Republic XF-12 Rainbow

The Republic XF-12 Rainbow was an American four-engine, all-metal prototype reconnaissance aircraft designed by the Republic Aviation Company in the late 1940s. Like most large aircraft of the era, it used radial engines, specifically the Pratt & Whitney R-4360 Wasp Major. The XF-12 was referred to as "flying on all fours" meaning: four engines, 400 mph (640 km/h) cruise, 4,000 mi (6,400 km) range, at 40,000 ft (12,000 m). The aircraft was designed to maximize aerodynamic efficiency. Although innovative, the jet engine and the end of World War 2 made it obsolete, and it did not enter production. A proposed airliner variant, the RC-2, was deemed uneconomical and cancelled before being built.