21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-1.7.3

A SENSITIVITY ANALYSIS OF CHAOS AT HIGH ANGLE OF ATTACK

Granasy P., Rohacs J.*
GE Lighting Tungsram, Hungary; *Technical University of Budapest, Hungary

Keywords: sensitivity analysis, chaos, high angle of attack

Modelling the aircraft motion at high angle of attack is necessary to obtain information on manoeuverability. Extended simulation based on a NASA wind tunnel test of HARV (High Alpha Research Vehicle) were made on the longitudinal motion of the aircraft. Investigating a single stable poststall equilibrium by sinusoidal excitation in thrust deflection several bifurcations and even chaos was found. At high angle of attack the aerodynamic coefficients itself contains some uncertainties. Considering this effect the drag, lift, moment coefficients and lift and moment derivatives due to pitch rate and alpha dot were changed with a linearly increasing relative error. Simulations were made on the bifurcation map to compare the effect of changes in the aerodynamic coefficients. The structure of the period doublings qualitatively remains the same. Small changes are observable at drag coefficient variation. The lift variation provides more deviation with vanishing some attractor and period doubling however the domain and character of chaotic attractor is basically unchanged. Modifying in the moment coefficient gives higher variation and the equilibrium got unstable. The system keeps its structure with small variation of derivatives. A conclusion could be draw the appeared nonlinear phenomena are robust against the aerodynamic contamination.

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