Noise-reducing technology on engine nacelle put through paces as part of collaborative research project

Boeing is preparing to begin flight tests of an engine nacelle equipped with “smart” noise-reducing chevrons on its Quiet Technology Demonstrator 2 (QDT 2).

Boeing Big

The effort is a collaborative research and development programme with General Electric, Goodrich Aerospace, NASA and All Nippon Airways, which is loaning a 777-300ER. The aircraft has been flying since the start of August with a modified nacelle on one side, and is expected to complete these tests around 23 August. The initial phase included tests of a new inlet lip with in-built noise-reduction treatment, a one-piece inlet liner and chevrons on the primary and secondary exhaust nozzles.

The next phase, due to start around mid-August, will include tests of a revised nacelle configuration that includes variable-geometry chevrons on the fan cowl. The chevrons are made of a sandwich including composite material and Nitinol (nickel titanium Naval Ordnance Lab), a shape-memory alloy that automatically bends into the airflow to reduce noise for take-off and landing, but which in cruise also reverts to streamlined position automatically.

The alloy reacts to temperature and will be trained to bend inwards with higher temperatures and return to “normal” when cooled by the lower temperatures at cruise. The combination of the inlet treatment and chevrons, either variable-geometry or non-moving, is generating “noticeable” noise reductions both outside the aircraft and within the cabin, particularly in the forward section, which suffers traditionally from “buzzsaw” fan noise, and the aft cabin, which encounters sonic shock interactions from the exhaust.

Full results will be known at the end of August. The tests are the second series of noise evaluations, and follow an earlier QTD1 programme conducted in 2001 with Rolls-Royce. These proved the effectiveness of the chevrons and other features. “QTD 2 is giving us a chance to validate that technology,” says Boeing product development vice-president Dan Mooney.

“It also gives us a chance to show off even more new technologies, such as the shape-memory alloy chevrons and the undercarriage fairings. It also gives us a chance to migrate this technology earlier into the product line,” he adds.

Around 70 flights have been conducted so far, with about 120 more expected to be made by the end of the programme.



Source: Flight International