The Montgolfier brothers used hot air to make a balloon rise. In 1783, early untethered crewed hot-air balloon flights in France opened a new chapter in aviation history.

Hydrogen balloons were also used around the same time. Both hot air and gases lighter than air provide lift, but their equipment and operating methods differ.

Balloons before human flight

A precursor of the hot air balloon was the sky lantern. Zhuge Liang of the Shu Han kingdom, during the Three Kingdoms era (220–280 CE), used these airborne lanterns for military signaling. The Mongolian army studied Kongming lanterns from China and used them in the Battle of Legnica during the Mongol invasion of Poland in the 13th century. This is the first time ballooning was known in the western world.

A later article dated on October 20, 1786, by the London Daily Universal Register would state that the inventor was able to raise himself by the use of his prototype. Also in 1709, the Portuguese Jesuit wrote Manifesto summário para os que ignoram poderse navegar pelo elemento do ar (Short Manifesto for those who are unaware that is possible to sail through the element air); he also left designs for a manned air vessel.

First manned flight

The French brothers Joseph-Michel and Jacques-Étienne Montgolfier developed a hot-air balloon in Annonay, Ardèche, France, and demonstrated it publicly on September 19, 1783, making an unmanned flight lasting 10 minutes. After experimenting with unmanned balloons and flights with animals, the first balloon flight with humans aboard, a tethered flight, performed on or around October 15, 1783, by Jean-Francois Pilatre de Rozier, who made at least one tethered flight from the yard of the Reveillon workshop in the Faubourg Saint-Antoine. Later that same day, Pilatre de Rozier became the second human to ascend into the air, reaching an altitude of 26 m (85 ft), the length of the tether. The first free flight with human passengers was made a few weeks later, on November 21, 1783.

King Louis XVI had originally decreed that condemned criminals would be the first pilots, but de Rozier, along with Marquis François d'Arlandes, petitioned successfully for the honor. The first military use of a hot air balloon happened on June 26, 1794 during the battle of Fleurus, when the French used the balloon l'Entreprenant for observation.

Modern balloons

Modern hot air balloons, with an onboard heat source, were developed by Ed Yost and Jim Winker, beginning during the 1950s; their work resulted in the first successful flight on October 22, 1960. The first modern hot air balloon to be made in the United Kingdom (UK) was the Bristol Belle, built in 1967. Presently, hot air balloons are used primarily for recreation.

Generating lift

Increasing the air temperature inside the envelope makes it less dense than the surrounding (ambient) air. The balloon floats because of the buoyant force exerted on it. This force is the same force that acts on objects when they are in water and is described by Archimedes' principle. The amount of lift (or buoyancy) provided by a hot air balloon depends primarily upon the difference between the temperature of the air inside the envelope and the temperature of the air outside the envelope. For most envelopes made of nylon fabric, the maximal internal temperature is limited to approximately 120 °C (250 °F).

The melting point of nylon is significantly greater than this maximal operating temperature—about 230 °C (450 °F)—but higher temperatures cause the strength of the nylon fabric to degrade more quickly over time. With a maximal operating temperature of 120 °C (250 °F), balloon envelopes can generally be flown for between 400 and 500 hours before the fabric needs to be replaced. Many balloon pilots operate their envelopes at temperatures significantly less than the maximum to extend envelope-fabric life.