1473. Determining Product of Inertia Using a Torsion Pendulum


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C L Jodry, Richard Boynton: 1473. Determining Product of Inertia Using a Torsion Pendulum. 1982.



This paper presents a method for determining the product of inertia of an object using a high accuracy torsion pendulum moment of inertia instrument. The method chosen requires only three different inertia measurements and minor calculations to determine the principal axes of the object. An air-to-air missile control surface was used as the test article. Simple fixturing was designed so the article could be rotated about its center of gravity, to facilitate making inertia measurements at different angles relative to the reference axes. The center of gravity of the article was determined using a gas bearing center of gravity instrument and utilizing a part of the moment of inertia fixture. Data reduction was handled automatically by the HP 85 computer incorporating a program written for this application. A listing of the program is included in the discussion. Test results were verified by constructing Mohr’s Circle for moments of inertia. Minimum and maximum inertia values agreed closely with the measured values. In summary, the method chosen seems to provide a simple and practical approach to product of inertia measurement for some applications.


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