Vev

Hi Maj Millard

Many thanks for your comments on this subject.

Apart from David’s (vK3auu) comments re a blow out in his exhaust system (this is the only 1st hand account I have been provided for an aircraft) I have yet to find one example of exhaust failure from wrapping, even after talking to a number of manufactures i've found none. However I have heard plenty about a mate of a mate stories, which mostly come to nothing (mostly poor maintenance and cleaning) when I have tried to follow them up, although I’m sure there must be some but I have yet to personally see one as a direct result. In any case I would like to know more about this as it will help me to make a more informed call about inspection frequency, so please pass on any specific 1st hand experiences you have.

My plan today is to do a visual before every flt day, which is only a 5 minutes job, and remove the wrap at 10hrs to do a closer inspection and then step it out when I feel comfortable that all is well. I suspect that if cracks appear before hand I should see exhaust gas leak stains around the wrap, just as one can see now at the header/muffler interface, owing to its deliberate loose fit.

To answer your question about cause … I can only tell you I think (meaning I don’t know for sure) there are a couple small design problems that effects CHT and oil temps in the 160: 1. the cowl design does not air scavenge as well as it could, which, I imagine, is why Jab have had a couple of goes with modes and variations of design to the cowl… I might add I have implemented the mod on my Jab as per the book. 2. I think (again this is an assumption) the exhaust scavenging is not as efficient as it could be, which is not allowing the incoming charge to help pull down the temps inside the combustion chamber through the latent heat of evaporation from the fuel as it goes through the inlet manifolds and ports. This is why to some extent the richer jetting (as prescribed by Jab) helps crudely cool things by wetting down the inlet track. 3. I think (educated guess again) the oil temp is affected by bad cowl design and some possible heat radiation from the headers being so close to the sump. I think the later is quite probable as I have already noticed an oil temp drop, intuitively I feel this has accrued from a reduction in radiated heat from the headers.

I also agree with you that an engine should be at the correct operating temp before flight for a whole stack of very good reasons … Personally I do make a point of seeing the oil & CHT temp needles get into green zones before I gas it up.

In terms of additional thrust from the exhaust … not sure what makes you think this was under consideration… in any case, I agree there will be zip.

Regards

Jack

Hi Ross,

The material I used is called Cool It by Thermo-tec I bought a 50’ roll of 1” which is more than enough for the 4 cylinder jab and should do a 6 cyc.

Before I used the wrap I did alter my bottom cowl with an extension as per Jabs advice, this only had a marginal effect in flt ops although it did seem to keep taxi temps down a little lower… however to honest it is a marginal call to say it really did a lot. I also increased my fuel burn by fitting a larger needle jet and a larger main jet, this increased my fuel flow in cruise by about 1ltph… I followed this strategy up and increased my main jet again which really helped pull down the CHT temps in climb and kept them away from the edge of the yellow and closer to about 310 - 320 deg.

It terms of the oil cooler I repositioned the angle on this and also improved the fit in the cowling … since then my oil temp never gets over 80deg c even on very hot days.

Whilst the wrap is a new thing and I only have a about 1.2hrs of flt time, it’s clearly a quantum leap in pulling down the CHT and oil temps. I will not be surprised that I may need to reduce air flow over the oil cooler on cold day (we get them in Melb) but I do feel very certain this is a real fix for pulling down the CHT... My climb temp last weekend was between 275 – 300 deg, which is excellent in my book.

In terms of fitting … I simply wrapped it and secured it with lock wire in several place (about 6) along the headers… I probably used more lock wire than I needed but I didn’t think there would be any prizes to be won if it came adrift and tangled up inside, it took a couple of hours to fit and it actually look very good too… I would send you a photo but I’m working overseas in Africa this week and not home until Sat week.

Once I get past the testing I will look at either going to ceramics as per the Captain’s (Geoff) suggestion or sick with this and make it pretty.

http://www.aircraftspruce.com/catalog/eppages/graphblkwrap.php

http://www.thermotec.com/

Hope this helps?

Best regards

Jack

Whilst it has taken me sometime I have installed the exhaust wrap today. I have yet to do any extensive testing, but so far I can tell you that I have seen approx 15deg F reduction in climb and a 10 deg F in cruise temps on my CHT. My oil temp is also showing about 10 deg c cooler. I can’t say I can feel any difference in power output at this stage but I will think about this a little more to try and find an objective proxy to measure performance.

For what it’s worth, I did a quick check my CHT gauge and have found it is over reporting by 4% … not a big deal but things are a little cooler than what the gauges says.

It’s still early days and will need to look at these numbers in relevant context of ambient temps and fuel flows. Never the less the sky didn’t fall in and all the numbers went the right way.

Cheers

Jack

I have decided to give the exhaust wrap a try as a starting point and may progress to ceramic coating if things look to be heading in the right direction. The wrap is something that is reversible and will allow me to undertake any procedure in a graduated way.

I will develop a test process to try and quantify any metrics I can obtain as well as institute a high frequency engine inspection and oil analysis programme to track any oxidation impact from thermal stress. I am hopeful accelerated oil oxidation will provide a good precursor for potential adverse engine problems caused from the wrap particularly around the cylinder head… I will also include wear metals analysis to keep a finger on engine fatigue. Whilst I won't be able to measure HP output I do have fitted a ground adjustable prop which may allow me to ascertain a proxy measurement and see if there is any +/-ive movements.

Once done I will share the outcomes.

Regards

Jack

Ps.

Yenn (Ian)……. I agree ceramics seem to have eluded engine builders so far, albeit Honda did actually build an oval piston motorcycle 4 stroke GP engine in the late 70's that seemed to work, even though it was uncompetitive against 500cc 2 strokes … Isuzu and a couple of others have built and ran engines in field trials but still seem to struggle with over all durability. Never the less there is a trend towards after market ceramic coating which are running successfully and showing some remarkable performance and durability improvements… I guess time will tell.

David,

This is one (thankfully) to be able to tell the grandchildren!

Regards

Jack

Hi Ian, I don’t think there is anything wrong with your thinking on exhaust fluid mechanics here, in fact I think this is precisely one of the actions that helps scavenge the exhaust gases effectively…. I guess the argument is about efficiency and if higher exhaust temps reduces gas density and frictional resistance enough to create better scavenging through the exhaust port. Whilst I could spend time calculating the fluid dynamics there is nothing like the real application to know if this is just nice theory or a practical option.

My interest in this technology is two fold; 1. reduce my CHT as I would like to see it slightly lower… my CHT is always in the green but I think a lower number will improve long term engine durability and safety. 2. see if I can find a few more HP without resorting to any engine modifications, albeit this is secondary outcome.

By the way, I have followed up on Geoff's suggestion and spoken to the chaps that do the ceramic coating … they tell me they have done this on a number of aircraft (almost all GA) and feedback has indicated that lower CHT have been achieved…. Sadly, he doesn’t have any metrics to quote!

Many thanks for your contribution … regards Jack

Composite report

Attached is a link re a Research and Analysis on Composite Materials undertaken by the Australian Government ATSB … if nothing else read the conclusion but there is quite a bit of useful info on safety for composite LSA a/c

http://www.atsb.gov.au/publications/2008/pdf/AR2007021.pdf

Regards

Jack

Geoff,

Thanks for this idea … I have heard the use of ceramics in this type applications which does sound like a nice approach. I presume you have managed to reduce your heat load inside the cowls, however can you quantify any values in terms of engine oil temp or CHT reductions?

Regards

Jack

Exhaust Wrap

Hi Nev,

Many thanks for your response … I share your concerns too. However the manufactures claim otherwise, which feels is a little counterintuitive to what one would expect, but there seems to be some technical logic. I have heard of this being fitted to RV's to improve HP and reduce heat build-up around the engine but I really don’t know any details and can't find much on the internet, other than automotive applications, hence my question for views, which I thank you for providing.

I have attached one of the manufactures claims .. I've removed the band (????) name.

"The original Exhaust Insulating Wrap was developed over 14 years ago by ???. Exhaust Insulating Wrap is an innovative way to create more horsepower and reduce under-hood temperatures. Wrapping headers maintains hotter exhaust gasses that exit the system faster through decreased density. Increased exhaust scavenging is produced along with lower intake temperatures. Exhaust insulating Wrap withstands continuous heat up to 2000°F, and contains no asbestos. ???? exhaust wrap will not over-insulate a system when properly installed due to a proprietary coating developed by ????. --Thermal Conduction Technology (TCT) -- that conducts heat across the wrap's surface. This coating controls heat build-up and dissipation".

Regards

Jack

Has anyone had any experience (or an opinion) with Exhaust Wrap in a Jab 160 and what has been the impact in terms of CHT/EGT/Oil Temp or power improvements?

Regards

Jack