SAIL THE SKIES

For as long as humans have watched birds in flight, they've considered ways to imitate them. The earliest attempts at such efforts are vaguely documented or mythical in nature. During this blog, we'll follow the progress of gliders as they become the recreational aircraft of today.

Though most people had the attitude that humans and flight did not mix for centuries, small groups of pathfinders were willing to take the risk to achieve flight by whatever means was available. For example, the Italian mathematician Giovanni Danti is reported to have attempted flight over Lake Trasimeno in Italy in the late 1500's. John Damian, another Italian, reportedly constructed a pair of wings and jumped off the wall of a castle belonging to King James IV of Scotland, with Damian breaking his leg in the process. Leonardo Da Vinci, a fifteenth century Italian artist, scientist and inventor, studied the possibility of human flight in detail. By utilization of comparative architectural, mathematical and zoological studies, Da Vinci realized that humans were too heavy to be kept aloft by feathered wings modeled on the wings of birds. Da Vinci concluded that batlike wings with the skin stretched over a lightweight skeleton were more likely to sustain human flight. Da Vinci was also credited with the design of some of the first parachute systems along with an ornithopter with flapping wings, which was an early precursor to the helicopter. While his concepts were valid, it would be three-hundred years before they would be put into practice.

Though not much activity took place in the realm of glider aviation during the next three centuries, a renewed interest in the potential of gliders began during the nineteenth century. Octave Chanute, a French immigrant, sought to interest engineers and other technical professionals in both the problems and possibilities of flight. Chanute began his career as a member of a surveying crew with the Hudson River Railroad. Attending private schools in New York City, Chanute then worked his way up through a series of successively responsible positions, to include that of chief engineer of the first bridge built across the Missouri River. Chanute then became a leader of major American engineering societies, which culminated in his appointment as the chief engineer of the Erie Railroad Company from 1873 to 1883. He corresponded with a number of aeronautical experimenters and inventors around the globe. As a result of his contacts, Chanute gained much information on the history and technology of flight. He compiled and published this information in a journal titled Progress In Flying Machines in 1894. Chanute also organized sessions on aeronautics at the meetings of major engineering societies, as well as arranging conferences on aeronautics at the World's Columbian Exposition in Chicago in 1883 and the Louisiana Purchase Exposition in St. Louis in 1904.

The history of aircraft structure parallels the history of aviation itself. Advances in materials and manufacturing processes have led to their evolution from simple wood truss structures to the sleek aircraft of today. Once it was proven that lift could be created by passing air over the top of a curved surface, the path was clear for the development of fixed and rotary-wing aircraft. George Cayley produced such an airfoil in a chambered configuration in the early 1800's, later producing manned gliders as well. As early as 1809, Cayley built a man-sized version of his glider with a wing surface of 300 square feet. His assistant was able to make a few short flights by hanging on to the craft. Cayley had conclusively proven the principles of flight, including the existence of lift, weight, thrust and drag. He also built the first stacked wing aircraft, a tri-wing glider which successfully flew a man in 1853. Cayley also utilized a crude form of rudder on his gliders, from which he was able to establish directional control. By the 1890's Otto Lilienthal of Germany, both an engineer and inventor, built upon Cayley's work by initially by studying the flight characteristics of storks and other birds by conducting a number of experiments. Lilienthal also developed at least a dozen models of planes, consisting of both wing-flapping and conventional biplane designs. Lilienthal's gliders were designed to precise tolerances in order to distribute weight as evenly as possible. They operated similar to modern hang gliders, in which the pilot could control them by shifting body weight. As a result of these efforts, Lilienthal was granted a US patent for his hang bar control system. Though he only flew gliders for five years, Lilienthal's experiments formed the basis of operating the hang gliders and ultralight aircraft of today. During a test flight in 1893 he flew a distance of 820 ft.-a world record at the time.

By the early 1900's, the Wright brothers began to test gliders and conducted gliding flights in the hills of Kitty Hawk, North Carolina. The Wrights built a series of gliders while experimenting with aerodynamics, which was critical to developing a workable control system. A number of historians, and the Wrights themselves, emphasized their overall plan was to learn flight control and become pilots by soaring, while their contemporaries rushed to add power to their aircraft without focusing on the flight control problems. Once Wilbur and Orville Wright had achieved powered flight in December 1903 by attaching an engine to one of their stacked glider designs, interest began to wane in the concept of glider flight. Achievements and records in powered flight became the driving force behind aviation in the early twentieth century. However, this began to change about 1920, as the sport of soaring got a new lease on life. Glider design was encouraged by developments in Germany, where the Treaty of Versailles banned flying powered aircraft, as well as an air force. This situation promoted the use of gliders in Germany and elsewhere as new forms of lift were discovered, including wind waves, which could lift a glider as high as 40,000 ft., making it possible to gain altitude and distance using previously unknown atmospheric properties. As proof, Dr. Wolfgang Klemperer broke the 1911 soaring record of the Wrights with a duration record of 13 minutes, by the use of a ridge lift. Austrian Robert Kronfeld proved that thermal lift could be used by a sailplane to gain altitude by a short flight in 1928. Flight by glider became became organized at the national level with the founding of the National Glider Association in 1929 in Detroit and the USA National Glider contest held at Elmira, New York in 1930.

It wasn't long before the military applications of gliders became obvious. The first large-scale military glider was the DFS-230 produced by Germany. On May 11, 1940 ten DFS-230's carrying seventy-eight glider troops attacked and captured fortress Eben Emael in Belgium, due in large measure to the element of surprise. Other countries quickly began to produce their own gliders as a result of the Eben Emael action. The United States produced thousands of the small TG-2 and TG-3 gliders, as well as larger gliders, such as the Laister-Kauffman CG-10A Trojan. The British also built large numbers of various types of gliders for use in aerial observation, in addition to troop and equipment transport, though glider troops and pilots often sustained high casualties due to the instability of the aircraft in high winds and damage when striking the ground. After World War II, gliding became a sport, since many inexpensive surplus military gliders became available.

By the mid-1950's recreational gliding became popular enough to drive enhancements in glider design, leading to the production of more streamlined and aerodynamic planes. New glider aircraft were built with a variometer, a small sensitive altimeter dating back to the late 1920's, which enabled glider pilots to monitor changes in altitude. New materials such as fiberglass, carbon-fiber, glass reinforced plastic (GRP) and Kevlar have made today's gliders both lighter and more durable. The success of glider aviation after World War II has spawned other forms of the sport, such as paragliding, in which a free-flying glider is launched by foot control and parasailing, in which a specially designed parachute is either towed by a boat or vehicle. Over the last thirty years, both forms of gliding have approached the popularity of gliding by aircraft.

We at Fly By Wire Air wish our viewers the Merriest Christmas and the Happiest New Year.