Approximate Formulae for Flutter Prediction

Abstract

On the basis of certain simplifying assumptions a general equation can be developed that provides an estimate of the flutter speed of a binary system. The equation includes aerodynamic stiffness derivatives, and in the absence of reliable derivatives for oscillatory motion it is suggested that derivatives derived from steady flow measurements can be used. The equation is applied to derive specific formulae for main surface flexure‐torsion flutter. The effects of compressibility on the derivatives for this particular case is deduced, and the derivatives are then used to estimate certain general effects of compressibility on flutter. It appears that many of the generally accepted features of flutter in the transonic region can be established by this approach, but the application of the formula is limited by the lack of reliable data for aerodynamic stiffness derivatives. A concentrated effort to establish these derivative values is likely to be more rewarding in the long run than flutter tests on innumerable models to establish overall flutter trends of limited application.