The Goppingen Go 9 was a German research aircraft built to investigate pusher designs, with the propeller placed far away from the engine. Its first flight was in 1941. Its fate is unknown. The tests led to the development of the Dornier Do 335.
In 1937, Claudius Dornier observed that adding more engines and propellers to an aircraft to increase speed would also create more drag. He believed that this could be minimized by adding the second engine in the rear of an aircraft. To prevent being tail heavy though, the engine would have to be placed farther up the fuselage. The Go 9 was then built to see if this theory would work.
The Go 9 was built with the Do-17's fuselage and wings, only at 40 % of their normal size. It was made entirely of wood, and had a tricycle undercarrige.