Horizontal datum + − Figure 6-3.  While the horizontal reference datum can be anywhere  the manufacturer chooses, some manufacturers choose the datum  line at or ahead of the most forward structural point on the  helicopter, in which case all moments are positive. This aids in  simplifying calculations. Other manufacturers choose the datum  line at some point in the middle of the helicopter, in which case  moments produced by weight in front of the datum are negative and  moments produced by weight aft of the datum are positive. Figure 6-2.  When making weight and balance computations, always  use actual weights if they are available, especially if the helicopter  is loaded near the weight and balance limits.  Oil weight is given in pounds per gallon while oil capacity is usually given in quarts; therefore, convert the amount of oil to  gallons before calculating its weight. Remember, four quarts  equal one gallon. * Chapter Summary Weight and Balance Calculations purposes. There is no fixed rule for its location. It may be  located at the rotor mast, the nose of the helicopter, or even  at a point in space ahead of the helicopter.  [Figure 6-3] The lateral reference datum is usually located at the center  of the helicopter. The location of the reference datum is  established by the manufacturer and is defined in the RFM.  [Figure 6-4] This chapter discusses the importance of computing the  weight and balance of the helicopter. The chapter also  discusses the common terms and meanings associate with  weight and balance.  When determining whether a helicopter is properly loaded,  two questions must be answered: To answer the first question, just add the weight of the items  comprising the useful load (pilot, passengers, fuel, oil [if  applicable] cargo, and baggage) to the basic empty weight of  the helicopter. Ensure that the total weight does not exceed  the maximum allowable gross weight. To answer the second question, use CG or moment  information from loading charts, tables, or graphs in the  RFM. It is important to note that any weight and balance  computation is only as accurate as the information provided.  Therefore, ask passengers what they weigh and add a few  pounds to account for the additional weight of clothing,  especially during the winter months. Baggage should be  weighed on a scale, if practical. If a scale is not available,  compute personal loading values according to each individual  estimate.  Figure 6-2  indicates the standard weights for  specific operating fluids. These values are used when  computing a helicopter’s balance. Balance is determined by the location of the CG, which  is usually described as a given number of inches from the  reference datum. The horizontal reference datum is an  imaginary vertical plane or point, arbitrarily fixed somewhere  along the longitudinal axis of the helicopter, from which all  horizontal distances are measured for weight and balance  Reference Datum Aviation Gasoline (AVGAS). . . . . . . . . . . . . . . . . . . . . 6 lb/gal Jet Fuel (JP-4). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 lb/gal Jet Fuel (JP-5). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 lb/gal Reciprocating Engine Oil. . . . . . . . . . . . . . . . . . . . . 7.5 lb/gal* Turbine Engine Oil. . . . . . . . . . Varies between 6 and 8 lb/gal* Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.35 lb/gal 6-4 1. Is the gross weight less than or equal to the maximum  allowable gross weight? 2. Is the CG within the allowable CG range, and will  it stay within the allowable range throughout the  duration of flight including all loading configurations  that may be encountered?