ORIGINAL: FAST-J
Hey richlstubbz, Was just readin your post and the props that you want to try will be a little to much for that engine,I am running the O.S. 91FX turning a APC 14x4w, a zinger 14x6 also works well but i seem to prefer the apc.
My calculations are from using Real Flight 3.5.
I have been going off of a "Real World" ref engine (ST-90 w/ 0% nitro) that has a 14x6 3blade maybe a 14x7 3blade running at about 10.5K RPM at full. I have taken that known ref and tuned it into the RealFlight and modified the engine with a 2 blade prop @ the same RPM. I came up with 15x6 or 16x5 in the same RPM range.
I don’t care for the engine to be a screamer (ideal 10-11k range) though I might end up doing a 15x4 or 16x4 beings "X"x5 is somewhat uncommon, from doing a tower search.
Also 16 may be out of the question too depending on how well it works at our field (I am not to sure what the clearance will look like yet)
I guess the question is what is the RPM’s like on the smaller props?
All is subject to change though and I plan on doing some experiments with it to find out what will work out best.