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Weight and Balance

Key Terms

  • Center of Gravity (CG): An imaginary point where the aircraft is balanced. Imagine a string tied to the CG symbol (a circle cut into four quadrants with two blacked out); the aircraft would balance on the end of that string. This balance occurs on three axes: fore and aft, side to side, and vertically.

  • CG Range: The specific range within which the center of gravity must fall. If the CG is outside this range, the aircraft will not balance or fly safely. You can find these limits in Chapter 6 of the Pilot Information Manual (PIM).

  • Datum (Reference Datum): An imaginary vertical plane or line from which all horizontal distances are measured for weight and balance calculations.

  • Station: A specific location on the aircraft (e.g., pilot seat, passenger seats, fuel tanks, baggage compartment).

  • Arm: The horizontal distance from the reference datum to a specific station, typically measured in inches.

  • Weight: The weight of an object at a specific station (e.g., the pilot, fuel, or baggage).

  • Moment: A physics term referring to a rotational or torquing force. It is the product of weight multiplied by the arm:

    Weight×Arm=MomentWeight \times Arm = Moment

Fuel Definitions

  • Unusable Fuel: The small amount of fuel that cannot be safely used by the engine. In aircraft like the Cessna 172, fuel pickups are located on the side of the tank (rather than the very bottom) to prevent dirt, grime, or sediment from clogging the system.

  • Fuel Load: Defined specifically as the weight of usable fuel only.

Loading Definitions

  • Useful Load: The weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil.

  • Payload: The weight of occupants, cargo, and baggage—essentially the load for which a commercial operator would be paid.

Empty Weight Variations

  • Standard Empty Weight: The weight of the airframe, engines, and all permanently installed operating equipment, including hydraulic fluid, unusable fuel, and full engine oil.

  • Basic Empty Weight: The standard empty weight plus the weight of optional equipment.

  • Licensed Empty Weight: Similar to basic empty weight, but excludes the weight of engine oil.

Note

When performing your calculations using Basic Empty Weight, you do not need to add the weight of unusable fuel separately, as it is already included in that definition.

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