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AGK Engines > Propeller Systems > Flashcards

Propeller Systems Flashcards

1
Q

What is the purpose of a reduction gearbox

A

On powerful designs used to translate large amounts of power generated at high engine rpm into large amounts of torque for a relatively slow turning propellor

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2
Q

What are propellor blades made off

A

Propellor hubs are metal. Blades are made from aluminium alloy or composites

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3
Q

What is the aerodynamic force in line with drive shaft

A

Thrust

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4
Q

What aerodynamic force acts parallel to and in the opposite direction to plane of rotation

A

Torque Drag.

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5
Q

How is thrust increased on a fixed pitch propeller

A

Increasing engine RPM.

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6
Q

What are the disadvantages to a fixed pitch propeller system

A

Only operates efficiently in a narrow range of RPM. Below or above this speed engine becomes less efficient.

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7
Q

What are the advantages of a variable pitch propeller system

A

Adjustable pitch angle to maintain the blade at the optimum AOA through speed range.

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8
Q

How is thrust increased on a variable pitch propeller

A

Thrust is increased by increasing blade AOA rather than propellor rpm.

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9
Q

What is the Power control unit (PCU)

A

Mechanism responsible for changing blade pitch angle.

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10
Q

How does the PCU work

A

Inside Prop hub a piston is connected tot pins/links on root of propeller blade. The linear motion of the piston is translated into rotational movement by the pins.

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11
Q

What drives the PCU

A

Electric motors or more commonly by oil pressure or combo or oil/spring pressure.

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12
Q

How does a single acting PCU work on a single engine aircraft

A

Pressurised oil is fed to one side of the piston only driving pitch angle towards coarse.

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13
Q

Role of single acting PCU on twin engine aircraft

A

Coarsen off blade to feather position in event of engine failure.
Counterweights on root of blade creates a couple to twist blade towards feathered position.

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14
Q

How does a double acting PCU work

A

Oil pressure supplied to both sides of piston. Switching system directs high pressure oil to appropriate side to either coarsen or fine-off propeller.

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15
Q

Why are double acting PCU’s needed

A

Used on larger propellor systems to overcome greater centrifugal and aerodynamic forces produced by the blades.

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16
Q

What is the purpose of a centrifugal latch

A

Minimise propeller drag during engine start to reduce load on engine. Stops the blades from moving to fully feathered position on engine shut-down.

17
Q

How does a centrifugal latch work

A

At low rpms (>1000) pins emerge and stop the piston from moving back towards feather position.

18
Q

What happens if engine torque exceeds torque drag and vice versa.

A

If it exceeds propeller will accelerate and if its less propellor will decelerate.

19
Q

What does a Control speed unit do

A

Match torque drag to engine torque.
If propellor rpm falls moves blades to finer pitch.
If propellor rpm rises moves blades to coarser pitch.

20
Q

What is CSU overspeed

A

As engine rpm increases the governors rotating flyweights are thrown outwards lifting valve against spring pressure. In lifted position landed valve directs pressurised oil to coarse side of PCU. Blades coarsen, propeller torque drag increases and engine rpm reduces.

21
Q

What is CSU underspeed

A

Governor flyweights move inwards and landed valve goes down. Valve directs high pressure oil to fine pitch side. Blade moves finer, propellor drag reduces below engine torque and propellor accelerates back to equilibriums.

22
Q

What is CSU on speed

A

Propeller torque=engine output. Governor moves inwards and landed vale lowered which shuts off supply of high pressure oil to valve chamber. Hydraulic lock created which holds propeller at selected pitch angle

23
Q

What does the propellor rpm lever do

A

Allows to select different RPM’s.

24
Q

How is the feathering system backed up

A

Key requirement is supply of high pressure oil for the PCU which comes from engine.
Backup system is a separate oil reservoir with sufficient oil to allow prop to be feathered. Supplemented by electric driven pump.

25
Q

What is the role of auto-feathering system

A

Take over engine shut down and prevent loss of control

26
Q

What is the beta range

A

Range of (v.fine) pitch angles available below flight idle. Ie reverse thrust

27
Q

What is the role of the power lever in Beta Range

A

Power lever controls blade pitch.

28
Q

What is cabin noise

A

Propellors in line with cabin. Noise created by pressure waves from blade tips hitting fuselage.

29
Q

What is the synchronising unit

A

Eliminates rhythmic amplitude by synchronising the propellors by rotating all at same RPM. One engine made a master and others slaves. Synchronising unit compares RPM of slaves and adjusts them so that they are same as Master.

30
Q

What is a synchrophasing unit

A

Once’s synchronised SP unit makes a very brief and temporary rpm adjustment to slave engines to adjust the position of the blades of each propeller. Reduces cabin nose levels.

31
Q

What is used as an indication of engine power for a constant speed propeller and a fixed speed propeller

A

Map gauge for constant speed. (Pressure of air passing through the inlet manifold)
RPM for fixed.

32
Q

What power measurement does a turboprop engine use.

A

Torque gauge which indicates amount of torque being applied by the engine to the propeller shaft.
Torque sensing can be done electronically or by measuring oil pressure.

33
Q

What does the fully fine setting do

A

Minimises torque drag allowing engine fo respond very quickly to changing power requirements.

34
Q

How can overboosting be prevented at low rpm

A

Rev up and throttle back.

35
Q

What are the CSU checks

A

Start- rpm lever opens to encourage oil flow. Look to see rise n fall rpm
Feathering check- momentarily set to feather, see rpm drop quickly before removing the rpm.
Rpm lever Fully forward for taxi and takeoff

AGK Engines (7 decks)

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