j / T O R E than twenty-five years ago, a rational 1 T A method of calculating the stability of airplanes was developed by Bryan and published in his Stability in Aviation. He laid the ground so well that in the main, no fundamental change in the method has appeared since. However, aerodynamic phenomena, wellunderstood at present, were not amenable to close evaluation at the time the method was first presented. It was, therefore, exceedingly difficult to predict the behavior of airplanes, when the calculation of the quantities to be substituted in the stability equations was, at best, uncertain. In the intervening time, research workers have, along with the general progress of aerodynamic science, developed improved methods of evaluating the so-called stability derivatives, on which the calculations rest. This has resulted in placing stability calculation, for the region below the stall at least, on a practical basis. Although the theory is based on the assumption of infinitesimally small disturbances, experience has demonstrated that stability may be predicted relative to disturbances normally experienced by an airplane in steady flight with sufficient precision for all practical purposes. The application of stability theory to the design of airplanes was pioneered in this country by Hunsaker whose work ' pointed out the desirability and practicability of such computation as early as 1915. Since that time the method has languished and the airplane designer has made little use of the only existent means of stability analysis which bears any relation to reality. Indeed, he is usually only vaguely aware of dynamic stability as something you don't have to worry about. However, in justice to the designer, it must be said that should he attempt to undertake such an analysis, it would be necessary for him., in order to obtain the required data, to search through a great many technical books and reports, only some of which are useful, and all couched in unfamiliar language. Further than this, such data are usually presented in a form not immediately applicable to the airplane designer's needs. The designer is usually content to insure that the airplane has a degree of static stability, determined by the