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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 could be full of it though!
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.I'm pretty sure oil consumption was an issue with most all of these large displacement aircraft engines, some probably worse than others.
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.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.
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.
Yup, .30 cal peashooters, no big stuff. When they went to .50s, things got awfully tight. Cannons not an option.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.
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.Yup, .30 cal peashooters, no big stuff. When they went to .50s, things got awfully tight. Cannons not an option.
Cheers,
Wes
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