Dynamics analysis of nose landing gear shimmy performance considering aircraft structural flexibility

Abstract

This study examines the sliding vibration characteristics of high-speed aircraft constructed with multi-layer composite materials and designed with a large cabin opening, which consequently leads to diminished overall structural integrity and lower natural vibration frequencies. To assess the influence of structural flexibility on the shimmy behavior of the nose landing gear during taxiing, a rigid-flexible coupling dynamic model was developed based on multi-body dynamics theory, integrating considerations of structural flexibility. The modal stiffness derived from this model was compared to that obtained from a finite element analysis, and simulations were performed to evaluate shimmy stability. The results reveal that fuselage motion enhances the damping coefficient for anti-shimmy while concurrently decreasing the oscillation frequency. When the structural frequency approaches the oscillation frequency, the stability of the system may be jeopardized. Therefore, it is crucial to prevent the alignment of the landing gear’s shimmy frequency with the structural frequency during the design process. Excessive flexibility in the fuselage can result in substantial lateral deformation, which disrupts the normal vibration pattern of the wheels’ angular motion and reduces the system’s capabilities for anti-shimmy and sliding control. Furthermore, when the fuselage demonstrates significant flexibility, the influence of the nose section on shimmy becomes pronounced, indicating that employing earpieces to simulate the body’s stiffness for shimmy analysis is not a suitable approach.