Boeing and Rolls-Royce work on a quieter future for commercial aviation

Citation

(2002), "Boeing and Rolls-Royce work on a quieter future for commercial aviation", Aircraft Engineering and Aerospace Technology, Vol. 74 No. 2. https://doi.org/10.1108/aeat.2002.12774bab.013

Boeing and Rolls-Royce work on a quieter future for commercial aviation

Keywords: Boeing Commercial Aeroplanes, Rolls-Royce, Aircraft, Noise levels

Boeing Commercial Aeroplanes and Rolls- Royce Aero Engines recently completed a noise reduction flight test programme that promises to deliver significant further reductions in engine noise for the Boeing 777.

Known as the Quiet Technology Demonstrator (QTD), a Rolls Royce Trent 800 engine was modified with a package of noise reduction technologies developed collaboratively by the two aerospace companies. Using a 777-200ER, the three week flight-test reportedly demonstrated noise levels significantly below those of a standard 777, which is known as one of the quietest aeroplanes in service today. Takeoff jet exhaust noise was said to be reduced by up to four decibels and inlet fan noise was reduced by up to 13 decibels.

Engineers used saw-tooth-shaped aerodynamic devices at the rear of the nacelle and on the exhaust nozzle to control the mixing of the hat jet exhaust, the bypass stream and the ambient air. The shape of the devices was determined by computational fluid dynamics modelling and verified in wind tunnel tests using scale models.

Fan noise also was reported to be reduced with extensive acoustic improvements to the redesigned engine nacelle inlet. A new technology called Amax (area maximisation) increased by 30 percent the area of acoustic treatment in the inlet casing. A new lining design was used that reduces objectionable "buzz saw" noise passengers often hear during takeoff and climb.

The flight tests, conducted at Boeing's Glasgow, Montana airfield are stated to have verified the computer and laboratory results. Some 200 microphones were placed on the ground along the flight path, and 100 microphones were affixed to the 777. Teamed with computers, the microphones became an "acoustic camera" that accurately and dynamically pinpointed high-frequency noise sources on the aeroplane as it took off, flew the flight test pattern and landed again. This ground noise monitoring capability was made possible by NASA sponsorship.

Although the purpose of the QTD program was to reduce noise heard on the ground, levels within the cabin equally important to the airlines also were analysed. Nearly 100 microphones placed along the entire length of the cabin are reported to have registered a reduction of forward cabin buzz-saw noise by seven decibels.

The culmination of years of work, these tests mark one of the final stages before QTD noise reduction technology is implemented in service. Combined with airframe noise reduction and engine redesign efforts being pursued separately, the new technologies can be incorporated on a new aeroplane program or as a retrofit to aeroplanes in service.