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picture of engine nacelleWhat is the purpose of the recent phenomenon of green being seen inside newer turbofan engine nacelles, just to the front of the fan blades?

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    $\begingroup$ Because it's better than black-- that wouldn't contrast with the fan blades, and you'd have less light bouncing around in there during visual inspections. $\endgroup$ Feb 24, 2023 at 19:05

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The green part of the fan case is an acoustic liner, used to dampen the engine noise. The liner is used both in the fan case and on the internal walls of the engine nacelle, but this particular segment is a part of the fan case. (please note that the fan case is an integral part of the engine, and is seperate from the nacelle).

Image 1

Image 2

enter image description here

Why is it painted green? It doesn't appear to be that way for any functional reason, just like there is no functional reason for the cyan colour of the Ultrafan blades; it's only a matter of looks.

In fact, it doesn't have to be painted green. On CFM56 for instance, the acoustic liner is painted white. Image 3

On GEnx, it is painted black, while on Trent XWB it is painted brown/red. So there is no fixed colour of choice for the acoustic liner.

Sources: PW1100: Fan case diagram, Engine image, Engine-on-wing image, Acoustic liner detail ; CFM56: Acoustic panel image.

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    $\begingroup$ I suspect modern liners are dyed, not painted. Paint would compromise its function. $\endgroup$
    – Therac
    May 26, 2023 at 19:25

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