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M17 > 17.3 > Flashcards

17.3 Flashcards

(65 cards)

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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
If engine is stopped what will be occurring in governing assembly?
No force on flyweights Pilot valve in position
26
Governing system positions in start-up to idle plus?
Flyweights move outward with increasing engine RPM, until constant (on) speed is reached. Landed valve/pilot valve in central position
27
The propeller rotates with a constant what?
RPM within its operating ranges
28
Changes in power are achieved by what?
Changes in torque
29
The propellers of turboprops have greater range of pitch change than those of what?
Piston engines
30
Propellers are only efficient a what RPM?
1000-1200 RPM
31
To match the propeller to the engine what is required?
A reduction gearbox
32
Reduction ratios are between approximately what?
6:1 and 20:1
33
Disadvantages of direct coupled engine arrangement?
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
Compounded engine arrangement advantages?
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
Disadvantage of compound engine arrangement?
Used on large engines mainly
36
Advantages of free power turbine engine arrangement?
Easier starting Independent control of engine and propeller Engine and propeller operate at optimum speed Lower fuel consumption
37
Disadvantages of free power turbine engine arrangement?
More Pilot intensive as he needs to know parameters and constantly maintain them
38
What is the engine stopped operation?
No centrifugal force on flyweight Speeder spring pushes pilot valve down Oil trapped in cylinder between piston and oil pump
39
What is start up to idle plus operation?
Flyweights move outwards Increasing RPM until constant speed reached Pilot valve central Propeller in fine pitch
40
What is increased to take off operation?
Speeder spring forced down against flyweights Fine pitch oil moves blades to a lower pitch for take off
41
What is take off operation?
As forward speed increases the angle of attack decreases Propeller load decreases and propeller tries to overspeed
42
What is increased to cruise operation?
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
What goes where during feathering condition?
Pilot valve lifts up Counterweights and spring pressure move blades to feathered position
44
The propeller governor moves to the over speed condition for what three main reasons?
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
Some systems have a what to provide a reserve of pressure to turn the blades?
Unfeathering accumulator
46
What do centrifugal latches do?
When engine shuts down they stop the piston moving and lock it into fine pitch
47
What is shaft horse power?
Power available from engine at propeller driveshaft
48
What is equivalent shaft horsepower?
Residual power from engine exhaust plus shaft horsepower
49
What type of turbines use direct control of fuel flow?
Free power turbines
50
What type of direct control is used when propeller follows engine?
Direct control of fuel flow
51
What type of direct control is used when engine follows propeller?
Direct control of blade angle
52
At max RPM more power is achieved by what?
By increasing fuel flow
53
Turbo prop pitch control system requirements?
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
What is ground fine pitch stop?
For starting, a stop on piston ensures the blades are at zero degree position -causes least drag
55
What is flight fine pitch stop?
-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
What is FFPS operated by and where is it controlled?
Operated by oil pressure Controlled electronically in cockpit
57
Two positions of FFPS?
Engaged Withdrawn
58
Requirements of FFPS?
-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
What does the electro-hydraulic stop do?
Coarsens the pitch of the blade preventing the propeller from drifting below flight fine pitch, should FFPS fail
60
What is automatic feathering?
During take off and cruise, if engine shuts down the feathering position system will take over
61
Advantages of beta range operation?
Reduce landing roll Reduce break wear Improved manoeuvrability on ground Reversing of the aircraft during taxiing
62
Disadvantages of beta range operation?
Reduced engine cooling when in reverse pitch Increased blade damage Complicated control system
63
Resetting of the beta valve is done through what?
Beta ring
64
Propeller governor ineffective in what range?
BETA range
65
How is beta range controlled?
Power lever

M17 (10 decks)

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