TM 1-1520-238-10 6-3 Section II. WEIGHT AND BALANCE 6.4 WEIGHT AND BALANCE. This section contains information needed to compute the weight and balance for an individual helicopter by using the prescribed standard charts and forms. 6.5 WEIGHT DEFINITIONS. 6.5.1 Basic Weight. The normal basic weight of this helicopter includes wing pylons, all fixed operating equip- ment, 30mm gun, all oil, and trapped fuel. It is only neces- sary to add the variables or expendables to these items for the missions. NOTE The basic weight of the helicopter will vary with mission requirements and structural modifications such as addition or removal of wing pylons, peculiar kits, 30mm gun, turret, ammo handling system, etc. A continuing record of an individual helicopter’s basic weight is maintained on Chart C – Basic Weight and Balance Record, DD Form 365-3. 6.5.2 Operating Weight. The operating weight of the helicopter is the basic weight plus those variables which remain substantially constant for a particular mission. These items include crew, baggage, rocket launchers, Hellfire launchers, and any emergency or extra equipment that may be required. 6.5.3 Gross Weight. The gross weight is the total weight of the helicopter and its contents. 6.6 BALANCE DEFINITIONS. 6.6.1 Reference Datum. The reference datum is an imaginary vertical plane from which all horizontal dis- tances are measured (in inches) for balance purposes. 6.6.2 Arm. For balance purposes, the term ARM is the horizontal distance (in inches) from the reference datum to the center of gravity of a given item. For special cases, ARM can be determined from figure 6-1. For the AH-64A helicopter, ARM and fuselage station (FS) are the same. 6.6.3 Moment. Moment is the weight of an item multi- plied by its arm. For the AH-64A helicopter, moment divid- ed by 100 (moment/100) is used to simplify calculations by reducing the number of digits. NOTE Throughout this chapter, moment/100 fig- ures have been rounded off to the nearest whole number. When moments from other sources are being used,they must be divid- ed by 100 and rounded off. 6.6.4 Average Arm. Average arm is the arm obtained by adding the weights and the moments of a number of items and dividing the total moment by the total weight. 6.6.5 Basic Moment. Basic moment is the sum of the moments of all items making up the basic weight with re- spect to the helicopter reference datum. 6.6.6 Center of Gravity (CG). Center of gravity is the point about which the helicopter would balance if sus- pended. Distance from the reference datum is found by di- viding the total moment by the gross weight of the helicop- ter. 6.6.7 CG Limits. The cg limits are the extremes of movement to which the helicopter cg can travel without endangering controllability or structural integrity. The cg of the loaded helicopter must remain within these limits at takeoff, throughout flight, and during landing. 6.7 LOADING DATA. The loading data in this chapter is intended to provide in- formation necessary to work loading problems for the heli- copter. From this data, weight and moment/100 are ob- tained for all variable load items and are added to the current basic weight and moment/100 from Chart C (DD Form 365-3) to determine the gross weight and mo- ment/100 using Form F (DD Form 365-4). The effect on helicopter cg of expending the fuel and armament in a log- ical sequence may be checked by subtracting the weight and moment/100 of each item from the takeoff gross weight and moment/100; then, checking the new moment (or helicopter cg) with the cg limits chart. This check should be made to determine if the cg will remain within limits during the entire flight. Refer to paragraph 6.10 for helicopter cg management. 6.8 CHART C – BASIC WEIGHT AND BALANCE RECORD, DD FORM 365-3. Chart C is a continuous history of the basic weight and moment resulting from structural and equipment changes in service. At all times, the last weight and moment/100 entries are considered the current weight and balance status of the basic helicopter.