I am running a UMS 5-100 on a 1/5th scale Ziroli AT-6 Texan although I haven't done the maiden yet. Long story about that but the maiden probably won't happen till the end of the year. As Tom has stated, the 5-100 is an easy to start, smooth running engine. I am turning a semi-scale Biela 25x14, turning 4400rpm's.