Pratt & Whitney is studying a "technical package" to hushkit JT9D engines to meet prospective Stage 4 noise rulesthat could be adopted by the International Civil Aviation Organisation as early as 2001.

Legislation is likely to require noise levels between 8dB and 11dB (as measured cumulatively) below current Stage 3 levels, placing the new limits beyond the reach of untreated JT9Ds. These were the first generation of high-bypass turbofans to enter commercial service, on the Boeing 747 in 1970. P&W estimates that over 2,500 JT9Ds are in service powering over 600 Airbus A300/A310s, Boeing 747s, 767s and McDonnell Douglas DC-10s.

The engine maker says the package will be offered if there is enough market interest and if the unknown factors surrounding the limits of Stage 4 and its implementation timetable are decided, says P&W. Another pre-requisite for the go-ahead of the JT9D hushkit will be clarification of the re-certification laws at the centre of a dispute between the European Union and USA. "This has got to be ready before we develop a hushkit for the engine," says P&W acoustics project engineer, Ernie Hinterkeuser.

The technical package under study draws on developments made for the PW2000 and PW4000 series, as well as the latest computer-based design methods used for the PW6000 and PW8000 projects. "We will look at improved acoustic liner designs and increased acoustic liner areas in the nacelles, the latter thanks to improved manufacturing techniques," says Hinterkeuser.

Other potential noise reduction work is focused on optimising the blade and stator counts of rotating stages, pylon flow matching and introducing sweep to fan stators. P&W says it is also examining "contour nozzles", or tabs on the exit of the primary nozzle. These metallic devices will promote greater mixing of the jet and free-flow air, and act in a similar way to General Electric's chevron nozzle.

Source: Flight International