When using a universal propeller protractor, how should it be zeroed?

Zeroing a universal propeller protractor is an important step in ensuring accurate measurements of propeller pitch. The correct method involves placing the aileron in the neutral position. This is crucial because it establishes a baseline reference that accounts for variations in wing attitude and ensures that any pitch measurements taken during further adjustments are consistent.

By setting the aileron to neutral, the aircraft's control surfaces are at a position representative of stable flight conditions. This allows the protractor to measure pitch angles accurately, without the bias introduced by control surface positions that could skew the readings during operation.

While other options may seem reasonable, they do not provide the accurate reference point needed for the protractor. For example, setting the propeller to maximum or minimum pitch may not correspond to the neutral flight attitude of the aircraft, and using the aircraft in level flight is more variable depending on how the aircraft is configured at that moment. Therefore, establishing the neutral position of the aileron is the most reliable way to zero the protractor for precise measurements.