Thermal exhaust wrap

[jrthomas]

Do any of you have your exhaust wrapped? Any thoughts pro or con? James Thomas Mod 4/912ul.

[Dave S]

James,

Haven't done it; and, not likely that I ever will on an airplane - but that's just me.

I know this is done on cars in some cases (hot rods, etc W/ Headers) however, the pipe materials are much heavier and most cars don't continuously operate at high power settings...even rolling down the freeway, few car engines are producing more than 15% of rated power - meaning a whole lot less heat out the exhaust compared to what we see on an airplane.

I'd be leery of doing this. Here's why. The wrapped exhaust pipe will operate at a much higher temperature - unless we have empirical data as to what that temperature will be and what effect it will have on the pipe regarding strength and integrity; also, considering the intensity and frequency of vibration the pipe is exposed to....and then know the limits of the metal the pipe is made of under those conditions (it's thinner that car pipes for weight saving), it's dealing with a lot of unknowns.

If a person could view the pipe where it is coming off the engine when cruising with 75% or 85% power you'd see that it glows - it's red. the pipe holding together is in part dependent on the pipe shedding heat as well as the nature of the metal it is made of.
Quite a lot of heat is shed off the exhaust - the exhaust gas cools quite a bit on its rather short trip through the pipes and muffler due to heat loss through the pipes.

If there is a need to insulate other under cowl components from the exhaust pipe heat, another strategy is to insulate the other components with ceramic fiber wrap, a metal shield, or similar.

On our aircraft, in one case, an aluminum shield was fabricated to reflect the exhaust heat away from a nearby component.

Sincerely,

Dave S
Kitfox 7 Trigear
912US Warp Drive

St Paul, MN

[Esser]

My exhaust is ceramic coated which does the same thing just a little bit better and a lot more money (I didn't pay for it, it came with the engine). I don't know how it performs as I have yet to fire it up.

Why do people want to heat wrap or coat their exhaust? (BTW I am not expert, this is the word on the street)

When parts get red hot (like turbo housings) and then cool down they go through a thermal cycle which over time can degrade the metal. Ceramic coatings help reduce the thermal cycle and reduce surface temperatures. It does this in a variety of ways.

Exhaust gases that flow through your system are extremely corrosive and can eat away at your exhaust system from the inside out. A good coating can be applied to the inside of pipes to help make sure the exhaust gases and moisture either exit quickly or are burned off

On turbo components the thermal cycle process can go from glowing red to cool. Over time this can weaken the cast housing. A high heat ceramic coating can provide protection, keeping the heat internal to the system.

On headers and exhaust piping the bends and curves where heat can concentrate at can thermally degrade the metal over time. These hot spots can also develop pin holes as exhaust gases erode the inner substrate.
So a good high heat coating over 1600 degrees F can protect your exhaust and turbo components from the problems associated with thermal cycling.

Ceramic coatings help increase the speed and maintain the quality of exhaust gas flow. It also helps with thermal tumbling which happens when hot spots develop in the metal due to thermal cycling. By coating your headers you can make sure that you have a smooth laminar flow of exhaust.

Finally you get rid of heat soak, which can in turn affect other parts of the engine. By keeping the heat in the pipes you lessen the risk of excess heat damaging other engine parts like plastic parts, wiring harnesses, and spark plug wires. My engine is fuel injected so this can help with vapour lock issues.

[jiott]

Go to the Rotax-Owner.com website and click on forums. Do search for wrapping the exhaust and you will find quite a bit of discussion on it. My recollection is that the general opinion is that it is a good thing if done properly for many of the reasons given by Esser.

[jrevens]

Specifically regarding wrapping, I'm with Dave S. There are situations where it can be helpful under the cowl, but my considered opinion is that it is not particularly good for your expensive exhaust system. The pipes are actually going to have a greater range of thermal cycling if wrapped - the pipe itself will get hotter. With the pipes being hidden under the wrap, cracks or corrosion that are forming can be hidden, etc.

As far as ceramic coatings go, there is some controversy about the brittleness of the coating actually causing a greater possibility of cracks developing. One thing is certain - if you do have to repair the system by welding, it's a real pain to try to remove the coating... many welders will not even consider doing it. I know this from experience. Exhaust gas downstream of a turbocharger is no hotter than it is without a turbocharger... in fact it's possibly cooler.

I prefer lightweight thermal shielding if necessary, as Dave suggested.

[Av8r3400]

To pull back just a bit, what is the benefit you would be looking for to wrap the exhaust?

Personally, I don't see the need for it. The risks of damage is more than any benefit potential. I would say the same for ceramic coating as well. Other than looking pretty (very pretty for sure!) the risk reward ratio is not there.

Just my opinion.

[Esser]

I think the theory behind is it it will cool slower and more evenly. But like I said, I am no expert.

[jrthomas]

I did a post on www.rotaxowner.com aimed at Roger Lee. I'm anxious to hear what he has to say. I don't have an opinion either way so I'm open to leaving the wraps on or taking them off. I'm flying the plane now with no issues. Thanks for your comments. James Thomas

[jrthomas]

I got an answer from Roger Lee. I consider him one of the best Rotax guys out there. He says that he knows a hundred others using thermal wraps with no issues and he has run wrap for over 8 years himself. He says that the advantage is that it cuts down on under the cowl heal, which I believe is a good thing and as long as it's done correctly shouldn't be a problem. James Thomas

[KFfan]

Are you able to expand regarding "done correctly"?
Thanks