WWII Inline engines: Daimler Benz vs Rolls Royce vs Allison vs Klimov vs Jumo

[joeblogs]

Yes.

Rolls Royce was hardly the only company to develop superchargers for high altitude performance. But they did develop the most efficient superchargers (generating more manifold pressure with less HP) than just about any other firm.

The only problem with adopting a larger single stage supercharger is that, in those day, blower efficiency falls with the diameter of the impeller. So putting in a larger impeller implies a larger penalty in HP well below the critical altitude. For gear driven superchargers this is a major problem. It was less of a problem on the DB designs because of the variable speed clutch you mentioned. Supercharger efficiency also falls off with impeller speed (at some point) so spinning the larger impeller less rapidly would mitigate some of those losses.

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[Viking]

Originally posted by Angus
Wasn't aware that the P51 used the 70…

They didn’t.

Originally posted by Nashwan
I don't think any Mossies used the Merlin 70. 70 series engines, yes, but not the 70 itself.
 

I’m sure you are correct.

Originally posted by Nashwan
As to numbers, about 1,000 Merlin 70s built, all used in Spitfires. Approx 400 Spitfire HF IXs, 160 HF VIIIs, an unknown number of PR XIs.

A very small number of Spits, as I said.

Originally posted by Nashwan
At the same time, the USAAF still had a lot of V-1650-3s in service, and the Germans had a lot of DB 605A. You have chosen a high alt German engine to compare with a low alt allied engine.

The -3 only served on P-51B’s, and many of them were later replaced with the -7 to standardize supply and maintenance. The -7 is not a low alt engine; it’s a medium alt engine. The Germans did not use DB 605A engined 109s in the West as escorts, only as bomber destroyers (with gondelwaffen and extra armor). Thousands of G-6/AS and G-14/AS saw service in 1944/45. I chose the allied Merlin engine that powered the most prolific allied fighter in the West in 1944/45 and that was the main threat to the LW at the time. You chose a Merlin that saw service with less than 1000 planes of different marks, only 400 as fighters. The proper opponent for such a rare bird would be the GM-1 equipped 109’s, and they out flew everything at high altitude.

Originally posted by Nashwan
And rather badly with the Merlin 70 using 100/150 fuel, which produced about 2000 hp.

Which compares poorly to the DB 605DC which produced 2200 hp with MW50. If you’re going to use “exotic” fuel then you must make this allowance for both sides of the argument, otherwise you’re just being dishonest. And C3 was far less exotic than 100/150 avgas, and far less problematic. One third of Germany’s avgas production was C3.

[joeblogs]

But notice ths significant difference in Displacement between these two engines. That is what makes the comparisons so interesting.

Now RR also increased displacement for the Griffon, but I think DB was ahead of them in developing their 605 (just my opinion).

-Blogs

Originally posted by Viking
The RR Merlin 68/ Packard Merlin V-1650-7 used by the P-51D. This engine has a FTH of 25,800 feet where it produces 1210 hp.

The DB 605AS using B4 fuel and no MW50 has a FTH of 26,200 feet (8 km) where it produces 1200 hp.

These two engines are for all intents and purposes identical in performance. Only difference being the different approach to supercharging. RR with its two-stage blower and the DB with its single-stage variable-speed blower.

[Viking]

Originally posted by gripen
Well, the Germans had certainly a need for better high altitude performance; the DB 605AS was a stop gap solution because the DB 605D was so late.

The DB 605D used the exact same supercharger as the DB 605AS: the supercharger developed for the DB 603. The DB 605D was an improved DB 605ASM. However the DB 605D was a real stopgap engine; the 109K was supposed to be powered by the DB 605L.

[Viking]

Originally posted by joeblogs
But notice ths significant difference in Displacement between these two engines. That is what makes the comparisons so interesting.

The difference is not so big as you might think just by looking at the numbers. The DB was a high compression, low-blown engine, while the RR was a low- compression, high-blown engine. Some of the DB engine volume was used up by the higher compression ratio. The RR’s supercharger had to “make up for the slack” of the RR’s lower compression to get the same amount of fuel mix compressed in the cylinders. The higher volume also allowed the DB to produce roughly the same amount of power using 87 octane fuel as the RR did with 130 octane. It is very evident that the DB engineers were fighting an uphill battle against RR with the deteriorating availability of strategic materials and fuel. It’s a testament to their skill and ingenuity that they manage to keep pace at all.

[MiloMorai]

Originally posted by Viking
Which compares poorly to the DB 605DC which produced 2200 hp with MW50. If you’re going to use “exotic” fuel then you must make this allowance for both sides of the argument, otherwise you’re just being dishonest. And C3 was far less exotic than 100/150 avgas, and far less problematic. One third of Germany’s avgas production was C3. [/B]

C3 had a rich mixture rating of 130 and late war, was pushing 140.

Some might find this of interest but no breakdown of fuel types,



What is of interest is that it looks like there was lots of stock, so the so called lack of fuel starting in the last half of the war could be possibly because of distribution problems.

[joeblogs]

Viking

That was my point. There is more than one way to skin a cat.

Originally posted by Viking
The difference is not so big as you might think just by looking at the numbers. The DB was a high compression, low-blown engine, while the RR was a low- compression, high-blown engine. Some of the DB engine volume was used up by the higher compression ratio. The RR’s supercharger had to “make up for the slack” of the RR’s lower compression to get the same amount of fuel mix compressed in the cylinders. The higher volume also allowed the DB to produce roughly the same amount of power using 87 octane fuel as the RR did with 130 octane. It is very evident that the DB engineers were fighting an uphill battle against RR with the deteriorating availability of strategic materials and fuel. It’s a testament to their skill and ingenuity that they manage to keep pace at all.

[Viking]

Yup, most certainly is.

Just a note to those that might think the 109G-6/AS or G-14/AS(M) were rare or "special" planes fielded only in small numbers: By late spring of 1944 the DB 605AM and DB 605AS(M), both producing 1800 hp with MW50, were the standard production engines for the 109G. The AM engines going mostly to the East where low to medium altitude performance mattered most, and the AS(M) engines to the West where high altitude performance was essential. During 1944 Germany produced over 14,000 109G's, the vast majority with 1800 hp AM or AS(M) engines.


And to quote another poster who paraphrases from a tv show that interviewed a P-51 pilot: (phew! is that even a proper sentence? )

Originally posted by AquaShrimp
I was watching "Wings" one day, and a P-51D pilot was talking about BF-109s being way above them (30,000+) as they were escorting bombers.  He said these were special high-alt equipped 109s, and that they had much better performance than the P-51s at such altitudes.

Any idea to what type of BF-109 he was referring to?

[gripen]

Originally posted by Viking
The DB 605D used the exact same supercharger as the DB 605AS: the supercharger developed for the DB 603. The DB 605D was an improved DB 605ASM. However the DB 605D was a real stopgap engine; the 109K was supposed to be powered by the DB 605L.

Actually not, the DB 605D was a whole new variant of the DB 605, it's developement started long before the DB 605AS was born. The DB 605AS was born because the delays in the DB 605D developement (for more information see Valtonen's article on DB 605AS in the SIHL).

The DB 605L was yet another 605 variant; basicly DB 605D with two stage super charger.

Originally posted by Viking
Just a note to those that might think the 109G-6/AS or G-14/AS(M) were rare or "special" planes fielded only in small numbers: By late spring of 1944 the DB 605AM and DB 605AS(M), both producing 1800 hp with MW50, were the standard production engines for the 109G. The AM engines going mostly to the East where low to medium altitude performance mattered most, and the AS(M) engines to the West where high altitude performance was essential. During 1944 Germany produced over 14,000 109G's, the vast majority with 1800 hp AM or AS(M) engines.

Well, if over the half of the BF 109s ever produced were G-6s, how can wast majority of the 1944 produced 14000 planes be with MW-50. The G-6 was produced until autumn 1944 and many of the practically similar G-14s lacked MW50.

[joeblogs]

Can you provide a more complete citation for Valtonen's article?

Originally posted by gripen
Actually not, the DB 605D was a whole new variant of the DB 605, it's developement started long before the DB 605AS was born. The DB 605AS was born because the delays in the DB 605D developement (for more information see Valtonen's article on DB 605AS in the SIHL).

The DB 605L was yet another 605 variant; basicly DB 605D with two stage super charger.

 

Well, if over the half of the BF 109s ever produced were G-6s, how can wast majority of the 1944 produced 14000 planes be with MW-50. The G-6 was produced until autumn 1944 and many of the practically similar G-14s lacked MW50.

[gripen]

Suomen Ilmailuhistoriallinen Lehti, 4/1995 p.15-16.
Hannu Valtonen: "Bf 109 G-6/AS, DB 605 AS moottorit Suomessa".

Written in Finnish and sources include BAMA, FAF AS papers etc.

[Viking]

Originally posted by gripen
Well, if over the half of the BF 109s ever produced were G-6s, how can wast majority of the 1944 produced 14000 planes be with MW-50. The G-6 was produced until autumn 1944 and many of the practically similar G-14s lacked MW50.

A 109G-6/AS(M) is still a G-6. And I sincerely doubt any DB 605 engine was produced without MW50 after June 1944, unless with GM1.

[MiloMorai]

Out of some 17,017 new build (neubau) 109s built from Jan 1944 to wars end, only 1377 were G-14/AS and 1 G-6/AS.

The G-6AS was mostly conversions, some 686.

So only 2064 /AS 109s or 12% of 109s.

A pdf file can be found here, post by ArtieBob, http://forum.12oclockhigh.net/showthread.php?t=2462&page=3&highlight=neubau

[Viking]

Thanks for posting it Milo, but downloading the attachment is only for registered users on that bbs I’m afraid. Note that I said the vast majority of 109’s produced in 1944 had AM or AS(M) engines. Some 2000+ AS(M) 109’s sounds about right. They would be the escort fighters on the Western Front. 12% of all 1944 109’s being high altitude variants is a significant number.

[Meyer]

Viking, I suggest you to register there. You won't regret

Yes, only 1377 109/AS, but also about 3600 with the 605D engine.