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这是由于直升飞机的“头”上有一个螺旋桨,它不停转动会使空气产生一种向上的浮力。当这种浮力和地球对飞机的吸引力相等时,直升飞机就可以稳稳当当地停在空中了。
This is due to a propeller on the “head” of the helicopter, which will cause the air to produce an upward buoyancy as it rotates. When this buoyancy and Earth's attraction to the aircraft equal, the helicopter can be stopped in the air steadily.