Time-Domain System Identification of Multipoint Loads Model for Flexible Aircraft

The aircraft loads monitoring plays a crucial role in the aviation industry, directly influencing both safety and operational efficiency. This importance arises from the need for aircraft manufacturers and operators to ensure safe continued airworthiness, optimize maintenance programs, and extend the lifespan of aircraft structures. This paper presents the development of an aeroelastic multipoint loads model based on flight test data using System-Identification in time domain. Building upon previous rigid-body loads model, the proposed methodology incorporates the effects of structural flexibility. Several strain sensors were calibrated to enable local loads measurements. Direct loads measurements at different positions of the flexible aircraft structure were used to extend the typical set of observation variables, in order to enable the prediction of local aerodynamic loads by this model. For this purpose, specific flight test maneuvers covering low and high frequency inputs at different airspeeds were performed, in order to excite both rigid-body and elastic degrees of freedom. The test platform is a high-performance sailplane equipped with special flight test instrumentation, in order to allow the modeling of the multipoint loads model at several aircraft load stations. The main contribution of this work is the extension of the conventional rigid-body System-Identification approach for enabling the simulation of aeroelastic local loads in real time. In other words, this paper aims to bridge the gap between conventional rigid-body loads models and the more complex, dynamic behavior of flexible structures in flight, providing significant insights into the complex aerodynamic-structural interactions in flexible aircraft. In this context, the multipoint model structure is outlined and a host of results from the identification of an aeroelastic seven-point loads model is presented.