Scramjet

A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forcefully before combustion (hence ramjet), but whereas a ramjet decelerates the air to subsonic velocities before combustion, the airflow in a scramjet is supersonic throughout the entire engine. That allows the scramjet to operate efficiently at extremely high speeds. A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forcefully before combustion (hence ramjet), but whereas a ramjet decelerates the air to subsonic velocities before combustion, the airflow in a scramjet is supersonic throughout the entire engine. That allows the scramjet to operate efficiently at extremely high speeds. During World War II, a tremendous amount of time and effort were put into researching high-speed rocket-powered aircraft, predominantly by the Germans. After the war, the US and UK took in several German scientists and acquired various military technologies through Operation Paperclip, including technology surrounding rocket engines. The Bell X-1 attained supersonic flight in 1947 and, by the early 1960s, rapid progress towards faster aircraft suggested that operational aircraft would be flying at 'hypersonic' speeds within a few years. Except for specialized rocket research vehicles like the North American X-15 and other rocket-powered spacecraft, aircraft top speeds have remained level, generally in the range of Mach 1 to Mach 3. In the 1950s and 1960s a variety of experimental scramjet engines were built and ground tested in the US and the UK. In 1958, an analytical paper discussed the merits and disadvantages of supersonic combustion ramjets. In 1964, Drs. Frederick S. Billig and Gordon L. Dugger submitted a patent application for a supersonic combustion ramjet based on Billig’s Ph.D. thesis. This patent was issued in 1981 following the removal of an order of secrecy. In 1981 tests were made in Australia under the guidance of Professor Ray Stalker in the T3 ground test facility at ANU. The first successful flight test of a scramjet was performed by the Soviet Union in 1991. It was an axisymmetric hydrogen-fueled dual-mode scramjet developed by Central Institute of Aviation Motors (CIAM), Moscow in the late 1970s. The scramjet flight was flown captive-carry atop the SA-5 surface-to-air missile that included an experimental flight support unit known as the 'Hypersonic Flying Laboratory' (HFL), 'Kholod'. Then from 1992 to 1998 an additional 6 flight tests of the axisymmetric high-speed scramjet-demonstrator were conducted by CIAM together with France and then with NASA. Maximum flight velocity greater than Mach 6.4 was achieved and scramjet operation during 77 seconds was demonstrated. These flight test series also provided insight into autonomous hypersonic flight controls. In the 2000s, significant progress was made in the development of hypersonic technology, particularly in the field of scramjet engines. The HyShot project demonstrated scramjet combustion on July 30, 2002. The scramjet engine worked effectively and demonstrated supersonic combustion in action. However, the engine was not designed to provide thrust to propel a craft. It was designed more or less as a technology demonstrator. A joint British and Australian team from UK defense company QinetiQ and the University of Queensland were the first group to demonstrate a scramjet working in an atmospheric test.