A point to be brought up is your engine itself. The rule of thumb when going from a two blade to a three is one size down in length and one up in pitch. The big however is your engine itself. The RCV engines in this country are almost never seen. I have only built one plane that I talked the owner into using the RCV, the one that looks like a honey comb. That was years ago and the plane has never been flown. The engines are gear driven and swing a big prop, you may want to go into the glow engine forum and ask about props for that engine and see what people that are really using it have done. The normal rules of prop selection may not be correct for the RCV. I know they have two different models but that's about it, we just don't see a lot of them in use and they are a bit different then any other engine. When I had the one I installed in the plane, A Hell Cat, I read the instructions and just the break in for the engine was different then anything I have seen before. Better to be safe then sorry, go ask some users of the engine and be safe. They really are cool but I still haven't seen one in use.