A baffling issue

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Rich
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A baffling issue

Post by Rich »

Not baffling as in "confusing", but rather an inquiry on remedying possible baffle issues in the plane.

The long story:

I haven't really had an issue with CHT's over the many years I've had the plane. But until last summer I was based out of Puget Sound and it doesn't really get hot enough there to give me a realistic sense of such a possibility. Only on occasions where I ventured into the heartland would I see CHT issues, and then only fleetingly - climb in hot weather. But two things have since happened:

1. Got my engine repaired last summer to a degree that required breaking it in again. This gave me higher CHTs right off the bat. This is considered normal during break in, so it didn't concern me greatly.
2. Relocated to Central Oregon where summers are considerably warmer. DA on the surface at my new home airport routinely hit 5500 ft, with daytime temperatures 80-90 deg F.

My CHTs seem normal right now, but it's not yet summertime warm, and the break-in period was ending as fall arrived. I had my cowling off a couple of weeks ago and seriously perused the baffling. There seems to be no big problem with the rubber strips at the top sealing against the cowling. At least if the scuffing on the upper cowl and the strips is any indication.

But the intersection of the front and rear composite shell pieces with the engine case is another matter. Of the four pieces that comprise this shell, three of them have a significant gap with the case. 3/16-1/4" I'd say. Lots of daylight shines though these gaps. These gaps would allow a significant leakage. My inclination is to get these gaps sealed up with RTV. Has anyone done anything like this? I searched the forum but haven't find anything.

NOTE: The one section where the gap is very small is the right front - the "Arizona Baffle". Though now standard this part was installed post-delivery and had the effect of lowering the #1 CHT and improved the balance of CHTs considerably in our plane.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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BlackMammoth
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Re: A baffling issue

Post by BlackMammoth »

I sealed the gaps in my baffles years ago using High Temperature RTV. Some areas took multiple passes as the gaps approached 3/8"!

I highly recommend this to all DA40 owners who have issues with cooling.
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Steve
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Re: A baffling issue

Post by Steve »

My DA-40 lives in S. TX and we have very hot summers. I don't think I have ever seen my CHT above 350 degrees. My baffling fits the engine case fairly closely, the gaps are more on the order of 3/16 inch in only a few localized areas, with the remainder flush to the case.

Since I've never had an issue with the CHTs, I haven't felt motivated to seal the gaps.

Steve
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Re: A baffling issue

Post by Antoine »

+ 1 to Phil. The gaps were huge on mine.
You'll find the first reference to this in Brock's supercharger thread.
Google: NASA Contractor Report 3405.
My take away: if you leave leaks, part of the cooling airflow is wasted (and turning into parasitic outflows from the wrong places of the cowling - more drag.
As a result your CHTs are hotter. You can't lean as much in the climb, so you waste fuel and/or performance because your engine is running unnecessarily rich.
Your A&P will hate you if you do though... they don't like unsticking parts when working on the engine!
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kjmeyers1
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Re: A baffling issue

Post by kjmeyers1 »

Steve wrote:My DA-40 lives in S. TX and we have very hot summers. I don't think I have ever seen my CHT above 350 degrees. My baffling fits the engine case fairly closely, the gaps are more on the order of 3/16 inch in only a few localized areas, with the remainder flush to the case.

Since I've never had an issue with the CHTs, I haven't felt motivated to seal the gaps.

Steve
I'm always at 360-380. I would love to never see 350+ :bow
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Diamond13
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Re: A baffling issue

Post by Diamond13 »

It is essential to fit the GRP baffles as close to the casing as possible. I have seen often, after an engine change, baffles re-installed with large gaps, CHT became a problem. The delta pressure is almost lost if gaps are too large. Normally becomes a problem at front & rear side of case......
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Charles
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Re: A baffling issue

Post by Charles »

Diamond13 wrote:It is essential to fit the GRP baffles as close to the casing as possible. I have seen often, after an engine change, baffles re-installed with large gaps, CHT became a problem. The delta pressure is almost lost if gaps are too large. Normally becomes a problem at front & rear side of case......
Thank you for this wonderful piece of advice. I always found my CHTs to be a bit high ever since I bought the plane 6 years ago. We replaced all the soft baffles at the top and ensured a very close fit with the cowling, which made no difference. We also installed the Arizona baffle, which reduced cyl #1 CHT by about 15F. But after reading this post, I looked carefully around the bottom of the engine to see if there were any gaps between the composite baffles and the engine and found that the baffle around the bottom of cylinder #3 toward the rear of the engine, instead of hugging the contour of the cylinder, had caught on something (cable or screw, not sure) and was lifted from the cylinder by about 1 cm (3/8"). I freed it and it fell nicely into place, closing the gap completely. Last flight showed CHTs lower by 20-30F on all cylinders :shock: This is almost miraculous.
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