Rockwell Displays Experimental Jet Designed to Turn and Aim Quickly
Ever since Orville Wright flew for the first time, aircraft have faced an insurmountable aerodynamic barrier. Known as stall, it occurs when wings fail to provide adequate lift and an aircraft plummets.
The new experimental X-31 jet fighter, which is supposed to break that barrier, was rolled out Thursday in Palmdale at ceremonies by Rockwell International and its West German partner, Messerschmitt-Bolkow-Blohm.
The fighter-type aircraft, built under joint funding by the Pentagon and the West German government, is expected to make its first flight late next month. The cost of developing the technology and building two planes is put at about $200 million, which includes 400 hours of flight testing.
The X-31’s capability of breaking the stall barrier should allow it to turn and point at targets much more quickly than conventional fighters, which could cause revolutionary changes in air combat.
If a current-generation fighter attempted such slow, sharp turns as the X-31 is expected to demonstrate, it would be likely to enter a stall, lose altitude and fall out of control.
“It is like disconnecting the steering wheel on your car at 65 miles per hour,” said Sam Iacobellis, Rockwell International executive vice president. “But in the X-31, you can get out of it. It is a natural progression in moving past that barrier.”
If the X-31 succeeds in radically improving an aircraft’s turning and pointing capability, it will open to question the very costly design philosophy in air combat that the military services have embraced for more than a decade.
That philosophy has been one that favors very high speeds, powerful air radars and long-range missiles that allow fighter pilots to enter battle at ranges well beyond the range of human eyesight.
But plans to conduct battles at long range are controversial, because missiles like the Phoenix, Sparrow and Amraam designed for such battles have yet to prove they can successfully destroy targets at medium and long ranges. Missile experts say the Sparrow was successful only 10% of the time in the Vietnam War.
An even more basic problem with long-range combat is the inability of electronic systems to determine which aircraft are hostile. In 1988, the U.S. Navy shot down an Iranian passenger jetliner with a medium-range missile, for example.
Rockwell is not attempting to become an industry maverick with the X-31, but the theory behind the plane suggests that modern jet fighters can benefit by having better close-in fighting capability and more agility.
“I’d rather have a cheap missile on an aircraft that comes back than an expensive missile that doesn’t come back,” said Leonard S. Freeman, a technical director at the Naval Air Systems Command, which is managing the X-31 program. “The X-31 gives another trick in the bag for the pilot.”
But pilots will have to be persuaded to forfeit high speed in combat in exchange for maneuverability. “If you run out of air speed, you run out of tricks--that’s the conventional wisdom,” Freeman said.
What makes the X-31 different is its ability to quickly restore lost speed. It is powered by a General Electric engine with thrust of 16,000 pounds at sea level, providing a powerful 1.25 to 1 thrust to weight ratio. The X-31 is 43 feet long and has a wing span of 24 feet.
The need for highly maneuverable aircraft emerged in the late 1970s, when missiles were developed that could shoot down aircraft in head-on engagements. Until then, pilots had to maneuver behind an enemy aircraft in dog fights.
Wolfgang Herbst, director for advanced design and technology at MBB, originated the concept for the X-31 but could not persuade the West German air force to fund it, he said Thursday in an interview.
He said he believes that while long-range combat is important, many engagements will quickly degenerate into short-range. Then, the aircraft that can turn and point its weapons fastest will win. Herbst said the X-31 will be able to execute a 180-degree turn in a diameter of roughly 100 meters at a speed of about 150 knots.
The maneuverability is provided by thrust vectoring of the engine, in which the exhaust stream from the engine is directed by three paddles. That system, in addition to small forward wings called canards, will enable it to fly at high angles of attack that enable the sharp turns. An angle of attack is something of a controlled slide through the air, in which the aircraft’s nose is pointed up while the plane continues in a horizontal line of flight.
A key measure of the maneuvering capability of a jet fighter is how sharp an angle of attack it can fly. Conventional fighters can fly at up to 35 degrees. The X-31 aims to double that.
“I think all future fighter aircraft will have thrust vectoring,” said John Pierro, president of Rockwell’s North American Aircraft unit, which built the X-31.
