Republic XF-12 Rainbow
The Republic XF-12 Rainbow was a four-engine, all-metal prototype reconnaissance aircraft designed in the 1940`s.
The proposal was for a reconnaissance aircraft which included a requirement for speed (400 mph), ceiling (40,000 ft), and range (4,000 nmi).It`s primary objective was for high-speed overflights of the Japanese homeland and key enemy installations.During World War II, due to the extended range requirements of operating in the Pacific, existing fighters and bombers were being used for missions for which they were never intended. The need existed for an aircraft specifically designed for the photo-reconnaissance mission with adequate speed, range, and altitude capabilities for its missions to be successful.
The XF-12's first flight was made on 4 February 1946.During the flight testing and development period,it demonstrated the capability of operating at 45,000 feet (14,000 m), at a speed of 470 mph (760 km/h), over a range of 4,500 mi (7,200 km), so it met and exceeded the design goals for which it had been designed.
It was powered by four of the new Pratt & Whitney R-4360-31 Wasp Major 28-cyl. four-row air-cooled radial piston engines,of 3,250 hp each.
The original design called for contra-rotating propellers,due to the added complexity and reliability issues,the propellers were never installed.The aircraft used standard four-bladed Curtiss Electric propellers for all flights.
The USAF canceled the entire XF-12 program in late 1948.The primary reason for its demise was the availability of both Boeing B-29 Superfortress and B-50 types to meet the long-range photo-reconnaissance requirement.
Republic had intended to also build an airline version of the aircraft to be known as the RC-2.This variant was supposed to be a "stretched" version of the XF-12, growing in length from 93 ft 9 in to 98 ft 9 in, with the addition of a fuselage "plug" in front of the wing.Also the complex Plexiglas nose section was supposed to be replaced with a solid metal nose,changes to the engines and superchargers were also included in the civil design.
Had the XF-12 Rainbow been available in 1944,it almost inevitably would have been ordered in quantity,and along with its civilian counterpart, the whole postwar structure of aircraft markets might have been altered. As it was, the XF-12 disappeared into oblivion, despite its graceful lines and high performance.
It`s high speed, near-perfect streamlined form, and neatly cowled engines make it a design classic, often unappreciated, and not very well known. The XF-12 was the fastest, four engine pure piston-powered aircraft of its day, and the only one ever to exceed 450 mph in level flight.
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