Weight & Balance

1. Weight & Balance

2. Basic Definitions Center of Gravity (CG) The point about which an aircraft would balance if it were possible to suspend it at that point. It is the mass center of the aircraft, or the theoretical point at which the entire weight of the aircraft is assumed to be concentrated. It may be expressed in inches from the reference datum, or in percent of MAC.

3. Basic Definitions CG Limits The specified forward and aft points within which the CG must be located during flight. These limits are indicated on pertinent aircraft specifications.

4. Basic Definitions Arm The horizontal distance in inches from the reference datum line to the CG of an item.

5. Basic Definitions Moment The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches (in-lb). Total moment is the weight of the airplane multiplied by the distance between the datum and the CG.

6. Basic Definitions Moment index (or index) A moment divided by a constant such as 100, 1,000, or 10,000. The purpose of using a moment index is to simplify weight and balance computations of aircraft where heavy items and long arms result in large, unmanageable numbers.

7. Basic Definitions Mean aerodynamic chord (MAC) The average distance from the leading edge to the trailing edge of the wing. Aircraft CG will be within the MAC.

8. Basic Definitions Basic Empty Weight The standard empty weight plus the weight of optional and special equipment that have been installed.

9. Basic Definitions Basic Operating Weight (BOW) The empty weight of the aircraft plus the weight of the required crew, their baggage and other standard items.

10. Basic Definitions Maximum zero fuel weight The maximum weight, exclusive of usable fuel.

11. Basic Definitions Maximum ramp weight The total weight of a loaded aircraft, and includes all fuel. It is greater than the takeoff weight due to the fuel that will be burned during the taxi and runup operations. Ramp weight may also be referred to as taxi weight.

12. Basic Definitions Maximum takeoff weight The maximum allowable weight for takeoff.

13. Basic Definitions Maximum landing weight The greatest weight that an aircraft normally is allowed to have at landing.

14. The Basic Formulas Weight X Arm = Moment Moment/Arm = Weight Moment/Weight = Arm Total moment / Total weight = CG

15. General Wt & Bal Computations • Based on this information, where would the CG be located? Weight No. 1 601 pounds at 45 inches aft of datum Weight No. 2 700 pounds at 145 inches aft of datum Weight No. 3 125 pounds at 185 inches aft of datum Weights X Arms = Moments 601 X 45 = 27045 700 X 145 = 101500 125 X 185 = 23125 1426 divided into 151670 = 106.36 inches

16. ADX Questions

17. ADX Questions

18. Stabilizer Trim

19. Stabilizer TrimDC-9 Stab Trim calibrated in percent of MAC B-737 Stab Trim calibrated in units of nose-up(ANU)

20. Stab Trim Setting • The reason we need the CG in % is to set the stab trim before takeoff. • Stab trim can be calculated: • In per cent of MAC, or • in units ANU • (Airplane Nose-Up). CG ANU 8 7 3/4 7 1/2 7 6 3/4 6 1/2 6 1/4 5 3/4 5 1/2 5 4 1/2 4 6 % 8 10 12 14 16 18 20 22 24 26 28

21. CG and MAC Relationship

22. CG and MAC Relationship Equation CG – LEMAC / MAC = CG as percentage of MAC

23. ADX Questions

24. Changing Load Conditions

25. Changing Load Conditions Weight shifted # Dist CG changed ---------------------- = ---------------------- Total GW # Dist wt changed

26. A cargo aircraft loaded to a maximum takeoff gross weight 165,000 lb. is tail heavy. How many 50 lb. boxes must be moved from station 1200 to station 710 to move the CG forward 3.2 inches? Weight shifted # Dist CG changed” Total GW # Dist wt changed”

27. Weight Shift Equation 165,000 710”-1200” 3.2” 1077.6 3.2” Weight shifted # Dist CG changed” Total GW # Dist wt changed” = 1 1 165,000# 490” fwd aft 1076.6 50 = 21.6 boxes 710” 1200” 2 3

28. ADX Questions

29. 1. Benefits of Aft CG • Loading toward aft CG limits = faster cruise (max TAS); better climb rate; & max range! • Tail-down force, while only an aerodynamic force, must be carried by the airplane. • Lower stall speed • Loaded aft, less tail-down force required to balance the aircraft, therefore… aft loaded aircraft require less lift.

30. 2. Fuel Burn with Sweptwing

32. 3. Fuel Burn from Center Tanks • Burn center tank fuel first leaving the wing tanks full. This reinforces the spar for turbulence penetration. • Suggestion - Leave 1000 – 2000 lb. in center tank to keep fuel pumps covered at all times.

33. Max Zero Fuel Weight Max cabin load With a big cabin load & not much fuel, the wings can be overstressed! Max cabin load Fuel load Fuel load MZFW limits designedto ensure cabin loads don’t overstress the wings in bending. Fuel may be added beyond MZFW, however, because it loads the wing outboard & actually reduces wing bending moments.

34. Effects of Overweight Aircraft • Higher takeoff speed. • Longer takeoff run. • Reduced rate & angle of climb. • Lower service ceiling. • Shorter range. • Reduced cruise speed. • Reduced maneuverability. • Higher stall speed. • Higher landing speed. • Longer landing roll. • Excessive loads on structure, ie landing gear.

35. FAA Enforcement Actions Position DescriptionFAA Initial ActionRegsFinal Action Captain Operated flt Notice of Proposed 91.5 14 day when wt cert. action; 14 day 121.89(c) suspension exceeded suspension ATP 91.9 ATP max allow. Co-pilot “ Notice of Proposed “ 14 day cert. Action; 14 day suspension suspension - all all cert. certificates

36. WEIGHT AND BALANCE • The weight and balance of each aircraft will be re- established at the specific re-weighing periods (36 months) or • Whenever the accumulated changes to the operating weight exceed plus or minus ½ of 1% of the maximum of the landing weight, or • Whenever the cumulative change to the center of gravity exceeds ½ of 1% of the mean aerodynamic chord.

37. WEIGHT AND BALANCE • The basic weight and balance log maintains a continuous record of all changes in aircraft weight and balance between weighings. • It maintains a current value for the basic empty weight and CG location. • The Weight and Balance Manual is maintained on each aircraft. • Weight and Balance Manual revisions are approved by the Senior Manager of Quality Control and Quality Assurance.

38. Center of Gravity Limits TAXI 170 FLIGHT (Flaps Up) 160 Do Not Operate In This Area When Landing Weight Exceeds 137,500 LB. 150 TAKE-OFF 140 GROSS WEIGHT 1000 LB 130 See weight limitations for Maximum Landing Weight. 120 FLIGHT (Gear and flaps Up) LANDING AND TAKE-OFF 110 ZERO Fuel Limits (Gear and Flaps Down) 100 90 15 20 25 30 35 40 CENTER OF GRAVITY - PERCENT MAC

39. 2.What is the maximum payload under these conditions? Basic operating weight 101,500 lb. Max zero fuel weight 138,000 lb. Max landing weight 142,500 lb. Max takeoff weight 184,200 lb. Fuel tank load 52,000 lb. Estimated fuel burn en route 45,500 lb.

40. Max Payload Max landing weight 142,500 +Burnoff to destination + 45,500 Step 1 =Allowable takeoff weight =188,000

41. Max Payload Max landing weight 142,500 +Burnoff to destination + 45,500 Step 1 =Allowable takeoff weight =188,000 (pick smaller number)Step 2 Max takeoff weight184,200

42. Max Payload Max landing weight 142,500 +Burnoff to destination + 45,500 Step 1 =Allowable takeoff weight =188,000 (pick smaller number)Step 2 Max takeoff weight 184,200 -Fuel load -52,000Step 3 =Allowable ZFW =132,200

43. Max Payload Max landing weight 142,500 +Burnoff to destination + 45,500 Step 1 =Allowable takeoff weight =188,000 (pick smaller number)Step 2 Max takeoff weight 184,200 -Fuel load -52,000 Step 3 =Allowable ZFW =132,200 (pick smaller number)Step 4 Max ZFW138,000

44. Max Payload Max landing weight* 142,500 +Burnoff to destination + 45,500 Step 1 =Allowable takeoff weight =188,000 (pick smaller number)Step 2 Max takeoff weight* 184,200 -Fuel load -52,000 Step 3 =Allowable ZFW =132,200 (pick smaller number)Step 4 Max ZFW* 138,000 -BOW -101,500Step 5 =Max payload ? =30,700