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According to Figure 7-12, the landing CG at station
297.5 is also within limits.
7–18
8–
8 Chapter Use of Computer for
Weight and Balance Computations
Almost all weight and balance problems involve only
simple math. This allows slide rules and hand-held
electronic calculators to relieve us of much of the tedium
involved with these problems. This chapter gives a
comparison of the methods of determining the CG of an
airplane while it is being weighed. First, determine the CG
using a simple electronic calculator, then solve the same
problem using an E6-B flight computer. Then, finally,
solve it using a dedicated electronic flight computer.
Later in this chapter are examples of typical weight and
balance problems (solved with an electronic calculator) of
the kind that pilots and the A&P mechanics and repairmen
will encounter throughout his or her aviation endeavors.
Using an Electronic Calculator to Solve Weight and
Balance Problems
Determining the CG of an airplane in inches for the
main-wheel weighing points can be done with any simple
electronic calculator that has addition (+), subtraction (-),
multiplication (x), and division (÷) functions. Scientific
calculators with such additional functions as memory (M),
parentheses (( )), plus or minus (+/-), exponential (yx),
reciprocal (1/x), and percentage (%) functions allow you to
solve more complex problems or to solve simple problems
using fewer steps.
The chart in Figure 8-1 includes data on the airplane used
in this example problem.
Figure 8-1. Weight and balance data of a typical nose wheel
airplane.
According to Figure 8-1, the weight of the nose wheel (F)
is 340 pounds, the distance between main wheels and nose
wheel (L) is -78 inches, and the total weight (W) of the
airplane is 2,006 pounds. (L is negative because the nose
wheel is ahead of the main wheels.)
To determine the CG, use this formula:
Key the data into the calculator as shown in red, and when
the equal (=) key is pressed, the answer (shown here in
green will appear.
(340)(x)(78)(+/-)(÷)(2006)(=) -13.2
The arm of the nose wheel is negative, so the CG is -13.2,
or 13.2 inches ahead of the main-wheel weighing points.
Using an E6-B Flight Computer to Solve Weight and
Balance Problems
The E6-B uses a special kind of slide rule. Instead of
its scales going from 1 to 10, as on a normal slide rule,
both scales go from 10 to 100. The E6-B cannot be used
for addition or subtraction, but it is useful for making
calculations involving multiplication and division. Its
accuracy is limited, but it is sufficiently accurate for most
weight and balance problems.
The same problem that was just solved with the electronic
calculator can be solved on an E6-B by following these
steps:
First, multiply 340 by 78 (disregard the - sign): [Figure 8-
2a.]
• Place 10 on the inner scale (this is the index) opposite
34 on the outer scale (this represents 340) (Step 1).
• Opposite 78 on the inner scale, read 26.5 on the outer
scale (Step 2).
8–
• Determine the value of these digits by estimating: 300
x 80 = 24,000, so 340 x 78 =26,500.
Then, divide 26,500 by 2,006: [Figure 8-2b.]
• On the inner scale, place 20, which represents 2,006,
opposite 26.5 on the outer scale. (26.5 represents
26,500) (Step 3)
• Opposite the index, 10, on the inner scale read 13.2 on
the outer scale (Step 4).
• Determine the value of 13.2 by estimating: 20,000 ÷
2000 = 10, so 26,500 ÷ 2,006 = 13.2.
• The arm (-78) is negative, so the CG is also negative.
The CG is -13.2 inches, or 13.2 inches ahead of the datum.
Figure 8-2a. E6-B computer set up to multiply 340 by 78.
Figure 8-2b. E6-B computer set up to divide 26,500 by 2,006.
8–
Using a Dedicated Electronic Flight
Computer to Solve Weight and Balance
Problems
Dedicated electronic flight computers like the one in
Figure 8-3 are programmed to solve many flight problems,
such as wind correction, heading and ground speed,
endurance, and true airspeed (TAS), as well as weight and
balance problems.
Figure 8-3. Dedicated electronic flight computers are programmed to
solve weight and balance problems, as well as flight problems.
The problem just solved with an electronic calculator
and an E6-B can also be solved with a dedicated flight
computer using the information shown in Figure 8-1.
Each flight computer handles the problems in slightly
different ways, but all are programmed with prompts that
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Aircraft Weight and Balance Handbook(30)
