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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
What happens in the event of an over speed condition?
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
26
Check previous two
27
If under speed what condition do the propellers want to be at?
Fine
28
The propeller of a turboprop rotates with what?
A constant RPM within its operating ranges
29
How are changes in power achieved?
Changes in torque
30
What differed the range of pitch change between turboprops and pristine engines?
Turboprops have a greater range
31
What speed do turboprop variable pitch propellers not exceed?
450mph
32
Pg 71
33
What are the 3 engine arrangements of a turbo prop engine?
. Direct connected . Compound . Free power turbine
34
What are the disadvantages of a direct connected engine regarding a propellor?
. 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
What is a compound engine?
A twin spool layout where the HP turbine drives the HP compressor and the LP turbine drives the LP compressor and reduction gearbox
36
What are the disadvantages of the compound engine?
. Only suitable for large engines
37
What are the advantages of a compound engine? It
. Engine free from surge , good flexibility . Good acceleration . Low power starting with a twin spool
38
How does a free power turbine engine work?
The compressors and propeller are mounted on different shafts and driven by independent turbines
39
What are the advantages of a free power turbine engine?
. Easier starting . Independent control of engine and propeller . Engine and prop can both operate at optimum speed which gives lower fuel consumption
40
When on speed is happening, explain what is happening to the governor??
. 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
What happens in the overspeed condition?
. 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
What happens to the governor in under speed condition?
. 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
When engine is stopped what is the condition of the flyweights and blade angle?
. No centrifugal force, therefore speeder spring pushes down on flyweights. Oil is trapped in cylinder between the piston and oil pump
44
When start up to idle plus what is the condition of the flyweights and blade angle?
. As engine rpm increased it causes the flyweights to move outward until the constant speed condition is reach
45
In the event of engine stopping in flight what must you do to stop wind milling?
The prop must be feathered
46
Page 67
47
After a feathering of the prop, the pilot may want to start the engine again, what must happens.
The prop must be moved to fine (low) pitch . Some systems equipped with an unfeathering accumulator to provide a reserve of pressure
48
How would the unfeathering condition be achieved?
By moving the power lever to a higher RPM position and relapsing the pressure stored in the accumulator
49
When engine is fitted in a single acting prop is shit down, what happens to oil pressure?
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
What prevents an unacceptable load from happening on the governor system?
Centrifugal latches
51
When are centrifugal latches engaged and disengaged?
Latches are engaged by spring pressure at low RPM (700-1000rpm) and disengaged by centrifugal forces as RPM increases
52
What does ESHP stand for?
Equivalent shaft horsepower
53
What is equivalent shaft horse power?
The sum of SHO and thrust. Indicates the total power available from the engine
54
For static condition I’d there is 1 HP, what thrust is this?
2.5 lbs of thrust
55
What rpm do turboprop gas generators run at?
100% RPM
56
Page 75
57
What does the NF do in a free power turbine??
Makes sure that the free power turbine doesn’t over spin
58
What are the 5 system requirements on a typical turboprop prop system?
. 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
What is ground fine pitch stop?
Used for starting and initial acceleration, ensures the blade is at 0 degrees position, causing the least drag
60
What is the flight fine pitch stop (FFPS)?
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
What two positions does the FFPS have?
Engaged and withdrawn
62
What is the purpose of the electro- hydaulic stop?
. A pitch coarsening mech to prevent too much fine pitch if a faliure of FFPS occurs
63
How is the electro- hydaulic stop activated?
. 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
What is the purpose of a hydaulic pitch lock?
. 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
Why is feathering selected?
To prevent excessive drag and negative torque (wind milling in the event of an engine faliure
66
When is automatic operation of the feathering system?
Take off and cruise and in the event of engine faliure
67
In the event of an engine faliure what happens for automatic feathering?
The centrifugal flyweights are automatically overridden and the electric feathering pump runs driving the prop to the feather position
68
What does constant speeding mean?
The giver enter is regulating the speed of the prop within a certain RPM
69
What does the beta range describe?
The range of blade angles which can be obtained when the aircraft is operating on the ground
70
What are the advatanges of reverse pitch?
. Reduce landing roll . Reduce brake wear . To improve manoeuvre on ground . Reversing of aircraft during taxi
71
What are the disadvantages of revere pitch?
. Reduced engine cooling when in reverse pitch . Increased blade damage . Complicated control system
72
In beta mode how is the blade angle changed?
Directly with the power lever, so that any angle between zero thrust and flight ideal can be selected
73
On modern aircraft prop pitch control systems are controlled by what?
Electronic control systems in same easy FADEC does
74
What are the 3 things the electronic pitch control consists of?
. Integrated Hugh pressure PCU pump and over speed governor unit . Pitch control unit . Propeller electronic control unit
75
What does the PCU do? (Pitch control unit)
. 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
What is the PEC?
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
The PCU also have independent circuits to perform what 2 saftey functions?
. Auto feathering . Under speed prop contro,
78
What does autofeather provide?
Automatic initiated propeller feathering and good operating engine power up trim following an engine faliure during take off
79
When would the ARM light turn on?
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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