| The helicopter water ditching can be divided into two stages, the first stage is water entry and the second stage is emergency floating. The emergency floating stability was mainly studied in this paper. Because of the influence on floating, the water entry was also studied in this paper.Numerical simulation of helicopter water entry has been done to analyze the changing of stress distribution of airbags during water entry. The effects of different water entry velocity, different water entry angle and different airbags arrangement on impact acceleration were also analyzed. The results showed that, during the water entry, the stress mainly concentrated in the connection part between airbags and connection cloth, as well as the connection part between connection cloth and links. The results also suggested that installation of airbags on the rear of a helicopter is good to reducing impact acceleration. The helicopter falling velocity has significant effects on the impact acceleration and the acceleration increases with the increase of falling velocity. About the water entry angle, the results show that 8° pitch angle got minimum impact acceleration and helicopter crash in water with a roll angle was good for decreasing the impact overload.In the emergency floating part, the theory has been used to analyze the heel stability of a helicopter simplified model. A numerical wave tank has been established to simulate the regular water wave which was used to provide wave environment for helicopter emergency floating. Effects of emergency airbags on heel stability and trim stability were analyzed. The results showed that equipment of emergency airbags on the head of helicopter was good for heel stability. The results also suggested that installation of airbags on the rear of a helicopter was bad for the trim stability. |
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