NACA-RM-A55A28

Abstract

<strong>INTRODUCTION</strong> <br>The calculation and prediction of dynamic stability has assumed considerable importance in recent years and, in fact, has become a necessary part of nearly all current airplane design. The phase of these calculations which is normally subject to the greatest uncertainty is the estimation of the dynamic stability derivatives for high speeds. The methods used in evaluating these derivatives include both theoretical and experimental techniques. A large number of purely theoretical reports have been published of which references 1 and 2 are examples. Wind-tunnel measurements include data taken at low speeds in the Langley stability tunnel (ref. 3), tests with a steadily rolling model at high speeds (ref. 4), and experiments with oscillating models (refs. 5 and 6). Flight measurements include tests with both piloted airplanes (refs. 7, 8, and 9) and rocket-propelled or freely falling models of aircraft (ref. 10). The literature on this subject is extensive and the above references are only representative examples of the different techniques. Summaries of the unclassified research on dynamic stability and estimation of the stability derivatives can be found in references 11 and 12. <br>The method used to obtain the data in this report represents a new approach to the measurement of dynamic stability derivatives in a wind tunnel (ref. 13). The technique should have considerable appeal to designers confronted with the problem of evaluating the dynamic performance of an airplane. The necessary stability derivatives are measured on a scale model at high speeds and under oscillatory conditions. With these experimental data and supplementary static-force test data it is shown herein that reasonably accurate estimates of the longitudinal and the lateral-directional dynamic stability characteristics can be made. Thus the most uncertain part of the dynamic stability estimate The evaluation of the derivatives - becomes amenable to wind-tunnel research. It is believed that methods such as this will permit the same assurance in estimating the oscillatory characteristics as wind-tunnel static-force tests have provided in static stability and control calculations. <br>Results of tests on an airplane model having a triangular wing and a triangular vertical tail are presented in this report. The principal emphasis has been placed on the presentation and discussion of the wind tunnel data, and comparison with existing methods of estimating the stability derivatives. Some typical dynamic stability calculations are presented for a representative airplane to illustrate the application of the data.