The X-Wing was an experimental hybrid helicopter/fixed wing aircraft built in 1986 by helicopter maker Sikorsky for NASA and the US army, it was based on a modified S-72 Rotor System Research Aircraft (RSRA) which could fly with or without rotor blades. The addition of large x-shaped rotor blades would, in theory, allow the aircraft to take off and land vertically. During flight, the rotor blades could be switched off and act as an additional pair of wings to provide lift when moving forward. Despite being built, it was never flown.