What is the 'moment' in a weight and balance worksheet?

• A. The product of weight (lb) and its arm (in).
• B. The sum of weights.
• C. The distance from datum to CG.
• D. The weight times distance from tail.

Answer: (B)

Moment is the turning effect a weight has about the reference point (the datum). It’s found by multiplying the weight by its arm: moment = weight (lb) × arm (in), with the result in inch-pounds. This product captures how far and how heavy the item is from the datum, illustrating how the weight tends to rotate the airplane about that point.

To balance the aircraft, you compute a moment for every item and then sum all those moments to get the total moment. The airplane’s center of gravity is then found by dividing this total moment by the total weight: CG location = total moment ÷ total weight. So the moment is about multiplying weight by how far it sits from the datum, and the total moment drives the CG calculation.

Why the other ideas don’t fit: the sum of weights is just total weight, not a moment. The distance from datum to CG describes where the balance point is, not the turning effect of a single weight. And the arm is measured from the datum, not from the tail, so using distance from the tail would not yield the correct moment.

Example: 1,000 lb at 50 in gives a moment of 50,000 in-lb; 500 lb at 70 in gives 35,000 in-lb; total moment 85,000 in-lb with total weight 1,500 lb, so CG is 85,000 ÷ 1,500 ≈ 56.7 in from the datum.