Inverted V engine vs. V engine
- Thread starter B-17engineer
- Start date
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Mustang nut
Banned
- 200
- Jun 14, 2011
DonL's data sources.....
updated graphs:
They begin to tell a story....
If I read the graph correctly it is weight to power so the most powerful enine for a given weight is the lower number, or am I wrong?
The graph does not make sense to me. Merlin 61 for example - late in 1940 engine? DB 605A - late 1941 engine? Latter seems correct for first protypes.. but in practice, service of these engines - both summer 1942...
Rest similiar. I think it correct for when single engine run for 15 minutes at power before falling pieces. Service type, different. Merlin 66, 2000 HP in mid-1942.. in practice, no Merlin 66 in service before 1943.. and type with 2000 HP... no before 1945.
Also dry weights - net weights. Interesting for labor.. but in practice, brutto weights are interesting - all inclusive. Propeller weight. Radiator weight. Booster weight. Kompressor weight. Fuel weight. Coolant weight, oil weight. This is engine in practice, in plane. Try fly with engine in plane with no propeller, no radiator.. and no coolant or oil in it! this is net dry weight. For this reason, I find graph stupid. It suggest: Merlin or DB can run 2000 HP without even oil or cooling.. yes.. couple of seconds.
So believe we are mixing data. Also enlightening for internal development progress, but fighter pilot do not care how well scientist do in labor. He cares about engine in his plane, running.
If you want comparison, you need to take a look how much complete powerplant weight with all above in plane. Does anyone know for example complete powerplant weight in Spitfire, Messerschmitt, Mustang, Mosquito etc? Propeller, engine, radiators, pipes, kompressor etc.
Rest similiar. I think it correct for when single engine run for 15 minutes at power before falling pieces. Service type, different. Merlin 66, 2000 HP in mid-1942.. in practice, no Merlin 66 in service before 1943.. and type with 2000 HP... no before 1945.
Also dry weights - net weights. Interesting for labor.. but in practice, brutto weights are interesting - all inclusive. Propeller weight. Radiator weight. Booster weight. Kompressor weight. Fuel weight. Coolant weight, oil weight. This is engine in practice, in plane. Try fly with engine in plane with no propeller, no radiator.. and no coolant or oil in it! this is net dry weight. For this reason, I find graph stupid. It suggest: Merlin or DB can run 2000 HP without even oil or cooling.. yes.. couple of seconds.
So believe we are mixing data. Also enlightening for internal development progress, but fighter pilot do not care how well scientist do in labor. He cares about engine in his plane, running.
If you want comparison, you need to take a look how much complete powerplant weight with all above in plane. Does anyone know for example complete powerplant weight in Spitfire, Messerschmitt, Mustang, Mosquito etc? Propeller, engine, radiators, pipes, kompressor etc.
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Tartle
Airman
Tante ju... I agree it is installed condition that counts... also the Rolls-Royce figures are mainly from type tests, so are valid; the DB figures I am not sure of, but as we are discussing how /\ and \/ engines compare I would say they are a valid comparison... if you can supply installed weights etc we could replot. My take from the graphs is that the major challenge on the development teams was external to the engines themselves- politics, disruption of access to materials, fuels, etc.- It may be that the /\ was marginally more challenging but the other factors were vital too. I suggest someone more knowledgeable than me on the aircraft perhaps plots the total aircraft weight vs power available to see if that yields a story.
As to the pilot... RR had a man at each base to get clear feedback on service issues which were fed into the service response and also the developemnt process... it was pilot feedback about FW190s that sparked the Merlin 60 series being fitted into a modified Spitfire V at Hucknall to create the IX which was then rushed into production. In Egypt it was feedback direct to RR that about the superiority of the FW190 over the Spitfire V... IXs were not yet allocated to Middle East... especially at 6,000ft so a communication back to Derby confirmed the way to get boost at 6,000 ft was to turn 3/4" off diameter of supercharger impeller... this was done in the local workshop and with 18 lbs boost speed went up 22 mph.
A THOUGHT: as we are talking \/ or /\ in this thread should we start one on 'pilots and developers -how they interacted'
As to the pilot... RR had a man at each base to get clear feedback on service issues which were fed into the service response and also the developemnt process... it was pilot feedback about FW190s that sparked the Merlin 60 series being fitted into a modified Spitfire V at Hucknall to create the IX which was then rushed into production. In Egypt it was feedback direct to RR that about the superiority of the FW190 over the Spitfire V... IXs were not yet allocated to Middle East... especially at 6,000ft so a communication back to Derby confirmed the way to get boost at 6,000 ft was to turn 3/4" off diameter of supercharger impeller... this was done in the local workshop and with 18 lbs boost speed went up 22 mph.
A THOUGHT: as we are talking \/ or /\ in this thread should we start one on 'pilots and developers -how they interacted'
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Tartle
Airman
Mustang nut... you are correct the lower the better! less weight or more power achieves this. I know that working with car companies as subcontractors in the shadow factory scheme enabled RR developers to pool expertise with car experts ... I think it was Morris and RR Hucknall that halved the weight of the radiators during the course of the war. So it was working on top and bottom of the equation that enabled the aircraft's performance.
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Tartle
Airman
Tante ju ...
some dates for 60 series
The Merlin 60 intended as insurance powerplant for high altitude Wellington ran early in 1941...
Realised it would work well in Spitfire to combat lack of high altitude performance of the mk V vs FW190, so Merlin 61 built and installed in a V... worked well so Merlin 61 ordered. After type testing and approval in autumn of 1941 manufacture started and the first production engine was ready for despatch on Christmas day 1941. deliveries of Spitfire IX began June 1942 and were operational with 42 Squadron in July, 1942.
The tactics of FW 190 pilots changed as they realised that whilst they were matched at high altitudes they could come down to around 18000ft and maintain superiority. So thw Merlin 66 was born and type tested prior to production in late 42. Production stared early 1943. Hope this gives some background to the points on the graphs.
some dates for 60 series
The Merlin 60 intended as insurance powerplant for high altitude Wellington ran early in 1941...
Realised it would work well in Spitfire to combat lack of high altitude performance of the mk V vs FW190, so Merlin 61 built and installed in a V... worked well so Merlin 61 ordered. After type testing and approval in autumn of 1941 manufacture started and the first production engine was ready for despatch on Christmas day 1941. deliveries of Spitfire IX began June 1942 and were operational with 42 Squadron in July, 1942.
The tactics of FW 190 pilots changed as they realised that whilst they were matched at high altitudes they could come down to around 18000ft and maintain superiority. So thw Merlin 66 was born and type tested prior to production in late 42. Production stared early 1943. Hope this gives some background to the points on the graphs.
Shortround6
Major General
Dry weights are what they are because accessories could change. Yes you need a starter but the type of starter can can change and therefore the installed weight. The generator can change, a plane with electric flaps and landing gear and such (or larger more powerful radios) needing a bigger generator. A bomber may need a bigger diameter propeller than a fighter.
Including such weights tells us little about the progress of engine development even though such weights tell us a lot about why certain engines were or were not used in certain applications.
Compressors (except turbos) were always included in the dry weight of the engine.
Including such weights tells us little about the progress of engine development even though such weights tell us a lot about why certain engines were or were not used in certain applications.
Compressors (except turbos) were always included in the dry weight of the engine.
Readie
Chief Master Sergeant
Hello SR6,
I have read all the threads and am still confused whether inversion brought any significant advantage over the traditional upright configuration.
Did it?
or, was it a solution that some maunfacturers sought to provide space for weapons?
Be glad of your opinions
Cheers
John
Shortround6
Major General
I don't believe it brought any significant advantage over an upright engine except perhaps in view and that depends in large part on were the cockpit is positioned in relation to the engine. What was intended vs what was achieved may not be the same thing.
BUT I also don't believe the inverted engines suffered any particular disadvantage compared to an upright engine.
Once a designer or company starts down a particular course they are often stuck with it. Flipping one of these engines over changes a lot of things. While either type can run inverted or negative "G" for a number of seconds or even a few minutes they are not designed to do it for minutes or hours on end. While changing oil pick up points can be done some parts were designed to supplied with oil by splash or run-off from another part. certain parts were cooled by oil flow as much as by the water/glycol system. A lot of testing would have to be done to make sure that such parts were still getting proper oil flow for hours on end if the engine was flipped.
Same with the coolant flow. The engineers spent a lot time figuring how much coolant was needed at what temperature in certain parts of the engine. The coolant might flow over(past) a number of different areas and if went past the hottest parts first it might not actually be able to cool some of the lower heat areas properly. Simply reversing the flow may not do the trick. Or larger passages might be needed meaning new casting patterns.
BUT I also don't believe the inverted engines suffered any particular disadvantage compared to an upright engine.
Once a designer or company starts down a particular course they are often stuck with it. Flipping one of these engines over changes a lot of things. While either type can run inverted or negative "G" for a number of seconds or even a few minutes they are not designed to do it for minutes or hours on end. While changing oil pick up points can be done some parts were designed to supplied with oil by splash or run-off from another part. certain parts were cooled by oil flow as much as by the water/glycol system. A lot of testing would have to be done to make sure that such parts were still getting proper oil flow for hours on end if the engine was flipped.
Same with the coolant flow. The engineers spent a lot time figuring how much coolant was needed at what temperature in certain parts of the engine. The coolant might flow over(past) a number of different areas and if went past the hottest parts first it might not actually be able to cool some of the lower heat areas properly. Simply reversing the flow may not do the trick. Or larger passages might be needed meaning new casting patterns.
One advantage I can see in a inverted V engine is the parts needing the most maintenance in high performance engines, the spark plugs and valvetrain, can be accessed from the ground or a low plantform. May not seem very important to us sitting at computers, but there is a big difference in changing spark plugs or valve springs from the ground with a inverted V, than having to climb up and down a ladder to do the same job on a upright V.
Readie
Chief Master Sergeant
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Readie
Chief Master Sergeant
Mustang nut
Banned
- 200
- Jun 14, 2011
Did g forces affect engine wear?
If a plane pulls say, 9G presumably that means the piston in effect gets 9 times heavier. Did high g affect engine wear or breakages. In a radial enine did the top cylinders big and little ends wear more than the side or bottom? for an inverted engine the weight is pulling on the con rods rather than pushing so is that an advantage?
I assume most planes pull the highest g in the positive.
If a plane pulls say, 9G presumably that means the piston in effect gets 9 times heavier. Did high g affect engine wear or breakages. In a radial enine did the top cylinders big and little ends wear more than the side or bottom? for an inverted engine the weight is pulling on the con rods rather than pushing so is that an advantage?
I assume most planes pull the highest g in the positive.
At any given second in any engine, inverted or upright, some pistons are going up, they would be resisted by gravity or G's. Some pistons are going down, they would be assisted by gravity or G's. That wouldn't change, it would just be different pistons and connecting rods.
Mustang nut
Banned
- 200
- Jun 14, 2011
Tyrodtom I agree as far as the power output. I was asking about the total load on the bearings and surfaces. In a vertical engine the force of combustion pushes down and High g would add to that force on the little and big end. In an inverted engine the force of combustion is up while the effect of high g is still down so they are subtracted. In a rotary engine the cylinders which are horizontal the effect of high g would press the piston into one side of the cylinder.
or wouldnt it
Shortround6
Major General
Considering the thrashing around pistons are doing I doubt that the orientation of the engine has much effect on them. I mean an engine with a 6 in stroke and turning even 2400rpm has pistons moving at 2400 fpm. or 40 ft/sec except that they are starting and stopping 40 times a second and hitting peak speeds of 80ft a second or so in about 3 in of travel. or zero to 54mph in 3 in and back to zero in another 3 in. Average (not peak) acceleration seems (if I have done the math right???) to be about 10Gs with an average of 10G deceleration 40 times a second. Every other revolution includes hundreds of pounds of pressure per square inch on the pistons surface.
Tartle
Airman
I have been emailing Jerry Wells, who wrote an Torquemeter article on ramp head Merlins and their problems and was drawn towards this post by Brian Abraham on work about the DBs done by Jerry which I reproduce here:
"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."
To be continued....(too long for one post)
"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."
To be continued....(too long for one post)
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Tartle
Airman
continued........
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. 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."
This is a challenging series of thoughts on the /\ in general and Db 600 series in particular.
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. 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."
This is a challenging series of thoughts on the /\ in general and Db 600 series in particular.
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Lighthunmust
Banned
Bravo! Magnificent post Tartle.
johnbr
2nd Lieutenant
+1
