Just finished my cap 580,with a os 70, not really sure what size prop i should use. flew it once with a 12x6 not enough power ,any suggestions. thanx kevin

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!

I'm running a APC 13x4w, I've heard people like the regular 13x4 better, I tried a 13x6 but didn't have enough vertical. I've also heard a 14x4 works well, but don't know if an OS 70 can swing that big a prop.

13x4 should do it. Remember, larger diameter less pitch gives better veritcal/climb and less speed. Smaller diameter and higher pitch gives less vertical and more speed. I found the 13x4 to be perfect with a os .61 FX.