EXHAUST INSULATING WRAP

This will be a personal choice and there is definitely some old wives tales and myths about it;

You'll get many different opinions here I'm sure. I've been using 2" wide header wrap on Rotax for 20 years now and never an issue. There is a right and wrong way to apply it. You only over wrap the edge of each previous wrap by 3/8" which some wraps actually have a mark on the outside edges to follow. Over wrapping can cause too much heat build up and that could cause an issue.  On the exhaust pipe bend coming out of the head you will have some over wrap, but isn't enough to cause an issue. You dampen the cloth NOT SOAK it. Use standard hose clamps to hold it in place. When I wrap down by the exhaust springs and knuckles I wrap under the springs around the joint 1.5 wraps and clamp it. Then these knuckles that often may have a little blow by exhaust leak going out is taken care off. It is easy to apply and the wrap can be obtained from many auto stores. I did a research project many years ago about under the cowl temps. The wrap made a difference and it keeps radiated and convected heat off wire insulation, hoses and rubber engine mounts. Wrap MFG's claim up to a 70% heat reduction. Now I don't always believe MFG's, but even if it's 50% that significant.Through the years I must know a hundred plus owners that have wrapped their exhaust. When done right I have never seen or had anyone complain that it caused an issue.

Roger, can it be done on just one pipe, or even on part of a pipe? The issue arise only when the pipe is close to other sensitive elements.

Thanks

Please Read SL-914-023 - https://legacy.rotaxowner.com/si_tb_info/serviceletter/sl-912-025.pdf

Use of exhaust insulation materials for ROTAX® Engine Type 916 i (Series), 915 i (Series), 912 i (Series), 912 and 914 (Series) ATA System: 78-10-00 Exhaust system

1.3) Reason Insulating the exhaust pipes (e.g. with exhaust wraps or ceramic coatings) leads to a significant increase in the component temperatures of all exhaust-relevant components. The significant additional thermal load generated inevitably reduces the proven durability of exhaust components. Exhaust wrap may also hold moisture, promoting corrosion. The use of any insulation material is not approved by ROTAX® and may result in exhaust component fatigue and damage.

This is like ethanol in the fuel. Rotax didn't approve it for decades and then they tested it and it was approved for 10% and yet others in the world have used up to 23% without incident.

I knew Rotax wasn't a fan of the header wrap, but many around the world do use it. When you are running the EGT's most are usually seeing around 1275F - 1450F depending on the plane, engine and use and setup. Rotax has a max temp of 1616F. The exhaust pipes are short and air still flows over them for cooling. The header wrap can't make it go higher in temp because the wrap isn't heat generating. All it can do is maintain the existing temp through the pipe. This is why race car drivers use it. To maintain the heat so the exhaust doesn't cool and slow the expulsion of the exhaust gas and knock down a little HP. 

 Rotax numbers: Nominal exhaust gas temperature: 800 °C (1470 °F),,  max. 850 °C (1560 °F) ,,   At take-off: max. 880 °C (1616 °F) 

I'm a science and research based kind of guy and believe in real time and field testing. After 20 years of using the wrap and knowing hundreds of Rotax engines that use it without incident this may be something Rotax wants to revisit. It cuts heat damage to wire insulation, rubber engine mounts, hoses and reduces the temps in the cowl to help keep the VR, ignition modules and other electrical components cooler and it helps reduce an incident where a hot exhaust burns through a hose that may be a little too close. I would bet worldwide there are thousands. I haven't seen or heard of a single failure when wrap was used PROPERLY and corrosion shouldn't be anymore of a factor with or without. If the pipes get wet and stay that way there may be some, but the stainless is pretty durable and resistant. If the pipes get wet in flight then the heat dries it fast and even if you washed your engine with water and started it within a few minutes it would be dry. I've had to replace may a wrap from old age and mechanic abuse and never seen any corrosion that would even raise an eyebrow.

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Hello Roger

We are not trying to go against what you are saying; we are only supplementing your information with what Rotax has released on the topic. When answering questions, we first reference the manuals/bulletins, and If we can't find the answer or solution, we then consult with our team of experts. 

Many times field experience is the only reference available.

Cheers!