Merlin vs. DB601

[Neil Stirling]

DB 601 N description

Neil.

 

[tomo pauk]

I'd really love if knowledgeable people (or/and those that can look after the original chart at Kew) would be so kind to 'dig out' the original chart posted here (by Kurfurst!). I've tried to make it more user-friendly, by drawing out the lines in different colors.
The Mk.VIII (for Fulmar I), was capable for 1275 HP on SL and for take off at +9 psi (not at +10 psi - that is for the Mk.X); +9 psi on 100 oct fuel was the maximum boost according to the Fulmar's manual.
The dark blue line should be for Mk.30. I'm not sure about two last lines, the part above ~15000 ft looks like Mk. 46/47, but those two engines were with single speed supercharger, unlike what we can see at the graph.
Combat powers are colored brown (Mk.VIII), red (X; just in low gear here), light green (III), yellow (XII).

Since the graph was of low quality, I'll again ask for clarifications, suggestions corrections

 

[tomo pauk]

Merlin fuel consumption could vary according to the fuel used and boost pressure: the BASIC specifications were:

<snip>

Merlin 45-50 series:

<snip>

Hello, Aozora,
The single speed engine mentioned there (Merlin 35, a.k.a. T-24-2) was the post war engine, not the Merlin 45-50. The supercharger gear ratio was, for Merlin 45, 9.089:1, vs. 8.588:1. The manual is probably post-war.

 

[Aozora]

Hello, Aozora,
The single speed engine mentioned there (Merlin 35, a.k.a. T-24-2) was the post war engine, not the Merlin 45-50. The supercharger gear ratio was, for Merlin 45, 9.089:1, vs. 8.588:1. The manual is probably post-war.

Ah ha, well spotted! Okay, looking at the Spitfire VA/VB Pilot's Notes, maximum consumption was 88 gall/hr @ 3,000 rpm and +9 lbs boost. It would have been much greater in the Merlin 55 operating at +18 lbs.

 

[tomo pauk]

No pain, no gain - one that wants power, will usualy pay it through increased consumption. The Merlins with suffix 'M' (= cropped supercharger) were capable for boosts of +18 psi, the 'regular' ones were capable for up to +16 psi.

The small story about the DB-601 would not be complete without taking a look at some other versions of the DB-601A. Eg. the DB-601A-0 (installed on Ju-52 in 1936, so more or less a prototype, or zero-series) was allowed for 2500 rpm for take off, the take off power, however, was still 1100 PS. Altitude power was a tad smaller than what the DB-601A of BoB era was capable for. Interestingly enough, the data sheet states that fuel injection not just enabled more power against the DB-600, it also enabled lower consumption (here, in German).
The 'real' 1st DB-601s were outfitted with a supercharger that was still not as good as the DB-601s of BoB vintage. If I'm not mistaking it badly, the 'old' supercharger have had 12 blades, each only 5mm wide. New supercharger was with 13 blades, each 12 mm wide. I assume the quoted width was measured at the circumference? The power with 'old' supercharger was 1020 PS at 4 km, vs. at 4.5 km with new supercharger, take off power remained the same. graph
Engines with new supercharger were some times named as DB-601A-1. People might be interested in this graph of the DB-601 (with new supercharger), kindly provided by krieghund:

On the bottom of the chart there are lines for power equivalent of the exhaust thrust available at 600 km/h, that goes from roughly 10% of the 'shaft power' at SL to ~12% at 4.5 km (the ram effect is not accounted for, however). Circa 130 HP was the worth at that altitude. The lines entitled with 'Staudruck = 1200 kg/cm^2' down to 0 kg/cm^2 are for engine power that uses different amounts of ram, ie. a real-world use of the engine in a flying aircraft.

The another important version was the DB-601Aa. The 'a' in the name means 'ausland', ie. engine intended for export. The likely consumers would be Yugoslavia (for their Bf-109E-3), Italy (probably only a small quantity for MC.202 and Re.2001, and for licence production), Japan (base for Ha-40, plus small quantity of actually bought engines?). The engine differed from the 'regualr' DB-601A by having a different (smaller?) supercharger, was capable for slightly greater RPM and manifold pressure, the power at lower altitudes was greater, while above 4.5 km it was producing just about 20 PS less than 'new' DB-601A.

This graph was also provided by krieghund.
The line marked with 2 arrows is for total (shaft HP, plus exhaust thrust equivalent) power, peaking at ~1230 at 3.7 km for airplane flying at 600 km/h. Again, unfortunately, that line does not take in account the effects of the ram at such speed. The lines named with 'Stau 1200 kg/cm^2' and lower pressures are for shaft power with ram accounted for. Probably the most interesting line is the one emanating from 1050 PS (2400 rpm, 1,35 ata), being at 1100 PS up until 3.7 km.
Seems like the DB-601Aa was also used by Luftwaffe, mostly for Jabos, because of better take off power?

As before, corrections and additions are welcomed

 

[Jugman]

From Whitney. The V-1710-39 (F3R) had 7,161 parts. There is about 700 different part types in an Allison. The V-1650-1 has about 11,000 parts total and 4500 different types of parts.

Author Robert J. Neal claims the Packard Merlin (most likely the two-stage models) has slightly over 14,000 parts as compared to the 4M2500's 10,000. I have seen somewhere that the two-stage Merlin had over 13,000 parts. But can not remember where I saw that though.

Whitney says of the V-3420; "There were only 340 parts unique to V-3240, accounting for 930 different pieces per engine, out of a total of 11,630 pieces in the engine."

The "typical" R-2800 had 13,000 parts and 1400 different part types.


Total part count for some Wright engines. (From Whitney)

R-2160 10,200
R-2600 8000
R-3350 10,150

If I recall correctly the WW2 era R-1820 had about 6,000 to 6,500 pats.

 

[GregP]

Since I counted the parts myself, I believe the 7,000 claim and don;t doubt 7,100. I cannot see that adding a second supercharger stage would add 2,000 parts under any circumstances.

It would add a second wheel case, the impeller and bearings, the gaskets, and the screws or bots and nuts, washers, and cotter pins (or pal nuts) to hold it together. plus the shaft connection and drive gears. That just isn't going to be 2,000 parts.

 

[GregP]

Hi Wuzak,

I went to the authority on semi-factual data, Wikipedia. I typed in "Daimler Benz DB 605" and got to a page.

At the bottom of the page, the DB 605AM is quoted as 1,324 kW for takeoff at 2,800 rpm with MW-50 injection. They don;t say when the power measurement was taken.

I convert that to 1,775.5 HP - the 550 ft-lbs/sec type HP. It is also 1,800 cv or PS horsepower, unless my math is wrong.

I did not question the great Wiki and concede that , though it has obviously never happened before, Wiki might be wrong. Obviously you think so?

Maybe we should use a lesser number than 1,324 kW? Suits me, no argument here.

Post a good number for the DB 605 - a typical wartime unit of, say, about mid-to-late 1944. Max power, with whatever injection was being used at the time.

 

[wuzak]

Hi Wuzak,

I went to the authority on semi-factual data, Wikipedia. I typed in "Daimler Benz DB 605" and got to a page.

At the bottom of the page, the DB 605AM is quoted as 1,324 kW for takeoff at 2,800 rpm with MW-50 injection. They don;t say when the power measurement was taken.

I convert that to 1,775.5 HP - the 550 ft-lbs/sec type HP. It is also 1,800 cv or PS horsepower, unless my math is wrong.

I did not question the great Wiki and concede that , though it has obviously never happened before, Wiki might be wrong. Obviously you think so?

Maybe we should use a lesser number than 1,324 kW? Suits me, no argument here.

Post a good number for the DB 605 - a typical wartime unit of, say, about mid-to-late 1944. Max power, with whatever injection was being used at the time.

Earlier versions used less boost and had less power. They were about 1450hp. As they developed the engine they were able to give it more boost and get more power.

Your comparison was with an early Merlin XX.

 

[GregP]

At 1,450 HP and 2,800 rpm, that would put the DB 604 at 12.97 Bar MEP.

HP = (Torque * rpm) / 5,252. So Torque = (5,252 * HP) / rpm.

BMEP (psi) = (150.8 * Torque (ft-lbs) / Displacement (cu in).

I converted psi to Bar after the calculation. 1 psi = 0.068947333 Bar.

 

[OldSkeptic]

The hydraulic supercharger drive was not more efficient; its variable speed was by deliberate slippage in a fluid coupling. This may have resulted in improved system performance, but it was not "more efficient."

The inverted-V may have helped visibility in some installations, but not when an annular radiator was used.

The side-mounted supercharger may have permitted an engine cannon, but it also forced some amount of asymmetry in the combustion conditions between the left and right banks of the engine.

Fuel injection was an advantage, especially over the float-type carburetors preferred by Rolls-Royce. The pressure-type carbs used by the US companies did not have that problem.

Correct, just like the impacts of a 'slush box' automatic transmissions, you get power losses due to hydraulic slippage. The advantage was a much smoother between gear (on a 2 speed engine) power curve, at the expense of less actual power at the peaks.

The individual point fuel injection was complex, expensive and probably a nightmare to maintain. It also reduced the efficiency of the engine, by not having the charge cooling effect of fuel being injected pre the supercharger. It did give the advantage of no negative G impacts, but carbs soon caught up with the anti G SUs and the Strombergs.
It also consumed some power as it was a mechanical system.

Naturally RR, when they added fuel injection in the late 100 series Merlins, used a single point injection prior to the supercharger to maintain the charge cooling effect.

Interesting was BMW's C3 injection, where they (over and above the multi point injection) added another fuel inlet before the supercharger, which allowed greater boost for short periods of time largely because of the charge cooling effect. Makes you wonder why they didn't just get rid of all the individual cylinder injection ports and just use the single pre supercharger one.....


Curiously RR originally planned the Merlin to be inverted, but Hawker and Supermarine both wanted it upright.

 

[tomo pauk]

Correct, just like the impacts of a 'slush box' automatic transmissions, you get power losses due to hydraulic slippage. The advantage was a much smoother between gear (on a 2 speed engine) power curve, at the expense of less actual power at the peaks.

How much the power was actually lost due to slippage - do we have actual numbers? The P&W went to similar system with the single stage R-2800-30W, installed in the F8F-2. The horse power in war emergency rating was 1800 HP at 23250 ft, ie. the power in WER was between two stage B and C series of engines. Allison also went for similar system to power the auxiliary stage of their 2-stagers, those engines quickly went to achieve considerable power.
The DB-601 was at lest comparable, in power, with single stage Merlin when using same fuel; the DB-601E was patiently more powerful than any single stage Merlin, on same fuel.

The individual point fuel injection was complex, expensive and probably a nightmare to maintain. It also reduced the efficiency of the engine, by not having the charge cooling effect of fuel being injected pre the supercharger. It did give the advantage of no negative G impacts, but carbs soon caught up with the anti G SUs and the Strombergs.
It also consumed some power as it was a mechanical system.

Few people will argue that multi-point injection is/was a as cheap as single carburetor. Comparing injection with several carburetors per engine, as used on Hispano/Klimov and Isota-Fraschini engines, it was a blessing. We can note that many minor powers used the engines with inection, and Italy and Japan went to produce, no other than DB-601 under licence. Seem not that utterly expensive complicated thing?
I'll argue about the claim that MP injection decreaces engine efficiency. The V-12 engines with a single, big carburetor need to have backfire screens in intake system, in order to prevent backfire. In V-1710 it cost between 1000 and 1500 ft in full throttle height.
The specific fuel consumption of DB-601 was lower than of 1-stage Merlin, by some 10%.
The (1-stage?) Merlin received SU carbs some time in second half of 1942, and the benefits were apparent immediately (" Table III shows that the aircraft is appreciably better than most other Spitfires, after allowing for differences in weight and wing span, the gain being about 1,500 ft. in ceiling and 8-10 m.p.h. in top speed. Both of these improvments may be attributed to the removal of the carburettor, causing a lower pressure drop of the engine air before entering the supercharger, and thus giving an appreciable rise in boost pressure"; here) - ie. float cabs were not susceptible for negative G conditions, but cost power.

Naturally RR, when they added fuel injection in the late 100 series Merlins, used a single point injection prior to the supercharger to maintain the charge cooling effect.

The Merlin 100 series still had the backfire screens?
The DB introduced water injection and better superchargers in DB-605AS/D/L and it took Griffon to beat them in altitude power. We can also recall that one of cures for the temperamental R-3350 was to introduce fuel injection, so each cylinder can receive exact amount of fuel.

Interesting was BMW's C3 injection, where they (over and above the multi point injection) added another fuel inlet before the supercharger, which allowed greater boost for short periods of time largely because of the charge cooling effect. Makes you wonder why they didn't just get rid of all the individual cylinder injection ports and just use the single pre supercharger one.....

The additional C3 injection did not take much hold. It was dispensed with when BMW-810D was cleared for greater manifold pressure, up to 1,65 ata - simmilar clearance procedure as when Merlins were cleared for greater boost due to availability of better fuel.

 

[Shortround6]

I believe the "loss" of power in the fluid coupling was on the order of 2-3% of the power to drive the supercharger when the fluid drive was fully locked up, ( full throttle height). At lower altitudes the the loss could be much higher.

However the fluid drives did heat up the oil used in the hydraulic coupling and since this was often shared oil with the engine it required larger oil coolers. An Allison V-1710-143 engine making 1600hp/3200rpm/sea level was adding 117hp worth of cooling load to the oil system because of the drive for the auxiliary supercharger.

 

[wuzak]

The DB introduced water injection and better superchargers in DB-605AS/D/L and it took Griffon to beat them in altitude power. We can also recall that one of cures for the temperamental R-3350 was to introduce fuel injection, so each cylinder can receive exact amount of fuel.

I suppose being of similar capacity. and not 30% less, was helpful for that!

 

[OldSkeptic]

I suppose being of similar capacity. and not 30% less, was helpful for that!

Well said. And the later, 100 series Merlins matched that.....

 

[Juha]

...The DB introduced water injection and better superchargers in DB-605AS/D/L and it took Griffon to beat them in altitude power. ..

Hello Tomo, 70 series Merlins were not powerless at altitude, combat power 1475bhp at 6800m.

Juha

 

[Juha]

db

 

[tomo pauk]

I suppose being of similar capacity. and not 30% less, was helpful for that!

Of course.
My comments at above post were to underscore that each engine have had it's advantages and shortcomings, and that engine developments was continuing during the war in all countries.

Hello Tomo, 70 series Merlins were not powerless at altitude, combat power 1475bhp at 6800m.

Juha

Agreed. It took Germans quite a time (about a year?) to come out with something comparable, ie. with DB-605AS.

 

[gjs238]

Wonder if direct injection V-1710's would have performed better in the P-38's at high altitude.

 

[gjs238]

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