Riding the Wind: How Hot Air Balloons Fly

Riding the Wind

1Have you ever seen a giant, colorful balloon drifting across the sky? A hot air balloon has no engine and no wings, yet it can carry people high above the treetops. How does it work?

2In 1783, two brothers in France, Joseph and Étienne Montgolfier, built a large balloon out of cloth and paper. They lit a fire beneath it, and the balloon rose into the sky. For one early test flight, the brothers sent up a sheep, a duck, and a rooster in a basket. The animals landed safely. Later that same year, two men became the first people to ride in a hot air balloon.

3At first, the brothers thought the smoke from the fire was what lifted their balloon. Scientists later explained that heat was the real reason. When air is heated, its tiny particles move faster and spread farther apart. As a result, a balloon full of hot air is lighter than the same space filled with cooler air. The heavier, cooler air all around the balloon pushes it upward, much like water pushes a cork up to the surface.

4A modern hot air balloon has three main parts. The huge fabric bag that holds the hot air is called the envelope, and it is usually made of strong, lightweight nylon. Below the envelope is the burner. Most burners use propane gas. The burner shoots a tall flame up into the envelope to heat the air inside. The pilot and passengers ride in the basket. Many baskets are woven from wicker because wicker is strong and flexible. It bends a little instead of breaking, which helps soften a bumpy landing.

5A pilot controls a balloon mostly by changing the temperature of the air inside it. To climb higher, the pilot turns on the burner and heats the air. To come down, the pilot can let the air cool slowly. To come down faster, the pilot pulls a cord that opens a vent at the top of the envelope. The vent lets some hot air escape, so the balloon sinks.

6Steering is the trickiest part of flying a balloon. A balloon has no steering wheel, so it cannot simply turn left or right. It travels wherever the wind carries it. However, winds at different heights often blow in different directions. A skilled pilot rises or sinks to find a wind that is heading the right way. Most balloon flights happen early in the morning or close to sunset, when the winds are usually calmer.

7Today, balloon pilots follow the same idea that the Montgolfier brothers discovered: heat the air inside a giant bag, and it will rise.