A cyclone in the tropics is caused by a smaller area of low pressure. 热带暴风是由小面积低压引起的。
An air craft which can take off and land vertically in a small area without the need for runways.The propellers is installed in the top of the helicopter, circumrotate flatly. 能直升直落及在空中停留的航空器，螺旋桨装在机身的上部，作水平方向旋转，可在小面积场地起落。
