RE: 1/2A ducted fan???
Ducted Fans need a lot of RPM.. Surestarts don't enjoy a suplus of Testicular Fortitude, so they make a poor choice for powering a Ducted Fan setup. I did some playing with EDF's a while back and found that at least from a load perspective the standard Speed 400 3" fan is about the same as a 4.7-4.7 prop. At that load and cell count the fan would be turning about 19,000 on a Astro 020, which is way out of the ballpark for a SureStart. Some of the newer GWS fans may have less load, it might be worth checking it out. The big problem you'll find is how to mount the engine and not take out so much of the fan center that you lose support for the engines and ruin stator rigidity. I'm dealing with this right now trying to get a TD .010 into a little GWS fan.