Fault Analysis and Solution of an Airplane Nose Landing Gear's Emergency Lowering

In this paper, the fault analysis of an aircraft nose landing gear's emergency lowering was conducted with a cosimulation method. The simulation was aimed at studying the dynamic response characteristics of landing-gear retraction/extension. Moreover, the equations of the mechanical and hydraulic system were derived and analyzed so as to acquire the boundary condition under which the landing-gear emergency lowering could fail. Based on the simulation platform computer aided engineering, a cosimulation model ( including a dynamic system and a hydraulic system) was developed, after which, by comparing the simulation results with the data of the ground test and flight test, the model was further verified. Additionally, the nose landing gear could succeed in emergency lowering with the premise that the critical dampings of different flight cases and temperatures were obtained. After that, a feasible scheme of emergency lowering was put forward. The results showed that, at the end of the landing-gear lowering process, the favorable moment saltation produced by the spring force could lag behind the unfavorable moment saltation of the aerodynamic force of the front and back cabin doors, thus resulting in the fault of emergency lowering and locking. Furthermore, when the method of decreasing the damping force was adopted, the landing gear would succeed in emergency lowering only by adjusting the force down to the critical value. However, due to the reduced damping force, the lowering process could be made so fast that there was a great impact load on the landing gear at the end of the trip. The solution laid in using the original damping value in normal extension and the reduced damping value in emergency lowering by a hydraulic selector valve.