W&B 3-9

Figure 3-18. Formula for determining the CG expressed in percent MAC. CG inches % MAC = Distance aft of LEMAC × 100 MAC = = 27.4 17 × 100 62 Figure 3-17. Large aircraft weight and balance calculation diagram. CG = 27.4% CG = 161 MAC TEMAC LEMAC Datum CG = 27.4% CGCG 1= 161161 MAC Station 144" Station 206" Figure 3-19. Formula for determining the CG in inches from the datum. CG inches from datum = LEMAC + MAC × CG % MAC 100 = 144 + = 160.9 62 × 27.4 100 CG = 161" In order to find the percent MAC, firs determine the distance of the CG from LEMAC. CG – LEMAC = Distance from LEMAC 161" – 144" = 17" The location of the CG expressed in percent MAC is determined using the formula found in Figure 3-18. The CG of the airplane is located at 27.4 percent MAC. It is sometimes necessary to determine the location of the CG in inches from the datum when its location in percent MAC is known. The CG of the airplane is located at 27.4 percent MAC. MAC = 206 – 144 = 62 LEMAC = station 144 Determine the location of the CG in inches from the datum by using the formula found in Figure 3-19. The CG of this airplane is located at station 160.9 inches aft of the datum. It is important for longitudinal stability that the CG be located ahead of the center of lift of a wing. Since the center of lift is expressed as percent MAC, the location of the CG is expressed in the same terms.