Identification of the Aerodynamic Coefficients of Longitudinal Motion of an Aircraft in the Operational Range of the Attack Angles

Abstract

This work presents a methodology for identification of aerodynamic coefficients of longitudinal motion of an aircraft in the operational range of the attack angles, taking into account the nonlinearities and changes in the engine operation. A solution to this problem envisages development of methodological, algorithmic and software support for the process of determination of the characteristics of stability and controllability of the aircraft, using flight experiments data and the results of the mathematical and semi-natural simulation. The paper discusses the basic steps of the identification technique and examples of its use. In the test-flights more than 100 test modes were performed with the purpose to obtain materials for identification of the aerodynamic coefficients for longitudinal movement and for the aerodynamic coefficients of the lateral movement. In order to assess the correctness of functioning of the on-board systems for measuring and recording a special algorithm was applied, based on the relationship between the flight parameters defined by the equations of spatial motion of the aircraft. The results of testing and the methodology on the example of a modern maneuverable aircraft are considered. The obtained estimates of the aerodynamic coefficients of the longitudinal motion of the aircraft in comparison with the a-priory wind-tunnel aerodynamic characteristics are presented. The method allows us to obtain reliable estimates of the aerodynamic coefficients of an aircraft within the operating range of the flight conditions, which is proved by the results of the flight data processing. The identification results will make it possible to reveal inaccuracies in the a-priory wind-tunnel aerodynamic characteristics, make adjustments and improve the mathematical model of an aircraft in accordance with the flight test data. A distinctive feature of the technique is the focus on the improvement of the identification procedures and development of a user-friendly graphic interface, which can be achieved due to specially developed algorithms and software.