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LOADING GRAPHS AND CG ENVELOPES
The weight and balance computation system, commonly called
the loading graph and CG envelope system, is an excellent and rapid method
for determining the CG location for various loading arrangements. This
method can be applied to any make and model of aircraft.
Aircraft manufacturers using this method of weight and balance computation
prepare graphs similar to those shown in figure 3-13 and 3-14 for each
make and model aircraft at the time of original certification. The graphs
become a permanent part of the aircraft records. Along with the graphs
are the data for the empty weight arm and moment (index number) for that
particular make and model aircraft.
The loading graph illustrated in figure 3-13 is used to determine the index
number of any item or weight that may be involved in loading the aircraft.
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To use this graph, find the point on the vertical
scale that represents the known weight. Project a horizontal line to the
point where it intersects the proper diagonal weight line (i.e., pilot,
copilot, baggage, etc.). From the point of intersection, read straight
downward to the horizontal scale to find the moment or index number.
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After the moment for each item of weight has been determined, all weights
are added and all moments are added. With knowledge of the total weight
and moment, project a line from the respective point on the CG envelope
shown in figure 3-14, and place a point at the intersection of the two
lines. If the point is within the diagonal lines, the loading arrangement
meets all balance requirements.
The following is an actual weight and balance computation using the
graphs in figure 3-13 and figure 3-14. For this example, assume that the
aircraft has an empty weight of 1,386.0 pounds and a moment of 52,772.0
pound-inches.
The index number for the empty weight of the aircraft is developed by
dividing the empty weight moment by 1,000. This gives an index number of
52.8 for the airplane's empty weight moment. Load the aircraft to determine
whether the CG will fall within the diagonal lines of figure 3-14. Arrange
item weights and index numbers in an orderly form to facilitate adding.
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