Technology Briefly Explained The Development of the Hot Air Balloon

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In our series "Technology Briefly Explained," we regularly present masterpieces of engineering and special developments. Today: the hot air balloon.

In the USA, June 5 is celebrated as "Hot Air Balloon Day" to commemorate the first balloon flight by the Montgolfier brothers on June 5, 1783. We take this as an opportunity to look at the development of the hot air balloon.

The history of the hot air balloon dates back to the 16th century. Leonardo da Vinci experimented with hot air lift as early as 1513 by launching hot air-filled figures made of canvas or paper at the inauguration of Pope Leo X. Jesuit priest Bartolomeu de Gusmão had also previously demonstrated some balloon models at the Portuguese court. In China, even earlier unmanned hot air balloons existed, the so-called Kongming lanterns.

Flies Like a Petticoat Over the Stove

However, the decisive breakthrough in the development of the hot air balloon as a practically usable aircraft came in the 18th century through the Montgolfier brothers, which is why they are also considered the true inventors of the hot air balloon.

Behind this was a simple yet attentive observation: Paper manufacturer Joseph-Michel Montgolfier noticed how a petticoat hung over a stove to dry puffed up and moved upward due to the influx of hot air. This observation, combined with his fascination for science, led him to the idea that heated air can make things rise.

Sparks and warm air currents from a fireplace eventually inspired Montgolfier to conduct initial experiments with heated air. His experiments demonstrated that an envelope made of paper and canvas filled with hot air could rise—the decisive step towards the invention of the hot air balloon, which was publicly demonstrated in 1783.

Initially With Animal Passengers in the Air

And indeed, the brothers Jacques and Joseph Montgolfier launched the first unmanned hot air balloon in the marketplace in Annonay, near Lyon, France. It ascended about 1,000 meters (0.62 miles) and flew approximately 2.5 kilometers (1.55 miles) in ten minutes.

The first unmanned hot air balloon rose about 1,000 meters and flew approximately 2.5 kilometers in ten minutes.

Only a short time later, on September 19, 1783, the second balloon flight took place in Versailles—this time with animal passengers. Since not enough was known about the conditions at high altitude, animals were initially used as test passengers: a rooster, a duck, and a sheep were the first living creatures to ascend into the air with a hot air balloon.

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How the First Hot Air Balloon was Built

The envelope of the first successful balloons was made of canvas, sealed with paper to make it as light and airtight as possible. To fill the balloon with hot air and thus generate lift, the inventors ignited combustible materials under the balloon’s opening—primarily straw and wool, as these produced a lot of smoke. It is said that the Montgolfiers initially and mistakenly believed that the smoke was crucial for the lift. The edge of the balloon opening was coated with alum, a copper-aluminum compound, presumably to make the material more fire-resistant.

How the Hot Air Balloon Works

• A burner heats the air to high temperatures inside the balloon envelope.

• The heated air expands, becomes lighter, and has a lower density than the cooler outside air.

• Since the balloon envelope is open at the bottom, the hot air cannot be fully enclosed, but partially escapes while cold air flows in from below.

• The buoyant force, which acts according to Archimedes' principle, is equal to the weight of the air displaced by the balloon envelope.

• The balloon can ascend if its total weight, i.e., the balloon envelope, basket, passengers, and air inside the balloon, is accordingly less than the weight of the displaced surrounding air.

• To ascend, the burner is ignited and more hot air is introduced. To descend, the air is allowed to cool, or a vent at the top of the balloon is deliberately opened to let hot air escape, allowing cooler, heavier air in and causing the balloon to lose lift.

To this day, the hot air balloon has not lost its fascination: In 2024, there were 1,075 registered balloons in Germany.

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