By the closing years of the 19th century, balloons and airships had become fairly commonplace, and attention turned to the possibility of flight using machines that did not depend upon buoyancy for their lifting ability.
Replica 1902 Wright Glider, Wright Cycle Company Museum, Dayton OH
One of the most important of these early aerial researchers was Otto Lilienthal. During the 1890s, Lilienthal built a number of crude gliders, big enough to carry a man, that he flew by jumping off hills into the wind. Through careful measurement, and by testing several potential wing sizes and shapes, he was able to publish data on such basic matters as lift and drag. In 1896, Lilienthal was killed in a crash of his “flying machine”.
In America, the publicity surrounding Lilienthal’s death caught the attention of two brothers in Ohio. Orville and Wilbur Wright ran a bicycle shop in Dayton. As kids, they had both a mechanical bent and an interest in flight, and now they decided to continue where Lilienthal had left off. After scouring the local libraries for information, they somewhat naively wrote to the Smithsonian Institution in 1899 asking for any information they might have about “aeronautics”, assuming that it could all be worked out in just a short time. (They knew that a number of other people in Europe and the US were also looking into the problem.) Instead, it was the beginning of a multi-year project in which the Wright brothers demonstrated their genius by not only solving all the problems of flight, but by designing and building all the testing machinery they would need to do it.
Almost immediately, they recognized that the real difficulty that needed to be solved in heavier-than-air flight was the problem of flight control—how to both keep the “aeroplane” steady while at the same time allowing for movement in three different axis (“pitch” for up-and-down, “roll” for spinning, and “yaw” for side-to-side). Nearly all of the other people working on the matter were trying to produce a design that was inherently stable and would automatically fly itself in a straight line. The Wright brothers, however, influenced by their work in designing bicycles, realized that a flying machine had to be inherently un-stable: rather than being something in which the occupant passively rode, it would have to be actively controlled by its operator, like a bicycle. This is what Lilienthal had done: his machines were steered by shifting one’s body weight around, similar to a modern hang-glider. But the Wrights decided that this method was too difficult and dangerous, and they sought a mechanical method of controlling their machine. At first, they experimented with a system of gears and levers to do this, but they quickly determined that this would make their machine too heavy to get off the ground. They needed a better way.
The answer came one day in the bicycle shop as Wilbur was talking with a customer and absent-mindedly twisting an empty cardboard box from an inner tube. As he twisted the box, the shape remained rigid, but one corner rose higher than the other—which in the air would, he quickly realized, produce more lift on one side and turn the aeroplane. The concept became known as “wing-warping”.
In July 1899, in their first actual experiments, the Wrights built a working model, five feet wide, from balsa and cloth, which they flew as a kite. The kite’s biplane wings were based on an 1896 design by French researchers Chanute and Herring. The upper and lower wings were attached to each other by struts to form a rectangular box structure, and four cables were attached to the wing edges and ran down to control levers held by the operator. And it worked. As the kite rode on the wind, the brothers found that they were able to turn and bank it at will using the control levers. It was a revolutionary breakthrough, and it put the Wrights far ahead of everyone else. (Though nobody else knew it: the brothers, afraid that someone would see and steal their deigns, were obsessed with secrecy, did all their testing out of the public eye, and did not publish any of their results.)
The next step was to build a model that was large enough to carry a person. Their first glider was finished in 1900. It used a bigger version of the biplane wing-warping system to control roll, and a small flat elevator at the front to control pitch. To keep the plane from side-slipping, it had a fixed vertical rudder. Testing the design required stronger and steadier winds than were available in Dayton, so, after an inquiry to the US Meteorological Service, the Wrights took their new glider to Kitty Hawk NC. Here, it was first flown a few times as a giant kite, then was launched from the top of nearby Kill-Devil Hill, piloted by one of the brothers. In 1901, after making a few changes, the Wrights built a second glider and made a number of flights with it.
The 1900-1901 experiments showed the brothers that they now had a workable control system. But there were still two big problems. The gliders proved to be unsteady in yaw: occasionally the aircraft would unexpectedly veer in the opposite direction and crash. After some thought, the brothers decided that this could be solved by making the rudder moveable and connecting it to the wing-warping controls to push the nose into a turn.
A bigger problem involved the plane’s lifting ability. They had based their wing design on the data published by Lilienthal, but in the actual tests the wings produced far less lift than expected. Now the Wright’s true genius came into play: they concluded that Lilienthal’s data was simply wrong and, to calculate it correctly, they designed and built their own wind tunnel at their bicycle shop, testing various wing shapes and measuring their lift and drag. After determining the best wing shape, they built a new glider in 1902 and took it to Kitty Hawk for testing.
The first tests, in which the 32-foot-wide glider was flown as a kite, showed a drastic improvement. In September and October 1902, the brothers made almost 1,000 flights from the top of Kill-Devil Hill (hauling the 100-pound glider back up the hill after each one), some of them lasting over 25 seconds and covering over 600 feet. The design proved to be fully controllable in all three axis. In effect, they had built an airplane. Since the 1902 Glider did not have an engine, the first powered flight would not happen for another year, but all of the basic systems of flight control had now been demonstrated, and when the Wright Brothers eventually got their patent for a heavier-than-air flying machine, it was based on the 1902 Glider.
After finishing their flight tests in 1902, the Glider was stored in a wooden shed at Kitty Hawk. When the Wrights returned in September 1903 with their powered Flyer, they first refreshed their piloting skills by reassembling the 1902 Glider and making over 1,000 flights with it. By December they were ready to try out the new Flyer.
After 1903 the Glider was unceremoniously abandoned at Kitty Hawk and deteriorated in the weather. Today, the only remaining original piece is a small section of wingtip, on display at the Smithsonian Air and Space Museum. A number of replicas were made later, some of them under the direct supervision of Orville Wright himself. One of these is on display inside the Wright Cycle Company Museum in Dayton OH, and another is on display at the Kitty Hawk National Monument in North Carolina.