DB 601Aa Dauerleistung power issue

[Mantis49]

Greetings everyone.

The datasheet found on kurfurst.org: Kurfürst - DB 601, 603, 605 datasheets - DB 601 Aa
claims that on Dauerleistung power setting, DB 601Aa has an output of 950PS at 0m and 880 PS at 4500m.

However, the way that the turbocharger on all DB 601 series engines works, their output at rated altitude is always slightly greater than the power they yield at sea level at the same RPM. Therefore, its is very unlikely that DB 601Aa should have whole 80 hp less at 4500m than it does at SL, especially considering that the former value is cited for a setting of some 100 RPM less than the latter.

My guess is that one of these values is simply a typing error. The big question is, which one's right - 850 and 880 PS, or 950 and 980 PS, correspondingly? This far, I've been unable to obtain the power curves for 601Aa, which would've solved the dilemma once and for all.

Does anyone have any documents on DB 601Aa not derived from this datasheet (values from NII VVS report certainly are), or any other info to provide insight on the matter?

 

[Shortround6]

We may be loosing something in translation.

The DB 600 series of engines did NOT have a turbocharger. They had a mechanical drive supercharger.

The supercharger spun at about 7 (not looking at the books so I don't remember the exact ratio)times the crankshaft speed at low altitude and as the hydraulic coupling tightened up as the plane gained altitude the ratio increased to the supercharger spinning at about 10 times the crankshaft speed. Since the power needed to drive the supercharger goes up with the square of the supercharger speed the supercharger took about TWICE the power to drive at high altitude as it did at low altitude.

Complicating things is that the fact that at "sea level" the throttle was not fully opened. Like the DB 605, the throttle was part closed at sea level and was opened as the plane climbed (with the supercharger staying at maximum slip) until somewhere around 2000 meters. At this point the throttle was fully opened and the engine made max power ( a bit above sea level power) and then as the plane climbed higher the supercharger began to slip less, until it reached a height at which the supercharger hit maximum rpm and power fell off much faster as the plane climbed.

 

[Denniss]

The 601A-0 datasheet (same supercharger) shows the same sharp power loss above rated alt, the 601A-1 with the improved supercharger was able to retain it's power far above rated alt.
Either there's a problem with these two datasheets or the improved supercharger was far more effective at alt than the original one (I assume old one was taken from DB 600).

Also visible: despite raising rated alt by just 500m the 5 min max power alt raised 800m while losing only 5 PS, 30 min max power raised by 900m although with 40 PS less.

 

[tomo pauk]

From the manual for the DB-605A/B:

 

[Mantis49]

We may be loosing something in translation.

The DB 600 series of engines did NOT have a turbocharger. They had a mechanical drive supercharger.

Oops, my mistake. Of course I meant supercharger here.

The 601A-0 datasheet (same supercharger) shows the same sharp power loss above rated alt, the 601A-1 with the improved supercharger was able to retain it's power far above rated alt.
Either there's a problem with these two datasheets or the improved supercharger was far more effective at alt than the original one (I assume old one was taken from DB 600).

Also visible: despite raising rated alt by just 500m the 5 min max power alt raised 800m while losing only 5 PS, 30 min max power raised by 900m although with 40 PS less.

Hmm... considering that Aa has the same supercharger as A-0 (I didn't know that), while A-1 and N-1, of course, have upgraded ones - maybe there's no typing error in the datasheets at all, as I initially assumed, and it's just that early DB601s had a much much sharper power drop-off above rated altitude. Thanks.

On a side- but related note, does anyone have any idea which of the DB601As can this chart and these power curves be attributed to?
RPM and power values at SL seem to be in line with the datasheet for DB 601A-1 from kurfurst.org. Figures at altitude, however, do not match at all

UPD: the power curves look identical to what tomo pauk posted, thanks. The question still stands - which version of the 601A exactly are they supposed to describe?

 

[tomo pauk]

Mantis, from the second link/picture:

If I'm reading it correctly, with the new supercharger (bei neuem Lader), having 13 vanes, each 12 mm wide 1 mm tick, the full throttle height was increased to 4,5km (verschiebt sich die Nennleistungohe auf 4,5 km), and supercharger was cutting in at 2,1 km now, instead of 1,6 km. All of that gave, for example, 50 HP at 6 km, and 40 HP at 2,1 km.

All in all, seeem like my chart is for DB-601A-1, and the chart from Williams' site is for DB-601A?

 

[krieghund]

Hi Gents, this is the chart for the DB601Aa engine. Looks like the higher critical altitude has the greater power.

 

[Mantis49]

All in all, seeem like my chart is for DB-601A-1, and the chart from Williams' site is for DB-601A?

Huh, I didn't notice the 500m diffference in full throttle altitude at first.
You're right - if we apply these corrections from this note to the curves form William's site, I guess we'll get the curves you posted as a result.

So yours indeed should be for the A-1, and the ones from wwiiaircraft - for the A-0.

Hi Gents, this is the chart for the DB601Aa engine. Looks like the higher critical altitude has the greater power.

Thanks a lot! This solves everything)

 

[tomo pauk]

For the DB-601Aa, the critical altitude, no ram, was at 3700m (5 min Kurzleistung, thicker continous line), engine making 1100 PS there. At 6 km it makes 825 PS. Ie. the FTH, or critical altitude, was 800 m lower than for A-1, and 300 m lower than for A.

The Aa ('a' is for 'ausland', ie. export engines) was sporting a reduced capability supercharger (vs. A-1), so the altitude performance was not that good as in A-1. However, since the supercharger was also drawing less power to drive, more power under full throttle height was available for the propeller, eg. 1100 PS at 1,6km vs. 1050 (5 min rating), or 1175 at sea level vs. 1100 (1 min rating), Aa vs. A-1. The DB601Aa beats DB-601A, however.

We can see that, at FTH, the exhaust thrust at 600 km/m was to add another 10 % of power equivalent.

IIRC the Aa engine found the way to the Luftwaffe, too?

 

[Mantis49]

IIRC the Aa engine found the way to the Luftwaffe, too?

I've just read about that recently:

Luftwaffe and Allied Air Forces Discussion Forum - View Single Post - DB601A-1 = Aa ??

 

[bruno_]

Just one question about the relationship between supercharger speed W and the power P the supercharger needs to work: is P proportional to W^2 or to W^3 ?

 

[davebender]

DB601 engine production wasn't expanded until 1940. Then you need about a year for factory construction. So engines were probably in short supply prior to mid 1941. Under such circumstances you use all available spare engines even if they are the wrong model.

 

[Denniss]

There were not really enough DB 601 availabe thus they cancelled the He 111P in favour of the Jumo 211 equipped H. But they didn't ground the P to recycle their engines for use in fighters so the situation can't be that bad.
The 601Aa was preferred for the bomb trucksand their low-alt raids with additional power for take-off and low-alt speed.
The 601N had even more power but proved to be problematic in its initial version.