Hi,

I would like to know which propeller to use, because OS doesn't recommend any propeller size for the break-in, only this:
Sport 12X7-8, 13X 6-7

Can I use an APC 12X6 or what?

Thanks

SDG666

I used a Graupner 12x7 for break-in and flying

Is there anything "touchy" for the tunning and breaking-in with that engine that I most know?

Nope

Set it rich, make sure it's reliable, and go fly it. I'm not a real proponent of extended break-ins on the ground. OS engines are known for their ease of use and relatively quick break in times.

They say to use the prop you are going to fly with. Also, most "break-in props" are smaller than the ones you would use for flight, so you will be just fine.

Engine is a breeze to start and tune; have fun with it!

The 12X6 will work just fine.
A question for gaRC. How would someone know what prop they are going to fly with??
Just wondering??

I don't know, it's just what the manual says

For my new 55AX, I know I've been enjoying 5pitch props on my previous planes with the 46, so I went to a larger prop diameter with the same pitch for the bigger engine. I imagine this will give me a bit more pull without increasing my speed too much. But of course I'll have to try it and see what happens. I also bought a 12x6 as I heard the plane flies well with that setup.

Yep and that's why I have so many props these days. Trying an odd ball prop has often given me some wonderful surprises. I spend A lot of time with A new plane changing props.
I like A lot of pull with the slowest speed I can find so I have A lot of low pitched props, even been trying out some of the 3-D props I have never used before and found I liked some of them.
I have been nipping off the tips of A few too, I'm having A ground clearence problem on A couple of planes, if I bounce on that three point they get just A bit shorter.