cutting cockpit noise?

[wildirishtime]

After upgrading from a Model 3 Rotax 582 to a Model 5 912ULS, the only complaint I've got - is engine noise in the cockpit. When that 912 cranks over about 4900 or 5000 it gets loud enough my Zulu's even have trouble drowning it out. Any suggestions on effective noise dampening? I have no noise padding anywhere.... a thin sheet seperating the firewall
padding and my feet, but none on the belly under my feet or anything - figured it wasn't doing much so i pulled it last annual

[jrthomas]

I've worn ear plugs along with the headset. It doesn't seem to bother my intercom or radio reception but it sure helps with the engine noise. It's an easy fix that works real well. James Thomas

[Monocock]

What prop are you spinning wildirishtime?

The reason I ask is because when I had a GSC prop the noise was deafening. I then tried out (ie borrowed) a Warp Drive (to solve some vibration issues that the GSC was causing) and it was a little bit quiter. I ended up buying a Kiev on advice from this forum and it is even quiter still, as well as being by far and away the best performer.

I don't think it's all directly the engine noise. Prop and exhaust noise are probably the main contributors. I don't have any soundproofing either, other than the metal fire wall.

I find 4650 (100mph) the most comfy power setting. If I need to get somewhere and I want to see 120mph I go for 5200, but it's certainly a fair bit noisier!!:eek:

[HighWing]

While building my first model IV, I went to an EAA meeting in the SF Bay Area and a sound engineer made the presentation. A couple of things stuck in my mind. Mass is what you need to attenuate noise. To eliminate the transmission of noise - through a thin firewall - you need to bulk up the weight bacause the thin sheet metal just vibrates and the sound passes right through. In aviation, this is not practical, so he gave some alternatives. Much of what we hear is reflected sound that just bounces around our enclosure. Upholstery and carpeting will help there. Then he mantioned a fairly effectve sound absorber which consisted of a rubbery type foam - like the temper foams - which is enhanced by a hard coating on one side like an aluminum skin. I found that ACS had such a thing and used that on the firewall. I also used a half inch foam sheet between the floorboard and bottom fabric to help with exhaust sounds.
Lowell

[wildirishtime]

...highwing you're hitting my question dead on. During my KF5 restoration I took all that crap out of the floorboard cause it was soaked with brake fluid (broken master cyl) and threw it away. Figured I didn't want the mass so I left it out. There is SOME dampening on the firewall side and that's not very efficient at this time to swap.

Do you, or anyone, have any 'before and after' experience to tell me "yes, put that metal back foam in the floorboards will make a measuarable decrease in engine/exhaust noise"?

Thanks guys!
~Wild

[wildirishtime]

Anyone have specific material recommendations they found to provide the best noise reduction? (comparisons preferably?)

[akarmy]

sorry, no comparisons, but this is the stuff I used on my RV9 a few years ago. Just cut it to fit the floor and firewall. Think it would dampen the firewall on the Kitfox, but myself I've not really had that much of an issue with it. I use active headsets which tame the Rotax for the most part.

http://www.aircraftspruce.com/catalog/appages/soundproofinstall.php

[wildirishtime]

I've been eyeballing that stuff and the other stuff from ACS. My noise is enough that my Zulu2's mics pic up a lot of ambient noise when making radio calls, and hearing the COM clearly is not easy at RPM's over 5000.... hoping to get that addressed. Thanks !

[rogerh12]

I "strongly" suggest any noise dampening material you use does not burn or absorb fuel (safety first guys !!!) Does anyone know if that Super Soundproofing Foam Mat for noise control (as linked below) supports combution or not?

[wildirishtime]

I second that question. Also, does anyone know of any online videos, or good online documentation on soundproofing? I am confident there is a lot of science behind it, but I don't find much good info on the EAA website about it strangely enough. Maybe I missed the details - if someone has links please let me know.

[Geowitz]

From Aircraft Spruce's website. It's hidden at the bottom...

"For instructions and lab flammability test reports from FAA certified lab, click here...

http://soundproofing.org/infopages/soundprf.htm "

From that link...

" It is a closed cell vinyl/nitrile insulating material which will not absorb water or oil. Materials that absorb liquids are not suitable because if they get wet, they will promote corrosion and increase their weight. The mat also conserves and blocks heat because it is an insulator. It has fire retardant qualities and we have the manufacturer’s assurance that, in thicknesses over 1/8″, it meets the requirements of FAR 25.853b. Therefore, it is suitable for aircraft use...

The test procedures of F.A.R. 853.b, U.L. 94 or “Class A” are intended only as measurements of the performance of materials under specific controlled conditions. These tests generally mean the material will burn, but not support a flame, or will not support an flame but will create smoke. You can get a good idea about any material you intend to use by burning a scrap of it with a match. Materials used by aircraft manufacturer’s years ago may not even meet present day “standards.” Generally, if a person is responsible for returning a certified aircraft to service as a shop or mechanic, he should use materials that are FAA approved and follow approved procedures. If it is in the experimental category, you can use whatever you wish. For certified aircraft, a letter is included here in this booklet certifying that it meets requirements of F.A.R 25.853b(3). One may wish to place the letter in the aircraft logbook."


This stuff is on my wish list for a future purchase.

[Esser]

Geowitz, For that closed cell stuff would you just do your firewall? Or are you planning on doing the floor as well?

[wildirishtime]

Mine personally has NOTHING on the firewall unfortunately (well a thin rubberized damper pad about 1/16" so I'll be doing the floors first (easiest) and the toekick area since my muffler sits there.... see how that turns out....

[Geowitz]

I'll just be putting that stuff on the interior side of the firewall. 1/2 inch thick and cutting out pieces to fit between the tubing, but if I had known about it before I covered my fuse I would have put it under the floor as well. Right now I do have 1/2 blue foam board (high density blue board from Lowe's) which should work reasonably well under the floor boards, but it's closed up and permanent now.

[rogerh12]

Geowiz;

I had that blue foam on my 601HDS. It worked great but I took it out after my header tank line leaked on it. Just poor some fuel on it and i think you will see what I mean. It just ate it right up to nothing after a while.

When it comes to foam, the high end memory foam I used later would not hardly burn at all and was more fuel resistant. Even with a lighter on it, it would not burn much and as soon as I removed the ligher, it went out. But the good stuff is not so easy to find (I don't know the chemical composition, it came in the seats).

[rogerh12]

I suggest everyone make their floor boards removable so they can access the flight control mounting bolts (so you can remove the control for inspections, greasing and other maintenance). Also, to inspect the airframe under the floors at annual.
I used the wood floor boards as patterns to make aluminum floor boards and they are split in half to allow removal and access to the second half, which of course is held down by the control mounting bolts (now I can access the nuts on the back side). The half-plates not held down by the control mounting bolts are held in place by using nutplates instead of loose nuts (nut plates are used with the rudder peddle mounts too).
It took me a while to figure it all out, but now the floorboards are tight and don't rattle or anything (plus the look kinda cool).

http://barnstormers.com/tmp_images/84/d0/.watermarked_2c3976a6bad78d959adb4a5696838774.jpg

http://barnstormers.com/tmp_images/d3/ce/.watermarked_5a5d201d9567f830e2d6e44fdff5d285.jpg

[jiott]

The SS7 kit's floorboards are easily removable, except for the small piece way forward under the pedal mounts. I used clipnuts on the prewelded floorboard mounting tabs instead of the sheet metal screws that came with the kit. Anyway, on this model, sound insulation could easily be added under the floor at any time.

I wonder if the sound insulation works better on the inboard or engine side of the firewall, without considering ease of installation?

Jim

[Esser]

jiott, that article said to put it on the cabin side. And for additional noise reduction make an engine side with fibreglass batting or any other soft flame resistant material.

[Geowitz]

Yeah, I forgot to mention that. I actually planned on the foam on the inside and a matt like this - http://www.aircraftspruce.com/catalog/eppages/coolit.php or similar on the engine side. I think it'll be plenty quiet enough for a Kitfox.

[High Country]

Sorry to get off topic but i was interested in your aluminum floorboards. how thick are they and how much do they weigh compared to the wooden floorboards

[rogerh12]

HIgh Country:

The Aluminum is just 5052-H33, which I have used before on floor boards for my sonerai and liked it as it is very corrosion resistant , cheapish and easy to work with. These plates are made from 0.040 thickness metal, but are really very stiff with the shimming in place, so I think I could have gone with 0.032 and been just fine. With shimming, seam-locks and large magnesium tube spacers in place (red and green block, see below), the total weight was 3 lbs 11 OZ.

I am not sure what wood floor boards weight, but these things are stiff as heck and strong enough too. Strong enough to act as penetration protect in the even I land on a fence or something.

With smaller spacers and shims, and using 0.032 thick metal, I think I could have built the floor boards under 3 lbs for sure.


Roger




http://barnstormers.com/tmp_images/2f/f0/.watermarked_2d42604ab8a3c5fd97b3aceb5e1afd01.jpg



http://barnstormers.com/tmp_images/20/bf/.watermarked_a5f5afa06d310a136a0a6571d6fbb8ef.jpg




http://barnstormers.com/tmp_images/f2/63/.watermarked_0f129257b8acc8ea2d718e073c9a0866.jpg

[dginok]

I meant to post this earlier. I wonder how this would work for firewall heat and sound reduction.

http://www.eastwood.com/thermo-coustic_barrier_video

[Dave Holl]

sounds good!!!
Wonder how fire resistant? and how heavy?
Dave

[dginok]

Looks like that Eastwood product is 0.75 lb per square foot.

[HansLab]

I always thought there isn't much one can do about sound-proofing in a tube-and-rag plane: you litterly sit next to the engine/prop combination....

Anyway: I used HeatBlock (pointed u=out on this very Forum, though): take a look at their site http://www.heatblok.com/product.html
The material comes with a couple of sheets report about heat, but Volvo uses it as a sound-absorber as well, so I guess that kind of info should be somewhere, out there.

[HighWing]

Looks like that Eastwood product is 0.75 lb per square foot.

Sounds like it fits all the requirements of the sound engineer at the EAA meeting. Heavy to prevent the material simply becoming a sound transmitter, rubbery to absorb vibration and with the aliminum skin. The engineer with a smile suggested we use a sheet of lead. I also like the hearing aid solution, except I suspect the sound is still beating on the ears even though we can't hear it.
Lowell