Hot air balloon
 A hot air balloon is partially inflated with cold air from a petrol-driven fan, before the propane burners are used for final
inflation
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 A hot air balloon is inflated by its propane burners, just before
dawn
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 A hot air balloon takes
off
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Hot air balloons are the oldest successful human flight technology, dating back to the Montgolfier brothers' invention in Annonay, France in 1783. The first flight carrying humans was made on November 21, 1783, in Paris by Pilâtre de Rozier and the Marquis d'Arlandes. Balloons that can be propelled through the air rather than just being carried along by the wind are known as airships.
Attractive aspects of ballooning include the exceptional quiet (except when the propane burners are firing), the lack of any perceptible feeling of movement and the birds-eye view. Since the balloon moves with the wind, the passengers feel absolutely no wind, except for brief periods during the flight when the balloon climbs or descends into air currents of different direction or speed. Recently, balloons have been made in fantastic shapes, such as hot dogs, rocket ships, and the shapes of commercial products.
History
Unmanned hot air balloons are mentioned in Chinese history. Zhuge Liang in the Three Kingdoms era used airborne lanterns for military signalling. These lanterns, known as Kongming lanterns (孔明灯) nowadays, are still being flown in China, despite the risk of causing a fire upon landing.
There is also some speculation that hot air balloons were used by the Nazca Indians of Peru some 1500 years ago as a tool for design vast drawings on the Nazca plain.
The first clearly recorded instances of balloons capable of carrying passengers used hot air to obtain buoyancy and were built by the brothers Josef and Etienne Montgolfier in Annonay, France. They were from a family of paper manufacturers who had noticed the ash rising in fires. After experimenting with uncrewed balloons and flights with animals, the first balloon flight with humans on board took place on 21 November 1783. King Louis XVI had originally decreed that condemned criminals would be the first pilots, but a young physicist named Pilâtre de Rozier and the Marquis Francois d'Arlandes successfully petitioned for the honor. Hot air balloons were basically paper bags with a smoky fire built on a grill attached to the bottom, so they had a tendency to catch fire and be destroyed on landing.
The first hot air balloon flight in the United States took place on January 9, 1793. The 45 minute flight started in Philadelphia and ended in Gloucester County, New Jersey. The flight was witnessed by George Washington.
Balloons were the first manifestation of air power. Hot air balloons such as The Enterprise were used by the North for artillery observation in the American Civil War and were used for communication during the Siege of Paris in 1871. They were also used for observation of trench warfare in World War I. However, as the development of balloons that used unheated gases (such as hydrogen) became more refined, hot air for ballooning receded to obscurity for most of the 1800's and the first half of the 1900's. Only with advances in material and fuel technology did hot air ballooing return to the fore.
The first modern hot air balloon was designed and built in 1960 by Ed Yost. Yost used a modified propane powered "weed burner" to heat the air and lightweight nylon fabric for the envelope material. He made the first free flight of such an aircraft in Bruning, Nebraska on 22 October 1960.
Today, hot air balloons are used primarily for recreation. There are some 7,000 hot air balloons operating in the United States.
Hot air balloons are able to fly to extremely high altitudes. On November 26, 2005, Vijaypat Singhania set the world altitude record for highest hot air balloon flight, reaching 69,852 feet (20.29 km). He took off from downtown Bombay, India and landed 150 miles south in Panchale. The previous record of 19,811 meters (64,980 ft) had been set by Per Lindstrand of Sweden on June 6, 1988 in Plano, Texas.
Construction and theory of operation
A hot air balloon for manned flight uses a single layered, fabric gas bag (lifting envelope), with an opening at the bottom called the throat. Attached to the envelope is a basket, or gondola, for carrying the passengers. Mounted above the basket and centered in the throat is an "air heater" or "burner" which injects a flame into the envelope, heating the air within. Raising the air temperature inside the envelope makes it lighter than the surrounding (ambient) air. This causes the balloon and its payload to rise.
Modern hot air balloons are usually made of synthetic fabrics such as ripstop nylon, a light weight fabric of high strength. During the manufacturing process, the material is cut in long sections known as "gores" and sewn together, along with structural load tapes (webbing) that carry the weight of the gondola or basket. The heater or burner is fueled by propane, a liquefied gas stored in pressure vessels, similar to high pressure forklift cylinders.
The amount of lift (or buoyancy) provided by a hot air balloon depends primarily upon the difference between the temperature of the air inside the envelope and the temperature of the air outside the envelope. For most envelopes made of nylon fabric, the maximum internal temperature is limited to approximately 120 °C (250 °F). It should be noted that the melting point of nylon is significantly higher than these maximum operating temperature -- about 230 °C (450 °F). However the lower temperatures are generally used because the higher the temperature, the more quickly the strength of the nylon fabric degrades over time. With a maximum operating temperature of 120 °C, balloon envelopes can generally be flown for between 400 and 500 hours before the fabric needs to be replaced. Many balloon pilots operate their envelopes at temperatures significantly below the maximum in order to extend the longevity of their envelope fabric.
For typical atmospheric conditions, a hot air balloon requires about 3 cubic meters of envelope volume in order to lift 1 kilogram (50 ft³/lb). The precise amount of lift provided depends not only upon the internal temperature mentioned above, but the external temperature, altitude above sea level, and humidity of the surrounding air.
In general, the lift provided by a hot air balloon decreases about 3% for each 1,000 meters (1% per 1,000 ft) of altitude gained.
A range of envelope sizes is available. The smallest, one-person, basket-less balloons (called " Hoppers" or " Cloudhoppers") have less than 1,000 cubic meters (35,000 ft³) of envelope volume. At the other end of the scale are the balloons used by large commercial sightseeing operations that carry well over two dozen people and have envelope volumes of up to 15,000 cubic meters (600,000 ft³). However, most balloons are roughly 2,500 cubic meters (100,000 ft³) and carry 3 to 4 people.
The Rozier type of hybrid balloon, called after its creator, Jean-François Pilâtre de Rozier, has separate chambers for a non-heated lifting gas (such as hydrogen or helium) as well as a heated lifting gas (as is used in a hot air balloon).
The direction of flight depends on the wind, but the altitude of the balloon can be controlled by changing the temperature of the air inside the envelope. The top of the balloon generally has a flap of fabric (often referred to as a parachute) that can be pulled partially open to release hot air in an emergency or for better control of the descent. The flap is pulled completely open to collapse the balloon after landing. In some advanced hot air balloons, side vents are fitted, which when open, cause the balloon to rotate. This is a useful manoeuvre to align the wider side of the basket for landing.
The lift of the balloon is determined by the temperature difference between the inside and outside air. On a hot day, the balloon cannot be loaded as much as on a cool day, because the temperature required for launch will exceed the maximum sustainable for nylon. Most hot air balloon launches are made during the cooler hours of the day, at dawn or two to three hours before sunset. This is also to avoid thermals, which are vertical air currents caused by ground heating, making controlling a balloon more difficult.
The largest manufacturer of hot air balloons in the world is Cameron Balloons of Bristol, England. Aerostar International Inc. of Sioux Falls, South Dakota is North America's largest balloon manufacturer and is a close second in world manufacturing. Firefly Balloons, formerly known as The Balloon Works, is another popular manufacturer of hot-air balloons located in Statesville, North Carolina.
Flight techniques
A hot air balloon flight starts with unpacking the balloon from its carrying bag. A gasoline powered fan is used to blow cold (outside) air into the envelope. The cold air partially inflates the balloon to establish its basic shape before the burner flame is aimed into the throat heating the air inside. A crew member stationed opposite the throat, holds a rope (crown line) tied to the apex (crown) of the envelope. The "crown-man" acts as a dead weight in order to slow the envelope's rise so that the envelope can achieve maximum inflation (volume) before standing erect. Once the balloon is upright, pilot and passengers climb into the basket. When the pilot is ready for launch, more heat is directed into the envelope and the balloon lifts off.
The crew then pack up inflation equipment and follow the balloon with the retrieval transport (also known as a "chase vehicle").
Once the balloon has landed, the envelope is deflated and detached from the basket. The envelope is then packed into its carrying bag. The burner and the basket are separated and all components are packed into the chase vehicle.
In competition, the pilots need to be able to read different wind directions at different altitudes. Balloon competitions are often called "races" but they're most often a test of accuracy, not speed. For most competitive balloon flights, the goal is to fly as close as possible to one or more exact points called "targets". Once a pilot has directed the balloon as close as possible to a target, a weighted marker with an identifying number written on it is dropped. The distance between a pilot's marker and that target determines his or her score. During some competitive flights, pilots will be required to fly to 5 or more targets before landing. To assist with navigation, topographic maps and GPS units are used.
Some experienced pilots are able to take a flight in one direction, rise to a different altitude to catch wind in a returning direction. With experience, luck, and the right conditions, some pilots are able to control a precision landing at the destination. On rare occasions, they may be able to return to the launch site at the end of the flight. This is sometimes called a box effect, usually when flying in valleys with drainage winds.
The dangers of the sport include excessive (vertical or horizontal) speed during landing, entangling with high voltage power lines, and mid-air collisions that may collapse the balloon.
In the United States, hot air balloon pilots must have an FAA license. There are two categories in the United States; private and commercial. In order to fly passengers and be paid for it in the United States, you must have a commercial certificate. The FAA requires balloons to fly under visual flight rules which means that they can only be flown during daylight hours. Tethered balloons are sometimes inflated at night for the impressive visual effects. In the United Kingdom a CAA Private Pilots Licence is required.
Gallery
 PREPARING FOR FLIGHT: the wicker balloon basket holds 16 passengers. The pilot is climbing out after some pre-flight tests |
 FINAL INFLATION: firing the propane burners to complete inflation |
 LANDING: an unusual top view of the basket, after tipping onto its side during landing at dusk |
 RETRIEVAL: the envelope is packed in to a bag for storage until the next flight |