Hi!
A 14.5x11 four blade prop is way way to much load for a 20cc four stroke.
back in the early nine-thies Quay Barber in Ohio manufactured 1/4 scale Formula 1 racers (pylon racers) for 1.20 four stroke engines and the prop of choice back then was a two blade 14x10 APC. I think our OS and Saito 20cc engines turned those props at around 9000-10000rpm on 5% nitro.
A 4 blade prop that would work on a .60 size fighter would only look ridiculous due to it small size.