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Cowl exhaust heat damage prevention

rv9aviator

Well Known Member
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.
DSC00394.jpg

DSC00396.jpg

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.
DSCN2810.jpg

Continued!
 
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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.
DSCN2814.jpg

Here are the after pictures.
DSCN2812.jpg

DSCN2815.jpg

Maybe this will help someone else down the road. I love my mufflers BTW!
 
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(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.
 
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.
 
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 :)
 
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
 
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:
 
My DAR mentioned during inspection that I will get this. I forgot then after couple hours of flight testing I noticed a brown spot.


cowl2hours.jpg



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


cowl50hours.jpg
 
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.
 
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.

After reading a few reports of this, I've been pondering this myself. One suggestion I've read is to try flaring the ends of the stainless steel tubes provided by Vetterman. That would add some mechanical support, instead of just friction between clamped rubber hose and steel tube. I tried that; it makes it a lot harder to assemble the hose onto the tube. I don't like the idea of the relatively sharp edge of the flare biting into the tube ID, since with heat already trying to kill the hose, this could shorten the life even more. I'm going to try an ISO bubble flaring tool next. Bubble flares are used on some automotive brake lines, among other things. It may assembly easier, while still providing a mechanical "stop" for the hose clamp to lodge against.

Is your system mounted per Vetterman's instructions (one set of hangers to the engine, the other to the motor mount)?
 
Find someone with a tool that creates the outward bulge just a 1/4" or so from each end.

Something like this but rounded instead of triangular

_______/\__

--------\/---
 
Find someone with a tool that creates the outward bulge just a 1/4" or so from each end.

Something like this but rounded instead of triangular

_______/\__

--------\/---

That would be an ISO bubble flaring tool :)
 
Another option:

Heat Shield Mat, self adhesive

I think Tony Bingelis provided a good solution that I used. Use some thin gauge aluminum sheet cut to size in the high heat areas and glue it down with a bead of RTV. Don't squish the bead flat, leaving about a 1/16" air gap between the aluminum and the cowling.

V
 
Another option:

Heat Shield Mat, self adhesive

This is what I used after having delamination problems with the stuff I got from Van's . I did lay a coat of plybond down before applying this material . This may have been an overkill , is has good adhesive on the product already . You want to make sure what ever shielding is used is secure , when the one from Van's came loose it shorted between the alt and exhaust stack, could have been ugly .
 
Find someone with a tool that creates the outward bulge just a 1/4" or so from each end.

Something like this but rounded instead of triangular

_______/\__

--------\/---

Ron,
The tool you are referring to is called a beading tool. Most of us have seen beeding done on the fuel filters we buy for small engines. Beading is also done for rubber coolant hose connections on our cars. You can find one here. See

http://www.earls.co.uk/earls/accessories/tools/beadingtools.html

http://www.aircraftspruce.com/catalog/topages/ezbeader.php

Charlie
 
Ron,
The tool you are referring to is called a beading tool. Most of us have seen beeding done on the fuel filters we buy for small engines. Beading is also done for rubber coolant hose connections on our cars. You can find one here. See

http://www.earls.co.uk/earls/accessories/tools/beadingtools.html

http://www.aircraftspruce.com/catalog/topages/ezbeader.php

Charlie

I wish you hadn't posted those links... more tools that I can't live without- there goes the budget ;)

I've used (borrowed) a KD Tools bubble flaring kit, but don't own one. The beader looks like a better tool for this job.
 
Grinding grooves into the stainless supports

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.

Jim,

I found that grinding grooves into the stainless metal tube hangers before they are inserted into the rubber hose creates enough grip for the hose not to slip once the clamps are tightened. I made the grooves using a grinding wheel. It works well for me after more than 300 hours.
 
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