316. An Arbitrary Axis Inertia Measuring System

Paper

Abstract

This paper was presented at the Twenty-first Annual National Conference of the Society of Aeronautical Weight Engineers at Seattle, Washington, May 14-17, 1962. This is a case history of a successful application of purely analytical instrument design. In consideration of the problems in aligning and leveling large packages, and in consideration of the availability of modern computing equipment, a more basic approach is made to the measurement of all inertial properties. Arbitrary suspension axes are used to minimize the mass and inertia of support structure. Thus the errors commensurate with large tares are required.
The technician simply measures two reference heights (or angles) on the specimen and one period of oscillation for each suspension. After several suspensions sufficient data are accumulated for the computer to solve for all inertial properties. Because of the arbitrary nature of the suspension, the human bias factor is eliminated from the recording of the specimen position. Better accuracy of inertial determination has been demonstrated. The system lends itself to a statistical approach which yields an appraisal of the reliability as well as the mean value of results.
Computation time is 30 seconds for all inertial properties expressed in three of the more common axis systems. Any computer capable of solving a 6 X 6 matrix will perform the computation. Since excellent computing service is as close as convenient as the telephone the cost of a special purpose computer is not justified.