Summary of Aircraft Weight and Balance Fundamentals

## Introduction Aircraft weight and balance ensures an airplane or helicopter is loaded so it can be flown safely and controllably. Proper weight and balance procedures protect structural limits, performance margins, and controllability throughout all phases of flight. > **Definition:** The aircraft's weight is the total mass (reported as weight) of the airplane and its contents; the arm is the distance from a reference datum to an item; the moment is the product of weight and arm and is used to compute center of gravity (CG). ## Key Concepts Broken Down ### Weight, Arm, and Moment - **Weight:** The force due to gravity acting on mass (reported in pounds or kilograms depending on unit system). - **Arm:** > **Definition:** The arm is the distance (in inches) an item is located forward or aft of the datum. It is obtained by actual measurement or from the aircraft weight-and-balance records. - Measured from the aircraft datum (a fixed reference point defined by the manufacturer). - Arms can be positive or negative depending on whether the item is aft or forward of the datum. - **Moment:** The turning effect of a weight about the datum, calculated as weight × arm. Moments let you compute the CG. Practical example: If a 150 lb pilot sits at an arm of 36 in, the moment is $150 \times 36 = 5400$ in·lb. ### Empty Weight, Tare, Residual, and Minimum Fuel - **Empty weight:** The aircraft weight including all required operating and installed equipment but excluding usable fuel, payload, and passengers. When records are missing, reweigh the aircraft to establish empty weight and empty weight CG. - **Tare weight:** > **Definition:** "Tare" is the weight of the extra equipment used for weighing the aircraft such as chocks, blocks, jacks, and chains. Tare weight must be subtracted from scale readings to obtain the actual aircraft weight. - Subtract tare from scale totals to report correct aircraft empty weight. - **Residual (undrainable) fuel:** > **Definition:** Residual fuel is fuel remaining in tanks, lines, and the engine after draining; it is considered part of the empty weight and is unusable for loading computations. - **Minimum fuel (for weight-and-balance):** > **Definition:** Minimum fuel is the quantity necessary for 30 minutes of operation at rated maximum continuous power. It is used in weight-and-balance computations when low fuel might create the most critical balance condition. - For loading, use either actual fuel or minimum fuel depending on which produces the more critical (worst-case) CG condition. ### Ballast and When to Use It - **Ballast:** > **Definition:** Ballast are items (lead bars, metal plates, shot bags, sandbags, etc.) added to the aircraft to achieve a desired CG location. - Use only when necessary to bring CG into allowable range. - Ballast must be secured and its weight/arm recorded in weight-and-balance logs. ### Differences Between Fixed-Wing and Helicopter CG Ranges - Helicopters often have much narrower CG ranges than fixed-wing aircraft; in some helicopters the allowable CG band can be less than three inches. This makes precise weight-and-balance especially critical for rotorcraft. ### Equipment Inclusion When Weighing - When you weigh an aircraft to determine empty weight and empty weight CG, include all operating equipment—required, optional, and special. These items become part of the empty weight and affect the CG. ### Manufacturer Empty Weight CG vs. Operational Use - Some manufacturers specify an "empty weight CG" position in the records even if the aircraft will not be operated at that empty weight. If the empty weight CG falls within the manufacturer’s empty-weight CG range, routine load checks may be unnecessary when standard loading and seating are used. ### Considering Aircraft Category - Aircraft category (e.g., normal, utility, acrobatic) affects maximum gross weights and CG ranges. Always use the appropriate limits for the category under which t