One week wonder update?

[gcm52]

I am perplexed hearing about these cooling issues. I installed a Rotax 912UL in a Zenith 701 using the factory FWF kit and flew that airplane for three years with perfect temperatures all year round. The engine ran perfectly from the first start up, never an issue. Based on that happy experience with the Rotax I installed a 912 ULS in my Onex. This time the FWF was a custom job done by me, although the cowling was closer to the Zenith design rather than the Sonex design. That is I didn't try to replicate the Sonex look to the cowling. Once again I had perfect temperatures from the first start up. Never a cooling issue of any kind. The airplane had tremendous climb performance, was fast and was a delight to fly. I think that the Rotax 100hp on a Sonex airframe is a fantastic combination.

[13brv3]

I've never had any cooling issues in my 912 Onex either. I used a chin scoop for the radiator, with oil cooler sealed to the back of the radiator. Zero cooling problems. I think the main issue is the fact that everyone wants to come up with some sort of "pretty" NACA duct, low drag solution which often ends up being more of a problem than a solution.

I'm sure I have some excess cooling drag, but it's not a racing plane. Heck, I even left the wheel pants off because they just don't make much difference. I had to widen the stock pants to fit my 500x5 tires, and they were never very effective. Some day I might add some of Van's pressure recovery pants, but probably not. I see 140 mph cruise at 5300 RPM, and almost 1200 fpm climb to 4000 ft. I can't really wish for more.

[gcm52]

Hang the proper radiator out in the wind, I do believe that is the secret.

[Kai]

Agreed- I can´t understand their cooling issues either. I went with a split radiator setup controlled by two 80C full flow thermostats. Cooling air inlets per standard Sonex dimensions- outlets by chutes in the bottom of the cowling and gills in the sides. No issues whatso ever, and temperatures stay pegged at set values. The cowling might be looking a little squarish, not at all so elegant as Casy´s, but it gets the job done.