Weight & Balance
| Weight and Balance
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.
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The airplane is balanced when weight and
distance is equal from the center of gravity balance point.
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5 pounds X 10 inches = 50 inch/pounds
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5 pounds X 10 inches = 50 inch/pounds
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If one of the weights is shifted, an imbalance will also exist.
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| 5 pounds X 5 inches = 25 inch/pounds
| 5 pounds X 10 inches = 50 inch/pounds
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If one of the weights is increased, an imbalance occurs.
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10 pounds X 10 inches = 100 inch/pounds
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5 pounds X 10 inches = 50 inch/pounds
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Shifting the weight will return the plane to a balanced condition.
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10 pounds X 5 inches = 50 inch/pounds
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5 pounds X 10 inches = 50 inch/pounds
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| 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
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| Loaded Center of Gravity
|
 (Total Moment) / (Total Weight)
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(185425 inch-pounds) / (2096.1 pounds)
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88.84 inches
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 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).
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