Radical Design May Result in New Slant on Aircraft

In a small wind tunnel once used to design the B-2 stealth bomber, Northrop Grumman Corp. engineers in El Segundo are developing an aircraft that could alter the skies.

Or never get off the ground.

Such are the promise and challenges in designing the so-called oblique flying wing, a concept that has eluded scores of engineers for 60 years.

The plane would have no fuselage or tail; early models resemble a cross between a giant boomerang and a surfboard. What it lacks in stability, it would more than compensate for with unequaled aerodynamic efficiency.

For commercial flight, such a plane could cut by half the time it would take to fly to Tokyo from Los Angeles -- all without burning the massive amounts of fuel that ultimately doomed the Concorde supersonic jet.

For the military, which is paying for Northrop’s design work, the aircraft could fly quickly to a war zone and then loiter at low speeds to extend the time to carry out its mission.

“It’s the holy grail of aerodynamics,” said Joe Pawlowski, the program’s manager.

As a 23-year company veteran, Pawlowski knows a thing or two about chasing grails. He has helped develop many of Northrop’s aircraft, including the radar-evading B-2, the first operational flying wing. He also worked on a pioneering experimental jet that could fly faster than the speed of sound without producing ear-piercing sonic booms.

“To me this is the most difficult challenge we’ve faced,” Pawlowski said of the oblique flying wing. “This is a real hard one.”

In high-speed flight, the aircraft would appear to be flying sideways, with one tip of the wing pivoted forward in the direction the aircraft is flying, while the opposite tip is angled backward.

At slower speeds the wing would be positioned in the traditional alignment to allow for greater control of the aircraft.

The goal for Northrop engineers is to design a plane that can attain supersonic speeds comparable to those of the fastest military jets, but then be able to slow to a glider-like pace.

That combination of capabilities has so far eluded aircraft designers.

When the wing is swept forward, the aircraft would encounter less drag, allowing it to fly faster and far more efficiently than the Concorde.

It also would not require the noisy afterburners that the Concorde used at takeoff. (That English-French collaboration ended in 2003, when the last plane was retired.)

Northrop’s project is being funded by the Pentagon’s research arm, the Defense Advanced Research Projects Agency, whose successes include early funding of the Internet as well as stealth airplanes.

The Pentagon has given Pawlowski and his colleagues $10 million and 20 months to come up with a design that can fly before committing more funds to build a full-size experimental aircraft that would be flight-tested in 2010.

Northrop’s expertise in designing flying wings could push development of the aircraft further than previous attempts, said Richard Aboulafia, aerospace analyst for aviation research firm Teal Group Corp.. But he is skeptical that the team can succeed in building an operational plane.

“It comes around now and then with not much to show for it,” Aboulafia said of the concept. “I think it’s more likely a way for the Pentagon to keep design departments intact. There is a real concern with the diminishing aerodynamic research base.”

The concept of the oblique flying wing seems deceptively simple -- and not unlike riding a snowboard. To gain speed, the rider points the front of the snowboard down the slope. To slow down, the rider angles the snowboard perpendicular to the slope.

In much the same way, the pilot of the flying wing would adjust the sweep of the wing. Pivoting the wing so it is closely aligned with the plane’s direction of travel would reduce drag, allowing the aircraft to go faster. Pivoting the wing so it is perpendicular to the direction of flight would provide added lift for takeoff and maneuvering at slower speeds.

But as any beginning snowboarder can attest, learning to navigate can take days of trial and error, during which the human brain learns how to process millions of calculations to control the interaction of the body, the control system and the snowboard.

As generations of engineers have found, an oblique flying wing is just as intrinsically unstable as a snowboard. The plane would need massive computing power, akin to that of the human brain, to continuously correct its course and attitude.

Since the concept was first proposed by legendary aircraft designer R.T. Jones in the 1940s, NASA, the Pentagon, university research labs and several major aerospace companies have attempted to develop such a craft.

Researchers at Stanford University, with the aid of NASA and Boeing Co., built a 20-foot model in 1994 that flew briefly and reached 65 mph, before the program was canceled because of lack of funding. The team had proved that an oblique wing could stay aloft, but doubts remained whether it could reach supersonic speeds.

Engineers at Northrop believe they have assembled sufficient computing power to rapidly analyze the aircraft’s movement and adjust the controls.

At the same time, advances in flight control systems, such as the digital fly-by-wire system used on B-2 bombers, could increase control of the unstable plane.

“We believe we now have the technology,” Pawlowski said. “It will be a matter of getting all the different technologies together.”

For now, Northrop engineers are focusing on creating the optimal shape for the aircraft and running hundreds of wind tunnel tests of more than a dozen designs.

Once a shape is selected -- candidates have included a wing resembling a boomerang and one that looks like a surfboard -- engineers will have to figure out what kind of propulsion system or jet engine it would have and how that would be mounted on the wing.

People and cargo probably would fly within the wing itself.

The first operational aircraft would probably be unmanned, controlled by computer or remotely by a pilot on the ground.

Aerodynamicists Eric Cooper and Yuto Shinagawa last month demonstrated a 2-foot-long steel model labeled Case M, placing it in a small wind tunnel. The model was one of more than a dozen shapes the Northrop engineers tested.

After adjusting one of the eight flaps on the wings, test engineer Chris Curnes cranked up the wind tunnel, sending 153-mph blasts at the model. As Curnes remotely maneuvered the wing and then pitched it up, it began to shake violently.

“Now that you don’t have a tail, how do you get it to behave?” Cooper mused, as Shinagawa wrote down the results for run No. 481.

“If we can get this to go,” Cooper said, “I think people will look back at these wind tunnel tests as a pivotal moment” in aviation.