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

[gripen]

Originally posted by Knegel

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.

I have used the best tested AS data I'm aware (it's from engine manufactiurer so the engine probably had been seen as OK).  The Mustang data I choosed were just the first ones with certain engines when browsing the page down in the site. The others have choosed the Spitfires to look.

Note that even the lowest FTH Spitfire (BS310) you listed, did over +9psi at 33k ie better than the specification for the AS.

Originally posted by Knegel

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.

The AS prototype did 8,3km at high speed with 1,3ata/2600rpm (the results were seen as good by Mtt staff), other one of the FAF G-6/AS did 8250m at the same setting.

Given the date 7.6.1944 and the designation of the engine (DB 605 A-S), it's certainly not an ASB but probably one of the first ASM engined planes in the engine manufacturers tests.

[Knegel]

Hi,

i have different datas for the G14AS and G6AS.

One is from a G14AS/G14-U2/K4 comparison and give
combat climb, 645km/h, 1140PS in 8800m
Sondernot, 680km/h, 1495PS in 7500m, what is 500m above GJ+FX.

Another is a G6AS, with a ASB engine(no MW50),  
combat/climb, 648km/h, 1135PS in 8800m
Start/Not,  660km/h, 1190PS in 9000m

btw, the DB605D had 1140PS in 9000m, combat climb.

A good Merlin70 seems to have a bit more power than a good 605ASM above 8000m, while the 605ASM is better below this, with a more smooth curve.

Since the Spitfire speeds in all three tests got corrected to around 3200kg, it would be interesting what weight the 109s had, cause 200kg below take off weight is already 2/3 of the 109´s fuel and 200kg in 10000m is a lot.
I realy doubt that any of this Spitfires did reach 1300HP at FTH, with this smal weight they should be faster then.  
The P51B probably did provide a better RAM effect, resulting in more power and a higher speed and a even better RAM effect and higher power.


Greetings,

Knegel

[gripen]

Originally posted by Knegel

i have different datas for the G14AS and G6AS.

One is from a G14AS/G14-U2/K4 comparison and give
combat climb, 645km/h, 1140PS in 8800m
Sondernot, 680km/h, 1495PS in 7500m, what is 500m above GJ+FX.

These sound very much like spec calculations from A/IV/...  and GL/C-E series.

Originally posted by Knegel

Another is a G6AS, with a ASB engine(no MW50),  
combat/climb, 648km/h, 1135PS in 8800m
Start/Not,  660km/h, 1190PS in 9000m

I have not ever heard about  the G6/AS with ASB engine, AFAIK the G-6 was about out of production when the ASB engines became available. What's the source?

The values are the same as calculated values in the GL/C-E sheet for the standard G-6/AS with 605AS engine.

Originally posted by Knegel

btw, the DB605D had 1140PS in 9000m, combat climb.

The DB 605D did roughly same high altitude performance as the 605 ASM.

Originally posted by Knegel

A good Merlin70 seems to have a bit more power than a good 605ASM above 8000m, while the 605ASM is better below this, with a more smooth curve.

That depends how you define "a bit". IMHO 100-200hp at high altitude is quite a lot.

The Merlin 70 was cleared for the +25lbs use if low altitude performance was needed.

Originally posted by Knegel

I realy doubt that any of this Spitfires did reach 1300HP at FTH, with this smal weight they should be faster then.

The static rating of the Merlin 70 for 2nd FTH at +18psi is 1475hp at 22250ft.

[Viking]

Originally posted by gripen
And generally I forgive quite a lot.

Well, don't bother. You're obviously arguing to "win", not to reason.

[Angus]

More of the climb, - Viking.
(And TY for the input)
Climb seems to be measured  at MIL in both camps. But the data is confusing. 109G in 1944 is still using 6 minutes to 20K, Rall also mentions the same figure. A Spitty in the same time will use some rough 5 with more weight

[Knegel]

Hi Angus,

climb is made with combat/climb and this is smaler in the DB605AS(M) than in the DB605A, while the later 109G´s had 40- 80kg more weight.
Unfortunately i never saw a climb chart of a 109G with Sondernot.

Hi Gripen,

its from a chart from the "General Luftzeugmeister/C-E2 13 Aug. and 01. Nov1944.
Since this plane had the typical low ground level performence of the AS and no MW50, i only can guess that this is a writing error and should be the AS, not ASB.
Also the high rated altitude is above that of the ASB.

The DB605D had 1565PS in 7500m and 1140PS in 9000m

Thats 70PS more Sondernot in FTH and a 200m higher FTH for climb/combat.

I never saw a powercurve of the DB605D, but its not much of a guess that the power with Start/Not would have been above 1140PS in 9000m, therefor i would say the DB605D had good advantages over the DB604AS(M) in high alt and was at least even to the Merlin70.
Also the service ceiling of the DB605D powered 109´s was 500m above the AS and only 600m below that of the good HF Spits and 300m(Spits with 3200kg), while one of the three tested HF Spits had the same service ceiling.

I realy cant see a huge advantage of the RR engines at all, specialy not, if i take into account that the DB605D´s and ASM´s  had a rather constant range of power, from sea level up to service ceiling, not to talk about GM1.

Greetings,

Knegel

[gripen]

Originally posted by Knegel

its from a chart from the "General Luftzeugmeister/C-E2 13 Aug. and 01. Nov1944.
Since this plane had the typical low ground level performence of the AS and no MW50, i only can guess that this is a writing error and should be the AS, not ASB.
Also the high rated altitude is above that of the ASB.

The lower 2nd FTH ASB if compared to the ASM is caused by higher MAP (1,8ata). These are mostly the same engines, the ASB is just a later version with higher CR etc. The output difference is very small.

Originally posted by Knegel

The DB605D had 1565PS in 7500m and 1140PS in 9000m

Thats 70PS more Sondernot in FTH and a 200m higher FTH for climb/combat.

These are with RAM and the differences are mostly caused by higher MAP too as well due to higher RAM of the K-4. The static difference in the specification above FTH is 5-20ps between the AS and D depending on data (actually some data show advantage for the AS).

Note that all these are calculations (before production began in the case K-4). And there is no compressibility effects accounted in the calculation.

[Charge]

"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)."

The pump does not cause a noticeable need of power. The power need comes directly from transmission from crankshaft to impeller, the power need for auxiliary equipment such as alternator and oil-pump is constant. In some two speed supercharged planes the cooling of the engine alone causes a lot of the 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"

So you have claimed. I haven't seen evidence of any noticeable overpressure which would cause the need for throttling. First there is "slip" and then there is "overpressure". The engineers at DB obviously could not design superchargers with small enough output...

"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."

In well designed engines the impeller speed can be controlled so there is no need for rotating the supercharger needlessly and thus regulating the air feed to the charger.

-C+

[Bronk]

Originally posted by Charge


The pump does not cause a noticeable need of power. The power need comes directly from transmission from crankshaft to impeller, the power need for auxiliary equipment such as alternator and oil-pump is constant. In some two speed supercharged planes the cooling of the engine alone causes a lot of the drag...



-C+

Yea I'm no AC expert. However I do have some auto experience. There is a noticeable difference HP/Torque loss in manual vs auto trans car at the rear wheels.

If you have a tech sheet with identical engines. One with a hydraulic driven SC the other mechanically driven that proves it. I'd like to see it.

Bronk

[gripen]

Originally posted by Charge

The pump does not cause a noticeable need of power. The power need comes directly from transmission from crankshaft to impeller, the power need for auxiliary equipment such as alternator and oil-pump is constant. In some two speed supercharged planes the cooling of the engine alone causes a lot of the drag...

Your original argument was that "it does not "use" more power other than the normal amount of a supercharger which needs to be turned". I don't know how much power did the two pumps use, but certainly these used some power. Von Gersdorf&co book has a graph which shows that at max oil flow, 2,5% slip, there is 5% performance loss (p. 149 in the edition I have), more at higher slip.

AFAIK all engines discused here needed quite a lot cooling but Von Gersdorf&co claim that the hydraulic coupling caused ca max 30% increase to needed oil cooling.

Originally posted by Charge

So you have claimed. I haven't seen evidence of any noticeable overpressure which would cause the need for throttling. First there is "slip" and then there is "overpressure". The engineers at DB obviously could not design superchargers with small enough output...

Just look the picture below, in this case at sealevel it did about 30% overpressure and between the 1st and 2nd FTH max overpressure was a bit over 15%. The pictures of the throttle system of the DB 605 can be found from the manual and there is a picture of system of the L in the Gersdorf&co.

Originally posted by Charge

In well designed engines the impeller speed can be controlled so there is no need for rotating the supercharger needlessly and thus regulating the air feed to the charger.

Well, the problem of the DB could not produce that kind of system. Basicly large part of the advantages of the hydraulic coupling was lost due to unaccurate adjustment of the supercharger speed and location of the throttle valve. If you compare curves of the DBs and the ideal DVL variable speed supercharger in the NACA paper, you can see that the loss is tens of ps between the 1st and 2nd FTH.

Below the 1st FTH the rate of the loss is also higher in the DBs than in the better designed engines. As an example the BMW 801D lost about 25-30ps/km while the DB 605A lost about 40-50ps/km; the BMW had throttle valves located before impeller while the DB had the throttle valve after the impeller.

[Charge]

"There is a noticeable difference HP/Torque loss in manual vs auto trans car at the rear wheels. "

That would be the case if the propeller was run on hydraulic clutch. It is not run by it directly but "secondarily" which means that the possible losses can be overcome without the solution having to cause power loss. In this case by simply rotating the impeller a bit faster but not so fast that it exceeds the limiting tip speed.

"I don't know how much power did the two pumps use"

I don't have any pictures of the system or functional descriptions so I don't know how it actually looks and but I don't understand why it would need two pumps. Just one input from the main pump and one or two regulating systems depending of how well it is done. Of course the pump needs to be able to support both the engine's pressure and coupling pressure so it needs to develop more pressure than that of the same engine with two stage charger -and that pressure in not free, but I doubt the increase is significant enough to show.

"AFAIK all engines discused here needed quite a lot cooling but Von Gersdorf&co claim that the hydraulic coupling caused ca max 30% increase to needed oil cooling."

That is a fact with variable speed unit. It surprises me that the additional cooling needed is that small after all. I thought it would be bigger since the NACA requests for 50% bigger oil displacement.

"Just look the picture below, in this case at sealevel it did about 30% overpressure and between the 1st and 2nd FTH max overpressure was a bit over 15%."

I see that the Gebläsedrück is higher after the first FTH but the Ladedrück remains constant. If the GBD would be less after the FTH we could prolly see a notch in LDD i.e. less power.

"Basicly large part of the advantages of the hydraulic coupling was lost due to unaccurate adjustment of the supercharger speed and location of the throttle valve."

Probably more because of worse fuel and unclean aerodynamics...

"Below the 1st FTH the rate of the loss is also higher in the DBs than in the better designed engines. As an example the BMW 801D lost about 25-30ps/km while the DB 605A lost about 40-50ps/km; the BMW had throttle valves located before impeller while the DB had the throttle valve after the impeller."

Well, the choice of the impeller size and gear ratio dictates the power at first FTH and the second FTH and the choice can be made more freely if you have two stages as in FW and as the NACA report states the the biggest power gain in two stage charger happens in first FTH and thats where it IS better than other solutions. The bigger the power gain in First FTH the smaller the deck speed and vice versa. But after the first FTH the power begins to drop and the depth of the drop is determined of how high the second stage has its  FTH. If it is very high the notch is very big, and that is where the variable speed keeps on pumping. It is visible in speed charts too. I don't see how much better the DBs could have done given the fuel they had to use.

Note: There are pros and cons in all systems and I am not claiming the variable speed system being superior to other systems. I think it was a good choice for that size and use of an aeroplane 109 was. Light and mechanically simple but requiring some automation stuff to make it work. With DBs engine construction it would have been much worse with either a turbo or a two stage charger because the weight gain would have been bigger than the gain in power. P47 and P38 could afford to run on turbo as the size of the aeroplane was so big and both Spit and Ponies had more leeway due to bigger wings and thus more load carrying capability although the weight gain  of two stage is not so big over the variable speed than that of turbo system over them both.  

-C+

[gripen]

Originally posted by Charge

I don't have any pictures of the system or functional descriptions so I don't know how it actually looks and but I don't understand why it would need two pumps.

You can find pictures of the system from the DDB 605 manual. There is a diagram showing how the oil flow of the second pump is regulated by the barometric valve.

I don't know what the DB engineers where thinking but they probably choosed two pump system for the increased cooling flow; the second pump is used to increase cooling flow when not used for the coupling.

Originally posted by Charge

That is a fact with variable speed unit. It surprises me that the additional cooling needed is that small after all. I thought it would be bigger since the NACA requests for 50% bigger oil displacement.

Cooling need was seen as a problem. As an documented example, just take a look to the PDF on Kawasaki DB developements Mike just posted to the thread on Russian and Japanese engines.

Originally posted by Charge

I see that the Gebläsedrück is higher after the first FTH but the Ladedrück remains constant. If the GBD would be less after the FTH we could prolly see a notch in LDD i.e. less power.

The "Gebläsedruck" is practically allways a bit higher than the "ladedruck" (MAP) due to pressure losses caused by the throttle valve and other control valves (three valves all together which restrict air flow somewhat).

If the "gebläsedruck" drops below the certain level, the MAP starts to drop despite it's lower than the "gebläsedruck". A good example can be seen here.

Originally posted by Charge

Probably more because of worse fuel and unclean aerodynamics...

This has absolute nothing to do with fuels nor unclean aerodynamics; the overpressure and performance losses were caused simply by unaccurate adjustment of the hydraulic coupling and the location of the throttle valve.

Originally posted by Charge

Well, the choice of the impeller size and gear ratio dictates the power at first FTH and the second FTH and the choice can be made more freely if you have two stages as in FW and as the NACA report states the the biggest power gain in two stage charger happens in first FTH and thats where it IS better than other solutions.

Hm... I quess you mean the two speed supercharger instead the two stage, right?

The DBs were variable speed systems only between 1st and 2nd FTH (the DVL system was variable speed from sealevel to it's FTH so its not the same), so it had advantage only at that altitude range, everywhere else the direct mechanical gearing is more efficient (above 2nd FTH it's even better than ideal DVL system).

Originally posted by Charge

I don't see how much better the DBs could have done given the fuel they had to use.

Just compare the concave shape of the power curve of the ideal DVL system to the convex shape of the DB power curves between 1st and 2nd FTH. And as noted above, this has absolute nothing to do with the fuels.

[Knegel]

Originally posted by gripen
The lower 2nd FTH ASB if compared to the ASM is caused by higher MAP (1,8ata). These are mostly the same engines, the ASB is just a later version with higher CR etc. The output difference is very small.

 

These are with RAM and the differences are mostly caused by higher MAP too as well due to higher RAM of the K-4. The static difference in the specification above FTH is 5-20ps between the AS and D depending on data (actually some data show advantage for the AS).

Note that all these are calculations (before production began in the case K-4). And there is no compressibility effects accounted in the calculation.

Hi,

according to my datas of the static power, i get this picture:

DB605AS:
Kurzleistung(combat/climb): fth 7800m, 1150PS
Dauerleistung: fth 7700m 1050PS

DB605ASM:
Kurzleistung: fth 7800m, 1150PS
Dauerleistung: fth 7100m, 1040PS

DB605ASB: (c3 fuel or MW50injection)
Kurzleistung: fth 6800m, 1285PS
Dauerleistung: fth 6500m, 1200PS

AS and ASB/M use different Spark plugs and ignition systems, who knows what else. All DB605 engines was rather similar, the different was the different between AS/ASB/ASM and D was in a different max usable presure and RPM. The D could run on higher rpm for longer time.

The DB605D datas are also from the 109G10, not only K4, but of course its the power with RAM, thats what we just compare(the Merlin datas are also with RAM and a even higher one, from the P51).
Combat power  at 9000m is 1140PS with 653km/h. The K4 show the G10 engine datas, but 670km/h.
The K4 tests(not corrected?), show the plane with 690km/h in 9000m with combat climb, therefor i guess 670km/h(K4), 653(G10) and the related power are corrected.

Greetings,

Knegel

[gripen]

Originally posted by Knegel

according to my datas of the static power, i get this picture:

DB605AS:
Kurzleistung(combat/climb): fth 7800m, 1150PS
Dauerleistung: fth 7700m 1050PS

DB605ASM:
Kurzleistung: fth 7800m, 1150PS
Dauerleistung: fth 7100m, 1040PS

These seem to be from here. These differences are most probably typos; there is no sense to have same output at certain altitude and different at another given that the engine is practically same except MW50 (not used for these power settings).

Originally posted by Knegel

DB605ASB: (c3 fuel or MW50injection)
Kurzleistung: fth 6800m, 1285PS
Dauerleistung: fth 6500m, 1200PS

This is a later model than the AS or ASM with different ratings and other differences like higher CR.

Originally posted by Knegel

AS and ASB/M...

Never heard about ASB/M, what's the source for this? And I can't find the reference for the G-6/AS with ASB you claimed, the sheet you claimed seem to contain standard G-6/AS Jäger with the DB 605AS.

Originally posted by Knegel

All DB605 engines was rather similar, the different was the different between AS/ASB/ASM and D was in a different max usable presure and RPM. The D could run on higher rpm for longer time.

There is considerable differences between the A and D series engine engines; as an example lubrication system was partially redesigned in the D.

Originally posted by Knegel

The DB605D datas are also from the 109G10, not only K4, but of course its the power with RAM, thats what we just compare(the Merlin datas are also with RAM and a even higher one, from the P51).

The difference here is that the values for the Mustang are measured  but the values you want to use for the Bf 109s are calculations. And there is plenty of evidence on problems with DBs to reach claimed performance.

[Viking]

Originally posted by Angus
More of the climb, - Viking.
(And TY for the input)
Climb seems to be measured  at MIL in both camps. But the data is confusing. 109G in 1944 is still using 6 minutes to 20K, Rall also mentions the same figure. A Spitty in the same time will use some rough 5 with more weight

I have no problem believing a late-war Spitfire could climb better than a contemporary 109 at MIL power. Remember that while the Merlin's whole power range (cruise, MIL and WEP) increased during the war, due to limitation in materials and fuel (having to use anti-knocking agents like MW50) the DB 605 mostly just increased in WEP power. The Spitfire's bigger wing also made up for some of the greater weight.

If we look at the planes in AH we can see that the Spit XVI does indeed out climb 109G-14 on MIL power. It even matches the K-4 on MIL power.

http://www.gonzoville.com/ahcharts/index.php