Research On The Dynamics During The Contact Between The Helicopter Blade And The Droop Stop

To investigate the dynamics during the contact between the helicopter blade and the droop stop, the dynamic equations of the system are derived by the Hamilton's principle. The finite element method is used to discrete the blade in several beam elements, and the global mass matrix, stiffness matrix, damping matrix and external load vector of the blade are obtained. The dynamic responses during the droops stop impact is obtain by the Newmark integration method. Three models are used to model the contact between the blade and the droop stop, and the dynamic responses of the blade are analyzed.The contact between the blade and the droop stop is modeled as a conditional hinged spring with a damper. The predicted dynamic responses are in good agreements with the test data. The maximum negative tip displacement error is 2.13%, and the time delay is 7.18%. The parameters, hinged spring stiffness, the damping ratio and the integration step, are investigated. The results indicate that the hinged spring stiffness has a strong influence on the convergence of the response. The damping has substantially small influence on the contact moment. Smaller integration step can get better convergence but with the degrade of the computation efficiency.Two elastic balls are utilized to model the contact process between the blade and the droop stop. The contact is equivalently modeled as a spring the a dashpot model. The predicted dynamic responses are in good agreement with the test data. The maximum negative tip displacement error is 2.07%, and the time delay is 7.40%. Different spring stiffness is investigated, and the results indicate the small difference.Three dimension finite element method is used to model the blade droop stop system. The implicit-explicit dynamic analysis is conducted. The dynamic responses are in good agreements with the test data. The prediction precision of the maximum negative tip displacement is improved and the time delay reduces. The contact moment is a little smaller than the values predicted by the previous other two methods. The contact process can last longer. The maximum contact moment increases and then decreases with the initial contact angle.