The Wrights reasoned that a wing makes lift when air meets it, so making different amounts of lift on each end of a wing would make one side rise more than the other and bank the whole aircraft. This was wing warping: twisting the tips of the wings in opposite directions with lines the pilot pulled. Because wing warping was based on the air and not on body weight, it did not limit the size of the aircraft, as shifting body weight did. Otto Lilienthal of Germany had used weight shifting as his only means of controlling his gliders, yet the Wrights believed he had collected the most reliable data of any researcher before them.
Their 1901 glider developed only one-third of the lift that Lilienthal's lift data predicted. The brothers made about 100 glides between July 27 and August 17, but the wings still did not produce enough lift. They also met a problem called adverse yaw: when the wings were warped to roll the aircraft, drag increased on the upper wing, and the aircraft twisted the opposite way. After that season Wilbur wrote that, considering the time and money spent and the distance yet to go, they considered their experiments a failure.
Rather than give up, the brothers tested the numbers themselves. To make wind for a test of Lilienthal's data, they rode a bicycle up and down the streets of Dayton as fast as possible. Then they built a wind tunnel, with a square tube for aiming the air, a fan that drove the air, and a balance mounted in the airstream. Testing wing shapes was tedious, because each wing shape had to be tested at 45 different angles. They recorded the results on scraps of wallpaper.
A multiplier of 0.005 for air pressure had been developed by John Smeaton in the 1700s to design windmills, and it had been accepted as true for almost 150 years. By mid-December 1901 the Wrights found, to their surprise, that Lilienthal's tables were largely correct and that Smeaton's coefficient was what was wrong. In 1902 they made the rudder movable and connected it to the wing-warping wires, so it turned the right way automatically, and their best glide that year went more than 600 feet and lasted 26 seconds.
Next came the engine. The Wrights built it themselves because they could not buy one light enough. They built the crankcase of aluminum to save weight, and the engine had no throttle, so it could run only at full speed. The first test, on February 12, 1903, ended with a seized engine and a shattered crankcase. The Wrights rebuilt it completely, and it was running smoothly by May. The finished engine made about 12 horsepower.
The Patent Office had received so many similar applications over 50 years that it decided to reject automatically all applications for machines that had not already flown. On December 17, 1903, at Kitty Hawk, the Flyer made four flights, and the longest went 852 feet in 59 seconds. Orville and Wilbur had promised their father never to fly together. On May 25, 1910, he allowed one six-minute flight near Dayton, and Orville then took his 82-year-old father on his first and only flight.
Words to know
- lift: upward push
- coefficient: multiplier number
- throttle: speed control
- crankcase: engine housing
