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British Super-/Turbocharger Development

Schneiderman

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There is no question that the UK had the necessary metallurgy to construct turbines, Whittle, Hooker and their peers would confirm that.
Rolls-Royce and Bristol, along with BTH and research at RAE etc. had been developing superchargers progressively since the mid 1920s and had acheived a high degree of efficiency in both intake and impeller design. In the Rolls-Royce 'R' racing engine of 1929 the power consumption of the supercharger was matched by the additional boost acheived in the intake duct, effectively taking the net power drain to zero. Furthermore the introduction of ejector exhausts to provide a modicum of thrust meant that not all the enegy in the exhaust was lost. All in all I doubt that the advantage of turbochargers in the war years was that significant.
 

iverson

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England had the technology to develop superchargers and could get the required materials and fuel from the US. But the two-stage, intercooled, mechanical supercharger met the RAF's requirements, which made turbocharger development a luxury that could be left to the Americans.

That said, the work of Hooker and Whittle on jet engine turbines is not, I believe, directly comparable with work on turbochargers. Jet-engine turbines work at significantly lower temperatures, closer to those produced by diesels. Indeed, most jet engines burn diesel or similar light oil fuel.

My main point was that the US had the success that it did with turbochargers for unique and largely fortuitous reasons--a large domestic gasoline industry and the accidental discovery of Vitallium. Turbochargers were being developed in WW1, if not before, and in many countries. But no one had much success until the US in the 1940s. Bristol turbocharged the Hercules, but did not persist with it once the two-stage Merlin proved successful.

Even then, success was marginal. Most American turbocharged engines had issues with overheating and turbine failures throughout the war--hence the many proposals for replacing turbocharged Allisons with Packard-Merlins in airplanes like the P-38.
 

iverson

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One more point, re the Rolls-Royce R engine. Racing engines are not a good parallel with service engines generally, and ram-air induction is a case in point. Ram-induction only works within the speed and altitude range for which the inlet duct was tuned. Under other conditions, the inlet geometry is likely to cause turbulence that hurts performance. So ram-air induction can work on a low-level racing engine that runs for a relatively short time. But it would be much harder to use in a service engine.

Ejector-type exhaust pipes are obviously more applicable to service conditions. They recover some of the exhaust energy by producing thrust. But they do not reduce the power consumed by the supercharger or attain the efficiency that is at least theoretically possible by compressing the intake charge using the turbine.

So I still maintain that, in wartime, the choice between turbocharging and the combination of exhaust thrust and mechanical supercharging was more a matter of requirements and history than of any theoretical, absolute advantage of one approach over the other.
 

Avimimus

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Thanks for the analysis. Engine design isn't something that is discussed enough.
 

Richard N

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“Even then, success was marginal. Most American turbocharged engines had issues with overheating and turbine failures throughout the war--hence the many proposals for replacing turbocharged Allisons with Packard-Merlins in airplanes like the P-38.”

That sounds more like an Allison issue than a turbocharging problem. Turbocharging seems to have worked well enough for the B-24, B-17, B-29, and P-47 on their air cooled radials.
 

Schneiderman

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Fair points but I still doubt that metalurgy would have slowed development of a turbo should it have been required. My reference to the 'R' was not regarding any ram effect but the rise in air pressure within the expanding intake duct as a result of the airflow slowing, this would be equally valid for any well designed intake on a military aircraft.
 

red admiral

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iverson said:
For the US, long range and thus fuel economy were greater concerns than they were for the European powers. The turbocharger had theoretical advantages in this respect. A mechanically supercharged engine burns a lot of fuel just to drive the supercharger and blows a lot of usable energy out the exhaust stacks. A turbocharged engine drives the supercharger using that otherwise wasted energy.
The exhaust energy from the exhaust stacks isn't actually wasted though, it provides a significant amount of thrust compared to the propellor, especially at high altitude and high speed. I seem to remember a figure of ~30mph boost.

I came across a nice comparison between turbocharged and supercharged engines many years ago. Turbocharged better at low speed and altitude. Supercharged being superior above ~400mph above 20,000ft i seem to remember. But not a massive difference.
 

iverson

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The exhaust energy from the exhaust stacks isn't actually wasted though, it provides a significant amount of thrust compared to the propellor, especially at high altitude and high speed. I seem to remember a figure of ~30mph boost.

I came across a nice comparison between turbocharged and supercharged engines many years ago. Turbocharged better at low speed and altitude. Supercharged being superior above ~400mph above 20,000ft i seem to remember. But not a massive difference.
I believe that your first point is correct in some cases but not in others. Like most technical issues, advantages--and performance--are relative to conditions and requirements. Thrust-producing exhaust stacks demand a lot of experimental tuning work to get them right. When they aren't right, they might even hurt performance, due to back pressure or poor scavenging. In the case of the Merlin, it took awhile before the right solution was found. Ejector stacks also raise operational concerns--they are problematic for military aircraft operating at night.

In your second point, I think you have mixed up the conditions. Supercharged (gear- or turbine-driven) will be superior at altitude. Unsupercharged or mildly supercharged engines will be superior at low level (hence the cropped supercharger impellers used when adapting Merlin engines for low level use).

With few exceptions, military and commercial aero engines never make more power than they do at sea level. Maximum power is usually needed when getting a loaded aircraft off the ground. The engine will not need more as it climbs and cruises, because lift will increase with speed, fuel burn will reduce weight, and drag will be less in less dense air. So, if maximum power output were the issue (as it would be in race cars and Schneider Trophy racers), there would be little point in having a supercharger. A gear or turbine-driven driven supercharger would just add weight and complexity. You can always get the power with a larger, lighter, and/or faster-turning engine.

But maximum power output is, of course, not the only issue in an working airplane. As the airplane climbs, the air density decreases and power/thrust decreases with it. There is less oxygen per intake stroke, less fuel burned per expansion stroke, and less high-pressure, high-velocity gas in the exhaust. So an engine's critical altitude--the altitude at which sea-level power begins to fall off due to decreasing air pressure--is what matters in practical (non-racing) applications. Superchargers (mechanical or turbo) are used to delay the point at which sea-level power falls off by artificially increasing the density of the intake air. As altitude increases. both have to do more work. But the power required for that work comes from different sources that have very different characteristics, costs, and benefits--and it is in this respect that mechanical and turbo superchargers have their respective advantages and disadvantages.

During the war, in England, the mechanical supercharger had the advantage of being very highly developed (largely due to Bristol's early lead in air-cooled engines and Rolls-Royce's pre-war investments and racing experience--Napier did not benefit). The mechanical approach was expensive and demanded a lot of development. The supercharger was driven by precision-machined gears and clutches and the whole installation was integral with and dedicated to a given engine design and model. Superchargers weren't interchangeable, mass-production units and couldn't be added to any desired engine (though Allison worked on some designs with this in mind). Mechanical superchargers were also efficient only within a fairly narrow altitude band. In general, to achieve a higher critical altitude, engineers had to redesign and/or add hardware. Rolls-Royce were the masters at addressing this. But the solutions--multi-speed drives, multi-stage impellers, and intercoolers, added weight and complexity. The parts had to be finely tuned and governed so that abrupt speed changes did not catastrophically damage components. The extra parts increased the power consumption of the supercharger and reduced the net gains. Complexity and weight yield diminishing returns. This is probably why two-stage engines were successful, but, with the exception of German diesels, three-stage engines were not. As several of us have rightly pointed out, tuned exhaust ejectors add thrust that can offset the power consumption of the supercharger, but only in the supercharger's designed operating range. At other altitudes, the supercharger will consume power without producing optimal power or exhaust thrust.

Turbochargers had the disadvantage of a relative lack of development prior to the war, largely due to fuel and metallurgical issues (see https://history.nasa.gov/SP-4306/ch3.htm, S.D heron's autobiography, and S.D Heron's Development of Aviation Fuels). During the war, this, arguably, limited its success vs. the mechanical supercharger. But post-war, turbochargers replaced their mechanical counterparts in almost all applications, from light airplanes to airliners. The turbo charger is relatively simple compared to a mechanical unit, because it lacks most of the multi-speed clutching and gearing. The units were mass produced in various sizes that could be more or less bolted on to a variety of of production engines. Performance-wise, the turbo charger had the huge advantage of automatically producing higher supercharger speed--and thus higher pressure--as altitude increased, up to the critical altitude. The compressor/impeller had to turn faster to produce sea level power, as in the case of the gear-driven unit. But the turbine had to overcome less back pressure and thus automatically spun the compressor faster. No gear trains. No clutches. No complex mechanical governors. A simple (if sometimes troublesome) blow-off valve prevented compressor over-speed/over-pressure problems by venting excess exhaust gas to the atmosphere. This was less efficient than a properly tuned ejector stack below critical altitude, but the inefficiency would be largely offset by the the lack of mechanical losses under these conditions. On the other hand, turbochargers did compress the intake air in close proximity to the exhaust, and components could get very hot. All war-time turbocharger installations suffered from fires, detonation, and overheating, a problem that was kept in bounds mainly by the abundant use of Anti Detonant Injection (ADI, water injection with alcohol as antifreeze) during take off and landing.

Overall, I suspect that the lower costs that result from suitability for mass production and interchangeability of parts explain why the USAAF preferred the turbo and why it replaced the mechanical supercharger in the post-war civil markets. When the performance differences aren't that great in theory and when cost and availability are critical, an off-the-shelf unit almost always wins over a multi-year bespoke engineering effort. In 1939, England had already completed that effort. So following through on the Merlin made sense. But it was a dead end (aside, of course, from all the expertise RR gained on the developing the compressor itself, which put them in the forefront of jet development, when coupled with a gas-turbine drive).

I said that there were few exceptions to the rule that military and commercial aero engines never make more power than they do at sea-level. The exceptions are the Austrian and German "super-compressed" engines of the first world war. These had compression ratios optimized for the intended operating altitude of the aircraft. As I understand them, a decompression lever on the camshaft let a ground crewman lower the compression enough to swing the prop and start the motor. The lever was then returned to the full compression position. From sea-level to the optimal altitude, the pilot had to operate the engine at part throttle--and low power--to avoid over stressing it. This was effective and met the immediate need, but was inflexible, inefficient, and unlikely to be good for durability.
 

iverson

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Schneiderman said:
Fair points but I still doubt that metalurgy would have slowed development of a turbo should it have been required. My reference to the 'R' was not regarding any ram effect but the rise in air pressure within the expanding intake duct as a result of the airflow slowing, this would be equally valid for any well designed intake on a military aircraft.
Please explain. What you describe is what I think of AS ram effect. Changes in section in the inlet are trading flow velocity for higher pressure, an effect which is proportional to speed with which the intake moves through the air. Thanks.
 

iverson

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Richard N said:
“Even then, success was marginal. Most American turbocharged engines had issues with overheating and turbine failures throughout the war--hence the many proposals for replacing turbocharged Allisons with Packard-Merlins in airplanes like the P-38.”

That sounds more like an Allison issue than a turbocharging problem. Turbocharging seems to have worked well enough for the B-24, B-17, B-29, and P-47 on their air cooled radials.
"Worked well enough" depends on the definition of "well enough". In war time, the USAAF accepted the trade-off between performance and problems/losses. But in peace time military or commercial service, things might have looked different.

As far as I know, all USAAF turbocharged engines suffered from overheating, fires, and waste-gate (blow-off valve) issues to some extent. Where the engines were at greatest risk--during high-load, high-weight take offs--ADI (Anti Detonant Injection) was used go limit problems. Water and alcohol would be injected into the engines to cool the fuel-air mixture in the cylinders. This prevented detonation that would otherwise destroy the engine. A large aircraft could carry quite a load of ADI, so I suspect that we have heard less about problems in the big radials than in the Allisons. Nonetheless, I've read that B-17s and B-24s frequently aborted due to turbo failures shortly after takeoff.

If my conjecture is true, the B-29 is the exception. It was notorious for engine fires, although how much of this was down to the turbo alone is debatable. The Curtiss-Wright R-3350 Duplex-Cyclone suffered from design issues, poor fuel/air distribution (which promotes detonation) and overall lack of development (all arguably down to a combination of lack of due-diligence and profiteering on the part of the manufacturer). The R-3350 overheated severely, both at takeoff and during cruise. Ambient temperatures were usually high at its bases. Long-range flight at high-altitude demanded lean mixtures, which were known to promote detonation even in the absence of turbocharging and poor fuel distribution. The problems were so bad that B-29 production was very nearly switched to a version re-engined with turbocharged, liquid-cooled, 24-cyclinder Allison V-3420s. These had the same power, fewer overheating problems, and offered higher performance due to reduced drag. But the disruption to production was considered too great.
 

iverson

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Schneiderman said:
Fair points but I still doubt that metalurgy would have slowed development of a turbo should it have been required. My reference to the 'R' was not regarding any ram effect but the rise in air pressure within the expanding intake duct as a result of the airflow slowing, this would be equally valid for any well designed intake on a military aircraft.
Alternate futures are always debatable. If you are interested, my source on this is mainly S.D. Heron, in the books quoted in my other reply on this topic. I found both amusing and worthwhile--comprehensible even for a non-engineer like me.
 

red admiral

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But post-war, turbochargers replaced their mechanical counterparts in almost all applications, from light airplanes to airliners.
Agree, but this overlooks that in the main performance driving application i,e. High speed high altitude fighters, piston engines were replaced by jets. The applications that remained were generally for low and slow, where the turbocharger has a performance advantage. Anything remotely high/fast soon switched to turbojets or turboprops.
 

CJGibson

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If my conjecture is true, the B-29 is the exception. It was notorious for engine fires, although how much of this was down to the turbo alone is debatable.

Wasn't that fixed by fitting cuffs to the roots of the propeller blades to increase airflow through the engine?

Chris
 

iverson

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CJGibson said:
If my conjecture is true, the B-29 is the exception. It was notorious for engine fires, although how much of this was down to the turbo alone is debatable.

Wasn't that fixed by fitting cuffs to the roots of the propeller blades to increase airflow through the engine?

Chris
That may have helped, as did better baffling for control of air flow, improved valve metallurgy to reduce detonation, improved oil distribution, better manifold designs, etc. But I believe that, ultimately, in the post-war period, direct fuel-injection had to be adopted before fuel distribution improved enough to control detonation.
 

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About Vitallium:

For high-temperature use in engines, particularly turbochargers, the first alloy used was Haynes Stellite No. 21, similar to Vitallium. This was suggested by the British engineer, and denture wearer, S.D. Heron during World War II. Although the characteristics of the material obviously suggested itself for making turbocharger blades, it was thought impossible to cast it to the precision needed. Heron demonstrated that it could be, by showing his Vitallium dentures.[2]
[Source]
 

riggerrob

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Dear Iverson,

Your description of super versus turbo charging is excellent.

If I may make an analogy to the gas-turbine, turbo-shaft engines installed in modern turbo-props and helicopters.
Early turbo-props drove their propellers directly from compressor shafts and need propeller speed reduction unit to slow propellers until their tips are sub-sonic.

OTOH free-turbine engines merely mount the power turbine in the exhaust manifold and let exhaust gas spin it. Free turbines are not directly connected to the core's turbine-to-compressor shaft. Free-turbines have fewer gears and fewer vibrations. They also allow mechanics to simply un-bolt power sections and replace them with over-hauled components.

The R-3350 engines installed in B-29 bombers suffered a variety of problems because they were rushed into production during WW2. Even simple engines need to be balanced, but balance is vastly more complex in 28 cylinder radial engines. Back in those days, they needed to break/burn out dozens of prototypes - test stands - before they could balnce the engine. An engine can only be perfectly balanced at one rpm, one altitude, one fuel-air mixture and a single boost pressure. Every other time is a compromise.
Without fuel injection to individual cylinders, it is extremely difficult to deliver consistent fuel-air mixtures to all cylinders.
Cooling rear cylinders is always more difficult.
R-3350 and R-4360 were so maintenance intensive that only a few trans-Atlantic airlines used them post WW2. The USAF Military Airlift Command was the biggest customer.
 

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Ironically the only people who had control & injection systems necessary to make a really really good turbocharger system were the Germans, about the only nation materially unable to build them. USAF turbo installations were very seriously impeded by poor boost controls, which with a turbo become really difficult once you have wastegates and prop pitch to add to the mix. You really do need a "Kommandogerat" to have the easiest time of a reliable turbo system.

Its a bit less critical with a mech supercharger as the shaft speeds are all kept constant relative to eachother. Its also very difficult to do a good multipoint injection system without a Kommandogerat (or systems to that function). Of course its all chicken-egg as the only reason you TRY to develop a Kommadogerat in the first place is if you want injection or turbos or both.

The DB601 sort of has the same functions, but the automation is distrubuted over separate control boxes on the injection pump and supercharger. The BMW and Jumo Kommandogerat is really just a consolidated neat box version of that, but including VPitch controls (early 601 has manually variable thumbwheel pitch controller).

British boost controls were pretty good, and auto prop pitch, but you still dont have proper mixture controls or supercharger speed control integration (auto rich/lean is still just a manual switch, it just keeps things lean or rich once you flip it either way).

USAF tech intellience people at Wright Field did a LOT of work on captured BMW801 kommandogerat`s for this reason, and had the war gone on the USA would have had their own version in operation by late 1945 in combat, probably with injection.

Theoretical studies by RAE and RR concluded that below about 20,000 feet the turbo fighter would probably be slower than mech supercharged versions, although for obvious reasons its basically impossible to do a meaningful back-back test to prove that (basically thats all about size, weight and exhaust thrust).

Basically thats a very longwinded way of saying I agree that in WW2 due to complexity, size, weight and controls problems - a turbo was not at all a means to guaranteed supremacy, although I think the P47 systems were really very good indeed, but thats what you needed. design the plane around the turbo - if you dont want to do that, your chance of installing one in an existing airframe without ending up with a horrible "frankensteins-airframe" shape - is very small indeed.
 

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Calum, I have a few questions for you, if I may.

a) Were there experimental "Kommandogeräte" from other german companies/institutions other than DB, Jumo or BMW, e.g. DVL, KHD, MAN or FKFS?
b) Are you aware of any advanced SUM-Vergaser-Gesellschaft carburettors?
c) Which turbosuperchargers were intended to equip the KHD`s Dz series?
 

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So, if maximum power output were the issue (as it would be in race cars and Schneider Trophy racers), there would be little point in having a supercharger. A gear or turbine-driven driven supercharger would just add weight and complexity. You can always get the power with a larger, lighter, and/or faster-turning engine.
The above statement is 100 % wrong. Supercharging, be it mechanical or turbocharger, is by far the best way to boost an engine's power even at sea level. A perfect example is that in all car racing in which supercharging is not banned, supercharged engines rule. Back in the golden days of Formula 1 racing when the makers could choose either a naturally-aspirated 3.5 litre or a 1.5 litre supercharged one, the latter won the power race hands down. In case of large aero engines, the advantages of power boosting through supercharging are even greater from the point of both size and weight.
 

Pasoleati

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All war-time turbocharger installations suffered from fires, detonation, and overheating, a problem that was kept in bounds mainly by the abundant use of Anti Detonant Injection (ADI, water injection with alcohol as antifreeze) during take off and landing.
This is another Bravo Sierra statement by Iverson. Turbochargers saw service in basically these aircraft: P-38, P-47, B-17, B-24 and B-29. Of these 5, only the P-47 had an ADI system fitted during the war in servive, the rest did not. It seems that Iverson has not even done the basics.
 

Pasoleati

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If my conjecture is true, the B-29 is the exception. It was notorious for engine fires, although how much of this was down to the turbo alone is debatable.

Wasn't that fixed by fitting cuffs to the roots of the propeller blades to increase airflow through the engine?

Chris
No. I strongly recommend reading the A.T.D.C. series written by Kevin Cameron in Torque Meter. That is the most thorough series in print I know on the issues with the R-3350.
 

Pasoleati

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... and R-4360 were so maintenance intensive that only a few trans-Atlantic airlines used them post WW2. The USAF Military Airlift Command was the biggest customer.
No. The R-4360 was a very reliable engine and per primary sources, cooled very well (statement made by a P&W representative during the the Joint Fighter Conference 1944. I strongly recommend Graham White's R-4360 book.
 

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Ironically the only people who had control & injection systems necessary to make a really really good turbocharger system were the Germans, about the only nation materially unable to build them. USAF turbo installations were very seriously impeded by poor boost controls, which with a turbo become really difficult once you have wastegates and prop pitch to add to the mix. You really do need a "Kommandogerat" to have the easiest time of a reliable turbo system.

Its a bit less critical with a mech supercharger as the shaft speeds are all kept constant relative to eachother. Its also very difficult to do a good multipoint injection system without a Kommandogerat (or systems to that function). Of course its all chicken-egg as the only reason you TRY to develop a Kommadogerat in the first place is if you want injection or turbos or both.

The DB601 sort of has the same functions, but the automation is distrubuted over separate control boxes on the injection pump and supercharger. The BMW and Jumo Kommandogerat is really just a consolidated neat box version of that, but including VPitch controls (early 601 has manually variable thumbwheel pitch controller).

British boost controls were pretty good, and auto prop pitch, but you still dont have proper mixture controls or supercharger speed control integration (auto rich/lean is still just a manual switch, it just keeps things lean or rich once you flip it either way).

USAF tech intellience people at Wright Field did a LOT of work on captured BMW801 kommandogerat`s for this reason, and had the war gone on the USA would have had their own version in operation by late 1945 in combat, probably with injection.

Theoretical studies by RAE and RR concluded that below about 20,000 feet the turbo fighter would probably be slower than mech supercharged versions, although for obvious reasons its basically impossible to do a meaningful back-back test to prove that (basically thats all about size, weight and exhaust thrust).

Basically thats a very longwinded way of saying I agree that in WW2 due to complexity, size, weight and controls problems - a turbo was not at all a means to guaranteed supremacy, although I think the P47 systems were really very good indeed, but thats what you needed. design the plane around the turbo - if you dont want to do that, your chance of installing one in an existing airframe without ending up with a horrible "frankensteins-airframe" shape - is very small indeed.
Calum, not so simple.

1. For example, the P-38J/L had simpler engine controls than the F6F-5. In flight the pilot did not need to operate the turbochargers separately at all.

2. British engine controls also evolved. For example, the Spitfire IX (and later marks too, except XII) had no longer a separate mixture control at all. Also the supercharger change was automatic with most Merlins and Griffons.

3. The single-lever control was not the ideal in all applications. In short-range interceptors yes, but not necessarily in bombers, patrol or transport aircraft where fuel economy in cruising may be of utmost importance. E.g. the DB 605A had a minimum s.f.c. at low altitude is around 205 - 210 g/hp/h. That of the R-1830 is 190 g and that withouut manual leaning, which was possible with American engines. Single-lever systems also prevented the use of high boost/low r.p.m. combinations for cruising.
 

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Calum, not so simple.

1. For example, the P-38J/L had simpler engine controls than the F6F-5. In flight the pilot did not need to operate the turbochargers separately at all.

2. British engine controls also evolved. For example, the Spitfire IX (and later marks too, except XII) had no longer a separate mixture control at all. Also the supercharger change was automatic with most Merlins and Griffons.

3. The single-lever control was not the ideal in all applications. In short-range interceptors yes, but not necessarily in bombers, patrol or transport aircraft where fuel economy in cruising may be of utmost importance. E.g. the DB 605A had a minimum s.f.c. at low altitude is around 205 - 210 g/hp/h. That of the R-1830 is 190 g and that withouut manual leaning, which was possible with American engines. Single-lever systems also prevented the use of high boost/low r.p.m. combinations for cruising."


1) Please identify where I say the word simple. or imply it conceptually - I seem to have missed it.

2) You are discussing british developments on later models, which were also not turbocharged or injected, ignoring all the early
problems in the war which is when it was actually much more important (plenty of controls for the pllot in the MkII hurricane, including
the supercharger speeds and many others besides)

3) Again, its you who are simplifiying by cherry-picking the P38L/ late model which had corrected the problems which plagued the early versions. The early reliability
problems were caused EXACTLY becuase the pilot WAS responsible for controls which could over-speed the turbo in combat. If you wish I can provide
the USAF reports demanding that a proper single lever system be made quickly because the existing system didnt work properly. The prior models
did NOT control the turbo`s automatically.

The DB605 you choose for the fuel economy comparison was never given a kommandogerat, (although DB were developing one), and it is simply
impossible to make a carburettor engine with better economy than multi-point injection, as the carburettor has to be tuned to provide
a safe mixture to the leanest cylidner, and therefore over-fuel all the others. Of course you can if you wish to put together
a set of data which under chosen conditions "proves" otherwise, but only by cherry picking.

All the investigations done by Rolls-Royce and the Royal Aircraft Establishment and Bristol Aero engines all proved that the German
engines had about 10% better fuel economy overall than the best carburettor engines, for the resons given. This may reduce slightly
in the case of a single-row radial as the pipes are all the same length and therefore the leanest>richest cylinder delta can be lower.

R-1830 was indeed a very good engine, powering a lot of useful aeroplanes - but none were notable fighters - so maybe not the best engine as a comparison....

As for single lever controls giving worse fuel economy, this is entirely depedant on how they are designed - and many were very clever indeed and were
much smarter than just tying the throttle to everything else with bits of string - there was often a lot of logic built in and would automatically
decide from the pilots throttle position if they were supposed to be in max-economny settings and so on.

All the best
 
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Wurger

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Calum, anything on these subjects?
a) Were there experimental "Kommandogeräte" from other german companies/institutions other than DB, Jumo or BMW, e.g. DVL, KHD, MAN or FKFS?
b) Are you aware of any advanced SUM-Vergaser-Gesellschaft carburettors?
c) Which turbosuperchargers were intended to equip the KHD`s Dz series?
 

Pasoleati

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Calum, I never spoke about "overall lower sfc". I am fully aware that e.g. the DB 605A Notleistung sfc was much lower than the comparable figure in any American or British engine.

As for the lack of "Kommandogerät" in the DB, well, the lowest cruising sfc figure I have ever seen for the BMW 801 is not below 200 g/hp/h.
 

Pasoleati

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1. Calum, you wrote: "USAF turbo installations were very seriously impeded by poor boost controls, which with a turbo become really difficult once you have wastegates and prop pitch to add to the mix. You really do need a "Kommandogerat" to have the easiest time of a reliable turbo system. " I do think this strongly implies that turbocharger installations had complicated controls for the pilot.

2. Since some 70 % of all P-38 production were either J or L models, I think it is perfectly logical to use them as the primary example.

3. The R-1830 was used in several fighters, of which two at least are very notable (Grumman F4F and Curtiss P-36)), other being e.g. Commonwealth Boomerang, Swedish J22, P-35 and Finnish VL Myrsky.

4. According to German pilot statements, the BMW 801 was at least in the Do 217 a very fragile and cranky engine despite the vaunted Kommangerät. Reliabilibility was nothing to vouch for.

5. I have in front of me an sfc curve of the DB 605A. The lowest figure is about 205 g/hp/h (that figure is also given in various DB Datenblätter). Based on some other data I have come across, the BMW 801 was definitely not more economical. Therefore I am quite confident that the lowest sfc of the BMW 801 with Kommandogerät is not lower than 205 g/hp/h. Now, based on engine manual data, I have calculated that e.g. the Bristol Hercules was able to achieve about 191 g/hp/h. No Kommandogerät. And of course, the Wright R-3350 Turbo Compound achieved about 168 g/hp/h. No Kommandogerät.

6. As for USAF reports demanding a single-lever system, pilots were NOT unanimous in that regard. The minutes from the Joint Fighter Conference held in October 1944 at NAS Patuxent River indicate that issue was discussed at some length. Some pilots wanted such control, some didn't. And these pilots present represented USAAF, USMC, USN, FAA, RAF and manufacturers.

7. One may also ask that if a Kommandogerät provided superior fuel economy, why wasn't the system adopted in post-war piston transport aircraft. Surely a 10 % reduction in fuel costs would have had airliner bean counters screaming for such a device.
 

Calum Douglas

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1) ?? I think we have some crossed-wires here Pasoleati ? - I dont think we are disagreeing....

2) Here in Europe the p38 failed to reach its potential,
in very large part due to turbocharger controls - this is a historical fact.

P38.png

3) I said "notable figters" and none of those are notable - seems like a communication cross-wires again.

4) German engine reliability was nothing to do with the kommandogerat, if you can - try to attend one of my lectures
to learn about this. Next one is in UK, in Oxford on 21st April hosted by the Institution of Mechanical Engineers, at Oxford Brookes
University. If you monitor my webpage you`ll find attendance details. I will inform a lot more about what was happening with the early 801-
its a mixture of fuel and metallurgy which is the major problem.

5) Fuel injected engines are more fuel efficient than those with a carburettor - this is a technical fact. Its really hard to compare
across totally different engines as it depends on their fuel "strategy" and all the mechanical considerations.
Kommandogerat doesnt "give" you fuel economy, you need one to have good injection, which is in itself where the fuel economy comes from.

The two systems are utterly inter-connected. This is from the Royal Aircraft Establishment in late 1940, after they ran German direct injection
engines on their test-beds.

Jumo_Economy.png

6) You can find a pilot who will say anything about anything if you search to have your own views proven.
Ask any fighter pilot today if they want to go back to old control systems...some early RAF pilots hated the
variable pitch propellor as they were used to the fixed pitch... and Rolls-Royce really worried they would not
want them - when they actually tried them in combat, nobody wants to go back.

7) A kommandogerat doesnt "automatically" give you good fuel economy, its REQUIRED to have injection, which
can itself provide the best fuel economy possible. Its pointless trying to compare economy on different engines
as they have too many other differences - we can see most clearly the difference in the German engines
before and after they were converted from carburettors to injection. This is not my "view" this is what
Rolls-Royce and the Royal Aircraft Establishment wrote in 1940 in their internal technical reports.

The big advantage of Kommandogerat is for fighter use, because they are subject to radically altering altitutde, speed
and power requirements in combat. Obviously of no use in transport aircraft. The cost of converting an entire airfleet
in civilian time to Kommandogerat`s and injection would be immense, so hardly a suprise that wasnt done.

Bristol, who had a very good history of powering civilian aircraft in the 30`s, were working on converting the Centaurus
to Direct Injection with automatic controls in the war. It was their intention to convert post-war civilian Centaurus to
injection.

Picking a turbo-compound engine as your example of why carburettors are better is really not very technically
sensible, as the compounding itself has a dramatic influence on fuel economy.
 
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Pasoleati

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Calum, to summarize: I am a fan of direct injection. But here is the problem: Why don't specific fuel consumption curves for German engines indicate that? For over 15 years I have been deeply interested in this subject, and whenever I have power and fuel consumption data, I calculate the sfc. I have never been able to find data on any major German engine (DB 605/601, Jumo 211/213, BMW 801), which gives an sfc of below 200 g/hp/h at any power setting. This is in direct contrast to data on several Allied engines (R-1830, R-1820, R-2800, Hercules). For example, a few days ago I took a look at B-17F engine curves and one setting gave less than 190 g/hp/h.

Now, I ask you: Do you have data that gives a minimum sfc of approximately 190 g/hp/h or less for any of the German engines listed above? I would be most happy to see such.

One more thing: Harry Ricardo states in an article in Shell Aviation News that a Napier Lion achieved an sfc of 123 g/hp/h (he uses the figure 0.27 lbs. /hp/h). Your take on this?
 

Calum Douglas

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Calum, to summarize: I am a fan of direct injection. But here is the problem: Why don't specific fuel consumption curves for German engines indicate that? For over 15 years I have been deeply interested in this subject, and whenever I have power and fuel consumption data, I calculate the sfc. I have never been able to find data on any major German engine (DB 605/601, Jumo 211/213, BMW 801), which gives an sfc of below 200 g/hp/h at any power setting. This is in direct contrast to data on several Allied engines (R-1830, R-1820, R-2800, Hercules). For example, a few days ago I took a look at B-17F engine curves and one setting gave less than 190 g/hp/h.

Now, I ask you: Do you have data that gives a minimum sfc of approximately 190 g/hp/h or less for any of the German engines listed above? I would be most happy to see such.

One more thing: Harry Ricardo states in an article in Shell Aviation News that a Napier Lion achieved an sfc of 123 g/hp/h (he uses the figure 0.27 lbs. /hp/h). Your take on this?
You will have a hard job trying to make correlations across such huge numbers of variables. For example do you know the calorific value of each fuel you are interested in ? If you dont know the exact calorific value of B4 and C3, its impossible to compare the actual energy consumption. The mass is meaningless because the fuels have different internal energy value.

Do you know the FMEP for each engine to see power lost in friction ?

Do you know the lambda value for each setting ?

Without doing a laboratory analysis (like the RAE did on the Jumo with the section of text I posted) its an entirely fruitless exersize to try to evaluate fuel consumption benefits of various induction systems across engines not even using the same fuel blends.

The Jumo211D recorded a min of 193g/hp.hr in 1940 at the RAE Labs, using British fuel - however this is also not definitive as you would need (to see the actual
best economy) to recalibrate the control unit to make the best use of the British fuel. They just ran it on 100 Octane without further adjustment, so we dont really
know if it could have done even better or not.

Unless you know the fuelling strategy and exact fuel characteristics of each fuel, its a total waste of time to discuss a topic like direct injection vs. carburettors across not only different engines, but different nations with different fuels, oils and requirements.

The best you can do is to read the original technical evaluations of the engine test engineers, and that shows conclusively that D.I. is better in this respect.

These engines also all have totally different compression ratios, further making any comparison of the sort of prescision with which you are hoping to achieve very unwise, further the valve overlap on the German engines is dramatically higher, which again makes comparisons across manufacturers incredibly complex.

The RAE concluded "The Merlin X has 19% greater specific fuel consumption that the Jumo211D at take off"

B17 engine is turbocharged, which will very significantly lower fuel economy over any mechanically driven SC engine because
you are loosing far less in SC drive losses, which for DB601 etc are easily 10% of full engine output. You cannot compare
fuel economy with respect to fuelling systems between mechanically and turbine boosted engines.

I cant comment on the Ricardo result beause I would need to know all the particulars of the engine the fuel and the test conditions.

If in spite of all that the numbers of german engines are still of interest for comparison.

verbrauch.png

If you dont like the RAE, you can always go with Wright-Field in the USA, who said this of a 211 they tested. Clearly the real fuel economy benefit
is not achived by expecting a vastly lower number for highest economy (although it actually IS lower at max economy than QUOTE
"comparable American engines".

The American and RAE tests are better (for comparison purposes) than German data-cards as they usually ran captured German engines on Allied
100 Octane fuel. Therfore eliminating one of the big differences. "Controls" refers to the automatic engine controls of the German engines.

NARA.png

Generally the Jumo series had better economy than the DB600 series, which is probably due to higher injection pressure and the use of 3 valve head, which tends to give better
performance at low engine speeds (when economy is in use).

The problems comparing ABSOLUTE consumption are examplified by this RAE report on the BMW801 and commenting on consumption on German fuel vs Allied 100,
which rather illustrates the point I`m trying to make.

BMW.png
 
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Pasoleati

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1. What is the injection pressure of Jumo 211/213 vs. DB 605/605? I have been under the impression that the DB used higher pressure (about 170 bars or so; the figure is given in the data card along a DB 605 injection pump on display at the Finnish AF museum) with the Jumo having less than half that. It is my understanding that the Jumo used much different injection nozzles ("open-type" whereas Bosch followed diesel-practice).

2. I have no doubt that at take-off setting a Merlin X has markedly higher sfc than the Jumo.

3. I know that turbocharging reduces the sfc. Nevertheless, I have a Twin Wasp manual curve for a mechanically supercharged variant on 87 octane fuel and it does give 190 g/hp/h.

4. I tried to check www.fischer-tropsch.org site where there are plenty of original reports on German fuels, but while finding some specs for the B4 and C3, no calorific value was given. It was mentioned however, that the C3 had high aromatic content.

5. The last extract in your post regarding the BMW 801 is in line with the reported characteristics in those F-T archive reports, i.e. that due to high aromatic content the C3 had high knock rating with rich mixture while not so good with lean.

6. There might be one easily comparable case: the R-3350 which had both carburetted and direct-injection variants.
 

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1. What is the injection pressure of Jumo 211/213 vs. DB 605/605? I have been under the impression that the DB used higher pressure (about 170 bars or so; the figure is given in the data card along a DB 605 injection pump on display at the Finnish AF museum) with the Jumo having less than half that. It is my understanding that the Jumo used much different injection nozzles ("open-type" whereas Bosch followed diesel-practice).

2. I have no doubt that at take-off setting a Merlin X has markedly higher sfc than the Jumo.

3. I know that turbocharging reduces the sfc. Nevertheless, I have a Twin Wasp manual curve for a mechanically supercharged variant on 87 octane fuel and it does give 190 g/hp/h.

4. I tried to check www.fischer-tropsch.org site where there are plenty of original reports on German fuels, but while finding some specs for the B4 and C3, no calorific value was given. It was mentioned however, that the C3 had high aromatic content.

5. The last extract in your post regarding the BMW 801 is in line with the reported characteristics in those F-T archive reports, i.e. that due to high aromatic content the C3 had high knock rating with rich mixture while not so good with lean.

6. There might be one easily comparable case: the R-3350 which had both carburetted and direct-injection variants.
I think you just need to decide what it is you are trying to find out/prove ?

Its a simple fact that if you have DI, you`ll have better fuel economy.

How this was implimented in wartime across vastly different engines, fuels, and manufacturers is another thing.

You could decide you were interested in who made the best DI system, or who had the best carburettor - but you really need to give up on trying to prove that a carburettor can give you equivalent fuel economy as a general operational principle.

Regarding injection pressure, its very complicated because they are mechanical plunger systems, the pressure curve has a parabolic curve, its not like a modern system
where you have a set rail pressure. However the Jumo system is slightly better in this respect (i.e the peak is higher).

If you have a catalogue showing that the fuel consumption of one engine is no higher with a mechanically driven SC, then something was extremely badly wrong with it as between 150 and 300 hp has gone missing ! :)
 
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Pasoleati

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Just a quickie now: Grumman FM-2 at sea level. 1450 rpm, 29 inHg. 30 U. S. g/h. Approx. 425 hp. Sfc=193 g/hp/h. Screenshot_20200229-042846.pngScreenshot_20200229-042917.pngScreenshot_20200229-043416.png
 

edwest

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To Calum Douglas,

Regarding your upcoming book about fighter engines, will there be some mention of propellers and propeller types?
 

Foo Fighter

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A fascinating discussion.
 

Calum Douglas

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edwest

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Thank you for that. Best of luck with your book.
 
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