Four-engined Junkers 288? <delurk>!

[Shortround6]

"We can also note that German V-12s will get better fuel mileage than Allied V-12s."

Any details on this? I would have thought the higher-octane fuel of the Allies on its own would have given the Allies lower specific fuel consumption.

Note that the DB605, in performance equivalent to a Merlin, was nearly the displacement of the Griffon.

Different engine designers emphasized different things in their designs and "fuel mileage" is a different attribute than "Performance" or hp per liter of displacement or hp per pound of engine weight. The Allies might have used the higher octane fuel for lower specific fuel consumption but they didn't. Instead they used it for higher specific power output per unit of displacement.
High cylinder compression ( a major element in low specific fuel consumption) is in direct opposition to high manifold pressure/boost ( a major element in high specific power output.)

The DB 605, while nearly the displacement of the Griffon was closer in weight to the Merlin and engine weight was much more important to the airframe designer than displacement.

 

[tomo pauk]

Part of the 'deal' for lower consumption was also the direct fuel injection, that took care that every cylinder gets exact amount of fuel, for a desired power setting. The engines with one big carburetor needed to run some of the cylinders a bit too rich, so no cylinder is run too lean.
Here are two tables. One is for the Packard Merlin V-1650-1, a sibling with early Merlin 20 series. Another is for the DB-601E. 445 l/h is about 117.5 US gal/hr, 1350 PS is 1331 HP (consumption and take off power for the DB-601E). Against 133 US gal/hr for 1300 HP for the V-1650-1.
300 l/h is 79 US gal/hr, 1040 PS is 1026 HP (maximum continuous power for the 601E); against 93 US gal/hr for 1010 HP for the V-1650-1.

 

[Shortround6]

And into somewhat more normal cruise settings the DB 601E can give 840 PS (828hp at 5100 meters/16830ft) on 240 liters per hour (63 gallons) while the Merlin on 63 gallons per hour can give 758hp at 16,000ft. A 9.3% advantage for the DB 601E

 

[Koopernic]

There was a great deal of smart technology in the DB601E/DB605 that to an extent the automotive world is still catching up on. DB605 even beats the Merlin on frontal area. However, the DB605 wasn't producing equal power outputs to the Merlin in service aircraft till about March 1944. It was then that the Water-Methanol versions started coming into service, the DB605AM. The German engine was 10%-20% behind the Merlin during the BoB which to an extent can be blamed on 100 octane fuel which allowed 12psi or 1310hp for the Merlin III and XII. The German DB601A1 engines could only provide 1100hp, there was a Db601Aa able to do 1170 but for one minute and usually only allowed on bombers for takeoff. The DB601Aa seems to have been an export version for the Swiss with a supercharger set for higher altitudes that was used as a stopgap while the DB601N was debugged and only equipped 25% of 109 and in general was no better than the DB601A1 apart from a slightly higher FTH. After the BoB after the DB's fell further and further behind. The gap closed for a very short time with Me 109F4 with the DB601E engine released to 1.42 ata and the Me 109G1 (and many argue that the Me 109F4 was better than the Spitfire V) but then the Spitifre IX was only 2 months away.

I believe the problem gets down to two things:
1 Spark plug quality. I suppose an aspect of spark plugs is their ability to cool themselves to avoid preignition, handle high temperatures and pressures without deteriorating or failing, to provide a high tension without breaking down to ensure reliable ignition in the prescience of fouling and water injection etc.
2 A Lubrication issue, one of the changes of DB601->DB605 was the replacement of the crankshaft roller bearings with more conventional journal bearings. The higher pressures in the lube system seem to have caused a 'frothing' at higher altitude that wasn't understood till much latter. I'm not sure about this as I am not using primary sources.
3 Fuel quality was an important issue but I think secondary to the above. There were strengthened pistons fitted prior to the release from 1.3 to 1.42 ata but they of themselves did not allow the release.

German pilots were at one point flying 1320hp Me 109G6's against 1700hp Spitfire IX, VIII with Merlin 66 and 70.

If the British had of been able to fit their Mk.V Spitfires with the two speed Merlin's that were assigned to try and make the inferior Hurricane compettive then the 109 would have been under the most dreadful pressure and the Fw 190 scourge blunted much earlier.

However fuel consumption at sustained high speed cruise and military power of the DB seems excellent.

 

[tomo pauk]

... However, the DB605 wasn't producing equal power outputs to the Merlin in service aircraft till about March 1944. It was then that the Water-Methanol versions started coming into service, the DB605AM.

The DB-605AM was been unable to solve the main shortcoming of the DB-605 line, namely the power above 7 km against turboed or two-stage engines fielded by W.Allies. That problem was addressed with the 605AS/ASM, but by then the air war in the ETO was decided.

The German engine was 10%-20% behind the Merlin during the BoB which to an extent can be blamed on 100 octane fuel which allowed 12psi or 1310hp for the Merlin III and XII.

Blamed?

The German DB601A1 engines could only provide 1100hp, there was a Db601Aa able to do 1170 but for one minute and usually only allowed on bombers for takeoff. The DB601Aa seems to have been an export version for the Swiss with a supercharger set for higher altitudes that was used as a stopgap while the DB601N was debugged and only equipped 25% of 109 and in general was no better than the DB601A1 apart from a slightly higher FTH.

The DB-601Aa was the export version of the 601A ('a' is for 'ausland' - foreign country), the supercharger was of lower capacity - good for lower alt, a bit worse for high altitudes. The FTH was at 3700 m, power there was a bit bigger than for the 601A - 1100 PS vs. 1020 PS. The take off power (1 minute duration) was 1175 PS, vs. 1100. We are informed n this forum that many 601Aa engines wound up in Jabo versions of Bf-109 and 110, exactly because of that extra power under 4 km.
The DB-601A have had two different superchargers, to add to the 601Aa. Earlier version gave 1010-1020 PS at 4 km, later version was doing 1020 PS at 4.5 km. Take off power was equal.
I doubt that DB-601N equipped more than a token of Bf-109 produced.

...
German pilots were at one point flying 1320hp Me 109G6's against 1700hp Spitfire IX, VIII with Merlin 66 and 70.

The Me-109G6 was also a much smaller A/C, with less guns ammo weight, and probably less radiators' bulk under wings - should even out a bit the speed comparison? The rate of climb was pretty much in Spitfire's favor, especially at high altitudes; ditto for high speed there.

If the British had of been able to fit their Mk.V Spitfires with the two speed Merlin's that were assigned to try and make the inferior Hurricane compettive then the 109 would have been under the most dreadful pressure and the Fw 190 scourge blunted much earlier.

Maybe splitting some hairs - there were no problems to install 2-speed Merlin in Spitfire V (it was installed in a handful of Spit IIs, and Spit V received two-speed, two stage Merlins, and also 1-stage 2-speed Griffons), but huge demand for those, mostly for multi-engined bombers, but also for Hurricane, made that task pretty much impossible.

 

[Koopernic]

The DB-605AM was been unable to solve the main shortcoming of the DB-605 line, namely the power above 7 km against turboed or two-stage engines fielded by W.Allies. That problem was addressed with the 605AS/ASM, but by then the air war in the ETO was decided.

Blamed?


The DB-601Aa was the export version of the 601A ('a' is for 'ausland' - foreign country), the supercharger was of lower capacity - good for lower alt, a bit worse for high altitudes. The FTH was at 3700 m, power there was a bit bigger than for the 601A - 1100 PS vs. 1020 PS. The take off power (1 minute duration) was 1175 PS, vs. 1100. We are informed n this forum that many 601Aa engines wound up in Jabo versions of Bf-109 and 110, exactly because of that extra power under 4 km.
The DB-601A have had two different superchargers, to add to the 601Aa. Earlier version gave 1010-1020 PS at 4 km, later version was doing 1020 PS at 4.5 km. Take off power was equal.
I doubt that DB-601N equipped more than a token of Bf-109 produced.

The Me-109G6 was also a much smaller A/C, with less guns ammo weight, and probably less radiators' bulk under wings - should even out a bit the speed comparison? The rate of climb was pretty much in Spitfire's favor, especially at high altitudes; ditto for high speed there.

Maybe splitting some hairs - there were no problems to install 2-speed Merlin in Spitfire V (it was installed in a handful of Spit IIs, and Spit V received two-speed, two stage Merlins, and also 1-stage 2-speed Griffons), but huge demand for those, mostly for multi-engined bombers, but also for Hurricane, made that task pretty much impossible.

Thanks for the "a = ausland" info. The Aa seems a tweek rather than an improvement. Playing around with the supercharger settings and short term power periods (WEP, takeoff) ie 1 minute of slightly greater emergency power instead of 5 minutes.

I wouldn't over emphasize the altitude problem. There was no significant 'high altitude problem' for either the Me 109 or the Fw 190A since 95% of their missions were below 6500m which is at or slightly above the full throttle height at which there is typically a rapid decline in speed and climb rate. From late 1943 and certainly 1944 even the USAAF seldom operated above this altitude and you will note that the moderate flying MF (66 series) and 5 series Packard Merlins came to dominate in both the Spitfire and Mustang. The enlarged supercharger of the DB605AS and its subsequent variants (DB605DM,DC/DB) certainly increased the full throttle height. It could have been better but it was enough.

There was certainly a power problem for the Me 109 and that was closed of as I say around March 1944 when engines in the 1700 hp class came in service eventually reaching 2000hp. The two engines, as you know are the:
DB605AM which was essentially a refined DB605A with Water Methanol added, it required C3 fuel AFAIKT, at least initially.
DB605ASM which had an enlarged supercharger as well as the MW50.
Both had the same power but the ASM at higher altitude.

What matters most is the power since the FTH of the DB605A and BMW801 is reasonable to begin with though the higher FTH is welcome and useful.

It's amazing that the Me 109 was able to function with this huge power gap, if the situation had of been reversed such that the Spitfire had 20% less power than the 109 I doubt the Spitfire would have done as well at all. This situation never arose. I think you'll find that the Spitfire IX and Me 109G6 have essentially the same weights.

There was a two stage DB605L, it worked rather well and there is a speed graph on the ww2 performance testing site but for an early version without the 4 blade prop it needed to cut into the thinner air.

There were nearly 1000 Me 109G with GM-1 nitrous oxide produced, they had fantastic performance when using mixture. The weight consumed by a few hundred pounds of turbo or intercooler can be used instead to carry the same weight in cryogenic nitrous and this was seen as the expedient solution but one needs the power rating to begin with.

 

[tomo pauk]

Thanks for the "a = ausland" info. The Aa seems a tweek rather than an improvement. Playing around with the supercharger settings and short term power periods (WEP, takeoff) ie 1 minute of slightly greater emergency power instead of 5 minutes.

I guess we might call the 601Aa a 'tweak'. The power of 1100 PS at 3.7 km was 5 minute rating, as it was 1020 at 4 or 4.5 km for the 601A.

I wouldn't over emphasize the altitude problem. There was no significant 'high altitude problem' for either the Me 109 or the Fw 190A since 95% of their missions were below 6500m which is at or slightly above the full throttle height at which there is typically a rapid decline in speed and climb rate. From late 1943 and certainly 1944 even the USAAF seldom operated above this altitude and you will note that the moderate flying MF (66 series) and 5 series Packard Merlins came to dominate in both the Spitfire and Mustang.

I'm not sure that there were 5 series Packard Merlins in operative use - it was either V-1650-3 or V-1650-7 in use in P-51s. As you've noted - the problem was not around before mid/late 1943, but then it vehemently backfired in LW's face.

The enlarged supercharger of the DB605AS and its subsequent variants (DB605DM,DC/DB) certainly increased the full throttle height. It could have been better but it was enough.

Indeed, the hi-alt performance was greatly improved with a big S/C, but it was too late to matter.

There was certainly a power problem for the Me 109 and that was closed of as I say around March 1944 when engines in the 1700 hp class came in service eventually reaching 2000hp. The two engines, as you know are the:
DB605AM which was essentially a refined DB605A with Water Methanol added, it required C3 fuel AFAIKT, at least initially.
DB605ASM which had an enlarged supercharger as well as the MW50.
Both had the same power but the ASM at higher altitude.

It took the DB-605D sub-variant, when using both C3 and MW-50 to attain 2 ata, ie. 2000 PS for take off. And that means 1945. I will not enter the quagmire of debating how regularly the 605D was operating on 2 ata

What matters most is the power since the FTH of the DB605A and BMW801 is reasonable to begin with though the higher FTH is welcome and useful.

The rated altitude (or FTH) also matters, if the enemy is throwing in it's A/C on high altitude. We can compare eg. DB-605A and 605AS, and then compare those with what Allies were fielding from 1942/43 on.

It's amazing that the Me 109 was able to function with this huge power gap, if the situation had of been reversed such that the Spitfire had 20% less power than the 109 I doubt the Spitfire would have done as well at all. This situation never arose. I think you'll find that the Spitfire IX and Me 109G6 have essentially the same weights.

It is not that amazing. The Bf-109 was considerably smaller A/C, and size matters. Once the Spitfire received two-stage engine, that, combined with generous wing area, contributed to the plane's competitivness at higher altitudes.

There was a two stage DB605L, it worked rather well and there is a speed graph on the ww2 performance testing site but for an early version without the 4 blade prop it needed to cut into the thinner air.

Indeed, the DB-605L shows the advantages of two-stage compressors - it was some 300 PS advantage over the DB-605D at 10 km.

There were nearly 1000 Me 109G with GM-1 nitrous oxide produced, they had fantastic performance when using mixture. The weight consumed by a few hundred pounds of turbo or intercooler can be used instead to carry the same weight in cryogenic nitrous and this was seen as the expedient solution but one needs the power rating to begin with.

The GM-1 system was offering advantages, but also the disadvantages. Like need to carry it at suitable altitude, while not taking advantage of it, but lugging it until the altitude is reached. A part of the dead weight is still aboard, even after use. The DB-605L did not used intercooler (and no intercooler weighted hundred of pounds), but MW-50 instead.

 

[Koopernic]

I don't believe there was ever a time when the Spitfire didn't have a 10% power advantage, I would say throughout preponderance of the war the Spitfire had generally a 20% power advantage over the Me 109.

Battle of Britain
Spitfire I Merlin III with 100 octane, power = 1030hp or 1310hp 9,000 ft (2,700 m) for 5 minutes using 12psi boost.
Spitfire II with Merlin XII power = 1150hp, this engine was able to use constant 12psi boost (1310hp+) and was free of the 5 minute restriction. Also used in BoB.

Me 109E3 with DB601A1 = 990ps, 1100 for 5 minutes. (note it's an A1 not just an A)
Me 109E4 with DB601Aa = 990ps, 1045 for 5 minutes, 1170ps for 1 minute. Doubtful if the 1 minute rating was of use.

Figures for the German engine are in metric horsepower so deduct 1.6%. In detail:

The DB 601A-1 with the old type supercharger, 1.30 ata for five min and 990 PS, and 1.40 ata for 1 min and 1100 PS. Rated altitude being 4000m.

The DB 601A-1 with the new type supercharger, 1.30 ata for five min and 990 PS, and 1.40 ata for 1 min and 1100 PS. Rated altitude being 4500m.

The DB 601N, 1.35 ata for five min and 1175 PS. Rated altitude being 4800m. (there was a second type of 601N, mounted in one in the 109F had better supercharger and IIRC 5200 m rated altitude) and 1260hp, which latter was also cleared for 1.42 ata along with the DB601E presumably giving Me 109F1/F2 the same performance as Me 109F4.


The DB 601Aa with the old type supercharger, 1.35 ata for five min and 1045 PS, and 1.45 ata for 1 min and 1175 PS. Rated altitude being 3700m (altitude output was otherwise very much like the DB 601A-1 / old s/c, though it is a question whether the new s/c was fitted to the Aa as well.)


In regards to your statement that the Spitfires "generous wing area" being an advantage; it may have been a disadvantage if the tables had of been turned in power and their size extracts a toll in drag. The high coefficients of lift the Me 109's wing can generate at high angles of attack due to its slats come at the disadvantage of even higher drag which leads to loss of height, speed and energy but only when pulling high G, in level flight the small wing is advantageous. With adequate power that can be overcome. I won't claim that with such the 109 could turn inside a Spitfire, though it would help, but what it would do is help greatly turn rates, acceleration, climb, speed, altitude and the 'energy' of a fighter; its ability to position itself favorably.

It should be noted that the DB601 didn't need a high pressure supercharging so much since it's bolt-less head design offered much higher swept volume, greater valve area while the higher compression ratio improved efficiency and power. Really one needs to look at a power versus altitude chart with the DB601 over layed to the Merlin since the altitude curves are radically different. Really, we don't know much about use of GM-1 operationally.

I'm not pushing the 1.98ATA band wagon apart from saying it was certainly used in the closing months of the war in 1945. An Me with the DB605L was tested at 1.75ATA but would have been interesting at 1.98ATA given the higher altitude, if it were possible that is given the higher temperatures resulting from higher pressure ratios. The 1800/1850 hp the DB601DB/DC achieved eliminated the gap to the Merlin except in the event that 100/150 fuel was available to the Merlin.

But, getting back on topic, it seems to me that 4 conventional engines either DB605 or Jumo 211, fitted to the Ju 288 or Fw 191 would have produced a rather excellent fast bomber able to rapidly take advantage of advances in these fighter engines development. No one tried a medium weight bomber with 4 engines. The only loss would be steep diving bombing, not really needed post 1942 with computing bomb sights.

 

[Shortround6]

Seems to be turning into another Sptifire vs 109 thread. Or Merlin vs DB 60? thread.

The Merlin XII was not free of the 5 min. restriction. What it could do was climb (1 hour) at 2850rpm and 9lbs boost instead of the Merlin III's climb rating of 2600rpm and 6 1/4lbs. Max cruise went from 2600rpm/4 1/2lb to 2650/7lbs.
Early testing and early service use used a 9lb boost limit at 3000rpm with 12lbs available, like the Merlin III, by operating the boost control cut-out.

It should be noted that the DB601 didn't need a high pressure supercharging since it's bolt-less head design offered much higher swept volume, greater valve area while the higher compression ratio improved efficiency and power.

While this is true (mostly) it is also true that the DB601 could not use high pressure supercharging with it's service fuel without wrecking the engine. 12lb boost being roughly 1.8 ata and 6lb boost being roughly 1.4 ata. High compression does improve efficiency but it actually limits peak power in a supercharged engine because a higher compression ratio limits the amount of boost that can be used with a given fuel.
Let us assume for arguments sake, that the British had a choice when they got 100 octane fuel of either raising the compression ratio or raising the boost limit. They did raise the boost limit and at 12lbs (everything being equal, which it often is not) the engine is consuming about 29% more air than at 6lbs boost. tracks the power change fairly well. Perhaps they could have kept the 6lb boost and fitted high compression pistons to boost the compression to 8 or 8.2 like the DB 601N. The trouble with this is approach is that while it increases the fuel economy by about 10% it only increases the power by about 11% (for an 8:1 compression ratio) yet it increases the peak pressure in the cylinder by around 35%. Granted using more boost will increase the peak pressure in the cylinder too, but obviously the high boost approach gives more power for the same fuel grade(Allison used a higher compression ratio than the Merlin and lagged a bit in power on a given fuel but since the Allison was about 5% bigger in displacement, that covered about 1/2 the power difference and a 5% difference in power doesn't amount to much in the real world unless you are using stop watches).

 

[tomo pauk]

I don't believe there was ever a time when the Spitfire didn't have a 10% power advantage, I would say throughout preponderance of the war the Spitfire had generally a 20% power advantage over the Me 109.

Agreed with Shotround6 - Spit vs. 109 deserves a thread on it's own, if not the whole sub-forum

Battle of Britain
Spitfire I Merlin III with 100 octane, power = 1030hp or 1310hp 9,000 ft (2,700 m) for 5 minutes using 12psi boost.
Spitfire II with Merlin XII power = 1150hp, this engine was able to use constant 12psi boost (1310hp+) and was free of the 5 minute restriction. Also used in BoB.

Covered by SR6. I'll add that we also need to state the rated height (or FTH) of contemporary engines - and it was above 16000 ft where Merlin III was doing it's 1030 HP (30 minutes limit?). Merlin XII even managed a bit a higher FTH, the power was some 10% greater above 10000 ft than Merlin III. The DB-601 was with FTH at 4 or 4.5 km (~13120 or 14700 ft), depending whether a new or old supercharger was installed.

Me 109E3 with DB601A1 = 990ps, 1100 for 5 minutes. (note it's an A1 not just an A)
Me 109E4 with DB601Aa = 990ps, 1045 for 5 minutes, 1170ps for 1 minute. Doubtful if the 1 minute rating was of use.
Figures for the German engine are in metric horsepower so deduct 1.6%. In detail:
The DB 601A-1 with the old type supercharger, 1.30 ata for five min and 990 PS, and 1.40 ata for 1 min and 1100 PS. Rated altitude being 4000m.
The DB 601A-1 with the new type supercharger, 1.30 ata for five min and 990 PS, and 1.40 ata for 1 min and 1100 PS. Rated altitude being 4500m.

Will you please be so kind to double-check the bolded part, or to give some source that can confirm that? The 1 minute rating was for take off, and as such is/was stated in contemporary documents.

The DB 601N, 1.35 ata for five min and 1175 PS. Rated altitude being 4800m. (there was a second type of 601N, mounted in one in the 109F had better supercharger and IIRC 5200 m rated altitude) and 1260hp, which latter was also cleared for 1.42 ata along with the DB601E presumably giving Me 109F1/F2 the same performance as Me 109F4.

The DB-601N is one of most mysterious German engines. This excerpts from the manual for the Bf-109F1/F2 states that, by my currently best ( ) translation, that 'regular' Steig- Kampfleistung was using 1.3 ata and 2400 rpm, and 1.42 and 2600 rpm was used for Start- Notleistung, that is limited to 3 minutes. Some engines were rated just for 1.25 ata for Kampfleistung, and 1.35 ata for Startleistung, and that means power down for 4.5% and 6% respectively. Hopefully someone with a better grasp of German language (and the awkward of the neo-gothic) will help us here
The German documents do state that a new type of supercharger is in use in the engines for the Bf-109F - that change allowed for 1.42 ata at same 4800 m? The Bf-109F topped in high speed at 5200 m, ie. the engine is using max possible amount of ram air.
A change from 1.30 ata (=1175 PS) to 1.42 ata is indeed making some ~1250 PS (6%)? A further thing in the DB-601N (in Bf-109F only?) was the clearance for 2800 rpm, allowed above FTH. That gave another healthy boost of power above 5 km - speed increse of 10 to 15 km/h at FTH.
(please open the pics separately; chart for the 601N kindly provided by krieghund; 'Ausgezogene' - full line; 'Gestrichelt' - dashed line)

The DB 601Aa with the old type supercharger, 1.35 ata for five min and 1045 PS, and 1.45 ata for 1 min and 1175 PS. Rated altitude being 3700m (altitude output was otherwise very much like the DB 601A-1 / old s/c, though it is a question whether the new s/c was fitted to the Aa as well.)

The power chart for the DB-601Aa, again kindly provided by krieghund. My guess is that the new S/C was fitted to the 601Aa - it made more power at all altitudes than the 601A with old S/C.

It should be noted that the DB601 didn't need a high pressure supercharging so much since it's bolt-less head design offered much higher swept volume, greater valve area while the higher compression ratio improved efficiency and power. Really one needs to look at a power versus altitude chart with the DB601 over layed to the Merlin since the altitude curves are radically different. Really, we don't know much about use of GM-1 operationally.

I'm not sure that bolt-less head design was to be credited for those benefits. Many countries were into big V-12s, much before DB-60? appeared. High compression ratio is a trade off.

I'm not pushing the 1.98ATA band wagon apart from saying it was certainly used in the closing months of the war in 1945. An Me with the DB605L was tested at 1.75ATA but would have been interesting at 1.98ATA given the higher altitude, if it were possible that is given the higher temperatures resulting from higher pressure ratios. The 1800/1850 hp the DB601DB/DC achieved eliminated the gap to the Merlin except in the event that 100/150 fuel was available to the Merlin.

The DB-605L, in case it was to be running on ~2 ata, would do so at lower altitudes than it was the case for 1.75 ata. The DB-605DC was making 1.98 ata at 4.9 km, but 'only' 1.8 ata at 6 km (no ram).

 

[wiking85]

But, getting back on topic, it seems to me that 4 conventional engines either DB605 or Jumo 211, fitted to the Ju 288 or Fw 191 would have produced a rather excellent fast bomber able to rapidly take advantage of advances in these fighter engines development. No one tried a medium weight bomber with 4 engines. The only loss would be steep diving bombing, not really needed post 1942 with computing bomb sights.

Why adapt those airframes when you could just do the four Jumo 211s or DB601/5s on a He177B? It would be ready by 1942 unlike either of the above. In fact the Bomber B adaptations would only be ready for flight testing in 1942 and wouldn't be production ready until late 1943 and operational until 1944. So that's a moot point. Much better just to go with the He177B with four DB601/5s or Jumos.

There was this later on though:
Focke-Wulf Fw 191 Luft '46 Prototypes Entry

One final attempt was made to save the Fw 191 program, this time the Fw 191C was proposed as a four engined aircraft, using either the 1340 horsepower Jumo 211F, the 1300 horsepower DB 601E, the 1475 horsepower DB 605A or the 1475 horsepower DB 628 engines. Also, the cabin would be unpressurized and the guns manually operated; a rear step in the bottom of the deepened fuselage being provided for the gunner.

 

[Koopernic]

Shortround6,

I agree fully with your well presented post. One needs to consider that Daimler Benz was probably driven by a few imperatives different to Rolls Royce. One was the severe limitation Germany had in producing 100 octane fuel in quantity and the other the need to keep fuel economy high for its main customers the Me 109G and Me 110G both of which had little hope of improvements in internal fuel volume. To me the 'large capacity' using a bolt-less head seems more appropriate.

What I find interesting is if we look at the situation at the close of 1944:

DB 605 DB/DC performance:
With C3 fuel 1800hp at sea level
With B4 +MW50 1850hp at sea level
Full throttle height is about 6000m.
With C3+MW50 power is 2000hp at sea level and full throttle height about 4900 meters.

The Merlin 66 with 110/150PN fuel at 25psig is producing
1860hp at sea level
2000hp at rated altitude.

I would regard 150PN fuel equal to the 96/130 C3 fuel +MW50 the DB605 used.

The Packard Merlin V-1650-9 with 150PN fuel plus ADI (water ethanol injection) could manage about 2200-2300hp but I would imagine the DB605 could manage this as well i given the fuel, there was supposedly a German 140PN fuel being developed and DB605 was benching 2.3 ata. (I have no proof only other posters claims) and of course there was a DB605L with two stage supercharger, for which only 1.75 ata rating data is usually provided, which no doubt could have generated the pressures required. The sloweness of getting two stage supechargers in service is probably explained by the Germans developing highly sophisticated types such as the DB605 based DB628 that proved to hard to put into production with the available airframes.

The point I wish to make is this. The DB605 engine and the Merlin ended up with the same power levels 1944/45, however for much of the war the DB was severely lagging the Merlin. Inferior Fuel explains some of this but it seems not all.

I do think the narrative in which the Spitfire is superior because it "out turns" the Me 109 would be different, even reversed, if these aircraft were equally matched in power.

Despite that, the evolution of the Jumo 211 shows a different possibility. This engine was closer to the configuration of the Merlin, Griffon, Allison in using a lower compression ratio and higher boost and perhaps beat even the Merlin 61 into service with an inter-cooler in 1942 when the Jumo 211J came into service on Ju 88A4.

It might even have made a better fighter engine in 1942 given the power of 1420hp on only B4 fuel (1500hp for the Jumo 211P on only B4 though it was not produced in numbers). It's curious to imagine this inter-cooled engine receiving two stage supercharger given the inter-cooler and two speed gearbox is already present and perhaps C3 fuel.

Something went wrong between 1942 to 1944 with German fighter engine performance particularly the DB, some item of technology was missing.

(Tomo, thanks for the data, one day I mean to overlay DB and RR power v altitude on dated charts. The bolt-less integral head design seems authentically DB technology, remeber Rolls Royce messed up the head design of the Merlin originally. I know that Hispano Suiza used a similar idea on the HS-12 series and this technology ended up in Soviet production in the form of the Mikulin engines but the HS-12 series was way down on DB601 performance, it was this rather than airframe issues that nobbled the Morane-Saulnier M.S.406 though the Dewoitine D.520 had hideous handling with a viscous completely unannounced stall)

 

[Aozora]

Shortround6,

I agree fully with your well presented post. One needs to consider that Daimler Benz was probably driven by a few imperatives different to Rolls Royce. One was the severe limitation Germany had in producing 100 octane fuel in quantity and the other the need to keep fuel economy high for its main customers the Me 109G and Me 110G both of which had little hope of improvements in internal fuel volume. To me the 'large capacity' using a bolt-less head seems more appropriate.

What I find interesting is if we look at the situation at the close of 1944:

DB 605 DB/DC performance:
With C3 fuel 1800hp at sea level
With B4 +MW50 1850hp at sea level
Full throttle height is about 6000m.
With C3+MW50 power is 2000hp at sea level and full throttle height about 4900 meters.

The Merlin 66 with 110/150PN fuel at 25psig is producing
1860hp at sea level
2000hp at rated altitude.

I would regard 150PN fuel equal to the 96/130 C3 fuel +MW50 the DB605 used.

While the Allies were using 100/150 grade fuel en masse from June 1944 the DB 605DC only ever used C3 + MW 50 on an experimental basis in one gruppe, II./JG 11, late 1944-early 1945, after which the use of 1.98 ata + MW 50 was banned until problems with the DC were solved (II./JG 11 was disbanded soon after testing stopped); there is no viable evidence that this combination was used operationally by 109G-10s or K-4s by wars end - best of intentions aside,and a single document stating that a small number western based Jagdgruppen were supposed to start using C3 + MW 50 1.98 ata from 27 March 1945 notwithstanding. AFAIK the BMW 801 engined Fw 190s had priority when it came to supply of C3 fuel.

 

[Koopernic]

The DB605DB/DC was cleared for 1.8 atmosphere's boost using B4(87 octane) +MW50 and achieved 1850hp at sea level, about the same incidentally as the Merlin 66 using 150PN fuel at sea level whose 2000hp MF gear WEP rating was only at about 2000ft and somewhat less at sea level. That's quite an achievement of the DB considering the low grade of the fuel and no doubt of enormous value in terms of supply logistics.

All of the engines certainly operated securely at 1.75 ata and up to 1800hp.

1.98 ata was clearly worked at Daimler Benz, was tried at the Luftwaffe's Rechlin Center, was tried at a Gruppen level, withdrawn in some cases reset down to 1.9 ata and then rescheduled to Gruppen that had C3 issued. It's highly plausible, I would say likely, that the engine was suitable for use this way given there was still nearly two months of war left and that was the intention.

I was clearly a ignition/detonation issue as the use of retarded ignition on the 1.9 ata units shows. In other words the use of 104/150PN or some other better fuel would have allowed the DB605D"x" to produce the same power as the Merlin. Given the allied oil bombing campaign and the damage it caused to the synthetic fuel industry its unlikely such a fuel could be manufactured. There was a great deal of research in this area including production of triptane (lean PN rating 160) use of analine etc. The solution seems to have been the use of the Beru F280 E43 spark plug though there may have been an attempt to tweak C3 fuel formulation, the characteristics of this fuel being rather difficult to manage at this time.

But I digress, the point is the difference between the DB605 on 1.8 ata with B4+MW50 at 1850hp versus the Merlin at 2000hp on 150PN is only 7.5% and then only at the Merlins 2000ft MF gear peak.

This gap is minimal and the smallest the gap ever was since the BoB.

 

[Shortround6]

The Allison, Merlin, DB 601 and Jumo 211 all started out fairly close to each other in power, weight and physical size.

The Hispano (and Russian M100 series) were roughly of a size (outside dimensions) but down on power even if a bit lighter.

It is power to weight that was much more important to aircraft performance than displacement. The next thing is that once a company or country is tooled up and producing an engine at hundreds per month (or thousands) it is more than just a bit difficult to switch horses in midstream. Unless the engine is an unmitigated disaster, every attempt will be made to extend it's life with a series of modifications rather than start over and loose the tooling/production knowledge.

Strangely enough the engines didn't finish that far apart in weight either. The Allison and Merlin both gained two stage superchargers that added several hundred pounds but then the DB 605 gained around 100 kg over the early 601s and the Jumo 211 porked up a bit even before trying for the 213 version.
Different materials and manufacturing techniques allowed more power with the same or better engine life in many later models compared to the late 1930s versions of the engines. The trick is rarely making large power for a few minutes, it is making large power for extended periods of time and still having a serviceable engine. For instance the Allison went through 4 different crankshaft versions ( at least) with the first 3 being identical to the eye in dimensions and weight. They started with a "plain" version, went to a shot peened model that could handle about 28% higher stress loads and then went to a nitrited model that could handle 33% more stress than the shot peened crank (and 71% more than the plain crank). They finished with a new crank with 26-27lb more counterweights but using the same size bearings/journals that can be dropped into early crankcases.
New casting techniques allowed for stronger engineblocks/crankcases that weighed just a bit less and had a lower scrap rate.
The Merlin and German engines are not quite as well documented as the Allison in regards to these internal modifications that allow the engine to survive at the higher powers.

 

[wuzak]

I do think the narrative in which the Spitfire is superior because it "out turns" the Me 109 would be different, even reversed, if these aircraft were equally matched in power.

The Spitfire out turns the Bf 109 whether it has more power, equal power, or less power. It is a function of the bigger wing.

Increased power would improve the Bf 109's straightline speed, climb and acceleration.

The small wing is part of the reason why the Bf 109 could be so fast on low power.

The bolt-less integral head design seems authentically DB technology, remeber Rolls Royce messed up the head design of the Merlin originally. I know that Hispano Suiza used a similar idea on the HS-12 series and this technology ended up in Soviet production in the form of the Mikulin engines but the HS-12 series was way down on DB601 performance, it was this rather than airframe issues that nobbled the Morane-Saulnier M.S.406 though the Dewoitine D.520 had hideous handling with a viscous completely unannounced stall)

The "ramp head" design was based on that which was used in their latest car engine. It showed well in single cylinder testing, but that did not translate to the full V-12.

 

[wuzak]

The DB605DB/DC was cleared for 1.8 atmosphere's boost using B4(87 octane) +MW50 and achieved 1850hp at sea level, about the same incidentally as the Merlin 66 using 150PN fuel at sea level whose 2000hp MF gear WEP rating was only at about 2000ft and somewhat less at sea level. That's quite an achievement of the DB considering the low grade of the fuel and no doubt of enormous value in terms of supply logistics.

According to Lumsden, Merlin 66 with PN100/150:
2000hp, 3000rpm, +25psi @ 5,250ft
1860hp, 3000rpm, +25psi @ 11,000ft

Merlin 66 with PN100/130:
1750hp, 3000rpm, +18psi @ 5,250ft
1625hp, 3000rpm, +19psi @ 12,500ft

 

[wiking85]

Given the discussion on the efficacy of the DB601/5 vs. the Merlin, and seeing how the Merlin provided to be a successful bomber engine, how would the DB 600 series have done as a bomber engine for a four engine bomber?

 

[Shortround6]

It depends on which engine and when and what you want the bomber to do.

Comparing a 20 series Merlin and a DB 605 without big supercharger or power boosting systems the DB gives perhaps 10% better fuel economy, which for a plane with 2500-3000 US gallons of fuel means either longer range/a bit higher cruise speed/ or a 1500-1800lb greater bomb load. Pick one. Of course a Merlin 20 series is about 145lbs lighter per engine so the difference is more like 630-930lbs.

The engines don't match power exactly but you can forget the over 1500hp power ratings of the later DB 605s for bomber use. Of course you can pretty much forget the over 18lb boost ratings for the 20 series too for 4 engine bomber use.
4 engine bombers often took 20-30 minutes to take-off and climb to operating altitudes. the 30-60min rating is much more important than the 1-5minute sprint rating. Take-off rating is important too and it should be a normal take-off rating for most purposes, not WEP or water injection ratings except for special missions. Increasing the maintenance man hours per mission is not a goal when in the planning stages. Once squadrons are equipped and operational you sometimes have to do what you have to do but planning ahead of time to use WEP/water injection take-offs during most of WW II wasn't a good idea. ( they got better at it as the war went on and post war commercial planes used it).

There doesn't seem to a be any reason why the DB 600 series wouldn't have worked on a 4 engine bomber. Both engines had advantages and disadvantages and the differences changed (either increased or decreased) depending on exact model available and fuel available.

The bomber has to match the engines to some extent, sticking two stage Merlins on the Short Sterling wasn't going to get you a high performance/high altitude bomber because of the fuselage (huge) and wing, for example.

 

[wiking85]

How about the DB605A of 1942 on the He177B? Despite being restricted in RPMs until 1943, it was about 200kg lighter as an engine than the DB603 the He177B was tested with in 1943.