The XF-103 was developed as a high-speed high-altitude aircraft specifically designed to intercept incoming enemy bombers. The XF-103 was proposed in the same contract competition that resulted in the Convair F-102 -- Project MX-1554 Interceptor Fighter Airplane. The Republic design, Model AP-57, underwent a design performance evaluation conducted by the Air Material Command. The results showed an estimated top speed of 1,438 knots. A limiting Mach number of 3.0 was quoted due to excessive (estimated) turbine inlet air temperature. The Republic AP-57 design was ranked eighth out of nine entries for design. The only aircraft scoring lower (as a design) was the Consolidated-Vultee (i.e. initial F-102 design) entry.
The USAF canceled the XF-103 development contract on Aug. 21, 1957, when the aircraft was in the mock-up phase.
Technical Evaluation - MX-1554
Section II (page 19)
Republic Model AP-57
27 March 1951 (Document # 51S-43239-A)
The Republic Model AP-57 has a Delta wing swept-back 55 degrees at the leading edge and incorporates a variable incidence feature. The horizontal tail is of the Delta configuration with a sweep-back angle of 60 degrees at the leading edge. The alighting gear is of the tricycle type and retracts into the fuselage. The turbo-jet is a Wright Aeronautical Corporation XJ-67-W-1 power plant with afterburner. A Ferri type two-dimensional engine air inlet is used. The thrust of the turbo-jet engine is limited at high Mach numbers by the allowable turbine inlet temperature. The air bypasses the engine compressor and turbine, and using the afterburner as a ram-jet combustion chamber, the available thrust is greatly increased above a Mach number of 2.0.
Six (6) MX-904 missiles and 36 2.75 in. FFA rockets internally stowed are proposed. The missile launching system is complex with six (6) individual tracks and actuating cylinders. Accessibility of all launchers for loading is adequate. Rockets and especially missiles are poorly located in the immediate area of the engine air scoop.
Most of the Electronic and Control system is located in a compartment adjacent to the radar equipment. Accessibility of the radar for checking in the airplane is not too good. A ladder is required for access to all components, unless the entire nose package is removed. This limits the use of test equipment and makes minor adjustments difficult. The entire collection of rack-mounted components may be removed in a detachable nose section along with the radar antenna and associated equipment for complete replacement or for major service.
Fuel is contained in five pressurized fuel cells. No self-sealing or armor is proposed for the fuel system.
The electrical system includes a 24-28 volt DC system and a three phase 4 wire 208 volt 400 cycle AC system. The electrical power source proposed will require the development of an alternator, constant speed drive and an air turbine.
Reached mock-up phase only
TECHNICAL NOTES (as designed): Armament: 36 unguided 2.75 inch "Mighty Mouse" FFAR rockets and six MX-904 "Falcon" guided missiles Engine: One Wright XJ67-W-1 rated at 15,000 lbs. thrust and one XRJ55-W-1 ramjet (afterburner section of the XJ67) of 18,800 lbs. thrust when operated at altitudes above 50,000 ft. Maximum speed: Mach 3+ Combat speed: Mach 2.2 at 75,000 ft. Combat radius: Approx. 450 miles Service ceiling: Approx. 80,000 ft. Span: 35 ft. 10 in. Length: 81 ft. 11 in. Height: 18 ft. 4 in. Weight: In excess of 40,000 lbs. Crew: One