flyrotary@lancaironline.net Mailing List Archive

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My oil cooler "diffuser" is almost identical to yours except mine tapers to zero distance from core at back end. Extensive wind tunnel tests (squirting compressed air nozzle at inlet and feeling where air came out of oil cooler) showed that most of it was at the back end (no big surprise). Already been some better permanent solutions suggested here but as a quick fix I put a piece of ridge vent material (very porous fiber stuff used to vent roofs) at the back end to equalize the flow through the core. Not a great solution but did show measurable improvement.

I took another look at the scoop today, and there's plenty of room for improvement. I believe I'll smooth out the bottom of the scoop in the rear to eliminate the wall. I'll also add a steering vane in the middle of the core. After looking at it today, I can easily imagine that the front quarter or so isn't getting much air due to the way the air has to turn to get to it. I can even imagine needing a second smaller vane just like what Al showed in his picture.

Only thing I would suggest is to carefully measure the pressure drop through the scat duct to throttle body. Possibly even worse than the pressure drop is the heat the air picks up going through that thing (at least that's my theory). I was flabbergasted at the improvement I got when I eliminated the scat. Mine was a bit longer than yours so the penalty may not be that much in your installation. Worth keeping in mind though.

I really went overkill with the scat tube this time. Mine is 3" ID, and it's hard to imagine it having much of a pressure drop. I'm sure there's some unwanted turbulence though, so eventually, I'll replace this run with something smooth. I never thought much about the heat issue either. By far, my biggest problem is the inlet located inside the radiator duct. It's got a big hole, but forces the air to make 90 degree turns to get in, which just can't be good. I still can't believe I'm really only getting 26" MAP in climb though, because I'm turning close to 6200 rpm at 120 mph. Since that's the same as what you were seeing, I find it pretty hard to imagine that I'm getting as much power as you had, but with 4" less MAP. I sure hope I'm wrong though :-)

I've made the decision that I'm not going to do either of the above fiberglass projects until I get my 40 hours flown off. After today's flight, I've only got 2.9 hours to go. I treated the airport to a full showoff climb today. I lifted off, kept the nose level to 100 mph, then pointed it upward at 90 mph. I forgot to look at the VSI though. I rolled on course as I leveled off a fraction of a minute later at 2000 ft, and the oil temp was up to about 190. Level at 2000 ft, and 5200 rpm, the oil stabilized at 185, and the water at 144. Just purred like a rotary kitten :-)

Cheers,

Rusty (zoom, zoom)