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Boeing
and General Electric have successfully completed airplane engine ground testing on noise-reduction improvements being incorporated into
the new Boeing 747-8. The test conducted by Boeing and GE indicates the 747-8
should meet its targets for noise reduction.
The three-week ground test on a GE90-115B engine conducted at GE's test facility in Peebles, Ohio, focused on noise-reduction technologies
planned for incorporation into the engine case and nacelle of GE's GEnx-2B, which will power the 747-8. An elaborate array of monitoring
equipment and microphones recorded engine operating conditions and noise levels at multiple locations in and around the engine. The test
results, combined with other noise-reduction technology applied to the 747-8, show projected reduction in noise levels on the order of 10
decibels (dB) relative to the 747-400. This noise reduction puts the 747-8 10 dB below International Civil Aviation Organization (ICAO) Chapter 4
standards.
"These results demonstrate our effort to design the 747-8 with the community and environment in mind," said Dan Mooney, vice president of the
747/747-8 Program, Boeing Commercial Airplanes. "The GEnx engine will play a key
role in achieving a 30% smaller noise footprint than its predecessor."
The GEnx engine nacelle will be fitted with a one-piece, sound-absorbent acoustic inlet liner, which will extend approximately one foot into the
forward fan case. This liner, along with the larger 104-inch fan diameter of the GEnx engine nearly doubles the noise absorption area and
reduces the weight compared to current designs in production.
The engine nacelle also will incorporate chevrons on both the hot-core-exhaust and fan-bypass nozzles. Each fan chevron will have a different
size and shape to take into account the three-dimensional nature of engine exhaust flow. The chevrons mix the air coming from the engine's
exhaust, reducing the turbulence and noise at takeoff, as well as the low-frequency noise heard in the aft cabin during climb and cruise.
"These new technologies are just part of noise-reduction improvements being made to the 747-8," said Billy Glover, director of Environmental
Strategy, Boeing Commercial Airplanes. "The engine nacelle will work in concert with the new GEnx engine, new wing design and
flight-management computer to further reduce the 747-8 noise levels."
Boeing is designing the 747-8 to meet the London Quota Count (QC) 2 metric, which dictates operating hours both into, and out of, London-area
airports based on noise levels. The 747-8 will meet the noise requirements for QC 2 classification on both Arrivals and Departures, and also has
a significant chance of achieving the next lower classification level (QC 1) for Arrival. This will allow operation at the major London airports
without a noise-imposed curfew.
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