Why a Balloon Needs a Fan Before Its Burner
A hot-air balloon’s envelope—the large fabric bag—is spread out on the ground with its mouth held open. A fan pushes ordinary outside air into it, turning a collapsed sheet of fabric into a broad, upright canopy. The air is still nearly the same temperature as the surrounding air, so this stage gives the balloon shape, not lift.
That distinction matters because the burner works best once there is room for its flame and heat to enter the envelope. Trying to heat a flattened mass of fabric would warm it unevenly and leave the balloon difficult to control. The fan supplies a steady volume of air without exposing the fabric to a concentrated flame.
Heat Creates the Lift
Once the envelope is mostly inflated, the pilot directs the burner into its opening. Heating the air inside makes it less dense than the cooler air outside. The surrounding air then exerts a greater upward buoyant force on the balloon; when that force exceeds the weight of the envelope, basket, passengers, and fuel, the balloon rises.
The fabric is not airtight, and some warm air gradually escapes, so the burner must keep adding heat during flight. The fan’s job is different and brief: it gets enough air inside to establish the balloon’s shape before the burner takes over. On the ground, the balloon’s dramatic ascent is therefore preceded by a quieter piece of equipment doing the essential work of unfolding it.
