In this chapter:
Hot-air balloons use hot air to rise and cool air to come down.
The Montgolfier brothers designed the first hot-air balloon to carry passengers.
Gas flames heat the air inside the balloon, which makes it float.
There are three main parts to a hot-air balloon - the balloon (envelope), the burners and the basket.
Hot-air balloons can only be directed up or down.
A hot-air balloon moves horizontally by using the wind.
This chapter discusses the use of hot air in the flight of hot-air balloons. Hot-air balloons are the oldest way humans have moved through the air. This chapter looks at the history of hot-air ballooning. The chapter also looks at the parts of a hot-air balloon and the means by which a hot-air balloon is steered and landed.
What is a hot-air balloon?
A hot-air balloon is a very large balloon with a basket attached to the bottom. It uses hot air to travel through the air. The balloon is shaped like an upside-down raindrop. Hot-air balloons were the first objects to fly with human passengers inside. Hot-air balloons use both hot and cold air to control rise and fall. The weather (winds) determines the direction of travel of the balloon.
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Today there are also hot-air balloons that can be propelled through the air with the use of engines. These are known as airships or blimps.
Hot-air balloon history
Hot-air balloon travel is the oldest way humans have moved through the air. The first hot-air balloon to carry human passengers was launched in Paris in 1783. Brothers, Joseph and Ettienne Montgolfier, came from a paper-manufacturing family and had observed how burnt paper from a fire rose into the air.
The brothers' first balloon experiment was in 1782. A year later they had successfully sent the first people into the air. The flight lasted for approximately 20 minutes. The pilots were two noblemen. The first hot-air balloons built by the brothers were just cloth bags, sometimes paper-lined, with a fire built underneath which released a lot of smoke.
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How a hot-air balloon floats
The air around us is made of many different things: gases, water vapour, cold air and warm air. It is the cold air and warm air that are used by a hot-air balloon. Hot air rises in the atmosphere because it is lighter, or less dense, than cold air. Place some feathers on top of a heater and see what happens. The hot air will rise and the feathers will rise with it. Hot-air balloons have made use of this basic knowledge since the 1700s.
Hot-air balloons use hot air to rise into the sky. Gas flames are used to heat air which then inflates the balloon, just like blowing up a smaller party balloon. This hot air is lighter than the cool air on the outside of the balloon, so it can move upwards. The hot air trapped inside the balloon starts to press against the inside of the balloon. This is called the upthrust force, or lift force. It is this force that raises the whole hot- air balloon off the ground. The more hot air forced into the balloon the higher it will go.
Staying in the air
Hot air cools as it rises and begins to fall back to Earth. To stop this from occurring in a hot-air balloon, the air needs to be continuously reheated. Gas flames from the hot-air balloon's burners are used to reheat the air. The pilot will fire the burner and a flame will shoot up into the balloon, reheating the air and stopping the balloon from floating back down towards the ground.
To bring the balloon back down to the ground, the air inside the balloon is left to cool down. The pilot can also control how fast a hot-air balloon floats back to Earth by again using the burners. If a hot-air balloon is falling too fast, then the pilot can fire a small flame into the balloon and partially heat the air.
When in the air, sideways movements of the hot-air balloon are mostly controlled by the winds. A pilot can only control the upward and downward movement, but not the sideways movement. Winds move in all different directions and a pilot needs to know what the weather is doing before going up into the air.
Parts of a hot-air balloon
A hot-air balloon is made up of three major parts - the balloon, the burners and the basket.
The balloon, or envelope, is what holds all the hot air and is the largest and most important part of the whole structure. These days the balloon is mostly made from a fabric called nylon. Nylon is heat resistant and able to handle the heated air without melting or burning. Further down the balloon, at the part closest to the burners (skirt), fire-resistant materials need to be used as a safety precaution.
The parachute valve
On top of the balloon there is a parachute valve that releases small amounts of hot air. This stops the hot-air balloon from floating into the higher levels of the atmosphere. It is difficult to cool air in a confined space quickly. A pilot can heat the air faster than it can be cooled.
The gores and panels
The balloon is strengthened with reinforced stitching in the nylon. These are called gores and panels. This reinforcement makes the balloon stronger and safer.
The burners sit just under the mouth of the balloon. The burners are controlled by the pilot, who decides when the burners need to be fired and for how long. The fire flame shoots straight up into the balloon and nowhere near the passengers.
The basket is attached to the balloon and hangs underneath. It is almost always made out of a material called wicker. Wicker is a strong, flexible and lightweight material. The basket not only holds the passengers, but also the gas (in tanks) that is needed for the burners.
Steering and landing
Steering a hot-air balloon requires the pilot to have a great deal of knowledge about the winds and the air. As the pilot can only steer up or down, the only way to achieve horizontal movement is if the balloon catches different winds. Weather reports and other wind testers are used by hot-air balloon pilots to determine what is happening in the atmosphere.
To land a hot-air balloon, the pilot needs to slowly cool the air inside the balloon. As hot air escapes via the valve at the top of the balloon, cooler air moves in to take its place. This cooler air stops the balloon from rising and will make it float to the ground. The pilot can influence this by controlling the rate at which the air cools. If the air is cooling too fast, the pilot will shoot a small about of heat back into the balloon.
The pilot will land a hot-air balloon in a large area. The balloon will then deflate and be packed up by the crew.