With a look at the possible future of high altitude transportation, the Air Force put a test vehicle in the air that used its high speed Scramjet engine to propel the craft to in excess of Mach 6, or six times the speed of sound. The hypersonic (more than 5 times the speed of sound) flight was very short but exceeded the old record for hypersonic flight by a factor of 15.
"The [X-51A Waverider]’s scramjet engine accelerated the vehicle to Mach 6, and it flew autonomously for 200 seconds before losing acceleration. At that point the test was terminated. The Air Force said the previous record for a hypersonic scramjet burn was 12 seconds. Joe Vogel, Boeing’s director of hypersonics, said, ‘This is a new world record and sets the foundation for several hypersonic applications, including access to space, reconnaissance, strike, global reach and commercial transportation.’ "
The idea of hypersonic flight has been around since the early 1960s. The reason so little has been made a part of the public consciousness is not one of a secret nature, but that there were problems to be worked out with reducing thermal loads on the structure of the vehicle, which is one reason why the other vehicles of the last century had been limited to a bit over Mach 3, such as the SR71 Blackbird. The shedding, and avoiding the creation, of heat is part of why many supersonic planes have forward wing profiles that are razor sharp.
The SR-71 Blackbird, one of the first really fast planes, and a test bed for dealing with the stresses of very high speed flight.
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