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Module 17 > 17.3 Propeller Pitch Control > Flashcards

17.3 Propeller Pitch Control Flashcards

1
Q

What speeds are fixed pitched propellers used for?

A

250 km/h (160 mph)

Up to 200kW performance

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2
Q

What pitch is preferred for gradual climb and cruising flight?

A

Coarse (higher) pitch.

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3
Q

What pitch is preferred for steep climb and towing?

A

Low (fine) pitch.

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4
Q

What reasons are fixed pitch propellers favourable for?

A

Production and maintenance costs.

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5
Q

What blade angle is usually used for fixed pitch propellers?

A

The best angle for cruising speeds, when propeller is most efficient.

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6
Q

What does a higher RPM do for the angle of attack?

A

Increases angle of attack.

Causing loss of thrust

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7
Q

Why is the take off for propellers inefficient?

A

Max RPM puts large loads on the engine at low speeds.

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8
Q

What blade angle is needed for take off?

A

A low (fine) angle.

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9
Q

What does air density do to the power of the engine?

A

Greater weight of air will absorb more engine power so more RPM is needed.

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10
Q

If the RPM is to double what must happen to the power in high density air?

A

Quadrupled.

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11
Q

What are the disadvantages of fixed pitch propellers?

A

Maximum efficiency only available at one pre-determined RPM and speed.

Power available at take off is reduced because of lower RPM.

Constant changes in RPM due to airspeed and altitude decreases efficiency.

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12
Q

What is the blade angle range usually between?

A

7 and 15 degrees.

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13
Q

How close should the blade angle be within the desired blade angle?

A

0.1 degrees.

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14
Q

What 2 controls does an aircraft with a controllable pitch propeller have?

A

Throttle control

Propeller control

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15
Q

What is one of the most popular controllable pitch propeller designs?

A

Beech-Roby propeller.

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16
Q

How is pitch change initiated in the cockpit?

A

Crank handle which directly drives a pinion gear.

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17
Q

What is a feathering position of blades?

A

Least drag.

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18
Q

How is thrust reverse produced on propellers?

A

Propellers turned into reverse pitch (air is accelerated forwards)

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19
Q

What is disc braking?

A

Adjusting the pitch to a “fine” pitch causing a negative angle of attack and a braking force.

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20
Q

What is the BETA range for blades?

A

Pilot controls the pitch on the ground.

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21
Q

What can the pitch change mechanism be sub divided into?

A

Moving piston

Moving cylinder

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22
Q

How are the pistons moved for varying the pitch of the blades?

A

Oil pressure

Or sometimes spring pressure.

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23
Q

What is a single acting propeller?

A

The oil pressure only moving the pitch of the blade in one direction only. (To coarse)

Movement of opposite direction done by spring pressure. (To fine)

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24
Q

What pitch stop position is optimal for restarting the engine?

A

Low pitch

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25
Q

What pitch would a centrifugal force turn the propeller blade?

A

To a low (fine) pitch.

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26
Q

If the centrifugal force turns the blade into a coarse pitch angle, what must be added to the blade root?

A

A flyweight.

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27
Q

What is a double acting propeller?

A

Oil pressure changing the pitch of the blade in both directions.

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28
Q

What is a CSU and a PSU?

A

Constant speed unit

Propeller control unit

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29
Q

What does a propeller governor assembly consist of?

A

A spur gear type pump.

A pilot valve.

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30
Q

Why is a safety spring fitted to the governor in the event of a control lever failure?

A

To move the pitch to the fine position to enable thrust to be maintained.

31
Q

What are the 2 levers in a twin lever for propeller control?

A

Power

Conditioning

32
Q

What do vertical flyweights do?

A

Create a hydraulic lock.

33
Q

What is propeller RPM determined by in a governor assembly?

A

Balance between engine power and braking moment of propeller blades.

34
Q

What happens to the flyweights as centrifugal force is added?

A

Move outwards until constant speed condition is reached.

35
Q

What happens to the angle of attack as speed increases.

A

Decreases.

36
Q

When would feathering be used?

A

If an engine happened to stop in flight.

37
Q

What pitch position must the the blades be in if trying to restart the engine?

A

Fine position.

38
Q

How are blade angles moved to fine when an engine has shut down to feather it?

A

Power lever to a high RPM and turning engine on starter motor to allow oil pressure to move the blades.

39
Q

What is an unfeathering accumulator?

A

Storage of pressure to move the blades to a fine position for engine restart after already feathered.

40
Q

What do centrifugal latches do?

A

Mechanically locking the blades in a fine position when the engine is not rotating.

(Engaged with spring pressure and disengaged with centrifugal force when RPM is increased)

41
Q

How are changes in power achieved?

A

Changes in torque.

42
Q

Where are turboprop engines generally used?

A

Where speeds do not exceed 450mph

43
Q

What RPM are turbo prop engines most efficient at?

A

1,000 to 1,200 RPM.

Large diameter limiting tip speeds.

44
Q

What reduction gearbox is used to reduced propeller speeds?

A

Compound epicyclic gearbox

Ratios between 6:1 and 20:1

45
Q

What are the 3 basic engine arrangements related to turboprop engines?

A

Direct connected
Compounded
Free turbine

46
Q

What is a direct connected engine arrangement?

A

Turbine drives the compressor through the reduction gearbox.

47
Q

What are disadvantages of direct connected engines?

A

Requires fine pitch for starting
Complex interconnection between throttle and propeller control.
Unstable with sudden changes in load.

48
Q

What is a compound engine only good for?

A

Large engines.

49
Q

What are advantages of compound engines?

A

Engine free from surge
Good flexibility
Good acceleration
Low power starting

50
Q

What is a free power turbine engine?

A

Compressor and propeller are mounted on different shafts

51
Q

What are advantages of free power turbines?

A

Easier starting
Independent control of engine and propeller
Engine and propeller can operate at optimum speed which reduces fuel consumption.

52
Q

What is 1 horsepower equal to in thrust?

A

2.5 lbs of thrust.

53
Q

What % RPM do most turboprop gas generators run at?

A

100%

54
Q

What is a CSU?

A

Constant speed unit.

Increases blade angle and to keep RPM constant.

55
Q

What is the BETA range generally associated with?

A

Reverse thrust on the ground.

56
Q

What selects the propeller pitch?

A

Governor

57
Q

What does the beta range of operation consist of?

A

Reverse function to idle.

58
Q

What are advantages of propeller reverse pitch?

A

Reduce landing roll
Reduce brake wear
Reverse of aircraft while taxiing.

59
Q

What are disadvantages of reverse pitch propellers?

A

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

60
Q

What pump is the integrated high pressure PCU pump and over speed governor unit?

A

Fixed displacement spur gear pump

Driven directly from reduction gearbox.

61
Q

What is a PCU?

A

Pitch control unit.

62
Q

Where is the PCU Mounted?

A

On the reduction gearbox.

63
Q

What is a PEC?

A

Propeller electronic control unit.

Dual channel microprocessor based controller.

64
Q

Where is a PEC mounted?

A

On the engine nacelle.

65
Q

When is autofeather only selected?

A

For take off.

66
Q

What would torque drop to trigger UPTRIM?

A

Below 25%

67
Q

How long is the auxiliary feathering pump activated for?

A

30 seconds.

Makes sure there is adequate oil pressure for feathering.

68
Q

What is the auxiliary feather pump for?

A

A backup source of oil pressure to the propeller pitch change mechanism.

69
Q

Is autofeather testing automatic or manual?

A

Automatic.

70
Q

What is the discing position?

A

Propellers in a zero degree position.

71
Q

What position do the blades move to at ground idle?

A

The discing position

72
Q

What is the purpose of feathering?

A

To prevent excessive drag and negative torque in the event of an engine failure

73
Q

What is lever position E for?

A

Take-off

Module 17 (6 decks)

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