Weight and Balance

• CG limits—the specified forward and aft points within • Moment index (or index)—a moment divided by a which the CG must be located during flight. These constant such as 100, 1,000, or 10,000. The purpose limits are indicated on pertinent aircraft specifications. of using a moment index is to simplify weight and balance computations of aircraft where heavy items • CG range—the distance between the forward and aft and long arms result in large, unmanageable numbers. CG limits indicated on pertinent aircraft specifications. • Payload (GAMA)—the weight of occupants, cargo, • Datum (reference datum)—an imaginary vertical and baggage. plane or line from which all measurements of arm are taken. The datum is established by the manufacturer. • Standard empty weight (GAMA)—aircraft weight Once the datum has been selected, all moment arms that consists of the airframe, engines, and all items of and the location of CG range are measured from this operating equipment that have fixed locations and are point. permanently installed in the aircraft, including fixed ballast, hydraulic fluid, unusable fuel, and full engine • Delta—a Greek letter expressed by the symbol r to oil. indicate a change of values. As an example, rCG indicates a change (or movement) of the CG. • Standard weights—established weights for numerous items involved in weight and balance computations. • Floor load limit—the maximum weight the floor These weights should not be used if actual weights can sustain per square inch/foot as provided by the are available. Some of the standard weights are: manufacturer. Gasoline.................................................. 6 lb/US gal • Fuel load—the expendable part of the load of the aircraft. It includes only usable fuel, not fuel required Jet A, Jet A-1 ....................................... 6.8 lb/US gal to fill the lines or that which remains trapped in the Jet B ......................................................6.5 lb/US gal tank sumps. Oil .........................................................7.5 lb/US gal • Licensed empty weight—the empty weight that Water .................................................8.35 lb/US gal consists of the airframe, engine(s), unusable fuel, and undrainable oil plus standard and optional equipment • Station—a location in the aircraft that is identified by as specified in the equipment list. Some manufacturers a number designating its distance in inches from the used this term prior to GAMA standardization. datum. The datum is, therefore, identified as station zero. An item located at station +50 would have an • Maximum landing weight—the greatest weight that arm of 50 inches. an aircraft is normally allowed to have at landing. • Useful load—the weight of the pilot, copilot, • Maximum ramp weight—the total weight of a loaded passengers, baggage, usable fuel, and drainable oil. aircraft including all fuel. It is greater than the takeoff It is the basic empty weight subtracted from the weight due to the fuel that will be burned during the maximum allowable gross weight. This term applies taxi and run-up operations. Ramp weight may also be to general aviation (GA) aircraft only. referred to as taxi weight. • Maximum takeoff weight—the maximum allowable Principles of Weight and Balance Computations weight for takeoff. It is imperative that all pilots understand the basic principles • Maximum weight—the maximum authorized weight of weight and balance determination. The following methods of the aircraft and all of its equipment as specified in of computation can be applied to any object or vehicle for the TCDS for the aircraft. which weight and balance information is essential. • Maximum zero fuel weight (GAMA)—the maximum By determining the weight of the empty aircraft and adding weight, exclusive of usable fuel. the weight of everything loaded on the aircraft, a total weight • Mean aerodynamic chord (MAC)—the average can be determined—a simple concept. A greater problem, distance from the leading edge to the trailing edge of particularly if the basic principles of weight and balance are the wing. not understood, is distributing this weight in such a manner • Moment—the product of the weight of an item that the entire mass of the loaded aircraft is balanced around multiplied by its arm. Moments are expressed in a point (CG) that must be located within specified limits. pound-inches (in-lb). Total moment is the weight of the airplane multiplied by the distance between the The point at which an aircraft balances can be determined by datum and the CG. locating the CG, which is, as stated in the definitions of terms, 10-5