Baffle mysteries

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Rich
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Baffle mysteries

Post by Rich »

Specifically I'm referring to a couple of interesting items regarding #3, but relevant to all to some degree.

As a result of the Surefly installation I wound up investigating cooling for #3 cylinder head. First of all there wasn't anything peculiar that I could see that would affect airflow from above that cylinder. There was a small gap associated with the #1 and #3 upper spark plug leads where they entered that upper plenum. I RTV'd it on general principles, as there was likely a bit of a leak there.

Then I looked at the rear baffle and for obstructions beneath #3 cylinder. I did find one culprit in the latter category which could have occurred when running up the engine after installation when we checked for oil leaks. It was the battery cooling SCAT that had wedged against the bottom of the #3 cylinder head fins - and right below the CHT temperature sensor. I rerouted it so as to clear the area. But I noticed something else.

The cooling baffles that wrap around the cylinder heads for #1, 2, and 4 were all pressed against the cooling fins, allowing no air to pass beyond the tips of said fins. When I pressed on these assemblies toward or pulled outward from each respective cylinder I could detect no flex whatever. This forced air from above to travel along the large areas of these fins, maximizing heat transfer away from the respective cylinder heads.

Not so #3. There was a visible gap pretty much all the way down. This picture doesn't quite do it justice:
N40XE No 3 baffle.jpeg
In addition, when I pressed inward on this it flexed against the #3 CH and was free to flex outward quite a bit, as well, which would widen the gap further. After much fiddling and issuing magical incantations I found that by loosening the 2 screws that held the baffle to the CH and pressing the baffle down and forward and tightening the screws, the gap was removed. The baffle now sat tight against the fins and would barely flex outward, though the very lower edge can be flexed a bit outward. OK, this seemed much better.

Now for the remaining mystery. Note that gob of RTV on the flange at the bottom of the baffle. This looks for all the world like it had been anchored against the #3 oil return pipe but there's too much gap. (This engine was pulled and extensively worked over in '15 and untouched since then.) I don't think it's necessary any more but I wonder if others have this gob o' goo on their planes.

There is still one other bit of obstruction below #3 and #1 cylinders (my highest and second highest CHTs, respectively) that is not so easily dealt with. It's the wiring to the starter and alternator. It also look like there's an opportunity to improve the flexible strips at the top of the right front baffle.
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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Steve
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Re: Baffle mysteries

Post by Steve »

Rich:

No gob on mine. I am wondering if you have the SS wire between the front and rear baffles on that side. On my installation that wire has an S-bend in the middle. Twisting that with a pliers pulls the bottom of each baffle toward the other of the pair, against the cooling fins of the cylinder.

DSCN6015.jpg
The arrow indicates the aforementioned S-bend.

Steve
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Re: Baffle mysteries

Post by Rich »

Steve wrote: Thu Jan 23, 2020 11:16 pm Rich:

No gob on mine. I am wondering if you have the SS wire between the front and rear baffles on that side. On my installation that wire has an S-bend in the middle. Twisting that with a pliers pulls the bottom of each baffle toward the other of the pair, against the cooling fins of the cylinder.

Steve
I do. But the #3 baffle isn't all that rigid between the cylinder section (where the wire is) and the cylinder head area. The others are shaped differently.
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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Steve
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Re: Baffle mysteries

Post by Steve »

I was out flying today, and looked at my CHTs in more detail than usual. Interestingly, on my airplane, #1 is hottest (by 10 degrees) and #3 is coolest (by 15 degrees). Hottest was 350 degrees. ROP at 6500 MSL.
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Rich
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Re: Baffle mysteries

Post by Rich »

I don't remember what the pattern was before installing the PowerFlow but aftward it changed the ranking of CHTs of highest to lowest. In climb-out right now #1 will show the highest. As I level off in cruise, #3 heats up and becomes the highest CHT. This happens before leaning, BTW. :scratch:
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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