Which type of propeller has a blade angle that cannot be changed by the pilot?

A fixed-pitch propeller is designed with blades that are set at a specific angle that cannot be altered during flight. This design means that the propeller operates efficiently at a predetermined flight condition, such as a specific speed or altitude. Pilots cannot adjust the blade pitch to optimize performance in varying flight situations, which can limit the versatility of the aircraft. A fixed-pitch propeller is typically simpler and lighter, making it common in smaller or more basic aircraft, where performance adjustments are less critical compared to larger, more versatile planes.

In contrast, other types of propellers, such as variable pitch, constant-speed, and adjustable pitch propellers, allow for alterations to the blade angle. These adjustments can enhance performance, fuel efficiency, and climb rates under different flying conditions. The inability to change the blade angle in a fixed-pitch propeller is a defining characteristic that distinguishes it from these other types.