Morphing engines might cut aeroplane noise

Paul Marks, senior technology correspondent

(Image: Paul Marks)

You may have heard of research into planes with more aerodynamically-efficient 'morphing' wing tips but how about morphing engines? A Boeing executive said today that in a bid to further cut airliner noise on future planes, smart engine enclosures that change shape in flight are being studied by the firm's design engineers.

Anyone who's seen Boeing's 787 airliner will have seen the cookie-cutter 'chevron' shapes cut into the rear of the jet engine. These cause destructive interference by mixing the emerging hot air blasting out of the jet core with the draggy eddy currents generated as the engine bites into the airflow around the engine. At the airport this reduces engine noise by 15 decibels and in the rear cabin by between 4 to 6 decibels.

But the technology could be even better at its job if it were subtly adaptive to flight conditions, says Boeing vice-president Randy Tinseth, who was unveiling plans for the firm's next version of its veteran workhorse jet, the 737, at the Royal Aeronautical Society in London today. While the 737 Max, as it is called, will have static chevrons when launched in 2017, that may not always be the case.

"One of the things we're looking at for the future is how airplane materials can change their characteristics as a flight progresses. And one of the things we're looking at, for example, is moving and changing the chevron shape so they optimise the noise footprint at different phases of flight," Tinseth says.

Boeing tested the basic principle in 2005, using a "temperature reactive alloy" that warped the chevrons on a test 777 engine into its jet exhaust to reduce noise during the high thrust of take-off. But a more graduated response is needed. "The technology isn't here today," says Tinseth. "But we're looking for the types of materials that can do it."

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