The aircraft becomes less stable as the CG is moved rearward.

The aircraft becomes less stable as the CG is moved rearward.

• A. True
• B. False
• C. Depends on airspeed
• D. Only with flaps

Answer: (A)

Moving the center of gravity toward the tail reduces longitudinal stability because the tail’s stabilizing effect relies on a lever arm from the CG to the tail. The tail normally provides a downward force to counter nose‑up tendencies. As the CG moves aft, that distance shortens, so for a given tail force the restoring pitching moment about the CG is smaller. This reduces the aircraft’s ability to return to trim after a disturbance. The concept of static margin describes this: moving the CG toward the neutral point lowers the static margin, making the airplane less stable and potentially neutrally stable or unstable if moved far enough. Flaps or airspeed can affect tail effectiveness and damping, but the basic effect of aft CG reducing stability holds.

Moving the center of gravity toward the tail reduces longitudinal stability because the tail’s stabilizing effect relies on a lever arm from the CG to the tail. The tail normally provides a downward force to counter nose‑up tendencies. As the CG moves aft, that distance shortens, so for a given tail force the restoring pitching moment about the CG is smaller. This reduces the aircraft’s ability to return to trim after a disturbance. The concept of static margin describes this: moving the CG toward the neutral point lowers the static margin, making the airplane less stable and potentially neutrally stable or unstable if moved far enough. Flaps or airspeed can affect tail effectiveness and damping, but the basic effect of aft CG reducing stability holds.