Centre of Gravity (C of G)

The point of balance of the aircraft. 

The point through which weight (the resultant of all gravitational forces) is said to act. 

Also called Centre of Mass. 

Usually expressed as a position relative to a datum such as the nose, firewall or leading edge of the wing.

C of G Position

The C of G's position depends on the weight distribution of all the individual parts of the aircraft as well as the fuel and payload. 

If the aircraft was suspended from its centre of gravity, it would balance evenly. 

The C of G position is critical to the control of the aircraft, and it must be kept within strict limits.

If the Centre of Gravity is forward, the distance to the horizontal stabiliser will be long and therefore encouraging longitudinal stability.