Definitions

EMPTY WEIGHT - The total weight of the aircraft including unusable fuel, undrainable oil, and the total quantity of engine coolant and hydraulic fluid. The passengers and crew, payload, usable fuel, and drainable oil are excluded.

ZERO FUEL WEIGHT - The maximum weight that can be concentrated in the fuselage (passengers and crew plus payload) in order to prevent wing bending stress. All additional weight must be in the form of fuel carried in the wings.

MAXIMUM TAKEOFF WEIGHT - The maximum allowable weight for takeoff.

MAXIMUM RAMP WEIGHT - A weight slightly higher than the MAXIMUM TAKEOFF WEIGHT that allows for fuel burn during taxi.

MAXIMUM LANDING WEIGHT - This weight is dependent upon field conditions such as altitude, temperature, pressure, wind, and slope.

USEFUL LOAD - The maximum allowable takeoff weight minus the empty weight. The weight of the crew, passengers, baggage, usable fuel and drainable oil.

DATUM - An imaginary reference line which serves as the starting point for all measurements of ARM. The location of the DATUM is determined by the manufacturer (usually at the tip of the spinner or the firewall).

STATION - A location in the aircraft represented by a number in inches from the DATUM. The DATUM station is always zero. The station and arm usually have the same number; thus, an item located at station +95 would have an ARM of 95 inches.

ARM - The distance in inches from the DATUM to a particular STATION in the aircraft, which represents the center of gravity of the item at that location. The ARM will be + if measured aft of the DATUM and - if measured forward of the DATUM.

MOMENT - The product (expressed in pound-inches) of the weight of an item multiplied by its ARM.

MOMENT INDEX - The MOMENT divided by a constant (such as 100 or 1000) in order to simplify weight and balance calculations.

TOTAL MOMENT - the sum of all the MOMENTS calculated by multiplying the total weight at each station by its corresponding ARM.

CENTER OF GRAVITY (CG) - The point about which an aircraft would be balanced (expressed in inches from the DATUM) if it could be suspended at that point. It is the theoretical center of mass of the aircraft which is determined by dividing the TOTAL MOMENT by the TOTAL WEIGHT.

CG LIMITS - the forward and aft limits of the CG (expressed in inches from the DATUM). The CG range is the distance between these limits. When making weight and balance calculations prior to flight, the resulting CG must fall within the acceptable range determined by the manufacturer or the aircraft will be unbalanced. If it is nose heavy it may be difficult to flare the aircraft on landing. If it is tail heavy it may stall.