Hot Air Balloon: Construction
A hot air balloon for manned flight uses a single-layered, fabric gas bag (lifting "envelope"), with an opening at the bottom called the mouth or throat. Attached to the envelope is a basket, or gondola, for carrying the passengers. Mounted above the basket and centered in the mouth is the "burner," which injects a flame into the envelope, heating the air within. The heater or burner is fueled by propane, a liquefied gas stored in pressure vessels, similar to high pressure forklift cylinders
Hot Air Balloon Envelope
The actual balloon is referred to as The Envelope, which is constructed from long nylon sections called gores. The gores extend from the base of the envelope to the crown and are made up of many smaller panels. The main part of the envelope (the bottom two thirds) is made from a combination of nylon or polyester, same material that use in parachutes. It is very tightly woven and is coated with a material that makes it extremely air tight and durable. Nylon works very well in balloons because it is very light, high melting temperature and fairly sturdy.
The bottom part of the envelope, referred to as the skirt (closest to the burner) is made from Nomex. Nomex is an industrial standard flame resistant material used in the suits of Firefighters. It is used near the base of the envelope as this is area prone to the most heat from the burner.
The material used nearer the top of the envelope is known as Hyperlast and used in the top 3rd of the envelope. What makes Hyperlast desirable to use is that Hyperlast has a silicone coating added to both sides of the fabric which helps to protect the envelope from the growth of mould or fungi.
|part of the envelope|
Hot Air Balloon Basket
The basket is the bottom part of the balloon. It carries the passengers, pilot and propane gas cylinders. Baskets come in a variety of different shapes and sizes, some smaller for the more intimate flights for 2-3 people, right through to the larger sizes (20+) used for public flights. Baskets are commonly made of woven wicker or rattan. These materials have proven to be sufficiently light, strong, and durable for balloon flight.
The basket must be extremely strong as it is constantly on the move, being shifted from place to place and also when the balloon actually lands there is a large amount of force exerted on it as it hits the floor and comes to a halt. The flexibility of the cane helps with the balloon landing as wicker material flexes a little, absorbing some of the energy. Such baskets are usually rectangular or triangular in shape.
|Hot air balloon basket|
Their size are vary from two people capacity to large enough to carry thirty. Larger baskets often have internal partitions for structural strengthen and to compartmentalize the passengers. Small holes may be woven into the side of the basket to act as foot holds for passengers to climb in or out.
Baskets may also be made of aluminium, especially a collapsible aluminium frame with a fabric skin, to reduce weight or increase portability. These may be used by pilots without a ground crew or who are attempting to set altitude, duration, or distance records. Other specialty baskets include the fully enclosed gondolas used for around-the-world attempts, and baskets that consist of little more than a seat for the pilot and perhaps one passenger.
Types of Hot Air Balloon basket
There are 2 main types of basket, Open and T-partition. The open type is an open space where the passengers, pilot and fuel are all placed in the basket in just 1 compartment and T-partition type is where the basket is split into sections so the passengers can be separated from the pilot and canisters. The T-partitions has more advantages than the Open type because T-partitions are stronger due to the extra struts and the balloon more balanced as weight can be spread evenly over each compartment.
Here are some examples of different basket types below:
|A single T-partitioned basket|
|A single Open basket 1|
|A double T-partitioned basket|
Hot Air Balloon Burner
The burner unit is like the engine of the Hot Air balloon; it mixes air with propane then ignites the mixture, and directs the flame and exhaust into the mouth of the envelope to make the balloon move upwards. There are many different types of burner available - single, double, up to quad systems configurations installed where more power is needed depending on the size of the balloon flying.
The propane is stored in cylinders which are kept in the balloon basket, along with the passengers and the pilot. The propane is highly compressed in the cylinders and flows to the burner in liquid form. When the pilot starts the burner up, the propane flows to it and is ignited by a pilot light. As the flame burns, it heats up the metal in the surrounding tubing and when the tubing becomes hot it heats the propane flowing through it. This process changes the propane from a liquid to a gas before it is ignited. The gas makes for a more powerful flame and an overall more efficient fuel consumption. When more than one burner is present, the pilot can use one or more at a time depending on the desired heat output.
A burner may have a secondary propane valve that releases propane more slowly and thereby generates a different sound. This is called a whisper burner and is used for flight over livestock to lessen the chance of spooking them. It also generates a more yellow flame and is used for night glows because it lights up the inside of the envelope better than the primary valve.
Hot Air Balloon Construction.