Balance control refers to the location of the cg of an aircraft. This is of primary importance to aircraft stability,which determines safety in flight.
The cg is the point at which the total weight of the aircraft is assumed to be concentrated, and the ch must be located within specific limits for safe flight. Both lateral and longitudinal balance are important, but the prime concern is longitudinal balance; that is, the location of the cg along the longitudinal or lengthwise axis.
An airplane is designed to have stability that allows it to be trimmed so it will maintain straight and level flight with hand off the controls. Longitudinal stability is maintained by ensuring the cg is slightly ahead of the center of lift this produces a fixed nose-down force independent of the airspeed. This is balanced by a variable nose-up force, which is produces by a downward aerodynamic force on the horizontal tail surfaces that varies directly with the airspeed.