What is the primary purpose of using a universal propeller protractor?

The primary purpose of a universal propeller protractor is to measure degrees of flap travel. This tool is specifically designed to help technicians and pilots accurately measure and set the flap angles of an aircraft, which are crucial for safe takeoff, landing, and overall flight performance. By ensuring that flaps are set to the correct angle, pilots can optimize lift and drag characteristics, essential factors in controlling aircraft during different phases of flight.

Flap travel measurement is a critical aspect of maintaining the aircraft's operational capabilities, as improper flap positioning can affect both performance and safety. Accurate readings from a protractor help ensure that the flaps function as intended, thus supporting the aircraft's aerodynamic efficiency.

Other options do not align with the specific use of the universal propeller protractor. For example, measuring speed, assessing fuel efficiency, or determining weight distribution are tasks that require different equipment and methods, rather than the direct measurement capabilities offered by a propeller protractor.