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Weight and Balance Handbook

FAA-H-8083-1B Version 2016
All Library Documents FAA Source

Chapter 10

Use of Computer for Weight and Balance Computations

Use this formula:

CG = –(D + (F × L) / W)

  1. Determine the CG in inches from the main wheels: (340)(×)(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).

Tailwheel 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 tailwheel (R) is 67 pounds, and the distance between main wheels and tailwheel (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:

CG = D + (R × L) / W

  1. Determine the CG in inches from the main wheels. (67)(×)(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.

Tailwheel Airplane With Datum Behind the Main Wheels

The datum (D) is 80 inches behind the main wheel weighing points, the weight of the tailwheel (R) is 67 pounds, and the distance between main wheels and tailwheel (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:

CG = –D + (R × L) / W

  1. Determine the CG in inches from the main wheels: (67)(×)(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.
Figure 10-6. Specifications for determining the CG of an airplane using weight and arm.
Figure 10-6. Specifications for determining the CG of an airplane using weight and arm.

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 10-6 contains the specifications for determining the CG using weights and arms.

Determine the CG by using the data in Figure 10-6 and following these steps:

  1. Determine the total weight and record this number: (830)(+)(836)(+)(340)(=) 2,006
  2. Determine the moment of each weighing point and record them: (830)(×)(128)(=) 106,240 (836)(×)(128)(=) 107,008 (340)(×)(50)(=) 17,000
  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.