The example of the X-51 points to the current direction of research into hypersonic propulsion: it has been said that the technology demonstrated in this project could be applied to the development of hypersonic missiles, currently underway in the USA. “Currently the useful life of a scramjet is in the order of minutes and they are not reusable, having only been tested in prototypes.” But despite these advances, “ scramjets still need significant technological advances for reliable use,” continues Bermejo-Moreno, who is studying how to improve scramjet performance. The latter, developed in the last decade, applied the waverider concept, a design intended to increase lift by relying on the shock waves generated by the aircraft itself when breaking the sound barrier. These include NASA’s X-43 unmanned aircraft and its successor, the USAF Boeing X-51A. Thanks to this technology, “in the last 20 years several experimental hypersonic propulsion projects have been successfully developed,” says the engineer. An artist’s conception of the X-43A Hypersonic Experimental Vehicle in flight. In exchange, its disadvantage is that “it needs to fly at hypersonic speeds to start operating, so it must reach that stage with other propulsion systems, such as jet engines, afterburners and ramjets,” notes Bermejo-Moreno. The advantage of this thruster is that it works with atmospheric oxygen, which is compressed in the engine thanks to the aircraft’s own speed, which avoids the use of turbines. The main alternative to rockets are ramjets, and more specifically their supersonic combustion variant: the scramjet. Air Force (USAF) X-15 and by NASA, which in October 1967 set the speed record for a manned, powered aircraft at Mach 6.7, or 7,274 km/h. These rocket engines have been tested in projects such as the U.S. In these cases, the spacecraft carries its own reserve of liquid oxygen for combustion, “which gives them autonomy outside the atmosphere, but increases weight and volume,” says Bermejo-Moreno. “Today, manned hypersonic flights are only possible with rocket propulsion, such as those used in space missions,” explains Iván Bermejo-Moreno, an aerospace engineer at the University of Southern California who specialises in hypersonic propulsion, to OpenMind. However, at hypersonic speeds the turbines would disintegrate, and therefore other types of thrusters without moving parts are needed. These turbochargers or turbofans are suitable even for supersonic flight. ![]() In most modern aircraft, fans compress the air needed to fuel combustion. The difference between supersonic flights -the Concorde used to fly at 2,180 km/h, approximately Mach 2, or twice the speed of sound- and hypersonic flights -Mach 5 and above- is not a question of just giving more gas to the engines, but will require certain technological advances. ![]() Nowadays, although there are plans underway to revive supersonic flight, there are those who are looking even further ahead, towards the hypersonic plane: from Europe to Australia and back taking the length of just a workday. ![]() The supersonic Concorde, which substantially cut transatlantic flight times, was only ever an option reserved for the elites. In the half century since, the evolution of commercial aircraft has brought us increasingly comfortable, efficient and safe aircraft, but one thing hasn’t changed: the length of the journeys. On March 2, 1969, the iconic Boeing 747, better known as the Jumbo Jet, first took to the skies.
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