Aircraft lubrication system helps in reducing the friction between moving parts of the engine by reducing metal-to-metal contact.
Main functions of lubrication system are –
- Reduces friction.
- It provides cushion between metal parts.
- Provides cooling.
- Provides protection against corrosion.
Types of Lubrication Oil
- Straight Mineral Oil – This type of oil oxidises when subjected to elevated temperature. It needs specification MIL-L-608B.
- Metallic Ash Detergent Oil – This type of oil is good nut its cleaning action loosens Carbon deposit and may clog tthe oil passage.
- Synthetic Oil – Due to its high operating temperature., this type of oil is mostly used. However, it has softening effects on rubber parts.
The two types of aircraft lubrication system are explained below.
Types of Aircraft Lubrication System
- Wet Sump Lubrication System
In this type of lubrication system, the entire oil supply is within the engine. Wet sump lubrication system consists of piston ring, gear, lubricating oil sump, bypass valve, piston, crankshaft and connecting rod.
Piston rings are in touch with cylinder and they get worn out as the piston operates in the cylinder. Filter filters out the impurities of the lubricating oil which is sent through gear type pump. Since the oil is under pressure, bypass valve opensand thus the oil goes to crankshaft and drips down where various parts are present and then it is collected in the sump.
The sump passes sufficient quantity of oil at the inlet of gear type oil pump. From the pump exit, oil is directed to the filter. In case, the filter is blocked, the bypass valve opens and permits the oil to flow directly from the pump to the filter outlet. The oil flows through the drill passage to the front of the engine for lubricating crankshaft, camshaft, connecting rods, various bearings, cylinder walls, pistons and piston rings.
After lubricating various parts of engine, the oil drains back into the sump and the cycle is repeated.
Disadvantage of this lubrication system is that oil supply is limited by some capacity and the oil temperature is high.
- Dry Sump Lubrication System
In this type of lubrication system, only small amount of oil is within the engine while most of it is in the external tank. Dry sump lubrication system consists of an external oil tank, oil pump, cylinder block (sump), scavenging pump, filter and bypass valve.
Oil pump draws the oil from the external tank and then circulates prssurised oil to various parts of the engine. Then, this oil is collected in the sump by the force of gravity and then it is removed by the scavenging pump.
A filter with bypass valve is placed between scavenging pump and external tank. If the main filter is blocked, the bypass valve allows the oil to flow. After passing through the filter, the oil returns to the external tank. From the external tank, oil is recirculated to various parts of the engine.
In this lubrication system, a seperate oil cooler is usually provided so as to remove the heat from the oil.