Hot air balloons are air transport vehicles that are supported in the air by the difference in density between the air outside and inside the balloon. Balloons are a clear example of fluid mechanics, since air is a fluid and Archimedes' principle applies to them.
This method of flying is usually used for transporting passengers on recreational trips or for advertising campaigns. Balloon championships, festivals and crossings such as the English Channel are also organised .
What is a hot air balloon?
A hot air balloon is essentially a non-motorized aircraft that is kept aloft by the difference in density between the warm air inside the balloon and the cold air outside.
The balloon consists of a large bag, called an envelope, containing hot air or a gas lighter than air, such as helium or hydrogen. At the bottom of the balloon is a basket or gondola where the passengers and the pilot sit.
Often the envelope has an opening at the bottom, allowing in hot air generated by a gas burner, which is the element that actually provides the upward force needed for the balloon to fly.
The different types of hot air balloons
There are several types of hot air balloons, although the most common is the hot air balloon. This type of balloon uses air heated by a propane burner, allowing the pilot to control the altitude of the aircraft by regulating the temperature of the air in the envelope.
The warmer the air inside the balloon, the lower its density and the greater the lifting force, allowing the balloon to ascend.
Another type of balloon uses gases such as helium or hydrogen. These gases, being lighter than air, provide lift without the need for burners to heat the air. However, gas balloons are less common today due to the flammability of hydrogen and the high cost of helium.
Physical explanation: Archimedes' principle and fluid mechanics
Hot air balloons work on Archimedes' principle, which states that any object submerged in a fluid experiences an upward force equal to the weight of the fluid displaced. In the case of a hot air balloon, the "fluid" is the air surrounding it.
When the air inside the balloon envelope is heated, its density decreases compared to the cold air outside, creating an upward force that allows the balloon to rise.
Thermodynamics also plays a crucial role in the flight of a hot air balloon. The chemical energy of the propane gas is converted into thermal energy by the burner, which heats the air in the envelope and allows the balloon to rise.
The pilot has fairly precise control over the altitude of the balloon by regulating the amount of heat introduced into the envelope. If the pilot wants to descend, he simply reduces the heat, allowing the air to cool and the balloon to lose buoyancy.
How many people can fly in a hot air balloon?
The number of people that can fly in a hot air balloon depends on the size and capacity of the balloon. Smaller balloons typically carry one to two people, ideal for more intimate flights or personal recreation.
However, larger balloons, designed for tourist or commercial activities, can carry more than 20 people at a time, including the pilot.
The total capacity is determined not only by the size of the balloon envelope, but also by the maximum weight that the hot air or gas used for lift can hold.
Safety: Hot Air Balloon Accidents
Although hot air balloon accidents are rare, when they do occur they can have serious consequences. One of the most common risks is the possibility of collision with obstacles such as buildings, trees or power lines, so pilots must be constantly alert and carefully plan their flight paths.
Good equipment condition is essential to ensure a safe flight. Before each flight, pilots must thoroughly check the balloon envelope, burners and amount of propane gas available to ensure everything is working properly.
In addition, weather conditions play a crucial role in flight safety. Strong winds or storms can pose a major danger to hot air balloons, so flights are only carried out when the weather is favourable.
The history of hot air balloons
The concept of flight has fascinated humans since time immemorial, but it was in the 18th century when brothers Joseph-Michel and Jacques-Étienne Montgolfier, two Frenchmen, achieved the first manned flight in a hot air balloon in 1783.
They used hot air to inflate a large silk and paper balloon that carried passengers over Paris, setting a new milestone in the history of aviation. This was the first documented human flight and represented a significant advance in the understanding of how humans could master the skies.
Since then, hot air balloons have evolved considerably in terms of technology, design and safety. Modern balloons are made from stronger materials, such as nylon, and use propane gas burners to heat the air, allowing for greater control over altitude and flight duration.
However, the basic principles of balloon flight have remained virtually unchanged since those early experiments by the Montgolfiers.