An aircraft had an empty weight of 998 pounds with an empty weight CG of 13.48 inches. After replacing the engine as described, the new empty weight CG is which value?

An aircraft had an empty weight of 998 pounds with an empty weight CG of 13.48 inches. After replacing the engine as described, the new empty weight CG is which value?

• A. 12.50 inches
• B. 12.90 inches
• C. 12.73 inches
• D. 13.48 inches

Answer: (C)

Center of gravity moves whenever the weight distribution changes, such as when the engine is replaced. The empty weight CG is found from the total moment about the datum divided by the total empty weight. So when you replace the engine, you must update both the empty weight and the total moment. First, update the empty weight: remove the weight of the old engine and add the weight of the new engine. Then update the moment: subtract the old engine’s moment (old engine weight × its arm) and add the new engine’s moment (new engine weight × its arm). The new CG is then the new total moment divided by the new empty weight. In this scenario, doing that calculation yields a new empty weight CG of about 12.73 inches. That forward shift relative to the original 13.48 inches happens because the new engine (or its placement) contributes a different weight and moment, pulling the balance point forward.

Center of gravity moves whenever the weight distribution changes, such as when the engine is replaced. The empty weight CG is found from the total moment about the datum divided by the total empty weight. So when you replace the engine, you must update both the empty weight and the total moment.

First, update the empty weight: remove the weight of the old engine and add the weight of the new engine. Then update the moment: subtract the old engine’s moment (old engine weight × its arm) and add the new engine’s moment (new engine weight × its arm). The new CG is then the new total moment divided by the new empty weight.

In this scenario, doing that calculation yields a new empty weight CG of about 12.73 inches. That forward shift relative to the original 13.48 inches happens because the new engine (or its placement) contributes a different weight and moment, pulling the balance point forward.