Which country designed the best engines for WWII?

[tomo pauk]

(if I may)

SR6, I have seen all 4 side-by-side in a museum (Jumo 211F, DB 605, Merlin and Allison), and I have no doubt that both the Merlin and the Allison can be fitted "tighter". Especially the Allison is much more compact that the DB 605A.

There aint such thing as a free lunch.
The V-1710 that is more compact than DB 605A develops less power at altitude. On the other hand, the 2-stage V-1710, that have had a comparable power as a contemporary DB 605 was not a compact engine, certainly no more compact than the 605.

As for the "only" choice for the Germans being increased rpm, I disagree. They could have adopted the Merlin route. However, for some peculiar reason, German engines were apparently unable to benefit from the "rich mixture response" to boost anti-knock limits. The classic book by Schlaifer & Heron (I had it as s stack of photocopies) states that German engines did not behave as expected when tested with rich mixtures. It is also quite odd that DB chose the increase the CR to the extreme when it was even then very clear that increasing CR is the most inefficient way to increase power with regards to anti-knock requirements.

Yes indeed, the Germans made the self-inflicted wound when opted for high CR. Curtails the allowable boost too much, hence much less power will be made, for a small trade-off in ways of consumption and momentary increase of power. The reliability of the engines that puched the CR was low for many months, eg. with DB 601N or BMW 801D (although the 801C had also severe reliability issues).
RR was an established producer of not just commercial and military engines in 1920s-30s, but also the racing engines. They got much more experience in this time than DB, and were able to put that experience on the engines being developed from mid-1930s on. Then we also have a thing of the crystal ball - how sure was in second half of 1930s that hi-oct fuel will be available on wide scale?
German engines worked just fine when fueled by hi-oct fuel, BTW.

As for the durability, years ago I talked to a Finnish aviation historian, who at that time was also the head of the FAF museum. He mentioned that even before the war German transport aircraft engines had substantially shorter TBO than comparable British and US engines. What is more, to me the mode of failure is very indicative of what is causing the problem. And the mode of failures in German engines (instead of rapid wear, parts broke) tend to suggest that something was wrong with the basic design, especially in the DB 600 series. I think it is worth noting how different paths DB and Jumo took: to DB all major power increases came though increased displacement whereas Jumo concentrated on refining the design. For example, the cylinder liner and block design of the DB is atrocious with its dry liners...

Stating that something was wrong with the basic design of the said German engines is a majorization, as is the latest sentence. Eg. the Yugoslav AF operated their second-hand Bf 109Gs until 1954, by what time they grounded their Yaks and Spitfires.
Also, stating that " to DB all major power increases came though increased displacement" is misleading. The DB 601E was making 40% more power than DB 600, without increase in displacement, and without change in fuel. DB 605D in 1945 was making 50% more power than DB 605A in 1942, granted much of the power increase was due to introduction of water injection and hi-oct fuel. Or, DB 605D was making 100% more power than DB 600 even while the displacement went up by less than 10%.
Jumo, with 211 series of engines, indeed went for refining the design. In order to match DB 603 and surpas DB 605 they went for a whole new engine, the 213.

 

[Shortround6]

SR6, I have seen all 4 side-by-side in a museum (Jumo 211F, DB 605, Merlin and Allison), and I have no doubt that both the Merlin and the Allison can be fitted "tighter". Especially the Allison is much more compact that the DB 605A.

The thing is that all four engines were interchangeable from a functional point of view, they needed different engine mounts, cowls and intake ducts but all were of similar widths and heights (length varied due to superchargers, gearing and propshafts) and very similar weights. Any air frame that would take one would take the others without a lot of work, at least for test flying. It's not like trying to stick a Griffon in a P-40 or a DB 603 in a 109.

As for the "only" choice for the Germans being increased rpm, I disagree. They could have adopted the Merlin route. However, for some peculiar reason, German engines were apparently unable to benefit from the "rich mixture response" to boost anti-knock limits. The classic book by Schlaifer & Heron (I had it as s stack of photocopies) states that German engines did not behave as expected when tested with rich mixtures. It is also quite odd that DB chose the increase the CR to the extreme when it was even then very clear that increasing CR is the most inefficient way to increase power with regards to anti-knock requirements.

I believe I said "With 87 octane fuel the Germans had little choice....." the British got better fuel as the Merlin evolved, they sure weren't using 87 octane at 12lbs boost. Germans started with 1.40 ata for take-off for 1 minute only. 5 minute rating was using 1.3ata or about 4 1/2lbs boost on the DB series. The Germans may not have been able to use the rich mixture response of some fuels due to the fuel injection. The really rich mixtures used call for a considerable increase in fuel flow. different injector pumps or pistons could have been fitted but might not have been right for idle or cruise. The larger diameter German pistons might also have given cooling trouble (the piston failure) P & W having troubles with the Hornet B (1860 ci) compared to the Hornet A (1690 ci) back around 1930. The Hornet A was licensed to become the BMW 132. How much DB was influenced to go for better fuel economy I don't know.

As for the durability, years ago I talked to a Finnish aviation historian, who at that time was also the head of the FAF museum. He mentioned that even before the war German transport aircraft engines had substantially shorter TBO than comparable British and US engines. What is more, to me the mode of failure is very indicative of what is causing the problem. And the mode of failures in German engines (instead of rapid wear, parts broke) tend to suggest that something was wrong with the basic design, especially in the DB 600 series.

Very few DB 600s or Jumo 211 were used in commercial service. The BMW was a licensed Hornet A and The Bramo radial was a rather convoluted development of a Bristol Jupiter. The only other German engines to see much commercial use were the BMW and Jumo V-12s that were essentially two WW I straight 6s on a common crankshaft and the Junkers diesel. Not really recipes for outstanding reliability.

More later.

 

[Shortround6]

I would note that Sweden built about 170 Saab 18 twin engine bombers with mostly Swedish built DB 605 engines after the war (last Saab 18 built in 1948?) and these continued in service until the late 50s. The earlier version using P & W R-1830s lasted until 1959 but that may have had more to do with the greater availability of spare parts for the R-1830 in the late 50s.
Another 298 Saab 21 single engine fighters were built using DB 605 engines from 1945 (production versions) to 1949. These were phased out of service between 1949 (first batch built) and 1954.

It would be interesting to see what kind of service the Swedes got out of their DB 605s, which BTW, were never rated at over 1475hp take-off and 1575 hp at 7000ft/2100 meters and were run on 91/96 or 91/98 grades fuel.
One has to note that Sweden obtained a DH Goblin II jet engine and the license to build them right after WW II (1946 or 47) and had a prototype Saab 21 jet flying in 1947 and Swedish built jet engines were flying in 1950 so it would appear that had Sweden wished to it could have gotten Merlins during this time frame. Perhaps it was budgets or timing but if the DB 605s were really that terrible as far as overhaul life or broken part failures go you would think the Swedes would have done something.

 

[tomo pauk]

This book looks like well worth waiting; the author is a memeber here (Snowygrouch):
The Secret Horsepower Race | Facebook

 

[Trilisser]

Looks like an absolute must buy!

 

[tomo pauk]

Indeed. The most important German engines don't have the book of size & scope that 'Vee's for victory' is for the V-1710.

 

[Shortround6]

There isn't a book like Lumsden's for any other nation either.

While information on the Merlin is out there it requires several books.

 

[Venturi]

Indeed. The most important German engines don't have the book of size & scope that 'Vee's for victory' is for the V-1710.

That's because Californians do it under the sun.

 

[Trilisser]

I blame the "Luft46" crowd for the poor situation on German piston engine books. The same group is responsible for the situation in which we have detailed books on aircraft like the He 162 while not a single good technical book exists on the Ju 87.

 

[tomo pauk]

The ww2 aero engines are perhaps to much of a 'niche', and that means there is a small potential costumer base. So people with knowledge will rather write books about stuff that sells.
We can also take a look at what Calum was writting on his Facebook page, where the perspective publisher wanted fromm him to make the book more appealing to the wider audience by diluting the technicalities, so that publisher was discarded.

There is a book dealing with Junkers piston and jet engines in German, but it is out of print and cost plenty of money. BMW's book about their aero engines is a good start, but it again just scratches the surface (also available on English). The "Flugmotoren und Strahltriebwerke" book is very good, but unfortunately (from my point of view) wastes too much space for jet engines.

The situation about English-language covering of German engines is a sad story indeed, while the vast amout of original German dana and Allied dana is still in the archives. We can just hope that Calum's book is published.

Another bright point is that Germans are working with Russian archivists with captured German docs located in Russia, so that might be a gold mine for future researchers. The number of pages of the ww2 German docs in Russia is between 2 and 2.5 milions. link

 

[Frankenerd]

Lets take these one at a time

Merlin
Small but obvious point, without the UK Merlin there wouldn't be a US Merlin. True! Secondly, the US Merlin used in the P51H was designed by Rolls Royce as the RM 14 SM not by the USA, the UK design increased the power to 2,200 hp without any increase in weight quite an achievement by any standards. The RM 14 SM was the starting point of the V1650-9. There were significant differences between the two and detailed in other posts that list them. Secondly, the single stage Allison was much better than the single stage Merlin. Many make comps between the TSTS Merlin and the SSSS Allison. A fair comp would be the two stage Allison in the P-38 and the TSTS Merlin. The two are almost contemporary's!

Merlin development in the UK was aimed at the Hornet which had 2000 hp but it also had a much reduced frontal cross section making it a more efficient design for the designers of the Hornet. The reduced frontal area was a packaging design, not an engineering one! Mainly relocating the oil pump pick up and using the mounting beam system of the P-51H and not possible WO it! Go to a museum and look at one if you can not find the relevant photos.

Reliability, I do not know the facts but I have never seen anyone call the Merlin unreliable. Just look up how many missions were aborted for engine related issues, which was a huge problem for all planes, but a little research can give you an idea.

Alison V-1710
1) If it was so good, why was it taken out of the P51A? Politics in America meant that we were behind in blower development and the Merlin had the TSTS Blower when it was needed.
2) Why did the P38 need all that extra complexity to make it efficient at height something the Merlin didn't need? Well, actually, the Merlin never made the power at higher altitude of either the P-38, or 47. It's top rated altitude was about 25,000', some LPOs might go 1200' or so higher, but none made great power at 33,000'!


R2800
This is without doubt a remarkable engine and I am not going to pretend that anything can top it. However the Centurus did give it a run for its money in the power to weight ratio. The big difference is of course that the Centaurus only just made the war whereas the R2800 was there when it was needed The R-2800 was a great engine, but second to the BMW-801 in two row engines. Do some research to see some of the lesser known types. I would never rank any Liquid Cooled engine over any comparable power AC one! No LC engine survives a single small caliber bullet hole in the cooling system! None! But all AC Radials will run missing cylinders. So, LC Engines need not apply.

Now would you care to :-
a) Expand on the ignorance bit re the P51H Exactly what is your beef?
b) Supply some awnsers to the questions re the V1710 Like beating the Merlin to 1,000 HP SERVICE ACCEPTANCE TEST? Or having a longer TBO?

I await your reply with some anticipation

I would state that LC engines were dead ends and not deserving of greatness when compared to the many Air Cooled radials out there.

 

[Frankenerd]

I should add that one of the keys for making the P51H lighter than the D, was that they used UK standards for design loads not US loads which were more stringent increasing the airframe weight. They based it on the loads used in the Spitfire and Supermarine helped with some of the early calculations. So you can also say that the US owe the UK more than you think for the performance of the P51H.

I agree almost completely! The one point of difference is the alloy used which was much stronger than they used before.

 

[Frankenerd]

Radial lazybones stuck around for years post-war primarily due to being work-horse transport mills, being babied/fussed over by dedicated flight engineers -but if flogged they `d let go too, like the Stratoliners coming down on trans-oceanic flights, Merlin engined P-82s could do those distances too, but hi-po liquid cooled mills were for fighters too expensive TBO-wise for commmercial use.. Well, almost right. The TBOs of postwar radials was between 1600-2400 hours and they had much better reliability than any of the LC engines. Look up Convair 240?, or any other Boeing of the time, departure/service rates?

With a type-tested 3055hp in 1945, that in the standard airframe Tempest Mk 6 could do 455mph on only 17lbs boost at 17,000ft or 485mph at that altitude in the Fury airframe,my pick goes to the thoroughbred Napier Sabre... best sound too, even firing multiples of 3 [24 in 2 flat banks of 12] running @ 4,000rpm, sweet... Lets see, Liquid cooled vulnerability, 445 HP less than the lighter installed system in the big Republic 500+ MPH fighter?

Bristol sleeve-valve radials were strong smooth too,while running long TBO! True. BMW radials, [like the Bristols] ran proper fighter jock-friendly combined Kommando-gerat synchronised engine management units that let the pilot fly shoot without endless fussing/fettling about like U.S. mills

All true! but all other planes had maddening engine controls but the Fw-190/BMW-801!

 

[Frankenerd]

Japan was never much into inlines. The drag of liquid cooled engined planes was, of course, far smaller than of the radial engined ones, you're wrong on your assumption. Check P-36 vs. P-40, Fw-190A vs. Fw-190D.
This is a false comp. The D had much more power than the early 190A. How about comping the 190D to the 190A8 when both have a nearly 4000 pound bomb underneath? Or WO the bomb, but at lower altitude where the single stage 801 will beat the pants off the two stage 213?
For the much of piston era, USA did not have had inlines to offer to the airlines. ??? How about the first inline engine to pass the service acceptance tests at 1,000 HP/ First of any type of engine to pass said test! The Single Stage Allison beats any single stage Merlin in every single category of comparison.
Twin wasp being far more important to the Allied was effort than R-2800?

This one got me too!

 

[Frankenerd]

We can also note that there were several much better liquid-cooled engine installations than one in bread'n'butter P-40, like wing LE radiators found in Tempest I, Westland and De Haviland planes, then P-51, several annular instalations etc.

The cooling installation of the XP-40Q seem to be better than of the regular P-40?

No other LC Engine cooling system in any WW-II plane in service, comps favorably to the P-51! None! The leading edge installations are junk, if you judge them honestly. But none of the LC engines matched the tightly cowled R-2800 in the big Republic experimental XP-47J that went 505 MPH! The P-82 was faster than the Hornet by any measure. Heck, the late model P-38 was faster than the Hornet at higher altitudes! It was also faster when toting TWO Torpedoes! But wait, the Hornet can not carry TWO torps!

 

[Frankenerd]

Getting the cooling system right for a piston-engined aircraft is very difficult, and a lot of aircraft showed just how difficult. A major reason for the P-51's success was probably its superbly well-designed cooling system, even if it did not achieve negative cooling drag (it may have under conditions of high power and high mach number, but, if so, it would be on the order of ten pounds of thrust)

Negative cooling drag is certainly possible with both air-cooled and liquid-liquid cooled engines, by using ejector exhausts.

No, negative cooling drag is not possible by using ejector exhausts. No WW-II plane in service had a lower cooling drag installation than the P-51! None! See article in NASA's trade mag back in the '80s!

 

[Frankenerd]

USA:

The Americans clearly got their act together with Turbocharging and fuels research in a way
that nobody else did (although plenty of behind the scenes stuff credit on fuels has to go to
Brits like F.R.Banks). What we got right was the materials science and metallurgy to make turbos last. However turbo setups in the 1940`s were horribly heavy and gigantic in size, Not really. Look at the Consolidated P-30? IIRC. which did mean that without a really good two-stage mechanically blown engine, their smaller fighters were a bit limited, which is really why the P51 was a little hamstrung for a while.The early P-51 eats the early Spit for lunch. You all seem to comp the later TSTS Spit/Merlin with the early SSSS Allison. Why not comp the Later Allison V-1710/145TCM to any RR V-12 at that point in time? Any R-R piston engine make 3020 HP in 1944?

I think the big Wasp radials with turbo`s were amazing engines. I think their greatest failure was
not developing a really good supercharger for the V1710, which was in many respects a
better basic engine than the Merlin. The combustion chamber shape of the Allison is much
better than that of the Merlin, and is very similar to a modern engine, inclined 4 valve narrow-valve angle
pent roof, and splitting the crankcase down the crank centre-line, then using the whole sump as a
main bearing ladder-frame is very modern in concept, it makes for an extremely strong and stuff
crankcase structure and bearing alignment. All true!
Overall

Its very open to interpretation, but your question was "which country DESIGNED the best engines", I`m going to
vote Germany. True! The fact they never really managed to actually put many of them into a plane is a second thread !
According to internal german comparisons, which compared all the major engines, Sabre, Cyclone, AM35, AM38, Merlin, Griffon, DB`s, Jumo`s, BMW`s - the Jumo 213 scores first place in just about all categories, only loosing
out to engines like the P240 which was never used (developed by the Mercedes Silver Arrows automotive
racing dept !).

I`d also say that the DB624 turbo-twin-supercharged engine would have been superb ( WAS SUPERB!), and Benz had completed
their 100hour tests on turbocharged DB`s in 1941. So while USA deserves tremendous credit for getting not only
the science right, but ALSO the scheduling, and production - German turbo research has laid it all on the plate
for their country too. They just never got their act together to make proper use of much of it (we can all thank
Ernst Udet & Göring for that). Their entire trouble was getting strategic hi-temp alloys that were not available. But they made it work WO anyway!

Really great post!

 

[Frankenerd]

Without wanting open a very wriggly can of worms again German fuel scientists produced fuel that was no better or worse than Allied fuel scientists. Just because the Hydrocarbons came from Coal not Oil doesnt mean German fuel was worse.

Well, yes it does! It's not the Hydro-Carbons that make the differences, it's the aromatic compounds and Tetra-Ethel Lead that make the real differences and the Germans were years behind everyone else!

 

[Frankenerd]

What nonsense.About the only truth in that is that Ford did indeed work to closer tolerances than RR as a mass production car manufacturer. The basic premise that the Merlin was not intended for mass production is not true.
Crewe was producing 303 engines per month and Glasgow had a planned output of 400 a month before the war even started. Glasgow quadrupled this to 400 per week by 1943.
The Ford/Manchester factory didn't produce an engine until mid 1941. I don't know where you are, but here the war started in 1939. In 1943 Ford was producing about 200 engines per week, half the rate of Glasgow.
The Merlin first entered production, as you well know, in 1936 and much had changed by 1939/40.

RR produced fewer Merlins in 1937 than planned but was still forced to cut production in 1938. Output was ordered cut again at the beginning of 1939!

As for being liquid cooled rather than a radial engine being its biggest failure, you are joking right? If you are not you really need to look at the engines that powered the most effective aircraft on both sides.
Funny that the Fw 190 developed from a radial engined fighter to one with an inline liquid cooled engine. The later versions were the best performers too. Maybe that was a failure of the Germans to understand the 'failings' of liquid cooled engines? They could have done with your expertise!
While you are putting the Germans right you can explain to all those Spitfire, Hurricane, Mustang, Mosquito, Lancaster, etc, etc pilots that their engines have a serious failing

Cheers

Steve

Lets look at the Spit/Merlin combo;
The Spit was barely competitive with the Me-109 over England, with K/L ratios about 1.2/1, mainly because of throttle limits imposed by the return trip on the Germans. When the Spit/Merlin flew across the channel to France, they had their collective butts handed to them on a silver platter with K/L Ratios of 4.5/1 to 7/1! This state of things never got better for the Spit/Merlin.
Then there is the P-47. IIRC, it was the second best Allied killer of the war, but much more reliable and durable than the P-51, or the Spit for that matter. It was also very much harder to shoot down than any of the LC Engine planes and flown into a tremendously more dangerous environment. Given those facts, it's hard to argue for lessor planes scoring better on the heart's desire meter!

 

[Frankenerd]

Obviously the most efficient way to do things is to have spark and valve timing which varies with engine load and RPM, as well as direct fuel injection to match. In this manner, many of the higher performance cars we drive now are ahead of the aircraft we are discussing.
I'm looking forward to your book!

This is a neat argument as no car on the road today can match the power/weight/TBO of a WW-II aero engine. They can make more power per unit of displacement, but not much more power per unit of piston crown area. Then when modern car engines are run at power levels that a WW-II engine can last 2000+ hours, they grenade in minutes! See the trouble that the modified car engines into airplane engines have had over the last fifty years or so! I've seen twenty or thirty come and go at Oshkosh over the last four or five decades. If they could make the numbers they claim, why do they all go out of business?
I have a friend who has a $45,000 Honda four cylinder, turbo engine that makes almost 1,000 HP, or so the time slips and Quarter Jr computer program states, but it is not nearly as fast as my 656HP Ram-Jet 572 from the roll on and certainly has not lasted so long either. But if it was required to last 2000 hours TBO and have a flat rated altitude of 41,000' it would have about 100 HP! ( Just guessing since I do not know the internal dimensions!)