If an airplane is loaded to the rear of its CG range, it will tend to be unstable about its

• A. vertical axis
• B. lateral axis
• C. longitudinal axis
• D. yaw axis

Answer: (A)

When the load is toward the rear of the CG, the aircraft becomes less statically stable in pitch. Pitching motion is rotation about the lateral axis, which runs wingtip to wingtip. With aft CG, the tail has less leverage to generate a restoring force, so after a disturbance the airplane tends to maintain or exaggerate the nose-up or nose-down attitude instead of returning to the trimmed state. This makes the aircraft unstable about the pitch (lateral) axis. Yaw stability (about the vertical axis) and roll stability (about the longitudinal axis) are influenced more by other factors like the vertical tail, dihedral, and wing design, and are not the primary effect of aft CG.