August 16, 2012
By Jim Moore
It has been a mixed bag on the cutting edge for Boeing this month.
An Aug. 7 maiden flight was celebrated by the aerospace giant, which teamed with NASA to produce the X-48C, an experimental blended wing body design that could significantly reduce the noise of future airlines. A week later, another Boeing design, this one aiming to speed past Mach 6, failed in testing.
The scramjet-powered X-51 was launched from a B-52 on Aug. 14, but lost control before the engine was fired, according to an unnamed source. U.S. Air Force photo/Chad Bellay.
The X-51A Waverider, an Air Force experiment so named because it is designed to ride its own shockwave at hypersonic speed, crashed into the Pacific Ocean after a control fin failed seconds after the X-51A separated from the rocket booster, according to an Air Force statement.
The sleek missile was designed to be dropped from a B-52 at altitude, and was supposed to demonstrate hypersonic technology—sustained speed above Mach 5, a challenge that has bedeviled generations of engineers. Many such efforts have never even made it off the drawing board, such as the X-30. Once dubbed the “new Orient Express” by President Ronald Reagan and envisioned to carry passengers from Washington to Tokyo in two hours, the X-30 was canceled in 1993 due to budget concerns, and disbelief that technical challenges could be overcome. It never flew.
The X-51A has now managed sustained flight just once in three attempts. The first flight in 2010 fell short on speed—Mach 4.88—but set a record for sustained flight under the power of an air-breathing scramjet at 143 seconds. (A scramjet compresses supersonic airflow with a Venturi tube, and without a turbine or related moving parts; a ramjet is basically a scramjet designed to operate at subsonic speeds.)
The two subsequent flights (three, if you count an attempt that aborted when the X-51A failed to detach from the B-52) fell well short of that.
A scale model of a future airliner designed by Boeing’s Phantom Works, the X-48C flew for the first time Aug. 7 in California.
In June 2011, the Pratt & Whitney Rocketdyne SJX61 dual-mode ramjet/scramjet engine failed to transition during flight from ethylene fuel used for engine start to the JP-7 fuel used for sustained flight, and wound up clocking just under 10 seconds around Mach 5 before taking its first and final swim.
The Aug. 14 failure of the third X-51A built also ended with a splash: None are designed for post-flight recovery, all wind up in the ocean—one way or another. Boeing is close to completing a fourth X-51A, though Aviation Week reports there is no funding allocated yet for the fourth to fly.
In contrast, the X-48C was celebrated by Boeing and NASA, which is backing a variety of futuristic aircraft designs—not including the X-51A, which is an Air Force effort.
The X-48C is a remote-control scale model (500 pounds with a 21-foot wingspan, 8.5 percent of the future version’s full size) flown out of NASA’s Dryden Flight Research Center on the grounds of Edwards Air Force Base. The X-48C climbed to 5,500 feet during a 9-minute maiden flight.
Boeing blended wing body designs have been tested since 2007, with the latest version powered by a pair of turbojets producing 89 pounds of thrust each and replacing a trio of 50-pound thrust engines used on the previous model. Boeing and NASA believe the blended wing body offers promise to deliver high-efficiency, heavy lift capability with significant noise reduction. The X-48C engines are mounted above the fuselage to help reduce its noise signature, and this version is specifically designed to test the effect of noise reduction modifications on low-speed control abilities previously demonstrated.
The National Aeronautic Association has awarded the Collier Trophy for “the first unmanned, autonomous air system operating from an aircraft carrier.”
AOPA and others urge FAA to quickly adopt regulations governing unmanned aerial systems (drones) to protect all airspace users.
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