Nicola Hetherington
School of Chemistry
University of Bristol

Lighter than air


Montgolfier brothers

Gas balloons

Airships and blimps

Modern hot air balloons

Rozier balloons

Special shapes

Modern hot air balloons

Airships overshadowed hot air balloons for many years until the 1960s when the hot air balloon was modernised. Nowadays, the craft is used mainly for recreation although ballooning is also reognised as a sport at numerous competition across the globe. Its usefulness is limited by the fact that a balloon can only be flown in calm, dry conditions. The modern balloon is a far cry from the Montgolfiers' original design.

Parts of a hot air balloon

Labelled diagram of a hot air balloons Envelope Parachute valve Parachute valve cord Gores Panels Basket Burner Skirt Propane
Click on the words in the diagram to find out more...

This is the colourful part of the balloon. In modern balloons, it is made of reinforced heat-resistant nylon. It is coated on the inside with a layer of polyurethane or silicon which helps to retain heat and air. Between flights the envelope is folded and rolled and stored in a bag around 1.5 metres in diameter.  The envelope is made up of panels between load tapes that run right through the envelope and attach to the basket. The load tapes carry all the strain in the envelope and the panels in between essentially just keep the air in. Hot air doesn't escape from the bottom of the envelope as buoyancy keeps it moving up.


Parachute valve
At the crown of the balloon is a large hole which is used to deflate the balloon on landing. Fortunately, during flight, this hole is sealed by a parachute valve. held in place by the pressure inside the balloon. The pilot can pull the parachute down out of hole via pulleys using the parachute valve cord that drops down to the basket.


Parachute valve cord
This allows the pilot to pull out the parachute valve to deflate the balloon.


These are panels of fabric cut at particulat angles which when sewn together form the shape of the balloon.


These make up the gores.


This is where the passengers and pilot stand during flight. It also contains the tanks of propane which are connected to the burners overhead. Balloon baskets are generally still made from traditional woven willow branches as no modern material gives the same combination of lightness, strength and flexibility. Flexibility is especially important to absorb the impact on landing and save the knees of the passengers. Very strong steel cords pass through and underneath the basket and are attached to the load tapes of the envelope. The basket may also contain instruments such as an altimeter and a radio to aid the pilot in their flight.


The burner is fuelled by the propane tanks below and is usually made of stainless steel. It is supported by plastic support poles that fit into the basket and is also connected to the basket by way of steel cords. Both the envelope and basket are attached to the burner frame which must be strong.


The very lowest part of the envelope is made from a flame resistant material and serves to deflect any wind from the burner flame allowing the flame to be directed staight up into the envelope. A scoop is a similar piece of fabric which directs air up into the mouth of the balloon helping the balloon to hold its shape.


Propane cylinders
These are located in the basket. The propane is highly compressed in the cylinders and so when released flows quickly through the hoses to the heating coil. On starting up the burner, the pilot will light a pilot light which ignites the propane which is in liquid form to begin with. As the flame burns, it heats up the metal in the surrounding tubing which converts the propane to a gas. Propane as a gas is a more efficient fuel and creates a stronger flame.


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