What is the purpose of setting tailplane incidence?

• A. It sets the tail airfoil angle of attack, thereby affecting tail lift and pitching moment
• B. It changes wing tip shape
• C. It alters fuselage length
• D. It adjusts engine thrust

Answer: (A)

Setting tailplane incidence establishes the tail’s angle of attack, so the tail generates a specific amount of lift (usually a downward force in conventional configurations) and a corresponding pitching moment about the aircraft’s center of gravity. This baseline moment lets the aircraft be trimmed for steady, level flight, and it also sets the stability characteristics: as the aircraft pitches, the tail’s lift changes in a way that provides a restoring moment toward the trimmed condition. By selecting the incidence, designers control how much tail lift or downforce the tailplane will produce at a given flight condition, which is essential for longitudinal stability and trim.

It’s not about changing wing tip shape, fuselage length, or engine thrust; those are unrelated design or performance factors. The tailplane incidence specifically tunes the tail’s angle of attack and the resulting lift and pitching moment that help keep the aircraft balanced.