System Identification of Flexible Aircraft in Time Domain

Abstract

The paper proposes and demonstrates the applicability of the system identification methodology in time domain to include the effects of structural motion on the flight dynamics of an aircraft treated as an elastic body. For this end, flight tests using a high-performance sailplane equipped with special flight test instrumentation were performed. The structural motion is represented in terms of those normal modes which influence and are influenced by the rigid-body response. The coupling between rigid-body and structural motion is obtained through aerodynamic forces in terms of generalized stability and control derivatives, which are estimated using the output error method in the time domain. The conventional rigid-body stability and control derivatives as well as the deflections of the normal modes at the measurement points are estimated. The model dynamics incorporate two anti-symmetric and three symmetric normal modes. A validation analysis shows the improvements obtained by using the integrated model when compared to the traditional rigid-body approach.