The tail on this glider, however, caused a new problem that had not occurred in their previous gliders. At times, when struck by a side gust of wind, the glider turned up sidewise and came sliding laterally to the ground in spite of the effort and skill of the operator in using the warping mechanism to control it. The brothers were experiencing tailspins, though that term did not come into use until several years later. When tailspins occurred, the glider would sometimes slide so fast that the movement caused the tail’s fixed vertical vanes to aggravate the turning movement instead of counteracting it by maintaining an equal speed at the opposite wingtips. The result was worse than if there were no fixed vertical tail. [Illustration: Wilbur Wright making right turn in glide from West Hill, Oct. 24, 1902 (Kill Devil Hill in background.)] [Illustration: High glide on Oct. 10, 1902. _Courtesy, Smithsonian Institution._] While lying awake one night, Orville thought of converting their vertical tail from two fixed vanes to a single movable rudder. When making a turn or recovering lateral balance, this rudder could be moved toward the low wing to compensate for the increased drag imparted to the high wing by its greater angle of attack. Wilbur listened attentively when Orville told him about the idea the next morning. Then, without hesitation, Wilbur not only agreed to the change but immediately proposed the further important modification of interconnecting the rudder control wires with those of the wing-warping. Thus by a single movement the operator could affect both controls. Through the brilliant interplay of two inventive minds, all the essentials of the Wright control system were completed within a few hours. The combination of warp and rudder control became the key to successful control of their powered machine and to the control of all aircraft since. (Modern airplanes—and indeed Wright planes after the middle of their 1905 experimental season—do not have the aileron and rudder controls permanently interconnected, but these controls can be and are operated in combination when necessary.) Together with the use of the forward elevator, it allowed the Wrights to perform all the basic aerial maneuvers that were necessary for controlled flight. The essential problem of how to control a flying machine about all three axes was now solved.