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Engine duct dimples

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Engine duct dimples

Old 28th Jan 2015, 06:08
  #1 (permalink)  
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Join Date: Sep 2008
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Engine duct dimples

Could find anything with a bit of a Google search, so I thought I would put it out there on the forum - with the engine intake of the turboprop I fly I've noticed the surface inside appears dimpled. Is this an intentional design (similar to golf ball dimples and the air flow around) or is it another reason, perhaps to do with rigidity?

Cheers all.
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Old 28th Jan 2015, 08:12
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Join Date: Jun 2001
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A picture is worth a thousand words.

Or maybe more specific information, like make and model.
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Old 28th Jan 2015, 09:44
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Without a photo this is just a guess........... Noise reduction measures.
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Old 28th Jan 2015, 10:16
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The type You refer to would be good to know. If it is the DH8, the lower innards of the engine intake are made from composite material; the honeycomb structure of the middle layer is rather well visible. As the main source of noise is the propeller and not so much the compressor (which is pretty much shielded behind a rather complicated duct structure), there are none of those noise reducing resonance holes that can be found on jet engines.

So my money would be on a bare composite structure that just happens to look like this without any bad intentions behind it.
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Old 28th Jan 2015, 13:58
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Another guess given the lack of a picture:

Certain manufacturers put dimples in the surfaces of the bass reinforcement ducts of their loudspeakers. They do this to "reduce turbulence [of the resonating air] and therefore improve the bass sound"

So if you are talking about dimples (as opposed to holes which are for noise reduction), maybe they are to reduce turbulence in the air intake?
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