The only negatives preserved in the Deutsches Museum in Munich were destroyed during World War II. Zhukovsky wrote that Lilienthal's flying machine was the most important invention in the aviation field. In 1867 Lilienthal began his experiments on the force of air in earnest interrupted when he volunteered to serve in the Franco-Prussian War.
". He was the first person to make well-documented repeated successful gliding flights. He followed an experimental approach establiOtto Lilienthald previously by Sir George Cayley.