Yep, I took the plunge and installed the louvers that have been sitting on the shelf for the past couple of months. I’m not going to post my hard data because I don’t feel like getting into the technical argument that always ensues. I went out and took pressure differential measurements in various phases of flight. Ok, got a base line, and the numbers seemed about right to me. The engine numbers that I’m expecting to be directly effected are Cylinder Head Temperatures and oil temperature.
Off came the cowl, chop, slice, dice, badda-bing, got louvers! Back on and time for a test flight. Wow. CHTs down around 20-30 degrees and oil temp down about 10-15 degrees. The measured pressure differential was up significantly. (How is that for generalities?)
Just for fun, I took off (OAT 88 deg) full power and basically hung it on the prop at about 85 kts. up to 5000′. Previously this wouldn’t really be feasible as CHTs would be climbing above 430+ by about 2500′. This time they came up to about 390 degrees and just parked there for the climb all the way up. Very neat. I did a little cruise speed testing and took some more plenum pressure measurements. I drug it back into the pattern slowly (heating up the oil) and did a full stop and taxied back to the run-up pad. This is the kind of thing that you wouldn’t find me doing much of because oil temps would be exceeding 200 by the time I got back out to takeoff, and CHTs would be starting out hotter. I tinkered around on the run-up pad (late in the evening on a week day, very quiet at the airport) and even shut down for a few minutes of heat soak. I took off again and did another “high performance” climb remaining in the pattern. Oil temp was well under 200 and one CHT just barely came up to touch 400 degrees at the top of the climb, and clearly wasn’t going to go much higher. One more lap remaining in the pattern and everything was very happy. Including the builder/pilot. This is going to be much more fun.
Why? Well, I do have some more things that I can/could work on for CHT and oil temps other than louvers. I still feel a little bit like the louvers are a bit of an easy way out. Actually when it comes right down to it, all of my current temps are totally within normal limits. But of course being the “junkie” that I am, and the fact that I want Tanya to be able to fly this thing easily without having to worry too much about the engine, I want it cooler. I could do some more testing on air inlet shape, and I could put a better oil cooler on, but these things are related. Keep in mind that we’ll be flying often in 100 degree OAT and this is an -A model with all kinds of nose gear stuff blocking some air outlet area. (excuses, excuses.) Finally, the thing that pushed me over the edge. I’ve been thinking more about paint. Just as soon as I get it all painted and pretty, next summer will surely roll around and I’ll be chopping up my nice paint job to install the louvers. Better to just get it over with now and get over the “shame” and enjoy the ride.
