Constant Speed Propeller

Question 1

What is the purpose of a constant-speed propeller?

Answer 1

To maintain a selected RPM by automatically adjusting blade pitch in response to changes in airspeed and engine power.

Image: Diagram showing RPM control via blade angle. Source: Boldmethod.

Question 2

What component controls the blade angle in a constant-speed propeller?

Answer 2

The propeller governor, which uses oil pressure to move a piston that changes blade pitch.

Image: Governor mechanism with flyweights and pilot valve. Source: Aircraft Engine Historical Society.

Question 3

Where does the oil used to control blade pitch come from?

Answer 3

From the engine’s lubricating system, with pressure boosted by a pump inside the governor.

Image: Oil flow from engine to governor. Source: Pilot Institute.

Question 4

What happens during an overspeed condition?

Answer 4

The governor senses high RPM and sends oil to increase blade pitch, creating more drag and reducing RPM.

Image: Overspeed response diagram. Source: Pilot Workshops.

Question 5

What happens during an underspeed condition?

Answer 5

The governor reduces blade pitch, allowing the propeller to spin faster and restore RPM.

Image: Underspeed correction flow. Source: Aviation Dictionary.

Question 6

What is the role of the pilot valve in the governor?

Answer 6

It moves in response to flyweights and directs oil flow to either increase or decrease blade pitch.

Image: Pilot valve movement diagram. Source: Jihostroj.

Question 7

What are the three speed conditions managed by the governor?

Answer 7

• Overspeed: RPM too high → increase pitch
• Underspeed: RPM too low → decrease pitch
• On-speed: RPM matches selected setting → no oil flow

Image: Governor response chart. Source: Pilot Institute.

Question 8

What mechanical part inside the propeller hub moves the blades?

Answer 8

A servo piston, which responds to oil pressure changes from the governor.

Image: Servo piston in hub. Source: ScienceDirect.

Question 9

Why is this system called “constant-speed”?

Answer 9

Because it maintains a constant engine RPM regardless of changes in flight conditions.

Image: RPM vs blade angle chart. Source: Boldmethod.

Question 10

What is the benefit of a constant-speed propeller?

Answer 10

Improved efficiency, performance, and fuel economy across a range of flight conditions.

Image: Efficiency comparison chart. Source: PilotMall.