To investigate helicopter vortex-ring state, the phenomenon and reason of helicopter vortex-ring state flight accident is analyzed from the view of helicopteraerodynamics.
针对直升机特有的涡环飞行状态，根据直升机空气动力学理论，分析了直升机涡环状态飞行事故的现象及成因。
2
Then the equation of helicopter pendulum is derived from the nonlinear differential equation and linear differential equation, with the principle of helicopteraerodynamics.