Ballooning World
“A hot air balloon is an aerostat in which the lifting force consists of hot air produced by a propane burner”.
The hot air balloon is remarkably simple in its conception and handling. The first air balloon flew in 1783 in Paris using the materials available at the time. It consisted of a large bag to collect the heat produced by a fire on the ground, attached to a gondola to carry people.
The modern hot air balloon consists of three main parts: the envelope (the large bag), the fuel system (burner with load frame and fuel cylinders) and finally a wooden basket to carry the pilot and passengers.
Apply heat and it goes up!
Stop the heat and it comes down!
The top of the envelope has a large hole, which is sealed with a fabric valve. It is held in place by the pressure inside the balloon. This fabric valve looks like a parachute and is therefore called the parachute valve.
The pilot can let hot air out of the balloon by controlling this valve with a rope whenever he wishes to descend quickly or land.
This valve returns to its place automatically when the rope is released.
Why does it fly?
Hot air rises. Most people know this, and a hot air balloon rises because it has hot air trapped inside the envelope. This air is hotter than the air outside the envelope and therefore less dense.
This means the air inside the balloon is lighter than the air outside. If enough of this lighter air is generated inside the envelope, the balloon will keep rising. It will fly!
The bigger the balloon, the more hot air it can hold, the greater the lift and the more people it can carry.
Even so, the air inside the balloon is continuously cooling, which is why it needs topping up all the time. This is why a constant source of heat in the form of a propane burner is required to maintain the flight. If combustion stops, the balloon will stop climbing as the temperature inside and outside the balloon become similar.
For a short period of time the balloon will be suspended, in equilibrium. After that, with no more heat applied, the balloon will descend gently.
