The longitudinal static stability of an aircraft is significantly influenced by the distance between the Centre of Gravity and the aerodynamic centre of the airplane.

If the CG moves forward, the airplane becomes more stable (greater moment arm between the aerodynamic centre and CG, and if too far forward will cause the airplane to be difficult for the pilot to bring nose-up as for landing.

If the CG is too far aft, the moment arm between it and the a.c. diminishes, reducing the inherent stability of the airplane and in the extreme going negative and rendering the airplane longitudinally unstable.