Control

The direction of flight depends on the wind, but the altitude of the balloon can be controlled by changing the temperature of the air inside the envelope. The pilot may open one or more burner blast valves to increase the temperature inside the envelope, thereby increasing lift, and thus ascend or slow or stop a descent. The pilot may also open a vent, if the envelope is so equipped, to let hot air escape, decreasing the temperature inside the envelope, thereby decreasing lift, and thus descend or slow or stop an ascent. Unless the pilot intervenes, the air inside the envelope will slowly cool, by seepage or by contact with cooler outside air, and slowly provide less lift.