Answers - Powerplant Lubrication Systems


1. c
The viscosity, or the resistance of oil to flow, changes with temperature. For example, as the temperature drops, highly viscous oils become extremely thick and do not circulate. Therefore, low viscosity oils are typically recommended for use in reciprocating engines operating in cold climates. However, if a low viscosity oil is used when an engine is operated in extremely high temperatures, the oil can become so thin that a lower than normal oil pressure can result.

2. c
Because of the unique operating requirements, synthetic oils are typically used in gas turbine engines. Furthermore, because of the differences between turbine and reciprocating engine oils, they should not be mixed or used interchangeably.

3. b
A wet-type engine-driven vacuum pump uses an air-oil separator to separate the oil that mixes with the air that passes through the pump. The separator is installed in the pump's discharge line where it removes oil from the air and returns it to the engine sump.

4. c
The viscosity of commercial aviation oils is measured by a testing instrument called a Saybolt Universal Viscosimeter. This instrument consists of a tube that holds a specific oil quantity at an exact temperature and a calibrated orifice. The time in seconds required for exactly 60 cubic centimeters of oil to flow through the orifice is recorded as the oil's viscosity.

5. b
Viscosity index is a measure of the change in an oil's viscosity for a given change in temperature. The smaller the change in viscosity for a given temperature change, the higher the viscosity index.


6. a
Viscosity index is a measure of the change in an oil's viscosity for a given change in temperature. The smaller the change in viscosity for a given temperature change, the higher the viscosity index. In other words, a high viscosity index indicates that an oil's viscosity does not change very much with changes in temperature.

7. c
Synthetic turbine engine oil has two principle advantages over petroleum oil. It has less tendency to deposit lacquer and coke, and is less likely to evaporate at high temperatures.

8. c
Reciprocating engines require large engine operating clearances because of the relatively large size of the moving parts and high operating temperatures. Therefore, the oil used in reciprocating engines must have relatively high viscosity in order to maintain an adequate film between moving parts.

9. a
The oil selected for aircraft engine lubrication must be thin enough to circulate freely, yet heavy enough to provide the proper film strength at operating temperatures.

10. b
In addition to reducing friction, one of the primary functions of oil is to circulate through the engine and absorb heat to aid in engine cooling. In addition, engine oil also helps to form a seal between the piston rings and cylinder walls, clean the engine interior by carrying foreign particles to the filter, coat engine parts to prevent corrosion, and act as a cushion between the metal parts during the combustion process. This cushioning effect is particularly important for such parts as crankshafts and connecting rods.

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