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Cork insulation for noise reduction

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dmac7

Joined: 05 Apr 2019
Posts: 48
Location: Canada

Posted: Tue Aug 29, 2023 6:10 am Post subject: Cork insulation for noise reduction

I have been reading a few article's regarding the properties of cork insulation, light weight, fire resistant, sound absorbing, and thermal insulation properties.  I was wondering if others considered it as a choice for aviation sound control? 



It is used by NASA on the Orion spacecraft and was used on the Space Shuttle fuel tank for thermal insulation.

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Area-51

Joined: 03 May 2021
Posts: 391

Posted: Wed Aug 30, 2023 9:15 am Post subject: Re: Cork insulation for noise reduction

You can use cork for making anything, shoes, wallets, jackets, chopping boards, gaskets, bowls, chairs, plates, doilies, curtains, car panels, emergency boat hull leak repair, pin boards, gloves, boats, canoes, pants, anything. Just go to Portugal and see for yourself! And it does not deteriorate with age either! You can drop it on the floor and it won't break! You can kick it and it just bounces around off stuff.... Terrrrrrible  fire wood though; worst fire wood ever.

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dmac7

Joined: 05 Apr 2019
Posts: 48
Location: Canada

Posted: Thu Aug 31, 2023 2:35 pm Post subject: Re: Cork insulation for noise reduction

Doing a small amount of research we learn that there are two ratings of interest when considering a material for sound control, NRC Noise Reduction Coefficient = sound absorption Cork said to be 0.7 NRC means 70% absorbed 30% reflected at specific frequencies 250, 500, 1000, 2000 HZ

STC Sound Transmission Class = ability to block noise, Cork said to be 89  that makes Cork rather unique it both blocks and absorbs noise, perhaps this is why it passed the lab testing at Airbus so successfully.



I came across a article from 16 years ago on airliners.net saying the next step for airbus was a two year test in the fuselage of one of their jets with Cork insulation. 

Then one must decide the best locations to place it, top cowl & firewall to start I suppose.

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n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Mon Sep 11, 2023 6:59 am Post subject: Re: Cork insulation for noise reduction

One of the things I wanted to address is possibly sound insulation of the wheel well metal firewall so this subject is interesting.



The material could be placed behind the firewall so the cork is not exposed to any direct flames. However, smoke generation would be a consideration. Any info available on that? I would also imagine that if cork is used on an airplane, a specific type should be used that is more suitable from a fire resistance and/or smoke standpoint.



Chris

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JohnFrance

Joined: 17 Sep 2014
Posts: 78
Location: Grenoble France

Posted: Tue Sep 12, 2023 1:57 am Post subject: Re: Cork insulation for noise reduction

Having flown a couple of hours recently in a friend’s WT9 I was amazed how quiet it is compared to my Europa. In the WT9 a conversation is possible even without headsets  whereas my Europa is very uncomfortable with headsets removed. 

I think there is a lot of direct noise transmission through the engine mounts as the rubber mounts are very hard and let’s face it arrives in the cockpit under our feet. 

Does anyone have any information on what lining all the front facing inside walls  of the cockpit module with 3mm of cork might have on sound attenuation?

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_________________
Europa mono Nr 192

peterz(at)zutrasoft.com
Guest

Posted: Tue Sep 12, 2023 2:20 am Post subject: Cork insulation for noise reduction

Indeed when I changed to the softer industry-std Lords for engine mounts, my cabin noise decreased markedly.  I find that at anything over 120knots and the airstream noise is greater than the engine noise. Prop noise (3 blade CS E-prop) is also noticeable over the engine noise.

Cheers,

PeteZ



On Tue, Sep 12, 2023 at 6:11 AM JohnFrance <77alembert(at)gmail.com (77alembert(at)gmail.com)> wrote:



 	  Quote: 	
		  --> Europa-List message posted by: "JohnFrance" <77alembert(at)gmail.com (77alembert(at)gmail.com)>

 

 Having flown a couple of hours recently in a friend’s WT9 I was amazed how quiet it is compared to my Europa. In the WT9 a conversation is possible even without headsets  whereas my Europa is very uncomfortable with headsets removed. 

 I think there is a lot of direct noise transmission through the engine mounts as the rubber mounts are very hard and let’s face it arrives in the cockpit under our feet. 

 Does anyone have any information on what lining all the front facing inside walls  of the cockpit module with 3mm of cork might have on sound attenuation?

 

 --------

 Europa mono Nr 192

 

 

 

 

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 http://forums.matronics.com/viewtopic.php?p=511421#511421

 

 

 

 

 

 

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n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Tue Sep 12, 2023 12:41 pm Post subject: Re: Cork insulation for noise reduction

Today I removed the engine and instrument module in my airplane in preparation for painting the fuselage. It was actually quite easy to do albeit, like everything, it did involve some work.



Although I was initially tempted to remove and insulate the firewall, I looked at it today and honestly don't want to remove it. Too much work and I had enough of disassembling stuff. So if I am going to apply sound insulation it will have to be on the engine side.



One thing I could consider is to try the Lord mounts since the engine is off so it would be easy to try.



I also think that our firewall could be a good source of noise since that thing is a nice drum and could use some sound proofing.



But I also agree with John that the engine mount, being attached to the wheel well, probably acts as a resonator and transmits a good deal of noise to the interior.



Chris

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Area-51

Joined: 03 May 2021
Posts: 391

Posted: Tue Sep 12, 2023 3:13 pm Post subject: Re: Cork insulation for noise reduction

Chris, the firewall from memory is about 6.0mm phenolic material and the drumming qualities are quite different to the rest of the fuselage; higher pitched around 2000hz. If you have a dB app on your phone you can work these out by going around tapping sharply with finger tip and noting all the areas identified. On 181's firewall this is the forward facing footwell surfaces and the upper vertical firewall/cabin surface. Engine vibration travels through the entire airframe.



These surfaces can often act more like a speaker cone vibrating when excited by another "modal" frequency impacting anywhere upon the body.



Technicals aside the DCI produced butyl mat only needs to be applied to 10% of the entire drumming surface area to still be most effective. Other brands will require 20% coverage due to density. It can be applied on the interior side of the firewall.



DCI also produce a 3M adhesive polyester backed AL sheet which I have used successfully lining automotive roof panels; it's very light weight, fire resistant, sound and heat insulating,  applied across entire panel, and looks great when the edges are folded over to form an edge bead.



The 3M adhesive is a "once on never comes off" solution. You get one chance only at putting on. On composites it will tear the base material layer away from the body before it comes away from the adhered surface. So finger tip size tacking points to align followed by soft paint roller application is required.

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