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Weight and Balance Handbook

FAA-H-8083-1B Version 2016
All Library Documents FAA Source

Chapter 3

Weighing the Aircraft and Determining the Empty Weight Center of Gravity

Figure 3-17. Large aircraft weight and balance calculation diagram.
Figure 3-17. Large aircraft weight and balance calculation diagram.

CG = 161″

In order to find the percent MAC, first determine the distance of the CG from LEMAC.

CG – LEMAC = Distance from LEMAC

161″ – 144″ = 17″

Figure 3-18. Formula for determining the CG expressed in percent MAC.
Figure 3-18. Formula for determining the CG expressed in percent MAC.

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.

CG = 27.4% MAC

MAC = 206 – 144 = 62

LEMAC = station 144

Figure 3-19. Formula for determining the CG in inches from the datum.
Figure 3-19. Formula for determining the CG in inches from the datum.

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.