Republic XF-12 Rainbow - Operational History

Operational History

The first prototype was damaged in landing on 10 July 1947. The aircraft was undergoing maximum landing weight tests. During one particularly hard landing, the right main gear was severed at the engine nacelle. The aircraft bounced hard, and staggered back into the air. The test pilot was able to maintain control, and climb to a safe altitude. He continued to fly the aircraft to burn off excess fuel, to both make the aircraft lighter and lessen the chance of fire. Once excess fuel was burned off, the pilot landed on the left main gear and the nose wheel. The pilot touched down, and while keeping the right wing up, scrubbed off as much speed as possible before it touched down. During the incident the aircraft suffered significant damage. The right wing spar was cracked, and the #3 and #4 engines and props needed to be replaced due to the ground contact. The aircraft was repaired by Republic, and later returned to service.

The only external difference between the first and second prototypes was the addition of cooling gills on the upper engine cowlings. Internally, the second prototype was far more "finished." This included its full operational reconnaissance equipment suite, to allow for further testing.

The XF-12 was later re-designated XR-12, when the U.S. Army Air Forces separated from the Army and became the U.S. Air Force.

The most successful part of the XF-12 flight history is "Operation Birds Eye." The mission was conceived to demonstrate the newly designated XF-12’s ultimate photo capabilities. On 1 September 1948, the second prototype XF-12 departed U.S. Air Force Flight Test Center at Muroc, California, and climbed westward to gain altitude over the Pacific Ocean. Upon reaching its 40,000 ft cruising altitude, the XF-12 headed eastward and began photographing its entire flight path over the United States. The crew shot a continuous 325 foot-long strip of film composed of 390 individual photos (10 inches per photo) covering a 490-mile-wide field of vision. The aircraft landed at Mitchel Field at Garden City, Long Island, New York, completing a flight lasting six hours and 55 minutes at 361 mph average speed (approx. 1m4s per photo). The record-shattering flight was featured in the 29 November 1948 issue of Life magazine and the actual filmstrip went on exhibit at the 1948 U.S. Air Force Association Convention in New York.

At the time this record flight was made, the U.S. Air Force had already canceled the entire XF-12 program. 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 until the far more capable Boeing RB-47 Stratojet was brought into service. The B-29 and B-50 gave the U.S. Air Force less costly "off the shelf" options.

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 with a bifurcated windshield. Fuel capacity would have been increased, and more powerful (at lower altitude) P&W R-4360-59s would have been substituted in place of the P&W R-4360-31s on the U.S. Air Force version. The engines also would have only had one General Electric turbosupercharger each, instead of the dual arrangement on the U.S. Air Force model. The aircraft would be lavishly appointed for the 46 passengers and seven crew. It would have been fully pressurized to sea level, air conditioned, with an electric galley providing hot meals and with an inflight lounge. It would have had the ability to cruise above the weather at 435 mph at 40,000 feet. No versions of this aircraft were ever built.

Without an order from the U.S. Air Force to offset the cost for development and tooling, the cost of building the civilian airliners went up exponentially. As a result, the two airlines (American Airlines and Pan-Am) that had originally placed tentative purchase orders, both cancelled due to the additional unit cost. Economically, the RC-2 wasn't as feasible as other designs available at the time, such as the Lockheed Constellation and the Douglas DC-6. Both of those aircraft could carry more people, at a lower cost per mile. In addition, after the hostilities ended in World War II, there were large collections of surplus military transports available for purchase, such as the Douglas C-54 Skymaster. These former transport aircraft lent themselves to be readily converted to airline service at a fraction of the cost of buying new aircraft. Without additional orders, Republic cancelled all further plans to build not only the XF-12 but also the RC-2, leaving just the two original prototypes.

On 7 November 1948, prototype number two, 44-91003, crashed at 1300 hrs. while returning to Eglin Air Force Base, Florida. The number 2 (port inner) engine exploded as the aircraft was returning from a photographic suitability test flight. The pilot was unable to maintain control due to violent buffeting, and he ordered the crew to bail out. Five of the seven crew escaped safely, including pilot Lynn Hendrix, rescued by Eglin crash boats and helicopters. The airframe impacted two miles south of the base in the Choctawhatchee Bay. Sgt. Vernon B. Palmer and M/Sgt. Victor C. Riberdy were killed. The first prototype, which returned to service in 1948, continued the flight testing and development phase. After the U.S. Air Force declined to order any additional aircraft, and with the loss of the second prototype, the flight testing period wound down. In June 1952, the first prototype, 44-91002, was retired (having flown just 117 additional hours from 1949 to 1952), was stricken from the U.S. Air Force inventory and ended up as a target on the Aberdeen Proving Ground, Maryland.

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. According to Machat, the Rainbow remains the ultimate expression of multi-engine, piston-powered aircraft design. Its 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 such ever to exceed 450 mph in level flight.