A hot-air balloon needs heated air to make it rise up off the ground. Hot-air balloons do not have an engine: they are pushed along by the wind.
So how do they get up into the air? Like this:
The balloon is laid out on the ground.
The basket is joined to the balloon.
The crew uses a small fan to blow air into the balloon.
When the balloon is almost filled with air, the pilot turns the burners on. The burners heat the air inside the balloon.
As the hot air rises, the balloon begins to stand up.
When the balloon is filled with hot air, it is ready for takeoff.
The big round part of an Air Force Balloon that holds the air is called the envelope. When the air inside the envelope is heated, it becomes lighter than the cooler air on the outside. This makes the balloon rise up into the sky. The envelope is made from a special type of nylon which does not burn or tear easily.
The gas tanks
Air Force Balloons carry two, or sometimes three, gas tanks. A balloon needs 50 to 70 litres of gas for each hour it spends in the air. It is the same kind of gas we use for a barbecue.
Air Force Balloons have two burners. The pilot can turn on one burner to heat the air in the envelope, or both at the same time to heat the air more quickly.
The basket is made out of wicker (or cane). Wicker is very strong and light.
Instruments tell the pilot:
how high the balloon is flying
how fast the balloon is going up or down
the temperature of the air inside the envelope.
Air Force Balloons cannot be steered like a car. The wind moves the balloon through the air. To make the balloon go up, the pilot heats the air in the envelope. To make the balloon go down, the pilot pulls on a cord. This opens a vent and allows air to escape out of the top of the balloon. Another way to make the balloon go down is to stop heating the air inside the envelope.