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  #1  
Old 07-21-2011, 10:13 AM
rv9aviator rv9aviator is offline
 
Join Date: Jan 2005
Location: Arkansas
Posts: 1,502
Default Cowl exhaust heat damage prevention

I have a Vetterman crossover exhaust with mufflers on my RV-9A and because the mufflers are much closer to the cowl than just the pipes I was getting heat damage to the lower cowl after only 2 hours of flight. This is how I fixed the problem. This would be something to do before you ever fly as it will most likely become necessary. I only have one heat muff installed so the side without the heat muff puts off much more heat. Here are pictures of the mufflers with and without the heat muffs.


I have to give Dan Horton all the credit for the materials and how I did this. You take some 1/16 thick fiberfrax from ACS and cut a piece big enough to cover the effected area and then cut a piece of the self adhesive aluminum sheet from VANS 2 inches larger each side around the piece of fiberfrax.

Continued!
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Last edited by rv9aviator : 07-21-2011 at 10:36 AM.
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  #2  
Old 07-21-2011, 10:30 AM
rv9aviator rv9aviator is offline
 
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Location: Arkansas
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The next step is to clean the lower cowl area to remove any oil and grease. I had to scuff the damaged area and add another layer of glass just to repair the charred layer. You simply lay the fiberfrax and aluminum sheet down and press the adhisive edges down to finish the job. I mixed up some epoxy and painted the edges of the aluminum sheet to keep it from peeling loose later. Don't know if that's necessary but it gave me the warm and fuzzy.
Here is the before picture.

Here are the after pictures.


Maybe this will help someone else down the road. I love my mufflers BTW!
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RV-9A N9JW 90919 SoldArkansas
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Last edited by rv9aviator : 07-21-2011 at 10:36 AM.
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  #3  
Old 07-21-2011, 11:49 AM
Lars Lars is offline
 
Join Date: Nov 2005
Location: Davis, CA
Posts: 814
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Quote:
Originally Posted by rv9aviator View Post
(snip...) Maybe this will help someone else down the road. I love my mufflers BTW!
It helps me, thanks. Added to the to-do list.

Did you see much difference in scorching from left to right?

The instructions that came with my system specified that cooling air be supplied to both mufflers, though Larry Vetterman has since told me that I could take the heat muff off the one not used for cabin heat, as you did. By the time I spoke with him I had already added an extra air inlet to the baffling, for the right side. I am considering hooking it up and dumping the hot air at the cowl exit, if it would help drop lower cowl temperatures.
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RV-7 Flying as of June 24, 2012
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  #4  
Old 07-21-2011, 02:27 PM
rv9aviator rv9aviator is offline
 
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The one without the heat muff was the one that burned the cowl. The other side probably would have survived but I didn't want to chance it. I would like to add another 2 inch scat hose and dump it overboard too but I already need to add a scat hose for the fuel pump and was afraid I would starve the cyclinders of air flow. I posted a question about adding hoses to the back baffling in another thread. My uneducated little mind tells me the more places I have for air to go the less will go thrugh the cylinders. BTW, don't forget to paint the whole inside of the cowl with epoxy before the first engine start to stop any oil from soaking into the fiberglass.
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RV-9A N9JW 90919 SoldArkansas
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  #5  
Old 07-21-2011, 03:46 PM
Lars Lars is offline
 
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Quote:
Originally Posted by rv9aviator View Post
The one without the heat muff was the one that burned the cowl. The other side probably would have survived but I didn't want to chance it. I would like to add another 2 inch scat hose and dump it overboard too but I already need to add a scat hose for the fuel pump and was afraid I would starve the cyclinders of air flow. I posted a question about adding hoses to the back baffling in another thread. My uneducated little mind tells me the more places I have for air to go the less will go thrugh the cylinders. BTW, don't forget to paint the whole inside of the cowl with epoxy before the first engine start to stop any oil from soaking into the fiberglass.
In that case, I'll hook up the left side. I'm pulling air off the left (pilot side) ramp via the same type of circular flange as supplied for the heater muff. And yeah, it's a cooling drag compromise for sure. Yet another opportunity for experimentation, once I get this thing in the air. Maybe I'll change my mind eventually. Not about the mufflers, though. Quiet = good, as far as I'm concerned.

The inside of my pepto pink cowling looks pretty much like yours- glossy from all the leftover epoxy I've painted on it from all the other small glass jobs- at a hundred bucks a gallon I hate to waste the stuff
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  #6  
Old 07-21-2011, 05:23 PM
tclaire tclaire is offline
 
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Location: Rayville Mo Midland Tx
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Quote:
Originally Posted by rv9aviator View Post
The one without the heat muff was the one that burned the cowl. The other side probably would have survived but I didn't want to chance it. I would like to add another 2 inch scat hose and dump it overboard too but I already need to add a scat hose for the fuel pump and was afraid I would starve the cyclinders of air flow. I posted a question about adding hoses to the back baffling in another thread. My uneducated little mind tells me the more places I have for air to go the less will go thrugh the cylinders. BTW, don't forget to paint the whole inside of the cowl with epoxy before the first engine start to stop any oil from soaking into the fiberglass.
When i installed my mufflers on my RV9A Larry said on the muffler that i did not use the heater on take off the heater shroud, and replace it with a thin piece of alumuim wrap half around and use the clamps from the heater shroud and leave the top open for air flow and heat removal, it seems to be working find after 150hrs
Tim
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Old 07-21-2011, 05:38 PM
rv9aviator rv9aviator is offline
 
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I remember that now. I'll add aluminum sheet the next time I have the cowl off.
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RV-9A N9JW 90919 SoldArkansas
http://www.jimsairplanes.com
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  #8  
Old 07-21-2011, 09:33 PM
Randy Means Randy Means is offline
 
Join Date: Apr 2008
Location: Cocoa Florida
Posts: 43
Default Cowl browning

Had the same issue on my 10 and used simular product on cowlinging with no adverse effect. Actually it was an easy fix for once.
Randy Means
N595RV:
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  #9  
Old 08-11-2011, 08:54 PM
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Vlad Vlad is offline
 
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My DAR mentioned during inspection that I will get this. I forgot then after couple hours of flight testing I noticed a brown spot.





I put aluminum foil Vans sells, checked yesterday during oil change the reflector works good. 51 hour later no damage so far.


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  #10  
Old 08-11-2011, 09:26 PM
rv9aviator rv9aviator is offline
 
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After the mods my cowl is doing OK but I am having a difficult time keeping the mufflers and tail pipes from moving around after a few hours. Right after I adjust the rubber hose hangers there is about 3/8 of an inch clearance between the back of the muffler and the cowl. After a few hours it will be down to 1/8 of an inch from touching the cowl. I sure wish there was a better system to support the exhaust than hose clamps and fuel hose. I bet it works OK with just pipes but the added weight of the mufflers may be the problem.
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