06.1 - Flight Dynamics and Control (Control & Modelling)
NONLINEAR UNSTEADY AERODYNAMIC MODELING AND LONGITUDINAL STABILITY ANALYSIS FOR AN AIRCRAFT MODEL
Y. Kong¹, K. He¹, M.H. Lowenberg², S.A. Neild², F. Cen¹; ¹China Aerodynamics Research and Development Center, China ;²University of Bristol, United Kingdom
The high angle-of-attack region has become more accessible to modern aircraft due to advanced aerodynamic design giving improved control authority. In this regime, flow conditions change rapidly and flow separation and vortex breakdown can occur. At the same time, rapid angular rates will influence the flow state as well. Therefore, classical linear steady models are not suitable under these conditions, which increases the challenge in evaluating the overall stability and performance of aircraft. In this paper, a nonlinear mathematical modeling method based on the Goman-Khrabrov approach is used to capture aircraft aerodynamic characteristics influenced by unsteady phenomena such as flow separation. Bifurcation analysis of the resulting state-space system is proposed as a means of evaluating and interpreting the model. It is intended that, through this analysis method, phenomena such as limit cycle oscillations observed in wind tunnel tests can be explained. Experimental results from wind tunnel tests using the University of Bristol multi-degree-of-freedom ‘maneuver rig’ are used as a test case for this method. It is shown that the combination of a Goman-Khrabrov formulation and bifurcation analysis can be effective in developing models for predicting the stability of aircraft in the high angle-of-attack region or during rapid maneuvers.