How do hot air balloons fly and how do you steer them?

Bristol International Balloon Fiesta is a huge event in the South West - but have you ever wondered how to fly a hot air balloon? Credit: PA

Hot air balloons work on a simple principle - hot air rises while cold air sinks.

This means the balloons fly because the hot air inside weighs less than the air on the outside - causing it to float upwards.

But how does a pilot steer a hot air balloon?

Before we start, there are few bits of ballooning terminology it would be helpful for you to know.

  • The envelope: The fabric balloon which holds the air

  • The basket: An easy one, this - it's where the pilot and passengers stand

  • The burners: The instrument used to heat the air in the envelope.

  • Parachute valve: A circle of fabric cut out of the top of the envelope controlled by a chord in the basket

Hot air balloons fly over South Bristol as part of a mass ascent Credit: PA

How do hot air balloons rise and fall?

When a pilot wants to make the balloon rise they turn on the burner, which makes the air inside the envelope hotter. The hotter the air, the less it weighs - and so the quicker the balloon will rise.

When pilots want to go down, they either let the air cool naturally or speed up the process by letting hot air out of the balloon by opening the parachute valve.

To keep the balloon at a stable level the pilot must use the burner at regular times during the flight to ensure the right amount of hot and cold air are present inside the envelope.

The heat of the air inside the balloon is used to control how it flies Credit: PA

How do you steer a hot air balloon?

Technically, a pilot is at the mercy of the wind when it comes to flying a hot air balloon - but there are a few things they can do to aid their travel.

By moving the balloon up or down, the pilot can move the balloon left or right as well. This is because the wind blows in different directions at different altitudes.

So if a pilot wants to go east, they move up or down to find the easterly wind, and then follow the current.

There is also a green and black cable in the basket itself, which helps to turn the basket to face the direction of travel.

Hot air balloon pilot Ian Martin explains how to fly a hot air balloon