A hot air balloon is an aircraft that flies due to the application of Archimedes’ Principle: “Any object immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object”.
A fluid can be taken to mean both a liquid and a gas.
In our case a balloon full of hot air is lighter than the volume of air displaced, therefore it is pushed upwards according to the same principle.
1 m3 of air at 15 °C weighs 1,225 g.
1 m3 of air at 100 °C weighs 887 g. (338 g. less).
When the hot air balloon is flying it is driven by the wind, therefore we can say that it is a “passive flight”. In fact, it is not possible to direct a hot air balloon as, unlike a navigable balloon, it does not have directional tools like propellers or motors. This makes it unique and gives the aerostatic flight a connotation with the flavour of times gone by.
A hot air balloon is essentially made up of three elements: the envelope, the burners and the basket.
The envelope of a hot air balloon is made up of a load bearing network structure to which special polyester panels are applied. At the base of the envelope we have the first row of panels and the scoop (a triangle that acts as protection from the flames). Both are made with a very heat resistant material called Nomex.
The burners are used to heat the air inside the envelope. They work using liquid propane gas (LPG) and normally each hot air balloon has two burners. The power developed by each burner is about 24,000,000 BTU.
The basket is built with steel tubes connected to the burner frame. Once the framework of the basket is finished, it is woven with wicker by skilful, experienced hands and then finished with special ropes and leather. The propane tanks and on-board instruments are positioned inside the basket.