The Constant Speed

Propeller

Introduction• Describe how power is controlled with a

Constant Speed Propeller

• Describe how the speed of the propeller is set and controlled

• State the limitations on the engine and propeller

• Describe the 2 elements of a Constant Speed Propeller Unit

• Describe the failure modes of the Constant Speed Propeller

Objectives

• State how to control power and engine RPM with a constant speed propeller

• State the limitations of RPM and engine power

• List the 2 main elements of a Constant Speed Propeller system

• Explain how the Pitch Change Mechanism and the Speed Governor work

• State the failure modes of the Constant Speed Propeller

Engine and Prop Controls

Manifold Air Pressure (MAP)

Control of Power (Low Power)

Control of Power (High Power)

Control of RPM (High RPM)

Control of RPM (Low RPM)

Control Indications

MAP Change with Altitude

Take –Off and Climb

Cruise

Limitations

• The Slingsby Firefly T67M-Mk2– The MAP must not exceed hundreds of RPM +4

• i.e. If the RPM is 2300, the max allowed MAP is 27”

– The RPM must not exceed 2700.

Two Main Elements

• Speed Governor– Senses speed of the engine– Provides pressurised oil, hydraulic lock or a

path to sump for oil to the pitch change mechanism

• Pitch Change Mechanism– Changes pitch of the blades depending on the

oil pressure from the Speed Governor

Speed Governor

Speed Governor RPM Control

Speed Governor and Pitch Change Mechanism

Pitch Change MechanismDecreasing Pitch

Pitch Change MechanismHolding Pitch

Pitch Change MechanismIncreasing Pitch

Failure ModeUnderspeed

• Underspeed• Caused by excessive pitch

– Loss of oil Pressure

– Failure of speed governor

– Failure of Pitch Change Mechanism

• Actions– Check oil pressure

– Check MAP above 15” If not open throttle

– Exercise RPM through whole range

– Refer to checklist

Failure ModeOverspeed

• Overspeed– Caused by excessively fine pitch

• Speed Governor failure

• Pitch Change Mechanism failure

– Actions• Use throttle to keep RPM within limits

• Leave RPM control at mid range

• Reduce speed 80kts

• Refer to failure checklist

Summary• How power is controlled with a Constant Speed

Propeller

• How the speed of the propeller is set and controlled

• Limitations on the engine and propeller

• The 2 elements of a Constant Speed Propeller Unit

• The failure modes of the Constant Speed Propeller

Questions

• State how to control power and engine RPM with a constant speed propeller

• State the limitations of RPM and engine power• List the 2 main elements of a Constant Speed

Propeller system• Explain how the Pitch Change Mechanism and the

Speed Governor work • State the failure modes of the Constant Speed

Propeller