Hot air balloon

Hot air balloons are the oldest successful human flight technology, dating back to the Montgolfier brothers' invention in Annonay, France in 1783. The first manned flight 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.

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 cargo to rise. Hot air balloons are able to fly extremely high in the sky. Some weather balloons are known to exceed 20 km above the Earth?s surface, much higher than normal aircrafts.

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Modern hot air balloons are usually made of synthetic fabrics such as ripstop nylon, a light weight fabric of relatively 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, which resembles a flamethrower, is fueled by propane, a liquefied gas stored in pressure vessels, similar to high pressure forklift cylinders.

Related Topics:
Nylon - Propane - Forklift

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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 in contrast to the air outside the envelope. For most envelopes made of nylon fabric, the maximum

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internal temperature is limited to approximately 120 degrees Celsius (about 250 degrees Fahrenheit). It should be noted that the melting point of nylon is significantly higher than these maximum operating temperature -- about 230 degrees Celsius or 450 degrees Fahrenheit. 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 Celsius, balloon envelopes can generally be flown for between 400 and 500 hours before the fabric needs to be replaced. This compromise between lifting capacity and envelope longevity is primarily a matter of convention and economics rather than any hard and fast rules. Many balloon

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pilots operate their envelopes at temperatures significantly below the maximum in order to extend the longevity of their envelope fabric.

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For typical atmospheric conditions, a hot air balloon requires about 3 cubic meters of envelope volume in order to lift 1 kilogram (or about 50 cubic feet per pound). 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.

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In general, the lift provided by a hot air balloon decreases about 3% for each 1,000 meters of altitude gained (1% per 1,000 feet).

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The range of envelope sizes varies a great deal amongst different designs. The smallest, one-person, basket-less balloons (called "Hoppers" or "Cloud Hoppers") have less than 1,000 cubic meters (35,000 cubic feet) 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 cubic feet). However, most balloons are roughly 2,500 cubic meters (100,000 cubic feet) and carry 3 to 4 people.

Related Topics:
Hoppers - Cloud Hoppers

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There is a special type of hybrid balloon that 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.) This is called a Rozier balloon after its creator, Jean-François Pilâtre de Rozier.

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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 open partially to release hot air in an emergency or for better control of the descent. The flap is pulled open completely 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.

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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.

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The largest manufacturer of Hot Air Balloons in the world is Cameron Balloons of Bristol, UK. Aerostar International Inc. of Sioux Falls, South Dakota is North America's largest balloon manufacturer and is a close second in world manufacturing.

Related Topics:
Cameron Balloons - Bristol - Sioux Falls, South Dakota

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