In our baseline data, what is the arm for the fuel weight?

• A. 60 inches
• B. 83 inches
• C. 96 inches
• D. 120 inches

Answer: (C)

The arm is the distance from the aircraft datum to the center of gravity of a given weight. Baseline data provides the standard arm values used to compute moments for each component, including fuel. For fuel, the arm represents where the fuel’s CG sits relative to the datum, which depends on where the wing tanks are located.

In this aircraft’s baseline data, the fuel weight has an arm of 96 inches. That means the center of gravity of the fuel sits 96 inches aft of the datum, so when you multiply the fuel weight by 96 you get the fuel’s moment contribution. The other distances would place the fuel’s CG at locations that don’t correspond to the actual tank geometry, leading to incorrect moments.