After a two-year upgrade of its test facilities, the AEDC Aerodynamic and Propulsion Test Unit at Arnold Air Force Base in Tennessee has finally been able to test the latest Northrop Grumman scramjet at simulated hypersonic speeds, setting a new thrust record in the process.
Scramjets, of course, can only operate at hypersonic speeds, as they rely on extreme intake air velocity to compress and heat the air before combustion can take place. Where a turbojet uses a compressor and a piston engine uses a compression stroke to achieve this effect, scramjets in some cases need no moving parts at all. Air comes in at hypersonic speeds, and is then forced into a narrowing channel which compresses it, and then fuel is added at the narrowest point, igniting and producing thrust as it leaves the chamber.
In this case, the test unit put out more than 13,000 pounds of thrust – a US Air Force record test figure for an air-breathing hypersonic engine. That might not sound very impressive, what with Boeing gearing up to put GE9X jets on its next model airliners that make more than a 100,000 pounds of thrust each, but hypersonic flight starts at five times the speed of sound and theoretically goes up to as fast as Mach 24, and this makes everything considerably more challenging.
Indeed, even testing the thing turned out to require a two-year upgrade of the AEDC's test facilities, because there wasn't a single test rig in the country capable of reproducing the airspeeds and thermal conditions needed to properly run this engine through its paces.
The scramjet engine in question was conceived during the X-51 test program around 10 years ago. At 18 ft (5.5 m) long, it's designed to handle 10 times the airflow the X-51 could, and is eventually slated to power a host of hypersonic military aircraft.
The nine-month test program subjected the Northrop Grumman engine to a total of more than 30 minutes of combustion time.
Source: Wright-Patterson AFB