Republic XF-12

Republic XF-12 Rainbow
Type:	Reconnaissance plane
Design country:	United States
Manufacturer:	Republic Aviation Company
First flight:	February 4, 1946
Commissioning:	Flight tests ended in 1948
Production time:	never mass-produced
Number of pieces:	2

The Republic XF-12 Rainbow (English for "rainbow") was an all-metal four-engine reconnaissance aircraft of the United States, designed by Republic Aviation in the late 1940s. The letter "F" in the designation stands for the mission designation Photographic Reconnaissance, which was used from 1930 to 1947 and must not be confused with the designation for fighter currently used by the USAF . In 1948 the name of the machine was changed to Republic XR-12A ( reconnaissance ).

Like most of the large Allied aircraft of this era, it had radial engines - in this case the Pratt & Whitney R-4360 "Wasp Major". The aircraft had excellent aerodynamic properties and could "fly on all fours" because it was faster than 400 miles per hour (643 km / h), had a range greater than 4000 nautical miles (7408 km) and had a service ceiling of 40,000 feet (12,190 m). Although the Rainbow was very innovative, it could not hold its own against the more modern nozzle technology and series production was never started.

development

Republic XF-12 Rainbow

The original tender for a new aircraft was sent to aircraft manufacturers in 1943 by the Air Technical Service Command of the US Army Air Forces . The order called for a reconnaissance aircraft that could exceed the said "four" (400 miles per hour, 40,000 feet service ceiling and 4,000 nautical miles range). The aircraft's primary purpose was high-speed overflights over Japan - warplanes and bombers were typically used for reconnaissance flights during World War II. The new scout was supposed to collect photographic information, and that required adequate speed, range, and service ceiling.

In August 1943, Colonel Elliot Roosevelt , commander of an F-5 reconnaissance squadron and son of US President Franklin D. Roosevelt , recommended the procurement of a suitable high-performance reconnaissance aircraft that would search for bomber targets in preparation for Allied air raids. Additional overflights after an attack would give officers the ability to attack undamaged targets again. Colonel Roosevelt's F-5 aircraft were converted P-38 Lightnings .

Republic Aviation then developed the Republic XF-12 to meet these requirements. Their main competition was the Hughes XF-11 , which was designed by Hughes. Both models were constructed at the same time and were equipped with the same engines. After the first flight of the Republic XF-12 on February 4, 1946, it succeeded in exceeding the requirements of the US Army Air Corps - the machine even reached 470 miles per hour (756 km / h), the service ceiling was 45,000 feet (corresponding to 13,716 Meters) and she flew 4500 nautical miles, that is 8334 km.

construction

Achieving low air resistance was the main concern of Republic engineers, who already had experience in the construction of fighter aircraft. In order to fulfill the role of reconnaissance, the XF-12 had three separate compartments behind the wings for flight photography - one of them for a vertical camera, one for split-vertical recordings (two cameras are mounted and there is a small overlap area between the Photographs) and finally a compartment for Trimetrogon photographs .

With the latter technology, three cameras each take a picture, and the middle one is directed vertically downwards, while the other two deviate from the vertical at a 60 ° angle. The result is a composite picture whose perspective extends from one horizon to the other. In order not to impair the aerodynamics, each flap for the camera openings opened inwards, which ensured a seamless outer skin. The XF-12 also had a complete darkroom in order to be able to develop and possibly evaluate the photographs while they were still in use.

history

The Republic XF-12 was used most successfully during Operation Birds Eye. The mission was designed to showcase the reconnaissance capabilities of the Republic XF-12. On September 1, 1948, the second prototype of the Republic XF-12 took off from Edwards Air Force Base , California, first ascending westward to service ceiling. When 40,000 feet were reached, the Republic XF-12 flew eastward over the United States and photographed its entire flight path to Mitchell Field ( Garden City , Long Island) on the east coast. During the 6-hour and 55-minute flight, a 325-foot (99-meter) long film was exposed on which there was space for 390 individual aerial photographs; the field of view on the strip of images was 788 kilometers wide. The record-breaking flight was featured in Life magazine on November 29, 1948, and the film strip was shown at the 1948 Air Force Association Convention in New York.

When the Republic XF-12 made this impressive “reconnaissance flight”, the Air Force had already canceled the Republic XF-12 program. The main reason for the decision was that both the Boeing B-29 Superfortress and its further development B-50 Superfortress were already in service and could be used temporarily for reconnaissance flights until the RB-47 Stratojet was put into service in 1951.

Republic then considered building a passenger version of the XF-12, the RC-2 - American Airlines and Pan American World Airways ( Pan-Am ) reluctantly ordered the RC-2, but they canceled the purchase because of additional costs. The main changes compared to the reconnaissance aircraft were a stretched fuselage, weaker, but more efficient engines at the lower flight altitude and additional volume for fuel. But when the military version was not ordered, Republic would have had to charge the civilian customers for the additional costs for further development and production - the civilian version would have become much too expensive.

In addition, Lockheed was already selling the Constellation and Douglas their Douglas DC-6  - both aircraft that could carry more passengers at a lower price per kilometer. Another difficulty was that after the end of the war there were many unneeded military transport aircraft for sale - such as the C-54 Skymaster , the army's DC-4 version. With no more orders coming in, only two Republic XF-12 prototypes were ever built.

Had the Republic XF-12 been available in 1944, Republic would have received many orders thanks to its superior aircraft and, along with a possible passenger version, this would have completely changed the post-war aircraft market. The Republic XF-12 fell into oblivion, despite being fast, almost perfectly streamlined, and cleverly disguised engines. But the Republic XF-12 therefore remains a design classic and is still one of the few piston-engine-powered aircraft that reached 450 mph in level flight.

Technical specifications

• Length: 28.56 m
• Span : 39.37 m
• Height: 8.55 m
• Wing area : 152.36 m²
• Empty weight: 29,483 kg
• Maximum take-off weight : 45,994 kg
• Engines: 4 × Pratt & Whitney R-4360-31 with four-blade propellers; the civil model would have had a weaker engine
• Top speed: over 756 km / h / 470 mph
• Range: 7,242 km
• Service ceiling: 13,716 m; Civil version RC-2: 12,200 m
• Climb rate : over 1,524 m / min / 5,000 ft / min

Web links

Commons : Republic XF-12 Rainbow  - Collection of images, videos and audio files

Individual evidence

1. ↑ http://www.map-reading.com/aptypes.php
2. ↑ This article is based on a partial translation of "XF-12" in the English language Wikipedia, version [1]