What distinguishes a variable pitch propeller from a constant speed propeller?

A variable pitch propeller is designed to allow the pilot or an automatic system to adjust the angle of the blades during flight, which optimizes performance for varying flight conditions. This means the blades can be positioned at different angles to manage thrust effectively. In contrast, a constant speed propeller not only allows for blade angle adjustments but also integrates a governor system that automatically adjusts the propeller pitch to maintain a consistent engine RPM regardless of flight conditions.

Both types of propellers have the capability to change the blade angle, but the distinction lies in how they manage RPM. The constant speed propeller maintains a specific RPM by continuously changing the blade angle in response to changes in load or airspeed, whereas a variable pitch propeller does not inherently control RPM in this way. Instead, while the angle can change to optimize thrust, the RPM may vary depending on the power settings and flight conditions.

The other options do not accurately reflect the operational capabilities of the different types of propellers. Fixed pitch propellers indeed don't allow for any change in blade angle, but that doesn't make them relevant to the distinction between variable pitch and constant speed propellers. Understanding these differences is crucial for pilots who need to manage their aircraft's performance effectively in various flight situations.