How would you present a weight and balance calculation if you have multiple stations with different arms?

• A. List each weight and its arm, compute its moment, sum weights and moments, then calculate CG = total moment ÷ total weight.
• B. Sum weights and moments, then calculate CG = total moment ÷ total weight.
• C. Only total weight is needed to determine CG.
• D. CG is equal to total moment divided by number of stations.

Answer: (A)

When stations have different arms, the balance is found by treating each load at its own location. For every item, multiply its weight by the arm of its station to get that item’s moment. Then add up all the weights to get the total weight and add up all the moments to get the total moment. The center of gravity is the total moment divided by the total weight.

If several items share the same arm, you can combine them into a single weight at that arm, but you still sum their moments to contribute to the total moment. This approach accounts for how weight is distributed along different arms.

Why not the other ideas? You need the total weight in the denominator because CG is the weighted average of the arms, weighted by the actual weights. Dividing a total moment by the number of stations doesn’t reflect how far the weight is spread, and considering only total weight loses information about where that weight sits along the fuselage.