As weighed, the empty weight of an aircraft is 5,862 pounds with a moment of 885,957. If 20 pounds of potable water are on board at +84 and 23 pounds of hydraulic fluid are in a tank at +101, what is the empty weight CG of the aircraft?

• A. 151.365 inches
• B. 150.000 inches
• C. 152.500 inches
• D. 151.000 inches

Answer: (A)

The key idea is that the center of gravity is found by dividing the total moment by the total weight. When weights are added, you add their moments (weight times its arm) to the existing moment, and you add the weights to the existing weight, then divide to get the new CG.

First, the empty-weight CG uses the empty weight and its moment:

CG_empty = M_empty / W_empty = 885,957 / 5,862 ≈ 151.14 inches.

If you actually place the two onboard items, you update both weight and moment:

Total weight = 5,862 + 20 + 23 = 5,905 lb.

Total moment = 885,957 + (20 × 84) + (23 × 101) = 885,957 + 1,680 + 2,323 = 889,960 in-lb.

CG with items on board = 889,960 / 5,905 ≈ 150.71 inches.

So the empty-weight CG is about 151.14 inches, and the loaded CG (with the water and hydraulic fluid) is about 150.71 inches. The general method—sum moments, sum weights, then divide—is the essential tool you’ll use for weight-and-balance problems.