The ramjet: a jet engine that only works once it's already flying fast
A ramjet has no spinning compressor. It simply scoops air by rushing forward, so it cannot start from a standstill and must be flung to speed first. Once there, it thrives, working best around Mach 3 and usable up to Mach 6. Pilots in the 1950s nicknamed it the flying stovepipe.
That nickname came from trade magazines contrasting the ramjet with the turbojet, whose turbines are intricate and costly. A ramjet is little more than a shaped tube where fast incoming air is squeezed, mixed with fuel and burned. The simplicity makes it ideal where speed matters in a small package, above all missiles, and designers have studied ramjet-boosted artillery: a 120 millimetre mortar round so fitted might reach 35 kilometres.
Arthur C. Clarke gave credit for the concept to Cyrano de Bergerac, whose satirical moon voyage of 1657 counts among the earliest science fiction. The engineering version came from the Frenchman René Lorin, who patented a design in 1913 but could never test it, because no aircraft of his day could fly fast enough. In 1915 the Hungarian Albert Fonó proposed attaching ramjets to artillery shells so light guns could fire heavy rounds far; the Austro-Hungarian army turned him down, though he later won a German patent in 1932.
Soviet engineers pressed ahead in the 1930s. Their GIRD-04, tested in April 1933, ran on hydrogen fed with air compressed to 200 bar to mimic supersonic flight, and shells fired from cannon with ramjets may have been the first jet-driven projectiles to pass the speed of sound. In December 1940 a modified Polikarpov biplane made the first flight powered partly by ramjets. Kawasaki in Japan and several German firms also built wartime test engines, the Germans at one point trying pressed coal dust as fuel when petrol ran short.
After the war, France flew the Leduc 0.10 in 1949 and the Nord Griffon reached Mach 2.19 in 1958. The United States built the Talos naval missile, which in May 1968 downed a fighter jet about 105 kilometres away, and no missile fired from a ship had ever shot down a hostile plane in battle before Talos did.
Source: Ramjet
