Lilienthal and others had also added horizontal surfaces behind each wing, called elevators, that controlled the glider's pitch up and down, and Lilienthal used a vertical rudder that could turn his glider right or left. But the third axis through which a glider could rotate—rolling to either left or right—remained problematic. Most experimenters of the day thought roll was something to be avoided and worked to offset it, but Wilbur Wright, the older of the brothers, disagreed. Wilbur's experience with bicycles had taught him that a controlled roll could be a good thing. Wilbur knew that when cyclists turned to the right, they also leaned to the right, in effect "rolling" the bicycle and thereby achieving an efficient, controlled turn. Wilbur realized that creating a proper turn in a flying machine would require combining the action of the rudder and some kind of roll control. While observing the flight of turkey vultures gliding on the wind, Wilbur decided that by twisting the wings—having the left wing twist upward and the right wing twist downward, or vice versa—he would be able to control the roll. He rigged a system that linked the twisting, called wing warping, to the rudder control. This coordination of control proved key. By 1902 the Wrights were flying gliders with relative ease, and a year later, having added an engine they built themselves, Orville made that historic first powered flight—on December 17, 1903.
As happens so often in engineering, however, the first solution turned out not to be the best one. A crucial improvement soon emerged from a group of aviation enthusiasts headed by famed inventor Alexander Graham Bell. The Wrights had shared ideas with Bell's group, including a young engine builder named Glenn Curtiss, who was soon designing his own airplanes. One of the concepts was a control system that replaced wing warping with a pair of horizontal flaps called ailerons, positioned on each wing's trailing edge. Curtiss used ailerons, which made rolls and banking turns mechanically simpler; indeed, aileron control eventually became the standard. But the Wrights were furious with Curtiss, claiming patent infringement on his part. The ensuing legal battle dragged on for years, with the Wrights winning judgments but ultimately getting out of the business and leaving it open to Curtiss and others.