The Air Force Balloon is Australian-made and constructed from a rip-stop nylon that is similar to parachute material. It has a polyurethane coating to make it less porous. The lower sections of the balloon are made from flame-retardant nomex (the same material used in pilots' flying suits).
Maximum temperature inside the envelope is 120°C. This temperature is monitored by a sensor at the top of the envelope that sends a signal to the pilot's instrument pack. There is also a tell-tale flag that drops if the temperature limit is exceeded. The envelope should then be strength-tested to check for damage.
The balloon uses a double-burner system. Each side can be run separately, or a cross-feed can be used to run either side off any fuel tank.
Each burner has two different internal systems. One is the main burner and feeds the fuel through a ring of jets to increase the pressure before igniting the gas as it passes a pilot light. The second system, known as 'liquid fire', bypasses the ring of jets and ignites the fuel with the pilot light. This system is quieter and is used over houses or stock, but it is also less powerful, less efficient and dirtier than the main burners.
The basket is constructed from wicker - a traditional material for balloon baskets that is flexible, strong for its weight and looks appropriate. However, the basket has an internal steel frame and is supported by cables that criss-cross under the basket and attach to the burner frame. The envelope then attaches to these cables via four karabiners. The maximum 'All Up Weight' of the balloon is approximately 1000kg.
The Air Force Balloon usually carries two or three gas tanks, each with a capacity of 76 litres. The fuel is LPG, usually near 100% propane. Fuel consumption is 50 to 70 litres per hour.
A combined instrument pack showing altitude, vertical speed and envelope temperature is carried.
Radio contact with Air Traffic Control is maintained with a VHF radio and the pilot communicates with ground crew and other balloons with a UHF CB radio.
The balloon may also carry a transponder for aircraft identification. This sends a signal in response to Air Traffic Control radar, without which the balloon would be invisible to radar.
The balloon cannot be steered – it can only travel downwind. However, some directional control can be achieved by finding different winds at different levels.
The pilot can increase altitude by heating the air in the envelope using the burners, which must also be used periodically to compensate for cooling. To descend, that pilot can use the burners less often or disperse hot air by opening a vent at the top of the envelope. The Air Force Balloons also have a rapid deflation system that allows a large amount of air to be dumped quickly. This system is only used on landings to stop the balloon from skipping along in windy conditions.
The balloon can also be rotated by vents on the side of the envelope that allow some air to escape and propel the envelope around.
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