1983-02-01

An Improved Method for Predicting Lateral-Directional Dynamic Stability Characteristics 830711

ABSTRACT

Current methods of predicting lateral-directional dynamic stability using closed form small perturbation equations are often inaccurate. Flight test data usually shows Dutch-roll characteristics; in particular, to be poorer than estimates. Two assumptions are inherent in these current methods that are inappropriate to General Aviation-type aircraft: First, that the control surfaces are fixed and, secondly, that the rate-of-change in sideslip (beta dot) stability derivatives are insignificant. These assumptions are discarded in this new method, and the system of equations describing the aircraft motion are expanded. Solution of the eigenvalues and eigenvectors of this system of partial differential equations yield the characteristics of the airplane and control system motions. Comparison of the predictions with the new method to that of the old show significant differences. Particularly noteworthy is the strong influence of the beta-dot terms on the damping of the Dutch-roll mode.

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