直面现实问题，寻求解决方案——访IATA理事长乔瓦尼·比西尼亚尼

从统计数据来看,全球航空运输业衰退的局面已经明显超出了预期。国际航协（IATA）理事长乔瓦尼·比西尼亚尼认为,全行业走出困境既需要各国政府政策上的支持,也要继续推进行业改革。     

AN EXPERIMENTAL STUDYOF ROTOR AERODYNAMICS IN GROUNDEFFECT AT LOW SPEEDS

Results of an experimental study of the aerodynamics of a helicopter rotor in ground . effect at low speeds are presented in this paper. Experiments of rotor wake flow visualization and induced velocity measurement near the rotor disc were conducted. At some advance ratio, the forward part of the rotor wake, after impinging on the ground, rolls up and recirculates near the rotor leading edge and large increase in induced velocity appears near the rotor leading edge. When the advance ratio increases, the rolled-up wake develops into a concentrated vortex, ground vortex, under the rotor, and the induced velocity near the rotor leading edge becomes much smaller. The ground vortex diminishes as the advance ratio further increases. Recirculation and ground vortex occur in a very narrow region of the advance ratio. These results explain the irregular variations of rotor forces and moments with advance ratio reported in previous works.