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

[Viking]

Originally posted by gripen
The 1st FTH is the altitude where the hydraulic coupling starts to increase the speed of the supercharger with second oil pump. Below this altitude it works like fixed speed unit because the slip of the drive was constant ie the supercharger used constant oil flow from the first oil pump.

In other words the DB supercharger was variable speed unit only at certain altitude range; between the altitude where the second oil pump started increase the speed of the supercharger and where the supercharger reached peak speed.

The 1st FTH was at ~5000 feet so the efficiency loss below this altitude is minimal compared to the Merlin 70's supercharger which has a 1st stage FTH of 11,900 feet. The barometric pressure at 5000 feet is only 14% less than at sea level, so at sea level the DB's supercharger is only producing 14% waste pressure. The Merlin 70 otoh produces 33%-34% wasted pressure at sea level.

Originally posted by joeblogs
Ok so below FTH 1, the only variable is the Throttle. Above this, is the throttle wide open, but the rotational speed of the supercharger increasing?

-Blogs

A short description of the DB 610’s supercharger which is similar in function to the Db 605’s:

Centrifugal supercharger on port side of engine driven through a fluid coupling by a shaft at right angles to crankshaft. This shaft is driven through bevel gears from the crankshaft, variation in propeller speed secured through variable filling of fluid coupling by two-stage engine driven pump receiving lubricating oil from the main pressure filter.

First stage delivers oil direct to coupling and second stage delivery is passed in varying proportions between crankcase and coupling by piston valve controlled by a capsule which is sensitive to inlet pressure. Second stage cuts in at approximately 5,000 ft. and full delivery occurs at approximately 11,500 ft.

Butterfly throttle which is capsule controlled regulates supercharger delivery, second throttle which is pilot operated controls air supply to engine and manifold pressure, first throttle subjected to pressure between two throttles, increased boost for take-off controlled by clockwork mechanism, mixture delivered by supercharger to looped manifold by large diameter pipe, dry-sump pressure-feed lubrication, gear type oil pumps, spray of oil directed upon reduction gears, main oil pressure line feeds crankshaft bearings, secondary line feeds supercharger fluid pump.

[gripen]

Originally posted by Viking
Errata: The FTH i have stated for the Merlin V-1650-7 of the P-51D is actually that of the V-1650-3 of the P-51B. The correct FTH's of the -7 is 7,000 feet (1st stage) and 18,000 feel (2ns stage). For comparison the FTH's of the Merlin 70 is 11,900 feet (1st stage) and 24,700 (second stage).

The DB 605AS(M) with a FTH of 7,9 km (~26,000 feet) has a higher FTH than all these Merlins.

Well, perhaps you should compare the reached output at altitude with RAM; say 10km:

P-51D with V-1650-7 from here: about 1000hp

P-51B with V-1650-3 from here: about 1200hp

Bf 109G (GJ+FX) with DB 605AS: DB test data gives about 1,1ata at 2800rpm ie roughly about 1000hp (or ps, I used a DB 605A chart and a AS does actually a bit less).

So basicly the DB 605AS did about same as V-1650-7.

[gripen]

Originally posted by Viking
The 1st FTH was at ~5000 feet so the efficiency loss below this altitude is minimal compared to the Merlin 70's supercharger which has a 1st stage FTH of 11,900 feet. The barometric pressure at 5000 feet is only 14% less than at sea level, so at sea level the DB's supercharger is only producing 14% waste pressure. The Merlin 70 otoh produces 33%-34% wasted pressure at sea level.

Pointless comparison, the Merlin 70 was a true high altitude engine.

Originally posted by Viking

A short description of the DB 610’s supercharger which is similar in function to the Db 605’s:

Well, that is about the same I have explained to you.

[Charge]

The power graph looks good to me. Fairly even up to the FTH. What is wrong with it?  

The ideal in that NACA report is not something you can do IRL It is lossless and the induced temperature to manifold is lower than can be normally attained. The matter is how close to that ideal you can get. The variable speed unit provides steady power output up to critical height.

-C+

[Viking]

Originally posted by gripen
Well, perhaps you should compare the reached output at altitude with RAM; say 10km:

P-51D with V-1650-7 from here: about 1000hp

P-51B with V-1650-3 from here: about 1200hp

Bf 109G (GJ+FX) with DB 605AS: DB test data gives about 1,1ata at 2800rpm ie roughly about 1000hp (or ps, I used a DB 605A chart and a AS does actually a bit less).

So basicly the DB 605AS did about same as V-1650-7.

I don’t have numbers at 10 km for the DB 605AS only at 8 km where it produces 1200 PS according to the Motorenblatt.

Originally posted by gripen
Pointless comparison, the Merlin 70 was a true high altitude engine.

The Merlin 70 had very similar performance to the V-1650-3.

Originally posted by gripen
Well, that is about the same I have explained to you.

Perhaps, but in better detail and without the negative connotations. In any case that part of the post was not meant for you.

[Charge]

"Between 1st and 2nd FTH hydraulic coupling has an advantage when the second oil pump starts to increase speed of the supercharger. "

The flow away from the clutch is regulated in two ways. It has only one oil pressure feed. The oil pump does not rotate the charger, the engine does.

"However, in the case of the DB, supercharger still does some overpressure because the speed of the supercharger is not adjusted according to MAP but simple barometric valve. In practice some of the theoretical advantage is lost due to this."

I don't follow your logic. The pressure is controlled due to barometric conditions. How is that inaccurate considering that the aneroid is working correctly.

"Note that the throttle valve was located after the supercharger so the losses due to throttling were higher than in the case where the valve is before supercharger (in the L series DBs this was fixed using the spin valve before the supercharger)."

The throttle is supposed to cause loss -without it the plane would not stop. The point is that at what altitude you can open the throttle fully and what charger configuration will not let you do it.  In DB you can open the throttle fully at any altitude and the charging control itself does not prevent it.

"Above 2nd FTH the hydraulic coupling works as a fixed speed supercharger again so there is no advantage but some disadvantage again due to higher losses of the hydraulic coupling."

Nope, the 4% loss can be compensated by simply rotating the impeller faster. The only drawback is the excess heat which needs to be get rid of.

-C+

[gripen]

Originally posted by Viking
I don’t have numbers at 10 km for the DB 605AS only at 8 km where it produces 1200 PS according to the Motorenblatt.

There is plenty of charts in the site linked above.

Originally posted by Viking

The Merlin 70 had very similar performance to the V-1650-3.

The V-1650-3 was a high altitude engine like the Merlin 70.

Originally posted by Viking

Perhaps, but in better detail and without the negative connotations. In any case that part of the post was not meant for you.

Are you saying that the problems of the DBs I mentioned above are not true?

Besides, perhaps you should investigate your own claims as well...

[Angus]

Originally posted by MiloMorai
No Viking, it is only when Barbi put on his hobnailed boots and started doing the goosestep. Someone had to counter the utter bs spewed by Barbi.

Yes Angus it was Barbi.

Here is another little trivia about German aero engines written by a German,

I don't know for shure about the alloys the Allies used for their aircraft engines - but the Germans made excessive use of ELECTRON for their engine's light-alloy-castings - that is: an alloy with up to 60 percent Magnesium to 40 percent Aluminium - throughout the entire engine.

By doing so, you can reduce the wheight of a casting down to 2/3rds of that of a sheer aluminium-alloy. Bad point is, that Electron-alloys must be coated to become oil- and water-tight, as Electron-castings tend to be porous.

Secondly, Electron-castings corrode like Hell: Electron is hysterically sensitive to water, due to it's high Magnesium-contence. The applied coating had to fight that corrosion, too. But it could do so only to a certain extent. as even the finest cracks, fissures and, punctures in the laquer-coating would allow enough humidity, if not sheer coolant liquid sip into the Electron and initiate intermolecular corrosion hat, it would render that specific casting scrap before long.

If you should ever have asked yourself, why there are so few airworthy genuine german engines from WWII left in the World - there you have the answer for this question: They are all corroded down to unairworthiness (if such a word should exist at all in English) - if not (white) dust...

Holy moly. So that's why. Well, makes sense to what Rall said, but what would be the cure? Wchich parts suffer and have to be refreshed? After all, he mentioned wear and loss of power after as little as 10 hours.
This also bothered me on a different quest when I was researching some claims by the 109 band. ROC.
ROC really needs a wing and power. Top speed is more like (mostly) parasite drag vs power, etc etc. So, using the Spitfire and the 109 as a comparison and calculating into NM's, they pull apart in ROC as the war proceeds, - i.e. the Spitfire gains. A Spitfire with a Merlin 66 or 70 weighting the same as a 109G will easily outclimb it. I have no other data. From SL to some 30K all combined that is.
I always tended to write that on to the wing, and not the Engine - the engines always seemed to be very very close, and since the closest match would be a Spit I (CS) and a 109E (almost same power with the 109 slightly above AFAIK), the difference in pulled Newtons was already close to 10%.
But if the DB was always being saved, or derated due to wear or tear, it upsets this a bit. I mean, why still be doing tests at 1,3/1,43 ATA still in 1944??????

[gripen]

Originally posted by Charge
"Between 1st and 2nd FTH hydraulic coupling has an advantage when the second oil pump starts to increase speed of the supercharger. "

The flow away from the clutch is regulated in two ways. It has only one oil pressure feed. The oil pump does not rotate the charger, the engine does.

Read my post please.

Originally posted by Charge
"However, in the case of the DB, supercharger still does some overpressure because the speed of the supercharger is not adjusted according to MAP but simple barometric valve. In practice some of the theoretical advantage is lost due to this."

I don't follow your logic. The pressure is controlled due to barometric conditions. How is that inaccurate considering that the aneroid is working correctly.

Needed supercharger speed (in ideal conditions) depends on MAP.

Originally posted by Charge
"Note that the throttle valve was located after the supercharger so the losses due to throttling were higher than in the case where the valve is before supercharger (in the L series DBs this was fixed using the spin valve before the supercharger)."

The throttle is supposed to cause loss -without it the plane would not stop. The point is that at what altitude you can open the throttle fully and what charger configuration will not let you do it.  In DB you can open the throttle fully at any altitude and the charging control itself does not prevent it.

The problem is that the DBs did not work that way, see above.

Originally posted by Charge
"Above 2nd FTH the hydraulic coupling works as a fixed speed supercharger again so there is no advantage but some disadvantage again due to higher losses of the hydraulic coupling."

Nope, the 4% loss can be compensated by simply rotating the impeller faster. The only drawback is the excess heat which needs to be get rid of.

Please read your own text, there is 4% loss.

[Viking]

Originally posted by gripen
There is plenty of charts in the site linked above.

For the DB 605AS as well? (I notice you did not post a link to a DB chart)

Originally posted by gripen
The V-1650-3 was a high altitude engine like the Merlin 70.

You chose to compare the DB 605AS with the V-1650-3 and -7 (that I compared it to earlier not realizing it actually was a -3).

Here is a piece of news that might surprise you: The DB 605AS is also a high altitude engine.

Originally posted by gripen
Are you saying that the problems of the DBs I mentioned above are not true?

Yes. They are not problems at all and the use of the word “problem” is inappropriate. You’re basically saying the supercharger had “problems” because it could have been even better than it already was.

Edit: The fact of the matter is that the DB supercharger was more efficient at a much wider altitude range than the RR supercharger. The RR supercharger was marginally (you mention 4%) more efficient at its two FTH’s, but those only peak at very narrow altitude bands.

[joeblogs]

I don't follow the logic here.

There are lots of sources of losses in driving a supercharger. Yes one of them is spinning the supercharger at a constant multiple of engine speed and NOT opening the throttle wide open. Everyone gets that.  

The losses I was referring to was the use of a single (and therefore larger) diameter impellor which is less efficient than a smaller impeller. This is offset, partially, by spinning the impeller at a smaller (but constant) multiple of engine RPM below the first throttle height if I understand what Grippen has said.

Now even a high altitude version of the Merlin is using two impellers, the smaller one at lower altitudes. That impeller will be more efficient than a larger impeller. Now with the Merlins, it is likely the engine is not running at full Throttle at sea level, and there are losses associated with spinning all this machinery and not pushing all the air you could through it.

The point is that the efficiency losses come from a variety of sources and they are all relevant to the comparisons.

-Blogs

Originally posted by Viking
The 1st FTH was at ~5000 feet so the efficiency loss below this altitude is minimal compared to the Merlin 70's supercharger which has a 1st stage FTH of 11,900 feet. The barometric pressure at 5000 feet is only 14% less than at sea level, so at sea level the DB's supercharger is only producing 14% waste pressure. The Merlin 70 otoh produces 33%-34% wasted pressure at sea level.

[Angus]

Merlin 70 = high alt engine.

[Viking]

Originally posted by joeblogs
The losses I was referring to was the use of a single (and therefore larger) diameter impellor which is less efficient than a smaller impeller.

The DB supercharger wasn’t that large. Remember that the DB was a low-blown high-compression engine, meaning the engine did much of the compression in the cylinders itself. The DB 605AS only runs at 1.42 ATA boost, meaning 142% of normal sea level atmosphere pressure.

Originally posted by joeblogs
Now even a high altitude version of the Merlin is using two impellers, the smaller one at lower altitudes. That impeller will be more efficient than a larger impeller. Now with the Merlins, it is likely the engine is not running at full Throttle at sea level, and there are losses associated with spinning all this machinery and not pushing all the air you could through it.

But they are pushing all the air they could though the supercharger at all times. They just dump what the engine can’t use at altitudes below the FTH’s, and that’s the source of the inefficiency. This is the inefficiency the Germans avoided by regulating how much engine power is used by the supercharger, thus reducing the “overproduction” of boost (a concept they nicked from the Polish).

[Viking]

Originally posted by Angus
Merlin 70 = high alt engine.

You too?

Originally posted by Viking
Here is a piece of news that might surprise you: The DB 605AS is also a high altitude engine.

[Meyer]

Originally posted by Angus
A Spitfire with a Merlin 66 or 70 weighting the same as a 109G will easily outclimb it. I have no other data. From SL to some 30K all combined that is.

I don't see any data there, just a wrong assumption... the Spitfire IX was heavier than most 109G versions.

And nowhere near a Spitfire from the same era in ROC. Except very high up?

The ROC in those charts is in the Steg-Kampfleistung regime, not in maximum power....

But if the DB was always being saved, or derated due to wear or tear, it upsets this a bit. I mean, why still be doing tests at 1,3/1,43 ATA still in 1944??????

I don't know what is wrong with doing tests at "1.3/1.43ata" in 1944, but I have no idea of what are you talking about here