EDWARDS AIR FORCE BASE, Calif. -- Although the second flight test of the X-51A Waverider scramjet ended prematurely, the coordination and performance of the Hypersonics Combined Test Force and the 419th Flight Test Squadron was flawless.
More than 100 people from both Edwards Air Force Base and Naval Air Station Point Mugu took part in the enormously complex flight test.
A B-52H Stratofortress on loan to Edwards released the experimental vehicle from an altitude of approximately 50,000 feet June 13, 2011. After release, the X-51 was initially accelerated by a solid rocket booster.
The hypersonic aircraft was successfully boosted to just over Mach 5 and the scramjet engine lit, but it failed to transition to full power.
From reconfiguring the release mechanism from the previous test attempt, to pushing the B-52 to its altitudinal limit, everyone involved had to be at the top of their game throughout the entire test process.
During a previous test attempt in March, the scramjet failed to release from the B-52 and the team went to work to create a solution.
"The configuration we used to eliminate the problem has never been used before," said Lt. Col. Todd Venema, Hypersonics Combined Test Force director.
Engineers had to reconfigure the release charges to ensure the X-51 would be released successfully.
"We were very pleased with the eventual solution. It was a lot of work over two months," said Colonel Venema.
The flight test had several challenges that had to be worked through and planned with extreme precision, such as the altitude required to launch the X-51.
"The B-52's flight envelope goes up to 50,000 feet, and that was the launch conditions for the X-51," said Colonel Venema. "The B-52's crew is flying right at the very edge of that aircraft's capability. It's quite surprising to me that a flight that would be perfectly normal at 40,000 feet would have a tremendous difference at 50,000 with difficulty and complexness."
He said the bomber has to work harder to keep pressurization, and the temperature at that height required waivers from the air crews.
For the X-51 to launch effectively, the B-52 was also required to fly as fast as possible.
"It's going absolutely as fast as it can, and it's not that much above a stall margin," he said.
Colonel Venema added that the F-18 chase planes during the test were at the edge of their envelope as well because the fighters had to fly as slow as they could.
"All of the aircraft in the area were right at the edge of their capabilities, and that is a very challenging thing," he said.
Fuel temperature was another constraint to the flight test. The X-51's fuel could not drop below a certain temperature. This required the B-52 to climb to the 50,000 level at an accelerated rate. That meant the B-52 needed to be lighter and it could not have any deviation from its course where extra fuel could be spent.
Barry Reed, Hypersonics CTF project engineer, said additional obstacles running up to the test also included making sure the ocean range was clear of ships and monitoring weather conditions.
"The morning of the test, even before the weather cleared, we got a boat," Mr. Reed said. "That one cleared and then we had another boat. Just one after another. We had to make radio contact with these guys and it wasn't until the last possible moment in our launch window that got a green range."
Boeing and Pratt & Whitney Rocketdyne built four X-51A flight test vehicles with the program goal of reaching Mach 6 in hypersonic flight. The next flight is tentatively scheduled for this fall.
"We're shooting for that Mach 6, 100-percent success mark," said Mr. Reed. "We've already done the 90-percent success test, now we want 100-percent success and to get more data to make sure the United States remains the leader in hypersonic technology development. We have two more vehicles left; we have two more opportunities to make even more history."