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Resource Group Mod 15 2024 > 15.10 Lubricating Systems > Flashcards

15.10 Lubricating Systems Flashcards

1
Q

What’s the main purpose of a Lubricating system?

A

Distribute oil to the engine bearing components and the gearboxes.

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2
Q

What are the two types of oil sump?

A
  • Wet sump.
  • Dry sump.
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3
Q

What’s a wet sump?

A

Where the oil is stored in the engine.

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4
Q

What’s a dry sump?

A

Where the oil is stored in an external supply tank, located on or near the engine.

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5
Q

What are the two classifications of lubrication systems?

A
  • Full-flow system.
  • Constant pressure system.
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6
Q

What’s the main charactersitic in a full-flow system, in terms of pressure?

A

There’s no way of regulating the pressure.

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7
Q

What factors affect the oil pressure, in a full-flow system?

A
  • N2 rotor speed.
  • Oil temperature.
  • The flow in areas downstream of the supply pump.
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8
Q

What is the effect of a higher N2 rotor speed on oil pressure, in a full-flow system?

A

Higher N2 speeds means higher oil pressure.

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9
Q

What is the effect of a higher oil temperature on oil pressure, in a full-flow system?

A

A higher oil temperature means a decrease in oil pressure.

(Oil is less viscous at higher temps, and thus has less resistance and flows easier, resuting in lower pressures).

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10
Q

What is the effect on oil pressure with a decrease in the flow area, in a full-flow system?

A

A decrease in the flow area will result in an increase in oil pressure.

(Flow area can be decreased by clogged oil nozzles).

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11
Q

What special type of oil leakage is hard to identify?

A

When oil pressure decreases but oil quantity remains the same.

(Caused by very low oil temp with very high N2 speeds)

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12
Q

What’s another name for the Constant Pressure lubricating system?

A

The regulated pressure system.

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13
Q

What’s the key component of the Constant Pressure type lubrication system?

A

The pressure regulating valve (PRV).

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14
Q

What’s the main function of the PRV?

A

Holds oil pressure to a given design value, at all N2 rotor speeds from idle to max.

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15
Q

How does oil temperature affect oil pressure in a Constant Pressure system?

A

It Doesn’t. Oil temperature has no effect on oil pressure in a Constant Pressure system.

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16
Q

What does the PRV ensure, with regards to pressure differential?

A

Ensures that the difference between supply pressure and vent pressure is held constant, giving the same flow level at all engine speeds.

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17
Q

What are the advantages of full-flow systems? (2)

A
  • Simpler.
  • No adjustments necessary during maintenance.
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18
Q

What are the disadvantages of full-flow systems? (2)

A
  • High oil pressures required at engine start means very high oil pressures develop at high engine speeds.
  • Significant rise in oil temp after power reduction, as flow rate decreases with engine speed.
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18
Q

What are the advantages of Constant Pressure systems? (2)

A
  • Pressure remains relatively low throughout.
  • No oil temp rise after power reduction.
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19
Q

What are the disadvantages of Constant Pressure systems? (3)

A
  • More complex.
  • Requires adjustments during maintenance.
  • PRV is often a source of trouble.
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20
Q

What component is a critical lubrication point, due to high temperatures?

A

Exhaust turbine bearing.

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21
Q

What can provide air cooling?

A

Cool bleed air from the early compressor stages.

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22
Q

What can air cooling help to reduce, in terms of oil?

A

It helps to reduce the oil quantity required for cooling.

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23
Q

What are the four sub-systems of a lubricating system?

A
  • Oil reservoir and supply system.
  • Scavenge system.
  • Vent system.
  • Monitoring system.
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24
Q

What are the 3 sub-systems of the oil system?

A
  • Storage.
  • Distribution.
  • Indicating.
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25
Q

What is an oil tank usually constructed of?

A

Aluminium alloy with a silicone coating for fire resistance.

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26
Q

What are the two methods for filling an oil tank?

A
  • Gravity.
  • Pressure.
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27
Q

What part of the oil filler catches foreign particles?

A

The strainer.

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28
Q

What’s the primary source of oil cooling?

A

The fuel-cooled oil cooler.

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29
Q

What does the check valve in the oil filter section do?

A

Stops oil and air from flowing back out of the filler port if the cap isn’t reinstalled correctly by an idiot.

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30
Q

What two types of elements can oil pumps have?

A
  • Supply element.
  • Scavenge element.
  • (Or both, usually).
31
Q

What is the number of elements used in an oil pump, dependent on?

A

The type and model of the engine.

32
Q

What element type has a greater pumping capacity, supply or scavenge?

A

The scavenge element has a greater pumping capacity.

33
Q

What are the two types of oil pump?

A
  • Gear pump.
  • Gerotor pump.
34
Q

What does a gear pump have to protect from overpressure?

A

Pressure relief valve.

35
Q

How is the correct output maintained in a gear pump?

A

The clearances between the gear-teeth, and sides of the pump wall and plate.

36
Q

What protection method does a gear pump employ, if it were to sieze?

A

It’s driven by a ‘shear-shaft’. The shaft will shear-off if the pump siezes.

37
Q

What elements does a gerotor pump usually consist of?

A

A single supply element and several scavenge elements.

38
Q

How is the capacity of the elements in a geretor pump controlled?

A

By varying the size of the gerotor elements.

39
Q

Which type of fuel pump is most commonly used?

A

Gear pump.

40
Q

Where is the oil pressure regulating valve usually located?

A

On the pressure side of the pressure pump.

41
Q

How does the oil pressure regulating valve operate?

A

It uses a spring, held under tension.

42
Q

What effect does increasing the tension on the spring of the pressure regulating valve have?

A

The pressure at which the valve opens also increases the system pressure.

43
Q

When would a pressure relief valve be required in the system? (2)

A
  • If the system does not have a pressure regulating valve.
  • Especially required in systems that use an oil cooler.
44
Q

Under what conditions should the pressure relief valve be closed?

A

Normal conditions.

45
Q

What is a ‘last-chance’ oil filter?

A

Used to protect the oil nozzles if supply filter is bypassed.

46
Q

What type of filter element is used for supply filters?

A

Pleated Woven Wire Mesh (25-35 microns).

Can be cleaned and reused.

47
Q

What type of filter element is used for scavenge filters?

A

Paper.

Must be disposed of and cannot be reused.

48
Q

What are the two types of heat exchanger tank system?

A
  • Hot tank system.
  • Cold tank system.
49
Q

What is the hot tank system?

A

Oil from the bearing compartments is not cooled before returning to the tank.

50
Q

Where is the hot tank system located?

A

In the supply line.

51
Q

What is the cold tank system?

A

Oil from the bearing compartments IS cooled before returning to the tank.

52
Q

Where is the cold tank system located?

A

In the scavenge line.

53
Q

What are the two types of oil cooler?

A
  • Fuel-cooled.
  • Air-cooled.
54
Q

Which type of oil cooler is primarily used?

A

Fuel-cooled oil coolers

55
Q

What can be used as an addtional cooler?

A

Air-cooled oil coolers.

56
Q

What types of engine mainly use air-cooled oil coolers?

A

Turboprop and APUs.

57
Q

How does the fuel and oil flow through a heat exchanger?

A

The fuel flows through tubes in the core, and the oil flows in passages circulating around the tubes.

58
Q

What provides an exit for the fuel and oil, if their passages become blocked?

A

Bypass valves. One for fuel, and one for oil.

59
Q

How many scavenge pumps (generalised) remove oil/contaminants from bearing compartments and gearboxes?

A

7 scavenge pumps.

60
Q

What is a ‘breather’ vent system?

A

Removes air from scavenge oil in external gearbox.

61
Q

What is a ‘de-aerator’ vent system?

A

Removes air from scavenge oil at the inlet.

62
Q

Where are quantity transmitters (Qty Tx) usually located, for ease of maintenance?

A

At the top of the oil tank, so they can be removed/changed without needing to drain all the oil.

63
Q

What are the two types of Qty Tx?

A
  • Capacitance type.
  • Reed type.
64
Q

How does the capacitance-type Qty Tx measure oil?

A

Two concentric tubes makes up the capacitance plates.

As the level of oil increases and fills the space between the plates, the capacitance increases.

65
Q

How does the Reed-type Qty Tx measure oil?

A

Has a metal tube with a float inside it, and holes to allow the oil to flow in.

The float has permanent magnet that activates a ladder of reed switches.

The switch closest to the magnet closes, and gives an indication.

66
Q

How do metal particles in oil, increases exponentially?

A

Metal particles cause more abrasion which results in more metal particles = more abrasion = even more particles etc..

67
Q

What does SOAP stand for?

A

Spectrometric Oil Analysis Program

68
Q

What does SOAP find and analyse in oil?

A

Analyses internal wear of parts by finding particles in oil that are 0.001mm to 0.02mm in size.

69
Q

How does SOAP analyse particles?

A

Uses an electric arc to vapourise particles, which then produce a light spectra that determines the type and size of the metal.

70
Q

What is the function of Mag-chip detectors?

A

To catch metal particles by attracting them to a magnet.

71
Q

How can a mag-chip be checked?

A

Manually, or automatically using the maintenance panel in the flight deck.

72
Q

How does the mag-chip give an indication in the flight deck?

A

The resistance decreases when the mag-chip picks up metal particles, until it reaches a point where it gives an indication.

73
Q

What must be done before checking the oil, on an aircaft without an anti-syphon system?

A

Wait 5-10 mins after engine shutdown to check the oil. The oil slowly feeds back into the tank.

Anti-syphon system prevents the slow flow back into the tank from the gearbox.

74
Q

What type of hose should be used on the overfill port, when pressure-filling oil on an aircraft without a sight glass?

A

A transparent hose, so that you can easily see when the oil is flowing out of the overfill port.

75
Q

How long should you wait before removing the oil filler cap after engine shutdown?

A

Up to 5 minutes, as high pressure my still be present in the system, causing hot oil to spill out of the filler port.

76
Q

Why are oil overfills dangerous?

A

Overfills can result in large amounts of oil being pumped through the vent line into the forward beaaring compartment, or the de-oiler.

Resource Group Mod 15 2024 (13 decks)

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