Hot air balloons are amazing application of science that lets everyone enjoy birds-eye-view of the world flying. The basic principle behind the working of hot air balloons is that as air inside the balloon gets heated up, it rises. As the air cools, it starts to descend.
There are just three important parts in the setup – burner, envelope and basket. There is a burner which is placed above the passengers which produces a huge flame to keep heating the air. The heated air is held inside a colorful fabric called an envelope. The basket carries the passengers. This basket is made of wicker which is a woven fiber formed into a strong material yet light weighted.
The fuel used for heating the air is propane, which is kept in a highly compressed inside a cylinder. We know that when gases are compressed, they occupy less space. Two or more lightweight propane cylinders are positioned inside the basket. A hose connects the cylinder to the burner. There is a propane valve which is opened /closed by the pilot. When the burner is started, propane flows out in liquid form and gets ignited. The more the valve is opened, bigger gets the flame and faster the balloon rises. To bring it down, the pilot opens a parachute valve that would let hot air inside the envelope to escape, decreasing the inner temperature.
By controlling the heat in the envelope, the pilot has a good control over up and down movements, though not a complete control due to wind currents. Hot air occupies a mere 7grams in one cubic foot of space, while in the same space, cold air occupies around 28grams. In order to carry around 10-20 people, it might need around 65,000 cubic feet of hot air. That’s why the hot air balloons are so huge. These balloons normally fly below 2000 feet.
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