Does anyone have any experince with diffent prop-sizes on this engine?
What is the best size for hovering etc.?

Try a APC 12.25x3.75 for hovering. This prop will produce lots of thrust for 3D flying. Hope this helps.

EdMan

Mine swings a APC 12 x 4 at 15,800 on Wildcat 10% Premium Xtra. I'm using a Performance Specialties muffler which increased the rpm by 1,500+. It is the best 2 stroke motor I own

I second that opinion on the 12.25x3.75 apc. It pulls my H9 ultrastick 40 straight up from a hover with authority.

With a 50 you might even go bigger 13x4?

I have one on my Magic with a 12x4 power point(wood) this gives me about 16000rpm on the ground with a mac header and tuned pipe. I kind of depends on what you are wanting to do other than hover and what plane. I like the wood props because they seem to rev up quicker and if you dump it in a low hover and hit the prop it will break it and not the firewall!!!!!!!
On mine the 12x4 hovers a little easyer but, put an 11x4 and it will loop almost a fast as a boom plane!

If your planning to do 3d/hovering then APC funfly props work pretty well, as said above 12.25 *3.75, 12*4 or 13*4, I have used them all on my 50 sized engine and their all pretty similar, I say try them all and pick the one you like best.

I do not know which I prefer. The APC 12-4 or 12.25x3.75.

The 12x4 spins up great. The 3.75 bites well with it's thick blade.

Perhaps you must experiment with your fuel and nitro preferences between those two. With Coolpower Pro-Pattern 20%, either is really great.

Lower nitro fuel may prefer using the thinner bladed 12-4?

Try it and see.

Mark

Maybe this is a stupid question, but do you use inch - sized props in Norway? if so, what brands are most available to you?

I use the 15% Cool power with the thin blade 12x4 so that my motor has almost instant response. One of the guys that I fly with runs the 30% heli fuel in all his motors and the 12x4 thin blade worked good for him.

Thanks for the help!
I think I have enough info now to get started. I have tried it with an APC 13X4 this weekend and it seemed fine. I might try out the 12.25X3.75 as soon as I find one.

I wouldn' t go with the 13x4 !
You will have much better results with the 12x4 APC or even better with the 12.25x3.75 APC . This of course is for fun flying doing 3d stuff and hovering. No speed barriers will be broken here.
I run mine on Wildcat YS20/20 fuel, and it just loves it !!! Not one dead stick after about 45 flights !!
As always, just my $0.02