At roughly the same time as the first experiments with full-scale aircraft powered with Wankel engines, model aircraft-sized versions were pioneered by a combine of the well-known Japanese O.S. Engines firm and the then-extant German Graupner aeromodeling products firm, under license from NSU/Auto-Union. By 1968, the first prototype air-cooled, single-rotor glow plug-ignition, methanol-fueled 4.9 cm3 displacement OS/Graupner model Wankel engine was running, and was produced in at least two differing versions from 1970 to the present day, solely by the O.S. firm after Graupner's demise in 2012.