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Air Show of Oshkosh (Wisconsin - United States), summer 1992. Among the hundreds of aircraft on static display or presented in flight, an ultra-light (here in the photo) attracts my attention: it has no engine but is equipped with a propeller; fixed trolley, one would say single-seater, with structure limited to the essential and extremely light. What is it about? And most importantly, how does it take off and stay in the air after take-off?