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M17 > M17.3 Propeller Pitch Control > Flashcards

M17.3 Propeller Pitch Control Flashcards

1
Q

Propellers are either push or pull tractor propellers, what are they subdivided into?

A

. Fixed pitch propeller
. Adjustable pitch propeller
. Controllable pitch propellers
. Constant speeding propeller

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2
Q

Constant speed propellers can either be?

A

Hydraulic amechanical or electrical

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3
Q

Multiple engine aircraft’s and motorised gliders should produce as little drag as possible, so what is in place? As well as when engine failure?

A

Blades can be moved into the feathering position (least drag)
Prevents windmilling when engine faliure

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4
Q

On large aircraft there is also another function to reduce distance for landing?

A

Reverse thrust

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5
Q

What is the purpose of discing braking?

A

Some propellers can move their blades to a very fine (low) pitch on landing. This causes a negative angle of attack and thus braking

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6
Q

When would you use BETA blade range?

A

Pilot controls the pitch on the ground

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7
Q

When would you use ground fine pitch blade range?

A

Used for engine starting and discing braking

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8
Q

When would you use Negative pitch (reverse) blade range?

A

Used for power in braking and manoeuvre

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9
Q

When would you use ALPHA blade range?

A

The constant speed range, the prop governor control the pitch (cruise)

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10
Q

When would you use max fine pitch blade range?

A

Used for rapid acceleration during take off allowing a shorter take off run

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11
Q

When would you use coarse (High) blade range?

A

Used for high forward speed

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12
Q

How does a moving piston work?

A

A piston is attached to the propeller blade lugs and move within a cylinder

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13
Q

How does a moving cylinder work?

A

The cylinder is attached externally to the propeller blades

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14
Q

How does a single acting propeller work?

A

. Oil pressure changes the pitch in one direction only .
. The opposite direction is done by a spring force and the torsion moments of the blades themselves

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15
Q

How do single acting propellers with a single engine aircraft work?

A

. Oil pressure moves the blades in high (coarse) pitch
. Spring moves it toward the low pitch

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16
Q

How do single acting propellers for multi engine aircraft’s work?

A

. Oil pressure moves blades in direction of low pitch (fine)
. The springs and torsional moments of blades move the blades towards high pitch
(If engine faliure goes from high pitch to feathered)

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17
Q

What do double acting propellers allow?

A

Pitch change mechanism are controlled both ways by oil pressure

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18
Q

How many oil transfers rubes must the double acting propeller have if the control valve is mounted behind the gearbox?

A

2

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19
Q

What are the different names for the propeller governor?

A

. Contacts speed unit (CSU)
. A propeller control unit (PCU)
. Propeller governor

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20
Q

What are the 3governor assembly?

A

. A spur gear type pump to provide a positive operating pressure for the system
. A pilot valve to control the oil flow to and from the pitch change mechanism
. . A saftey spring

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21
Q

What is the job of a safety spring on a governor?

A

Fitted at the top of the governor so that in the event of a control lever failure, the spring will drive the governor to low pitch position

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22
Q

In on condition, what position is the governor assembly in?

A

Neutral

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23
Q

In on speed condition, where do the flyweights sit?

A

Vertical flyweights to maintain the pilot valve in a position that allows no oil to flow into or out of the governor assembly. Thus creating a hydualic lock at 250psi

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24
Q

What happens in the event of an under speed condition?

A

The flyweights would be in the inward position which pushes the spring down allows oil trapped to drain away

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25
Q

What happens in the event of an over speed condition?

A

The flyweights are in an outward position which pulls the spring up because of Hugh centrifugal forces. Thais then forms a hydaulic brake at 250 psi to drain the oil away

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26
Q

Check previous two

A
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27
Q

If under speed what condition do the propellers want to be at?

A

Fine

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28
Q

The propeller of a turboprop rotates with what?

A

A constant RPM within its operating ranges

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29
Q

How are changes in power achieved?

A

Changes in torque

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30
Q

What differed the range of pitch change between turboprops and pristine engines?

A

Turboprops have a greater range

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31
Q

What speed do turboprop variable pitch propellers not exceed?

A

450mph

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32
Q

Pg 71

A
33
Q

What are the 3 engine arrangements of a turbo prop engine?

A

. Direct connected
. Compound
. Free power turbine

34
Q

What are the disadvantages of a direct connected engine regarding a propellor?

A

. Requires fine pitch for starting
. Omplex interconnection between throttle and propeller control
. May be unstable with sudden changes in load due to attitude of the aircraft

35
Q

What is a compound engine?

A

A twin spool layout where the HP turbine drives the HP compressor and the LP turbine drives the LP compressor and reduction gearbox

36
Q

What are the disadvantages of the compound engine?

A

. Only suitable for large engines

37
Q

What are the advantages of a compound engine? It

A

. Engine free from surge
, good flexibility
. Good acceleration
. Low power starting with a twin spool

38
Q

How does a free power turbine engine work?

A

The compressors and propeller are mounted on different shafts and driven by independent turbines

39
Q

What are the advantages of a free power turbine engine?

A

. Easier starting
. Independent control of engine and propeller
. Engine and prop can both operate at optimum speed which gives lower fuel consumption

40
Q

When on speed is happening, explain what is happening to the governor??

A

. Neutral position
. No oils moving
. Speeder spring tension is equal to centrifugal force required to keep to keep the flyweights in the vertical position

41
Q

What happens in the overspeed condition?

A

. Pilot requires lower RPM, new speed
. Lever moves rearwards
. Less tension on the speeder spring
. Centrifugal force moves pilot valve up, pushes pilot valve up
. Piston moves forward
. Increases propeller brake moment (blade pitch)
. Engine RPM decreases down till hydaulic lock on new on speed condition

42
Q

What happens to the governor in under speed condition?

A

. Pilot requires high RPM, new speed
. Lever goes forwards
. More tension on speeder spring
. Overcomes centrifugal force moves pilot valve down
. Piston moves rearwards
. Reduces prop brake moment
. Engine RPM increases until hydaulic lock (new on condition speed)

43
Q

When engine is stopped what is the condition of the flyweights and blade angle?

A

. No centrifugal force, therefore speeder spring pushes down on flyweights. Oil is trapped in cylinder between the piston and oil pump

44
Q

When start up to idle plus what is the condition of the flyweights and blade angle?

A

. As engine rpm increased it causes the flyweights to move outward until the constant speed condition is reach

45
Q

In the event of engine stopping in flight what must you do to stop wind milling?

A

The prop must be feathered

46
Q

Page 67

A
47
Q

After a feathering of the prop, the pilot may want to start the engine again, what must happens.

A

The prop must be moved to fine (low) pitch
. Some systems equipped with an unfeathering accumulator to provide a reserve of pressure

48
Q

How would the unfeathering condition be achieved?

A

By moving the power lever to a higher RPM position and relapsing the pressure stored in the accumulator

49
Q

When engine is fitted in a single acting prop is shit down, what happens to oil pressure?

A

Oil pressure is trapped in the cylinder, which may cause a leakage therefore the blades would be forced toward a coarse pitch, which causes an unacceptable load on starter system

50
Q

What prevents an unacceptable load from happening on the governor system?

A

Centrifugal latches

51
Q

When are centrifugal latches engaged and disengaged?

A

Latches are engaged by spring pressure at low RPM (700-1000rpm) and disengaged by centrifugal forces as RPM increases

52
Q

What does ESHP stand for?

A

Equivalent shaft horsepower

53
Q

What is equivalent shaft horse power?

A

The sum of SHO and thrust. Indicates the total power available from the engine

54
Q

For static condition I’d there is 1 HP, what thrust is this?

A

2.5 lbs of thrust

55
Q

What rpm do turboprop gas generators run at?

A

100% RPM

56
Q

Page 75

A
57
Q

What does the NF do in a free power turbine??

A

Makes sure that the free power turbine doesn’t over spin

58
Q

What are the 5 system requirements on a typical turboprop prop system?

A

. Provide constant speed control
. Minimum drag in a failed engine
. Minimum starting spray
. Create high drag for aircraft braking
. Limit the degrees of fine pitch in flight

59
Q

What is ground fine pitch stop?

A

Used for starting and initial acceleration, ensures the blade is at 0 degrees position, causing the least drag

60
Q

What is the flight fine pitch stop (FFPS)?

A

A retractable stop used to limit the fine (low) pitch a viable during flight. The FFPS is in locked position automatically as power lever is advanced to take off.

61
Q

What two positions does the FFPS have?

A

Engaged and withdrawn

62
Q

What is the purpose of the electro- hydaulic stop?

A

. A pitch coarsening mech to prevent too much fine pitch if a faliure of FFPS occurs

63
Q

How is the electro- hydaulic stop activated?

A

. System is activated by a micro switch which will energise the system if the prop angle should decrease below the FFPS by 2 degrees

64
Q

What is the purpose of a hydaulic pitch lock?

A

. A spring operated valve which is designed to prevent the prop from moving to a finer pitch in the event of an operating oil supply faliure

65
Q

Why is feathering selected?

A

To prevent excessive drag and negative torque (wind milling in the event of an engine faliure

66
Q

When is automatic operation of the feathering system?

A

Take off and cruise and in the event of engine faliure

67
Q

In the event of an engine faliure what happens for automatic feathering?

A

The centrifugal flyweights are automatically overridden and the electric feathering pump runs driving the prop to the feather position

68
Q

What does constant speeding mean?

A

The giver enter is regulating the speed of the prop within a certain RPM

69
Q

What does the beta range describe?

A

The range of blade angles which can be obtained when the aircraft is operating on the ground

70
Q

What are the advatanges of reverse pitch?

A

. Reduce landing roll
. Reduce brake wear
. To improve manoeuvre on ground
. Reversing of aircraft during taxi

71
Q

What are the disadvantages of revere pitch?

A

. Reduced engine cooling when in reverse pitch
. Increased blade damage
. Complicated control system

72
Q

In beta mode how is the blade angle changed?

A

Directly with the power lever, so that any angle between zero thrust and flight ideal can be selected

73
Q

On modern aircraft prop pitch control systems are controlled by what?

A

Electronic control systems in same easy FADEC does

74
Q

What are the 3 things the electronic pitch control consists of?

A

. Integrated Hugh pressure PCU pump and over speed governor unit
. Pitch control unit
. Propeller electronic control unit

75
Q

What does the PCU do? (Pitch control unit)

A

. The hydro mechanical PCU is mounted on the reduction gearbox and is designed to control the pitch of the prop by directing oil to either side

76
Q

What is the PEC?

A

Propeller electronic control unit
. Mounted on engine nacelle and is a duel channel microprocessor that utilises inputs from aircraft, pro control system sensors and engine control system to control the prop pitch and RPM

77
Q

The PCU also have independent circuits to perform what 2 saftey functions?

A

. Auto feathering
. Under speed prop contro,

78
Q

What does autofeather provide?

A

Automatic initiated propeller feathering and good operating engine power up trim following an engine faliure during take off

79
Q

When would the ARM light turn on?

A

When both engine torques exceed a minimum value of 50% and both power levers are advatanges beyond 60% PLA

M17 (12 decks)

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