LOS ANGELES — A closely watched test flight of an experimental aircraft designed to travel up to 3,600 mph ended in disappointment when a part failed, causing the unmanned cruiser to plummet into the Pacific Ocean, the Air Force revealed.
The X-51A WaveRider was launched in the Point Mugu Naval Air Test Range over the Pacific in a key test Tuesday intended to fine-tune its hypersonic scramjet engine.
This is the third time the WaveRider has flown. Not one flight has gone the distance.
The aircraft, built and tested in Southern California, was designed to hit Mach 6, or six times the speed of sound, and fly for five minutes. But that didn’t happen. The engine never even roared into action.
About 15 seconds into the flight, a problem was detected in one of the WaveRider’s control fins — a relatively small part of the aircraft — and the cruiser was not able to maintain control and was lost.
“It is unfortunate that a problem with this subsystem caused a termination before we could light the scramjet engine,” Charlie Brink, program manager for the Air Force Research Laboratory, said in a statement Wednesday.
“All our data showed we had created the right conditions for engine ignition, and we were very hopeful to meet our test objectives.”
Engineers thought they were on the right track with the WaveRider program in May 2010 when the Wave-Rider made its first flight. The WaveRider sped west for about 2 minutes, 23 seconds — less than half its scheduled five-minute flight — at 3,500 mph before plunging into the ocean as planned.
But in a June 2011 flight, a lapse in airflow to the jet engine caused a premature shutdown.
In the test Tuesday, a B-52 took off from Edwards Air Force Base with the Wave-Rider attached and flew to 50,000 feet near Point Mugu.
Once there, the B-52 dropped the aircraft and it fell like a bomb for about four seconds before its booster rocket engine ignited and propelled the aircraft.
It was then supposed to separate from the rocket and streak across the sky, powered by the air-breathing hypersonic engine, but the control-fin issue caused it to fail.
The Air Force said that “program officials will now begin the process of working through a rigorous evaluation to determine the exact cause of all factors at play.”
One of the four WaveRider aircraft remains. But officials have not decided when — or if — that vehicle will be used.
Aerospace engineers say that developing technology capable of sustaining hypersonic speeds — going five times the speed of sound or more — is crucial to the next generation of missiles, military aircraft, spacecraft and even passenger planes.
But engineers have been trying to sustain hypersonic flight since the 1960s and have had few positive results.
One of the more recent attempts at hypersonic flight was in August 2011 when the Pentagon’s research arm, the Defense Advanced Research Projects Agency, carried out a test flight of an arrowhead-shaped unmanned aircraft, dubbed Falcon Hypersonic Technology Vehicle 2.
It’s designed to travel in excess of 20 times the speed of sound. The launch had received worldwide attention and much fanfare. But minutes into the flight, searing heat from high speeds caused portions of the Falcon’s skin to peel from the aerostructure, and the flight ended prematurely.
The Pentagon said it has spent as much as $2 billion over the last 10 years on hypersonic technologies and supporting engineering. The Pentagon is funding six major hypersonic technology programs.
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Work on the WaveRider was done by Boeing Co.’s research center in Huntington Beach and Pratt & Whitney Rocketdyne in Canoga Park. The program cost an estimated $140 million, according to Globalsecurity.org, a website for military policy research.
But that number doesn’t include classified money and other additional funds, said John Pike, director of Globalsecurity.org. He also noted that the WaveRider program is years behind schedule.
Pike attributes some of the WaveRider’s problems to the fact that there aren’t wind tunnels that can simulate the conditions in which the aircraft will fly. So the engineers are finding out what’s wrong with the plane the old-fashioned way: by flying it.
“They have to go out there and make mistakes and then learn from those mistakes,” he said. “Evidently, going Mach 6 is hard to do.”
Still the Pentagon wants to prove the concept and will most likely attempt a fourth flight with the last remaining WaveRider, Pike said.
“I’m sure they’ll take whatever they think they learned from this flight and have another go-round.”