Tip: Cowl insulation with mufflers

rv9aviator · #1 06-25-2011, 06:50 AM

I installed a Vetterman crossover exhaust on my RV-9A and found very quickly I had a problem with heat scortching the bottom cowl. The muffler being a larger diameter puts them much closer to the fiberglass. I only have one muffler hooked up for cabin heat and Larry Vetterman said to remove the heat muff from the muffler that wasn't connected to cabin heat. My engine is a carbureted Lycoming 0-320 E3D. After only 2 hours of flight time I noticed some darkening of the fiberglass on the side with the heat muff and much more on the side without the heat muff. Left alone this would surely ruin the cowl. Dan Horton suggested taking a piece of 1/16 fiberfrax from Aircraft Spruce and putting that next to the cowl with a piece of Van's aluminum self adhesive material cut 2 inches bigger all around and taping that down over the fiberfrax. It worked great. Problem solved and everyone tells me my RV is very quiet but has a nice sound.

rivetshaver · #2 06-25-2011, 09:42 AM

I have the same set up but it is still a half year from completion. Can you tell us your observations of the effects of the mufflers on cabin noise, and make a comparison to non mufflered set up if you have flown in one?

Greg.

rv9aviator · #3 06-25-2011, 06:27 PM

Since this my first RV I can't really tell you the difference. I've only ridden in other RV's for a short time and with good head sets on. One of the forum members that does transition training and flies lots of hours says it is less fatiguing at the end of the day and much quieter. I know listening to my plane from the ground it is much quieter than a non muffled RV. Maybe some one else with mufflers will comment.

chaskuss · #4 06-25-2011, 09:00 PM

Jim,
I just checked your builder's page. Could you post a few photos of your completed exhaust system with the mufflers either to your builder's site or to this thread? I'd like to see your system.
Charlie Kuss

rv9aviator · #5 06-26-2011, 05:13 AM

Here is the only picture I have right now.

I have the cowl off right now so I can take more pictures. Is there any certain view you would like?

jsharkey · #6 06-26-2011, 06:15 AM

The heat muffs shown are heat exchangers to extract heat from the exhaust and divert it to the cabin. They aren't sound mufflers like in a motor car - although I believe that Vetterman sell alternative end pipes that do include a sound muffling element.

I have a cabin heat muff on the RH pipe and it just clears the cowl. I don't think it would fit on the LH pipe without hitting the cowl. Also I'm sure that the muff can runs much cooler than the pipe since it has cooling air running through it all the time.

I experienced some charring on the cowl near the LH pipe and RTVed a thin aluminum plate to the cowl below the pipe per the Vetterman instructions. This helped but I was still getting charring at the transition of the cowl and snorkel. Since it was too hard to form a plate here I removed the charred glass and core material - and in the process making more clearance for the pipe - repaired with a couple of layers of glass epoxy and covered with a couple of layers of self adhesive aluminum tape - the type used on the fire wall insulation joints that AC Spruce sells.

Still looks good many hours later.

I also notice that the pipes tend to naturally drift leftward off centerline on their swivel joints opening up cowl clearance on the RHS and tightening it up on the LHS. I was considering some lateral bracing but haven't got that far yet.

Hope this helps

Jim Sharkey
RV-6

rv9aviator · #7 06-26-2011, 08:27 AM

What you are looking at is indeed a muffler with a heat muff around the muffler. I will post a picture later of the other side which is just the muffler with the heat muff removed.
Here is the picture from Larry's website showing the crossover system with mufflers and heat muffs. Sorry if there is a problem with reposting from Larry's website. Just please remove it if so.

Dan B · #8 06-26-2011, 11:43 AM

Jim,

Had the same problems with high heat on the cowling. I used a heat insulation material, available at your local auto/aircraft supply store. The material has a reflective tape, insulating material and self adhesive. I covered the cowl beneath my exhaust stacks and mufflers.

rv9aviator · #9 06-26-2011, 12:09 PM

Hi Dan, Keep a close watch on the tape to make sure it isn't coming loose. Pierre Smith had some come loose and blocked the outlet air which caused overheating issues real quick. I painted a strip of epoxy aroud all the edges of mine to add a little extra insurance.

chaskuss · #10 06-26-2011, 02:27 PM

Quote:

Originally Posted by rv9aviator

Here is the only picture I have right now.

I have the cowl off right now so I can take more pictures. Is there any certain view you would like?

Jim,
I spotted that photo on your builder's page. The photo shown earlier[complete system shown from above] is very helpful. I would like to see both left and right views of the mufflers and the related SCAT tubing and heat boxes.
Charlie