H. Tourajizadeh - Assistant professor, Department of mechanical engineering, Faculty of engineering, Kharazmi University, Tehran,
S. Zare - M. Sc. Student of mechanical Engineering, Kharazmi University, Tehran

In this paper, an optimal active controller is designed to prevent the shimmy vibrations of the aircraft nose landing gear. Shimmy vibration is the lateral and torsional vibrations in the wheel that is self-excited and causes instability in high speed performances. This phenomenon is highly impressive since this malfunction for a long period of time can damage the landing gear of the aircraft, its fuselage and even it can hurt the passengers. Thus, control and suppressing of this vibration is extremely important. The controllers in this paper are designed according to the both of nonlinear and linearized system while the input is implemented on the real non-linear plant. The linear quadratic regulator (LQR) is used to design the linear controller and the state-dependent Riccati equation (SDRE) is used to design the nonlinear controller. Both of optimal controllers guarantee the asymptotic stability of the closed-loop system and effectively suppress the shimmy vibration of aircraft landing gear at the same time. To estimate the states of the system which are not measurable using ordinary sensors, an observer is designed and implemented using separation principal. The validity of the proposed controllers is verified by numerical simulation. To do so, vibration response of the open loop system is compared with the closed loop response of the designed optimal controllers. Considerable improvement can be seen in the performance of the closed loop system since not only the vibrations are effectively damped but also the consumption of energy is minimized. Finally, LQR controller is also compared with the SDRE controller which again shows an improvement for SDRE response because of its nonlinear nature.

optimal control, shimmy vibration, state dependent Riccati controller, linear quadratic regulator