Republic XF-103
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The Republic XF-103 was an American project to develop a powerful
missile In military terminology, a missile is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles are thus also called guided missiles or guided rockets (when a previously unguided rocket i ...
-armed
interceptor aircraft An interceptor aircraft, or simply interceptor, is a type of fighter aircraft designed specifically for the defensive interception role against an attacking enemy aircraft, particularly bombers and reconnaissance aircraft. Aircraft that are cap ...
capable of destroying
Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
bomber A bomber is a military combat aircraft designed to attack ground and naval targets by dropping air-to-ground weaponry (such as bombs), launching aerial torpedo, torpedoes, or deploying air-launched cruise missiles. The first use of bombs dropped ...
s while flying at speeds as high as Mach 3. Despite a prolonged development, it never progressed past the
mockup In manufacturing and design, a mockup, or mock-up, is a scale or full-size model of a design or device, used for teaching, demonstration, design evaluation, promotion, and other purposes. A mockup may be a ''prototype'' if it provides at leas ...
stage.


Development

In 1949, the
USAF The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Sign ...
issued a request for an advanced
supersonic Supersonic speed is the speed of an object that exceeds the speed of sound ( Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately . Speeds greater than five times ...
interceptor to equip the
Air Defense Command Aerospace Defense Command was a major command (military formation), command of the United States Air Force, responsible for continental air defense. It was activated in 1968 and disbanded in 1980. Its predecessor, Air Defense Command, was est ...
. Known formally as Weapon System WS-201A, but better known informally as the
1954 interceptor 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 De ...
, it called for a supersonic aircraft with all-weather capability, powerful airborne interception radar, and
air-to-air missile The newest and the oldest member of Rafael's Python family of AAM for comparisons, Python-5 (displayed lower-front) and Shafrir-1 (upper-back) An air-to-air missile (AAM) is a missile fired from an aircraft for the purpose of destroying a ...
armament.
Republic A republic () is a "state in which power rests with the people or their representatives; specifically a state without a monarchy" and also a "government, or system of government, of such a state." Previously, especially in the 17th and 18th c ...
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 The Convair XF-92 (re-designated from XP-92 in 1948) 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 ...
that evolved into the
F-102 The Convair F-102 Delta Dagger was an American interceptor aircraft designed and manufactured by Convair. Built as part of the backbone of the United States Air Force's air defenses in the late 1950s, it entered service in 1956. Its main purpos ...
, a Lockheed design that led to the
F-104 The Lockheed F-104 Starfighter is an American single-engine, supersonic air superiority fighter which was extensively deployed as a fighter-bomber during the Cold War. Created as a day fighter by Lockheed as one of the "Century Series" of fi ...
, and Republic's AP-57. AP-57 was an advanced concept to be built almost entirely of
titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
and capable of Mach 3 at altitudes of at least . 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. Work on the prototypes was delayed by continued problems with the titanium construction, and more by continuing problems with the proposed
Wright J67 The Rolls-Royce Olympus (originally the Bristol B.E.10 Olympus) was the world's second two- spool axial-flow turbojet aircraft engine design, first run in May 1950 and preceded only by the Pratt & Whitney J57, first-run in January 1950. It is ...
engine. The contract was later reduced to a single prototype. 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 The Wright J65 was an axial-flow turbojet engine produced by Curtiss-Wright under license from Armstrong Siddeley. A development of the Sapphire, the J65 powered a number of US designs. Design and development Curtiss-Wright purchased a license f ...
, a much less powerful engine. The project was eventually cancelled on 21 August 1957 with no flying prototypes ever being completed. 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 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 ...
. Part of this project was the development of the advanced
Hughes AN/ASG-18 The Hughes AN/ASG-18 Fire Control System was a prototype airborne fire control radar system for the planned North American XF-108 Rapier interceptor aircraft, and the Lockheed YF-12 for the United States Air Force. It was the US's first Pulse-Dopp ...
pulse-doppler radar A pulse-Doppler radar is a radar system that determines the range to a target using pulse-timing techniques, and uses the Doppler effect of the returned signal to determine the target object's velocity. It combines the features of pulse radars an ...
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 40 inch antenna, which required the nose section to be scaled up considerably. Nothing ever came of the proposal, and testing of the ASG-18/GAR-9 was carried out on a modified
Convair B-58 Hustler The Convair B-58 Hustler, designed and produced by American aircraft manufacturer Convair, was the first operational bomber capable of Mach 2 flight. The B-58 was developed during the 1950s for the United States Air Force (USAF) Strategic Air ...
instead.


Design


Propulsion

Mach 3 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
intake An intake (also inlet) is an opening, structure or system through which a fluid is admitted to a space or machine as a consequence of a pressure differential between the outside and the inside. The pressure difference may be generated on the ins ...
s 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 Mach 2.5 were difficult to achieve. The solution to this problem is the removal of the turbine. The
ramjet A ramjet, or athodyd (aero thermodynamic duct), is a form of airbreathing jet engine that uses the forward motion of the engine to produce thrust. Since it produces no thrust when stationary (no ram air) ramjet-powered vehicles require an ass ...
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 The Lockheed X-7 (dubbed the "Flying Stove Pipe") was an American unmanned test bed of the 1950s for ramjet engines and missile guidance technology. It was the basis for the later Lockheed AQM-60 Kingfisher, a system used to test American air def ...
, were reaching speeds as high as Mach 4. There are numerous problems with the ramjet engine, however. Fuel economy, or
thrust specific fuel consumption Thrust-specific fuel consumption (TSFC) is the fuel efficiency of an engine design with respect to thrust output. TSFC may also be thought of as fuel consumption (grams/second) per unit of thrust (newtons, or N), hence ''thrust-specific''. This fig ...
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 Mach 1.
Alexander Kartveli Alexander Kartveli, born Aleksandre Kartvelishvili, ( ka, ალექსანდრე ქართველიშვილი) (September 9, 1896 – July 20, 1974) was a Georgian aeronautical engineer and an aviation pioneer in the United ...
, Republic's Chief Designer, devised a solution to these problems. He proposed using a
Wright J67 The Rolls-Royce Olympus (originally the Bristol B.E.10 Olympus) was the world's second two- spool axial-flow turbojet aircraft engine design, first run in May 1950 and preceded only by the Pratt & Whitney J57, first-run in January 1950. It is ...
turbojet The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and ...
(a license-built derivative of the
Bristol Olympus The Rolls-Royce Olympus (originally the Bristol B.E.10 Olympus) was the world's second two- spool axial-flow turbojet aircraft engine design, first run in May 1950 and preceded only by the Pratt & Whitney J57, first-run in January 1950. It is ...
) supplemented by an RJ55-W-1
ramjet A ramjet, or athodyd (aero thermodynamic duct), is a form of airbreathing jet engine that uses the forward motion of the engine to produce thrust. Since it produces no thrust when stationary (no ram air) ramjet-powered vehicles require an ass ...
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 40,000 lbf (180 kN) 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 Republic F-105 Thunderchief is an American supersonic fighter-bomber that served with the United States Air Force from 1958 to 1984. Capable of Mach 2, it conducted the majority of strike bombing missions during the early years of the Viet ...
. 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 wing A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (Δ). Although long studied, it did not find significant applications until the Jet Age, when it proved suitabl ...
s. 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 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 Landing gear is the undercarriage of an aircraft or spacecraft that is used for takeoff or landing. For aircraft it is generally needed for both. It was also formerly called ''alighting gear'' by some manufacturers, such as the Glenn L. Martin ...
. 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, 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
aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...
s, 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 tank In aviation, a drop tank (external tank, wing tank or belly tank) is used to describe auxiliary fuel tanks externally carried by aircraft. A drop tank is expendable and often capable of being jettisoned. External tanks are commonplace on modern ...
s were available at about of the way out from the wing root. 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. This fin folded to the right, as seen from behind, during takeoff and landing to avoid hitting the ground. 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 In naval architecture and aerospace engineering, the fineness ratio is the ratio of the length of a body to its maximum width. Shapes that are short and wide have a low fineness ratio, those that are long and narrow have high fineness ratios. A ...
for low drag at supersonic speeds. The design was developed prior to the discovery of the
area rule The Whitcomb area rule, named after NACA engineer Richard Whitcomb and also called the transonic area rule, is a design procedure used to reduce an aircraft's drag at transonic speeds which occur between about Mach 0.75 and 1.2. For supersonic ...
, 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 The Avro 730 was a planned Mach 3 reconnaissance aircraft and strategic bomber that was being developed by Avro Aircraft for the Royal Air Force (RAF). It had been originally envisioned as a very high-speed aircraft to perform aerial reconna ...
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.Jenkins and Landis 2004 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 A Fresnel lens ( ; ; or ) is a type of composite compact lens developed by the French physicist Augustin-Jean Fresnel (1788–1827) for use in lighthouses. It has been called "the invention that saved a million ships." The design allows the c ...
arrangement directly in front of the pilot. In 1955, the periscope concept was tested on a modified
F-84G The Republic F-84 Thunderjet was an American turbojet fighter-bomber aircraft. Originating as a 1944 United States Army Air Forces (USAAF) proposal for a "day fighter", the F-84 first flew in 1946. Although it entered service in 1947, the Thun ...
, which was flown on a long, cross-country flight with the pilot's forward vision blocked.Baugher, Joe
"Republic XF-103."
''Joe Baugher's Encyclopedia of American Military Aircraft'', 4 December 1999. Retrieved: 16 February 2011.
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.Pace 1991, p. 128.


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.


Specifications (XF-103, as designed)


See also


Notes


Citations


Bibliography

* Crickmore, Paul
''Lockheed Blackbird: Beyond the Secret Missions.''
Oxford, UK: Osprey, 2004. . * 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. . * Jenkins, Dennis R. and Tony R. Landis. ''Valkyrie: North American's Mach 3 Superbomber''. North Branch, Minnesota: Specialty Press Publishers & Wholesalers, 2004. . * Pace, Steve. ''X-Fighters: USAF Experimental and Prototype Fighters, XP-59 to YF-23''. St. Paul, Minnesota: Motorbooks International, 1991. .


External links


USAF Museum: XF-103
{{USAF system codes Ramjet-powered aircraft Cancelled military aircraft projects of the United States F-103 Mixed-power aircraft Mid-wing aircraft