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

[Knegel]

Originally posted by gripen
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).

Yep, right, iam aware of this, but made the same typo, i was up to point to the different to the ASB, where you wrote before that its very similar to the AS and ASM.

Originally posted by gripen

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

Yes, and same like the DB605D it had a different output.

Originally posted by gripen

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.

AS, ASM+B would have been less confusing,eh?


As i wrote before, i thinks thats a typo and should be AS.

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

 
Yes, and this different also brough a different poweroutput.

Originally posted by gripen
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.

The 109K4 tests show a smaler FTH, but the performence is avove the calculated one and the SpitfireIXc tests dont show the great power output of the P51B engine. With "Drehzahlsteigerung" the K4´s best combat power(also max power) speed in 9km alt is around 705km/h(maybe not corrected, with a new propeller). Even with correction and the default propeller, the Vmax is still above that of the best Spitfire HF, despite the K4 is as heavy as the Spits and the heavy wingload also dont will be a advantage in this hight.
Thats why i still think its more the P51 airframe that provide better circumstances for the engine, than the engine itslef.
The big airinlet of the P51 probably provide a better RAM effect and this provide the outstanding power and highspeed performence of the P51B in high alt, despite its high wingload.
I guess the DB605D or AS in the P51 airframe would provide same results.

Greetings,

Knegel

[gripen]

Originally posted by Knegel
Yep, right, iam aware of this, but made the same typo, i was up to point to the different to the ASB, where you wrote before that its very similar to the AS and ASM.

What I wrote above is that the AS and the D performed very similarly at high altitude and that the differences between earlier AS engines (AS and ASM) and later AS engines (ASB, ASC) are caused by different ratings. Just read the later pages of the same doc where the static output at 10km is given for 2800rpm:

AS  925ps
D 930ps

That means that there is no practical difference at high altitude between the AS (any model) and D (production model with large supercharger).
 

Originally posted by Knegel

AS, ASM+B would have been less confusing,eh?
...
As i wrote before, i thinks thats a typo and should be AS.

That is from the Monogram Close-Up series with typo, the original (from NASM microfilms) states clearly AS.

Please don't invent new designations.

Originally posted by Knegel

The 109K4 tests show a smaler FTH, but the performence is avove the calculated one and the SpitfireIXc tests dont show the great power output of the P51B engine. With "Drehzahlsteigerung" the K4´s best combat power(also max power) speed in 9km alt is around 705km/h(maybe not corrected, with a new propeller). Even with correction and the default propeller, the Vmax is still above that of the best Spitfire HF, despite the K4 is as heavy as the Spits and the heavy wingload also dont will be a advantage in this hight.

I don't see any properly corrected tests on the K-4 here. The compressibility correction for the 705km/h at 9km at can be more than 50km/h depending on conditions (edited for calculation error).

BTW what's the source and the FTH in the tests?

[Charge]

"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."

That looks abnormal. This looks normal.
   
"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."

Yes, that is what you keep saying, I don't buy it.

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

Yes. I wasn't aware that there were actual two-stage chargers but they actually existed. They have the advantage of better designed impellers for both critical altitudes but they are heavier designs.

"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)."

Of course, the DB has a single stage and thus its performance is that of a generously designed (altitude optimized) single stage with the option that its charge pressure does not need to be restricted but of course it is possible to put such impeller into two speed system that exceeds the power output of a variable speed system -but it comes with a price. There is a surge of inlet temperature rise in two stage system that calls for the drop in charging pressure in a two speed system, causing the notch in powercurve, a defect that a variable speed system does not have. Clearly seen in NACA document, too.

"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."

Actually I think that with 130-150 grade fuel the performance and design of DB or any German aeroengine could have been quite a bit different. With 100 octane or less they had to stick with larger displacement and thus larger engine which dictated that all the auxiliaries needed to be light and thus the variable speed unit was absolutely a correct choice for DB fit in 109s. A drawback was the larger oil-cooler requirement but in turn it needed less cooler capacity than higher charged engines. E.g. Jumo213 had a two-speed charger and the weight was almost 200kg more (the 190D9 seems to have smaller notch in speed curve that both Spit and Pony have?).

In case I didn't need extreme high altitude speed I'd take variable speed unit anytime. No need for LFs or HFs or whatever...

-C+

[gripen]

Originally posted by Charge

That looks abnormal.

That is exactly how it should theoretically be. Note that there is measured point at 3000m where the MAP drops and gebläsedruck is at lowest point.

Originally posted by Charge

This looks normal.

That is a drawing error at 2500m, there is no measured point at that altitude. Above 2nd FTH there is logical difference between the MAP and gebläsedruck just like in the several other graphs in the same data set.
   

Originally posted by Charge

Yes, that is what you keep saying, I don't buy it.

This is an impeller speed adjustment issue, it's there regardsless the fuel used or the aerodynamic condition of the plane.

We can simply disagree, if you don't want to believe me. No problem.

Originally posted by Charge

Yes. I wasn't aware that there were actual two-stage chargers but they actually existed. They have the advantage of better designed impellers for both critical altitudes but they are heavier designs.

Hm... the weight difference between single speed and two speed systems seem to be generally around 20-30kg if I look Merlin and some Radials. So the difference is quite small. It's difficult to figure out the weight of the hydraulic coupling + other needed gear but I quess it's in the same ballpark.

Originally posted by Charge

Of course, the DB has a single stage and thus its performance is that of a generously designed (altitude optimized) single stage with the option that its charge pressure does not need to be restricted but of course it is possible to put such impeller into two speed system that exceeds the power output of a variable speed system -but it comes with a price. There is a surge of inlet temperature rise in two stage system that calls for the drop in charging pressure in a two speed system, causing the notch in powercurve, a defect that a variable speed system does not have. Clearly seen in NACA document, too.

I don't know how many times it should be pointed out to you:

The ideal DVL variable speed supercharger in the NACA paper is continously adjustable at whole altitude range and the speed of the supercharger is supposed to be exactly needed below the FTH. Therefore the DVL supercharger runs at full throttle at entire adjustment range.

The DB supercharger is adjustable only at certain altitude range and there is no mechanism to adjust supercharger speed to match needed MAP. Therefore the DBs run more or less throttled up to the (near) 2nd FTH as the gebläsedruck curves show.  Below 1st FTH the DB had the same losses as direct mechanical connection and in addition location of the throttle valve and coupling itself caused some more.

Originally posted by Charge

Actually I think that with 130-150 grade fuel the performance....

This has absolute nothing to do with the fuels...

Originally posted by Charge

E.g. Jumo213 had a two-speed charger and the weight was almost 200kg more (the 190D9 seems to have smaller notch in speed curve that both Spit and Pony have?).

The reason is that the Jumo 213 utilized spin type throttle (copied from the Mikulin AM-35 series) as was planned for the L series DBs. In addition the Jumo 213 did not run at constant MAP.

[Knegel]

Originally posted by gripen
What I wrote above is that the AS and the D performed very similarly at high altitude and that the differences between earlier AS engines (AS and ASM) and later AS engines (ASB, ASC) are caused by different ratings. Just read the later pages of the same doc where the static output at 10km is given for 2800rpm:

AS  925ps
D 930ps

That means that there is no practical difference at high altitude between the AS (any model) and D (production model with large supercharger).

As far as i understand there is a significant different in the time to use this powersetting. Further more 5PS static power will result in a higher RAM power different.

Originally posted by gripen

I don't see any properly corrected tests on the K-4 here. The compressibility correction for the 705km/h at 9km at can be more than 50km/h depending on conditions (edited for calculation error).

BTW what's the source and the FTH in the tests?

The source is the 109K4 speed curve from 19.01.45 for the DB605d/ASB mit MW50, mit Dünnblattschraube 9-12199.
Afaik thats the only available 109K4 test.
Vmax @9km with the default propeller is 690-695km/h, thats still 25-50km/h faster than the HF Spits in this altitude, despite the heavy wingload of the 109K4(same T/O weight like the Spits).

Of course we could assume that engeeners of the nation, who did develop planes like the 252, 163, flying wing , who had highspeed windtunnels etc  made speed curves with a mistake of 50km/h, otherwise we also could assume the DB605D was pretty even or maybe better than the Merlin70 in the Spitfire.

Greetings,

Knegel

[gripen]

Originally posted by Knegel
As far as i understand there is a significant different in the time to use this powersetting. Further more 5PS static power will result in a higher RAM power different.

Given that the tolerance for the DBs was 2,5%, the 5ps difference is neglible.

Originally posted by Knegel

The source is the 109K4 speed curve from 19.01.45 for the DB605d/ASB mit MW50, mit Dünnblattschraube 9-12199.

Hm... that sounds a lot like the A/IV/42/44; those are calculations, not test data and not accounting the drag rise due to compressibility (not the same thing as compressibility correction of the test data). Note that in these later calculations they use somewhat more realistic FTH, another story is if the engines reached claimed performance (even these lower specs).

BTW this thread is about the engines and the test data is used just to check out if the engines were up to the specs. However, for one reason or another you tend to bring in plane related arguments just like you did in Stoney's thread on airplane design.

[Knegel]

Hi,

actually you came up with the RAM power of the Merlin70/V-1650-3, and RAM power is in big degree related to the airframe.

If we talk about the engines only static power is valid, or we need to use the same or a similar airframe for the comparison.

I brought in the Spitfire HF performence and 109K4 performence to show that the engine power is very much related to the used airframe.

The datas say:

V-1650-3:
combat/climb: 1055HP at 8231m
max power: 1380HP at 7100m,


DB605AS:
combat/climb: 1150PS at 7800m
max power: 1200PS at 8000m

DB605D:
combat/climb: 1200HP at 7400m
max power: 1280PS at 7600m

Again its not that easy to compare this values, it simply depends to the time of usage and altitude.  The Merlin have a the known high peak, but at a rather low altitude, while the DB´s have a good combat climb power.

Imho thats rather similar.

Greetings,

Knegel

[gripen]

Originally posted by Knegel

actually you came up with the RAM power of the Merlin70/V-1650-3, and RAM power is in big degree related to the airframe.

That is simply because the test data shows if an engine delivers claimed performance. Note that even the lowest performing Merlin 70 you choosed gave closer to specs performance than the tested DBs.

Originally posted by Knegel

If we talk about the engines only static power is valid, or we need to use the same or a similar airframe for the comparison.

The problem with that is the chronic tendency of the DBs to not live up to the specs. Therefore test data gives better picture.

Originally posted by Knegel

I brought in the Spitfire HF performence and 109K4 performence to show that the engine power is very much related to the used airframe.

You brought in calculated data (accounts no drag rise due to compressibility) which you claimed to be flight tested.

Besides even the lowest performing Merlin 70 test data you choosed delivers higher output at high altitude than the calcudated data for the DBs.

[Charge]

"That is exactly how it should theoretically be. Note that there is measured point at 3000m where the MAP drops and gebläsedruck is at lowest point."

Nope. That notch is not normal IMO.

"This is an impeller speed adjustment issue, it's there regardsless the fuel used or the aerodynamic condition of the plane.

We can simply disagree, if you don't want to believe me. No problem."

Yes we do, fine for me too. I'll study this matter more if I can and let you know if I discover I was wrong.

"Hm... the weight difference between single speed and two speed systems seem to be generally around 20-30kg if I look Merlin and some Radials. So the difference is quite small. It's difficult to figure out the weight of the hydraulic coupling + other needed gear but I quess it's in the same ballpark."

I have no idea of the weight gain, only that that NACA doc claims there is some. It could well be insignificant depending on how it is done, though.

"I don't know how many times it should be pointed out to you:
The ideal DVL variable speed supercharger in the NACA paper is continously adjustable at whole altitude range and the speed of the supercharger is supposed to be exactly needed below the FTH. Therefore the DVL supercharger runs at full throttle at entire adjustment range."

The DB charger provides steady ATA from the deck to the highest FTH. I think it performs quite well looking the speed figures too. Maybe it could have been better, maybe not -but for a long time it certainly was good enough.

"The DB supercharger is adjustable only at certain altitude range and there is no mechanism to adjust supercharger speed to match needed MAP. Therefore the DBs run more or less throttled up to the (near) 2nd FTH as the gebläsedruck curves show. Below 1st FTH the DB had the same losses as direct mechanical connection and in addition location of the throttle valve and coupling itself caused some more."

It seems so. It also appears that DB did not have such abrupt temp rise as the two speed units had requiring not as radical throttling between speed change point to prevent detonation. The arch troubles me though and it is a potential place for throttling, but I don't understand why it is there. But even there the Ladendrück remains even so it does not effect speed negatively.

"This has absolute nothing to do with the fuels..."

The fuel dictated the path DB and German engine designers had to stay on. More displacement for more power and more ATA only if proper materials and fuel were available. More displacement generally means more power and thus  more weight unless the engine can be lightened from some place. Wiht heavily charged engines there is not such pressures to increase displacement but the make the engine withstand more stress from increased charging pressures.

"The reason is that the Jumo 213 utilized spin type throttle (copied from the Mikulin AM-35 series) as was planned for the L series DBs. In addition the Jumo 213 did not run at constant MAP."

The point was that Jumo was heavier than DB, maybe because of its charger arrangement or again maybe not, and that its two speed charger was maybe better done than those of its allied contemporaries. That is visible in TA152s speed figure too. Two stages, three speeds and the speed of the a/c does not drop at gear/speed change, maybe because off less radical temperature changes in charged air or less sensitiveness to those changes.

-C+

[MiloMorai]

Charge, can you use italics for you quotes to help with the reading.

[gripen]

Originally posted by Charge

Nope. That notch is not normal IMO.

The point was to show the relation between the gebläsedruck and MAP ie the gebläsedruck is practically allways higher than MAP.

Do you disagree?

Originally posted by Charge

Yes we do, fine for me too. I'll study this matter more if I can and let you know if I discover I was wrong.

OK. I have given the the sources to look for, most sources can be found from FAF museum library (Von Gersdorf&co there is my former copy).

Originally posted by Charge

The DB charger provides steady ATA from the deck to the highest FTH. I think it performs quite well looking the speed figures too. Maybe it could have been better, maybe not -but for a long time it certainly was good enough.

Generally it does steady MAP up to the 2nd FTH but there is no direct connection between barometric valve and MAP control so the system rarely runs impeller at optimal speed below 2nd FTH.

If barometric valve starts to redirect flow from the second pump too late, the MAP drops just like in the case discused above.

If barometric valve redirects flow too early or too much oil from the the second pump, the impeller spins too fast and throttling is needed (supercharger does overpressure) . As can be seen from the gebläsedruck curves, that is the situation most of time below the 2nd FTH.

Originally posted by Charge

It seems so. It also appears that DB did not have such abrupt temp rise as the two speed units had requiring not as radical throttling between speed change point to prevent detonation. The arch troubles me though and it is a potential place for throttling, but I don't understand why it is there. But even there the Ladendrück remains even so it does not effect speed negatively.

As pointed out by comparing the power curves of the BMW 801D and DB 605A, the losses due to throttling are higher in the case of the DB due to location of the throttle valve. In the L series engines the throttle valve was relocated before the impeller and the throttle was changed to the spin type like in the Jumo 213 (there is a picture of the system in the Von Gersdorf&co).

Originally posted by Charge

The fuel dictated the path DB and German engine desig...

The points discused above are there regardless the used fuel, in other words the fuels has nothing to do with this.

Originally posted by Charge

The point was that Jumo was heavier than DB...

I just pointed out the reason for the properties of the power curve.

The DB 605 is more comparable with the Jumo 211 than the Jumo 213, roughly same weight and roughly same output as used in service before mid 1944 (later DB got MW50 etc. but that time Junkers was focused to the more advanced Jumo 213).

[joeblogs]

I just want to throw out a few things raised in the last few posts:

Two stage superchargers do add a significant amount of weight. It is not just the weight of the second blower itself, it is the weight and drag associated with an intercooler. The accessory drive also has to be redesigned to manage the effects of a second, more highly geared blower. And at lower altitudes all this weight is added for little purpose. It only becomes useful at higher altitudes.

As an example, the two stage blown Twin Wasp on the F4f was a fine engine for good high altittude performance (once the kinks were worked out), but for low altitudes better performance was attained using a lighter Cyclone with a single stage supercharfer (hence the FM version of the Wildcat)

Second there are sometimes differences in engine performance when comparing charts for a particular engine and looking at numbers for that same engine in a particular airplane. That does not mean that an engine chart without reference to a particular plane is necessarily reporting only "static" power. RAM air is easily simulated on the test bed and this was often done. There are plenty of P&W engine charts that include data with RAM air. Now whether a particular plane can deliver this RAM air to the engine is a different question and that is one reason why there can be differences in the charts I alluded to above (another is differences in cooling).

-Blogs

[gripen]

The DB was going towards the two stage concept in high altitude engines; atleast in paper the DB 605L is comparable to the best 100 series Merlins at high altitude. The weight difference between the DB 605D and the L seem to be rather low (30-40kg depending on source) if compared to the Merlins (about 90kg). That might be partially explained by aftercooler of the Merlin. The concept of the two stage supercharger in the L was similar as seen in the Merlin and Jumo213; integral unit featuring two impellers in series in the same axle.

The American system was to use external auxilary stage (turbo or mechanical) for two stage engines. This is less compact and probably somewhat heavier arrangement. However, production wise the american system was much easier because the base engine is practically unchanged regardless the supercharging used.

[joeblogs]

Sounds about right. The difference in the dry weight of a single stage vs. A two stage supercharged Twin Wasp is about 51kg, a 7.5 percent increase in weight.

-Blogs

Originally posted by gripen
... The weight difference between the DB 605D and the L seem to be rather low (30-40kg depending on source) if compared to the Merlins (about 90kg). That might be partially explained by aftercooler of the Merlin. ...
.

[joeblogs]

For the double wasp, the weight increase between otherwise comparable models with single or two stage supercharging appears to be about 95kg, or roughly a 9 percent increase in engine weight.

Originally posted by joeblogs
Sounds about right. The difference in the dry weight of a single stage vs. A two stage supercharged Twin Wasp is about 51kg, a 7.5 percent increase in weight.

-Blogs