Republic XF-103

XF-103 Thunderwarrior
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Type	Interceptor
Manufacturer	Republic Aviation Company
Status	Cancelled at mockup stage.
Unit cost	US$104 million for the program

The Republic XF-103 Thunderwarrior was an American project to develop a Mach 3 interceptor aircraft to destroy Soviet bombers. Despite a prolonged development, it never flew.

Development

In 1949 the USAF issued a request for an advanced supersonic interceptor, known as the "1954 interceptor" project, or Weapon System WS-201A. It was to be a supersonic aircraft with all-weather capability, radar, and air-to-air missile armament. Republic was one of six companies to submit proposals. On 2 July 1951 three of the designs were selected, Convair's scaled-up XF-92, a Lockheed design, and Republic's AP-57.

AP-57 was an extremely advanced design intended to be built almost entirely of titanium, capable of speeds up to Mach 4 (2,600 mph/4,160 km/h) at 80,000 ft (24,400 m). To provide such performance it was intended to have a Wright J67 turbojet (a license-built version of the Bristol Olympus engine) supplemented by an RJ55-W-1 ramjet. At "low" speeds the ramjet was turned off and the aircraft was powered by the J67 and its afterburner. At high speeds, starting at about Mach 2, the jet engine would be shut down and the ramjet operated alone. At full power, the engines provided a total of 37,400 pounds thrust in a 55,000 pound gross weight aircraft. Both engines were fed by a large ventral Ferri intake, which featured a prominent swept-forward lip, a design that would re-appear on their F-105 Thunderchief design, albeit on the fuselage sides.

All of the control surfaces were pure delta wings. The main wing was swept at 55 degrees, and could be rotated around the spar to provide variable incidence. For takeoff and landing the wing was "tilted up" to increase the angle of attack while keeping the fuselage more horizontal in order to improve visibility. The system also allowed the fuselage to fly "flat" to the airflow at various speeds, setting the trim angle independent of the aircraft as a whole. This decreased trim drag and thereby improved range. The wing was "cut" at about 2/3rds span, the portion outside of this line able to rotate independently of the rest of the wing in order to act as large ailerons, or as Republic referred to them, "tiperons". In order to keep the surfaces area in front and behind the pivot point somewhat similar, the "cut line" was closer to the fuselage in front of the pivot. Large conventional flaps ran from the fuselage to the tiperons. The horizontal stabilizers were seemingly undersized, and mounted below the line of the wing. The larger vertical fin was supplemented by a ventral fin for high-speed stability, and was folded to the right (as seen from behind) during takeoff and landing. Two "petal" style air brakes were mounted directly behind the horizontal surfaces, opening out and up at about a 45 degree angle into the gap between the horizontal and vertical surfaces. A provision for a breaking parachute is not evident on the mockup or the various artwork, although this was a common addition for planes of the era.

The fuselage was completely smooth, with a high fineness ratio for low drag at supersonic speeds. The design was created prior to the introduction of the area rule, and thus lacks the "coke bottle" appearance of later designs. It was mostly cylindrical, but was blended into the intake starting around the wing area, giving it a rounded-rectangular profile through the middle, before reverting to a pure cylinder again at the engine nozzle.

The cockpit was completely buried in the fuselage, with only two windows on the side for direct viewing, and a periscope for forward view during takeoff and landing in a "mini-canopy" on top. In 1955, the periscope concept was tested on a specially modified F-84G, which was flown on a long cross-country flight with the pilot's forward vision blocked. The XF-103 was not the only aircraft to use this sort of arrangement, the Avro 730 high speed bomber used a very similar system.

The entire cockpit area would be ejected below the aircraft in an emergency, along with a small portion of the fuselage that created a stable shape at high speeds. To enter and exit the aircraft, the entire ejection module was lowered on rails out of the bottom of the aircraft, allowing the pilot to simply walk into the seat, sit down, and raise the module back up. During an emergency, a shield stored in front of the seat would slide up into place in front of the pilot, sealing him into a capsule formed out of the shield and the seat back. Only the basic flight instruments were included in the "normal" cockpit area, most of the equipment was mounted around the pilot on the inside of the fuselage. This allowed the pilot to continue operating the aircraft with the capsule "locked up", as in the case of depressurization. It is not clear if the small number of instruments inside the capsule continued to operate after ejection.

The entire nose of the aircraft was taken up by the large Hughes radar set, which offered (what was then) long detection ranges. Guidance and fire control was to be provided by the same MX-1179 package being developed for all of the 1954 Interceptor designs. Hughes had won this contract with their MA-1 fire control system, which was under development at the time. Weapons were carried in bays located on the sides of the fuselage behind the cockpit, which opened by flipping upward and thereby rotating the missiles out of their bays. It was to be armed with six AIM-4 Falcon missiles (then still known as MX-904) and thirty-six 2.75-inch "Mighty Mouse" FFAR's.

A full-scale mockup was built and was inspected in March 1953. A contract for three prototypes followed in June 1954. Work on the prototypes was delayed by continued problems with the titanium construction, and more notably by continued problems with the engine. The contract was later reduced to a single prototype. In the end, the J67 never entered production, and the variety of aircraft that had selected it were forced to turn to other designs, or were cancelled outright. Continuing delays and cost overruns caused the program to be cut back to only one prototype. Republic suggested replacing the J67 the Wright J65, but this was a much smaller engine and entirely unrealistic. The project was eventually cancelled on 21 August 1957, and no flying prototypes were ever completed.

Specifications (XF-103, as designed)

General characteristics

• Crew: one pilot
• Length: 77 ft (23.5 m)
• Wingspan: 34 ft 5 in (10.5 m)
• Height: 16 ft 7 in (5.1 m)
• Wing area: 401 ft² (37.2 m²)
• Empty: 24,949 lb (11,317 kg)
• Loaded: 38,505 lb (17,466 kg)
• Maximum takeoff: 42,864 lb (19,443 kg)
• Powerplant: Wright XJ67-W-3 turbojet with 15,000 lbf (66.7 kN) thrust, augmented by one Wright XRJ55-W-1 ramjet with 18,800 lbf (83.6 kN) thrust

Performance

• Maximum speed: 1,985 mph (3,195 km/h) at altitude, 2,600 mph (4,180 km/h) with ramjet
• Combat radius: 245 mi (394 km)
• Ferry range: 1,545 mi (2,486 km)
• Service ceiling: 69,000 ft (21,000 m)
• Rate of climb: 19,000 ft/min (5,800 m/min)
• Wing loading: 96 lb/ft² (470 kg/m²)
• Thrust-to-Weight: 0.57:1 (afterburner, no ramjet); 0.95:1 (afterburner and ramjet)

Armament

• internal weapons bays in fuselage sides for six GAR-3 Falcon air-to-air missiles and 36x 2.75-in (70 mm) FFAR rockets.

References

• Titanium Titan: the story of the XF-103, Airpower, January 2004

External links

• USAF Museum: XF-103

Related content

Related development:

Comparable aircraft:

• XF-108 Rapier

Designation sequence: F-100 - F-101 - F-102 - XF-103 - F-104 - F-105 - F-106