Noise Reduction Insulation Techniques?!?!?

Discussion in 'General Experimental Aviation Questions' started by HomeBuilt101, Jan 24, 2016.

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  1. Jan 26, 2016 #41

    SVSUSteve

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    For the behind the panel, etc....the option for extinguishing is the same as an engine compartment fire: basically use one of the little extinguishers that remotely deploy which are sold for racing.

    I figured it was partly a bad choice of words. You're one of the brighter folks on the forum and thus the idea of blindly following any suggestion didn't seem to fit with my experience with you.

    My first time in an RV made me wonder what all the fuss was about actually. It was one of the noisiest closed cockpits I have over been in even with, as you said, headphones on. They handle beautifully though- if anything a little too responsive but it fits with the "poor man's fighter" look- and I guess that's an acceptable tradeoff for the thousands of people who own them. I certainly wouldn't turn up my nose at one and completely understand why they are basically the yardstick against which homebuilts are generally judged.

    I don't want quite business jet plush either (mostly because that sort of luxury makes me want to sleep and/or drink when sitting in it) but I also don't want to feel like I found my "getting from point A to point B" ride by jacking it from the poor end of a grass strip either or that I got lazy and never finished the cockpit. There's a happy medium somewhere in the middle there.

    Thanks for all of the other input. I appreciate getting my views questioned, critiqued and corrected when necessary by those with the experience and education to be able to point me in the right direction.
     
  2. Jan 26, 2016 #42

    Midniteoyl

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    What am I missing here? I sure thought that anyone running a water cooled engine would simply and logically use a heater core.. At least to me it seemed so logical that I didnt even think of any other way.
     
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  3. Jan 26, 2016 #43

    SVSUSteve

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    Bob's idea: "Here's another thought--how about a system with a heat exchanger that uses exhaust heat to heat a glycol/water mix that you can pipe into the cabin to another heat exchanger? I bet such a system wouldn't need more than about half a gallon of liquid. It would require some specialized parts and plumbing, but would not have the inherent CO risk of a typical heater muff, nor would it add any load to the engine."

    Basically, the same concept you'd see on a liquid cooled engine but on an air-cooled one. You have a heater muff but instead of running the heated air back through the firewall you run a heated liquid which then heats the ventilation system. Other than a small pump and some insulation....sounds pretty straightforward.
     
  4. Jan 26, 2016 #44

    BJC

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    Steve:

    150 amps for avionics? Building something custom with redundant Crays?


    BJC
     
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  5. Jan 26, 2016 #45

    rv6ejguy

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    Just looking at this thread now. Yes, Marc, I think between the flight testing Dan and me did, we can conclude that liquid cooling is more efficient overall than air cooling. Always wanted to put that one to rest...

    I use a coolant heat exchanger in my drafty RV6A slider and it works very well down to my personal limit of about -15C to get into the thing.

    Lycoming RVs have a lot of noise from the exhaust pulses drumming the floor skin. My turbo Subie is much quieter than most of those but still not very quiet.

    The turbo takes a lot of the bark out of the exhaust note as well.
     
    Last edited: Jan 27, 2016
  6. Jan 27, 2016 #46

    Marc Zeitlin

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    So the question would be, what's the definition of "efficiency" here. I would argue that efficiency is defined as the minimum possible power consumed by the cooling system divided by the actual power consumed by the cooling system. So the comparison of two cooling systems would be a measurement of the relative power consumed by the cooling systems. One way to achieve this comparison (but hardly the only way) would be to install a best-case air cooling system on an air-cooled engine of a given HP on an aircraft and measure the speed at various power outputs. Then, without modifying ANYTHING on the aircraft except the cooling system (inlets identical, outlets identical, CG identical, weight identical, etc.), measure the speed of the aircraft at the same various power outputs. Obviously the second case would have to have a liquid cooled engine which can make the same power at the same RPM as the air-cooled engine, but other than that, nothing would be allowed to change.

    I will agree 100% that most air-cooled engines have FAR from optimal cooling systems, and that there's a lot of improvement that's possible (witness some of the aftermarket kits available for certificated aircraft, as well as the infinitesimally small inlets on many optimized racing aircraft), and that at least in theory it's easier to optimize the cooling of liquid cooled engines due to the flexibility of radiator shapes and positioning, but if we're comparing the theoretical cooling efficiencies, there's nothing that says that liquid cooling is more efficient. More flexible, probably. Easier to optimize, also probably. But that's not the same as more efficient, which was the original claim.
     
  7. Jan 27, 2016 #47

    rv6ejguy

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    Dan did extensive instrumented testing on his modified RV8 (adjustable cowl flap) with temperature probes and pressure probes throughout. I did the same on my RV6A liquid cooled design. You'll find lots of information here on HBA regarding the test and conclusions plus I wrote a Kitplanes article on my testing.

    To sum up the main points:

    1. Liquid cooling uses slightly less mass flow per unit temperature than air cooling due to much higher heat transfer rates of radiators vs. engine cooling fins despite the much higher delta T in air cooled installations. Less mass flow. That is more efficient.

    2. Optimized liquid cooled systems have substantially lower momentum losses compared to air cooled installations. I was able to generate net thrust in my installation at coolant temperatures above 75C. Air cooled momentum never gets anywhere close to parity. That is less drag= more efficient.

    Mass X momentum loss = cooling drag.

    I spent over 400 hours converting my cooling system over to something more efficient, instrumenting and flight testing it to prove/ disprove the the generally held notions and conjecture about the topic and assumptions that it was all about delta T and that liquid cooling couldn't be as efficient. This also goes without saying that my installation on an RV is far from being fully optimized compared to a clean sheet design. On an air cooled layout, little can be done past what Dan has done on his -8 to avoid the known losses.
     
    Last edited: Jan 27, 2016
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  8. Jan 27, 2016 #48

    SVSUSteve

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    There's a lot of redundancy in the avionics but it's not quite that level of computing power. LOL

    It'll probably end up being a lot less. I don't have the spreadsheet on my laptop at the moment but since it's mainly a matter of designing for structural loads at this point I figured it's best to assume the worst (having to install the 150 A alternator) and then not need that weight than to have to go back and beef up the engine mount later.
     
  9. Jan 27, 2016 #49

    gtae07

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    Ooooooooh... I like that idea.

    <ponders>

    I'll probably have time to kill while I save up for the engine and avionics...

    <ponders more>

    Sounds like a good, fun project! :grin: And it's a systems project, so it's something right up my alley for once!
     
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  10. Jan 27, 2016 #50

    Himat

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    Or an oil - water heat exchanger in series with the oil cooler?
     
  11. Jan 27, 2016 #51

    Himat

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    This an interesting observation. To me it then look like other RV's could be made quieter with revising where and how the exhaust system ends. Adding a longer tail pipe might make for a quieter ride.

    I searched for an illustration with a long tail pipe and did find this image, that might not be representative but lead to some observations:
    [​IMG]

    First, there is the heating muff. If the air do come from the engine compartment and not an external intake, a leaking exhaust, not only a leaking heating muff can give CO poisoning. Next trouble is that with any oil leak or other malfunction that gasses of, the gasses can enter the cabin.

    Next, back to acoustics and interior noise. By taking ventilation air from or trough the engine compartment a path for noise to enter the cabin have been provided. Depending on the details, the ventilation air intake will not only provide air, clean or polluted, to the cockpit, but also a noise source. Moving the ventilation air intake to take air from the outside of the plane will probably make a quieter cockpit.

    Actually the pictured solution for cockpit heat do look bad to me. There is the possibility of noise and polluted air entering the cockpit and it may breach the firewall in case of a engine compartment fire. Probably the only good thing with this system is the long tail pipe muffling the exhaust noise and emitting it aft of the cockpit.

    Edit, added picture of a Rallye with twin long muffled tailpipes.
    This have been installed to lover environmental noise impact, but they may prove a quieter cockpit too.
    (I have seen other Rallye airplanes with a single long muffled tailpipe on the engine exhaust sysem.)
    [​IMG]
     
    Last edited: Jan 27, 2016
  12. Jan 27, 2016 #52

    NoStealth

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    I haven't heard anyone suggest an extra shielded oil cooler as a heat exchanger in the cockpit - could be plumbed many ways.
    There is a lot to said for the simplicity of an easy to check-remove-install heat muff.
    I have also had-seen a number of electrical fires and vehicles burn to the ground.

    I highly recommend people take a look at the flammability of stuff in the cockpit..
     
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  13. Oct 12, 2019 #53

    DanH

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    If I may correct a few misconceptions...

    The FAA test standard for firewalls is 5" x 5" patch at 2000F for 15 minutes. Although one might argue the standard is excessive or unrealistic, it remains the standard.

    Many firewall products are advertised as meeting FAR 25-853. That particular standard applies to cabin wall insulation, as found in big tube airliners. FAR 253.853 materials are fire resistant, not fireproof. Although a fine choice for cabin walls, the standard has nothing to do with firewalls. In fact , FAR 25 has nothing to do with small GA aircraft. Think Little Johnny playing with his father's cigarette lighter in the bathroom.

    Testing examined the performance of various materials placed in contact with the 25 sq inch hot patch. No material was ever exposed to open flame; the test materials were heated only by contact with, and radiation from, the red hot SS sheet. Very few materials were found acceptable, the criteria being limited smoke and no open flame. Quite a few popular "firewall insulation" products are outrageously bad, in particular the rubber and/or plastic variety. One popular product, when investigated, turned out to be Thermozite polyester based fiber...recycled plastic water bottles. It ignited less than 15 seconds into the test. This photo was taken at about 30 seconds. Good luck with detecting an engine compartment fire and shutting off the fuel.

    [​IMG]

    The only tested materials found to be fire safe on the cabin side were classic ceramic wool refractory products which did not incorporate an organic binder. However, those products generally come with a fiber-based cancer risk, so if used, they must be fully encapsulated in an envelope. BTW, common Fiberfrax felt was not acceptable on the cabin side; the organic binder is flammable.

    In the end, the only practical approach was insulating the forward side of the firewall. I'm not going into it here, except to say the basic principle is to place a reflector over an insulator. The common, very practical installation is a 1/16" or 1/8" layer of fiberfrax felt under a very thin stainless steel foil. In the event of an engine compartment fire, it will prevent the cabin side from glowing red hot and radiating like a toaster oven. In normal operation, the cabin side will be comfortable.

    I don't care if anyone does or does not insulate the forward side. The key point is simply "Don't put stupid things on the cabin side of a metal firewall".
     
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  14. Oct 12, 2019 #54

    Toobuilder

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    Nice to see you over here Dan. Hope you stick around.
     
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  15. Oct 12, 2019 #55

    pictsidhe

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    +1 Dan, that saved me some typing!
    Back to sound insulation. Sealing air leaks makes a huge difference.
    While weight is generally the acoustic insulators friend, it is not one of ours. For troublesome panels, constrained layer damping is usually the most weight effective. I have had some success with an adhesive flashing product from a big box a few years back Thick tarry stuff and thin Al sheet. Not something to put on the inside of a firewall, though! There are more optimised constrained layer products.
    I like the idea of using oil cooler heat to the cabin. Intake should probably be away from the FWF to avoid fire and smoke issues should the unthinkable happen.
     
  16. Oct 15, 2019 #56

    pfarber

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    Well, no.

    Water can hold many more BTUs than air for any given volume. Air's capacity to 'hold heat' is affected by humidity and pressure. Water not so much, more the difference in the temps.

    Water is controllable (flow and pressure) and additives can actually benefit heat transmission. Air is whatever you got a that point in time.

    Water cooling on AC suffers from the compromises made. You want a proper radiator, with the proper plenums and controls. But you also want light weigh and reduced drag. Let me hold up the P-51 as the poster child for water cooling efficiency.

    You may say 'but you have to dump that heat into the air' so air is better (or the same) well yes, but as in the P-51 the answer is 'well designed system'. The P-51 radiator made thrust to actually offset cooling drag. And water has a much larger thermal mass (aka can 'hold' more heat).

    The only reason water cooling hasn't been widely incorporated into new AC design is because Cessna or Diamond or whomever would end up offering a more expensive plane for sale. And the pilot doesn't really care how the engine is cooled.

    Let me just throw this last little bit of water on 'air cooling is better'.

    Your air cooled engine would seize up in minutes without OIL COOLING. Oil is a liquid, is it not?
     
  17. Oct 15, 2019 #57

    PTAirco

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    Back on the noise topic: I found that pulling back on that black knob in the middle of the panel reduces noise considerably.
     
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  18. Oct 15, 2019 #58

    narfi

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    If you think that makes things quieter, you should try pulling back the red one.....
     
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  19. Oct 15, 2019 #59

    SoaringEagleRick

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    Well, we even try to make our gliders more quiet.
     
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  20. Oct 31, 2019 #60

    Gyrojeffro

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    https://www.aircraftspruce.com/catalog/pdf/howtosoundproof.pdf

    I insulated the cabin cockpit of my himax with 1/4" foam board and doubled and trippled the thickness where more sound deadening is needed such as the firewall. I then went over that with light weight carpeting similar to what is used to cover speaker boxes. Weight is very minimal maybe added 3 pounds at most. I'm not sure how good it works because I haven't installed Windows in my plane, I may do that when it gets colder out. I do have a set of noise cancelling headsets I just got but haven't tried them out.
     

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