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Cat B- Mod 11 Aircraft Systems > 11.11 Hydraulic Power > Flashcards

11.11 Hydraulic Power Flashcards

1
Q

How efficient are hydraulic systems?

A

Nearly 100%

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2
Q

What two types of hydraulic pressure are there?

A

Hydrostatic and Hydrodynamic

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3
Q

What is hydrostatic pressure?

A

Pressure produced by static or nearly static fluids.

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4
Q

What is hydrodynamic pressure?

A

Pressure produced by fluids with no internal friction.

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5
Q

Which type of pressure is used in aircraft?

A

Hydrostatic

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6
Q

What is an open centre hydraulic system?

A

An open-centre system is one having fluid flow, but no pressure in the system when the actuating mechanisms are idle.

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7
Q

Unlike the closed centre system what are the selector valves of the open centre system always?

A

Connected in series with one another.

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8
Q

If a constant delivery pump is used in a closed system circuit then what must the pressure be?

A

Regulated

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9
Q

What is the advantage of an open loop system over a closed?

A

The need for constant pressurisation is eliminated.

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10
Q

Why are closed centre systems more commonly used?

A

Due to their instant operation.

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11
Q

What is a hydraulic power pack?

A

A small self contained unit which reduces weight and system maintenance.

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12
Q

If a fluid is hygroscopic what does it have the tendency to do?

A

Absorb water.

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13
Q

Which is more hygroscopic, mineral or synthetic?

A

Synthetic

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14
Q

What is used to measure viscosity?

A

Viscometer or a Viscosimeter

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15
Q

What does a Saybolt Viscometer measure?

A

The time required for 60mm of fluid to pass through an orifice at specified temps between 21-99 degrees c.

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16
Q

What are the units given from a Saybolt Viscometer?

A

Saybolt universal seconds or saybolt flurol seconds

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17
Q

What is chemical stability?

A

Ability to resist oxidisation and deterioration over time.

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18
Q

What is a localised hot spot?

A

The point where liquid under pressure is forced through a small orifice making the part warm up.

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19
Q

What are the three principal categories of hydraulic fluids?

A

Minerals
Polyalphaolefins
Phosphate esters

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20
Q

What is the oldest hydraulic fluid?

A

Mineral MIL-H-5606

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21
Q

Can MIL-H-5605 be mixed with 6083?

A

Yes, 6083 is just the rust inhibiting version.

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22
Q

What is a Phosphate Ester hydraulic fluid known as?

A

Skydrol

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23
Q

What types of skydrol are used today?

A

Types IV and V

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24
Q

What classes of Skydrol IV are there?

A

Class I- Low density
Class II- Standard density

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25
Q

Why are type V skydrol fluids being developed?

A

The industries requirement for more thermally stable fluids.

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26
Q

What are two general contaminants found in hyd fluid?

A

Abrasives
Non-Abrasives

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27
Q

What are the two main service activities for hydraulic systems?

A

Reservoir filling
Fluid sampling

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28
Q

When should hydraulic systems be sampled?

A

Once a year or 3000 flight hours.

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29
Q

What two classifications of reservoir are there?

A

Pressurised and Non-pressurised

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30
Q

Where is the return pipe located on a resevoir?

A

Bottom

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31
Q

Contrary to their name, non-pressurised reservoirs do actually have some pressure, why is this?

A

To ensure positive supply of fluid to the inlet ports of the pumps.

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32
Q

For what reasons are reservoirs pressurised?

A

Provide positive flow and also prevents foaming, evaporation, and cavitation of the hydraulic fluid.

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33
Q

What does the reservoir pressurisation module do?

A

Supplies aircraft bleed air to the reservoir.

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34
Q

When a reservoir is filled correctly the top sight glass and bottom sight glass show what?

A

Top-red
Bottom-black

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35
Q

What is the purpose of an accumulator?

A

To accumulate energy and smooth pulsations

36
Q

What type of accumulator operation is commonly used today?

A

Hydro-Pneumatic piston type.

37
Q

What classifications of pump are there?

A

Positive displacement and Non-positive

38
Q

What are centrifugal and impeller pumps examples of?

A

Non positive displacement

39
Q

What is a gerotor pump?

A

Similar to a rotary engine, it is a positive displacement fixed volume pump.

40
Q

What type of mounting bases do piston pumps have?

A

Flanged mounting bases for mounting the pumps on the accessory drive cases of aircraft engines.

41
Q

What protects a cylinder pump from damage if it seizes?

A

There is a shear shaft between the splines.

42
Q

What type of pump is the EDP?

A

VDP

43
Q

What are air driven pumps driven by?

A

Typically the RAT

44
Q

When are ADP’s used?

A

When the EDP is not consistent enough.

45
Q

What types of hand pump are there?

A

Single action
Double action
Rotary

46
Q

How is emergency and back up pressurisation acheived?

A

RAT, PTU and ACMP.

47
Q

What is an ACMP?

A

Alternating current motor pump

48
Q

What type of pump is the RAT?

A

VDP

49
Q

Why do systems have filters?

A

Because 85% of failures are due to clogs.

50
Q

What is a wire mesh filter for?

A

Made of steel, this type of filter is usually used for surface cleaning.

51
Q

What filter material gives the best filtration?

A

Micro glass

52
Q

What micron element does a micro glass filter prevent from passing through?

A

Greater than 10 microns

53
Q

What is the advantage of cellulose paper filters?

A

They can be recycled

54
Q

What is the service life of a pressure filter, return filter and case drain filter?

A

Pressure 3000 hours
Return 1500 hours
Case Drain 600 hours

55
Q

What are the most common types of pressure relief valve?

A

Ball
Sleeve
poppet

56
Q

What are skydrol seals made from?

A

Butyl rubber or ethylene-propylene elastomers.

57
Q

What three main classes of seal are used?

A

Packing
Gasket
Wipers

58
Q

Hydraulic seals used internally on a sliding or moving assembly are normally called?

A

Packing

59
Q

Hydraulic seals used between non-moving fittings and bosses are normally called?

A

Gaskets

60
Q

What is the part number for v ring seals?

A

AN6225

61
Q

Where are U ring seals used?

A

Brake assemblies

62
Q

In what pressures are u ring seals used?

A

Less than 1000psi

63
Q

What is the operating temps of o rings?

A

-54 to 135 degrees c

64
Q

What does a red stripe indicate on an o ring?

A

Fuel compatible

65
Q

What does a blue stripe indicate on an o ring?

A

Hydraulic compatible.

66
Q

What are static seals used for?

A

Steady or pulsating pressure.

67
Q

What are dynamic (buffer) seals used?

A

Stroking or rotational movements

67
Q

What are some common gasket materials?

A

Asbestos
Copper
Cork
Rubber

68
Q

What are asbestos gaskets good for?

A

Heat resistance

69
Q

What does an open centre selector valve allow?

A

Allows a continuous flow of system hydraulic fluid through the valve, even when the selector is not able to actuate a unit.

70
Q

What is the purpose of a shuttle valve?

A

To isolate the normal system from an alternate or emergency system.

71
Q

What are hydraulic fuses used on?

A

Brake system
Leading edge flap and slat extend and retract lines
Nose landing gear up and down lines
Thrust reverser pressure and return lines

72
Q

What does a hydraulic fuse react too?

A

Sudden increase in flow.

73
Q

What does a hydraulic actuating cylinder do?

A

Transforms energy in the form of fluid pressure into a mechanical force, or action, to perform work.

74
Q

What two types of actuating cylinder are there?

A

Single
Double

75
Q

What angles can rotary actuators acheive?

A

Up to and beyond 720 degrees

76
Q

What can pressure sensors be divided into?

A

Pressure switches
Pressure transducers

77
Q

What is a pressure switch?

A

Active electromechanical device which measures the pressure in a system.

78
Q

What is a pressure transducer?

A

Samples and records the pressure in the system.

79
Q

What is a pressure transducers input and output voltage?

A

Input under 10v
Output can be hundreds of thousands volts

80
Q

What does HMDGS stand for?

A

Hydraulic motor driven generator,

81
Q

What does an HMDGS do?

A

Provides electrical power of 400Hz in the event of a primary gen failure.

82
Q

Why has power by wire come into existence to replace FBW?

A

The disadvantage of FBW is that if a single actuator fails then the entire hydraulic system has to be stopped.

83
Q

What is an Electro Hydrostatic Actuator?

A

A self-contained, modular, and compact actuator system, used in the power by wire technology.

84
Q
A

Cat B- Mod 11 Aircraft Systems (28 decks)

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