Abstract Summary
The motivation to accurately model the dynamics of flexible aircraft grew with the development of great aspect ratio aircraft and the great research effort for the development of energy efficient and ecologically correct aircraft, such as those powered by solar energy. These configurations have, as a common characteristic, lower natural frequencies of the first structural modes in relation to more conventional aircraft. This decrease in structural frequencies can result in coupling with the rigid body response. The development of a suitable model that accurately represents the flight dynamics of a flexible aircraft has been pursued by industry and aeronautical research organizations during the last decades. Many groups have proposed a number of different approaches in this direction. And one direction of these approaches is to address the problem of finding a flexible aircraft model using systems identification methods. Recent work on flight tests showed the possibility of adopting the Output Error Method in the time domain to identify and model the dynamics of a flexible aircraft. In this work, the objective is to apply an integrated model containing longitudinal and lateral directional rigid body dynamics, coupled to the first eight flexible body modes, for identification and validation from flight test data. That is, it represents an extension of the current use of the time domain system identification methodology to obtain dynamic models with a wider application frequency range, which can be especially useful for flight control systems projects, in which Structural sway control is intended to improve passenger comfort or reduce structural loads. To carry out this work, an aircraft with a flexible wing, EOLO, from the Aeronautical Systems Laboratory of the Aeronautics Institute of Technology was used. Initially, a finite element structural model (FEM) based on beam elements, concentrated masses, and rigid bars was used. Furthermore, the quasi-stationary panel model based on the Vortex Lattice Method (VLM) was adopted for the aerodynamic model. After obtaining the interpolation between the structural and aerodynamic models, the concept of the mean axes reference system was used in the motion equations of flexible aircraft, and a simulation of the aircraft's dynamics was obtained, consequently, the maneuvers were designed to excite dynamic modes during flight. After the flight test, the identification was produced. For aircraft identification, instead of obtaining stability derivatives, commonly obtained in several identification works, two diagonal matrices were used to correct the matrix of aerodynamic influence coefficients (AIC) obtained via VLM, pre and post-multiplication. The estimation of the main diagonal elements of each matrix was obtained through the Output Error Method in the time domain. After the identification stage, a validation analysis was carried out, which shows the improvements obtained by using the integrated model when compared to the traditional rigid body approach. In addition, it is beneficial to get correction matrices instead of stability derivatives, since they can be used more directly in the correction of aeronautical design stages and also observe the behavior of the aircraft in relation to loads described in space, such as gust loads.
