The following alteration was performed on an aircraft: A model B engine weighing 175 pounds was replaced by a model D engine weighing 185 pounds at a -62.00-inch station. The aircraft weight and balance records show the previous empty weight to be 998 pounds and an empty weight CG of 13.48 inches. What is the new empty weight CG?

The following alteration was performed on an aircraft: A model B engine weighing 175 pounds was replaced by a model D engine weighing 185 pounds at a -62.00-inch station. The aircraft weight and balance records show the previous empty weight to be 998 pounds and an empty weight CG of 13.48 inches. What is the new empty weight CG?

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

Answer: (C)

The concept to use is moment balance: CG = total moment / total weight, and total moment is the sum of each weight times its arm. When an engine is replaced, update both the total weight and the total moment based on the engine’s weight change and its location. Original empty weight is 998 lb with an empty weight CG of 13.48 in, giving an original moment of 998 × 13.48 = 13,453.04 in-lb. The new engine weighs 185 lb instead of 175 lb, a gain of 10 lb, and sits at the -62.00 in station. That creates a moment change of 10 × (-62) = -620 in-lb, which moves the total moment downward (forward). New empty weight = 998 + 10 = 1008 lb. New total moment = 13,453.04 − 620 = 12,833.04 in-lb. New empty weight CG = 12,833.04 / 1008 ≈ 12.731 in, which rounds to 12.73 inches. So the new empty weight CG is about 12.73 inches, reflecting a forward shift due to the heavier engine located forward of the datum.

The concept to use is moment balance: CG = total moment / total weight, and total moment is the sum of each weight times its arm. When an engine is replaced, update both the total weight and the total moment based on the engine’s weight change and its location.

Original empty weight is 998 lb with an empty weight CG of 13.48 in, giving an original moment of 998 × 13.48 = 13,453.04 in-lb. The new engine weighs 185 lb instead of 175 lb, a gain of 10 lb, and sits at the -62.00 in station. That creates a moment change of 10 × (-62) = -620 in-lb, which moves the total moment downward (forward).

New empty weight = 998 + 10 = 1008 lb. New total moment = 13,453.04 − 620 = 12,833.04 in-lb. New empty weight CG = 12,833.04 / 1008 ≈ 12.731 in, which rounds to 12.73 inches.

So the new empty weight CG is about 12.73 inches, reflecting a forward shift due to the heavier engine located forward of the datum.