I was asked this question and it has got me wondering. An inverted mounted aircraft engine must still have oil running down the cylinder walls and a little must get past the oil rings as it does in the bottom cylinders if a radial engine. I understand about ‘dry sump’ systems as used in all high performance engines but when the ‘sump’ is the piston skirts do they fill up and fling the oil back up or does the oil system recover it? I was looking at a cutaway drawing of a DH Gypsy engine and could see the oil drain pipes at the bottom of the engine.
I hope there is an engineer who can explain it easily for my old brain!
mmitch.
By: mmitch - 13th September 2010 at 13:49
Thanks again for replies.
mmitch.
By: low'n'slow - 13th September 2010 at 13:16
While more sophisticated inverted engines use a scavenge pump to return oil to the tank, some such as earlier Gipsy Majors and Walter Mikrons don’t bother with such complexity
The oil is pumped up to the crankcase by the pressure pump, then after being flung around the engine by the movement of crankshaft and pistons, is collected in galleries on the lower part of the crankcase. After that, good old gravity does the rest, draining the oil back to the tank via external oil pipes.
By: mmitch - 13th September 2010 at 06:34
Thanks for that Truculent AME. I think that explains what I suspected. it must have quite a nightmare designing the oil system with all the changing G forces involved!
Thanks again. mmitch
By: Truculent AME - 13th September 2010 at 03:18
mmitch
Hope this helps a bit???
When the engine is running the oil pressure system is supplying oil flow to the rod bearings and the movement of the pistons inside the crankcase will fling oil all over – this oil is collected by the crankcase sump and a scavenge pump driven by the engine will then return the oil to the tank – same way as the valve train in rocker boxes are scavenged.
On shutdown – some engines requires a short higher rpm just before shutting off the engine to ensure those sumps are in fact scavenged as completely as possible.
After shutdown – the residual oil will drain down to the lowest points – which will include the piston skirt area. Depending on the thickness of the oil – the temperature – and the condition of the rings to cylinder sealing the oil may seep past the rings into the combustion chamber. Thus the requirement to ensure no hydraulic lock before starting the engine again. Some engines are good at sealing others are not so good – thus the joke about “If a radial engine is not dripping oil – there is none left in it!!!”
On starting the oil will be flung all around again by the motion of the piston and crank parts and once again will be scavenged back to the tank.
Is this what you are looking for??
Regards,
Truc
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September 12, 2010 at 3:36 pm