Weight and Balance

An aircraft may only be flown loaded within its weight and centre-of-gravity envelope. Weighing requires the aircraft level on calibrated scales in the configuration the manual specifies, including unusable fuel and full oil. Empty weight plus useful load equals gross weight.

Each item contributes a moment equal to its weight multiplied by its arm, the distance from the datum. The centre of gravity is the total moment divided by the total weight. Adding, removing or shifting load moves the centre of gravity in a predictable direction along the aircraft.

A forward centre of gravity is stable but makes the controls feel heavy; an aft centre of gravity is light and responsive but can become uncontrollable or unrecoverable beyond the published aft limit. Ballast corrects an out-of-envelope load only when the manual permits it. Helicopters add a lateral centre-of-gravity limit. Every loading is computed in writing, signed, and kept with the flight papers.