Engine cooling/baffling

[dave]

I reduced my inlet openings on my plane by 50% about a month ago. In the winter I have a hard time keeping the jugs warm enough. They would read around 200 degrees on the front two and about 250 on the back jugs.

Reducing the inlet size brought the temps up as expected. The front were around 250 and the back cylinders about 375 at cruise. However the oil temp was getting around 210 to 225.

After reading an article on the web about wraping the tin tight around the cylinders and only having a gap of 1-1/2 " on the bottom I tried it out. The top of the cylinders have an opening around 3" wide and I sealed every possable leak with red silicone. The engine already had a plenum.

I tried it out today. In a continuous climb from 2000' to 8000' the jugs got up to 320 degrees. All jugs within 5 degrees! The oil temp peaked at 210 but settled down to 190 when I leveled off.

Continuous wide open throttle at 8000' the oil temp stabilized at 200 and the cylinders were at 310.

This was with a Lycoming but the principle should apply to any aircooled flat 4.

Dave

[dave]

The web address of the site was www.x-jets.com/a_cooling_efficiency.html.

[n3480h]

Good information, Dave. Any pics of your installation? Couldn't get the link to work.

Tom

[dave]

Tom,

Try googling x-jets The Experimental Workshop, when it opens up look under articles for cooling efficiency. They have pictures in there. They got their info from an old NACA report.

Dave

[JoeB]

Try this: www.x-jets.com/a_cooling_efficiency.html

(The period '.' at the end was killing the linky)

[n3480h]

Thanks Dave and Joe. Good article.

Tom

[dave]

I have to change my prop in the next while. When I do I will take pics up the bottom of the jugs and try to post them. I didn't have the baffling exit ducts extend down as long as shown in the drawing. There is not enough room as it would interfere with the leads from the CHT probes.

The exit baffle ducts are around 1" long.

Frankly when I started to do the cylinder wrap I was a bit nervous as before the tin merely divided the top half of the cylinder from the bottom. Wraping around seemed counter intuitive. It worked far better than I expected. I did not bother with the flow divider as shown. I thought with the reduction of the inlet opening I would have seen an increase in speed. Unfortunately there was none.

[Schmleff]

Thanks for posting that!