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Several years ago, in an office building near the 787 Dreamliner factory, a small group of Boeing engineers were quietly working on a lofty goal.
"We were trying to make the 787 airplane come out the quietest airplane of its size and capability," recalls noise engineer Mark Sandstrom.
Sandstrom and his colleagues set out to look for ways to make the jetliner quieter from tip to tail, participating in every facet of the Dreamliner's design.
In the video above, you can hear the results as two 787 test airplanes were brought to Glasgow, Montana for tests of its community noise levels.
First, flight test engineers embedded ultra-sensitive microphones along the runway of a secluded airfield. Then, Boeing test pilots performed multiple takeoffs and approaches, testing each engine thrust setting to see how much noise the airplane generated.
The 787's noise footprint will be as much as 60% smaller than today's comparable airplanes.
"For the approaches, you'll come in, you'll pitch the airplane over," says Boeing test pilot Captain Craig Bomben. "You have to pitch over at a certain location and then the pilot's responsibility is to hold air speed as constantly as possible. Any deviations in air speed up to say 5 knots, 4 to 5 knots, could affect the signature of the airplane as it goes through the air.
For many of the test conditions, the 787 is so quiet as it approaches that you can hear birds chirping and cameras clicking until the airplane is right on top of the runway.
"We have to publish numbers to the one-tenth of a decibel, which is your human ear can't hear the difference," explains Sandstrom. "We have to define to that level of numerical precision."
Early data show the 787's noise footprint will be as much as 60% smaller than today's comparable airplanes, thanks to a host of design improvements.
Sandstrom says the 787's lightweight composite fuselage and more aerodynamic wing don't just help the airplane fly more efficiently, it also affects what people hear on the ground.
"If you climb higher on the same amount of energy and fuel, you've gotten further away from ears and microphones," says Sandstrom.
The results represent a big leap not only for Boeing but for the aviation industry.
"We have gone to great strides to try to reduce the noise signature of the airplanes to be better stewards of the environment, better stewards of the community," says Capt. Bomben.
"We can't expect to grow the number of airplanes higher and higher unless their environmental impact is minimized," says Sandstrom.