Large round inflatable sacks filled with hot air that rise above the ground, towing compartments for passengers or cargo.
Hot-air balloons inaugurated the concept of human flight. The hot-air balloon proved for the first time that a human being could survive at some height above the earth. This was a notable scientific achievement, since prior to the advent of balloons many people had no clear understanding of how high the breathable atmosphere extended. With the advent of the balloon, the dream of leaving the confines of the earth was realized. This was the dawn of a new era, the preamble to the space age.
Two French brothers, Joseph-Michel and Jacques-Étienne Montgolfier, invented the hot-air balloon in 1783. Their inspiration was the observation that a paper bag placed over an indoor smoking fire rose in the air. As a test, they lined a large cloth bag with paper and caused it to rise by filling it with black smoke and hot air from an outdoor straw fire. Later, the Montgolfiers sent animals aloft first on tethered balloons and then on a free flight in order to prove that the animals could survive above the earth. They succeeded: The animals lived. After the free flight, King Louis XVI of France was persuaded to allow the required permission for humans to attempt a test flight. With approval, two other Frenchmen, Jean-François Pilâtre de Rozier and the Marquis François-Laurent d’Arlandes, made the first human free-flight balloon ascent on November 21, 1783. In a 70-foot-high, 46-foot-diameter Montgolfier balloon, they flew for 25 minutes, traveling for several miles over the city of Paris. The balloon carried its own grated fire pot, to which the pilots frequently added straw. Although the pilots had to extinguish small fires when parts of the balloon’s flimsy material ignited from sparks, they landed safely. This flight was witnessed by thousands of Parisians. The second human free-flight balloon ascension was made by Professor Jacques Alexandre César Charles and a passenger on December 1, 1783, in a hydrogen-filled balloon.
Hydrogen-filled balloons, filled with dangerously combustible gas, nevertheless had the advantage of requiring only one-third the gas volume of hot-air balloons for the same buoyancy. The larger hot-air balloons were more difficult to handle and transport. The risk of balloon material igniting from the sparks of open fires made them hazardous, and smoke from the fire choked the riders. Flight time was limited by the fuel supply. In contrast, the hydrogen balloon was well suited to long-term scientific and military observation. Its gas was not expelled until a descent was desired. For these reasons, hot-air balloons became rare during the years between 1800 and 1960, while hydrogen types flourished.
A rebirth of hot-air ballooning occurred on October 10, 1960, in Bruning, Nebraska, when an American, Ed Yost, performed a free-flight test in his prototype balloon. His new design featured a polyurethane-coated nylon envelope and a propane-powered burner. This system was much safer and more rugged than that of the previous era. In 1963, Yost and a partner, Don Piccard, traveled to Britain and made the first English Channel crossing by hot-air balloon.
By the 1970’s, hot-air balloon manufacturers had flourished in the United States, Britain, and France. A hot-air balloon could be obtained for the price of an expensive motorcycle, thus bringing it within the budget of many sports enthusiasts. Many balloonists started businesses offering one-hour chartered flights for one hundred dollars.
High cost and adventurous record-breaking attempts also continued in the twentieth century. Bertrand Piccard and Brian Jones achieved the first nonstop circumnavigation of the globe in March, 1999, in a combination hot-air-and-helium balloon. They launched their Breitling Orbiter 3 from Switzerland, traveled around the world in twenty days, and landed in Egypt.
The main parts of a modern hot-air balloon are the envelope, the burner-fuel system, and the basket. The envelope is the bag, or air sack, containing hot air. It is constructed of pieces of fabric, usually nylon. Each slice of fabric, called a gore, consists of panels and stretches from the top to the bottom of the balloon. Forming the gores in specific dimensions determines the overall shape of the balloon. Round, oblong, and special shapes such as those of a piggy bank, a soda can, and even Mickey Mouse have been constructed, often for advertising.
The envelope top, or crown, is constructed with a parachute valve, a piece of fabric in the shape of a parachute. It is attached in such a manner that a section can be pulled away when a pilot pulls a connected cord. This action releases some of the hot air through the top of the balloon, reduces the overall inside air temperature, and causes the balloon to descend. At the base, which is open, there is usually a short, cylindrical fabric section called the skirt. It is coated with fire-resistant material, because it is close to the flame. The burner is mounted in a frame attached between the basket and the skirt.
Propane from a tank is ignited by the burner’s pilot light. An on-off valve allows the pilot to control fuel flow. The amount of fuel available determines the amount of time the balloon can stay aloft. Baskets, which usually hold from two to five people in addition to propane fuel tanks, are still made of wicker because the shock-absorbent material helps provide a soft landing for passengers and pilots.
In the United States, hot-air balloons must be registered with the Federal Aviation Administration (FAA). Pilots are certified in one of three classes: student, private, or commercial. Hot-air balloons lift off by inflating their containing envelope with heated air. Because hot air expands, the heated air becomes lighter than the ambient, cooler surrounding air, which pushes upward against the air bag and provides the lift necessary for flight. Within the envelope, the heated, lighter air rises and displaces the cooler, heavier air, which descends.
Prior to launch, the pilot checks weather conditions for local winds and any possible storm indications. Storms are hazardous for several reasons: Lightning strikes can electrocute people and damage the balloon; rain, hail, or snow can cause damage, present visibility problems, and make the balloon heavier; and high wind makes launching and landing dangerous. To check the weather conditions, a pilot can either consult a weather service or go to the launch site and send up a small party-size helium balloon. From the balloon’s changing position as it ascends, the pilot can gauge both the speed and the direction of the wind.
Because the air inside the envelope of a hot-air balloon is lighter than the air outside, the relative pressure is upward, and air does not pour out of the open-ended base. To prepare for launching, the deflated envelope is laid out on the ground, then the gas-fired burner is positioned to force heated air into the envelope opening. Another method uses a powerful fan to initially provide a partial cold-air inflation. The balloon, as it inflates, gradually rises from horizontal to vertical. The balloon basket is anchored to prevent a gust of wind from blowing the balloon away prior to launch. The ground crew also holds the basket down until pilot and passengers are ready to launch.
Once the balloon is fully inflated, more lift can be generated by continuing to heat the air within it. When the lift of the heated air is greater than the total weight of the balloon, basket, equipment, and occupants, the balloon rises. Just prior to this point, all tie-lines are released, and the crew releases the basket. The pilot fires the burner again, and the balloon lifts off. Whenever the burner is turned off, the air in the bag gradually cools, and the balloon slowly descends. Neither the heating nor the cooling causes an instant effect. There is a thermal time lag, usually of a half-minute or more, due to the large amount of air to heat or cool. To maintain one particular altitude, the pilot periodically turns the burner on and off. If the pilot is skilled, the balloon will neither rise nor fall to any appreciable degree during this operation. In addition to keeping the burner off, the pilot can also cause a descent by momentarily opening the parachute valve and allowing some of the hot air to escape.
Because a hot-air balloon has no propulsion system, the horizontal direction and speed of the balloon are determined by the prevailing winds. Riding with the wind, passengers feel no wind except for gusts. Winds generally blow in different directions at different altitudes. The pilot seeks out the desired wind to carry the balloon in the desired direction.
There is an upper limit to balloon ascension, even if the burner is left on continuously. As elevation above the ground increases, the air becomes thinner. Eventually, the air becomes so thin that it provides no further lift. The pilot uses an onboard altimeter to determine the balloon’s altitude and a variometer to indicate the rate of ascent or descent. A Global Positioning System (GPS) device can be used to obtain a readout on the balloon’s latitude, longitude, and elevation.
Normally, the pilot tries to land in a large, flat, open area, such as a field, meadow, flatland, or desert, with no nearby obstructions, such as power lines, telephone poles, trees, or fences. In the case of a no-wind landing, the touchdown can be very gentle. If there is wind, the basket will drag along the ground until stopped by friction. After the basket has stopped, the pilot can fully open the parachute valve, causing the balloon to collapse completely. The ground crew tracks the balloon’s path in a recovery vehicle and meets it at the landing site.
There are thousands of hot-air balloon pilots worldwide, and periodic balloon festivals are held in many countries. These festivals usually feature competitions and mass ascensions, in which as many as five hundred balloons float in the air at the same time. The annual October festival in Albuquerque, New Mexico, is one of the largest festivals, with more than 850 balloons aloft in cooperative weather.
Cowl, Clayton T., et al. “Factors Associated with Fatalities and Injuries from Hot-Air Balloon Crashes.” Journal of the American Medical Association 279, no. 13 (April, 1998). Summarizes data collected by the Civil Aeronautics Board and the National Transportation Safety Board covering the years from 1964 to 1995, with causes and types of injuries and deaths due to crashes. Heppenheimer, T. A. A Brief History of Flight: From Balloons to Mach 3 and Beyond. New York: Wiley, 2001. An overview of the important developments in aeronautical history, including the contributions of the Montgolfier brothers. Scott, Phil. The Shoulders of Giants: A History of Human Flight to 1919. Reading, Mass.: Addison-Wesley, 1995. An in-depth account of the balloon flights of the Montgolfier brothers. Wirth, Dick. Ballooning: The Complete Guide to Riding the Wind. New York: Random House, 1980. Focuses on all types of hot-air balloons, from 1783 to 1980, with ample sketches and more than 120 color photographs.
History of human flight