At first I used a APC 12 1/4 - 3 3/4 ran ok probably under propped a bit was making a bit of noise in the air, then went to a master air screw 13-4 as I just wanted the plane for 3D flying and I really just want to do a lot of hovering or hanging it off the prop so thought that 13-4 would give me plenty of pull being big diameter small pitch should hold the plane nice in a hover anyway at this time had a accident with my thumb and a prop so couldn't really master the rudder with my thumb bandaged so 3D flying was on hold for a few week's, 13-4 master air screw was barking at full noise as could only fly in circles with the thumb the way it was had to pull back to half throttle as the boy's said It was hard hearing each other lol,, so then I went to a 12-5.5 still made noise but not as bad as the 13-4 and also made the plain fly a lot betteras it was a windt day. Explained that the 13 -4 was for hovering or hanging it off the prop it wasn't really for normal flying. Still don't know how the 13-4 will go hovering the FunFly yet to try as of my injury .
I am up for any suggestions on prop sizes for the 55AX