Republic XF-103
Encyclopedia
The Republic XF-103 was an American
project to develop a high speed interceptor aircraft
capable of destroying Soviet
bomber
s. Despite a prolonged development, it never progressed past the mock-up stage.
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, intercept 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 Mach
3 at altitudes of at least 60,000 ft (24,400 m).
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 notably by continued problems with the proposed Wright J67 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
, 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 led to the XF-108 Rapier
. Part of this project was the development of the advanced Hughes AN/ASG-18
pulse-doppler radar
and the GAR-9
missile. Republic proposed adapting the F-103 as a testbed for these systems, 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 B-58 instead.
s to slow the speed of the supersonic air to a usable figure. The energy lost in this process heats the air, which means the engine has to operate at ever-higher temperatures in order 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 extremely 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 air around the engine. Experimental ramjet aircraft of the era, like the Lockheed X-7
, were reaching speeds as high as Mach 4. There are numerous problems with the ramjet engine, however. Fuel economy, or thrust specific fuel consumption in aircraft terms, of ramjet engines 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 start to operate efficiently above Mach 1.
Alexander Kartveli
, Republic's Chief Designer, came up with 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 was 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 around the jet engine and directly into the XJ5. 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 of the engines were located behind a single very large ventral Ferri intake, which featured a prominent, swept-forward lip, a design feature employed on the Republic RF-84F
and later F-105. The J67 was installed just behind the intake, angled with the intake below the centerline of the aircraft. The XJ55 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.
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 up" to increase the angle of attack
while keeping the fuselage more nearly horizontal. 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 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
s, or as Republic called them, "tiperons". In order to keep the surface 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. Hard points for drop tank
s were available at about 1/3 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 a common addition for aircraft of the era.
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.
selecting a very similar system, and the Air Force demanded that it be used on the F-103. The system that emerged 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 specially modified F-84G, which was flown on a long, cross-country flight with the pilot's forward vision blocked.
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.
A unique supersonic escape capsule (SEC) 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. The SEC was fully pressurized, allowing the pilot to continue operating the aircraft without a pressure suit when the capsule was "locked up".
(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" FFAR
s.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
project to develop a high speed interceptor aircraft
Interceptor aircraft
An interceptor aircraft is a type of fighter aircraft designed specifically to prevent missions of enemy aircraft, particularly bombers and reconnaissance aircraft. Interceptors generally rely on high speed and powerful armament in order to complete their mission as quickly as possible and set up...
capable of destroying Soviet
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
s. Despite a prolonged development, it never progressed past the mock-up stage.
Development
In 1949, the USAF issued a request for an advanced supersonicSupersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
interceptor to equip the Air Defense Command. Known formally as Weapon System WS-201A, but better known informally as the "1954 Interceptor
1954 interceptor
The 1954 interceptor, formally WS-201A, was a US 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, XF-103 Thunderwarrior and, indirectly, the...
", it called for a supersonic aircraft with all-weather capability, intercept radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
and air-to-air missile
Air-to-air missile
An air-to-air missile is a missile fired from an aircraft for the purpose of destroying another aircraft. AAMs are typically powered by one or more rocket motors, usually solid fuelled but sometimes liquid fuelled...
armament. Republic
Republic Aviation Company
The Republic Aviation Corporation was an American aircraft manufacturer based in Farmingdale, Long Island, New York. Originally known as the Seversky Aircraft Company, the company was responsible for the design and production of many important military aircraft, including the P-47 Thunderbolt, F-84...
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
Convair XF-92
The Convair XF-92 was the first American delta-wing aircraft. Originally conceived as a point-defense interceptor, the design was later made purely experimental...
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
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
and capable of Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
3 at altitudes of at least 60,000 ft (24,400 m).
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 notably by continued problems with the proposed Wright J67 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
Wright J65
|-See also:-External links:*...
, 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 led to the XF-108 Rapier
XF-108 Rapier
The North American XF-108 Rapier was a proposed long-range, high-speed interceptor aircraft designed by North American Aviation. Initiated to defend the United States from supersonic Soviet bombers, the program, initially called NA-257, was cancelled in 1959 due to a shortage of funds and the...
. Part of this project was the development of the advanced Hughes AN/ASG-18
Hughes AN/ASG-18
The Hughes AN/ASG-18 was a prototype fire control system and radar, originally intended for the XF-108 Rapier interceptor aircraft, for the United States Air Force....
pulse-doppler radar
Pulse-doppler radar
Pulse-Doppler is a 4D radar system capable of detecting both target 3D location as well as measuring radial velocity . It uses the Doppler effect to avoid overloading computers and operators as well as to reduce power consumption...
and the GAR-9
AIM-47 Falcon
The Hughes AIM-47 Falcon, originally GAR-9, was a very long-range high-performance air-to-air missile that shared the basic design of the earlier AIM-4 Falcon. It was developed in 1958 along with the new Hughes AN/ASG-18 radar fire-control system intended to arm the Mach 3 XF-108 Rapier interceptor...
missile. Republic proposed adapting the F-103 as a testbed for these systems, 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 B-58 instead.
Propulsion
Mach 3 performance in the 1950s was very difficult to achieve. Jet engines work by compressing the incoming air then mixing it with fuel and igniting the mixture, the expansion of gases and heat produces thrust. Engines generally can ingest air only at subsonic speeds, using advanced intakeIntake
An intake , or especially for aircraft inlet, is an air intake for an engine. Because the modern internal combustion engine is in essence a powerful air pump, like the exhaust system on an engine, the intake must be carefully engineered and tuned to provide the greatest efficiency and power...
s to slow the speed of the supersonic air to a usable figure. The energy lost in this process heats the air, which means the engine has to operate at ever-higher temperatures in order 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 extremely difficult to achieve.
The solution to this problem is the removal of the turbine. The ramjet
Ramjet
A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill...
engine consists mostly of a large tube, and is relatively easy to air-cool by forcing air around the engine. Experimental ramjet aircraft of the era, like the Lockheed X-7
Lockheed X-7
-See also:-External links:*...
, were reaching speeds as high as Mach 4. There are numerous problems with the ramjet engine, however. Fuel economy, or thrust specific fuel consumption in aircraft terms, of ramjet engines 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 start to operate efficiently above Mach 1.
Alexander Kartveli
Alexander Kartveli
Alexander Kartveli 1896–1974, born Kartvelishvili) was a famous and influential aircraft engineer and a pioneer of American aviation history. Kartveli achieved important breakthroughs in military aviation in the time of turbojet fighters...
, Republic's Chief Designer, came up with 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
Ramjet
A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill...
behind it. Connecting the two were a series of movable ducts that could route air between the engines. At "low" speeds the aircraft was 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
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
, the jet engine would be shut down and the airflow from the intake around the jet engine and directly into the XJ5. 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 of the engines were located behind a single very large ventral Ferri intake, which featured a prominent, swept-forward lip, a design feature employed on the Republic RF-84F
F-84F Thunderstreak
The Republic F-84F Thunderstreak was an American-built swept-wing turbojet fighter-bomber. While an evolutionary development of the straight-wing F-84 Thunderjet, the F-84F was a new design. The RF-84F Thunderflash was a photo reconnaissance version....
and later F-105. The J67 was installed just behind the intake, angled with the intake below the centerline of the aircraft. The XJ55 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 wingDelta wing
The delta wing is a wing planform in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta .-Delta-shaped stabilizers:...
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 up" to increase the angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
while keeping the fuselage more nearly horizontal. The system also allowed the fuselage to fly "flat" to the airflow at various speeds, setting the trim angle
Angle of incidence
Angle of incidence is a measure of deviation of something from "straight on", for example:* in the approach of a ray to a surface, or* the angle at which the wing or horizontal tail of an airplane is installed on the fuselage, measured relative to the axis of the fuselage.-Optics:In geometric...
independent of the aircraft as a whole. This decreased trim drag and thereby improved range.
The wing was "cut" 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
Aileron
Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...
s, or as Republic called them, "tiperons". In order to keep the surface 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. Hard points for drop tank
Drop tank
In aeronautics, a drop tank is used to describe auxiliary fuel tanks externally carried by aircraft. A drop tank is expendable and often jettisonable...
s were available at about 1/3 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 a common addition for aircraft of the era.
Fuselage
The fuselage was completely smooth, with a high fineness ratioFineness ratio
Fineness ratio is a term used in naval architecture and aerospace engineering to describe the overall shape of a streamlined body. Specifically, it is the ratio of the length of a body to its maximum width; shapes that are "short and fat" have a low fineness ratio, those that are "long and skinny"...
for low drag at supersonic speeds. The design was developed prior to the discovery of the area rule
Area rule
The Whitcomb area rule, also called the transonic area rule, is a design technique used to reduce an aircraft's drag at transonic and supersonic speeds, particularly between Mach 0.75 and 1.2....
, 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 730Avro 730
|-See also:-References:CitationsBibliography* Bartlett, Christopher John. "The Long Retreat: A Short History of British Defence Policy, 1945-70". Macmillan, 1971.* Brookes, Andrew J. "V-Force: The History of Britain's Airborne Deterrent ". Jane's, 1982....
selecting a very similar system, and the Air Force demanded that it be used on the F-103. The system that emerged used two large oval windows on the cockpit sides, and a periscope system projecting an image onto a fresnel lens
Fresnel lens
A Fresnel lens is a type of lens originally developed by French physicist Augustin-Jean Fresnel for lighthouses.The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design...
arrangement directly in front of the pilot. 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.
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.
A unique supersonic escape capsule (SEC) 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. The SEC was fully pressurized, allowing the pilot to continue operating the aircraft without a pressure suit when the capsule was "locked up".
Avionics and armament
The entire nose of the aircraft was taken up by the large Hughes radar set, which offered (then) 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 FalconAIM-4 Falcon
The Hughes AIM-4 Falcon was the first operational guided air-to-air missile of the United States Air Force.-Development:Development of a guided air-to-air missile began in 1946. Hughes Aircraft was awarded a contract for a subsonic missile under the project designation MX-798, which soon gave way...
(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" FFAR
Mk 4/Mk 40 Folding-Fin Aerial Rocket
The Mk 4 Folding-Fin Aerial Rocket , sometimes called the Mighty Mouse, was a 2.75 in diameter unguided rocket weapon commonly used by U.S. military aircraft. It was intended as an air-to-air weapon to allow interceptor aircraft to shoot down enemy bombers with greater range and effectiveness than...
s.
Specifications (XF-103, as designed)