If an airplane is loaded to the rear of its CG range, instability is exhibited about which axis?

If an airplane is loaded to the rear of its CG range, instability is exhibited about which axis?

• A. Longitudinal axis
• B. Lateral axis
• C. Vertical axis
• D. Diagonal axis

Answer: (B)

Pitch stability is governed by the axis that runs wingtip to wingtip—the lateral axis—which is the axis about which the airplane rotates when it pitches up or down. When the airplane is loaded toward the rear, the center of gravity moves closer to the tail, and the tail’s ability to provide a restoring moment during a pitch disturbance is diminished. With the tail less effective at opposing a nose-up or nose-down movement, the airplane becomes less resistant to pitching disturbances and can become unstable about the lateral axis. In contrast, roll stability involves the longitudinal axis, and yaw stability involves the vertical axis, so a rearward CG mainly affects pitch stability.

Pitch stability is governed by the axis that runs wingtip to wingtip—the lateral axis—which is the axis about which the airplane rotates when it pitches up or down. When the airplane is loaded toward the rear, the center of gravity moves closer to the tail, and the tail’s ability to provide a restoring moment during a pitch disturbance is diminished. With the tail less effective at opposing a nose-up or nose-down movement, the airplane becomes less resistant to pitching disturbances and can become unstable about the lateral axis. In contrast, roll stability involves the longitudinal axis, and yaw stability involves the vertical axis, so a rearward CG mainly affects pitch stability.