The stability around the vertical axis is called which?

• A. Lateral stability
• B. Longitudinal stability
• C. Directional stability
• D. Vertical stability

Answer: (C)

Stability about the vertical axis is directional stability. It describes how the aircraft resists yaw motions—left or right turning about the vertical axis—and tends to return to a straight-ahead heading after a disturbance. The vertical tail (and its distance from the center of gravity) creates a restoring yawing moment when the airplane yaws, similar to a weather vane that aligns with the wind and then resists further turning. That restoring effect is what keeps the aircraft from spiraling into persistent sideslip.

Lateral stability relates to roll about the longitudinal axis, affecting how the airplane returns from a banked condition. Longitudinal stability concerns pitch about the lateral axis, influencing whether a nose-up or nose-down tendency dampens after a disturbance. The term directional stability specifically targets yaw about the vertical axis, which is why it is the correct concept here.