STABILITY ANALYSIS OF GROUND RESONANCE PHENOMENON IN HELICOPTERS: EXPERIMENTAL INVESTIGATIONS
Leonardo Sanches1; Guilhem Michon2; Alain Berlioz2; Domingos Alves Rade1; Daniel Alazard2
1 Universidade Federal de Uberlândia; 2 Université de Toulouse
Resumo
Helicopter ground resonance is an unstable dynamic phenomenon which can lead to the total destruction of the aircraft during take-off or landing phases. Coleman and Feingold were the earliest research in this domain around the 1960 decade. Their study leads to the prediction of instability by using classical procedure, when assuming all blades with the same mechanical properties (i.e.: isotropic rotor). Under this condition, the periodical equations of motion are simplified by introducing a change of variable, known as Coleman Variable Transformation. However, this assumption is no more valid for a helicopter under the aging effects. In fact, the mechanical properties of the blades may modify randomly with time and be different from each other (i.e.: anisotropic rotor). Recently, studies have been developed, by using the Floquet's Theory, in order to verify the influence of stiffness dissimilarities between blades. Stability chart highlights the appearance of new instability zones as function of the perturbation introduced on the lead-lag stiffness of one blade. In order to further understand the phenomenon and valid the theoretical results, this paper leads with the design and development of a new experimental setup. Different rotor configurations are investigated and the boundaries of instabilities are determined. Beyond the good correlation between both results, the new instability zones are found in asymmetric rotors. The temporal responses of the measured signals highlight the exponential divergence at the instability regions.
Palavras-chave: Ground Resonance; Experimental Setup; Stability Analysis; Nonlinear Dynamics