For the stability control of ground resonance of coaxial rotor helicopters,a dynamic model of coaxial rotor helicopter to analyze the stability of ground resonance is derived based on the principle of Hamilton.The model is verified by the test data of ground resonance of a model helicopter.Based on the dynamics model,the influence of the parameters on the ground resonance of the coaxial rotor helicopters is discussed.The parameters include the lag hinge offset,the distance between the lower rotor and the gravity of the body,the distance between the lower rotor and upper rotor,the lag natural frequency,the body roll and pitch frequency.The analyses show that increasing the lag hinge offset,the distance between the lower rotor and the mass center of fuselage,the distance between the two rotors,lag natural frequency,or reducing the body roll frequency can reduce the instability introduced by the coupling between the rotor regressive lag mode and the fuselage rolling mode.The ground resonance can be effectively controlled by adding enough damping to the upper rotor,the lower rotor and the fuselage.The vacancy of any type of these dampers may lead to the instability.Compared with the hydraulic damper with the same damping,the fluidlastic damper can have a smaller unstable region.For the completely controllable system,the state feedback control can be used to design the closed-loop system,and the open-loop unstable system can be transferred to a closed-loop stable system.Because the system is complete controllability,the poles of the system can be configured arbitrarily.Given the poles,the feedback matrix can be calculated.The feedback matrix determines the dynamic performance of the closed-loop system.Adjusting the poles of the system can change the dynamic performance,such as regulation time,maximum overshoot,and steady-state error.Finally,the test system to demonstrate the ground resonance of a model helicopter with coaxial rotors is designed.This system consists of a rotor,a positive-reverse driving device,a model fuselage,a universal joint,and a pedestal.The function of each subsystem is analyzed. |