EVENDALE, OHIO - GE Aircraft Engines has been instrumental in helping the United States' aircraft fleet reach an historic aircraft noise reduction milestone.
In a report submitted to Congress, the Transportation Department and the U.S. Federal Aviation Administration declared the nation's commercial jet aircraft fleet the quietest in history, and predicted record-low noise levels into the next century.
The report also states that, for the seventh consecutive year, both foreign aircraft flying into the United States and domestic operators have been ahead of requirements for transitioning to quieter aircraft.
Federal requirements state that all civil aircraft must meet quieter "Stage 3" noise regulations by January 1, 2000. Stage 3 aircraft are roughly five times quieter than Stage 2 aircraft.
While jet engine noise is very complex, with different sounds radiating from different parts of the engine, GE Aircraft Engines has minimized the actual creation of engine noise, as well as muffling the remaining sound, paying particular attention to the most annoying characteristics of sound that humans find most objectionable.
The big fan at the front of modern engines tends to create the two sounds humans find most irritating: the deeper-toned, buzz-saw noises, and the high-pitched whine. The compressor and turbine, and the process of burning fuel, also contribute to the sound. The exhaust makes the most noise of all, especially at full power, as compressed, high-speed gases shear through the surrounding air.
To reduce these noises, GE has been refining the shape, spacing, and number of airfoils in engines, and has been incorporating new types of sound-absorbing materials. In the past ten years, these materials have become lighter and significantly more effective. Engineers are also improving compressor and turbine designs to generate the least amount of sound possible.
GE has made much progress at the exhaust end, also. The newer, large-fan engines compress air to produce thrust much more efficiently than older turbojet engines, and their lower exhaust velocities translate into significantly reduced noise levels.
Most recently, GE's introduction of the GE90 with its higher-than-typical bypass ratio, has set a new standard for engine noise in terms of decibels per pound of thrust. The GE90-powered Boeing 777 is quieter than the CF6-powered Boeing 767, even though the 777 is 35 percent heavier than the 767.
GE's CF6 family is also quiet, with the CF6-80C2 and CF6-80E1 exceeding Stage 3 requirements without any trades in takeoff, sideline, or approach noise levels.
This is also true of CFM56 engines, which are produced by CFM International, a 50/50 joint company between Snecma of France and General Electric of the United States. The CFM56-5C2, for example, features a long-duct, mixed-flow nacelle that produces an acoustic signature that is well below Stage 3 requirements.
GE's new CF34-8C engine, under development to power next-generation regional jets, is designed using the latest technology advances and newest design tools. More stringent airport noise constraints have been factored directly into its design, as well as current and anticipated future certification requirements.
Another good example of progress in noise reduction is provided by the U.S. Air Force's fleet of KC-135 tankers. Replacing their 1950s-technology engines with modern CFM56 powerplants has made an astounding reduction in noise.
"As we move into the 21st century, we at GE, together with the aviation industry, continue our long-standing commitment to the environment by investing in research and development and identifying new technologies that will make today's engines even quieter," said Fred Herzner, chief engineer at GE Aircraft Engines. "It is clear that together, we recognize the need and are fully committed to reducing noise and emissions levels and meeting the challenge of maintaining and improving our environment."