Exhaust Insulating Wrap

hgerhardt · #1 10-05-2006, 01:31 PM

Anyone have any negative reports associated with wrapping the exhaust tubes? Dan C, you've got many hours on your wrap job by now, so how's it holding up?

Heinrich Gerhardt
RV-6, almost flying

dan · #2 10-05-2006, 02:13 PM

The wrap has broken down a little bit and loosened here and there. I just wrap some safety wire around the loose spots when I find 'em during oil changes.

I can't quantify the effect of wrapping the exhaust -- although numerically speaking, I did see peak EGTs rise about 30F across the board after wrapping. Hot starts seem to be easier. The temp of "hand to cowl" after a flight "feels" cooler. Again, I don't have any data to quantify any of this.

Before I get flamed about wrapping being bad for the exhaust, I know it is! My feeling is...it's cheaper to replace the exhaust than it is lots of other items under the cowling.

sf3543 · #3 10-05-2006, 03:52 PM

I wrapped the exhaust on my RV6 and after a few months, I had to take the exhaust off and some of the wrap. Even though I had Vetterman SS exhaust, it was all discolored and basically looked like it was going to corrode. At any rate, I had a hard time wrapping it and keeping it on. I took it off.
On the RV8, I had the exhaust ceramic coated. It looks nice and is cool to the touch after a flight almost as quickly as I can get out and bend over to check it. No ticking sounds after a flight, associated with cooling.
I can't submit a report as to how things have changed, since it was applied during the build, but I do believe it keeps things cooler under the cowling. Can't remember the exact cost, but it was about $275 for the exhaust. (I also had the intake pipes coated to keep the heat out.)

gmcjetpilot · #4 10-05-2006, 05:36 PM

Quote:

Originally Posted by hgerhardt

Anyone have any negative reports associated with wrapping the exhaust tubes? Dan C, you've got many hours on your wrap job by now, so how's it holding up?

Heinrich Gerhardt
RV-6, almost flying

Look you heat soak to pipes and they crack. The wrap is subject to absorbing oil becoming flammable. If you need local heat shields you can use a stainless steel shield clamped on (like cars have heat shields around the cat converter). You can also insulate or protect objects that are too close to the pipes.

The state of the art is ceramic coating on the inside and out side. Don't know if that can be done to old pipes, but if they can be cleaned why not. You do not want to just ceramic coat the outside, that is like cooking the steel, similar to wrapping it. Vetterman I hear does not condone coating and definitly wrap on his exhaust. He will not warranty it. I don't know? That is too bad because if done properly it's really is a good thing, but its his product and I understand he wants to be nice to the pipes. We know the pipes love to get rid of their heat and cool down. Unfortunately a lot of that heat goes into the cowl area and cooks everything. I think ceramic coating has all the advantage but none of the drawbacks. It does cost money however.

The down side of ceramics is we use heat muffs for carb and cabin heat. I personally would not like to stop and start the ceramic coating in one section of a pipe. My theory is it will create a thermal stress concentration due to the coating discontinuity. My work around is I have 4 separate pipes going into 1 collector. I coated 3 out of 4 pipes, leaving the one with the heat muff completely uncoated. Since the whole pipe is uncoated from the cylinder to the collector which is a slip joint there is not coating discontinuity.

RV6_flyer · #5 10-05-2006, 06:31 PM

I have 1,953 hobbs hours on my RV-6. Have had wrap on the pipes all but the first 75 or so hours. Read Dan's post as my thoughts are the same.

The only down side is if you got an oil or gas leak that sprayed on the wrap, it MAY hold some of that but only the fuel / oil would burn but and the wrap would not.

I do not see this as much of a problem. Others may think it is. I agree to disagree with them. To have a fire, you need fuel, ignition, and O2. Adding warp does not add any of those items. Yes it may hold a small amout of fuel more than it would without but the quanity will not make any difference in an actual fire. The same amount of fuel that gets on the wrap would still be the same amount of fuel even if the wrap were not there. Ok, maybe there would be one tablespoon more fuel wicked up in the weave of the wrap. Is one tablespoon more fuel on the fire going to make a difference? I say no it will not.

I believe that the advantages out way the diadvantages. The safety issue is overstated.

My next exhast will be ceramic coated.

penguin · #6 10-05-2006, 07:04 PM

My advice is not to wrap your exhaust. I bought an RV-6A with 250 hrs on the clock in a couple of years and a wrapped exhaust. The wrap was beginning to break down and get very brittle, so I took it all off. A while later I had to send the exhaust back to Larry Vetterman. Larry commented that the exhaust had become badly over heated and had required one tube to be replaced, while the others were slightly damaged but OK. When I mentioned that it had been wrapped he explained that it was a bad idea as aircraft exhausts are made from much lighter tubing than cars use. The thinner tubes are much less able to withstand the heating they get when wrapped - as they need a constant supply of cooling air. In bad cases I believe a wrapped exhaust can warp due to the heating and the crack. I think that ceramic coating does the same thing as wrapping and is similarly a bad idea.

Pete

gmcjetpilot · #7 10-05-2006, 08:59 PM

There you have it, 5 opinions and all different or almost all

-Wrap will hurt the pipes but don't care, buy new pipes
-Wrap is a pain and made the pipes look distressed, but the ceramic is working well so far
-Wrap is bad, ceramic good (inside and out)
-Wrap is wounderful and Dan is the Man!
-Wrapping destroyed or nearly destroyed my pipes, ceramic coating is also bad.

ha ha ha

I just like to say, well done!

frankh · #8 10-05-2006, 09:03 PM

When I saw Dan had wrapped his exhaust I had fully expected to hear about cracks in his system. The reason being is that as the system cannot loose heat being wrapped it will heat up more and the tubes will get longer than if they were not wrapped.

I have had a few (second hand) reports of Vetterman systems cracking and I put it down to this tube lengthening effect. I am a little surprised that Dan's system has not cracked....I guess as long as the slip joints do in fact slip as the system warms up it won't crack but its hard to imagine these joints work perfectly.

The more serious issue for me is that if you do get a crack how will you spot it under the insulation?...CO poisoning being the risk here.

picking up on George's point about heat sheilding, My invert oil tubes run Very close to my exhaust...So close that I could only just get a half baked heat shield in there and insulate the oil line with firesleeve.

Just to be sure I buried a thermocouple under the firesleeve on each of the oil lines, connected to a handheld temperature meter.

To my amazement I have never gotten the thermocouples to read more than 225F.....Petty amazing.

So George is right in that heat sheilding plus a firesleeve works very well.

Now I want to insulate the intake tubes for another pony or two.

Cheers

Frank

RV6_flyer · #9 10-05-2006, 09:53 PM

Quote:

Originally Posted by gmcjetpilot

There you have it, 5 opinions and all different or almost all

-Wrap will hurt the pipes but don't care, buy new pipes
-Wrap is a pain and made the pipes look distressed, but the ceramic is working well so far
-Wrap is bad, ceramic good (inside and out)
-Wrap is wounderful and Dan is the Man!
-Wrapping destroyed or nearly destroyed my pipes, ceramic coating is also bad.

ha ha ha

I just like to say, well done!

George:

Just another "Old Wives Tale" on exhaust system failing if wrapped. Same as LOP and Over Square operation. You will find the same agreement to disagree on those subjects.

I have more hours with Exhaust Wrap than anyone I know. I got the idea from two different "Airshow" Pilots based at the same airport as I. Both airwshow pilots are IAs and one is also a Professional Engineer, FAA Designated Engineering Representive, along with a few other non-aviation credentials.

From an OLD RV-3A that was based at my home base, he had an Allen Tolle exhaust that cracked all the time. Wrapping it and the exhaust cracked less. When it did crack under the wrap, the wrap would blow out near the crack so it was as easy to find.

The trick to getting it to stay on is use Hose Clamps. Safety wire only allows the wrap to go away more quickly.

As for me, I am only a high time RV builder / Pilot that is also an A&P and DAR. Make up your own mind if exhaust wrap is right for you.

BTW. The exhausts we use all turn black and look distressed even if not wrapped after 50 hours.

dan · #10 10-05-2006, 09:53 PM

Quote:

Originally Posted by frankh

The more serious issue for me is that if you do get a crack how will you spot it under the insulation?...CO poisoning being the risk here.

I didn't wrap any of the slip joints, Ys, or ball joints. The likely spots for cracks. They're inspectable. Flame on, it's HORRIBLE for the exhaust!!!