Removing sound insulation make inside louder in flight?

[pinkiedog64]

Hello guys, one of my first posts here. I have N1351D, 1951 170A, sn 19927. I am in the middle of an owner-assist annual. I am removing the old and ratty (original?) headliner to install BAS front seat shoulder harnesses. The headliner is in bad shape and I am probably not going to re-install it this annual after I get the harnesses installed. The airplane is a “rat” so not having a headliner doesn’t bother me much, at least for a while. The airplane has what I am assuming is the original sound insulation glued to the roof and side skins. Kind of a yellow-orange fiberglass-ish material. It is falling down in chunks so I am going to just remove it all where it was glued to roof and side skins.

My question is: for those who have removed headliner and sound insulation, is it noticeably louder inside in flight? I use noise-cancelling headsets so I am hoping I won’t hear much of a difference, but if it will be significantly louder I may go ahead and do new insulation and headliner this annual, though I am hoping to postpone interior/cosmetic work for a while. The airplane is only has a partial interior as it sits right now, anyway, so I'm guessing it is louder than average and it isn't a bother right now.

Thanks,

Stephan

[c170b53]

I’d say not much difference. Remove that old stuff (you’re on you way to making it perdy), you’ll likely find a bit of corrosion around the glue, usually just surface, clean it up if you can. You may want to prime afterwards and you can (like many) go for the closed foam insulation option. You can go about it one section at a time. Many like the san headliner look, then again later you can put the headliner in and lose rat category points. Ask Bruce on how to win that award if you decide to get serious..

[gfeher]

I didn’t notice a difference when I removed mine. There are a couple more reasons to remove it. It collects moisture, causing the corrosion Jim mentioned. Also, it attracts mice, even if the plane is stored in a hangar. I know both from personal experience. I never replaced my insulation with anything. I don’t feel the need to.

[counsellj]

I have flown several airplanes that have the headliner removed. All of them are noticeably cooler and draftier than with a headliner installed. Something to consider.

[GAHorn]

Congratulations on undertaking an intrior renewal! That always gives a rewarding result…. AFTER the job is finished!

It might be helpful to consider when and why Cessna installed fiberglass insulation in the overhead of the headliner…. In the 1940s/50s few civilian airplanes used headsets and when they did, the headsets used had virtually no noise-reducing capabilities. Therefore the insulation offered a reduction in sound level as well as a change in “tone” (as compared to prop-blast bleating against sheet-metal. Additionally, while taxying there is considerable “oil canning” and thumping that is pretty loud when no headset is worn. These days few pilots are aware of this because of improved passive headsets and when a noise-cancelling headset is used (especially with headliners and sound “proofing” is installed.)

Fiberglass is better at shedding moisture than foam, and if used, closed-cell foam is best. But be aware that the weight of aluminum-foil-backed-foam adds up… and not only in weight…but also in cost.

My B-model was restored using plenty of foil-backed-foam and frankly I was surprised at how noisy the airplane was without a headset. (I never owned a noise-cancelling headset until I bought a 170, and the headsets I used predominately at the time were the small Telex Airman 750 series…nothing more than lightweight foam ear-pads which worked great in the day-job jets I flew most of the time and even the occasional King-Air…. but ferrying my new-to-me, fresh-restored 170B home set me to shopping for different headsets!

The MOST NOISE REDUCTION I was able to obtain was by installing good door and window seals! (And I also installed a sheet-metal back-wall behind the bag-shelf to reduce oil-canning noise coming forward from the fuselage while taxying.)

If I were more interested in a “spartan look” in one of these airplanes I’d be inclined to remember the interiors of WW2-period aircraft that had visible zinc-chromate-treated exposed sheet-metal, stringers, and bulkheads….that has a certain ambiance I like……. and then with the money saved I’d provide good quality noise-cancelling headsets for everyone. The weight-savings would certainly be helpful, IMO.

[bgiesbrecht]

I just did this recently. You'll notice a bit different tone/wind noise but not necessarily an INCREASE in noise. It's fine - remove that stuff, make sure you wear gloves and respirator.

[pinkiedog64]

Great, thanks all. I'll remove it and clean up any corrosion while I'm there. I used to be an engineer at Mooney. This original style insulation reminds me of the stuff Mooney used to use between the aluminum fuselage skins and steel tube fuselage frame. There was a service bulletin about it where you removed the insulation, inspected/addressed corrosion, then installed new closed cell foam.

I don't know what Bruce's airplane looks like, but I think mine would give his a run for the money in the rat category. As soon as I get the annual wrapped up and finish private license (almost there, just a few hours/items to go!) then I'll start going to some of the 170 fly-ins and y'all can judge the rattiness of mine. I'll be it scores high!

Thanks again.

Stephan