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solicit you to input the required data so you do not need
to memorize any formulas. Weight and arms are input as
called for, and a running total of the weight, moment, and
CG are displayed.
Typical Weight and Balance Problems
A hand-held electronic calculator like the one in Figure
8-4 is a valuable tool for solving weight and balance
problems. It can be used for a variety of problems and has
a high degree of accuracy. The examples given here are
solved with a calculator using only the (X),(÷),(+),( - ),
and (+/-) functions. If other functions are available on your
calculator, some of the steps may be simplified.
Figure 8-4. A typical electronic calculator is useful for solving most
types of weight and balance problems.
Determining CG in Inches From the Datum
This type of problem is solved by first determining
the location of the CG in inches from the main-wheel
weighing points, then measuring this location in inches
from the datum. There are four types of problems
involving the location of the CG relative to the datum.
Nose Wheel Airplane with Datum Ahead of the Main
Wheels
The datum (D) is 128 inches ahead of the main-wheel
weighing points, the weight of nose wheel (F) is 340
pounds, and the distance between main wheels and
nose wheel (L) is 78 inches. The total weight (W) of the
airplane is 2,006 pounds. Refer to Figure 3-5 on page 3-5.
Use this formula:
1. Determine the CG in inches from the main wheel:
(340)(x)(78)(÷)(2006)(=) 13.2
2. Determine the CG in inches form the datum:
(128)(-)(13.2)(=) 114.8
The CG is 114.8 inches behind the datum.
8–
Nose Wheel Airplane with Datum Behind the Main
Wheels
The datum (D) is 75 inches behind the main-wheel
weighing points, the weight of the nose wheel (F) is
340 pounds, and the distance between main wheels and
nose wheel (L) is 78 inches. The total weight (W) of the
airplane is 2,006 pounds. Refer to Figure 3-6 on page 3-5.
Use this formula:
1. Determine the CG in inches from the main wheels:
(340)(x)(78)(÷)(2006)(=) 13.2
2. Determine the CG in inches from the datum:
(75)(+)(13.2)(=) 88.2
The minus sign before the parenthesis in the formula
means the answer is negative. The CG is 88.2 inches
ahead of the datum (-88.2).
Tail Wheel Airplane with Datum Ahead of the Main
Wheels
The datum (D) is 7.5 inches ahead of the main-wheel
weighing points, the weight of the tail wheel (R) is 67
pounds, and the distance between main wheels and tail
wheel (L) is 222 inches. The total weight (W) of the
airplane is 1,218 pounds. Refer to Figure 3-7 on page 3-6.
Use this formula:
1. Determine the CG in inches from the main wheels.
(67)(x)(222)(÷)(1218)(=) 12.2
2. Determine the CG in inches from the datum:
(7.5)(+)(12.2)(=) 19.7
The CG is 19.7 inches behind the datum.
Tail Wheel Airplane with Datum Behind the Main
Wheels.
The datum (D) is 80 inches behind the main-wheel
weighing points, the weight of the tail wheel (R) is 67
pounds, and the distance between main wheels and tail
wheel (L) is 222 inches. The total weight (W) of the
airplane is 1,218 pounds. Refer to Figure 3-8 on page 3-6.
Use this formula:
1. Determine the CG in inches from the main wheels:
(67)(x)(222)(÷)(1218)(=) 12.2
2. Determine the CG in inches from the datum:
(80)(+/-)(+)(12.2)(=) -67.8
The CG is 67.8 inches ahead of the datum.
Determining CG, Given Weights and Arms
Some weight and balance problems involve weights and
arms to determine the moments. Divide the total moment
by the total weight to determine the CG. Figure 8-5
contains the specifications for determining the CG using
weights and arms.
Determine the CG by using the data in Figure 8-5 and
following these steps:
1. Determine the total weight and record this number:
(830)(+)(836)(+)(340)(=)(2006)
2. Determine the moment of each weighing point and
record them:
(830)(x)(128)(=)106240
(836)(x)(128)(=) 107008
(340)(x)(50)(=) 17000
Figure 8-5. Specifications for determining the CG of an airplane
using weight and arm.
8–
3. Determine the total moment and divide this by the total
weight:
(106240)(+)(107008)(+)(17000)(=)(÷)(2006)(=) 114.8
This airplane weighs 2,006 pounds and its CG is 114.8
inches from the datum.
Determining CG, Given Weights and Moment Indexes
Other weight and balance problems involve weights and
moment indexes, such as moment/100, or moment/1,000.
To determine the CG, add all the weights and all the
moment indexes. Then divide the total moment index
　
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