Hot Air Balloons
Hot air balloons are the oldest method of air transportation. The first flight of this nature occurred in Annonay, France on June 4, 1783. A hot air balloon is basically a large envelope that contains heated air. There is a wicker basket called a gondola suspended beneath this canopy that carries the passengers and the source of heat. The heated air causes the envelope to rise because it is lower in density than the colder air outside it.
The hot air balloons of today are made of a bag or envelope made from strong fabrics, such as nylon or Dacron. The material is cut into panels and then sewn together to contain structural tapes that will hold the weight of the basket and its occupants. The individual sections are called gores and one envelope can have from 4 to 24 of these gores. They run from the throat to the top of the envelope. There is a crown ring at the top of the envelope made of aluminum. The hoop, which is about 12 inches in diameter, has strong ropes attached to it. There is also a range of sizes of envelopes for hot air balloons. The smallest ones do not have any baskets and the largest are commercial balloons designed to take passengers on sightseeing flights.
The fabric is coated with a sealer, such as silicone or polyurethane, so that it is impermeable to the air. Once this coating weakens, the balloon can no longer fly. It is not the fabric that is most important but the amount of coating it has. Heat, moisture and mechanical wear and tear are some of the things that can cause degradation of the coating.
There are vents at the top of the balloon, the most common of which is a disk-shaped flap of fabric. The fabric is gathered around the edges of the vent to resemble a parachute and the vent lines are connected to a control line in the basket. When you pull on the control line, you open the vent lines in the top. The vent is opened completely to collapse the balloon after it lands.
The basket is usually made of wicker or rattan because these materials are light enough to float in the air and will not weigh down the envelope even though they are durable. They are usually shaped like a rectangle or a triangle and vary in size being able to accommodate different numbers of people. There are usually small holes in the side of the basket to make it easier for passengers to get in and out. Some baskets are made of aluminum to further reduce the weight and increase the level of portability.
Every hot air balloon has to have a burner or it will not lift off the ground. The fuel used is liquid propane. When ignited the flame and exhaust are directed into the mouth of the envelope. A balloon may have one or two burners and each one has a metal coil of propane tubing through which the flame shoots in order to prevent overheating. The fuel is stored in small cylindrical tanks attached to the burner with a fuel gauge and a pressure gauge.
Some hot air balloons also have a range of instruments to help the pilot in guiding the balloon. These include such things as an altimeter, a speed gauge and temperature gauges for the envelope and the air. A GPS helps to determine location and a wireless radio allows the pilot to maintain ground contact.