In weight and balance calculations, what is the purpose of the datum line?

In weight and balance calculations, what is the purpose of the datum line?

• A. To determine total aircraft weight
• B. To define a reference point from which arms are measured
• C. To locate fuel quantity
• D. To compute drag coefficient

Answer: (B)

The datum line is the fixed reference point from which all arms are measured. In weight and balance, each item’s arm is the horizontal distance from the datum to the item’s center of gravity, and the moment is found by multiplying that weight by its arm. By using a single datum, you can sum all moments and then find the center of gravity by dividing the total moment by the total weight. The datum line does not determine total weight, locate fuel, or compute drag—those are handled by summing weights, using fuel gauges and tank locations, and considering aerodynamics, respectively.

The datum line is the fixed reference point from which all arms are measured. In weight and balance, each item’s arm is the horizontal distance from the datum to the item’s center of gravity, and the moment is found by multiplying that weight by its arm. By using a single datum, you can sum all moments and then find the center of gravity by dividing the total moment by the total weight. The datum line does not determine total weight, locate fuel, or compute drag—those are handled by summing weights, using fuel gauges and tank locations, and considering aerodynamics, respectively.