Retaining the same basic bat-like configuration of the Éole, the Avion III was equipped with two engines driving two propellers. While the earlier aircraft had no means of directional control at all, this one was equipped with a small rudder.
Trials of the aircraft began at the Satory army base near Versailles on 12 October 1897, with the aircraft taxiing along a circular track. The first flight was attempted on 14 October and most sources agree ended almost immediately in a crash without ever leaving the ground. Late in his life, Ader would claim that there had been a flight of 100 m (328 ft) on this day, and said he had two witnesses to confirm it. Whatever actually happened, the French military was unimpressed with the demonstration and cancelled any further funding.