Determination of directional stability using torsional pendulum concept for preliminary design of aerospace vehicles

Abstract

Static and dynamic directional stabilities are important features of an aircraft in design phase and to study transient response characteristics. Torsional pendulum, used to measure moment of inertia, has been employed to determine the method of finding directional stability of an aircraft because of a relation between moment of inertia and directional stability. Mathematical relation for moment of inertia using torsional pendulum and constrained yawing motion has been formulated and directional (dynamic) stability characteristics of scale down model have been experimentally determined by mounting the model in wind tunnel. The results obtained have been compared with theoretical ones, and are found to be in agreement. Hence Torsional pendulum concept has been used to accurately determine directional (dynamic) stability characteristics under various flight conditions. The Torsional pendulum has also been employed for the proper distribution of mass on aircraft so that (static) stability characteristics can be optimized. Moreover, it can be used to experimentally determine the mass moment of inertia of an aircraft to confirm the values calculated as it is one of the most accurate methods for experimental determination of moment of inertia. For this purpose, an aircraft body is integrated into a vibratory system such as a pendulum. This method of determining directional stability using a simple torsional pendulum concept helps in the correct prediction of aircraft yawing moment under various conditions, especially under cross wind conditions by making a suitable scale down model (PREMILINARY DESIGN), and then testing it in the wind tunnel.