The Republic XF-103 originated in an early 1949 request for the USAF for an advanced interceptor capable of surpassing in speed and altitude the new Soviet intercontinental bombers soon to be available in quantity according to American CIA officials. The North American F-86D Saber, the Northrop F-89 Scorpion, and the Lockheed F-94 Starfire were subsonic aircraft, and did not offer sufficient room for improvement to counter this threat.
This project is known as "interceptor 1954", after the year the new interceptor was supposed to enter service. At that time, the USAF realized that the increasing complexity of modern weapons made it very difficult to develop airframes, electronics, engines, and other components in isolation.
To solve this problem, the USAF introduced the "WEAPON SYSTEM" concept, in which the components of the new interceptor would be integrated with each other from the start, ensuring that the various systems would be compatible once incorporated into the final plane. The project received the designation WS-204A and was a weapons system consisting of air-to-air guided missiles, and an all-weather search and fire control radar, all housed in a fuselage capable of supersonic flight.
The electronic module for the new WS-204A system was developed first. The MX-1179 project was the designation given to this part of the project devoted to the armament and electronic fire control system of the 1954 interceptor. In October 1950, Hughes Aircraft Company won the MX-1179 contract. Hughes' proposal was the Falcon air-to-air missile MA-1 fire control system. For a time, the Falcon missile was designated F-98.
The airframe part of the project was designated MX-1554. The USAF submitted the project to the industry on June 18, 1950. By January 1951, nine proposals had been submitted by six different manufacturers. Republic had submitted three different proposals, North-American two, and Chance-Vought, Douglas, Lockheed, and Convair one each.
On July 2, 1951, the USAF announced that projects from Convair, Lockheed, and Republic had been selected for preliminary development. Each of the three companies was to proceed with development to the mock-up stage, with the most promising project at that point receiving a production contract. Later, the USAF considered it too expensive to develop three programs in parallel, and canceled the Lockheed project.
Republic's project took the factory designation AP-57. It was a development of the AP-48, a 1948 proposal for a high-altitude all-weather fighter. The AP-57 project was an extremely advanced aircraft capable of flying at Mach 4 (4183 km/h) up to an altitude of 24,000 meters. The AP-57 was to be constructed entirely of titanium, this metal being chosen because of its resistance to aerodynamic heating at these speeds.
This phenomenal performance for the time (and still today) was to be achieved by the adoption of a two-cycle (turbo-stato) propulsion system. On takeoff and cruise, the F-103 was to be powered by a Wright XJ67-W-3 turbojet engine, rated at 6800 kgp dry and 9980 kgp with afterburner. The XJ67 was a licensed version of the Bristol Olympus. At high speed, the thrust of the turbojet engine had to be supplemented by an XRJ55-W-1 ramjet, capable of providing a thrust of 8535 kgp.
Since the thrust of the reactor is limited, at high mach numbers, by the maximum temperature allowed at the turbine inlet, the air admitted can bypass the compressor, the turbine and the combustion chamber to operate the post-combustion like a ramjet ( the same principle as that adopted later for the Lockheed A12/SR-71 family). In this way, engine thrust was expected to increase with speed beyond Mach 2. A total thrust of 17,000 kgp was to be available at high altitude. The engines were fed by a large air intake mounted under the fuselage.
The fuselage was smooth from nose to tail, even the pilot's cockpit was fully integrated into the fuselage. The cockpit was equipped with only two small side windows. The forward view was obtained by a periscope. In 1955, the periscope concept was tested on an F-84G during a long flight with the canopy obscured in front. For the emergency evacuation of the pilot, a downward ejection capsule was adopted.
The small wings had a delta configuration with a leading edge angled at 55 degrees, but Republic's aircraft was not a true delta, since it had a horizontal tailplane in a delta with an angle of 60 degrees. A ventral fin was also mounted on the rear fuselage, and retracted to the side during takeoffs and landings.
The landing gear was of the tricycle type and retracted into the fuselage. The armament was to consist of six Hughes GAR-3 air-to-air missiles housed in various internal compartments of the fuselage, plus 36 unguided rockets. The estimated take-off weight of the AP-57 was more than 18 tons.
Here is an excerpt from the USAF report on the device:"The missile launch system is complex with six individual internal rails. The accessibility of the missiles for loading is correct. The rockets and especially the missiles are poorly located at immediate proximity to the air inlet of the reactor.
Most of the on-board electronics are located in a compartment adjacent to the radar equipment. The accessibility of the radar for control is not very good. A ladder is required to access most components unless the nose of the unit is removed. This limits the use of test equipment and requires minor adjustments. The complete set of equipment can be dismantled thanks to a removable nose section.
The fuel is contained in five pressurized tanks. There is no shielding or automatic refueling device for the fuel system. The electrical system includes a continuous 24-28 volt DC three phase 208 volt 400 cycle AC system. The proposed electrical power source requires the development of an alternator, controlled at constant speed and a dynamic turbine driven by air pressure".
The Republic AP-57 was clearly a technological leap forward for the early 1950s. That would be a challenge even today (but perhaps already met with the Lockheed Aurora). Convair's competing project was an enlarged version of his experimental XF-92 delta-winged aircraft. On September 11, 1951, Convair received a contract for this aircraft under the designation F-102. Work on the Republic project is also allowed, and this aircraft takes the designation XF-103. A complete inspection of the model took place in March 1953. Republic then received a contract for three prototypes in June 1954.
But the development will be slowed by a number of problems, such as the difficulties encountered in the manufacture of the titanium alloy used in the structure, the delay in the development of the two-cycle propulsion system, and finally massive cost overruns. The Wright XJ-67 engine ultimately never materialized and plans to use the Wright J-65 turbojet engine proved to be unrealistic. The USAF finally threw in the towel on August 21, 1957, canceling the entire XF-103 project. It is clear that the XF-103 was far too innovative to be a realistic competitor for the "1954" interceptor project.
Republic XF-103 Features:
Dimensions:
Wingspan :10.6 meters
Arrow :55 degrees.
Wing area :?
Overall length :24.7 meters
Height :5.6 meters
Masses:
Laden:> to 18 tons
Performance:
Max speed :Mach 3+
Ceiling :Approximately 24,000 meters
Range :Approximately 720 km
Motorization :1 Wright XJ67-W-1 engine of 6800 kgp dry and 9980 kgp with afterburner.
1 ramjet XRJ55-W-1 Thrust:8535 kgp
Armament :36 unguided 2.75 inch "Mighty Mouse" rockets and six GAR-3 "Falcon" guided missiles
Crew :1