Definition: All manner of flight that is not powered by any mechanical or electrical source of energy. Wind-powered flight can be in an aerostat, which is a lighter-than-air aircraft such as a gas-filled balloon, or in an aerodyne, which is a heavier-than-air craft such as a glider.
Significance: All modern aircraft has its origins in wind-powered flight. Early aeronautical engineers studied, designed, constructed, and flew balloons and later gliders; many perished in the attempt. Wind-powered flight is now mainly for recreation and sport (ballooning, gliding, parasailing, and skydiving), for military purposes (troop and equipment parachute drops), and for scientific research (weather balloons).
Early History
Historians refer to several early attempts at wind-powered flight. In the ancient Greek myth, Icarus wore wings of feathers held together by wax; when he flew too close to the sun, the wax on his wings melted, and he plummeted to the sea. A Persian legend dating from 1500 b.c.e. relates the story of a king who used tethered eagles to fly him to China. In 850 b.c.e., a legendary English king made a pair of wings, attached them to his arms, and tried to fly, but he crashed and died.
For centuries, humans continued to pursue the concept of wearing artificial wings and attempting to fly like a bird. John Damian constructed wings from chicken feathers in early sixteenth century Scotland and tried to fly from the walls of Stirling Castle. A century later, a Frenchman made his wings out of wood and taffeta and tried to fly from a rooftop. Another Frenchman tried to fly with wings on his arms in 1712, and died in the attempt. Thirty years later, a man wearing wings on his hands and feet tried to fly across the Seine in Paris; he survived his fall. At about the same time in Germany, a man fastened large taffeta wings to his arms and tried to fly off a mountain.
Because of the failure to fly by attaching wings and jumping from great heights, early aeronautical engineers began investigating the idea of flying in lighter-than-air crafts. Roger Bacon, an English monk and scientist in thirteenth century England, wrote about lighter-than-air flight in Secrets of Art and Nature, a work that was not studied by aviation enthusiasts until the sixteenth century.
Aerostat Flight
Gas-Filled Balloons. A balloon is an aerostat in that it will lift in a static air mass and move horizontally with a moving air mass. Balloons work according to the buoyancy principle. The principle, attributed to Archimedes, states that the pressure in any stationary fluid, liquid or gas, increases with depth. A balloon is filled with a fluid, heated air, or a lighter-than-air gas, and the total weight of the balloon and its gas is less than the air that is surrounding the balloon. As a result, the balloon rises to that point of elevation at which the density of the air outside the balloon is the same as the density of the fluid inside the balloon; at this point the difference between the pressures at the top and bottom surfaces of the balloon is not longer great enough to propel the balloon upward. Because the density of atmospheric air reduces with elevation, a balloon filled with a gas that is lighter than air will rise to a point in the atmosphere where the gas in the balloon has the same density as the atmospheric air. To rise higher, the gas in the balloon must be heated further to reduce its density even more, or the pilot must jettison ballast, such as sand bags, to make the balloon lighter and thus able to ascend.
History of Balloon Flight. In 1670, Father Francesco Lana, an Italian priest, was the first person to apply scientific principles to the design of an aerostat. He sketched a figure that was basically a boat with large copper spheres; when emptied of air, de Lana theorized, the boat would rise and float in the air.
Almost forty years later, another priest, Father Bartholomeu de Gusmao, designed and built a model of a hot-air balloon that he demonstrated at the court of King John V in Lisbon, Portugal. De Gusmao’s miniature aircraft contained a small fire to heat the air in the balloon; as the device rose, it collided with the curtains, crashed, and started a fire. Aviation chronicles credit de Gusmao with building the first aerostat in history.
The first successful passenger-carrying hot-air balloon was launched by the Montgolfier brothers in France in 1783. After observing that warm air in their fireplace caused paper to rise up the chimney, Joseph-Michel and Jacques-Etienne Montgolfier designed and built a hot-air balloon large enough to carry a human. They constructed it with a large linen bag and filled it with air that was heated beneath by small fire; their first passengers in the September 19,1783, flight were a sheep, a rooster, and a duck. The animals traveled about two miles and then landed safely ten minutes later.
French physicist Jacques-Alexander-Cesar Charles experimented with a hydrogen-filled balloon; he knew that the weight of hydrogen was about 7 percent of the weight of air, so he theorized that not only would a balloon filled with hydrogen ascend higher than one filled with heated air, but it would also be safer as no fire was required to heat the air. On August 27, 1783, Charles launched his un-crewed hydrogen balloon; it rose to a height of 3,000 feet and flew for about an hour.
The first crewed hot-air balloon flight occurred on October 15, 1783, when Jean-Francois Pilatre de Rozier ascended in a tethered balloon. The following month, he and a fellow Frenchman made the first untethered crewed balloon flight. Their beautifully decorated balloon rose to a height of several hundred feet above Paris, drifted about 5 miles and landed safely almost thirty minutes later. They used a charcoal-burning brazier to heat the air for theirbal-loon. De Rozier died in 1785 in an attempt to cross the English Channel in a hydrogen-filled balloon; a spark ignited the hydrogen and the balloon fell to the ground.
On December 1, 1783, Jacques-Alexander-Cesar Charles made the first flight in a hydrogen-filled balloon. He and his passenger flew 27 miles and used sand bags to control their altitude. Charles then made a solo flight and reached an altitude of 10,000 feet; he was the first person to make a solo balloon flight. The next year the first woman to fly in an untethered balloon was Madame Elisabeth Thible. With his balloon flight on October 4, 1784, James Sadler became the first British aeronaut. On January 7, 1785, Jean-Pierre Blanchard and John Jeffries crossed the English Channel by balloon. The first crewed flight in a hydrogen balloon in the United States took place in January, 1793; President George Washington personally honored the pilot.
Balloons in the Military. By the end of the eighteenth century, balloon flight had been adapted for military use. In April, 1794, the world’s first military air service was established in France. French troops used balloons to observe Austrian troop movements, and in the Franco-Prussian War of 1870-1871, the French interior minister escaped Paris in aballoon. Balloons were also used for observation by the North and South during the American Civil War. In 1883, the British Army established its balloon school, and the army’s First Balloon Section left in 1899 to serve in the Boer War. Japan sent thousands of balloons filled with explosives across the Pacific and rigged them to descend and detonate on American cities; a few hundred did land but did little damage.
Scientific Balloons. Balloon flights specifically for meteorological research began in the nineteenth century. On September 5, 1862, English meteorologist James Glaisher and a colleague filled their balloon with scientific equipment and ascended to 30,000 feet, where both men lost consciousness; the balloon finally began its descent, and the men recovered and the balloon landed safely. A German meteorologist also ascended to 30,000 feet in his balloon in early 1894.
The main problem facing the aeronauts in their scientific expeditions was the low temperatures at such high altitudes. In 1930, Swiss balloonist Auguste Piccard designed an enclosed and pressurized compartment in which the scientists could conduct their research and still be protected from the cold air at elevations as high as 70,000 feet. Uncrewed balloons continued to be used for upper atmosphere research throughout the twentieth century and into the twenty-first century. These balloons, made of rubber or polyethylene and filled with hydrogen or helium, carry scientific equipment to measure the speed and direction of the wind and air temperature and pressure.
Recreational Balloons. Balloon flight in the late twentieth century developed into a popular recreational activity for sports enthusiasts and adventurers. Sport ballooning relies on hot-air balloons that utilize butane or propane burners or a combination of both hot air and lighter-than-air gases. Adventurers continue to use balloons to set altitude and distance records. In the late 1990′s, several international teams attempted to circumnavigate the world in balloons that combined both a hot-air bag and a helium-filled bag, a method that allowed balloonists to reach higher altitudes. Bad weather, however, prevented the successful completion of their trips. In August, 2001, American adventurer Steve Fossett failed in his fifth attempt to travel around the world in a balloon.
Aerodyne Flight
Gliders. Gliders are heavier-than-air machines, meaning that they are heavier than the air that they displace. A glider’s lift is due to the movement of air over the glider’s surfaces that in turn causes lift.
Gliders are designed so as to increase lift and decrease drag. Lift is the force that is perpendicular to the direction of motion. Lift is created by the difference between the high pressure on the lower surface of the wing and the lower pressure above the wing. Drag is the force that is parallel but opposite to the direction of motion and thus resists the forward motion of the plane. Drag is created by the friction and pressure forces. The long wings of the glider increase its lift; the shape of the streamlined fuselage decreases the drag. Because it lacks a power source, a glider needs some method to launch it into flight. A powered vehicle, such as a truck or an engine-driven aircraft, can launch a glider; also, the pilot of the glider can take off by accelerating down a slope. Once aloft, the glider soars by riding rising warm air currents, or thermals, to higher altitudes; as the atmospheric air cools, the glider will descend unless it finds another thermal.
History of Gliders. The “Father of Aeronautics” is Sir George Cayley, the first person to understand and apply aerodynamic principles in the design of an aircraft. Cayley designed gliders with fixed wings for lift and a tail with horizontal and vertical surfaces for control; his wing and tail designs are remarkably similar to those of modern aircraft. The first crewed flight in a glider was in 1853, when a young boy flew in one of Cayley’s fixed-wing gliders.
The greatest glider of the late nineteenth century was German Otto Lilienthal, an engineer and aviation pioneer. He experimented with fixed-wing gliders, and in 1891 made his first glider flight. By the time he died in a glider accident in 1896, Lilienthal had made more than two thousand glides in several different gliders he designed and built; they were elegant constructions that usually consisted of a willow and bamboo frame covered with waxed cotton. His method of flying was to race down a hill with his glider, and the momentum created lift over the curved wings. The air currents enabled him to sail hundreds of feet. He controlled the glider by gripping the framework bar and shifting his weight. He directed the glider by means of a harness around his forehead that was attached to the glider’s moveable elevator. When Lilienthal lowered his head, the glider would aim upward; when he raised his head, the glider would go down. Lilienthal flew almost every day and kept meticulous records of the details of his flights; he was widely photographed in journals and newspapers. On August 9, 1896, his glider crashed 50 feet to Earth after a sudden shift of wind, and he died the next day.
American Octave Chanute, a civil engineer, followed Lilienthal and experimented with fixed-wing gliders. Chanute designed and flew several different models and wrote a detailed topic about the history of human attempts to fly. He also gave technical advice to the Wright brothers, the two American men who made the most momentous contribution to aviation.
The Wright Brothers. Orville and Wilbur Wright followed a specific scientific approach in their early experimental flights with kites and gliders. To research flight, they contacted the Smithsonian Institution on June 2, 1899, and requested any information about the construction of a flying machine. They then read every publication from the Smithsonian, including Chanute’s Progress in Flying Machines, and learned more about Lilienthal’s work with gliders. Lilienthal had used elevators to regulate the pitch of his gliders and had used rudders for steering right or left. The Wright brothers discovered that Lilienthal had not known how to control yaw, or the side-to-side rolling, other than by simply shifting his weight as he flew. Wilbur Wright wanted to solve the problem of yaw; he studied buzzards as they flew and observed how they dropped one of their wings to maintain balance. He believed that the movement of the wing lifted the bird by increasing the air pressure under that wing. Wilbur and his brother tested this theory by building a biplane kite and manipulating the opposite wing tips with strings to turn either up or down, with the result that they were able to control the yaw of the kite.
In 1900, they built a glider and tested it near Kitty Hawk, North Carolina. It was a 52-pound biplane with a wingspan of about 17 feet; the pilot lay prone at center of the lower wing. The wings of the glider were made of fabric, and it was flown as a kite. They chose the beach in North Carolina because the Weather Service informed them that the strong winds at Kitty Hawk would be able to keep the glider up in the air. After a flight of ten minutes, the glider was able to make a soft landing on the sandy beach.
A year later they tested a second glider; this one was bigger in order to have more lift, but it was so big that it stalled dangerously in midair. In order to solve the problem, the Wright brothers tested wing profiles. They also designed and built a small wind tunnel in Dayton, Ohio, and carefully tested 150 different wing shapes to measure aerodynamic forces on wing sections and to solve lift and drag problems. They equipped their tethered gliders with mechanical instrumentation to measure the force of the wind upon the aircraft. Applying their findings, they designed a new glider that had longer and narrower wings and implemented a wing warping technique. In 1902, Wilbur and Orville flew almost one thousand times in their new glider. The next step was to add an engine, and their December 17, 1903, flight was the first heavier-than-air powered flight in history.
Recreational Gliding. Gliders, or sailplanes as they are also called, are now the mainstay of the international sport of gliding and soaring in which the pilot flies through the air using thermals, or rising currents of warm air, to maintain the desired altitude. Modern sailplanes are constructed of fiberglass with a wingspan between 15 and 20 meters (50 to 65 feet). They are launched most often by powered aircraft at a height of about 2,000 feet. Biannual competitions sponsored by the Federation Aeronautique Internationale award the Lilienthal Medal to the winner.
Kites. A kite is a tethered device made of a lightweight frame covered with a thin layer of cloth or paper. Most probably invented by the Chinese more than two thousand years ago, kites were early wind-powered vehicles used frequently by scientists in the eighteenth century. In Scotland, Alexander Wilson used paper kites in 1749 to carry thermometers aloft to measure atmospheric temperatures at various altitudes. American Benjamin Franklin flew a kite in his famous experiment about the conduction of electricity in 1752. The British Army’s balloon school set up a human-lifting kite section in 1894. In the same year, Australian Lawrence Hargrave invented the box kite; his design became the standard model for early airplanes, including the Wright brothers’ planes. By the end of the century, Orville and Wilbur Wright tested their theory of wing warping on a biplane kite. In 1904, Samuel Cody crossed the English Channel in a boat pulled by a large kite.
The following year, the British Army’s balloon factory hired a kiting instructor and planned to teach observation and signal transmission using kites. In 1907, a kite built by Alexander Graham Bell carried a man aloft to 168 feet for a seven-minute flight. By the late twentieth century, kites were popular in recreational and competitive sports throughout the world, and also as a method of signaling in rescue operations at sea.
Parachutes. Leonardo da Vinci’s 1495 sketch was one of the earliest drawings of a parachute. He theorized that a human being could safely descend from any height provided he was wearing a tent like apparatus. Parachutes were not made until the eighteenth century, however, when aeronauts realized that they needed a quick escape if their balloons caught on fire. Joseph-Michel Montgolfier and Jean-Pierre Blanchard, both famous eighteenth century French balloonists, are said to have jumped with a parachute from their balloons. Another Frenchman, Andre-Jacques Garnerin, made the first exhibition parachute jump over Paris in 1797. His jump was marred by severe oscillation, however, and Sir George Cayley then designed a cone-shaped chute that he believed would decrease the oscillation. This design was notable for causing the first fatality of a parachutist in 1837, when the chute collapsed and the jumper fell several thousand feet to his death. Subsequently, a small opening at the top of the parachute was added. With the increased popularity of ballooning in the nineteenth century, parachutes, too, became more widespread.
By the twentieth century, parachuting had evolved into an exhibition sport, extremely popular in the United States. Military forces around the world were reluctant to adopt the parachute for their pilots. Indeed, World War I pilots at first considered it cowardly to jump with a parachute from their burning aircraft. Balloonists who served in the war, however, did not hesitate to wear parachutes and thus escape their balloons if shot down. In 1916, an Austrian pilot parachuted safely from his burning airplane; soon afterward, all Austrian and German pilots were finally equipped with parachutes. Allied pilots, however, did not agree to use parachutes until World War II. By the end of that war, almost 100,000 people had parachuted to safety.
By the 1970′s, parachuting had evolved into the recreational and competitive international sport of skydiving. Parachuters jump from an airplane at about 10,000 feet in solo jumps or in a group of several skydivers. They can travel at speeds as high as 150 miles per hour during their free fall, and can change their speed by maneuvering their bodies. Many perform rehearsed maneuvers during their free fall until they are at an altitude of approximately 4,000 feet, at which point they deploy their chute. Skydivers use controls to steer left or right, or to slow their descent.
Hang Gliders. Hang gliding is another type of wind-powered flight that, like skydiving, became popular in the 1970′s; it relies on the same aeronautical principles first explained by Lilienthal and Chanute, who wrote about using air and gravity to fly and land lightweight aircraft.
Hang gliders have a frame and a kitelike sail; the person flying the hang glider wears a harness and is supported by holding on to the frame. The pilots self-launch the hang glider by running into an updraft; they control the aircraft by shifting their weight either forward or back, left or right. The primary designer and developer of the skysail or hang glider was Francis Rogallo, an aeronautical engineer. Working with his wife, Rogallo designed a successful paraglider with a flexible wing and received a patent for it in 1951. The Rogallo skysail is portable, inexpensive, and consists of two sails mounted on a frame.
Parasailing. The water sport of parasailing became popular in different countries in the late twentieth century. Parasailing developed from parascending, a method of training parachutists invented by Pierre Lemoigne in 1960. In parascending, the parachutist’s harness lines were connected to a car, which then drove until the chutist was airborne. In 1961, a Connecticut company marketed the parachute as a “Parasail,” and parasailing became adapted as a water sport with the parachutist being tethered to a boat in the water and being hoisted into the air by the moving boat. To land, the parasailer maneuvered the lines to return to the shore. The inventor and pioneer of the safe and popular sport of modern parasailing is Mark McCulloch, who in 1974 invented a launch and retrieval apparatus, known as a winchboat. He also designed and patented a single passenger device and a tandem passenger chair; the seating device remains tethered to the boat and is launched from and returns to a platform, also designed and patented by McCulloch, by means of a winch on a small boat.
