Ramjet

A ramjet, sometimes referred to as a flying stovepipe or an athodyd (aero thermodynamic duct), is a form of airbreathing jet engine that uses the engine's forward motion to compress incoming air without an axial compressor or a centrifugal compressor. Because ramjets cannot produce thrust at zero airspeed, they cannot move an aircraft from a standstill. A ramjet-powered vehicle, therefore, requires an assisted take-off like a rocket assist to accelerate it to a speed where it begins to produce thrust. Ramjets work most efficiently at supersonic speeds around Mach 3 (2,300 mph; 3,700 km/h). This type of engine can operate up to speeds of Mach 6 (4,600 mph; 7,400 km/h). Ramjets can be particularly useful in applications requiring a small and simple mechanism for high-speed use, such as missiles. Weapon designers are looking to use ramjet technology in artillery shells to give added range; a 120 mm mortar shell, if assisted by a ramjet, is thought to be able to attain a range of 35 km (22 mi). They have also been used successfully, though not efficiently, as tip jets on the end of helicopter rotors. Ramjets differ from pulsejets, which use an intermittent combustion; ramjets employ a continuous combustion process. As speed increases, the efficiency of a ramjet starts to drop as the air temperature in the inlet increases due to compression. As the inlet temperature gets closer to the exhaust temperature, less energy can be extracted in the form of thrust. To produce a usable amount of thrust at yet higher speeds, the ramjet must be modified so that the incoming air is not compressed (and therefore heated) nearly as much. This means that the air flowing through the combustion chamber is still moving very fast (relative to the engine), in fact it will be supersonic—hence the name supersonic-combustion ramjet, or scramjet. L'Autre Monde: ou les États et Empires de la Lune (Comical History of the States and Empires of the Moon) (1657) was the first of three satirical novels written by Cyrano de Bergerac, that are considered among the first science fiction stories. Arthur C Clarke credited this book with inventing the ramjet, and being the first example of a rocket-powered space flight. The ramjet was conceived in 1913 by French inventor René Lorin, who was granted a patent for his device. Attempts to build a prototype failed due to inadequate materials. In 1915, Hungarian inventor Albert Fonó devised a solution for increasing the range of artillery, comprising a gun-launched projectile which was to be 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 of jet propulsion, in May 1928 describing an 'air-jet engine' which he described as being 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 after four years of examination (German Patent No. 554,906, 1932-11-02). 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 a great deal of research into ramjet engines. 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 20,000 kilopascals (200 atm), 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.