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In Cockpit Noise - How to reduce?


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The quoted cabin noise of a Jab is 95db.

Others like Sling and Technam I have flown seem to be about the same when you take the headphones off.

Any ideas on how to lower in cockpit noise.

For example any quite aftermarket exhaust systems for rotax or jab engines being made without loss of HP.

Any idea of prop noise level in cruise?

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Sound deadening or have 2 jet engines way up the back. Prop noise where it's bad is usually tip speed and less when revs drop. Makes Catalina's very noisy so I didn't buy one. nev

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I found things got a lot quieter when I unplugged her headset..............

Yes, I have found that to work well. Or turn the ICS down..

 

 

The quoted cabin noise of a Jab is 95db.

Others like Sling and Technam I have flown seem to be about the same when you take the headphones off.

Any ideas on how to lower in cockpit noise.

For example any quite aftermarket exhaust systems for rotax or jab engines being made without loss of HP.

Any idea of prop noise level in cruise?

Have you correctly identified the source of the noise?

I had an 80hp 912 with a kit exhaust that was 95db in the cockpit. With careful internal baffling, I got down to 85 dB, in cruise, most which is wind noise. I don’t think it’s any quieter than a proper Rotax exhaust, but even at full power it gets quieter as you pull the nose up and slow down. Anyway, the point being, is it all engine noise or is it airframe noise?

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Lightspeed Sierra works for me.

Yeah, that's partial fix though. I was very surprised just how much less fatigued I felt after noise reduction, even with an ANR headset.

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I would speculate (some experience): that composite aircraft, motivated by relativly slow turning propellers (Rotax 912 range) are likely to be considerably quieter than their metal relatives ("spam cans") with a noise gradient somewhere in between, for mixtures of construction/motivation thereof.

 

There are things that can be done to mitigate noise":

  • Do not get sucked into a straight through exhaust system (keep the muffler) - there a few if any benefits for aircraft not used for racing and you will annoy all the "neighbours" you fly over
  • Operate the engine at some comfortable point below max continuose cruise power - makes a big difference to vibration/noise and improved fuel consumption.
  • Line the cockpit with light weight, fire retardant, carpet - cheap, comes in variose colours/shades, easy to apply and improved temperature insulation.
  • Cover the firewall with a fire resistant "blanket" - addition benefits are reduced heat into cockpit
  • Make sure all firewall holes/pass through's are well sealed - in addition to noise mitigation, reduces the chance of CO poisoning.
  • Seal up canopy/fuselage gaps (gap sealing tape. caulking, replacing rubbers, etc) and keep vents closed, if not required - wind noise can be a significant noise generator on some aircraft.
  • Etc

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The quoted cabin noise of a Jab is 95db

There quite a few smartphone apps that will measure noise levels. I don't know how accurately they measure db, but they are good for comparisons to see if you made it better or worse and seeing which flight conditions are louder or quieter.

Having the prop in front is the main problem; it dirties up all the air behind it.

Have you tried it with the fan off? You may be surprised just how much noise is generated by the airflow over "dirty" bits of the airframe.

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Bose (in my experience) may help.. I've also heard good reviews from Lightspeed Zulu and some other ANR headsets.

If that doesn't help, try flying in some aircraft with more power (150hp and above), then return to Jab.

I've never flown Jab, but I've seen (and heard) them departing. I was surprised how quiet they are.

 

The only downside of Bose is $ cost which is in my opinion way overpriced for headsets made in Mexico or E/SE Asia.

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Makes Catalina's very noisy so I didn't buy one. nev

I’ve always wondered how engineers on Catalinas tolerated the engine noise when they were stuck up on their elevated perch between the two of them. They’ll must all have gone deaf.

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  • Line the cockpit with light weight, fire retardant, carpet - cheap, comes in variose colours/shades, easy to apply and improved temperature insulation.
  • Cover the firewall with a fire resistant "blanket" - addition benefits are reduced heat into cockpit

 

Hi Skippy,

 

Any tips on where to source the lightweight carpet and firewall blanket? I have to start thinking of cabin finish soon.

 

Thanks, Marty

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Car sound deadening - Dynamat from super cheap auto on inside of firewall and forward skin panels. A bit more in the center of any bulkhead that might resonate. Marine polypropylene boat liner mounted with double sided tape for interior upholstery. Floor mats held down with velcro. Treat it all with spray on fire retardant just in case.

 

‘’You can actually talk in the cockpit with a running rotax 912.

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Sound proofing is heavy so not so good for AC.

ANR aviation headsets are not even close to the best headsets for active noise reduction they are generations behind the best consumer ones.

If you want the very best active noise reduction headset you have to look at headsets like the Sony WH-1000XM3 these smoke my Bose A20's you do need a mic but this company has the solution. NFlight Nomad Pro Aviation Microphone

This gives you a way better more comfortable headset with the latest generation of active noise canceling. Oh it is cheaper to :)

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Hi Skippy,

 

Any tips on where to source the lightweight carpet and firewall blanket? I have to start thinking of cabin finish soon.

 

Thanks, Marty

 

Got mine from a Sydney wholesaler.

Go on line, find the stuff with a fire & UV rating (avoid anything else). When you know what you want Google suppliers.

Best to make your colour/texture/weight selection either by visiting the store or asking for sample swatches.

Ships Chandlers/Boat Supply are probably your best bet

I used three three different grades; a very lightweight flexible, for cabin walls etc , a denser heavier grade for floor mats and a slightly stiff black mat for an anti glare,on my instrument panel (dash) top

You will need nice sharp scissors, sharp craft knife or similar, a clean flat working surface, marking chalk (for drawing a pattern) and flat "square", strait edge & dressmakers measuring tape

This stuff, has no "grain" & cut edges do not fray, can be easily moulded & slightly stretched, if need be, around bulges/corners etc. "Dry" fit everything befor sticking

The side walls are all contact adhesive attached, (its easier to use the spray adhesive but you will need to do a preliminary coat on the fabric - let dry befor applying second coat) the floor mats and "dash" matt (black) are sticky backed Velcro (dont purchase the cheap no name stuff) in place-

 

For engine side - Proper fire wall "blanket" material needs to come from aircraft or race car supply. If you blanket the cabin side of the firewall, you could use a denser thicker version of the light weight stuff with "space blanket" glued on.

 

I would steer away from any automotive/boat heavy sound insulation - adds too much mass.

 

Like Walrus #15 - I can have a non shouted non headset conversation in flight (912 ULS). Active Noise Reducing headsets are not required

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About the noisiest plane I've flow is the 145 HP Auster with short exhaust stubs. Fabric doesn't keep much noise out. I think some basic RV's are pretty noisy if not well muffled and no sound deadening. It will ruin your ears.. Eventually if not sooner.. Planes need sound deadening and it must be fireproof. I can't recall any Jabiru I've flown being objectionally noisy either to the occupants or others. Lots of big engines have no mufflers at all and some have very noisy props. While nut cases like me find the noises inspiring I'm sure plenty of others don't and a coupla thousand hours near 4 P&W R-2000's consigned my hearing to the wastebasket, unfortunately. with crackling HF radios when a long way from civilisation helping also.. LOOK AFTER your hearing. Nev

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I think that you could add a lot of heavy sound insulation and not affect the sound levels in the cabin at all. The slightest gap in sound insulation nullifies the effect. If the noise is coming from the propeller tips, the noise would come straight through the windscreen. If you insulated the firewall, engine noise would come straight through the cowel and then the windscreen. You would need to soundproof the cowel. I would not even try.

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The best solution that I am aware of is to wear foam ear plugs and an ANR headset. If you have a passenger, they will need to wear the earplugs too, or the required volume from the intercom might be too different for each of you. The best foam earplugs are the ones that are cylindrical, and coloured yellow or beige. The earplugs that are are rounded at one end, like a bullet, distort the sound as well as reduce it. I suggest that you wear a type in the car and see if they distort the radio. I prefer to wear earplugs and ANR headphones. The radio and intercom are still able to be more than loud enough.

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Operators removed the sound deadening from the companys aircraft to carry more weight. B**ger the pilots..It does make quite a bit of difference but your point of a thin window is valid. A lot of insulation is not particularly heavy.. Underbonnet sound deadening is common ?universal in good road vehicles. Nev

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The best solution that I am aware of is to wear foam ear plugs and an ANR headset...

Even better is custom-made earplugs, which you can mould in your ear yourself. The kits are cheap as chips and available on eBay.

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ANR headset not available ? certainly poor fitting headset ear cups make for position and fitting sensitivity in a noisy cockpit, even if they are ANR.

In high noise environments I am involved in, best solution is a silicone ear bud that pushes into the ear canal- IE the air tube earphones.

 

I would suggest, for a cheapie, using pneumatic ear buds, with custom eartips if possible. (yes I do this for a living- headsets, earbuds, noise reduction )

 

https://www.ebay.com.au/itm/In-Ear-Straight-Insert-Stereo-With-Microphone-Air-Tube-Music-Play-Mono-Earphone/114361391206

 

but you have to deal with the aircraft audio interface.

and maybe some of that transparent aluminium from Star Trek for a thicker windscreen ? ALTHOUGH an insensitive sound level meter with a good super cardioid shotgun microphone would tell you where it is getting in.

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The best solution that I am aware of is to wear foam ear plugs and an ANR headset.

If you use your "hierarchy of control", PPE comes in last.

1. Elimination- You could eliminate the risk by not flying....Not going to happen

2. Substitution- you could go in a glider.....not going to happen

3. Isolation- Still not going to work

4. Engineering controls- What the OP was looking for... There are several things that can be done from engine mufflers to cockpit soundproofing and so on.

5. Administrative controls- Won't do anything unless you use the paper as soundproofing.

6. PPE- Flash headsets, are great, and they work even better when you start by getting the cockpit as quiet as practicable to start with.

 

There is more to high noise than just hearing loss. As I mentioned earlier, I have recently knocked about 10 db off cockpit noise and didn't think that much of it until a few longer flights over 2-3 hours and found that I walked away feeling way less fatigued than I had previously( even with ANR headsets). I had been thinking about it for some time but hadn't changed anything because people I fly with said it sounded great. It got the better of me and now I wish I had done it when I rebuilt it a few years ago. The noise generators that I have left will be very difficult to remove, but it's much more comfortable that it was.

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