GUY NORRIS / LOS ANGELES
Initial results from the Quiet Technology Demonstrator (QTD) test programme show the noise reduction package developed by Boeing and Rolls-Royce is significantly more effective than expected.
The three-week flight test of the modified Trent 800 on an American Airlines-owned 777-200 showed jet noise was cut by up to 4dB, against the 3dB predicted. Inlet fan noise was reduced by 13dB, versus the 7dB initially expected by the engineering test team. Noise reductions were produced by chevrons around the primary and secondary nozzles, as well as by extending the area of the acoustically treated inlet liner by more than 30% over the current Trent 800.
"The test results came out better than we expected, particularly the inlet noise," says Boeing noise engineer Belur Shivashankara.
Two versions of the primary chevron design were tested, one of which was configured with sawtooth extensions protruding deeper into the jet flow. "Both worked pretty well," says Shivashankara, who adds that the overall results also verified the analytical and predictive tools used to develop the shapes in the windtunnel.
Tests of the modified secondary nozzle and revised inlet lining also proved beneficial.
In all, a total of eight major combinations of noise reduction features were tested over more than 60 flight test hours.
Boeing says the evaluation also proved the "producability" of the primary nozzles, which were fabricated by Washington-based Exotic Metals, and the secondary nozzle made at Boeing's Wichita, Kansas operating site.
"Lessons learned" from the tests are now being fed into windtunnel tests of 747 derivatives with low noise nacelles.
Boeing is also expected to begin offering existing 747 customers a low noise upgrade package, incorporating QTD features, in 2003.
Source: Flight International
