Ramjet


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 and can operate up to.
Ramjets can be particularly appropriate in uses requiring a compact mechanism for high speed, such as missiles. Weapons designers are investigating ramjet technology for use in artillery shells to increase range; a 120 mm ramjet-assisted mortar shell is thought to be able to travel. They have been used, though not efficiently, as tip jets on the ends of helicopter rotors.

History

France

Cyrano de Bergerac

L'Autre Monde: ou les États et Empires de la Lune was the first of three satirical novels written by Cyrano de Bergerac that are considered amonged the first science fiction stories. Arthur C Clarke credited this book with conceiving the ramjet, and as the first fictional example of rocket-powered space flight.

René Lorin

The ramjet was designed in 1913 by French inventor René Lorin, who was granted a patent for his device. He could not test his invention due to the unavailability of adequate equipment since there was no way at the time for an aircraft to go fast enough for a ramjet to function properly. His patent showed a piston internal combustion engine with added 'trumpets' as exhaust nozzles, expressing the idea that the exhaust from internal combustion engines could be directed into nozzles to create jet propulsion.

René Leduc

The works of René Leduc were notable. Leduc's Model, the Leduc 0.10 was one of the first ramjet-powered aircraft to fly, in 1949.

Nord Aviation

The Nord 1500 Griffon reached in 1958.

Austria-Hungary

Albert Fonó

In 1915, Hungarian inventor Albert Fonó devised a solution for increasing the range of artillery, comprising a gun-launched projectile united with a ramjet propulsion unit, thus giving a long range from relatively low muzzle velocities, allowing heavy shells to be fired from relatively lightweight guns. Fonó submitted his invention to the Austro-Hungarian Army, but the proposal was rejected. After World War I, Fonó returned to the subject. In May 1928 he described an "air-jet engine" as suitable for high-altitude supersonic aircraft, in a German patent application. In an additional patent application, he adapted the engine for subsonic speed. The patent was granted in 1932.

Soviet Union

In the Soviet Union, a theory of supersonic ramjet engines was presented in 1928 by Boris Stechkin. Yuri Pobedonostsev, chief of GIRD's 3rd Brigade, carried out research. The first engine, the GIRD-04, was designed by I.A. Merkulov and tested in April 1933. To simulate supersonic flight, it was fed by air compressed to 200 bar, and was fueled with hydrogen. The GIRD-08 phosphorus-fueled ramjet was tested by firing it from an artillery cannon. These shells may have been the first jet-powered projectiles to break the speed of sound.
In 1939, Merkulov did further ramjet tests using a two-stage rocket, the R-3. He developed the first ramjet engine for use as an auxiliary motor of an aircraft, the DM-1. The world's first ramjet-powered airplane flight took place in December 1940, using two DM-2 engines on a modified Polikarpov I-15. Merkulov designed a ramjet fighter "Samolet D" in 1941, which was never completed. Two of his DM-4 engines were installed on the Yak-7 PVRD fighter during World War II. In 1940, the Kostikov-302 experimental plane was designed, powered by a liquid fuel rocket for take-off and ramjet engines for flight. That project was cancelled in 1944.
In 1947, Mstislav Keldysh proposed a long-range antipodal bomber, similar to the Sänger-Bredt bomber, but powered by ramjet instead of rocket. In 1954, NPO Lavochkin and the Keldysh Institute began development of a Mach 3 ramjet-powered cruise missile, Burya. This project competed with the R-7 ICBM developed by Sergei Korolev, but was cancelled in 1957.

Japan

Several ramjets were designed, built, and ground-tested at the Kawasaki Aircraft Company's facility in Gifu during the Second World War. Company officials claimed, in December 1945, that these domestic initiatives were uninfluenced by parallel German developments. One post-war U.S. intelligence assessment described the Kawasaki ramjet's centrifugal fuel disperser as the company's "most outstanding accomplishment... eliminat a large amount of the fuel injection system normally employed." Because of excessive vibration, the engine was only intended for use in rocket, or catapult-launched pilotless aircraft. Preparations for flight testing ended with the Japanese surrender in August 1945.

Germany

In 1936, Hellmuth Walter constructed a test engine powered by natural gas. Theoretical work was carried out at BMW, Junkers, and DFL. In 1941, Eugen Sänger of DFL proposed a ramjet engine with a high combustion chamber temperature. He constructed large ramjet pipes with and diameter and carried out combustion tests on lorries and on a special test rig on a Dornier Do 17Z at flight speeds of up to. Later, as petrol became scarce in Germany, tests were carried out with blocks of pressed coal dust as a fuel, which were not successful due to slow combustion.

United States

Stovepipe was a popular name for the ramjet during the 1950s in trade magazines such as Aviation Week & Space Technology and other publications such as The Cornell Engineer. The simplicity implied by the name came from a comparison with the turbojet engine which employs relatively complex and expensive spinning turbomachinery.
The US Navy developed a series of air-to-air missiles under the name of "Gorgon" using different propulsion mechanisms, including ramjet propulsion on the Gorgon IV. The ramjet Gorgon IVs, made by Glenn Martin, were tested in 1948 and 1949 at Naval Air Station Point Mugu. The ramjet was designed at the University of Southern California and manufactured by the Marquardt Aircraft Company. The engine was long and in diameter and was positioned below the missile.
In the early 1950s the US developed a Mach 4+ ramjet under the Lockheed X-7 program. This was developed into the Lockheed AQM-60 Kingfisher. Further development resulted in the Lockheed D-21 spy drone.
In the late 1950s the US Navy introduced a system called the RIM-8 Talos, which was a long range surface-to-air missile fired from ships. It successfully shot down enemy fighters during the Vietnam War, and was the first ship-launched missile to destroy an enemy aircraft in combat. On 23 May 1968, a Talos fired from USS Long Beach shot down a Vietnamese MiG at a range of about. It was also used as a surface-to-surface weapon and was modified to destroy land-based radars.
Using technology proven by the AQM-60, In the late 1950s and early 1960s the US produced a widespread defense system called the CIM-10 Bomarc, which was equipped with hundreds of nuclear armed ramjet missiles with a range of several hundred miles. It was powered by the same engines as the AQM-60, but with improved materials to endure longer flight times. The system was withdrawn in the 1970s as the threat from bombers subsided.

THOR-ER

In April 2020, the U.S. Department of Defense and the Norwegian Ministry of Defense jointly announced their partnership to develop advanced technologies applicable to long range high-speed and hypersonic weapons. The Tactical High-speed Offensive Ramjet for Extended Range program completed a solid fuel ramjet vehicle test in August 2022.

Dual-mode ramjet

In 2023, General Electric demonstrated a ramjet with rotating detonation combustion. It is a turbine-based combined-cycle engine that incorporates a
In the late 1950s, 1960s, and early 1970s, the UK developed several ramjet missiles.
The Blue Envoy project was supposed to equip the country with a long range ramjet powered air defense against bombers, but the system was cancelled. It was replaced by a shorter range ramjet missile system called the Bloodhound. The system was designed as a second line of defense in case attackers were able to bypass the fleet of defending English Electric Lightning fighters.
In the 1960s the Royal Navy developed and deployed a ramjet powered surface to air missile for ships called the Sea Dart. It had a range of and a speed of Mach 3. It was used successfully in combat against multiple types of aircraft during the Falklands War.

Fritz Zwicky

Eminent Swiss astrophysicist Fritz Zwicky was research director at Aerojet and holds many patents in jet propulsion. Patents and are for ram accelerators. The U.S. Navy would not allow Zwicky to publicly discuss his invention, is for the Underwater Jet, a ramjet that performs in a fluid medium. Time magazine reported on Zwicky's work.

Design

The first part of a ramjet is its diffuser in which the forward motion of the ramjet is used to raise the pressure of its working fluid as required for combustion. Air is compressed, heated by combustion and expanded in a thermodynamic cycle known as the Brayton cycle, before being passed through a nozzle to accelerate it to supersonic speeds and generate forward thrust.
Ramjets are much less complex than turbojets or turbofans, requiring only an air intake, a combustor, and a nozzle to be built. Additionally, ramjets have little to no moving parts - liquid-fuel ramjets have only a fuel pump, whilst solid-fuel ramjets lack even this.
By comparison, a turbojet uses a compressor driven by a turbine, which generates its own compressed air in order to generate thrust.

Construction

Diffuser

The diffuser converts the high velocity of the air approaching the intake into high pressure required for combustion. High combustion pressures minimise entropy rise during heat addition, thus minimising wasted thermal energy in the exhaust gases
Subsonic and low-supersonic ramjets use a pitot-type opening for the inlet. This is followed by a widening internal passage to achieve a lower subsonic velocity that is required at the combustor. At low supersonic speeds a normal shock wave forms in front of the inlet.
For higher supersonic speeds the pressure loss through the shock wave becomes prohibitive and a protruding spike or cone is used to produce oblique shock waves in front of a final normal shock that occurs at the inlet entrance lip. The diffuser in this case consists of two parts: the supersonic diffuser, with shock waves external to the inlet, followed by the internal subsonic diffuser.
At higher speeds still, part of the supersonic diffusion has to take place internally, requiring external and internal oblique shock waves. The final normal shock has to occur in the vicinity of a minimum flow area known as the throat, which is followed by the subsonic diffuser.