The pioneer era of aviation was the period of aviation history between the first successful powered flight, generally accepted to have been made by the Wright Brothers on 17 December 1903, and the outbreak of the First World War in August 1914. Once the principles of powered controlled flight had been established there was a period in which many different aircraft configurations were experimented with. By 1914 the tractor configuration biplane had become the most popular form of aircraft design, and would remain so until the end of the 1920s. The development of the internal combustion engine—primarily from their use in early automobiles even before the start of the 20th century—which enabled successful heavier-than-air flight also produced rapid advances in lighter-than-air flight, particularly in Germany where the Zeppelin company rapidly became the world leader in the field of airship construction. During this period aviation passed from being seen as the preserve of eccentric enthusiasts to being an established technology, with the establishment of specialist aeronautical engineering research organizations and university courses and the creation of major industrial aircraft manufacturing businesses, and aviation became a subject of enormous popular interest. Flying displays such as the Grande Semaine d'Aviation of 1909 and air races such as the Gordon Bennett Trophy and the Circuit of Europe attracted huge audiences and successful pilots such as Jules Védrines and Claude Grahame-White became celebrities. An emerging technology Although the Wright brothers made their first successful powered flights in December 1903 and by 1905 were making flights of significant duration, their achievement was largely unknown to the world in general and was widely disbelieved. After their flights in 1905 the Wrights stopped work on developing their aircraft and concentrated on trying to commercially exploit their invention, attempting to interest the military authorities of the United States and then, after being rebuffed, France and Great Britain. Consequently, attempts to achieve powered flight continued, principally in France. To publicize the aeronautical concourse at the upcoming World's Fair in St. Louis, Octave Chanute gave a number of lectures at aero-clubs in Europe, sharing his excitement about flying gliders. He showed slides of his own glider flying experiments as well as some of the Wrights glider flying in 1901 and 1902. All these talks were reproduced in club journals. The lecture to members of the Aéro-Club de France in April 1903 is the best known, and the August 1903 issue of