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Quiet Cabin

BruceMe

Well Known Member
My non-insulated RV-4 is much noisier than I'd prefer. What is the least weight simplest and effective way to improve it? Bubble wrap, foam insulation, carpet? Wondering what others have done, other posts, articles or ways to make it flyable. Objective results would be best (db lost per lb added)

-Bruce
 
Just adding Carpet made a significant difference to one of our local 7 guys .. he put a layer of foam and then carpet on the floor and in the luggage department .. didn't bother with the side panels it made such a difference.
 
A good ANR headset.
That was my original plan as well, but what I failed to consider was that every time I keyed my mic, all that cockpit noise was being broadcast to ATC. The noise was so loud that they could barely understand me. Here's how I solved that problem:
1. I added sound insulation to the cabin and improved the canopy seals.
2. I added a full 1" of foam insulation to the cabin side of the firewall.
3. I added foam/rubber insulation to the floor.
4. I bought a Sigtronics S-20 headset with a noise-cancelling mic
5. I added a Mic Muff over the microphone
6. I added down turns on my exhaust pipes
7. I adjusted my Icom A-210 as follows:
INCOM LVL = 051
MIC 1 GAIN = 10
MIC SQL = 026​
 
By far, the most effective thing I did on the 1st -4 I owned was to seal up air leaks.

Sealing leaks can be a lot of work, but should add minimal weight and minimal expense.

After that, just a good set of headphones; either noise cancelling or 'plug' type like QT Halos. If ear plugs don't bother you, the passive in-ear models can have noise reduction as good as, or better than the active over-ear models. And no batteries, and no head vise, and no weight on your head.
 

2. I added a full 1" of foam insulation to the cabin side of the firewall.

Careful here, with a fw fwd fire the foam could offgas/melt into stuff you don't want in your lungs. There is a thread on this on the forum, some of the foam insulation breaks down into seriously nasty stuff when heated.
 
...the foam could offgas/melt into stuff you don't want in your lungs.
I used Super Soundproofing Foam from ACS which supposedly "has fire retardant qualities and meets FAR 25.853a Appendix F, Pt1". I have no illusions that the stuff won't burn and give off toxic fumes, but I decided that I would rather take my chances. I did install a temperature sensor in my lower cowling so I would (might) know if there was a fire up front. I also installed a spray header in the engine compartment leading back to a receptacle on my panel that my Halon fire extinguisher will fit into.
 
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Sound Reducing

Bruce
There are sometimes presentations at fly-ins from sound engineers like Oshkosh and others. Their content reduced to the executive summary is:

1. Seal gaps. Gaps is the number 1 source of sound getting into the cabin.
2. Stop vibrations. This is number 2. Use foam with an aluminum foil on one side to add a little weight which changes the natural frequency of aluminum skin so it doesn't vibrate in the wind as much. This is damping. (Note there is no such word as dampening). Sound engrs say, "Dampen vibrations).
3. Absorb noise. This is the least effective, but the most attempted. Just use thick foam or other sound absorbing material. Carpet is an absorb-er.
 
I also installed a spray header in the engine compartment leading back to a receptacle on my panel that my Halon fire extinguisher will fit into.

Has anybody demonstrated that this would work on an engine fire, what with the volume/velocity of air moving around under the cowling? I'm not saying it wouldn't, I'm very curious...
 
I think Dave Anders won a competition for quiet cockpit, and I remember seeing pics of his -4 completely covered in black egg crate foam..Im sure it was quiet, but in my -4, I dont want the sides any closer than the skin for arm room and simplicity. My wife and I both use Halo QT's, and I have never heard anyone tell me I have noise through radio transmission. The Halo's will spoil you and are perfect in the small cockpit for every reason. I don't consider my -4 all that loud actually.
 
Hey, now there's an idea :) Bet I could find enough scrap anechoic foam at work to really deaden the noise LOL! Make the interior look something like this:

100714klabtestphotos07eif.jpg
 
Has anybody demonstrated that this would work on an engine fire..
Not that I know of. I ran the spray bar about 4" fwd of the firewall near the top. Underneath it are the oil filter, oil cooler, gascolator, boost pump, fuel lines, and oil lines. I doubt my little 1 lb. Halon bottle would stop a raging fire, but it might help for long enough for me to get on the ground. "It's experimental" :eek:
 
I think that is a fairly recent change, brought about by the near-universal misuse of the term to the point that it was effectively redefined by our culture.

My thought from going to Scouse skools in the 60's was that the terminology was correct.

It even appears as far back as 1890, written by a colonial...:)

https://books.google.com/books?id=P...hBh4Q6AEITjAH#v=onepage&q="dampening"&f=false

Added - I'll throw this one in for 1898 Marine Engineering...

https://books.google.com/books?id=r...HY4ChDoAQhMMAg#v=onepage&q=dampening &f=false

It may be that millennials actually resurrected the original use of the word... :D
 
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Wing Roots

One other source of noise is the wing roots. The prop blast beats on the wing roots and that drumming can get into the cockpit if not insulated.
 
Look into tacmat

I used dynamat Tacmat, an aerospace thermo-acoustical liner in my T-51 and it made a big difference in temp and noise at a minimal weight. It's made for aircraft cabins and reasonably priced..

Mike
 
So what if Webster has it? Probably written by some Millennial!

No self-respecting Vibration or Flutter Engineer would use the term "dampening". :D It's DAMPING when used in an Engineering context! :D



As an aside, note that the amplitude of vibration can be reduced by adding damping, without necessarily changing the natural frequency of the vibration mode.
Oh my, now this is so funny! ROFLAL!! I am speechless! Engineers arguing over semantics of the use of the English language. :p:p:p
 
It's the improper use of a *technical* term that gets us upset.
Which is the exact point that makes me laugh. One could think of every word as a *technical* word when communicating such as we do on a forum such as this, or for that matter, anytime technical information is being shared in whatever format.

Just a handful of highly *technical* words in the English language that are NOT interchangeable:
Where/were
bring/take
brake/break
ran/run
to/too/two
see/saw/seen
by/buy/bye


Engineers will go to fisticuffs over *technical* words but consider the correctness of the rest of their communication to be inconsequential -
"It is not important that I spell the word correctly or use the correct grammar to explain something as long as the reader can get the gist of what I am saying from the words I choose to use."

Just too funny! :rolleyes:

Oh by the way:
1001100 1001001 1010110 1000101 0100000 1001100 1001111 1001110 1000111 0100000 1000001 1001110 1000100 0100000 1010000 1010010 1001111 1010011 1010000 1000101 1010010
 
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I'm all about the weight. If I drop it, and it doesn't fall UP I don't want it in my plane. :rolleyes:
I bought a Decibel meter (Ebay cheapy) and tested the effect of exhaust system changes when I was running my Turbocharged Mazda Rotary.
If you do not verify your alterations, you might just be adding useless weight!
1) use decibel meter to get a sound pressure baseline
2) Install our new idea
3) repeat baseline test record new data
4) Compare.
5) Remove your new idea if it does not work

A little off topic, but removing my experimental engine and replacing it with a lightened O-360 narrow deck with Catto wood prop netted me a 70 pound weight reduction. I lost about 11 Knots top speed, but gained rate of climb, range and payload. Also gained ability to compete in IAC aerobatics, and That is Something!
 
I used Super Soundproofing Foam from ACS which supposedly "has fire retardant qualities and meets FAR 25.853a Appendix F, Pt1". I have no allusions that the stuff won't burn and give off toxic fumes, but I decided that I would rather take my chances.

In John's defense (and if I recall correctly), his early Lancair firewall is (from front to back) glass or steel sheet, fiberfrax, 3/4 plywood, then more glass. The assembly should not allow the quick ignition of plastic or rubber foam on the cabin side, as heat transfer will be low. Two caveats; any opening not well protected may transfer the fire, as will steel hardware and copper wire.

As for RV builders, the stainless steel firewall will ignite the foam very quickly, and from that point, the only good news is that the smoke may kill before you burn. Don't do it.

I also installed a spray header in the engine compartment leading back to a receptacle on my panel that my Halon fire extinguisher will fit into.

The cowls are set up to provide a minimum cooling air flow of roughly two lbs per second, which (for example) would be about 33 cubic feet per second at 8000 feet. How many cubic feet of Halon is released in one second?
 
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I was able to get the cabin noise in my RV4 down to 91.0 dBA on a short field take off which was read outside the plane in 2 locations, one at the starting point and one at as you passed over it on the departure end. At lower speeds and power settings in cruise you could take off your headset and talk back and forth to the rear passenger in a fairly normal speaking volume.
It all was heavy, complex and very difficult to do it right. It requires the use of the right materials in the different places. If you do a poor job, like miss an 1/8" seam here or there, it decreases it's effectiveness.
Make certain nothing is bumping against anything, and nothing is vibrating.
A quiet prop is essential. I used a special made Whirlwind prop that was 4 dBA quieter then my Hartzell.
A good muffler is necessary. i made mine but even though it was light for a muffler if you threw it up it came back down. It weighed about 7 lbs.
A GREAT canopy seal is required. You wouldn't believe how loud leaks are. Use a dba meter like SHIPCHIEF recommended.
Even with anechoic foam on the thin skins and canopy skirts, you can't do much about the wind noise through our thin canopy glass and as you go faster it just gets louder.
I also placed fiberglass insulation in every compartment under the floor, filling every speck of space, and installed anechoic foam in the baggage compartment behind the passenger seat.
It added about 15+ lbs to the plane and i couldn't wait to take it all back out after the competition.
Just get good noise canceling headset!!!!
 
I think that is a fairly recent change, brought about by the near-universal misuse of the term to the point that it was effectively redefined by our culture.
I fear we have also lost the battle on proper use of apostrophes. The plural of RV is not RV's.
 
If you do a poor job, like miss an 1/8" seam here or there, it decreases it's effectiveness.

Dave is making a point that is often overlooked.

If you have ever been in a high noise industrial environment where a sound proof door is used you would notice that the moment the door is cracked open just a tiny amount, the noise level increases to almost the full level that you will hear with the door fully opened.
 
The examples you list below drive me absolutely buggy as well. My Mom was an English teacher and I strive for precision and correctness in my writing. However, I have become largely inured to the brutality visited on the language by most people on the Internet. I spent years as an engineering manager reviewing reports written by my employees and trying to get them to write better. It pains me that engineers are seen (othen correctly) as not caring about language, and that they often live up to the stereotype.



Just a handful of highly *technical* words in the English language that are NOT interchangeable:
Where/were
bring/take
brake/break
ran/run
to/too/two
see/saw/seen
by/buy/bye


Engineers will go to fisticuffs over *technical* words but consider the correctness of the rest of their communication to be inconsequential -

Just too funny! :rolleyes:

Oh by the way:
1001100 1001001 1010110 1000101 0100000 1001100 1001111 1001110 1000111 0100000 1000001 1001110 1000100 0100000 1010000 1010010 1001111 1010011 1010000 1000101 1010010
 
The examples you list below drive me absolutely buggy as well. My Mom was an English teacher and I strive for precision and correctness in my writing. However, I have become largely inured to the brutality visited on the language by most people on the Internet. I spent years as an engineering manager reviewing reports written by my employees and trying to get them to write better. It pains me that engineers are seen (othen correctly) as not caring about language, and that they often live up to the stereotype.

Spelling, grammar or syntax errors in reports and documents from my engineers drive me nuts. I make them go back and fix them. There's no excuse for it, really.

I get that occasionally, a typo occurs (but that's what proof-reading and review is for). But bad grammar or poor syntax is just a product of not carefully crafting your work. Part of the blame, I think, is the over-reliance on Powerpoint to present work; it causes one to use short phrases, rather than whole sentences. The Intertubes also bear a big share of the blame. English as a second language can have an effect (not "affect"), so I tend to be gentler with non-native speakers. :)

But in the end, it's the person doing the writing who really is at fault.

BTW, as far as aviation-related errors, there are quite a few to go around:
You keep your plane in a *hangar*, not a hanger
You stop the plane with brake *pedals*, not peddles
You *transit* an airspace, you don't transition it
And everyone's favorite in EAB: it's a *condition* inspection, not a conditional inspection.

:)
 
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Dave is making a point that is often overlooked.

If you have ever been in a high noise industrial environment where a sound proof door is used you would notice that the moment the door is cracked open just a tiny amount, the noise level increases to almost the full level that you will hear with the door fully opened.

Boy, I must be prescient. ;-) (See post #7.)

BTW, if you're going to use a dB meter, do yourself a favor & don't use an A weighted meter, if you want an honest noise measurement. The A scale was apparently (er, obviously) invented to give manufacturers a pass when they're required to meet noise level standards. The A scale is an average young human's hearing response curve, at absolute minimum sound levels (think quiet bedroom in the middle of the night, without your a/c running). But that's not what you're worried about. Our concern is our ear's response curve in the area of 100 dB and up, and more importantly, the damage that can be done to your hearing by that noise. Look at the A curve. Trust me, a 100 Hz noise at 100 dB is *not* going to do 1/100th the damage to your hearing that a 1kHz noise at 100dB will do (which is what the A scale says, if you use it to evaluate loud noise).

https://www.noisemeters.com/help/faq/frequency-weighting.asp

https://en.wikipedia.org/wiki/Equal-loudness_contour


Charlie
(no Holiday Inns recently, but sound engineer in a previous life)
 
Boy, I must be prescient. ;-)

Not sure what you mean because the comment I made was not in the context of air leaks (though those are very important also).

I was just re-emphasizing Daves comment that if you go to all of the effort to install materials for noise reduction, even the smallest gaps left untreated can make your efforts largely a waste of time.
 
I'm new to this forum but have read many informative and well reasoned posts that would not have passed muster with any of my esteemed educators many years ago. I had no trouble understanding what they were trying to convey and that's what matters. If we turn this forum into a freshman level English lit exercise these guys will probably take a hike, and justifiable so.

While acknowledging that all the criticisms were probably technically correct (composition was not my forte) some may find these criticisms belittling and/or demeaning.

Give me a minute to pull on my flack vest :)
 
I'm new to this forum but have read many informative and well reasoned posts that would not have passed muster with any of my esteemed educators many years ago. I had no trouble understanding what they were trying to convey and that's what matters.

And you'll note that they are almost *never* criticized for any of those errors in those threads themselves. That would be ?ber-pedantic. But sometimes, these sorts of generalized discussions come up elsewhere, and then I think it's pretty okay and harmless, or at least meant only in the hopes that someone may learn a correct aeronautical term. I, for one, would never call someone out on a post for a spelling or grammar error...very bad netiquette (plus, doing so almost guarantees that the caller-outer will have an error in their own post :) ).
 
And you'll note that they are almost *never* criticized for any of those errors in those threads themselves. That would be über-pedantic. But sometimes, these sorts of generalized discussions come up elsewhere, and then I think it's pretty okay and harmless, or at least meant only in the hopes that someone may learn a correct aeronautical term. I, for one, would never call someone out on a post for a spelling or grammar error...very bad netiquette (plus, doing so almost guarantees that the caller-outer will have an error in their own post :) ).

Phew, hopefully this means my "observation" was free of any gross grammatical, structural or spelling errors. :D Of course, that does not mean I'm simply not full of ****. Someone spent a lot of time constructing the "naughty word" exclusion file for this forum, it just kicked cr#p. It's a shame the same effort cannot be directed to signing up with a cloud outfit that will handle proprietary hosting of the common picture file types.
 
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Spilling

To paraphrase Andrew Jackson our 7th President " It takes a small mind to only be able to spell a word one way "
 
Jon Meacham wrote a rather flattering bio of Jackson (American Lion) a couple of years ago, before lauding the achievements of a populist was blasphemy :) Surprising, considering Jon's political leanings. Many consider Jackson the father of the democratic party, interesting how things change over 195 years.
 
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