No facility in the country could safely hold the test, so they had to build one.
- Scramjets use experimental engines that are powered partially by air, and the Air Force Research Laboratory just tested on in excess of Mach 4.
- They’re been theoretical for a long time, but the Air Force broke its own record for thrust while trying to develop one.
A team of engineers at the Air Force Research Laboratory and Air Force Test Center have set a record for the highest thrust produced by an air-breathing hypersonic engine in the military branch’s history. The test were done in service of the latest Northrop Grumman scramjets, where combustion takes place in a supersonic airflow.
During the nine months of testing, the 18-foot engine experienced a full half-hour of accumulated combustion time. During the tests, the engine operated at conditions above Mach 4, or 3,069 MPH.
“AFRL, in conjunction with Arnold Engineering Development Complex and Northrop Grumman, achieved over 13,000 pounds of thrust from a scramjet engine during testing at Arnold Air Force Base,” said Todd Barhorst, AFRL aerospace engineer and lead for the Medium Scale Critical Components program, in a press statement.
Scramjets need the intensity of hypersonic speeds to function properly. They carry fuel on board their engines, like rockets, but make their fuel explosive in very different ways. Rockets carry an oxidizer on board. Scramjets use the surrounding oxygen as an oxidizer, giving them an endless and weightless supply at the right atmospheric levels. The trade-off is that their use is limited to suborbital flight.
It’s an idea that makes sense in theory but has had difficulty getting off the ground, so to speak. As recently as 2012, Air Force scramjet tests were failing. But there have been improvements, especially in India, where the country’s military research and development program had a successful scramjet flight earlier this year.
“The series of tests, ran in conjunction with AEDC and AFRL, on this fighter-engine sized scramjet was truly remarkable,” said Pat Nolan, vice president, missile products, Northrop Grumman. “The scramjet successfully ran across a range of hypersonic Mach numbers for unprecedented run times, demonstrating that our technology is leading the way in delivering large scale hypersonic platforms to our warfighters.”
“The plan for a larger and faster hypersonic air breathing engine was established 10 years ago during the X-51 test program, as the Air Force recognized the need to push the boundaries of hypersonic research,” Barhorst said. “A new engine with 10-times the flow of the X-51 would allow for a new class of scramjet vehicles.”
There were numerous challenges facing the test, and they weren’t just related to the complexity of scramjets. Because of the power needed for the test, no test facility in America was deemed capable of handling them. The Arnold Engineering Development Complex (AEDC), based in middle Tennessee, was forced to undergo a massive two-year upgrade just to meet the testing conditions.
“Our collective team has worked hard over the past few years to get to where we are today,” said Sean Smith, lead for the AEDC Hypersonic Systems Combined Test Force ground test team. “We’ve encountered numerous challenges along the way that we’ve been able to overcome thanks to the dedication and creativity of the team. We’ve learned quite a bit, and I’m proud of what we’ve accomplished. These groundbreaking tests will lead the way for future hypersonic vehicles for a range of missions.”
The Air Force has gotten mixed reviews on some of its latest planes, like the F-35, especially among neighbors who have to live near their noise.