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  • Canada, US Step up War on Airframe Noise
    Posted by Graham Warwick 2:29 PM on Oct 27, 2011

    As engines get quieter, airframe-generated sound is becoming a dominant contributor to aircraft noise on the approach to landing. As a result, research is accelerating into understanding airframe noise and developing quieter landing gear and flaps.

    Key to this is the availability of design tools and test facilities to isolate the noise sources, understand their interaction and evaluate solutions. To that end,
    Canada's National Research Council (NRC) has commissioned a wind tunnel to help manufacturers measure the noise generated by landing gear.

    blog post photo
    Photo: NRC Aerospace

    In Ottawa, one of the eight tunnels operated by NRC Aerospace has been fitted with an acoustic liner and precision noise-measurement equipment. This tunnel can simulate conditions during landing-gear deployment and on approach, at speeds up to 150kt. Using the tunnel, NRC can measure the noise generated by airflow around each component as well as that caused by components interacting. 

    So far, NRC Aerospace has tested a full-scale Bombardier Learjet 60 landing gear. “We looked at the gear struts and axles individually, but also the interaction between such components,” says researcher Jerry Syms. “The drag-strut/main-strut combination, gear doors, brake lines, wheel wells and other components generate enough noise on their own to merit attention.”

    NASA, meanwhile, has completed initial tests on a Goodrich-designed quiet main gear (below) in a wind tunnel at Virginia Tech {info updated - see note* below). This is to be followed by tests of the 18%-scale G550 model in NASA Langley's 14x22ft tunnel as part of a colloborative effort with Gulfstream that is planned to lead to acoustic flight tests of the most promising noise-reduction technologies in 2013 or 2014.


    blog post photo

    Goodrich quiet gear (left) and pressure fluctuations before (middle) and after (right) modification - blue is good, red bad for noise (Graphic: NASA)

    NASA conducted baseline tests on the quiet gear in September, and says full acoustic tests are planned for next year after an improved noise measurement array is installed in the Langley tunnel. Gulfstream and NASA are also looking at ways to reduce flap noise on the approach. These include the Flexible Side-Edge Link (FLEXSEL) - a flexible panel that fills the gap between wing and flap edges (below, left), as well as flap edges that are porous or use metallic rods (below, right) to reduce noise.


    blog post photo
    Graphic: NASA


    UPDATE: Nasa says "The Goodrich quiet main landing gear model, jointly designed by NASA and its partners Goodrich, Gulfstream, and Exa, was tested in the Virginia Tech wind tunnel by Avec Company (under contract to Goodrich) during September 6-14. The test was focused on obtaining aeroacoustic measurements of the quiet gear model as a standalone component with and without the noise reduction concepts installed. 

    "More than eighty configurations were studied during the six days of tunnel entry including the baseline, solid fairings, NASA developed porous fairings, and other combinations.  A preliminary analysis of the measured acoustic data revealed that moderate to substantial levels of noise reduction, both in the sideline and flyover directions, were achieved. This corroborated the computationally driven noise reduction design process."



    Tags: awt, environment, NASA

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