Hot Air Balloons

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 Pil‰tre de Rozier and the Marquis d'Arlandes.

Hot air balloons that can be propelled through the air rather than just being carried along by the wind are known as airships or, more specifically, thermal 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.

A hot air balloon consists of a bag called the envelope that is capable of containing hot air. Suspended beneath is the gondola or wicker basket (in certain, long distance or high altitude balloons, a capsule) which carries a source of heat capable of producing a sufficient temperature gradient between the air inside the envelope and the surrounding air mass to give enough lift to keep the balloon and its passengers aloft. Unlike gas balloons, the envelope does not have to be sealed at the bottom since the rising hot air only exerts pressure on the upper hemisphere of the balloon to provide lift. In today's sports balloons the envelope is generally made from nylon fabric and the mouth of the balloon (closest to the burner flame) is made from fire resistant material such as Nomex.

Recently, balloon envelopes 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, Shu Kingdom, used airborne lanterns for military signaling. These lanterns are known as Kongming lanterns .

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 designing 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 unmanned balloons and flights with animals, the first balloon flight with humans on board took place on October 19, 1783 with the physician Pil‰tre de Rozier, the manufacture manager, Jean-Baptiste RŽveillon and Giroud de Villette, at the Folie Titon in actual Paris. Officially, the first fly was 1 month later, 21 November 1783. King Louis XVI had originally decreed that condemned criminals would be the first pilots, but a young physicist named Pil‰tre de Rozier and the Marquis Francois d'Arlandes successfully petitioned for the honor. The first hot air balloons were basically cloth bags (sometimes lined with paper) with a smoky fire built on a grill attached to the bottom. They had a tendency to catch fire and be destroyed upon landing.

The first military use of aircraft took place during the French Revolutionary Wars, when the French used a tethered hydrogen balloon to observe the movements of the Austrian army during the Battle of Fleurus (1794). Hot air balloons were employed during the American Civil War. Though the military balloons used by the Union Army Balloon Corps under the command of Prof. Thaddeus S. C. Lowe were limp silk envelopes inflated with coke gas or hydrogen, the Confederate Army did attempt to counter with a rigid Montgolfier style hot air, or "hot smoke balloon." Captain John R. Bryant inflated his rigid cotton balloon with a fire of oil-soaked pine cones. The balloon was soon captured by Union forces as the Confederate's techniques of balloon handling were not competent.

The first modern hot air balloon was designed and built in 1960 by Ed Yost. He made the first free flight of such an aircraft in Bruning, Nebraska on 22 October 1960. Initially equipped with a plastic envelope and kerosene fuel, Yost's designs rapidly moved onto using a modified propane powered "weed burner" to heat the air and lightweight nylon fabric for the envelope material.

Today, hot air balloons are used primarily for recreation. There are some 7,500 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 21,290 meters (69,852 feet). He took off from downtown Bombay, India and landed 240 km (150 miles) south in Panchale. The previous record of 19,811 meters (64,980 ft) had been set by Per Lindstrand on June 6, 1988 in Plano, Texas. However, like all registered aircraft, oxygen is needed for all crew and passengers for any flight that reaches and exceeds an altitude of 12,500 feet.

The furthest that a hot air balloon has ever been flown is 7,671.91 km. On January 15, 1991, the Virgin Pacific Flyer balloon completed the longest flight in a hot air balloon when Per Lindstrand (born in Sweden, but resident in the UK) and Richard Branson of the UK flew from Japan to Northern Canada.

With a volume of 74,000 m (2,600,000 ft), the balloon envelope was the largest ever built for a hot air craft. Designed to fly in the trans-oceanic jetstreams the Pacific Flyer recorded the highest ground speed for a manned balloon at 245 mph (394 km/h).

The longest duration hot air balloon flight ever made is 50 hours and 38 minutes made by Michio Kanda and Hirosuke Tekezawa of Japan on January 2, 1997.

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 mouth or throat. Attached to the envelope is a basket, or gondola, for carrying the passengers. The basket is usually made of wicker and ratan, but can be made of aluminum. 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.

Modern hot air balloons are usually made of light-weight and strong synthetic fabrics such as ripstop nylon, or dacron (a polyester). During the manufacturing process, the material is cut into panels and sewn together, along with structural load tapes (webbing) that carry the weight of the gondola or basket. Vertical rows of panels are referred to as gores due to their triangular shape. Envelopes can have as few as 16 gores or as many as 24 or more. The use of more gores usually means a smoother shape.

The fabric (or at least part of it, the top 1/3 for example) may be coated with a sealer, such as silicone or polyurethane, to make it impermeable to air. It is often the degredation of this coating and the corresponding loss of impermiability that ends the effective life of an envelope, not weakening of the fabric itself. Heat, moisture, and mechanical wear-and-tear during set up and pack up are the primary causes of degredation. Once an envelope becomes too porous to fly, it may be retired and used as a 'rag bag': cold inflated and opened for children to run through.

Envelopes often have a crown ring at their very top. This is a hoop of smooth metal, usually aluminum and approximately 1 foot in diameter, to which vertical load tapes attach.

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 ft) 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 ft). However, most balloons are roughly 2,500 cubic meters (100,000 ft) and carry 3 to sometimes 4 people.

Raising the air temperature inside the envelope makes it lighter than the surrounding (ambient) air. This causes the balloon and its payload to rise. 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 ˇC (250 ˇF). It should be noted that the melting point of nylon is significantly higher than these maximum operating temperature - about 230 ˇC (450 ˇF). 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 ˇC, 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 ft/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. 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 envelope fabric.

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

The Rozier type of hybrid balloon, called after its creator, Jean-FranŤois Pil‰tre de Rozier, has separate cell for helium as well as a cone below for hot air (as is used in a hot air balloon) to heat the helium at night.

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.

One of the tricks involved in flying a balloon is learning to deal with the delayed response. To slow or stop a descent requires the pilot to light the burner. This sends hot combustion exhaust through the mouth into the envelope where it expands and forces some cooler air out of the mouth. This lightens the total weight of the system and increases its buoyancy, but not immediately. From the time that the burner is lit until the balloon slows or stops its descent can take 30 seconds or more, depending on its rate of decent and how cold it has become. This delay requires a great deal of anticipation on the part of the pilot.

The top of the balloon usually has a vent of some sort. The most common type of vent is a disk-shaped flap of fabric called a parachute vent. The fabric is connected around its edge to a set of "vent lines" that converge in the center. (The arrangement of fabric and lines looks roughly like a parachute -- thus the name.) These "vent lines" are themselves connected to a control line that runs to the basket. A parachute vent is opened by pulling on the control line. Once the control line is released, the pressure of the remaining hot air pushes the vent fabric back into place. A parachute vent can be opened briefly while in flight to initiate a rapid descent. (Slower descents are initiated by allowing the air in the balloon to cool naturally.) The vent is pulled completely open to collapse the balloon after landing.

An older, and today less commonly used, style of vent is called a "Velcro-style" vent. This too is a disk of fabric at the top of the balloon. However, rather than having a set of "vent lines" that can repeatedly open and close the vent, the vent is secured by "hook and loop" fasteners (such as Velcro) and is only opened at the end of the flight. Balloons equipped with a "Velcro-style" vent typically have a second "maneuvering vent" built into the side (as opposed to the top) of the balloon.

Some hot air balloons have turning vents which are side vents which, when opened, cause the balloon to rotate. Such vents are particularly useful for balloons with rectangular baskets in order to align the wider side of the basket for landing.

Instrumentation - A balloon may be outfitted with a variety of instruments to aid the pilot. These commonly include an altimeter, a rate of climb (vertical speed) indicator, envelope (air) temperature, and ambient (air) temperature. A GPS receiver can be useful to indicate ground speed (traditional aircraft air speed indicators would be useless) and direction.

Flight techniques - Most hot air balloon launches are made during the cooler hours of the day, at dawn or two to three hours before sunset. At these times of day, the winds are typically light making for easier launch and landing of the balloon. Flying at these times also avoids thermals, which are vertical air currents caused by ground heating that make it more difficult to control the balloon. In the extreme, the downdrafts associated with strong thermals can exceed the ability of a balloon to climb and can thus force a balloon into the ground.

Additional Information





My Journey in a Hot Air Balloon
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