EAA Chapter 838
Batten International Airport
3333 N. Green Bay Rd.
Racine, Wisconsin 53404
262.634.7575
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Lift generated by the airplane wing must be able to carry the weight of the airplane, its passengers, and baggage. Too much weight, and the plane will not get off the ground. Not only is weight a factor, but also where in the airplane the weight is placed.
Take a look at a teeter totter. If equal an amount of weight is placed on both ends, the board remains balanced. If more weight is added to one end, or the weight is moved to a different position, the teeter totter becomes unbalanced. An airplane in flight reacts the same way. Too much weight in the front, and the airplane flies nose heavy. Too much weight in the back, the airplane will fly tail heavy. This can cause problems with controlling the airplane.
To make sure the airplane is able to fly, the pilot before each flight will do a weight and balance. The location of each weight such as passengers, baggage and fuel is measured along a line through the front to the back of the airplane. An imaginary point on the airplane, called the Datum, is the starting point. The arm, is the distance in inches, from the Datum to each of the individual weights. Each individual weight multiplied by it’s arm results in a moment measured in inch/pounds. The sum of all the moments divided by the sum of all the weights gives the pilot the loaded Center of Gravity (CG) or balance point of the airplane. If the CG falls inside a graph called an envelope, the airplane is safe to fly. If the CG falls outside the envelope, the pilot must either re-distribute the weight, or take weight off in the form of baggage or even a passenger. The pilot then has to recalculate the weight and balance.
5 pounds X 10 inches = 50 inch/pounds
5 pounds X 10 inches = 50 inch/pounds
The airplane is balanced when weight and distance is equal from the center of gravity balance point.
5 pounds X 5 inches = 25 inch/pounds
5 pounds X 10 inches = 50 inch/pounds
If one of the weights is shifted, an imbalance will also exist.
10 pounds X 10 inches = 100 inch/pounds
5 pounds X 10 inches = 50 inch/pounds
If one of the weights is increased, an imbalance occurs.
10 pounds X 5 inches = 50 inch/pounds
5 pounds X 10 inches = 50 inch/pounds
Shifting the weight will return the plane to a balanced condition.
| Item | Weight (pounds) | Arm(inches) | Moment(Inch-Pounds) |
| Aircraft Empty Weight | 1336.1 | 84.94 | 113488.0 |
| Oil 6 quarts (1.8 lbs/qt) | 15 | 32.5 | 487.5 |
| Front Seats (Pilot 190 lbs passenger 130 lbs) | 320 | 85.5 | 2736.0 |
| Fuel (50 gals @ 6 lbs/gal) | 300 | 95.5 | 28650 |
| Rear Passenger | 75 | 117.0 | 8775.0 |
| Baggage | 50 | 133.3 | 6665.0 |
| Total | 2096.1 | XXX | 185425 |
| Loaded Center of Gravity |  (Total Moment) / (Total Weight) |
(185425 inch-pounds) / (2096.1 pounds) |
88.84 inches |
The black line at the nose is the Datum. The colored arm lines locate the concentration of weight for each item listed on the chart above. Once the total weight and loaded C.G. is determined, the figures are plotted on the graph to the right. If the point of intersect of the two lines fall within the red lines, the airplane is safe to fly. The acceptable CG range is illustrated in the pink portion of the airplane below.
The vertical lines through the airplane from front to back represent the Datum (black), oil (light yellow), CG envelope (pink), front passenger and pilot (dark blue), loaded CG (green - see green line on CG graph), rear passenger (purple), and rear baggage (blue).
