Weight and Balance

Example Example Weight shifted ∆CG (change of CG) Given: = Total weight Distance weight is shifted Aircraft total weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6,860 lb CG station. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80.0 in 100 = ∆CG 8,000 120 Determine the location of the CG if 140 pounds of baggage is added to ∆CG = 1.5 in station 150. The change of CG is added to (or subtracted from when appropriate) Solution: the original CG to determine the new CG: Added weight ∆CG 77 + 1.5 = 78.5 inches aft of datum = New total weight Distance between weight and old CG The shifting weight proportion formula can also be used to determine 140 lb ∆CG how much weight must be shifted to achieve a particular shift of the CG. = 6,860 lb + 140 lb 150 in − 80 in The following problem illustrates a solution of this type. 140 lb ∆CG = 7,000 lb 70 in Example CG = 1.4 in aft Given: Aircraft total weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7,800 lb Add ∆CG to old CG CG station. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.5 in New CG = 80 in + 1.4 in = 81.4 in Aft CG limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80.5 in Determine how much cargo must be shifted from the aft cargo compart- Example ment at station 150 to the forward cargo compartment at station 30 to move the CG to exactly the aft limit. Given: Aircraft total weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6,100 lb Solution: CG station. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80.0 in Weight to be shifted CG = Total weight Distance weight is shifted Determine the location of the CG if 100 pounds is removed from station 150. Weight to be shifted = 1.0 in 7,800 lb 120 in Solution: Weight to be shifted = 65 lb Weight removed = ∆CG New total weight Distance between weight and old CG 100 lb ∆CG A simpler solution may be obtained by using a computer = 6,100 lb − 100 lb 150 in − 80 in or calculator and a proportional formula. This can be done 100 lb ∆CG because the CG will shift a distance that is proportional to 6,000 lb = 70 in the distance the weight is shifted. CG = 1.2 in forward Subtract ∆CG from old CG Weight Addition or Removal New CG = 80 in − 1.2 in = 78.8 in In many instances, the weight and balance of the aircraft will be changed by the addition or removal of weight. When this In the previous examples, the rCG is either added or happens, a new CG must be calculated and checked against subtracted from the old CG. Deciding which to accomplish is the limitations to see if the location is acceptable. This type best handled by mentally calculating which way the CG will of weight and balance problem is commonly encountered shift for the particular weight change. If the CG is shifting when the aircraft burns fuel in flight, thereby reducing the aft, the rCG is added to the old CG; if the CG is shifting weight located at the fuel tanks. Most small aircraft are forward, the rCG is subtracted from the old CG. designed with the fuel tanks positioned close to the CG; therefore, the consumption of fuel does not affect the CG to Chapter Summary any great extent. Operating an aircraft within the weight and balance limits The addition or removal of cargo presents a CG change is critical to flight safety. Pilots must ensure that the CG is problem that must be calculated before flight. The problem and remains within approved limits throughout all phases of may always be solved by calculations involving total a flight. For additional information on weight, balance, CG, moments. A typical problem may involve the calculation and aircraft stability refer to the FAA handbook appropriate of a new CG for an aircraft which, when loaded and ready to the specific aircraft category. for flight, receives some additional cargo or passengers just before departure time. 10-11