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M17 > 17.3 > Flashcards

17.3 Flashcards

1
Q

Two types of propellers?

A

Push or pull tractor propellers

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2
Q

Methods for changing pitch for controllable or constant speed propellers?

A

Hydraulic
Mechanical
Electrical

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3
Q

A shut down engine should be what to minimise drag?

A

Feathered

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4
Q

What is discing braking?

A

Moves props to a very low pitch on landing, causing negative angle of attack and thus a braking force

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5
Q

When is feathering done and why?

A

Done at engine failure to prevent engine windmilling

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6
Q

When is the BETA range used?

A

Pilot controls pitch on ground.
Pilot directly controls pitch of prop through throttle

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7
Q

When is ground fine pitch used?

A

Engine starting

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8
Q

When is reverse pitch used?

A

Braking and manoeuvring

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9
Q

What is ALPHA range?

A

Also known as the constant speed range.
The propeller governor controls the pitch.

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10
Q

When is max fine pitched used?

A

Used for rapid acceleration during takeoff
-allowing a shorter runway

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11
Q

When is Coarse (High) pitch used?

A

Used for high forward speed

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12
Q

How does a moving piston work?

A

A piston attached to the propeller blade lungs and moves within a cylinder

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13
Q

How does a moving cylinder work?

A

The cylinder is attached externally to the propeller blade

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14
Q

How do single acting propellers work?

A

Oil pressure changes the pitch in one direction only
Spring force and the torsion moments of the blades

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15
Q

How do single acting propellers for single engine aircraft work?

A

Oil pressure moves the blades in the direction of high (coarse) pitch and the spring moves it towards low pitch

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16
Q

How does single acting propellers work for multi engine aircraft?

A

-Oil pressure moves blades in direction of low (fine) pitch
-Springs and torsional moments of blades, move the blades towards high pitch
-Engine failure- decreasing oil pressure the blades move in the high (coarse) pitch direction

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17
Q

How does a double acting propeller work?

A

Pitch change are controlled both ways by oil pressure
Usually constructed as co-axial tubes, one containing oil for pitch and other for fine pitch

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18
Q

If control valve is mounted behind gear box, the propeller shaft must have what?

A

Must have two oil transfer tubes for each side of the piston

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19
Q

Where is propeller governer usually mounted?

A

On propeller reduction gearbox

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20
Q

Different names for governer?

A

Propeller governor
Constant speed unit
Propeller control unit

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21
Q

Different components of governor system?

A

-Spur gear pump to provide operating pressure
-Pilot valve which controls oil flow through the pitch change mechanism.
-Speeder spring pushes the valve downwards
-Centrifugal flyweights within the governor oppose the spring pressure and move the landed valve up to provide a coarser angle
-safety spring fitted to permanently set the blades to a fine pitch position in the event of control lever failure

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22
Q

What is on speed condition?

A

Flyweights are vertical and in position where no oil can flow in or out of governor assembly- creating a hydraulic lock

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23
Q

What is the under speed condition?

A

-Pilot requires higher RPM
-Lever forwards
-More tension on speeder spring
-Pilot valve down
-Piston move rearwards
-Engine RPM increased until new hydraulic lock

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24
Q

What is overspeed condition?

A

-Pilot selects lower speed,
-reduces tension on the speeder spring
-centrifugal force of flyweights to lift up the pilot valve
-Oil is now directed into pitch becomes coarser, slows RPM
-This happens until the speeder spring and centrifugal force tension is balanced again
-Creates new hydraulic lock

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25
Q

If engine is stopped what will be occurring in governing assembly?

A

No force on flyweights
Pilot valve in position

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26
Q

Governing system positions in start-up to idle plus?

A

Flyweights move outward with increasing engine RPM, until constant (on) speed is reached.
Landed valve/pilot valve in central position

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27
Q

The propeller rotates with a constant what?

A

RPM within its operating ranges

28
Q

Changes in power are achieved by what?

A

Changes in torque

29
Q

The propellers of turboprops have greater range of pitch change than those of what?

A

Piston engines

30
Q

Propellers are only efficient a what RPM?

A

1000-1200 RPM

31
Q

To match the propeller to the engine what is required?

A

A reduction gearbox

32
Q

Reduction ratios are between approximately what?

A

6:1 and 20:1

33
Q

Disadvantages of direct coupled engine arrangement?

A

Requires fine pitch stop for starting
Complex connection between throttle and prop control
Can be unstable with outside loads introduced with aircraft at different attitudes

34
Q

Compounded engine arrangement advantages?

A

Due to engine operating at constant RPM, it is free from surge
Good acceleration
Low power starting as HP compressor on a different spool (twin spool engine)

35
Q

Disadvantage of compound engine arrangement?

A

Used on large engines mainly

36
Q

Advantages of free power turbine engine arrangement?

A

Easier starting
Independent control of engine and propeller
Engine and propeller operate at optimum speed
Lower fuel consumption

37
Q

Disadvantages of free power turbine engine arrangement?

A

More Pilot intensive as he needs to know parameters and constantly maintain them

38
Q

What is the engine stopped operation?

A

No centrifugal force on flyweight
Speeder spring pushes pilot valve down
Oil trapped in cylinder between piston and oil pump

39
Q

What is start up to idle plus operation?

A

Flyweights move outwards
Increasing RPM until constant speed reached
Pilot valve central
Propeller in fine pitch

40
Q

What is increased to take off operation?

A

Speeder spring forced down against flyweights
Fine pitch oil moves blades to a lower pitch for take off

41
Q

What is take off operation?

A

As forward speed increases the angle of attack decreases
Propeller load decreases and propeller tries to overspeed

42
Q

What is increased to cruise operation?

A

Propeller rpm increases
Centrifugal force overcomes spring force
Pilot valve up
Blades turn more coarse
RPM decreases until flyweights and speeder springs are in balance

43
Q

What goes where during feathering condition?

A

Pilot valve lifts up
Counterweights and spring pressure move blades to feathered position

44
Q

The propeller governor moves to the over speed condition for what three main reasons?

A
  1. Aircraft goes into a dive increasing forwards speed, AOA is decreased
  2. When speeder spring force on flyweights is reduced
  3. When Pilot increases fuel flow by moving the throttle forward

Under-speed condition results in reverse of above

45
Q

Some systems have a what to provide a reserve of pressure to turn the blades?

A

Unfeathering accumulator

46
Q

What do centrifugal latches do?

A

When engine shuts down they stop the piston moving and lock it into fine pitch

47
Q

What is shaft horse power?

A

Power available from engine at propeller driveshaft

48
Q

What is equivalent shaft horsepower?

A

Residual power from engine exhaust plus shaft horsepower

49
Q

What type of turbines use direct control of fuel flow?

A

Free power turbines

50
Q

What type of direct control is used when propeller follows engine?

A

Direct control of fuel flow

51
Q

What type of direct control is used when engine follows propeller?

A

Direct control of blade angle

52
Q

At max RPM more power is achieved by what?

A

By increasing fuel flow

53
Q

Turbo prop pitch control system requirements?

A

Provide constant speed control
Minimum drag on failed engine
Minimum starting drag
Create high drag for A/C braking
Limit fine pitch during flight

54
Q

What is ground fine pitch stop?

A

For starting, a stop on piston ensures the blades are at zero degree position
-causes least drag

55
Q

What is flight fine pitch stop?

A

-Retractable stop to limit the amount of fine pitch available during flight
-This ensures thrust is given when needed
-Fine pitch would cause engine to overspeed
-Withdrawn for starting and ground operations

56
Q

What is FFPS operated by and where is it controlled?

A

Operated by oil pressure
Controlled electronically in cockpit

57
Q

Two positions of FFPS?

A

Engaged
Withdrawn

58
Q

Requirements of FFPS?

A

-Energise both engine lock withdrawal solenoids
-Provide cockpit indication that circuit is energised
-De-energise electro hydraulic stop circuit when the FFPS circuit is energised

59
Q

What does the electro-hydraulic stop do?

A

Coarsens the pitch of the blade preventing the propeller from drifting below flight fine pitch, should FFPS fail

60
Q

What is automatic feathering?

A

During take off and cruise, if engine shuts down the feathering position system will take over

61
Q

Advantages of beta range operation?

A

Reduce landing roll
Reduce break wear
Improved manoeuvrability on ground
Reversing of the aircraft during taxiing

62
Q

Disadvantages of beta range operation?

A

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

63
Q

Resetting of the beta valve is done through what?

A

Beta ring

64
Q

Propeller governor ineffective in what range?

A

BETA range

65
Q

How is beta range controlled?

A

Power lever

M17 (10 decks)

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