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What is the general consensus of Rotax 912 ULS operators about wrapping the exhaust pipes with
"automotive exhaust manifold tape" to reduce the under cowl temps... looking for ways to get rid of heat to reduce my oil temp slightly on high ambient OAT days.
What did you see or experience
What product and from which source did you use
Any other caveats
Phil Smith CH 70wonderful
I know you're familiar with my discussion "Heatshield Armor" exhaust insulation and just wanted to give you a longer-term followup - could be that the material might have an application in the Rotax exhaust system? Typical exhaust wraps are going to be much easier to install and conform to the bends in header pipes and the "Heatshield Armor" works well on large surfaces such as mufflers. I have found the Heatshield Armor material to be much more durable - on my muffler, it looks like it is going to probably be permanent or at least will last for years. I had previously wrapped my muffler with a premium fabric wrap but it was already starting to break down within a year or so. I didn't think to check the temps with an infrared thermometer, but I'm fairly certain the muffler's radiated heat is much less with the Heatshield Armor vs the previous exhaust wrap.
I put it on mine and it is definitely cooler. I get high oil temps when its hot out during climbs. I have opened up the cowl bottom and put a 2 inch lip that draws air out of the cowl. my oil lines are 5 years old now so will change soon and put springs in them where they bend, Roger Lee said this helps alot as the lines bend collaspe? when the oil gets hot and slows the flow of oil to the cooler. I might try a cowl flap instead of the lip I have so could regulate it when cold because then it stays too cold. PS I also put sticky heatshield on the water lines where they were near the exhaust just to protect them. Yesterday 86 degrees on climb at 70 mph up to 5K got as high as 228 so leveled out cooled down and went back to 212-216. Hot engines are scary.
Chris, Like you I have added a lip to the cowl exit on the bottom - have also made a scoop for the oil inlet and a scoop for the radiator to possibly get more air. Both of these have helped a little. Have ordered some exhaust pipe wrap as my next attack point - I might take another look at the water hoses for areas that I haven't wrapped. Been thinking of wrapping the cowl to cooler ducting with insulation.
Still looking for more info from those of you that have tried something and won or failed.
If you wrap/insulate exhaust pipes to retain radiant heat in pipes, the pipes will run hotter and the steel will be prone to higher thermal oxidation (long-term breakdown). If there is an alternate way to reduce cowl temps other than wrapping pipes, I'd go that route.
In a car with wrapped pipes, if a pipe ruptures from high heat, you just pull over to the side of road. In flight, a ruptured pipe can make life highly unpleasant.
If you wrap/insulate exhaust pipes to retain radiant heat in pipes, the pipes will run hotter and the steel will be prone to higher thermal oxidation (long-term breakdown).
Isn't that more of a concern with mild steel pipes vs stainless? I don't have the headers wrapped on my Jab 3300, but the entire exhaust system is stainless. When I took exhaust wrap off the stainless muffler to install the "Heatshield Armor," the stainless muffler appeared totally unaffected by the wrap, but of course the muffler surface temperature is much lower vs the headers.
The ultimate treatment would be to coat the pipes inside and out with a ceramic coating such as "Jet Hot." I had auto headers treated with it and it looked same-as-new even after several years!
You are correct in that any oxidation breakdown is a function of temperature and time. And the chrome in SS resists that breakdown. But if you operate for prolonged times at 1300F with pipes wrapped, they will eventually oxidize, even SS.
You could keep wraps on and periodically inspect for problems like micro cracks. The higher grades of stainless like 316 or 321 will have more resistance to breakdown and lower grades like 304 will have lesser resistance.
When you use a coating to keep oxygen from the steel, any minor crack in the coating will allow O2 in and start the process. Expansion/contraction from thermal cycling can initiate cracks in coating. Much better to have intrinsic oxidation resistance of pipes from selection of base material.
I woke up tonight with the thought that I made a mistake in logic. If the SS pipe inherently withstands the 1300F exhaust gas, then wrapping it does not increase the gas temp, it just extends the distance that the pipe stays hot. So wrapping the SS pipe should not effect it's longevity. I stand corrected.
As I previously pointed out, I don't have the headers wrapped so no issues there, anyway - with there being 6 of them very closely crowded together, it's just too complex to wrap them or cover them without making inspection and maintenance too difficult. But I did wrap and later used "Heatshield Armor" on the muffler to cut down radiated heat to the carb above it to avoid vapor lock problems. I thought this would help in addition to the carb's aluminum heat deflector that was between it and the muffler.
However, a second reason for the insulation applies exactly to your corrected logic. The only vacant exhaust pipe space for a cabin heat muff was on the exhaust immediately downstream of the muffler. I reasoned that insulating the muffler would transfer some of the heat further downstream and enhance the effectiveness of the cabin heat muff. I also insulated the exterior of the cabin heat muff to cut down on radiated heat losses there, too. Works great!
Here a picture of my installation. Engine temps are good.
Good discussion here https://www.rotax-owner.com/en/912-914-technical-questions/8434-914...
Put it on last year...because of some health issues didn't get to do much flying to observe temps...always next summer