Stο Stipa-Caproni, was an experimental Italian aircraft designed in 1932 by Luigi Stipa and built by Caproni. It had a hollow barrel-shaped shaft with the engine and propeller completely surrounded by the fuselage. In essence, the whole fuselage was a simple conduit. Although Regia Aeronautica (Italian Royal Air Force) was not interested in continuing the development of Stipa-Caproni, its design inspired the development of the jet engine.