CENTER OF GRAVITY COMPUTATION— By totaling the weights and moments of all components and objects car- ried, you can determine the point where a loaded heli- copter would balance. This point is known as the center of gravity. The lateral reference datum, is usually located at the center of the helicopter. The location of the reference datums is established by the manufacturer and is defined in the rotorcraft flight manual. [Figure 7-4] Since weight and balance is so critical to the safe oper- ation of a helicopter, it is important to know how to check this condition for each loading arrangement. Most helicopter manufacturers use one of two meth- ods, or a combination of the methods, to check weight and balance conditions. With the computational method, you use simple math- ematics to solve weight and balance problems. The first step is to look up the basic empty weight and total moment for the particular helicopter you fly. If the cen- ter of gravity is given, it should also be noted. The empty weight CG can be considered the arm of the empty helicopter. This should be the first item recorded on the weight and balance form. [Figure 7-5] ARM — The horizontal distance from the datum to any component of the helicopter or to any object located within the helicopter is called the arm. Another term that can be used interchangeably with arm is station. If the component or object is located to the rear of the datum, it is measured as a positive number and usu- ally is referred to as inches aft of the datum. Conversely, if the component or object is located for- ward of the datum, it is indicated as a negative num- ber and is usually referred to as inches forward of the datum. Next, the weights of the oil, if required, pilot, passen- gers, baggage, and fuel are recorded. Use care in recording the weight of each passenger and baggage. Recording each weight in its proper location is extremely important to the accurate calculation of a CG. Once you have recorded all of the weights, add them together to determine the total weight of the loaded helicopter. MOMENT— If the weight of an object is multiplied by its arm, the result is known as its moment. You may think of moment as a force that results from an object’s weight acting at a distance. Moment is also referred to as the tendency of an object to rotate or pivot about a point. The farther an object is from a pivotal point, the greater its force. Now, check to see that the total weight does not exceed the maximum allowable weight under existing condi- tions. In this case, the total weight of the helicopter is under the maximum gross weight of 3,200 pounds. 7-4 Figure 7-5. In this example, the helicopter’s weight of 1,700 pounds is recorded in the first column, its CG or arm of 116.5 inches in the second, and its moment of 198,050 pound- inches in the last. Notice that the weight of the helicopter, multiplied by its CG, equals its moment. Figure 7-4. The lateral reference datum is located longitudi- nally through the center of the helicopter; therefore, there are positive and negative values. WEIGHT AND BALANCE METHODS COMPUTATIONAL METHOD Weight Arm MomentGLYPH<.notdef> (pounds) (inches) (lb/inches) Basic Empty WeightGLYPH<.notdef> OilGLYPH<.notdef> PilotGLYPH<.notdef> Forward PassengerGLYPH<.notdef> Passengers AftGLYPH<.notdef> BaggageGLYPH<.notdef> FuelGLYPH<.notdef> TotalGLYPH<.notdef> CG 1,700GLYPH<.notdef> 12GLYPH<.notdef> 190GLYPH<.notdef> 170GLYPH<.notdef> 510GLYPH<.notdef> 40GLYPH<.notdef> 553GLYPH<.notdef> 3,175 116.5GLYPH<.notdef> 179.0GLYPH<.notdef> 65.0GLYPH<.notdef> 65.0GLYPH<.notdef> 104GLYPH<.notdef> 148GLYPH<.notdef> 120GLYPH<.notdef> GLYPH<.notdef> 109.9 198,050GLYPH<.notdef> 2,148GLYPH<.notdef> 12,350GLYPH<.notdef> 11,050GLYPH<.notdef> 53,040GLYPH<.notdef> 5,920GLYPH<.notdef> 66,360GLYPH<.notdef> 348,918 Max Gross Weight =  3,200 lbs . CG Range 106.0 –114.2 in . LateralGLYPH<.notdef> Datum + – + – Front View Top View