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Why do gas turbine engines use a synthetic oil?
It is better suited for high temperatures.
Why are liquid lubricants the best type for use in gas turbine engines?
They effectively dissipate heat
What is the designation of the most common synthetic oil used by the military?
What are the advantages of a synthetic oil over a petroleum base oil?
(1) Stability at high temperatures
(2) less coke/lacquer deposits.
Are synthetic base and petroleum base oils compatible with each other?
No, cuases a sticky mass when mixed and poor lubricating qualities.
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.
How does the shelf life of synthetic oil compare to that of petroleum oil?
Six months vs indefinite
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.
Resistance to flow
What is the relationship between temperature and viscosity?
Temperature increases, viscosity decreases, and vice versa.
What is the difference between a wet and dry sump system?
Wet sump-oil stored internally
Dry sump- external oil tank
What does an oil reservoir contain to ensure a constant oil supply during all flight attitudes and G loads?
a weighted swivel outlet assembly
What are the two functions of pumps used in the lubrication system?
to supply oil under pressure and scavenge oil
What is the main advantage of a dry sump system?
the temperature/viscosity can be better regulated.
What does oil pressure system use a relief valve for?
To vent off excess fluid pressure.
Where is oil pressure monitored? Why?
After the oil pump. It can indicate a pump malfunction.
What does the filter bypass valve do?
Ensures continuous oil supply to the engine in the event the filter becomes clogged.
What are the two types of oil coolers?
Fuel-oil heat exchanger and air-oil cooler
What is the fuel-oil heat exchanger designed to do?
Heat the fuel and cool the oil
Does fuel always go through the fuel-oil heat exchanger?
Yes, if the aircraft is designed with that component.
Does oil always go through the fuel-oil heat exchanger?
Does airflow always go through the air-oil cooler?
What are the three subsystems of the engine lubrication system?
Pressure, Scavenge, and Breather Pressurizing
What does the pressure subsystem do?
Supplies oil under pressur to the engine main bearings and accessory drive gear.
What does the scavenge subsystem do?
Returns oil to the tank from the bearings and accessory section. Provides cooling for the oil.
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.
Where is oil temperature monitored?
Prior to netering the engine bearing compartments.
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.
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.
Book Questions Chapter 9