Which country designed the best engines for WWII?

[wuzak]

As soon as multiple smaller impellers started to be used the efficiency went up. This resulted in less intake air heating (more hp!) as well as less parasitic power loss (more hp!) from the s/c at a given boost. It also allowed for greater absolute compression ratios as altitude went ever higher (more hp at 30k ft). Not to mention that there is always "some" loss of efficiency in such a fluid-coupled system.

Single stage superchargers were more efficient for lower pressure ratios (ie lower boost). IIRC Rolls Royce figured that the change-over happened around a PR of 3.5:1.

Note that boost depended on pressure ratio and inlet pressure (altitude). For a given boost a higher pressure ratio is required for a higher altitude.

 

[Shortround6]

Actually the two stage superchargers were almost always more efficient than a single stage supercharger, at least from a power in for amount of compression and lower heat rise of the compressed charge stand point.
However that doesn't mean they were the best choice when you figure in weight, volume, cost and a few other things.
SO it may depend on how you define efficiency.
Below 3.5:1 the two stage wasn't worth the extra complexity/cost.
And nobody got a single stage centrifugal compressor past 4.0:1 with anything approaching usable efficiency until several years after WW II.

At sea level a 3.0:1 supercharger could give you (roughly) 30lbs of boost or 90in manifold Pressure.
At 10,000ft a 3.0:1 supercharger could give you (roughly) 15-16lbs of boost or 61.7in manifold Pressure.
At 20,000ft a 3.0:1 supercharger could give you (roughly) 5 1/2lbs of boost or 41.26in manifold Pressure.

Please note that 1.4 Ata is roughly 42in.
I Know Greg has a more accurate conversion but that gives the general idea.
At 23,500ft a Merlin 61 needs 5.06-5.1:1 to reach 15lbs of boost. (or roughly 2.0 Ata).

 

[gjs238]

What nonsense.About the only truth in that is that Ford did indeed work to closer tolerances than RR as a mass production car manufacturer. The basic premise that the Merlin was not intended for mass production is not true.
Crewe was producing 303 engines per month and Glasgow had a planned output of 400 a month before the war even started. Glasgow quadrupled this to 400 per week by 1943.
The Ford/Manchester factory didn't produce an engine until mid 1941. I don't know where you are, but here the war started in 1939. In 1943 Ford was producing about 200 engines per week, half the rate of Glasgow.
The Merlin first entered production, as you well know, in 1936 and much had changed by 1939/40.

RR produced fewer Merlins in 1937 than planned but was still forced to cut production in 1938. Output was ordered cut again at the beginning of 1939!

As for being liquid cooled rather than a radial engine being its biggest failure, you are joking right? If you are not you really need to look at the engines that powered the most effective aircraft on both sides.
Funny that the Fw 190 developed from a radial engined fighter to one with an inline liquid cooled engine. The later versions were the best performers too. Maybe that was a failure of the Germans to understand the 'failings' of liquid cooled engines? They could have done with your expertise!
While you are putting the Germans right you can explain to all those Spitfire, Hurricane, Mustang, Mosquito, Lancaster, etc, etc pilots that their engines have a serious failing

Cheers

Steve

Next time just spray on a little of this:

 

[Venturi]

At sea level a 3.0:1 supercharger could give you (roughly) 30lbs of boost or 90in manifold Pressure.
At 10,000ft a 3.0:1 supercharger could give you (roughly) 15-16lbs of boost or 61.7in manifold Pressure.
At 20,000ft a 3.0:1 supercharger could give you (roughly) 5 1/2lbs of boost or 41.26in manifold Pressure.

Please note that 1.4 Ata is roughly 42in.
I Know Greg has a more accurate conversion but that gives the general idea.
At 23,500ft a Merlin 61 needs 5.06-5.1:1 to reach 15lbs of boost. (or roughly 2.0 Ata).

Excellent points.
Given that the aviation fuel DB engines were using was 87 octane, it is likely a maximum of 42"Hg is all they could work with. Thus it may very well have been DB's calculus that a higher displacement was the better way to go for more power, rather than incur the extra cost and complexity of a two-stage s/c.

The DB601 was 33L in swept volume (the DB605 being nearly 36L!) while the Merlin was 27L. That is a 22% larger actual displacement than the Merlin from the DB601, and a whopping 33% more displacement than the Merlin from the DB605!

For all that extra displacement,
the DB601E powering the Bf109F-4 produced a maximum of 1410hp at 42"Hg/2700rpm at 7000' (best power altitude).
the DB605A-1 powering the Bf109G-6 produced a maximum of 1510hp at 42"Hg/2800rpm at 7000' (best power altitude).

Whereas the contemporary 27L Merlin 61 powering the Spitfire MkIX, with two-stage, two-speed supercharger at 61"Hg/3000rpm operating at 11000' (best power altitude), produced 1565hp.

Now imagine an Allison V-1710 (28L displacement) operating with a two-stage, two-speed supercharger...

 

[Shortround6]

I would note that the early DB 601s ran at 2400rpm instead of the 3000 rpm of the Merlin so if both were operating at the same boost the DB601 is only flowing about 98% of the air the Merlin was. Higher RPM in the later versions (and the DB 605) flowed more air (more air means more power) but required the engine to be beefed up (more weight).

 

[Venturi]

Yes, and since air-fuel ratios are "fairly" consistent for any given airflow through an engine, that means ultimate fuel economy really depends on how low an rpm the engine can operate, which in turn boils down to cam and ignition timing and engine behavior. At low throttle settings often engines which tolerated lower rpm well could run a bit leaner mix, too.

A "peaky" thoroughbred engine will not tolerate being run at low rpm...

Lots more to look at than peak power if one wants to go that route. But ultimately, aerodynamics and airframe fuel capacity will trump low rpm engine running for creating greater mission range. This is why the P51D with the Merlin could get such good range.

It is an interesting debate and I enjoy it, but maybe the better question would have been, "which nation produced the best mass-produced piston engines for [x mission here]?"

 

[GregP]

I believe 90 inches of manifold pressure is about 29.51 inches (close enough to 30, but inches) of boost in British terms, not about 30 pounds. But Shortround is probably more knowledgeable about engines than I am, so I wouldn't discount his explanations.

I show 1.4 ata as 40.541 inches MAP, so Shortround is very close. Nice estimates, Shortround.

In case anybody wants it, the file is attached. I have protected the worksheets (I think) but there is no password. If you choose to unprotect it, it will do that. But I'd do that on a copy if I were you, not the original file.

If you find any issues, please let me know either in a post addressed to me or via PM. If there IS an issue, I'll fix it and re-post the file.

 

[wuzak]

90inHg MAP = 44.2psi (ABS) ~ 29.5psi boost (gauge).

 

[Deleted member 68059]

Hi,
All good conversations - but please be VERY careful equating air flow to both BHP and/or Air/Fuel Ratio.

In the case of almost ANY German engine after 1941/2 the relation between flow and power/fuel totally breaks
down because they all went to extreme valve overlaps. To give you a rough number on this, some were
blowing 15% of the ENTIRE supercharger flow straight out the exhaust pipes during overlap - hence
from a chemical point of view, this air mass took no part in combustion.

This caused both German engineers problems at the time (and the British at Farnborough who were running all
these German engines on their own test-beds) because their equations didnt work anymore (they measured
the volume of air being drawn into the supercharger, and then measured the fuel flow rate, to calculate
air/fuel ratios). The Farnborough engineers had to modify their mathematics to produce realistic figures
with the DB601E onwards for this reason.

Engine speed has some direct affect on overall efficiency because friction goes up (sometimes disproportionatly) with engine speed - and also at a certain point it gets hard to complete the combustion in time when really high speeds are used. However it is perhaps a little ambitous to say that low rpm gives high economy by default. Much more important for economy were steps such as
going to direct injection; because you no longer have to pour in enough fuel to ensure that the leanest cylinder is "ok", (
which usually means some of the other 11 are running considerably too rich). When you can tune each cylinder individually
you make large gains in economy for this reason (10>15% according to the Royal Aircraft Establishment in their comparisons
of Jumo211 to the Merlin 3).

Regards

 

[MiTasol]

Hi,
All good conversations

Agreed Snowy

For those interested in the technology behind some lesser known engines may I suggest a visit to
World War II | Old Machine Press and
Aircraft Engines | Old Machine Press

Note that although one link is a subdirectory of the other there is a lot in common between them and you need to look at both to get the full detail
I just accidentally discovered this site (though I am sure many other members have been there before me and maybe even linked to it) when looking for a Russian engine I saw details on aeons ago that also used a long valve overlap to scavenge all combusted gasses from the cylinder in order to gain extra power. No joy on that one damn it.

 

[Venturi]

This is the reason variable valve timing was invented. Because when a engine is operating at lower rpms, valve overlap is wasteful. When operating at design rpms, valve overlap is beneficial as it increases a/f entry into, as well as exhaust scavenging from, the cylinder. Of course this necessitates separate intake and exhaust cams.

However regardless of fuel delivery, lower rpms do result in lower amounts of fuel being used, and lower mix does as well. Ultimately a engine with better tolerance of low rpms (see my comment on cam timing, which SETS valve overlap) will be more suited to low rpm economy cruise than one which does not (also see characterization of Allison v1710 vs Merlin in this regard).

Direct fuel injection certainly increases efficiency when comparing engines on test stands, but more germanely, a major reason why it is important is that when looking at engines which also have a high valve overlap, it provides a way to deliver fuel more precisely during the combustion cycle (I.e. only when the exhaust valve is closing or nearly closed) rather than necessitate a generalized a/f "mix" which was available to all cylinders, anytime the intake valve opens...

Obviously the most efficient way to do things is to have spark and valve timing which varies with engine load and RPM, as well as direct fuel injection to match. In this manner, many of the higher performance cars we drive now are ahead of the aircraft we are discussing.

I'm looking forward to your book!

 

[Frankenerd]

Lot of good ones. Merlin was certainly a great engine. No doubt about it. So was the P&W R-2800. Another great. Also the Wright Cyclone.

Germans had the BMW 800 and Diamler Benz 600.

Russians had a bunch as well (sorry I'm not specific here).

But throughout WW2, all sides sort of "kept up" with each other as much as possible. The Japenese definitely lagged as did the Italians and other smaller countries. But the big players (US, Britian, Germany and Russia) all managed to produce engines that were roughly parrallel to each other in power.

I guess that it all depends on how you describe "Best"?
The best Radial built in large numbers was the BMW 801 and variants based on Power, P/W and P/FA.
The best inline was the DB-603 and variants using the same criteria as above. A distant second would be the Packard Merlin-9 in the P-51H which had far and away the best total integration of any plane in the War, or after, but it was >700 HP shy of the big Benz DB-624, IIRC with it's integral turbocharger installation.
While the best engine cowl was the "low frontal area cowl" used on the Hornet.
Which brings us back to the original question; How do you decide which is best?

 

[Shortround6]

Which brings us back to the original question; How do you decide which is best?

but it was >700 HP shy of the big Benz DB-624, IIRC with it's integral turbocharger installation.

I guess it depends,
do you count engines run on tests stands on the ground?
Engines that flew in test bed (test mules) aircraft?
Engines that actually powered service aircraft?
Engines that actually powered service aircraft that flew combat operations in WW II? (doesn't mean they actually engaged in air combat, just flew in a combat zone).

The DB-624 is a fail on all but the first condition (and that might be doubtful?)

 

[GrauGeist]

How about one question that takes that one step further:
Which engine was developed, produced, reliably powered aircraft during the war and continued in reliable service well after the war?

The Wright R-1820 was developed before the war, powered several successful aircraft types types during the war (SBD, B-17, FM-2, etc.), licensed by other countries and was even adapted for use in Armored vehicles. If this wasn't a good enough legacy, it was also developed into the R-2600 which in it's own right, was an engine used in successful types like the A-20, TBF, PBM, SB2C, B-25 and so on.

There are plenty of other engines like this, the R-1820 being one example.

It's one thing to have a monsterous, complex engine that produces brutal horsepower for a certain type of aircraft, but it's an entirely different matter to have a reliable engine which was capable of providing power to a multitude of applications and still finds itself useful long after it's deemed "obsolete".

 

[wuzak]

If this wasn't a good enough legacy, it was also developed into the R-2600 which in it's own right, was an engine used in successful types like the A-20, TBF, PBM, SB2C, B-25 and so on.

And not forgetting the R-3350.

 

[Shortround6]

Production of the Wright R-1820 started in 1930 and was pretty much an R-1750 (over 500 built) with a 1/8in bore job. R-1750s were first SOLD in 1927. Production of the R-1820 ended in Wright factory/s in 1963 which pretty much sets a record for large western piston engines. Russian licence version from the 30s was developed through several different models and production continued (at low levels) in Poland until at least 2007 which may be some sort of record for any type of piston engine. (anybody making Ford flat head V-8s for 70 years?)

Granted some versions of the R-1820 had no interchangeable parts with some previous versions.

 

[wuzak]

I guess that it all depends on how you describe "Best"?
The best Radial built in large numbers was the BMW 801 and variants based on Power, P/W and P/FA.
The best inline was the DB-603 and variants using the same criteria as above. A distant second would be the Packard Merlin-9 in the P-51H which had far and away the best total integration of any plane in the War, or after, but it was >700 HP shy of the big Benz DB-624, IIRC with it's integral turbocharger installation.
While the best engine cowl was the "low frontal area cowl" used on the Hornet.
Which brings us back to the original question; How do you decide which is best?

The DB624 was abandoned in 1943. It did not have 700hp more than the V-1650-9. In fact, it had less power.

GED0112

It may have had more power at altitude thanks to the turbo.

 

[GrauGeist]

And not forgetting the R-3350.

Yes, that's a good point...once it had it's bugs worked out, it was a great workhorse powering several notable types.

The Douglas A-1 would be perhaps the best example of longevity out of that application.

 

[fastmongrel]

Production of the Wright R-1820 started in 1930 and was pretty much an R-1750 (over 500 built) with a 1/8in bore job. R-1750s were first SOLD in 1927. Production of the R-1820 ended in Wright factory/s in 1963 which pretty much sets a record for large western piston engines. Russian licence version from the 30s was developed through several different models and production continued (at low levels) in Poland until at least 2007 which may be some sort of record for any type of piston engine. (anybody making Ford flat head V-8s for 70 years?)

Granted some versions of the R-1820 had no interchangeable parts with some previous versions.

The Zhuzhou Aero-Engine Factoryin China can still build you a HS-5 which is a license built Shvetsov Ash-62 which is of course developed from the R1820. Its probably built from spare parts stock but it still counts as production.

 

[tomo pauk]

I guess that it all depends on how you describe "Best"?
The best Radial built in large numbers was the BMW 801 and variants based on Power, P/W and P/FA.
The best inline was the DB-603 and variants using the same criteria as above. A distant second would be the Packard Merlin-9 in the P-51H which had far and away the best total integration of any plane in the War, or after, but it was >700 HP shy of the big Benz DB-624, IIRC with it's integral turbocharger installation.
While the best engine cowl was the "low frontal area cowl" used on the Hornet.
Which brings us back to the original question; How do you decide which is best?

The best big radial used in ww2 was R-2800. Period.
The best V12 was RR Griffon, second best was the RR Merlin. Merlin was the most important engine for the outcome of ww2, 1st in defense then both defense and attack.

DB 603 was plagued with reliability problems for 15 months (give or take) after introduction. DB 624 was supposed to operate on 2900 rpm, not to have 2900 HP.

I define 'the best in ww2' as combination of power at all altitudes used, reliability, usability, role played in the war; in this order; obviously disregarding the engines that were produced in small numbers.