# Merlin vs. DB601



## wiking85 (Jan 10, 2014)

Which engine was better the Merlin or DB601? From what I can tell the Merlin had a lower displacement, but the same weight (roughly) as the DB; why was that? What did the Merlin have that made it capable of the same or better HP at lower displacement than the DB?


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## davebender (Jan 10, 2014)

> What did the Merlin have that made it capable of the same or better HP at lower displacement



RR Merlin employed higher compression and/or supercharger boost. 

Higher RPM is the other primary method for getting more power out of small displacement engines.


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## GregP (Jan 10, 2014)

The Germans were operating on lower octane (or performance number if greater than 100) fuels and so could not use the same compression ratio and rpm. They had to limit cylinder pressure to prevent detonation.

In my view, the DB 6 series were excellent engines with very few negatives. That the Germans used manual starting was their own choice. Today an DB can be fitted with an electric starter. One main issue in a wartime pistion was reliability and the DB seems to me to have been VERY reliable.

We know the Merlin was good one.

Which was best? Can't say but, in terms of engineering, neither took a back seat. We KNOW the DB 601 / 605's propelled Bf 109's up to 35,000+ feet with hydraulically-driven superchargers quite effectively.

I have not seen any average TBO's for the DB, but Merlins were in the neighborhood of 250 hours or less. Well. let me temper that, the military prescribed overhaul was around 250 - 400 hours. The Allison was anywhere from 300 - 1,000 hours depending on the expected engine stress in the installation. Typical was around 450 hours. 

I've seen a 1942 review of the DB 601 in "Flight" magazine that estimated overhaul every 100 hours, but would love to see real overhaul numbers for the DB series as well as the Jumos. The DB 601 manual I saw never mentioned overhaul, but did require a major inspection at 150 hours. Canada has interpreted this as 150 hour TBO for the Russel Bf 109E.

So ... I can't pick which is "better" and would gladly fly behind eitther the Merlin or a DB. I HAVE flow behind a Merlin (and Allison) on a couple of occasions and would love to have the chance to ride in or fly a DB-powered aircraft. The only major wartime engines I might decline to ride behind are the Japanese Aichi Atsuta (unless they drilled the front gearcase oil hole that was left out on the original Japanese version) and an early Nakajima Homare (had a lousy reliability reputation). I might think really hard about riding behind a Russian WWII piston engine, but that is due more to the state of the current part supply than the design of the engines. 

I can tell you the Nakajima Sakae 21 in our A6M5 Model 52 Zero has been flawlesssly reliable. 

Nothing to do with the Merlin or the DB, but is just for info.

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## davebender (Jan 10, 2014)

Water injection became common on aircraft engines during 1944 and it made quite a HP difference. Not sure why it wasn't employed earlier.


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## tomo pauk (Jan 10, 2014)

I reckon it you are talking about single stage Merlin? 
The things were very much 'fluid', power-wise, with newer engines quickly supplanting older ones.

At any rate, Merlin turned notably bigger rpm than DB-601A (3000 rpm vs 2400). It's supercharger intake section were probably designed for greater flow of air (1030 HP at ~16000 ft vs. 1006 HP at 14500 ft). Merlin was using one of lowest compression ratios (6:1), that meant it was able to use much greater boost levels than other engines. RR took advantage of that, and Merlin III was able to produce 1300 HP at 9000 ft, boost pressure being there +12 lbs per in^2 (vs. +6 lbs per in^2 on 87 oct fuel). Please note that benefits of better fuel were confined at lower altitudes - Merlin III was producing same power above 16000 ft be it with 87 oct fuel or with 100 oct. The DB-601 was later (later in 1940) allowed for 2600 rpm, here, though the increased power is not noted?
The DB-601 have had advantage of having the variable supercharger drive - instead of only one supercharger drive ratio in Merlin III, the DB-601 was able to vary the speed of it's supercharger, so it will take just a small power to drive it under 2 km of altitude (= more power left for the propeller). The net benefit is that take off power was 1100 PS (~1085 HP), vs. 880 HP of the Merlin III.
RR was aware of this Merlin's shortcomings, so they introduced Merlin X (2-speed supercharger) and Merlin XII (improved Merlin III, with reinforced internals so it was able to withstand +12 lbs boost even with engine in static position). The Merlin XII (Spitfire II) was able to give 1175 HP for take off, and, due to changes in supercharger system, a bit more power higher up. Merlin X never went in the fighters, the power was comparable with Merlin III above 16000 ft, take off power was 1065 HP.

Germans also moved on, with DB-601N. It was using C3 fuel (roughly 100 oct?), vs. B4 fuel (~87 oct). The RPM were increased to 2600, so power at altitude also went up considerable - at ~15700 ft, the 1-minute power was ~1160 HP, the 30-minute power was 1035 HP at about same altitude. Take off power also increased (+75 PS), and 1-minute rating was available at all altitudes, vs. only SL to ~2km for the 601A. At 3 km (~9700 ft), the 601N was giving ~1220 PS, vs. 1040 for the DB-601A. Benefits of better fuel? Though, it seems like benefits of better fuel were not used maximally (boost pressures were about the same as at 601A).The rev limit was upped to 2800 rpm quickly (again, in late 1940), but I don't know how much the power was increased.

British introduced, in about the same time as the Germans introduced the DB-601N (~2nd half of 1940), the Merlin XX. Stanley Hooker redesigned the supercharger system, so now the power high up was about 1150 HP at 18000 ft, take off power went to 1280 HP. Engine was used on Hurricane II with those power levels. Combat power (usually limited to 5 minutes) was equal or better than 1400 HP, under 14000 ft. The Merlin 45 (for Spitfire V) was basically the XX, but single speed supercharger. High gear was used only, so the power above ~10000 ft was about as what the XX was capable for, the power between SL and 10000 ft was slightly lower (1185 HP for take off). 

Shortly after that, DB introduced the DB-601E. It reverted back to B4 fuel, introduced changes in supercharger, valve timing other stuff (see here for more), allowed initially for 2500 rpm and 1,30 at boost. The power curve was comparable with Merlin 45. Some time in early 1942 (January, probably), the DB-601E was allowed for 2700 rpm and 1,42 ata, and power was notably increased on all altitudes (vs. Merlin 45 and XX: slightly more power above 15500 ft, slightly less under ~12000 ft; better TO power vs. Merlin 45, almost 150 HP).

Basically: power-wise, both engines were competitive enough, advantage see-sawing through time and desired altitude. The DB-601 series was a better choice if a country have had problems acquiring high octane fuel. The DB engines were also to accommodate a cannon firing through the prop shaft.

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## GregP (Jan 10, 2014)

Pretty good summation, tomo.

Maybe we should undertake to do one for a few more engines, including some radials.

Perhaps a discussion of Merlin - Griffon - Sabre contrasted with the DB - Junkers Jumo (probably at least the 213 used in the Fw 190D) contrasted with the Allison contrasted with the Klimov and Mikulin. Maybe in a new post as not to hijack this one.

I left out the Aichi Atsuta since the Japanese never quite got it right.


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## Milosh (Jan 10, 2014)

Greg, afaik the DB601 engines used 6.9:1 CR. This compares to 6:1 for the Merlins.

The DB601N engine used C3 fuel which late war had a PN of 140+ and had a CR of 8.2:1.

The DB engines were more fuel efficient due to fuel injection.

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## tomo pauk (Jan 10, 2014)

Could you post some numbers comparing the consumption, Milosh?


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## GregP (Jan 10, 2014)

Hi Milosh,

Right on about the CR. Merlin was 6.0 and the British could thus use higher boost before detonation set in. It's kind of that way at Reno these days. The winning engines are running a CR of about 5.0 and insane boost numbers. I've heard 145 inches (56 psi or so) being bandied about by some in the unlimited gold pits ... unofficially, that is. For comparative purpose, 1.42 ata equates to 41 inches of MAP or 5.5 psi of boost, so racing these days is stressful on the engines, to say the least.

According to the German fuels report I read and recorded, six samples of C-3 fuels averaged 95.7 Octane lean (95 to 97.5) and a rich mixture rating of 123.75 (118.5 to 125). Another report said they found two different 50-gallon samples that averaged 95.5 lean with one sample being 150 rich and the other 145 rich. These were German reports.

So we have eight samples from varying times, taken from German reports, all near 95 lean and varying from 118.5 to 150 rich. Sounds like some wartime variation was happening for sure, and you could NOT be sure what rich rating of fuel you would get. So, a good pilot who knew his engine might do some leaning and get some benefit, but a prudent commander would simply order them to use what the average could be expected to be unless in a fight for life ... and then you might as well melt the engine or die since it WAS a fight for life.

I would assume that you could NOT expect most samples to be 140+ since 6 of 8 samples from the German reports were below that number.

Note: All C-3 samples were about 40% aromatics, 37% parafins, and 21% Napthenes with specific gravities of 0.7705 - 0.7706.

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## Aozora (Jan 10, 2014)

tomo pauk said:


> Could you post some numbers comparing the consumption, Milosh?



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

Merlin II (and III) from an R-R handbook issued in May 1938:







Supplements from 1939 1941 (Merlin X specs)










Merlin 45-50 series:










Merlin 60, 70, 85 series (A.P. 1590P,S U Volume 1):











To ask whether one engine was better than the other is a little simplistic; both were fine aero engines, designed to different formulas, albeit for a similar purpose and power requirement.

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## GregP (Jan 10, 2014)

If I compare the Allison V-1710 (F-30R) against a Merlin XX against a DB 601 against a DB 605, I get data as follows:

1) Allison F-30R:
Displ (cu in) = 1710.6; rpm = 3,000; power (HP) = ,1500. MEP = 15.97 Bar (sea level, takeoff).

2) Merlin XX:
Displ. (cu in) = 1649; rpm = 3,000, power (HP) = 1,480. MEP = 16.34 Bar (sea level, takeoff).

3) DB 601:
Displ. (cu in) = 2073.9; rpm = 2,500; power (HP) = 1,159. MEP = 12.21 )sea level, takeoff).

4) DB 605:
Dsipl (cu in) = 2,180.5; rpm = 2,800; power (HP) = 1,775; MEP = 15.88 Bar (sea level, takeoff). 

So the Merlin XX is 33.8% better than the DB 601. But if we drop the DB 601 and only compare the DB 605, the difference between the best and the worst is only 2.9% in MEP! Pretty damned close, if you ask me, and I know you didn’t. I dropped the DB 601 because it was supplanted in production early-on.

The only real "apples-toapples) comparison in engines is using Mean Effective Pressure, and thsi shows them all to be VERY close to one another, as I expected before I started. For reference, I used the model that came up in Wiki for the numbers, but chose the Merlin XX since I had access to all. The merlin starts to look better up high with the 2-stage units, but not at takeoff, which is where these come from.

I think if we compared and earlier Allison, an earlier Merlin, and the DB 601. they'd all be VERY close in MEP.

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## Aozora (Jan 10, 2014)

GregP said:


> The only real "apples-toapples) comparison in engines is using Mean Effective Pressure, and thsi shows them all to be VERY close to one another, as I expected before I started. For reference, I used the model that came up in Wiki for the numbers, but chose the Merlin XX since I had access to all. The merlin starts to look better up high with the 2-stage units, but not at takeoff, which is where these come from.



Again, this depends on which version of the 2-stage Merlin is being discussed; for example, the Merlin 66 running on 150 grade at +25lbs boost is a very different animal from the Merlin 61 running on 100/130 grade at +18 lbs










It can be _so_ hard to make comparisons, particularly when comparing variations of the same basic item:

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## GregP (Jan 10, 2014)

I like the one without all those distracting clothes, myself.

However, in this case, the cup sizes are the same, whereas in the case of the engines above, the DB 605 is the busty one with the prop shaft poking out of the cup centerline. I still say they're very close ... but beauty is in the eye of the beholder, after all, and each person must pick their favorite. Somebody MUST want Phyllis Diller! Huh?

I'll stick with someone like Barbara Eden in her prime. I'd post a drawing, but it probably violates forum guidelines.

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## wuzak (Jan 11, 2014)

GregP said:


> If I compare the Allison V-1710 (F-30R) against a Merlin XX against a DB 601 against a DB 605, I get data as follows:
> 
> 1) Allison F-30R:
> Displ (cu in) = 1710.6; rpm = 3,000; power (HP) = ,1500. MEP = 15.97 Bar (sea level, takeoff).
> ...



Which DB 605 made 1775hp and when?


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## Aozora (Jan 11, 2014)

wuzak said:


> Which DB 605 made 1775hp and when?



That would be the DB 605AS/ASM series, from early 1944, or the DB 605DB from late 1944


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## R Pope (Jan 11, 2014)

The Germans fitted a captured Spitfire with a DB engine (not sure which one) and there was very little performance difference noted. The Spaniards put Merlins on 109's with little diff, too. Small advantages in some flight conditions, losses in others, I believe.


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## cimmex (Jan 11, 2014)

Well, power wise both contemporary engines were rather close. IMO the DBs offered some advantages. 
Inverted V-design offered better view over the nose, 
fuel injection ensured supply at all flight situations,
hydraulic supercharger drive was more efficient, 
side mounted supercharger allowed an engine cannon.
cimmex


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## wuzak (Jan 11, 2014)

Aozora said:


> That would be the DB 605AS/ASM series, from early 1944, or the DB 605DB from late 1944



Thanks for the info Aozora.

Regarding Greg's analysis, an equivalent period single stage Merlin would make more power than the 1480hp of the 1941/42 Merlin XX.

The Merlin 24 had a take-off rating of 1610hp, low blower of 1640hp @ 2000ft and high blower of 1500hp @ 9500ft. These are at +18psi boost.

The two stage Merlins were similar in weight to the DB 605 - the XX and 24 were lighter.

Of course, the major performance emphasis on the Merlin was the 2 stage engines. And their BMEPs were higher, though probably not at sea level.

A Merlin 76/77 was rated at 1710hp in MS gear, +18psi boost and 3000rpm, giving a BMEP of 18.9 bar, or about 18% more than the DB 605.


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## Milosh (Jan 11, 2014)

Greg, please look at the dates those fuel samples were obtained. I think you will find that most of them were early to mid war.


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## tomo pauk (Jan 11, 2014)

As for fuel consumption - the DB-601E was using 445 L/h, for 1350 PS, take off. Or, circa 118 US gals per hour. The V-1650-1 (basically, the Merlin XX), 133 US gals for 1300 HP, take off power. Maximum continuous powers: 300 L/h for DB-601E (about 79 us gals/hr) for 1040 PS; the V-1650-1 was using 93 us gals for 1010 HP. The DB-601A was using 300 L/hr when producing 960 (hi-alt) or 990 PS (SL).
So, yes - DB-601 was more fuel efficient than Merlin. But, not because of fuel injection, but because of notably higher compression ratio?


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## cimmex (Jan 11, 2014)

tomo pauk said:


> So, yes - DB-601 was more fuel efficient than Merlin. But, not because of fuel injection, but because of notably higher compression ratio?


can you please explain. I cannot see any relationship between compression ratio and fuel consumption.
cimmex


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## wuzak (Jan 11, 2014)

cimmex said:


> can you please explain. I cannot see any relationship between compression ratio and fuel consumption.
> cimmex



Higher CR means less boost required from the compressor, thus less power expended in driving the compressor, thus less fuel used for the same (or more) power output.


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## cimmex (Jan 11, 2014)

wuzak said:


> Higher CR means less boost required from the compressor, thus less power expended in driving the compressor, thus less fuel used for the same (or more) power output.


Sounds reasonable but I don’t buy it. It would be far easier to increase the CR than improve the charger to get more boost. I wonder why RR didn’t go that way.
cimmex


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## Shortround6 (Jan 11, 2014)

Actually higher compression means a higher expansion ratio in the cylinder. More work is extracted from the fuel burn before the exhaust valve opens and dumps the remaining pressure to atmosphere. However you only have so many BTUs of energy in the fuel/air mixture in the cylinder. The supercharger crams more fuel/air into the cylinder so you have more BTUs to begin with. More power even if a bit less efficient. Rounding off a Merlin at 12lb boost (27lbs total) compared to one at 6lbs boost (21lbs total) was cramming 28% more fuel and air into the cylinders. You need a *LOT* of compression to get 28% more power. 
Superchargers heat the intake mixture more than just the simple heat of compression unless they are 100% efficient (never happens) and a hot mixture is less dense even at the same pressure (less mass). A better supercharger needs a bit less power to drive, heats the air less for the same amount of boost.


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## stona (Jan 11, 2014)

cimmex said:


> Well, power wise both contemporary engines were rather close. IMO the DBs offered some advantages.
> Inverted V-design offered better view over the nose,
> fuel injection ensured supply at all flight situations,
> hydraulic supercharger drive was more efficient,
> ...



The inverted V requirement dates back to a committee of 1928, made up of various German experts. They decided that future liquid cooled aero engines should incorporate the following principal design features.

- mono-block cylinder banks,
- wet cylinder liners,
- propeller reduction gear,
- supercharger,
- fuel injection,
- high temperature glycol cooling,
- provision of a cannon tunnel in the V

These requirements were presented to the manufacturers as a fait accompli. Tender documents were sent to Daimler-Benz, Junkers and B.M.W., all of which eventually produced a V-12 engine model in response although none was able to incorporate all of the required features immediately. The DB600 had dry liners and carburettors, the JU210 also had only carburettors and the B.M.W. 116/117 only got as far as the prototype stage.

Wolfram Eisenlohr, in 1928 head of the DVL power plant division and a member of that committee, was interviewed in 1980 about the 1928 requirement for inverted V-12s and he cited three reasons for the decision.

- more compact installation,
- better pilot view for single engine aircraft,
- less exhaust flame dazzle during night flying.

The manufacturers were much less keen to turn their engines upside down.

A report was made by a British team which visited Germany immediately after the war, interviewing many of their German counterparts. The Report is called, "Comments on Visit to Germany, July 24th 1945 to August 12th 1945”.

10 persons made up the visiting party, including P. G. Barlow and E. Wolsey (M.A.P.), Mr A. Thomas (Armstrong Siddeley Motors), Mr N. Quinn (Bristol Aero Co.), Mr R. Chamberlin (D. Napier Son) and Mr G. Morris (Rolls-Royce Ltd).

Page 3 of the Report says, 

"A good example of Air Ministry [RLM] control lies in the inverted Daimler-Benz engine. The D.B. people said that both from a technical and production point of view they would have preferred to make an upright engine but they were compelled to make it inverted by the Air Ministry." 

Later. 

"With the inverted engine, they [engineers from DB] said it was very difficult to obtain consistent oil consumptions and due to the rotation of the crankshaft, one bank gets more oil than the other. For this reason the engine is built with a lower compression ratio on one bank than the other."

So it seems inversion also caused problems that the German engineers would rather not have had to deal with.

I don't think that the minimal peripheral advantages of such an installation ultimately justified the engineering challenges it raised, with the possible exception of the cannon tunnel.

Cheers

Steve

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## tomo pauk (Jan 11, 2014)

cimmex said:


> can you please explain. I cannot see any relationship between compression ratio and fuel consumption.
> cimmex



SR6 explained that well. 



cimmex said:


> Sounds reasonable but I don’t buy it. It would be far easier to increase the CR than improve the charger to get more boost. I wonder why RR didn’t go that way.
> cimmex



RR was of opposite opinion - they 1st improved Merlin's supercharger with Merlin XX in 1940, then introduced two-stage supercharger with Merlin 60, already in second half of 1941 in token numbers.


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## cimmex (Jan 11, 2014)

tomo pauk said:


> SR6 explained that well.
> 
> 
> 
> RR was of opposite opinion - they 1st improved Merlin's supercharger with Merlin XX in 1940, then introduced two-stage supercharger with Merlin 60, already in second half of 1941 in token numbers.


Sorry, cannot see any hint in SR’s post that higher CR lowers the fuel consumption.
cimmex


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## tomo pauk (Jan 11, 2014)

It's in the 2nd sentence of the post #24.


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## cimmex (Jan 11, 2014)

Increasing the CR at car engines by skimming the cylinder head was a common tuning action in my youth. We got some more power but I never noticed a lower consumption, mostly higher.
cimmex


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## tyrodtom (Jan 11, 2014)

cimmex said:


> Increasing the CR at car engines by skimming the cylinder head was a common tuning action in my youth. We got some more power but I never noticed a lower consumption, mostly higher.
> cimmex


 I've done the same, but if you modify a engine to make more power, and you use that additional power, then of course your fuel mileage goes down.
But I noticed WHEN I drove the modified higher compression engine for mileage, ( which wasn't often) it was more efficient and got better mileage.


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## tomo pauk (Jan 11, 2014)

Aircraft engines were designed from ground-up for certain CR, the CR being there in most designer's equations from day one. Nobody skimmed the heads in some depot hundreds or thousands miles away from factory. Plus, increased CR will reduce the allowable boost pressure, so more would be lost than gained.
The influence between CR and consumption was mentioned several times in 'Vee's for victory', where Allison went with no less than 6.65:1 when designing the V-1710; lower CR than that was deemed to increase the consumption. Allison was envisioning the V-1710 as air-ship and bomber engine, where consumption is a major thing. Later/post war, consumption was sidetracked, the CR went to 6:1 with G series of engines, so the boost could be increased and the engine output be closer to the same generation of Merlins.

There might be no way for people skimming heads to note decrease of consumption - they were eager to use up the newly-acquired power, consumption was not their aim. We do not now, however, the specific consumption (ie. consumption per HP produced).


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## fastmongrel (Jan 11, 2014)

You cant just increase compression ratio you need new cam profiles, new valves, you need to retime the magnetos and design a new exhaust and inlet system. You cant cram as much fuel air mix in so you have to lower supercharger ratio or the tops of the pistons and the valve heads will disintegrate. Also more compression and you have to start strengthening parts as there aint no such thing as a free lunch. 

My forum name Fastmongrel comes from a bike I used to race an Aermacchi 350cc air cooled pushrod single, a mongrel mix of several different bikes. It was fast for an old thumper but it could be blown away by a japanese 250 2 stroke twin, I decided it was time for more speed I fitted a bigger carb, bigger exhaust, bigger valves, lumpier camshaft, new crank, piston and rod and skimmed the head to raise CR. After all this work it went faster in a straight line but the power had been shoved too high up the rev range and it had no mid range power, it actually went slower round a twisty circuit it had lost the flexibility. I ended up taking it all back to original apart from the piston, rod and crank.


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## cimmex (Jan 11, 2014)

I’m aware of all you said but Tomo stated that the DB engine was more fuel efficient because of higher CR and this is what I doubt.
cimmex


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## BiffF15 (Jan 11, 2014)

wiking85 said:


> Which engine was better the Merlin or DB601? From what I can tell the Merlin had a lower displacement, but the same weight (roughly) as the DB; why was that? What did the Merlin have that made it capable of the same or better HP at lower displacement than the DB?



Wiking85,

An add on to this would be service life and maintainability. Which had better longevity and which were more easily repaired. 

I remember reading an article in, I think Air and Space, about the various WW2 fighter motors. The author made points that the German engines (DB and Jumo-213) both had 1/3 less parts than the RR Merlin. More parts means more chances for failure. I think he also went on to mention that the Allison could be overhauled in the field, while the Merlin, DB and Jumo could not. 

Cheers,
Biff


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## davebender (Jan 11, 2014)

> Allison could be overhauled in the field, while the Merlin, DB and Jumo could not.



Modern aircraft and tank engines are designed to be quickly replaced in the field. Removed engine is shipped back to factory or rear area depot for rebuild. If WWII era U.S. Army rebuilt engines in a field environment then our operational doctrine was behind the times.


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## Aozora (Jan 11, 2014)

davebender said:


> Modern aircraft and tank engines are designed to be quickly replaced in the field. Removed engine is shipped back to factory or rear area depot for rebuild. If WWII era U.S. Army rebuilt engines in a field environment then our operational doctrine was behind the times.



That's not quite correct; while the ideal situation is to have plug-in components, in wartime conditions it might not be possible to depend on rear-echelon services being available when or where they were needed - ground crews might be forced to work with what is available in front of them because there are no replacements. During WW 2 there were numerous examples of supposedly unserviceable aircraft and engines being made serviceable.

Packard, for instance, recognised this and issued a V-1650-3 7 Maintenance Manual with this revision:


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## tomo pauk (Jan 11, 2014)

Fine contribution (not only) in this thread, Aozora


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## davebender (Jan 11, 2014)

Your reference is for emergency repair and replacement. Everyone does that. It's not the same as an engine overhaul.


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## Shortround6 (Jan 11, 2014)

Sometimes authors get misled by simple numbers. I have no doubt that a R-R Merlin had more total "parts" than some other engines but many of these "parts" were screws and bolts used to hold thing together or on the engine. Rolls-Royce, even on their cars, liked to use more small screws/bolts spaced closer together to hold on things like cam covers than many other manufacturers. Lets face it, with a V-12 engine there are only 12 pistons now matter who makes it, there is only one crankshaft and so on. Things were you can get more parts are in the valve train. Merlins used 4 valves per cylinder but so did some other V-12 engines, triple vs double valve springs? A more complicated oil pump or more of them? German fuel injection used way more parts than the British carburetor. 
DB roller bearing connecting rods used 72 rollers per pair of connecting rods and so on.

With out a meaningful break down of the number of critical or even just "moving" parts the "total" number of parts actually doesn't tell us much about the reliability of an engine although it may tell us a bit about how hard it was to overhaul. Having to deal with a significantly higher number of fasteners could be a pain in the butt even if they make no real difference to the life of the engine. 

There are any number of text books about engine design that go into compression ratio. Many from the 1930s and 40s can be found online for $10-20 ALL of the ones I have seen say that higher compression will give better gas mileage or fuel consumption. In some case they will give the result of tests done on test stands with the engine connected to a dyno. Sometimes they have charts/graphs showing the theoretical increase in power by changing the compression ratio with everything else staying the same. Theory and formulas were sometimes backed up by experiments like ones for friction and pumping losses in which a test engine was spun by an electric motor with various parts removed to find out what each part or group of parts contributed to the total friction. Bare crankshafts were spun in the main bearings, "L" head cylinder head was removed to measure crankshaft and piston/ring friction without compression. Power to run fan and so on. 

I think I will take their word for what was going on inside some of these engines.

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## Aozora (Jan 11, 2014)

Shortround6 said:


> Sometimes authors get misled by simple numbers. I have no doubt that a R-R Merlin had more total "parts" than some other engines but many of these "parts" were screws and bolts used to hold thing together or on the engine. Rolls-Royce, even on their cars, liked to use more small screws/bolts spaced closer together to hold on things like cam covers than many other manufacturers. Lets face it, with a V-12 engine there are only 12 pistons now matter who makes it, there is only one crankshaft and so on. Things were you can get more parts are in the valve train. Merlins used 4 valves per cylinder but so did some other V-12 engines, triple vs double valve springs? A more complicated oil pump or more of them? German fuel injection used way more parts than the British carburetor.
> DB roller bearing connecting rods used 72 rollers per pair of connecting rods and so on.
> 
> With out a meaningful break down of the number of critical or even just "moving" parts the "total" number of parts actually doesn't tell us much about the reliability of an engine although it may tell us a bit about how hard it was to overhaul. Having to deal with a significantly higher number of fasteners could be a pain in the butt even if they make no real difference to the life of the engine.
> ...



Small changes in the design of critical components can have a big influence on how well an engine performs in service. For example, the Merlin needed several small modifications to enable it to run at +18 lbs boost; these changes led to improvements which enabled higher power outputs:

View attachment Lovesey on Merlin extract.pdf


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## GregP (Jan 12, 2014)

The Merlin has 11,000 parts. The Allison, also a V-12 of similar displacement and performance, has 7,000.

4,000 is a LOT of screws and bolts, especially considering that the Allison is also held together with screws and bolts! And Allisons don't leak anymore than Merlins do.

The seal between the top and bottom crankcase on an Allison is metal to metal with one small silk thread all the way around with overlapping ends as the entire gasket. The rest is just tightseal, which can be used on ANY engine. Nothing wrong with the Merlin design, but one or two people can get an Allison mostly apart in about a day and a half or less. Ditto for reassembly. The hard part is prepping the parts for proper fit, just as in ANY piston engine. Correct prep is everything.

You have to torque the cylinders on a Merlin every 25 hours or so. Allison cylinders are torqued once, upon assembly, and are never a problam after that. Of course, the cylinders are of Different design and Allison cylinder nuts require 2,200 foot-pounds of torque!

And as a matter of information, I looked at our Merlin for the Hiapano and was wrong. It is a Merlin 224, not a 228. Being a 20-series, it has a 2-speed supercharger and the gearshit is at the bottom of the supercharger case on the left side. Once I was looking for it, the lever was quite obvious and was confirmned by Steve Hinton. Sorry, no pics. The camera was 1/2 mile away at the time.


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## fastmongrel (Jan 12, 2014)

Until someone gets 2 engines an Allison V1710 and a RR Merlin in equivalent condition with the same accesories then strips them down to the very last washer and enters the details into a spreadsheet no one is going to know how many parts there are in each engine. We dont even know which engines supposedly had 11,000 or 7,000 parts it might be comparing a 1930s prototype V1710 and a Merlin 131 with the reversible prop. 

Is the number of parts for a V1710 a bare engine is the parts number for a "Merlin Power Egg" an engine with everything bolted on from the prop shaft to the little link that moves the widget that pushes the doofer that starts the waffle pump that turns the flange that spins the dickey that makes the engine go BRMMMM.

I have never worked on a RR aero engine but I have worked on older RR car engines and every single nut, bolt or screw had a washer, every single cable, hose and pipe was clamped in at least 1 place sometimes 2, with a fibre pad under the clamp and a washer on the bolt, nut or screw. Oh how I wish modern cars were put together the same way rather than a thousand brittle plastic clips that require special tools to open and a box of spare clips to replace the half dozen you break every time.

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## Shortround6 (Jan 12, 2014)

I certainly don't have the experience to tell where all the "extra" parts are but lets be logical. Like I said earlier, a Merlin, an Allison and a DB 600 series all use the same number of pistons, connecting rods, piston pins, valves, etc, so were do the "thousands" of extra pieces go? Nuts, bolts, washers (fiber or metal) clamps? they all used shaft drives to the cams, not gear towers. 

I can certainly understand how, with extra parts, the Merlin could be more of a pain (need more man hours) to tear down and re-assemble. That does NOT mean it would be less reliable or break down more often. That would assume that ALL the parts were made of the same materials, were manufactured the same way, and had to handle identical stresses. I don't know how many changes were made to an item like the Merlin or DB crankshaft. We do know that the Allison went through at least 4 changes in crankshaft and that just shot peening the crankshaft _without any other changes in dimensions or material_ added significantly to it's fatigue life. 
There is too much we don't know about the engines to make the assumption that the relative number of parts had anything to do with either reliability or longevity. Assuming the engines were assembled with due care. 

For all I know the R-R use of smaller but closer spaced fasteners allowed for better sealing (anyone with experience with _most_ old English gaskets can appreciate this) or lighter cam covers or other access plates due to less 'bending' near the fasteners.


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## RCAFson (Jan 12, 2014)

How many Allison engines had two stage, two speed SCs? Are we comparing apples to oranges?


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## swampyankee (Jan 12, 2014)

cimmex said:


> Well, power wise both contemporary engines were rather close. IMO the DBs offered some advantages.
> Inverted V-design offered better view over the nose,
> fuel injection ensured supply at all flight situations,
> hydraulic supercharger drive was more efficient,
> ...



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.


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## davebender (Jan 12, 2014)

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



1930s German fighter aircraft designs did not employ an annular radiator. So the inverted V12 design helped fighter aircraft visibility in all circumstances prior to fall 1944 Fw-190D9.


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## cimmex (Jan 12, 2014)

swampyankee said:


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


Here I disagree. Only the lower Prop axis of an inverted V-engine allowed the use of an annual radiator. I don’t know any plane with an upright V-engine which had an annual radiator
cimmex


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## GregP (Jan 12, 2014)

Hi Shortround,

In your post above you state higher CR makes for better fuel consumption. I believe that is for naturally aspirated engines. Once you start adding boost, the CR is not as important as the final cylinder pressure, and that is controlled almost exclusively by how you employ the boost. If you are running a CR of 5.0 and are running 140 inches of MAP up near the limits of detonation, the cylinder pressure is equivalent to a CR of 7.0 and some reduced boost at the same detonation limit. Do you agree?

Now if you are running at cruise, then you'd have to adjust the boost to give equivalent cylinder pressure to get equivalent fuel consumption. The performance might not be quite the same since the gearing also might not be, but the fuel consumption should be very close at identical internal cylinder pressures.

As for the parts count, I worked at a shop specializing in Allisons and ONLY Allisons. I think we know how many parts it has since we were assembling them. We never built or have seen a "C" engine inside the shop (DO have some parts), though we could certainly have added a "C" type nose case to any existing -89 or above is anyone really wanted a "C" nosecase (if anyone can find one ... try South America in a museum or barn ... that's where the last 2 -3 of them were found). The parts count is for a typical E, F, or G engine. Most of the E and F engines we built were of the -89 / -91 series and up. The difference in parts count between an "E" and an "F" is miniscule. Both have a nosecase and internal bearings, the "F" has internal gears. The difference is that the "F" has a shaft designed to mount a propeller and the "E" has a mounting flange designed to interfce with a U-joint for driveshaft operation of a remote gearbox such as in a P-39 or P-63. The same nose case can be used in a PT boat or a tank, but is usually replaced with a case employing a flywheel weight for smoother non-aviation operation. The parts count delta might be 5 - 8 parts between an "E" and an "F". Within a count of 7,000 it makes zero difference.

The "G" is the last of the higher-power Allisons and has the same parts count as an "E" or "F" but some of the parts are stronger. All the front-running Merlins at Reno are running Allison "G" series rods since the Merlin rods will not live at the power levels they are producing today.

The 11,000 count for the Merlin is for a single stage, single speed engine, but the count is almost identical for a 2-stage engine, no matter the speeds. Adding an impeller, 3 - 4 gears and 2 - 4 bearings makes almost NO diference in parts count at a level of 11,000 parts, and the case is a unit with minimal parts count increase (some extrra bolts). The total delta between a single-stage and a 2-stage might by as high as 50 or so parts out of an 11,000 count. The percent parts difference is well less than 1%, so it makes zero diffrence in an analysis of parts count.

As for the 2-stage Allisons, I am not interested in anything bedore the -7 engine since they were all pretty much experimental before that. If you are interested, you can research them. Starting with the V-1710-7 there were 75 models through the V-1710-149. Of these, 12 models had auxilliary supercharger stages, These were the -93, -97, -103, -109,-109A, -111, -113, -117, -119, -121, and -123.

The V-1710-57 had a single-stage, 3-speed supercharger.

If the Government had funded an integral 2-stage unit, it might have been nice. Unfortunately, it didn't happen.


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## swampyankee (Jan 12, 2014)

cimmex said:


> Here I disagree. Only the lower Prop axis of an inverted V-engine allowed the use of an annual radiator. I don’t know any plane with an upright V-engine which had an annual radiator
> cimmex



There were; they were used on US aircraft in the 1920s.


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## cimmex (Jan 12, 2014)

never heard, what type?


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## fastmongrel (Jan 12, 2014)

> As for the parts count, I worked at a shop specializing in Allisons and ONLY Allisons. I think we know how many parts it has since we were assembling them



Did an accountant with a spreadsheet and a complete parts list down to the last widget check every part. Is it an about number or an exact number that is being bandied about, people forget how many small parts there are in an engine. 

Take a Conrod is it one part or is it 1 x rod 1 x end cap 1 x gudgeon pin 2 x circlips 1 x gudgeon pin sleeve 1 x small end roller bearing or journal bearing 2 x rod bolts 2 x rod nuts 2 x end cap bolt washers plus depending on design maybe some kind of bolt retainer 2 x big end shells and some old engines also have 2 x gudgeon pin end float control washers. Thats about 15 parts for one rod but is it one part because a lot of people call it one part. 

I stripped, refurbished and rebuilt a 32cc Lawn Mower engine just before Xmas from 2 boxes of parts and I couldnt tell you how many parts are in the engine I know the carb was about 20 parts because I rebuilt the thing about 5 times till I found out I had the main jet upside down


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## Aozora (Jan 12, 2014)

swampyankee said:


> 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.



Flight magazine had several pre-war articles debating the merits of carburettors vs fuel injection; one of them is from March 1939:

Aviation History from 1939. Browse historical aircraft from 1939
fuel injection | carburetter system 1939 | 0839 

A description of the Stromberg pressure-injection carburettor starts here:

Aviation History from 1941. Browse historical aircraft from 1941

Plus an article on the different systems, starting here:

Aviation History from 1941. Browse historical aircraft from 1941


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## Aozora (Jan 12, 2014)

fastmongrel said:


> I stripped, refurbished and rebuilt a 32cc Lawn Mower engine just before Xmas from 2 boxes of parts and I couldnt tell you how many parts are in the engine I know the carb was about 20 parts because I rebuilt the thing about 5 times till I found out I had the main jet upside down



A couple of years ago I helped my grandad strip down and overhaul the gearbox/engine unit of his ancient, but immaculate, Morris 1100. How many parts? Dunno. How easy was it to pull apart and rebuild?  I never realised that such a small engine could be so !!!!!! Not the best example of British engineering...


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## GregP (Jan 12, 2014)

I think you are arguing just to argue fastmongrel. The exact method arrived at for the count is easy if you (and anyone else who is interested) know how.

I decline to participate going forward, but please feel free to make a count on your own.

If you elect to do so, you'll come out VERY close unless you miscount. The diference is not worth the effort unless you have it all on computer and can simply look at the total count when you're finished right at the bottom of the database.

Go for it and good luck.


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## Balljoint (Jan 12, 2014)

Compression ratio is basically the volume at TDC vs. volume at BDC, though blow down requirements affect the ideal. If, for a given fuel mixture charge, the mixture is confined to a smaller volume at TDC, the fuel charge in the smaller volume will be at greater pressure and produce a greater force on the top of the piston for the given fuel charge. The greater force will persist but relatively diminish as the piston moves toward EVO. Thus for a given fuel charge, more power and efficiency result from a higher CR until the higher pressure and temperature result in fuel detonation or pre-ignition. Too high CR cause the oxygen to become hyper reactive (changing the electron spin to a higher state) in response to raising temperature and pressure. Octane rating is a measure of fuel susceptibility to this failing.

Supercharging lowers mean thermal efficiency by cramming more fuel mixture into a given volume, i.e. more than atmospheric pressure would. Thus the combustion products have less relative expansion volume so more energy is wasted during blow down opening of the exhaust valve.


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## fastmongrel (Jan 12, 2014)

Aozora said:


> A couple of years ago I helped my grandad strip down and overhaul the gearbox/engine unit of his ancient, but immaculate, Morris 1100. How many parts? Dunno. How easy was it to pull apart and rebuild?  I never realised that such a small engine could be so !!!!!! Not the best example of British engineering...



My dad had a Austin 1100 (same car different badge) and it was a pretty poor example, we used to joke and say it did 5 miles per hour. That is for every 5 miles Dad drove it he spent an hour fixing it


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## tomo pauk (Jan 12, 2014)

Oh, boy - you people mean this? picture

Rest assured - my dad's 1st car, bought in 1971 (or was it in 1972?). He drove it maybe 7-8 years, once some mechanical issues arose it became a challenge to keep it running. Body panels (ie. sheet metal) were, by his words, 'as good as in the Mercedes', on the other hand.


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## fastmongrel (Jan 12, 2014)

GregP said:


> I think you are arguing just to argue fastmongrel. The exact method arrived at for the count is easy if you (and anyone else who is interested) know how.
> 
> I decline to participate going forward, but please feel free to make a count on your own.
> 
> ...



I am not arguing for arguings sake people have stated the Allison and the DB had 7,000 parts and the Merlin had 11,000. Where did these numbers come from are they genuine GM DB and RR numbers or are they someones guesstimate. We can spend whole threads discussing a 1,000 feet of altitude or 10 pounds of fuel but somehow an unsupported bunch of numbers becomes fact with no discussion allowed and if you know an easy method of counting engine parts please link to this method of counting engine parts I am genuinely interested.


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## stona (Jan 12, 2014)

fastmongrel said:


> I am not arguing for arguings sake people have stated the Allison and the DB had 7,000 parts and the Merlin had 11,000. Where did these numbers come from are they genuine GM DB and RR numbers



That's a fair point. The provenance of the numbers IS relevant. Also, there may well have been different standards or methods used by different companies, never mind different nationalities, for ascertaining these figures.
I neither know nor care which engine had more parts, I don't see any relationship between that and reliability or ease of maintenance, but just stating unreferenced numbers, arrived at by who knows what method, as comparative facts seems to me a very risky business.
Cheers
Steve


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## wuzak (Jan 12, 2014)

Shortround6 said:


> I certainly don't have the experience to tell where all the "extra" parts are but lets be logical. Like I said earlier, a Merlin, an Allison and a DB 600 series all use the same number of pistons, connecting rods, piston pins, valves, etc, so were do the "thousands" of extra pieces go? Nuts, bolts, washers (fiber or metal) clamps? they all used shaft drives to the cams, not gear towers.
> 
> I can certainly understand how, with extra parts, the Merlin could be more of a pain (need more man hours) to tear down and re-assemble. That does NOT mean it would be less reliable or break down more often. That would assume that ALL the parts were made of the same materials, were manufactured the same way, and had to handle identical stresses. I don't know how many changes were made to an item like the Merlin or DB crankshaft. We do know that the Allison went through at least 4 changes in crankshaft and that just shot peening the crankshaft _without any other changes in dimensions or material_ added significantly to it's fatigue life.
> There is too much we don't know about the engines to make the assumption that the relative number of parts had anything to do with either reliability or longevity. Assuming the engines were assembled with due care.
> ...



I think most of the extra parts of the Merlin are screws and bolts.

On 2 piece Merlin blocks, for instance, there are an extra set of bolts to clamp the cylinder head to the block. I don't think the Allison uses them. There are also ferrules to transfer coolant between the block and head (4 per cylinder) and, IIRC, o-ring seals for each end of those ferrules.


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## wuzak (Jan 12, 2014)

cimmex said:


> Here I disagree. Only the lower Prop axis of an inverted V-engine allowed the use of an annual radiator. I don’t know any plane with an upright V-engine which had an annual radiator
> cimmex



That is not the case at all.

In the case of both the upright and inverted vees, at least of WW2 vintage, the prop drive tended to be offset to the centre of the frontal area of the engine. There is nothing precluding the use of an annular radiator with an upright V-12.

The V-12s with annular radiators in the 1920s didn't, in reality have annular radiators - they had car type radiators mounted ahead of the engine with the prop drive through the radiator.


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## fastmongrel (Jan 12, 2014)

stona said:


> I neither know nor care which engine had more parts, I don't see any relationship between that and reliability or ease of maintenance, but just stating unreferenced numbers, arrived at by who knows what method, as comparative facts seems to me a very risky business.
> Cheers
> Steve



Bingo exactly what I am trying to get to only you put it more succinctly. I couldnt care less if a Merlin had more parts than a Space Shuttle and the Allison and DB had the same number of parts as a clockwork toy.


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## fastmongrel (Jan 12, 2014)

wuzak said:


> The V-12s with annular radiators in the 1920s didn't, in reality have annular radiators - they had car type radiators mounted ahead of the engine with the prop drive through the radiator.



What is the definition of an annular radiator does it have to be a circular radiator wrapped round the propshaft.


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## GregP (Jan 12, 2014)

If you don't see the relationship between parts count and ease of maintenance, then you've never taken one apart and put it back together. 4,000 more parts take a LONG time to install or remove, and there is a LOT more opportunity to drop one inside an engine. That requirs even MORE time to disassemble it and find the part if it goes inside the engine.

There is a strong relationship between number of MOVING parts and relaibility. More moving parts means more parts to fail, simple math of reliability engineering. Parts count matters in reliability and MTBF.

I do not have an estimate of the number of MOVING parts in an Allison versus a Merlin, but I KNOW from being inside both the Allison has fewer moving parts.

When properly assembled, tuned and operated, both engines give excellent service, with the Merlin requiring more maintenance. For instance, you have to torque the Merlin cylinder liners every 25 hours or so while the Allison cylinder liners must be torqued once when being assembled and are never touched until disassembly after that. The Merlin method of torqueing in the valve seats is just plain stupid and involves turning it in until the new seat shank snaps off. There is some minimum torque, but no defined torque. That they used a method that produces no defined torque value for the seat does NOT make the Merlin a bad engine, it means there no defined torque for the valve seats, that's all. In operation, it doesn't seem to make much difference, but most good engineers don't design that way.


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## wuzak (Jan 12, 2014)

More moving parts?

Which would those be Greg?

Clutches for the multiple speed supercharger drive? Not needed on the Allison since it didn't have a multi-speed drive.
Crankshaft torsional vibration damper? Well, the Merlin didn't have one, but the Allison did.
Roller cam followers? Again, featured on the Allison, and not the Merlin.

Do you count retaining bolts as moving parts?


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## wuzak (Jan 12, 2014)

fastmongrel said:


> What is the definition of an annular radiator does it have to be a circular radiator wrapped round the propshaft.



Well, yes.

It has to be in the form of an annulus.

"In mathematics, an annulus (the Latin word for "little ring", with plural annuli) is a ring-shaped object, especially a region bounded by two concentric circles. The adjectival form is annular (as in annular eclipse)."

Annulus (mathematics) - Wikipedia, the free encyclopedia


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## swampyankee (Jan 12, 2014)

cimmex said:


> never heard, what type?



Well, there was this: Verville VCP - Wikipedia, the free encyclopedia and this: Curtiss XP-22 - fighter

This one was British: Bristol Scout E / F

It was also pretty common for aircraft with Liberty V-12s to have radiators in front of the engine, with the propshaft passing through the radiator. This is, of course, topologically identical to an annular one 

Outside of Germany, annular radiators were not particularly popular. I suspect this was because they were viewed as equally as draggy as a radial installation, because they didn't permit the nice pointy nose that a V-12 with a radiator under the wing permits. Even in Germany, it seems to have had relatively few proponents -- Focke Wulf (or Kurt Tank at FW), Junkers, and Kurt Tank. I don't think the annular radiator is a bad idea, as it permits nice, short coolant lines, but I don't see it has any other particular benefits.


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## GregP (Jan 12, 2014)

Hi Wuzak,

Bolts, nuts, and washers that are attached to moving parts (think of bolts, washer, and nuts on a crankshaft) ARE moving parts. They are subject to more vibration and stress than non-moving parts which, by defintion, may be moving through the sky, but are NOT moving relative to the crankcase (think of engine mount bolts).


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## Shortround6 (Jan 12, 2014)

Merlin used 6 bolts per pair of connected rods. One pair on the center rod end cap and one pair on _each_ of the forked rod's end caps. Pretty much the same as the Allison? 

The Merlin may very well have a few dozen (or even a few hundred) more moving parts than the Allison, that is a far cry from the 3-4,000 "total" number of parts.

I won't argue that the Allison was easier to take apart or put back together, shear number of parts argues otherwise. But to argue that the "number" of parts affected reliability or durability to any great extent leaves out too many other variables to be taken seriously. Maybe the number did parts did and maybe it didn't but since a number of the parts were NOT made of exactly the same materials, or heat treated/processed the exact same, or in some cases perhaps not "finished" the same (surface finish or polish prevented the start of fatigue cracks, how much polish was enough?) the variables are too great to dismiss.


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## GregP (Jan 12, 2014)

No they aren't SR. 4,000 more parts take a long time to both remove and reinstall. The time to complete an overhaul HAS to be greater for a Merlin, even if everything else was equal, just due to that many parts.

Military TBO may have been similar, but use in peacetime shows the Allison to last quite a bit longer than a Merlin. Of course, in military service the engines were overhauled at very similar intervals, so it didn't make that much difference at that time. It doesn't help if the engine life was 1,000 hours but you overhauled it at 400 hours anyway.

Rolls Royce generally uses more parts to do the same thing that Allison does or, perhaps from another point of view, Allison generally uses less parts to do what Rolls-Royce does. Go watch a teardown and rebuild somewhere near you and you may well come away with the same opinion I have after having done that, including helping with the allison function.

This is not a "one is better than the other" argument here. It is just noting that one has many more parts than the other, and that is a fact, not a question. Wartime service generally required rebuild before wearout was reached anyway, so the difference in lifetimes was never very apparent until after military service.

Both are good engines.


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## cimmex (Jan 13, 2014)

wuzak said:


> That is not the case at all.
> 
> In the case of both the upright and inverted vees, at least of WW2 vintage, the prop drive tended to be offset to the centre of the frontal area of the engine. There is nothing precluding the use of an annular radiator with an upright V-12.


Obviously you don’t see what I mean. Of course all V engines had a reduction gear which shifts the prop axis offset to the crank axis but at the upright V to the wrong direction. Imagine a radiator around the actual spinner position at a Mustang or a Spitfire and then try to imagine how the view over the nose would be.
cimmex


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## Aozora (Jan 13, 2014)

cimmex said:


> Obviously you don’t see what I mean. Of course all V engines had a reduction gear which shifts the prop axis offset to the crank axis but at the upright V to the wrong direction. Imagine a radiator around the actual spinner position at a Mustang or a Spitfire and then try to imagine how the view over the nose would be.
> cimmex



Gotta agree with cimmex; the reduction gears on an upright vee wouldn't allow a conventional annular radiator installation. There is a myth which says that annular radiators were used on the Avro Lincoln's Merlin 80 series "universal" power-plant installation, but these used semi-circular "chin" radiators. Looking at this installation, its clear that an annular radiator would restrict vision over the nose:

universal power | power plant | flight universal | 1947 | 0233 | Flight Archive

AFAIK the only annular radiator installations tested by the British were on Napier Sabres which, being of H-24 configuration, lent themselves to the configuration.

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## stona (Jan 13, 2014)

GregP said:


> If you don't see the relationship between parts count and ease of maintenance, then you've never taken one apart and put it back together. 4,000 more parts take a LONG time to install or remove, and there is a LOT more opportunity to drop one inside an engine. That requirs even MORE time to disassemble it and find the part if it goes inside the engine.



There are obviously many here who have some experience maintaining or servicing engines of one type or another. Even I have stripped and rebuilt a single cylinder Ducati engine (complete with 'desmodronic' valve system). Actually I gave up and took it to a nice man in Wisbech who did it for me but that's another story  
Most engines can be 're-built' without being reduced to component parts. The total number of parts in an engine, down to the last fibre washer and circlip has nothing to do with its ease of maintenance. How many Merlins or Allisons were stripped to their thousands of individual components between leaving the factory and being loaded on a truck bound for the scap heap? 
The way an engine is put together and also how it is installed are FAR more relevant than the total number of parts. This is something Davebender touched on a while ago.
The lengths someone might go to today to recover or restore an old aero engine would be very different to those that a service depot in WW2 might go to in order to fix something that was essentially a disposable item. Stripping for spares isn't reducing to components either.
Cheers
Steve


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## wuzak (Jan 13, 2014)

cimmex said:


> Obviously you don’t see what I mean. Of course all V engines had a reduction gear which shifts the prop axis offset to the crank axis but at the upright V to the wrong direction. Imagine a radiator around the actual spinner position at a Mustang or a Spitfire and then try to imagine how the view over the nose would be.
> cimmex



In an inverted vee the prop shaft is shifted down relative to the crankshaft, which is at the top. In an upright vee the prop shaft is shifted up from the crankshaft, which is mounted at the bottom.

The annular radiator wouldn't know if it were an upright or an inverted V-12 behind it.

As regards to the Spitfire and Mustang, if they were to have an annular radiator the engine and thrust line would have to be moved down.

The view over the nose would be worse than the standard planes, but that is true of any V-12 behind an annular radiator - being round they are wider than the engine is by some margin.

An upright vee behind an annular radiator:











I believe that is an (upright) Allison V-1710 powering the Flugwerks Fw 190D replica.

You can also see that the annular radiator is much bigger than the engine. That is because it was fitted to an aircraft originally designed for a radial, and the point of using an annular radiator was to be able to bolt up either the radial or in-line engine module.


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## wuzak (Jan 13, 2014)

And when you think about it, if you take the inverted V-12/annular radiator module and rotate it 180° about the prop axis you have an upright V-12 with an annular radiator.


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## cimmex (Jan 13, 2014)

I would like to see a Spitfire or a Mustang with the engine moved down by around 30 cm.
cimmex

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## fastmongrel (Jan 13, 2014)

cimmex said:


> I would like to see a Spitfire or a Mustang with the engine moved down by around 30 cm.
> cimmex



I wouldnt they might still work but would look ugly as sin


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## tomo pauk (Jan 13, 2014)

Looking at this upright V-12 installation (drawing for P-40E), it does not seem that installation of annular radiator would've hampered any way the pilot's vision.

Here is a Spitfire with inverted V-12, a DB-605 - a 'surprisingly good fit' indeed:
http://spitfiresite.com/2010/04/wolf-in-sheeps-clothing-modelling-captured-db605-powered-spitfire.html


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## cimmex (Jan 13, 2014)




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## tomo pauk (Jan 13, 2014)

Guess you mean something like this:


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## Aozora (Jan 13, 2014)

wuzak said:


> In an inverted vee the prop shaft is shifted down relative to the crankshaft, which is at the top. In an upright vee the prop shaft is shifted up from the crankshaft, which is mounted at the bottom.
> 
> The annular radiator wouldn't know if it were an upright or an inverted V-12 behind it.
> 
> As regards to the Spitfire and Mustang, if they were to have an annular radiator the engine and thrust line would have to be moved down.



Moving the thrust line of a upright-vee engine enough to accommodate an annular radiator, in the way you're suggesting, means the entire airframe would have to be redesigned, all for very little gain in efficiency or performance. Plus, for the likes of the Spitfire, without an almost complete redesign of the airframe, the cg would move significantly. In practice, during wartime no manufacturer would risk such a radical redesign.


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## wuzak (Jan 13, 2014)

Maybe look at a Griffon Spitfire, as they have lower thrust lines. Preferably a Mk XII, not the XIV, as the XIV has the engine titled down slightly for visibility.

As for the P-40, the early models with the lower thrust line are better for visualising them.

http://th06.deviantart.net/fs71/PRE/f/2011/106/f/6/f6cd4af00c6d4659d5abeee037f1ed5d-d3e3vfk.jpg


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## wuzak (Jan 13, 2014)

tomo pauk said:


> Guess you mean something like this:
> 
> View attachment 251990



Yeah....but start with a P-36. Take off the radial and bolt on a new QEC.


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## wuzak (Jan 13, 2014)

Aozora said:


> Moving the thrust line of a upright-vee engine enough to accommodate an annular radiator, in the way you're suggesting, means the entire airframe would have to be redesigned, all for very little gain in efficiency or performance. Plus, for the likes of the Spitfire, without an almost complete redesign of the airframe, the cg would move significantly. In practice, during wartime no manufacturer would risk such a radical redesign.



I never suggested it was wise or advantageous to do so.

Annular radiators worked best on aircraft, particularly fighters, which were designed to be used with radial engines. That was certainly the case for the Hawker Tempest - if you see the engine installation there is a lot of space around the engine.


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## wuzak (Jan 13, 2014)

My point is that the notion that only inverted V-12s can have annular radiators is ridiculous.


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## cimmex (Jan 13, 2014)

Keep on dreaming, I’M out here.


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## wuzak (Jan 13, 2014)

Dreaming...it has been done.







That is a V-1710 upright V-12 in an Fw 190D-9 replica with an annular radiator. The cowling is larger than the engine, but it is probably no larger than on the original.


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## Milosh (Jan 13, 2014)

Who says the radiator has to be centered on the prop shaft?


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## stona (Jan 13, 2014)

Here's a good picture showing the radiator installation on a restored DB engine from the NASM's He 219.






This type of annular radiator arrangement is the so called 'drum' installation as the radiators do not face the direction of flight, air is ducted to them. This is apparently more efficient.

I can't see why a system like this couldn't be fitted to a V-12 engine in any orientation. Maybe I'm missing something?

Cheers

Steve


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## tomo pauk (Jan 13, 2014)

The Jumo-213A in regular layout, and turned, by your's truly, upside down . Does not seem like the annular radiator would be an awkward thing on an upright V-12.


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## GregP (Jan 13, 2014)

Hey Wuzak,

That pic of the Allison in the Fw 190D will certainly tell you the nose case is not stock. The prop shaft is about 8 inches to a foot too low. As I recall, the prop reduction gear came from Ross Aero here in the States. Also as I recall, it doesn't fly much. And, if it WORKS, that is too bad. I'd love to see it in the air.

We heard about that one while I was at Joe's and also heard it was not done very well from an engineering standpoint, so I'd love to hear about any flight time that aircraft has on it. From what we heard, it is fixable, but the correct people aren't being asked to fix it.

That is heresay; I have no first hand information on it. I hope what we heard is wrong and i runs just fine, but have not seen or heard of airshow appearances or flights as yet. I could simply have not heard about it and hope that is the case.

Purests might skoff at an Allison in an Fw 190D replica, but the lines are supposed to be true to scale and I'd love to see it fly. Seeing a 100% full scale replica fly is second only to seeing a real Fw 190D fly.


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## wuzak (Jan 13, 2014)

Greg, I expect that to be used in an annular radiator situation you would need an extended nose case - certainly over the standard V-1710 and Merin nose cases. The Sabre with annular radiator certainly had a longer nose case.


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## gjs238 (Jan 13, 2014)

*Merlin*





*DB series*

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## gjs238 (Jan 13, 2014)




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## wuzak (Jan 13, 2014)

For a Merlin with an annular radiator you may have to change a few accesories, to remove them from under the sump. ANd use a downdraft carby.

Something like the Merlin 130/131


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## Aozora (Jan 13, 2014)

wuzak said:


> For a Merlin with an annular radiator you may have to change a few accesories, to remove them from under the sump. ANd use a downdraft carby.
> 
> Something like the Merlin 130/131




So more like






rather than




*?*

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## GregP (Jan 13, 2014)

OK, I did a quick (OK, most of an afternoon and evening) spreadsheet of the parts in an F-series Allison.

Without taking into account all the little clamps and finishing items I get 6,828 parts.

Adding in clamps, hoses and small hose interconnects, levers to operate all the items, linkages between them, and washers, nuts, cotter pins and bolts for them will get use VERY close to 7,000 parts, maybe very slightly over. If so, not by much. Could be very slightly under.

Considering we came up very close to 7,000 at Joe's, this independent confirmation makes me a believer. If it doesn't you, get a manual and just DO it. Youll be a believer. Remember flat lock washers and cotter pins. They add up quickly.

Oh and, about working on something and not knowing how many parts, there is a BIG difference between working on , say, a lawn mower, and bulding them for a living. The people who do it for a living are very well aware of the number of parts. I bet any car manufacturer knows EXACTLY how many parts are in a particular engine since they make or buy them. Easy if you stock the parts and must account for them when it is assembled.

Somebody esle can do the Merlin.

Use a single stage engine, single or multi-speed ... doesn't matter much. In fact, even a 2-stage wouldn't change the part count much.


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## tomo pauk (Jan 14, 2014)

A chart with power-to-altitude values for DB-601A and Merlin III. 
Thin red graph is for power available with 87 oct fuel (and, of course, also with a fuel of better octane value), +6 lbs per sq in ('psi' from now on) of boost was available from take off until 4960 m. The thick red line shows power available with 100 oct fuel, +12 psi boost was available from SL until 2790 m. Between 2790 and 4960 m, the boost pressure was gradually decreased to +6 psi, and then further decreased with altitude - supercharger was been able to provide ever less of compressed air with ever greater altitude. Use of boost pressure above +6 psi was for 'short periods' (probably not more than 5 min?)
We can note how much the 100 oct fuel increased the power of the Merlin, it delivered 20-30% more power than DB-601A under 4 km (the dotted line was take off power, 1 min rating for the DB-601A), and still about 10% more above 5 km. Merlin XII offered slightly more power above, than Merlin III, slightly less under 3 km, but it was cleared to use +12 psi boost even for take off.


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## tomo pauk (Jan 14, 2014)

People will notice that, in the graph, I did not take into account the over-revving of the DB-601A (allowed in late 1940, to be used above full throttle height of 4.5 km) - that should yield more power than Merlin III was been able to do. Another thing to have in mind is that 'maximum climbing condition' for the Merlin III was listed as '2600 rpm, +6.25 psi' - perhaps people might drop a line or two about pilots adhering or not to this limit while in combat, as well as adding something more about over-revving the DBs (other than it's written on Kurfurst's site)?

The Merlin XII was actually allowed for +12.5 psi for take off (red dash at 1190 PS), not just for +12 psi. The 'maximum climbing condition' listed at '2850 RPm and +9 psi'. 
In the following chart, red lines are for Merlin XI. Thicker lines are for boost pressures above +9 psi, the 'upward going' line is for +12 psi boost, ending at ~1300 PS. Thinner lines are for boosts under +9 psi, the 'upward going' line for +9 psi, max being ~ 1170 PS at 4.5 km.

The 'violet' coloured line is for Merlin 45, maximum boost represented as +9 psi (from SL to ~5.5 km). Again, I'd really love to know when increased boost levels were introduced for Merlin 45, at least the +12 psi boost should've been available by the time Spit V entered combat? The +12 psi was take off limit (here).
This document states boost of 54.5 in Hg (~ +12.5 psi?) as used until Jan 3rd of 1942, the 60.5 in Hg (+15.5 psi?) to be used from that date. With +16 lbs boost, the power was ~ 1530 PS at ~3.4 km.


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## Neil Stirling (Jan 14, 2014)

Flights DB 601a article 1940 | 3152 | Flight Archive

Neil.


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## Neil Stirling (Jan 14, 2014)

DB 601 N description






Neil.


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## tomo pauk (Jan 15, 2014)

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


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## tomo pauk (Jan 15, 2014)

Aozora said:


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


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## Aozora (Jan 15, 2014)

tomo pauk said:


> 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.


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## tomo pauk (Jan 16, 2014)

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


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## Jugman (Jan 16, 2014)

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.


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## GregP (Jan 16, 2014)

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.


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## GregP (Jan 16, 2014)

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.


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## wuzak (Jan 17, 2014)

GregP said:


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



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.

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## GregP (Jan 17, 2014)

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.


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## OldSkeptic (Jan 25, 2014)

swampyankee said:


> 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.
> 
> ...



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.


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## tomo pauk (Jan 25, 2014)

OldSkeptic said:


> 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.

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## Shortround6 (Jan 25, 2014)

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.


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## wuzak (Jan 25, 2014)

tomo pauk said:


> 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!


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## OldSkeptic (Jan 26, 2014)

wuzak said:


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



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


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## Juha (Jan 26, 2014)

tomo pauk said:


> ...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


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## Juha (Jan 26, 2014)

db


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## tomo pauk (Jan 26, 2014)

wuzak said:


> 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.



Juha said:


> 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.


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## gjs238 (Jan 26, 2014)

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


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## gjs238 (Jan 26, 2014)

...


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## tomo pauk (Jan 26, 2014)

The V-1710 did have problems with engine's intake (ie. between supercharger and pistons), where the fuel would cease to be 'atomized', and started to revert into fluid as it was before exiting carburetor nozzles. Low temperatures worsened the situation, ie. when aircraft was flying high, and proper intercooler was used (as in P-38J/L, and the P-38J was seriously plagued with the problem, especially if low boost was used). The solution was to insert a venturi pipe in the intake duct, so the air stream was sucking any of the fuel from the bottom of the duct and re-atomize it. That way V-1710 also got rid with backfire screens (wire mesh, located just before the pistons), thus gaining 1000 ft in full throttle altitude (single stage engines, eg. installed in late P-39Qs) or 1500 ft (in P-38L).
On the opposite side, the earlier P-38s have had low-capacity intercoolers, and fuel in the duct didn't plagued them? The fuel injected there might've helped to cool the compressed air slightly better? They still have had the backfire screens, though, and these do lower the engine output.

So, after this lengthly intro - IMO, the direct injection would've improved the V-1710. We can take a look at the two stage V-1710 for the P-82 - those were without the screens, but backfired violently when pushed to the limits. The NAA installed backfire screens on their own, but GM (owner of Allison) was against that and managed to cancel the NAA's effort, employing political pressure. At the end of the day, the Allison engined P-38 have had slightly less performance vs. Merlin-engined ones. Edgar Shmued was very bitter on that GM's move.


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## thedab (Jan 26, 2014)

well it looks close to me (DB605AS+MW-50 v merlin 63+ 21lb Boost (1ps=0.9863hp)










how much do the DB605ASM with it MW-50 system weigh compare to the merlin 63 with all it's bit's

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## tomo pauk (Jan 26, 2014)

The quirk with the Merlin chart is that it includes the effects of ramming the air, ie. aircraft speed 'helps' the supercharger to do it's job. Note the remark at the bottom of the chart. Another thing with the chart is that it lumps together the distinctively different 2-stage Merlins together.
Without, or with small ramming, ie. the engine is on the test stand, or plane is at low speed, the altitude power is lower. You can check out the power of different Merlins here, including the Mk.70 (=1475 HP at 23250 ft, or 1500 PS at ~7090 m). Or, almost 200 PS more than DB-605ASM, and a tad better than DB-605D.
The Merlin 66 (for LF Spitfires) have had more power down low (~1620 PS at 4890 m), but less at higher altitudes, both vs. Merlin 70 and late was DB-605s. The mid-alt Merlin 63 have had ~1525 PS at 6400m, ie. it's power at altitude was between the AS/ASM and D. The main shortcoming of the DB-605AS and later was not so much the power they developed (the small and light Bf-109 was the major user anyway), but that they emerged too late to influence the income of the war.
Weight of the late war DB-605s with MW system and 2-stage Merlins (+ intercooler) was in the ball park?

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## gjs238 (Jan 26, 2014)

Wonder how the DB's would have performed with Allied fuel.


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## fastmongrel (Jan 26, 2014)

gjs238 said:


> Wonder how the DB's would have performed with Allied fuel.



Which Allied fuel there were plenty of different blends, late war 100 octane was different to early war 100 octane and early US and UK blends of 87 and 100 were vastly different. Once the DB engineers tuned the engines for the different fuel probably much the same at altitude. The late war 130 and 150 octane Allied fuels might have made a difference at lower levels.


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## tomo pauk (Jan 26, 2014)

gjs238 said:


> Wonder how the DB's would have performed with Allied fuel.



By 'Allied fuel' I reckon you mean 100 oct and better? German C3 fuel was roughly comparable with Allied hi-oct fuel, at least it seems so by GregP's post here. This chart, belonged to DB-605G, the engine later named DB-605AM. 
With B4 fuel, the manifold pressure was 1.42 ata up to 5.7 km. With C3 fuel, the manifold pressure was 1.7 ata, but only up to 4 km. Greater manifold pressure means more power - up to ~230 HP more with better fuel, but under 5.7 km. We can draw paralels with Merlin here - better fuel increased power since it enabled greater manifold pressure before detonation occurred. Above those altitudes, the supercharger was limiting engine power, and it did not mattered whether C3 or B4 were used above 5.7 km. For greater power high up, new supercharger was needed, and the DB-605A 1st received the supercharger from DB-603, thus becoming DB-605AS. 
In the graph we can see that internal mixture cooling (accomplished via MW-50 system) was still providing 1.7 ata under 4 km, but was packing more mixture in cylinders, since it was colder, thus the engine was capable for even more power. The benefits were falling sharply above 4 km.


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## GregP (Jan 26, 2014)

I'm pretty sure the DB's would do fine with Allied fuel, so long as they were jetted and tuned for the differences between the blends.

Conversely, the Allied engines would do fine with the German fuels provided THEY were jetted and tuned for it. They might make slightly less power on German fuels depending on which one was used, but would run just fine if set up for it.

The trick is to get your engine running well on the fuel it must use. It's no good to have a thoroughbred Spitfire turned for 150 fuel if your local supply is 100 grade.


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## tomo pauk (Jan 26, 2014)

An interesting experiment was tried in KIngdom of Yugoslavia just prior ww2. They have had license for Hurricanes, the engines should be purchased. Since they received a bit more DB-601 engines that needed for their Bf-109E3s, they mated the DB with Hurricane airframe (that particular airframe was purchased in UK, though). Resulting fighter (LVT-1, or, roughly "Fighter, by aero-techic section") was notably better than their stock Hurricane, especially during climb - Yugoslavia was operating the Hurricanes with 2-blade prop and likely on 87 oct fuel. The Yugoslavs were intending to produce 24 such fighters, but ww2 canceled the operation. link

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## GregP (Jan 26, 2014)

Here is a drawing of the LVT-1:

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## Gixxerman (Jan 27, 2014)

Great illustration GregP, interesting how the Hurricane (like the Spit similarly modded) still looks 'right' even with the inverted DB motor....something which I don't think quite works the same way with the RR equipped Spanish Me (Bf) 109's?

But that's just my opinion.... we all know what they say about them


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## tomo pauk (Jan 27, 2014)

The story about single stage Merlin has another chapter, namely the engines that came after Merlin 45. 
The Merlin 46 and 47 received bigger supercharger, with diameter of 10.85 in - compared with 10.25 in most of the single stage Merlins. Bigger supercharger gave better high altitude performance, at +9 psi boost it was capable for 1100 bhp at 22000 ft, or almost as good as the 2-stage V-1710 that was installed in P-63A! Emergency power was, on +16 psi, 1440 HP at 14500 ft. Here the Merlin turned the tables vs. the contemporary DB-601E, offering more power above ~13000 ft, but less under that altitude. 
The altitude performance of the Mk.46 47 came at cost - low altitude performance was, without using the short term emergency power, barely above 1000 HP at 15000 ft. Unfortunately, the supercharger drive was still a single speed unit, and that, coupled with big supercharger, meant that supercharger itself was using too much power and heated the charge too much at lower altitudes; more power there was available with engine doing 2850 rpm, than 3000 rpm. 
We can drive parallels here with Mikulin's AM-35/35A engine - fine at 5 km and above, but not that good at 2-3 km of altitude. The Spitfire V and VI received the Merlin 46s and 47s, not many of those engines were produced. The next Merlin installment, Mk.50, reverted to standard sized supercharger, and was, for all intents and purposes, similar in power as Merlin 45.
People will notice that I do not make much mention of Merlins with either smaller ("cropped", mostly 9.50 in diameter) supercharger, or the ones with decreased supercharger's drive ratio - those were used mostly for FAA needs, and for low-level Spitfires, and do not have a DB-601 variant that is directly comparable (apart from DB-601Aa?).


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## Shortround6 (Jan 27, 2014)

I think you can see the same effect with the DB 605 engines, the later ones with big supercharger had slightly less power for take-off and low altitude _at the same pressures_ than the earlier small supercharger engines even with the variable drive although that helped considerably.


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## tomo pauk (Jan 27, 2014)

Yep - the DB-605AS (= big supercharger) have had 1435 PS for take off, vs. 1475 PS for the DB-605A. 
OTOH, one might wonder what would've do the Merlin 46/47 with water-alcohol injection...


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## thedab (Jan 27, 2014)

A Merlin with water injection






I know it was bit late


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## Reluctant Poster (Feb 13, 2014)

"The specific fuel consumption of DB-601 was lower than of 1-stage Merlin, by some 10%."
This is one of those internet numbers which is not based on a real apples to apples comparison. Flight magazine published an interesting comparison of a Merlin X vs a Jumo 211D. This article claims the Merlin's fuel consumption was actually lower. Admittedly this was written by a Rolls Royce engineer so there may be a bit of bias. It does point out that the Merlin is penalized by 3% due to its lower compression ratio. There are more differences between engines that can account for differences in fuel consumption than just fuel delivery. The only truly valid comparison would be based on engines that are identical save for the method of delivery. There is no reason to suppose that the Bosch direct injection system was better than the good old fashioned carb given the technology of the day. It took the invention of the microprocessor to make fuel injection truly effective. The direct injection system was an adaptation of the diesel system and proved to be an evolutionary dead end. Modern fuel injection system are not direct injection (at least until very recently) and do not meter the fuel using the mechanical jerk pump as used by Boschn The float type carb was actually a pretty precise instrument at the time and it took a very long time for fuel injection to replace it in gasoline engines, at least in cars.


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## Reluctant Poster (Feb 13, 2014)

The Flight article on the Merlin X Jumo 211D comparison is attached along with one on the Bendix Stromberg Carb


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## GregP (Feb 13, 2014)

The two hottest Merlins in the world are both running very low compression. That's how they can run 140 inches of boost at Reno.

If they were running 6.0 : 1, you couldn't get that level of boost without detonation and blowing out the tops of the pistons.

Wasn't particularly practical for war use, but makes for a FAST racer. Neither Strega nor Voodoo would ever make Berlin and back on the race engines ... even if they had the fuel capacity (which they don't anymore).

Thanks for the linked articles ReluctantPoster!

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## tomo pauk (Feb 14, 2014)

Reluctant Poster said:


> "The specific fuel consumption of DB-601 was lower than of 1-stage Merlin, by some 10%."
> This is one of those internet numbers which is not based on a real apples to apples comparison. Flight magazine published an interesting comparison of a Merlin X vs a Jumo 211D. This article claims the Merlin's fuel consumption was actually lower. Admittedly this was written by a Rolls Royce engineer so there may be a bit of bias. It does point out that the Merlin is penalized by 3% due to its lower compression ratio. There are more differences between engines that can account for differences in fuel consumption than just fuel delivery. The only truly valid comparison would be based on engines that are identical save for the method of delivery. There is no reason to suppose that the Bosch direct injection system was better than the good old fashioned carb given the technology of the day. It took the invention of the microprocessor to make fuel injection truly effective. The direct injection system was an adaptation of the diesel system and proved to be an evolutionary dead end. Modern fuel injection system are not direct injection (at least until very recently) and do not meter the fuel using the mechanical jerk pump as used by Boschn The float type carb was actually a pretty precise instrument at the time and it took a very long time for fuel injection to replace it in gasoline engines, at least in cars.



Hello, Reluctant Poster,

I do have some remarks re. this post. 
You unfortunately did't bother to quote the relevant part of the original post, or at least the post number. Then, I've posted the consumption numbers here, for the Merlin XX and DB-601E, that you unfortunately either did not read, or, you did read, but didn't offer your data math. Further, DB sheet about DB-601A states that benefits of fuel injection, vs. carburated DB-600, are greater power and lower fuel consumption. The float type carb penalized Merlin's performance, and part of the British test that I've quoted here clearly states so. It's just under the sentence you quoted in the post #135


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## DonL (Feb 15, 2014)

For the WWII aircraft engines tomo pauk has posted all relevant data's and arguments.

A comment to:



> The direct injection system was an adaptation of the diesel system and proved to be an evolutionary dead end. *Modern fuel injection system are not direct injection (at least until very recently) and do not meter the fuel using the mechanical jerk pump as used by Boschn* The float type carb was actually a pretty precise instrument at the time and it took a very long time for fuel injection to replace it in gasoline engines, at least in cars.



This is a very wrong claim for modern gasoline engines.

Gasoline direct injection - Wikipedia, the free encyclopedia

Here in Europe nearly every very modern gasoline engine has direct fuel injection.


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## Milosh (Feb 15, 2014)

I missed that comment DonL. All I can say is that any British carb whether it was on a car or motorcycle had to be *continually* fiddled with.


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## thedab (Feb 15, 2014)

How long does a late 43 DB605A goes for on 1.42 ata boost? (i.e.what the time limit at maximum boost)

and what are time limits for the DB605AM?


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## drgondog (Feb 15, 2014)

Amen to Milosh - particularly Solex carbs


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## fastmongrel (Feb 15, 2014)

drgondog said:


> Amen to Milosh - particularly Solex carbs



Milosh was talking about British Carbs. Solex were French now part of Magnetti Marelli.


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## Reluctant Poster (Nov 14, 2015)

DonL said:


> For the WWII aircraft engines tomo pauk has posted all relevant data's and arguments.
> 
> A comment to:
> 
> ...



That's exactly why I said: "at least until recently". In fact I've owned a car with direct fuel injection since 2006. The point is that it took 50 years after WWII for it to become a truly viable system. In addition modern systems do not meter fuel in the same way as the WWII systems. Today's systems use a common rail with fuel metering via electronically controlled fuel injectors. Such a system is only possible due to the enormous processing power of modern microprocessors. 

I have found a truly "apples to apples" comparison test of carburetors, indirect fuel injection and direct fuel injection that was conducted by NACA in 1939. A single cylinder engine with a Wright R-1820-G air cooled cylinder was used. The results are quite specific "The values of minimum specific fuel consumption with each method of mixing fuel and air were the same." The paper does indicate that fuel injection has advantages in the distribution of fuel to individual cylinders, which was the main impetus for its adoption on the Wright R-3350.

I've attached the NACA Paper

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## GregP (Nov 14, 2015)

People tend to think fuel injection is the be-all, end-all. A good carb is just fine if coupled with a good intake. It is easier to get fuel injection right these days because of microprocessors. Before that, using cams for injection adjustment, it was about as good as a carb with the added benefit of not cutting out under negative g.

The engines of today have a host of improvements that allow them to go 100,000 miles between tuneups ... not just digital fuel injection. I wouldn't trade a digital new engine for an old carbureted engine ... but, if the carbs had the development DFI has had, they might be VERY comparable in fact.

We know they haven't but, then again, nobody has made the effort to do it. Since DFI is so well understood, nobody may EVER make the effort. Had they done so, carbs might still be in the mainstream. Maybe not. I can say I had a Suzuki 100 with 4 carbs that ran absolutely great for years. I had a DFI GPZ 100 Kawasaki that also ran great for years. To this day I'm not sure which one ran better. The only thing I know for sure is the Suzuki had a choke and, if you left it ON, the bike was very slow after it warmed up ... I did that only once.


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## Koopernic (Nov 15, 2015)

The big advantage of direct injection from the DB601E onwards was that a large valve overlap between intake valve and exhaust valve allowed scavenging and tuned ports that flushed our the last 15% of exhaust in the system. This was not possible on a carburator system since the fuel was premixed and would tend to be flushed out during scavenging. With direct injection the fuel could be injected after scavenging. This kind of tunning caused a problem with rough idling at low RPM so the DB601E and DB605 had variable length induction ports to aid idling and engine starting by tunning the length.

Apart from flushing in more air for combustion it also disposed of residual endgases that could cause pre-ignition. This helped greatly with low octane fuels. The injection also helped engine starting in the cold.

This technique was also used in the BMW801 but not as aggressively as intake ports could not be made variable length(instead they experimented with variable exhaust valves on the BMW802). 

When German fuel improved from about 94/115 octane to about 96/125 in 1943 the BMW801 boost could be increased from 1.42 ata to 1.65 ata, thus giving the aircraft 1900hp instead of 1700hp.

Those aircraft tasked for ground attack were given what was called "C3 einspritzing" or C3 injection whereby the fuel during special increased emergency power could be fed instead to the intake of the engine ahead of the supercharger thus precooling the air/fuel mix and allowing increased power to 2050hp. Effectively the BMW801 acted like it had a carburettor when in War Emergency Power.

The direct fuel injection thus provided very good high speed cruise and military power while C3 einspritzung added a little more power again at a cost in efficiency.

The DB601/605 was a better engine than the Merlin for the Germans.

Had Britain been forced to operate all of its bomber force and over half of its fighter force on 87 octane they probably would have lost the war. It would have been hard to get much above 1030hp.

I imagine the best way forward, without 100/130 or even 100 was to introduce Water injection as soon as possible and move onto the Griffon XII spitfire in 1943 with water injection.


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## GregP (Nov 15, 2015)

About 3/4 of the way down you posted: "The direct fuel injection thus provided very good high speed cruise and military power while C3 einspritzung added a little more power again at a cost in efficiency."

Perhaps you meant valve overlap thus provided same. All fuel injection did was to change the method of fuel metering, unless I miss my logic here. Could be.

I've certainly seen carbureted engines outperform fuel injected engines. All you have to do is go to an NHRA drag race to see it. Since that is true in 2015, it was probably true in 1940. The NHRA top fuel racer today, on a carburetor, is making 10,000 HP from 500 cubic inches and going 1,000 feet in less than 4 seconds. No fuel injected piston engines are going any quicker, anywhere in the world. So they probably didn't either in 1940. What they DID do is not lose power under negative g-force. That was a major advantage for the Bf 109 in 1940.


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## wuzak (Nov 15, 2015)

Top fuel cars do not use carburettors - they use direct fuel injection.


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## GregP (Nov 15, 2015)

If you say so ...

Here's a nice top fuel pump demo ...
_View: https://www.youtube.com/watch?v=xGTbQuhhluY_

The sound is the fuel pump. NO reason why it couldn't be injected. It's just a fuel delivery system. Neither one is superior to the other unless one can be controlled better. At this point, digital fuel injection SHOULD be better by a wide margin simply due to the ability to be controlled instantaneously. But the main need is 1.3 - 1.5 gallons per second.


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## fastmongrel (Nov 15, 2015)

I dont think there are any Top Fuelers or Funnys still using carbs but in the lower classes carbs are still regulary used. The top Pro Stock cars in Europe were using carbs last time I looked. Dont know if NHRA rules are the same.


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## Milosh (Nov 15, 2015)

Again I can't load an image.

Twin fuel pump schematic
http://images109.fotki.com/v782/photos/4/41615/228570/TwinFuelPumpSchematic-vi.jpg


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## tomo pauk (Nov 15, 2015)

thedab said:


> How long does a late 43 DB605A goes for on 1.42 ata boost? (i.e.what the time limit at maximum boost)
> 
> and what are time limits for the DB605AM?



The time limit for the DB 605A for 1.42 ata was 5 minutes. Not sure for the 605AM, though.



Reluctant Poster said:


> That's exactly why I said: "at least until recently". In fact I've owned a car with direct fuel injection since 2006. The point is that it took 50 years after WWII for it to become a truly viable system. In addition modern systems do not meter fuel in the same way as the WWII systems. Today's systems use a common rail with fuel metering via electronically controlled fuel injectors. Such a system is only possible due to the enormous processing power of modern microprocessors.



Was driving the 4 carb Alfa 33 1.5 TI, consumption was horrible. The injected, though not directly injected, 1.7 was giving more, while being more frugal with fuel.



> I have found a truly "apples to apples" comparison test of carburetors, indirect fuel injection and direct fuel injection that was conducted by NACA in 1939. A single cylinder engine with a Wright R-1820-G air cooled cylinder was used. The results are quite specific "The values of minimum specific fuel consumption with each method of mixing fuel and air were the same." The paper does indicate that fuel injection has advantages in the distribution of fuel to individual cylinders, which was the main impetus for its adoption on the Wright R-3350.



Both Bristol and NACA were testing fuel injection on a 'wrong' engine type - a single row radial engine. The V-12 engine does not feature the inlet manifolds that are of same length and layout, as it was the case with the single row radial. A eupercharged V-12 with one carb will hence run some of the cylinders on a little more rich the mixture, in oder that other cylinders get just the mixture they need. 
However, the gain in fuel consumption via injection on the ww2 era German aero engines was probably in single digits, the other part of a bit better consumption was due to the greater compression ration; both of these were not without trade-offs, though.



Koopernic said:


> ...
> The direct fuel injection thus provided very good high speed cruise and military power while C3 einspritzung added a little more power again at a cost in efficiency.



The very good hi-speed cruise and military power from BMW 801 was due to the engine being of 'decent' displacement and RPM 



> The DB601/605 was a better engine than the Merlin for the Germans.



Maybe. The capacity for engine gun/cannon on the DB probably kept the Bf-109 competitive until the end of ww2 without a major airframe modification being necesarry.



> Had Britain been forced to operate all of its bomber force and over half of its fighter force on 87 octane they probably would have lost the war. It would have been hard to get much above 1030hp.



I'm afraid that youre wrong on both accounts. Once the USSR and USA were in the fight vs. Germany, there was no way that UK will loose the war. 
The RR have had in production, prior the war, the Merlin X, that was giving 1130 HP in low gear on 87 oct fuel. That is before Hooker improved the supercharger sytem (gaining in both rated height and brake horsepower), and before tests with intercooled both Merlin XX and 45 that showed further gain in power and rated height on those engines.



> I imagine the best way forward, without 100/130 or even 100 was to introduce Water injection as soon as possible and move onto the Griffon XII spitfire in 1943 with water injection.



Yep, water injection is a way to circumvent the lack of hi-oct fuel. The Merlin 46/47 with WI would've been an really interesting engine, let alone the 2-stage Merlin and Griffon.


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## bobbysocks (Nov 15, 2015)

fastmongrel said:


> I dont think there are any Top Fuelers or Funnys still using carbs but in the lower classes carbs are still regulary used. The top Pro Stock cars in Europe were using carbs last time I looked. Dont know if NHRA rules are the same.



are they using jetted carbs or throttlebody....which is the first type of fuel injection....a carb body with an injector instead of jets.


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## fastmongrel (Nov 16, 2015)

bobbysocks said:


> are they using jetted carbs or throttlebody....which is the first type of fuel injection....a carb body with an injector instead of jets.



In Pro Stock it is Jetted Carbs iirc. The engines are stock apart from you can build them with forged cranks, rods, pistons and heads. Though everything must be dimensionally similar to stock and only have 2 valve heads. Thats the extent of my knowledge without googling it comes from a programme I kept from the last drag race I went to.


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## EKB (Nov 17, 2015)

GregP said:


> I can say I had a Suzuki 100 with 4 carbs that ran absolutely great for years. I had a DFI GPZ 100 Kawasaki that also ran great for years. To this day I'm not sure which one ran better. The only thing I know for sure is the Suzuki had a choke and, if you left it ON, the bike was very slow after it warmed up ... I did that only once.



When I was a teenager I rode a 4-cyl Yamaha Seca 550. With 50 hp, I thought it was pretty fast in stock trim. 

That is until I rode a Kawasaki 750 triple that was built in the 1970s. Factory specs on the H2 Mach IV motor was 75 hp but the owner did some minor upgrades (tuned to about 100 hp). Even though the bike was ten years old, he was running 11 second ETs at the local 1/4 mile strip. I did not ride the bike to its limits and I recall having problems keeping the front wheel on the ground. The two-stroke triples were the budget superbikes of their day. Just insanely quick off the line and often wrecked by inexperienced riders.


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## Koopernic (Nov 17, 2015)

tomo pauk said:


> The very good hi-speed cruise and military power from BMW 801 was due to the engine being of 'decent' displacement and RPM
> 
> Maybe. The capacity for engine gun/cannon on the DB probably kept the Bf-109 competitive until the end of ww2 without a major airframe modification being necesarry.
> 
> ...



Wikipedia specifically states the Merlin X producing that power in 100 octane fuel (not 100/130 but just 100) not 87 octane.

See:
"At the start of the war the Merlin I, II and III ran on the then standard 87 octane aviation spirit and could generate just over 1,000 horsepower (750 kW) from its 27-litre (1,650-cu in) displacement: the maximum boost pressure at which the engine could be run using 87 octane fuel was +6 pounds per square inch (141 kPa; 1.44 atm).[nb 8] However, as early as 1938, *at the 16th Paris Air Show*, Rolls-Royce displayed *two versions of the Merlin rated to use 100 octane fuel*. The Merlin *R.M.2M* was capable of 1,265 horsepower (943 kW) at 7,870 feet (2,400 m), 1,285 horsepower (958 kW) at 9,180 feet (2,800 m) and 1,320 horsepower (984 kW) on take-off; while a *Merlin X* with a two-speed supercharger in high gear generated 1,150 horsepower (857 kW) at 15,400 feet (4,700 m) and 1,160 horsepower (865 kW) at 16,730 feet (5,100 m).[48]"

It further states this was at 9 psig which is beyond the 6 psig possible on 87 octane at the time. I think the head design had to be strnghtend and 70/30 glycol were needed to get to 12psig but either way greater than 6psig was not possible with 87.

A gain of 100 hp is a great deal merely for a gear speed change. Seems possible only with extreme optimisation for low altitude WEP.

Another section of Wiki gives
1,130 hp (843 kW) at 3,000 rpm at 5,250 ft (1,600 m) with maximum boost pressure +10 psi (69 kPa); this was the first production Merlin to use a two-speed supercharger; Used in Halifax Mk.I, Wellington Mk.II, and Whitley Mk.V bombers. First production Merlin X delivered 5 December 1938.[6] It also gives 1,280 hp (954 kW) at 3,000 rpm, +10 psi (69 kPa) boost, sea level

there is a useful chart here:
https://en.wikipedia.org/wiki/List_of_Rolls-Royce_Merlin_variants
This is where I'm lifted the quote from.
https://en.wikipedia.org/wiki/Rolls-Royce_Merlin


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## GregP (Nov 18, 2015)

The Kawasaki 750 triple and the original KZ900 had mild steel frames, and you'd get into frame flex if you hit the poower hard ina turn. The 750 triple had head shake when the front end came down, but the KZ900 did not ... or at least MINE didn't, but DID have a bit of head shake if you got into washboard while turning. I had ample opportunity to sample that behavior. I added a steering damper and it was better at high speed. The only real cure for frame flex was an aftermarket chromolly frame and swing arm.


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## tomo pauk (Nov 18, 2015)

Koopernic - I don't know why going to the Wikipedia, when on this site there is far more accurate data on the Merlin X. 
Eg. in the post #10 of this very thread, Aozora kindly posted data for different early Merlins, and it is stated that in the 1st gear max power was 1130 HP on the Merlin X on 87 oct fuel, while for anything above that the 100 oct fuel is needed. The power settings requiring 100 oct fuel are marked with asterisk (*).
As for the boost level that is feasible on 87 oct fuel - the Jumo 213 was god for 1.6 to 1.8 ata without MW 50, or +8 to +11 psig. The Merlin featured an even lower CR than Jumo 213, so we can still expect it t do at least that boost, if not greater. 



> A gain of 100 hp is a great deal merely for a gear speed change. Seems possible only with extreme optimisation for low altitude WEP.



Bingo for the 1st sentence, totally wrong on the second.


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## Denniss (Nov 18, 2015)

One has to be careful with power comparisons as one may refer to power available for take-off at sea level and another may refer to maximum available power at altitude.


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## tomo pauk (Nov 18, 2015)

Of course. 
This chart (http://ww2aircraft.net/forum/aviation/merlin-vs-db601-39722-7.html#post1092184) shows that Merlin X will give some 1075 HP at sea level, 1130 HP at 5000 ft, all on +5.75 psi.


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## Gixxerman (Nov 18, 2015)

Wow, some H2 owners here, nice. Always fancied one but never did.
I was ( am) mostly into Suzuki's. I love 2 strokes had all the Gts (except for the 750 triple, which a few friends had so I know them reasonably well). I took a while to get into 4 strokes but the big Gsx11's were ( currently the Gsxr11w) are my thing. Even the 80's Gsx11 weren't exactly the best handling bikes (all that weight basic physics) but the Gsxr's are so much better (more compact, lighter, much better suspension, brakes tyres - despite the power hike - make the big difference I think).

All a carb per pot, the earlier ones ran well enough (nothing quite like a well set up crisp 2 stroke hitting its power-band) but the later ones are harder to set up right but run extremely well at all speeds, the more recent bikes with fuel injection, digital ignition 'closed loop computerised control systems seem much easier to mess with (just get out your laptop, get a Dynojet Power Commander exhaust 'sniffer' when you put it on the rolling road)


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## GregP (Nov 19, 2015)

Gi Gixxerman,

I had a Suzy Water Buffalo. I liked it except when it was decelerating. OK, but nothing to write home about stock. When setup up for drag racing, it was something like a 10-time national champion. About 60 - 75 HP stock, depending on the state of tune. Over 160 HP when setup up for racing, with a LOT of the weight gone.

Doesn't seem like much these days, but it was in the 1970's and 1980's. Heck, a Yamaha TZ750 only had about 160 hp, and won several world titles in road racing. When it came on the pipe, you could NOT keep the front end down ... you had to control the rise with throttle. That assumes you were within 20° of being vertical. If you were leaned over and hit the pipe, you did an instant low-side.

Meanwhile, back to airplane engines .... especially Merlins and DB 601s. I have often wondered why more DB 601/603/605's are not avialable. There were thousands sitting around after the war. Why didn't they save a few more than they did? Hard to imagine just scrapping them ... for no good reason, when they could run and be generators, or whatever. Power is power.

They used Allisons for a few decades as water pump / farm engines in the USA. Why not DB's in Germany?

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## tomo pauk (Nov 19, 2015)

Price of gasoline wrecks the idea for most of the world, let alone in post war Germany.

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## fastmongrel (Nov 19, 2015)

Outside of the US after the war everyone was short of money, raw materials and cash. In Britain people tried to run cars and motorbikes on Petrol mixed with Lamp Oil, waste engine oil, heating oil and other horrible brews because Petroleum was so expensive and rationed. In 1945 Germans didnt have shoes, Coal and food never mind running a gas guzzling aero engine as a generator. A lump of high quality metal scrap was worth a whole lot more.

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## GregP (Nov 19, 2015)

THANKS!

Makes sense now. I always wondered ... seems such a waste to scrap engines that run well ... if nothing else, preserve them for use later. I have several V-8's for cars that are "pickled" for later use in hobby vehicles as I get the time and inclination. One has been pickled for 15 years and , because I treated it well, it has no corrosion and is ready for rebuild. I can turn it over by hand with the spark plugs out.

I have a good friend who JUST rebuilt a Chevrolet 409 (750 HP Version) after the engine had been pickled for 20 years. The car runs GREAT and will do a quarter mile so quickly it will scare you ... if you are riding. If driving, it is just plain old FUN, but hard on the tires.

We should ALL have such problems ...

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## fastmongrel (Nov 19, 2015)

I have a BSA B50 engine thats sitting in a box smothered in grease waiting for the right time and frame. I put it in the box for a few weeks whilst I got on with something else that was 12 years ago.

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## Snowygrouch (Dec 28, 2015)

Hi,
The benz fluid drive coupling power loss follows this equation (RAE ref E/2410/2/6/13.D).

P_v=P_comp ((N_in-N_out)/N_out ) 

Where, Pv is power to oil heating, Pcomp is supercharger impeller compressor drive power and N is shaft speed. 

In other words the losses to oil
are highest when the coupling is doing its thing. The slip was around 2.5 %, the power loss
at locked condition was hence less as per equation above. The tests show
that at 0.7/1 (max slip) you`re loosing 42% of the supercharger drive power to oil.

For a 601-E, at 1.3Ata at GND>5000feet zone the coupling looses 39bhp in pure oil heating alone,
at 1.15ata (hence lower compressor pressure ratio) its reduced to 24bhp. So it doesnt take
long to imagine whats happening with fairly moderate boost increases. Going up 0.15 Ata
boost puts 61% more power to oil. 

Once you`re at 17,000feet or above thats reduced to nominally insignificant (in the case
of this particular engine in that particular condition, it depends on how the secondary
control pump is set to come online).

Not too bad as long as you`re just going up and down once. But evidently if you do any sort of 
time in the band between min and max slip, you need a much bigger oil cooler. I do not
know much about air operations as I`m just an engines man - but just saying that is the
case with this type of drive. Conversely it was stated by other studies that in a pure intercept
and return home scenario the coupling was actually quite nice, as it warmed the engine up
fast, and then the losses become small above rated height. So it all depends (like all 
engines) on deciding what the exact nature of the application is.

Geoffery Wilde at Rolls did a study on the coupling for Stanley Hooker, as he had worked
previously with these couplings and knew their workings. Because the Merlin was a smaller 
engine they knew they would have to boost it considerably higher than the DB in order to 
have a chance. This means higher compressor air power, hence in a Merlin with a higher 
pressure ratio compressor, the power lost to the coupling will go up and up. 

Geoffery worked out that a Merlin equipped with a fluid drive (there are layout drawings
and a complete theoretical set of curves), that with projected boost developments, 
that the drag of the required oil cooler would almost nullify the advantage of the 
coupling (which is basically that it "fills-in" the area under the "saw-tooth"
pattern of a gearbox equipped supercharged aero engine).

This is further complicated by the characteristics of the Fottinger coupling, 
which follows this mathematical behaviour.

Pt=ρ x d^5 x n^3 x c 

Where Pt = power transmission capacity (Watts), d= outer diameter of coupling (m), ρ= oil density (kg/m^3), n= shaft speed (rads/sec) and c=a geometry constant (depending on the shape of internal ribs of the particular coupling and so on). 

To get a compact installation Geoffrey worked out that running it off the back of a crank (like a automatic gearbox in a modern car) you`d need a huge toriod. 
So (like Benz) realised it needed to be speeded up (see the n^3 term). However once you do this the viscous heating losses go up further. 

This tended to sludge up the couplings, because the oils were pretty awful back then compared to what we run now, so you would often find the superchargers
on the DB not performing to factory spec at the mid-end of their lives. I`ve got a coupling here thats in "as used" condition and it extremely gummed up
inside. Not a design error really, just something that one aspect of tech. of the day didnt quite deliver on in real life. I think if Geoffery had
done the study for Stanley 6 months prior, they would definetly have at least built a test-stand. 

Geoffery and Stanley hooker both visited Sinclair Fluid Drives in person to discuss
developing the coupling into the Merlin - but within a month hostilities officially
started and all efforts swung into "get the most out of what we`ve got now". 

Hence the Merlin with fluid drive never happened for these two reasons.

In other words, if you want a larger lower boosted engine the fluid drive is better,
because the losses into oil are less and hence smaller oil cooler = lower drag = more speed.

If you study the Merlin vs DB series compressor power - you`ll see the Merlin expends
considerably more shaft power driving its impeller. Which it would as it was nearly
always running at a higher pressure ratio than the DB. Another very good reason 
why DB used methods to increase power late-on that didnt involve running
extremely high pressure ratios in their compressors (eg Nox), as
that power comes from direct chemical energy not increasing the compressor
pressure ratio.

Kind Regards

Calum

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## fastmongrel (Dec 28, 2015)

Good first post and I learnt something new.


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## stona (Dec 28, 2015)

Well done! Even I managed to follow the arguments and learn something new and I am definitely not an engines man.
Cheers
Steve


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## Snowygrouch (Dec 28, 2015)

For your interest, this is a rather well used DB605-A fluid drive
supercharger coupling. Dismanted for your delectation under laboratory
conditions (my PC desk).

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## bobbysocks (Dec 29, 2015)

if you have that kind of stuff laying around I would love to dig through your attic!!


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## gjs238 (Dec 29, 2015)

Snowygrouch said:


> Hi,
> The benz fluid drive coupling power loss follows this equation (RAE ref E/2410/2/6/13.D).
> 
> P_v=P_comp ((N_in-N_out)/N_out )
> ...



What is that playing on the TV in the background?


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## GregP (Dec 29, 2015)

Looks fairly easy to clean up and make good again. That assumes it isn't magnesium.

I hope you have the rest of it around somewhere.


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## Balljoint (Dec 29, 2015)

Since the DB 601 et al was the larger engine but weighed about the same as the Merlin it would seem to be the better execution of a V -12 design. For a given fuel flow the larger displacement allowed for greater conversion of heat energy to power. Conversely, the Merlin would have a hotter exhaust that saw low efficiency in power extraction as through exhaust thrust and such. Both greater stress through higher boost and larger components tend to drive engine weight. Just an opinion but I see the Merlin as the result of evolution that involved compromises (of spec creep) while the DB was more of a clean sheet of paper design.


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## gjs238 (Dec 29, 2015)

Wonder what the DB series would have been capable of with US fuel.


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## tomo pauk (Dec 29, 2015)

Provided they fulfil the original specs, that was not the case always, the power at lower and mid altitudes would've increased with higher oct fuel.


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## Aozora (Dec 29, 2015)

Snowygrouch said:


> Hi,
> The benz fluid drive coupling power loss follows this equation (RAE ref E/2410/2/6/13.D).
> 
> P_v=P_comp ((N_in-N_out)/N_out )
> ...



Thanks for that, even I understood! For comparison, attached is an interesting article from AEHS (Aircraft Engine Historical Society), describing Rolls-Royce's methods for testing the Merlin's power and supercharger efficiency in 1940 and comparing the results with NACA tests.

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## gjs238 (Dec 29, 2015)

Snowygrouch said:


> Hi,
> The benz fluid drive coupling power loss follows this equation (RAE ref E/2410/2/6/13.D).
> 
> P_v=P_comp ((N_in-N_out)/N_out )
> ...



So I guess one is faced with the choice of a multi-speed geared supercharger drive, a torque converter driven supercharger, or a turbo charger.
The latter seems to avoid some of the issues of the former, while creating some of its own.


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## fastmongrel (Dec 29, 2015)

Balljoint said:


> Since the DB 601 et al was the larger engine but weighed about the same as the Merlin it would seem to be the better execution of a V -12 design. For a given fuel flow the larger displacement allowed for greater conversion of heat energy to power. Conversely, the Merlin would have a hotter exhaust that saw low efficiency in power extraction as through exhaust thrust and such. Both greater stress through higher boost and larger components tend to drive engine weight. Just an opinion but I see the Merlin as the result of evolution that involved compromises (of spec creep) while the DB was more of a clean sheet of paper design.



It doesnt quite work that way on a supercharged engine, its not about fuel, compression ratio or capacity though bigger is often better. Its all about how much *Air* you can move into and out of the engine and thats down to the air compressor and the intercooler. 

Take a look at BMWs M12 Formula 1 engine of the 80s, it was a 1500cc 4 cylinder engine with an Iron block from a saloon car that ended up producing 1,400 hp in practice trim and 1,000 hp in race trim with the boost wound back to save fuel. The Turbo just got bigger and bigger and the engine became almost a gas generator bolted to a Turbine. If BMW had kept on strengthening the engine (it was Iron because Aluminium technology couldnt cope) and making the Turbo bigger and the radiators bigger its mind boggling to imagine what power they could have achieved if the FIA hadnt changed the regulations to try and slow the cars down.


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## tomo pauk (Dec 30, 2015)

gjs238 said:


> So I guess one is faced with the choice of a multi-speed geared supercharger drive, a torque converter driven supercharger, or a turbo charger.
> The latter seems to avoid some of the issues of the former, while creating some of its own.



Both the multi-speed and torque converter are supercharger drive systems, they add flexibility, not altitude capability. Compare Merlin III vs. Merlin X, or Merlin 45/50 vs. Merlin 20 series.
The addition of turbo adds another impeller, thus it adds capability.


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## gjs238 (Dec 30, 2015)

.


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## Balljoint (Dec 30, 2015)

fastmongrel said:


> It doesnt quite work that way on a supercharged engine, its not about fuel, compression ratio or capacity though bigger is often better. Its all about how much *Air* you can move into and out of the engine and thats down to the air compressor and the intercooler.
> 
> Take a look at BMWs M12 Formula 1 engine of the 80s, it was a 1500cc 4 cylinder engine with an Iron block from a saloon car that ended up producing 1,400 hp in practice trim and 1,000 hp in race trim with the boost wound back to save fuel. The Turbo just got bigger and bigger and the engine became almost a gas generator bolted to a Turbine. If BMW had kept on strengthening the engine (it was Iron because Aluminium technology couldnt cope) and making the Turbo bigger and the radiators bigger its mind boggling to imagine what power they could have achieved if the FIA hadnt changed the regulations to try and slow the cars down.



Scroll down to the 9/03/15 entry;

McCabism

I think we’re saying pretty much the same thing. Cooling aside, with a stoichiometric mixture fuel mixture, air or fuel are a function of each other. I’m assuming that both DB and RR designed so there was an optimum of both engine strength and weight. The FIA BMW obviously has a great overhead in strength at the cost of avoidable weight.


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## kool kitty89 (Apr 18, 2016)

fastmongrel said:


> It doesnt quite work that way on a supercharged engine, its not about fuel, compression ratio or capacity though bigger is often better. Its all about how much *Air* you can move into and out of the engine and thats down to the air compressor and the intercooler.


Superchargers (mechanically driven or otherwise) add compression and increase mass flow, but are only ONE of the factors contributing to that. The bare (normally aspirated) engine will induce air into the manifold through the vacuum created by the cylinders themselves, and larger displacement and higher RPM mean larger volumes of air being drawn in (and of course, superchargers of similar mass flow will provide lower pressure to a large displacement engine than a small one).

Engine displacement, RPM, throttle body/plate design, and overall intake manifold design are all factors that come into play for mass flow through an engine. (manifold design was the key difference between the Merlin X and XX series, more aerodynamically clean and un-kinked supercharger+intake manifold improving mass flow and compression while reducing charge heating -reduced drag/friction- and thus improving performance without increasing supercharger size or engine power consumed to drive it) 

The V-1710 had a known manifold bottleneck as well around the carburetor/throttle body, but it was never corrected due to some combination of war-time expediency and lack of funding. (as well as relative irrelevance for turbocharged installations using low gear ratios for the integral supercharger -for the 8.8 and especially 9.6 geared engines, it was a major bottleneck both for mass flow and charge heating, and is the main factor that prevented the 9.6:1 engines from matching or exceeding the performance of the Merlin 45 in both power and altitude performance) Similar overhead on the production line is likely why 2-speed gearing was never used on the V-1710, and external auxiliary supercharger stages were preferred due to not disrupting existing manufacturing tooling. (the integral supercharger and manifold arrangement remained unchanged)

Junkers adopted an annular throttle plate (swirl throttle) that avoided aerodynamic losses common to conventional butterfly style throttle plates and greatly improved power curves for both single and multi-speed supercharger drive when employing this mechanism. (gains were most significant at sea level and critical altitude for higher gear speeds where the throttle plate does the most constricting of the intake, little or nothing is gained when the throttle is allowed to be wide open, but the swirl arrangement greatly improves airflow characteristics at partial throttle to the point power curves are often best at low level for any given supercharger speed, and dropping slightly in power as critical altitude is reached rather than loosing massive amounts of power to intake drag at lower altitudes and failing to take advantage of the denser atmosphere -which in theory, should allow the supercharger to work somewhat less hard, and is demonstrated in practice with a well designed swirl throttle)


There's also the issue of cylinder compression ratio, but this doesn't impact mass flow, but instead improves power and fuel efficiency though higher peak compression in the cylinder, and smaller volume of the charge when ignited. (ie the cylinder extends slightly further at full stroke in higher compression ratio configurations)

German engine designers typically opted for higher compression ratio over higher boost pressures for engines targeting higher octane fuels. This had the advantage of avoiding larger and more power-sapping superchargers and the intercooling necessary to use such (or charge heating suffered without such cooling) while offering an increase in power at all altitudes without increasing fuel consumption. (the V-1710 is a bit of an interesting case there given it uses a slightly higher displacement and higher compression ratio than the V-1650, but not nearly to the extent of any of the German V-12s of that power class ... of course the V-1710 was bottlenecked by politics and funding issues)

Ever increasing engine RPM was the primary way german engines developed higher and higher capacity throughout the war, and one of the reasons they needed larger (or faster running) superchargers as well, in spite of little (or sometimes no) increase in boost pressure. (mass flow increased due to the increased operating RPM) Aside from the case of the DB-605 increasing the 601's bore and volume. (prior to that the 601 had increased its operating speed continually, and had it not been for the roller bearing shortage, would have been worth continuing development to that end -along with introducing high altitude versions using the DB-603 supercharger a la DB-605AS) The Jumo 211 and Jumo 213 progression to higher and higher RPM without increase in volume is an exceptional example of this progression, particualrly with the impressive operating speed of the 213. (The V-1710 might have been rated too conservatively in this respect too given that, unlike the Merlin/V-1650, there had been fairly dramatic improvements in crankshaft design that should have allowed reliable operation well above 3000 RPM and well above the limits of the early-war C-series engines present on the P-40B/C/Tomohawk, though like overboosting there may have been quite a lot of unofficially sanctioned operation of the V-1710 beyond its official specifications -unlike the Merlin which didn't function well enough under such conditions to tolerate some of that sort of abuse and was also noted to run too rough to allow low-RPM cruise like the V-1710 offered, the crankshaft not being as well balanced and not nearly as tolerant to high or low RPM beyond its general sweet-spot for operation; I suspect part of the V-1710's conservative rating was lack of funds for more extensive testing but also due to more conservative USAAF standards in general and particularly due to some of the failures experienced with the C series V-1710 when pilots/crews operationally pushed them out of spec -notably the Flying Tigers- and suffered failures with those much less tolerant early series engines -the crankshaft design in particular was both less suited to overreving and running at higher torque levels, so overboosting to excessive power levels at lower RPM would also overstress it)


Rolls Royce (and several American engien designers) also seemed to have more capable centrifugal compressor engineering than German designs, or at least a significant number of cases, so relying less on supercharger performance also sidestepped this serious bottleneck. Junkers Jumo's pre-war superchargers were particularly poor with the 210 and (pre-F series) 211 using a somewhat ridiculous looking 'spouted' impeller with a series of square outlets formed into the outer edge of a shrouded impeller and thus producing a substantial amount of drag when spinning. This was replaced with a far better designed and somewhat novel fully-shrouded impeller in the 211F, though probably still not as aerodynamically efficient as most Allied engines impellers it seems to have been a good design and one Junkers stuck with and built on for their later war designs (and multi-stage superchargers) and did have the advantage of simplifying the supercharger casing itself. (an unshrouded impeller requires very tight tolerances in the casing to maximize compression and avoid leakage and drag around the edge of the impeller blades/vanes, the shroud effectively has a built-in casing that contains and guides the airflow into the diffuser independent of the outer casing)

http://www.enginehistory.org/Sarah Clark/Finding Aid/Jumo211A SC.jpg (Jumo 211A supercharger -note the 'spouted' impeller, yes that's one solid piece that rotates at high speed inside the casing ... years ago when I first saw it, I assumed it was 2 parts with those spouts being part of the diffuser guide vanes)

Access forbidden! (nice allied report on the 211F including details on its supercharger)

To be fair, American supercharger design had been pretty awful when General Electric had been the only supplier (super, not turbochargers) and engine manufacturers finally decided to go it alone and develop their own, superior centrifugal compressor designs (and consequently forcing GE to both step up their own game in compressor design and to focus more on turbocharger development).

With that in mind, it's surprising Hans Von Ohain and Whittle both did as well as they did with their impeller designs. (Ohain making some compromises to allow sheet metal blades rather than a machined aluminum disc, but still rather well designed compared to plenty of late-30s superchargers, particularly Jumo's ... perhaps another reason axial compressors were pursued more heavily by some was due to the underdeveloped nature of centrifugal compressor designs? -often claimed to be a mature technology of the time, but really not, Whittle in particular targeting unheard of 4:1 and higher compression ratios on a single stage -Ohain's 2.8:1 in the HeS 3 was pretty much cutting edge for 1939, while the Halford H.1 remained within the range of Ohain's early work until later in development when pushed over 3:1 when approaching its full RPM and 2,700 lbf design thrust and 3.3:1 in the post-war Goblin II with improved diffuser casing and combustion chamber design)

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## blau (Aug 20, 2021)

GregP said:


> The only real "apples-toapples) comparison in engines is using Mean Effective Pressure, and thsi shows them all to be VERY close to one another, as I expected before I started. For reference, I used the model that came up in Wiki for the numbers, but chose the Merlin XX since I had access to all. The merlin starts to look better up high with the 2-stage units, but not at takeoff, which is where these come from.




But Greg, according Wikipedia - Mean effective pressure - Wikipedia:
W=Pme x Vd; 
work or power directly depends on displacement (Vd), power is product of Pme (MEP) and Vd (displacement) so if you talk power and want "apple to apples comparison" then displacement should be included, isn't it?
There is an old saying - no replacement for displacement

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## blau (Aug 20, 2021)

tomo pauk said:


> But, not because of fuel injection, but because of notably higher compression ratio?


I can say for DB60x series only - without comparison to Merlin.
A higher compression at DB601 was (is) possible due to fuel injection... There is no fuel injection as a factor in basic power equation for internal combustion engine per cycle (W=Pme x Vd). 

By the rule, if we have two identical engines, one without and with fuel injection then fuel injected version is more efficient. There is an example of Db600 vs. Db601. 






Of course, there is a big technical issue of building controlling unit for injection - but assuming it solved, injection of fuel (direct or indirect) must make the engine more efficient - mostly due to cooling effect of injection and atomization - even if there are other positive effects of fuel injection. Controlling issue is far more simple to be solved for stationary regime engines (let say aircraft engines) than than ever changing (cars). Fuel injection is nothing new or modern - is as old as internal engine itself (Fuel injection - Wikipedia) - by the way, it wasn't mentioned there, but even Nikolaus Otto himself, filed a for a patent on direct fuel injection in 1877. 

Regards

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