Airbus and CFMI also move to quieten A321 to meet ICAO Chapter 4 regulations

Boeing is expanding its engine noise reduction programme to test scarfed inlets and treated lips following 777 Quiet Technology Demonstrator (QTD) flight tests last year, which have resulted in design changes being incorporated on the 777 production line.

Boeing technical fellow, environmental performance strategy Belur Shivashankara told the Association Aeronautique et Astronautique de France aircraft noise reduction conference in Arcachon, France, earlier this month that the scarfed inlet proposal would extend the lower lip of the engine inlet, deflecting more sound upwards and shielding the ground from direct fan noise. Boeing hopes to test the inlet on a Pratt & Whitney PW4098-powered 777 next year.

The second concept involves pumping hot bleed air through micro-perforated titanium panels on the inlet lip, and is also due for flight tests next year. Shivashankara says ground tests predict a forward-radiated noise reduction of 3-5dB using the scarf, with a further reduction of up to 10dB promised by inlet lip treatment.

The QTD tests last year involved an American Airlines 777-200ER fitted with a modified Rolls-Royce Trent 800 flying over a phased array of 187 microphones in Glasgow, Montana. The modifications resulted in significant jet and inlet fan noise reductions (Flight International, 20-26 November, 2001). During the programme Boeing engineers noticed a distinct 2kHz tone emanating from the 777's wing leading edge. Shivashankara said: "By taping over de-icing holes on subsequent tests, the tones were eliminated, and Boeing has since incorporated redesigned non-whistling holes on production 777s."

Meanwhile, Airbus and CFM International aim to reduce A321 aircraft and engine noise to comply fully with International Civil Aviation Organisation Chapter 4 noise regulations, and London Heathrow's Quota Count 2 (QC2) noise levels.

The A321's sideline noise levels currently fall outside the limits imposed by these regulations (ICAO Chapter 3 minus 10dB). Airbus and CFMI are to begin flight testing an A321 early next year featuring with a CFM56-5 engine fitted with a chevron nozzle and other noise reducing components from CFMI's wider TECH56 programme. Testing was due to begin this year, but the programme has been pushed back by Airbus.

Source: Flight International