| Hypersonic jet program gains speed NASA says May test could make history 04/13/2001 By Peter Pae / Los Angeles Times
For more than four decades, scientists have been trying to develop a jet-powered aircraft that could zip across the sky at five times the speed of sound, a feat that has been harder to accomplish than sending a man to the moon.
But in a hangar in California's Mojave Desert, engineers are putting the finishing touches on a new plane that they think could meet that milestone and lead one day to an airliner flying from Los Angeles to New York in 30 minutes.
A 12-foot experimental airplane is scheduled to make its maiden flight next month, flying over the Pacific Ocean at more than 5,000 mph.
Though the first flight of the unmanned X-43A is expected to last about 10 seconds – covering about 14 miles – it would mark a dramatic turning point for the decades-long effort to develop a hypersonic aircraft, a vehicle that is powered not by a rocket but by an air-breathing jet engine.
"We're finally getting down to testing the basic science of a new propulsion system that could ultimately alter commercial aerospace and national security," said Charles Vick, acting director of space policy for the Federation of American Scientists. "It's a big step forward for aerospace technology."
It would come after repeated setbacks to design of a hypersonic craft. A $2.5 billion Reagan-era hypersonic program, based in Southern California, was scuttled. The total cost of the X-43A program is $185 million.
With one short flight, to begin off the coast of Los Angeles, National Aeronautics and Space Administration officials say dreams of a commercial airliner that can fly from Los Angeles to Tokyo in two hours instead of 10 is one step closer to reality. The military's vision calls for a bomber that would be too fast to shoot down.
NASA officials plan to disclose the date of the test flight at a Wednesday news conference at Dryden Flight Research Center at Edwards Air Force Base, where the plane is being prepared. The plane, dubbed Hyper-X, was designed by Boeing Co. and built by Micro Craft in Ontario, Calif., and Tullahoma, Tenn.
Micro Craft is a 700-employee aerospace concern that initially began as a maker of aircraft models for wind-tunnel testing. The company has benefited from NASA's move to cut costs by farming out work to smaller companies who can do it cheaply and quickly.
"It will be an aviation first," said Vincent Rausch, NASA's Hyper-X program manager. "No one has ever flown an engine like this at the velocity we are talking about."
For scientists, the flight will represent a significant milestone in the development of propulsion systems and aerodynamic designs.
The plane, resembling a boogie board with twin tail fins, will be propelled by a supersonic combustion ramjet engine – a "scramjet" – essentially a rectangular copper box mounted to the belly.
Technological barrier
But looks are deceiving, because the science behind the scramjet has been one of the more difficult technological barriers to overcome.
The common turbojet uses turbines inside the engine to compress air, which ignites with kerosene to create combustion and then thrust. Though the turbojet is efficient at subsonic speeds of conventional airliners, air flows too slowly and overheats the engine at high speeds.
Ramjets are basically a hollow tube with no moving parts, resolving the temperature problem. They can propel an aircraft past Mach 2, or twice the speed of sound. Air flow into the front of the ramjet is compressed and mixed with fuel. The resulting combustion creates thrust as it exits the engine.
But the ramjet cannot power an aircraft past Mach 5. That requires a scramjet, in which gases can flow at supersonic speeds.
Although it is mechanically simple, it is vastly more complex aerodynamically than a jet engine. For instance, the front end of the X-43A, such as the flat nose, helps compress the oxygen before it enters the copper alloy chamber, where it mixes with hydrogen and burns, creating pressure from the expanding gas to propel the plane forward.
In essence, the propulsion system and the airframe are interdependent, a radical new concept in aircraft design, NASA officials said.
"It's a subtle difference but you have to think of the plane and the engine as one," said Joel Sitz, NASA's project manager for the X-43A at Dryden. "The plane is integrated into the engine, and that makes it much more efficient."
But for a scramjet to kick in, the aircraft must already be flying fast to suck in enough oxygen for combustion to occur. As such, the X-43A will be mounted to an Orbital Science Corp. Pegasus rocket, which boosts the aircraft to the required speed, or about Mach 5 or greater.
Once detached from the booster rocket, the aircraft will be able to fly between seven and 10 times the speed of sound, or about 4,725 mph to 6,750 mph depending on altitude and atmospheric conditions. Most commercial jets cruise at about 500 mph and the world's fastest plane, the Air Force's SR-71 Blackbird, flies at about 2,100 mph.
Help from bomber
For the test flight, a modified B-52 bomber with the X-43A attached to the wing will fly to the California coast from Edwards and launch the aircraft along with the booster rocket near San Nicolas Island southwest of Los Angeles.
The X-43A will fall away from the B-52 as it is cruising westward at about 20,000 feet. About five seconds later, after it is clear of the carrier aircraft, the booster rocket will fire, lifting the X-43A to about 100,000 feet, where the hypersonic plane will separate and fly on its own for about 10 to 15 seconds before plunging into the ocean. By comparison, the Wright Flyer flew for 12 seconds and covered about 120 feet when it made aviation history in 1903.
If all goes according to plan, the X-43A should reach a speed of Mach 7, or about 5,000 mph, breaking the record for both air-breathing and rocket-powered airplanes, surpassing even the Mach 6 record set by the rocket-powered X-15 in 1967.
Two additional X-43A planes are under assembly for flights planned within the next year.
NASA officials said there are no plans to recover the vehicles, which will primarily be used to gather data and test the propulsion system for the next generation of hypersonic planes.
Distributed by Los Angeles Times/Washington Post News Service.
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