## 04.2 - Aerostructures Design, Structural Dynamics, Aeroelasticity## A PERTURBATION ANALYSIS OF NONLINEARITY IN LANDING-GEAR SHIMMY OF A FLEET AIRCRAFT
The shimmy damper of a fleet aircraft is hydraulic motor in which exist more frictions and freeplay compared to the other forms of shimmy damper?in addition, freeplay of the nose landing gear will increase in later service. A perturbation analysis of nonlinear shimmy in the landing gear of is presented. The method is used to obtain general expressions for the limit cycle amplitude and frequency which are functions of ground speed. The analysis shows that stable or unstable limit cycles can exist for taxi speeds above or below a critical value with stability of the limit cycles being determined by the sign of a computed coefficient. The solution method is applied to a dual tire nonlinear shimmy model. The analysis shows that when only Coulomb friction is present, an unstable limit cycle exist beyond the critical velocity; When only freeplay is present, a stable limit cycle exists below the critical velocity. Both freeplay and Coulomb friction is present, a stable limit cycle exists below the critical velocity; Pilot should do his best to reduce disturbance when landing to avoid shimmy and to decrease taxi speed below the critical velocity; If possible, increasing the critical velocity by strengthening twist stiffness of nose landing gear of the fleet aircraft. |