Experimental tiltwing aircraft converted from a Chase YC-122C, 49-2883. Strangely named Propelloplane by Hiller. Two Allison T40 turboprops from the XFV and XFY Pogo programmes but the X-18 also needed a J34 turbojet in the fuselage for jet reaction pitch control. First flown at Moffett Field on 24 November 1959, then moved to Edwards were photo is assumed to have been taken. A malfunction caused the aircraft to enter a spin on 20th flight in July 1962 but test pilot George Bright managed to land. Not flown again but damaged when its ground test platform collapsed and subsequently scrapped.