The constant-speed propeller
The governor, how manifold pressure and rpm work together, and the order the levers move in.
15 min read · The complex airplane
After this lesson you can
- Explain why a fixed-pitch propeller is a compromise and how a constant-speed propeller removes it.
- Describe how the governor senses and corrects engine rpm using oil pressure.
- State the standard sequence for increasing and decreasing power, and why it exists.
- Interpret manifold pressure and rpm together, and recognize the tachometer's green arc and red line.
A fixed-pitch propeller is tuned for exactly one condition — usually cruise, sometimes climb — and it loses efficiency everywhere else. A constant-speed propeller removes that compromise by continuously changing the blade angle to hold whatever rpm the pilot selects, which means the propeller can be efficient at the low speed and high power of takeoff and at the high speed and reduced power of cruise, in the same flight.
For the pilot, that gain comes with a new control and a new way of thinking. The propeller lever no longer moves the throttle; it moves a governor that manages rpm on its own. Pilots who keep reasoning as though they were still flying a fixed-pitch airplane end up commanding combinations of manifold pressure and rpm the engine does not like, which is exactly the failure mode this lesson is built to prevent.
The rest of this lesson
- 1.The problem a fixed-pitch propeller cannot solve
- 2.The governor
- 3.Which way blade pitch fails, and why it depends on the design
- 4.Reading manifold pressure and rpm together
- 5.The order the levers move
- 6.Ground checks and the limits on the gauges
These 6 sections, their figures, the checks along the way and the end-of-lesson quiz come with the CPL track. Paid once, yours for good.
Key terms
Try to recall each definition before turning the card.