What is meant by a moment index?

• A. A measure of force acting over time.
• B. The aircraft's center of gravity.
• C. The product of weight and arm.
• D. A moment divided by a constant such as 10, 100, or 1,000.

Answer: (D)

A moment index is a scaled version of the rotational moment used in weight-and-balance calculations. The moment itself is the product of weight and its arm (distance from the reference point). To keep the numbers practical for charts and tables, this moment is divided by a constant such as 10, 100, or 1,000, yielding the moment index. This preserves the relative effects of different loads while producing simpler, smaller numbers for plotting or comparison.

For example, a load of 2,000 lb at 50 inches has a moment of 100,000 lb-in. Dividing by 100 gives 1,000; dividing by 1,000 gives 100. These scaled values are easier to work with on balance charts.

The other ideas don’t fit because the moment index isn’t about force over time (that would be impulse), nor is it a location like the aircraft’s center of gravity, and it isn’t the raw moment itself (weight times arm) but a scaled version of that moment.