Stability and the centre of gravity

An aircraft is stable if, after a gust disturbs it, it tends to return to where it was.

• Longitudinal stability (pitch) comes from the tailplane and the position of the centre of gravity (CG) ahead of the centre of pressure of the wing.
• Lateral stability (roll) comes mainly from dihedral and a high wing.
• Directional stability (yaw) comes from the fin — like the feathers on an arrow.

If the CG is too far forward the aircraft is very stable but heavy on the controls and needs more speed to land. If it is too far aft it becomes unstable and may be impossible to recover from a stall or spin. That is why pilots always do a weight and balance calculation before flight.