SonexBuilders.net

Hey all,
Last couple of flights the outside temps were right around freezing. My oil heated to 155F in climb, and stabilized at 145F in cruise. CHTs were around 160. I made some block off plates out of flashing and speed taped them on. I have a flange at the opening and much of it has a little curve to mate to the cowl.

I'm blocking off about 50%. Too much, too little, or just right? Looking for any advice and experience.

I don’t think I have ever seen anyone block off the oval openings behind the prop. I would worry that it would cause uneven cooling and make the front cylinders run very hot and overheat quickly while the rear cylinders ran pool. Most of us control the engine temps in the winter by limiting airflow to the oil cooler. On the old style lower cooler we would block off the opening that feeds the cooler right under the prop. On the top mount oil cooler, the cooler itself gets blocked off with either some high temp foil tape or a piece of sheet metal. I have even seen someone make an adjustable opening to the cowling exit hole by the exhaust pipes using a cable run into the cockpit. If it is extremely cold outside then you could also remove the oil cooler all together. It’s experimental aviation so you don’t need to always follow the norm. Maybe your solution will work better, maybe not. Let us know how the test flight goes.

In any case, you aren’t scoring any extra judging points for aesthetics :)

GordonTurner wrote:In any case, you aren’t scoring any extra judging points for aesthetics :)

Did you see that return flange though? Maybe I should polish the tape.

We used to do something very similar for the C140. If my CHTs are only getting to 160, I don't see the oil getting that warm. I'll share my results. First flight will be local.

Ah, well, with seeing the whole system and all that shiny tape, I reserve the right to refine my opinion :)

Ok, here are my results. We just flew for 1.4 hours and we both reset our night currency. Ambient was about 39F when we started, and 37F when we finished. It was dark. A lot warmer than our recent cold days, and I am sure the days will be colder yet.

Startup, warmup, runup, and taxi got things warmer than usual for these temps. We saw 295F max CHT and oil got up to 180 or so. Full power climb to 3000' MSL, about 2200' AGL, and 80 kts. CHT got a little over 300 and oil got to 213. Pulled back to cruise and did some orbits. CHTs came back to about 250 and oil went to 200F. Did this for about 20 minutes, then entered the pattern. Went around 6 times, 3 each, and it got a little hotter on the ground each time. Before the last takeoff CHT peaked about 318 and oil was 212ish. In the air those temps always dropped even in the full power climb. The fact that we could do 6 patterns in a row says we had adequate cooling. Overall I'm pretty happy because it isn't even that cold yet. I'm going to leave it as is, especially since it looks so nice, and see how it does as we get back to the 20s and teens.

32F today and low ceilings. Spent 1.2 in the pattern. Oil temp on the ground 200F and cools off to 190 in flight. CHTs 250ish.

Hi Bryan, I have tried an opposite approach. I fitted hinges on the outlet dams so I can open and close them, but only on the ground so it's just a summer/winter thing. They seem to have a large effect and would ideally be adjustable in flight but I have opted to keep it simple. It would be nice to be able to close them off for long descents so I might try to fit a cable operated mechanism in the future.

Peter

Peter,
That seems like a cool idea. Then you can maximize cooling for climb and minimize drag for cruise.

Or do something like this...

https://antisplataero.com/products/ez-cool-cowl-flap