumption drove the design of US bombers. When the USAAF actually had to deal with an enemy with a powerful air force defending its cities, it found its bombers wouldn't get through without unsustainable losses (I think they also found that one or two raids wouldn't cause an enemy to sue for terms).

Designing a lightly armed or unarmed strategic bomber would require the concomitant design of a high-performance, long ranged escort fighter. (No doubt somebody will blame Congress, but before doing, they should remember that the USAAF leadership was politically well-connected enough so that Congress would generally follow the USAAF's priorities; the pot of money may not have been infinite, but the USAAF had a great deal of influence over how their share of that pot was distributed, and they didn't distribute it to long-ranged escort fighters) Here, I think that the Luftwaffe, with its flawed _zerstorer_ concept was actually considering enemy fighters as a serious threat to its bombers, showed somewhat better planning than did the USAAF. The USN, which included fighters in its carrier aviation planning, was also considering enemy fighters were a problem -- those fighters were there, at least partly, to prevent enemy fighters from decimating attack aircraft -- also showed a greater level of foresight.


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## BiffF15 (Dec 18, 2017)

Swampyankee,

I think it could be said they (Germany, USN, and USAAC) all had foresight. Hindsight has shown some was more accurate than others.

Cheers,
Biff

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## Koopernic (Dec 18, 2017)

The early B17s seemed capable of up to 318mph. Even as engine performance increased the aircraft slowed down. The engine performance increase was mainly due to a higher critical altitude from turbo charger limits but Short term power also increased from 1200hp to about 1380ph.

So I thought strip of the dorsal turret and ventral ball turret. Tidy up the nose to B-26 standards and I think you would have quite a fast aircraft at 25,000ft to 30,000ft. We’ve also removed thousands of pounds of weight. Not only the turrets but it’s supporting structure and also armour.

We can still retain the tail gunner, a single nose gun, maybe the radio room gun.

It’s probably possible to do a speed calculation from the drag of the two deleted turrets since the can be treated as a sphere.

So I did. I modeled the ball and dorsal turret as a 1 square meter area sphere with A Cd of 0.5. At 312mp at about 28000ft the turrets absorb 343kW/450hp. Assuming 70% prop efficiency that’s about 480kw/630hp at the shaft.
So getting rid of the turrets is equal to 20% increase in power for a B17E/F which 4800hp total. The cube root of 1.2 is 1.06 so we might be able to get our B17 up by 6% or 330 mph. Perhaps more with a tidy up and maybe Allison’s another 10mph. So 340mph perhaps 350mph. I’d imagine maximum cruise would be about 310mph.

An Me 109G6 could manage 380mph at that altitude, 28000ft.

To me it sounds plausible and a worthwhile trade off especially if escorts can be provided.


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## Shortround6 (Dec 18, 2017)

swampyankee said:


> Yes. See, for example, the Mosquito. Before that, the US B-9 was faster than its contemporary fighter aircraft.







A nice picture which shows the problem rather nicely.
*IF* the bomber can use technology the fighter is not using then the bomber can be faster. The B-9 was NOT faster than the P-26. It was faster than the biplane fighters. In part because the P-26 used a smaller, lighter engine that gave the same power as the engines in B-9, despite the fixed landing gear and wire bracing. 
What happens to the B-9 if the opposing fighters use unbraced monoplane wings and retracting landing gear? 
Granted the perspective is a bit off but which airplane needs more hours of design work (including blueprints) and more hours of construction to bring to the prototype stage? 





> You're correct that progress was moving quickly in the mid to late 1930s, but that progress was equally beneficial for large aircraft as for fighters. In any case, I think the main barrier to the pre-war development of an unarmed or minimally armed, fast heavy bomber was not technological but internal air force ideology, that being that the bomber will always get through _without fighter escort_; this assumption drove the design of US bombers. When the USAAF actually had to deal with an enemy with a powerful air force defending its cities, it found its bombers wouldn't get through without unsustainable losses (I think they also found that one or two raids wouldn't cause an enemy to sue for terms).
> 
> Designing a lightly armed or unarmed strategic bomber would require the concomitant design of a high-performance, long ranged escort fighter. (No doubt somebody will blame Congress, but before doing, they should remember that the USAAF leadership was politically well-connected enough so that Congress would generally follow the USAAF's priorities; the pot of money may not have been infinite, but the USAAF had a great deal of influence over how their share of that pot was distributed, and they didn't distribute it to long-ranged escort fighters) Here, I think that the Luftwaffe, with its flawed _zerstorer_ concept was actually considering enemy fighters as a serious threat to its bombers, showed somewhat better planning than did the USAAF. The USN, which included fighters in its carrier aviation planning, was also considering enemy fighters were a problem -- those fighters were there, at least partly, to prevent enemy fighters from decimating attack aircraft -- also showed a greater level of foresight.



In reverse, the Navy example is flawed because the Navy aircraft were restricted in size and power. They had to fit on the carrier and they had to be single engine. If you are using the same engine in your fighter and in your attack aircraft (carrying 500-1000lb bomb or a torpedo) then the attack aircraft is going to be slower than the fighter and perhaps shorter ranged when carrying the strike load. All have to take off and land from a certain sized "runway". 

The Army can use twin engine bombers (some foreign nations used three) and gain range/payload over single engine aircraft. 
By the time you get to the Martin B-10 




you have a plane at the end of 1933 that had a normal range of around 590 miles, a max range of 1240 miles and a ferry range of 1830 miles. 
or would when it became the B-10B. In any case the ranges were beginning to exceed what single engine fighters could achieve and still keep their performance. With the Armies interest in the B-15 and B-17 the range of fighters was falling further behind what the bombers could do. 
The Boeing 299 was credited with a range of 2040 miles while carrying 2573 lbs of bombs. This was in 1935 with 750hp P & W Hornet engines. No single engine fighter in existence or in the planning stages could come close to that range using the engines available or promised at the time.


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## swampyankee (Dec 18, 2017)

Shortround6 said:


> View attachment 476243
> 
> 
> 
> ...



I disagree with your dismissal of the USN example; while the USN had restricted its operational carrier aircraft to have one engine*, the navy planners could have come to the conclusion that "the bomber will always get through" just as easily as could the USAAC or it could have decided that using fighters to defend carriers from air attack was pointless, and build heavily armored carriers instead. The basic specifications of the B-17 are interesting: here's an aircraft that is tasked with bombing _somebody_, but the most likely somebodies are Japan, clearly impossible to attack from US bases, and Europe, also impossible to attack from US bases. About the only countries that could be bombed from US bases would be Mexico and Canada. Was the B-17 really designed to attack foreign cities or was it really designed as a long-range adjunct to coastal artillery?



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* The USN had operated twin-engined aircraft from carriers in the 1920s and early 1930s, the T2D. I suspect they found it to be feasible but not cost-effective.


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## Shortround6 (Dec 18, 2017)

They didn't really operate twin engine aircraft from carriers in a normal sense. 
Douglas T2D.





Yes they were operated from the Langley but lowering them over the side and recovering by crane are not normal carrier operation. 
Most were used from shore bases. With a 57ft wing span and 42 foot length their ability to operated from carriers was limited. No mention of wing folding and getting something that size down the elevators probably wasn't happening. 

" _About the only countries that could be bombed from US bases would be Mexico and Canada. Was the B-17 really designed to attack foreign cities or was it really designed as a long-range adjunct to coastal artillery_?"

doesn't really matter from the point of view of an escort fighter. You simply couldn't build an escort fighter with the range required to stay with the B-17 no matter what target was intended. In fact building fighters to escort the B-18 was going to be difficult. With 882 gallons on board a B-18 could fly 1200 miles while ferry range was 2225 miles. 

I would also note that the B-17 was sort of an interim bomber. It wasn't what the Army really wanted which is why they were building the B-15, the B-19 and funding other design studies of very large bombers. It use air cooled engines which the Army bought because they were available but the army was funding the "hyper" engine/s and the Allison as they thought they were better suited to turbo operation at high altitudes for long range. 
If you can't build a fighter to escort your "interim" less than optimal bomber/s what chance do you have of building escort fighters for the really big bombers they were planning for the future?


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## KiwiBiggles (Dec 19, 2017)

swampyankee said:


> Was the B-17 really designed to attack foreign cities or was it really designed as a long-range adjunct to coastal artillery?


The clue is in the name. Early B-17s were not covered in guns; they were dubbed Fortresses as they were designed to act as a longer-ranged coastal defence fortress.


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## swampyankee (Dec 19, 2017)

KiwiBiggles said:


> The clue is in the name. Early B-17s were not covered in guns; they were dubbed Fortresses as they were designed to act as a longer-ranged coastal defence fortress.



That disagrees with, among other sources, Boeing's web site: "Richard Smith dubbed the new plane, with its many machine-gun mounts, the 'Flying Fortress,' a name that Boeing quickly adopted and trademarked" (Boeing: Historical Snapshot: B-17 Flying Fortress) 

On the other hand, the idea that the USAAC/USAAF bomber force was intended as long-range coastal defense makes a great deal of sense, in that the number of defending aircraft a bomber performing maritime attack would need to contend with would be fairly small.


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## Shortround6 (Dec 19, 2017)

The USAAF had "plan" that stretched over years if not over 1-2 decades. Much like the RAF and what would become Bomber Command. They wanted to become, at the least, fully the equal of the Navy and the ground army and at best, the premier military service in the Country. Much like the RAF ordering hundreds (or thousands) of Fairey Battles and Blenheims to build the RAF while they waited for better designs. The USAAF had to order interim aircraft to train crews, establish a position in the "budget wars" (get the congress or higher ups used to the idea of funding bombers) build bases,etc while they worked towards their "dream" aircraft, which would have intercontinental range. 
The requirement that lead to the XB-15 called for a 5000 mile range. 
It also resulted in the XB-16 design study




which morphed from 4 to six engines. The range requirement was restated as "maximum practical"
Boeing also came up with the XB-20 to compete with the XB-19 but as the XB-20 was pretty much a slightly bigger XB-15 with bigger engines it wasn't as advanced as the XB-19 and was not funded. 
Please note that only the XB-16 proposal used liquid cooled engines and the Army was sticking to the "idea" that liquid cooled engines (buried in the wings) were the _preferred _power plant for their _ ultimate _bomber. 
There may have been a lot of paper doodles that never got an official designation. 

In the political climate of the US in the 1930s, publicly announcing you wanted intercontinental bombers would have been career suicide so euphemisms or fuzzy mission statements were the order of the day. 

There was"talk" of putting those flat engines into the wings of a "fighter", but think about that. SIngle engine fighter with flat fuselage? twin engine fighter? 
There may be some drawing/s somewhere. Please remember that one of the "concept" drawings for the P-38 shows a plane with two engines in the fuselage driving props on the wings through extension shafts and right angle drives to eliminate nacelles on the wing.

It is hard to figure out exactly what they were thinking during the 30s but the movers and shakers in the USAAF were certainly dreaming of very long range bombers and put more money and effort into the idea than any other country. It just took until the B-29 to actually pay off. (and air to air refueling)


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## FLYBOYJ (Dec 19, 2017)

KiwiBiggles said:


> The clue is in the name. Early B-17s were not covered in guns; they were dubbed Fortresses as they were designed to act as a longer-ranged coastal defence fortress.


_Upon touring the Boeing plant and witnessing the first B-17s roll off the assembly line, “An awestruck reporter called the aircraft a ‘Flying Fortress,’ and the name stuck.”_

How Did The B-17 Get Its Name? « Dr Burt


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## Shortround6 (Dec 19, 2017)

The name date back longer than that. One magazine article calls the B-9 a "Flying Fortess" and it might not have been original then?






See first sentence of text. Any heavily armed bomber may have been referred to as a "flying fortress" at the time and perhaps reporters weren't any more creative then than they are now.

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## FLYBOYJ (Dec 19, 2017)

Shortround6 said:


> perhaps reporters weren't any more creative then than they are now.



But there was still "fake news"!

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## pbehn (Dec 19, 2017)

FLYBOYJ said:


> But there was still "fake news"!


There was always fake news, Elizabeth the firsts speeches were re written after she died, and don't even start a discussion about Noahs Ark!

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## wuzak (Dec 31, 2017)

pbehn said:


> For daylight operations it is true that the defensive fire was significant, the raids that were considered a disaster like Schweinfurt also imposed heavy losses on the LW.



I suppose it depends on what you count as a heavy loss.

The Luftwaffe lost 20-odd fighters in the first Schweinfurt mission. Almost all due to the fighter escort of P-47s and Spitfires. 

The Allied fighter pilots claimed slightly more kills than was actually the case. Gunners on the bombers claimed more aircraft killed than the Luftwaffe put into the air, by some margin.

Bombing raids became far more costly to the Luftwaffe when escort was provided all the way to target.


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## wuzak (Dec 31, 2017)

Shortround6 said:


> which morphed from 4 to six engines. The range requirement was restated as "maximum practical"
> Boeing also came up with the XB-20 to compete with the XB-19 but as the XB-20 was pretty much a slightly bigger XB-15 with bigger engines it wasn't as advanced as the XB-19 and was not funded.
> Please note that only the XB-16 proposal used liquid cooled engines and the Army was sticking to the "idea" that liquid cooled engines (buried in the wings) were the _preferred _power plant for their _ ultimate _bomber.



The XB-15 and XB-19 were originally intended to use liquid cooled engines (X/V-3420s, I believe) but these were unavailable and would not be available for some time.

So they ended up with what was available.


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## swampyankee (Dec 31, 2017)

wuzak said:


> The XB-15 and XB-19 were originally intended to use liquid cooled engines (X/V-3420s, I believe) but these were unavailable and would not be available for some time.
> 
> So they ended up with what was available.



For the XB-15, more likely V-1720s; see Boeing: Historical Snapshot: XB-15 Bomber/Transport.


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