Air Force Balloon
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How Do the Air Force Balloons Fly?
Air Force Balloons are fantastic to see in the skies, but there is much more to these balloons than meets the eye!
Preparation for Takeoff
- The balloon is laid out on the ground and attached to the basket.
- The crew use an 'inflation fan' - a small motor turning a propeller that blows air into the balloon (this is called 'cold inflation', because cold air is being blown into the balloon).
- Once the balloon is partly filled, the pilot ignites the burners and heats the air inside the balloon (this is called 'hot inflation').
- The balloon then begins to stand up as the heated air rises.
- When fully inflated and upright, the balloon is ready for takeoff.
The Balloon Systems
Envelope
The envelope is the name for the part of the balloon that holds the air. When the air inside the envelope is heated, it expands and becomes lighter and less dense than the cooler air surrounding the balloon. This temperature difference will cause the lighter air, and the balloon containing it, to rise.
The Air Force Balloon envelopes are Australian-made and are mainly constructed from a nylon fabric that is similar to parachute material. The lower sections of the balloon envelope, closer to the burners, are made from the same flame-retardant material that is used in pilots' flying suits.
The envelope gets very hot, so there is a sensor at the top that monitors the temperature and sends a signal to the pilot's instrument pack to ensure that the temperature is kept below the safe operating limit of 120°C. Temperatures above this could damage the balloon fabric. As an additional safety measure, there is also a tell-tale flag that drops down from the top of the envelope if the temperature is getting too high.
Gas Tanks
Air Force Balloons carry at least two, and sometimes three, gas tanks. Each tank contains 76 litres of Liquid Petroleum Gas (LPG), also known as propane, which is ignited by the burners to heat the air in the balloon's envelope. The balloons use 50 to 70 litres of fuel for each hour spent in the air.
Burner System
Air Force Balloons have two burners that can be turned on one at a time, or together, depending on how quickly the pilot wants to heat the air in the envelope (this is referred to as a double LPG burner system).
Basket
The basket is made out of wicker (or cane) - a traditional material for balloon baskets. It is flexible and very strong for its weight. The basket has a steel frame inside and is supported by cables that criss cross under it, attaching it to the burner frame.
Avionics
Each balloon carries a combined instrument pack that shows the pilot the altitude, the vertical speed, and the envelope temperature of the balloon.
The pilot keeps in contact with Air Traffic Controllers using a VHF (Very High Frequency) radio and communicates with ground crew and other balloons using a UHF CB (Ultra High Frequency Citizens' Band) radio.
The balloon may also carry something called a transponder, which is used to identify the aircraft. The pilot can ask Air Traffic Control to provide a unique four-digit code (such as 5643) over the radio, which is keyed into the balloon's transponder. Then, when in the air, the transponder will automatically send the code to the Air Traffic Controller's radar screen. This assists the Air Traffic Controller to keep other aircraft clear of the balloon.
Control Systems
The balloon cannot be steered; it can only travel with the direction of the wind! The pilot directs the balloon by moving it up and down to find different wind speeds and directions. To make the balloon go higher, the pilot can control the burners to increase the flame that heats the air in the envelope.
The pilot can make the balloon descend by pulling on a cord that opens a valve to release air from the top of the envelope (this is called venting), or by allowing the air to cool naturally.
The balloons have a rapid deflation system that allows a large amount of air to be vented quickly. This system is only used when landing in order to stop the balloon from skipping across the ground in windy conditions.
The balloons can also be rotated either clockwise or anticlockwise by opening vents on the side of the envelope that allow some air to escape, propelling the balloon around.