When is the blade angle of a fixed pitch propeller set for optimum performance?

The blade angle of a fixed pitch propeller is set for optimum performance during cruise. In this phase of flight, the aircraft is typically operating at a constant speed and altitude, allowing the propeller to perform efficiently at that specific thrust and speed condition. The fixed pitch blade angle is designed to provide the best compromise between thrust and efficiency at cruise conditions, maximizing the aerodynamic properties of the propeller and leading to better fuel efficiency and reduced drag.

Setting the blade angle during other phases, such as takeoff or landing, would not provide optimal performance since the requirements for thrust and efficiency vary significantly during these different stages of flight. For example, during takeoff, maximum thrust is typically required, while during landing, lower speeds and thrust levels are in play. Thus, the configuration of the propeller for cruising is essential for achieving the best overall performance of the aircraft during its most sustained and efficient phase of operation.