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

[gripen]

Originally posted by Knegel

GJ + FX is a G14AS, with DB605ASM, with the more weight due to the MW50 installation, this plain will have a disadvantage with combat climb to the 109G6AS.

I'm refering high speed values and values are higher than other AS data at high altitude, lower at low altitude. Probably because not corrected for compressibility, the specification calculation is certainly without compressibility correction (directly said in the Mtt datasheet).

Originally posted by Knegel

Therefor the GJ + FX had around 1,5 ata in 10000m alt for 2 x 10min combat.

Hm... I read something like 1,1ata at 10000m at high speed (very hard to read again).

Originally posted by Knegel

If i compare the Speeds of the GJ + FX with the Spitfire IX BS. 551 (Merlin 70
 ( http://www.spitfireperformance.com/bs543.html , the other HF Spits show a rather similar result), the Vmax performences seems to be very similar.

Probably not because probably no compressibility correction.

Originally posted by Knegel

The 109G14AS is better with Sondernot, but less good with combat climb, the RAM FTH of this Spit is a bit below that of the DB605ASM with combat climb, at 8350m.

Hm... the GJ+FX had FTH 6800m with MW50 where it did 1495ps according to the specs. The BS 543 had FTH about 8350m where it did 1475hp according to the specs.

BTW there is only high speed FTHs in GJ+FX sheet.

[Viking]

Originally posted by gripen
Hm... the GJ+FX had FTH 6800m with MW50 where it did 1495ps according to the specs.

Negative. The DB 605 ASM makes 1,435 PS at 1,42 ata according to the Leistungsblatt. With 2800 rpm according to the GJ+FX chart the engine was running 1.7 ata at 6.8 km. According to the same chart the engine was running on 1.3 ata at well over 9 km at 2800 rpm. The DB 605 ASM produces over 1300 PS at 1.3 ata and 2600 rpm. At 10 km it still runs on ca. 1.15 ata at 2800 rpm. And according to the Leistungsblatt for the DB 605 AS without MW50 (and thus without charge cooling) the engine was producing 925 PS at 10 km at 2800 rpm.

And according to this table the Merlin V-1650-3 was making 985 hp at 35,000 feet (10.6 km):

http://www.wwiiaircraftperformance.org/mustang/mustangtest.html

[joeblogs]

Here is one more figure, which is a nice measure of relative performance. It plots the maximum horsepower the engine can develop (at any altitude), divided by its dry weight (i.e. without coolant):

http://mysite.verizon.net/vze479py/sitebuildercontent/sitebuilderfiles/power_wt.pdf

I have left out the German engines for the reason Viking mentioned earlier. If I did plot them, they would look average in my data. When corrected to reflect war time boost systems, they would look reasonably good. One reason why they would, as pointed out by others in this thread, is the generally higher compression ratio of the German engines.

You could draw a 45 degree vertical line through the data and see the strong, stable correlation between weight and power. Engines above that line are better, at least by this metric.

The outstanding engines in this figure are the late model Napier Sabres, the RR Griffons & Merlins. The Packard Merlins and the Allisons are about average, because they are reletively heavy (I don't know why).

I left out the Italian and Japanese liquid cooled engines; they are below average.

Some lesser known standouts include Contentinental's Hyper engine, which did not see production and Klimov's M107.

The Hisso and the Kestrel are engines of an earlier generation, but the Hisso seems ahead of its time. Some of those were also high compression engines.

Originally posted by 1K3
In the radial department, nothing beats the Pratt & Whitney series.  Not even the BMW radials can beat P&W.

When it comes to Inline liquid-cooled engine, which company made THE best inline engine


[ EDIT:  Jumo is added to the list ]

[Meyer]

From a post of George Hopp in the TOCH board

IIn response to the discussion on which fuels the DB engines could use, this is from a top secret DB internal memo on a conference of 3 Oct 44 on the Bf 109/DB 605 combo:

Motortype Brennstoff Startleistung Höhenleistung in 10km

DB 605 AM B4+MW 50 1830 PS 800 PS
DB 605 AM C3+MW 50 2000 PS 800 PS
DB 605 ASM+D B4+MW 50 1850 PS 950 PS
DB 605 ASM+D C3+MW 50 2000 PS 950 PS
DB 605 L C3+MW 50 1700 PS 1275 PS

[gripen]

Originally posted by Viking
Negative. The DB 605 ASM makes 1,435 PS at 1,42 ata according to the Leistungsblatt.

That value is for sealevel. The specification is 1200ps at 1,42ata at 8000m while the GJ+FX did that at a bit over 8000m with RAM (hard to read again)

Originally posted by Viking

With 2800 rpm according to the GJ+FX chart the engine was running 1.7 ata at 6.8 km. According to the same chart the engine was running on 1.3 ata at well over 9 km at 2800 rpm. The DB 605 ASM produces over 1300 PS at 1.3 ata and 2600 rpm. At 10 km it still runs on ca. 1.15 ata at 2800 rpm.

If I put a paper following 10000m line from the above, it reaches the 2800rpm line at the point where the 2800rpm line ends ie closer to 1,1ata.

Originally posted by Viking
And according to the Leistungsblatt for the DB 605 AS without MW50 (and thus without charge cooling) the engine was producing 925 PS at 10 km at 2800 rpm.

You see the problem, the DBs had problems to live up to the specs; even assuming 1,15ata, the GJ+FX did around 1050ps at 10000m and a bit below 1000ps at 1,1ata.

Originally posted by Viking

And according to this table the Merlin V-1650-3 was making 985 hp at 35,000 feet (10.6 km):

Well, Knegel's reading was something like a bit below 1150hp at 10000m.

[gripen]

BTW the V-1650-3 data there is for 11,5' diameter impeller (Merlin 61), not for the 12' impeller (Merlin 70).

[Knegel]

Hi,

i made a typo and was up to write 1,15, not 1,5.

With help of a paint program, by adding the ata steps, out of the 1,3 and 1,7 ata avlues, visible that its between 1,1 and 1,15.

Regarding the FTH i wrote the "combat/climb" FTH of the DB605ASM is above that of the Merlin70.

The Vmax performence of the SpitIXc HF and 109G14AS is very similar at hight, so is the engine power.

Greetings,

Knegel

[gripen]

Originally posted by Knegel

With help of a paint program, by adding the ata steps, out of the 1,3 and 1,7 ata avlues, visible that its between 1,1 and 1,15.

I don't see much reason to argue about that small difference (about 0,02ata); the original claim, roughly about 1000ps is certainly at right ballpark.

Originally posted by Knegel

Regarding the FTH i wrote the "combat/climb" FTH of the DB605ASM is above that of the Merlin70.

What is the point comparing those? The Merlin 70 still does something like 150hp higher output at that altitude.

Originally posted by Knegel

The Vmax performence of the SpitIXc HF and 109G14AS is very similar at hight, so is the engine power.

Well, the GJ+FX results are probably not corrected for compressibility and the error is around 15-20km/h at FTH according to spec sheet. Otherwise the GJ+FX would had been 15-20km/h faster than spec at around 8000m despite the FTH was below the spec.

[Viking]

Originally posted by gripen
Hm... the GJ+FX had FTH 6800m with MW50 where it did 1495ps according to the specs.

Originally posted by Viking
With 2800 rpm according to the GJ+FX chart the engine was running 1.7 ata at 6.8 km.

Forgive me if I'm repeating myself, but I can't seem to find your response to this. Surely the DB was producing more than 1495 PS at 1.7 ata at full pressure height? Or am I reading the chart wrong?

[Viking]

Originally posted by gripen
What is the point comparing those? The Merlin 70 still does something like 150hp higher output at that altitude.

Because this particular discussion that has been going on for the last six pages was not initially about the engines’ power output but about the superchargers and the claim I made when entering this discussion:

Originally posted by Viking
… The DB's already had a supercharger with a similar FTH to that of the two stage supercharged Merlins. …

… to which there was an uproar of polite dissent.


Now I think it has been conclusively documented that the DB 605 AS(M) had a similar FTH to that of the two stage Merlins. The difference in FTH between the DB 605AS(M) and the Merlin 70 is less than 10%, and the DB 605AS(M) FTH is higher than all other two-stage Merlins.

Now, we can continue the discussion on which engine produced the most hp at altitude which is dependent on a lot more factors than supercharger performance; it is an interesting topic (and perhaps even more on-topic), but I consider my initial claim about the DB supercharger to have been validated.

[gripen]

Originally posted by Viking
Forgive me if I'm repeating myself, but I can't seem to find your response to this. Surely the DB was producing more than 1495 PS at 1.7 ata at full pressure height? Or am I reading the chart wrong?

These values are taken directly from the GL/C-E data for the G-14/ASM Jäger,  both values are naturally for 1,7ata:

V-hmax-NNot am boden km/h-km 560-1740
V-hmax-NNot im VH km/h-km 680-1495-7,5

You don't seem to understand that the hydraulic coupling uses increasing amount of power when the speed of the impeller increases between 1st and 2nd FTH.

And generally I forgive quite a lot.

Originally posted by Viking

Because this particular discussion that has been going on for the last six pages was not initially about the engines’ power output but about the superchargers and the claim I made when entering this discussion:
...

Now I think it has been conclusively documented that the DB 605 AS(M) had a similar FTH to that of the two stage Merlins. The difference in FTH between the DB 605AS(M) and the Merlin 70 is less than 10%, and the DB 605AS(M) FTH is higher than all other two-stage Merlins.

Now, we can continue the discussion on which engine produced the most hp at altitude which is dependent on a lot more factors than supercharger performance; it is an interesting topic (and perhaps even more on-topic), but I consider my initial claim about the DB supercharger to have been validated.

Well, there is no point at all to compare 30min rating FTH of the DB to the 5min rating FTH of the Merlin; the Merlin 70 has 30min rating FTH (IIRC +15psi, higher if lower MAP) well over 9000m with RAM. At both FTHs (combat and military rating) the Merlin 70 does clearly higher output than the DB.

[Knegel]

Hi,

the Vmax(RAM FTH) of the merlin 70 powered Spits, on the "Spitfire Performence testing",  was @ 7700m, 8100m and 8475m, while the V-1650-3 chart at WEP show 8840m.

The RAM FTH of the GJ + FX with Start/Not (1,42ata) was in 8200m.

The V-1650-3 datas are made with around 705km/h, while the Spit and 109 speeds are good below this and therefor the RAM effect is smaler. Probably the P51 Aitframe also provide a better RAM effect, but that dont make the engine better, but confirm my thought that no engine can get seen without the airframe.

The Merlin70 in the Spitfire is very similar to the DB605ASM in the 109G, while the V-1650-3 in the P51 airframe reach better values, but with a not that long time of usage.

Greetings,

Knegel

[Charge]

"You don't seem to understand that the hydraulic coupling uses increasing amount of power when the speed of the impeller increases between 1st and 2nd FTH."

Hmm... it does not "use" more power other than the normal amount of a supercharger which needs to be turned. If the heat from the clutching cannot be wasted the engine needs to be throttled and only then power is lost. It is a different thing than that of mechanical supercharger which needs to be throttled to prevent it from over boosting in nearly every other instance than at first and second FTH. That is the case where supercharger really hogs power from the engine.

I read an article where German pilots used to go up and down just at the altitude where the Spit had its gear change point and watch them struggle with gear change.

-C+

[gripen]

Originally posted by Knegel

the Vmax(RAM FTH) of the merlin 70 powered Spits, on the "Spitfire Performence testing",  was @ 7700m, 8100m and 8475m, while the V-1650-3 chart at WEP show 8840m.

The RAM FTH of the GJ + FX with Start/Not (1,42ata) was in 8200m.

Hm... according to G-6/AS specs the DB 605AS did 1190ps at FTH with that rating (as usual tested FTH is well below spec, 9km). The Merlins you listed did around 1300hp at that altitude.

Note that in that site the AAF No. 43-12093 had a V-1650-3 with 11,5" first stage impeller while the production engine had 12" impeller. Strange thing is that the claimed power difference between the AAF No. 43-12093 and the AAF No. 43-6883 is only 22hp despite the first one runs at 60,5" and later one at 67". According to RR charts, the difference should be around 80hp.

Originally posted by Knegel

The Merlin70 in the Spitfire is very similar to the DB605ASM in the 109G, while the V-1650-3 in the P51 airframe reach better values, but with a not that long time of usage.

Well, the Merlin 70 does considerably more power at altitude and the Spitfire seem to be faster given the specs (and probably GJ+FX data as well) does not account the compressibility effects.

Originally posted by Charge

Hmm... it does not "use" more power other than the normal amount of a supercharger which needs to be turned.

Even in the ideal case the supercharger with hydraulic coupling uses more power for the given impeller RPM because the slip and the power used by the pump (in addition needed oil cooling increases drag).

In the case of the DBs (before the L version) the supercharger also produces some amount of overpressure all the way up to the 2nd FTH which also increases power consumption

Originally posted by Charge

If the heat from the clutching cannot be wasted the engine needs to be throttled and only then power is lost. It is a different thing than that of mechanical supercharger which needs to be throttled to prevent it from over boosting in nearly every other instance than at first and second FTH. That is the case where supercharger really hogs power from the engine.

Because the throttle valve is located before the impeller in the well designed engines, the main wastage is increased charge temperature due to throttling below the FTHs, there is no overpressure produced like in the DBs. It took about ten years for DB to fix this problem and the fix came too late.

[Knegel]

Hi,

as the very different FTH´s  of the different Merlin 70 Spitfires show, also the Merlin wasnt that constant.

Using only the best chart of the Merlin vs a rather bad one of a DB605ASM, while other, also rather bad Merlin70 performences are available isnt that logical.

The speed of the GJ+FX is maybe not corrected, but even if we reduce all by 15km/h, the speed is still around the same like that of the Spitfire IXc HF, depending to the used test, a bit faster or a bit less fast.

Since GJ + FX´s RAM FTH is good below what the engine should offer, it simply dont make sence to compare it only with the best tested Spitfire/Merlin, specialy not with the P51 engine and the much greater RAM effect, due to much more speed.

Of course we also can assume that most DB605ASM´s was so much below the official datas, but we also could assume that GJ+FX dont use a DB605ASM, but a ASB, where the FTH was 600m more low.

Greetings,

Knegel