Which reference point does a CG location expressed as a percentage of MAC relate to when measuring distance?

Which reference point does a CG location expressed as a percentage of MAC relate to when measuring distance?

• A. LEMAC
• B. Datum
• C. MAC
• D. Wing root

Answer: (A)

When CG is expressed as a percentage of the mean aerodynamic chord (MAC), the distance is measured from the Leading Edge of the MAC (the LEMAC) along the MAC to the CG, then divided by the MAC length and multiplied by 100. This reference from the LEMAC provides a consistent, aerodynamically meaningful scale for comparing balance across different aircraft and wings. The LEMAC is the starting point because the MAC represents the spanwise distribution of aerodynamic forces, and using its leading edge as the zero point keeps the percent-of-MAC value meaningful regardless of wing shape or size. Other references like the datum or wing root are used for raw arm computations, but they do not define the percent-of-MAC CG location.