Helicopter flight dynamic axis coupling identification

Abstract

The paper reviews the research that combines dedicated modelling approaches in a nonlinear environment with parameter estimation and system identification methods to pursue two goals simultaneously. First, the improvement of helicopter axis coupling prediction capabilities and second, to gain an insight into the physical mechanisms leading to the phenomena by analysing the identification results. Axis coupling behaviour of helicopters is discussed and the knowledge of the phenomena is compiled to lay the foundation for the modelling and simulation task. The specific modelling approach applied is based on the Parametric Wake Distortion (PWD) theory that yielded a closed mathematical formulation for the treatment of pitch-roll cross coupling. In order to make use of this combined nonlinear analytical/parametric formulation, system identification and parameter estimation methods are used to quantify the effects involved. The methods based on the maximum likelihood output error estimation are presented and explained. The actual optimisation task is applied to BO 105 flight test data and is thoroughly analysed with regard to the stated objectives. The method proved to be suited to support the goals postulated for this research. As per the two stated goals, the results are interpreted twofold. The improvement of simulation fidelity and the conclusions to be obtained regarding the involvement of the addressed physical effects. The resulting values of the estimated parameters of the optimized result yields an insight into the participation of the addressed phenomenon in the improvement of the simulation result. The paper concludes with an assessment of the methods.