There's a whole thread (over 600 replies and over 25,000 hits) with all kinds of discussion (what works, what doesn't work, etc. etc. etc.) on this airplane just below! I fly mine with an OS70FS using a Graupner 12.5 X 7 three-blade and it flies it really nice. I've also used two-blade APC 13 x 4 and a Masterairscrew 13 X 6 that are also good matches for this engine!