Glider Planes

Definition: A winged, heavier-than-air craft having no internal propulsion source other than gravity. Sailplanes are a specific type of glider that can ascend and descend.

Significance: Gliders were the predecessors to motorized flight. The information gained from experiments with gliders made the motorized flight possible.

A glider is launched from a raised elevation and can only move forward through the air while simultaneously losing altitude. The relation between forward momentum and loss of altitude is a glider’s sink rate, and gliding is the motion of the craft’s controlled descent. The history of glider development is essentially the process of experimentation to minimize a glider’s sink rate while giving the glider pilot increasing control over the movement or flight of the glider while airborne. Eventually, after centuries of experimentation, aviation technology developed to the point where gliders could be constructed and flown in ways that permitted the glider pilot to slow and even reverse the rate of descent. Flying a glider using the energy from thermal air currents to regain altitude lost by the downward force of gravity is called soaring. The type of glider capable of being flown in such a way is a sailplane. It is a high-performance glider explicitly designed for soaring. Post-World-War-II gliders are more correctly called sailplanes to distinguish them from earlier glidersregardless of size and precise configurationthat were incapable of regaining lost altitude in a controlled manner after being launched.

Earliest History

The experimentation with gliders that led to modern sailplanes took place over centuries. As long as humans watched birds in flight, they wanted to imitate them. Many of the earliest attempts at human flight are thinly documented or are mythological. One of the earliest stories of human flight is the account of Daedalus and his son, Icarus. As related in Metamorphoses (8 C.E.; Eng. trans. 1567), a collection of tales by the Roman writer Ovid, Daedalus was imprisoned by the Cretan king Minos. While watching seagulls in flight, Daedalus got the idea to fashion wings from discarded gull feathers held together with candle wax. Using these birdlike wings, Daedalus and Icarus escaped. Daedalus wisely kept a course midway between Earth and Heaven, but Icarus flew too close to the sun. The wax holding his wings together melted, and he plummeted to his death. This cautionary tale of Daedalus and Icarus set the stage for much later thinking about human flight. Most people thought that humans had no business trying to fly, but a small group of adventurers and inventors disregarded this opinion.

Medieval Attempts at Flight

Numerous undocumented passages in medieval historical sources state that humans achieved flight aboard or attached to gigantic kites, perhaps similar to present-day hang gliders. The Italian mathematician Giovanni Danti reportedly tried to fly over Lake Trasimeno in Italy in the late 1500s. 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. He plummeted to Earth, breaking his leg. Leonardo da Vinci, a fifteenth-century Italian artist, scientist, and inventor, seriously examined the possibility of human flight. Using comparative zoology and architectural and mathematical studies, da Vinci concluded that humans were too heavy to be kept aloft by feathered wings modeled on birds' wings. Da Vinci thought that batlike wings in which the skin is stretched over a lightweight skeleton were more likely to sustain the weight of a human in flight. Da Vinci also designed rudimentary parachutes and a type of ornithopter or bird-imitating flapping machine that is considered an early prototype of the modern helicopter. Although da Vinci's flying inventions are theoretically possible, it was almost three hundred years before they were built, tested, modified, and implemented.

Nineteenth Century

The Englishman Sir George Cayley systematically examined the problems associated with human flight. In 1809, he published the results of his experiments with small, uncrewed glider models, each with V-shaped wings and a tail stabilizer. Cayley performed a brief, barely controlled glider flight in 1853 using his horses to supply the forward momentum. William Henson tried to develop Cayley's experiments further by adding a steam-powered motor to the aircraft. Such an engine made the aircraft far too heavy to get off the ground, but Henson improved Cayley's glider designs, eventually designing a fixed, single-wing glider with a bird-tail-shaped tail, a rudder, and landing gear. Henson's friend John Stringfellow built a small model glider with a small steam engine that could fly under specific circumstances, but he needed to create a bigger model to carry the weight of a human. F. H. Wenham, another Englishman, also studied birds to investigate possibilities for human flight. Wenham concluded that a slightly arched wing set at an angle, rather than a flat wing surface, could lift more weight. He also thought that a connected series of shorter, arched wings rather than one set of long, flat wings might sustain a person in flight if only a means could initially lift the craft off the ground.

Frenchmen Jean-Marie Le Bris and Felix Du Temple built uncrewed, motorless gliders. Le Bris fashioned his glider as an albatross, and Du Temple constructed the first propeller-driven aircraft to lift off from the ground under its power. Neither craft could stay aloft for over a few seconds, nor could their flight path be controlled. In the late nineteenth century, the German Otto Lilienthal built numerous single-winged gliders, each with a fixed tail for stability. The pilot stood in the glider's center with the glider frame attached around his waist. By making over two thousand flights off a small hill, Lilienthal learned how to move his weight to steer the glider. His longest flight was approximately 200 feet. On August 9, 1896, Lilienthal attached a small motor to his glider and launched himself off the hill. The wind shifted, and he crashed, suffering fatal injuries. Percy Pilcher, a Scotsman who knew Lilienthal, modified his triplane glider based on Lilienthal's experiments. Pilcher conducted numerous glider flights, one as long as 750 feet, before being killed in a glider accident in September 1899. Lilienthal's experiments also influenced a naturalized American, Octave Chanute. He designed numerous gliders and tested them on the beach at Lake Michigan near Chicago, Illinois. He had two-, three-, and five-winged models with rear stabilizers, each controlled in flight by shifts in the pilot's weight. Chanute kept careful records of his experiments with equilibrium while aloft, information he shared with the Wright brothers.

Early Twentieth Century

Wilbur Wright and his brother Orville Wright grew up primarily in Dayton, Ohio. They initially made their living repairing bicycles while pursuing aeronautical experiments as a hobby. Beginning with a series of kites, the Wright brothers developed a system of wing-warping that significantly increased the pilot's ability to control the flight of an aircraft. The Wright brothers spent part of each year from 1900 to 1905 at Kitty Hawk, North Carolina, testing gliders they had designed in Dayton. The 1900 glider weighed 52 pounds and had eighteen by five-foot wings. It was not substantial enough to lift a pilot in a controlled flight. In 1901, the glider was much more significant, having twenty-two by seven-foot wings. The longest piloted flight, by Wilbur, was 400 feet. During the winter of 1901, the Wright brothers reworked information from Chanute and Lilienthal to solve problems with both lift and control. Using this new information, the 1902 biplane glider weighed 116 pounds and had a 32-foot wingspan. It incorporated various design changes to provide more lift, including a forward monoplane elevator and a fixed rudder linked to the wing-warping or shaping system, allowing the pilot to control the glider's flight. The longest flight of the 1902 testing session was 622 feet, lasting 26 seconds. The original patent issued to the Wright brothers covered the modifications included in the 1902 glider design. Returning to design experiments, the Wrights constructed a glider that could carry a 12-horsepower engine with two propellers. On December 17, 1903, Wilbur Wright flew 852 feet, staying aloft for 59 secondsthe first documented pilot-controlled motorized flight in history. The Wrights continued to refine their aircraft designs in 1904 and 1905, gradually increasing the length of and control over motorized flights. In 1911, Orville returned briefly to gliders, setting a glider flight record of nine minutes and 45 seconds.

World War II

Once the motorized flight had been demonstrated, gliders seemed rather primitive. All the major powers in World War I used motorized airplanes, not gliders. After the end of World War I, however, attention returned to gliders. The Treaty of Versailles ended the war and prohibited the Germans from building new planes with engines. The treaty did not mention the building of motorless gliders. Thus, throughout the 1920s and early 1930s, thousands of young German men learned to fly as glider pilots. They formed the core of the Nazi Luftwaffe in World War II. In 1930, the three Schweizer brothers—Bill, Paul, and Ernest—began to build gliders for sale to enthusiasts in the United States. In 1932, the Soaring Society of America was founded to regulate the small but growing hobby in America. Soaring Magazine, still in publication, debuted in 1937.

The Germans were the first to recognize the potential military applications of gliders. The first army glider capable of carrying troops and equipment was the DFS-230. On May 11, 1940, ten DFS-230s carrying seventy-eight glider troops attacked and captured Eben Emael in Belgium due in considerable measure to the element of surprise. Other countries quickly took notice. The United States produced thousands of small TG-2 and TG-3 gliders and jumbo gliders, such as the Laister-Kauffman CG-10A Trojan. The British also built large numbers of gliders to use in aerial observation and in troop and equipment transport.

The idea of parachute troops or airborne infantry began in early World War II. Rather than trying to coordinate hundreds of individual soldiers in parachute drops, the conventional wisdom of the time thought it made more sense to airlift troops in platoons in gliders. Unfortunately, glider pilots and troops suffered very high casualty rates, over 50 percent. The Germans tried an unsuccessful glider assault on Crete. Many gliders were blown off course; some crashed, and some landed intact but far from the designated landing zone. On July 9, 1943, the Allies tried a joint American-British glider assault on Sicily. Of the 144 troop gliders involved in the assault, 69 landed in the ocean rather than on land, ten were shot down, 12 could land intact, and only four landed within the designated landing zone. The Allies also tried glider assaults in Burma, with similar disastrous results.

Post-World War II

After World War II, many military pilots turned to glide as a recreational pursuit. Inexpensive military surplus gliders were readily available. By the mid-1950s, there was a large enough recreational market to spur further refinements in glider design. Invented in 1928, the variometer, a piece of equipment that allowed the pilot to measure even slight differences in altitude, became standard on every glider, which became technically sailplanes, able to both ascend and descend. National and international championships are held annually for different design classifications of sailplanes, with various contests for speed, altitude, duration of flight, distance covered, and accuracy in landing at a designated spot. All rules and standards concerning sailplane construction and classification, as well as sailplane pilot training requirements in the United States, are regulated by the Federal Aviation Administration.

Drones as Powered Gliders

In the late twentieth and early twenty-first century, military drones (or unmanned aerial vehicles-UAVs), such as General Atomic's MQ-1 Predator and MQ-9 Reaper, gained great notoriety in battlefields such as Bosnia, Iraq, and Afghanistan. These aviation assets were particularly suited for long-duration flights. This was because they were essentially powered gliders. Their design, particularly their relatively low weight, and long wingspans enabled them to stay aloft for missions approaching a complete twenty-four-hour cycle. In 2024, reports emerged of the newest generation of military UAVs. One such was named the Ultra Long-Endurance Tactical Reconnaissance Aircraftor ULTRA. Photographs of ULTRA indicated a glider-like design and media reports suggested flight durations of up to 80 hours. Future projected missions for glider-like drones include cargo resupply of military personnel. Futurists envision such gliders being dropped from larger aircraft while laden with cargo. The gliders would navigate to ground troops operating beyond enemy lines.

Bibliography

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