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Constant Speeding Variable Pitch Propeller System

Propeller Control Unit (PCU)

Operation

How the PCU changes propeller pitch and maintains

constant engine speeds

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The Pilot moves the throttle lever which, as well as

changing fuel flow and therefore engine power, selects

an RPM for the engine to run at.

The PCU maintains the selected speed by adjusting

propeller pitch.

This eases pilot workload :-

Especially during combat as the engine is automatically

prevented from over speeding and therefore potential

destruction and the pilot can concentrate on defeating

the enemy

Basic Principal of Operation

And during civilian/transport duties giving the same

engine safeguards as above allowing the pilot to

concentrate on flying the aircraft, and therefore deliver

the passengers and/or cargo safely to their destination

(You will see later that the throttle is connected to both the Fuel Control Unit and the PCU)

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Propeller HubEngine Mounted

Simplified System

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Start

& Idle

Cruise

Take

Off

Throttle

Positions: -

Pilot Input

Signal

Hydraulic

Pressure

Supply

Hydraulic

Return

Operation Piston

Spinner

Connecting Linkage

Hydraulic

Connections

PCU

Sliding

Collar

Engine RPM Signal

(Mechanical Drive)

Spring

Hydraulic

Valve

Counter

Balance

Weights

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PROPELLER SYSTEM

VARIABLE PITCH CONTROL

FMU PCU

Piston Engine driven propeller

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PROPELLER SYSTEM

VARIABLE PITCH CONTROL

FMU PCU

Jet Engine driven propeller Turbo-Prop

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Start

& Idle

Cruise

Take

Off

Throttle

Positions

Pilot Input

Signal

Engine Stationary

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Start

& Idle

Cruise

Take

Off

Throttle

Positions

Pilot Input

Signal

Start Initiated Engine Begins to Rotate

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Start

& Idle

Cruise

Take

Off

Throttle

Positions

Engine At Idle

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Start

& Idle

Cruise

Take

Off

Throttle

Positions

Take Off Selected

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Start

& Idle

Cruise

Take

Off

Throttle

Positions

Engine Running at Take Off Speed

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Throttle

Positions

Start

& Idle

Cruise

Take

Off

Aircraft Starts Dive

Throttle (and Engine) at Cruise

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Throttle

Positions

Start

& Idle

Cruise

Take

Off

RPM Increases

Throttle at Cruise

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Throttle

Positions

Start

& Idle

Cruise

Take

Off

RPM Increases - Prop Goes to Coarser Pitch

Throttle at Cruise

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Flying straight and level

Flying straight and level

Looked at how the PCU changes propeller pitch

and maintains constant engine speeds during

Dive commencement

In all these manoeuvres, all the pilot is doing is flying (redirecting) the aircraft, the throttle is not touched.

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Now at Level Out

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Throttle

Positions

Throttle at Cruise

Start

& Idle

Cruise

Take

Off

Aircraft Levels Out

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Throttle

Positions

Start

& Idle

Cruise

Take

Off

RPM Reduces

Throttle at Cruise

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Throttle

Positions

Start

& Idle

Cruise

Take

Off

Prop Pitch Reduces

Throttle at Cruise

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Propeller HubEngine Mounted

PROPELLER SYSTEM

VARIABLE PITCH CONTROL

Throttle

Positions

Start

& Idle

Cruise

Take

Off

RPM Restored

Throttle (and Engine) at Cruise