Warm Wx Numbers

[Dorsal]

I am planning on closing the gap under the radiator at the back of the NACA scoop. Have others done this and did it make a difference?

[War Eagle]

I fly with the 914 so we aren't comparing apples to apples, but I made sure the fit of the NACA duct scoop for the radiator cooling was a very close fit (but not rubbing). I also sealed the gap under the radiator before I flew the plane in the beginning so I can't really compare a before and after. I knew the 914 was going to be a furnace so I started off wanting to close off every gap where air could bypass the radiator.

I run the Evans product as well and I see temps in the 240-245 if I am getting after it on a warm day. But Evans is good for something like 275 or so. I wouldn't want to run my temps up there but at least I have margin in the coolant. Coolant temps of 245 haven't been a concern to me at all.

I have the oil cooler mounted behind the cowling where the lower air inlet enters. I run a semi synthetic oil that allows for temps up to around 245-250 degrees but I can get there really quick on high power settings and warm ambient temps. I have to watch this temp really closely or I could sail right past it. Even though the 914 uses a bigger oil cooler than the 912s, I am concerned about the oil temps and am looking for ways to build in more margin on it.

My egt's have not been as issue and cht's are basically coolant temps.

[HighWing]

I fly a Model IV, so take this for what it's worth - But. I helped a guy build a Lancair IV and monitored the forums during the two and a half years that project took. The oft suggested solution to high operating temps there was to reduce the size of the air inlets on the cowl. What the guys claimed is that the ratio of inlet area to outlet area should be about 1 to 1.5. The air should enter the cowl then slow down a bit as it progresses around the engine then exit out the larger lower opening. It is a low pressure system and the air has no problem entering the cowl.

Then I helped a friend finish a Series V with the Series 7 FWF. When we measured the inlet to outlet ratio, it is almost exactly the opposite of what is recommended. In other words, more air can enter than can escape so in the theory of the Lancair guys, some of the air sees the high internal pressures and simply bypasses the inlet. We added an adjustable flap over the NACA duct on the V to close it off a bit to see if the theory holds with the Kitfox design. Unfortunately he was transferred by his work and is still not flying so no report there.

Then there is the relative inefficiency of the Evans Coolant - it helps in an over temp situation by tolerating the high temps, but then hurts a bit by not being an efficient heat transfer agent.

In actuality it is very likely an air flow issue as the problems with the earlier models with the much smaller external radiator, is trying to get up to operating temps - lots of duct tape.

Just suggesting some food for thought.
Lowell