# Superchargers?



## tomo pauk (Feb 24, 2014)

What I'm after is this: is there a one-stop on-line reference around? Specifically, I'm interested about supercharger systems used in piston engines, from late 1930s to late 1940s. Preferably, with as small flag-waving as possible


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## Shortround6 (Feb 24, 2014)

I am not even sure there is a one stop print reference 

You can certainly find books with chapters on supercharger theory and formulas but actual details of individual superchargers seems to be pretty spread out. 

The Merlin was pretty prolific as far as superchargers go, with a variety of gear ratios and different sized impellers (at least 4) and at least 3 different inlets on the single stage superchargers alone. Maybe somewhere there are documents with supercharger maps or charts for all the variations. 

Same with a number of other companies. The superchargers were modified over time with not only different sized impellers but different numbers of 'blades', the geometry of the inlets changed, the number and shape of the inlet vanes changed and the diffuser changed even for superchargers that kept the same nominal impeller diameter. These changes could affect air flow and efficiency even at the same gear ratios. These records may or may not exist in company records anymore.


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## tomo pauk (Feb 24, 2014)

Guess you're on the money there. I'm a bit more interested in applications, than in theory, but will look at anything decent that I can learn from.


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## Balljoint (Feb 24, 2014)

For what it's worth;

Supercharger Development in the U.S. During the Inter-War Period


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## tomo pauk (Feb 25, 2014)

A worthly reading. Guess I'll try to make a set of articles about supercharger systems of ww2


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## Shortround6 (Feb 25, 2014)

This site _may_ have a fair amount of the information you need. Unfortunately it may be scattered through a number of threads.


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## rinkol (Feb 25, 2014)

You can find a number of NACA reports on superchargers and various other aeronautical topics in the NACA archive on the NASA web site (I tried posting a link, but this was forbidden for some reason). In some cases, these are translations of foreign documents.


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## OldSkeptic (Feb 26, 2014)

tomo pauk said:


> What I'm after is this: is there a one-stop on-line reference around? Specifically, I'm interested about supercharger systems used in piston engines, from late 1930s to late 1940s. Preferably, with as small flag-waving as possible



Read Stanley Hookers biography "Not much of an Engineer", put quite few equations in there.


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## tomo pauk (Feb 26, 2014)

Thanks for feedback, people.


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## Shortround6 (Feb 27, 2014)

The "Flight Magazine" archives : Aviation History - Browse the History of Flight from 1909

Have a number of articles on superchargers although you have to dig for them. You may also have to allow for a bit of bias or war time censorship.


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## Balljoint (Apr 23, 2014)

Apparently NACA was tasked with improving the supercharger performance but found the engine itself was lacking. Just an opinion, but it would seem that the engine may have been unlike their previous experience with radials and turbocharging.

http://history.nasa.gov/SP-4306/ch2.htm


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## tomo pauk (Apr 23, 2014)

I take it you mean this, from the NACA's page:



> The Allison engine, however, never met the expectations of the Army Air Forces. The Cleveland Laboratory's work on the Allison engine increased its horsepower through the use of water injection and supercharging. However, from Ben Pinkel's point of view, this work was a "tremendous waste of effort" because of the basic flaws in the engine's design. Only after the Army substituted the British Merlin engine, in the P-51 Mustang did the United States finally have a fighter for high-altitude flight.



Am I the only one that finds this except misleading?


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## gjs238 (Apr 23, 2014)

tomo pauk said:


> I take it you mean this, from the NACA's page:
> 
> 
> 
> Am I the only one that finds this except misleading?



There were several misleading statements in that document.


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## Balljoint (Apr 23, 2014)

Two things struck me as pregnant. I had thought that the Allison supercharger problem was the result of Allison’s lack of corporate funds and lack of military concern. But Arnold was apparently on top of the matter and requested the NACA effort. However, the NACA guy Pinkel was a turbo man with good results on the B-17 but at sea as to how to package and drive a supercharged inline engine. It may be reading a bit too much into a few lines, but not at least replicating and adapting the extant Merlin supercharger tech meant the escort P-51 was delayed. It should have been doable.


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## m37b1 (Apr 23, 2014)

tomo pauk said:


> I take it you mean this, from the NACA's page:
> 
> 
> 
> Am I the only one that finds this except misleading?



I'd call it a bit misleading, or at least in need of expanding on. The basic mechanics of the reciprocating assembly of the Allison, were very much the equal of the Merlin. I'd say the combustion chamber was actually superior on the Allison. I'll never take any of the excellence away from the Merlin, but that statement really needs to be backed up with detail.


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## Shortround6 (Apr 24, 2014)

Something to remember is that Army power plant division thought that the IV-1430 hyper engine was the "answer" to the liquid cooled engine question for quite some time. Continental simply built bits and pieces to Army specifications. Some of the Army "experts" had a lot of prestige and pride invested in the hyper concept. How much of this transferred over to the NACA I don't know.

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## tomo pauk (Apr 25, 2014)

Fine points there. 
We might see that failure of the IV-1430 was never mentioned in the article, yet Arnold's condemning comments about US engines' manufacturers can be read easily: 



> Arnold blamed the engine companies for the country's dismal aircraft engine situation, but he expected the NACA to correct it. On October 14, 1942 he issued an official directive that the NACA must "do everything practicable to improve the performance of existing engines". The engine companies had failed to provide the nation with "small, light, high performance, highly supercharged engines" suitable for fighter airplanes. Their exclusive focus on large, heavy, air-cooled radial engines reflected their drive for profits at the cost of preparedness. "Our engines were nearly all built as all-purpose engines, with an eye on the world market, and not specifically for fighter aircraft".2 The United States could not enjoy the luxury of fundamental research until the problems of reciprocating engines then in production-the Wright 2600 and 3350, the Pratt Whitney 1830 and 4360, and the Allison V-1710 had been resolved.



In late 1942, both UK and Germany were trying to develop the engines that were neither small, nor light (Sabre, Griffon, Centaurus, DB-603, Jumo 213/222, BMW-802). The USAC/USAF never put much faith before 1942 in two-stage engines either - why all of the sudden accusing the manufacturers for not designing the stuff the main costumer isn't asking for? If there was no USN and P&W cooperation, the P&W 2-stage ('highly supercharged') engines would've likely never existed. Even Wright produced 2-stage variant of the R-2600, though just as prototype (prototypes?).
Contrary to that, USAC/USAF favored turbo, and that does not mean small, and by extension, does not mean light. Insistence for turbo meant that engine-stage compressors were of modest size, too. 



> As the country's aircraft engine needs intensified during World War II, fundamental engine research took a back seat to trouble-shooting to solve the problems of engines in production. The wartime mission of the new engine laboratory was simple. It had to assist the engine companies to make their engines more powerful and reliable. General Arnold wanted engines that were comparable to the best European models. He ordered Pratt Whitney and Wright Aeronautical to develop fuel injection systems within 12 months to make their engines comparable to the German BMW-801, at that point the world's best aircraft engine.



That is dated as of "3 November 1941". 
The R-2800 was at that time (and any other time) a far better engine than BMW-801. In late 1941, the lack of fuel injection was not a thing holding back the R-2600, but a better layout of exhaust, that was solved mid-war. The 801 was somewhat smaller, but R-2600 was far more reliable, despite some Curtiss muddling.

Here is the reply (dated 11 December 1942) from P&W to the Arnold's accusations of 14 October 1942, a footnote from same web site:



> Debate over the engine situation in the Power Plants Committee resulted in a stinging response to Arnold's charges by Arthur Nutt of Wright Aeronautical and Leonard S. Hobbs of Pratt Whitney. Hobbs went so far as to insist that a long rebuttal be inserted in the revised minutes of the meeting. *The Army Air Forces, he argued, had demanded speed "to the exclusion of other qualities, and as far as he knew, they had obtained it" He felt that there was a basic fallacy in Arnold's assessment of the nation's engine needs. Small engines would never be superior to large ones, and he believed that reliance on "small engines to eventually get the initiative and step above the Germans was simply the continuation of a basic error which could not be corrected by any kind or amount of concentrated laboratory work*


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## Shortround6 (Apr 25, 2014)

Kind of a case where the right hand didn't know what the left hand was doing. You are not going to build "small" (1200-1400 cu in engines) that are "highly supercharged" without fuel well in advance of the plain 100 octane stuff the US was using in 1940 and into 1941. It is also a bit amusing in that _both_ the Lycoming 1230 and Continental 1430, which had the most Army input (read meddling ) weighed about the same as the Allison and, at least in length, were significantly longer.


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## OldSkeptic (Apr 29, 2014)

Shortround6 said:


> Kind of a case where the right hand didn't know what the left hand was doing. You are not going to build "small" (1200-1400 cu in engines) that are "highly supercharged" without fuel well in advance of the plain 100 octane stuff the US was using in 1940 and into 1941. It is also a bit amusing in that _both_ the Lycoming 1230 and Continental 1430, which had the most Army input (read meddling ) weighed about the same as the Allison and, at least in length, were significantly longer.



Thank god for Roll Royce then. It was powerful enough and tough enough (under the great Hives) to ignore that nonsense from idiots.

People, especially Americans (who have a talent for reinventing history), underestimate how important RR was to creating the Merlin Mustangs. The USAAF didn't want it, NA had some vague ideas but were trying to survive against official obstruction from the USAAF (it's only customer really was the British). The Air Ministry didn't want it (especially Portal) , MAP didn't want it, there were official instructions from those to RR to NOT DO IT, Hives ignored them and told it team to go ahead... hence the Merlin Mustang X... which was a god send to Arnald trying to get some, against endless US and UK opposition, a decent LR fighter.

To be fair I think NA then stuffed up because it took nearly another year to produce the P-51B... it would have been much better to just slap Merlins into P-51As and get them out of the door fast (like a Spit V to Spit IX thing). So instead of P-51Bs arriving in late '43 in very small numbers could have been lots of P-51x's in say March/April 43... but hey Govt/corporate politics....heck the Merlin X was superior to the (much) later P-51B....at least it had guns that fired....

Thinking about it it would have been much smarter to ship P-51 shells across to the UK and let RR convert them....since NA took soooo long to produce a fast, but fairly average and buggy plane, with rubbish and unreliable guns and crappy vision (and a tendency to lose tails). RR was far better at that sort of thing and as master of mass production could have (given their clout with the UK Govt, not even Portal would dare to cross swords with RR, though he did quite happily do that with Arnold) converted heaps of them to become superb planes long before they actually did.

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## tomo pauk (Apr 29, 2014)

<gets popcorn>.


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## rinkol (Apr 29, 2014)

tomo pauk said:


> Fine points there.
> We might see that failure of the IV-1430 was never mentioned in the article, yet Arnold's condemning comments about US engines' manufacturers can be read easily:
> 
> 
> ...



The BMW 801 enjoyed an inflated reputation early in the war due to the reputation of the FW 190. Certainly, the FW 190 engine installation was advanced in some respects and fuel injection did avoid problems being encountered with larger engines, such as mixture uniformity.

It may be that Arnold was well aware of the shortcomings of the US engines, both real and imagined, while being unaware of the growing difficulties the Germans were finding themselves in.


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## tomo pauk (Apr 29, 2014)

I'm not sure how one can be aware of imaginary shortcomings 
Why the free world owes plenty to Arnold and NACA, I'll state this again: 
Arnold did not, at least not what is reported on the article, said that Army was betting on some of the wrong horses. He does not acknowledge that Navy was right to support 2-stage engines development. He either does not know, or won't admit that R-2800 is better than BMW-801. He does not remeber that Army was pushing for turbocharged engines, that equates with low-capability engine-stage superchargers. Forgets that Allison/GM was blackmailed to forget 900 000 US$ for the development of the V-1710. 
The article drums Arnold's accusations and requests without any critical distance. The P&W's rebuttal is posted as a footnote, instead just after Arnold's accusation. It claims that Merlin Mustang was the 1st US high-altitude fighter. It claims that V-1710 have had "the basic flaws in the engine's design", not because that is backed with facts and figures, but because someone says so. When someone says that V-1710 was tested/tried to improve with "water injection and supercharging" - that implies that V-1710, as-is, was devoid of a supercharger. The article is silent about the dead-end engines (Continental, Lycoming, Chrysler) that Army was wery keen of. They also seem unaware (at least going by the article) that R-2800 was better engine than BMW-801, let alone that R-2800 was also available in 2-stage and turbo flavor. Ditto for V-1710 (along with water injection) and R-1830.

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## Balljoint (Apr 29, 2014)

When an agency such as NACA writes its own history there’s going to be a good bit of puffery and over claiming. What they say about others and inadvertently is more important. Arnold is probably correct that the commercial engine manufacturers offered essentially commercial engines to the military -that’s what they know not some devious plot. Since the DC-3 wasn’t pressurized, it’s not surprising that supercharging, and particularly turbo charging, wasn’t their area of expertise. I expect that the Wright engineers had a good bit of work to do to implement the turbo after NACA’s proof of concept. Arnold was a bomber man so he should have been overjoyed with the B-17 engine wise.
The Allison issue strikes me as a bit cryptic. Did Arnold want a supercharged Allison so he could have a USAAF interceptor like the Spit or BF-109, or was he starting to see the need for an escort fighter to save the daylight bombing doctrine? I see nothing to suggest that the promise of the P-51 was at all linked to the Allison supercharger request. But maybe there’s a bit of Arnold’s metamorphosis from the bombers will get through to calling for a long range escort in the request. It should have been easier to tool up for an Allison supercharger –perhaps with help from R-R- than to respec the Merlin and tool up for the entire engine.


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## Shortround6 (Apr 29, 2014)

According to others (who may be equally biased) the Army started the whole "hyper" engine thing back in the very early 30s. They had been fooling with turbo superchargers since the 20s (GE and Dr Moss had been fooling with them since WW I) and there were a number of experimental or small batches (3-5) of aircraft equipped with turbo chargers for service testing. This 'series' ended with the 50 P-30A fighters equipped with turbochargers ONLY (there was NO engine driven supercharger) delivered in the summer of 1936. These were also the last of the Curtiss liquid cooled V-12 Military engines which dated back to the mid 20s. The Turbo 'merely" allowed sea level power to be maintained to much higher altitudes and very little boost in manifold pressure was used.
Army thinking was that air cooled engines would NOT cool properly in the thinner High altitude air, only 1/2-1/3 of the _mass_ of air flowing over the fins so liquid cooled engines were essential to a high altitude bomber force. Of course at this time a bomber wing could be 4-5 feet thick so there was a lot of interest in flat engines that could be 'buried" in the wing for less drag. 
Obviously some of these Army requirements/wishes would have lead to engines that were NOT really marketable on the commercial scene. 
Wright and P&W both increased the amount of fin area per cylinder by leaps and bounds during the 1930s. Better baffles to force more of the air that entered the cowling to pass _close_ to the cooling fins also helped. They finally figured that air that passed _more_ than 3/16 of inch away form the fins did no good at all. 

Army also hoped that the flat engines would fit in the wings of smaller aircraft than "large" bombers but had to give up the idea of buried engine as wings got thinner and thinner. Also the engines were never quite as _flat_ as the Army hoped. Things like intake manifolds and accessories like generators and pumps tended to bulk them up a bit. 

The "hyper" engines were going to require both high boost and high rpm to get the desired output. Army was trying for 1 hp per cubic inch of displacement. They were trying for this bench mark (or setting this goal) when production engines were producing 1/2 hp per cubic in even for liquid cooled engines. It is little wonder than the commercial engine builders didn't want to play this game.


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## gjs238 (Apr 29, 2014)

OldSkeptic said:


> NA had some vague ideas but were trying to survive against official obstruction from the USAAF (it's only customer really was the British).



Just to clarify, you mean NA's only customer for the *P-51*?
In contrast to, say, the B-25.


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## Koopernic (Apr 29, 2014)

tomo pauk said:


> "They also seem unaware (at least going by the article) that R-2800 was better engine than BMW-801, let alone that R-2800 was also available in 2-stage and turbo flavor. ".



Why would you say that? The BMW 801 was an R-2560 engine, some 8.1% smaller than the PW-R2800. It's progress in development shows it was yielding 2200 metric horsepower by the end of 1944 while a new version with a stronger crankshaft was yielding 2580hp. The R-2800 relied on either 110/150 octane fuel or 100/130 fuel with ADI (water/ethanol injection) to get 2800hp on the R-2800-57C. The R-2800 was effectively redesigned/re-engineered twice, once in 1940 and again for the C series. What we are seeing is the effect of smaller volume, inferior fuel and perhaps a few months lag in BMW introducing its innovations which is to be expected given the bombing campaign at this stage.

Allied 100/130 fuel was at least 102/130 while German C3 fuel was around 96/125 (they fiddled with it several times, started out around 93/115 at the BoB)

I really don't seem much difference at all.


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## rinkol (Apr 30, 2014)

Shortround6 said:


> According to others (who may be equally biased) the Army started the whole "hyper" engine thing back in the very early 30s. They had been fooling with turbo superchargers since the 20s (GE and Dr Moss had been fooling with them since WW I) and there were a number of experimental or small batches (3-5) of aircraft equipped with turbo chargers for service testing. This 'series' ended with the 50 P-30A fighters equipped with turbochargers ONLY (there was NO engine driven supercharger) delivered in the summer of 1936. These were also the last of the Curtiss liquid cooled V-12 Military engines which dated back to the mid 20s. The Turbo 'merely" allowed sea level power to be maintained to much higher altitudes and very little boost in manifold pressure was used.
> Army thinking was that air cooled engines would NOT cool properly in the thinner High altitude air, only 1/2-1/3 of the _mass_ of air flowing over the fins so liquid cooled engines were essential to a high altitude bomber force. Of course at this time a bomber wing could be 4-5 feet thick so there was a lot of interest in flat engines that could be 'buried" in the wing for less drag.
> Obviously some of these Army requirements/wishes would have lead to engines that were NOT really marketable on the commercial scene.
> Wright and P&W both increased the amount of fin area per cylinder by leaps and bounds during the 1930s. Better baffles to force more of the air that entered the cowling to pass _close_ to the cooling fins also helped. They finally figured that air that passed _more_ than 3/16 of inch away form the fins did no good at all.
> ...



It is a valid point that there was considerable logic behind the Army's thinking. Things went wrong with practical details. The idea of burying engines in the wings of bombers to reduce drag sounded good, but in practice led to structural and maintenance problems and complicated the task of finding space for the landing gear and fuel. Furthermore, as conventional engine installations were improved, the aerodynamic benefits turned out to be more apparent than real.

There would seem to have been a chicken and egg situation when aircraft manufacturers must have recognized the risks involved in having to tailor aircraft designs to engines that might or might not be available in the future and engine manufacturers did not want to invest their resources in specialized projects for which the market was uncertain at best.

There are more recent examples where efforts to develop technologies targeted at military requirements that were perceived to be unique went nowhere - the Very High Speed Integrated Circuit (VHSIC) program in the 1980s and ADA programming languages come to mind.


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## FLYBOYJ (Apr 30, 2014)

OldSkeptic said:


> Thinking about it it would have been much smarter to ship P-51 shells across to the UK and let RR convert them....since NA took soooo long to produce a fast, but fairly average and buggy plane, with *rubbish and unreliable guns *and crappy vision (and a tendency to lose tails). RR was far better at that sort of thing and as master of mass production could have (given their clout with the UK Govt, not even Portal would dare to cross swords with RR, though he did quite happily do that with Arnold) converted heaps of them to become superb planes long before they actually did.


 

NA didn't produce the guns and at least on the initial US order had little decision on what type of guns were used, they just installed them per customer request and the guns were probably "GFE."

*NA produced 41,900 T-6s, P-51s and B-25s. Masters of production?*

I don't think RR "would have" been in a postion to do an "AIRFRAME" mod to support a Merlin installation on an early P-51 when there were other UK airframe manufacturers more than capable of doing this. Come to think of it, RR was an ENGINE manufacturer (and a damned good one) weren't they??? - not an AIRFRAME manufacturer or mod center.



gjs238 said:


> Just to clarify, you mean NA's only customer for the *P-51*?
> In contrast to, say, the B-25.



Don't forget the T-6...


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## tomo pauk (Apr 30, 2014)

Sorry for the late reply 



> Koopernic said:
> 
> 
> > Why would you say that? The BMW 801 was an R-2560 engine, some 8.1% smaller than the PW-R2800.
> ...


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## tomo pauk (May 1, 2014)

Okay, since I have no popcorn handy:



OldSkeptic said:


> Thank god for Roll Royce then. It was powerful enough and tough enough (under the great Hives) to ignore that nonsense from idiots.



RR saved the day back in BoB era, when thing were far more sticky than in 1944. For the USAF, thank god for Allison and P&W delivering useful engines to power US fighters. Thank god for Dr. Moss and GE for having turbo systems ready by the time US went to war. We might also thank to the USAF, for pushing for turbo R-2800 and licence production of Merlins.



> People, especially Americans (who have a talent for reinventing history), underestimate how important RR was to creating the Merlin Mustangs. The USAAF didn't want it, NA had some vague ideas but were trying to survive against official obstruction from the USAAF (it's only customer really was the British). The Air Ministry didn't want it (especially Portal) , MAP didn't want it, there were official instructions from those to RR to NOT DO IT, Hives ignored them and told it team to go ahead... hence the Merlin Mustang X... which was a god send to Arnald trying to get some, against endless US and UK opposition, a decent LR fighter.



RR was indeed very important for the creation of Merlin Mustang. They issued their study in June 1942 about the project involving Merlin 61 in Mustang air-frame. However, you are as wide from the mark as possible about USAFs opposition to it, as well as NAA ideas. USAF gave a contract to the NAA for two XP-78s (= future XP-51B) already in June 1942. Hopefully that is fast enough? NAA received the contract for 400 P-51B-1NA at Aug 26th. Same question.
NAA flew the XP-51B for the 1st time at Nov. 30th 1942; engine overheating cuts the 1st flight short, the radiator and cooling air scoop must be redesigned. Just slap the Merlin on the Mustang I and go your merry way? Don't think so. The 1st conversion in UK flies earlier, in October, and that fight is aborted when a piece of cowling leaves the aircraft.
USAF was ignoring the Allison Mustang, and they can look guilty for that today (NAA successful bidding for A-36 basically saved the program). Contrary to that, Merlin Mustang was made possible much due to USAF and NAA (and RR and some other people in the UK) enthusiasm about it. 



> To be fair I think NA then stuffed up because it took nearly another year to produce the P-51B... it would have been much better to just slap Merlins into P-51As and get them out of the door fast (like a Spit V to Spit IX thing). So instead of P-51Bs arriving in late '43 in very small numbers could have been lots of P-51x's in say March/April 43... but hey Govt/corporate politics....heck the Merlin X was superior to the (much) later P-51B....at least it had guns that fired....



Again a shot that is loud, but hits away from the target. 
It was not fault of NAA that Packard was somewhat late with 2-stage Merlins. By July 1943, the NAA received only 173 Merlins, against 534 air-frames the NAA completed. Slapping the 2-stage Merlin on Mustang I airframe will take time. RR took 3 months for a fastest conversion of the previous Mustang, and how much for the slowest of 5 completed? Things can happen in case radiators are not properly engineered and installed, as seen above. From where the British 2-stage Merlins would come from, and what aircraft won't have them - Spit VII, XI, up-engined Mossie? What was wrong with Govt/corporate politics in case of P-51B? Mustang X (I take it you mean that, not Merlin X) was not superior to the P-51B in any way. You want to go with .30s against Luftwaffe in 1944, if the .50s were that bad? Who managed to kill plenty of LW hardware and pilots in 1st half of 1944? The Mustang I never had fuselage tank installed.



> Thinking about it it would have been much smarter to ship P-51 shells across to the UK and let RR convert them....since NA took soooo long to produce a fast, but fairly average and buggy plane, with rubbish and unreliable guns and crappy vision (and a tendency to lose tails). RR was far better at that sort of thing and as master of mass production could have (given their clout with the UK Govt, not even Portal would dare to cross swords with RR, though he did quite happily do that with Arnold) converted heaps of them to become superb planes long before they actually did.



Okay. Let's continue with production of Spitfire Vs, because we're short with 2-stage Merlins. Maybe forget the Mosquito with 2-stage engines? NAA was not guilty a single bit about how much it took to produce P-51B. 
Your mud throwing at the Mustang is not worth a reply. Ditto for it's guns. RR was never in airframe business, a conversion of handful of airframes does not equate with major airframe modification company.

added: the Mustang X, as a modification of the Mustang I, was not outfitted to carry drop tanks. So we can forget long range from that one. 
The racks, once hopefully installed, will cut 12 mph from 422 mph at 22500 ft (the Merlin 61 was not as powerful as Merlin 63/66, or V-1630-3/-7; how much of the drag was induced by slapped-on intercolers?), so our nifty Mustang X is now as fast as Fw-190A-5 and Bf-109G-2. It is slower than P-47 above 25000 ft.

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## OldSkeptic (May 2, 2014)

tomo pauk said:


> Okay, since I have no popcorn handy:
> 
> 
> 
> ...



Few things. 
The P-51A was equipped for drop tanks with options of the 75 or (ferry) 150 US gals ones.
They used the Merlin 65 for the Mustang X since it was similar in performance as the 66 (as used in the LF Mk IX).

Merlins (either XX series or 60 series) had been explored by RR in early 42, but there was no US interest. RR put forward a XX series engined Mustang as an 'interim' model.
Wright field (the US testing area) had very little interest (in fact antipathy) to the Mustang, one that got sent there early on was just left sitting there, while they tested everything else around, it was given the lowest priority.
The other manufacturers naturally pushed their own stuff as the 'solution'.

Within the USAAF there was also considerable opposition to a LR escort fighter, firstly because there was a large school of thought that felt it was unnecessary, secondly because it was thought to be impossible. Arnold swung a bit both ways, though he agreed, at the beginning, that the US bombers would get through all right, he did leave the door open (unlike Portal) for an escort fighter and he had been briefed early on on the prospects for a RR engined one with superior performance (we are talking about mid 42)
So he was primed and far sighted enough, in a sense, for when it all went pear shaped in '43* and RR and NA had done enough background work to prove the viability and production was starting up.

_*the 'unescorted bomber' myth was proven to be that ... a myth. And the shortcomings of the P047 and P-38 had by then become apparent._

In a more rational world, without all the opposition, you would have seen Mustang development going something like this:
P-51A - Allison.
P-51B - March/April 42. P-51A with a Packard Merlin XX series, huge improvement in mid altitude performance and easily a match for the 109s and 190s of the time (excepting maybe the 109s at very high altitude), with little or no structural changes. Rear tank optional.
P-51C - Sept-Dec 42. Modified P-51A for fitting with RR Merlins in the UK (since Packard was not up speed on them at that time). Moderate structural modifications, like tail and engine mounts, an interim type. Rear tank fitted. Roughly 420mph class, because of the intercooler drag (still faster than anything else at the time).
P-51D - Early '43. Very similar to the actual P-51B with Packard Merlins (now in full production), probably with better/more guns. Rear tank fitted. 440mph class
P-51E - Early '44, same as the original P-51D, the delay was because of the time needed to develop the technology to make the canopies.

Going by that timeline the USAAF could have had a fair number of Mustang escorts (mostly XX series with some 60 series engined) by late '42, with more 60 series coming on-stream as time went on, at least to the (roughly) 350 mile combat radius (500+ with the rear tank).


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## tomo pauk (May 3, 2014)

OldSkeptic said:


> Few things.
> The P-51A was equipped for drop tanks with options of the 75 or (ferry) 150 US gals ones.



RAF's name for the P-51A was Mustang II. The 1st P-51A was accepted in March 1943, 1st combat taking place in Summer of that year. RR was converting the Mustang I, ie. the version without racks.
Compared with Mustang I, the Mk.II have had also a different engine ( a bit more power above 14000 ft, a bit less under ~7000) and different weapon layout. The Mustang Ia was cannon armed, the US designation being P-51.



> They used the Merlin 65 for the Mustang X since it was similar in performance as the 66 (as used in the LF Mk IX).



Thanks, I stand corrected.



> Merlins (either XX series or 60 series) had been explored by RR in early 42, but there was no US interest. RR put forward a XX series engined Mustang as an 'interim' model.



Part of the problem with USAF and Mustang/XX was of subjective nature, part was of objective nature. Mustang was nobody's 'child', nobody from the USAF brass invested any personal prestige on it, so there were no personal gains in case the project succeeds; that would count under 'subjective'. Objectively, the production of the P-47 was to start in three factories, while P-38 was already in service. The Mustang I, for all of it's qualities, was ill suited for intercepting and killing the perceived bomber threat flying above 20000 ft, and that was the role of USAF's fighter force in 1941/early 1942, at least under the current doctrine. The USAF just started tests of the XP-51 in March 1942 - how realistic is that USAF will agree to the RR's proposal for the Merlin XX before the flight tests of the XP-51 are done? 
In the other hand, USAF lost no time in giving their support for the P-51 with 2-stage Merlin, after RR's study of July 1942.



> Wright field (the US testing area) had very little interest (in fact antipathy) to the Mustang, one that got sent there early on was just left sitting there, while they tested everything else around, it was given the lowest priority.
> The other manufacturers naturally pushed their own stuff as the 'solution'.



Solution means that there is problem. What USAF's problem did you have in mind, for the time between XP-51 arrival at Wright Field and the time the tests were done (ie. between Aug. 24th 1941 and March/April 1942)? 
On the other hand, I agree that it was a rather big mistake not to start flight tests as early as Aug 25th 1941.



> Within the USAAF there was also considerable opposition to a LR escort fighter, firstly because there was a large school of thought that felt it was unnecessary, secondly because it was thought to be impossible. Arnold swung a bit both ways, though he agreed, at the beginning, that the US bombers would get through all right, he did leave the door open (unlike Portal) for an escort fighter and he had been briefed early on on the prospects for a RR engined one with superior performance (we are talking about mid 42)



Yep, USAF was very much favoring the 'self-defending, high-flying bomber' doctrine by the time they got involved in the ETO.



> So he was primed and far sighted enough, in a sense, for when it all went pear shaped in '43* and RR and NA had done enough background work to prove the viability and production was starting up.



I'd again give credit to the USAF, too - their contracts with NAA in second half of 1942 pushed Merlin Mustang on the forefront.



> In a more rational world, without all the opposition, you would have seen Mustang development going something like this:
> P-51A - Allison.
> P-51B - March/April 42. P-51A with a Packard Merlin XX series, huge improvement in mid altitude performance and easily a match for the 109s and 190s of the time (excepting maybe the 109s at very high altitude), with little or no structural changes. Rear tank optional.
> P-51C - Sept-Dec 42. Modified P-51A for fitting with RR Merlins in the UK (since Packard was not up speed on them at that time). Moderate structural modifications, like tail and engine mounts, an interim type. Rear tank fitted. Roughly 420mph class, because of the intercooler drag (still faster than anything else at the time).
> ...



I'd opt for a more aggressive time line:
- once the deal is struck with Packard, ship a couple of the Merlin XXs from UK and give them to the NAA to incorporate it to the NA-73X (another Merlin is a reserve)
- change the contract, so the Mustang will use Packard Merlins (from British part of Packard contract).
- the first 30 engines will be shipped from the UK
- the 1st dozen of Mustang Is arrive in the UK in late 1941
- the 1st service use is at May 1942
- USAF tests the fighter, and buys 1000 of them
- the version with drop tanks is in production from Autum 1942 on
- in the mean time, the 2-stage version is in the works; RR provides 50 engines in winter of 1942/43


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## Koopernic (May 4, 2014)

When talking about aircraft engine performance one has to put dates and altitudes to claims about power. No point claiming that a R-2800 of 1944 was better than a 1942 BMW801.

The basic 1730 hp (metric horsepower) BMW801D one sees mentioned so often is an 1942 engine. The engine produced less prior to that time and more thereafter.

Around that time BMW had worked out that the 'welding' together of the exhaust's of cylinders of 9 + 10 and 5 + 6 into a single was costing 80hp, causing vibration, rough running, damaging spark plugs and injectors. Fixing this by the time the Fw 190A6 came into service one can say:

Power at Sea Level at 1.42 ata, 2700 rpm = 1800hp 
Power at 5.8km , 2700 rpm = 1490hp (5.8km = 20000ft)

This is in not inferior to the contemporary R-2800 which has 9.5% higher volume as well as a better fuel, German green dyed fuel C3=96/125 versus allied 100/130 which was 102/130.

The Fw 190A with this engine was faster at all altitudes to 22500ft ft and climbed much better than the P-47.

Between 1942 and 1943 BMW, Focke-Wulf conducted experiments using Fw 190A-4 to improve engine power.

a/ Injection of water methanol into the supercharger, MW-50 to cool intake air so that it contracted and more 'oxygen' was available. T
b/ Simply increasing the pressure going into the engine, from 1.42 ata to 1.68 ata in 2nd gear and 1.57 ata in 1st. Advances in spark plugs, fuels, lubricants
made this possible. This was known as Ladedruckerhöhung. (supercharger pressure increase)
c/ C3 injection into the supercharger of C3 to precool and contract the air in the manner of MW50. The correct term was *C3 - Zusatzeinspritzung* which means C3 supplementary injection.

C3 injection produced more power than MW50 injection, furthermore it didn't require any additional tankage and the center of gravity issues that would create. There was some minor damage found to the engines pistons from MW50 testing but this was over 30 hours of accumulated running.

It's just not right to claim that the BMW 801 was not suitable for water injection, C3 injection was just better and fewer issues eg adding extra tanks, plumbing, C of G adjustments.

The result of this work meant that in 1944 the Luftwaffe introduced *not one* but *two* different boosting systems.

Simple boost pressure increases initially went to the Fw 190A8 series fighters, the approval being in Jan 1944 though it doesn't seem to be coming out of production till june 1944.

C3 injection went to the Fw 190F and G series bombers. C3 injection was more powerful and boosted the speed of the Fw 190G 45km/h when it was carrying 3 x SC250kg bombs. They were essentially uncatachable by soviet aircraft till the LaGG 5 came out.

The two system were also combined. This is still the BMW 801D2 we are referring to here, the engine having incorporated advances from the advanced BMW 801E and BMW 801F programs.

BMW 801D2 1.42 ata 2700rpm
power at sea level 1800 ps metric horse power
Power at 5.8km 1490 ps metric horse power

BMW 801D2 1.57 ata 2700rpm
power at sea level 2060 ps metric horse power
power at 5.9km 1695 ps metric horse power

Allied intelligence completely missed detecting these boost systems for 8 months, the first note being March 1945.
http://www.deutscheluftwaffe.de/arc...steigerung/BMW 801 D Leistungssteigerung.html 

Using these systems all the A/F/G variants of the BMW engined Focke Wulf 190 increase climb rates by 27% at 8000m.

Speed of the Fw 190A-8 was 22km/h faster at sea level and 25km/h faster at altitude. When carrying bombs the speed increase was 45km/h.

For C3 injection, when released from 1km limit in Jan 1944.
Before
Fw 190 A-8 644 km/h at 6.3 km and 548 km/h Sea Level.
After 
Fw 190 A-8 667 km/h at 6.3 km and 570 km/h Sea Level.

In Imperial
Before
Fw 190 A-8 399.5 mph at 21500 ft and 340 mph Sea Level.
After boost increase
Fw 190 A-8 414.0 mph at 21500 ft and 353 mph Sea Level, in fact you'll find tests showing a 360mph speed at sea level and 414 at altitude.

It's worth looking at What the P-47 was doing at the time. ADI did not make it into service till early 1944. P-47DE04 and P-47RE05 were equipped with tanks and plumbing to inject water but couldn't actually do so. First production were the P47DE10 and P47RE11, the earlier versions had to be retrofitted in the field.

P-47 Performance Tests

P-47D10 with ADI (water injection), cooling cuffs, boosted to 2300hp 56 inches of mercury.
P-47D10 406mph at 20000ft and 333mph at sea level. (This is 10 mph slower than the A8 without boost and 20mph with the A8 with boost)

From this data its clear that the Fw 190A-8 with or without C3 injection boost has a significant speed advantage over the P-47D10 with ADI at altitude up to 22500ft-25000ft.

Furthermore while a Fw 190 might take 14 minutes to get to 30000ft the P-47 would take 20 minutes (Me 109 12 minutes).

P-47 pilots were told not to fight at low altitude. See what non other than Hubert Zemke has to say.

P-47 Thunderbolt Vs. Bf 109G/K: Europe 1943-45 - Martin Bowman - Google Books

Lets look at the introduction of the *2800hp* in the late 1944 C series engine using higher levels of ADI boost.







As you can see a Fw 190A-8 with either 1800ps or 2060ps is not disadvantaged in speed to the 2800hp P-47 below 20000ft. Same for climb. The P-47M (which saw service in small numbers) and the P-47N (which never saw service in Europe) don't outclass the Fw 190 till 20000ft.


At this point, October 1944, the Luftwaffe has the Fw 190A9 in service with the more capable BMW801TS engine. The BMW 801D2 used on the A8 has reached its limit and would need new components. There "Q" engine entering service at this time in the form of the TU Power egg but it has the same performance as the D2. The designations are about such things as gun mounts, replacement of electrical controls with hydraulic etc.

The BMW 801TS is also a 2000ps engine but it does not need to use short term emergency boost to achieve that. I is well within its detonation limits without either water injection, c3 injection or rich mixtures. (boost on the D2 was limited to 3 x 10 minute bursts per mission with 10 minutes military power in between). Emergency boost is only added a few months latter and they use MW50 because C3 injection wastes fuel.

The Fw 190A9 without boost is 3mph slower than the A8 with boost at sea level due to its greater weight (due to the engine armoring going from 6mm to 10mm) it is however faster at 22500ft being able to do 414mph.

The BMW 801TS is made out of 801E and 801F components. The 801F was supposed to be in production in early 1944 but the Germans are having factory and tooling problems.

The 801TS does not have C3 injection. In fact it will receive the MW50 injection first tested in 1942 in Luftwaffe service in December/January 1944. I have had documents cited that this produced 2400hp, this 20% increase being made up of a combination of the higher charge pressure of 1.82 ata and the charge cooling/contracting effect of the MW50 but I am reluctant to accept more than 2200hp since I have not seen them.

Either way the 2600hp 801F, whose development was complete was to enter production in early 1945. So the 801F bar a few months would have ended up producing 2600ps while the larger R-2800 produced 2800hp.

I do not accept your statement about German C3 fuel achieving 140 PN. If you can provide a citation I would be overjoyed. I have poured over the allied intelligence files at fischer-trospch.org and there is no evidence that C3 ever reached 140. C3 was continuously tested by the allies. C3 was 96/125 around 1943 and a little more, 97/130 somewhat later in the war. Either way this fuel was never available to the BMW801.

The R-2800 was in some ways inferior to the BMW801. For one the poor speed of the P-47 at low altitude was due to its inferior installation. Kurt Tank didn't put a cooling fan and a tight streamline cowl on for aesthetic reasons. 

The fact that low altitude speed of the P-47 with 2800hp was so mediocre points to the inferiority of P-47 aerodynamics since with only 2000hp Fw 190 could keep up with it. The Fw 190 itself was aerodynamically inferior to aircraft such as the P-51, Tempest V, Seafury etc with their laminar flow wings which could delay compressibility drag. Both the Fw 190 and the P-47D/M/N are out of date.

The Fw 190 could use cryogenic GM-1 (nitrous oxide) to match the P-47 engine at altitude and the 115L multipurpose tanks usefulness was improved by C of G changes made possible by the increased weight of the engine. It was a moot given that GM-1 was more likely to be used in the Me 109 and that The Fw 190D13 was promising the same kind of 390-400mph sea level speeds as the Mustang by using brute force of the Jumo 213EB while retaining high altitude ability, a speed likely well beyond the P-47 and its 2800hp R2800. GM-1 was inconvenient given the need to develop a cryogenic handling system, having said that it awkwardness is overstated because the oxygen used in the Fw 190 was also cryogenic. In reality it was too difficult to deploy given the breakdown of the Reich's manufacturing capacity.

There never was a 3500hp C series R-2800 engine in an airframe, that only worked in a test rig force blown by an external supercharger.


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## Denniss (May 4, 2014)

Both 1800 and 2050 PS given on that page/document is the pure engine power, not the engine system power. 70 PS for the fan have to be substracted.
The BMW 801 retained the dual-exhaust for cylinders 9/10 in the D-2/Q-2, dunno with the S.


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## Aozora (May 5, 2014)

Koopernic said:


> When talking about aircraft engine performance one has to put dates and altitudes to claims about power. No point claiming that a R-2800 of 1944 was better than a 1942 BMW801.
> 
> The basic 1730 hp (metric horsepower) BMW801D one sees mentioned so often is an 1942 engine.



Who mentions the 1942 1,730 hp BMW801D so often? 



Koopernic said:


> Around that time BMW had worked out that the 'welding' together of the exhaust's of cylinders of 9 + 10 and 5 + 6 into a single was costing 80hp, causing vibration, rough running, damaging spark plugs and injectors. Fixing this by the time the Fw 190A6 came into service one can say:
> 
> Power at Sea Level at 1.42 ata, 2700 rpm = 1800hp
> Power at 5.8km , 2700 rpm = 1490hp (5.8km = 20000ft)
> ...



What "contemporary" R-2800 are we discussing here? There were several variants, but if we are discussing the R-2800-21 fitted to the P-47D-10-RE it was producing 2,000 hp at all altitudes up to 23,800 ft, after which power started dropping off:






from http://www.wwiiaircraftperformance.org/p-47/P-47D_42-74616_Eng-47-1649-A.pdf

Considerably more than 1,490 hp at 20,000 ft. The reason Tank started designing the Fw 190 B, C D series with alternative engines was because the 801 started running out of puff at 20,000 feet, a considerable disadvantage for a fighter that was supposed to be intercepting high altitude American bombers.

Further down you say the BMW 801D-2 produced 1800 PS which actually = 1,775 hp 1,490 PS = 1,469 hp, so which figures do we go with?



Koopernic said:


> The Fw 190A with this engine was faster at all altitudes to 22500ft ft and climbed much better than the P-47.



The P-47 and the R-2800-21 was designed to fly and fight at high altitudes, at exactly those altitudes at which the BMW 801's power dropped off so rapidly. To claim the R-2800 was somehow inferior to the BMW 801 because the much bigger, heavier P-47 had inferior performance to the Fw 190 below 22,500 feet is a nonsense. These were aircraft designed for different purposes and to different specifications. How did the Fw 190 perform against the P-47 - and P-51B/C/D - above its rated altitude? 

Did BMW ever successfully design and build in quantity a BMW 801 with a decent high-altitude rated supercharger or turbo-charger? It was a decent enough engine once the bugs had been worked out?



Koopernic said:


> The R-2800 was in some ways inferior to the BMW801. For one the poor speed of the P-47 at low altitude was due to its inferior installation. Kurt Tank didn't put a cooling fan and a tight streamline cowl on for aesthetic reasons.
> 
> The fact that low altitude speed of the P-47 with 2800hp was so mediocre points to the inferiority of P-47 aerodynamics since with only 2000hp Fw 190 could keep up with it. The Fw 190 itself was aerodynamically inferior to aircraft such as the P-51, Tempest V, Seafury etc with their laminar flow wings which could delay compressibility drag. Both the Fw 190 and the P-47D/M/N are out of date.



On the one hand you say the R-2800 was in some ways inferior to the 801, yet you then go on to blame the inferior installation in the P-47, plus the P-47's "inferior" aerodynamics, ignoring the fact that the P-47 could fly and fight at altitudes where the 190 struggled. With only 2,000 hp the 190 could not keep up with the 2,800 hp P-47M's 473 mph maximum speed, nor the P-47D's 432 mph



Koopernic said:


> The Fw 190 could use cryogenic GM-1 (nitrous oxide) to match the P-47 engine at altitude and the 115L multipurpose tanks usefulness was improved by C of G changes made possible by the increased weight of the engine. It was a moot given that GM-1 was more likely to be used in the Me 109 and that The Fw 190D13 was promising the same kind of 390-400mph sea level speeds as the Mustang by using brute force of the Jumo 213EB while retaining high altitude ability, a speed likely well beyond the P-47 and its 2800hp R2800. GM-1 was inconvenient given the need to develop a cryogenic handling system, having said that it awkwardness is overstated because the oxygen used in the Fw 190 was also cryogenic. In reality it was too difficult to deploy given the breakdown of the Reich's manufacturing capacity



You are contradicting yourself by stating that the 190 could use GM-1 to match the P-47 at altitude, but didn't use it because the 109 was more likely to use it and anyway the 190D-13 (built AFAIK in very small numbers) could likely outperform the P-47M/N - the latter statement with no evidence. Both statements show that the BMW powered 190 could not match the P-47's performance at altitude because a) it didn't use GM-1 and b) because the Fw 190D-13 used the Jumo 213 specifically because the BMW 801 was not great at higher altitudes.


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## ohogain (May 5, 2014)

Balljoint said:


> For what it's worth;
> 
> Supercharger Development in the U.S. During the Inter-War Period



Another set of articles from same site: Superchargers


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## Shortround6 (May 5, 2014)

Many of us focus a bit too much on the _displacement_ of various engines when arguing over which was better. In reality war had _no_ displacement classes. 
Best fighter with engine of 36.1-42 liters?
best fighter with engine of 42.1-46 liters?
best fighter with engine of 33.1-36 liters? 

What mattered was weight and drag. How much power for how much weight and how much drag for the installation. 

What is also often left out is the service life as that was always a trade off between _acceptable_ power levels and _acceptable_ service life. Russians in particular sacrificed engine life for higher power. How much the Germans did it vs not having certain alloys I don't know but the R-2800 was generally a longer lived engine than the BMW 801. Had the Allies been willing to accept the service life of the BMW 801 one wonders what the power level might have been?


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## tomo pauk (May 5, 2014)

Koopernic said:


> When talking about aircraft engine performance one has to put dates and altitudes to claims about power. No point claiming that a R-2800 of 1944 was better than a 1942 BMW801.
> The basic 1730 hp (metric horsepower) BMW801D one sees mentioned so often is an 1942 engine. The engine produced less prior to that time and more thereafter.



Nobody was claiming that about the 1944 R-2800s. By the Pearl Harbor attack, the P&W has in production not just the B series of R-2800 with single stage supercharger, but also the two-stage B series (2000 HP for TO, but also 1650 HP at 21-22000 ft, and 1800 HP up to 15500 ft; no ram). link (pdf, ww2 engine production in USA)
The BMW 801D entered service some time in early 1942, but was restricted to 1.35 ata and 2450 rpm, in both supercharger speeds. Ie. it was about as good as the BMW-801C. Following the work to debug the issues, the restrictions were lifted in October 1942.








> Around that time BMW had worked out that the 'welding' together of the exhaust's of cylinders of 9 + 10 and 5 + 6 into a single was costing 80hp, causing vibration, rough running, damaging spark plugs and injectors. Fixing this by the time the Fw 190A6 came into service one can say:
> Power at Sea Level at 1.42 ata, 2700 rpm = 1800hp
> Power at 5.8km , 2700 rpm = 1490hp (5.8km = 20000ft)



Covered by Dennis - the power for the fan need to be deduced from those 1490 *PS*, meaning 1440 PS was available for the prop at *5.7* km. Similar goes for supposed 1800 *PS* for power at 0.6 km; the take off power (ie. at SL) was at ~1700 PS. The engines were using 'regular' settings already with later examples of Fw-190A-3. Data from flight manual for the 190A-5: pic. 
Table for different power settings and speed values; please note the interesting inscription saying 'an Luftshraube PS', or, roughly, 'power (in PS) available for propeller':








> This is in not inferior to the contemporary R-2800 which has 9.5% higher volume as well as a better fuel, German green dyed fuel C3=96/125 versus allied 100/130 which was 102/130.



Covered above, re. 1st part. The German C3 fuel could use a dedicated thread; it took quite some time for the BMW-801 to fully use even the 125 PN rich rating anyway.



> The Fw 190A with this engine was faster at all altitudes to 22500ft ft and climbed much better than the P-47.



Not sure why out of sudden the P-47 here - should we compare a tiny Fw-190 with it? 



> Between 1942 and 1943 BMW, Focke-Wulf conducted experiments using Fw 190A-4 to improve engine power.
> <snip>
> C3 injection produced more power than MW50 injection, furthermore it didn't require any additional tankage and the center of gravity issues that would create. There was some minor damage found to the engines pistons from MW50 testing but this was over 30 hours of accumulated running.
> It's just not right to claim that the BMW 801 was not suitable for water injection, C3 injection was just better and fewer issues eg adding extra tanks, plumbing, C of G adjustments.



The extra fuel tankage also an extra tank, plumbing, CoG adjustments - not sure what is the point? The article you've provided the link says flatly: "Schlechte Ergebnisse mit MW 50", ie. "Bad results with MW 50". The article mentions burned pistons in case MW was used. It also says that duration of the tests with MW 50 was only 4.43 flying hours: " Erprobt wurde diese Anlage mit der Fw 190, Werknummer 231, und dem SKZ SB + IK über einen Zeitraum von insgesamt 4,43 Flugstunden."



> The result of this work meant that in 1944 the Luftwaffe introduced *not one* but *two* different boosting systems.
> Simple boost pressure increases initially went to the Fw 190A8 series fighters, the approval being in Jan 1944 though it doesn't seem to be coming out of production till june 1944.
> C3 injection went to the Fw 190F and G series bombers. C3 injection was more powerful and boosted the speed of the Fw 190G 45km/h when it was carrying 3 x SC250kg bombs. They were essentially uncatachable by soviet aircraft till the LaGG 5 came out.
> The two system were also combined. This is still the BMW 801D2 we are referring to here, the engine having incorporated advances from the advanced BMW 801E and BMW 801F programs.



So the two boosting systems were combined??? Source, please. You do know that LaGG-5 entered combat in late 1942?
C3 injection was used only in low gear, ie. under 1 km of altitude (no ram). The 'Erhoehte Notleistung' was applicable both in second gear. 



> BMW 801D2 1.42 ata 2700rpm
> power at sea level 1800 ps metric horse power
> Power at 5.8km 1490 ps metric horse power
> 
> ...



Unfortunately, here the renown Dietmar Hermann makes some mistakes. 1st, he does not deduce the power requred for the fan. 2nd (a bgger mistake) he gives a higher FTH for the over-boost (used in 'Erhoehte Notleistung') than for 'normal' boost (used in 'Notleistung'). Going by this chart (link), we can easily see that FTH for over-boost at second gear (for 1.65 ata) is about 1.2 km lower than for 1.42 ata. 



> Allied intelligence completely missed detecting these boost systems for 8 months, the first note being March 1945.
> BMW 801 D Leistungssteigerung
> Using these systems all the A/F/G variants of the BMW engined Focke Wulf 190 increase climb rates by 27% at 8000m.
> Speed of the Fw 190A-8 was 22km/h faster at sea level and 25km/h faster at altitude. When carrying bombs the speed increase was 45km/h.



The boosted A-8 have had no adverse effect on allied operations in 1944 in the ETO - 1st, the overboost affected the speed and RoC mostly under 6 km, and that is way too low to matter, 2nd, the heavy A-8 needed any help to push it above 650 km/h, even if that's at 6 km. We can wonder how much the LW intelligence needed time to recognize a wide use of 100, 130 and finally 150 PN fuel , along with water injection for P-47. Stuff for another thread?



> For C3 injection, when released from 1km limit in Jan 1944.
> Before
> Fw 190 A-8 644 km/h at 6.3 km and 548 km/h Sea Level.
> After
> ...



I'm not sure from where do you pull those figures for overboosted A-8. This chart (link) gives speed of 652 km/h at 5.5 km for the A-8 using 1.65 ata. This chart shows the same, plus it shows that both A-8 and A-9 don't have MW-50 aboard, but the rear tank instead.



> It's worth looking at What the P-47 was doing at the time. <snip>



Same as above - comparison with 2 distinctively different aircraft.



> The BMW 801TS is also a 2000ps engine but it does not need to use short term emergency boost to achieve that. I is well within its detonation limits without either water injection, c3 injection or rich mixtures. (boost on the D2 was limited to 3 x 10 minute bursts per mission with 10 minutes military power in between). Emergency boost is only added a few months latter and they use MW50 because C3 injection wastes fuel.



Wrong re. MW-50.



> The Fw 190A9 without boost is 3mph slower than the A8 with boost at sea level due to its greater weight (due to the engine armoring going from 6mm to 10mm) it is however faster at 22500ft being able to do 414mph.



Nope - the A-9 was faster also at the SL, it's engine making 1.65 ata vs. A-8 making 1.58 ata. Per chart posted just above; grante, just a few km/h.



> The 801TS does not have C3 injection. In fact it will receive the MW50 injection first tested in 1942 in Luftwaffe service in December/January 1944. I have had documents cited that this produced 2400hp, this 20% increase being made up of a combination of the higher charge pressure of 1.82 ata and the charge cooling/contracting effect of the MW50 but I am reluctant to accept more than 2200hp since I have not seen them.



The 801TS does not need C3 injection. It will happily do 2000 PS at SL (minus 70 PS for the fan) at 1.65 ata. With 1.82 overboost, that would be some 2200 PS (again, minus power for the fan). 
BTW - you have had documents cited, mentoning 2400 PS, but you did not see the documents?



> I do not accept your statement about German C3 fuel achieving 140 PN. If you can provide a citation I would be overjoyed. I have poured over the allied intelligence files at fischer-trospch.org and there is no evidence that C3 ever reached 140. C3 was continuously tested by the allies. C3 was 96/125 around 1943 and a little more, 97/130 somewhat later in the war. Either way this fuel was never available to the BMW801.



I'd start the thread about the C3 fuel asap.

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## tomo pauk (May 5, 2014)

part 2:



> The R-2800 was in some ways inferior to the BMW801. For one the poor speed of the P-47 at low altitude was due to its inferior installation. Kurt Tank didn't put a cooling fan and a tight streamline cowl on for aesthetic reasons.
> 
> The fact that low altitude speed of the P-47 with 2800hp was so mediocre points to the inferiority of P-47 aerodynamics since with only 2000hp Fw 190 could keep up with it. The Fw 190 itself was aerodynamically inferior to aircraft such as the P-51, Tempest V, Seafury etc with their laminar flow wings which could delay compressibility drag. Both the Fw 190 and the P-47D/M/N are out of date.



Oh dear. Comparing the huge P-47 with tiny Fw-190, in order to prove the Fw-190 have had a 'better' engine.



> The Fw 190 could use cryogenic GM-1 (nitrous oxide) to match the P-47 engine at altitude and the 115L multipurpose tanks usefulness was improved by C of G changes made possible by the increased weight of the engine. It was a moot given that GM-1 was more likely to be used in the Me 109 and that The Fw 190D13 was promising the same kind of 390-400mph sea level speeds as the Mustang by using brute force of the Jumo 213EB while retaining high altitude ability, a speed likely well beyond the P-47 and its 2800hp R2800. GM-1 was inconvenient given the need to develop a cryogenic handling system, having said that it awkwardness is overstated because the oxygen used in the Fw 190 was also cryogenic. In reality it was too difficult to deploy given the breakdown of the Reich's manufacturing capacity.



?? Let's start lumping in the one-offs in this thread. 



> Either way the 2600hp 801F, whose development was complete was to enter production in early 1945. So the 801F bar a few months would have ended up producing 2600ps while the larger R-2800 produced 2800hp.
> There never was a 3500hp C series R-2800 engine in an airframe, that only worked in a test rig force blown by an external supercharger.



The 801F is rated in the book 'Flugmotoren und Strahltriebwerke' as having 2400 PS power for TO, while 2600 PS was made on the test bench.

edit: this one slipped through:


> Power at 5.8km , 2700 rpm = 1490hp (5.8km = 20000ft)



Make it 5.7 km, the altitude where 1440 PS was obtained (no ram). That would be 18700 ft; 20000 ft = ~6100 m.

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## ohogain (May 5, 2014)

I'd like to switch topics slightly. I've read often that the French Hispano-Suiza engines were criticized for their lack of a two speed or two stage supercharger. Since France fell in mid-1940, is this criticism fair?

I only joined this forum yesterday as a result of a discussion I read that took place on this forum back in 2008 that I found while researching superchargers. To quote one of the comments from that thread:

Shortround6
I think people get confused as to what was low altitude and high altitude in the late 30s. in 1939 ANYTHING and EVERYTHING that did not have a turbo charger was "low altitude". There were NO workable 2 stage mechanical blowers in any country and the 2 speed single stage super charger was only 6-7 years old and the ONLY production engines with 2 speed superchargers were the British Armstrong Siddeley Tiger, Bristol Pegasus and Merlin X, The American Wright Cyclone (since 1937) and the P &W Twin Wasp (after the Cyclone), and the German inverted V-12s.

While behind the English and the Germans in the deployment of 2-speed superchargers, the French were beginning to use the Szydlowsky-Planiol supercharger on their 12Y-45 and had mounted a 3-speed compressor in 1938 on their 12Y-5.


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## Shortround6 (May 5, 2014)

It is not fair to criticize them for the lack of a two stage supercharger. The Szydlowsky-Planiol supercharger was sort of a stage and half or maybe a stage and 1/3. But it doesn't seem to have actually performed quite as claimed although a significant improvement over the Hispano supercharger used up until then. 
The lack of a 2 speed supercharger is a little harder to excuse. A number of companies offered a variety of different supercharger gears on the same engines so the benefits of the different gear ratios was known. Several companies had experimented with 2 speed engines and Armstrong-Siddeley had one in production by the summer of 1937 if not a bit early and it was written up in the magazines of the day: 1937 | 2141 | Flight Archive

I would note that experiments are one thing and production engines are another, Bristol set world records with a *2 stage* supercharged in the Bristol 138 aircraft : Bristol Type 138 - Wikipedia, the free encyclopedia

But never got a _production_ 2 stage supercharger into service. 

Several French companies _announced_ power figures for new models of engines in 1939/40 but the versions of those engines offered for sale in 1946-48 were rated a bit lower in power or altitude or both than the pre-war engines despite the common availability of 100/130 fuel which didn't exist in 1940. Perhaps the engines were de-rated in the interest of longevity? 

I am sure that the French engines would have advanced beyond what they were in 1940 if development continued but I think they were flogging a dead horse in 1940 with the Hispano 12Y and 12Z. Post war versions gained several hundred pounds, new cylinder heads with more valves, fuel injection and other improvements yet struggled to get beyond 1500hp or so. (Swiss, Spanish and French programs)


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## ohogain (May 5, 2014)

Shortround6 said:


> It is not fair to criticize them for the lack of a two stage supercharger. The Szydlowsky-Planiol supercharger was sort of a stage and half or maybe a stage and 1/3. But it doesn't seem to have actually performed quite as claimed although a significant improvement over the Hispano supercharger used up until then.
> 
> The lack of a 2 speed supercharger is a little harder to excuse. A number of companies offered a variety of different supercharger gears on the same engines so the benefits of the different gear ratios was known. Several companies had experimented with 2 speed engines and Armstrong-Siddeley had one in production by the summer of 1937 if not a bit early and it was written up in the magazines of the day: 1937 | 2141 | Flight Archive
> 
> ...I am sure that the French engines would have advanced beyond what they were in 1940 if development continued but I think they were flogging a dead horse in 1940 with the Hispano 12Y and 12Z. Post war versions gained several hundred pounds, new cylinder heads with more valves, fuel injection and other improvements yet struggled to get beyond 1500hp or so. (Swiss, Spanish and French programs)



So basically you are saying that the French were remiss in not developing a two-speed supercharger, but even if they had, the HS 12Y/12Z engines were past their prime and a new engine needed to be developed, which makes sense considering the basic design goes back to 1928 with the 12N. Did the Russians ever come up with a two-speed supercharger for their variation of the 12Y? If so, do you know when?


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## Aozora (May 5, 2014)

Note that the drive for the two-speed supercharger developed for the Rolls-Royce Merlin X/XX series was based on pre-war design by the French Farman company, which licensed Rolls-Royce to use it in 1938.


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## Koopernic (May 6, 2014)

ohogain said:


> I'd like to switch topics slightly. I've read often that the French Hispano-Suiza engines were criticized for their lack of a two speed or two stage supercharger. Since France fell in mid-1940, is this criticism fair?
> 
> I only joined this forum yesterday as a result of a discussion I read that took place on this forum back in 2008 that I found while researching superchargers. To quote one of the comments from that thread:
> 
> ...



The swiss developed the MS.406 and its HS12 engine into a 1500hp 422mph fuel injected monster, so it would be wrong to assume the engine lacked development potential. The aircraft would be the Swiss Dornier D.3803 and the engine the Saurer YS-3, the name may be familiar from Formula F1.


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## Koopernic (May 6, 2014)

Thanks Thommo,

In regards to the debate re BMW801 versus PW R-2800. I am asserting that the BMW engine wasn't inferior. The evolution of power in consideration of the fact that the R-2800 versus BMW 801 was 9.5% larger and had better fuel was about the same.

Sure the turbocharged variants of the PW-2800 were vastly superior in power above 25000ft but that came at the cost of over 600lbs of turbo charger and more for the airframe to house it. At low altitude I argued that the R-2800 was in fact inferior to the BMW801 in respect of the fact that at sea level even with 2600hp of water injected ADI the P-47D was still slower than a 1800hp let alone the 2000hp Fw 190A8. I know that's a bigger airframe but that's a lot more power. Even the 2800hp of the clipped wing P-47M didn't lead to a spectacular increase in speed at low altitude. I put this down to the high drag installation of the R-2800 which lacked the forced induction and tight cowling of the BMW 801 power egg. At high altitude drag became less important since at 20000ft air density is 50% while at 33000ft it is 33% but at low altitude the P-47 clearly suffered from drag.

BMW clearly could produce a turbo charged engine and they did in the form of the BMW 801TJ. It shows the same power densities as the R-2800 though it never had Water injection added this was planned and was designed for higher altitudes(which in my view was what delayed them). BMW were getting 2580 out of the 801F which means that an turbocharged version of this engine could develop that sort of power.

Given German shortages of nickel and chromium using large amounts of the material for turbochargers and their turbines and ducting doesn't make a great deal of sense given that engines using inter-cooled multistage superchargers could produce almost the same power at high altitude. That doesn't mean that the 801 was inferior, it just doesn't make sense to develop it, certainly not for fighters.

I don't accept the claims about the forced fan of the BMW 801 costing 80hp under all conditions. At 20000ft air density is 50% and you can't tell me the engine fan is still drawing 80hp. Likewise with dynamic effects from aircraft speed. The laws of physics don't usually work that constantly. I'm saying that the 80hp is already accounted for as for the data you provide above AFAIKT the exhaust stub issue was fixed on the Fw 190A6 leading to the extra power.

I note above that in the table above that as the aircraft speeds up that its power increases.

One can see a lag in BMW introducing power boosting methods by about 6 months over PW (mid 44 instead of early 1944 for increased pressure and C3 injection versus Water injection for the R-2800) but I suspect that if Canada and Mexico had of been populated by 400 million angry Germans sending over 3000 bombers and 6000 fighters aircraft per day and 20000 tanks that Pratt and Whitney might have a few delays as well.


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## Shortround6 (May 6, 2014)

Koopernic said:


> The swiss developed the MS.406 and its HS12 engine into a 1500hp 422mph fuel injected monster, so it would be wrong to assume the engine lacked development potential. The aircraft would be the Swiss Dornier D.3803 and the engine the Saurer YS-3, the name may be familiar from Formula F1.



The Saurer YS-2 was good for 1300 hp/2600rpm/5.7lbs at take-off and 1410 hp at 15,700ft on 93 octane fuel but weighed 1510lbs, single speed supercharger. Uses fuel injection. 
Spanish Hispano 12Z-89 was good for 1300 hp/2800rpm/8.6lb at take-off and 1410 hp/2800rpm at 15,700ft on 92 octane fuel but weighed 1510lbs, single speed Szydlowsky-Planiol supercharger. Uses fuel injection.
The French 12Z-1 was good for 1800 hp/2800rpm/7.7lb at take-off, 1600 hp/2800rpm at 8,200ft, 1320/2800rpm at 26,200ft on 100/130 octane fuel but weighed 1367lb, two speed supercharger. Uses fuel injection.
Russian M-107A was good for 1600 hp/2800rpm/11.2lb at take-off, 1600 hp/2800rpm at 5,600ft, 1500 hp/2800rpm at 14,800ft on 95 octane fuel but weighed 1323lb, two speed supercharger. Uses carburetors. 
Saurer YS-3 was good for 1500 hp/2800rpm/8.6lbs at take-off and 1600 hp at 15,400ft on 100/130 octane fuel weight not given, single speed supercharger. Uses fuel injection.
Saurer YS-4 was good for 1600 hp/2800rpm/8.6lbs at take-off and 1580 hp at 15,300ft on 100/130 octane fuel weight 1555lbs, variable speed supercharger. Uses fuel injection.

please note that ALL of these are post war engines (or pretty much) and that the Saurer YS-4 shows up in late 1947 or early 1948. 
Please also note that the figures for the French engine are almost too good to be true. It had also disappeared from Wilkenson's "Aircraft engines of the World" 1948 edition, the one were the Saurer-3 4 show up. Getting 1500-1600hp at 15-16,000ft on 100/130 octane fuel from a 1500lb engine in 1947-48 doesn't really qualify as a "monster" engine.


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## tomo pauk (May 6, 2014)

Koopernic said:


> Thanks Thommo,



Thank you, I love debating about engines.



> In regards to the debate re BMW801 versus PW R-2800. I am asserting that the BMW engine wasn't inferior. The evolution of power in consideration of the fact that the R-2800 versus BMW 801 was 9.5% larger and had better fuel was about the same.



The fuel rating (in rich setting) was in the ballpark; the USA did not initially (1941) have had 100/130 fuel either. 100/120? 
We can see that, good as it was, the BMW 801D was, from late 1942 on, making the same manifold pressure on C3 fuel as the DB-601E and Jumo 211F on B4 fuel in early 1942. In other words, the qualities of the C3 were not used up until Autumn of 1943 (experiments) or early 1944 (service use). 1.42 ata is about +5.5 lbs/sq in, or about 41 in Hg.
I'll cover inferiority/superiority down the post.



> Sure the turbocharged variants of the PW-2800 were vastly superior in power above 25000ft but that came at the cost of over 600lbs of turbo charger and more for the airframe to house it. At low altitude I argued that the R-2800 was in fact inferior to the BMW801 in respect of the fact that at sea level even with 2600hp of water injected ADI the P-47D was still slower than a 1800hp let alone the 2000hp Fw 190A8. I know that's a bigger airframe but that's a lot more power. Even the 2800hp of the clipped wing P-47M didn't lead to a spectacular increase in speed at low altitude. I put this down to the high drag installation of the R-2800 which lacked the forced induction and tight cowling of the BMW 801 power egg. At high altitude drag became less important since at 20000ft air density is 50% while at 33000ft it is 33% but at low altitude the P-47 clearly suffered from drag.



Leaving aside comparison between complete aircraft (that really belong to some other thread), few things:
- the main benefit of the turbocharged R-2800 was that it was there, working as advertised and when needed. Unlike handful of turbo BMWs, it was produced in like 10000 examples, and gave sterling service
-the P-47M did not have clipped wings
-the 'forced induction' of the BMW-801 gave more trouble than it was worth - the handful of Fw-190s (and I'm not talking about lighthened examples) with external intakes were better in high altitudes than those run-on-the-mill.



> BMW clearly could produce a turbo charged engine and they did in the form of the BMW 801TJ. It shows the same power densities as the R-2800 though it never had Water injection added this was planned and was designed for higher altitudes(which in my view was what delayed them). BMW were getting 2580 out of the 801F which means that an turbocharged version of this engine could develop that sort of power.



There is no doubt that there was plenty of unused potential in the 801. Quirk is that BMW was trying to develop like half a dozen engines in short span of time, and that was their undoing. Should've concentrated on the 801.



> Given German shortages of nickel and chromium using large amounts of the material for turbochargers and their turbines and ducting doesn't make a great deal of sense given that engines using inter-cooled multistage superchargers could produce almost the same power at high altitude. That doesn't mean that the 801 was inferior, it just doesn't make sense to develop it, certainly not for fighters.



The benefits of two-stage supercharging were known in Germany even before ww2 started. Alas, they took that path too late to matter, with Jumo 213E/F and DB-605/603L



> I don't accept the claims about the forced fan of the BMW 801 costing 80hp under all conditions. At 20000ft air density is 50% and you can't tell me the engine fan is still drawing 80hp. Likewise with dynamic effects from aircraft speed. The laws of physics don't usually work that constantly. I'm saying that the 80hp is already accounted for as for the data you provide above AFAIKT the exhaust stub issue was fixed on the Fw 190A6 leading to the extra power.



No one was claiming that 80 PS need to be deduced for every altitude. At 5.7 km, it was just 50 PS. The flight manual for A-5 and A-8 gives the same power, 1730 or 1440 PS, depending on supercharger gear. 



> I note above that in the table above that as the aircraft speeds up that its power increases.



Guess you mean the use of ram effect? All the power figures I gave are without ram, that levels the playing field. BTW, if you take a look at the chart (link)for over-boosted A-5 (ie. a lighter and 'cleaner' sibling of the A-8), you will note that even with maximum ram (= max speed), the power is 1650 PS at 5.25 km. And 1900 PS at 400 m.



> One can see a lag in BMW introducing power boosting methods by about 6 months over PW (mid 44 instead of early 1944 for increased pressure and C3 injection versus Water injection for the R-2800)



Lag was much bigger. The single stage, B series R-2800-41 was capable in low gear for 52 in Hg (=2000 HP up to 1500 m), or 49.5 in Hg at 3500 ft (1920 HP); no ram. That would be ~1.79 ata and ~1.71 ata respectively. Power rating on 100/130 fuel. Those engines powered the B-26B and C. It took BMW some 2.5 years to equal or better this result with service engines, when 1.82 was available for 801S. 
In high gear, up to 47 in Hg (=1.62 ata) was available for the -41 up to ~15000 ft; again, the BMW was able to equal or better this some 2 years for service engines. Link for R-2800-41/-43. 

Two stage engines (R-2800-8, 10), used on fighters, were rated more aggressively, even without water injection. In low gear (or 'intermediate', as called by RAF), it was 54 in Hg (~1.9 ata) at 15500 ft (=1800 HP) and ~52.5 in (~1.81 ata) at (at least) 21000 ft for 1650 HP. That is military power (5 minute); please note that BMW-801D was allowed for only 3 min for Notleistung. In 1944, military power was allowed for 15 min of duration. And this is early 1942 we are talking about. At those 21000 ft, the BMW-801D was making about 1250 HP (a bit better than 1-stage R-2800), once cleared for 1.42 ata and 2700 rpm.
Water injection enabled up to 60 in Hg (and was flight tested for 65 in Hg) at 100/130 fuel. 60 in Hg is about 2 ata.

The C3 injection was used unly under 1000 m.



> but I suspect that if Canada and Mexico had of been populated by 400 million angry Germans sending over 3000 bombers and 6000 fighters aircraft per day and 20000 tanks that Pratt and Whitney might have a few delays as well.



As above - lack of focus was as much an issue as Allied bombing.


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## ohogain (May 6, 2014)

Aozora said:


> Note that the drive for the two-speed supercharger developed for the Rolls-Royce Merlin X/XX series was based on pre-war design by the French Farman company, which licensed Rolls-Royce to use it in 1938.



Very interesting. I was totally unaware of that fact. What can you tell me about the Farman 2-speed supercharger - a link, maybe?


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## wuzak (May 6, 2014)

Koopernic said:


> The swiss developed the MS.406 and its HS12 engine into a 1500hp 422mph fuel injected monster, so it would be wrong to assume the engine lacked development potential. The aircraft would be the Swiss Dornier D.3803 and the engine the Saurer YS-3, the name may be familiar from Formula F1.



The Swiss team in F1 are Sau*b*er, not Sau*r*er.

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## Aozora (May 6, 2014)

ohogain said:


> Very interesting. I was totally unaware of that fact. What can you tell me about the Farman 2-speed supercharger - a link, maybe?



Indeed I can:

http://www.wwiiaircraftperformance.org/100-octane/Development_of_Aircraft_Engines.pdf

A description of the Farman supercharger from Flight May 2 1935: Farman two-stage supercharger or







So it can be seen that the French could have had two-stage superchargers for their military aircraft engines in 1940.

Plus an interesting article from Flight 1943:

View attachment Aircraft Supercharger Development 1943.pdf

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## vikingBerserker (May 6, 2014)

That was pretty interesting, thanks for posting!


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## ohogain (May 7, 2014)

tomo pauk said:


> What I'm after is this: is there a one-stop on-line reference around? Specifically, I'm interested about supercharger systems used in piston engines, from late 1930s to late 1940s. Preferably, with as small flag-waving as possible



I just found this book today on Google Books:

Development of Aircraft Engines: Two Studies of Relations Between Government ... - Robert Schlaifer - Google Books

Development of Aircraft Engines by Schlaifer and Heron. The discussion of the Merlin supercharger begins on page 219, but there are references about superchargers, how they work, and the history of their development scatter about consistently.

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## tomo pauk (May 7, 2014)

Thanks for the tip 
The book can be dowloaded from here, one page at time, or complete if one has the password:

Development of aircraft engines Two studies of ... . - Full View | HathiTrust Digital Library | HathiTrust Digital Library

A bit about P&W two-stage compressors (though the power claimed, 1050 HP at 22500 ft, is a good deal optimistic; maybe with plenty of ram?):

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## Aozora (May 7, 2014)

tomo pauk said:


> Thanks for the tip
> The book can be dowloaded from here, one page at time, or complete if one has the password:
> 
> Development of aircraft engines Two studies of ... . - Full View | HathiTrust Digital Library | HathiTrust Digital Library
> ...



Attached is NACA Technical Note #794 on two-stage supercharging written in early 1941 by Richard E Buck of Pratt Whitney; this may have helped form the basis of Pratt Whitney's development of the supercharger:

View attachment Two-Stage Supercharging.pdf


Also attached is a 1940 research paper on the limits of single-stage superchargers

View attachment Limits of single-stage supercharging.pdf


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## snelson (May 8, 2014)

first off let me say that you guys are the Kings of knowledge when it comes to all things plane or engine related. 

but do have a question about turbo's and superchargers. what i would like is break down on the different's of the two type's. or was just a way to say the same thing with two words turbo and supercharger


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## Koopernic (May 8, 2014)

snelson said:


> first off let me say that you guys are the Kings of knowledge when it comes to all things plane or engine related.
> 
> but do have a question about turbo's and superchargers. what i would like is break down on the different's of the two type's. or was just a way to say the same thing with two words turbo and supercharger



Supercharger = a compressor that is driven by a gearbox driven by the engine crankshaft. In an aircraft there may be two or even three or four speeds as well as two stages. Sometimes even infinitely variable drive.
There is a type of valve (butterfly valve corliss valve) that is regulated (usually automatically) to prevent excess pressure damaging the engine. The altitude this can be fully open is refered to as full throttle height.

Turbosupercharger = a compressor that is driven by an exhaust gas turbine. The speed of the turbine is regulated by a waste gate valve that bleeds of excess exhaust. This is more effective than the gear driven supercharger alone but requires special high temperature alloys. Developed by an American called Sanford Moss who should've invented the jet engine as well. The altitude the wast gate is fully shut is the critical altitude, which is analogous tothe full throttle height.

Intercooler: = a heat exchanger that is placed between the engine and compressor to cool the air down thereby preventing preignition and knocking in the engine. Also reduces the workload in pumping in the air though it is actually throwing away energy.

Turbocompound = a gas turbine whose power is driven into the main engine crankshaft via a hydraulic coupling or some sort of infinitely variable drive. In this situation a mechanical supercharger is used. Turbocompounds don't need a waste gate, nor do diesels. Used in some diesel trucks as well as post war US piston engines.

The boost pressure is the pressure in the manifold of the engine.
WW2 Germans used atmosphere abbreviated as ATA so an unboosted engine was 1.0 ATA. 
British used psig pounds square inch guage above the 14.2psi that was a standard atmosphere. Hence a Merlin running at 12psgi actually had 26.2psi (14.2 plus 12) in the manifold.
Americans used inches of mercury with 30 inches equaling 1.0 ata or 0 psig boost. 60 inches of Mercury would be called 2.0 ata or 14psig.

The power out put of the engine is approximately linearly proportional to the pressure. Double the pressure you double the power, roughly. There are odd little effects such as engines initially producing more power as they climb due to less exhaust back pressure, mechanical load of the supercharger, jet thrust.

Most cars that have superchargers like a Subaru WRX or Porche Carrera use exhaust driven turbo superchargers. The compressor is invariably a centrifugal rotary type. Such compressors are non linear.

A few cars like certain Mercedes Benz's models may use a "Kompressor" that is driven of the engine. This is G shaped scroll device, a positive displacement air pump, that produces an air flow proportional to engine RPM thereby helping preventing lag effects . One or two cars have used Lysholm twin scrolls or even roots blowers.

Felix Wankel, a German who invented the Wankel Rotary engine seen in Mazda RX8 cars invented the concept as a compressor. Rolls Royce actually built diesel Wankel Rotary engines supercharged by a Wankel Rotary Compressor.


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## RpR (May 8, 2014)

snelson said:


> first off let me say that you guys are the Kings of knowledge when it comes to all things plane or engine related.
> 
> but do have a question about turbo's and superchargers. what i would like is break down on the different's of the two type's. or was just a way to say the same thing with two words turbo and supercharger


Both are super-chargers.

Simple "supercharger" usually refers to a mechanically driven one.

What is now often simply called a "turbo" refers to an exhaust driven supercharger.
Turbo refers to the turbine that gives the charge.
There are turbine type mechanical units but terminology makes reference to an exhaust driven supercharger simple by saying "turbo".

The difference is that simple.


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## snelson (May 8, 2014)

is one really better than the other? i use to drive a ford diesel that had a turbo and it seemed to have some lag time from when you punched it till it really took off, but once it got rolling it gave a lot of power.


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## Shortround6 (May 8, 2014)

While turbo lag can affect cars and trucks it has a lot less effect in aircraft. In cars or trucks there is _only_ one supercharger. It is _either_ mechanical driven or a turbo and the turbos, for the most part, did have lag. 

In aircraft, after about 1935/36, the planes with turbos had TWO superchargers, ONE turbo and ONE mechanical with the turbo feeding the the mechanical in a two stage system. While it may take time for the turbo to "spool up" this will be masked by the engine supercharger providing _some_ immediate response, at least until full throttle or full RPM is reached. You also have the propeller acting as a 300-500lb flywheel depending on engine and propeller. You may, depending on actual cruise conditions, have the propeller changing pitch as the engine accelerates.


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## RpR (May 8, 2014)

snelson said:


> is one really better than the other? i use to drive a ford diesel that had a turbo and it seemed to have some lag time from when you punched it till it really took off, but once it got rolling it gave a lot of power.


One serious drawback to a turbocharger is heat.

Now it is not as bad as it once was but the heat wears out any turbo unit, far, far sooner than any other engine related part.
As a Porsche mechanic once told me, it is not if, but when it will go out.


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## tomo pauk (May 8, 2014)

Turbo-supercharger ('turbo' from now on here), in ww2 engines, was one of the stages of what was a 2-stage system; sometimes it was noted as 'auxiliary supercharger'. Other stage, often called 'engine stage', was another supercharger, this one driven by the engine itself. The B-29 used two turbos to compress the air, that was then compressed by engine-stage compressor and pushed into intake manifolds and then into cylinders. The another role for the engine-stage supercharger was to provide an uniform air-fuel mixture, the fuel being injected just before the impeller of the e-stage S/C.

In case the engine was outfitted with just one stage of supercharging (one impeller), the turbo version offered far more power at altitude; the cost of weight and size was justified. In case the engine was outfitted with 2-stage system, where both stages were driven by engine itself, that supercharger system was often equal in performance at altitude, once we account for additional size weight of turbo installation. The engine-driven 2-stage system was usually better under 20000 ft than turbo.

The turbo in cars is the only supercharger, much of the need for the separate one was avoided by injection of the fuel either in intake manifold or directly in cylinders/cylinder heads. The turbo in today's cars has barely noticeable turbo lag, due to introduction of variable-geometry turbines, and/or use of sequential turbos (smaller for low power and low lag, bigger one for greater power). The variable geometry turbines likely draw the ideas from Szydlowski-Planiol supercharger, 1st used on Hispano Suiza 12Y engine that powered the Dewoitine D.520. Those two gentlemen founded the company, named 'Turbomeca', in late 1938 - the rest is history, as often said.

Koopernic said:



> Intercooler: = a heat exchanger that is placed between the engine and compressor to cool the air down thereby preventing preignition and knocking in the engine. Also reduces the workload in pumping in the air though it is actually throwing away energy.



Intercooler was a trade-off that pays off. Cooler air is more dense. So more air can be crammed into intake manifold(s) and cylinders, and more power can be provided by the engine. It was even useful with low-boost, single stage engine like Jumo 211J. US and UK militaries were asking for 50% of 'intercooling'. Shortcoming of the intercooler is that can provide a drag penalty, in case it is not smartly faired in the airframe. There is some weight penalty, too. Benefit is that intercooling also helps on all power settings, not just at maximum boost. 

The air (or air-fuel mixture) can be also cooled via injecting the water in a convenient spot. Alcohol was added to the water, it's role being anti-freeze. Sometimes both intercooler and water injection were used to improve engine power, sometimes only one of them. Benefit of water injection is that drag penalty is as good as zero (there is some weight penalty), shortcoming is that its duration was limited, mostly between 5 and 15 minutes.


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## Shortround6 (May 8, 2014)

The US turbo chargers in WW II had an overhaul life about equal to the overhaul life of the engine/s they were used on or a bit more. 

It was possible for a turbo to fail, sometimes catastrophically, but since nothing else offered the same sort of altitude performance (turbo can help cruise performance for hours on end) the extra maintenance and danger were accepted.


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## snelson (May 8, 2014)

thanks guys i've heard these terms for years without really knowing how they worked. at least now i understand better how they work


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## Shortround6 (May 22, 2014)

Do not exceed flight times for GE turbos varied a bit as time went on but reached 1300 hours late in the war.


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## ohogain (Jun 8, 2014)

In round numbers, what be the altitude differential and performance differential between a single-stage, two-speed supercharger vs a two-stage supercharger? 

I read in "Two-Stage Supercharging" by Richard S Buck, that a single-stage, single-speed supercharger provided adequate performance up to 14,000 feet. A two-stage supercharger increased that altitude to 32,000 feet. What altitude performance could be expected from a single-stage, two-speed supercharger?

From what I've read, due to shortages in two-stage superchargers, while the F4F-3 Wildcat had two-stage superchargers, the F4F-3A Wildcat had single-stage, two-speed superchargers. According to Wikipedia, the F4F-3A's "poorer performance made it unpopular with U.S. Navy fighter pilots." How much poorer?

Thanks.


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## Shortround6 (Jun 9, 2014)

The altitude depends on the amount of boost desired and the year. A single stage supercharger could compress the air around 3 times the ambient intake pressure. A little less in 1939, a little more in 1944. Adding extra speeds to the drive didn't change the altitude (high) all that much. Most engines in the 1930s were _called_ either fully supercharged or moderately supercharged depending on the altitude of the engine. The moderately supercharged engines had less power at high ( over 9,000ft or so) altitude but more power for take-off and low altitude. The two speed drive simple gave you both. There is a limit to how fast you can turn the impeller and most of the fully supercharged engines were getting close. The two speed Merlin X picked up about 1500ft over the single speed Merlin III. 

If your engine needed 9lb of boost (48in) and your supercharger could provide a 2.8:1 pressure ratio then your altitude was a bit under 15,000ft. _IF_ your engine needed 4 1/2lbs boost(39in) and your supercharger provided 2.8:1 pressure ratio then you had an altitude of around 19,500ft. 

These are simply figures and do not take into account the heating of the air in the supercharger which means a less dense charge.


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## Koopernic (Jun 9, 2014)

As an indication: The Germans made widespread use of single stage two speed superchargers in the BMW801D, Jumo 211 and Jumo 213A and they seemed to be quite satisfactory to 6500m or about 21500ft. Below that altitude they matched the allied fighters with turbos or the two stage Merlin in speed, above that they started falling behind. The exception being the Mustang which had an aerodynamic advantage. They latter improved their supercharger fluid dynamics and added about 1000m, something not well documented but mentioned in Rudiger Kosins "the German Fighter". The DB605 did a little better due to its unique design and latter enlarged supercharger. 

When the Allison V1710 and latter DB605L received two stage superchargers, both with infinitely variable drives, they did not use inter coolers but instead relied on water injection to obtain full power. Inter cooling or turbo adds some bulk that cuts out a little bit of the advantage. One variant of the Jumo 211 had a single stage two speed supercharger with inter cooler.


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## tomo pauk (Jun 9, 2014)

The DB-605 was doing okay because it was big enough ( 34? vs. 27 L for the Merlin and V-1710) and strong and heavy enough, while powering a fighter that was initially designed around ~20 L engine with 600-650 HP and 2 LMGs - no wonder that more than twice the power will transform a decent fighter into a performer, despite the additions of guns, ammo, fuel and protection. 
It can be argued that, with intercooler, any engine will provide more power. Again, if one starts with 34 liters, it can be pardoned not to have an intercoller that the 27L engine dearly needs. The 2-stage V-1710s were about as good as single stage DB-605s, but not that good as 2-stage Merlins until it was too late to matter (ie. before ww2 ended; applicable for service machines).



ohogain said:


> In round numbers, what be the altitude differential and performance differential between a single-stage, two-speed supercharger vs a two-stage supercharger?
> 
> I read in "Two-Stage Supercharging" by Richard S Buck, that a single-stage, single-speed supercharger provided adequate performance up to 14,000 feet. A two-stage supercharger increased that altitude to 32,000 feet. What altitude performance could be expected from a single-stage, two-speed supercharger?



Stating those altitudes is applying a too wide a brush to paint an accurate picture. Not all engines with two-stage S/C were capable to do at 32000 ft what a decent engine with single stage S/C was doing at 14000 ft. Then we have a question whether an intercooler was installed, or was there an anti-detonant system aboard (water-alcohol injection usually), or maybe both of those?

The single stage superchargers were capable, in quite a number of engines, to provide a good power at altitudes of 18-22000 ft. Merlin XX and 45, BMW 801D, DB-605, Mikulin AM-35A, for example. Their superchargers being driven either via a single speed, two speed, or infinite speed drives. Some of these engines were being outfitted with enlarged superchargers, like the DB-605AS or 605D, or Merlin 46 and 47, were quite useful even at 25000 ft, or above. In case the engines were outfitted with a 'smallish' S/C from the get-go (like V-1710, R-2600 and single stage R-2800), they were topping at 12-16000 ft, depending on the variant and year. 
In case the bigger supercharger was used, and was driven via a single-speed drive (like Merlin 46 47), the power at lower levels was suffering, since the S/C was using up too much power, and was heating the compressed air too much. The AM-35A was using sort of a 'swirl throttle' to circumvent those issues. 



> From what I've read, due to shortages in two-stage superchargers, while the F4F-3 Wildcat had two-stage superchargers, the F4F-3A Wildcat had single-stage, two-speed superchargers. According to Wikipedia, the F4F-3A's "poorer performance made it unpopular with U.S. Navy fighter pilots." How much poorer?
> Thanks.



You might want to check out the wwiiaircraftperformance.com, and compare different Widlcats/Martlets with different engines.

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## ohogain (Jun 17, 2014)

tomo pauk said:


> The DB-605 was doing okay because it was big enough ( 34? vs. 27 L for the Merlin and V-1710) and strong and heavy enough, while powering a fighter that was initially designed around ~20 L engine with 600-650 HP and 2 LMGs - no wonder that more than twice the power will transform a decent fighter into a performer, despite the additions of guns, ammo, fuel and protection.
> It can be argued that, with intercooler, any engine will provide more power. Again, if one starts with 34 liters, it can be pardoned not to have an intercoller that the 27L engine dearly needs. The 2-stage V-1710s were about as good as single stage DB-605s, but not that good as 2-stage Merlins until it was too late to matter (ie. before ww2 ended; applicable for service machines).
> 
> 
> ...



Thanks.


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## ohogain (Jun 17, 2014)

Shortround6 said:


> The altitude depends on the amount of boost desired and the year. A single stage supercharger could compress the air around 3 times the ambient intake pressure. A little less in 1939, a little more in 1944. Adding extra speeds to the drive didn't change the altitude (high) all that much. Most engines in the 1930s were _called_ either fully supercharged or moderately supercharged depending on the altitude of the engine. The moderately supercharged engines had less power at high ( over 9,000ft or so) altitude but more power for take-off and low altitude. The two speed drive simple gave you both. There is a limit to how fast you can turn the impeller and most of the fully supercharged engines were getting close. The two speed Merlin X picked up about 1500ft over the single speed Merlin III.
> 
> If your engine needed 9lb of boost (48in) and your supercharger could provide a 2.8:1 pressure ratio then your altitude was a bit under 15,000ft. _IF_ your engine needed 4 1/2lbs boost(39in) and your supercharger provided 2.8:1 pressure ratio then you had an altitude of around 19,500ft.
> 
> These are simply figures and do not take into account the heating of the air in the supercharger which means a less dense charge.



Sorry for my ignorance, but why would an engine need different boosts? Was it engine specific? Did one engine require 9lb of boost and a different one 4.5lb of boost?


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## Shortround6 (Jun 17, 2014)

Depends on fuel and engine design, A lot of mid 1930s engines used under 4 1/2lbs of boost (39 in or _around_ 1.3ata) The British began pushing things with 6lbs (42in) of boost in the Merlin on 87 octane ( and British 87 octane may NOT have been the same as other peoples 87 octane. depends on the amount aromatic compounds used in the fuel) and the US was changing to _US specification_ 100 octane ( with 2% or less aromatic compounds so the rich mixture response, (not measured at that time) didn't change much. It did allow boosts of 44in or a bit more more in Allison, Wright and P&W engines. 

The Germans and French tended to use larger displacement engines with less rpm and lower boost than the British and Americans. You have to know what the supercharger was actually doing if you want to compare the _supercharger design_ and not claim one was better than another based on the "full Throttle height" of the engine when the two different engines might very well have superchargers providing rather different pressures even though the engines power and height performance were similar.


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## rinkol (Jun 17, 2014)

The issue is the allowable amount of boost in absolute units measured after the supercharger. There are various design parameters that affect the ability of the engine to operate without detonation for a given level of supercharger boost:

- fuel octane and whether water injection was used or other means of cooling the charge (such as the use of a rich air-fuel mixture)
- compression ratio (a lower compression ratio should allow increased supercharger boost)
- the amount of charge heating contributed by the supercharger (depends on supercharger efficiency and the intercooler performance (if used))
- cylinder head design (airflow and temperature)

There were also physical constraints such as the strength of the critical engine components and the ability to maintain acceptable temperatures. Engines such as the HS 12Y and various Gnome Rhone 14K derivatives were designed to operate with fuels available in the early/mid 1930s and lacked the strength to benefit from really high boost levels.

Rolls Royce deserves comment for making particularly effective use of increases in fuel octane to obtain high power levels from the Merlin, a relatively small engine. This did involve progressive improvements to the supercharger and the mechanical components of the engine though, interestingly, it was achieved without changes to the engine RPM or compression ratio. There is a paper by Lovesy, "Development of the Rolls-Royce Merlin from 1939 to 1945," that can be found on the web and is well worth reading.


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## tomo pauk (Apr 9, 2019)

In order not to clog another thread, I've moved this here.



ThomasP said:


> In response to Shortround6 post#25 and the other posts related to the GE, P&W, Wright, and German superchargers,
> 
> The Germans had figured out the supercharger problems by about late-1942, if by no other way than the reverse engineering of the Merlin XX and later engines. The US also had figured out the supercharger problems, if by no other way than through the UK providing the Merlin XX and 60 series supercharger designs.



Germans probably have had nothing new to learn from supercharger installed on Merlin XX and the like. They experimented with 2-stage superchargers on DB 601C/D, luckily nothing came out from these engines.
US have figured in 1930s that 1 stage of supercharging is not good enough past 20000 ft, thus USAAC went with turbos (thus havig two stages of supercharging for engines), while USN co-funded 2-stage superchargers at P&W (and probably at Wright)



> However, both the Germans and the US (US in the early part of the war at least) had other fish to fry, so to speak.
> 
> The Germans had to plan on maybe not having high quality aviation fuel, and the Eastern Front was using up most of their focus and resources. In addition they used direct fuel injection on all(?) their high performance engines, which had some advantages over carburetor types, but did not allow for the fuel injection into the eye of the supercharger.



Advantage of not having a carburetor is that there is no obstruction to the airflow due to the carb, plus one can have better consumption figures. No problems with icing, either (thus no need for ice guard, heating passages for airflow, de-icing carbs etc).



> The US had institutional inertia to overcome, and not just relative to the turbo installations. *The Allison V-1710 did not evolve to the level of the single-stage Merlin until the Rolls Royce Allison Merlin V-1710'G' series.* The V-1710'G' could aptly be described as a 'Merlinized' and 'Hookerized' model with a slightly modified Merlin ⌀10.25" impeller, Merlin 6:1 cylinder compression ratio, and Hooker geometry for the airflow (I am not sure where the fuel was injected in the P-38L V-1710'G' series system). P&W did not come into their own until late-1944 with their R-2800 'C' series engines, and Wright not until their R-2600 'C' series? in 1945? (maybe not during the war?)



(by bold)
There was no 'institutional inertia' vs. non-turbo engines at US Navy. At USAAC/AAF, turboed engines worked well in service before RR 2-stage engines went in service. Let's not think that Bristol and Napier engines employed 2-stage engines, institutional inertia or not.
V-1710G was not a Merlinized V-1710 - no common-shaft impellers, no intercooler, no cooling of S/C housing, no flame trap, no 2-speed S/C drive. Hooker geometry for airflow??
P-38L never used V-1710G. P&W R-2800 2-stage engine powered the XF4U-1 (prototype Corsair) in 1940, mass production of 2-stage R-2800s started by early 1942, mass production of 2-stage R-1830s started by late 1940. The 2-stage R-2600-10 powered XF6F-1 (prototype Hellcat) in 1942.
Bolded part is load of bull, even if it is a joke.



> What I am saying by the above, any jokes aside, is why did the Germans and the US not simply put the Merlin supercharger on their engines? The answer is the very large amount of design, retooling, and trouble shooting that would be required. I can not say for sure how long the delay/disruption in production such a switch would have caused in 1942-43, but even today it would take a year, plus or minus a couple of months. For the US at least, while what they had for superchargers may not have been upto comparison with the Merlin, it was 'good enough' in an operational sense for the most part.



Far less of a trouble would've been making 2-stage supercharged DB 605 and/or Jumo 211 than making brand-new DB 603 and/or Jumo 213s.
US produced perhaps 10 times the turboed engines than RR produced 2-stage S/Ced engines.



> For the Germans, leaving out the fuel quality issue leaves engines that are pretty much equal to the US and UK engines in any operational sense, at least until it no longer really mattered.



Germans, to their detriment, lagged by at least 2-years with the engine as capable as 2-stage Merlin, Griffon or R-2800, let alone turbo R-2800 - the very reason why LW was unable to compete above 20000 ft against Allied best fighters.
2-stage engines can work with 87 oct fuel.


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## Shortround6 (Apr 9, 2019)

tomo pauk said:


> 2-stage engines can work with 87 oct fuel.




They can but it is an awful lot harder. A Merlin 61 at 23,500ft to get 12lbs of boost (54in) was compressing the outside air about 4.6 times. (on book claims 5.1 times) 

A DB605 to run at 1.42 Ata (42.5 inches) needs to compress the air 3.58 times at the same altitude. It's supercharger would require less power to run and heat the intake air less. 


Now if you want to fly around at 30,000ft where the air is 8.88in Hg instead of the 11.85in Hg at 23,500ft you are really going to have to compress the air and you need a really good way to cool it off before trying to use in the engine if you are using 87 octane fuel. It can be done but you are going to need bigger or better intercoolers (more weight/drag) or use water injection sooner (or more of it) for more installed weight. 

The Allied planes with their, oh so terrible, carburetors were running very rich and using the extra fuel as both a charge coolant and an internal coolant for the engine. I don't think the German injection systems were set up to provide the range of mixtures the allied planes were.


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## tomo pauk (Apr 9, 2019)

Shortround6 said:


> They can but it is an awful lot harder. A Merlin 61 at 23,500ft to get 12lbs of boost (54in) was compressing the outside air about 4.6 times. (on book claims 5.1 times)
> 
> A DB605 to run at 1.42 Ata (42.5 inches) needs to compress the air 3.58 times at the same altitude. It's supercharger would require less power to run and heat the intake air less.
> Now if you want to fly around at 30,000ft where the air is 8.88in Hg instead of the 11.85in Hg at 23,500ft you are really going to have to compress the air and you need a really good way to cool it off before trying to use in the engine if you are using 87 octane fuel. It can be done but you are going to need bigger or better intercoolers (more weight/drag) or use water injection sooner (or more of it) for more installed weight.



Both Jumo 213E and DB 603LA used 87 oct fuel. 213E was not allowed to use water-injection when in 3rd gear beacuse it was found out that S/C drive is not strong enough. Jumo 213F run on 87 oct, non intercooled, but required water injection.
The DB 605L, with it's high CR (8.6:1 vs. 6.5:1 for Jumo 213 engines) and no intercooler required both C3 fuel and water injection already for 1.4 ata.



> The Allied planes with their, oh so terrible, carburetors were running very rich and using the extra fuel as both a charge coolant and an internal coolant for the engine. I don't think the German injection systems were set up to provide the range of mixtures the allied planes were.



Allied carbs ranged from excellent to terrible.


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## ThomasP (Apr 9, 2019)

Hey tomo pauk, re your post#73,

"P-38L never used V-1710G." Sorry, my mistake. I should have used the F-82 in my example.

The Hooker geometry airflow is due to the fact that Hooker was a theoretical mathematician. Using mathematic analysis he figured that pretty much all of the superchargers in service at the time were 'choking' the airflow, causing unnecessary heat build-up and using additional HP. The result of this change allowed an increase in efficiency. If I am remembering correctly, just the redesigned geometry of the inlets and expansion chamber allowed about a 10% increase in efficiency over any other in service. The geometry was actually Hooker's first contribution to the supercharger heat problem.

The R-1830 and early- to mid-war R-2800 2-stage superchargers still used the typical less efficient airflow geometry of the time (all the pre-war/early-war US superchargers used basically the same geometry with about a 60-65% efficiency) and did not use the fuel to help cool the supercharged air in the supercharger. The Hookerized superchargers in the Merlin XX achieved about 90% efficiency, with a consequent reduction in HP absorbed by the supercharger.

P&W did not revamp their supercharger geometry for the R-2800 until the 'C' series entered service. I do not know if they ever incorporated the use of fuel to cool the charge during compression in the supercharger?

Fuel injection also allows slightly higher cylinder compression ratios (everything else being equal) without detonation.

There is always institutional inertia (not to be confused with institutional incompetence or stupidity) and I was not referring to any resistance to not using a turbo. Usually it manifests in the form of "if it aint broke don't fix it" or "this is the way we have always done it". Until Hooker figured out the math, no one else understood the problem, hence there was no reason to change. Once the math was figured out, there was an institutional inertia effect in the sense that it takes time and effort to change what the institution is doing - in technical knowledge dissemination, in manufacturing methods, in tooling up for new production, in developing a logistics train, in training of maintenance personal, etc. This always causes delays/disruptions in switching over to new designs when you have limited manufacturing resources.

Also, I did not realize you had switched to this thread, so I have already posted again on the "was the me 262 delay only hitler fault?" thread.


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## tomo pauk (Apr 9, 2019)

ThomasP said:


> ...
> The Hooker geometry airflow is due to the fact that Hooker was a theoretical mathematician. Using mathematic analysis he figured that pretty much all of the superchargers in service at the time were 'choking' the airflow, causing unnecessary heat build-up and using additional HP. The result of this change allowed an increase in efficiency. If I am remembering correctly, just the redesigned geometry of the inlets and expansion chamber allowed about a 10% increase in efficiency over any other in service. The geometry was actually Hooker's first contribution to the supercharger heat problem.



Agreed pretty much.



> The R-1830 and early- to mid-war R-2800 2-stage superchargers still used the typical less efficient airflow geometry of the time (all the pre-war/early-war US superchargers used basically the same geometry with about a 60-65% efficiency) and did not use the fuel to help cool the supercharged air in the supercharger. The Hookerized superchargers in the Merlin XX achieved about 90%, with a consequent reduction in HP absorbed by the supercharger.



Seems like the Merlin's superchargers went to 75% efficiency at pressure ratio between 2.5:1 to 3:1 - link, Fig.11.
P&W engines used fuel to help cool the compressed air, as all non-injected engines. Granted, some used it better than others.



> P&W did not revamp their supercharger geometry for the R-2800 until the 'C' series entered service. I do not know if they ever incorporated the use of fuel to cool the charge during compression in the supercharger?



R-2800 was a wholy revamped engine, with most parts being new, and managed extra 100 rpm vs. B series. At inlet of S/C, the fixed guide vanes were installed. All of that, cupled with improved S/Cs, certainly improved altitude power.



> There is always institutional inertia (not to be confused with institutional incompetence or stupidity) and I was not referring to any resistance to not using a turbo. Usually it manifests in the form of "if it aint broke don't fix it" or "this is the way we have always done it". Until Hooker figured out the math, no one else understood the problem, hence there was no reason to change. Once the math was figured out, there was an institutional inertia effect in the sense that it takes time and effort to change what the institutional is doing - in technical knowledge dissemination, in manufacturing methods, in tooling up for new production, in developing a logistics train, in training of maintenance personal, etc. This always causes delays/disruptions in switching over to new designs when you have limited manufacturing resources.



Interestingly enough, there was next to no resistance for the Packard-made Merlins by the USAAC/AAF. The brass was of opinion that too much of AAC fighter force hangs on succes or failure of V-1710 - thus P-44/P-47B (with R-2180/2800) and V-1650 for, initially, P-40s.
By the time Hooker improved the Merlin (spring/summer of 1940), V-1710 was not installed in a service-worthy fighter, so indeed further development would've meant USAAC of 1940/41 having 320 mph (and that is not certain) P-36s as best fighters.
AAC was certainly not the one to languish on the past, even with depression of 1930s and subsequent lack of money - they were funding 2- and 4-engined bombers, 2-engined fighters, 1-engined 2000 HP fighters, turbo engines in bombers and fighters alike, were the 1st to part with biplanes, they switched to V12 engines despite predominance of radials in US production.
Like anyone, they made their fair share of mistakes - no crystal ball and that jazz.



> Also, I did not realize you had switched to this thread, so I have already posted again on the "was the me 262 delay only hitler fault?" thread.



Nobody will mind


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## fliger747 (Apr 10, 2019)

The R2800 (even the C series) used auto rich and auto lean selections, the rich for high power and climb to provide additional cooling as the richer mixture burned at a lower temperature and additional mass flow carried heat out of the engine. The use of water injection for temporary higher boost values allowed more power due to a change to a better power mixture, the cooling effect being provided instead of by the water meth mixture. USN investigated fuel injection but concluded that the mixture distribution was more efficient with the carb setup! 

The biggest issue with shaft driven super chargers, even those with 2 additional stages, was they drew off a lot of power. In high blower at altitude the R2800 used 400 hp just to run the blower! So the 2000 hp SL engine in neutral blower became a 1600 HP engine in high blower at optimum altitude.


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## ThomasP (Apr 10, 2019)

Hey tomo pauk,

My understanding is that adding the fuel after the air is already compressed (i.e. after the supercharger) is significantly less effective at reducing the charge temperature before it enters the cylinders.

I believe the 75% shown in the chart ( link, Fig.11) is only taking into account the actual mechanical aspect of the supercharger, and does not include the cooling effect of adding the fuel to the mix before/during the compression. The use of the fuel as coolant in the supercharger reduced the charge temperature at entry into the cylinder by 25ºC, which is equal to about 17% increase in efficiency at SL. This added the other 15% to give the 90% efficiency.

About 15 years ago I built a spread sheet using the standard physics for such things and incorporated Hookers changes into the mix. The results (charge temperature, IHP, S/C HP loss, BHP) for an engine with Merlin XX single-stage characteristics were within 1.5% of historical test records at all altitudes from SL to 40,000 ft when using an overall S/C efficiency factor of 90%. In order to get historical test results for power curves of the Merlin III, V-1710, R-1820, R-1830, R-2600, and R-2800 early- to mid-war engines I had to use between 55% and 65% supercharger overall efficiency factors. The 55% was for the R-1830 2-stage supercharger at high altitude, the 65% was for the single-stage engines. The Merlin III required a 65% supercharger overall efficiency factor, and the Merlin 61 ended up with a 86% overall supercharger efficiency factor at high altitude. In order to reduce the overall efficiency factor to 55% to 65% I had to leave out the 25ºC charge cooling effect of the fuel introduction at the supercharger.


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## tomo pauk (Apr 10, 2019)

ThomasP said:


> Hey tomo pauk,
> 
> My understanding is that adding the fuel after the air is already compressed (i.e. after the supercharger) is significantly less effective at reducing the charge temperature before it enters the cylinders.



Depends who you're asking. On 2-stage V-1710s, relocating the carb from the entry of 1st stage to the entry of 2nd stage earned ~2500 ft worth of rated altitude for military power (1125 HP).



> I believe the 75% shown in the chart ( link, Fig.11) is only taking into account the actual mechanical aspect of the supercharger, and does not include the cooling effect of adding the fuel to the mix before/during the compression. The use of the fuel as coolant in the supercharger reduced the charge temperature at entry into the cylinder by 25ºC, which is equal to about 17% increase in efficiency at SL. This added the other 15% to give the 90% efficiency.
> 
> About 15 years ago I built a spread sheet using the standard physics for such things and incorporated Hookers changes into the mix. The results (charge temperature, IHP, S/C HP loss, BHP) for an engine with Merlin XX single-stage characteristics were within 1.5% of historical test records at all altitudes from SL to 40,000 ft when using an overall S/C efficiency factor of 90%. In order to get historical test results for power curves of the Merlin III, V-1710, R-1820, R-1830, R-2600, and R-2800 early- to mid-war engines I had to use between 55% and 65% supercharger overall efficiency factors. The 55% was for the R-1830 2-stage supercharger at high altitude, the 65% was for the single-stage engines. The Merlin III required a 65% supercharger overall efficiency factor, and the Merlin 61 ended up with a 86% overall supercharger efficiency factor at high altitude. In order to reduce the overall efficiency factor to 55% to 65% I had to leave out the 25ºC charge cooling effect of the fuel introduction at the supercharger.



Granted, the 2-stage S/C of the R-1830 was probably the worst of mass-used 2-stage superchargers - about as good as 1-stage superchargers on Merlin XX or DB 601E.
Goes without saying that I'd love to see the tests or math predictions for S/C efficiency. Have you calculated in the losses due the carb being present?


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## Shortround6 (Apr 10, 2019)

The improvement for "Hookerizing" a DB engine might be very slight.






the opening to the supercharger is pretty well unobstructed. there is going to be some piping with a 90 degree bend (or close) and that is it. 

On a Merlin X engine.




the carb mount is made in one piece with the supercharger front cover and inlet. One can see the abrupt change in direction the airflow has to make and indeed one can imagine that not areas of the inlet to the supercharger (or the impeller) were handling the same airflow. In fact it is worse that this photo shows





Air from the carb has to flow up around the depression in the center of the housing to reach the upper area of the intake to the supercharger. 

Back to the 109




Air intake to supercharger is well centered with little obstruction. Note mating hole in the cowl panel at the top of the picture. 

There may have been a number of other differences between the DB superchargers and RR superchargers but the inlets of the DB superchargers don't appear to have the problems the early RR superchargers had.

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## fliger747 (Apr 10, 2019)

Looks that there is a possibility for the air in the plenum prior to the actual impeller inlet beginning a swirl of the air and an acceleration through the wasp waisted impeller inlet housing. The larger the difference between the inlet and the circumference of the impeller, the more compression possible. Hard to tell mach about the DB setup due to the engine mount.


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## fliger747 (Apr 10, 2019)

Perhaps a bit more informative illustration?


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## fliger747 (Apr 10, 2019)

DB 601, looks to be a sidewinder type setup.


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## ThomasP (Apr 11, 2019)

Hey tomo pauk,

re: "Depends who you're asking. On 2-stage V-1710s, relocating the carb from the entry of 1st stage to the entry of 2nd stage earned ~2500 ft worth of rated altitude for military power (1125 HP)."

I may be wrong but I think we are saying the same thing here, just using the carburetor in front of 2nd stage instead in front of the 1st stage on the Merlin 60 series or the only stage (on the Merlin XX anyway). The 2-stage Merlin cut-away that fliger747 linked above shows the carburetor position relative to the compressor stages. I do not know exactly how the 2-stage V-1710 is layer out, but I think the 1st and 2nd stage were separate assemblies? They may not have had a practical choice of where to put the carburetor if they wanted to get the same cooling effect from the fuel.

re: "Goes without saying that I'd love to see the tests or math predictions for S/C efficiency."

I did not download it when I ran across it back in the early 2000s, but there is a UK memorandum/wartime report/(or some other name thing) with Hooker's findings, including the mathematical descriptions . I am not a theoretical mathematician (I am a semi-retired mechanical/automotive/systems/manufacturing engineer & machinist/fabricator) but I got the general idea of it. If you are up for the math it is quite interesting. Otherwise, the Rolls Royce Heritage Trust published a small booklet on Hooker's work on the supercharger in combination with the Merlin XX which gives a good explanation of what was done and why, but without the more complicated mathematical descriptions of the problem. I am sorry but I do not remember the title.

re: "Have you calculated in the losses due the carb being present?"

No. But, assuming the carburetor design had the airflow volume capability necessary, there should not be a significant impact on efficiency except when transitioning through power settings (I think?). The rammed air 'column' (my name for it) should already have been constricted to the area of the throat of the carburetor or less, and the area of the throat would be enough that only the airflow control valve should cause any increased back pressure. Pretty much the same as for a throttle body on a car but modified for higher velocity/pressure air at the entry orifice. Makes sense?Maybe?


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## tomo pauk (Apr 11, 2019)

ThomasP said:


> Hey tomo pauk,
> 
> re: "Depends who you're asking. On 2-stage V-1710s, relocating the carb from the entry of 1st stage to the entry of 2nd stage earned ~2500 ft worth of rated altitude for military power (1125 HP)."
> 
> I may be wrong but I think we are saying the same thing here, just using the carburetor in front of 2nd stage instead in front of the 1st stage on the Merlin 60 series or the only stage (on the Merlin XX anyway). The 2-stage Merlin cut-away that fliger747 linked above shows the carburetor position relative to the compressor stages. I do not know exactly how the 2-stage V-1710 is layer out, but I think the 1st and 2nd stage were separate assemblies? They may not have had a practical choice of where to put the carburetor if they wanted to get the same cooling effect from the fuel.



What the Allison accomplished with carb relocated, IMO, was that it removed a source of turbulent air before a supercharger stage. That being a practical choice - fuel injected into carb cools down the compressed air after the 1st stage of compression.
Pictures of 2-stage supercharged V-1710 are easily available on the 'net, so are manuals. One picture (here) unfortunately refers the auxiliary S/C as 2-nd stage, but never the less it shows the carb attached to the inlet of auxiliary stage. Short, horizontal pipe that is used to transfer the compressed air between the stages can be also seen.



> re: "Goes without saying that I'd love to see the tests or math predictions for S/C efficiency."
> 
> I did not download it when I ran across it back in the early 2000s, but there is a UK memorandum/wartime report/(or some other name thing) with Hooker's findings, including the mathematical descriptions . I am not a theoretical mathematician (I am a semi-retired mechanical/automotive/systems/manufacturing engineer & machinist/fabricator) but I got the general idea of it. If you are up for the math it is quite interesting. Otherwise, the Rolls Royce Heritage Trust published a small booklet on Hooker's work on the supercharger in combination with the Merlin XX which gives a good explanation of what was done and why, but without the more complicated mathematical descriptions of the problem. I am sorry but I do not remember the title.



Thank you, I've skimmed through the paper years ago, though I don't have a book.



> re: "Have you calculated in the losses due the carb being present?"
> 
> No. But, assuming the carburetor design had the airflow volume capability necessary, there should not be a significant impact on efficiency except when transitioning through power settings (I think?). The rammed air 'column' (my name for it) should already have been constricted to the area of the throat of the carburetor or less, and the area of the throat would be enough that only the airflow control valve should cause any increased back pressure. Pretty much the same as for a throttle body on a car but modified for higher velocity/pressure air at the entry orifice. Makes sense?Maybe?



It does make sense.
On the other hand, carb was not a 'no loss, just gains' mechanism. Especially the float-type carb, used also on UK-made Merlin XX (and a host of other engines), so we have a situation where replacing that type with pressure-type carb ('fuel pump' device in UK parlance) gains 8-10 mph and 1500 ft to ceiling to a Spitfire V. Test report, especially this (my bold):
_The normal float type carburettor has certain inherent weaknesses, such as insufficiently precise fuel metering and distribution coupled with inability to withstand negative "g" without cutting. A fundamentally better system is to use a mechanically driven pump as the metering device with suitable compensation for altitude and boost, etc.; *the metered fuel under pressure may then be injected into the supercharger intake, or direct into each cylinder.* _
and:
_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. *_

Also this report by NACA, where the removal of carburetor from the 2-stage V-1710 gained between 9.5 and 25% of airflow. Carb being of pressure-injection type, so we can wonder how much of airflow would've been lost if a float-type carb was installed instead.


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## fliger747 (Apr 11, 2019)

Any fuel injection system, even direct injection, needs a metering section for measuring the mass flow and adjusting such flow to effect throttling. Indeed the metering functions would perhaps have somewhat less "drag" than the restriction required to create low enough pressure in the venturi to such the fuel out in sufficient quantity for a big engine. 

However the limiting factors for the engine are the ability to pack the engine with enough of a dense enough mixture to meet it's mechanical limits. Superchargers take significant engine power and the more efficient they are flow wise the less the power loss for a giver effect. The Navy was happy with their injection carburetors given the tactical environment and more moderate altitudes for Pacific combat. 

Everything is a compromise and some optimal solution is chosen for some particular environment. Weight, complexity, may provide advantages in some situations and be adverse in others. Good engineering of a "simple" system is often the best.


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## mad_max (Apr 11, 2019)

This youtube video might be of interest. You can see tests, papers and such that you could look up on the net from it.

Turbo vs Supercharging in WW2 Airplanes

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## tomo pauk (Apr 11, 2019)

Past a few nit-picks, a very good video.


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## Snowygrouch (Apr 11, 2019)

fliger747 said:


> Any fuel injection system, even direct injection, needs a metering section for measuring the mass flow and adjusting such flow to effect throttling. Indeed the metering functions would perhaps have somewhat less "drag" than the restriction required to create low enough pressure in the venturi to such the fuel out in sufficient quantity for a big engine.



WW2 fuel injection systems did not use what we would call "mass flow" meters now, which were in primative form basically "Moving Vane" later refined to "Hot-wire" systems where a heated platinum wire has its resistance measured. The Moving Vane meter incites a significant pressure drop as it restricts the flow as the air is required to basically "move" a hinge. The modern hot-wire system basically has zero resistance.

In WW2 the determination of the required fuel flow was determined by virtue of a temperature sensor in the inlet tract, and a pressure sensors giving signals of external atmospheric pressure (to determine correction for exhaust backpressure) and also providing boost pressure correction relative to external pressure, which also provides correction for ram (i.e forward speed of the aircraft, in addition to normal supercharger boost). With pressure and temperature known, the mass flow can be calculated. Thus the WW2 system (although not that accurate in modern terms) does not induce ANY significant pressure drop to the inlet charge. A carburettor (except a pressure carburettor, which is basically just a primative single point fuel injector) induces a VERY significant power loss on the engine as the venturi`s needed to restrict the flow to induce the required pressure differential to suck fuel out of the float-bowl increase the pressure drop at the supercharger inlet, thereby requiring a higher supercharger pressure ratio than that requried by a fuel injected engine to achieve the same boost pressure.

Hence the direct injection metering systems provide a great deal more than just "somewhat less drag", it results in an engine power increase of about 50bhp at rated height in the case of the Merlin 46 looking at the power increase purely as a result of removing the carburettor chokes (so basically +3.5% engine power- this figure is from actual WW2 dynamometer testing, not guesswork).

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## fliger747 (Apr 11, 2019)

Since it's a British engine some understatement is permissible. 3.5% isn't a whole bunch in the scheme of things. I am aware that WWII technology didn't include the sophistication of modern accessories, but in effect determining mass flow was what they were _trying_ to do, match a mass of airflow to a quantity of fuel to obtain a desired mixture ratio. The DHC2 Beaver R985 which I have a lot of experience driving had fairly low volumetric power available compared to larger radials. Some of that is due to the float carb, much due to the low RPM at which it runs. 

Small increments in many areas do provide meaningful engine improvement. The C series R2800 revised the oil scavenging system and in effect gained significant HP by reducing the amount of oil being slung around in the case.


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## Elvis (Apr 11, 2019)



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## Shortround6 (Apr 11, 2019)

fliger747 said:


> Perhaps a bit more informative illustration?





fliger747 said:


> DB 601, looks to be a sidewinder type setup.



The illustration is for a a two stage Merlin.

I was trying to show that Hooker had improved the basic RR single stage supercharger. Which , BTW, was the best supercharger in production in 1939 before Hooker modified it. And the first modification/s that he did were to the inlet cover/elbow. He continued on to do a lot more with the two stage supercharger. 

DB superchargers went through a lot of changes over the years, however "Hookerizing" (modifying the inlet) wasn't going to get then much because they already had a pretty good inlet.
there may have been a few other problems with the DB supercharger though.

https://www.flightglobal.com/FlightPDFArchive/1942/1942 - 0144.PDF

Not all superchargers used the same style/type of impeller. Or housing/diffuser.

Just about all DB engines used a sidewinder supercharger (it left room for the through the prop hub gun) but since the supercharger faced the left a view from the right side obscures the inlet. Jumo engines put the supercharger (still a sidewinder) on the right side of the engine.


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## ThomasP (Apr 12, 2019)

Hey Elvis,

LOL! and thanks for the laugh.

Hey tomo pauk,

I may be wrong, but:

When I look at the Merlin 2-stage cut-away I see the carburetor introducing the fuel into the eye of the rightmost, i.e. 1st supercharger stage.

For the V-1710-E11(-93) picture, what I see is the injection carburetor, which sits on top of the auxiliary stage (Allison's terminology) supercharger, metering the incoming air, and then injecting the fuel just in front of the engine stage (Allison's terminology) supercharger via the thick flexible fuel hose above the air passage tube.

In either case the fuel will absorb heat (presumably about 25ºC worth ) from the compression of air.

In the Merlin the fuel is injected and absorbs heat during the 1st stage compression, the cooled air then goes to the 2nd stage where it is heated up again, the heated air is then sent through the after cooler, then to the intake manifold.

In the V-1710-93 the air is heated by compression through the auxiliary stage supercharger, the air is then passed via the tube to the engine stage supercharger, the fuel is injected into the compression heated air at the entry to the engine stage supercharger, the injected fuel then absorbs some of the heat in the already compressed air and heat due to compression in the engine stage supercharger, the air is then sent to the intake manifold.

If both superchargers have similar mechanical efficiencies, then the following will apply:

Merlin 2-stage
Ta + T1 - 25 + T2 - TAC = MT

V-1710-93
Ta + Taux + Teng - 25 = Tm

where

Ta = Temperature of the ambient air the altitude
T1 = Temperature increase due to compression in the 1st stage
T2 = Temperature increase due to compression in the 2nd stage
TAC = Temperature decrease due to aftercooling
Taux = Temperature increase due to compression in the auxiliary stage
Teng = Temperature increase due to compression in the engine stage
Tman = Temperature in the intake manifold

If we assume that each stage is going to absorb the same amount of HP then both stages (before use of fuel for cooling) will generate the same amount of heat. If we assume the altitude is 20k ft for an ambient temperature of -25ºC, and assume the heat due to compression generated by each stage is 50ºC, then we get:

Merlin 2-stage
-25 + 50 - 25 + 50 = +50ºC - TAC

V-1710-93
-25 + 50 + 50 - 25 = +50ºC

Since the TAC will always be greater than 0, again assuming similar supercharger mechanical efficiencies, the Merlin 2-stage will be more efficient and either allow more boost at a given altitude or absorb less HP for a given amount of boost.


re: power loss due to carburetor

Sorry, I thought you meant relative to the constriction of the air flow due to the throttle valve and any other projections into the sir stream. You are of course right that the float type carburetor "draws vacuum" at the point where it sucks the fuel into the airstream. And yes the injection type carburetors are more efficient relative to this problem.


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## Snowygrouch (Apr 12, 2019)

tomo pauk said:


> Depends who you're asking. On 2-stage V-1710s, relocating the carb from the entry of 1st stage to the entry of 2nd stage earned ~2500 ft worth of rated altitude for military power (1125 HP).



Something that Hookers equivalent at DB wrote in his memoirs is that in the case of a mult-stage compressor system, the priority must be given to the efficiency of the 1st stage, as detrimental inflow characteristics into the 1st stage have a far worse impact on overall compressor performance than the same restriction being applied to the 2nd or 3rd stage of a compressor. Hence if the 1710 carburettor was in any way restrictive or produced an unpleasant flow into the 1st stage compressor, it is not at all unreasonable to imagine that relocating this restriction to the 2nd stage inlet could in theory produce a gain in power. This would not be suggesting its the thermodynamic best place to put the fuel in, but reflective of the extreme importance of the 1st stage of any multi-stage compressor being optimised.

The 1710 setup with the 1st stage driven by the hydraulic coupling looks very restrictive for packaging as it sticks out the back so much , and it may well be it was impossible length wise to put the carb on the 1st stage inlet in a way that the air-path was in any way decent. However thats my opinion from photos not from consulting reports.

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## Shortround6 (Apr 12, 2019)

Somebody may have said that on a two stage supercharger any mistake or problem with the first stage is _multiplied _by the 2nd stage.


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## fliger747 (Apr 12, 2019)

It would appear that as a first order approximation that the radial engine designers had some advantages given the greater frontal area they had available for designing efficient ducting. Certainly the Dual Sidewinder superchargers installed on late model Corsairs benefited from "space" available. The DB supercharger probably lost some of it's effectiveness from the external intake, at least as far as external form drag goes without regard to any intake loss.


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## tomo pauk (Apr 12, 2019)

Shortround6 said:


> The illustration is for a a two stage Merlin.
> 
> I was trying to show that Hooker had improved the basic RR single stage supercharger. Which , BTW, was the best supercharger in production in 1939 before Hooker modified it. And the first modification/s that he did were to the inlet cover/elbow. He continued on to do a lot more with the two stage supercharger.



All very true. A cutaway of a real Merlin III posted at Calum's FB page (link) - the fresh air 'arrives' from the bottom, circulates a bit around the entry, and then enters the impeller.
Hooker got rid of that, his design allowed for a more direct path of the fresh air. Picture of air intake of Merlin 45 just before the S/C, the air again comes upwards, turns by 90 deg and encounters the impeller (not shown).



> DB superchargers went through a lot of changes over the years, however "Hookerizing" (modifying the inlet) wasn't going to get then much because they already had a pretty good inlet.
> there may have been a few other problems with the DB supercharger though.
> 
> https://www.flightglobal.com/FlightPDFArchive/1942/1942 - 0144.PDF



Of the German superchargers, DB's were probably the best before Junkers 213 was designed? The one at Jumo 211F (designed by DVL) and later were also much better than earlier on the 211s.
The BMW 801A/C/D didn't have had a very efficient S/C, using straight blades, but impeller was big (13 inches diameter) partially compensating for it. The 801E/F/S introduced a much better S/C, with curved entry blades. That, with some tweaking of the intake, meant they were providing 1.65 ata at altitudes where the D and previous were making 1.42 ata (= worth up to 200 HP).



fliger747 said:


> It would appear that as a first order approximation that the radial engine designers had some advantages given the greater frontal area they had available for designing efficient ducting. Certainly the Dual Sidewinder superchargers installed on late model Corsairs benefited from "space" available. The DB supercharger probably lost some of it's effectiveness from the external intake, at least as far as external form drag goes without regard to any intake loss.



Side-mounted intake added drag. The only user of DB engines with 'blended' air intake that I'm aware was the He 100 - less drag, but air has to make a few turns before entering the S/C, so it is a trade-off.
DB's and Jumo's S/C gained in efficiency, since the incoming fresh air have had only one 90 deg turn to make before entering the impeller working area.


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## Shortround6 (Apr 12, 2019)

Not sure why you think that.

The intake on the Hurricane MK II was good for anywhere from 27.7hp to 14.1 hp of Air intake momentum drag from 15,000 to 35,000ft.

You don't quite get "RAM" for free. You want to turn the forward speed of the plane into higher pressure air (than ambient) going into the carb or supercharger inlet you are going tohave to pay for it in both form drag ( intake scope external aerodynamics) and internal duct drag (internal aerodynamics) and if you are compressing the ambient air in the intake duct/scoop that compression has to be paid for somehow even if it is only 1-2 psi.

The 109F and G may have increased the effectiveness of the intake compared to the E by moving the intake further away from the fuselage (boundary layer/turbulent air) and going to the round shape instead of square (corners don't do a lot for air flow)

as for the Corsair, they didn't quite fit the new engine and supercharger set up in the old fuselage.





Notice the "cheek" scoops to supplement the wing root intakes and the fact that the fuselage is bulged behind the cowl flaps over the wing roots. On an F4U-4 the cowl flaps go much further down the cowl.

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## Shortround6 (Apr 12, 2019)

German planes had supercharger intakes sticking out the sides instead of sticking out underneath (Hurricane, Spitfire and ???) or mounted on top of the cowl (P-39/P-40/P-51 Allison) 

Can't figure out why there would be much difference in drag due to location. 
Differences in drag due to shape or form yes.


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## tomo pauk (Apr 12, 2019)

Shortround6 said:


> Not sure why you think that.
> 
> The intake on the Hurricane MK II was good for anywhere from 27.7hp to 14.1 hp of Air intake momentum drag from 15,000 to 35,000ft.



Nobody ever accused Hurricane to be a miracle of aerodynamics.
Hoerner's analysis of the Bf 109G pointed out to the ram air intake as source of a drag, while at the Fw 190D and Ta 152 the side-mouted intake accouted between 4.3 and 5.9 % of total drag (or about as much as weapon-related drag). For comparison, the internal intakes on the Fw 190A represented 0.6% of total drag.



> You don't quite get "RAM" for free. You want to turn the forward speed of the plane into higher pressure air (than ambient) going into the carb or supercharger inlet you are going tohave to pay for it in both form drag ( intake scope external aerodynamics) and internal duct drag (internal aerodynamics) and if you are compressing the ambient air in the intake duct/scoop that compression has to be paid for somehow even if it is only 1-2 psi.



The 'no free lunch rule' applies as ever



> The 109F and G may have increased the effectiveness of the intake compared to the E by moving the intake further away from the fuselage (boundary layer/turbulent air) and going to the round shape instead of square (corners don't do a lot for air flow)



Agreed.



> as for the Corsair, they didn't quite fit the new engine and supercharger set up in the old fuselage.
> Notice the "cheek" scoops to supplement the wing root intakes and the fact that the fuselage is bulged behind the cowl flaps over the wing roots. On an F4U-4 the cowl flaps go much further down the cowl.



Fuselage was more or less old. The engine section was changed (and obviously the powerplant itself); old air intakes were insufficient to provide enough of airflow for oil coolers, inter-coolers and engine itself all int the same time, thus the -4 gained one extra intake, and -5 two (possitioned so the air flow towards the two impellers of the 1st stage is as direct as possible).


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## Shortround6 (Apr 12, 2019)

tomo pauk said:


> Nobody ever accused Hurricane to be a miracle of aerodynamics.
> Hoerner's analysis of the Bf 109G pointed out to the ram air intake as source of a drag, while at the Fw 190D and Ta 152 the side-mouted intake accouted between 4.3 and 5.9 % of total drag (or about as much as weapon-related drag). For comparison, the internal intakes on the Fw 190A represented 0.6% of total drag.



and there is the trade off. 

Is 4-6% more drag worth several thousand feet of FTH on the engine? 

as for the Hurricane. 






Most anything would have been an improvement as far as streamlining goes. 
One also wonders about the efficiency of the boundary layer splitter on the radiator with the turbulence generator air scoop only few feet in front of it.


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## tomo pauk (Apr 12, 2019)

Shortround6 said:


> and there is the trade off.
> 
> Is 4-6% more drag worth several thousand feet of FTH on the engine?



It will depend on use? Going against the B-17s (with or without an assorted escort) will favor greater FTH. Prominent/external intakes also allow for installation of air filters (useful if the aircraft is used on dusty African or steppe airfields). 
In case that much of increase in FTH is not of an interest (East front, mostly), lower drag might be preferred.


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## Snowygrouch (Apr 12, 2019)

Shortround6 said:


> Somebody may have said that on a two stage supercharger any mistake or problem with the first stage is _multiplied _by the 2nd stage.



This is from a strict theoretical perspective true. However the practicalities of actually joining the airpaths together means than in practise a 2-stage SC tends to end up having
the pressure heads added not multiplied, such are the losses incurred from bending the airflow around so many corners (180 deg turn between stages 1 & 2 in the case of something like a Merlin 61). In pure "maths-world" of little boxes on paper with the compression ratios written on them, they ought to multiply...the multiplication takes no account of any of the inefficiencies of a real system. Hence Merlin 45 might have an ACTUAL pressure ratio of something like 3.5:1 and a Merlin-61 6.5:1 (both stages considered as one bloc, in perfect-land it ought to be something like 10:1).


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## ThomasP (Apr 12, 2019)

Hey Snowygrouch,

I believe you are mistaken as to how the air is traveling through the Merlin 2-stage supercharger. The only relatively sharp radius is at the 90º elbow at the turn from the inlet duct/carberetor to the eye of the 1st stage impeller. After that the air is routed to the 2nd stage by circumferential and spiral ducts to the 2nd stage, and the same from the 2nd stage to the entry into the engine intake manifold. There is kind of a large radius 90º turn at the entry to the engine intake manifold.

Also, in the language of physics (and mathematics is considered the language of physics) the 1st and 2nd stage in centrifugal superchargers add, they do not multiply. In the same sense as the 1st stage adds heat to the air (i.e. by doing work) and the 2nd stage then adds more heat to the air (i.e. by doing additional work), the 2nd stage adds its work of compression to the already accomplished 1st stage compression. I think where the confusion comes in is that once you have determined how much the effective increase/addition in compression is, you can then determine the resulting ratio and use that ratio as a descriptive multiplier. (If I misunderstood what you were saying I apologize.)


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## fliger747 (Apr 12, 2019)

It might be that the scoop in front of the radiator would help compensate for the gap in the gear doors? Wow, what miracles would a detail cleanup of the exterior of the "Hurri" have done?

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## Shortround6 (Apr 12, 2019)

In practical terms they multiply. Each unit operates at a pressure ratio (which varies with the rpm and a few other things) 

this is from a modern turbo but the principle is the same.




the output is going to be a certain ratio of pressure compared to the input (most cars and certainly most planes don't use flow meters (measure the mass moving through the system)'

so if you take in air at 15in Hg and compress it to 37.5in Hg you have compressed it 2.5 times, 

Now you add a second unit in series. It should not be identical as it won't flow the required mass. But if it takes in air at 37.5 in Hg (and I would agree with Snowygrouch that this is ideal and not real world) and it compresses it 2.5 times you will wind up with air at 93.75in Hg. 
In practice you will find that no fuel that was in service use in WW II would stand up to that so there was no incentive to design such a system. That or the superchargers were running into the choke limit. 





another modern turbo map running at sea level. The unit simply won't flow more than about 95-97lb/min no matter how fast you turn the impeller. 

Don't confuse cause and effect. Most two stage systems in use in WW II didn't exceed an overall pressure ratio of around 6-7 to 1 but they were designed that way in order to use the lowest amount of power and heat the intake the charge the least. The different gear ratios in the V-1650-7 from the V-1650-3 were to limit the total amount of possible boost and lower the power needed to drive the supercharger and heat the intake charge less to give more power at lower altitudes. Using oversized/over capacity/higher pressure ratio superchargers than needed for the application limited power at other points in the flight envelope. 

one of the few (only?) exceptions were the late model P-47s (M & N) which could pull 72in of Hg at 32,000ft including ram or to 27,500ft while climbing which is performance that probably could not be matched if you added the ratios of two superchargers instead of multiplying them, this was possible because the the turbo allowed for a much wider variation in speed of the auxiliary stage impeller than any mechanical system.


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## ThomasP (Apr 13, 2019)

Hey Shortround6,

I am sorry, but your statement "In practical terms they multiply." is actually the direct opposite of how it works. In practice they cannot multiply - if they could they would have to be 100% efficient - which is an impossibility. The inability to describe compression using multiplication was discovered back in the early days of mechanical compression systems, when the engineers, physicists, and mathematicians tried to develop formulas that could predict the effect of 2 steps or more of compression, and were unable to do so using multiplication.

The actual formula for multiple stage compression is similar to the formula I used to show the pattern of heat rise in the compressed air in my post#94 earlier in this thread:

Ta + T1 - 25 + T2 - TAC = MT

If you substitute P for each T increase , and substitute i for each temperature decrease you get:

Pa + P1p - P1i + P2p - P2i = MP

simplified to

P1e + P2e = MP

where

Pa = ambient air pressure
P1p = Pressure increase due to work that could be done by 1st stage if there was no inefficiency (i.e. p = perfect)
P1i = Pressure increase not achieved due to inefficiency of 1st stage
P1e = effective Pressure after the 1st stage
P2p = Pressure increase due to work that could be done by 2nd stage if there was no inefficiency (i.e. p = perfect)
P2i = Pressure increase not achieved due to inefficiency of 2nd stage
P2e = effictive Pressure after the 2nd stage
MP = Manifold Pressure

If you substitute values for the above variables I believe you will find that there is no way to use any form of multiplication to arrive at the correct answer until after you have already used the above formula to calculate the resulting MP. Once you have done so you can then use the values for P1e, P2e, and MP to generate ratios that can be used as a descriptive multiplier.

The physics principle illustrated above is a pattern followed by everything in the universe (at least everything so far discovered). The principle being that the universe is additive, not multiplicative.

Make sense?


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## wuzak (Apr 13, 2019)

ThomasP said:


> Make sense?



No.

Consider the MetroVick F2/2. The 9 stage compressor had an overall pressure ratio of 3.5:1. 

If the final pressure ratio is the sum of the pr of the stages, the average pr would be about 0.4:1.

If you take the multiple of the stages, the stage pr would be about 1.15:1.


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## wuzak (Apr 13, 2019)

ThomasP said:


> Hey Shortround6,
> 
> I am sorry, but your statement "In practical terms they multiply." is actually the direct opposite of how it works. In practice they cannot multiply - if they could they would have to be 100% efficient - which is an impossibility.



Multiplication does not require 100% efficiency, as it does not say anything about the power required to drive the system


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## Snowygrouch (Apr 13, 2019)

ThomasP said:


> Hey Snowygrouch,
> 
> I believe you are mistaken as to how the air is traveling through the Merlin 2-stage supercharger. The only relatively sharp radius is at the 90º elbow at the turn from the inlet duct/carberetor to the eye of the 1st stage impeller. After that the air is routed to the 2nd stage by circumferential and spiral ducts to the 2nd stage, and the same from the 2nd stage to the entry into the engine intake manifold. There is kind of a large radius 90º turn at the entry to the engine intake manifold.
> 
> Also, in the language of physics (and mathematics is considered the language of physics) the 1st and 2nd stage in centrifugal superchargers add, they do not multiply. In the same sense as the 1st stage adds heat to the air (i.e. by doing work) and the 2nd stage then adds more heat to the air (i.e. by doing additional work), the 2nd stage adds its work of compression to the already accomplished 1st stage compression. I think where the confusion comes in is that once you have determined how much the effective increase/addition in compression is, you can then determine the resulting ratio and use that ratio as a descriptive multiplier. (If I misunderstood what you were saying I apologize.)



I have engineering drawings (not magazine sketches) of the 61 supercharger and have spent time at Rolls-Royce poking at the real parts (below is actually my 100 series
pic as its a better photo to show this particular part of the supercharger).






The inter-stage area has turning vanes to try to make the flow have an easy time flowing between stages 1 and 2, but its still a huge loss which cannot be recouped by any means. Its a package layout problem not a design flaw. If you removed the turning vanes and the 1st stage volute exit, the air from the 1st stage would fly off into space still needing to be rotated about 180 degrees to make it back to the 2nd stage inlet eye.

Compressor *work* can only be ADDED when it is decribed in the form of work, i.e. for example in WW2 German practice as: "Adiabatic pressure head" (Had).






When compressor work is written as m.kg/kg (work done per mass unit) then one CAN simply add together the individual stage work to get to the actual total compressor work result.

FYI an Merlin-61 supercharger in reality makes about 12,500 m.kg/kg Had compressor work by the above equation. This is a useful representation as you can multiply this by the mass flow rate and it gives you the power required to drive the supercharger, and it also (roughly) tells you the height up to which the compressor can maintain sea-level pressure. I.e. the Merlin-61 supercharger can (by this rough measure) maintain sea level pressure to 12,500meters alititude (41,500feet), so its a useful visual guide to how effective a compressor might be in an aeroplane.


With regards to the figures discussed for axial stages by a later poster, it is not at all uncommon that each axial stage might only produce a pressure ratio of something like 1.2:1 - hence
why you do need loads of axial stages to do anything useful.

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## ThomasP (Apr 13, 2019)

Hey wuzak,

The problem is that if you do not already know that the MetroVick F2/2 9-stage compressor had an overall pressure ratio of 3.5:1, you would not have any way of figuring the average or any possible inverse power (i.e. 1.15^9) of the stages, let alone the actual values. If the 1st stage achieves a 1.5:1 effective compression (P1e in the formula) instead of 1.15, what is the effective compression of the 2nd stage (P2e), the 3rd stage,...? Do all the stages achieve the same multiple for the effective compression ratio? or don't they? The reason that multiplication cannot be used is because it does not take into account the wasted power (Pi in the formula), just the work (physics term meaning change in energy state - in this case the effective increase in pressure (Pe in the formula)) achieved at the last measured stage. There are only 2 ways to determine the effective increase in pressure (Pe) done by a system:

1. Build the 1st compressor stage, build the 2nd stage, test each one separately and then attach (i.e. add) them to each other and measure their combined pressure increase, repeat the process with 3rd through 9th stage. Assuming the MetroVick F2/2 3.5:1 ratio is achievable at sea level, the MP (I know, the out put of the MetroVick is not going into an intake manifold, you can substitute another acronym if you wish) value of 51.45 lb/in^2 (3.5 x 14.7 lb/in^2) would be the sum of the original 14.7 lb/in^2 (Pa) + the 1st stage work (P1e) + the 2nd stage work (P2e) + the 3rd ....., + the 9th stage work (P9e).

2. Use a formula similar to the one above, which previously accepted values for similar systems.


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## ThomasP (Apr 13, 2019)

Hey Snowygrouch,

re: "why you do need loads of axial stages to do anything useful."

In axial flow turbo- and fan-jets the main reason is to spread the work (physics term) done over more material (i.e. more stages, vanes, shafts, etc. ) without overloading the parts in terms of stress and heat, while keeping the diameter of the overall engine as small as possible. In other words, to decrease the chance of breaking or melting something while keeping the potential drag to a minimum.


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## Shortround6 (Apr 13, 2019)

ThomasP said:


> Hey Shortround6,
> 
> I am sorry, but your statement "In practical terms they multiply." is actually the direct opposite of how it works. In practice they cannot multiply - if they could they would have to be 100% efficient - which is an impossibility. The inability to describe compression using multiplication was discovered back in the early days of mechanical compression systems, when the engineers, physicists, and mathematicians tried to develop formulas that could predict the effect of 2 steps or more of compression, and were unable to do so using multiplication.
> 
> ...



No it does not because you are measuring two different things. Amount of work done from an efficiency standpoint is not pressure rise. 

A single stage compressor multiplies the pressure of the air flowing through it. 
if you have 30in Hg going in and the supercharger has a pressure ratio of 2.2 at a certain rpm and mass flow you will get 66in Hg at the output. Now there is no mention of power used to drive the supercharger or the efficiency of the supercharger (what percent of the power is used to actually compress the air).

If you climb to an altitude to where you have only 17.6in Hg going in you will get 38.72 coming out (or very close) 

Now what happens when you run two impellers in series?

You are asking us to believe that two 2.2 pressure ratio supercharges (they would not be identical due to airflow considerations) would only give us a total rise of 4.4 times the original inlet pressure instead of the 4.84 that multiplication would give us. It gets worse if the pressure ratios are higher. two 2.25 superchargers should give 5.086.
In practice it would be rare to have two stages operating at identical pressure ratios. 

However as Calum has shown us there are losses between the two stages, despite these losses two stage systems show an ability to operate at pressure ratios higher than simple addition would account for. 

Superchargers (or centrifugal compressors) got better as the war went on (doesn't mean that all engines got new superchargers) but state of the art at the close of WW II was under 4.0 for a single stage compressor in useable form (not test compressor on the bench.) 

I have no idea what RR did to the impeller closest to the engine, if anything, on the two stage engines besides cropping the diameter a fraction of inch. (fewer blades, different shape/depth, etc) but they ran the impellers a lot slower on the two stage engines.


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## wuzak (Apr 13, 2019)

Snowygrouch said:


> With regards to the figures discussed for axial stages by a later poster, it is not at all uncommon that each axial stage might only produce a pressure ratio of something like 1.2:1 - hence
> why you do need loads of axial stages to do anything useful.



I am aware of the small pressure ratios that axial flow compressor stages have.

My point is that in order for the method espoused by Thomas of adding the pressure ratios together to get the overall ratio, since it would require ratios less than 1:1


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## wuzak (Apr 13, 2019)

ThomasP said:


> Hey wuzak,
> 
> The problem is that if you do not already know that the MetroVick F2/2 9-stage compressor had an overall pressure ratio of 3.5:1, you would not have any way of figuring the average or any possible inverse power (i.e. 1.15^9) of the stages, let alone the actual values. If the 1st stage achieves a 1.5:1 effective compression (P1e in the formula) instead of 1.15, what is the effective compression of the 2nd stage (P2e), the 3rd stage,...? Do all the stages achieve the same multiple for the effective compression ratio? or don't they? The reason that multiplication cannot be used is because it does not take into account the wasted power (Pi in the formula), just the work (physics term meaning change in energy state - in this case the effective increase in pressure (Pe in the formula)) achieved at the last measured stage. There are only 2 ways to determine the effective increase in pressure (Pe) done by a system:
> 
> ...



There is the method MetroVick actually used. Calculate the output conditions based on the input conditions, the profile and length of the blades for the rotors and stators, the rpm, etc, long hand iteratively.

All this before cutting metal and being able to check their calculations.

Probably all stages were considered part of one system, since each stage affects the last.


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## Snowygrouch (Apr 13, 2019)

ThomasP said:


> 2. Use a formula similar to the one above, which previously accepted values for similar systems.



This is a WW2 German set of compressor maps for a 2 stage supercharger (centirifugal) showing the performance of each stage
and the combined performance. Theses are in Had, adiabatic pressure head (work) in which the total compressor work can be
represented as the work of each stage ADDED. which you can see as its basically 6000+6000=12,000 m.kg/kg

This does not work for pressure ratio, and needs to be caculated as per the equation I previously posted

(look for "314" which is the impeller tip speed in m/s)


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## pbehn (Apr 13, 2019)

Snowygrouch said:


> This is a WW2 German set of compressor maps for a 2 stage supercharger (centirifugal) showing the performance of each stage
> and the combined performance. Theses are in Had, adiabatic pressure head (work) in which the total compressor work can be
> represented as the work of each stage ADDED. which you can see as its basically 6000+6000=12,000 m.kg/kg
> 
> ...


I appreciate your posts Callum, I just wish I could understand them. Great stuff.


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## ThomasP (Apr 14, 2019)

Hey Snowygrouch,

Thank you for supporting my post#105, 108, and 112 on the additive nature of supercharging.

re: my statement "I believe you are mistaken as to how the air is traveling through the Merlin 2-stage supercharger."

My description is based on what I read a number of years ago as to how the air was channeled from the output of the 1st stage to the 2nd stage inlet. Maybe I misunderstood? I can not tell from the actual engine cut-away picture you posted.


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## Snowygrouch (Apr 14, 2019)

ThomasP said:


> Hey Snowygrouch,
> 
> Thank you for supporting my post#105, 108, and 112 on the additive nature of supercharging.
> 
> ...



Be a bit careful, I`m stating that multi-stage compressor WORK is additive when presented in that manner...

I think the fact that the air has to travel around a "u" bend is fairly clear from the picture. The fact that the flow exits the impeller with a strong tangential component, does not alter the fact that its flow direction must be altered by 180 degrees to make it back to the 2nd stage inlet eye.


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## ThomasP (Apr 14, 2019)

Hey Snowygrouch,

Please see my 2nd paragraph post#105 and 1st paragraph post#112 re work.

I think the only difference we see re the Merlin 2-stage air flow is that I read the route from the 1st stage outlet to the 2nd stage inlet was a spiral instead of a U?


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## tomo pauk (Apr 14, 2019)

Snowygrouch said:


> This is a WW2 German set of compressor maps for a 2 stage supercharger (centirifugal) showing the performance of each stage
> and the combined performance. Theses are in Had, adiabatic pressure head (work) in which the total compressor work can be
> represented as the work of each stage ADDED. which you can see as its basically 6000+6000=12,000 m.kg/kg
> 
> ...





pbehn said:


> I appreciate your posts Callum, I just wish I could understand them. Great stuff.



The 1st diagram (Bild 4), says roughly: _"supercharger map of the 1st stage of 2-stage blower, calculated per Diagram 1 (Bild 1)"._ 
2nd diagram (Bild 5) says roughly: _"supercharger map of the 2nd stage of a 2-stage blower, calculated per Diagram 3 (Bild 3)". _
3rd diagram_: "supercharger map of a 2-stage blower, calculated per Diagrams 4 and Diagram 5"_
(impeller tip speed in m/sec; VL in m^3/sec is the weight of air the blower is 'moving', Had in m.kg/kg is blower's work, efficiency is noted being, for example, 0,75 = 75%, or 0.65 = 65%)


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## wuzak (Apr 14, 2019)

ThomasP said:


> The actual formula for multiple stage compression is similar to the formula I used to show the pattern of heat rise in the compressed air in my post#94 earlier in this thread:
> 
> Ta + T1 - 25 + T2 - TAC = MT
> 
> ...



Your direct correlation between pressure and temperature presupposes that the volume remains constant.

In fact pressure temperature and volume are interconnected.

In a 2 stage system, the second stage pressure ratio is determined by the pressure, temperature and mass flow of the air fed by the first stage.

The second stage and feed ducts cause a back pressure for the first stage, changing its performance. 

Once all those factors are considered, the overall pressure ratio is the product of each stage’s ratio.


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## wuzak (Apr 14, 2019)

And regarding calculating the pressure ratio of axial compressor, I believe the Navier-Stokes equations were applied.


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## pbehn (Apr 14, 2019)

tomo pauk said:


> The 1st diagram (Bild 4), says roughly: _"supercharger map of the 1st stage of 2-stage blower, calculated per Diagram 1 (Bild 1)"._
> 2nd diagram (Bild 5) says roughly: _"supercharger map of the 2nd stage of a 2-stage blower, calculated per Diagram 3 (Bild 3)". _
> 3rd diagram_: "supercharger map of a 2-stage blower, calculated per Diagrams 4 and Diagram 5"_
> (impeller tip speed in m/sec; VL in m^3/sec is the weight of air the blower is 'moving', Had in m.kg/kg is blower's work, efficiency is noted being, for example, 0,75 = 75%, or 0.65 = 65%)


Thanks Tomo but my German is good enough to understand the German but my knowledge of fluid dynamics and all the other laws of physics is overloaded, I can however follow the basic principles and find it all interesting.


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## ThomasP (Apr 14, 2019)

Hey Wuzak,

re: from your post#115. "My point is that in order for the method espoused by Thomas of adding the pressure ratios together to get the overall ratio, since it would require ratios less than 1:1"

This illustrates some of the confusion over additive work (physics term) processes.

If we use the MetroVick F2/2 9-stage compressor as an example, and it is capable of achieving a 3.5:1 pressure ratio at sea level, the actual pressure rise is from 14.7 lb/in^2 to 51.45 lb/in^2, a difference of 36.75 lb/in^2. If each of the stages achieved the same amount of work (physics term), then (as you said) each stage would add ~.4, not as a ratio, but as 4 lb/in^2 (4.083 to be more precise) to that stage's intake pressure. So we get:

14.7 + 4.083 + 4.083 + 4.083 + 4.083 + 4.083 + 4.083 + 4.083 + 4.083 + 4.083 = 51.45

However, since we are starting at an ambient air pressure that is greater than 0 (in this case 14.7 lb/in^2) none of the stages would have a ratio of less than 1:1. So we get the following ratios for the individual stages:

1st stage ratio = (14.7 + 4.083) / 14.7 = 18.783 / 14.7 = 1.278:1
2nd stage ratio = (18.783 + 4.083) / 18.783 = 22.866 / 18.783 = 1.217:1
3rd stage ratio = (22.866 + 4.083) / 22.866 = 26.949 / 22.866 = 1.179:1
4th stage ratio = (26.949 + 4.083) / 26.949 = 31.032 / 26.949 = 1.151:1
5th stage ratio = (31.032 + 4.083) / 31.032 = 35.115 / 31.032 = 1.132:1
6th stage ratio = (35.115 + 4.083) / 35.115 = 39.198 / 35.115 = 1.116:1
7th stage ratio = (39.198 + 4.083) / 39.198 = 43.281 / 39.198 = 1.104:1
8th stage ratio = (43.281 + 4.083) / 43.281 = 47.364 / 43.281 = 1.094:1
9th stage ratio = (47.364 + 4.083) / 47.364 = 51.447 / 47.364 = 1.086:1

If you then multiply the ratios you get:

1.278 x 1.217 x 1.179 x 1.151 x 1.132 x 1.116 x 1.104 x 1.094 x 1.086 = 3.497

3.497 = 3.5 (almost )


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## Shortround6 (Apr 14, 2019)

My knowledge of fluid dynamics and all the other laws of physics may be somewhat on the elementary side so let's try a little example and perhaps people can point out the flaws in my thinking.

Lets say we have a 2 stage supercharger that operates on a 3 to ratio in the first stage and a 2 to ratio in the second stage. The first stage (in theory) will raise the pressure from 15lb/sq/in to 45 lb/sq/in and the 2nd stage raises it from 45 lb/sq/in to 90lb/sq/in. 

Now is the 2nd stage "work" _result_ added to the 1st stage or has it multiplied it? 

Now please note I have made no mention of power required in each stage or temperature rise or any other factors. 

lets also assume, as a variation on this that this was a design goal and for some reason the 1st stage didn't achieve it's goal of 45lb/sq/in output and only made 42 lb/sq/in, what happens?

My theory/line of thinking says the 2nd stage multiples the 42 lb/sq/in by 2 to 84lb/sq/in. 
Other, less likely lines of thinking may call for an "additive" (second stage miraculously still adds 45lbs/sq/in to the total for 87 psi total?) or some other total?

My working knowledge of fluid dynamics (such as it is) is from working with water which is not compressible so a lot my experience may not apply. 

In my example the 2nd stage may be doing more actual "work" since it is compressing the air by 45psi vs the 30psi of the first stage but then it is only reducing the volume to 1/2 the starting volume vs 1/3 like the 2st stage.


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## pbehn (Apr 15, 2019)

I find the discussion interesting, from the theoretical physics then to the practical application which throws up news laws of physics to be got around, then the whole lot has to be mounted in an aircraft and perform at all sorts of altitudes and speed. Finally when talking about temperature pressure and flow rates how do you measure and control them with 1940s tech.


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## Shortround6 (Apr 15, 2019)

They could measure them in test houses/on test stands but in operational aircraft everything had to be on the conservative side (as much as possible) to take care of unknowns/weather-temperature variations.

Pilots didn't care about most of the technical details and the pressure gauge was simple, cheap, and worked close enough to get by with. In a test house they could rig pressure gauges at various points in the intake tract and measure the exhaust pressure. It was possible (although not easy) to measure the amount of air (at least the cubic ft) per minute goring through the system.

For flying there were often test aircraft










with one or more positions for engineers/technicians to monitor banks of gauges.


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## ThomasP (Apr 15, 2019)

Hey wuzak,

re your post#124 "And regarding calculating the pressure ratio of axial compressor, I believe the Navier-Stokes equations were applied."

The Navier-Stokes series of equations can and have been used in the development of compressive systems, like the airflow around an airfoil (i.e. a turbine blade), compression in a confined space (i.e. within the confines of a cylinder), and resulting momentum of the air flow (i.e. the mass of the air being moved times the velocity of the air), which can then be used to calculate the Kinetic Energy (KE) of the airflow (i.e. the energy contained in the exhaust), which when applied to a real world mechanism (such as a jet engine) can give you the theoretical thrust. In and of themselves the Navier-Stokes equations will not give you an exact real world value, but said value (if you substitute solvable sub-formula for the variables) should get pretty close to the real world values after refinement. A couple of the equations that can be used to solve the problems of motion of/in a system are below.

I am sure you have heard the term Reynolds number used in the calculation of the modeling of airflow around an airfoil (i.e. usable to help figure the pressure decrease/increase and overall lift of a wing, or the equivalent effect relative to a turbine blade)






and this set of equations used in the modeling of 3-dimensional movement of a body/system (i.e. perhaps a spiral vortex flow of compressible gas with changing radii and varying radial and axial velocities, aka the airflow through a jet engine).






Please note all the adding and subtracting going on.


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## wuzak (Apr 15, 2019)

What if the inlet condition is 1/2 atmosphere?

In your example of the MetroVick F.2/2 does each stage give a 4psi rise still?


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## ThomasP (Apr 16, 2019)

Hey wuzak,

re: "What if the inlet condition is 1/2 atmosphere?"

If you are talking about having 1/2 standard pressure at SL but with the same air temperature as the standard day (15ºC), you would add 1/2 the pressure gain listed above for each stage( i.e. 4.083 / 2 = 2.0415 lb/in^2, so +2.0415) and the resulting CR of 3.5:1 would be the same. If, however, you are asking what the compression ratio would be at 18,000 ft (where the ambient pressure is 1/2 the standard pressure at SL and the standard temperature is -20.6ºC) the pressure gain would be 2.196 lb/in^2, with resulting CR of 3.76:1. The achievable CR at 33,800 ft (where the pressure is 1/4 SL and the temperature is -51.8ºC) would be 4.04:1. From 36,000 ft on up the temperature remains the same (-56.5ºC) and the achievable CR would remain the same at 4.08:1. This is assuming the engine is not moving and the turbine rpm remains the same at all heights.

Altitude______CR
36,000 ft+___4.08:1
33,800 ft____4.04:1
18,000 ft____3.76:1
S.L._________3.5:1


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## wuzak (Apr 16, 2019)

I must admit that I had been under the impression that you were summing the pressure ratios, not the pressure deltas.

I wrote down your addition method in terms of pressure ratios.

That is:
dP1 = P0 x R1 - P0 = P0(R1 - 1)

And you do that for all stages, it comes out as:

P = P0.R1.R2.....Rn

So if you do know the individual pressure ratios you can multiply them to get the overall ratio.

You are correct that you can’t directly calculate the pressure ratio of a stage. You have to go through the process of calculating the pressure at each stage.


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## Buster01 (Apr 18, 2019)

Here is a link to a table of characteristics. Here is a link to an article on turbochargers with a lot of historical data.


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## ThomasP (Apr 19, 2019)

Hey Buster01,

Great article, thanks for the link. I have visited the Engine History website but had not noticed the article.


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