The Republic XF-103 was an American project to develop a powerful missile-armed interceptor aircraft capable of destroying Sovietbombers while flying at speeds as high as Mach 3. Despite a prolonged development, it never progressed past the mockup stage.
In 1949, the USAF issued a request for an advanced supersonic interceptor to equip the Air Defense Command. Known formally as Weapon System WS-201A, but better known informally as the 1954 interceptor, it called for a supersonic aircraft with all-weather capability, powerful airborne interception 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 for further development, Convair's scaled-up XF-92 that evolved into the F-102, a Lockheed design that led to the F-104, and Republic's AP-57. AP-57 was an advanced concept to be built almost entirely of titanium and capable of Mach3 at altitudes of at least 60,000 feet (18km).
A full-scale mock-up of the AP-57 was built and inspected in March 1953. A contract for three prototypes followed in June 1954.[1] Work on the prototypes was delayed by continued problems with the titanium construction, and more by continuing problems with the proposed Wright J67 engine. The contract was later reduced to a single prototype.[1] In the end, the J67 never entered production and the aircraft it had been chosen for were forced to turn to other engine designs, or were cancelled outright. Republic suggested replacing the J67 with the Wright J65, a much less powerful engine. The project was eventually cancelled on 21 August 1957 with no flying prototypes ever being completed.[1]
The design was given a brief reprieve as part of the Long-Range Interceptor – Experimental (LRI-X) project that ultimately led to the North American XF-108 Rapier. Part of this project was the development of the advanced Hughes AN/ASG-18pulse-doppler radar and the GAR-9 missile. Republic proposed adapting the F-103 as a testbed for these systems with additional fuel tanks taking up much of the original weapon bay spaces, although it wouldn't be able to come close to meeting the range requirements of LRI-X. Some work was carried out adapting the mockup to house the 40inch antenna, which required the nose section to be scaled up considerably. Nothing ever came of the proposal,[2] and testing of the ASG-18/GAR-9 was carried out on a modified Convair B-58 Hustler instead.[3]
Design
A mock-up of the F-103 was built at the Republic factory. In this image, the pilot's capsule is shown in its lowered position.
Propulsion
Mach3 performance in the 1950s was difficult to achieve. Jet engines compress incoming air, then mix it with fuel and ignite the mixture. The resulting expansion of gases produces thrust. The compressors generally can ingest air only at subsonic speeds. To operate supersonically, aircraft use advanced intakes to slow the supersonic air to a usable speed. The energy lost in this process heats the air, which means the engine has to operate at ever-higher temperatures to provide net thrust. The limiting factor in this process is the temperature of the materials in the engines, in particular, the turbine blades just behind the combustion chambers. Using materials available at the time, speeds much beyond Mach2.5 were difficult to achieve.
The solution to this problem is the removal of the turbine. The ramjet engine consists mostly of a large tube, and is relatively easy to air-cool by forcing extra air around the engine. Experimental ramjet aircraft of the era, like the Lockheed X-7, were reaching speeds as high as Mach4. There are numerous problems with the ramjet engine, however. Fuel economy, or thrust specific fuel consumption in aircraft terms, is extremely poor. This makes general operations like flying from one airbase to another expensive propositions. More problematic is the fact that ramjets rely on forward speed to compress the incoming air, and only become efficient above Mach1.
Alexander Kartveli, Republic's Chief Designer, devised a solution to these problems. He proposed using a Wright J67 turbojet (a license-built derivative of the Bristol Olympus) supplemented by an RJ55-W-1 ramjet behind it. Connecting the two were a series of movable ducts that could route air between the engines. At low speeds the aircraft would be powered by the J67, with the RJ55 acting as a traditional afterburner, producing a total of about 40,000lbf (180kN) thrust. At high speeds, starting above Mach 2.2, the jet engine would be shut down and the airflow from the intake would be routed around the jet engine and directly into the RJ55. Although the net thrust was reduced by shutting down the jet, operating on the ramjet alone allowed the aircraft to reach much higher speeds.
Both engines were located behind a single very large ventral Ferri-type intake, which used a prominent, swept-forward lip, a configuration also used for the wing-root inlets on the F-105 Thunderchief. The J67 was installed just behind the intake, angled with its intake below the centerline of the aircraft. The RJ55 was installed inline with the fuselage in the extreme rear, as if it were the exhaust of a conventional engine installation. There was a significant empty space above the J67 for ducting.
Wings and control surfaces
All of the control surfaces were pure delta wings. The main wing was swept at 55degrees, and could be rotated around the spar to provide variable incidence. For takeoff and landing, the wing was tilted upwards to increase the angle of incidence while keeping the fuselage nearly horizontal. The length of the fuselage made it difficult to achieve the same end by tilting the entire aircraft upwards, which would have required a very long extension on the landing gear. The system also allowed the fuselage to fly flat to the airflow at various speeds, setting the angle of incidence independent of the aircraft as a whole. This decreased trim drag, thus improving range.
The wing was split at about two-thirds of the span. The portion outside of this line able to rotate independently of the rest of the wing. These movable portions acted as large ailerons, or as Republic called them, tiperons. To keep the surface area in front and behind the pivot point somewhat similar, the split line was closer to the fuselage in front of the pivot. Large conventional flaps ran from the fuselage to the tiperons. Hard points for drop tanks were available at about 1⁄3 of the way out from the wing root.
The horizontal stabilizers were seemingly undersized, and mounted below the line of the wing. Two petal-style air brakes were mounted directly behind the horizontal surfaces, opening out and up at about a 45° angle into the gap between the horizontal and vertical surfaces. A provision for a braking parachute is not evident on the mock-up or the various artwork, although this was common for aircraft of the era.
Fuselage
The fuselage was completely smooth, with a high fineness ratio for low drag at supersonic speeds. The design was developed prior to the discovery of the area rule, and does not display any of the wasp waisting common to aircraft primarily developed after 1952. The fuselage contours were mainly cylindrical, but blended into the intake starting around the wing root, giving it a rounded, rectangular profile through the middle, before reverting to a pure cylinder shape again at the engine nozzle.
Cockpit
The cockpit design originally featured a canopy, but low drag requirements for high speed suggested that it be removed. The idea of using a periscope arrangement for forward viewing on high speed aircraft was then in vogue, the Avro 730 selecting a very similar system. The Air Force demanded that it be used on the F-103. Kartveli was opposed to this layout, and continued to press for the use of a "real" canopy. Design documents throughout the program continued to include this as an optional feature, along with performance estimates that suggested the difference would be minimal.[2]
The system shown on mockups used two large oval windows on the cockpit sides, and a periscope system projecting an image onto a Fresnel lens arrangement directly in front of the pilot. In 1955, the periscope concept was tested on a modified F-84G, which was flown on a long, cross-country flight with the pilot's forward vision blocked.[1][N 1]
A unique supersonic escape capsule was designed for the XF-103. The pilot's seat was located in a shell with a large movable shield in front that was normally slid down into the area in front of the pilot's legs. In the case of depressurization, the shield would slide up in front of the pilot, sealing the seat into a pressurized pod. Basic flight instruments inside the capsule allowed the aircraft to be flown back to base, and a window in the front of the shield allowed the periscope system to be used. In an emergency, the entire capsule would be ejected downward, along with a small portion of the aircraft fuselage that provided a stable aerodynamic shape. To enter and exit the aircraft, the 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 into the aircraft. The capsule was fully pressurized, allowing the pilot to continue operating the aircraft without a pressure suit when the capsule was locked up.[5]
Avionics and armament
The entire nose of the aircraft was taken up by the large Hughes radar set, which (at the time) offered long detection ranges. Guidance and fire control were to be provided by the same MX-1179 package being developed for all of the WS-201 designs. Hughes had won this contract with their Hughes MA-1 fire control system, which was under development. Weapons were carried in bays located on the sides of the fuselage behind the cockpit, which opened by flipping upward, thereby rotating the missiles out of their bays. It was to be armed with six GAR-1/GAR-3 Falcon (then known as MX-904), with a likely arrangement of three or four each GAR-1s and GAR-3s, fired in pairs (one each radar and infrared guided) to improve the odds of a hit. The XF-103 also was to feature 36 2.75-inch "Mighty Mouse" FFARs.
Jenkins, Dennis R. "Titanium Titan: The Story of the XF-103." Airpower, January 2004.
Jenkins, Dennis R. and Tony R. Landis. Experimental & Prototype U.S. Air Force Jet Fighters. Minnesota: Specialty Press, 2008. ISBN978-1-58007-111-6.
Jenkins, Dennis R. and Tony R. Landis. Valkyrie: North American's Mach 3 Superbomber. North Branch, Minnesota: Specialty Press Publishers & Wholesalers, 2004. ISBN1-58007-072-8.
Pace, Steve. X-Fighters: USAF Experimental and Prototype Fighters, XP-59 to YF-23. St. Paul, Minnesota: Motorbooks International, 1991. ISBN0-87938-540-5.
A ramjet is a form of airbreathing jet engine that requires forward motion of the engine to provide air for combustion. Ramjets work most efficiently at supersonic speeds around Mach 3 and can operate up to Mach 6.
The North American Aviation XB-70 Valkyrie is a retired prototype version of the planned B-70 nuclear-armed, deep-penetration supersonic strategic bomber for the United States Air Force Strategic Air Command. Designed in the late 1950s by North American Aviation (NAA) to replace the aging B-52 Stratofortress and B-58 Hustler, the six-engined, delta-winged Valkyrie could cruise for thousands of miles at Mach 3+ while flying at 70,000 feet (21,000 m).
The McDonnell XF-88 Voodoo was a long-range, twinjet fighter aircraft with swept wings designed for the United States Air Force. Although it never entered production, its design was adapted for the subsequent supersonic F-101 Voodoo.
The Republic XF-91 Thunderceptor is a mixed-propulsion prototype interceptor aircraft, developed by Republic Aviation. The aircraft would use a jet engine for most flight, and a cluster of four small rocket engines for added thrust during climb and interception. The design was largely obsolete by the time it was completed due to the rapidly increasing performance of contemporary jet engines, and only two prototypes were built. One of these was the first American fighter to exceed Mach 1 in level flight.
The Lockheed YF-12 was an American Mach 3+ capable, high-altitude interceptor prototype, developed and manufactured by American aerospace company Lockheed Corporation.
The North American XF-108 Rapier was a proposed long-range, high-speed interceptor aircraft designed by North American Aviation intended to defend the United States from supersonic Soviet strategic bombers. The aircraft would have cruised at speeds around Mach 3 with an unrefueled combat radius over 1,000 nautical miles, and was equipped with radar and missiles offering engagement ranges up to 100 miles (160 km) against bomber-sized targets.
The Bell D-188A was a proposed eight-engine Mach 2–capable vertical take-off and landing (VTOL) tiltjet fighter that never proceeded past the mock-up stage.
The Sukhoi Su-9 was a single-engine, all-weather, missile-armed interceptor aircraft developed by the Soviet Union.
The Convair XF-92 was an American, delta wing, first-generation jet prototype. Originally conceived as a point-defence interceptor, the design was later used purely for experimental purposes and only one was built. However, it led Convair to use the delta-wing on a number of designs, including the F-102 Delta Dagger, F-106 Delta Dart, B-58 Hustler, the US Navy's F2Y Sea Dart as well as the VTOL FY Pogo.
The North American F-107 is North American Aviation's entry in a United States Air Force tactical fighter-bomber design competition of the 1950s, based on the F-100 Super Sabre. It incorporated many innovations and radical design features, notably the over-fuselage air intakes. The competition was eventually won by the Republic F-105 Thunderchief, and two of the three F-107 prototypes ended their lives as test aircraft. One is on display at the National Museum of the United States Air Force and a second at Pima Air and Space Museum.
A supersonic aircraft is an aircraft capable of supersonic flight, that is, flying faster than the speed of sound. Supersonic aircraft were developed in the second half of the twentieth century. Supersonic aircraft have been used for research and military purposes, but only two supersonic aircraft, the Tupolev Tu-144 and the Concorde, ever entered service for civil use as airliners. Fighter jets are the most common example of supersonic aircraft.
The Nord 1500 Griffon was an experimental ramjet-powered interceptor aircraft designed and built by French state-owned aircraft manufacturer Nord Aviation. The Griffon was developed to become a Mach 2 follow on to the supersonic Nord Gerfaut research aircraft. Development of the aircraft began in earnest after the receipt of a letter of intent in 1953 for a pair of unarmed research aircraft. The design featured an innovative dual propulsion turbojet-ramjet configuration; the former being used to takeoff and attain sufficient speed to start the latter.
The Republic XF-84H "Thunderscreech" was an American experimental turboprop aircraft derived from the F-84F Thunderstreak. Powered by a turbine engine that was mated to a supersonic propeller, the XF-84H had the potential of setting the unofficial air speed record for propeller-driven aircraft, but was unable to overcome aerodynamic deficiencies and engine reliability problems, resulting in the program's cancellation. Its name, Thunderscreech, is a reference to its extremely loud supersonic propeller.
WS-201A, informally known as the 1954 Interceptor, was a United States Air Force project to develop a dedicated interceptor aircraft that would enter service in 1954. Several aircraft were developed as part of the project, leading to the F-102 Delta Dagger, F-106 Delta Dart, Republic XF-103 and, indirectly, the F-101B Voodoo and F-104 Starfighter. The electronics and weapons developed for the program would become common on US designs, including the AIM-4 Falcon missile and a variety of Hughes Aircraft–supplied radar and fire control systems. The project also led, eventually, to the upgrading of the SAGE battle control computers to directly control the interceptors for much of their flight. Although greatly delayed, the resulting systems operated for approximately 20 years, into the 1980s.
The Vickers Type 559 was a supersonic interceptor aircraft design by the British aircraft company Vickers-Armstrongs and was their submission for Operational Requirement F.155 in 1955.
The Lockheed XF-104 Starfighter was a single-engine, high-performance, supersonic interceptor prototype for a United States Air Force (USAF) series of lightweight and simple fighters. Only two aircraft were built; one aircraft was used primarily for aerodynamic research and the other served as an armament testbed, both aircraft being destroyed in accidents during testing. The XF-104s were forerunners of over 2,500 production Lockheed F-104 Starfighters.
The Leduc 022 was the prototype of a mixed-power French interceptor built in the mid-1950s. Designer René Leduc had been developing ramjet-powered aircraft since before World War II and had flown a series of experimental aircraft, the Leduc 0.10 and Leduc 0.21, throughout the 1950s before he was awarded a contract for two examples of a short-range supersonic interceptor armed with two air-to-air missiles (AAMs).
The SNCASO SO.9000 Trident is a French mixed-power interceptor aircraft built by aircraft manufacturer SNCASO during the 1950s. As part of a wider effort to re-build French military power during the late 1940s and to furnish France with advanced, new domestically produced designs, a request for a supersonic-capable point-defence interceptor aircraft to equip the French Air Force was issued to SNCASO. In response, the firm designed the mixed-propulsion Trident, powered by a single SEPR rocket engine, which was augmented by wingtip-mounted turbojet engines, and the Air Force ordered two prototypes.
The Nord CT.41 Narwhal was a French target drone, designed and built by Nord Aviation during the late 1950s for the purpose of providing training in the interception of supersonic bomber aircraft.
The Mikoyan-Gurevich I-7 was a development of the Mikoyan-Gurevich I-3 experimental fighter. Planned as a Mach 2-class aircraft, the I-7 was the second of a series of three experimental fighter aircraft from the Mikoyan-Gurevich design Bureau. Like the Mikoyan-Gurevich I-3, the I-7 was to be one of the components of the automated Uragan-1 then under development by protivovozdushnaya oborona strany, the Soviet defense system.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
