NACA-TN-1370

Abstract

INTRODUCTION <br>Until recently the effects of the product of inertia usually have been neglected in lateral stability analyses because the lateral-stability studies of reference 1 indicated that these effects were relatively unimportant for conventional airplanes. Calculations in reference 2, however, show that the product of inertia may have a pronounced effect on the lateral stability of some high-speed airplanes because of high wing loadings, large differences between yawing and rolling moments of inertia, high operational altitudes, and sweepback. The sweepback may cause high effective dihedral and high angles of attack and, consequently, large angles between the principal longitudinal axis of inertia and the wind axis. <br>In order to obtain an experimental check of lateral-stability calculations including the product-of inertia terms, a systematic series of flight tests have been made in the Langley free-flight tunnel. A model having a 42&#176; sweptback wing was used to determine experimentally the effects of the product of inertia on the lateral stability of the free-flying model for correlation with the calculated stability characteristics of the model. In order to provide a comprehensive check of the calculations, the directional stability of the model was varied by changing the vertical-tail size and tail length and the quantitative effects of the product of inertia, were varied by changing the vertical-tail size and tail length and the quantitative effects of the product of inertia were varied by changing the wing incidence and thereby changing the inclination of the principal axes of inertia relative to the wind axes.