The correct name for the "balloon" is the bag or envelope, and is made of rip stop material or dacron. The material is very lightweight and coated on the inside to prevent leaks. Hot air is lighter than cold so when the air in the balloon is heated the surrounding cold air pushes the balloon upwards.
It takes about four or more people to inflate the balloon as it is difficult to manage on the ground especially in gusty winds. This can be a particularly fun part of ballooning and a definite group activity. To begin with the envelope needs to be stretched along the ground and attached to the basket that will be lying on its side. A petrol powered fan blows air into the balloon, the burner is then turned on to heat the air in the balloon causing the balloon to stand upright.
Usually hot air balloons range from 1840 to 2973 cubic metres in volume and stand at approximately 21 metres tall. Commercial and special shapes are usually much bigger. Once in flight, the balloons travel as fast as the wind surrounding them.
Strictly speaking balloons are unable to be steered. There are however some limited ways of navigating through valving gas (releasing gas) to descend into different layers of different directional wind, or heating the air in the balloon to ascend into different directional wind. A drag rope can also be dragged over the ground to stabilise and slow the balloon at low altitudes.
The best time to fly is when the wind is at its stillest. This usually occurs just after sunrise and around sunset.
Usually most balloons fly between 500 feet (152 metres) and 1000 feet (304 metres) high although they can fly both higher and lower than this. The length of time a hot air balloon can stay up depends on the amount of fuel (liquid propane) it carries. Most balloons will carry enough propane to remain in flight for around two hours (110 -150 litres), but the length of time that the fuel lasts depends on factors such as the weather, weight and the temperature.
The propane remains in a liquid form while pressurised in tanks. When the valves are opened the propane atomises (turns into a gas) and is ignited by the burners, causing the flame we observe.
A chase vehicle and crew follows the balloon while it is in flight and should be ready to assist the balloon as it lands. The balloon and passengers are then returned to base.
In many countries a licence is required to fly a hot air balloon and can be obtained by meeting a series of requirements set by each country's aviation authority. Some of the requirements within the US, for example, include passing a written and practical test and flying a prescribed number of hours including solo and at various altitudes. In New Zealand there is no specific balloon pilot licence system although work is being done with the Civil Aviation Authority (CAA) to establish criteria for one. Most New Zealand pilots are trained by other pilots, many of whom have received their training overseas.
A gas balloon is completely enclosed and contains a gas such as helium, which causes it to rise. A hot air balloon is only partially enclosed and the air inside is heated, which causes it to rise.
Balloons can be used for reporting readings about the weather. The balloons are equipped with a weather instrument package called a radiosonde that sends readings about the weather back to the balloon's base as it passes through the atmosphere.