What is the difference between a controllable propeller and a constant-speed propeller?

What is the difference between a controllable propeller and a constant-speed propeller?

• A. The propellers have different numbers of blades.
• B. The materials and construction differ.
• C. Basically, it is the control system. A controllable-pitch propeller uses a manually operated oil valve to control the pitch, and a constant-speed propeller uses a governor to control the valve.
• D. They both use the same control system; there is no difference.

Answer: (C)

The difference lies in how the blade pitch is controlled. A controllable-pitch propeller lets the pilot set the blade angle using an oil-valve system—pitch is adjusted manually and is not automatically tied to engine speed. A constant-speed propeller is a type of controllable-pitch propeller, but its pitch is automatically managed by a governor. The governor senses engine RPM and modulates oil pressure to move the blades to the correct angle to hold the selected RPM, adapting to changes in throttle, power, and airspeed. So the key distinction is the control system: manual pitch adjustment versus automatic, governor-controlled pitch. The other factors like blade count or materials don’t define this difference, and saying they share the same control system isn’t accurate.

The difference lies in how the blade pitch is controlled. A controllable-pitch propeller lets the pilot set the blade angle using an oil-valve system—pitch is adjusted manually and is not automatically tied to engine speed. A constant-speed propeller is a type of controllable-pitch propeller, but its pitch is automatically managed by a governor. The governor senses engine RPM and modulates oil pressure to move the blades to the correct angle to hold the selected RPM, adapting to changes in throttle, power, and airspeed. So the key distinction is the control system: manual pitch adjustment versus automatic, governor-controlled pitch. The other factors like blade count or materials don’t define this difference, and saying they share the same control system isn’t accurate.