Instability zones for isotropic and anisotropic multiblades rotor configurations

Abstract

Helicopter ground resonance is an unstable dynamic phenomenon which can lead to the total destruction of the aircraft during take-off or landing phases. The earliest research in this domain was done by Coleman and Feingold around the 60's decade. The prediction of the instability was possible by using classical procedures once the rotor was considered as isotropic and, consequently, the periodic equations of motions could be simplified to a system with constant coefficients by introducing a change of variables, knew as Coleman Variable Transformation. With the goal of further comprehend the phenomenon and the influence of the anisotropic properties of rotors, analysis in the periodic set of equations of motions is envisioned. For this, Floquet's theory (Floquet's Method – FM) is used. In the present work, analyses of predicting the ground resonance phenomenon in isotropic and anisotropic rotor configurations are explored. The conclusions lead to verify the appearance of bifurcation points depending on the anisotropic characteristic present in the rotor.