US Air Force working on new hypersonic scramjet capable of Mach 5 speeds

Curtis Moldrich Read more June 3, 2015

The US Air Force has confirmed it’s working on a new type of scramjet, capable of speeds up to Mach 5 (3,806mph at sea level). The technology has already been tested, but engineers are now looking to incorporate it into a hypersonic aircraft by 2023.

The X-51A

The US Air Force has already tested scramjet technology. In 2013, the Boeing X-51A “WaveRider” achieved hypersonic flight 60,000ft above the Pacific Ocean. The aircraft was initially taken to an altitude of 50,000ft by a B-52H Stratofortress before the X-51A accelerated to Mach 5.1. More than five times the speed of sound, hypersonic speed is classed as anything above Mach 5.

Now, following the $100 million proof of concept, the US Air Force is ready to incorporate scramjet technology into a more conventional air vehicle. There are many engineering and technological challenges ahead – and the data collected during the X-51A’s test flight will be essential to overcoming them.

“They are trying to build the whole system so that it isn’t only about the engine. You need materials that can operate at the kind of temperatures you see when travelling at hypersonic speeds,” said US Air Force Chief Scientist Mica Endsley.

“You need guidance systems that will function when you’re going at those speeds. There are a number of technological challenges that will have to be addressed to make a functioning system.”

Future uses

Scramjet technology represents a faster, more efficient method of air travel, and the US Air Force’s decision to develop it hints at some possible uses. Current cruise missiles can achieve top speeds of 600mph, while scramjet technology can reach up to Mach 10 (7,612mph). This would enable missiles to travel far more efficiently over huge distances, opening up a range of military uses.

NASA also believes a scramjet represents a cheaper, safer way to get people and cargo into space. Unlike conventional rockets, scramjets don’t require their own supply of oxygen – reducing the need to carry more expensive, volatile fuels.

Scramjet technology could also reduce the five-hour trip from Los Angeles to New York to only 30 minutes, although no plans exist at present for a manned aircraft; as a result of superfast levels of acceleration, the g-forces generated by scramjets are well beyond what we humans can handle.

How does a scramjet work?

Normal jets work by inducting air at subsonic speeds, compressing it and then mixing it with fuel before combustion. Although some jets can fly at supersonic speeds, air travels much more slowly inside their engines.

In contrast, scramjets maintain supersonic airspeeds throughout the combustion process. Scramjets even use the speed of the air to cause sufficient compression, so they don’t require the moving parts of conventional jets. As well as making them highly efficient, they’re capable of even greater speeds than conventional jet engines.

The catch? Scramjets need supersonic airflow to work properly, so they need to be brought up to speed by a more conventional propulsion system.