Which term best describes the theoretical pitch of a propeller?

• A. Geometric pitch
• B. Effective pitch
• C. Actual pitch
• D. Real pitch

Answer: (A)

Theoretical pitch is geometric pitch. It represents the distance the propeller would advance in one revolution if there were no slip between the blade and the air—the advancement dictated purely by the blade geometry and pitch angle. In actual flight, slip occurs because air offers resistance, so the real forward distance per revolution is less than this geometric value, which is why the term “effective pitch” is used for real operating conditions. Terms like actual or real pitch aren’t standard descriptors for this concept. So the geometric pitch is the best description of the theoretical advancement.