The forces of multiple ventilatons can be superimposed, creating stacked ventilators or ''pusfans[[pus]]fans''. A double ventilator will life a paper ball faster than a single ventilator. A 6-pusfan can slowly lift the [[wooden ball]] with a mass of 1.9 tons (when increasing the number of ventilator to around 10, the rising speed is similar to the rising speed provided by 1 ventilator to a paper ball), and a 32-pusfan can lift a [[stone ball]] with a mass of 10 tons. The force of the pusfans on the paper ball will also increase accordingly, so that it can produce the effect of "flying into the sky".