Up, Up and Away with LPG

There are few things more colourful than a hot air balloon race. 

Hot air balloons are also the oldest form of human flight, going back to 1783! 

But exactly how do they work?

Hot Air Rises

The basic principle of hot air balloon flight is based on the fact that hot air rises. 

The air within the “envelope” (fabric air bag) is heated by an LPG burner. 

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Elgas LPG hot air balloon

The fact that the air inside of the envelope is warmer than the ambient surrounding air makes it less dense, so it rises.

The amount of lift is dependent upon a number of factors. 

The greater the temperature differential between the envelope air and the ambient air the greater the lift. 

The size of the envelope is also critical, as larger loads require a larger envelope. 

Altitude is also a factor, as lift decreases, along with the ambient air density, the higher you go.

That’s a Lot of Hot Air

The envelope size required to lift 4 or 5 people is about 3,000m3

Large commercial size envelopes, used for group rides, could be as much as 6X that volume.

The envelopes are typically made from Nylon or Dacron with fire resistant material used at the bottom, closest to the burner. 

At least some of the fabric, especially parts toward the top of the balloon, may be coated with a sealer that is air impermeable.

Flight Controls

The pilots control the rate of climb or descent using the burners. 

To increase altitude, they run the burners to heat the air within the envelope. 

To descend, they just let the air naturally cool. 

The envelopes also have some kind of venting to release the hot air more quickly, when a rapid descent is desired.


A balloon would typically be equipped with a number of instruments to help the pilot control the flight. 

Altimeters, ambient and envelope air temperature thermometers, and a GPS would be amongst the usual instrumentation. 

Another device, called a variometer, shows the rate of climb or descent so the pilot knows if he is going up or down and how fast it's happening.

LPG Hot Air Burners

LPG burner for hot air balloonThe air within the air bag envelope is heated with LPG. 

The LPG is mixed with air in the burner and resulting flame and exhaust are directed into the envelope.

A balloon would typically have 2, 3 or 4 burners. 

The balloon pilot operates a valve to control the burners and how much heat is added to the air within the envelope.

The burners themselves can either hang from the bottom of the envelope or be mounted to framework on the top of the basket (gondola). 

The burners can even be adjusted to produce a more yellow coloured flame to make the envelope glow brighter, when used at night.

Flying Gas Bottles

The LPG gas bottles are typically lightweight aluminium or stainless steel. 

Due to the lower temperatures at altitude, the gas bottles will also typically have insulation covers to keep them warm. 

This helps maximise the vapourisation of the gas.

Forklift size bottles are common and can be mounted inside or outside the basket. 

Multiple gas bottles are customary, with the number and capacity dictated by the desired duration of the flight and the size of the envelope that must be heated.

Exceptional Energy

LPG is Exceptional Energy and an amazingly versatile fuel. 

Hot air ballooning is just another example of what LPG can do.




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The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.

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