Update! See New Baffle Kit, Diffusers and Plenum V.2
New Baffle kit, Diffusers and plenum have been made. Below you will find my first version and the basic principles.
Cooling drag is one thing that many experimental aircraft have a lot of. Many systems get the job done, but not very well. Chris Zavatson pioneered the way for many LNC2 builders in regards to cooling drag. I’m still learning, so rather then me explain, read up on his cooling system evaluation. Then, once you understand the idea, check out the improvements article. A very well done article. So, my aircraft already had his cowling and diffusers installed. It was just a matter of forming up a mold to make the top cooling plenum. As noted in the report, 55% of cooling air is lost through a typical baffle system. This plenum would achieve 100% of the cooling air was passed over the engine and through the oil cooler. To make the mold I used some styrofoam my dad had out at the lake house. I cut down the under side of the foam to lay on the complex engine shape. Then I was able to sand the foam down to a shape that would fit under the cowl. Once that was complete, I layed the glass directly on top of my mold and around the edges to create a sealing surface. O’Riley’s had some cheap weatherstrip that I used to seal the plenum to the baffle. It isn’t the greatest stuff, but so far it has done well considering how many times I have had to remove the plenum.
The results lowered my CHT by about 30 deg F. and moved all 4 cylinders to within 2-3 deg F. More importantly was the oil temperature. I have always been fighting high oil temps, and this plenum took almost 20 deg F. off the oil temperature. Recently I found some more “leaks” around the oil cooler that should net me even more cooling ability, but this has not been tested yet.
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