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Why do gas turbine engines use a synthetic oil?
It is better suited for high temperatures.
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Why are liquid lubricants the best type for use in gas turbine engines?
They effectively dissipate heat
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What is the designation of the most common synthetic oil used by the military?
MIL-L-23699
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What are the advantages of a synthetic oil over a petroleum base oil?
- (1) Stability at high temperatures
- (2) less coke/lacquer deposits.
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Are synthetic base and petroleum base oils compatible with each other?
No, cuases a sticky mass when mixed and poor lubricating qualities.
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List the various types of oil contamination. What is the most common type of contamination?
Metallic particles, carbon, sand, fuel, over age synthetic oil.
Metallic particles from engine wear.
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How does the shelf life of synthetic oil compare to that of petroleum oil?
Six months vs indefinite
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What is the purpose of a lubrication system?
To provide an adequate supply of clean oil to bearings and gears at the proper temperature and pressure.
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Define viscosity.
Resistance to flow
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What is the relationship between temperature and viscosity?
Temperature increases, viscosity decreases, and vice versa.
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What is the difference between a wet and dry sump system?
- Wet sump-oil stored internally
- Dry sump- external oil tank
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What does an oil reservoir contain to ensure a constant oil supply during all flight attitudes and G loads?
a weighted swivel outlet assembly
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What are the two functions of pumps used in the lubrication system?
to supply oil under pressure and scavenge oil
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What is the main advantage of a dry sump system?
the temperature/viscosity can be better regulated.
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What does oil pressure system use a relief valve for?
To vent off excess fluid pressure.
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Where is oil pressure monitored? Why?
After the oil pump. It can indicate a pump malfunction.
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What does the filter bypass valve do?
Ensures continuous oil supply to the engine in the event the filter becomes clogged.
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What are the two types of oil coolers?
Fuel-oil heat exchanger and air-oil cooler
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What is the fuel-oil heat exchanger designed to do?
Heat the fuel and cool the oil
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Does fuel always go through the fuel-oil heat exchanger?
Yes, if the aircraft is designed with that component.
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Does oil always go through the fuel-oil heat exchanger?
No
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Does airflow always go through the air-oil cooler?
No
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What are the three subsystems of the engine lubrication system?
Pressure, Scavenge, and Breather Pressurizing
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What does the pressure subsystem do?
Supplies oil under pressur to the engine main bearings and accessory drive gear.
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What does the scavenge subsystem do?
Returns oil to the tank from the bearings and accessory section. Provides cooling for the oil.
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Where is the oil temperature regulator valve located and what does it do?
1. At the entrance of the fuel-oil heat exchanger. 2. Thermostatically operated to direct flow of oil either through or past the heat exchanger.
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Where is oil temperature monitored?
Prior to netering the engine bearing compartments.
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Where is the fuel temperature sensing switch located and what does it do?
On the fuel exit of the fuel-oil cooler. It controls the operation of the air-oil cooler doors.
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What is the funtion of the breather pressurizing subsystem?
Ensures sea level pressure is maintained in the oil tank and scavenge subsystem to prevent oil leaks.
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