Daimler-Benz DB 605 Oil System...I Don't Understand

[Djarum41]

Hello forum members....
Regarding the DB605 engine, I don't understand why many quarts of oil aren't pulled by gravity past the crankshaft & into the cylinder bores & into the undersides of the pistons? Obviously this doesn't happen...clearly the engine design is successful as the engine runs....I just don't understand the oiling system & can't figure out the inverted design oiling. Thanks

 

[Crimea_River]

There's a good diagram of the lubrication system here but it's in Italian: http://www.museomotori.unipa.it/posters/26.jpg



Oil is pumped under pressure to the crankcase and runs by gravity down a path between the cylinders into the camshaft covers where there are camshaft driven pumps to return out to the header tank. I'm not certain of this but, in regard to 0the colleciton of oil in the cylinder bores, I would suggest that it probably does but that, when the engine is running, the oil is constantly being splashed back up into the crank case to eventually run down to the camshaft covers.

 

[Crimea_River]

I could not edit the above post to insert a clip so here is the diagram I was referring to:

 

[Djarum41]

Thanks a lot...that helps explain why & it makes sense now. I knew it must've worked, the planes actually flew, just couldn't get my head around the upside down V with oil everywhere. Guess those oil control rings did a good job. That's a great diagram of the 605 oiling system, I couldn't find anything like that myself when I searched. There's something sorta cool about a canon in the middle of your engine

 

[stona]

The inverted engine did pose problems with oil supply and consumption. The British sent a team to Germany immediately after WW2 to investigate the German engines and speak to German engineers. The British team comprised men from the Ministry of Aircrat Production and all the British aero engine manufacturers (including Armstrong Siddeley Motors, Bristol Aero Co., D. Napier & Son and of course Rolls Royce). They produced a report, 'Comments on Visit to Germany, July 24th 1945 to August 12th 1945'. In it they recorded that Daimler Benz engineers would have preferred an upright 'V', but the inverted layout was a requirement of the RLM (actually it predated the RLM, back to 1928).
They made the point that it was very difficult to get even oil consumption as the rotation of the crankshaft caused one bank to get more oil than the other. It's why the compression ratio is lower on one bank than the other.
Cheers
Steve
Edit: Quote from report:
"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."

 

[Old Wizard]

Interesting!

 

[MiTasol]

The same issue technically applies to many radial cylinders but the speed the pistons move ensures that the vast majority of the oil gets thrown up and finding its way into the sumps while the engine is running.

Once the engine stops naturally relatively large amounts of oil accumulate in the down facing cylinders on radials so it is essential that the engine is pulled through before starting to ensure there are no cylinders with a hydraulic lock.

I presume this also applied to the inverted V engines but have never seen it written anywhere (and my German is ultra basic so German manuals can not help me)

 

[Guv]

Funny but not surprising that this style of engine has basically disappeared since the end of WW2. It's main advantage had to be cowl gun placement, no Spitfires of Hurricanes with cowl guns. I'm pretty sure that when the engine was running any oil collecting on the back side of the piston would get slung back towards the crankshaft. It was still a very well engineered aircraft engine that was very good for it's intended purpose. Also, I'm pretty sure oil consumption was an issue with most all of these large displacement aircraft engines, some probably worse than others.

 

[stona]

Wolfram Eisenlohr, who was on the original committee, when interviewed long after the events, gave three reasons for the 1928 preference for of an inverted vee.
1. More compact installation
2. Better pilot view for single engine aircraft.
3. Less exhaust dazzle during night flying

The requirement for a 'cannon tunnel' in the vee was part of the resulting specification, with other specifications like mono-block cylinder banks, wet cylinder liners, propeller reduction gear, supercharger, fuel injection, and high temperature glycol cooling. None of the designs submitted by Daimler-Benz, Junkers and B.M.W. met all the specifications, the BMW 116 never got beyond the prototype stage.

Cheers

Steve

 

[mad_max]

They made the point that it was very difficult to get even oil consumption as the rotation of the crankshaft caused one bank to get more oil than the other. It's why the compression ratio is lower on one bank than the other.

That maybe true about the oil,but from my studies of the DB600 series engines the reason for the difference in compression ratios is from the different length of the intake runners to the left and right banks of cylinders from the supercharger.

I also investigated the problem with oil foaming in the 601, which can very well be from the way oil was moved around from the crank, pistons, and valve train with the oil exiting from the valve covers. Hence the development of a new oil defoaming unit.

I could be full of it though!

 

[stona]

That maybe true about the oil,but from my studies of the DB600 series engines the reason for the difference in compression ratios is from the different length of the intake runners to the left and right banks of cylinders from the supercharger.

I could be full of it though!

That may have been a factor for all I know. I'm only posting what the Germans told the British party, as in their report, when questioned about the inverted arrangement. I can't imagine that the German engineers had any reason to be secretive or to lie, the war had been lost.
Cheers
Steve

 

[XBe02Drvr]

I'm pretty sure oil consumption was an issue with most all of these large displacement aircraft engines, some probably worse than others.

Big difference! Air cooled engines (such as radials) must operate at a wide range of cylinder temperatures, thus requiring looser tolerances in pistons and rings, which increases oil consumption significantly. Liquid cooled engines, on the other hand are able to keep their cylinder temperatures pretty constant, allowing tighter tolerances, more efficiency, and reduced oil consumption.
Cheers,
Wes

 

[Shortround6]

Going by Wilkinson's "Aircraft Engines of the World" there doesn't seem to be any rhyme or reason for the different oil consumptions listed. They range from about 0.009lb/hp/hr (at cruise) to over 0.025lb/hp/hr with both aircooled engines and liquid cooled engines being on both ends of the range.
Granted these are advertised figures and real consumption may vary as will the consumption at different power levels.
A few companies claim the exact same oil consumption for ALL models of engines while other companies show a wide variation even though the engines may use the same cooling system.

 

[XBe02Drvr]

Going by Wilkinson's "Aircraft Engines of the World" there doesn't seem to be any rhyme or reason for the different oil consumptions listed. They range from about 0.009lb/hp/hr (at cruise) to over 0.025lb/hp/hr with both aircooled engines and liquid cooled engines being on both ends of the range.
Granted these are advertised figures and real consumption may vary as will the consumption at different power levels.
A few companies claim the exact same oil consumption for ALL models of engines while other companies show a wide variation even though the engines may use the same cooling system.

In WWII days, almost no engine manufacturers built both air cooled and liquid cooled engines, and every manufacturer had their own standards for estimating and advertising such things as service life and oil consumption. Air cooled builders in particular tended to be a bit optimistic on oil consumption.
My engines instructor at A&P school had been a mechanic with the 8th AF in War II, and he said the heavies were flying longer missions than the engine designers ever envisioned, and the engine oil tanks weren't big enough for the consumption they were experiencing. The planes had auxiliary oil tanks installed in the fuselage/wing center section with distribution pumps to top off the engine oil tanks.
I actually got to change out a failed distribution pump on Collings Foundation's B-24 when it visited our local airport. (I still have the oil-strained shirt, with "Genuine Liberator Blood" scrawled on it in Magic Marker!)
Cheers,
Wes

 

[wuzak]

Funny but not surprising that this style of engine has basically disappeared since the end of WW2. It's main advantage had to be cowl gun placement, no Spitfires of Hurricanes with cowl guns. I'm pretty sure that when the engine was running any oil collecting on the back side of the piston would get slung back towards the crankshaft. It was still a very well engineered aircraft engine that was very good for it's intended purpose. Also, I'm pretty sure oil consumption was an issue with most all of these large displacement aircraft engines, some probably worse than others.

The P-40 had an upright V-12 and had cowl guns.

The A-36 (and P-51/P-51A?) had synchronised guns in the lower engine cowling.

 

[XBe02Drvr]

The P-40 had an upright V-12 and had cowl guns.
The A-36 (and P-51/P-51A?) had synchronised guns in the lower engine cowling.

Yup, .30 cal peashooters, no big stuff. When they went to .50s, things got awfully tight. Cannons not an option.
Cheers,
Wes

 

[stona]

The requirement for the inverted V12 wasn't for cowl guns, it was for a 'cannon tunnel' allowing a weapon to fire through the spinner, something the Germans finally, more or less, perfected with the Bf 109 F in 1940. The two are entirely different installations. Given that the specification was issued in 1928/29 and that the first engines built vaguely to the requirements were produced in the early 1930s, it took a while.
Cheers
Steve

 

[Shortround6]

Yup, .30 cal peashooters, no big stuff. When they went to .50s, things got awfully tight. Cannons not an option.
Cheers,
Wes

The cowl guns on the P-40 and Allison P-51/A-36 were .50 cal, not .30s and the .50 Browning was a big gun, at least compared to most other 12.7-13mm machineguns.

 

[XBe02Drvr]

I stand corrected. I thought they were originally designed for .30s, but upgraded to .50s.
Cheers,
Wes

 

[wuzak]

The requirement for the inverted V12 wasn't for cowl guns, it was for a 'cannon tunnel' allowing a weapon to fire through the spinner, something the Germans finally, more or less, perfected with the Bf 109 F in 1940. The two are entirely different installations. Given that the specification was issued in 1928/29 and that the first engines built vaguely to the requirements were produced in the early 1930s, it took a while.
Cheers
Steve

I would even dispute that, since the system would have worked if the engine was inverted or upright.

The main differences between the DBs and the Merlin and V-1710 were the placement (and size) of the supercharger and the intake manifolding.

These are what make the hub gun possible, not the inverted layout.

I would have though the inverted V was in order to gain better view for the pilot, especially downwards at the front.