Messerschmitt Bf 109 to be built new in Bavaria again!
Bf to Me Changeover
If you look up Messerschmitt on Wikipedia, it gives this description for the change from Bf to Me. It certainly sounds plausible.
It appears that there was a Bf163 (STOL observation aircraft) and Me163 (the well known rocket powered Komet).
Willy Messerschmitt joined the company (BFW) in 1927 as chief designer and engineer, and formed a design team.
One of the first designs, the Messerschmitt M20, was a near-catastrophe for the designer and the company. Many of the prototypes crashed, one of them killing Hans Hackman, a close friend of Erhard Milch, the head of Lufthansa and the German civil aviation authorities. Milch was upset by the lack of response from Messerschmitt and this led to a lifelong hatred towards him. Milch eventually cancelled all contracts with Messerschmitt and forced BFW into bankruptcy in 1931. However, the German re-armament programs and Messerschmitt's friendship with Hugo Junkers prevented a stagnation of the careers of him and BFW, which was started again in 1933. Milch still prevented Messerschmitt's takeover of the BFW until 1938, hence the designation "Bf" of early Messerschmitt designs.
Messerschmitt promoted a concept he called "light weight construction" in which many typically separate load-bearing parts were merged into a single reinforced firewall, thereby saving weight and improving performance. The first true test of the concept was in the Bf 108 Taifun sports-plane, which would soon be setting all sorts of records. Based on this performance the company was invited to submit a design for the Luftwaffe's 1935 fighter contest, winning it with the Bf 109, based on the same construction methods.
From this point on Messerschmitt became a favorite of the Nazi party, as much for his designs as his political abilities and the factory location in southern Germany away from the "clumping" of aviation firms on the northern coast. BFW was reconstituted as Messerschmitt AG on July 11, 1938, with Willy Messerschmitt as chairman and managing director. The renaming of BFW resulted in the company's RLM designation changing from Bf to Me for all newer designs after the acquisition date. Existing types, such as the Bf 109 and 110, retained their earlier designation in official documents, although sometimes the newer designations were used as well, most often by subcontractors. In practise, all BFW/Messerschmitt aircraft from 108 to 163 (not the same plane as the Me 163) were prefixed Bf, all later types with Me.
One of the first designs, the Messerschmitt M20, was a near-catastrophe for the designer and the company. Many of the prototypes crashed, one of them killing Hans Hackman, a close friend of Erhard Milch, the head of Lufthansa and the German civil aviation authorities. Milch was upset by the lack of response from Messerschmitt and this led to a lifelong hatred towards him. Milch eventually cancelled all contracts with Messerschmitt and forced BFW into bankruptcy in 1931. However, the German re-armament programs and Messerschmitt's friendship with Hugo Junkers prevented a stagnation of the careers of him and BFW, which was started again in 1933. Milch still prevented Messerschmitt's takeover of the BFW until 1938, hence the designation "Bf" of early Messerschmitt designs.
Messerschmitt promoted a concept he called "light weight construction" in which many typically separate load-bearing parts were merged into a single reinforced firewall, thereby saving weight and improving performance. The first true test of the concept was in the Bf 108 Taifun sports-plane, which would soon be setting all sorts of records. Based on this performance the company was invited to submit a design for the Luftwaffe's 1935 fighter contest, winning it with the Bf 109, based on the same construction methods.
From this point on Messerschmitt became a favorite of the Nazi party, as much for his designs as his political abilities and the factory location in southern Germany away from the "clumping" of aviation firms on the northern coast. BFW was reconstituted as Messerschmitt AG on July 11, 1938, with Willy Messerschmitt as chairman and managing director. The renaming of BFW resulted in the company's RLM designation changing from Bf to Me for all newer designs after the acquisition date. Existing types, such as the Bf 109 and 110, retained their earlier designation in official documents, although sometimes the newer designations were used as well, most often by subcontractors. In practise, all BFW/Messerschmitt aircraft from 108 to 163 (not the same plane as the Me 163) were prefixed Bf, all later types with Me.
Last edited by Mechta; 20th Dec 2009 at 11:15. Reason: Clarification of Bf/Me163
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The correct designation is a subject of much debate. Janes says it was originally known as Bf, but with the reconstruction of the company as Messerschmitt A.G. the designation was changed to Me, and the first aircraft to carry this designation was the Me 109E which went to war in September, 1939. The linage of the company is Udet Flugzegbau G.m.b.H of Munchen, succeeded by Bayerische Flugzeugwerke of Augsberg in 1926, because of the depression in 1931 the company was taken over by Messerschmitt Flugzeugbau which then became Messerschmitt A.G. in 1938. A bit convoluted.
Originally the aircraft was designated as Bf 109 by Reichsluftfahrtministerium (German Aviation Ministry, RLM), since the design was submitted by the Bayerische Flugzeugwerke (literally "Bavarian Aircraft Factory") company. However, the company was renamed Messerschmitt AG after July 1938 when Erhard Milch finally allowed Willy Messerschmitt to acquire the company. Subsequently, all Messerschmitt aircraft that originated after that date, such as the Me 210, were to carry the "Me" designation. Despite regulations by the RLM, wartime documents from Messerschmitt AG, RLM and Luftwaffe loss and strength reports continued to use both designations, sometimes even on the same page. All extant airframes are described as "Bf 109" on identification plates, including the final K-4 models, with the noted exception of aircraft either initially built or re-fitted by Erla Flugzeugwerke, which sometimes bore the Me 109 stamping.
With the exception of the fuel injection on the DB it is considered by the experts to be a fairly crude engine when compared to the Merlin. It took a capacity of 35.7 litres to produce 1,475 HP at a weight of 1,663 Lbs compared to the Merlin with a capacity of 27 litres for an output of 1,440 HP (weight 1,375 Lbs Spitfire I) to 1,650 HP (weight 1,650 Lbs) in later marks.
Problems with the DB
Spark plug placement was considered to reduce power output by some 8%.
Compared to the gallery-type oil feed used on the DB, the end-feed system is vastly superior because, with the former, as bearing wear takes place there is an increased leakage of oil from the mains journals resulting in less supply to the big-ends. As oil has to be forced into the crankshaft against centrifugal pressure, it gives a reduction in lubrication to the big-ends with increasing crankshaft rotational speed. The limit of life of bearings is the time when the main journal clearances have increased to the extent that the big-ends get insufficient oil, even though the main journal bearings can run on quite satisfactorily with increased clearance.
The advantages of end-feed. lubrication include:
1) The entry of oil into the crankshaft interior not being opposed by the centrifugal force generated by the spinning crankshaft.
2) Making possible a much better proportioning of oil quantities between the main and crankpin bearings,
3) Permitting a reduction in the total oil flow because with the gallery system, excess oil must be given to the mains in order to ensure there is enough for the big-ends.
4) Allowing the deletion of holes and grooves in the main bearings thereby increasing their load carrying capacity.
5) Use of much lower oil pump pressures. In most engines, oil pressure is usually regarded as a vital indication of the health of the functioning engine - any fluctuation signals impending disaster. End feed engines can operate quite satisfactorily on just a few psi if necessary.
At the insistence of the Air Ministry, and against the advice of DB, the engine was made as of an inverted V configuration. This led to excessive oil reaching the combustion chambers and so reducing the octane rating of the fuel, hence further reducing power output. Such was this problem that the two banks of cylinders had different compression ratios, because windage from the crankshaft forced more oil into one bank than the other, thereby reducing the octane rating on one bank more than the other.
The apparently insoluble oil control problems plagued the DB 600 series for the whole of its production life.
Originally the aircraft was designated as Bf 109 by Reichsluftfahrtministerium (German Aviation Ministry, RLM), since the design was submitted by the Bayerische Flugzeugwerke (literally "Bavarian Aircraft Factory") company. However, the company was renamed Messerschmitt AG after July 1938 when Erhard Milch finally allowed Willy Messerschmitt to acquire the company. Subsequently, all Messerschmitt aircraft that originated after that date, such as the Me 210, were to carry the "Me" designation. Despite regulations by the RLM, wartime documents from Messerschmitt AG, RLM and Luftwaffe loss and strength reports continued to use both designations, sometimes even on the same page. All extant airframes are described as "Bf 109" on identification plates, including the final K-4 models, with the noted exception of aircraft either initially built or re-fitted by Erla Flugzeugwerke, which sometimes bore the Me 109 stamping.
With the exception of the fuel injection on the DB it is considered by the experts to be a fairly crude engine when compared to the Merlin. It took a capacity of 35.7 litres to produce 1,475 HP at a weight of 1,663 Lbs compared to the Merlin with a capacity of 27 litres for an output of 1,440 HP (weight 1,375 Lbs Spitfire I) to 1,650 HP (weight 1,650 Lbs) in later marks.
Problems with the DB
Spark plug placement was considered to reduce power output by some 8%.
Compared to the gallery-type oil feed used on the DB, the end-feed system is vastly superior because, with the former, as bearing wear takes place there is an increased leakage of oil from the mains journals resulting in less supply to the big-ends. As oil has to be forced into the crankshaft against centrifugal pressure, it gives a reduction in lubrication to the big-ends with increasing crankshaft rotational speed. The limit of life of bearings is the time when the main journal clearances have increased to the extent that the big-ends get insufficient oil, even though the main journal bearings can run on quite satisfactorily with increased clearance.
The advantages of end-feed. lubrication include:
1) The entry of oil into the crankshaft interior not being opposed by the centrifugal force generated by the spinning crankshaft.
2) Making possible a much better proportioning of oil quantities between the main and crankpin bearings,
3) Permitting a reduction in the total oil flow because with the gallery system, excess oil must be given to the mains in order to ensure there is enough for the big-ends.
4) Allowing the deletion of holes and grooves in the main bearings thereby increasing their load carrying capacity.
5) Use of much lower oil pump pressures. In most engines, oil pressure is usually regarded as a vital indication of the health of the functioning engine - any fluctuation signals impending disaster. End feed engines can operate quite satisfactorily on just a few psi if necessary.
At the insistence of the Air Ministry, and against the advice of DB, the engine was made as of an inverted V configuration. This led to excessive oil reaching the combustion chambers and so reducing the octane rating of the fuel, hence further reducing power output. Such was this problem that the two banks of cylinders had different compression ratios, because windage from the crankshaft forced more oil into one bank than the other, thereby reducing the octane rating on one bank more than the other.
The apparently insoluble oil control problems plagued the DB 600 series for the whole of its production life.
Thanks Mechta, that is good information and I'll pass it on. Thanks for the quick reply, I stuck my neck out abit by saying, "I'll find that out". It's never as easy as one first assumes!
No problem George.
Brian, Your info on the company and engine is also appreciated here too. I would also welcome clarification of how end and gallery fed oil systems work, respectively.
Its very easy to get muddled on designations; I've lost count the number of times I have seen ANT-* aicraft referred to as Antonov, when they are in fact early designs from A.N.Tupolev! Antonov are just AN-* of course.
Brian, Your info on the company and engine is also appreciated here too. I would also welcome clarification of how end and gallery fed oil systems work, respectively.
Its very easy to get muddled on designations; I've lost count the number of times I have seen ANT-* aicraft referred to as Antonov, when they are in fact early designs from A.N.Tupolev! Antonov are just AN-* of course.
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i think that the argument as to whether the Merlin or the DB was the better engine gets muddied by the fact that from fairly early in the war, we had access to 100 octane and later, even higher octane fuel. The Germans were stuck with 87 octane throughout the war. The Merlin was able to be developed to produce ever higher powers through higher boost pressures with no increase in capacity, whereas the Germans had to resort to short term boost gimmicks such as GM-1 and MW 50 or use bigger engines.
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on the subject of engine's,
was the mounting of the 109's engine "upside down" really a good idea?
after all, everyone else (uk,usa,france etc) saw fit to mount their V12's the "right" way up.
was the mounting of the 109's engine "upside down" really a good idea?
after all, everyone else (uk,usa,france etc) saw fit to mount their V12's the "right" way up.
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Further thread drift. While the Germans used methanol-water and nitrous-oxide injection to boost power it was not unknown in the Allies high powered radials to use water/meth. Nitrous oxide was used in some Mosquito night fighters. Most German aero engines used 87 octane fuel (called B4), some high-powered engines used 100 octane (C2/C3) fuel.
There is a common misapprehension about wartime fuel octane numbers. There are two octane numbers for each fuel, one for lean mix and one for rich mix, rich being always greater. So, for example, a common British aviation fuel of the later part of the war was 100/125. The misapprehension that German fuels have a lower octane number (and thus a poorer quality) arises because the Germans quoted the lean mix octane number for their fuels while the Allies quoted the rich mix number for their fuels. Standard German high-grade aviation fuel used in the later part of the war (given the designation C3) had lean/rich octane numbers of 100/130. The Germans would list this as a 100 octane fuel while the Allies would list it as 130 octane.
After the war the US Navy sent a Technical Mission to Germany to interview German petrochemists and examine German fuel quality, their report entitled "Technical Report 145-45 Manufacture of Aviation Gasoline in Germany" ( Technical Report 145-45 - The Manufacture of Aviation Gasoline in Germany ) chemically analysed the different fuels and concluded "Toward the end of the war the quality of fuel being used by the German fighter planes was quite similar to that being used by the Allies" ie 150 octane by our standard.
Will get back on the oil question.
There is a common misapprehension about wartime fuel octane numbers. There are two octane numbers for each fuel, one for lean mix and one for rich mix, rich being always greater. So, for example, a common British aviation fuel of the later part of the war was 100/125. The misapprehension that German fuels have a lower octane number (and thus a poorer quality) arises because the Germans quoted the lean mix octane number for their fuels while the Allies quoted the rich mix number for their fuels. Standard German high-grade aviation fuel used in the later part of the war (given the designation C3) had lean/rich octane numbers of 100/130. The Germans would list this as a 100 octane fuel while the Allies would list it as 130 octane.
After the war the US Navy sent a Technical Mission to Germany to interview German petrochemists and examine German fuel quality, their report entitled "Technical Report 145-45 Manufacture of Aviation Gasoline in Germany" ( Technical Report 145-45 - The Manufacture of Aviation Gasoline in Germany ) chemically analysed the different fuels and concluded "Toward the end of the war the quality of fuel being used by the German fighter planes was quite similar to that being used by the Allies" ie 150 octane by our standard.
Will get back on the oil question.
Last edited by Brian Abraham; 20th Dec 2009 at 22:27. Reason: Mossie info
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With all due respect, I think the least authoritative voices as to whether it was an Me or a Bf were those of the young pilots who bravely flew against it.
regardless of their courage, they really had no idea whether Willy Messerschmitt or Bavarian Flugzeugwerk built it
It's in a sense as though you asked an Iraq War pilot 50 years from now to confirm that his A-10 was named Thunderbolt II. "You mean the WARTHOG?" he'd laugh...
regardless of their courage, they really had no idea whether Willy Messerschmitt or Bavarian Flugzeugwerk built it
It's in a sense as though you asked an Iraq War pilot 50 years from now to confirm that his A-10 was named Thunderbolt II. "You mean the WARTHOG?" he'd laugh...
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"...was the mounting of the 109's engine "upside down" really a good idea?"
The urban legend, and I suspect it's exactly that, is that back in the mid-'30s when the Germans and their British friends were exchanging technical teams, a Daimler group visited Rolls-Royce and saw Merlin prototypes on display. Their DB-600 was very similar, but they decided that to mitigate claims that they'd "copied the Brits," they'd at least invert the engine.
As I said, almost certainly a myth.
But beyond that, what's wrong with "inverting" a dry-sump engine of any configuration? The only reason engines were ever upright (by our definition) in the first place was to keep the oil down where it wouldn't do silly things. Once you separate the oil supply from the engine, you can do such things as--what a revolutionary thought, no pun--put all the cylinders in a circle, so that some of them are upright, some upside-down, some sideways and some in-between. The pistons and cylinders don't know the difference.
The urban legend, and I suspect it's exactly that, is that back in the mid-'30s when the Germans and their British friends were exchanging technical teams, a Daimler group visited Rolls-Royce and saw Merlin prototypes on display. Their DB-600 was very similar, but they decided that to mitigate claims that they'd "copied the Brits," they'd at least invert the engine.
As I said, almost certainly a myth.
But beyond that, what's wrong with "inverting" a dry-sump engine of any configuration? The only reason engines were ever upright (by our definition) in the first place was to keep the oil down where it wouldn't do silly things. Once you separate the oil supply from the engine, you can do such things as--what a revolutionary thought, no pun--put all the cylinders in a circle, so that some of them are upright, some upside-down, some sideways and some in-between. The pistons and cylinders don't know the difference.
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Re the oil question. In a conventional in line engine lubrication system, the oil is conveyed to the main bearings through galleries, which are holes drilled in the crankcase joining up with the main bearings. A groove machined in the main bearing transfers the oil to the connecting rods journals through holes drilled in the crankshaft. In the "end to end" lubrication system oil was fed into the crankshaft from both ends. This arrangement offered several advantages. The requirement for an oil distribution groove in the main bearing was eliminated and centrifugal force aided the oil pressure instead of the oil pump having to fight centrifugal force when pumping oil into the main bearing.
Inverted engines, including radials, have a voracious appetite - for oil. The B-29 for example has 85 US gallons per engine. Flight manuals for aircraft of the period have notes "ensure the oil is full for extended flights". Often the fuel endurance exceeded that of the oil supply. The DC-4 despite its 22 gallon supply per engine had a 50 gallon tank just behind the cockpit on some aircraft to ensure an adequate supply on long range flights.
Inverted engines, including radials, have a voracious appetite - for oil. The B-29 for example has 85 US gallons per engine. Flight manuals for aircraft of the period have notes "ensure the oil is full for extended flights". Often the fuel endurance exceeded that of the oil supply. The DC-4 despite its 22 gallon supply per engine had a 50 gallon tank just behind the cockpit on some aircraft to ensure an adequate supply on long range flights.
The Merlin was apparently originally planned to be inverted but changed by the Air Ministry or whatever it was that week. There's a picture of an early wooden mock-up in "Spitfire - The History". Rumour, or possibly just one of the many accusations of copying, is that's what the Daimler chappies saw.
IIRC, only the later Merlins had end feed. I'm fairly certain it's mentioned in one of the RRHT books, but I can't find the book...
IIRC, only the later Merlins had end feed. I'm fairly certain it's mentioned in one of the RRHT books, but I can't find the book...
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"Inverted engines, including radials, have a voracious appetite - for oil."
The examples you mention are all air-cooled, and I certainly would agree, as a Porsche 911 owner, that air-cooled engines used more oil than liquid-cooled ones, due at least in part to the substantial differences in the coefficient of expansion of various materials. But I didn't know that liquid-cooled inverted engines use more oil than do upright ones. I'd be interested if you can cite any examples (but don't waste any time on it if nothing comes to mind immediately).
The examples you mention are all air-cooled, and I certainly would agree, as a Porsche 911 owner, that air-cooled engines used more oil than liquid-cooled ones, due at least in part to the substantial differences in the coefficient of expansion of various materials. But I didn't know that liquid-cooled inverted engines use more oil than do upright ones. I'd be interested if you can cite any examples (but don't waste any time on it if nothing comes to mind immediately).
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The Merlin did start out in an inverted configuration but the aircraft manufacturers are said to have preferred an upright. Don't know why, though do have a reference directing to a source explaining the reasons.
The following is excerpted from a letter by Jerry Wells in "Torque Meter" Volume 2, Number 2 (Spring 2003) - magazine of the Aircraft Engine Historical Society. As can be adjudged from the article, little is known about German WWII aero engines, but this article is the "best guess" from experts in the field. A factual, definitive answer would seem still to await us ie original German documentation which as likely as not no longer exists being lost in the annuls of time and the massive destruction of WWII.
On a further point of interest regarding CRs, J.J. notes, quite correctly, the 8.3/9.5 figures that pertain to the left and right cylinder banks of the Daimler-Benz 603 when running on 100 octane fuel.
One of the great curiosities in aero-engine literature is that authors often meticulously list the differential CRs of the DB 603/605 V-12s, but never get round to explaining why the engine manufacturer deemed it necessary to do this! By any standards, it is an odd thing to do - I cannot think of any other piston engine that was supplied with the CR for some cylinders deliberately set lower than others.
Hunting through the literature, three theories materialize - perhaps an indication of how little we know about the German WWII aero-engines. The first suggests the differential CRs were due to articulated con-rods, the reasoning being that in a V-engine the pistons moved by the articulated rods would always travel slightly further in completing each stroke compared to their master-rod counterparts. All else being equal, this would produce a slightly higher CR on the link-side of the engine. However, this theory falls down very quickly on two counts:
1) It is a relatively simple matter to adjust the shape of a combustion chamber or piston top to compensate for the slightly longer stroke.
2) The DB 600 series V-12s were never fitted with anything but fork and blade con-rod pairs!
Theory two centers on the fact that the supercharger on the DB 600 V-12s as located on the left hand side of the engine and, thus, from such position would naturally provide mere “huff” to the cylinder bank nearest to it. In order not to (relatively) over-boost the left hand bank, the CR would have to be lowered slightly on that side.
In their book, Die deutsche Luftfahrt - Vol 2, (if you haven't got a copy of this in your library, you're missing a treat) ven Gersdorff & Grasmann write, regarding the DB 603, “Die Verdichtung der beiden Zylinderreihen war unterschiedlich, die linke hatte 7,3 din rechte 7,5, um die durch die unterschiedliche Lange der Ladeluftleitung – bedingt durch den einseitig angeordneten Lader- geringen Ladedruckunterschiede auszugleichen.” An exact translation of this reads, “The compression ratio of the two cylinder banks was different, the left had 7.3:1, the right had 7.5:1, in order to balance the small boost-pressure differences due to the differing lengths of the supercharger air delivery pipes resultant from the off-set arrangement of the supercharger.”
One hesitates to question the veracity of two such respected German authors (especially when they are writing about German Flugmoteren (aircraft engines)) but their explanation appears to be flawed. For one thing, even though the the DB supercharger was offset, the delivery pipe to the inlet manifolds actually has a gentler, less angular pathway down to the midpoint between the two cylinder banks than is the case with a cross mounted Allison/Merlin supercharger installation. If it discharges at or very near to the midpoint between the banks then only equal pressure will be fed to each side. Having reached the midpoint of the rear most cylinders, the DB induction pipe bifurcates to feed the two banks. However, the two branches do not end blindly at the forward-most cylinder but instead rejoin at this point so that the entire manifold is ring-shaped, making the likelihood of any one-sided pressure differences impossible.
The third possibility is that the lubrication system was at the heart of the matter. One of the disadvantages of an engine design which features inverted or downward pointing cylinders is that the cylinder and piston interiors form containers into which the oil flows and accumulates due to gravity. While this augers well for piston cooling and cylinder lubrication, the problem of oil moving past the pistons and into the combustion chambers in excess quantities crops up. Mixing oil with petrol (gasoline) rapidly causes a lowering of the octane rating of the fuel thus increasing the likelihood of detonation.
Tucked away in one of the very early editions of the R-RHT magazine, Archive is a reprint of, “Comments on a Visit to Germany - July 24th to August 12th, 1945.” Two paragraphs are of particular interest: “A good example of the (excessive) Air Ministry control lies in the inverted DB engine. The DB people said that both from a technical and production point of view they would have preferred to make an upright engine but they are compelled to make it inverted by the (German) Air Ministry.”
“With the inverted engine, they said it was very difficult to obtain consistent oil consumption and due to the rotation of the crankshaft one cylinder bank got more oil (spray) than the other. This oil got past the pistons into the combustion chambers and reduced the anti-knock value of the charge. For this reason the engine was built with a lower cylinder compression ratio on this (?) bank than on the other.”
In the light of this evidence, the third theory seems to be the most plausible. The situation was probably exacerbated by the use of roller bearings in the con-rod big ends. Assuming theory three is true, lowering the CR of one bank of cylinders does seem to be an extraordinary, almost desperate attempt to solve the problem. It also makes an absolute mockery of all the much vaunted, supposed advantages of fitting these engines with precision made, high pressure fuel injection systems. If six of the twelve cylinders per engine were suffering from chronic, unpreventable oil contamination then accurate fuel metering would count for very little. As it was, the DB601 had enough combustion problems due to poor fuel burning resultant from the location of both spark plugs per cylinder on the same (exhaust) side. This undesirable feature alone was responsible for a power loss of seven to eight percent.
From all of this, two other questions beg consideration.
1) Why did predecessors to the DB603/605, i.e. the DB600/601 not also have differential cylinder bank CRs?
2) Did the oil consumption problem affect the well known, close contemporary to the DB 600-series V-12s, vis a vis the Junkers Jumo 211?
In answer to Question 1, it is most likely that the left bank oil burning problem was with the 601 model from the beginning of its production and that the first opportunity to do something about it came with the introduction of the 605/603 types. Even so, as mentioned above, DB's answer to the difficulty was crude to say the least.
With regard to Question 2, it becomes obvious from just a brief comparison of the Jumo 211 and the DB 600 series that apart from being inverted, having a cannon tunnel and featuring an off-set supercharger, the design features of the two makes of engine were very different.
Nowhere is this more apparent than in the respective lubrication systems. The DB had a conventional gallery-type arrangement where, from a central feed-pipe branch lines admitted oil to each main bearing block, thence the oil was forced through holes and grooves into each bearing shell and then into the crankshaft interior via more holes and grooves in the crankshaft main bearing journals. From there, 3/8” pipes took the oil to the hollow crankpin for distribution to the big-end bearings, both roller and plain.
The Junkers' engineers on the other hand, perhaps anticipated possible oil control problems due to the compulsory inverted installation requirement, designed the Jumo 211 with an end-feed system where the oil was fed into the front end of the crankshaft and from this single entry point it was moved along the length of the crankshaft to be fed by centrifugal force to the main and big end bearings. Compared to the gallery-type, the end-feed system is vastly superior because, with the former, as bearing wear takes place there is an increased leakage of oil from the mains journals resulting in less supply to the big-ends. As oil has to be forced into the crankshaft against centrifugal pressure, it gives a reduction in lubrication to the big-ends with increasing crankshaft rotational speed. The limit of life of bearings is the time when the main journal clearances have increased to the extent that the big-ends get insufficient oil, even though the main journal bearings can run on quite satisfactorily with increased clearance.
The advantages of end-feed. lubrication include:
1) The entry of oil into the crankshaft interior not being opposed by the centrifugal force generated by the spinning crankshaft.
2) Making possible a much better proportioning of oil quantities between the main and crankpin bearings,
3) Permitting a reduction in the total oil flow because with the gallery system, excess oil must be given to the mains in order to ensure there is enough for the big-ends.
4) Allowing the deletion of holes and grooves in the main bearings thereby increasing their load carrying capacity.
5) Use of much lower oil pump pressures. In most engines, oil pressure is usually regarded as a vital indication of the health of the functioning engine - any fluctuation signals impending disaster. End feed engines can operate quite satisfactorily on just a few psi if necessary.
An illustration of the tight control of oil flow through the main and crankpin bearings is provided by the Rolls-Royce experience of changing the Merlin over to end-feed late in the WW II period. When the Merlin 60 was introduced (the first two speed, two stage, intercooled, and aftercooled version) they began to suffer main bearing failures, which was solved by the simple expedient of changing from the gallery supply system to end feed. An addition problem they found that on the test engines the pistons were in danger of seizing in the bores due to significantly reduced amounts of oil spray coming from the crankpins. They had to modify the design to deliberately make it more “leaky”.
Thus, it is entirely possible that the adoption of the end-feed type of lubrication system spared the Jumo 211 engines of the apparently insoluble oil control problems that plagued the DB 600 series for the whole of its production life.
The following is excerpted from a letter by Jerry Wells in "Torque Meter" Volume 2, Number 2 (Spring 2003) - magazine of the Aircraft Engine Historical Society. As can be adjudged from the article, little is known about German WWII aero engines, but this article is the "best guess" from experts in the field. A factual, definitive answer would seem still to await us ie original German documentation which as likely as not no longer exists being lost in the annuls of time and the massive destruction of WWII.
On a further point of interest regarding CRs, J.J. notes, quite correctly, the 8.3/9.5 figures that pertain to the left and right cylinder banks of the Daimler-Benz 603 when running on 100 octane fuel.
One of the great curiosities in aero-engine literature is that authors often meticulously list the differential CRs of the DB 603/605 V-12s, but never get round to explaining why the engine manufacturer deemed it necessary to do this! By any standards, it is an odd thing to do - I cannot think of any other piston engine that was supplied with the CR for some cylinders deliberately set lower than others.
Hunting through the literature, three theories materialize - perhaps an indication of how little we know about the German WWII aero-engines. The first suggests the differential CRs were due to articulated con-rods, the reasoning being that in a V-engine the pistons moved by the articulated rods would always travel slightly further in completing each stroke compared to their master-rod counterparts. All else being equal, this would produce a slightly higher CR on the link-side of the engine. However, this theory falls down very quickly on two counts:
1) It is a relatively simple matter to adjust the shape of a combustion chamber or piston top to compensate for the slightly longer stroke.
2) The DB 600 series V-12s were never fitted with anything but fork and blade con-rod pairs!
Theory two centers on the fact that the supercharger on the DB 600 V-12s as located on the left hand side of the engine and, thus, from such position would naturally provide mere “huff” to the cylinder bank nearest to it. In order not to (relatively) over-boost the left hand bank, the CR would have to be lowered slightly on that side.
In their book, Die deutsche Luftfahrt - Vol 2, (if you haven't got a copy of this in your library, you're missing a treat) ven Gersdorff & Grasmann write, regarding the DB 603, “Die Verdichtung der beiden Zylinderreihen war unterschiedlich, die linke hatte 7,3 din rechte 7,5, um die durch die unterschiedliche Lange der Ladeluftleitung – bedingt durch den einseitig angeordneten Lader- geringen Ladedruckunterschiede auszugleichen.” An exact translation of this reads, “The compression ratio of the two cylinder banks was different, the left had 7.3:1, the right had 7.5:1, in order to balance the small boost-pressure differences due to the differing lengths of the supercharger air delivery pipes resultant from the off-set arrangement of the supercharger.”
One hesitates to question the veracity of two such respected German authors (especially when they are writing about German Flugmoteren (aircraft engines)) but their explanation appears to be flawed. For one thing, even though the the DB supercharger was offset, the delivery pipe to the inlet manifolds actually has a gentler, less angular pathway down to the midpoint between the two cylinder banks than is the case with a cross mounted Allison/Merlin supercharger installation. If it discharges at or very near to the midpoint between the banks then only equal pressure will be fed to each side. Having reached the midpoint of the rear most cylinders, the DB induction pipe bifurcates to feed the two banks. However, the two branches do not end blindly at the forward-most cylinder but instead rejoin at this point so that the entire manifold is ring-shaped, making the likelihood of any one-sided pressure differences impossible.
The third possibility is that the lubrication system was at the heart of the matter. One of the disadvantages of an engine design which features inverted or downward pointing cylinders is that the cylinder and piston interiors form containers into which the oil flows and accumulates due to gravity. While this augers well for piston cooling and cylinder lubrication, the problem of oil moving past the pistons and into the combustion chambers in excess quantities crops up. Mixing oil with petrol (gasoline) rapidly causes a lowering of the octane rating of the fuel thus increasing the likelihood of detonation.
Tucked away in one of the very early editions of the R-RHT magazine, Archive is a reprint of, “Comments on a Visit to Germany - July 24th to August 12th, 1945.” Two paragraphs are of particular interest: “A good example of the (excessive) Air Ministry control lies in the inverted DB engine. The DB people said that both from a technical and production point of view they would have preferred to make an upright engine but they are compelled to make it inverted by the (German) Air Ministry.”
“With the inverted engine, they said it was very difficult to obtain consistent oil consumption and due to the rotation of the crankshaft one cylinder bank got more oil (spray) than the other. This oil got past the pistons into the combustion chambers and reduced the anti-knock value of the charge. For this reason the engine was built with a lower cylinder compression ratio on this (?) bank than on the other.”
In the light of this evidence, the third theory seems to be the most plausible. The situation was probably exacerbated by the use of roller bearings in the con-rod big ends. Assuming theory three is true, lowering the CR of one bank of cylinders does seem to be an extraordinary, almost desperate attempt to solve the problem. It also makes an absolute mockery of all the much vaunted, supposed advantages of fitting these engines with precision made, high pressure fuel injection systems. If six of the twelve cylinders per engine were suffering from chronic, unpreventable oil contamination then accurate fuel metering would count for very little. As it was, the DB601 had enough combustion problems due to poor fuel burning resultant from the location of both spark plugs per cylinder on the same (exhaust) side. This undesirable feature alone was responsible for a power loss of seven to eight percent.
From all of this, two other questions beg consideration.
1) Why did predecessors to the DB603/605, i.e. the DB600/601 not also have differential cylinder bank CRs?
2) Did the oil consumption problem affect the well known, close contemporary to the DB 600-series V-12s, vis a vis the Junkers Jumo 211?
In answer to Question 1, it is most likely that the left bank oil burning problem was with the 601 model from the beginning of its production and that the first opportunity to do something about it came with the introduction of the 605/603 types. Even so, as mentioned above, DB's answer to the difficulty was crude to say the least.
With regard to Question 2, it becomes obvious from just a brief comparison of the Jumo 211 and the DB 600 series that apart from being inverted, having a cannon tunnel and featuring an off-set supercharger, the design features of the two makes of engine were very different.
Nowhere is this more apparent than in the respective lubrication systems. The DB had a conventional gallery-type arrangement where, from a central feed-pipe branch lines admitted oil to each main bearing block, thence the oil was forced through holes and grooves into each bearing shell and then into the crankshaft interior via more holes and grooves in the crankshaft main bearing journals. From there, 3/8” pipes took the oil to the hollow crankpin for distribution to the big-end bearings, both roller and plain.
The Junkers' engineers on the other hand, perhaps anticipated possible oil control problems due to the compulsory inverted installation requirement, designed the Jumo 211 with an end-feed system where the oil was fed into the front end of the crankshaft and from this single entry point it was moved along the length of the crankshaft to be fed by centrifugal force to the main and big end bearings. Compared to the gallery-type, the end-feed system is vastly superior because, with the former, as bearing wear takes place there is an increased leakage of oil from the mains journals resulting in less supply to the big-ends. As oil has to be forced into the crankshaft against centrifugal pressure, it gives a reduction in lubrication to the big-ends with increasing crankshaft rotational speed. The limit of life of bearings is the time when the main journal clearances have increased to the extent that the big-ends get insufficient oil, even though the main journal bearings can run on quite satisfactorily with increased clearance.
The advantages of end-feed. lubrication include:
1) The entry of oil into the crankshaft interior not being opposed by the centrifugal force generated by the spinning crankshaft.
2) Making possible a much better proportioning of oil quantities between the main and crankpin bearings,
3) Permitting a reduction in the total oil flow because with the gallery system, excess oil must be given to the mains in order to ensure there is enough for the big-ends.
4) Allowing the deletion of holes and grooves in the main bearings thereby increasing their load carrying capacity.
5) Use of much lower oil pump pressures. In most engines, oil pressure is usually regarded as a vital indication of the health of the functioning engine - any fluctuation signals impending disaster. End feed engines can operate quite satisfactorily on just a few psi if necessary.
An illustration of the tight control of oil flow through the main and crankpin bearings is provided by the Rolls-Royce experience of changing the Merlin over to end-feed late in the WW II period. When the Merlin 60 was introduced (the first two speed, two stage, intercooled, and aftercooled version) they began to suffer main bearing failures, which was solved by the simple expedient of changing from the gallery supply system to end feed. An addition problem they found that on the test engines the pistons were in danger of seizing in the bores due to significantly reduced amounts of oil spray coming from the crankpins. They had to modify the design to deliberately make it more “leaky”.
Thus, it is entirely possible that the adoption of the end-feed type of lubrication system spared the Jumo 211 engines of the apparently insoluble oil control problems that plagued the DB 600 series for the whole of its production life.
