It is stated that the key is to determine the vortex-ring boundary the result and the characteristic of vortex-ring state test research are summarized and the rationality of some kinds of vortex-ring state criterion which determine the vortex-ring boundary is analyzed .

指出研究直升机 涡环状态的关键是确定涡 环状态的边界，分析了各种涡环边界试验的结果及特点，并比较了计算确定涡环边界所需的各种边界判据的特点。

Investigation of Blade-pitch Effect on Helicopter Vortex-ring State Using BP Method

使用BP算法研究桨叶安装角对直升机 涡 环状态的影响

Research on data process of helicopter vortex-ring test

直升机 涡 环 状态试验数据处理研究

To investigate helicopter vortex-ring state the phenomenon and reason of helicopter vortex-ring state flight accident is analyzed from the view of helicopter aerodynamics .

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。

Helicopter vortex-ring state influence flight safety badly whose flow characteristic is very complex and hard to calculate accurately .

直升机 涡 环状态严重影响飞行安全，其气流特性非常复杂，难以准确计算。

The result shows that the model of neural network can predict the effect of blade negative-twist on helicopter vortex-ring state .

计算结果表明，神经网络模型能够准确预测桨叶负扭度对直升机 涡 环状态的影响。