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  #1  
Old 04-19-2022, 07:35 PM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 2,247
Default Cowl/fiberfrax modification

There are some areas on the lower cowl on my RV6 build that are pretty close to the exhaust pipes. I would like to protect these areas with 1/8” fiberfrax and the aluminum self adhesive cowl shield I got from Vans. Question for those who have done this - what did you use, if anything, to attach the fiberfrax to the cowl? My cowl surface is still unprotected. My plan is to seal it with bilge paint from my local boating shop. I’ve tried it on the inside of my wheel pants (old kit), and it seals very well, and is made to protect the fiberglass bilge area of a boat from oil, fuel, hydraulic fluids, etc. Should the fiberfrax/aluminum shield be put on over this bilge treatment, or before?
I’m unsure what would stick to fiberfrax, or if being held down by the adhesive back aluminum is enough.

Picture of the bilge paint:

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SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019/sold2021
RV6/Used kit purchased 2021 building
Cincinnati, OH/KHAO
JAN2022
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  #2  
Old 04-19-2022, 07:46 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,886
Default

Scott,

I didn't think big chunks of fiberfrax would hold their shape if I simply laid a bigger piece of tape over them. So I applied the fiberfrax in small strips - maybe 3" wide, covered with the aluminum tape. Then I overlapped another piece of fiberfrax right up to where the first layer of fiberfrax ended, and covered the new strip of fiberfrax with the aluminum tape, overlapping the previous layer of aluminum tape. Basically like shingling a house.

Ultimately, the only excess material and weight was in the form of an extra layer or two of aluminum tape in a few places.
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Marietta, GA
2001 RV-6 N46KB
2019(?) RV-10
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  #3  
Old 04-19-2022, 08:09 PM
CJ in EP CJ in EP is offline
 
Join Date: Apr 2017
Location: Eden Prairie, MN
Posts: 86
Default Try a small dab of bondo

I think it was Bruce Hill that documented his use of small dabs of bondo to secure the fiber, and once set (which is only 15 minutes or so) cover with foil tape. It worked great for me.
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Chris Hrabe
Eden Prairie, MN
RV-9A
N111CT
Phase II
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  #4  
Old 04-19-2022, 08:12 PM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 2,247
Default

Kyle,
Thanks, that makes a lot of sense. I have two areas I want to protect that are 4” wide, and two shorter areas that are 6” wide, so two 2” strips in each of the narrower areas, and 3” strips in the others. Should work fine and I’ll put down the bilge paint first, since the aluminum shield will stick fine to that.
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SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019/sold2021
RV6/Used kit purchased 2021 building
Cincinnati, OH/KHAO
JAN2022
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  #5  
Old 04-19-2022, 08:19 PM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 2,247
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Quote:
Originally Posted by CJ in EP View Post
I think it was Bruce Hill that documented his use of small dabs of bondo to secure the fiber, and once set (which is only 15 minutes or so) cover with foil tape. It worked great for me.
I might do that too. I’ll rough up those spots with 80 grit before applying the bondo - not sure bondo would stick well to bilge painted fiberglass.
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SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019/sold2021
RV6/Used kit purchased 2021 building
Cincinnati, OH/KHAO
JAN2022
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  #6  
Old 04-19-2022, 09:30 PM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,909
Default

All my three RVs have had a full 1/16" layer of fiberfrax on the lower cowl covered with Aluminum from VANS. Spruce sells a glue for fiberfrax but it was worthless for my use and did not stick. But if you take care and extend your aluminum table a good 1.5" beyond the fiberfrax, it will not come off. Between the three planes I have well over 1000 hours and it stayed on with no issues. The cowl remains very cool and easy to touch right after landing.
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N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - SOLD
N258SM RV14A - IO390EXP119 - Out of Paint shop & flying
Dues paid
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  #7  
Old 04-19-2022, 10:04 PM
Stevea Stevea is offline
 
Join Date: Jun 2008
Location: San Jose, CA
Posts: 189
Default exhaust pipe heat shields

So why not use one or more exhaust pipe heat shields instead?

https://www.aircraftspruce.com/catal...atedshield.php

Way easier than bonding fiberfrax to the inside of the cowl and covering it with the AL foil.

I only have the AL foil on my lower cowl (no fiberfrax). Heat shields were used where exhaust pipes were too close to fluid lines and wire runs. Maybe my exhaust doesn’t come as close to the cowl as yours does.
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RV-6A - sloooowwww build
First flight - 3/8/14
Phase II - 5/19/14

Last edited by Stevea : 04-19-2022 at 10:11 PM.
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  #8  
Old 04-20-2022, 06:40 AM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 2,247
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Quote:
Originally Posted by Stevea View Post
So why not use one or more exhaust pipe heat shields instead?

https://www.aircraftspruce.com/catal...atedshield.php

Way easier than bonding fiberfrax to the inside of the cowl and covering it with the AL foil.

I only have the AL foil on my lower cowl (no fiberfrax). Heat shields were used where exhaust pipes were too close to fluid lines and wire runs. Maybe my exhaust doesn’t come as close to the cowl as yours does.
I will have a couple of those shields for a couple areas, but they won’t fit where the tail pipe ball joint/springs come the closest to the cowl. Fiberfrax/aluminum is only planned for certain areas on the bottom cowl. There’s a couple places where the exhaust tail pipe/ball joint is about 1 - 1.5” away from the cowl at the edge of the chin scoop radius.
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SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019/sold2021
RV6/Used kit purchased 2021 building
Cincinnati, OH/KHAO
JAN2022
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  #9  
Old 04-20-2022, 07:17 AM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,754
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No need for a large area of fiberfrax. Just shadow the pipes. In strips, nothing is needed to hold the fiberfrax except the aluminum foil cover.

In general, the adhesive on foils and tapes always sticks better to a smooth painted surface. Scott, a simple test. Cut two equal width strips of foil. Stick one to the fender of your truck, and the other to the bilge paint. Peel them. If they require the same effort to peel, the bilge paint is a good surface for tape.

The installation below has been in place over 1000 hours.
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  #10  
Old 04-20-2022, 09:19 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,559
Default

The 8 has more room down there than my 7, and I did use a larger area for the fiberfrax, I used 3M spray contact cement and with 200 hrs it still sticks well. I do have a couple of areas that have lots of acoustic noise (or vibration) and fractures the aluminum overlay, but the insulation stays in place.

YMMV.
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