In the process of weighing toward obtaining the CG, the arms from the weighing points always extend which way?

• A. Parallel to the centerline of the airplane
• B. Perpendicular to the centerline of the airplane
• C. Along the fuselage
• D. Radially from the datum

Answer: (A)

The weight and balance process finds the center of gravity by summing moments about a fixed datum, so each weight’s moment is its weight times the distance along the airplane’s length from the datum. That distance, the arm, is taken parallel to the aircraft’s centerline (the longitudinal axis). Extending arms perpendicular to the centerline would measure sideways distances that don’t affect the longitudinal CG, and radial directions from the datum don’t align with how moments are defined for CG. So the arms extend parallel to the centerline to correctly capture forward/aft moments.