Ssshhh, we're flying a plane around here

A Boeing-led team is working to make quiet jetliners even quieter

BY BOB BURNETT

Every morning, usually before dawn, Boeing test pilots take off from an isolated Montana airstrip in an experimental 777 jetliner to see how quietly they can fly.

Equipped with a specially modified engine and packed with microphones and other sound-measuring equipment, the aircraft—the Quiet Technology Demonstrator Two—is the focus of a remarkable collaborative research and development program. The ultimate goal: to reduce cabin and community noise to the point where it is no longer an issue for passengers or people who live near airports.

A small army of engineers and technicians aboard the plane and on the ground use computers to generate acoustic maps and graphs to pinpoint specific noise sources and document noise reductions. Microphones are draped across the airplane seats and positioned on the runway to record every sound.

This was the scene during three weeks of QTD2 flight testing last August at Boeing's Glasgow Flight Test Center, a former Cold War bomber base in a remote corner of northeast Montana.

Today's jetliners are dramatically quieter than their predecessors. But the next generation—beginning with the Boeing 787 Dreamliner—will be significantly quieter.

"This demonstration program is the perfect mechanism for us and our partners to work together and accelerate the development of noise-reduction technology," says Walt Gillette,
Boeing Commercial Airplanes vice president for 787 Engineering, Manufacturing, and Partner Alignment.

Boeing and its QTD2 partners—General Electric Aircraft Engines, Goodrich Corporation, NASA, and All Nippon Airways—made significant progress toward that long-term goal during testing.

"This program achieved or exceeded all our expectations," says Gillette. "What we learned from QTD2 will help make the 787 better for people—better for the passengers inside the airplane, and better for the people who live in the communities around airports."

Gillette says the sound-reduction measures validated by QTD2 would permit the 787 to fly later at night and earlier in the morning, "giving airlines and airports more flight operations without having to add runways or terminals."

"We see this technology making a big difference on the 787, the 747 Advanced, the next-generation single-aisle airplane, and all new generations of aircraft from here forward," he says.

Noise reduced as fleet doubles

Boeing estimates a worldwide market for 25,700 new aircraft over the next 20 years—doubling the size of the current fleet. Reducing airplane noise is critical because airport noise regulations are increasingly stringent, especially in the hot Asian and European markets.

QTD2 targeted two of the biggest sources of airplane noise: the engines and the landing gear. To attenuate sound generated by the fan at the front of the engine, Boeing and Goodrich developed a one-piece acoustic barrel to line the inside of the engine nacelle inlet and also redesigned the inlet lip to enable sound-absorption without compromising deicing effectiveness. The barrel liner and the lip liner make almost the entire inner wall of the nacelle inlet sound absorbent.

To combat the sound of jet-blast from the rear of the engine, Boeing, General Electric, and NASA developed serrated edges called chevrons for the back of the nacelle and the engine exhaust nozzle. The chevrons reduce jet blast noise by controlling the way the air mixes after passing through and around the engine.

The acoustic liners and chevrons are such effective noise suppressors that several hundred pounds of sound insulation may be eliminated from the fuselage. Less weight translates to greater operational efficiency for airlines.

The team also tested variable-geometry chevrons made with a temperature-reactive alloy. These "smart" chevrons automatically warp into the jet exhaust flow to reduce noise during takeoff and landing and revert to a streamlined position at cruise altitude.

NASA and Goodrich developed toboggan-like fairings installed between the main landing-gear wheels to reduce the sound the landing gear makes when it is deployed into the ambient flow. NASA also provided computer-modeling software, hardware, and wind-tunnel testing.

All Nippon Airways let Boeing use the airline's newest Boeing 777-300ER as a flying testbed. Equipped with General Electric GE90-115B engines, the 777 is an excellent yardstick for noise testing because it is already the quietest airplane in its class.

"This brand-new airplane is a very valuable piece of equipment for All Nippon Airways, and yet they let us borrow it for a month because they valued what we were doing for them and their passengers," says Gillette. "It is really important that Boeing has an airline partner like ANA who has vision for the future, just like we do."

Where the rubber leaves the runway

During flight testing, Boeing test pilots Mike Carriker, Van Chaney, Mark Feuerstein, and Christine Walsh logged almost 80 hours of precision flying as they followed predetermined tracks around the airport to simulate takeoff, climb, cruise and landing without actually touching down on the runway. It required precision flying skills.

"It takes a lot of concentration to put the airplane exactly where the engineers expect it to be," Chaney, says. "You're required to maintain airplane heading, pitch, thrust, and airspeed within very, very tight tolerances. And then you throw in the weather, the wind and the thermal activity, and it's a challenge."

The ANA 777's left engine was a standard production model, but the team repeatedly modified the right engine to test the nacelle liners and various chevron options.

"We are always looking to improve the environmental characteristics of our product," says Gareth Richards, the GE-90 program manager for General Electric Aircraft Engines. "We are using the GE-90 as the vehicle for this testing because it's the framework of a whole family of new engines, including the GENX engines for the 787. Features of this technology program will find their way into production very quickly."

Colin Cramp, vice president for Research and Development, Quality, Technical Compliance and Manufacturing Technology, Goodrich Aerostructures, says the Montana flight tests showcased the QTD team's technical depth, commitment and professionalism.

"We have Ph.D.s through skilled technicians and mechanics, and they all work very well together," he says. "It's great to be working with partners on technology that is so near to coming to market. ...I'm already thinking about how to transition from a development program and put this into production."

"It's a really great example of collaborative R&D," says Dan Mooney, Boeing Commercial Airplanes vice president for Product Development. "Each partner brought a certain expertise and technology background to the table. Everybody shared the development costs, and Boeing integrated it into the airplane."

"This program is a marvelous example of how we can work together," echoed Herb Schlickenmaier, NASA deputy director for Vehicle Systems. "None of us individually could produce this technology. But together: wow!"

It was the second time in four years that acoustics researchers have descended on Glasgow. Some of the noise-reduction technologies validated by the first Quiet Technology Demonstrator program in 2001 have already been implemented on current-production 777s and designed into the 787, which will enter service in 2008.

"Everyone understood the importance of the program, and they were excited about doing something so useful," says Belur Shivashankara, QTD2 program manager. "There is a tremendous amount of ownership and enthusiasm. With its extensive flight-test program, QTD2 represented a significant investment from the program partners."