L-1011 Weight and Balance: Mean Aerodynamic Cord

The Mean Aerodynamic Cord (MAC) by definition is the cord of an imaginary air foil which throughout the flight range has the same force vectors as the three dimensional wing. In the example above, we have a rectangular wing with a cord root of 100 inches and a tip root of 50 inches. In order to graphically locate the MAC, we simply add 50 inches to the lower half of the cord root and 100 inches to the upper half of the cord tip. The line connecting the two extremes will intersect a line drawn from the center of the root to the center of the tip. The point of intersection then represents the Mean Aerodynamic Cord, at the trailing edge we have the trailing edge MAC. At the leading edge we have the Leading Edge MAC. Note that the MAC is not the average cord, but is the cord to the centroid of area. Centroid is the center of mass.