hot-air balloon
Where was the hot-air balloon first invented?
What principle allows hot-air balloons to ascend and descend?
What are the differences between hot-air balloons and gas balloons?
hot-air balloon, large balloon filled with heated air that floats in the sky with a basket underneath for people to ride in. For a full treatment of all types of manned and unmanned balloon craft, see also balloon flight.
History
Balloons were used in the first successful human attempts at flying. Experimentation with balloonlike craft may have begun as early as 1709 with the work of Bartolomeu Lourenço de GusmĂŁo. The Portugal-born priest was reportedly inspired upon seeing a soap bubble float above a candle, coming to the conclusion that objects lighter than air could technically fly. He presented a small âflying machineâ (a miniature hot-air balloon, in essence) to the Royal House in August 1709, which was received with enthusiasm by King John V. The full-size balloon, however, would be invented in France in the late 18th century.
The Montgolfier brothers
Credit for the invention of the hot-air balloon goes to brothers Joseph-Michel and Jacques-Ătienne Montgolfier of Annonay, a small town just south of Lyon, France. According to one, possibly apocryphal, story, the brothers took inspiration from watching Josephâs wifeâs skirts as they billowed from the heat of a charcoal burner being used to dry laundry.
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The Italian-born English scientist Tiberius Cavallo had recently demonstrated that Archimedesâ principle is applicable to airborne objects by successfully floating hydrogen-filled soap bubbles. When he attempted to duplicate this with animal bladders, though, they proved too heavy to ascend. Fortunately, the provincial Montgolfiers were not constrained by laboratory techniques and created their hot-air balloon on a cruder and much larger scale. In 1782 they discovered that heated air, when collected inside a large lightweight paper or fabric bag, caused the bag to rise. On June 4, 1783, the brothers made a public demonstration in Annonay with a 10.5-meter- (35-foot-) diameter unmanned cloth-and-paper balloon, using the heat from a straw fire. The balloon rose into the air about 1,000 meters (3,000 feet), remained there some 10 minutes, and then settled to the ground more than 2.4 km (1.5 miles) from where it rose.
Galvanized by their success, the Montgolfiers traveled to Versailles, where they repeated the experiment with a larger balloon. On September 19, 1783, the brothers sent a sheep, a rooster, and a duck aloft as passengers in the same balloon, which floated for about 8 minutes before landing safely about 3.2 km (2 miles) from the launch site. On November 21, 1783, the first crewed untethered flight took place in a Montgolfier balloon with Jean-François Pilâtre de Rozier and François Laurent, marquis dâArlandes, as passengers. The balloon sailed over Paris for 9 km (5.5 miles) in about 25 minutes.
The rip panel and drag rope
Important later additions were the rip panel, first used on April 27, 1839, by the American aeronaut John Wise, and the drag rope, invented about 1830 by the English aeronaut Charles Green. A rip panel is an elongated section of the balloon that is lightly fixed in place and can be quickly ripped or pulled open at the moment of landing. It adds greatly to the safety of ballooning by making quick deflation possible. The drag rope, or compensator, is a long, heavy rope that trails the balloon in order to slow down the balloonâs vertical and horizontal speed in landing operations before the basket touches down.
Elements of a hot-air balloon
Early hot-air balloons burned straw and alcohol spirits for fuel, though by 1900 these fuels had been replaced with petroleum. Compressed liquefied propane is used almost exclusively today. Hot-air balloon burners use vaporizing coils to preheat the fuel for efficient combustion. Most of these coils are made of stainless steel, but copper coils also work adequately. The burners are mounted, often on gimbals, on the suspension concentration ring between the basket and the mouth of the balloon. Most systems have redundant burners to compensate for problems with defective controls or contaminated fuel. A particularly notorious early problem was leaking seals on control valves.
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A variety of materials has been used for the actual balloon, or envelope. Cotton, nylon, and polyester are common for the envelopes of hot-air balloons. Cotton, having a poor weight-to-strength ratio, is only favored for carnival âsmokeâ balloons. In addition to the choice of envelopes, an even greater variety of systems for carrying the load or passengers has been used. For sport ballooning, the traditional wicker basket, albeit with a stainless steel frame, is popular. Criteria for evaluation of a basket design should include toughness, energy absorption, and electrical resistance, but style and marketability are more often the governing factors.
Mechanics
As the Montgolfier brothers had referred to earlier, Archimedesâ principle states that if the weight of an object is less than that of the displaced fluid (liquid or, in this case, gas), the object rises. This net result, buoyancy, is the main principle by which hot-air balloons operate.
Modern hot-air balloons operate on the same principles as the hot-air balloons of the 18th and 19th centuries. In essence, because hot air is lighter than cold air, a pilot can adjust a propane burner to either increase or decrease the heat in the balloonâs envelope, allowing it to ascend or descend.
Heating the air inside the balloon creates hotter air that is less dense than the surrounding air, pushing the hot-air balloon upward. To come back down, the gas heaters are turned off and the air inside the balloon starts to cool. A vent at the top of the balloon is also opened to allow more surrounding cool air to move into the balloon as the hot air cools, increasing the density of the air inside the balloon as the balloon slowly descends.
Doing the math
A balloon can carry the difference between its weight and the weight of the air that it displaces. Consider this example: 28 cubic meters (1,000 cubic feet) of hot air, at normal hot-air balloon operating temperatures, weighs about 22.5 kg (50 pounds). Thus, the lifting force of the hot air at low altitudes can be obtained by subtracting its weight from the typical weight of the same volume of air (about 34 kg, or 75 pounds, in this example).
Because the atmosphere is compressed by its own weight, it is less dense at higher altitudes. At 3,600 meters (about 12,000 feet) the atmosphere is approximately two-thirds as dense and so will provide two-thirds the buoyancy. This effect continues progressively, so that at 15,000 meters (50,000 feet) it is only one-tenth as dense, at 30,000 meters (100,000 feet) one-hundredth, and at 45,000 meters (150,000 feet) one-thousandth. In order to carry the same load at an altitude of 50 km (30 miles) as at sea level, a balloon would have to be 1,000 times as big and yet weigh the same (that is, keeping everything constant except the balloonâs volume).
Controlling buoyancy and altitude
The buoyancy of a hot-air balloon is controlled by heating the air in the balloon or by changing the amount of ballast (extra weight). Tiny changes in one of these components can force dramatic changes in a balloonâs flight. Just a one- or two-degree change in temperature in a hot-air balloon or a few grams of ballast dropped will make a balloon ascend or descend accordingly. On the other hand, in violent maneuvers (such as during a storm), whole bags of sand or great blasts of heat from a balloonâs burner may be required for a proper correction. To help in rapid atmospheric cooling, modern hot-air balloons also have very large hot-air release vents in the form of a parachute that can seal and unseal an opening in the top of the balloon.
Changing the altitude of a balloon will permit it to follow different air currents. A 20- or 30-degree difference in wind direction usually occurs in the first few thousand meters of altitude, but a full circle of wind directions (âbox windsâ) can also occur. Albuquerque, New Mexico, is famous for its box winds, which can be used to climb and descend back to the original launch site. If there is only a simple and stable wind pattern, no additional control is possible. With superior weather monitoring, use of the Global Positioning System (GPS), and radio or satellite communication, remarkable flight control is possible.
Hot-air balloons versus gas balloons
Although they are often treated the same way in popular culture, hot-air balloons differ significantly from gas balloons in how they operate. Gas balloons use either helium or hydrogen gas to lift the balloon. The gases do not require heat; rather, they are stored in the balloon from the start of a balloon flight. The amount of gas (and thus, the level at which the balloon floats) can be adjusted by releasing gas (to lower the balloon) or by dropping sandbags (to lift the balloon higher).
Recreation and sport
In addition to quiet morning or afternoon flights drifting cross-country to enjoy the view, many balloonists enjoy competitive sporting events and attempting to set new records. A balloonist may fly alone in the basket or carry several passengers. Often, many balloons meet to launch together without any competitive goals. Individual flights generally last from one to three hours and may go several kilometers, though they often land very close to the takeoff point.
Balloon rallies may consist of just a few balloons for a one-day outing or up to several hundred balloons for a weeklong festival. Competitive events include distance within a time limit, spot landing, and âhare and houndâ races. Hare and hound races are easy to organize and judge since they only require one (hare) balloon to launch first and fly a reasonable distance. The competitors attempt to land as close as possible to the hareâs landing position. In crowded conditions, markers are often dropped to simulate the landings, and the balloons fly on to more open locations.
Commercial ride operators are in business almost everywhere in the world. Some ride balloons carry 10 to 20 passengers at a time in gigantic partitioned baskets. In California and France, wine-country flights are popular tourist attractions. African safari flights, at low altitude over vast game preserves, are perhaps the pinnacle of ride ballooning.
In media and popular culture
Media
Hot-air balloons have been a fixture in popular culture ever since their invention. Jules Verneâs classic novel Around the World in Eighty Days (published serially in 1872) does not actually include a hot-air balloon, but film adaptations released in 1956 and 2004 feature hot-air balloon as a method by which the protagonist travels the world.
In the film The Wizard of Oz (1939), it is revealed that the Wizard had arrived in Oz by way of a hot-air balloon, which he then leaves in. After Dorothy exits the balloonâs basket to retrieve her dog, the balloon takes off before she can climb back in, unfortunately leaving her behind. Many of the citizens of Oz had believed in the Wizardâs powers because of his unconventional arrival in the giant balloon.
Festivals
Every year colorful festivals celebrating hot-air balloon flight are held worldwide, the largest of which takes place in Albuquerque, New Mexico. Originally featuring just 13 balloons in 1972, the Albuquerque International Balloon Fiesta has grown to include more than 500 balloons per year and has been called âthe worldâs most photographed event.â Major festivals in the United States are also held in Readington, New Jersey, and Charlotte, North Carolina. Other annual hot-air balloon festivals occur in many cities around the world, including Cappadocia, Turkey; Saint-Jean-sur-Richelieu, Quebec, Canada; Saga, Japan; Canberra, Australian Capital Territory; Taitung, Taiwan; and Bristol, England.