Otto Lilienthal turned the problem of flight into a replicable experimental program, combining observation of bird flight, aerodynamic measurement, and more than 2,000 glider flights between 1891 and his death in a flying accident in 1896. His work Der Vogelflug als Grundlage der Fliegekunst (1889) systematized the aerodynamic data that provided a direct technical basis for the next generation of aviators. The Wright brothers explicitly acknowledged their debt to Lilienthal. He died practicing what he researched.