L.: Measurement of the Moments of Inertia of an Airplane by a Simplified Method

A simplified method for the experimental determination of the moments of inertia, product of inertia, and inclination of the princi-pal axes; the associated equipment and techniques; and the application of this method to a conventional 13,000-pound airplane are described. Measurements were made with the landing gear retracted for full and empty fuel conditions. The equipment, which consisted primarily of knife—edge supports and restraining springs for the pitch and roll axes and a single—shaft torsional pendulum for the yaw axis, was designed for increased accuracy as well as for simplicity of operation and ease of handling as compared with previous methods. At no time was it necessary to hoist or jack the airplane in an abnormal fashion. Analysis showed the maximum possible error of the inertia measure-ments to be ±1.7, ±1.2, and ±0.6 percent of the true moments of inertia about the X, Y, and Z axes, respectively. For each suspension system, measured moments of inertia of known masses of simple form agreed within 0.5 percent with the calculated values. The results of brief tests have indicated that suitable application of the torsional pendulum would permit evaluation of the inclination of the principal axes to within less than ±0.1°, which corresponds to an error of less than ±35 slug-feet squared in the product of inertia of the test airplane