In this paper, the effect of incomplete similarity of inertial properties of dynamically scaled models of the airplane is investigated. The approach of flying quality analysis is presented to examine the possibility of using the approximate similar model to obtain reliable data from the flight test. Relationships are proposed for the longitudinal and lateral-directional flying qualities between the full-scale airplane and its model. Sensitivity analysis of flight characteristics for changes in the moment of inertia is performed. Results of analyses on Boeing-747 showed that the 7% changing the moment of inertia in the lateral mode and 13% in longitudinal mode can change the level of flying quality based on MIL-8785C standard. The proposed method improved the previous methods and can give the definite range for allowable deviations of moments of inertia errors for acceptance of the model as a research tool. Keywords: approximate similarity, inertial properties, dynamically similar/scaled model, simulation, flight test, flying quality, integral performance index.
