The Principles of Flight

Hot-air balloons work on the scientific principle that hot air rises. It rises because as the air is heated it becomes less dense, i.e. lighter than the surrounding air. If enough hot air is trapped in a lightweight bag then the bag will rise until the temperature of the air inside and outside the bag is roughly the same. When the air in the bag cools it will start to descend.

Balloon Manufacture

The hot air balloon bag or envelope as it is properly known is manufactured from rips top nylon which is a lightweight fabric that is specially woven with crisscross threads to help prevent tearing. Some balloons have a slightly heavier and more durable fabric called 'hyperlast' in the top section of the balloon. 

These materials are available in a whole spectrum of colours and are ideal for balloons because they can withstand temperatures in excess of 120 degrees Celsius - well above the boiling point of water.

The fabric is cut into shaped panels which are sewn together using a double overlapped seam called a 'French felled seam'  which is twin lock stitched for strength and reliability. These long panels or gores are then sewn to a web of heavy-duty nylon load bearing tapes that pass around the balloon. It is these tapes, rather than the rips top nylon panels, that carry the loads suspended beneath the balloon envelope. 

At this stage of construction the envelope has large holes in the top and bottom. The bottom opening is large enough to allow the balloon to be inflated and the air heated with a burner. Around the hole, or mouth as it is generally known, are panels made from fire-resistant Nomex.

When the balloon is fully inflated the top hole is sealed by a 'parachute valve'. This can be opened and closed by the pilot when he wants to vent hot air quickly to descend or land. 

The Burner

The balloon load tapes are attached to stainless steel flying wires that connect the envelope to a frame which holds the burner. This can be gimballed to allow the flame to be directed into the envelope and to compensate for any slight deflection of the flame caused by wind.

The flame itself is controlled by a blast valve that permits a mixture of vaporised and liquid propane to be ignited by a pilot light. To avoid upsetting animals when flying over the countryside most balloon burners also incorporate a 'Whisper' system which is considerably quieter than the main burner.

The Basket

The basket and load is carried by strong stainless steel wires which go down underneath the basket and are connected to the envelope at the burner frame.

The basket is woven by craftsmen from cane and willow and usually has a padded ridge of foam rubber around the top covered with suede or leather. Some baskets also have padded floors and side walls for passenger comfort and safety. Other materials such as plastics and aluminium have been tried as substitutes for basket wicker but they lacked the resilience and charm of the traditional material.

The Fuel System

The cylinders containing liquid propane gas, normally stand in each corner of the basket. These can be either aluminium, stainless steel or titanium and typically hold 45 or 60 litres of fuel. 

Padded covers surround the cylinders again for passenger comfort and safety and rubber-encased armoured pipes carry the fuel up to the burner which is supported above the basket on flexible nylon rods.

Flight Instruments

Although instruments are not used to control the balloon they provide practical information for the balloon pilot, such as altitude and rate of ascent and descent. 

The modern Flytec has a digital display of altitude in feet or metres, QNH pressure setting, variometer showing rate of ascent and descent, envelope temperature, ambient temperature and time.

Also useful for competition ballooning is a GPS to display position, speed and track and very useful for advising the retrieve crew exactly where the balloon has landed.

A VHF radio is also carried on board to communicate with air traffic services and to advise the retrieve crew of balloon track and possible landing sites.  

Balloon Size

The number of people a balloon can carry depends on its size. This varies from small one-man balloons to the larger balloons that can carry twenty passengers or more. Big balloons tend to be used by commercial operators to carry fare paying passengers while the more usual sport balloons will carry the pilot and a couple of friends in the basket and these often carry advertising for a sponsor which helps towards the operating costs.

The most popular size of balloon is described as a '77' because the envelope holds 77,000 cubic feet (2190 cubic metres) of air. The 77 can often carry four people (depending on their weight and the ambient temperature) which makes it ideal for family, club or syndicate use.

Inflation

To launch a balloon requires four people. When the envelope is laid out on the ground it is cold inflated with a powerful fan. 

Two crew members hold the mouth of the balloon open while the pilot operates the burner. The fourth crew member holds the crown line which is attached to the top of the balloon to prevent the envelope rocking from side to side or from moving into the vertical position too quickly.

When the balloon lifts off the retrieve crew follow by road and are usually in radio communication with the pilot so that they can be close by when the balloon lands. The retrieve crew get clearance from the landowner to enter the field and help to pack up the balloon ready for the next flight.