For an OS 40 you need to run a 10" prop (unless you are racing, then a 9" prop).

A 46 would use an 11" prop (except for racing or 3D).

These prop sizes are suggested to keep the engine from over revving (prop to small ) or bogging down from too much of a prop load (prop to large ).

The Rascal 40 is a "floater". Even with a low idle plan on having A LOT of runway to land.

Because the Rascal is such a floater, I recommend a Master Airscrew (the black one) 10x5 prop.

An APC is to efficient and will not allow the plane to slow down enough to land. The MAS are less efficient so the plane will slow down enough to land. I have an OS 46FX on my Rascal and I use a MAS 11x5 on it. It is either that or kill the engine in order to land (had to do that before I got the MAS prop for the plane).

Hope this helps and answers your questions.

FWIW - The Rascal will do a nice knife edge and other basic aerobatic manuvers. Depending on your skill level AND radio, I suggest low rates while learning and high rates for the aerobatic manuvers.