Information

How a balloon flies

A hot-air balloon has three main parts: the envelope that holds the hot air, the burner that heats it, and the basket that carries the passengers. The envelope — the balloon itself — holds at least 250 m³ to lift one person; the burner delivers a flame 3 to 6 m long beneath its mouth; the wicker or rattan basket takes three people and the fuel cylinders. It is the hot air inside the envelope that keeps the balloon up, so a burner and fuel are needed to keep that air hot.

The difference in density with the cooler air around it creates the lift that holds the balloon up. Two laws of physics are at work here. Archimedes' principle, which states that the force on a body immersed in a gas is equal to the weight of the gas it displaces. And the ideal gas law, by which pressure (P) times volume (V) is proportional to the temperature (T) of the gas (PV = nRT).

Air balloon (basket and envelope) out of the hangar and still in the trailer

The air ballon envelope is held on the ground by the crew

Activating the burners to maintain altitude

View over the city from the air balloon (the red stroke is a part of the basket frame)

The air balloon next to us has already take-off

Morning and misty view on and around Brindas

The envelope of the air balloon is being emptied of some of its air

Bakset and balloon folded into a ball and placed in a bag

There is no sense of vertigo, and no jolting. The flight is so smooth that you would almost forget the hundreds of metres between you and the ground — were it not for the magnificent view from up there...

Come and see the rest of the story, and the pictures from the balloon flight I made in October 2011. I hope it gives you the urge to take to the air yourself.

From 1709 to today

It was the Brazilian Bartolomeu Lourenço de Gusmão who, in Portugal in 1709, first flew small hot-air balloons. And it was the Montgolfier brothers, Joseph-Michel and Jacques-Étienne, who invented the hot-air balloon in 1782. The first official flight took place at Annonay on 4 June 1783; then on 19 September, at Versailles, a rooster, a sheep and a duck made the first flight to carry passengers. Finally, on 21 November 1783, Jean-François Pilâtre de Rozier and the Marquis d'Arlandes became the first people to fly: theirs was a second flight, but it is the one officially commemorated as the first.

Hot-air balloons were soon supplanted by gas balloons — hydrogen, town gas — which were easier to work with: a hot-air balloon needed a straw fire beneath it to heat the air, and care not to set the envelope alight. It was revived in the late 1950s, when nylon for the envelope and propane for fuel made it both easy and safe to fly.

The balloon had military uses in its early days — the Battle of Fleurus, the First World War — but today it flies mostly for pleasure.

Questions / Answers

How do you steer a balloon?: You don't really steer it: it goes where the wind takes it. But the wind blows in different directions and at different speeds depending on altitude, so the game is to find the height at which it blows the way you want to go.
When do balloons fly?: Just after sunrise (around 6am) and an hour or two before sunset (around 6pm): these are the times when the wind is calmest and the air most stable.
How far does a balloon travel?: Typically between 5 and 15 kilometres, though it depends greatly on the wind. Winds are usually light at low altitude and faster higher up.
How high does a balloon go?: Most flights stay between 300 and 450 metres, though this too varies a great deal.
How long is a flight?: The flight itself lasts about an hour, varying of course with the direction and the speed of the wind.
How is the balloon recovered?: A chase crew follows the balloon by van during the flight — where the roads allow, otherwise by GPS — and collects it when it lands.