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

[Angus]

I meant "IF" in the case of weight, sorry. You'd have to strip the Spit to get the lower weight.
A Spitfire Mk VIII trop from 1943 weighting more than i.e. a 109G from 1943/44 in a test (1.3/1.43 ATA) will hit 20K like some minute ahead.
I always presumed it to be mostly the wing while the engine output in the band could be similar, so I'm just scratching my head over whether there is an engine power issue as well.
The difference in NM's seems to increase as the power goes more and the aircraft heavier, so that would point a finger at the wing, but how does a 605A with 1,3/43 compare to a Merlin 66 or 70(not a cropped one)???

[Angus]

Oh, and if I understand things right the DB turbo layout is then much more flexible, while the Merlins were optimized for narrower alt bands, yes?

[joeblogs]

You may be right, I don't have the numbers in front of me. But the amount of manifold pressure a supercharger develops does not, in itself, tell you the size of the impeller.

I am not sure where this language about dumping and waste comes from when talking about gear driven superchargers. Now a turbo has a waste gate, so that is understandable. Gear driven superchargers don't have waste gates and they don't "dump" air. What ever air the supercharger takes in will go into that engine. The only question is how much air goes into that engine per stroke and per minute. Below full throttle height, manifold pressure is held back by (1) limiting RPM and (2) throttling the engine. Having expended the energy to drive the supercharger in the first place, this is wasteful.

If what you are trying to say is that by spinning the supercharger less rapidly, you can save some energy by not pushing more air per stroke as you need, that is certainly true.

-Blogs

Originally posted by Viking
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.


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]

Angus, Meyer’s point is valid; climb to altitude times are for the climb & combat power setting, not emergency power. And we both know the DB gets more power from emergency power setting than a similarly rated Merlin. The Merlin has a higher continuous power output, and thus a better climb rate in non-combat “friendly” climbs. Once you push that big red button on the 109’s instrument panel the 109 handily out climbs a contemporary Merlin Spit.

Edit: About the Spit's wings: Yes you're right that a Spit will out climb a 109 if they have the same power and weight. The wings were larger. The oval shape did not help however since climbing is done at low speeds.

[Viking]

Originally posted by joeblogs
If what you are trying to say is that by spinning the supercharger less rapidly, you can save some energy by not pushing as much air per second as you need, that is certainly true.

That's what I have been trying to say (and what the Germans did). I thought they dumped the extra pressure through a valve/waste gate system, but I'm not sure. Just throttling the engine seems even worse since then the supercharger would have to fight the build-up of pressure.

[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.

I did. The advantage is not "when the second oil pump starts to increase speed etc. but all the way to critical altitude if need be. The choice of impeller gear ratio could be more radical but that would mean more excess heat generated by the clutch which would again need to be wasted. So it needs to be a compromise.

 
    "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.

Yes, which again depends on barometric pressure, a very very important factor in aeroengine performance. I see no reason why it would produce overpressure unless something is not adjusted 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.

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

The clutch does the controlling of charge pressure, not the butterfly valve. The valve is used for other reasons, not to regulate the power as a primary function.


    "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.

I don't have to as I wrote it, but let me expalin a bit more: 4% slip i.e. loss of the power that is needed to turn the supercharger. Not 4% loss of the engine power because all of the engine power is not used to turn the charger.

***

The speed of the tips of the impeller is a major factor in impeller design. When the speed gets too high the air suddenly gets hotter which causes a surge in intake temperature which causes knocking which again needs to be countered by either more intercooling or by dropping the impeller speed.

If you have a big impleller it can still move air at high altitude without too much tip speed where as a smaller impeller reaches its critical tip speed and thus altitude earlier.

-C+

[joeblogs]

Tip speed is increasing in the diameter of the impeller. Just think of the distance the tip is covering as the impeller rotates - it is the circumference of the impeller.

This is the same principal as the propeller - the end of the propeller reaches Mach 1 before the disc does. That is one reason why there is a twist on propeller blades. It is also one of the reasons for reduction gearing on engines that turn higher than 2000 RPM.

-Blogs

Originally posted by Charge

If you have a big impleller it can still move air at high altitude without too much tip speed where as a smaller impeller reaches its critical tip speed and thus altitude earlier.

-C+

[gripen]

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

The DB 605AS as well as the DB 605A charts can be found from Valtonen's article and Raunio's article in SILH 1/2005. Charts on GJ+FX can be found from TOCH.

Originally posted by Viking

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.

As you can see, at 10000m so called high altitude DB was nearly equall with low altitude (or medium altitude if that suits your needs better) version of the two stage Merlin.

Originally posted by Viking

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.

Have a look here.

Ladedruck = manifold pressure
Gebläsedruck = pressure between impeller and the throttle valve

As you can see the DB does quite large overpressure all the way up to the 2nd FTH. That means that large part of the theoretical advantage is lost.

Besides the oil system of the supercharger caused continous problems.

Originally posted by Viking

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.

 

Perhaps you should actually try to understand the data posted above. Direct mechanical supercharger is more efficient everywhere else except between the 1st and 2nd FTH.

Originally posted by Charge

The advantage is not "when the second oil pump starts to increase speed etc. but all the way to critical altitude if need be. The choice of impeller gear ratio could be more radical but that would mean more excess heat generated by the clutch which would again need to be wasted. So it needs to be a compromise.

 

Well, the possible advantage lies only in the area where hydraulic coupling works enough effectively. The DB 605AS had 1st FTH around 2500m without RAM and around 3000m with RAM while roughly comparable V-1650-7 had 1st FTH around 1900m and around 3000m with RAM so there is no any advantage for the DB but losses due slip and heat (direct mechanical gear has no these losses).

Originally posted by Charge

 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.

Aneroid does not measure MAP but outside pressure on it's orifice . The optimal impeller speed depends on needed MAP. See the link above giving the MAP and "Gebläsedruck".

Basicly the aneroid using outside pressure gives just rough adjustment and rest is done with throttle valve, therefore the engine is running more or less throttled up to the 2nd FTH. Just look the MAP and Gebläsedruck values in the graph linked above (there is several similar graphs in that site).

Originally posted by Charge

 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.

You see the problem; you don't understand at all how the adjustment of the hydraulic coupling and MAP worked in the DBs. That NACA report presents just optimal case which is not reality with the DBs.

Originally posted by Charge
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.

Well, direct mechanical gear does the same with less power and without losses due to heat and slip. Other way to think the same issue is that at same gear ratio on direct mechanical gear spins 4% faster and without losses due to slip and heat.

[Angus]

Originally posted by Viking
Angus, Meyer’s point is valid; climb to altitude times are for the climb & combat power setting, not emergency power. And we both know the DB gets more power from emergency power setting than a similarly rated Merlin. The Merlin has a higher continuous power output, and thus a better climb rate in non-combat “friendly” climbs. Once you push that big red button on the 109’s instrument panel the 109 handily out climbs a contemporary Merlin Spit.

Edit: About the Spit's wings: Yes you're right that a Spit will out climb a 109 if they have the same power and weight. The wings were larger. The oval shape did not help however since climbing is done at low speeds.

Could you tell me why I find NO SOURCE for this??????????????????????
I have been begging for 109 tests for years, yet half of what I have just popped up in this thread. While the Spitfire climbing tests give me some data and not nearly enough, they are vastly more that all combined as a good reliable source of the Db & 109.

So, need to get clearer on this, - after all, comparing MIL to WEP is a bit of a ...wop

Are the Spit performance tests done at absolute peak power?

As for the wings, you are wrong. The oval  shape helps overcome (lift) induced drag, which is much more noticable at lower speed or if you you  prefer, larger A.o.A.. The bigger wings would then become a handicap in the end run where the biggest factor is parasite drag, - like in a dive.

[joeblogs]

Now I am confused.

I thought that up to the 1st FTH, the impeller spun at a constant multiple of crankshaft speed. As the plane climbed, the pilot would continue to open the throttle (which I believe also regulated RPM if I understand the German automatic controls correctly) until it was wide open at the 1st FTH. Thereafter, I thought all the action was done by the clutch, which countinuously increased the multiple of crank speed until the 2nd FTH was obtained. Am I wrong?

-Blogs

Originally posted by gripen
...

Basicly the aneroid using outside pressure gives just rough adjustment and rest is done with throttle valve, therefore the engine is running more or less throttled up to the 2nd FTH. Just look the MAP and Gebläsedruck values in the graph linked above (there is several similar graphs in that site). ...

 [/B]

[gripen]

Originally posted by joeblogs

I thought that up to the 1st FTH, the impeller spun at a constant multiple of crankshaft speed.

Yes, the impeller runs constant speed until the second oil pump starts to increase the speed of the impeller at 1st FTH by increasing the oil flow through the hydraulic coupling which decreases the slip of the clutch.

Originally posted by joeblogs

 As the plane climbed, the pilot would continue to open the throttle (which I believe also regulated RPM if I understand the German automatic controls correctly) until it was wide open at the 1st FTH.

The pilot has no direct control of the throttle valve, he just chooses the wanted MAP/RPM combination and the automatic controls does the rest (that is why throttle control stick used by pilot is called "leistung hebel" in the Bf 109).

Originally posted by joeblogs

Thereafter, I thought all the action was done by the clutch, which countinuously increased the multiple of crank speed until the 2nd FTH was obtained. Am I wrong?

You have the same misunderstanding as Charge; the aneroid has no information about the current MAP, so it just starts to reflow more oil to clutch just based on outside pressure regardless the MAP. So the automatic controls do the fine tuning of the MAP using the throttle valve between the impeller and intake manifolds. You can see the amount of throttling needed by looking the "ladedruck" and "gebläsedruck" curves linked above.

[Knegel]

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.

Hi.

in that chart i see the V-1650-3 with less than 1150hp at 10000m(32800ft)

The DB605AS had 1200PS @ 8000m, not rammed.
From the DB605A we know that the Vmax got reached at around 6700m altitude, so around 1000m above static FTH. The DB605AS max power with RAM @ 10000m must have been rather similar to that of the high alt Merlins, specialy when the speed and so the RAM effect was the same.

Greetings,

Knegel

[gripen]

Originally posted by Knegel
,in that chart i see the V-1650-3 with less than 1150hp at 10000m(32800ft)

Well, the chart is hard to read but the value is in the ballpark anyway. The GJ+FX power value is overestimated as well because I used the DB 605A chart.

Originally posted by Knegel

The DB605AS had 1200PS @ 8000m, not rammed.
From the DB605A we know that the Vmax got reached at around 6700m altitude, so around 1000m above static FTH. The DB605AS max power with RAM @ 10000m must have been rather similar to that of the high alt Merlins, specialy when the speed and so the RAM effect was the same.

I'm refering flight tested values of the GJ+FX at high speed. Generally the DB 605s had continous problem to reach specified performance; as an example the DB 605A did it's claimed unrammed FTH at about climb speed (ie with some RAM). The GJ+FX has the highest tested FTH at the high speed of the AS data I have and it's still below the specification.

[Charge]

GJ+FX? You mean this? http://kurfurst.allaboutwarfare.com/Performance_tests/109G_DB-G6AS_wMW/DB_109G6_ASM.html

How much below specification is it?

"the impeller runs constant speed until the second oil pump starts to increase the speed of the impeller at 1st FTH by increasing the oil flow through the hydraulic coupling which decreases the slip of the clutch."

There is no sense in using a specific oil pump to feed the clutch but to use the  oil pressure from pump that feeds the engine and just do what ever you do to regulate the pressure after the clutch and thus control the rotation speed.

"Ladedruck = manifold pressure
Gebläsedruck = pressure between impeller and the throttle valve

As you can see the DB does quite large overpressure all the way up to the 2nd FTH. That means that large part of the theoretical advantage is lost."

I don't see such thing. The system maintains steady ATA and delivers good power at low FTH and high FTH without large fluctuations in power output. Looks good.

"Besides the oil system of the supercharger caused continuous problems."

What kind of problems? Blown engines because of over pressure or just no pressure?

The only thing I know was low engine oil pressure because of which de-aerators were installed but that did not solve the problem.

"Tip speed is increasing in the diameter of the impeller. Just think of the distance the tip is covering as the impeller rotates - it is the circumference of the impeller."

Of course, but as the impeller is larger it is capable of moving more air but it is rotated slower than a smaller one because the tip moves faster and thus reaches the speed limit earlier.

-C+

[joeblogs]

Gripen:

No I don't have the same confusion as Charge. I know the clutch works off external atmoshperic pressure - I've seen the engineer's drawings. I am simply asking for some precision about the source of power increases above the 1st Full Throttle Height as altitude is increased.

Up to the 1st FTH, increased power with altitude can only come from increases in RPM and opening the throttle. I understand the German controls choose the combination of RPM and throttle automatically.

Now, at the 1st FTH, is it the case the engine is at maximum RPM with the throttle open or not? If the answer is yes, the only gain in power at altitudes above the 1st FTH must come from spinning the supercharger at ever increasing multiples of crankshaft speed. Tthis seems entirely possible.

But it does not have to work that way. There is no law of physics that says the engineers would set the 1st FTH where the engine is opened wide up. In that case, increases in power above the 1st FTH would come from a combination of (1) increased multiples of supercharger speed relative to crankshaft speed, (2) increased RPM, and (3) opening the throttle.

So which is it?

Originally posted by gripen
You have the same misunderstanding as Charge; the aneroid has no information about the current MAP, so it just starts to reflow more oil to clutch just based on outside pressure regardless the MAP. So the automatic controls do the fine tuning of the MAP using the throttle valve between the impeller and intake manifolds. You can see the amount of throttling needed by looking the "ladedruck" and "gebläsedruck" curves linked above. [/B]