BOEING IS about to submit "better than expected" noise data on the 777 to the US and European Joint Airworthiness Authorities. The noise data are essential for the type to qualify under Stage 3 requirements at certification, expected in late April 1995.
Boeing 777 noise-engineering supervisor, Billy Glover, says that Boeing is "...doing better than we predicted and the overall 85dBA footprint area is smaller than expected."
Flight data show that the Pratt & Whitney PW4084-powered 777 is "within 1dB" of 1993 predictions for approach, cutback, take-off and sideline noise, and in all cases is no less than 4.5EPNdB (environmentally perceived noise decibels) below Stage 3 limits.
Of the four major noise parameters, it is only the sideline measurement where the aircraft is noisier than expected. Flight data indicate noise levels of -6EPNdB relative to Stage 3, compared with predictions of nearly -7.
"If it has to be over anywhere, that's the best area," says Glover. "We're in very good shape on approach-noise levels," he says, adding that most of the noise is produced by airframe noise.
Interior noise levels are "right on nominal", although Glover says that the profile (noise) "...increases as you go back towards the rear of the cabin, as do the low-frequency sounds". Flight-test engineers aimed for an internal noise target of around 75-80dBA during the cruise, which is similar to the 767.
Meanwhile, Boeing is expected to begin the first static noise tests of the Rolls-Royce Trent 800 by the end of January, with noise flight-testing expected in late August 1995. Static tests of the General Electric GE90 are due in February and noise-measuring flight tests are expected in April and May 1995. A static mini-test of the GE90 was completed in December 1994.
Source: Flight International
