Chapter 3 - Engine Systems

Question 1

What is the purpose of an engine oil system?

Answer 1

To lubricate and cool the main bearings and other load bearing parts of an engine.

Question 2

What are the nine uses of oil in an aircraft?

Answer 2

Reduce friction

Reduce wear

Cleaning

Minimise corrosion

Cooling

Heating (oil to fuel heat exchange)

Hydraulic fluid

Chip detection

Engine status (oil Ts and Ps, torque)

Question 3

What does fluid effectiveness as a lubricant depend on?

Answer 3

The viscosity of the fluid

Question 4

What can friction between two surfaces cause?

Answer 4

Intense heat may be generated at points of contact, however small, and this can lead to localised welding. Subsequent damage is then caused when the two surfaces are torn apart.

Intense heat can also cause expansion and deformation of an entire surface/part, or even melting in extreme cases.

Question 5

What are the two basic phases of lubrication?

Answer 5

Hydrodynamic (fluid film) lubrication

Boundary lubrication

Question 6

What is Hydrodynamic (Film) lubrication?

Answer 6

Layer of oil between two surfaces is relatively thick

Keeps the two surfaces apart

Amount of friction generated is very small

Question 7

What is Boundary lubrication?

Answer 7

Layer of oil between two surfaces is very THIN

Caused by high bearing loads, inadequate viscosity, oil starvation or loss of oil pressure

Thin oil film can rupture, which can increase wear, temperature and then lead to failure

Often occurs during starting conditions

Not a desirable phase

Question 8

What is Mixed lubrication?

Answer 8

In practice, both Hydrodynamic (film) and Boundary lubrication phases occur at some time, giving mixed film lubrication.

Has qualities of both hydrodynamic and boundary lubrication regimes.

Generated lubricant film is not enough to separate the body completely, but hydrodynamic effects are present.

Question 9

What is the Viscosity Index (VI) of a fluid?

Answer 9

An empirical measure of its change of viscosity with temperature.

Oil with a high VI preferable to one with a low VI.

Question 10

What are the components of an engine oil system?

Answer 10

Oil tank

Oil pump

Filter assembly

Oil cooler

Monitoring instruments

Magnetic chip detectors

Question 11

What oil pumps are present in an engine oil system?

Answer 11

Pressure Pump

Scavenger Pumps

Question 12

Why is sump venting required?

Answer 12

Some air is returned to the sump by the scavenger pumps due to air leakage into the bearing housing. need to get rid of it.

Question 13

What can be found in the oil filter assembly?

Answer 13

Filter

Bypass (in case filter blocks)

Blockage indicator

Non Return Valve (NRV) - Stops fuel flowing the wrong way back through the filters.

Question 14

How does the bypass filter work in an oil filter assembly?

Answer 14

Opens when it detects a differential pressure across the filter.

Sends an indication to the cockpit.

Question 15

What types of oil cooler may be found on aircraft?

Answer 15

Air-cooled = Fine for turboprop but impractical at high speeds due to drag

Fuel-cooled

Question 16

LEARN + BE ABLE TO LABEL THE DIAGRAM IN THE COURSE MANUAL

Answer 16

Look at now

Question 17

What is the purpose of magnetic chip detectors in an engine oil system?

Answer 17

Collect ferrous debris from the bearing chamber that can be analysed to monitor bearing performance and assess engine life.

Question 18

What are the components of an Engine Fuel System?

Answer 18

Low Pressure (LP) cock

Fuel cooled oil cooler (FCOC)

Fuel filter

High Pressure (HP) fuel pump

Throttle valve

Fuel Control Unit

HP Shut-off valve

Question 19

What is the LP fuel cock the boundary between?

Answer 19

The airframe fuel and the engine fuel

Final component in the airframe system

Question 20

What is the primary function of the Fuel Cooled Oil Cooler (FCOC)?

Answer 20

Remove heat from the engine oil

Question 21

What are the secondary functions of the Fuel Cooled Oil Cooler (FCOC)?

Answer 21

Heat the fuel

Removes ice crystals

Increases volatility (of fuel) for more efficient fuel ignition

Note - Turboprops use an air-cooled oil cooler instead as they fly at lower speeds so the drag penalty incurred is not too major

Question 22

What is the purpose of the High Pressure (HP) fuel pump?

Answer 22

Driven by the engine

Provides a sufficient supply of fuel for engine operation

Raises the pressure of the fuel received from the aircraft fuel system to a level where efficient burner operation is possible

Question 23

What is the purpose of a Fuel Control Unit (aka fuel control Valve)?

Answer 23

Modulates the pilot’s movement of the throttle to prevent the engine being overstressed/damaged fi handled poorly.

Controlled by the Engine Control Unit, which receives info from sensors within the engine.

Question 24

What is the role of the HP shut-off valve?

Answer 24

Shuts off fuel to the engine burners

Question 25

Note - Look in manual and learn diagram for engine fuel system + be able to label.

Answer 25

Look now

Question 26

What device attracts ferrous debris in an engine oil system?

Answer 26

Magnetic chip detector

Question 27

What provides oil pressure throughout the system?

Answer 27

Oil pumps

Question 28

Would you put an oil cooling device in the low pressure or high pressure system?

Answer 28

In the LP system

Means the cooler does not need reinforcing (bigger + heavier) to withstand the pressure of the HP fuel

Question 29

Note - Learn + be able to label and distinguish between the HP and LP systems and all their parts.

Answer 29

Look in manual now + learn

Question 30

What is the purpose of oil pumps?

Answer 30

Create pressure and therefore flow to pump the oil through the oil system (LP or HP??)