Ceramic Coated Exhaust

[SkyKing]

Happened to browse the Trade-A-Plane ads and I note that the owner of N90BK has installed a "ceramic coated exhaust" to the rear engine. Anybody have details on this procedure and the possible benefits? Seems the heat transfer to nearby engine components and the rear engine mount would be minimized.

SkyKing

[GMAs]

Coating your exhaust parts is a old thing... as the cermic stuff will plate out.. but, the heat that is given off is not uniform .. thus you will develope cracks in the exhaust system usually around the inside radi... the reason the exhaust system is so paper thin.. is because it gets rid of heat quicker that way.. and keeps it more uniform without stress riser... shure it gets red.. ever see one on a turbo do a run up at night... glows bright orange ... except for the bad cyc.. their it is a dull red... but, the air passing thru the engine will keep the heat down.. if you have a radiation problem from the heat.. then you need to shield the part not the exhaust tube... and coating them with asbestos, fiberglass or cermic is not the answer...

Any shielding should be done so that the exhaust part can expand and contract freely...

And while were on this subject... lets talk a litte about the stanless steel parts... and springs... smile.. one of my more favorite things to discuss...

Mechanics love stanless steel.. yep we do... we make lots of money off of it... when you cant get the bolt out anymore... we get called in to remove the little bugger.... where as steel parts are actually stronger (by 30% more for the same weight) than their counterpart of SS steel... now drop one of the SS parts and how do you get it out... yep you have to go grab it... but, the steel part.. we use a magnet on and retreve it quite easly... Oh and does SS rust... well the grade that they are using.. or selling.. yep it does ... and when you put the wrench on it.. to take the nut off.. and round it off..so that no wrench known to man can remove it... now what... on the steel ones you take a little grinder and your good in a matter of mins... or drill out the bolt section from the head... but, the SS... well thats a different story... it requires that you take a carbide cutter wheel.. and cut the part off.. sometimes damaging the fixed part that you don't want to mess up...

Do SS parts hold up longer.. not from what we have seen... they actually seem to have about the same life... but, they add a new dimension to the other parts that will start to corrode and rust because of their valance level... where they make up a small battery... because of dissimalar metals...

So SS parts should be limited to Safety wire and kotter pins... leave the SS bolts and hardware alone... expecially around the hot sections unless the manufacture says to use them their... stick with the cheeper... less costly (ss cost about twice as much... to put it in other words.. you can buy two steel bolts for the same price as one ss bolt)... and more reliable... (higher strenght is in the steel bolts).

and remember we mechanics just love SS steel parts... because we can make more money off of you... when it comes time to remove it... and believe me.. it will come a time.. smile...

GMAs

[SkyKing]

GMAs,

Your good counsel echos my thoughts exactly regarding the stuff placed on the exhaust system and especially the stainless steel 'flash' items... Yes, I've seen the asbestos and ceramic wraps on a lot of funny cars and drag racers, but never on aircraft exhauses.

Isn't it funny, most macho-"PILOT's" just have to have that bright, shiny hardware, or the plane don't fly right and those who see the plane aren't impressed unless the sun flickers off the screws! My, my... such important egos... and of course, catered to by most of the parts houses with 'complete' stainless steel "screw kits". I'm not sure who is getting the screwing!

I wonder how many others that have the P-models have had or are having surface erosion of the long upward tilting angle piece on the left side of their rear engine mount that sits next to the left-side exhaust and turbo? I see mine is going to be needing a bit of clean-up and touch-up with the high-temp black stove paint. The previous owner had a 1 and 1/2 inch wide heat shield made out of a thicker piece of what appears to be aluminum that attaches with two hose clamps at either end, but when we cleaned it up last year, I left it off... the radiant heat must be flaking the high-temp paint off... just one of those yearly fix-its.

SkyKing

[Kevin McDole]

SkyKing,

Do you have a digital camera? I'm having trouble picturing the erosion & heat sheild you're describing. A picture would be worth a 1,000 words ...

[rick bell]

my turbo/wastegate backet had to be replaced when we changed out the engines (major parts were eaten away).
the back engine was always vaporlocking and i assumed that if i coated the exhaust with white hi temp paint the engine compartment would be cooler, made no change. the only thing that stopped the vaporlocking was insulating all the fuel lines, it has never vaporlocked from then on.

[SkyKing]

Kevin (SFO) and Rick,

Nope, don't have a digital camera... the part of the rear engine mount I was referring to is the long upward diagonal on the left side from the lower firewall weld of the frame that slants upward to join near the left Lord shock mount. The exhaust pipe is closest at the forward part of this diagonal and of course is near the rear of the turbo at the far aft end. Hope this makes since. The former owner had fabricated a shield that attached with two band-type clamps, one at each end, with the shield facing toward the exhaust/engine area.

Notice you also have a 1977 P337 ... ours is S/N 286... how 'bout yours? And are you having any heat erosion or flaking of paint in this area on the rear mount? Former owner had a habit of parking sometimes outside with rear cowl flaps opened and the rear of the plane facing into the wind... and with all the rain, I'm sure some of this is attributable to a bit of rust that was never completely wire-brushed off and sanded properly. We cleaned it up and recoated with some high-temp paint and didn't put the shield on as it was a temporary fix-it until annual.

Hope this helps.

And Rick, regarding the rear engine fuel lines... not sure that yours, I think a 1973, has the same routing... but we have the gear door removal and of course the fuel strainer and lower fuel line below the lower firewall is exposed to the environment... have thought about having these insulated, think the main tube is 1/2-inch or so.

Were your vaporlocking probs at start-up after heat-soaking, or what?

SkyKing

[rick bell]

i insulated all the rear ones (also had doors removed). the vapor locking only occured at cruise mp 27 & rpm 2600 and fuel flow around 65pds, usally occure between 8,5-15k

[Richard]

Well, I have to admit it. I've ceramic coated all my Skymasters and Lances exhaust. I wouldn't fly without it.

How many of you can shut off your engine after landing. Open the door, get out, walk over the to exhaust pipe, and place your hands on it? I'm going to guess, not many of you. Well... I can. The taxpayers paid the millions to research ceramic coatings for the aerospace industry. Proven it works and then not use it? I've never had a cracked pipe. Never had any corrosion or problems of any kind with the coatings coming off. (In fact, you will have to GRIND it off if you do put it on) My oil temps never see over 210, and head temps are reduced an honest 20 degrees. I think the problems people have seen are the nice looking, cheap, automotive coatings. The ones I've always used are always one manf. and they are thick and ugly. But.... they warranty your metal for life against corrosion of any kind. Costs about $400-500 for each engine. The cheap guys, shiney finshes would cost you about 150-250. That's my two cents. If you want a demonstration of getting out of the plane and grabing your exhaust pipes, let me know, and I'll let you grab'em.


One more thing. Interesting fact. When you run the exhaust hot. Then de-cowl. You will notice you can touch ANYWHERE on the coated exhaust. Even at the head, BUT... you can't touch any uncoated parts (clamps, probes, nuts) they are too hot, and will burn you. Amazing products.

Richard

[Kevin McDole]

Where can you get your exhaust parts coated? Does the ceramic coated exhaust require any approvals?

[Richard]

I don't think it is approved. All the AI's have looked at it and said "nice exhaust". I think it's one of those, don't ask, don't tell items. I use Jet Hot exclusively. Their 2000 black coating is done in only one place in the states, Pessagula, MS. Not cheap, but I feel it is worth it. A lot of complaints I hear about ceramic coating it due to the fact they use a lower quality coatings. Most standard coatings are good to 1600 degrees intermittent. This coating can withstand 2000 degrees continuous or 2400 degrees intermittent.

They do alot of aircraft exhaust and advise... If it is a turbo model only do outside only. They've never had it come off, but...... on the non turbo model I've done inside and out. Makes those mufflers last forever. I also do the turbine housing on the turbo. Keeps heat soaking on nearby parts down.

[Jim Rainer]

Richard, is that Jet Hot in Pascagoula, MS?

My rear engine oil temp will heat up if held for take off for longer than 10 mins on a warm day. The CHT is in the green, byt the oil temp approaches the redline. In your opinion will the ceramic coatings help keep the rear engine oil less hot on the ground on a hot, windless day? My 337 is normally aspirated, not turbo.

[Richard]

I had the EXACT same problem in my NA Skymaster. Had people telling me to check baffling. I put new baffling all the way around. Pluged every hole with red RTV and still the same problem.

Got sick of having to shut off the rear engine on the taxi ways at busy airports while waiting. Enriching the mixture to cool some, then reducing power in the climb so it doesn't overheat.... yep been there.

Don't think the ceramics solved all of my problems, but helped. Some people are pretty sinical on some of these subjects. I'd suggest calling the companies themselves and doing some of the research yourself. Some non biased groups have done some pretty good studies.

A U.S. government study was done just a year or two ago suggesting using ceramic coatings on EVERYTHING in an airplane.

"The overall goal of this project is to replace the environmentally hazardous chromium treatment with the environmentally friendly ceramic coatings"

NASA and the government are experimenting with ceramic coated piston rings and cylinder liners at this time too.

More recently they are researching ceramic coatings on the pistons and valves. The study is trying to see if these coatings on the pistons will lower emissions.

Sounds like if NASA is willing to coat their pistons, exhaust, valves, and piston rings......

Do your homework, and make up you own mind.

[SkyKing]

Richard,

In my many travels over the years, about the only place I've ever seen the coatings your talking about are on race cars and the like. Seems one WOULD run into a big problem with having the airplane signed-off at annual with a non-certificated item under the TCDS... and any IA who would sign-off on it would be hanging his ticket out in the breeze for all sorts of liability! Probably why I've never seen such coatings on any airplanes.

SkyKing

[Richard]

Your probably right. Not for everyone.

[SkyKing]

You must have a VERY 'friendly' IA!