This glossary is written for virtual airline and flight simulation use within Virtual Air Canada Airline. It is not intended as a real-world aviation reference.
MAC
Mean Aerodynamic Chord
The Mean Aerodynamic Chord is a reference measurement representing the average chord length of a tapered or complex wing, used as a standard unit for expressing the position of the aircraft’s centre of gravity (CG). The chord of a wing is the straight-line distance from the leading edge to the trailing edge at any given spanwise station. Because most aircraft wings are tapered or swept, the chord length varies along the span, so the MAC provides a single representative value that accounts for the wing’s aerodynamic properties. CG is expressed as a percentage of MAC - for example, a CG of 25% MAC means the centre of gravity is located at a point one quarter of the way aft along the mean aerodynamic chord.
The allowable CG range for any aircraft is defined in the Aircraft Flight Manual and expressed in percentage of MAC or sometimes as a moment arm in inches. A forward CG increases longitudinal stability but raises stall speed and increases the trim drag required to maintain level flight. An aft CG reduces stability, decreases stall speed, and can lead to control difficulties or departure from controlled flight if the CG exceeds the aft limit. Loadmasters and dispatchers calculate the planned CG based on payload distribution, and pilots verify the CG is within limits before each departure using the load and trim sheet.