System identification methods have played an essential role in the research and industry projects at the Institute of Flight System Dynamics of the Technical University of Munich. Besides the application of the established system identification approaches to multiple aircraft, novel methods have been developed at the institute to deal with the challenges associated with fixed- and rotary-wing aircraft system identification in the time and frequency domains. This paper provides an overview of these new developments, as well as practical application examples from the past and ongoing projects at the institute. After a brief introduction to the work at the institute, the paper describes the new advancements in the fields of time domain system identification and optimal input design by introducing optimal control methods. It continues with an alternative problem formulation for applying frequency domain system identification and parameter estimation methods to a novel flight control design and tuning approach. Additional topics from the past and ongoing research at the institute such as novel methods and practical findings in rotorcraft system identification and flight path reconstruction for different applications will be discussed and referenced.

In this paper, the Blade Element Momentum Theory (BEMT) hast been applied to setup a nonlinear model structure for a coaxial helicopter with a maximum take-off weight (MTOW) of 600kg. The model includes unknown aerodynamic parameters, which are estimated using flight test data. An extensive flight test campaign, with a fully instrumented CoAx 600 helicopter has been carried out to generate the required flight test data for parameter estimation. In this study, we use the maneuvers performed in the vicinity of the hover flight condition for system identification. The nonlinear model can be trimmed and linearized for the analysis of the system dynamics and control design. This has been done for one trim point in the study and the corresponding pole plan has been provided.

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A method of path following, utilized in the theory of position differential games as a tool for establishing theoretical results, is adopted in this paper for tracking aircraft trajectories under windshear conditions. It is interesting to note that reference trajectories, obtained as solutions of optimal control problems with zero wind, can very often be tracked in the presence of rather severe wind disturbances. This is shown in the present paper for rather realistic and highly nonlinear models of aircraft dynamics.

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