da Rock

Unfortunately, with the choice of props nowadays, there really isn't a good way using theory.

I'm running a 13x8(3) that is the absolute best performer on one airplane. That airplane flies really well on 2bladers also. Maybe the best 2blader is the Evolution 14x6. Landing speed at idle is decided by me. OK, it's decided by the stall. The idle rpm and pitch really don't play a significant part. Because the sucker will not stall until it's almost zero airspeed (ok, that's exaggerating, but it's SLOW, trust me) and the idle rpm/pitch work about the same with 2 or 3 blade. The 2 bladers pitch does seem to give a different slow speed, but not much. The point is that the 8" pitch on the 13x8(3) in practice does not equal theory.

What we read on the props for pitch is nice to read, but don't bet the farm on it.

At low speeds, the efficiency and blade area and fan area mean a bunch.

The most effective way to "work out the sort of" prop that will work is to try whatever props you can find to buy. I've been working with 3 bladers for a year or so now. I started because of the sillyism "3 blades are less efficient than 2" that everyone seems to think means "3 bladers won't work as well as 2 bladers". Turns out that I've found an excellent 3blader for my 61s, 75, 91s. And yet to find an excellent one for my 46s, but I've not really tried.

What I've found is that I need to try every diameter that seems appropriate and to pretty much ignore the pitch. And test fly. Our glow engines operate well over a broad range of rpms. Unless you're trying to race that is. The range has worked great for the 75 and 92s. I've had to work diameter for the 61.