An unmanned free balloon shall refer to a freely drifting inflatable object which is driven with no power, is piloted by nobody, is lighter than air, and whose gross mass is more than 4 kilograms.
无人驾驶自由气球，是指无动力驱动、无人操纵、轻于空气、总质量大于4千克自由漂移的充气物体。
2
While the requests of AUV design performance are met, the objectives of minimizing gross weight and maximizing propeller power and payload length are achieved.
This scenario would also apply to the situation of using irrigation waters from a farm dam to provide power because the water level, and therefore the Gross Head, would vary enormously.