The quantitative effect of a flexible fuselage on the symmetric torsional modes of the wings of a large airplane

Abstract

Using Holzer's method of frequency calculation, the natural frequencies for the first two modes of torsional vibration of the wing were determined for a representative conventional airplane (B24-C) in the customary manner, the fuselage being considered as a rigid body. Next, using a method developed by N. O. Myklestad of the Guggenheim Aeronautics Laboratory at the California Institute of Technology, combined with Holzer's method, the natural frequencies for the same two modes of vibration were again determined, but with the fuselage this time being considered as flexible. A comparison of results of the two methods indicates that in considering the fuselage as being flexible, a decrease in the natural frequency of torsional vibration may be expected. For the particular airplane selected, this decrease amounted to 6.68% for the first mode of vibration and to 39.1% for the second. The investigation reported in this paper was entirely theoretical and was performed during the 1943-1944 school year at the Guggenheim Aeronautics Laboratory at the California Institute of Technology, Pasadena, California under the direction and supervision of Dr. N. O. Myklestad, research associate in aeronautics at the Institute.